Abstract:
A power supply system includes a plurality of electrical storage devices, a distributor configured to distribute electric power between the plurality of electrical storage devices in a desired distribution mode, and an electronic control unit. The electronic control unit configured to (i) set the desired distribution mode based on at least one of a magnitude relation between first rates of change in dischargeable power of the corresponding electrical storage device to a charge state value indicating a remaining level of charge of the corresponding electrical storage device, or a magnitude relation between second rates of change in chargeable power of the corresponding electrical storage device to the charge state value, and (ii) control the distributor such that electric power is distributed in the set distribution mode.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a technical field of a power supply system including a plurality of electrical storage means. 
         [0003]    2. Description of Related Art 
         [0004]    There is known a power supply system including a first electrical storage device, a second electrical storage device and a converter that distributes electric power between these first electrical storage device and second electrical storage device (see, for example, Japanese Patent Application Publication No. 2009-261183 (JP 2009-261183 A)). The first electrical storage device and the second electrical storage device each are, for example, a rechargeable direct-current power supply, such as a secondary battery and a capacitor. Particularly, a power supply system described in JP 2009-261183 A determines a distribution ratio in the following manner. The distribution ratio is the ratio of electric power that is distributed to the first electrical storage device and electric power that is distributed to the second electric storage device. Specifically, the power supply system described in JP 2009-261183 A, when the first electrical storage device and the second electrical storage device are charged, determines a distribution between an electric power that is charged into the first electrical storage device and an electric power that is charged into the second electric storage device (distribution ratio) on the basis of the ratio of an available charge energy of the first electrical storage device and an available charge energy of the second electrical storage device. Each available charge energy is a parameter that is calculated on the basis of a difference between a charge state value (SOC) indicating a current state of charge of the corresponding electrical storage device and a charge state value of the corresponding electrical storage device at the timing at which an electric power (Win) that is chargeable into the corresponding electrical storage device begins to be limited. Similarly, the power supply system described in JP 2009-261183 A, when the first electrical storage device and the second electrical storage device are discharged, determines a distribution between an electric power that is discharged from the first electrical storage device and an electric power that is discharged from the second storage device (distribution ratio) on the basis of the ratio of an available discharge energy of the first electrical storage device and an available discharge energy of the second electrical storage device. Each available discharge energy is a parameter that is calculated on the basis of a difference between a current charge state value of the corresponding electrical storage device and a charge state value of the corresponding electrical storage device at the timing at which an electric power (Wout) that is dischargeable from the corresponding electrical storage device begins to be limited. 
       SUMMARY OF THE INVENTION 
       [0005]    However, when only the distribution ratios are determined on the basis of the ratio of available charge energies and the ratio of available discharge energies, there may occur a situation that the efficiency of the overall power supply system does not become optimal. Specifically, when only the distribution ratios are determined on the basis of the ratio of available charge energies and the ratio of available discharge energies, there may occur a situation that a dischargeable power of the overall power supply system or a chargeable power of the overall power supply system is excessively limited. In other words, for the method of determining the distribution ratios, described in JP 2009-261183 A, there may be room for improvement in terms of suitably ensuring a dischargeable power of the overall power supply system or a chargeable power of the overall power supply system. 
         [0006]    As an example, such, situations can occur when the plurality of electrical storage devices have different power supply characteristics. For example, the charge state value of each individual electrical storage device at the timing at which a dischargeable power (Wout) of the corresponding electrical storage device begins to be limited is not always the same among all the electrical storage devices. In this case as well, the power supply system described in JP 2009-261183 A is configured to distribute electric power between the plurality of electrical storage devices uniformly at the distribution ratio that is determined merely on the basis of the ratio of available discharge energies without consideration of a difference in the charge state value of each individual electrical storage device at the timing at which the dischargeable power of the corresponding electrical storage device begins to be limited. As a result, particularly, after the dischargeable power of each individual electrical storage device has begun to be limited, there may occur a situation that the dischargeable power of the overall power supply system is excessively limited. In other words, for a method of determining the distribution ratios, described in JP 2009-261183 A, particularly, after the dischargeable power of each individual electrical storage device has begun to be limited, there may be room for improvement in terms of suitably ensuring the dischargeable power of the overall power supply system. This also applies to the case after the chargeable power (Win) of each individual electrical storage device has begun to be limited. 
         [0007]    A task that the invention intends to solve includes the above-described one as an example. The invention provides a power supply system that suitably ensures the dischargeable or chargeable power of an overall power supply system including a plurality of power supplies. 
         [0008]    An aspect of the invention provides a power supply system. The power supply system includes a plurality of electrical storage devices, a distributor configured to distribute electric power between the plurality of electrical storage devices in a desired distribution mode, and an electronic control unit. The electronic control unit is configured to set the desired distribution mode based on at least one of a magnitude relation between first rates of change in dischargeable power of the corresponding electrical storage device to a charge state value indicating a remaining level of charge of the corresponding electrical storage device, or a magnitude relation between second rates of change in chargeable power of the corresponding electrical storage device to the charge state value. The electronic control unit is configured to control the distributor such that electric power is distributed in the set distribution mode. 
         [0009]    The power supply system includes the plurality of electrical storage devices and the distributor. Each of the plurality of electrical storage devices is a power supply that is able to discharge or charge electric power. The distributor distributes electric power between the plurality of electrical storage devices in the desired distribution mode. For example, the distributor is configured to distribute electric power such that a distribution between electric powers that are respectively discharged from the electrical storage devices becomes a distribution based on the desired distribution mode. Alternatively, for example, the distributor is configured to distribute electric power such that a distribution between electric powers that are respectively charged into the electrical storage devices becomes a distribution based on the desired distribution mode. 
         [0010]    The electronic control unit is configured to set the mode (that is, the distribution mode) in which the distributor distributes electric power. Particularly, the electronic control unit is configured to determine the distribution mode on the basis of at least one of the magnitude relation between the first rates of change or the magnitude relation between the second rates of change. 
         [0011]    Each of the first rates of change indicates the rate of change in dischargeable power of the corresponding electrical storage device to the charge state value of the corresponding electrical storage device. For example, when the correlation between the dischargeable power and charge state value of an electrical storage device is shown by a graph, the first rate of change of the electrical storage device indicates the slope of the graph. Alternatively, for example, when the dischargeable power of an electrical storage device changes by a second predetermined amount as the charge state value of the electrical storage device changes by a first predetermined amount, the first rate of change of the electrical storage device indicates a value expressed by Second predetermined amount/First predetermined amount. The first rate of change may be directly the rate of change in dischargeable power to the charge state value (that is, the rate of change that takes into consideration the sign) or may be the absolute value of the rate of change in dischargeable power to the charge state value (that is, the rate of change that does not take into consideration the sign). 
         [0012]    Each of the second rates of change indicates the rate of change in chargeable power of the corresponding electrical storage device to the charge state value of the corresponding electrical storage device. For example, when the correlation between the chargeable power and charge state value of an electrical storage device is shown by a graph, the second rate of change of the electrical storage device indicates the slope of the graph. Alternatively, for example, when the chargeable power of an electrical storage device changes by a fourth predetermined amount as the charge state value of the electrical storage device changes by a third predetermined amount, the second rate of change of the electrical storage device indicates a value expressed by Fourth predetermined amount/Third predetermined amount. The second rate of change may be directly the rate of change in chargeable power to the charge state value (that is, the rate of change that takes into consideration the sign) or may be the absolute value of the rate of change in chargeable power to the charge state value (that is, the rate of change that does not take into consideration the sign). 
         [0013]    The dischargeable power indicates an electric power that is dischargeable from each individual electrical storage device. The electric power that is dischargeable from each individual electrical storage device is an electric power that is allowed to be discharged from each individual electrical storage device or an upper limit value of an electric power that is discharged from each individual electrical storage device. The chargeable power indicates an electric power that is chargeable into each individual electrical storage device. The electric power that is chargeable into each individual electrical storage device is an electric power that is allowed to be charged into each individual electrical storage device or an upper limit value of an electric power that is charged into each individual electrical storage device. The charge state value indicates the remaining level of electric power that is stored in each individual electrical storage device (remaining level of charge). 
         [0014]    The electronic control unit is configured to control the distributor such that electric power is distributed in the set distribution mode. As a result, the distributor distributes electric power between the plurality of electrical storage devices in the set distribution mode. That is, the distributor is configured to distribute electric power between the plurality of electrical storage devices on the basis of at least one of the first rates of change (that is, the rates of change in dischargeable power) or the second rates of change (that is, the rates of change in chargeable power). 
         [0015]    According to the above aspect, the electronic control unit is able to suitably control the power supply system such that electric power is distributed in consideration of the magnitude relation between the first rates of change (that is, the rates of change in dischargeable power) between the plurality of electrical storage devices. Thus, the electronic control unit is able to, while taking the first rates of change into consideration, control the power supply system (cause the distributor to distribute electric power) such that the dischargeable power of the overall power supply system is relatively difficult to be limited. The electronic control unit is able to, while taking the first rates of change into consideration, cause the distributor to distribute electric power such that the dischargeable power of the overall power supply system is relatively difficult to be limited. That is, the electronic control unit is, able to control the power supply system such that the dischargeable power of the overall power supply system is relatively difficult to be limited in comparison with an electronic control unit according to a comparative embodiment in which the power supply system is controlled without taking the first rates of change into consideration. That is, the electronic control unit is able to control the power supply system such that the dischargeable power of the overall power supply system is suitably ensured. 
         [0016]    Specifically, for example, the dischargeable power of each electrical storage device is limited in a case where the current charge state value of each electrical storage device is relatively low. That is, when the current charge state value of each electrical storage device is relatively low, the dischargeable power of each electrical storage device is gradually limited with a discharge from the corresponding electrical storage device. On the other hand, the dischargeable power of each electrical storage device gradually recovers with a charge into the corresponding electrical storage device. As the first rate of change increases, the dischargeable power is limited at a relatively higher rate with a discharge. Similarly, as the first rate of change increases, the dischargeable power recovers at a relatively higher rate with a charge. That is, the magnitude of the first rate of change influences a mode in which the dischargeable power is limited. Therefore, by taking the magnitude relation between the first rates of change into consideration, the electronic control unit is able to control the power supply system such that the dischargeable power of the overall power supply system is relatively difficult to be limited in comparison with the electronic control unit according to the comparative embodiment in which the power supply system is controlled without taking the first rates of change into consideration. 
         [0017]    Similarly, the electronic control unit is able to suitably control the power supply system such that electric power is distributed in consideration of the magnitude relation in the second rate of change (that is, the rate of change in chargeable power) between the plurality of electrical storage devices. Thus, the electronic control unit is able to, while taking the second rates of change into consideration, control the power supply system (cause the distributor to distribute electric power) such that the chargeable power of the overall power supply system is relatively difficult to be limited. The electronic control unit is able to, while taking the second rates of change into consideration, cause the distributor to distribute electric power such that the chargeable power of the overall power supply system is relatively difficult to be limited. That is, the electronic control unit is able to control the power supply system such that the chargeable power of the overall power supply system is relatively difficult to be limited in comparison with the electronic control unit according to a comparative embodiment in which the power supply system is controlled without taking the second rates of change into consideration. That is, the electronic control unit is able to control the power supply system such that the chargeable power of the overall power supply system is suitably ensured. 
         [0018]    Specifically, for example, the chargeable power of each electrical storage device is limited when the current charge state value of each electrical storage device is relatively high. That is, when the current charge state value of each electrical storage device is relatively high, the chargeable power of each electrical storage device is gradually limited with a charge into the corresponding electrical storage device. On the other hand, the chargeable power of each electrical storage device gradually recovers with a discharge from the corresponding electrical storage device. As the second rate of change increases, the chargeable power is limited at a relatively higher rate with a charge. Similarly, as the second rate of change increases, the chargeable power recovers at a relatively higher rate with a discharge. That is, the magnitude of the second rate of change influences a mode in which the chargeable power is limited. Therefore, by taking the magnitude relation between the second rates of change into consideration, the electronic control unit is able to control the power supply system such that the chargeable power of the overall power supply system is relatively difficult to be limited in comparison with the electronic control unit according to the comparative embodiment in which the power supply system is controlled without taking the second rates of change into consideration. 
         [0019]    In the above aspect, the electronic control unit may be configured to when a current charge state value of each electrical storage device is lower than or equal to a first threshold in a discharge situation that each electrical storage device is discharged, set the distribution mode such that an allocation of electric power that is discharged from one of the plurality of electrical storage devices, which has a relatively low first rate of change, is large, as compared to the allocation of electric power that is discharged from the one of the plurality of electrical storage devices when the current charge state value of each electrical storage device is higher than the first threshold in the discharge situation. The electronic control unit may be configured to when the current charge state value of each electrical storage device is higher than or equal to a second threshold higher than the first threshold in the discharge situation, set the distribution mode such that an allocation of electric power that is discharged from one of the plurality of electrical storage devices, which has a relatively high second rate of change, is large, as compared to the allocation of electric power that is discharged from the one of the plurality of electrical storage devices when the current charge state value of each electrical storage device is lower than the second threshold in the discharge situation. 
         [0020]    According to the above aspect, when the current charge state value of each electrical storage device is lower than or equal to the first threshold (that is, the current charge state value of each electrical storage device is relatively low) in the discharge situation, the electronic control unit is able to control the power supply system such that electric power is distributed in consideration of the magnitude relation between the first rates of change (that is, the rates of change in dischargeable power). 
         [0021]    Specifically, the electronic control unit is able to control the power supply system such that an allocation of electric power that is discharged from one of the electrical storage devices, having the relatively low first rate of change, in the case where the current charge state value of each electrical storage device is lower than or equal to the first threshold in the discharge situation is larger than the allocation of electric power that is discharged from the one of the electrical storage devices in the case where the current charge state value of each electrical storage device is not lower than or equal to the first threshold in the discharge situation. That is, the electronic control unit is able to control the power supply system such that the allocation of electric power that is discharged from one of the electrical storage devices, having the relatively low rate of change, in the case where the current charge state value of each electrical storage device is lower than or equal to the first threshold in the discharge situation is larger than the allocation of electric power that is discharged from the one of the electrical storage devices in the case where the current charge state value of each electrical storage device is not lower than or equal to the first threshold in the discharge situation. 
         [0022]    From the other way around, the electronic control unit is able to control the power supply system such that the allocation of electric power that is discharged from one of the electrical storage devices, having the relatively high first rate of change, in the case where the current charge state value of each electrical storage device is lower than or equal to the first threshold in the discharge situation is smaller than the allocation of electric power that is discharged from the one of the electrical storage devices in the case where the current charge state value of each electrical storage device is not lower than or equal to the first threshold in the discharge situation. That is, the electronic control unit is able to control the power supply system such that the allocation of electric power that is discharged from one of the electrical storage devices, having the relatively high first rate of change, in the case where the current charge state value of each electrical storage device is lower than or equal to the first threshold in the discharge situation is smaller than the allocation of electric power that is discharged from the one of the electrical storage devices in the case where the current charge state value of each electrical storage device is not lower than or equal to the first threshold in the discharge situation. 
         [0023]    As described above, as the first rate of change increases, the dischargeable power is limited at a relatively higher rate with a discharge. Therefore, the electronic control unit is able to control the power supply system such that the electrical storage device of which the dischargeable power is limited at a relatively lower rate with a discharge (that is, the electrical storage device having the relatively low first rate of change) is preferentially discharged in the discharge situation. In other words, the electronic control unit is able to control the power supply system such that the electrical storage device of which the dischargeable power is limited at a relatively, higher rate with a discharge (that is, the electrical storage device having the relatively high first rate of change) is difficult to be discharged in the discharge situation. As a result, the electronic control unit is able to control the power supply system such that the dischargeable power of the overall power supply system is relatively difficult to be limited in comparison with the electronic control unit according to the comparative embodiment in which the power supply system is controlled without consideration of the first rate of change. 
         [0024]    Similarly, according to this aspect, when the current charge state value of each electrical storage device is higher than or equal to the second threshold (that is, the current charge state value of each electrical storage device is relatively high) in the discharge situation, the electronic control unit is able to suitably control the power supply system such that electric power is distributed in consideration of the magnitude relation between the second rates of change (that is, the rates of change in chargeable power). 
         [0025]    Specifically, the electronic control unit is able to control the power supply system such that the allocation of electric power that is discharged from one of the electrical storage devices, having the relatively high second rate of change, in the case where the current charge state value of each electrical storage device is higher than or equal to the second threshold in the discharge situation is larger than the allocation of electric power that is discharged from the one of the electrical storage device in the case where the current charge state value of each electrical storage device is not higher than or equal to the second threshold in the discharge situation. That is, the electronic control unit is able to control the power supply system such that the allocation of electric power that is discharged from one of the electrical storage devices, having the relatively high second rate of change, in the case where the current charge state value of each electrical storage device is higher than or equal to the second threshold in the discharge situation is larger than the allocation of electric power that is discharged from the one of the electrical storage devices in the case where the current charge state value of each electrical storage device is not higher than or equal to the second threshold in the discharge situation. 
         [0026]    From the other way around, the electronic control unit is able to control the power supply system such that the allocation of electric power that is discharged from one of the electrical storage devices, having the relatively low second rate of change, in the case where the current charge state value of each electrical storage device is higher than or equal to the second threshold in the discharge situation is smaller than the allocation of electric power that is discharged from the one of the electrical storage devices in the case where the current charge state value of each electrical storage device is not higher than or equal to the second threshold in the discharge situation. That is, the electronic control unit is able to control, the power supply system such that the allocation of electric power that is discharged from one of the electrical storage devices, having the relatively low second rate of change, in the case where the current charge state value of each electrical storage device is higher than or equal to the second threshold in the discharge situation is smaller than the allocation of electric power that is discharged from the one of the electrical storage devices in the case where the current charge state value of each electrical storage device is not higher than or equal to the second threshold in the discharge situation. 
         [0027]    As described above, as the second rate of change increases, the chargeable power recovers at a relatively higher rate with a discharge. Therefore, the electronic control unit is able to control the power supply system such that the electrical storage device of which the chargeable power recovers at a relatively higher rate with a discharge (that is, the electrical storage device having the relatively high second rate of change) is preferentially discharged in the discharge situation. In other words, the electronic control unit is able to control the power supply system such that the electrical storage device of which the chargeable power recovers at a relatively lower rate with a discharge (that is, the electrical storage device having the relatively low second rate of change) is difficult to be discharged in the discharge situation. As a result, the electronic control unit is able to control the power supply system such that the chargeable power of the overall power supply system is relatively difficult to be limited in comparison with the electronic control unit according to the comparative embodiment in which the power supply system is controlled without consideration of the second rate of change. 
         [0028]    In the above aspect, the electronic control unit may be configured to when a current charge state value of each electrical storage device is lower than or equal to a first threshold in a charge situation that each electrical storage device is being charged, set the distribution mode such that an allocation of electric power that is charged into one of the plurality of electrical storage devices, which has a relatively high first rate of change, is large, as compared to the allocation of electric power that is charged into the one of the plurality of electrical storage devices when the current charge state value of each electrical storage device is higher than the first threshold in the charge situation. The electronic control unit may be configured to when the current charge state value of each electrical storage device is higher than or equal to a second threshold higher than the first threshold in the charge situation, set the distribution mode such that an allocation of electric power that is charged into one of the plurality of electrical storage devices, which has a relatively low second rate of change, is large, as compared to the allocation of electric power that is charged into the one of the plurality of electrical storage devices when the current charge state value of each electrical storage device is lower than the second threshold in the charge situation. 
         [0029]    According to the above aspect, when the current charge state value of each electrical storage device is lower than or equal to the first threshold (that is, the current charge state value of each electrical storage device is relatively low) in the charge situation, the electronic control unit is able to control the power supply system such that electric power is distributed in consideration of the magnitude relation between the first rates of change (that is, the rates of change in dischargeable power). 
         [0030]    Specifically, the electronic control unit is able to control the power supply system such that an allocation of electric power that is charged into one of the electrical storage devices, having the relatively high first rate of change, in the case where the current charge state value of each electrical storage device is lower than or equal to the first threshold in the charge situation is larger than the allocation of electric power that is charged into the one of the electrical storage devices in the case where the current charge state value of each electrical storage device is not lower than or equal to the first threshold in the charge situation. That is, the electronic control unit is able to control the power supply system such that the allocation of electric power that is charged into one of the electrical storage devices, having the relatively high first rate of change, in the case where the current charge state value of each electrical storage device is lower than or equal to the first threshold in the charge situation is larger than the allocation of electric power that is charged into the one of the electrical storage devices in the case where the current charge state value of each electrical storage device is not lower than or equal to the first threshold in the charge situation. From the other way around, the electronic control unit is able to control the power supply system such that the allocation of electric power that is charged into one of the electrical storage devices, having the relatively low first rate of change, in the case where the current charge state value of each electrical storage device is lower than or equal to the first threshold in the charge situation is smaller than the allocation of electric power that is charged into the one of the electrical storage devices in the case where the current charge state value of each electrical storage device is not lower than or equal to the first threshold in the charge situation. That is, the electronic control unit is able to control the power supply system such that the allocation of electric power that is charged into one of the electrical storage devices, having the relatively low first rate of change, in the case where the current charge state value of each electrical storage device is lower than or equal to the first threshold in the charge situation is smaller than the allocation of electric power that is charged into the one of the electrical storage devices having in the case where the current charge state value of each electrical storage device is not lower than or equal to the first threshold in the charge situation. 
         [0031]    As described above, as the first rate of change increases, the dischargeable power recovers at a relatively higher rate with a charge. Therefore, the electronic control unit is able to control the power supply system such that the electrical storage device of which the dischargeable power recovers at a relatively higher rate with a charge (that is, the electrical storage device having the relatively high first rate of change) is preferentially charged in the charge situation. In other words, the electronic control unit is able to control the power supply system such that the electrical storage device of which the dischargeable power recovers at a relatively lower rate with a charge (that is, the electrical storage device having the relatively low first rate of change) is difficult to be charged in the charge situation. As a result, the electronic control unit is able to control the power supply system such that the dischargeable power of the overall power supply system is relatively difficult to be limited in comparison with the electronic control unit according to the comparative embodiment in which the power supply system is controlled without consideration of the first rate of change. 
         [0032]    Similarly, according to this aspect, when the current charge state value of each electrical storage device is higher than or equal to the second threshold (that is, the current charge state value of each electrical storage device is relatively high) in the charge situation, the electronic control unit is able to suitably control the power supply system such that electric power is distributed in consideration of the magnitude relation between the second rates of change (that is, the rates of change in chargeable power). 
         [0033]    Specifically, the electronic control unit is able to control the power supply system such that the allocation of electric power that is charged into one of the electrical storage devices, having the relatively low second rate of change, in the case where the current charge state value of each electrical storage device is higher than or equal to the second threshold in the charge situation is larger than the allocation of electric power that is charged into the one of the electrical storage devices in the case where the current charge state value of each electrical storage device is not higher than or equal to the second threshold in the charge situation. That is, the electronic control unit is able to control the power supply system such that the allocation of electric power that is charged into one of the electrical storage devices, having the relatively low second rate of change, in the case where the current charge state value of each electrical storage device is higher than or equal to the second threshold in the charge situation is larger than the allocation of electric power that is charged into the one of the electrical storage devices in the case where the current charge state value of each electrical storage device is not higher than or equal to the second threshold in the charge situation. 
         [0034]    From the other way around, the electronic control unit is able to control the power supply system such that the allocation of electric power that is charged into one of the electrical storage devices, having the relatively high second rate of change, in the case where the current charge state value of each electrical storage device is higher than or equal to the second threshold in the charge situation is smaller than the allocation of electric power that is charged into the one of the electrical storage devices in the case where the current charge state value of each electrical storage device is not higher than or equal to the second threshold in the charge situation. That is, the electronic control unit is able to control the power supply system such that the allocation of electric power that is charged into one of the electrical storage devices, having the relatively high second rate of change, in the case where the current charge state value of each electrical storage device is higher than or equal to the second threshold in the charge situation is smaller than the allocation of electric power that is charged into the one of the electrical storage devices in the case where the current charge state value of each electrical storage device is not higher than or equal to the second threshold in the charge situation. 
         [0035]    As described above, as the second rate of change increases, the chargeable power is limited at a relatively higher rate with a charge. Therefore, the electronic control unit is able to control the power supply system such that the electrical storage device of which the chargeable power is limited at a relatively lower rate with a charge (that is, the electrical storage device having the relatively low second rate of change) is preferentially charged in the charge situation. In other words, the electronic control unit is able to control the power supply system such that the electrical storage device of which the chargeable power is limited at a relatively higher rate with a charge (that is, the electrical storage device having the relatively high second rate of change) is difficult to be charged in the charge situation. As a result, the electronic control unit is able to control the power supply system such that the chargeable power of the overall power supply system is relatively difficult to be limited in comparison with the electronic control unit according to the comparative embodiment in which the power supply system is controlled without consideration of the second rate of change. 
         [0036]    In the above aspect, the electronic control unit may be configured to set the distribution mode such that the plurality of electrical storage devices are charged or discharged in descending order of the first rate of change, or are charged or discharged in ascending order of the first rate of change. The electronic control unit may be configured to set the distribution mode such that the plurality of electrical storages device are charged or discharged in descending order of the second rate of change, or are charged or discharged in ascending order of the second rate of change. 
         [0037]    According to the above aspect, the electronic control unit is able to suitably control the power supply system such that electric power is distributed in consideration of the magnitude relation between the first rates of change (that is, the rates of change in dischargeable power). Thus, the electronic control unit is able to, while taking the magnitude between the first rates of change into consideration, suitably control the power supply system such that the dischargeable power of the overall power supply system is suitably ensured. 
         [0038]    Similarly, the electronic control unit is able to suitably control the power supply system such that electric power is distributed in consideration of the magnitude relation between the second rates of change (that is, the rates of change in chargeable power). Thus, the electronic control unit is able to, while taking the magnitude between the second rates of change into consideration, suitably control the power supply system such that the chargeable power of the overall power supply system is suitably ensured. 
         [0039]    In the above aspect, the electronic control unit may be configured to set the distribution mode such that the plurality of electrical storage devices are discharged in ascending order of the first rate of change, when a current charge state value of each electrical storage device is lower than or equal to a first threshold in a discharge situation that each electrical storage device is being discharged. The electronic control unit may be configured to set the distribution mode such that the plurality of electrical storage devices are discharged in descending order of the second rate of change, when the current charge state value of each electrical storage device is higher than or equal to a second threshold higher than the first threshold in the discharge situation. 
         [0040]    According to the above aspect, when the current charge state value of each electrical storage device is lower than or equal to the first threshold in the discharge situation, the electronic control unit is able to control the power supply system such that the plurality of electrical storage devices are discharged in ascending order of the first rate of change. For example, the electronic control unit is able to control the power supply system such that the following discharge operation is repeated. That is, a discharge from the ath electrical storage device having the ath lowest first rate of change (where a is an integer larger than or equal to 1) completes, and then a discharge from the (a+1)th electrical storage device having the (a+1)th lowest first rate of change is started. Therefore, the electronic control unit is able to control the power supply system such that the dischargeable power of the overall power supply system is relatively difficult to be limited in comparison with the electronic control unit according to the comparative embodiment in which the power supply system is controlled without consideration of the first rate of change. 
         [0041]    Similarly, when the current charge state value of each electrical storage device is higher than or equal to the second threshold in the discharge situation, the electronic control unit is able to control the power supply system such that the plurality of electrical storage devices are discharged in descending order of the second rate of change. For example, the electronic control unit is able to control the power supply system such that the following discharge operation is repeated. That is, a discharge from the bth electrical storage device having the bth highest second rate of change (where b is an integer larger than or equal to 1) completes, and then a discharge from the (b+1)th electrical storage device having the (b+1)th highest second rate of change is started. Therefore, the electronic control unit is able to control the power supply system such that the chargeable power of the overall power supply system is relatively difficult to be limited in comparison with the electronic control unit according to the comparative embodiment in which the power supply system is controlled without consideration of the second rate of change. 
         [0042]    In the above aspect, the electronic control unit may be configured to set the distribution mode such that the plurality of electrical storage devices are charged in descending order of the first rate of change, when a current charge state value of each electrical storage device is lower than or equal to a first threshold in a charge situation that each electrical storage device is being charged. The electronic control unit may be configured to set the distribution mode such that the plurality of electrical storage devices are charged in ascending order of the second rate of change, when the current charge state value of each, electrical storage device is higher than or equal to a second threshold higher than the first threshold in the charge situation. 
         [0043]    According to the above aspect, when the current charge state value of each electrical storage device is lower than or equal to the first threshold in the charge situation, the electronic control unit is able to control the power supply system such that the plurality of electrical storage devices are charged in descending order of the first rate of change. For example, the electronic control unit is able to control the power supply system such that the following charge operation is repeated. That is, a charge into the cth electrical storage device having the cth highest first rate of change (where c is an integer larger than or equal to 1) completes, and then a charge into the (c+1)th electrical storage device having the (c+1)th highest first rate of change is started. Therefore, the electronic control unit is able to control the power supply system such that the dischargeable power of the overall power supply system is relatively difficult to be limited in comparison with the electronic control unit according to the comparative embodiment in which the power supply system is controlled without consideration of the first rate of change. 
         [0044]    Similarly, when the current charge state value of each electrical storage device is higher than or equal to the second threshold in the charge situation, the electronic control unit is able to control the power supply system such that the plurality of electrical storage devices are charged in ascending order of the second rate of change. For example, the electronic control unit is able to control the power supply system such that the following charge operation is repeated. That is, a charge into the dth electrical storage device having the dth lowest second rate of change (where d is an integer larger than or equal to 1) completes, and then a charge into the (d+1)th electrical storage device having the (d+1)th lowest second rate of change is started. Therefore, the electronic control unit is able to control the power supply system such that the chargeable power of the overall power supply system is relatively difficult to be limited in comparison with the electronic control unit according to the comparative embodiment in which the power supply system is controlled without consideration of the second rate of change. 
         [0045]    When the current charge state value of each electrical storage device is higher than the first threshold and is lower than the second threshold (where the second threshold is higher than the first threshold), the electronic control unit may set the distribution mode such that the charge state values of the plurality of electrical storage devices respectively reach corresponding target values at the same time. In this case, the electronic control unit may set the distribution mode such that electric power is distributed at the ratio of available discharge energies of the plurality of electrical storage devices (where each available discharge energy is a difference between the current charge state value of the corresponding electrical storage device and the charge state value of the corresponding electrical storage device at the timing at which the dischargeable power of the corresponding electrical storage device begins to be limited) in the discharge situation in which each electrical storage device is being discharged. The electronic control unit may set the distribution mode such that electric power is distributed at the ratio of available charge energies of the plurality of electrical storage devices (where each available charge energy is a difference between the current charge state value of the corresponding electrical storage device and the charge state value of the corresponding electrical storage device at the timing at which the chargeable power of the corresponding electrical storage device begins to be limited) in the charge situation in which each electrical storage device is being charged. 
         [0046]    Such operations and other advantages of the invention are further become apparent from embodiments that will be described below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0047]    Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
           [0048]      FIG. 1  is a block diagram that shows an example of the configuration of a vehicle according to an embodiment; 
           [0049]      FIG. 2A  is a graph that shows the correlation between both Wout 1  and Win 1  and SOC 1 ; 
           [0050]      FIG. 2B  is a graph that shows the correlation between both Wout 2  and Win 2  and SOC 2 ; 
           [0051]      FIG. 3  is a flowchart that shows the general flow of operations of controlling a vehicle (substantially, operations of controlling a power supply system, and operations of distributing electric power between a first power supply and a second power supply) according to the embodiment; 
           [0052]      FIG. 4  is a flowchart that shows the flow of first control operations that are executed when none of Wout 1 , Wout 2 , Win 1  and Win 2  is limited; 
           [0053]      FIG. 5  is a flowchart that shows the flow of second control operations that are executed when the vehicle is carrying out powering (that is, the first power supply and the second power supply are being discharged) in a situation that Wout 1  and Wout 2  are limited; 
           [0054]      FIG. 6  is a flowchart that shows the flow of third control operations that are executed when the vehicle is regenerating electric power (that is, the first power supply and the second power supply are being charged) in a situation that Wout 1  and Wout 2  are limited; 
           [0055]      FIG. 7  is a flowchart that shows the flow of fourth control operations that are executed when the vehicle is carrying out powering (that is, the first power supply and the second power supply are being discharged) in a situation that Win 1  and Win 2  are limited; 
           [0056]      FIG. 8  is a flowchart that shows the flow of fifth control operations that are executed when the vehicle is regenerating electric power (that is, the first power supply and the second power supply are being charged) in a situation that Win 1  and Win 2  are limited; 
           [0057]      FIG. 9A  to  FIG. 9C  are graphs that show a mode of change in SOC 1  and SOC 2  and a mode of change in total Wout of the overall power supply system when the second control operations are executed; 
           [0058]      FIG. 10A  to  FIG. 10C  are graphs that show a mode of change in SOC 1  and SOC 2  and a mode of change in total Wout of the overall power supply system when the third control operations are executed; 
           [0059]      FIG. 11A  to  FIG. 11C  are graphs that show a mode of change in SOC 1  and SOC 2  and a mode of change in total Win of the overall power supply system when the fourth control operations are executed; and 
           [0060]      FIG. 12A  to  FIG. 12C  are graphs that show a mode of change in SOC 1  and SOC 2  and a mode of change in total Win of the overall power supply system when the fifth control operations are executed. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0061]    Hereinafter, an embodiment of a case where the power supply system according to the invention is applied to a vehicle  1  including a motor generator  10  will be described as an example of a mode for carrying out the invention with reference to the accompanying drawings. The power supply system according to the invention may be applied to not only the vehicle  1  including the motor generator  10  but also any device that utilizes electric power that is supplied from the power supply system. 
         [0062]    The configuration of the vehicle  1  according to the present embodiment will be described with reference to  FIG. 1 .  FIG. 1  is a block diagram that shows an example of the configuration of the vehicle  1  according to the present embodiment. 
         [0063]    As shown in  FIG. 1 , the vehicle  1  includes the motor generator  10 , an axle  21 , wheels  22 , a power supply system  30 , and an electronic control unit (ECU)  40 . The ECU  40  is one specific example of a “power supply control apparatus (that is, including setting means and control means)”. 
         [0064]    During powering, the motor generator  10  mainly functions as an electric motor that supplies power (that is, power that is required to propel the vehicle  1 ) to the axle  21  by being driven with electric power that is output from the power supply system  30 . During regeneration, the motor generator  10  mainly functions as a generator for charging a first power supply  31  and a second power supply  32  that are provided in the power supply system  30 . 
         [0065]    The axle  21  is a transmission shaft for transmitting power to the wheels  22 . The power is output from the motor generator  10 . 
         [0066]    The wheels  22  transmit power to a road surface. The power is transmitted via the axle  21 .  FIG. 1  shows an example in which the vehicle  1  includes the wheels  22  one by one at each of the right and left sides. Actually, the vehicle  1  preferably includes the wheels  22  one by one at each of the front and rear right and left sides (that is, the four wheel  22  in total). 
         [0067]      FIG. 1  illustrates the vehicle  1  including the single motor generator  10 . The vehicle  1  may include two or more motor generators  10 . In addition, the vehicle  1  may further include an engine in addition to the motor generator  10 . That is, the vehicle  1  according to the present embodiment may be an electric vehicle or a hybrid vehicle. 
         [0068]    During powering, the power supply system  30  outputs, to the motor generator  10 , electric power that is required for the motor generator  10  to function as an electric motor. During regeneration, electric power that is generated by the motor generator  10  that functions as a generator is input to the power supply system  30  from the motor generator  10 . 
         [0069]    The power supply system  30  includes the first power supply  31 , the second power supply  32 , an electric power converter  33 , a smoothing capacitor  34  and an inverter  35 . The first power supply  31  is one specific example of “electrical storage means (electrical storage device)”. The second power supply  32  is one specific example of the “electrical storage means (electrical storage device)”. The electric power converter  33  is one specific example of “distribution means (distributor)”. 
         [0070]    Each of the first power supply  31  and the second power supply  32  is a power supply that is able to receive electric power (that is, to be charged) or output electric power (that is, to be discharged). At least one of the first power supply  31  or the second power supply  32  may be a storage battery that is able to be charged or discharged by utilizing, for example, an electrochemical reaction (that is, a reaction to convert chemical energy to electric energy). Examples of such a storage battery, for example, include a lead acid battery, a lithium ion battery, a nickel-metal hydride battery, a fuel cell, and the like. Alternatively, at least one of the first power supply  31  or the second power supply  32  may be a capacitor that is able to be charged or discharged by utilizing a physical action or chemical action to accumulate electric charge (that is, electric energy). Examples of such a capacitor, for example, include an electric double layer capacitor, and the like. 
         [0071]    Each of Wout indicating an allowable value of electric power that is dischargeable from the first power supply  31  and Win indicating an allowable value of electric power that is chargeable into the first power supply  31  can fluctuate depending on the state of charge (SOC) of the first power supply  31 . Similarly, each of Wout indicating an allowable value of electric power that is dischargeable from the second power supply  32  and Win indicating an allowable value of electric power that is chargeable into the second power supply  32  can also fluctuate depending on the SOC of the second power supply  32 . 
         [0072]    Hereinafter, for the sake of convenience of description, Wout of the first power supply.  31  is referred to as “Wout 1 ”. Win of the first power supply  31  is referred to as “Win 1 ”. The SOC of the first power supply  31  is referred to as “SOC 1 ”. Wout of the second power supply  32  is referred to as “Wout 2 ”. Win of the second power supply  32  is referred to as “Win 2 ”. The SOC of the second power supply  32  is referred to as “SOC 2 ”. In this case, each of Wout 1  and Wout 2  is one specific example of “dischargeable power”. Each of Win 1  and Win 2  is one specific example of “chargeable power”. The “SOC” is one specific example of “charge state value”. 
         [0073]    The correlation between both Wout 1  and Win 1  and SOC 1  will be described with reference to  FIG. 2A . The correlation between both Wout 2  and Win 2  and SOC 2  will be described with reference to  FIG. 2B .  FIG. 2A  is a graph that shows the correlation between both Wout 1  and Win 1  and SOC 1 .  FIG. 2B  is a graph that shows the correlation between both Wout 2  and Win 2  and SOC 2 . 
         [0074]    Hereinafter, in description of Wout 1  and Win 1 , for the sake of convenience, an electric power that is discharged from the first power supply  31  is defined as a positive electric power. An electric power that is charged into the first power supply  31  is defined as a negative electric power. Thus, typically, Wout 1  is provided by a positive value. On the other hand, Win 1  is provided by a negative value. This also applies to Wout 2  and Win 2 . 
         [0075]    As shown in  FIG. 2A , Wout 1  is limited when SOC 1  becomes lower than a lower limit value TL 1 . Specifically, in a region in which SOC 1  is lower than the lower limit value TL 1 , Wout 1  is more limited (decreases in the example shown in  FIG. 2A ) as SOC 1  decreases. Wout 1  becomes zero when SOC 1  becomes lower than a minimum lower limit value LL 1 . That is, the minimum lower limit value LL 1  indicates a discharge limit of the first power supply  31 . 
         [0076]    Win 1  is limited when SOC 1  becomes higher than an upper limit value TH 1 . Specifically, in a region in which SOC 1  is higher than the upper limit value TH 1 , Win 1  is more limited (increases in the example shown in  FIG. 2A ) as SOC 1  increases. Win 1  becomes zero when SOC 1  becomes higher than a maximum upper limit value HL 1 . That is, the maximum upper limit value HL 1  indicates a charge limit of the first power supply  31 . 
         [0077]    As shown in  FIG. 2B , Wout 2  and Win 2  change in modes similar to those of Wout 1  and Win 1 . However, for the second power supply  32 , the minimum lower limit value LL 1 , lower limit value TL 1 , upper limit value TH 1  and maximum upper limit value HL 1  of the first power supply  31  are respectively replaced with a minimum lower limit value LL 2 , a lower limit value TL 2 , an upper limit value TH 2  and a maximum upper limit value HL 2 . In the present embodiment, it is assumed that the minimum lower limit value LL 1  is the same as the minimum lower limit value LL 2  and the maximum upper limit value HL 1  is the same as the maximum upper limit value HL 2 . In addition, in the present embodiment, it is assumed that the lower limit value TL 1  is lower than the lower limit value TL 2  and the upper limit value TH 1  is lower than the upper limit value TH 2 . However, the minimum lower limit value LL 1  may be lower than the minimum lower limit value LL 2  or may be higher than the minimum lower limit value LL 2 . The maximum upper limit value HL 1  may be lower than the maximum upper limit value HL 2  or may be higher than the maximum upper limit value HL 2 . The lower limit value. TL 1  may be higher than the lower limit value TL 2  or may be the same as the lower limit value TL 2 . The upper limit value TH 1  may be higher than the upper limit value TH 2  or may be the same as the upper limit value TH 2 . 
         [0078]    Each of the lower limit value TL 1  and the lower limit value TL 2  is one specific example of “first threshold”. The upper limit value TH 1  is one specific example of “second threshold”. 
         [0079]    Referring back to  FIG. 1 , the electric power converter  33 , under control of the ECU  40 , converts electric power that is output from the first power supply  31  and electric power that is output from the second power supply  32  on the basis of required electric power that is required by the power supply system  30 . The required electric power that is required by the power supply system  30  is typically, an electric power that should be output from the power supply system  30  to the motor generator  10 . The electric power converter  33  outputs the converted electric powers to the inverter  35 . In addition, the electric power converter  33 , under control of the ECU  40 , converts electric power that is input from the inverter  35  on the basis of required electric power that is required by the power supply system  30 . The electric power that is input from the inverter  35  is, in other words, electric power generated as a result of regeneration of the motor generator  10 . The required electric power that is required by the power supply system  30  is, typically, electric power that should be input to the power supply system  30 , and is substantially electric power that should be input to the first power supply  31  and the second power supply  32 . The electric power converter  33  outputs the converted electric power to at least one of the first power supply  31  or the second power supply  32 . As a result of such electric power conversion, the electric power converter  33  is substantially able to distribute electric power between both the first power supply  31  and the second power supply  32  and the inverter  35  and distribute electric power between the first power supply  31  and the second power supply  32 . 
         [0080]    In order to carry out such conversion of electric power, the electric power converter  33  includes a first converter  331  and a second converter  332 . The first converter  331  converts electric power (converts voltage) between the first power supply  31  and the inverter  35 . The second converter  332  converts electric power (converts voltage) between the second power supply  32  and the inverter  35 . Each of the first converter  331  and the second converter  332  converts electric power under control of the ECU  40 . 
         [0081]    During powering, the smoothing capacitor  34  smoothes electric power that is supplied from the electric power converter  33  to the inverter  35 . Fluctuations in electric power that is supplied from the electric power converter  33  to the inverter  35  are substantially fluctuations in voltage in a power supply line between the electric power converter  33  and the inverter  35 . Similarly, during regeneration, the smoothing capacitor  34  smoothes fluctuations in electric power that is supplied from the inverter  35  to the electric power converter  33 . Fluctuations in electric power that is supplied from the inverter  35  to the electric power converter  33  are substantially fluctuations in voltage in the power supply line between the electric power converter  33  and the inverter  35 . 
         [0082]    During powering, the inverter  35  converts electric power (direct-current power), which is output from the electric power converter  33 , to alternating-current power. After that, the inverter  35  supplies electric power, converted to alternating-current power, to the motor generator  10 . In addition, during regeneration, the inverter  35  converts electric power (alternating-current power), generated by the motor generator  10 , to direct-current power. After that, the inverter  35  supplies electric power, converted to direct-current power, to the electric power converter  33 . 
         [0083]    The ECU  40  is an electronic control unit configured to be able to control the overall operation of the vehicle  1 . The ECU  40  includes a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and the like. 
         [0084]    Particularly, the ECU  40  controls a distribution of electric power in the above-described electric power converter  33 . More specifically, when the power supply system  30  is outputting electric power to the motor generator  10 , the ECU  40  sets a discharge distribution ratio. The discharge distribution ratio indicates a distribution between electric power that is discharged from the first power supply  31  and electric power that is discharged from the second power supply  32 . The fact that the power supply system  30  is outputting electric power to the motor generator  10  is, in other words, the fact that the power supply system  30  is being discharged. After that, the ECU  40  controls the electric power converter  33  such that electric power is distributed at the set discharge distribution ratio. In addition, when the motor generator  10  is outputting electric power to the power supply system  30 , the ECU  40  sets a charge distribution ratio. The charge distribution ratio indicates a distribution between electric power that is charged into the first power supply  31  and electric power that is charged into the second power supply  32 . The fact that the motor generator  10  is outputting electric power to the power supply system  30  is, in other words, the fact that the power supply system  30  is being charged. After that, the ECU  40  controls the electric power converter  33  such that electric power is distributed at the set charge distribution ratio. 
         [0085]    Hereinafter, the operations of distributing electric power between the first power supply  31  and the second power supply  32  under control of the ECU  40  will be described in detail. 
         [0086]    In the above description, the power supply system  30  includes the two power supplies (that is, the first power supply  31  and the second power supply  32 ). However, the power supply system  30  may include three or more power supplies. 
         [0087]    The operations of controlling the vehicle  1  according to the present embodiment will be described with reference to  FIG. 3  to  FIG. 8 . The operations of controlling the vehicle  1  according to the present embodiment are substantially the operations of controlling the power supply system  30 , and mean the operations of distributing electric power between the first power supply  31  and the second power supply  32 . 
         [0088]    Initially, the general flow of the operations of controlling the vehicle  1 , according to the present embodiment will be described with reference to  FIG. 3 .  FIG. 3  is a flowchart that shows the general flow of the operations of controlling the vehicle  1  according to the present embodiment. 
         [0089]    As shown in  FIG. 3 , the ECU  40  determines whether current SOC 1  is higher than or equal to the upper limit value TH 1  and current SOC 2  is higher than or equal to the upper limit value TH 2  (step S 01 ). That is, the ECU  40  determines whether Win 1  is limited and Win 2  is limited. In addition, the ECU  40  determines whether current SOC 1  is lower than or equal to the lower limit value TL 1  and current SOC 2  is lower than or equal to the lower limit value TL 2  (step S 02 ). That is, the ECU  40  determines whether Wout 1  is limited and Wout 2  is limited. 
         [0090]    In order to carry out determinations of step S 01  and step S 02 , the ECU  40  may acquire a current input to or output from the first power supply  31  and a voltage of the first power supply  31 , and may calculate SOC 1  on the basis of the acquired current and the acquired voltage. Similarly, the ECU  40  may acquire a current that is input to or output from the second power supply  32  and a voltage of the second power supply  32 , and may calculate SOC 2  on the basis of the acquired current and the acquired voltage. 
         [0091]    As a result of the determinations of step S 01  and step S 02 , when it is determined that current SOC 1  is not higher than or equal to the upper limit value TH 1  or current SOC 2  is not higher than or equal to the upper limit value TH 2  and it is determined that current SOC 1  is not lower than or equal to the lower limit value TL 1  or current SOC 2  is not lower than or equal to the lower limit value TL 2  (No in step S 01  and No in step S 02 ), it is estimated that none of Wout 1 , Wout 2 , Win 1  and Win 2  is limited. In this case, the ECU  40  executes first control operations that are executed when none of Wout 1 , Wout 2 , Win 1  and Win 2  is limited. Thus, the ECU  40  executes the operations of distributing electric power between the first power supply  31  and the second power supply  32  (step S 1 ). The first control operations will be described in detail later with reference to  FIG. 4 . 
         [0092]    On the other hand, as a result of the determinations of step S 01  and step S 02 , when it is determined that current SOC 1  is lower than or equal to the lower limit value TL 1  and current SOC 2  is lower than or equal to the lower limit value TL 2  (No in step S 01  and Yes in step S 02 ), the ECU  40  subsequently determines whether the vehicle  1  is being powered (step S 03 ). For example, when a vehicle required output that is required of the vehicle  1  is a positive value, the ECU  40  may determine that the vehicle  1  is being powered. On the other hand, when the vehicle required output that is required of the vehicle  1  is not a positive value, the ECU  40  may determine that the vehicle  1  is not being powered (that is, the vehicle  1  is regenerating electric power). 
         [0093]    As a result of the determination of step S 03 , when it is determined that the vehicle  1  is being powered (Yes in step S 03 ), it is estimated that the vehicle  1  is being powered in a situation that Wout 1  and Wout 2  are limited. That is, it is estimated that the power supply system  30  is outputting electric power to the motor generator  10  in a situation that Wout 1 , and Wout 2  are limited (that is, the first power supply  31  and the second power supply  32  are being discharged). In this case, the ECU  40  executes the operations of distributing electric power between the first power supply  31  and the second power supply  32  by executing second control operations that are executed when the vehicle  1  is being powered in a situation that Wout 1  and Wout 2  are limited (step S 2 ). The second control operations will be described in detail later with reference to  FIG. 5 . 
         [0094]    On the other hand, as a result of the determination of step S 03 , when it is determined that the vehicle  1  is not being powered (No in step S 03 ), it is estimated that the vehicle  1  is regenerating electric power in a situation that Wout 1  and Wout 2  are limited. That is, it is estimated that the motor generator  10  is outputting electric power to the power supply system  30  (that is, the first power supply  31  and the second power supply  32  are being charged) in a situation that Wout 1  and Wout 2  are limited. In this case, the ECU  40  executes the operations of distributing electric power between the first power supply  31  and the second power supply  32  by executing third control operations that are executed when the vehicle  1  is regenerating electric power in a situation that Wout 1  and Wout 2  are limited (step S 3 ). The third control operations will be described in detail later with reference to  FIG. 6 . 
         [0095]    On the other hand, as a result of the determinations of step S 01  and step S 02 , when it is determined that current SOC 1  is higher than or equal to the upper limit value TH 1  and the current SOC 2  is higher than or equal to the upper limit value TH 2  (Yes in step S 01 ), the ECU  40  subsequently determines whether the vehicle  1  is being powered (step S 04 ). 
         [0096]    As a result of the determination of step S 04 , when it is determined that the vehicle  1  is being powered (Yes in step S 04 ), it is estimated that the vehicle  1  is being powered in a situation that Win 1  and Win 2  are limited. That is, it is estimated that the power supply system  30  is outputting electric power to the motor generator  10  (that is, the first power supply  31  and the second power supply  32  are being discharged) in a situation that Win 1  and Win 2  are limited. In this case, the ECU  40  executes the operations of distributing electric power between the first power supply  31  and the second power supply  32  by executing fourth control operations that are executed when the vehicle  1  is being powered in a situation that Win 1  and Win 2  are limited (step S 4 ). The fourth control operations will be described in detail later with reference to  FIG. 7 . 
         [0097]    On the other hand, as a result of the determination of step S 04 , when it is determined that the vehicle  1  is not being powered (No in step S 04 ), it is estimated that the vehicle  1  is regenerating electric power in a situation that Win 1  and Win 2  are limited. That is, it is estimated that the motor generator  10  is outputting electric power to the power supply system  30  (that is, the first power supply  31  and the second power supply  32  are being charged) in a situation that Win 1  and Win 2  are limited. In this case, the ECU  40  executes the operations of distributing electric power between the first power supply  31  and the second power supply  32  by executing fifth control operations that are executed when the vehicle  1  is regenerating electric power in a situation that Win 1  and Win 2  are limited (step S 5 ). The fifth control operations will be described in detail later with reference to  FIG. 8 . 
         [0098]    In the example shown in  FIG. 3 , the ECU  40  executes all the second control operations to fifth control operations. However, the ECU  40  may execute at least part of the second control operations to the fifth control operations, while may not execute at least the other part of the second control operations to the fifth control operations. When the ECU  40  does not execute at least the other part of the second control operations to the fifth control operations, the ECU  40  may execute the first control operations instead of the at least the other part of the second control operations to the fifth control operations. 
         [0099]    Subsequently, the flow of the first control operations that are executed, when none of Wout 1 , Wout 2 , Win 1  and Win 2  is limited will be described with reference to  FIG. 4 .  FIG. 4  is a flowchart that shows the flow of the first control operations that are executed when none of Wout 1 , Wout 2 , Win 1  and Win 2  is limited. 
         [0100]    As shown in  FIG. 4 , the ECU  40  determines whether the vehicle  1  is being powered (step S 11 ). 
         [0101]    As a result of the determination of step S 11 , when it is determined that the vehicle  1  is, being powered (Yes in step S 11 ), the ECU  40  calculates an available discharge energy R 1  of the first power supply  31  and an available discharge energy R 2  of the second power supply  32  (step S 12 ). The available discharge energy R 1  corresponds to the amount of electric power that is dischargeable from the first power supply  31  until SOC 1  reaches the lower limit value TL 1 . That is, the available discharge energy R 1  is calculated from, the mathematical expression expressed by R 1 =Storage capacity of the first power supply  31 ×(Current SOC 1 −Lower limit value TL 1 ). Similarly, the available discharge energy R 2  corresponds to the amount of electric power that is dischargeable from the second power supply  32  until SOC 2  reaches the lower limit value TL 2 . That is, the available discharge energy R 2  is calculated from the mathematical expression expressed by R 2 =Storage capacity of the second power supply  32 ×(Current SOC 2 −Lower limit value TL 2 ). 
         [0102]    After that, the ECU  40  sets the discharge distribution ratio to R 1 :R 2  (step S 13 ). That is, the ECU  40  sets the discharge distribution ratio such that (electric power that is discharged from the first power supply  31 ):(electric power that is discharged from the second power supply  32 ) becomes R 1 :R 2 . 
         [0103]    After that, the ECU  40  controls the electric power converter  33  such that electric power is distributed at the discharge distribution ratio set in step S 13  (step S 14 ). In this case, the first power supply  31  and the second power supply  32  are discharged such that SOC 1  and SOC 2  respectively reach the lower limit value TL 1  and the lower limit value TL 2  at the same time. 
         [0104]    On the other hand, as a result of the determination of step S 11 , when it is determined that the vehicle  1  is not being powered (No in step S 11 ), the ECU  40  calculates an available charge energy C 1  of the first power supply  31  and an available charge energy C 2  of the second power supply  32  (step S 15 ). The available charge energy C 1  corresponds to the amount of electric power that is chargeable into the first power supply  31  until SOC 1  reaches the upper limit value TH 1 . That is, the available charge energy C 1  is calculated from the mathematical expression expressed by C 1 =Storage capacity of the first power supply  31 ×(Upper limit value TH 1 −Current SOC 2 ). Similarly, the available charge energy C 2  corresponds to the amount of electric power that is chargeable from the second power supply  32  until SOC 2  reaches the upper limit value TH 2 . That is, the available charge energy C 2  is calculated from the mathematical expression expressed by C 2 =Storage capacity of the second power supply  32 ×(Upper limit value TH 2 −Current SOC 2 ). 
         [0105]    After that, the ECU  40  sets the charge distribution ratio to C 1 :C 2  (step S 16 ). That is, the ECU  40  sets the charge distribution ratio such that (electric power that is charged into the first power supply  31 ):(electric power that is charged into the second power supply  32 ) becomes C 1 :C 2 . 
         [0106]    After that, the ECU  40  controls the electric power converter  33  such that electric power is distributed at the charge distribution ratio set in step S 16  (step S 14 ). In this case, the first power supply  31  and the second power supply  32  are charged such that SOC 1  and SOC 2  respectively reach the upper limit value TH 1  and the upper limit value TH 2  at the same time. 
         [0107]    In the above description, in calculating the available discharge energies R 1 , R 2 , the lower limit value TL 1  and the lower limit value TL 2  are respectively used. However, in calculating the available discharge energies R 1 , R 2 , a first target value different from the lower limit value TL 1  and a second target value different from the lower limit value TL 2  may be respectively used. When the available discharge energies R 1 , R 2  are calculated in this way, the first power supply  31  and the second power supply  32  are discharged such that SOC 1  and SOC 2  respectively reach the first target value and the second target value at the same time. 
         [0108]    Similarly, in the above description, in calculating the available charge energies C 1 , C 2 , the upper limit value TH 1  and the upper limit value TH 2  are respectively used. However, in calculating the available charge energies C 1 , C 2 , a third target value different from the upper limit value TH 1  and a fourth target value different from the upper limit value TH 2  may be respectively used. When the available charge energies C 1 , C 2  are calculated in this way, the first power supply  31  and the second power supply  32  are charged such that SOC 1  and SOC 2  respectively reach the third target value and the fourth target value at the same time. 
         [0109]    Subsequently, the flow of the second control operations that are executed when the vehicle  1  is being powered (that is, the first power supply  31  and the second power supply  32  are being discharged) in a situation that Wout 1  and Wout 2  are limited will be described with reference to  FIG. 5 .  FIG. 5  is a flowchart that shows the flow of the second control operations that are executed when the vehicle  1  is being powered in a situation that Wout 1  and Wout 2  are limited. 
         [0110]    As shown in  FIG. 5 , the ECU  40  determines whether the slope of Wout 1  is smaller than or equal to the slope of Wout 2  (step S 21 ). 
         [0111]    The slope of Wout 1  means the slope of the graph that represents the correlation between Wout 1  and SOC 1 , shown in  FIG. 2A . Thus, the slope of Wout 1  means the rate of change in Wout 1  to SOC 1 . That is, the slope of Wout 1  means ΔWout 1 /ΔSOC 1 . In addition, the “slope of Wout 1 ” is the slope of Wout 1  in the region in which SOC 1  is lower than or equal to the lower limit value TL 1 . That is, the “slope of Wout 1 ” is the slope of Wout 1  in the region in which Wout 1  is limited. This also applies to the slope of Wout 2 . 
         [0112]    The correlation between Wout 1  and SOC 1  is a characteristic unique to each individual power supply. Thus, the ECU  40  preferably stores the correlation between Wout 1  and SOC 1  (or information that directly or indirectly indicates the slope of Wout 1 ). This also applies to Wout 2 . 
         [0113]    As a result of the determination of step S 21 , when it is determined that the slope of Wout 1  is smaller than or equal to the slope of Wout 2  (Yes in step S 21 ), the ECU  40  sets the discharge distribution ratio to 100% (first power supply  31 ):0% (second power supply  32 ) (step S 221 ). That is, the ECU  40  sets the discharge distribution ratio such that (electric power that is discharged from the first power supply  31 ):(electric power that is discharged from the second power supply  32 ) becomes 100%:0%. In other words, the ECU  40  sets the discharge distribution ratio such that the first power supply  31  having a relatively low (that is, minimum) Wout is discharged and the power supply other than the first power supply  31  (that is, the second power supply  32 ) is not discharged. 
         [0114]    After that, the ECU  40  controls the electric power converter  33  such that electric power is distributed at the discharge distribution ratio set in step S 221  (step S 222 ). In this case, the first power supply  31  is discharged, while the second power supply  32  is not discharged. Such a distribution of electric power at the discharge distribution ratio set in step S 221  is continued (No in step S 223 ) until SOC 1  becomes lower than or equal to the minimum lower limit value LL 1 . 
         [0115]    After SOC 1  becomes lower than or equal to the minimum lower limit value LL 1  (Yes in step S 223 ), the ECU  40  sets the discharge distribution ratio to 0% (first power supply  31 ):100% (second power supply  32 ) (step S 224 ). That is, the ECU  40  sets the discharge distribution ratio such that (electric power that is discharged from the first power supply  31 ):(electric power that is discharged from the second power supply  32 ) becomes 0%:100%. In other words, the ECU  40  sets the discharge distribution ratio such that the second power supply  32  having a relatively high (that is, the second lowest) Wout is discharged and the power supply other than the second power supply  32  (that is, the first power supply  31 ) is not discharged. 
         [0116]    After that, the ECU  40  controls the electric power converter  33  such that electric power is distributed at the discharge distribution ratio set in step S 224  (step S 225 ). In this case, the first power supply  31  is not discharged, while the second power supply  32  is discharged. Such a distribution of electric power at the discharge distribution ratio set in step S 224  is continued (No in step S 226 ), until SOC 2  becomes lower than or equal to the minimum lower limit value LL 2 . 
         [0117]    On the other hand, as a result of the determination of step S 21 , when it is determined that the slope of Wout 1  is not smaller than or equal to the slope of Wout 2  (No in step S 21 ), the ECU  40  sets the discharge distribution ratio to 0% (first power supply  31 ):100% (second power supply  32 ) (step S 231 ). That is, the ECU  40  sets the discharge distribution ratio such that the second power supply  32  having a relatively low (that is, the lowest) Wout is discharged and the other power supply other than the second power supply  32  (that is, the first power supply  31 ) is not discharged. 
         [0118]    After that, the ECU  40  controls the electric power converter  33  such that electric power is distributed at the discharge distribution ratio set in step S 231  (step S 232 ). In this case, the first power supply  31  is not discharged, while the second power supply  32  is discharged. Such a distribution of electric power at the discharge distribution ratio set in step S 231  is continued (No in step S 233 ) until SOC 2  becomes lower than or equal to the minimum lower limit value LL 2 . 
         [0119]    After SOC 2  becomes lower than or equal to the minimum lower limit value LL 2  (Yes in step S 233 ), the ECU  40  sets the discharge distribution ratio to 100% (first power supply  31 ):0% (second power supply  32 ) (step S 234 ). That is, the ECU  40  sets the discharge distribution ratio such that the first power supply  31  having a relatively high (that is, the second lowest) Wout is discharged and the power supply other than the first power supply  31  (that is, the second power supply  32 ) is not discharged. 
         [0120]    After that, the ECU  40  controls the electric power converter  33  such that electric power is distributed at the discharge distribution ratio set in step S 234  (step S 235 ). In this case, the first power supply  31  is discharged, while the second power supply  32  is not discharged. Such a distribution of electric power at the discharge distribution ratio set in step S 234  is continued (No in step S 236 ) until SOC 1  becomes lower than or equal to the minimum lower limit value LL 1 . 
         [0121]    In the above-described second control operations, when the slope of Wout 1  is smaller than or equal to the slope of Wout 2 , the electric power converter  33  is controlled such that the first power supply  31  is discharged and then the second power supply  32  is discharged. On the other hand, when the slope of Wout 1  is not smaller than or equal to the slope of Wout 2 , the electric power converter  33  is controlled such that the second power supply  32  is discharged and then the first power supply  31  is discharged. Therefore, the second control operations are considered as operations of controlling the electric power converter  33  such that the first power supply  31  and the second power supply  32  are discharged in ascending order of the slope of Wout. That is, in the present embodiment, when the first power supply  31  and the second, power supply  32  are discharged in a situation that Wout 1  and Wout 2  are limited, the electric power converter  33  is controlled such that the power supplies are discharged in ascending order of the slope of Wout. 
         [0122]    However, the electric power converter  33  is controlled such that the power supplies are discharged in ascending order of the slope of Wout in the case where Wout is defined as a positive value. That is, the electric power converter  33  is controlled such that the power supplies are discharged in ascending order of the slope of Wout in the case where electric power that is discharged from each power supply is defined as positive electric power and electric power that is charged into each power supply is defined as negative electric power. If Wout is defined as a negative value, the second control operations are preferably operations of controlling the electric power converter  33  such that the power supplies are discharged in descending order of the slope of Wout. That is, when electric power that is discharged from each power supply is defined as negative electric power and electric power that is charged into each power supply is defined as positive electric power, the second control operations are preferably operations of controlling the electric power converter  33  such that the power supplies are discharged in descending order of the slope of Wout. That is, when Wout is defined as a negative value, the determination in step S 21  of  FIG. 5  is “determination as to whether the slope of Wout 1  is “larger than or equal to” the slope of Wout 2 ”. In this case, when the slope of Wout 1  is larger than or equal to the slope of Wout 2 , the operations of step S 221  to step S 226  are executed. On the other hand, when the slope of Wout 1  is not larger than or equal to the slope of Wout 2 , the operations of step S 231  to step S 236  are executed. In order to execute the same determination operation irrespective of such definition of the sign of electric power, “the absolute value (that is, a value irrespective of the sign) of the slope of Wout” is preferably used as “the slope of Wout”. 
         [0123]    Next, the flow of the third control operations that are executed when the vehicle  1  is regenerating electric power (that is, the first power supply  31  and the second power supply  32  are being charged) in a situation that Wout 1  and Wout 2  are limited will be described with reference to  FIG. 6 .  FIG. 6  is a flowchart that shows the flow of the third control operations that are executed when the vehicle  1  is regenerating electric power in a situation that Wout 1  and Wout 2  are limited. 
         [0124]    As shown in  FIG. 6 , the ECU  40  determines whether the slope of Wout 1  is larger than or equal to the slope of Wout 2  (step S 31 ). 
         [0125]    As a result of the determination of step S 31 , when it is determined that the slope of Wout 1  is larger than or equal to the slope of Wout 2  (Yes in step S 31 ), the ECU  40  sets the charge distribution ratio to 100% (first power supply  31 ):0% (second power supply  32 ) (step S 321 ). That is, the ECU  40  sets the charge distribution ratio such that (electric power that is charged into the first power supply  31 ):(electric power that is charged into the second power supply  32 ) becomes 100%:0%. In other words, the ECU  40  sets the charge distribution ratio such that the first power supply  31  having a relatively high (that is, the maximum) Wout is charged and the power supply other than the first power supply  31  (that is, the second power supply  32 ) is not charged. 
         [0126]    After that, the ECU  40  controls the electric power converter  33  such that electric power is distributed at the charge distribution ratio set in step S 321  (step S 322 ). In this case, the first power supply  31  is charged, while the second power supply  32  is not charged. Such a distribution of electric power at the charge distribution ratio set in step S 321  is continued (No in step S 323 ) until SOC 1  becomes higher than or equal to the lower limit value TL 1 . 
         [0127]    After SOC 1  becomes higher than or equal to the lower limit value TL 1  (Yes in step S 323 ), the ECU  40  sets the charge distribution ratio to 0% (first power supply  31 ):100% (second power supply  32 ) (step S 324 ). That is, the ECU  40  sets the charge distribution ratio such that (electric power that is charged into the first power supply  31 ):(electric power that is charged into the second power supply  32 ) becomes 0%:100%. In other words, the ECU  40  sets the charge distribution ratio such that the second power supply  32  having a relatively low (that is, the second highest) Wout is charged and the power supply other than the second power supply  32  (that is, the first power supply  31 ) is not charged. 
         [0128]    After that, the ECU  40  controls the electric power converter  33  such that electric power is distributed at the charge distribution ratio set in step S 324  (step S 325 ). In this case, the first power supply  31  is not charged, while the second power supply  32  is charged. Such a distribution of electric power at the charge distribution ratio set in step S 324  is continued (No in step S 326 ) until SOC 2  becomes higher than or equal to the lower limit value TL 2 . 
         [0129]    On the other hand, as a result of the determination of step S 31 , when it is determined that the slope of Wout 1  is not larger than or equal to the slope of Wout 2  (No in step S 31 ), the ECU  40  sets the charge distribution ratio to 0% (first power supply  31 ):100% (second power supply  32 ) (step S 331 ). That is, the ECU  40  sets the charge distribution ratio such that the second power supply  32  having a relatively high (that is, the maximum) Wout is charged and the power supply other than the second power supply  32  (that is, the first power supply  31 ) is not charged. 
         [0130]    After that, the ECU  40  controls the electric power converter  33  such that electric power is distributed at the charge distribution ratio set in step S 331  (step S 332 ). In this case, the first power supply  31  is not charged, while the second power supply  32  is charged. Such a distribution of electric power at the charge distribution ratio set in step S 331  is continued (No in step S 333 ) until SOC 2  becomes higher than or equal to the lower limit value TL 2 . 
         [0131]    After SOC 2  becomes higher than or equal to the lower limit value TL 2  (Yes in step S 333 ), the ECU  40  sets the charge distribution ratio to 100% (first power supply  31 ):0% (second power supply  32 ) (step S 234 ). In other words, the ECU  40  sets the charge distribution ratio such that the first power supply  31  having a relatively low (that is, the second highest) Wout is charged and the power supply other than the first power supply  31  (that is, the second power supply  32 ) is not charged. 
         [0132]    After that, the ECU  40  controls the electric power converter  33  such that electric power is distributed at the charge distribution ratio set in step S 334  (step S 335 ). In this case, the first power supply  31  is charged, while the second power supply  32  is not charged. Such a distribution of electric power at the charge distribution ratio set in step S 334  is continued (No step S 336 ) until SOC 1  becomes higher than or equal to the lower limit value TL 1 . 
         [0133]    In the above-described third control operations, when the slope of Wout 1  is larger than or equal to the slope of Wout 2 , the electric power converter  33  is controlled such that the first power supply  31  is charged and then the second power supply  32  is charged. On the other hand, when the slope of Wout 1  is not larger than or equal to the slope of Wout 2 , the electric power converter  33  is controlled such that the second power supply  32  is charged and then the first power supply  31  is charged. Therefore, the third control operations are considered as operations of controlling the electric power converter  33  such that the first power supply  31  and the second power supply  32  are charged in descending order of the slope of Wout. That is, in the present embodiment, when the first power supply  31  and the second power supply  32  are charged in a situation that Wout 1  and Wout 2  are limited, the electric power converter  33  is controlled such that the power supplies are charged in descending order of the slope of Wout. 
         [0134]    However, the electric power converter  33  is controlled such that the power supplies are charged in descending order of the slope of Wout in the case where Wout is defined as a positive value. That is, the electric power converter  33  is controlled such that the power supplies are charged in descending order of the slope of Wout in the case where electric power that is discharged from each power supply is defined as positive electric power and electric power that is charged into each power supply is defined as negative electric power. If Wout is defined as a negative value, the third control operations are preferably operations of controlling the electric power converter  33  such that the power supplies are charged in ascending order of the slope of Wout. That is, when electric power that is discharged from each power supply, is defined as negative electric power and electric power that is charged into each power supply is defined as positive electric power, the third control operations are preferably operations of controlling the electric power converter  33  such that the power supplies are charged in ascending order of the slope of Wout. That is, when Wout is defined as a negative value, the determination in step S 31  of  FIG. 6  is “determination as to whether the slope of Wout 1  is “smaller than or equal to” the slope of Wout 2 ”. In this case, when the slope of Wout 1  is smaller than or equal to the slope of Wout 2 , the operations of step S 321  to step S 326  are executed. On the other hand, when the slope of Wout 1  is not smaller than or equal to the slope of Wout 2 , the operations of step S 331  to step S 336  are executed. In order to execute the same determination operation irrespective of such definition of the sign of electric power, “the absolute value (that is, a value irrespective of the sign) of the slope of Wout” is preferably used as “the slope of Wout”. 
         [0135]    Subsequently, the flow of the fourth control operations that are executed when the vehicle  1  is being powered (that is, the first power supply  31  and the second power supply  32  are being discharged) in a situation that Win 1  and Win 2  are limited will be described with reference to  FIG. 7 .  FIG. 7  is a flowchart that shows the flow of the fourth control operations that are executed when the vehicle  1  is being powered in a situation that Win 1  and Win 2  are limited. 
         [0136]    As shown in  FIG. 7 , the ECU  40  determines whether the slope of Win 1  is larger than or equal to the slope of Win 2  (step S 41 ). 
         [0137]    The slope of Win 1  means the slope of the graph that represents the correlation between Win 1  and SOC 1 , shown in  FIG. 2A . Thus, the slope of Win 1  means the rate of change in Win 1  to SOC 1 . That is, the slope of Win 1  means ΔWin 1 /ΔSOC 1 . In addition, the “slope of Win 1 ” is the slope of Win 1  in the region in which SOC 1  is higher than or equal to the upper limit value TH 1 . That is, the “slope of Win 1 ” is the slope of Win 1  in the region in which Win 1  is limited. This also applies to the slope of Win 2 . 
         [0138]    The correlation between Win 1  and SOC 1  is a characteristic unique to each individual power supply. Thus, the ECU  40  preferably stores the correlation between Win 1  and SOC 1  (or information that directly or indirectly indicates the slope of Win 1 ). This also applies to Win 2 . 
         [0139]    As a result of the determination of step S 41 , when it is determined that the slope of Win 1  is larger than or equal to the slope of Win 2  (Yes in step S 41 ), the ECU  40  sets the discharge distribution ratio to 100% (first power supply  31 ):0% (second power supply  32 ) (step S 421 ). That is, the ECU  40  sets the discharge distribution ratio such that the first power supply  31  having a relatively high (that is, the maximum) Win is discharged and the power supply other than the first power supply  31  (that is, the second power supply  32 ) is not discharged. 
         [0140]    After that, the ECU  40  controls the electric power converter  33  such that electric power is distributed at the discharge distribution ratio set in step S 421  (step S 422 ). In this case, the first power supply  31  is discharged, while the second power supply  32  is not discharged. Such a distribution of electric power at the discharge distribution ratio set in step S 421  is continued (No in step S 423 ) until SOC 1  becomes lower than or equal to the upper limit value TH 1 . 
         [0141]    After SOC 1  becomes lower than or equal to the upper limit value TH 1  (Yes in step S 423 ), the ECU  40  sets the discharge distribution ratio to 0% (first power supply  31 ):100% (second power supply  32 ) (step S 424 ). That is, the ECU  40  sets the discharge distribution ratio such that the second power supply  32  having a relatively low (that is, the second highest) Win is discharged and the power supply other than the second power supply  32  (that is, the first power supply  31 ) is not discharged. 
         [0142]    After that, the ECU  40  controls the electric power converter  33  such that electric power is distributed at the discharge distribution ratio set in step S 424  (step S 425 ). In this case, the first power supply  31  is not discharged, while the second power supply  32  is discharged. Such a distribution of electric power at the discharge distribution ratio set in step S 424  is continued (No in step S 426 ) until SOC 2  becomes lower than or equal to the upper limit value TH 2 . 
         [0143]    On the other hand, as a result of the determination of step S 41 , when it is determined that the slope of Win 1  is not larger than or equal to the slope of Win 2  (No in step S 41 ), the ECU  40  sets the discharge distribution ratio to 0% (first power supply  30 ):100% (second power supply  32 ) (step S 431 ). That is, the ECU  40  sets the discharge distribution ratio such that the second power supply  32  having a relatively high (that is, the maximum) Win is discharged and the power supply other than the second power supply  32  (that is, the first power supply  31 ) is not discharged. 
         [0144]    After that, the ECU  40  controls the electric power converter  33  such that electric power is distributed at the discharge distribution ratio set in step S 431  (step S 432 ). In this case, the first power supply  31  is not discharged, while the second power supply  32  is discharged. Such a distribution of electric power at the discharge distribution ratio set in step S 431  is continued (No in step S 433 ) until SOC 2  becomes lower than or equal to the upper limit value TH 2 . 
         [0145]    After SOC 2  becomes lower than or equal to the upper limit value TH 2  (Yes in step S 433 ), the ECU  40  sets the discharge distribution ratio to 100% (first power supply  31 ):0% (second power supply  32 ) (step S 434 ). That is, the ECU  40  sets the discharge distribution ratio such that the first power supply  31  having a relatively low (that is, the second highest) Win is discharged and the power supply other than the first power supply  31  (that is, the second power supply  32 ) is not discharged. 
         [0146]    After that, the ECU  40  controls the electric power converter  33  such that electric power is distributed at the discharge distribution ratio set in step S 434  (step S 435 ). In this case, the first power supply  31  is discharged, while the second power supply  32  is not discharged. Such a distribution of electric power at the discharge distribution ratio set in step S 434  is continued (No in step S 436 ) until SOC 1  becomes lower than or equal to the upper limit value TH 1 . 
         [0147]    In the above-described fourth control operations, when the slope of Win 1  is larger than or equal to the slope of Win 2 , the electric power converter  33  is controlled such that the first power supply  31  is discharged and then the second power supply  32  is discharged. On the other hand, when the slope of Win 1  is not larger than or equal to the slope of Win 2 , the electric power converter  33  is controlled such that the second power supply  32  is discharged and then the first power supply  31  is discharged. Therefore, the fourth control operations are considered as operations of controlling the electric power converter  33  such that the first power supply  31  and the second power supply  32  are discharged in descending order of the slope of Win. That is, in the present embodiment, when the first power supply  31  and the second power supply  32  are discharged in a situation that Win 1  and Win 2  are limited, the electric power converter  33  is controlled such that the power supplies are discharged in descending order of the slope of Win. 
         [0148]    However, the electric power converter  33  is controlled such that the power supplies are discharged in descending order of the slope of Win in the case where Win is defined as a negative value. That is, the electric power converter  33  is controlled such that the power supplies are discharged in descending order of the slope of Win in the case where electric power that is discharged from each power supply is defined as positive electric power and electric power that is charged into each power supply is defined as negative electric power. If Win is defined as a positive value, the fourth control operations are preferably operations of controlling the electric power converter  33  such that the power supplies are discharged in ascending order of the slope of Win. That is, when electric power that is discharged from each power supply is defined as negative electric power and electric power that is charged into each power supply is defined as positive electric power, the fourth control operations are preferably operations of controlling the electric power converter  33  such that the power supplies are discharged in ascending order of the slope of Win. That is, when Win is defined as a positive value, the determination in step S 41  of  FIG. 7  is “determination as to whether the slope of Win 1  is “smaller than or equal to” the slope of Win 2 ”. In this case, when the slope of Win 1  is smaller than or equal to the slope of Win 2 , the operations of step S 421  to step S 425  are executed. On the other hand, when the slope of Win 1  is not smaller than or equal to the slope of Win 2 , the operations of step S 431  to step S 435  are executed. In order to execute the same determination operation irrespective of such definition of the sign of electric power, “the absolute value (that is, a value irrespective of the sign) of the slope of Win” is preferably used as “the slope of Win”. 
         [0149]    Next, the flow of the fifth control operations that are executed when the vehicle  1  is regenerating electric power (that is, the first power supply  31  and the second power supply  32  are being charged) in a situation that Win 1  and Win 2  are limited will be described with reference to  FIG. 8 .  FIG. 8  is a flowchart that shows the flow of the fifth control operations that are executed when the vehicle  1  is regenerating electric power in a situation that Win 1  and Win 2  are limited. 
         [0150]    As shown in  FIG. 8 , the ECU  40  determines whether the slope of Win 1  becomes smaller than or equal to the slope of Win 2  (step S 51 ). 
         [0151]    As a result of the determination of step S 51 , when it is determined that the slope of Win 1  is smaller than or equal to the slope of Win 2  (Yes in step S 51 ), the ECU  40  sets the charge distribution ratio to 100% (first power supply  31 ):0% (second power supply  32 ) (step S 521 ). That is, the ECU  40  sets the charge distribution ratio such that the first power supply  31  having a relatively low (that is, the minimum) Win is charged and the power supply other than the first power supply  31  (that is, the second power supply  32 ) is not charged. 
         [0152]    After that, the ECU  40  controls the electric power converter  33  such that electric power is distributed at the charge distribution ratio set in step S 521  (step S 522 ). In this case, the first power supply  31  is charged, while the second power supply  32  is not charged. Such a distribution of electric power at the charge distribution ratio set in step S 521  is continued (No in step S 523 ) until SOC 1  becomes higher than or equal to the maximum upper limit value HL 1 . 
         [0153]    After SOC 1  becomes higher than or equal to the maximum upper limit value HL 1  (Yes in step S 523 ), the ECU  40  sets the charge distribution ratio to 0% (first power supply  31 ):100% (second power supply  32 ) (step S 524 ). That is, the ECU  40  sets the charge distribution ratio such that the second power supply  32  having a relatively high (that is, the second lowest) Win is charged and the power supply other than the second power supply  32  (that is, the first power supply  31 ) is not charged. 
         [0154]    After that, the ECU  40  controls the electric power converter  33  such that electric power is distributed at the charge distribution ratio set in step S 524  (step S 525 ). In this case, the first power supply  31  is not, charged, while the second power supply  32  is charged. Such a distribution of electric power at the charge distribution ratio set in step S 524  is continued (No in step S 526 ) until SOC 2  becomes higher than or equal to the maximum upper limit value HL 2 . 
         [0155]    On the other hand, as a result of the determination of step S 51 , when it is determined that the slope of Win 1  is not smaller than or equal to the slope of Win 2  (No in step S 51 ), the ECU  40  sets the charge distribution ratio to 0% (first power supply  31 ):100% (second power supply  32 ) (step S 531 ). That is, the ECU  40  sets the charge distribution ratio such that the second power supply  32  having a relatively low (that is, the minimum) Win is charged and the power supply other than the second power supply  32  (that is, the first power supply  31 ) is not charged. 
         [0156]    After that, the ECU  40  controls the electric power converter  33  such that electric power is distributed at the charge distribution ratio set in step S 531  (step S 532 ). In this case, the first power supply  31  is not charged, while the second power supply  32  is charged. Such a distribution of electric power at the charge distribution ratio set in step S 531  is continued (No in step S 533 ) until SOC 2  becomes higher than or equal to the maximum upper limit value HL 2 . 
         [0157]    After SOC 2  becomes higher than or equal to the maximum upper limit value HL 2  (Yes in step S 533 ), the ECU  40  sets the charge distribution ratio to 100% (first power supply  31 ):0% (second power supply  32 ) (step S 534 ). In other words, the ECU  40  sets the charge distribution ratio such that the first power supply  31  having a relatively high (that is, the second lowest) Win is charged and the power supply other than the first power supply  31  (that is, the second power supply  32 ) is not charged. 
         [0158]    After that, the ECU  40  controls the electric power converter  33  such that electric power is distributed at the charge distribution ratio set in step S 534  (step S 535 ). In this case, the first power supply  31  is charged, while the second power supply  32  is not charged. Such a distribution of electric power at the charge distribution ratio set in step S 534  is continued (No in step S 536 ) until SOC 1  becomes higher than or equal to the maximum upper limit value HL 1 . 
         [0159]    In the above-described fifth control operations, when the slope of Win 1  is smaller than or equal to the slope of Win 2 , the electric power converter  33  is controlled such that the first power supply  31  is charged and then the second power supply  32  is charged. On the other hand, when the slope of Win 1  is not smaller than or equal to the slope of Win 2 , the electric power converter  33  is controlled such that the second power supply  32  is charged and then the first power supply  31  is charged. Therefore, the fifth control operations are considered as operations of controlling the electric power converter  33  such that the first power supply  31  and the second power supply  32  are charged in ascending order of the slope of Win. That is, in the present embodiment, when the first power supply  31  and the second power supply  32  are charged in a situation that Win 1  and Win 2  are limited, the electric power converter  33  is controlled such that the power supplies are charged in ascending order of the slope of Win. 
         [0160]    However, the electric power converter  33  is controlled such that the power supplies are charged in ascending order of the slope of Win in the case where Win is defined as a negative value. That is, the electric power converter  33  is controlled such that the power supplies are charged in ascending order of the slope of Win in the case where electric power that is discharged from each power supply is defined as positive electric power and electric power that is charged into each power supply is defined as negative electric power. If Win is defined as a positive value, the fifth control operations are preferably operations of controlling the electric power converter  33  such that the power supplies are charged in descending order of the slope of Win. That is, when electric power that is discharged from each power supply is defined as negative electric power and electric power that is charged into each power supply is defined as positive electric power, the fifth control operations are preferably operations of controlling the electric power converter  33  such that the power supplies are charged in descending order of the slope of Win. That is, when Win is defined as a negative value, the determination in step S 51  of  FIG. 8  is “determination as to whether the slope of Win 1  is “larger than or equal to” the slope of Win 2 ”. In this case, when the slope of Win 1  is larger than or equal to the slope of Win 2 , the operations of step S 521  to step S 525  are executed. On the other hand, when the slope of Win 1  is not larger than or equal to the slope of Win 2 , the operations of step S 531  to step S 535  are executed. In order to execute the same determination operation irrespective of such definition of the sign of electric power, “the absolute value (that is, a value irrespective of the sign) of the slope of Win” is preferably used as “the slope of Win”, as described in the description of the fourth control operations. 
         [0161]    Next, the technical advantageous effects that are achieved by executing the second control operations to the fifth control operations will be described with reference to  FIG. 9A  to  FIG. 12C . 
         [0162]    Initially, the technical advantageous effects that are achieved by the second control operations will be described with reference to  FIG. 9A  to  FIG. 9C .  FIG. 9A  to  FIG. 9C  are graphs that show a mode of change in SOC 1  and SOC 2  and a mode of change in total Wout of the overall power supply system  30  when the second control operations are executed. Hereinafter, as shown in  FIG. 9A , description will be made by focusing on the second control operations that are executed when the slope of Wout 1  is larger than the slope of Wout 2 . 
         [0163]    When Wout 1  and Wout 2  are not limited, the first control operations are executed. Therefore, as shown in  FIG. 9B , as a result of a discharge of the first power supply  31  and the second power supply  32 , the SOC 1  and the SOC 2  respectively reach the lower limit value TL 1  and the lower limit value TL 2  at the same time (see the section  2 A in  FIG. 9B ). After that, when Wout 1  and Wout 2  are limited as a result of a discharge of the first power supply  31  and the second power supply  32 , the second control operations are executed. Thus, initially, the second power supply  32  having the minimum slope of Wout is discharged, with the result that SOC 2  decreases to the minimum lower limit value LL 2  (see the section  2 B in  FIG. 9B ). After that, the first power supply  31  having the second smallest slope of Wout is discharged, with the result that the SOC 1  decreases to the minimum lower limit value LL 1  (see the section  2 C in  FIG. 9B ). On the other hand, if the first control operations are continued even after Wout 1  and Wout 2  are limited as a result of a discharge of the first power supply  31  and the second power supply  32 , SOC 1  and SOC 2  decrease at the same time as indicated by the dashed line in  FIG. 9B . 
         [0164]    Total Wout (that is, Wout 1 +Wout 2 ) of the overall power supply system  30  in the case where the second control operations are executed in this way is indicated by the continuous line in  FIG. 9C . On the other hand, total Wout in the case where the first control operations are continuously executed instead of executing the second control operations is indicated by the dashed line in  FIG. 9C . As shown in  FIG. 9C , total Wout in the case where the second control operations are executed is improved particularly in the region in which Wout 1  and Wout 2  are limited as compared to total Wout in the case where the first control operations are continuously executed (that is, the absolute value of total Wout increases). This is because of the following reason. 
         [0165]    Initially, when SOC is relatively low, Wout is gradually limited with a discharge. As shown in  FIG. 9A , as the slope of Wout increases, Wout is limited at a relatively higher rate with a discharge. Therefore, in the present embodiment, the ECU  40  controls the power supply system  30  such that the power supply of which Wout is limited at a relatively low rate with a discharge (that is, the power supply having a relatively small slope of Wout, and the second power supply  32  in  FIG. 9A  to  FIG. 9C ) is discharged preferentially or in first. On the other hand, in a comparative embodiment in which the first control operations are constantly executed without consideration of the slope of Wout, not only the power supply of which Wout is limited at a relatively low rate with a discharge is discharged but also the power supply of which Wout is limited at a relatively high rate with a discharge (that is, the power supply having a relatively large slope of Wout, and the first power supply  31  in  FIG. 9A  to  FIG. 9C ) is also discharged at the same time. Therefore, in the present embodiment, in comparison with the comparative embodiment in which the first control operations are constantly executed without consideration of the slope of Wout, the power supply system  30  is controlled such that total Wout is relatively difficult to be limited. 
         [0166]    In order to control the power supply system  30  such that total Wout is difficult to be limited in comparison with the comparative embodiment in which the first control operations are constantly executed without consideration of the slope of Wout, the discharge distribution ratio that is set in the second control operations may not necessarily be 100%:0% (0%:100%). For example, in the second control operations, the discharge distribution ratio may be set such that the discharge distribution ratio of the power supply having a smaller slope of Wout increases and the discharge distribution ratio of the power supply having a larger slope of Wout decreases with reference to the discharge distribution ratio (R 1 :R 2 ) that is set in the first control operations. Specifically, for example, when Slope of Wout 1 ≦Slope of Wout 2 , the discharge distribution ratio may be set to R 21  (where R 21 &gt;R 1 ):R 22  (where R 22 &lt;R 2 ). On the other hand, for example, when Slope of Wout 1 &gt;Slope of Wout 2 , the discharge distribution ratio may be set to R 23  (where R 23 &lt;R 1 ):R 24  (where R 24 &gt;R 2 ). 
         [0167]    Next, the technical advantageous effects that are achieved by the third control operations will be described with reference to  FIG. 10A  to  FIG. 10C .  FIG. 10A  to  FIG. 10C  are graphs that show a mode of change in SOC 1  and SOC 2  and a mode of change in total Wout of the overall power supply system  30  when the third control operations are executed. Hereinafter, as shown in  FIG. 10A , description will be made by focusing on the third control operations that are executed when the slope of Wout 1  is larger than the slope of Wout 2 . 
         [0168]    When Wout 1  and Wout 2  are limited, the third control operations are executed. Thus, initially, the first power supply  31  having the maximum slope of Wout is charged, with the result that SOC 1  increases to the lower limit value TL 1  (see the section  3 A in  FIG. 10B ). After that, the second power supply  32  having the second largest slope of Wout is charged, with the result that SOC 2  increases to the lower limit value TL 2  (see the section.  3 B in  FIG. 10B ). On the other hand, if the first control operations are executed even when Wout 1  and Wout 2  are limited, SOC 1  and SOC 2  increase at the same time as indicated by the dashed line in  FIG. 10B . After that, when Wout 1  and Wout 2  are not limited as a result of a charge of the first power supply  31  and the second power supply  32 , the first control operations are executed. Therefore, as shown in  FIG. 10B , the first power supply  31  and the second power supply  32  are charged such that SOC 1  and SOC 2  respectively reach the upper limit value TH 1  and the upper limit value TH 2  at the same time (see the section  3 C in  FIG. 10B ). 
         [0169]    Total Wout (that is, Wout 1 +Wout 2 ) of the overall power supply system  30  in the case where the third control operations are executed in this way is indicated by the continuous line in  FIG. 10C . On the other hand, total Wout in the case where the first control operations are continuously executed instead of executing the third control operations is indicated by the dashed line in  FIG. 10C . As shown in  FIG. 10C , total Wout in the case where the third control operations are executed is improved particularly in the region in which Wout 1  and Wout 2  are limited as compared to total Wout in the case where the first control operations are continuously executed (that is, the absolute value of total Wout increases). This is because of the following reason. 
         [0170]    When SOC is relatively low, Wout gradually recovers with a charge. As shown in  FIG. 10A , as the slope of Wout increases, Wout recovers at a relatively higher rate with a charge. Therefore, in the present embodiment, the ECU  40  controls the power supply system  30  such that the power supply of which Wout recovers at a relatively high rate with a charge (that is, the power supply having a relatively large slope of Wout, and the first power supply  31  in  FIG. 10A  to  FIG. 10C ) is charged preferentially or in first. On the other hand, in the comparative embodiment in which the first control operations are constantly executed without consideration of the slope of Wout, not only the power supply of which Wout recovers at a relatively high rate with a charge is charged but also the power supply of which Wout recovers at a relatively low rate with a charge (that is, the power supply having a relatively small slope of Wout, and the second power supply  32  in  FIG. 10A  to  FIG. 10C ) is also charged at the same time. Therefore, in the present embodiment, in comparison with the comparative embodiment in which the first control operations are constantly executed without consideration of the slope of Wout, the power supply system  30  is controlled such that total Wout is relatively difficult to be limited. 
         [0171]    In order to control the power supply system  30  such that total Wout is difficult to be limited in comparison with the comparative embodiment in which the first control operations are constantly executed without consideration of the slope of Wout, the charge distribution ratio that is set in the third control operations may not necessarily be 100%:0% (0%:100%). For example, in the third control operations, the charge distribution ratio may be set such that the charge distribution ratio of the power supply having a larger slope of Wout increases and the charge distribution ratio of the power supply having a smaller slope of Wout decreases with reference to the charge distribution ratio (C 1 :C 2 ) that is set in the first control operations. Specifically, for example, when Slope of Wout 1 ≧Slope of Wout 2 , the charge distribution ratio may be set to C 31  (where C 31 &gt;C 1 ):C 32  (where C 32 &lt;C 2 ). On the other hand, for example, when Slope of Wout 1 &lt;Slope of Wout 2 , the charge distribution ratio may be set to C 33  (where C 33 &lt;C 1 ):C 34  (where C 34 &gt;C 2 ). 
         [0172]    Next, the technical advantageous effects that are achieved by the fourth control operations will be described with reference to  FIG. 11A  to  FIG. 11C .  FIG. 11A  to  FIG. 11C  are graphs that show a mode of change in SOC 1  and SOC 2  and a mode of change in total Win of the overall power supply system  30  when the fourth control operations are executed. Hereinafter, as shown in  FIG. 11A , description will be made by focusing on the fourth control operations that are executed when the slope of Win 1  is smaller than the slope of Win 2 . 
         [0173]    When Win 1  and Win 2  are limited, the fourth control operations are executed. Thus, initially, the second power supply  32  having the maximum slope of Win is discharged, with the result that SOC 2  decreases to the upper limit value TH 2  (see the section  4 A in  FIG. 11B ). After that, the first power supply  31  having the second largest Win is discharged, with the result that SOC 1  decreases to the upper limit value TH 1  (see the section  4 B in  FIG. 11B ). On the other hand, if the first control operations are executed even when Win 1  and Win 2  are limited, SOC 1  and SOC 2  decrease at the same time as indicated by the dashed line in  FIG. 11B . After that, when Win 1  and Win 2  are not limited with a discharge of the first power supply  31  and the second power supply  32 , the first control operations are executed. Therefore, as shown in  FIG. 11B , the first power supply  31  and the second power supply  32  are discharged such that SOC 1  and SOC 2  respectively reach the lower limit value TL 1  and the lower limit value TL 2  at the same time (see the section  4 C in  FIG. 11B ). 
         [0174]    Total Win (that is, Win 1 +Win 2 ) of the overall power supply system  30  in the case where the fourth control operations are executed in this way is indicated by the continuous line in  FIG. 11C . On the other hand, total Win in the case where the first control operations are continuously executed instead of executing the fourth control operations is indicated by the dashed line in  FIG. 11C . As shown in  FIG. 11C , total Win in the case where the fourth control operations are executed is improved particularly in the region in which Win 1  and Win 2  are limited as compared to total Win in the case where the first control operations are continuously executed (that is, the absolute value of total Win increases). This is because of the following reason. 
         [0175]    When SOC is relatively high, Win gradually recovers with a discharge. As shown in  FIG. 11A , as the slope of Win increases, Win recovers at a relatively higher rate with a discharge. Therefore, in the present embodiment, the ECU  40  controls the power supply system  30  such that the power supply of which Win recovers at a relatively high rate with a discharge (that is, the power supply having a relatively large slope of Win, and the second power supply  32  in  FIG. 11A  to  FIG. 11C ) is discharged preferentially or in first. On the other hand, in a comparative embodiment in which the first control operations are constantly executed without consideration of the slope of Win, not only the power supply of which Win recovers at a relatively high rate with a discharge but also the power supply of which Win recovers at a relatively low rate with a discharge (that is, the power supply having a relatively small slope of Win, and the first power supply  31  in  FIG. 11A  to  FIG. 11C ) is also discharged at the same time. Therefore, in the present embodiment, in comparison with the comparative embodiment in which the first control operations are constantly executed without consideration of the slope of Win, the power supply system  30  is controlled such that total Win is relatively difficult to be limited. 
         [0176]    In order to control the power supply system  30  such that total Win is difficult to be limited in comparison with the comparative embodiment in which the first control operations are constantly executed without consideration of the slope of Win, the discharge distribution ratio that is set in the fourth control operations may not necessarily be 100%:0% (0%:100%). For example, in the fourth control operations, the discharge distribution ratio may be set such that the discharge distribution ratio of the power supply having a larger slope of Win increases and the discharge distribution ratio of the power supply having a smaller slope of Win decreases with reference to the discharge distribution ratio (R 1 :R 2 ) that is set in the first control operations. Specifically, for example, when Slope of Win 1 ≧Slope of Win 2 , the discharge distribution ratio may be set to R 41  (where R 41 &gt;R 1 ):R 42  (where R 42 &lt;R 2 ). On the other hand, for example, when Slope of Win 1 &lt;Slope of Win 2 , the discharge distribution ratio may be set to R 43  (where R 43 &lt;R 1 ):R 44  (where R 44 &gt;R 2 ). 
         [0177]    Next, the technical advantageous effects that are achieved by the fifth control operations will be described with reference to  FIG. 12A  to  FIG. 12C .  FIG. 12A  to  FIG. 12C  are graphs that show a mode of change in SOC 1  and SOC 2  and a mode of change in total Win of the overall power supply system  30  when the fifth control operations are executed. Hereinafter, as shown in  FIG. 12A , description will be made by focusing on the fifth control operations that are executed when the slope of Win 1  is smaller than the slope of Win 2 . 
         [0178]    When Win 1  and Win 2  are not limited, the first control operations are executed. Therefore, as shown in  FIG. 12B , as a result of a charge of the first, power supply  31  and the second power supply  32 , SOC 1  and SOC 2  respectively reach the upper limit value TH 1  and the upper limit value TH 2  at the same time (see the section  5 A in  FIG. 12B ). After that, when Win 1  and Win 2  are limited with a charge of the first power supply  31  and the second power supply  32 , the fifth control operations are executed. Thus, initially, the first power supply  31  having the minimum slope of Win is charged, with the result that SOC 1  increases to the maximum upper limit value HL 1  (see the section  5 B in  FIG. 12B ). After that, the second power supply  32  having the second smallest slope of Wout is charged, with the result that SOC 2  increases to the maximum upper limit value HL 2  (see the section  5 C in  FIG. 12B ). On the other hand, if the first control operations are executed even after Win 1  and Win 2  are limited with a charge of the first power supply  31  and the second power supply  32 , SOC 1  and SOC 2  increase at the same time as indicated by the dashed line in  FIG. 12B . 
         [0179]    Total Win (that is, Win 1 +Win 2 ) of the overall power supply system  30  in the case where the fifth control operations are executed in this way is indicated by the continuous line in  FIG. 12C . On the other hand, total Win in the case where the first control operations are continuously executed instead of executing the fifth control operations is indicated by the dashed line in  FIG. 12C . As shown in  FIG. 12C , total Win in the case where the fifth control operations are executed is improved particularly in the region in which Win 1  and Win 2  are limited as compared to total Win in the case where the first control operations are continuously executed that is, the absolute value of total Win increases). This is because of the following reason. 
         [0180]    Initially, when SOC is relatively high, Win is gradually limited with a charge. As shown in  FIG. 12A , as the slope of Win increases, Win is limited at a relatively higher rate with a charge. Therefore, in the present embodiment, the ECU  40  controls the power supply system  30  such that the power supply of which Win is limited at a relatively low rate with a charge (that is, the power supply having a relatively small slope of Win, and the first power supply  31  in  FIG. 12A  to  FIG. 12C ) is charged preferentially or in first. On the other hand, in a comparative embodiment in which the first control operations are constantly executed without consideration of the slope of Win, not only the power supply of which Win is limited at a relatively low rate with a charge but also the power supply of which Win is limited at a relatively high rate with a charge (that is, the power supply having a relatively large slope of Win, and the second power supply  32  in  FIG. 12A  to  FIG. 12C ) is also charged at the same time. Therefore, in the present embodiment, in comparison with the comparative embodiment in which the first control operations are constantly executed without consideration of the slope of Win, the power supply system  30  is controlled such that total Win is relatively difficult to be limited. 
         [0181]    In order to control the power supply system  30  such that total Win is difficult to be limited in comparison with the comparative embodiment in which the first control operations are constantly executed without consideration of the slope of Win, the charge distribution ratio that is set in the fifth control operations may not necessarily be 100%:0% (0%:100%). For example, in the fifth control operations, the charge distribution ratio may be set such that the charge distribution ratio of the power supply having a smaller slope of Win increases and the charge distribution ratio of the power supply having a larger slope of Win decreases with reference to the charge distribution ratio (C 1 :C 2 ) that is set in the first control operations. Specifically, for example, when Slope of Win 1 ≦Slope of Win 2 , the charge distribution ratio may be set to C 51  (where C 51 &gt;C 1 ):C 52  (where C 52 &lt;C 2 ). On the other hand, for example, when Slope of Win 1 &gt;Slope of Win 2 , the charge distribution ratio may be set to C 53  (where C 53 &lt;C 1 ):C 54  (where C 54 &gt;C 2 ). 
         [0182]    The invention may be modified as needed without departing from the scope or idea of the invention that can be read from the appended claims and the specification, and the technical idea of the invention also encompasses power supply control apparatuses having such modifications.