Patent Description:
In recent years, in view of the global warming problem, there has been an increased use of a power generation and transmission system that is intended to generate power by using renewable energy, such as sunlight and wind power, and stabilize the output by using a battery energy storage system (BESS). In view of emission control, such a battery energy storage system is widely used also for a mobile traffic system, such as of automobiles.

A conventional, typical battery energy storage system includes: a battery that includes multiple battery cells combined with each other; a cooling system that cools the battery to regulate the temperature; a battery management apparatus that performs charge and discharge control and maintains the system in a safe state.

Battery energy storage systems mounted on electric vehicles, hybrid vehicles and the like are required to correctly obtain battery states, such as a state of charge (SOC), a state of health (SOH), and the maximum permissible power, in order to facilitate to optimize vehicle control while maintaining the battery in the safe state. These battery states are obtained based on measured values, such as current, voltage and temperature, through sensors. One of the battery states used for such battery energy storage systems is available energy. The available energy represents the total amount of electrical energy remaining in the battery, and corresponds to electrical energy that can be discharged until the battery reaches a permissible use limit. The available energy is used to calculate the travelable distance of a vehicle until the battery reaches a fully discharged (use limit) state, for example.

As for calculation of the available energy of a battery, a technique described in Patent Literature <NUM> has been known. Patent Literature <NUM> discloses a method including: obtaining a battery's initial available energy; calculating the battery's accumulative consumption energy consumed while a vehicle is travelling a current accumulative driving distance; calculating the battery's remaining available energy from these values; calculating a final electric efficiency corresponding to driving the current accumulative driving distance; and calculating a travelable distance of the vehicle. Patent document <NUM> discloses a storage battery management device which includes a chargeable/dischargeable capacity table that stores therein a chargeable/dischargeable capacity corresponding to a temperature, a state of charge (SOC), a required charge rate or discharge rate, and a battery degradation rate of a secondary battery.

According to the method in Patent Literature <NUM>, during calculation of the accumulative consumption energy of the battery, the errors of a voltage sensor and a current sensor are accumulated. Accordingly, in particular, after the vehicle travels a long distance, it is difficult to correctly estimate the available energy of the battery.

The above is solved by the subject-matter as provided in the appended claims. In particular, it is described herein a battery management apparatus according to the present invention for managing a chargeable and dischargeable battery, the apparatus including: a battery state calculator that calculates a state of charge, a capacity deterioration degree, and a resistance deterioration degree of the battery; a mid voltage calculator that corrects the calculated resistance deterioration degree, corrects a mid resistance of the battery corresponding to a respective mid voltage according to a correction coefficient in accordance with the corrected resistance deterioration degree, and calculates a mid voltage that is present between a charge-discharge voltage in a current state of charge of the battery, and a charge-discharge voltage in a minimum state of charge or a maximum state of charge of the battery, based on the corrected mid resistance; a remaining capacity calculator that calculates a remaining capacity or a chargeable capacity of the battery, based on the calculated state of charge and the capacity deterioration degree; and an available energy calculator that calculates available energy or chargeable energy of the battery, based on the calculated mid voltage and the remaining capacity, or on the calculated mid voltage and the chargeable capacity.

A battery management method according to the present invention is a method for managing a chargeable and dischargeable battery, the method including, by a computer: calculating a state of charge, a capacity deterioration degree and a resistance deterioration degree of the battery; correcting the calculated resistance deterioration degree; correcting a mid resistance of the battery corresponding to a respective mid voltage, according to a correction coefficient in accordance with the corrected resistance deterioration degree; calculating a mid voltage that is present between a charge-discharge voltage in a current state of charge of the battery, and a charge-discharge voltage in a minimum state of charge or a maximum state of charge of the battery, based on the corrected mid resistance; calculating a remaining capacity or a chargeable capacity of the battery, based on the calculated state of charge and capacity deterioration degree; and calculating available energy or chargeable energy of the battery, based on the calculated mid voltage and remaining capacity, or on the calculated mid voltage and chargeable capacity.

A battery energy storage system according to the present invention includes: the battery management apparatus; a chargeable and dischargeable battery; and a charge-discharge apparatus that charges and discharges the battery, based on available energy or chargeable energy of the battery calculated by the battery management apparatus.

The present invention can correctly estimate the available energy of the battery.

Embodiments of the present invention are hereinafter described.

<FIG> is a schematic configuration diagram of a battery energy storage system according to one embodiment of the present invention. The battery energy storage system (BESS) <NUM> shown in <FIG> includes an assembled battery <NUM>, a battery management apparatus <NUM>, a current sensor <NUM>, a cell controller <NUM>, a voltage sensor <NUM>, a temperature sensor <NUM>, and relays <NUM>. The battery energy storage system <NUM> is coupled to a load <NUM>, such as an AC motor, via an inverter <NUM>. The battery energy storage system <NUM> and the inverter <NUM> are coupled to an upper level controller <NUM> via a communication circuit, not shown.

The assembled battery <NUM> includes multiple chargeable and dischargeable battery cells coupled in series and in parallel. For drive operation of the load <NUM>, DC power discharged from the assembled battery <NUM> is converted by the inverter <NUM> into AC power, and is supplied to the load <NUM>. For regenerative operation of the load <NUM>, AC power output from the load <NUM> is converted by the inverter <NUM> into DC power, with which the assembled battery <NUM> is charged. Such operation of the inverter <NUM> charges and discharges the assembled battery <NUM>. The operation of the inverter <NUM> is controlled by the upper level controller <NUM>.

The current sensor <NUM> detects current flowing in the assembled battery <NUM>, and outputs the detection result to the battery management apparatus <NUM>. The cell controller <NUM> detects the voltage of each battery cell of the assembled battery <NUM>, and outputs the detection result to the battery management apparatus <NUM>. The voltage sensor <NUM> detects the voltage (total voltage) of the assembled battery <NUM>, and outputs the detection result to the battery management apparatus <NUM>. The temperature sensor <NUM> detects the temperature of the assembled battery <NUM>, and outputs the detection result to the battery management apparatus <NUM>. The relays <NUM> switches the coupling state between the battery energy storage system <NUM> and the inverter <NUM> according to control by the upper level controller <NUM>.

The battery management apparatus <NUM> controls charge and discharge of the assembled battery <NUM> based on the detection results of the current sensor <NUM>, the cell controller <NUM>, the voltage sensor <NUM> and the temperature sensor <NUM>. At this time, the battery management apparatus <NUM> calculates various types of battery states as indicators that indicate the states of the assembled battery <NUM>. The battery states calculated by the battery management apparatus <NUM> include, for example, a state of charge (SOC) (specifically, e.g., the charging rate of the battery), a state of health (SOH) (specifically, e.g., the deterioration degree of the battery), the maximum permissible power, and the available energy. By controlling the charge and discharge of the assembled battery <NUM> by using these battery states, the battery management apparatus <NUM> safely controls the assembled battery <NUM>. As a result, an upper level system (an electric vehicle, a hybrid vehicle, etc.) provided with the battery energy storage system <NUM> can be efficiently controlled. The battery management apparatus <NUM> performs information communication required to control the charge and discharge of the assembled battery <NUM>, with the upper level controller <NUM>.

Note that in this embodiment, the available energy described above is defined as the total amount of electrical energy that the assembled battery <NUM> can discharge, in the electrical energy accumulated in the assembled battery <NUM>. This corresponds to the total electric energy (Wh) dischargeable without each battery cell falling below the minimum voltage Vmin, until the SOC of each battery cell reaches SOCmin, which is the minimum SOC value permitted for the corresponding battery cell, in a case where each battery cell of the assembled battery <NUM> is discharged with a constant discharge current IC0,DCh. Note that the discharge current value IC0,Dch is preset depending on the operation mode and the like of the battery energy storage system <NUM>.

<FIG> illustrates the available energy. In <FIG>, a broken line indicated by a symbol <NUM> represents an SOC-OCV curve that indicates the relationship between the SOC and the open-circuit voltage (OCV) of each battery cell of the assembled battery <NUM>. A solid line indicated by a symbol <NUM> represents a discharge curve when each battery cell of the assembled battery <NUM> is discharged with the constant discharge current IC0,DCh from the current SOC to SOCmin. Note that in <FIG>, the current SOC is indicated by a broken line <NUM>, and the SOCmin is indicated by a broken line <NUM>.

The discharge curve <NUM> indicates the relationship between the SOC and the closed-circuit voltage (CCV) during discharge from each battery cell of the assembled battery <NUM>. That is, the CCV of each battery cell during discharge of the assembled battery <NUM> continuously changes, according to the discharge curve <NUM>, from the voltage value <NUM> corresponding to the current SOC to the voltage value <NUM> corresponding to SOCmin when discharge is finished, in a range where the voltage does not fall below the minimum voltage Vmin indicated by a broken line <NUM>.

Here, provided that the C-rate during discharge corresponding to the discharge curve <NUM> is represented as C<NUM>, the discharge current IC0,Dch can be represented as IC0,DCH = C<NUM> × Ahrated. In this expression, Ahrated represents the rated capacity of each battery cell.

The available energy of each battery cell during discharge is defined by the following (Expression <NUM>).

In (Expression <NUM>), CCV(t) represents the CCV of each battery cell at a time t, i.e., the value of a discharge voltage, tpresent represents the current time, and tend represents a time when the SOC of each battery cell reaches SOCmin and discharge is finished. This (Expression <NUM>) represents the integral value of the discharge curve <NUM> from the current SOC to SOCmin shown in <FIG>. That is, in <FIG>, the area of an area <NUM> that is encircled by the discharge curve <NUM> and the broken lines <NUM> and <NUM> and is indicated by hatching corresponds to the available energy of each battery cell.

For example, in a case where the battery energy storage system <NUM> is mounted on a vehicle, the available energy of the assembled battery <NUM> is required to be calculated in real time in order to achieve appropriate and safe vehicle control. However, during vehicle traveling, the current sequentially changes. Consequently, (Expression <NUM>), which is a calculation expression assuming a constant discharge current IC0,Dch, cannot be applied. In one embodiment of the present invention, according to a calculation method described below, the available energy of the assembled battery <NUM> can be directly calculated in real time without using (Expression <NUM>).

<FIG> is a concept diagram of a method of calculating the available energy according to one embodiment of the present invention. In <FIG>, the SOC-OCV curve <NUM> and the discharge curve <NUM> correspond to those in <FIG>. In <FIG>, in addition to these curves, an area <NUM> indicated by hatching is depicted. The area <NUM> is defined as the remaining capacity of each battery cell, i.e., the area of a rectangle having a long side that is a difference ΔSOC between the current SOC and SOCmin, and a short side that is a mid voltage <NUM> that is present between the voltage value <NUM> corresponding to the current SOC on the discharge curve <NUM> and the voltage value <NUM> corresponding to the SOCmin when discharge is finished.

In one embodiment of the present invention, the mid voltage <NUM> that is present on the discharge curve <NUM> is obtained such that the area of the area <NUM> in <FIG> matches the area of the area <NUM> in <FIG>. Accordingly, the area of the rectangular area <NUM> by multiplying the mid voltage <NUM> by the remaining capacity (ΔSOC), thereby allowing the area of this area <NUM> in <FIG>, i.e., the available energy, to be calculated.

Note that in <FIG>, a point <NUM> on the SOC-OCV curve <NUM> represents the OCV value (mid OCV) corresponding to the mid voltage <NUM>. The mid OCV is present between the OCV value in the current SOC and the OCV value in the SOCmin. A point <NUM> on the abscissa axis represents a SOC value (mid SOC) corresponding to the mid voltage <NUM> and the mid OCV. The mid SOC is present between the current SOC and the SOCmin.

The method of calculating the available energy for units of battery cells has been described above. In this embodiment, it is preferable to calculate the available energy for the entire assembled battery <NUM>. For example, for each of the battery cells constituting the assembled battery <NUM>, the available energy is calculated with respect to each battery cell, and the calculation results of the available energy of the individual battery cells are summed up, which can obtain the available energy of the entire assembled battery <NUM>. Alternatively, the available energy may be calculated on an assembled battery <NUM> basis by applying the calculation method described above to the entire assembled battery <NUM>.

Subsequently, a method of calculating the available energy in this embodiment where the aforementioned concept is specifically implemented is described.

<FIG> shows functional blocks of the battery management apparatus <NUM> pertaining to an available energy calculation process according to a first embodiment of the present invention. The battery management apparatus <NUM> of this embodiment includes functional blocks including a battery state calculator <NUM>, a mid voltage calculator <NUM>, a remaining capacity calculator <NUM>, and an available energy calculator <NUM>. These functional blocks can be achieved by causing a computer to execute a predetermined program, for example.

The battery state calculator <NUM> obtains current I, closed-circuit voltage CCV, and battery temperature Tcell detected when the assembled battery <NUM> is charged or discharged, from the current sensor <NUM>, the voltage sensor <NUM> and the temperature sensor <NUM>, respectively. Based on the pieces of information, state values representing the current state of the assembled battery <NUM> are calculated; the state values are the open circuit voltage OCV, the state of charge SOC, the polarization voltage Vp, the charge capacity fade SOHQ (specifically, e.g., the deterioration rate of the capacity (e.g., an example of the deterioration degree)), and an internal resistance rise SOHR (specifically, e.g., the increase rate of the internal resistance, in other words, the deterioration rate of the internal resistance (an example of the deterioration degree)). Note that the details of the method of calculating these state values by the battery state calculator <NUM> are described later with reference to <FIG>.

The mid voltage calculator <NUM> obtains the state of charge SOC and the internal resistance rise SOHR among the state values of the assembled battery <NUM> calculated by the battery state calculator <NUM>, while obtaining the battery temperature Tcell from the temperature sensor <NUM>. Based on the obtained pieces of information, the mid voltage <NUM> described in <FIG> is calculated. Note that the details of the method of calculating the mid voltage by the mid voltage calculator <NUM> are described later with reference to <FIG>.

The remaining capacity calculator <NUM> obtains the state of charge SOC and the charge capacity fade SOHQ among the state values of the assembled battery <NUM> calculated by the battery state calculator <NUM>. Based on the obtained pieces of information, the remaining capacity of the assembled battery <NUM> at the present time is calculated. Note that the details of the method of calculating the remaining capacity by the remaining capacity calculator <NUM> are described later.

The available energy calculator <NUM> calculates the available energy of the assembled battery <NUM> based on the mid voltage calculated by the mid voltage calculator <NUM> and the remaining capacity calculated by the remaining capacity calculator <NUM>. Specifically, as represented in the following (Expression <NUM>), the available energy of the assembled battery <NUM> is calculated by multiplying the mid voltage by the remaining capacity.

The available energy of the assembled battery <NUM> calculated by the battery management apparatus <NUM> is transmitted from the battery management apparatus <NUM> to the upper level controller <NUM>, and is used to control the inverter <NUM>. Accordingly, the available energy of the assembled battery <NUM> is calculated in real time in the battery energy storage system <NUM>, and charge and discharge control of the assembled battery <NUM> is performed.

<FIG> shows functional blocks of the battery state calculator <NUM>. The battery state calculator <NUM> includes a battery model unit <NUM>, and a state-of-health detector <NUM>.

The battery model unit <NUM> stores a battery model obtained by modeling the assembled battery <NUM>, and obtains the open circuit voltage OCV, the state of charge SOC, and the polarization voltage Vp, using this battery model. The battery model in the battery model unit <NUM> is configured depending on the numbers of serial couplings and parallel couplings of battery cells in the actual assembled battery <NUM>, and the equivalent circuit of each battery cell, for example. The battery model unit <NUM> can obtain the open circuit voltage OCV, the state of charge SOC and the polarization voltage Vp depending on the state of the assembled battery <NUM>, by applying, to this battery model, the current I, the closed-circuit voltage CCV and the battery temperature Tcell obtained respectively from the current sensor <NUM>, the voltage sensor <NUM> and the temperature sensor <NUM>.

<FIG> shows an example of the equivalent circuit of the battery cell in the battery model configured in the battery model unit <NUM>. The equivalent circuit of the battery cell shown in <FIG> includes an open voltage source <NUM> having a voltage value Voc, an internal resistance <NUM> having a resistance value Ro, and a polarization model as a parallel circuit that includes a polarization capacity <NUM> having a capacitance value Cp and a polarization resistance <NUM> having a resistance value Rp; these components are coupled in series. In this equivalent circuit, the voltage across the opposite ends of the open voltage source <NUM>, i.e., the voltage value Voc, corresponds to the open circuit voltage OCV, and the voltage across the opposite ends of the parallel circuit of the polarization capacity <NUM> and the polarization resistance <NUM> corresponds to the polarization voltage Vp. A value obtained by adding applied voltage I×Ro at the internal resistance <NUM> and the polarization voltage Vp when the current I flows through the equivalent circuit, to the open circuit voltage OCV, corresponds to the closed-circuit voltage CCV. Furthermore, the value of each circuit constant in the equivalent circuit in <FIG> is defined depending on the battery temperature Tcell. Accordingly, based on these relationships, the battery model unit <NUM> can obtain the open circuit voltage OCV and the polarization voltage Vp of the entire assembled battery <NUM> from the current I, the closed-circuit voltage CCV and the battery temperature Tcell, and further obtain the state of charge SOC from the calculation result of the open circuit voltage OCV.

Returning to the description on <FIG>, the state-of-health detector <NUM> detects the state of health of the assembled battery <NUM>, and obtains the charge capacity fade SOHQ and the internal resistance rise SOHR depending on the state of health. Each battery cell of the assembled battery <NUM> progressively deteriorates by being repetitively charged and discharged. Depending on the state of health, reduction in charge capacity and increase in internal resistance occur. The state-of-health detector <NUM> preliminarily stores, for example, information representing the relationship between the current, voltage and temperature and the state of health of the assembled battery <NUM>, and detects the state of health of the assembled battery <NUM>, through use of this information, based on the current I, the closed-circuit voltage CCV and the battery temperature Tcell obtained respectively from the current sensor <NUM>, the voltage sensor <NUM> and the temperature sensor <NUM>. Based on the preliminarily stored relationship between the state of health, charge capacity fade SOHQ and internal resistance rise SOHR, the charge capacity fade SOHQ and internal resistance rise SOHR that correspond to the detection result of the state of health of the assembled battery <NUM> can be obtained.

As described above, increase in internal resistance occurs depending on the state of health of the assembled battery <NUM>. In a case where the initial resistance value of the internal resistance is represented as Ro,new, and the resistance value of the internal resistance at the current time t is represented as Ro(t), the internal resistance rise SOHR(t) at the current time t is represented by the following Expression (<NUM>).

<FIG> shows functional blocks of the mid voltage calculator <NUM> according to the first embodiment of the present invention. The mid voltage calculator <NUM> includes a mid OCV table <NUM>, a mid DCR table <NUM>, a discharge current setting unit <NUM>, and an SOHR corrector <NUM>.

The state of charge SOC obtained from the battery state calculator <NUM>, and the battery temperature Tcell obtained from the temperature sensor <NUM> are each input into the mid OCV table <NUM> and the mid DCR table <NUM>. Based on the input pieces of information, the mid OCV table <NUM> and the mid DCR table <NUM> obtain the mid OCV and the mid DCR depending on the current state of the assembled battery <NUM> through table search. Note that the mid DCR is a DC resistance value of the assembled battery <NUM> corresponding to the mid voltage.

In the mid OCV table <NUM>, MidOCV indicating the value of the mid OCV is set for each combination of the state of charge SOC and the battery temperature Tcell. For example, the value of the battery temperature Tcell is represented as Ti (i = <NUM> to p), and the value of the state of charge SOC is represented as SOCj (j = <NUM> to q). With respect to each combination thereof, p × q voltage values MidOCVi,j(V) represented by the following (Expression <NUM>) are set in the mid OCV table <NUM>.

In the mid DCR table <NUM>, MidDCR indicating the value of the mid DCR for each combination of the state of charge SOC and the battery temperature Tcell, is set. For example, the value of the battery temperature Tcell is represented as Ti (i = <NUM> to p), and the value of the state of charge SOC is represented as SOCj (j = <NUM> to q). With respect to each combination thereof, p × q resistance values MidDCRi,j(Ω) represented by the following (Expression <NUM>) are set in the mid DCR table <NUM>. <MAT>
where <NUM> ≤ i ≤ p and <NUM> ≤ j ≤ q. Each of the values of MidOCVi,j in the mid OCV table <NUM>, and each of the values of MidDCRi,j in the mid DCR table <NUM> can be preset based on an analysis result on a discharge test result of the assembled battery <NUM>, and on a result of simulation using an equivalent circuit model of the assembled battery <NUM>. For example, these preset values are written into a memory, not shown, included in the battery management apparatus <NUM>, thereby allowing the mid OCV table <NUM> and the mid DCR table <NUM> to be formed in the battery management apparatus <NUM>. In a design phase of the battery energy storage system, an experiment of discharge at a C-rate may be performed. In this experiment, the voltage value MidOCVi,j and the resistance value MidDCRi,j may be obtained based on the current value, the voltage value and the battery temperature respectively obtained from the current sensor <NUM>, the voltage sensor <NUM> and the temperature sensor <NUM> through the experiment. Although not shown, the mid DCR table <NUM> may have resistance values MidDCRi,j respectively for Ro and Rp.

The mid voltage calculator <NUM> obtains what corresponds to the input current state of charge SOC and battery temperature Tcell of the assembled battery <NUM> among the voltage values MidOCVi,j and the resistance values MidDCRi,j represented by (Expression <NUM>) and (Expression <NUM>), from the mid OCV table <NUM> and the mid DCR table <NUM>, respectively. The mid voltage described with reference to <FIG> is calculated by the following (Expression <NUM>), based on the obtained values, the discharge current IC0,Dch preset in the discharge current setting unit <NUM>, and SOHR for MidDCR (corrected SOHR) input from the SOHR corrector <NUM>.

In (Expression <NUM>), MidVoltage(t) represents the value of the mid voltage at the current time t. MidOCV(t) and MidDCR(t) respectively represent the values of the mid OCV and the mid DCR at the current time t, and are respectively obtained from the mid OCV table <NUM> and the mid DCR table <NUM>. SOHR for MidDCR (t) is a value after the value of the internal resistance rise SOHR calculated by the battery state calculator <NUM> at the time t is corrected by the SOHR corrector <NUM>, and represents an SOHR value to be used to correct the mid DCR (MidDCR). An example of the open-circuit mid voltage (the open-circuit mid voltage corresponding to the mid voltage) at the current time t is MidOCV(t). An example of the mid dropped voltage (the potential difference between the opposite ends of the battery caused by the mid DCR when a predetermined charge-discharge current is caused to flow) at the current time t is "IC0,DCh × MidDCR(t) × SOHR for MidDCR(t)/<NUM>" in (Expression <NUM>). The SOHR corrector <NUM> is described later.

Note that MidOCV(t) and MidDCR(t) in (Expression <NUM>), i.e., the values of the mid OCV and the mid DCR corresponding to the current state of charge SOC and battery temperature Tcell, may be obtained, through interpolation, from the mid OCV table <NUM> and the mid DCR table <NUM>. For example, interpolation using any of various known interpolation methods, such as linear interpolation, Lagrange interpolation, and nearest neighbor interpolation, can be performed. Accordingly, even for a combination of the state of charge SOC and the battery temperature Tcell that is not described in the mid OCV table <NUM> or the mid DCR table <NUM>, an appropriate voltage value and resistance value as the mid OCV and the mid DCR can be obtained.

For example, it is assumed that the values of the state of charge SOC and the battery temperature Tcell at the time t are represented as SOC(t) and Tcell(t), respectively, and these satisfy the relationships in the following (Expression <NUM>). In this case, MidOCV(t) and MidDCR(t) corresponding to the combination of SOC(t) and Tcell(t) are not described in the mid OCV table <NUM> or the mid DCR table <NUM>.

In the case described above, the mid voltage calculator <NUM> can obtain MidOCV(t) at the time t by the following (Expression <NUM>), through interpolation, from the four types of voltage values corresponding to four combinations that combine Ti or Ti+<NUM> and SOCj or SOCj+<NUM> in the mid OCV table <NUM>, i.e., MidOCVi,j, MidoCVi+<NUM>,j, MidOCVi,j+<NUM> and MidOCVi+<NUM>,j+<NUM>.

The mid voltage calculator <NUM> can obtain MidDCR(t) at the time t by the following (Expression <NUM>), through interpolation, from the four types of resistance values corresponding to four combinations that combine Ti or Ti+<NUM> and SOCj or SOCj+<NUM> in the mid DCR table <NUM>, i.e., MidDCRi,j, MidDCRi+<NUM>,j, MidDCRi,j+<NUM> and MidDCRi+<NUM>,j+<NUM>.

In (Expression <NUM>) and (Expression <NUM>), f and g represent interpolation processes executed for the mid OCV table <NUM> and the mid DCR table <NUM>, respectively. The details of these processes vary depending on the interpolation method in the case of interpolation.

The SOHR corrector <NUM> is described in detail. The SOHR corrector <NUM> corrects SOHR in order to improve the accuracy of the available energy to be calculated. As a result of earnest investigation on practical application of a battery management apparatus allowing real-time calculation of the available energy of the assembled battery <NUM> by the inventors of the present application, the following knowledge has been gained. That is, as shown in <FIG>, an equivalent circuit of a battery cell includes two types of resistors that are of an internal resistance <NUM> having a resistance value Ro and a polarization resistance <NUM> having a resistance value Rp. These two types of resistances deteriorate due to repetition of charge and discharge of the assembled battery <NUM> and at least one of the ambient situations. The deterioration mechanism of the internal resistance <NUM> having the resistance value Ro, and the deterioration mechanism of the polarization resistance <NUM> having the resistance value Rp are not completely the same (for example, different by the characteristics of the battery cell (e.g., the material used for the battery cell)). SOHR depends not only on R0 but also on Rp. Consequently, SOHR according to (Expression <NUM>) does not necessarily have a value sufficiently accurate to calculate the mid DCR (MidDCR) after occurrence of deterioration of the resistance. Accordingly, in this embodiment, the SOHR corrector <NUM> is provided. The SOHR corrector <NUM> corrects the SOHR calculated by the battery state calculator <NUM>. Specifically, an element depending on the different deterioration mechanisms of the internal resistance <NUM> and the polarization resistance <NUM> (in other words, an element dependent on the deterioration degree of the DC resistance component of the assembled battery <NUM> and the deterioration degree of the polarization resistance component of the assembled battery <NUM>) is reflected in the SOHR. The corrected SOHR is used to correct MidDCR obtained from the mid DCR table <NUM>. The corrected SOHR is SOHR for MidDCR described above. Consequently, in (Expression <NUM>), "SOHR for MidDCR(t)/<NUM>" corresponds to the correction coefficient for the mid DCR (the correction coefficient corresponding to the corrected SOHR of the assembled battery <NUM>), and "MidDCR(t)×SOHR for MidDCR(t)/<NUM>" corresponds to the corrected MidDCR(t) corrected using SOHR for MidDCR(t) (corrected SOHR(t)).

SOHR for MidDCR(t) (corrected SOHR(t)) is represented by the following (Expression <NUM>).

h is the element depending on the different deterioration mechanisms of the internal resistance <NUM> and the polarization resistance <NUM>. <FIG> shows an example of h for each of different battery temperatures.

According to discussion by the inventor of the present application, the internal resistance <NUM> and the polarization resistance <NUM> are affected by the battery temperature, and SOHR for MidDCR linearly depends on SOHR calculated by the battery state calculator <NUM>. For the battery temperatures T<NUM> and TN shown in <FIG>, the following (Expression 11a) and (Expression 11b) hold. <MAT> <MAT>.

λ<NUM> (λ<NUM> > <NUM>) is the slope of a straight line <NUM> representing the relationship between SOHR and SOHR for MidDCR at a battery temperature T<NUM>. λN (λN > <NUM>) is the slope of a straight line <NUM> representing the relationship between SOHR and SOHR for MidDCR at a battery temperature TN.

An element h to be reflected in SOHR calculated by the battery state calculator <NUM> is not limited to the example shown in <FIG>. The element h may be determined based on the result of analyzing the test result on the assembled battery <NUM>, and on the simulation result on the assembled battery <NUM>.

After MidOCV(t) and MidDCR(t) through interpolation are successfully obtained as described above, the mid voltage calculator <NUM> applies these values to (Expression <NUM>) described above, thereby allowing the mid voltage MidVoltage(t) at the current time t to be calculated.

The remaining capacity calculator <NUM> calculates the remaining capacity of the assembled battery <NUM> by the following (Expression <NUM>) based on the state of charge SOC and the charge capacity fade SOHQ obtained from the battery state calculator <NUM>.

In (Expression <NUM>), RemainingCapacity(t) represents the value of the remaining capacity at the current time t. Ahrated represents the rated capacity of the assembled battery <NUM>, i.e., the remaining capacity of the assembled battery <NUM> at the start of use when being fully charged.

The first embodiment of the present invention described above exerts the following working effects.

Next, a second embodiment of the present invention is described. In this embodiment, instead of the constant discharge current IC0,Dch described in the first embodiment, a method is described that calculates the available energy of the assembled battery <NUM> by using discharge current ICk,DCh determined in consideration of an actual traveling state of a vehicle provided with the assembled battery <NUM>. Note that a configuration of a battery energy storage system according to this embodiment is similar to the battery energy storage system (BESS) <NUM> in <FIG> described in the first embodiment. Accordingly, the description thereof is omitted.

In this embodiment, unlike the discharge current IC0,Dch in the first embodiment, the value of the discharge current ICk,DCh is not a preset value, and is determined by the battery management apparatus <NUM> based on an immediately previous traveling state of the vehicle. That is, the available energy of the assembled battery <NUM> in this embodiment corresponds to the total electric energy (Wh) dischargeable without each battery cell falling below the minimum voltage Vmin, until SOC of each battery cell reaches SOCmin, which is the minimum SOC value permitted for the corresponding battery cell, in a case where each battery cell of the assembled battery <NUM> is discharged with the discharge current ICk,DCh.

<FIG> shows functional blocks of the battery management apparatus 102a pertaining to an available energy calculation process according to the second embodiment of the present invention. The battery management apparatus <NUM> of this embodiment includes functional blocks including a battery state calculator <NUM>, a mid voltage calculator 502a, a remaining capacity calculator <NUM>, an available energy calculator <NUM>, and a C-rate calculator <NUM>. These functional blocks can be achieved by causing a computer to execute a predetermined program, for example.

The battery state calculator <NUM>, the remaining capacity calculator <NUM> and the available energy calculator <NUM> in <FIG> are similar to those in the battery management apparatus <NUM> in <FIG> described in the first embodiment. Accordingly, hereinafter, the operations of the mid voltage calculator 502a in <FIG> provided instead of the mid voltage calculator <NUM> in <FIG>, and the newly provided C-rate calculator <NUM> are mainly described, and description of the other functional blocks in <FIG> is omitted.

The C-rate calculator <NUM> calculates the C-rate during discharge of the assembled battery <NUM>, i.e., the rate of the magnitude of the discharge current to the capacitance of the assembled battery <NUM>. For example, measured values of discharge current obtained from a predetermined time period before to the present time are averaged, and the average value is divided by the rated capacity of the assembled battery <NUM>, thereby calculating the C-rate during discharge. The value of the C-rate calculated by the C-rate calculator <NUM> is input into the mid voltage calculator 502a.

The mid voltage calculator 502a obtains the state of charge SOC and the internal resistance rise SOHR among the state values of the assembled battery <NUM> calculated by the battery state calculator <NUM>, while obtaining the battery temperature Tcell from the temperature sensor <NUM>. Furthermore, the C-rate is obtained from the C-rate calculator <NUM>. Based on the obtained pieces of information, the mid voltage <NUM> described in <FIG> in the first embodiment is calculated.

<FIG> shows the functional blocks of the mid voltage calculator 502a according to the second embodiment of the present invention. The mid voltage calculator 502a includes a mid OCV table group <NUM>, a mid DCR table group <NUM>, an SOHR corrector <NUM>, and a gain setting unit <NUM>.

The state of charge SOC obtained from the battery state calculator <NUM>, the battery temperature Tcell obtained from the temperature sensor <NUM> and the C-rate obtained from the C-rate calculator <NUM> are input into the mid OCV table group <NUM> and the mid DCR table group <NUM>. Based on the input pieces of information, the mid OCV table group <NUM> and the mid DCR table group <NUM> obtain the mid OCV and the mid DCR depending on the current state of the assembled battery <NUM> through table search.

In the mid OCV table group <NUM>, MidOCV indicating the value of the mid OCV is set for each combination of the C-rate, the state of charge SOC and the battery temperature Tcell. Specifically, multiple tables in each of which the value of MidOCV is set for each combination of the state of charge SOC and the battery temperature Tcell, are set depending on the value of the C-rate. For example, it is assumed that the value of the C-rate is represented as Ck (k = <NUM> to N). Tables similar to the mid OCV table <NUM> described in the first embodiment are set with respect to each Ck, and the total number thereof is N. The value of MidOCV in each table is set to a value at the corresponding Ck.

Likewise, in the mid DCR table group <NUM>, MidDCR indicating the value of the mid DCR is set for each combination of the C-rate, the state of charge SOC and the battery temperature Tcell. Specifically, multiple tables in each of which the value of MidDCR is set for each combination of the state of charge SOC and the battery temperature Tcell, are set depending on the value of the C-rate. That is, as described above, it is assumed that the value of the C-rate is represented as Ck (k = <NUM> to N). Tables similar to the mid DCR table <NUM> described in the first embodiment are set with respect to each Ck, and the total number thereof is N. The value of MidDCR in each table is set to a value at corresponding Ck. The value of MidDCR may be provided for both Ro and Rp.

The mid voltage calculator 502a obtains the values of the mid OCV and the mid DCR corresponding to the input current state of charge SOC, battery temperature Tcell and value of the C-rate of the assembled battery <NUM>, from the mid OCV table group <NUM> and the mid DCR table group <NUM>.

The gain setting unit <NUM> sets the rated capacity Ahrated in (Expression <NUM>) described in the first embodiment, as the gain for the input C-rate. By multiplying the value of the C-rate by the rated capacity Ahrated, the discharge current ICk,DCh is calculated.

The mid voltage calculator 502a calculates the mid voltage described with reference to <FIG> by the following (Expression <NUM>) based on the values of the mid OCV and the mid DCR obtained respectively from the mid OCV table group <NUM> and the mid DCR table group <NUM>, the discharge current ICk,DCh output from the gain setting unit <NUM>, and the SOHR for MidDCR (corrected SOHR). Here, provided that the value of the C-rate at the current time t is represented as C(t), ICk,DCh = C(t) × Ahrated.

Similar to (Expression <NUM>) described in the first embodiment, MidVoltage(t) represents the value of the mid voltage at the current time t in (Expression <NUM>). MidOCV(t) and MidDCR(t) respectively represent the values of the mid OCV and the mid DCR at the current time t, and are respectively obtained from the mid OCV table group <NUM> and the mid DCR table group <NUM>. SOHR for MidDCR(t) represents the value of corrected SOHR at the time t.

Similar to the first embodiment, also in this embodiment, MidOCV(t) and MidDCR(t) in (Expression <NUM>), i.e., the values of the mid OCV and the mid DCR corresponding to the current state of charge SOC and battery temperature Tcell, may be obtained, through interpolation, from the mid OCV table group <NUM> and the mid DCR table group <NUM>. Accordingly, even for a combination of the C-rate, the state of charge SOC and battery temperature Tcell that is not described in the mid OCV table group <NUM> or the mid DCR table group <NUM>, an appropriate voltage value and resistance value as the mid OCV and the mid DCR can be obtained.

For example, it is assumed that the state of charge SOC, the battery temperature Tcell and the values of the C-rate at the time t are represented as SOC(t), Tcell(t) and C(t), respectively, and these satisfy the relationships in the following (Expression <NUM>). In this case, MidOCV(t) and MidDCR(t) corresponding to the combination of SOC(t), Tcell(t) and C(t) are not described in the mid OCV table group <NUM> or the mid DCR table group <NUM>.

In the above description, first, the mid voltage calculator 502a calculates a table corresponding to C(t), through interpolation, from two tables corresponding to Ck and Ck+<NUM> in the mid OCV table group <NUM>. In the calculated table, four types of voltage values corresponding to four combinations that combine Ti or Ti+<NUM> and SOCj or SOCj+<NUM> are extracted as MidOCVi,j(Ck, Ck,<NUM>), MidOCVi+<NUM>, j(Ck, Ck+<NUM>), MidOCVi,j+<NUM> (Ck, Ck+<NUM>), and MidOCVi+<NUM>, j+<NUM> (Ck, Ck+<NUM>). From these voltage values, MidOCV(t) at the time t can be obtained by the following (Expression <NUM>), through interpolation.

The mid voltage calculator 502a calculates a table corresponding to C(t), through interpolation, from two tables corresponding to Ck and Ck+<NUM> in the mid DCR table group <NUM>. In the calculated table, four types of resistance values corresponding to four combinations that combine Ti or Ti+<NUM> and SOCj or SOCj+<NUM> are extracted as MidDCRi,j(Ck, Ck+<NUM>), MidDCRi+<NUM>,j(Ck, Ck+<NUM>), MidDCRi,j+<NUM>(Ck, Ck+<NUM>), and MidDCRi+<NUM>,j+<NUM>(Ck, Ck+<NUM>). From these resistance values, MidDCR(t) at the time t can be obtained by the following (Expression <NUM>), through interpolation.

After MidOCV(t) and MidDCR(t) through interpolation are successfully obtained as described above, the mid voltage calculator 502a applies these values to (Expression <NUM>) described above, thereby allowing the mid voltage MidVoltage(t) at the current time t to be calculated.

According to the aforementioned second embodiment of the present invention, in addition to the working effects (<NUM>) and (<NUM>) described in the first embodiment, the following working effects are further exerted.

Next, a third embodiment of the present invention is described. Hereinafter, the difference from the first embodiment is mainly described, and description of points in common with the first embodiment is omitted or simplified.

<FIG> shows functional blocks of a battery management apparatus 102b pertaining to an available energy calculation process according to the third embodiment of the present invention. The battery management apparatus 102b of this embodiment includes a battery state calculator 501b and a mid voltage calculator 502b respectively instead of the battery state calculator <NUM> and the mid voltage calculator <NUM> shown in <FIG>. These functional blocks can be achieved by causing a computer to execute a predetermined program, for example.

The difference between the battery state calculator <NUM> and the battery state calculator 501b is as follows. That is, the battery state calculator 501b calculates SOHR for Ro and SOHR for Rp, instead of SOHR calculated by the battery state calculator <NUM>. SOHR for Ro is SOHR with respect to Ro. SOHR for Rp is SOHR with respect to Rp. For example, SOHR for Ro(t) = {Ro(t)/ Ro,new} × <NUM>, and SOHR for Rp(t) ={Rp(t)/ Rp,new} × <NUM> may be adopted. SOHR for Ro(t) is SOHR for Ro at the time t. Ro(t) is Ro at the time t. Ro,new is an initial Ro. SOHR for Rp(t) is SOHR for Rp at the time t. Rp(t) is Rp at the time t. Rp,new is an initial Rp.

The difference between the mid voltage calculator <NUM> and the mid voltage calculator 502b is as follows. The mid voltage calculator 502b receives SOHR for Ro and SOHR for Rp calculated by the battery state calculator 501a instead of SOHR.

<FIG> shows functional blocks of the mid voltage calculator 502b according to the third embodiment of the present invention. The mid voltage calculator 502b includes an SOHR corrector 1610a instead of the SOHR corrector <NUM> shown in <FIG>.

The difference between the SOHR corrector <NUM> and the SOHR corrector 1610a is as follows. The SOHR corrector 1610a receives SOHR for Ro and SOHR for Rp calculated by the battery state calculator 501a instead of SOHR. The SOHR corrector 1610a calculates SOHR for MidDCR, based on SOHR for Ro and SOHR for Rp. SOHR for MidDCR may be, for example, based on SOHR for Ro and its weight A and on SOHR for Rp and its weight B. The weight A and the weight B may be absolute weights or relative weights. For example, SOHR for MidDCR may be a weighted sum of SOHR for Ro and SOHR for Rp as shown by the following (Expression <NUM>).

Each of the weights A and B may be a constant, or a variable value changed depending on a parameter, such as the battery temperature. The parameter described here may be, for example, a parameter determined based on the result of the experiment of discharge at the C-rate with various battery deterioration degrees.

According to the aforementioned second embodiment of the present invention, in addition to the working effects (<NUM>) to (<NUM>) described in the first embodiment, the following working effects are further exerted. (<NUM>) The calculated resistance deterioration degree SOHR is the internal resistance deterioration degree SOHR for Ro that is the deterioration degree of the internal resistance <NUM> of the assembled battery <NUM>, and the polarization resistance deterioration degree SOHR for Rp that is the deterioration degree of the polarization resistance <NUM> of the assembled battery <NUM>. The mid voltage calculator 502b calculates the corrected resistance deterioration degree (SOHR for MidDCR), based on the calculated SOHR for Ro and the weight A of SOHR for Ro, and on the calculated SOHR for Rp and the weight B of SOHR for Rp. Accordingly, both Ro and Rp are reflected in the corrected SOHR. Consequently, the accuracy of SOHR that is an element for calculation of the available energy is improved. As a result, it is expected that the accuracy of the calculated available energy is high.

Note that in each embodiment described above, application examples to the battery energy storage systems mounted on electric vehicles, hybrid vehicles and the like have been described. Likewise, the present invention is applicable also to battery energy storage systems used for other applications, for example, battery energy storage systems and the like coupled to a power grid and used.

In each embodiment described above, the method of calculating the available energy when the assembled battery <NUM> is discharged is described. Alternatively, similar calculation methods are also applicable to chargeable energy when the assembled battery <NUM> is charged. Here, the chargeable energy is defined as the total amount of electrical energy chargeable when the assembled battery <NUM> is charged from a certain state of charge. This corresponds to the total electric energy (Wh) with which each battery cell can be charged until SOC of each battery cell reaches SOCmax, which is the maximum SOC value permitted for the corresponding battery cell, in a case where each battery cell of the assembled battery <NUM> is charged with a constant discharge current.

In the case of application to calculation of the chargeable energy, the mid voltage <NUM> described with reference to <FIG> is present between the voltage value corresponding to the current SOC and the voltage value corresponding to SOCmax when charging is completed, on a charge curve representing change in charge voltage from the current SOC of the assembled battery <NUM> to the SOCmax. The mid voltage <NUM> is then obtained such that a value obtained by multiplying the mid voltage <NUM> by the chargeable capacity defined as the difference between the current SOC and SOCmax matches the integral value of the charge curve from the current SOC to SOCmax. Specifically, the mid voltage during charging can be obtained by using those similar to the mid voltage calculator <NUM> described in the first embodiment, and the mid voltage calculator 502a described in the second embodiment. Note that the mid voltage (CCV) during charging increases in voltage by what is for the internal resistance more than the mid OCV. Accordingly, (Expression <NUM>) and (Expression <NUM>) described above may be changed to the following (Expression <NUM>') and (Expression <NUM>') and used. <MAT> <MAT>.

The mid voltage during charging obtained as described above is multiplied by the chargeable capacity obtained by the following (Expression <NUM>), thereby allowing the chargeable energy to be calculated. Note that in (Expression <NUM>), ChargeableCapacity(t) represents the value of the chargeable capacity at the current time t. Ahrated represents the rated capacity of the assembled battery <NUM>, i.e., the remaining capacity of the assembled battery <NUM> at the start of use when being fully charged.

The third embodiment may be applied not only to the first embodiment but also to the second embodiment. Specifically, for example, the battery state calculator <NUM> in the embodiment in <FIG> may be replaced with the battery state calculator 501b in the third embodiment. The SOHR corrector <NUM> in the second embodiment may be replaced with the SOHR corrector 1610a in the third embodiment. In the case where the third embodiment is reflected in the second embodiment, the working effect (<NUM>) described above is exerted in addition to the working effects (<NUM>) to (<NUM>) and (<NUM>) to (<NUM>) described above.

Claim 1:
A battery management apparatus for managing a chargeable and dischargeable battery, comprising:
a battery state calculator (<NUM>) that calculates a state of charge, a capacity deterioration degree, and a resistance deterioration degree of the battery;
a mid voltage calculator (<NUM>) that corrects the calculated resistance deterioration degree, corrects a mid resistance of the battery corresponding to a respective mid voltage according to a correction coefficient in accordance with the corrected resistance deterioration degree, and calculates a mid voltage that is present between a charge-discharge voltage in a current state of charge of the battery, and a charge-discharge voltage in a minimum state of charge or a maximum state of charge of the battery, based on the corrected mid resistance;
a remaining capacity calculator (<NUM>) that calculates a remaining capacity or a chargeable capacity of the battery, based on the calculated state of charge and the capacity deterioration degree; and
an available energy calculator (<NUM>) that calculates available energy or chargeable energy of the battery, based on the calculated mid voltage and the remaining capacity, or on the calculated mid voltage and the chargeable capacity.