Power supply system and method for controlling the same

A power supply system that supplies electric power to a load includes a first power storage device, a second power storage device, a power line for transmitting electric power input and output to and from the load, a converter for executing bidirectional DC voltage conversion between the first power storage device and the power line, and a switch connected between the second power storage device and the power line. When the switch is OFF, the control device performs voltage control of the converter so that a voltage value of the power line becomes a voltage command value, and when the switch is ON, the control device performs current control of the converter so that a current value of the first power storage device becomes a current command value.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/JP 2011/071987 filed Sep. 27, 2011, the contents of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

This invention relates to a power supply system and a method for controlling the power supply system, and more particularly to controlling of a power supply system on which a plurality of power storage devices are mounted.

BACKGROUND ART

In a power supply system applied to an electric powered vehicle, a power conversion apparatus that converts output electric power of a power storage device mounted on the vehicle into electric power for driving a drive motor is configured with a combination of a converter that can step-up the output voltage of the power storage device, and an inverter that converts output DC voltage of the converter into AC voltage and applies the AC voltage to the inverter.

Japanese Patent Laying-Open No. 2009-159663 (PTD 1) discloses a power supply system that includes a plurality of power storage devices, and a plurality of converters provided between DC power lines connected to inverters and the plurality of power storage devices, respectively. In the power supply system described in PTD 1, one of two converters is controlled in accordance with voltage control for bringing a voltage value of a DC power line to a prescribed voltage target value, while the other converter is controlled in accordance with current control for bringing the charge and discharge current of a corresponding power storage device to a prescribed current target value.

CITATION LIST

Patent Document

SUMMARY OF INVENTION

Technical Problem

In the power supply system described in PTD 1 described above, a converter for controlling charge and discharge power of each power storage device is provided for each power storage device associated with the converter. This allows charge and discharge into and from each power storage device to be performed independently.

However, upon charge and discharge into and from each power storage device, power loss occurs in the converter. Moreover, in order to extend the mileage of an electric powered vehicle, it is desirable to increase the number of power storage devices mounted to achieve an increased charge and discharge capacity of the power storage devices. This, however, also necessitates increasing the number of converters, leading to an increase in power loss, and an increase in size and costs of the power supply system. It is therefore necessary to construct a mechanism for making effective use of a plurality of power storage devices, while ensuring the function of variable control of DC voltage by converters.

Accordingly, this invention was made to solve the problems as described above, and an object of the invention is to simply and efficiently configure a power supply system on which a plurality of power storage devices are mounted, while ensuring the function of variable control of DC voltage.

Solution to Problem

In accordance with one aspect of this invention, a power supply system that supplies electric power to a load includes a first power storage device, a second power storage device, a power line for transmitting electric power input and output to and from a load, a converter for executing bidirectional DC voltage conversion between the first power storage device and the power line, a switch connected between the second power storage device and the power line, and a control device that controls ON/OFF of the switch and the converter. When the switch is OFF, the control device performs voltage control of the converter so that a voltage value of the power line becomes a voltage command value, and when the switch is ON, the control device performs current control of the converter so that a current value of the first power storage device becomes a current command value.

Preferably, the control device includes a switching unit that switches ON and OFF of the switch in accordance with an operating state of the load, a voltage control unit that performs voltage control of the converter in accordance with an output of a voltage feedback control element including at least an integral element that integrates a deviation of the voltage value of the power line from the voltage command value, and a current control unit that performs current control of the converter in accordance with an output of a current feedback control element including at least an integral element that integrates a deviation of the current value of the first power storage device from the current command value. When switching the switch from ON to OFF, the voltage control unit takes over from the current control unit the output of the integral element in the current feedback control element, as an initial value of the integral element in the voltage feedback control element.

Preferably, when switching the switch from OFF to ON, the current control unit takes over from the voltage control unit the output of the integral element in the voltage feedback control element, as an initial value of the integral element in the current feedback control element.

Preferably, the voltage control unit includes a voltage control calculation unit that performs a proportional integral calculation of the deviation of the voltage value of the power line from the voltage command value, and outputs a calculated control amount as the current command value, and a current control calculation unit that performs a proportional integral calculation of the deviation of the current value of the first power storage device from the current command value output from the voltage control calculation unit, and outputs a calculated control amount as a duty ratio command value to the converter. When the switch is ON, the current control calculation unit is configured to receive the current command value set in accordance with an electric power target value to be shared by the first power storage device, in place of the current command value output from the voltage control calculation unit, thereby functioning as the current control unit.

Preferably, the load includes an electric motor that generates vehicle driving force by receiving electric power supplied from the power supply system. The voltage control unit calculates a minimum required voltage of the power line in accordance with a torque and a rotational speed of the electric motor and sets the voltage command value in a range not lower than the minimum required voltage. The current control unit calculates required electric power of the electric motor in accordance with the torque and the rotational speed of the electric motor and determines an electric power target value to be shared by the first power storage device in accordance with the required electric power of the electric motor, and sets the current target value by dividing the electric power target value by a voltage of the first power storage device.

In accordance with another aspect of this invention, in a method for controlling a power supply system that supplies electric power to a load, the power supply system includes a first power storage device, a second power storage device, a power line for transmitting electric power input and output to and from a load, a converter for executing bidirectional DC voltage conversion between the first power storage device and the power line, and a switch connected between the second power storage device and the power line. A controlling method includes the step of, when the switch is OFF, performing voltage control of the converter so that a voltage value of the power line becomes a voltage command value, and when the switch is ON, performing current control of the converter so that a current value of the first power storage device becomes a current command value.

Advantageous Effects of Invention

According to the present invention, in the power supply system on which a plurality of power storage devices are mounted, even though a converter is provided only for some power storage devices, electric power can be supplied to a load through cooperative use of the plurality of power storage devices. Consequently, electric power can be supplied to the load with the effective use of the plurality of power storage devices, so that the power supply system can be configured to be smaller and efficiently at low cost.

DESCRIPTION OF EMBODIMENTS

Embodiments of this invention will hereinafter be described in detail, referring to the drawings. In the drawings, the same or corresponding portions are indicated by the same characters.

[Basic Structure of Vehicle]

FIG. 1is a schematic block diagram of an electric powered vehicle to which a power supply system according to an embodiment of the present invention is applied.

Referring toFIG. 1, in the embodiment of the present invention, a case where the drive system that generates driving force of an electric powered vehicle5corresponds to a load10will be described by way of example. Electric powered vehicle5runs by transmitting driving force generated with electric power supplied to load10from a power supply system20to a driving wheel260. Moreover, during regeneration, electric powered vehicle5causes electric power to be generated from kinetic energy with load10, and recovers the power into power supply system20.

Electric powered vehicle5is typically a hybrid vehicle, which includes an internal combustion engine (engine)220and electric motors (MG: Motor Generator), and runs with driving forces from the respective components controlled at an optimum ratio. A plurality of (two, for example) power storage devices for supplying electric power to these motor generators are mounted on electric powered vehicle5. During start-up of the system of electric powered vehicle5, these power storage devices can be charged by receiving mechanical power generated by the operation of engine220, and during stoppage of the system of electric powered vehicle5, they can be charged by being electrically connected to a power supply external to the vehicle via a connection portion not illustrated.

Note that in the present embodiment, an example in which electric powered vehicle5includes two motor generators and inverters corresponding thereto will be described; however, the present invention is also applicable to a case where electric powered vehicle5includes one motor generator and an inverter, and a case where three or more motor generators and inverters.

Electric powered vehicle5includes load10, power supply system20, and control device300. Load10includes an inverter120, motor generators MG1, MG2, a power split device250, an engine220, and driving wheel260.

Each of motor generators MG1, MG2is an AC rotating electric machine, and is, for example, a permanent magnet type synchronous motor that includes a rotor in which a permanent magnet is embedded, and a stator having a three-phase coil arranged in a Y-connection at the neutral point.

Output torque of motor generators MG1, MG2is transmitted to driving wheel260via power split device250, whereby electric powered vehicle5is run. At the time of regenerative braking of electric powered vehicle5, motor generators MG1, MG2can generate electric power by rotational force of driving wheel260. The generated electric power is then converted by a converter110and inverter120into electric power for charging power storage device(s)100and/or150.

Motor generators MG1, MG2are also coupled to engine220via power split device250. Then, motor generators MG1, MG2, and engine220are cooperatively operated by control device300, whereby required vehicle driving force is generated. Moreover, motor generators MG1, MG2can generate electric power by rotation of engine220, and power storage device100and/or150can be charged with this generated electric power. Note that in the present embodiment, motor generator MG2is used mainly as an electric motor for driving wheel260, and motor generator MG1is used mainly as a power generator driven by engine220. That is, motor generator MG2corresponds to an “electric motor” for generating vehicle driving force.

Power split device250is configured to include a planetary gear mechanism (planetary gear) for splitting mechanical power of engine220between driving wheel260and motor generator MG1.

Current sensors230,240detect motor currents (namely, inverter output currents) MCRT1, MCRT2flowing in motor generators MG1, MG2, respectively, and output the detected motor currents to control device300. Note that since the sum of instantaneous values of currents iu, iv, and iw of U-, V-, and W-phases is zero, current sensors230,240may be disposed to detect the motor currents of two phases of U-, V-, and W-phase (for example, V-phase current iv and W-phase current iw).

Rotation angle sensors (for example, resolvers)270,280detect rotation angles θ1and θ2of motor generators MG1, MG2, respectively, and transmit the detected rotation angles θ1and θ2to control device300. At control device300, rotational speeds and angular velocities of motor generators MG1, MG2can be calculated based on rotation angles θ1, θ2. Note that the provision of rotation angle sensors270,280may be omitted by using control device300to directly calculate rotation angles θ1,742from the motor voltages and currents.

Inverter120carries out bidirectional power conversion between DC electric power between a power supply line HPL and a ground line NL1, and AC electric power input and output to and from motor generators MG1and MG2. That is, power supply line HPL corresponds to a “power line” for transmitting electric power input and output to and from motor generators MG1and MG2.

Inverter120includes a first inverter for driving motor generator MG1and a second inverter for driving motor generator MG2, although not illustrated. First inverter mainly converts AC electric power generated by motor generator MG1with the output of engine220into DC electric power, in response to a control signal PWI from control device300, and supplies the DC electric power to power supply line HPL and ground line NL1. At this time, converter110is controlled by control device300to operate as a step-down circuit. In this way, during running of the vehicle as well, power storage device100and/or power storage device150can be actively charged with the output of engine220.

At the time of starting engine220, the first inverter also converts DC electric power from power storage device100and power storage device150into AC electric power, in accordance with control signal PWI from control device300, and supplies the AC electric power to motor generator MG1. Engine220can thus start motor generator MG1as a starter.

The second inverter converts DC electric power supplied via power supply line HPL and ground line NL1into AC electric power, in accordance with control signal PWI from control device300, and supplies the AC electric power to motor generator MG2. Motor generator MG2thus generates driving force for electric powered vehicle5.

Meanwhile, at the time of regenerative braking of electric powered vehicle5, motor generator MG2generates AC electric power along with deceleration of driving wheel260. At this time, the second inverter converts AC electric power generated by motor generator MG2into DC electric power, in response to control signal PWI from control device300, and supplies the DC electric power to power supply line HPL and ground line NL1. Power storage device100and/or power storage device150are/is thus charged during deceleration or running downhill.

Power supply system20includes power storage device100corresponding to “a first power storage device”, power storage device150corresponding to “a second power storage device”, a system main relay190, relays RL1to RL3and a resistance R2, converter110, and smoothing capacitors C1, C2.

Each of power storage devices100,150is a rechargeable power storage element, and typically adopts a secondary battery such as a lithium ion battery or a nickel-metal hydride battery. Hence, power storage device100and power storage device150will hereinafter also be referred to as battery100and battery150, respectively. It is noted that each of power storage devices100,150may also be constituted by a power storage element other than a battery, such as an electric double layer capacitor, or of a combination of a battery and a power storage element other than a battery.

Moreover, power storage devices100and150may be constituted by power storage devices of the same type or different types.

Each of batteries100and150is constituted by a plurality of battery cells connected in series. That is, the rated value of the output voltage of each of batteries100and150depends on the number of the battery cells connected in series.

Battery100is provided with a battery sensor105for detecting battery voltage Vb1and battery current Ib1. Similarly, battery150is provided with a battery sensor155for detecting battery voltage Vb2and battery current Ib2. Detection values from battery sensors105,155are transmitted to control device300. System main relay190includes relays SMR1to SMR3and a resistance R1.

Relays SMR1, SMR2are inserted through power supply line PL1and ground line NL1, respectively. Relay SMR3is connected in parallel with relay SMR2, and connected in series with resistance R1. That is, a circuit in which relay SMR3and resistance R1are connected in series is connected in parallel with relay SMR2. Relays SMR1to SMR3are controlled to be turned ON (closed)/OFF (opened) in response to relay control signals SE1to SE3given from control device300.

Relay RL1is connected between a power supply line HPL and a positive electrode terminal of power storage device150. Relay RL2is connected between a negative electrode terminal of power storage device150and ground line NL1. Relay RL3is connected in parallel with relay RL2and connected in series with resistance R2. That is, a circuit in which relay RL3and resistance R2are connected in series is connected in parallel with relay RL2. Relays RL1to RL3are controlled to be turned ON (closed)/OFF (opened) in response to relay control signals SR1to SR3given from control device300. Relay RL1is used as a representative example of a “switch” that is capable of disconnecting the electrical connection between power storage device150and power supply line HPL. That is, a switch of any type can be adopted in place of relay RL1.

Converter110is configured to execute bidirectional DC voltage conversion between power storage device100and power supply line HPL that transmits a DC link voltage of inverter120. That is, the input/output voltage of power storage device100and the DC voltage between power supply line HPL and ground line NL1are bidirectionally stepped up or down.

Specifically, converter110includes a reactor L1having one end connected to power supply line PL1, switching elements Q1, Q2connected in series between power supply line HPL and ground line NL1, and diodes D1, D2connected in parallel with switching elements Q1, Q2, respectively. As the switching elements, IGBTs (Insulated Gate Bipolar Transistors), bipolar transistors, MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), or GTOs (Gate Turn Off Thyristors), for example, are typically used. In the present embodiment, a case where IGBTs are used as the switching elements is described as an example.

The other end of reactor L1is connected to the emitter of switching element Q1and the collector of switching element Q2. The cathode of diode D1is connected to the collector of switching element Q1, and the anode of diode D1is connected to the emitter of switching element Q1. The cathode of diode D2is connected to the collector of switching element Q2, and the anode of diode D2is connected to the emitter of switching element Q2.

Switching elements Q1, Q2are controlled to be turned ON or OFF by a control signal PWC from control device300.

Smoothing capacitor C1is connected between power supply line PL1and ground line NL1, and reduces voltage fluctuations between power supply line PL1and ground line NL1. A voltage sensor170detects a voltage VL across the terminals of smoothing capacitor C1, and outputs the detected voltage to control device300. Converter110steps up the voltage across the terminals of smoothing capacitor C1. A current sensor160is inserted through power supply line PL1, and detects a current (equivalent to the current involving charge and discharge of power storage device100) IL flowing in reactor L1, and outputs the detected current IL to control device300. It is noted that current sensor160is not indispensable, and current IL may be replaced with battery current Ib1detected by battery sensor105provided for power storage device100.

A smoothing capacitor C2is connected between power supply line HPL and ground line NL1, and reduces voltage fluctuations between power supply line HPL and ground line NL1. That is, smoothing capacitor C2smoothes the voltage stepped up by converter110. A voltage sensor180detects a voltage VH across the terminals of smoothing capacitor C2, and outputs the detected voltage to control device300. Voltage VH (that is, the DC-side voltage of inverter120) across the terminals of smoothing capacitor C2will hereinafter be also referred to as “system voltage VH”.

Control device300includes a CPU (Central Processing Unit), memory, and an input/output buffer, all of which are not illustrated, and controls converter110and inverter120. It is noted that such control can be performed not only by software processing, but also by dedicated hardware (electronic circuit) constructed therefor.

Control device300receives detection values of motor currents MCRT1and MCRT2flowing in motor generators MG1, MG2, respectively, detected by current sensors230,240. Control device300receives detection values of rotation angles θ1, θ2of motor generators MG1, MG2detected by rotation angle sensors270,280. Control device300also receives detection values of voltages VL, VH across smoothing capacitors C1, C2detected by voltage sensors170,180, and a detection value of current IL involving charge and discharge of power storage device100detected by current sensor160. Control device300also receives an ignition signal IG indicating the ON/OFF state of an ignition switch that is not illustrated.

Control device300generates control signal PWC of converter110, based on voltages VL, VH across smoothing capacitors C1, C2. Control device300then causes converter110to perform a step-up or step-down operation, by driving switching elements Q1, Q2of converter110with control signal PWC.

Control device300also generates a control signal PWI for driving inverter120, based on motor currents MCRT1, MCRT2flowing in motor generators MG1, MG2, respectively, detected by current sensors230,240, and rotation angles θ1, θ2of motor generators MG1, MG2detected by rotation angle sensors270,280. Control device300then converts AC electric power for driving motor generators MG1, MG2into DC electric power supplied from converter110, by driving switching elements of inverter120with control signal PWI.

Control device300generates relay control signals SE1to SE3based on ignition signal IG. Control device300then controls ON/OFF of relays SMR1to SMR3of system main relay190with relay control signals SE1to SE3. Specifically, when ignition signal IG is switched from the OFF state to the ON state by a driver turning ON the ignition switch, control device300first turns ON relays SMR1, SMR3with relay SMR2being kept in the OFF state. At this time, a portion of the current is consumed by resistance R1to reduce the current flowing into smoothing capacitor C1, thereby preventing inrush current into smoothing capacitor C1. Thereafter, upon completion of precharge of smoothing capacitor C1, relay SMR2is turned ON, and relay SMR3is subsequently turned OFF.

Control device300generates relay control signals SR1to SR3, based on operating states of motor generators MG1, MG2, and a detection value of each sensor. Control device300then controls ON/OFF of relays RL1to RL3with relay control signals SR1to SR3. Specifically, when power storage device150is electrically connected to power supply line HPL, control device300first turns ON relays RL1, RL3with relay RL2being kept in the OFF state. At this time, a portion of the current is consumed by resistance R2to reduce the current flowing into smoothing capacitor C2, thereby preventing inrush current into smoothing capacitor C2. Thereafter, upon completion of precharge of smoothing capacitor C2, relay RL2is turned ON, and relay RL3is subsequently turned OFF.

As described above, power supply system20according to the embodiment of the present invention is configured to include a plurality of power storage devices100and150. Power storage device150is directly electrically connected to power supply line HPL, without converter110being interposed therebetween. Therefore, when relays RL1, RL2are ON, system voltage VH cannot be increased over battery voltage Vb2.

On the other hand, power storage device100is connected to power supply line HPL with converter110being interposed therebetween. Even while battery voltage Vb1is lower than system voltage VH, therefore, electric power can be supplied to power supply line HPL from power storage device100, and power storage device100can be charged with the electric power on power supply line HPL.

Thus, the rated value of the output voltage of power storage device100is preferably set to be lower than the rated value of the output voltage of power storage device150. In this way, even if the number of battery cells connected in series at power storage device100is reduced, power storage devices100and150can be used in parallel.

Next, a relation between the operating states of motor generators MG1, MG2and system voltage VH will be described in detail.

In order to smoothly drive motor generators MG1, MG2, it is necessary to appropriately set system voltage VH in accordance with operating points of motor generators MG1, MG2, specifically, in accordance with rotational speed and torque. First, since there is a certain limitation on a modulation factor of power conversion at inverter120, with respect to system voltage VH, there is an upper limit torque that can be output.

FIG. 2is a conceptual diagram showing a relation between the system voltage and an operable region of each of the motor generators.

Referring toFIG. 2, the operable region and an operating point of each motor generator are shown by a combination of rotational speed and torque. A maximum output line200represents a limit for the operable region when system voltage VH=Vmax (upper limit voltage). Maximum output line200has a portion restricted by T×N, which corresponds to output power, even when torque T<Tmax (maximum torque) and rotational speed N<Nmax (the maximum rotational speed). As system voltage VH decreases, the operable region becomes narrower.

For example, an operating point P1can be achieved when system voltage VH=Va. When electrically powered vehicle5is accelerated from this state by a user's operation of the accelerator, a requested value for vehicle driving force increases. This increases the output torque of motor generator MG2, thus changing the operating point to P2. Operating point P2, however, cannot be attained unless system voltage VH is increased to Vb (Vb>Va).

A lower limit value (minimum required voltage VHmin) of system voltage VH at each operating point (rotational speed, torque) of each of motor generators MG1, MG2can be found based on the relation between system voltage VH and boundaries of operating regions shown inFIG. 2.

Moreover, induced voltage corresponding to the rotational speed is generated in each of motor generators MG1, MG2. If this induced voltage becomes higher than system voltage VH, current in each of motor generators MG1, MG2will be out of control. Thus, while electrically powered vehicle5is running at high speed with an increased rotational speed of each of motor generators MG1, MG2, minimum required voltage VHmin of system voltage VH increases.

From these standpoints, it is understood that, in correspondence with an operating point of each of motor generators MG1, MG2, minimum required voltage VHmin for ensuring an output in accordance with the operating point can be calculated in advance.

FIG. 3is a flowchart for explaining a first example of control processing in the power supply system according to an embodiment of the present invention. InFIG. 3and other figures, processing at each step in each of the flowcharts shown below is carried out by software processing or hardware processing performed by control unit300. Further, a series of control processing operations according to each of the flowcharts shown below is carried out by control unit300at every prescribed control cycle.

Referring toFIG. 3, at step S01, control device300calculates minimum required voltage VHmin based on an operating state of each of motor generators MG1, MG2, using the above-described map of required voltages. Control device300then sets voltage command value VH* in consideration of minimum required voltage VHmin. Voltage command value VH* is set to be not less than minimum required voltage VHmin. For example, when there is a voltage at which loss in power supply system20and load10is minimum, compared with when VH>VHmin, it is preferred that voltage command value VH* be set to that voltage, in favor of fuel efficiency. On the other hand, when it is desirable to actively use power storage device150, voltage command value VH* is preferably lower, and thus, may be set to VH*=VHmin.

Accordingly, voltage command value VH* can be calculated in correspondence with an operating point of each of motor generators MG1, MG2, in consideration of minimum required voltage VHmin. For this reason, a map (voltage command value map) for calculating, in correspondence with an operating point of each of motor generators MG1, MG2, voltage command value VH* in accordance with the operating point, can be created in advance. The voltage command value map is stored in a memory (not illustrated) in control device300. Accordingly, in the electrically powered vehicle according to the present embodiment, system voltage VH is variably controlled, in order to smoothly and efficiently drive each of motor generators MG1, MG2. That is, a voltage amplitude (pulse voltage amplitude) applied to each of motor generators MG1, MG2is variably controlled in accordance with the operating state of each of motor generators MG1, MG2(rotational speed and torque).

In step S02, control device300reads battery information based on the detection values from battery sensors105,155shown inFIG. 1. The battery information contains at least battery voltage Vb2.

In step S03, control device300compares battery voltage Vb2with voltage command value VH* set in step S01. When battery voltage Vb2is not less than voltage command value VH* (when it is determined as YES in S03), control device300proceeds to the processing in step S04, where relays RL1, RL2are turned ON. Power storage device150is thus connected to power supply line HPL.

Converter110controls charge and discharge of power storage device100so that current IL from power storage device100(equivalent to battery current Ib1) matches a prescribed current target value Ib1*, using a below-described method. In this way, charge and discharge power Pb1of power storage device100can be adjusted in an arbitrary manner, and hence, charge and discharge power Pb2of power storage device150can also be indirectly controlled. Consequently, power storage devices100,150can be used in parallel to allow control of charge and discharge into and from load10. When electric powered vehicle5is regeneratively braked in this state, power storage devices100,150can be charged in parallel.

On the other hand, when battery voltage Vb2is below voltage command value VH* (when it is determined as NO in S03), control device300proceeds to the processing in step505, where relays RL1, RL2are turned OFF. Power storage device150is thus disconnected from power supply line HPL. As described above, since voltage command value VH*≧VHmin, relays RL1, RL2are reliably turned OFF, at least when Vb2<VHmin.

In this case, charge and discharge of electric power to and from load10is controlled using power storage device100only via converter110. Converter110controls charge and discharge of power storage device100so that system voltage VH matches prescribed voltage command value VH*, using a below-described method. When electrically powered vehicle5is regeneratively braked in this state, only power storage device100is charged.

As described above, with the electric powered vehicle according to the present embodiment, in the power supply system using the plurality of power storage devices100,150, even though a converter is provided for power storage device100only, variable control of system voltage VH in accordance with the operating state of each of motor generators MG1, MG2can be achieved. Consequently, a power supply system capable of extending the mileage obtained by the output of motor generators MG1, MG2using electric power from the plurality of power storage devices100,150can be configured simply and efficiently.

In particular, a high-voltage region of system voltage VH for handling acceleration of the vehicle and the like can be attained by disconnecting power storage device150, whose output voltage is lower than the voltage command value (minimum required voltage), from power supply line HPL, and stepping up the output voltage of power storage device100with converter110. Furthermore, when the output voltage of power storage device150is higher than the voltage command value (minimum required voltage) and power storage device150can be used, power storage devices100,150can be used in parallel. In this way, electric power can be supplied to motor generators MG1, MG2with the effective use of the plurality of power storage devices100,150, so that the power supply system can be configured to be smaller and efficiently at low cost.

(Controlling Voltage Conversion of Converter)

As described above, in power supply system20according to the present embodiment, a first mode in which power storage device150is used or a second mode in which power storage device150is not used is selected. For each of the first and second modes, control device300controls the voltage conversion operation at converter110as follows.

FIG. 4is a flowchart for explaining control processing for the converter in the power supply system according to the embodiment of the present invention.

Referring toFIG. 4, control device300determines in step S11whether the first mode in which power storage device150is used is selected or not. Where the first mode in which power storage device150is used is selected (when it is determined as YES in step S11), control device300calculates in step S12an electric power target value (that is, a target value of charge and discharge power Pb1of power storage device100) Pb1* to be shared by power storage device100, of the electric power supplied from power supply system20to load10.

Here, in the first mode in which power storage device150is used, power storage devices100,150are used in parallel. Hence, a sum of charge and discharge power Pb1of power storage device100and charge and discharge power Pb2of power storage device150corresponds to the electric power charged to load10and discharged from power supply system20. This charge and discharge power of load10includes electric power Pg generated/consumed by motor generator MG1and electric power Pm generated/consumed by motor generator MG2; therefore, a relation between charge and discharge power Pb1of power storage device100and charge and discharge power Pb2of power storage device150, and the charge and discharge power of load10is expressed by the following equation (1):
Pb1+Pb2=Pg+Pm(1)

When power storage devices100,150are being used in parallel, charge and discharge power Pb2of power storage device150is determined along with the control of charge and discharge of power storage device100by converter110. That is, charge and discharge power Pb2of power storage device150is determined by circumstances. Thus, in the first mode, control device300controls converter110so that the electric power to be shared by power storage device100(charge and discharge power Pb1), of the electric power supplied from power supply system20to load10, becomes prescribed electric power target value Pb1*. In this way, charge and discharge power Pb1of power storage device100can be adjusted in an arbitrary manner, and hence, charge and discharge power Pb2of power storage device150can also be indirectly controlled. Consequently, electric power can be supplied to motor generators MG1, MG2through cooperative use of power storage devices100,150.

Specifically, control device300calculates electric power target value Pb1* in step S12, and then in step S13, divides electric power target value Pb1* by battery voltage Vb1of power storage device100to calculate current command value Ib1* of power storage device100. Then in step S14, control device300controls converter110so that current IL from power storage device100becomes current command value Ib1*. In this way, converter110performs the voltage conversion operation in accordance with the current control, in order to achieve the electric power distribution at power storage device100.

On the other hand, when the second mode in which power storage device150is not used is selected (when it is determined as NO in step S11), control device300calculates voltage command value VH* in step S15. The calculation of voltage command value VH* is executed by the processing shown in step S01inFIG. 3.

In step S16, control device300controls converter110so that system voltage VH becomes voltage command value VH*. Converter110therefore performs the voltage conversion operation in accordance with the voltage control, so as to stabilize system voltage VH.

FIG. 5is a diagram for illustrating an exemplary configuration of a control block for implementing current control of converter110in control device300.

Referring toFIG. 5, control device300includes, as a configuration for performing the current control of converter110, an electric power target value generation unit30, a division unit32, a subtraction unit34, a PI control unit36, and a transfer function (Gi)38.

Electric power target value generation unit30calculates electric power target value Pb1* of power storage device100within a range of electric power in which power storage device100can be charged and discharged. It is noted that the range of electric power in which power storage device100can be charged and discharged is defined by a charge power upper limit value and a discharge power upper limit value.

Division unit32divides electric power target value Pb1* by battery voltage Vb1of power storage device100to calculate current target value Ib1* of power storage device100, and outputs the result to subtraction unit34.

Subtraction unit34calculates a current deviation AIL from a difference between current target value Ib1* and current IL, and outputs the result to PI control unit36. PI control unit36generates a PI output corresponding to current deviation ΔIL in accordance with a prescribed proportional gain and a prescribed integral gain, and outputs the PI output to transfer function38. PI control unit36constitutes a current feedback control element.

Specifically, PI control unit36includes a proportional element (P), an integral element (I), and an addition unit. The proportional element multiplies current deviation ΔIL by a prescribed proportional gain Kp and outputs the result to the addition unit, and the integral element integrates current deviation ΔIL with a prescribed integral gain Ki (integral time: 1/Ki) and outputs the result to the addition unit. The addition unit then adds the outputs from the proportional element and the integral element to generate a PI output. This PI output corresponds to a feedback control amount for implementing the current control. PI control unit36generates a duty ratio command value Di for the current control, in accordance with a sum of the feedback control amount and a feedforward control amount DiFF. Duty ratio command value Di is a control command that defines on-duty of switching element Q2(FIG. 1) of converter110in the current control. Feedforward control amount DiFF in the current control is set in accordance with a difference in voltage between voltage command value VH* and voltage Vb1of power storage device100. Transfer function (Gi)38is equivalent to a transfer function of converter110with respect to power storage device100that operates as a current source.

FIG. 6is a diagram for illustrating an exemplary configuration of a control block for implementing voltage control of converter110in control device300.

Referring toFIG. 6, control device300includes, as a configuration for performing the voltage control of converter110, a voltage command value generation unit40, a subtraction unit42, a PI control unit44, a transfer function (Gi)38, and a transfer function (Gv)46.

Voltage command value generation unit40sets voltage command value VH* based on the operating state of each of motor generators MG1, MG2. As explained withFIG. 2, voltage command value generation unit40calculates minimum required voltage VHmin based on the operating state of each of motor generators MG1, MG2, and sets voltage command value VH* in consideration of minimum required voltage VHmin calculated.

Subtraction unit42calculates a voltage deviation ΔVH from a difference between voltage command value VH* and system voltage VH, and outputs the result to PI control unit44. PI control unit44generates a PI output corresponding to voltage deviation ΔVH in accordance with a prescribed proportional gain and a prescribed integral gain, and outputs the PI output to transfer function38. PI control unit44constitutes a voltage feedback control element.

Specifically, PI control unit44includes a proportional element, an integral element, and an addition unit. The proportional element multiplies voltage deviation ΔVH by a prescribed proportional gain Kp and outputs the result to the addition unit, and the integral element integrates voltage deviation ΔVH with a prescribed integral gain Ki (integral time: 1/Ki) and outputs the result to the addition unit. The addition unit then adds the outputs from the proportional element and the integral element to generate a PI output. This PI output corresponds to a feedback control amount for implementing the voltage control. PI control unit44generates a duty ratio command value Dv for the voltage control, in accordance with a sum of the feedback control amount and a feedforward control amount DvFF. Duty ratio command value Dv is a control command that defines on-duty of switching element Q2(FIG. 1) of converter110in the voltage control. Feedforward control amount DvFF in the voltage control is set in accordance with a difference in voltage between voltage command value VH* and voltage Vb1of power storage device100. Transfer function (Gi)38and transfer function (Gv)46are equivalent to transfer functions of converter110with respect to power storage device100that operates as a voltage source.

As described above, converter110performs the voltage conversion operation in accordance with the current control, in the first mode in which power storage device150is used, and performs the voltage conversion operation in accordance with the voltage control, in the second mode in which power storage device150is not used. Thus, each time switching between the first mode and the second mode occurs, switching between the current control and the voltage control occurs in converter110, and the switched control is applied. At the timing at which the control is switched, therefore, system voltage VH that is the output voltage of converter110may fluctuate.

Therefore, in the power supply system according to the embodiment of the present invention, at the time of switching between the current control and the voltage control, the output of the integral element (integral term) of the feedback control elements in the control before switching is taken over as an initial value of the integral element of the feedback control elements in the control after switching.

Specifically, in the control block shown inFIG. 5, PI control unit36calculates a feedback control amount ILfb of current IL, based on a control calculation based on current deviation ΔIL, and typically, based on a proportional integral (PI) calculation in accordance with the following equation (2):

In equation (2), ILfb (P) is the proportional term, and ILfb (I) is the integral term. Moreover, ΔIL is the current deviation in a present control cycle, and Kp and Ki are feedback gains.

At the time of switching from the first mode to the second mode, that is, at the time of switching from the current control to the voltage control, control device300uses integral term ILfb (I) in equation (2) as an initial value of the integral element in PI control unit44of the control block shown inFIG. 6. That is, at the time of switching from the current control to the voltage control, PI control unit44outputs a value obtained by adding a product of current deviation ΔIL and integral gain Ki in the present control cycle to an integral term calculated in a previous control cycle, as the integral term in the present control cycle. In this way, by taking over the integral term in the feedback control amount between PI control unit36and PI control unit44, it is possible to prevent discontinuity of the feedback control amount at the time of switching the control. Consequently, the occurrence of fluctuations in system voltage VH can be avoided.

A configuration of the control block for implementing switching between the current control and the voltage control of converter110in control device300will be described hereinafter.

FIG. 7is a diagram for illustrating an exemplary configuration of the control block for implementing switching between the current control and the voltage control of converter110in control device300.

Referring toFIG. 7, control device300includes a mode determination unit50, a command value generation unit52, a switching unit54, a division unit32, a subtraction unit42, a PI control unit44, transfer functions38,46, and switches SW1, SW2.

When one of the first mode in which power storage device150is used and the second mode in which power storage device150is not used is selected in accordance with the flowchart shown inFIG. 3, mode determination unit50selects one of the current control and the voltage control in accordance with the selected mode. Mode determination unit50generates a signal indicating which of the current control and the voltage control is selected, and transmits the signal to command value generation unit52and switching unit54.

Command value generation unit52generates one of electric power target value Pb1* and voltage command value VH*, in accordance with the control selected by mode determination unit50. Specifically, where the current control is selected, command value generation unit52calculates electric power target value Pb1* of power storage device100within a range of electric power in which power storage device100can be charged and discharged. On the other hand, where the voltage control is selected, command value generation unit52sets voltage command value VH* based on the operating state of each of motor generators MG1, MG2. That is, command value generation unit52functions both as electric power target value generation unit30shown inFIG. 5and voltage command value generation unit40shown inFIG. 6.

In the configuration shown inFIG. 7, subtraction unit42, PI control unit44, transfer function (Gi)38, and transfer function (Gv)46form a voltage feedback loop for performing the voltage control of converter110. This voltage feedback loop has the same control structure as the control block shown inFIG. 6.

Specifically, subtraction unit42calculates voltage deviation ΔVH from a difference between voltage command value VH* and system voltage VH, and outputs the result to PI control unit44. PI control unit44includes a voltage control calculation unit440, subtraction unit34, and a current control calculation unit442.

Voltage control calculation unit440carries out a control calculation (proportional integral calculation) for making system voltage VH match voltage command value VH*, using voltage deviation ΔVH. Voltage control calculation unit440then outputs the calculated control amount as current command value IL*. That is, voltage control calculation unit440generates current command value IL* corresponding to voltage deviation ΔVH by carrying out the control calculation for making system voltage VH match voltage command value VH*.

Subtraction unit34calculates current deviation ΔIL from a difference between current IL and current command value IL* output from voltage control calculation unit440, and outputs the result to current control calculation unit442.

Current control calculation unit442carries out a control calculation (proportional integral calculation) for making current IL match current command value IL*, using current deviation ΔIL. Current control calculation unit442then generates a duty ratio command value D for the voltage control, in accordance with a sum of the calculated control amount and a feedforward control amount. That is, current control calculation unit442carries out a control calculation for making current IL match current command value IL*, taking a PI output of voltage control calculation unit440as current command value IL*. In this way, if a deviation of system voltage VH from current command value VH* occurs, current command value IL* is corrected to remove the deviation, and the current control is executed so that current IL matches current command value IL*.

In the voltage feedback loop shown inFIG. 7, subtraction unit42, current control calculation unit442, subtraction unit34, current control calculation unit442, and transfer functions38,46form a main loop for making system voltage VH match voltage command value VH*, and subtraction unit34, current control calculation unit442, and transfer function38form a minor loop for making current IL match current command value IL*.

In control device300, division unit32is added to this minor loop, so that the minor loop also functions as a current feedback loop for performing the current control of converter110. This current feedback loop has the same control structure as the control block shown inFIG. 5.

Specifically, division unit32divides electric power target value Pb1* by battery voltage Vb1of power storage device100to calculate current target value Ib1* of power storage device100, and outputs the result to subtraction unit34.

Subtraction unit34calculates current deviation ΔIL from a difference between current target value Ib1* and current IL, and outputs the result to current control calculation unit442.

Current control calculation unit442carries out a control calculation (proportional integral calculation) for making current IL match current command value IL*, using current deviation ΔIL. Current control calculation unit442then generates a duty ratio command value D for the current control, in accordance with a sum of the calculated control amount and a feedforward control amount. That is, current control calculation unit442carries out a control calculation for making current IL match current command value IL*, taking current IL calculated from electric power target value Pb1* as voltage command value IL*. In this way, if a deviation of charge and discharge power Pb1of power storage device100from electric power target value Pb1* occurs, current command value IL* is corrected to remove the deviation, and the current control is executed so that current IL matches current command value IL*.

Switch SW1is provided between subtraction unit42and voltage control calculation unit440in the above-described voltage feedback loop. Switch SW2is provided between division unit32and subtraction unit34in the above-described current feedback loop. ON/OFF of each of switches SW1, SW2is controlled by a control signal from switching unit54.

Specifically, switching unit54generates a control signal for turning ON or OFF each of switches SW1, SW2, in accordance with the control selected by mode determination unit50. When the current control is selected by mode determination unit50, switching unit54generates a control signal for turning ON switch SW2while turning OFF switch SW1. Therefore, at the time of the current control, division unit32and subtraction unit34are connected to form the above-described current feedback loop.

On the other hand, when the voltage control is selected by mode determination unit50, switching unit54generates a control signal for turning OFF switch SW2while turning ON switch SW1. Therefore, at the time of the voltage control, subtraction unit42and voltage control calculation unit440are connected to form the above-described voltage feedback loop.

Moreover, with the configuration in which the minor loop in this voltage feedback loop functions also as the current feedback loop, at the time of switching from the current control to the voltage control, the control amount (integral term) calculated before switching by current control calculation unit442by means of the control calculation (proportional integral calculation) of current deviation ΔIL can be taken over as an initial value of a control amount (integral term) calculated after switching by current control calculation unit442by means of the control calculation of current deviation ΔIL. In this way, at the time of switching from the first mode in which power storage device100is used to the second mode in which power storage device150is not used, the occurrence of fluctuations in system voltage VH can be avoided.

Furthermore, at the time of switching from the voltage control to the current control, in addition to taking over the control amount (integral term) in current control calculation unit442as the initial value of the control amount in the current control, a final value of current command value IL* output from voltage control calculation unit440can be taken over to current control calculation unit442. In this way, also at the time of switching from the second mode to the first mode, the occurrence of fluctuations in system voltage VH can be avoided.

FIG. 8is a flowchart showing a procedure of processing by control device300for implementing the above-described switching between the current control and the voltage control of converter110. Although each of the steps in the flowchart shown inFIG. 8is basically implemented by software processing by control device300, it may also be implemented by hardware processing, such as an electronic circuit provided in control device300.

Referring toFIG. 8, control device300determines in step S21whether the first mode in which power storage device150is used is selected or not, that is, determines whether converter110is being controlled in accordance with the current control or not.

Where the first mode is selected, that is, where converter110is being controlled in accordance with the current control (when it is determined as YES in step S21), control device300next determines in step S22whether the second mode is selected or not, that is, determines whether the voltage control is selected or not. Where the second mode is not selected (when it is determined as NO in step S22), the processing is terminated without thereafter performing the processing of switching the control.

On the other hand, where the voltage control is selected in accordance with the selection of the second mode (when it is determined as YES in step S22), control device300generates in step S23a control signal for turning OFF switch SW2while turning ON switch SW1, and outputs the control signal to switches SW1, SW2. Moreover, control device300proceeds to the processing in step S24to turn OFF relays RL1, RL2. Once power storage device150is disconnected from power supply line HPL and becomes out of use, control device300controls converter110in accordance with the voltage control in step S25.

On the other hand, where the second mode is selected, that is, where converter110is being controlled in accordance with the voltage control (when it is determined as NO in step S21), control device300next determines in step S26whether the first mode is selected or not, that is, determines whether the current control is selected or not. Where the first mode is not selected (when it is determined as NO in step S26), the processing is terminated without thereafter performing the processing of switching the control.

On the other hand, where the current control is selected in accordance with the selection of the first mode (when it is determined as YES in step S26), control device300generates in step S27a control signal for turning ON switch SW2while turning OFF switch SW1, and outputs the control signal to switches SW1, SW2. Moreover, control device300proceeds to the processing in step S28to turn ON relays RL1, RL2. Once power storage device150is connected to power supply line HPL, control device300controls converter110in accordance with the current control in step S29.

As described above, according to the embodiment of this invention, in the power supply system provided with the plurality of power storage devices100,150, even though a converter is provided for power storage device100only, converter110is controlled in accordance with the current control so that the electric power to be shared by power storage device100becomes a prescribed electric power target value, which allows charge and discharge power of power storage device150to be also indirectly controlled. In this way, electric power can be supplied to the load through cooperative use of power storage devices100,150. Consequently, electric power can be supplied to the load with the effective use of the plurality of power storage devices100,150, so that the power supply system can be configured to be smaller and efficiently at low cost.

Furthermore, at the time of switching converter110between the current control and the voltage control in accordance with switching between use and disuse of power storage device150, the output of the integral element (integral term) of the feedback control elements in the control before switching is taken over as an initial value of the integral element of the feedback control elements in the control after switching. Consequently, the occurrence of fluctuations in system voltage VH at the time of switching the control can be avoided.

It is noted that the configuration of load10(i.e., the drive system) of electrically powered vehicle5shown inFIG. 1is not limited to that illustrated herein. That is, the present invention is similarly applicable to an electrically powered vehicle on which an electric motor for running is mounted, such as an electric vehicle, a fuel cell vehicle, or the like. It is also described for confirmation that load10is not limited to the drive system that generates vehicle driving force, but is also applicable to an apparatus that consumes electric power.

It is to be understood that the embodiments disclosed herein are only by way of example, and not to be taken by way of limitation. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

Industrial Applicability

This invention is applicable to a power supply system on which a plurality of power storage devices are mounted.

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