Power supply system and vehicle including the same, and method of controlling the same

When power storage units and are both in a normal condition, system relays are maintained in an ON state. A converter performs a voltage conversion operation in accordance with a voltage control mode, and a converter performs a boost operation in accordance with an electric power control mode. If some kind of fault condition occurs in the power storage unit and the system relay is driven to an OFF state, the converters stop the voltage conversion operation and maintain an electrically conducting state between the power storage units and a main positive bus, a main negative bus.

TECHNICAL FIELD

The present invention relates to a power supply system having a plurality of power storage units and a vehicle including the same, and a method of controlling the same, and particularly to a control technique in a case where a power storage unit is disconnected from the power supply system.

BACKGROUND ART

Recently, considering environmental issues, a hybrid vehicle that runs based on efficient combination of an engine and a motor has been put into practical use. Such a hybrid vehicle includes a power storage unit that can be charged or discharged and generates drive force by supplying electric power to a motor at the time of start or acceleration while it recovers kinetic energy of the vehicle as electric power during running down a slope or during braking. Therefore, a nickel metal hydride battery, a lithium-ion battery or the like adapted to large input/output electric power and charge/discharge capacity has been adopted as the power storage unit included in a hybrid vehicle.

A configuration called “plug-in” allowing charge/discharge of a power storage unit by using external power supply such as commercial power supply has been proposed for such a hybrid vehicle. The plug-in configuration aims to enhance overall fuel consumption efficiency by driving a relatively short distance, for example for commuting or shopping, with electric power stored in advance in the power storage unit from the external power supply while the engine is maintained in a non-operating state.

In a running mode using only electric power from the power storage unit, that is, in what is called an EV (Electric Vehicle) running mode, steady output of electric power is necessary. Accordingly, a charge/discharge capacity greater than that of a power storage unit included in a normal hybrid vehicle is required in the power storage unit in the plug-in configuration, whereas input/output electric power thereof may be relatively small.

Thus, in a hybrid vehicle adapted to the plug-in configuration, power storage units different in performance are necessary. Therefore, a configuration including a plurality of power storage units different in a charge/discharge characteristic is desirable. Regarding a configuration incorporating a plurality of power storage units, for example, U.S. Pat. No. 6,608,396 discloses a power control system providing desired high DC voltage levels required by a high voltage vehicle traction system. The power control system includes a plurality of power stages for providing DC power to at least one inverter, each stage including a battery and boost/buck DC-DC converter, the power stages wired in parallel, and a controller controlling the plurality of power stages so as to maintain a voltage output to at least one inverter by causing uniform charge/discharge of the batteries of the plurality of power stages.

In general, the power storage unit stores a relatively large amount of electric energy. Accordingly, from the viewpoint of safety, the power storage unit is always monitored for a fault condition based on a status value of the power storage unit. For example, a degree of deterioration is determined based on an internal resistance value of the power storage unit. If determination as fault is made, the power storage unit should electrically be disconnected from the system.

In the power control system disclosed in U.S. Pat. No. 6,608,396 described above, no attention is paid to a case where a fault condition occurs in a battery (power storage unit), and a configuration for electrically disconnecting the power storage unit where a fault condition occurs is not disclosed. Therefore, if only one of a plurality of power storage units is in the fault condition, the entire system should inevitably be stopped.

DISCLOSURE OF THE INVENTION

The present invention was made to solve such problems, and an object of the present invention is to provide a power supply system capable of continuing supply of electric power to a load device even when any power storage unit among a plurality of power storage units is electrically disconnected for some reason, a vehicle including the same, and a method of controlling the same.

According to one aspect of the present invention, a power supply system for supplying electric power to first and second load devices is provided. The power supply system includes a first electric power line pair electrically connected to the first load device, a plurality of rechargeable power storage units, and a plurality of voltage conversion units arranged corresponding to the plurality of power storage units respectively. The plurality of voltage conversion units are connected in parallel to the first electric power line pair and each of the plurality of voltage conversion units is configured to perform a voltage conversion operation between the first electric power line pair and the corresponding power storage unit. The power supply system further includes a plurality of disconnection units arranged corresponding to the plurality of power storage units respectively, each for electrically disconnecting the corresponding power storage unit and the corresponding voltage conversion unit from each other, a second electric power line pair having one end electrically connected between a first voltage conversion unit representing one of the plurality of voltage conversion units and the corresponding disconnection unit and another end electrically connected to the second load device, and a control unit. The control unit controls the plurality of voltage conversion units, when one disconnection unit among the plurality of disconnection units electrically disconnects corresponding the power storage unit and corresponding the voltage conversion unit from each other, such that electric power supply to the first load device and electric power supply to the second load device are continued through the first electric power line pair and through the second electric power line pair respectively by using electric power from remaining power storage unit.

Preferably, the power supply system further includes a fault condition detection unit for detecting a fault condition for each of the plurality of power storage units. Each of the plurality of disconnection units is configured to electrically disconnect the corresponding power storage unit and the corresponding voltage conversion unit from each other in response to detection of a fault condition in the corresponding power storage unit by the fault condition detection unit.

Preferably, the fault condition detection unit detects a fault condition of each of the plurality of power storage units based on at least one of a temperature, a voltage value, a current value, and an internal resistance value of the corresponding power storage unit.

Preferably, the control unit controls the voltage conversion unit corresponding to the remaining power storage unit such that electric power from the remaining power storage unit is supplied to the first load device through the first electric power line pair and controls the first voltage conversion unit such that electric power is supplied from the first electric power line pair through the second electric power line pair to the second load device, when the first voltage conversion unit and the corresponding power storage unit are electrically disconnected from each other by the corresponding disconnection unit.

Further preferably, the control unit stops an electric power conversion operation between the first electric power line pair and the corresponding power storage unit and thereafter sets an electrically conducting state therebetween, for each of the plurality of voltage conversion units.

Further preferably, each of the plurality of voltage conversion units includes a switching element connected in series to an inductor and arranged between one electric power line out of the first electric power line pair and one electrode of the corresponding power storage unit, capable of electrically connecting and disconnecting one electric power line and one electrode of the corresponding power storage unit to/from each other, and a line for electrically connecting another electric power line out of the first electric power line pair and another electrode of the corresponding power storage unit to each other. The control unit maintains a conducting state by setting the switching element to an ON state, for each of the plurality of voltage conversion units.

In addition, preferably, the control unit controls the remaining voltage conversion unit except for the first voltage conversion unit such that electric power from the corresponding power storage unit is supplied to the first electric power line pair after it is boosted, and controls the first voltage conversion unit such that electric power from the first electric power line pair is supplied to the second load device after it is down-converted.

Further preferably, the control unit controls the first voltage conversion unit in accordance with a first control mode for attaining a value of a down-converted voltage supplied to the second load device to a prescribed target value.

Further preferably, the control unit controls at least one of the remaining voltage conversion units in accordance with a second control mode for attaining a value of a boosted voltage supplied to the first electric power line pair to a prescribed target value.

Further preferably, while the first voltage conversion unit and the corresponding power storage unit are electrically connected to each other, the first voltage conversion unit is set to the second control mode to perform a voltage conversion operation, and each remaining voltage conversion unit is set to a third control mode for attaining a value of electric power supplied and received between the first electric power line pair and the corresponding power storage unit to a prescribed target value to perform a voltage conversion operation. The control unit switches between the control modes for at least one of the remaining voltage conversion units and the first voltage conversion unit in response to electrical disconnection between the first voltage conversion unit and the corresponding power storage unit by the corresponding disconnection unit.

According to another aspect of the present invention, a vehicle including the power supply system described above and a drive force generation unit for generating drive force for running as the first load device is provided.

Preferably, the vehicle further includes an auxiliary machinery group for vehicle as the second load device.

According to yet another aspect of the present invention, a method of controlling a power supply system for supplying electric power to first and second load devices is provided. The power supply system includes a first electric power line pair electrically connected to the first load device, a plurality of rechargeable power storage units, and a plurality of voltage conversion units arranged corresponding to the plurality of power storage units respectively. The plurality of voltage conversion units are connected in parallel to the first electric power line pair and each of the plurality of voltage conversion units is configured to perform a voltage conversion operation between the corresponding power storage unit and the first electric power line pair. The power supply system further includes a plurality of disconnection units arranged corresponding to the plurality of power storage units respectively, each for electrically disconnecting the corresponding power storage unit and the corresponding voltage conversion unit from each other, and a second electric power line pair having one end electrically connected between a first voltage conversion unit representing one of the plurality of voltage conversion units and the corresponding disconnection unit and another end electrically connected to the second load device. The method includes the steps of: detecting whether a fault condition is present or not for each of the plurality of power storage units; electrically disconnecting, when the fault condition of any one power storage unit among the plurality of power storage units is detected, the power storage unit of which fault condition has been detected and the corresponding voltage conversion unit from each other by using the corresponding disconnection unit; and controlling the plurality of voltage conversion units such that electric power supply to the first load device and electric power supply to the second load device are continued through the first electric power line pair and through the second electric power line pair respectively by using electric power from the remaining power storage unit except for the disconnected power storage unit.

According to the present invention, a power supply system capable of continuing supply of electric power to a load device even when any power storage unit among a plurality of power storage units is electrically disconnected for some reason, a vehicle including the same, and a method of controlling the same can be obtained.

BEST MODES FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described in detail with reference to the drawings. It is noted that the same or corresponding elements in the drawings have the same reference characters allotted and description thereof will not be repeated.

First Embodiment

FIG. 1is a schematic configuration diagram showing a substantial part of a vehicle1including a power supply system100according to a first embodiment of the present invention.

Referring toFIG. 1, vehicle1includes power supply system100, a first inverter (INV1)40, a second inverter (INV2)42, a third inverter (INV3)44, motor-generators (M/G) MG1, MG2, a drive ECU (Electronic Control Unit)50, an air-conditioning apparatus70, low-voltage auxiliaries82, a down converter80, and a sub power storage unit SB.

In the present first embodiment, power supply system1including two power storage units10,20will be described by way of example of the power supply system including a plurality of power storage units.

Inverters40,42, motor-generators MG1, MG2, and drive ECU50constitute a “drive force generation unit” for generating drive force for running vehicle1. The “drive force generation unit” herein is illustrated as a “first load device.” Namely, vehicle1runs by transmitting to wheels (not shown), drive force generated by electric power supplied to the drive force generation unit from power supply system100. In addition, air-conditioning apparatus70, low-voltage auxiliaries82, down converter80, and sub power storage unit SB constitute an “auxiliary machinery group” for vehicle. The “auxiliary machinery group” herein is illustrated as a “second load device.”

A configuration capable of continuing electric power supply not only to the “drive force generation unit” corresponding to the “first load device” but also to the “auxiliary machinery group” even when any “power storage unit” is electrically disconnected from the power supply system is illustrated herein. Various situations where the “power storage unit” should electrically be disconnected are assumed. In the present first and second embodiments and variations thereof, an example where it is determined that the power storage unit should electrically be disconnected from the power supply system because the power storage unit is in a fault condition is illustrated.

(Configuration of Drive Force Generation Unit)

Inverters40,42are connected in parallel to a main positive bus MPL and a main negative bus MNL forming a first electric power line pair, and supply/receive electric power to/from power supply system100. That is, inverters40,42convert electric power (DC electric power) supplied through main positive bus MPL and main negative bus. MNL to AC electric power and supply the AC electric power to motor-generators MG1, MG2respectively. Meanwhile, inverters40,42convert AC electric power generated by motor-generators MG1, MG2to DC electric power and return the resultant DC electric power as regenerative electric power to power supply system100. For example, inverters40,42are constituted of a bridge circuit including switching elements of three phases, and perform electric power conversion by performing a switching (circuit opening/closing) operation in response to switching instructions PWM1, PWM2received from drive ECU50.

Motor-generators MG1, MG2are configured to be able to generate rotational drive force by receiving AC electric power supplied from inverters40,42respectively and to be able to generate electric power by receiving external rotational drive force. For example, motor-generators MG1, MG2are implemented by a three-phase AC electric rotating machine including a rotor having permanent magnets embedded. Motor-generators MG1, MG2are mechanically connected to a not-shown engine via a power split device46.

Drive ECU50performs operational processing such that an optimal ratio between the drive force generated by the engine and the drive force generated by motor-generators MG1, MG2is attained. More specifically, drive ECU50executes a program stored in advance, so as to determine drive force to be generated in the engine and motor-generators MG1, MG2based on a signal transmitted from each not-shown sensor, a running state, variation in an accelerator position, a stored map, or the like. It is noted that motor-generator MG1may serve solely as the generator while motor-generator MG2may serve solely as the motor.

(Configuration of Auxiliary Machinery Group)

Air-conditioning apparatus70is an apparatus for mainly air-conditioning a passenger room in a vehicle, and includes an inverter72connected to a low-voltage positive line LPL and a low-voltage negative line LNL forming a second power supply line pair and a compressor74driven by inverter72. Inverter72converts DC electric power supplied from power supply system100to AC electric power and supplies the AC electric power to compressor74. Compressor74is an apparatus for achieving air-conditioning by generating heat of vaporization through a refrigeration cycle (not shown) in which compression and expansion of a coolant (such as chlorofluorocarbons) are repeated, and compresses the coolant with rotational drive force generated by the AC electric power supplied from inverter72.

Low-voltage auxiliaries82are collective denotation of auxiliaries that are driven at a voltage lower (for example, 12V or 24V) than a voltage value (for example, 288V) of electric power supplied from power supply system100. For example, low-voltage auxiliaries82include a car navigation system, a car audio system, an interior light, an indicator within a vehicle, and the like. In addition, low-voltage auxiliaries82are driven by DC electric power at a low voltage supplied from down converter80or sub power storage unit SB.

Down converter80is a device for down-converting electric power supplied from power supply system100. Down converter80is connected to low-voltage positive line LPL and low-voltage negative line LNL and supplies down-converted DC electric power to low-voltage auxiliaries82and sub power storage unit SB. For example, down converter80is implemented by what is called a “trans”-type circuit that converts DC electric power to AC electric power, performs voltage conversion by using a winding transformer, and converts again the voltage-converted AC electric power to DC electric power.

Sub power storage unit SB is implemented, for example, by a lead-acid battery, connected to an output side of down converter80, and charged with output DC electric power, while it supplies charged electric power to low-voltage auxiliaries82. Namely, sub power storage unit SB also has a function as an electric power buffer for compensating for unbalance between output electric power from down converter80and electric power demanded by low-voltage auxiliaries82.

In addition, in the present first embodiment, inverter44is connected to main positive bus MPL and main negative bus MNL, in parallel to inverters40,42. Inverter44is a charging device for charging power storage units10,20included in power supply system100by using external electric power from outside the vehicle. Specifically, inverter44is electrically connected to a commercial power supply (not shown) in a house or the like outside the vehicle through a charge connector60and a supply line ACL such that electric power can be received from the external power supply. Then, inverter44converts the electric power from the external power supply to DC electric power for supply to power supply system100. For example, inverter44is representatively implemented by a single-phase inverter so as to adapt to a manner of electric power feed of the commercial power supply used in the house (not shown) outside the vehicle.

The plug-in configuration is not limited to the configuration shown inFIG. 1, and the configuration may be such that electrical connection with an external power supply is established through neutral points of motor-generators MG1and MG2.

(Configuration of Power Supply System)

Power supply system100includes a smoothing capacitor C, power storage units10,20, converters (CONV)18,28, temperature detection units12,22, voltage detection units14,24,52, current detection units16,26,54, system relays SMR1, SMR2, a battery ECU32, and a converter ECU30.

Smoothing capacitor C is connected between main positive bus MPL and main negative bus MNL, and reduces a fluctuating component contained in electric power supplied or received between power supply system100and the drive force generation unit.

Voltage detection unit52is connected between main positive bus MPL and main negative bus MNL, detects a bus voltage value Vc indicating a voltage value of electric power supplied and received between power supply system100and the drive force generation unit, and outputs the result of detection to converter ECU30. In addition, current detection unit54is inserted in main positive bus MPL, detects a bus current value Ic indicating a current value of electric power supplied and received between power supply system100and the drive force generation unit, and outputs the result of detection to converter ECU30.

Power storage units10,20are elements for storing chargeable/dischargeable DC electric power, and for example, they are implemented by a secondary battery such as a nickel metal hydride battery or a lithium-ion battery, or by an electric double layer capacitor.

Converters18and28are voltage conversion units connected in parallel to main positive bus MPL and main negative bus MNL and configured to perform an electric power conversion operation between corresponding power storage units10,20and main positive bus MPL, main negative bus MNL, respectively. More specifically, converters18and28boost discharged electric power from respective corresponding power storage units10,20to a prescribed voltage for supply to the drive force generation unit, while they down-convert regenerative electric power supplied from the drive force generation unit to a prescribed voltage for charging respective corresponding power storage units10,20. For example, converters18,28are both implemented by a “chopper” type circuit.

Temperature detection units12,22are arranged in the proximity of battery cells and the like constituting power storage units10,20respectively, detect temperatures Tb1, Tb2of power storage units10,20, and output the result of detection to battery ECU32. It is noted that temperature detection units12,22may be configured to output a representative value obtained based on values detected by a plurality of detection elements arranged in correspondence with a plurality of battery cells constituting power storage units10,20.

Voltage detection unit14is connected between a positive line PL1and a negative line NL1electrically connecting power storage unit10to converter18, detects a voltage value Vb1involved with input and output to/from power storage unit10, and outputs the result of detection to battery ECU32and converter ECU30. Similarly, voltage detection unit24is connected between a positive line PL2and a negative line NL2electrically connecting power storage unit20to converter28, detects a voltage value Vb2involved with input and output to/from power storage unit20, and outputs the result of detection to battery ECU32and converter ECU30.

Current detection units16,26are inserted in positive lines PL1, PL2connecting power storage units10,20to converters18,28respectively, detect current values Ib1, Ib2involved with charge/discharge of corresponding power storage units10,20respectively, and output the result of detection to battery ECU32and converter ECU30.

System relay SMR1is inserted in positive line PL1and negative line NL1electrically connecting power storage unit10and converter18to each other, and electrically connects or disconnects power storage unit10and converter18to/from each other in response to a system ON instruction SON1from battery ECU32which will be described later. In the description below, an electrically connected state is also referred to as the “ON” state, and an electrically disconnected state is also referred to as the “OFF” state.

In addition, low-voltage positive line LPL and low-voltage negative line LNL are connected to positive line PL1and negative line NL1at a position between system relay SMR1and converter18, respectively. Thus, a part of electric power that flows through positive line PL1and negative line NL1can be supplied to the auxiliary machinery group for vehicle. If system relay SMR1is in a disconnection state, power storage unit10is electrically disconnected from the drive force generation unit and the auxiliary machinery group.

Similarly, system relay SMR2is inserted in positive line PL2and negative line NL2electrically connecting power storage unit20and converter28to each other, and electrically connects or disconnects power storage unit20and converter28to/from each other in response to a system ON instruction SON2from battery ECU32which will be described later.

Thus, in the present first embodiment, system relays SMR1, SMR2correspond to the “plurality of disconnection units.”

Battery ECU32is a device for monitoring and controlling power storage units10,20, and maintains a state of charge (SOC; hereinafter also referred to as “SOC”) of power storage units10,20within a prescribed range in coordination with converter ECU30connected through a control line LNK1. Specifically, battery ECU32calculates SOC of power storage units10,20based on temperatures Tb1, Tb2received from temperature detection units12,22, voltage values Vb1, Vb2received from voltage detection units14,24, and current values Ib1, Ib2received from current detection units16,26.

In addition, battery ECU32detects a fault condition for each of power storage units10,20based on temperatures Tb1, Tb2, voltage values Vb1, Vb2, current values Ib1, Ib2, an internal resistance value, and the like of power storage units10,20. If power storage units10,20are both in a normal condition, battery ECU32activates system ON instructions SON1, SON2in response to an ignition ON instruction (not shown) issued by a driver's operation, and drives system relays SMR1, SMR2to the ON state. On the other hand, if a fault condition has occurred in any of power storage units10and20, battery ECU32determines that electrical disconnection is necessary, inactivates corresponding system ON instruction SON1, SON2, and electrically disconnects corresponding power storage unit10,20from power supply system100.

Converter ECU30controls the electric power conversion operation in converters18,28such that an electric power value requested by the drive force generation unit can be allotted to power storage units10and20at a prescribed ratio, in coordination with battery ECU32connected through control line LNK1and drive ECU50connected through a control line LNK2. Specifically, converter ECU30provides switching instructions PWC1, PWC2in accordance with a control mode selected in advance from among a plurality of control modes which will be described later, for respective converters18,28.

In particular, in power supply system100according to the present first embodiment, when power storage units10,20are both in a normal condition, any one of converters18and28operates as “master” and the other one operates as “slave”. The converter operating as “master” is controlled in accordance with a “voltage control mode (boost)” for setting a voltage value of electric power supplied from power supply system100to the drive force generation unit (bus voltage value Vc across main positive bus MPL and main negative bus MNL) to a prescribed voltage target value. On the other hand, the converter operating as “slave” is controlled in accordance with an “electric power control mode” for setting electric power allotted to the corresponding power storage unit (electric power supplied and received between that power storage unit and main positive bus MPL, main negative bus MNL) out of electric power supplied from power supply system100to the drive force generation unit to a prescribed electric power target value. Here, a part of electric power discharged from power storage unit10is supplied to the auxiliary machinery group.

Here, when a fault condition occurs in power storage unit10and power storage unit10is electrically disconnected from power supply system100, converter28continues the voltage conversion operation such that electric power supply from power storage unit20to the drive force generation unit is continued, while converter18performs the voltage conversion operation such that a part of electric power that flows through main positive bus MPL, main negative bus MNL is supplied to the auxiliary machinery group. Here, converter28corresponding to power storage unit20should operate as “master”. Accordingly, if converter28is operating as “slave” immediately before power storage unit10is electrically disconnected, mode switching is made such that converter28operates as “master” simultaneously with electrical disconnection of power storage unit10.

In contrast, if a fault condition takes place in power storage unit20and power storage unit20is electrically disconnected from power supply system100, converter18performs the voltage conversion operation such that electric power supply from power storage unit10to the drive force generation unit and the auxiliary machinery group is continued, while converter28stops the voltage conversion operation. Here, converter18corresponding to power storage unit10should operate as “master”. Accordingly, if converter18is operating as “slave” immediately before power storage unit20is electrically disconnected, mode switching is made such that converter18operates as “master” simultaneously with electrical disconnection of power storage unit20.

As described above, in the present embodiment, even when a fault condition takes place in any one of power storage units10and20, electric power supply to the drive force generation unit and the auxiliary machinery group can be continued.

In the present embodiment, converter ECU30corresponds to the “control unit”, and battery ECU32corresponds to the “fault condition detection unit.”

Referring toFIG. 2, converter18according to the first embodiment of the present invention, during discharge from power storage unit10, boosts DC electric power supplied from power storage unit10, while converter18, during charging to power storage unit10, down-converts DC electric power supplied through main positive bus MPL and main negative bus MNL, in response to switching instruction PWC1from converter ECU30(FIG. 1). Converter18includes transistors Q1A, Q1B serving as a switching element, an inductor L1, a line LNC1, diodes D1A, D1B, and a smoothing capacitor C1.

Transistor Q1B is connected in series to inductor L1and arranged between positive line PL1(positive electrode side of power storage unit10) and main positive bus MPL. Transistor Q1B has a collector connected to positive bus MPL. Transistor Q1B electrically connects or disconnects positive line PL1and main positive bus MPL to/from each other in response to a second switching instruction PWC1B included in switching instruction PWC1. Line LNC1electrically connects negative line NL1(negative electrode side of power storage unit10) and main negative bus MNL to each other. Transistor Q1A is further connected between a connection point of transistor Q1B and inductor L1and line LNC1. Transistor Q1A has an emitter connected to line LNC1. Transistor Q1A electrically connects or disconnects positive line PL1and negative line NL1in response to a first switching instruction PWC1A included in switching instruction PWC1.

In addition, diodes D1A, D1B allowing a current flow from the emitter sides to the collector sides are connected between the collectors and the emitters of transistors Q1A, Q1B, respectively. Moreover, smoothing capacitor C1is connected between positive line PL1and negative line NL1(or line LNC1), and reduces the AC component contained in the electric power supplied and received between power storage unit10and converter18. Further, when system relay SMR1(FIG. 1) makes transition from the OFF state to the ON state and power storage unit10and converter18are electrically connected to each other, smoothing capacitor C1is charged until it substantially attains to a voltage value of power storage unit10. Thus, smoothing capacitor C1also achieves an effect to prevent failure of transistor Q1A, Q1B, diode D1A, D1B or the like due to an inrush current that is produced at the moment of transition of system relay SMR1(FIG. 1) to the ON state.

The voltage conversion operation (boost operation and down-conversion operation) of converter18will be described hereinafter.

During the boost operation, converter ECU30(FIG. 1) maintains transistor Q1B in the ON state (duty ratio=100%) and turns ON/OFF transistor Q1A at a prescribed duty ratio lower than 100%. In the following, the duty ratio is also denoted as “Duty”.

While transistor Q1A is in the ON state (conducting state), a first current path from the positive electrode side of power storage unit10to main positive bus MPL and a second current path from the positive electrode side of power storage unit10through inductor L1back to the negative electrode side are formed. Here, a pump current that flows through the second current path is stored as electromagnetic energy in inductor L1. As transition from the ON state to the OFF state (non-conducting state) of transistor Q1A is made, the second current path is opened and the pump current is cut off. Then, as inductor L1will maintain the value of the current that flows through itself, inductor L1releases stored electromagnetic energy. The released electromagnetic energy is superimposed on the current output from converter18to main positive bus MPL. Consequently, electric power supplied from power storage unit10is output after it is boosted by a voltage value corresponding to the electromagnetic energy stored in inductor L1.

On the other hand, during the down-conversion operation, converter ECU30(FIG. 1) turns ON/OFF transistor Q1B at a prescribed duty ratio and maintains transistor Q1A in the OFF state (Duty=0%).

While transistor Q1B is in the ON state, a current path from main positive bus MPL to the positive electrode side of power storage unit10is formed. On the other hand, when transistor Q1B makes transition from the ON state to the OFF state (non-conducting state), that current path is opened and the current is cut off. In other words, as it is only a period of time when transistor Q1B is in the ON state that electric power is supplied from main positive bus MPL to power storage unit10, an average voltage of DC electric power supplied from converter18to power storage unit10is equal to a value obtained by multiplying a voltage value across main positive bus MPL and main negative bus MNL (bus voltage value Vc) by the duty ratio.

As the configuration and the operation of converter28are also similar to those of converter18described above, detailed description will not be repeated.

(Outline of Electric Power Management)

Electric power supply to the drive force generation unit and the auxiliary machinery group according to the present first embodiment will be described hereinafter with reference toFIGS. 3A to 6B. As described above, in the present first embodiment, a converter to operate as “master” can freely be selected, and in addition, even when any of power storage units10and20is disconnected from power supply system100, electric power supply to the drive force generation unit and the auxiliary machinery group should be continued.

In the description below, the following four cases will separately be described, for each converter to operate as “master” and for each power storage unit disconnected from power supply system100:

(1) A case where power storage unit10is disconnected while converter18is operating as “master”;

(2) A case where power storage unit10is disconnected while converter28is operating as “master”;

(3) A case where power storage unit20is disconnected while converter18is operating as “master”; and

(4) A case where power storage unit20is disconnected while converter28is operating as “master”.

FIGS. 3A and 3Bare diagrams showing outlines (case 1) of electric power supply to the drive force generation unit and the auxiliary machinery group according to the first embodiment of the present invention.FIG. 3Ashows a case where power storage units10and20are in a normal condition, whileFIG. 3Bshows a case where a fault condition takes place in power storage unit10.

Referring toFIG. 3A, if power storage units10and20are both in a normal condition, system relays SMR1and SMR2are maintained in the ON state. Thus, discharge electric power Pb1is discharged from power storage unit10, a part thereof is supplied to the auxiliary machinery group, and the remaining part thereof is supplied to the drive force generation unit. In addition, discharge electric power Pb2from power storage unit20is supplied to the drive force generation unit in its entirety. Therefore, relation of
discharge electric powerPb1+discharge electric powerPb2=supply electric powerPc+supply electric powerPs
discharge electric powerPb1>supply electric powerPs

is satisfied between supply electric power Pc and Ps supplied to the drive force generation unit and the auxiliary machinery group respectively and discharge electric power Pb1and Pb2discharged from power storage units10and20.

Here, in order to stabilize a voltage value of supply electric power Pc supplied to the drive force generation unit, that is, a voltage value across main positive bus MPL and main negative bus MNL (bus voltage value Vc), converter18operating as “master” performs the voltage conversion operation in accordance with the voltage control mode (boost). Namely, converter18is controlled such that bus voltage value Vc attains to a prescribed voltage target value Vc*. On the other hand, converter28operating as “slave” performs a boost operation in accordance with the electric power control mode in order to achieve electric power allotment between power storage units10and20(electric power management). Namely, converter28is controlled such that a value of electric power supplied and received between corresponding power storage unit20and main positive bus MPL, main negative bus MNL attains to a prescribed electric power target value Pb2*. As discharge electric power Pb2from power storage unit20can thus arbitrarily be adjusted, discharge electric power Pb1from power storage unit10can also indirectly be controlled.

Here, a voltage value of supply electric power Ps supplied to the auxiliary machinery group through low-voltage positive line LPL and low-voltage negative line LNL fluctuates depending on SOC or the like of power storage unit10. Inverter72(FIG. 1) included in air-conditioning apparatus70or down converter80, however, has a voltage adjustment function. Therefore, even when prescribed voltage fluctuation occurs in power storage unit10, the auxiliary machinery group can normally operate.

Here, if some kind of fault condition occurs in power storage unit10, system relay SMR1is driven to the OFF state as shown inFIG. 3Band power storage unit10is electrically disconnected from power supply system100. When power storage unit10is electrically disconnected, electric power cannot be supplied from power storage unit10to the auxiliary machinery group. Therefore, the control mode in converters18and28should be switched such that electric power can be supplied from power storage unit20to the auxiliary machinery group.

In the present first embodiment, for example, a configuration for switching converters18and28to the conducting mode will be described. Specifically, when power storage unit10is disconnected from power supply system100, converters18and28stop the voltage conversion operation and maintain the electrically conducting state between power storage units10,20and main positive bus MPL, main negative bus MNL, respectively.

Then, discharge electric power Pb2from power storage unit20is supplied to main positive bus MPL, main negative bus MNL through corresponding converter28. A part of discharge electric power Pb2is supplied to the drive force generation unit and the remaining part thereof is supplied to the auxiliary machinery group through converter18and low-voltage positive line LPL, low-voltage negative line LNL. Thus, even after power storage unit10is electrically disconnected from power supply system100, electric power supply to the drive force generation unit and the auxiliary machinery group is continued. Here, relation of
discharge electric powerPb2=supply electric powerPc+supply electric power

is satisfied between discharge electric power Pb2discharged from power storage unit20and supply electric power Pc and Ps supplied to the drive force generation unit and the auxiliary machinery group respectively.

FIGS. 4A and 4Bare diagrams showing outlines (case 2) of electric power supply to the drive force generation unit and the auxiliary machinery group according to the first embodiment of the present invention.FIG. 4Ashows a case where power storage units10and20are in a normal condition, whileFIG. 4Bshows a case where a fault condition takes place in power storage unit10.

Referring toFIG. 4A, as inFIG. 3Aabove, if power storage units10and20are both in a normal condition, system relays SMR1and SMR2are maintained in the ON state. Thus, discharge electric power Pb1is discharged from power storage unit10, a part thereof is supplied to the auxiliary machinery group, and the remaining part thereof is supplied to the drive force generation unit. In addition, discharge electric power Pb2from power storage unit20is supplied to the drive force generation unit in its entirety.

In the case shown inFIG. 4A, converter28operates as “master”, and converter18operates as “slave”. Namely, converter28operating as “master” is controlled such that bus voltage value Vc attains to prescribed voltage target value Vc*. On the other hand, converter18operating as “slave” is controlled such that a value of electric power supplied and received between corresponding power storage unit10and main positive bus MPL, main negative bus MNL attains to a prescribed electric power target value Pb1*.

Here, if some kind of fault condition occurs in power storage unit10, system relay SMR1is driven to the OFF state as shown inFIG. 4Band power storage unit10is electrically disconnected from power supply system100. In this case, as inFIG. 3B, converters18and28stop the voltage conversion operation and maintain the electrically conducting state between power storage units10,20and main positive bus MPL, main negative bus MNL, respectively.

Then, discharge electric power Pb2from power storage unit20is supplied to main positive bus MPL, main negative bus MNL through converter28. A part of discharge electric power Pb2is supplied to the drive force generation unit and the remaining part thereof is supplied to the auxiliary machinery group through converter18and low-voltage positive line LPL, low-voltage negative line LNL. Thus, even after power storage unit10is electrically disconnected from power supply system100, electric power supply to the drive force generation unit and the auxiliary machinery group is continued.

FIGS. 5A and 5Bare diagrams showing outlines (case 3) of electric power supply to the drive force generation unit and the auxiliary machinery group according to the first embodiment of the present invention.FIG. 5Ashows a case where power storage units10and20are in a normal condition, whileFIG. 5Bshows a case where a fault condition takes place in power storage unit20.

Referring toFIG. 5A, as inFIG. 3Aabove, if power storage units10and20are both in a normal condition, system relays SMR1and SMR2are maintained in the ON state. Thus, discharge electric power Pb1is discharged from power storage unit10, a part thereof is supplied to the auxiliary machinery group, and the remaining part thereof is supplied to the drive force generation unit. In addition, discharge electric power Pb2from power storage unit20is supplied to the drive force generation unit in its entirety.

In the case shown inFIG. 5A, as inFIG. 3A, converter18operates as “master”, and converter28operates as “slave”. Namely, converter18operating as “master” is controlled such that bus voltage value Vc attains to prescribed voltage target value Vc*. On the other hand, converter28operating as “slave” is controlled such that a value of electric power supplied and received between corresponding power storage unit20and main positive bus MPL, main negative bus MNL attains to prescribed electric power target value Pb2*.

Here, if some kind of fault condition occurs in power storage unit20, system relay SMR2is driven to the OFF state as shown inFIG. 5Band power storage unit20is electrically disconnected from power supply system100. In this case, converter28stops the voltage conversion operation and sets an electrically open state between system relay SMR2and main positive bus MPL, main negative bus MNL. Namely, the control mode of converter28is switched from the voltage control mode (boost) to an open mode.

On the other hand, as converter18operating as “master” is performing the voltage conversion operation in accordance with the voltage control mode (boost), bus voltage value Vc across main positive bus MPL and main negative bus MNL can continuously be stabilized without being affected by disconnection of power storage unit20from power supply system100or switching of the control mode of converter28. Thus, even after power storage unit20is electrically disconnected from power supply system100, electric power supply to the drive force generation unit and the auxiliary machinery group is continued by using electric power from power storage unit10.

FIGS. 6A and 6Bare diagrams showing outlines (case 4) of electric power supply to the drive force generation unit and the auxiliary machinery group according to the first embodiment of the present invention.FIG. 6Ashows a case where power storage units10and20are in a normal condition, whileFIG. 6Bshows a case where a fault condition takes place in power storage unit20.

Referring toFIG. 6A, as inFIG. 3Aabove, if power storage units10and20are both in a normal condition, system relays SMR1and SMR2are maintained in the ON state. Thus, discharge electric power Pb1is discharged from power storage unit10, a part thereof is supplied to the auxiliary machinery group, and the remaining part thereof is supplied to the drive force generation unit. In addition, discharge electric power Pb2from power storage unit20is supplied to the drive force generation unit in its entirety. In the case shown inFIG. 6A, as inFIG. 4A, converter28operates as “master”, and converter18operates as “slave”. Namely, converter28operating as “master” is controlled such that bus voltage value Vc attains to prescribed voltage target value Vc*. On the other hand, converter18operating as “slave” is controlled such that a value of electric power supplied and received between corresponding power storage unit10and main positive bus MPL, main negative bus MNL attains to prescribed electric power target value Pb1*.

Here, if some kind of fault condition occurs in power storage unit20, system relay SMR2is driven to the OFF state as shown inFIG. 6Band power storage unit20is electrically disconnected from power supply system100. In this case, converter28stops the voltage conversion operation and sets an electrically open state between system relay SMR2and main positive bus MPL, main negative bus MNL. Namely, the control mode of converter28is switched from the voltage control mode (boost) to the open mode.

As the control mode of converter28is switched, bus voltage value Vc across main positive bus MPL and main negative bus MNL cannot be stabilized. Therefore, converter18operating as “slave” is switched to operate as “master”. Namely, the control mode of converter18is switched from the electric power control mode to the voltage control mode (boost). Thus, even after power storage unit20is electrically disconnected from power supply system100, electric power supply to the drive force generation unit and the auxiliary machinery group is continued by using electric power from power storage unit10, while bus voltage value Vc across main positive bus MPL and main negative bus MNL is stabilized.

(Operating State of Converter in Conducting Mode)

FIG. 7is a diagram showing a state of operation of converters18,28in the conducting mode shown inFIGS. 3B and 4B.

Referring toFIG. 7, transistors Q1B and Q2B connected to main positive bus MPL in converters18and28respectively are both maintained in the ON state. Specifically, a switching instruction indicating the duty ratio of 100% is given from converter ECU30(FIG. 1) to transistors Q1B and Q2B. On the other hand, transistors Q1A and Q2A connected to main negative bus MNL in converters18and28respectively are both maintained in the OFF state. Specifically, a switching instruction indicating the duty ratio of 0% is given from converter ECU30(FIG. 1) to transistors Q1A and Q2A.

Consequently, positive line PL1is electrically connected to main positive bus MPL through inductor L1and transistor Q1B, and negative line NL1is directly connected to main negative bus MNL. In addition, positive line PL2is electrically connected to main positive bus MPL through an inductor L2and transistor Q2B, and negative line NL2is directly connected to main negative bus MNL.

Accordingly, from the viewpoint of power storage unit20(FIG. 1), two current paths, that is, a current path through converter28to the drive force generation unit and a current path through converter28and converter18to the auxiliary machinery group are formed.

As described above, converters18and28are configured with a chopper-type circuit. Therefore, unlike the trans-type circuit, the “conducting mode” can be implemented. Specifically, converters18and28are non-insulating-type voltage conversion circuits and an electrically conducting state between an input side and an output side can readily be established by maintaining a transistor on a current path in the ON state. On the other hand, in a voltage conversion unit configured with a trans-type circuit as in down converter80(FIG. 1), a winding transformer insulates the input side and the output side from each other, and hence it is difficult to implement the “conducting mode” as in the present embodiment.

(Control Structure in Battery ECU)

A control structure for implementing switching between the control modes as above will be described hereinafter in detail.

FIG. 8is a block diagram showing a control structure in battery ECU32for detecting a fault condition of power storage unit10.FIG. 9is a block diagram showing a control structure in battery ECU32for detecting a fault condition of power storage unit20.

Referring toFIG. 8, battery ECU32detects a fault condition of power storage unit10based on temperature Tb1, voltage value Vb1, current value Ib1, and an internal resistance value. It is not necessary to use all of four determination elements consisting of temperature Tb1, voltage value Vb1, current value Ib1, and the internal resistance value. Namely, at least one of these determination elements should only be included, and another determination element may be added.

A control structure of battery ECU32includes a logical sum unit320, a deactivating unit328, comparison units321,322,323,325,326, and327, and a division unit324.

Logical sum unit320operates the logical sum of a result of determination based on each determination element which will be described later and issues a fault condition detection signal FAL1for notification of the fault condition in power storage unit10. Specifically, when an output from any of comparison units321,322,323,325,326, and327which will be described later is activated, logical sum unit320outputs fault condition detection signal FAL1to the outside as well as to deactivating unit328.

Deactivating unit328sets system ON instruction SON1to inactive (OFF) in response to fault condition detection signal FALL. Then, system relay SMR1(FIG. 1) is driven to the OFF state and power storage unit10is electrically disconnected from power supply system100.

Comparison units321and322are units for monitoring voltage value Vb1of power storage unit10, and determines whether voltage value Vb1is within a prescribed voltage value range or not (a threshold voltage value α2<Vb1< a threshold voltage value α1). Specifically, comparison unit321activates the output when voltage value Vb1exceeds threshold voltage value α1. Alternatively, comparison unit322activates the output when voltage value Vb1is lower than threshold voltage value α2.

Comparison unit323is a unit for monitoring current value Ib1of power storage unit10and determines whether an excessive current flows in power storage unit10or not. Specifically, comparison unit323activates the output when current value Ib1exceeds a threshold current value α3.

Division unit324and comparison unit325are units for monitoring the internal resistance value of power storage unit10and determines whether the internal resistance value has excessively increased or not due to deterioration. Specifically, division unit324calculates an internal resistance value Rb1by dividing voltage value Vb1of power storage unit10by current value Ib1thereof, and comparison unit325determines whether calculated internal resistance value Rb1has exceeded a threshold resistance value α4or not. Then, comparison unit325activates the output when the internal resistance value exceeds threshold resistance value α4.

Comparison units326and327are units for monitoring temperature Tb1of power storage unit10, and determines whether temperature Tb1is within a prescribed temperature range or not (a threshold temperature α6<Tb1< a threshold temperature α5). Specifically, comparison unit326activates the output when temperature Tb1exceeds threshold temperature a5, and comparison unit327activates the output when temperature Tb1is lower than threshold temperature α6.

Referring toFIG. 9, battery ECU32further detects a fault condition of power storage unit20based on temperature Tb2, voltage value Vb2, current value Ib2, and an internal resistance value. It is not necessary to use all of four determination elements consisting of temperature Tb2, voltage value Vb2, current value Ib2, and the internal resistance value. Namely, at least one of these determination elements should only be included, and another determination element may be added.

The control structure of battery ECU32further includes a logical sum unit330, a deactivating unit338, comparison units331,332,333,335,336, and337, and a division unit334. As a function of each of these units is the same as that of logical sum unit320, deactivating unit328, comparison units321,322,323,325,326, and327, and division unit324, detailed description will not be repeated.

It is noted that threshold values α1to α6shown inFIGS. 8 and 9can experimentally be obtained in advance or they may be set based on a design value of power storage units10,20. If power storage unit10and power storage unit20are different from each other in characteristics, threshold values α1to α6shown inFIGS. 8 and 9may be different therebetween.

(Control Structure in Converter ECU)

FIG. 10is a block diagram showing a control structure involved with generation of switching instructions PWC1, PWC2in converter ECU30.

Referring toFIG. 10, the control structure of converter ECU30includes a switching instruction generation unit300and an allotment unit302.

Switching instruction generation unit300generates switching instructions PWC1, PWC2for controlling the voltage conversion operation of converters18,28in accordance with electric power target values Pb1*, Pb2*, a voltage target value Vh*, and the like. In addition, switching instruction generation unit300includes a control system (for normal condition)304and a control system (for fault condition)306, and activates any one of them in response to fault condition detection signals FAL1(FIG. 8), FAL2(FIG. 9) from battery ECU32. Each of control system (for normal condition)304and control system (for fault condition)306generates switching instructions PWC1, PWC2in accordance with a predetermined control mode, based on current values Ib2, voltage values Vb1, Vb2, and the like.

Allotment unit302divides requested electric power Ps* from drive ECU50(FIG. 1) into electric power target values Pb1*, Pb2* to be allotted to power storage units10,20respectively and provides the target values to switching instruction generation unit300. Here, allotment unit302determines a ratio of division based on SOCs (not shown) or the like of power storage units10,20provided from battery ECU32(FIG. 1).

FIG. 11is a block diagram showing a control structure of control system (for normal condition)304corresponding toFIGS. 3A and 5A.

In the operation state shown inFIGS. 3A and 5A, if power storage units10and12are both in a normal condition, converter18is controlled in accordance with the “voltage control mode (boost)” and converter28is controlled in accordance with the “electric power control mode.”

Referring toFIGS. 2 and 11, a control structure of control system (for normal condition)304includes modulation units (MOD)402,404, a division unit410, subtraction units412,416, and a PI control unit414as a configuration for controlling converter18in accordance with the “voltage control mode (boost).”

Modulation unit402generates second switching instruction PWC1B for driving transistor Q1B (FIG. 2) of converter18in accordance with a given duty ratio instruction. Specifically, modulation unit402generates second switching instruction PWC1B by comparing the duty ratio instruction with carrier wave generated by a not-shown oscillation unit. As transistor Q1B (FIG. 2) is maintained in the ON state when converter18performs the voltage conversion operation in accordance with the “voltage control mode (boost),” “1” (100%) is input to modulation unit402.

Modulation unit404generates first switching instruction PWC1A for driving transistor Q1A (FIG. 2) of converter18in accordance with a duty ratio instruction provided from subtraction unit416as will be described later.

Subtraction unit416subtracts a PI output from PI control unit414from a theoretical duty ratio from division unit410and provides the result as the duty ratio instruction to modulation unit404.

Division unit410calculates the theoretical duty ratio (=Vb1/Vc*) corresponding to a boost ratio of converter18by dividing voltage value Vb1of power storage unit10by voltage target value Vc* and outputs the result to subtraction unit416. Namely, division unit410generates a feedforward component for implementing the “voltage control mode (boost).”

Subtraction unit412calculates voltage deviation ΔVc of bus voltage value Vc from voltage target value Vc* and provides the result to PI control unit414. PI control unit414generates a PI output complying with voltage deviation ΔVc based on prescribed proportional gain and integral gain and outputs the same to subtraction unit416.

Specifically, PI control unit414includes a proportional element (P)418, an integral element (I)420, and an addition unit422. Proportional element418multiplies voltage deviation ΔVc by prescribed proportional gain Kp1and outputs the result to addition unit422, and integral element420integrates voltage deviation ΔVc with respect to prescribed integral gain K11(integral time: 1/Ki1) and outputs the result to addition unit422. Then, addition unit422adds outputs from proportional element418and integral element420and generates the PI output. The PI output corresponds to a feedback component for implementing the “voltage control mode (boost).”

In addition, a control structure of control system (for normal condition)304includes modulation units (MOD)406,408, a division unit430, a multiplication unit434, subtraction units432,438, and a PI control unit436as a configuration for controlling converter28in accordance with the “electric power control mode.”

Modulation unit406generates a second switching instruction PWC2B for driving transistor Q2B (FIG. 2) of converter28. As modulation unit406is otherwise the same as modulation unit402described above, detailed description will not be repeated.

Modulation unit408generates a first switching instruction PWC2A for driving transistor Q2A (FIG. 2) of converter28in accordance with a duty ratio instruction provided from subtraction unit438as will be described later. Subtraction unit438subtracts a PI output from PI control unit436from a theoretical duty ratio from division unit430and provides the result as the duty ratio instruction to modulation unit408.

Division unit430calculates the theoretical duty ratio (=Vb2/Vc*) corresponding to a boost ratio of converter28by dividing voltage value Vb2of power storage unit20by voltage target value Vc* as in division unit410described above and outputs the result to subtraction unit438.

Multiplication unit434calculates discharge electric power Pb2from power storage unit20by multiplying current value Ib2by voltage value Vb2. Then, subtraction unit432calculates electric power deviation ΔPb2of discharge electric power Pb2calculated by multiplication unit434from electric power target value Pb2* and provides the result to PI control unit436. Namely, the configuration in the “voltage control mode (boost)” described above is such that the voltage deviation is provided to the PI control unit, whereas the configuration in the “electric power control mode” is such that the electric power deviation is provided to the PI control unit.

PI control unit436generates the PI output complying with electric power deviation ΔPb1based on prescribed proportional gain Kp2and integral gain Ki2, and outputs the same to subtraction unit438. In addition, PI control unit436includes a proportional element440, an integral element442, and an addition unit444. As functions of these units are the same as those in PI control unit414described above, detailed description will not be repeated.

FIG. 12is a block diagram showing a control structure of control system (for normal condition)304corresponding toFIGS. 4A and 6A.

In the operation state shown inFIGS. 4A and 6A, if power storage units10and12are both in a normal condition, converter18is controlled in accordance with the “electric power control mode” and converter28is controlled in accordance with the “voltage control mode (boost).”

Referring toFIG. 12, the control structure of control system (for normal condition)304further includes modulation units (MOD)402,404, division unit410, a multiplication unit474, subtraction units472,416, and PI control unit414as a configuration for controlling converter18in accordance with the “electric power control mode.” As a function of each of these units is the same as that of modulation units (MOD)406,408, division unit430, multiplication unit434, subtraction units432,438, and PI control unit436inFIG. 11above, detailed description will not be repeated.

In addition, the control structure of control system (for normal condition)304further includes modulation units (MOD)406,408, division unit430, subtraction units482,438, and PI control unit436as a configuration for controlling converter28in accordance with the “voltage control mode (boost).” As a function of each of these units is the same as that of modulation units (MOD)402,404, division unit410, subtraction units412,416, and PI control unit414inFIG. 11above, detailed description will not be repeated.

FIG. 13is a block diagram showing a control structure of control system (for fault condition)306corresponding toFIGS. 3B and 4B.

Referring toFIGS. 8 and 10, if a fault condition occurs in power storage unit10and power storage unit10is electrically disconnected from power supply system100, control system (for fault condition)306is activated. Referring toFIGS. 7 and 13, in control system (for fault condition)306, “1” (Duty=100%) is provided to both of modulation units402and406and “0” (Duty=0%) is provided to both of modulation units404and408. Consequently, in converters18and28, transistors Q1B and Q2B are maintained in the ON state and transistors Q1A and Q2A are maintained in the OFF state.

FIG. 14is a block diagram showing a control structure of control system (for fault condition)306corresponding toFIGS. 5B and 6B.

As shown inFIGS. 9 and 10, if a fault condition occurs in power storage unit20and power storage unit20is electrically disconnected from power supply system100, control system (for fault condition)306is activated. In control system (for fault condition)306, converter18is controlled in accordance with the control structure similar to that of control system (for normal condition)304shown inFIG. 11. Namely, referring toFIG. 14, the control structure of control system (for fault condition)306includes modulation units (MOD)402,404, division unit410, subtraction units412,416, and PI control unit414as a configuration for controlling converter18in accordance with the “voltage control mode (boost).” As the function of each of these units has been described above, detailed description will not be repeated.

In contrast, converter28is controlled to enter the “open mode”. Specifically, in control system (for fault condition)306, “0” (Duty=0%) is provided to modulation units406and408. Therefore, transistors Q2A and Q2B of converter28are maintained in the OFF state. Consequently, converter28sets an electrically open state between system relay SMR2and main positive bus MPL, main negative bus MNL.

FIG. 15is a flowchart of a method of controlling power supply system100according to the first embodiment of the present invention. It is noted that the flowchart shown inFIG. 15can be implemented by execution of one or more program stored in advance by converter ECU30and battery ECU32.

Referring toFIG. 15, battery ECU32obtains temperature Tb1, voltage value Vb1and current value Ib1of power storage unit10(step S100). Then, battery ECU32calculates internal resistance value Rb1of power storage unit10from voltage value Vb1and current value Ib1, and determines whether a fault condition has occurred in power storage unit10or not based on temperature Tb1, voltage value Vb1, current value Ib1, internal resistance value Rb1, and the like of power storage unit10(step S102). Namely, whether power storage unit10should electrically be disconnected or not is determined.

If a fault condition has occurred in power storage unit10(YES in step S102), that is, if power storage unit10should electrically be disconnected, battery ECU32drives system relay SMR1to the OFF state and electrically disconnects power storage unit10from power supply system100(step S104). At the same time, battery ECU32transmits fault condition detection signal FAL1to converter ECU30(step S106).

In response to fault condition detection signal FAL1from battery ECU32, converter ECU30stops the voltage conversion operation in converters18and28(step S108) and switches converters18and28to the conducting mode (step S110). Then, the process ends.

In contrast, if there is no fault condition in power storage unit10(NO in step S102), battery ECU32obtains temperature Tb2, voltage value Vb2and current value Ib2of power storage unit20(step S112). Then, battery ECU32calculates an internal resistance value Rb2of power storage unit20from voltage value Vb2and current value Ib2, and determines whether a fault condition has occurred in power storage unit20or not based on temperature Tb2, voltage value Vb2, current value Ib2, internal resistance value Rb2, and the like of power storage unit20(step S114). Namely, whether power storage unit20should electrically be disconnected or not is determined.

If a fault condition has occurred in power storage unit20(YES in step S114), that is, if power storage unit20should electrically be disconnected, battery ECU32drives system relay SMR2to the OFF state and electrically disconnects power storage unit20from power supply system100(step S116). At the same time, battery ECU32transmits fault condition detection signal FAL2to converter ECU30(step S118).

In response to fault condition detection signal FAL2from battery ECU32, converter ECU30determines whether converter18is operating as “master” or not (step S120). If converter18is not operating as “master” (NO in step S120), converter18is switched to the voltage control mode (boost) to operate as “master” (step S122).

Further, after converter18is switched to the voltage control mode (boost) (after step S122is performed) or if converter18is operating as “master” (YES in step S120), converter ECU30switches converter28to the open mode (step S124). Then, the process ends.

In contrast, if there is no fault condition in power storage unit20(NO in step S114), that is, if it is not necessary to electrically disconnect power storage unit20, the process returns to the initial step.

According to the first embodiment of the present invention, when a fault condition occurs in power storage unit10and power storage unit10is electrically disconnected from power supply system100, converters18and28are both set to the conducting mode. Thus, electric power is supplied from power storage unit20through main positive bus MPL, main negative bus MNL to the drive force generation unit and a part of electric power supplied to main positive bus MPL, main negative bus MNL is supplied to the auxiliary machinery group.

Alternatively, when a fault condition occurs in power storage unit20and power storage unit20is electrically disconnected from power supply system100, converter18is set to the voltage control mode (boost) and converter28is set to the open mode. Thus, electric power is supplied from power storage unit10through main positive bus MPL, main negative bus MNL to the drive force generation unit and electric power is supplied through low-voltage positive line LPL and low-voltage negative line LNL to the auxiliary machinery group.

Thus, even though any one of power storage units10and20is electrically disconnected from power supply system100, electric power supply to the drive force generation unit and the auxiliary machinery group can be continued.

In addition, according to the first embodiment of the present invention, when any one of power storage units10and20is electrically disconnected from power supply system100, converters18and28both stop the electric power conversion operation, and hence switching loss involved with electric power supply from the corresponding power storage unit to main positive bus MPL, main negative bus MNL can be reduced. Therefore, even though a value of current that flows through converter28becomes relatively high along with electric power supply only from power storage unit20, unnecessary generation of loss can be suppressed.

[Variation of First Embodiment]

In the present first embodiment, the power supply system including two power storage units has been described, however, expansion to a power supply system including three or more power storage units is also similarly applicable.

FIG. 16is a diagram showing outlines of electric power supply to the drive force generation unit and the auxiliary machinery group according to a variation of the first embodiment of the present invention.

Referring toFIG. 16, a power supply system according to the variation of the present first embodiment representatively includes converter18operating as “master” and converters28_1to28_N operating as “slave”. In correspondence with converters28_1to28_N, power storage units20_1to20_N and system relays SMR2_1to SMR2_N are provided. If all of power storage unit10and power storage units20_1to20_N are in a normal condition, converter18performs the boost operation in accordance with the voltage control mode (boost) and converters28_1to28_N perform the boost operation in accordance with the electric power control mode.

Here, if a fault condition occurs in power storage unit10and power storage unit10is disconnected from the power supply system, all converters, that is, converter18and converters28_1to28_N, are switched to the conducting mode. Consequently, as in the first embodiment described above, electric power supply to the drive force generation unit and the auxiliary machinery group is continued.

As the power supply system is otherwise the same as power supply system100according to the first embodiment, detailed description will not be repeated.

According to the variation of the first embodiment of the present invention, as the number of power storage units constituting the power supply system is not limited, an appropriate number of power storage units can be provided, depending on magnitude of an electric power capacity of the drive force generation unit and the auxiliary machinery group. Therefore, in addition to the effect in the first embodiment of the present invention described above, the power supply system having a power supply capacity variable in a flexible manner can be obtained.

Second Embodiment

In the first embodiment described above, when power storage unit10is disconnected from power supply system100, electric power having a voltage substantially equal to voltage value Vb2of power storage unit20is supplied to the drive force generation unit. Meanwhile, in order to be able to supply electric power having a higher voltage, the voltage conversion operation in converters18and28may positively be performed.

As the overall configuration of a power supply system according to the second embodiment of the present invention is the same as power supply system100according to the present first embodiment shown inFIG. 1, detailed description will not be repeated. Referring again toFIGS. 3B and 4B, in the present second embodiment, if some kind of fault condition occurs in power storage unit10and power storage unit10is electrically disconnected from power supply system100, converter28is switched to the “voltage control mode (boost)” and converter18is switched to the “voltage control mode (down-conversion).”

FIG. 17is a diagram showing a state of operation of converters18,28in the voltage control mode (boost/down-conversion) shown inFIGS. 3B and 4B.

Referring toFIG. 17, converter28supplies discharge electric power from corresponding power storage unit20to main positive bus MPL, main negative bus MNL after it is boosted such that the voltage value of the discharge electric power attains to prescribed voltage target value Vc*. On the other hand, converter18supplies a part of electric power that flows through main positive bus MPL, main negative bus MNL to the auxiliary machinery group through positive line PL1, negative line NL1after it is down-converted such that the voltage value of the electric power attains to prescribed voltage target value Vb*.

As a result of such an operation, electric power having a voltage value substantially equal to that before disconnection of power storage unit10can be supplied to the drive force generation unit and electric power having voltage target value Vb* close to voltage value Vb1of power storage unit10can be supplied to the auxiliary machinery group. Therefore, the drive force generation unit and the auxiliary machinery group can continue substantially the same operation, regardless of electrical disconnection of power storage unit10.

More specifically, in converter28performing the boost operation, transistor Q2A performs the switching operation at a duty ratio in accordance with the boost ratio (=Vb2/Vc*) and transistor Q2B is maintained in the ON state (duty ratio=100%).

In addition, in converter18performing the down-conversion operation, transistor Q1A is maintained in the OFF state (duty ratio=0%) and transistor Q2B performs the switching operation at a duty ratio in accordance with a down-conversion ratio (=Vb*Nc).

(Control Structure in Converter ECU)

In a control structure in a converter ECU30A according to the present second embodiment, a control system (for fault condition)308is provided instead of control System (for fault condition)306in converter ECU30according to the present first embodiment shown inFIG. 10. As the control structure is otherwise the same as in the first embodiment described above, detailed description will not be repeated.

FIG. 18is a block diagram showing a control structure of control system (for fault condition)308corresponding toFIGS. 3B and 4B. It is noted that control system (for fault condition)308is activated when a fault condition occurs in power storage unit10and power storage unit10is electrically disconnected from the power supply system.

Referring toFIGS. 17 and 18, the control structure of control system (for fault condition)308includes modulation units (MOD)402,404and a division unit450as a configuration for controlling converter18in accordance with the “voltage control mode (down-conversion).”

Division unit450calculates a theoretical duty ratio (=Vb*/Vc) corresponding to a down-conversion ratio in converter18by dividing voltage target value Vb* by bus voltage value Vc and outputs the duty ratio to modulation unit402. Namely, division unit450generates a feedforward component for implementing the voltage conversion operation in accordance with the “voltage control mode (down-conversion).” Modulation unit402generates second switching instruction PWC1B for driving transistor Q1B (FIG. 11) of converter18in accordance with a signal output from division unit450.

In addition, as “0” is provided to modulation unit404, the duty ratio of first switching instruction PWC1A is fixed to 0% and transistor Q1A (FIG. 11) of converter18is maintained in the OFF state.

In addition, the control structure of control system (for fault condition)308includes modulation units (MOD)406,408, a division unit452, subtraction units454,458, and a PI control unit456as a configuration for controlling converter28in accordance with the “voltage control mode (boost).”

Division unit452calculates a theoretical duty ratio (=Vb2/Vc*) corresponding to the boost ratio in converter28by dividing voltage value Vb2of power storage unit20by voltage target value Vc* and outputs the duty ratio to subtraction unit458. Namely, division unit452generates a feedforward component for implementing the boost operation in accordance with the “voltage control mode (boost).”

PI control unit456generates a PI output complying with voltage deviation AVc of bus voltage value Vc from voltage target value Vc* calculated by subtraction unit454, based on prescribed proportional gain Kp3and integral gain Ki3and outputs the same to subtraction unit458. The PI output corresponds to a feedback component for implementing the “voltage control mode (boost).” In addition, PI control unit456includes a proportional element460, an integral element462, and an addition unit464. As these units are the same as those in PI control unit414described above, detailed description will not be repeated.

Subtraction unit458provides a value obtained by subtracting the PI output from PI control unit456from the theoretical duty ratio from division unit452to modulation unit408as the duty ratio instruction. Modulation unit408generates first switching instruction PWC2A for driving transistor Q2A (FIG. 17) in converter28, in accordance with the output value from subtraction unit458.

In addition, as “1” is provided to modulation unit406, the duty ratio of second switching instruction PWC2B is fixed to 100% and transistor Q2B (FIG. 17) in converter28is maintained in the ON state.

As described above, switching from control system (for normal condition)304to control system (for fault condition)308is made in response to occurrence of the fault condition in power storage unit10, so that the drive force generation unit and the auxiliary machinery group can continuously operate even after power storage unit10is electrically disconnected from the power supply system.

As the configuration is otherwise the same as in power supply system100according to the first embodiment described above, detailed description will not be repeated.

According to the second embodiment of the present invention, after power storage unit10is electrically disconnected from the power supply system, converter28performs the boost operation and converter18performs the down-conversion operation. Accordingly, electric power discharged from power storage unit20is supplied to the drive force generation unit after it is boosted by converter28and a part of electric power boosted by converter28is supplied to the auxiliary machinery group after it is down-converted by converter18. Thus, voltage ranges electric power supplied to the drive force generation unit and the auxiliary machinery group are maintained in ranges the same as before power storage unit10is electrically disconnected. Therefore, even after power storage unit10is electrically disconnected, an operating range (speed range) of motor-generators MG1and MG2constituting the drive force generation unit can be ensured and hence running performance or the like of the vehicle can be maintained.

[Variation of Second Embodiment]

In the present second embodiment, the power supply system including two power storage units has been described, however, expansion to a power supply system including three or more power storage units is also similarly applicable.

FIG. 19is a diagram showing outlines of electric power supply to the drive force generation unit and the auxiliary machinery group according to a variation of a second embodiment of the present invention.

Referring toFIG. 19, a power supply system according to the variation of the present second embodiment includes converter18operating as “master” and converters28_1to28_N operating as “slave”, as in the power supply system according to the variation of the present first embodiment shown inFIG. 16. In correspondence with converters28_1to28_N, power storage units20_1to20_N and system relays SMR2_1to SMR2_N are provided.

If all of power storage unit10and power storage units20_1to20_N are in a normal condition, converter18performs the voltage conversion operation in accordance with the voltage control mode (boost) and converters28_1to28_N perform the voltage conversion operation in accordance with the electric power control mode.

Here, if a fault condition occurs in power storage unit10and power storage unit10is disconnected from the power supply system, converter18is switched to the “voltage control mode (down-conversion)” and at least one of converters28_1to28_N is switched to the “voltage control mode (boost).” This is done so that bus voltage value Vc supplied to the drive force generation unit is controllable and bus voltage value Vc is stabilized when any one converter performs the electric power conversion operation in accordance with the “voltage control mode (boost).” Though all of converters28_1to28_N may be set to the “voltage control mode (boost),” from the viewpoint of electric power management in the overall power supply system, the number of converters maintained in the “electric power control mode” is desirably great.

As the power supply system is otherwise the same as the power supply system according to the second embodiment, detailed description will not be repeated.

According to the variation of the second embodiment of the present invention, as the number of power storage units constituting the power supply system is not limited, an appropriate number of power storage units can be provided, depending on magnitude of an electric power capacity of the drive force generation unit and the auxiliary machinery group. Therefore, in addition to the effect in the second embodiment of the present invention described above, the power supply system having a power supply capacity variable in a flexible manner can be obtained.

In the first and second embodiments of the present invention and the variations thereof, such a configuration that, when power storage unit10or20is in a fault condition, determination that the power storage unit in the fault condition should electrically be disconnected from the power supply system is made is illustrated, however, the present invention is not limited as such. For example, in such a manner of use that one power storage unit is successively selected from among a plurality of power storage units and each selected power storage unit is discharged to its limit in using a vehicle including the power supply system according to the present invention in the EV running mode, the power storage unit discharged to its limit should be disconnected from the power supply system. The power supply system according to the invention of the subject application is also applicable to such a manner of use.

In addition, in the first and second embodiments of the present invention and the variations thereof, a configuration including the drive force generation unit and the auxiliary machinery group is illustrated by way of example of the first and second load devices, however, the load device is not limited as such. Moreover, the power supply system according to the present invention is applicable to an apparatus having two types of load devices consuming electric power, in addition to an example where it is mounted on a vehicle.

In the invention of the subject application, even when the “first electric power line pair” is alternatively read as the “smoothing capacitor provided on the input side of the first load device,” the technical concept thereof is essentially identical.