Input/output controller for secondary battery and vehicle

An input/output controller for a secondary battery installed in a hybrid vehicle includes a temperature sensor detecting a battery temperature of a battery, a voltage sensor detecting battery voltage of battery, and a control unit for receiving temperature detected by temperature sensor and battery voltage detected by voltage sensor and setting a limit value of electric power to be inputted to or outputted from battery. Control unit changes a change ratio of the limit value to be inputted or outputted relative to battery voltage in accordance with temperature.

This is a 371 national phase application of PCT/JP2007/069333 filed 26 Sep. 2007, claiming priority to Japanese Patent Application No. 2006-303066 filed 08 Nov. 2006, the contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an input/output controller for a secondary battery and a vehicle.

BACKGROUND ART

Recently, a hybrid vehicle and an electric vehicle are drawing a great deal of attention as an eco-friendly vehicle. Then, the hybrid vehicle is partially put into a practical use.

This hybrid vehicle is a vehicle having a DC power source, an inverter and a motor driven by the inverter as a power source in addition to a conventional engine. That is, while the power source is obtained by driving the engine, direct voltage from the DC power source is converted into alternating voltage by the inverter and the power source is obtained by rotating the motor by the converted alternating voltage. The electric vehicle is a vehicle having a DC power source, an inverter and a motor driven by the inverter as a power source.

In general, a secondary battery is installed in the hybrid vehicle or the electric vehicle as the DC power source. By demonstrating a performance of the secondary battery more, a performance of the vehicle can be improved.

For example, Japanese Patent Laying-Open No. 2005-039989 discloses an output management device for a secondary battery. In a case where the secondary battery is required to output exceeding a rated output, this output management device sets a quantity of the output and a duration time for the output based on a temperature of the secondary battery.

In general, internal resistance of a battery has dependence on the temperature. For example, the internal resistance of the battery is increased as a temperature around the battery is lowered. When the internal resistance of the battery is increased, a change in battery voltage relative to a change in electric power inputted to or outputted from the battery is increased. When the change in the battery voltage is increased, the battery voltage may exceed an upper limit value of a use range or fall below a lower limit value of the use range. However, Japanese Patent Laying-Open No. 2005-039989 does not particularly disclose such a problem.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide an input/output controller for a secondary battery capable of properly controlling battery voltage in accordance with a battery temperature, and a vehicle provided with the above device.

In summary, the present invention provides an input/output controller for a secondary battery, including a temperature sensing unit for sensing a battery temperature of the secondary battery, a voltage sensing unit for sensing battery voltage of the secondary battery, and a setting unit for receiving the battery temperature sensed by the temperature sensing unit and the battery voltage sensed by the voltage sensing unit and setting a limit value of electrical power to be inputted to or outputted from the secondary battery. The setting unit changes a change ratio of the limit value relative to the battery voltage in accordance with the battery temperature.

Preferably, the setting unit includes an operation unit for performing control operation based on a deviation between target voltage of the secondary battery and the battery voltage. The operation unit changes control gain used in the control operation in accordance with the battery temperature. The setting unit further includes an initial value setting unit for setting an initial value of the limit value, and a limit value determining unit for determining the limit value based on the initial value and an operation result of the operation unit.

More preferably, the operation unit determines the control gain so that the control gain is decreased as the battery temperature is lowered.

More preferably, the control operation is proportional integral operation. The control gain includes proportional gain and integral gain. The operation unit has a coefficient setting unit, a proportional operation unit, an integral operation unit and an adding unit. The coefficient setting unit sets first and second coefficients in accordance with the battery temperature. The proportional operation unit sets the proportional gain by multiplying the first coefficient by fixed first gain not in accordance with the battery temperature and operates a proportional value of the deviation with using the proportional gain. The integral operation unit sets the integral gain by multiplying the second coefficient by fixed second gain not in accordance with the battery temperature and operates an integral value of the deviation with using the integral gain. The adding unit adds the proportional value and the integral value.

In accordance with another aspect of the present invention, a vehicle includes a secondary battery, and an input/output controller for controlling an input and an output of the secondary battery. The input/output controller includes a temperature sensing unit for sensing a battery temperature of the secondary battery, a voltage sensing unit for sensing battery voltage of the secondary battery, and a setting unit for receiving the battery temperature sensed by the temperature sensing unit and the battery voltage sensed by the voltage sensing unit and setting a limit value of electrical power to be inputted to or outputted from the secondary battery. The setting unit changes a change ratio of the limit value relative to the battery voltage in accordance with the battery temperature.

Preferably, the setting unit has an operation unit for performing control operation based on a deviation between target voltage of the secondary battery and the battery voltage. The operation unit changes control gain used in the control operation in accordance with the battery temperature. The setting unit further has an initial value setting unit for setting an initial value of the limit value, and a limit value determining unit for determining the limit value based on the initial value and an operation result of the operation unit.

More preferably, the operation unit determines the control gain so that the control gain is decreased as the battery temperature is lowered.

More preferably, the control operation is proportional integral operation. The control gain includes proportional gain and integral gain. The operation unit has a coefficient setting unit, a proportional operation unit, an integral operation unit and an adding unit. The coefficient setting unit sets first and second coefficients in accordance with the battery temperature. The proportional operation unit sets the proportional gain by multiplying the first coefficient by fixed first gain not in accordance with the battery temperature and operates a proportional value of the deviation with using the proportional gain. The integral operation unit sets the integral gain by multiplying the second coefficient by fixed second gain not in accordance with the battery temperature and operates an integral value of the deviation with using the integral gain. The adding unit adds the proportional value and the integral value.

Therefore, according to the present invention, the battery voltage can be properly controlled in accordance with the battery temperature.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. It should be noted that the same or corresponding parts in the drawings are given the same reference symbols and description thereof will not be repeated.

FIG. 1is a schematic diagram showing a configuration of a vehicle provided with an input/output controller for a secondary battery according to the present embodiment.

Hybrid vehicle1further includes a battery12arranged on the rear side of the vehicle, a voltage boosting unit32for boosting voltage of direct current power outputted by battery12, an inverter36for supplying or receiving the direct current power to or from voltage boosting unit32, a motor generator MG1for receiving mechanical power of engine2via planetary gear16and generating electric power, and a motor generator MG2having a rotation shaft connected to planetary gear16. Inverter36is connected to motor generators MG1and MG2so as to convert alternating current power and the direct current power from a voltage boosting circuit.

Planetary gear16has first to third rotation shafts. The first rotation shaft is connected to engine2, the second rotation shaft is connected to motor generator MG1, and the third rotation shaft is connected to motor generator MG2.

Gear4is attached to this third rotation shaft. By driving gear6, this gear4transmits the mechanical power to differential gear18. Differential gear18transmits the mechanical power received from gear6to front wheels20R and20L, and also transmits rotation force of front wheels20R and20L to the third rotation shaft of the planetary gear via gears6and4.

Planetary gear16plays a role of dividing the mechanical power among engine2and motor generators MG1and MG2. That is, when rotation of two of three rotation shafts of planetary gear16is determined, rotation of the remaining one rotation shaft is inevitably determined. Therefore, while engine2is operated in the most efficient area, electric generating capacity of motor generator MG1is controlled so as to drive motor generator MG2. Thereby, vehicle speed is controlled and a wholly energy-efficient vehicle is realized.

Battery12serving as a DC power source is, for example, formed by a nickel hydride secondary battery, a lithium ion secondary battery or the like for supplying the direct current power to voltage boosting unit32and being charged by the direct current power from voltage boosting unit32.

Voltage boosting unit32boosts direct voltage received from battery12, and supplies the boosted direct voltage to inverter36. Inverter36converts the supplied direct voltage into alternating voltage, and controls drive of motor generator MG1at the time of starting the engine. After starting the engine, the alternating current power generated by motor generator MG1is converted into the direct current by inverter36and converted into voltage suitable for charging battery12by voltage boosting unit32so that battery12is charged.

Inverter36drives motor generator MG2. Motor generator MG2assists engine2and drives front wheels20R and20L. At the time of braking, the motor generator performs a regenerating operation and converts rotation energy of the wheels into electric energy. The obtained electric energy is returned to battery12via inverter36and voltage boosting unit32.

System main relays28and30are provided between voltage boosting unit32and battery12, and high voltage is cut off at the time of not operating the vehicle.

Battery12includes internal resistance Rb. In general, internal resistance Rb has dependency on a temperature. For example, internal resistance Rb is increased as the temperature is lowered.

Hybrid vehicle1further includes a temperature sensor24and a voltage sensor26attached to battery12, and a control unit14for controlling engine2, inverter36and voltage boosting unit32in accordance with outputs of temperature sensor24and voltage sensor26. Temperature sensor24detects and transmits a temperature T of the battery to control unit14. Voltage sensor26detects and transmits voltage between terminals of battery12(battery voltage VB) to control unit14.

Control unit14receives temperature T and battery voltage VB and sets a limit value of electric power to be inputted to or outputted from battery12. Control unit14changes a change ratio of the limit value relative to a change in battery voltage VB in accordance with temperature T.

Specifically, control unit14decreases the change ratio of the limit value relative to the change in battery voltage VB as temperature T is lowered, and increases the change ratio of the limit value relative to the change in battery voltage VB as temperature T is raised. Thereby, even when the temperature of battery12is changed, battery voltage VB can be brought closer to target voltage.

FIG. 2is a block diagram of an input/output control system of battery12included in control unit14ofFIG. 1. It should be noted that the input/output control system shown inFIG. 2may be realized by software or by hardware.

With reference toFIG. 2, an input/output control system114in the present embodiment forms a feedback control system. Input/output control system114includes a target value generating unit121, a subtracting unit122, a PI control unit123, an initial value setting unit124, a final value determining unit125, and an input/output processing unit126.

Target value generating unit121generates and outputs target voltage VB0serving as a target value of the voltage of battery12. Target voltage VB0may be a fixed value or, for example, a value to be set in accordance with a deterioration state of battery12.

Subtracting unit122subtracts battery voltage VB from target voltage VB0and outputs a subtracting result thereof to PI control unit123.

PI control unit123performs proportional integral operation taking a deviation between target voltage VB0and battery voltage VB as an input and outputs an operation result thereof to final value determining unit125. PI control unit123changes control gain (hereinafter also referred to as the “feedback gain”) in accordance with temperature T. A configuration of PI control unit123will be described later.

Initial value setting unit124sets an initial value of a limit value Win of electric power inputted to battery12(initial value Win0) and an initial value of a limit value Wout of electric power outputted from battery12(initial value Wout0). A method of setting initial values Win0and Wout0is not particularly limited. For example, initial value setting unit124may preliminarily store a map for correspondence between battery voltage VB and initial value Win0and a map for correspondence between battery voltage VB and initial value Wout0. In this case, initial value setting unit124determines initial value Win0or initial value Wout0based on battery voltage VB detected by voltage sensor26ofFIG. 1.

Final value determining unit125receives initial value Win0from initial value setting unit124and the operation result of PI control unit123. Final value determining unit125compensates initial value Win0with using the operation result of PI control unit123and determines limit value Win of the electric power to be inputted to battery12.

Similarly, final value determining unit125receives initial value Wout0from initial value setting unit124and the operation result of PI control unit123. Final value determining unit125compensates initial value Wout0with using the operation result of PI control unit123and determines limit value Wout of the electric power to be inputted to battery12. That is, PI control unit123changes a compensation amount of limit value Win and a compensation amount of limit value Wout of the electric power in accordance with the temperature.

Input/output processing unit126charges battery12based on limit value Win given from final value determining unit125. Electricity is discharged from battery12based on limit value Wout given from final value determining unit125. Input/output processing unit126operates voltage boosting unit32, inverter36and engine2shown inFIG. 1so that battery12is charged or the electric power is discharged from battery12.

FIG. 3is a diagram showing a configuration of PI control unit123ofFIG. 2.

With reference toFIG. 3, PI control unit123includes a proportional operation unit131, an integral operation unit132, a coefficient setting unit134, and an adding unit135. Integral operation unit132includes an amplifying unit136and an integrating unit137.

Proportional operation unit131operates a proportional value of the deviation (VB0−VB) with using proportional gain (kP(T)×kPD) determined by the product of a coefficient kP(T) to be inputted and predetermined gain kPD. Integral operation unit132operates an integral value of the deviation (VB0−VB) with using integral gain (kI(T)×kID) determined by the product of a coefficient kI(T) to be inputted and predetermined gain kID.

kPD and kID are gain when a battery temperature is a predetermined temperature (such as −30° C.) (hereinafter, referred to as the “default”). kP(T) and kI(T) are coefficients changed in accordance with the temperature. Therefore, the proportional gain in proportional operation unit131and the integral gain in integral operation unit132are changed in accordance with the temperature.

Amplifying unit136amplifies the deviation (VB0−VB) with using integral gain (kI(T)×kID). Integrating unit137time-integrates an output of amplifying unit136. It should be noted that integrating unit137may be provided in a previous stage of amplifying unit136.

Coefficient setting unit134changes coefficients kP(T) and kI(T) in accordance with temperature T. For example, coefficient setting unit134refers to a map shown inFIG. 4so as to determine coefficients kP(T) and kI(T). Coefficient setting unit134outputs coefficients kP(T) and kI(T) to proportional operation unit131and integral operation unit132respectively.

Adding unit135adds an operation result (proportional value) of proportional operation unit131and an operation result (integral value) of integral operation unit132. An operation result in adding unit135is an output of PI control unit123.

FIG. 4is a diagram for illustrating a map referred by coefficient setting unit134ofFIG. 3.

With reference toFIG. 4, when the battery temperature is a predetermined value TL (−30° C. in the above example), both coefficients kP(T) and kI(T) are 1. As the battery temperature is raised from predetermined value TL, coefficients kP(T) and kI(T) are increased. It should be noted that a change ratio of coefficients kP(T) and kI(T) relative to a change in the temperature is not limited to an inclination of a curve shown inFIG. 4but properly determined in accordance with a characteristic of battery12, a response property in the feedback control system or the like.

Next, an effect by the input/output controller of the present embodiment will be described. It should be noted that hereinafter, a case where the electric power is taken out from battery12will be mainly described.

FIG. 5is a diagram for illustrating a relationship between discharged electric power of battery12and battery voltage VB.

With reference toFIG. 5, curves c1to c3are curves showing the relationship between the electric power of battery12at the time of electric discharge and battery voltage VB. Curves c1and c3show the relationship between the discharged electric power of battery12and battery voltage VB in a state where the internal resistance of the electric battery is relatively low and in a state where the internal resistance of the electric battery is relatively high respectively. Curve c2shows the relationship between the discharged electric power of battery12and battery voltage VB in a middle state between the state where the internal resistance of the electric battery is relatively low and the state where the internal resistance of the electric battery is relatively high.

In any of curves c1to c3, as the discharged electric power is increased, battery voltage VB is lowered from voltage VO serving as open circuit voltage.

Next, the change in the temperature in a minute change amount of electric power P relative to a minute change amount of battery voltage VB will be described. When electromotive force of battery12shown inFIG. 1is Eo, a resistance value of internal resistance Rb is R, and current passing through battery12is I, battery voltage VB is represented as (Eo−I×R). Electric power P outputted from battery12is represented as I×VB. Therefore, a relationship shown in the following equation (1) is established with regard to electric power P and battery voltage VB.
P={(Eo−VB)}/R×VB  (1)

Here, the change amount of electric power P relative to the change amount of battery voltage VB is dP/dV. dP/dV is equal to a result of differentiating electric power P shown in equation (1) with respect to battery voltage VB. Therefore, dP/dV is represented as the following equation (2).
dP/dV=(Eo−2VB)/R(2)

In general, as the battery temperature is lowered, the internal resistance of the battery is increased. That is, in a case where (Eo−VB) is fixed, as the battery temperature is lowered, dP/dV is decreased. Conversely, this indicates that as the battery temperature is lowered, (dV/dP) is increased.

Curves c1to c3show a relationship of dV/dP mentioned above. InFIG. 5, the minute change amount of electric power P is ΔP. In curves c1to c3, the change amounts of battery voltage VB corresponding to ΔP are ΔV1, ΔV2and ΔV3respectively. A relationship of ΔV1<ΔV2<ΔV3is established with regard to ΔV1, ΔV2and ΔV3. Therefore, a relationship of (ΔV1/ΔP)<(ΔV2/ΔP)<(ΔV3/ΔP) is established. This indicates that as the temperature of battery12is lowered, sensitivity of battery voltage VB is increased relative to the change in electric power P.

FIG. 6is a diagram for illustrating a possible problem caused in a case where the feedback gain in PI control unit123ofFIG. 2is set to be constant with the temperature.

With reference toFIG. 6, provided that the discharged electric power of the battery is controlled so that the discharged electric power of the battery is changed by ΔP around Po. Here, voltage VL is a lower limit value of battery voltage VB determined based on, for example, a performance of the battery, a use state (deterioration state) of the battery or the like. By maintaining battery voltage VB higher than voltage VL, for example, over-discharge of the battery can be prevented.

In curves c1and c2, even when the discharged electric power of the battery is changed by ΔP, battery voltage VB is always higher than voltage VL. On the other hand, in curve c3, the change in battery voltage VB relative to the change in the discharged electric power is large. Therefore, when the discharged electric power of the battery is changed by ΔP, battery voltage VB is lower than voltage VL.

FIG. 7is a diagram for illustrating an effect in a case where the feedback gain in PI control unit123ofFIG. 2is changed in accordance with the temperature.

With reference toFIG. 7, ΔP1, ΔP2and ΔP3show change amounts of the discharged electric power of battery12when battery voltage VB is changed from target voltage V130to voltage V1in curves c1to c3respectively.

With reference toFIGS. 7 and 2, in a case where the internal resistance is small, that is, in a case where the battery temperature is high, the feedback gain in PI control unit123is set to be large. In this case, the feedback gain is set so that the discharged electric power of the battery is changed along curve c1so to speak.

In the case where the battery temperature is high, the internal resistance of the battery is decreased. Therefore, the change in battery voltage VB relative to the change in outputted electric power of the battery is small. In the present embodiment, in the case where the battery temperature is high, the feedback gain is increased so as to increase the compensation amount of limit value Wout. Thereby, the change in limit value Wout can be increased. Even when the change in battery voltage VB is small, the response property of input/output control system114can be enhanced. Therefore, battery voltage VB can be brought closer to target voltage VB0for a short time.

On the other hand, in a case where the internal resistance is large, that is, in a case where the battery temperature is low, the feedback gain in PI control unit123is set to be small. In the case where the battery temperature is low, the change in battery voltage VB relative to the change in the outputted electric power of the battery is large. Therefore, the feedback gain relative to the deviation between target voltage VB0and battery voltage VB (that is, VB0−VB) is increased more than necessary, for example, overshoot of battery voltage VB, undershoot of battery voltage VB, hunting of battery voltage VB or the like may be caused.

In the present embodiment, in the case where the battery temperature is low, the feedback gain is decreased. Thereby, the compensation amount of limit value Wout is decreased and the change in limit value Wout relative to the change in battery voltage VB can be decreased. Thereby, since fluctuation of battery voltage VB can be decreased, the overshoot, the undershoot, the hunting and the like of battery voltage VB can be prevented.

As a result, in the present embodiment, in a case where the electric power is taken out from the battery, the electric power to be outputted from the battery can be controlled so that the lower limit value of battery voltage VB (voltage V1) is higher than voltage VL. That is, the voltage of the battery can be properly controlled in accordance with the battery temperature.

FIG. 8is a flowchart showing processing performed by input/output control system114shown inFIG. 2. The processing of this flowchart is executed whenever a predetermined condition is met, or at a fixed intervals.

With reference toFIGS. 8 and 2, input/output control system114obtains a value of battery voltage VB and a value of temperature T (Step S1). Next, with reference toFIGS. 8 and 3, processing of Steps S2and S3will be described.

In Step S2, coefficient setting unit134calculates coefficients kP(T) and kI(T) based on temperature T and the map (refer toFIG. 4).

In Step S3, PI control unit123sets the feedback gain by multiplying default gain by the coefficient. Specifically, in Step S3, proportional operation unit131sets the proportional gain by multiplying the default gain (gain kPD) by coefficient kP(T). Similarly, in Step S3, integral operation unit132sets the integral gain by multiplying the default gain (gain kID) by coefficient kI(T).

With reference toFIGS. 8 and 2again, processing of Step S4will be described. In Step S4, input/output control system114executes feedback control (PI control) based on a voltage exceeding amount (that is, deviation (VB0−VB)). When the processing of Step S4is finished, the entire processing is returned to Step S1again.

It should be noted that not only in a case where the electric power is outputted from the battery, but also in a case where the electric power is inputted to the battery, the input/output controller of the present embodiment can be applied.

FIG. 9is a diagram for illustrating a relationship between charged electric power of battery12and battery voltage VB.

With reference toFIG. 9, curves c4to c6are curves showing the relationship between the electric power of battery12at the time of electric charge and battery voltage VB. Curves c4and c6show the relationship between the charged electric power of battery12and battery voltage VB in a state where the internal resistance of the battery is relatively low and in a state where the internal resistance of the battery is relatively high respectively. Curve c5shows the relationship between the charged electric power of battery12and battery voltage VB in a middle state between the state where the internal resistance of the battery is relatively low and the state where the internal resistance of the battery is relatively high.

In any of curves c4to c6, as the charged electric power is increased, battery voltage VB is increased. At the time of charging battery12, as the internal resistance of battery12is raised, a change ratio of battery voltage VB relative to the change in the charged electric power is increased.

Voltage VH is an upper limit value of battery voltage VB determined based on, for example, the performance of the battery, the use state (deterioration state) of the battery or the like. By maintaining battery voltage VB lower than voltage VH, for example, over-charge of the battery can be prevented. ΔP4, ΔP5and ΔP6show change amounts of the charged electric power when battery voltage VB is changed from voltage V2to voltage V3in curves c4to c6, respectively. It should be noted that target voltage VB0is between voltage V2and voltage V3.

In a case where the internal resistance is small, that is, in a case where the battery temperature is high, the feedback gain in PI control unit123ofFIG. 2is set to be large. On the other hand, in a case where the internal resistance is high, that is, in a case where the battery temperature is low, the feedback gain in PI control unit123is set to be small.

In a case where the battery temperature is high, the feedback gain is increased. Therefore, the compensation amount of limit value Win is increased. As a result, the change in the charged electric power is increased. Therefore, even when the change in battery voltage VB is small, the response property of input/output control system114can be enhanced. On the other hand, in a case where the battery temperature is low, the change in battery voltage VB relative to the change in the outputted electric power of the battery is increased but the feedback gain is decreased. In this case, since the compensation amount of limit value Win is decreased, the change in limit value Win relative to the change in battery voltage VB can be decreased. Thereby, the overshoot, the undershoot, the hunting and the like of battery voltage VB can be prevented.

That is, as well as a case where the electric power is taken out from battery12, in a case where battery12is charged, the fluctuation of battery voltage VB relative to the electric power inputted to the battery can be suppressed (battery voltage VB can be brought closer to target voltage VB0) not in accordance with the battery temperature.

As a result, the electric power to be inputted to the battery can be controlled so that the upper limit value of battery voltage VB (voltage V3) is lower than voltage VH. In such a way, according to the present embodiment, the voltage of the battery can be properly controlled in accordance with the battery temperature.

It should be noted that in the present embodiment, a flowchart showing processing in a case where battery12is charged is the same as the flowchart shown inFIG. 8. Therefore, description thereof will not be repeated.

With reference toFIG. 1, the input/output controller for the secondary battery in the present embodiment will be comprehensively described. The input/output controller for the secondary battery is provided with temperature sensor24detecting the battery temperature of battery12(temperature T), voltage sensor26detecting the battery voltage of battery12(battery voltage VB), and control unit14receiving temperature T detected by temperature sensor24and battery voltage VB detected by voltage sensor26and setting the limit value (Win/Wout) to be inputted to or outputted from battery12. Control unit14changes the change ratio of the limit value relative to battery voltage VB in accordance with temperature T.

With reference toFIG. 2, preferably, control unit14includes the operation unit (PI control unit123) performing control operation based on the deviation between target voltage VB0of battery12and battery voltage VB. PI control unit123changes the control gain used for the control operation in accordance with temperature T. Control unit14further includes initial value setting unit124setting the initial value (Win0/Wout0) of the limit value, and final value determining unit125determining the limit value (Win/Wout) based on the initial value of the limit value and the operation result of PI control unit123.

More preferably, PI control unit123determines the control gain so that the control gain is decreased as temperature T is lowered.

With reference toFIG. 3, more preferably, the control operation of the operation unit (PI control unit123) is the proportional integral operation. The control gain includes the proportional gain and the integral gain. PI control unit123has coefficient setting unit134, proportional operation unit131, integral operation unit132, and adding unit135. Proportional operation unit131sets coefficients kP(T) and kI(T) (first and second coefficients) in accordance with temperature T. Proportional operation unit131sets the proportional gain by multiplying coefficient kP(T) by fixed gain kPD not in accordance with temperature T and operates the proportional value of the deviation with using the proportional gain. Integral operation unit132sets the integral gain by multiplying coefficient kI(T) by fixed gain kID not in accordance with temperature T and operates the integral value of the deviation with using the integral gain. Adding unit135adds the proportional value and the integral value.

In such a way, in the present embodiment, the voltage of the battery can be properly controlled in accordance with the battery temperature. Therefore, an electric storage performance and a discharge performance of the battery can be sufficiently exhibited.

According to the present embodiment, hybrid vehicle1is provided with the input/output controller for the secondary battery described in any of the above descriptions and battery12. Since the electric storage performance and the discharge performance of the battery can be sufficiently exhibited by the input/output controller, a performance of the vehicle can be sufficiently exhibited.

It should be noted that the above descriptions show an example that the input/output controller for the secondary battery of the present embodiment is applied to a series/parallel type hybrid system capable of dividing and transmitting the mechanical power of the engine into a wheel axle and a generator by a power split device. However, the present invention can be also applied to a series type hybrid vehicle of using an engine only for driving a generator and generating drive force of a wheel axle only by a motor using electric power generated by the generator or an electric vehicle traveling only by a motor.

The embodiment disclosed here is only an example in all respects but not restrictive. The scope of the present invention is shown not by the above descriptions but the claims and all the modifications within similar meanings and ranges of the claims are to be included.