Control method for fuel cell vehicle, and fuel cell vehicle

This control method for a fuel cell vehicle includes: a target motor output power obtaining step which obtains a target motor output power corresponding to an accelerator opening degree; and a high output power control step which controls operations of a first DC-DC converter and a second DC-DC converter, such that an output voltage of a power source becomes equal to or larger than a predetermined voltage that is required for securing a desired motor output power, when the target motor output power is larger than a predetermined output power threshold value.

BACKGROUND OF THE INVENTION

Priority is claimed on Japanese Patent Application No. 2006-026965, filed Feb. 3, 2006, the contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a control method for a fuel cell vehicle, and a fuel cell vehicle.

DESCRIPTION OF THE RELATED ART

A conventional power controller is known which is provided with, for example: a charging controller which converts output voltage of a fuel cell to charging voltage of a secondary battery; and a discharging controller which converts discharging voltage of the secondary battery to output voltage of the fuel cell, wherein the output voltage of the fuel cell and the discharged voltage of the secondary battery which was converted so as to be substantially equivalent to the output voltage of the fuel cell, are input to a converter of a power converter (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2003-208913).

In addition, a conventional fuel cell system is known which: when electrical power consumed by a load is larger than electrical power generated by a fuel cell, the shortage with respect to the electrical power consumed by the load is compensated by electrical power equal to or less than predetermined threshold electrical power purchased from a commercial power supply (for example, night electrical power or the like) and discharged electrical power from a power storage cell; and when the electrical power consumed by the load is less than the electrical power generated by the fuel cell, a surplus of the output electrical power is charged into the power storage cell (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2004-39506).

In the above-mentioned conventional power controller, since the output voltage of the fuel cell and the discharged voltage of the secondary battery which was converted so as to be substantially equivalent to the output voltage of the fuel cell are input into the converter of the power converter, it was impossible to appropriately change the ratio between the output power input from the fuel cell into the converter of the power converter, and the output power input from the secondary battery into the converter of the power converter. Therefore, it was difficult to secure desired output power, while, for example, protecting the fuel cell and the secondary battery in accordance with operation state of the fuel cell and charging state of the secondary battery.

In addition, in the conventional fuel cell system, since distributions of the electrical power to be supplied from the fuel cell and the power storage cell to the load is merely set in accordance with the electrical power purchased from the commercial power supply, it was difficult, for example, to appropriately set the distribution of each electrical power to be supplied from the commercial power supply, the fuel cell, and the power storage cell to the load, while considering each switching losses at an AC/DC converter connected to the load, and at a DC/DC converter arranged between the fuel cell and the power storage cell.

The present invention was made in view of the above-mentioned circumstances and has an object of providing a control method for a fuel cell vehicle, and a fuel cell vehicle which can perform an efficient electrical power converting operation to a power source formed from a fuel cell and a power storage device while preventing deterioration in traveling performance of a vehicle by securing desired motor output power.

SUMMARY OF THE INVENTION

In order to achieve the above-mentioned object, the present invention employed the followings.

That is, the present invention employed a control method for a fuel cell vehicle including a motor being a driving source of the fuel cell vehicle, a motor controller for controlling an operation status of the motor, and a fuel cell system being a power source for the motor. The fuel cell system includes: a fuel cell which receives reaction gasses and performs electrochemical reactions to generate an electrical power; a power storage device which is charged with the generated electrical power from the fuel cell and a regeneration power from the motor; a first DC-DC converter provided between the power storage device and the motor controller; and a second DC-DC converter provided between the fuel cell and the motor controller. The control method for a fuel cell vehicle includes: a target motor output power obtaining step which obtains a target motor output power corresponding to an accelerator opening degree; and a high output power control step which controls operations of the first DC-DC converter and the second DC-DC converter, such that an output voltage of the fuel cell system becomes equal to or larger than a predetermined voltage that is required for securing a desired motor output power, when the target motor output power is larger than a predetermined output power threshold value.

According to the control method for a fuel cell vehicle, even when, for example, the motor output power decreases from the desired motor output power in accordance with reducing voltage to be applied to the motor in a range where the reducing voltage becomes equal to or less than the predetermined voltage, it is possible to prevent the motor output power from becoming less than the desired motor output power by controlling the first DC-DC converter and the second DC-DC converter such that the output power voltage of the hybrid-type power source constructed from the fuel cell and the power storage device (i.e., voltage to be supplied to the motor controller constructed from the inverter which applies voltage to the motor, and the like) becomes equal to or over the predetermined voltage. Accordingly, even in a high output power state in which the target motor output power becomes larger than the predetermined output power threshold value, it is possible to secure the motor output power corresponding to the target motor output power.

The high output power control step may include: a remaining capacity determination step which determines whether remaining capacity of the power storage device is equal to or less than a predetermined remaining capacity threshold value; a voltage-increasing step which controls a voltage-increasing operation of the second DC-DC converter when the remaining capacity is determined to be equal to or less than the predetermined remaining capacity threshold value in the remaining capacity determination step; and a power storage device output power limiting step which controls an operation of the first DC-DC converter such that an output electrical power of the power storage device becomes equal to or less than a predetermined electrical power threshold value when the remaining capacity in the remaining capacity determination step is determined to be equal to or less than the predetermined remaining capacity threshold value.

According to the control method for a fuel cell vehicle, when the remaining capacity of the power storage device is determined to be equal to or less than the predetermined remaining capacity threshold value, by controlling an operation of the first DC-DC converter such that the output electrical power of the power storage device becomes equal to or less than the predetermined electrical power threshold value, it is possible to prevent problems such as deterioration of the power storage device due to, for example, excessive reduction in the remaining capacity of the power storage device.

Furthermore, it is possible to secure the desired motor output power in response to the accelerator opening degree, since the motor controller constructed from an inverter that applies voltage to the motor, and the like, is supplied with the voltage obtained by the voltage-increasing operation to the output power of the fuel cell by the second DC-DC converter.

The high output power control step may include: a direct connecting step which sets the second DC-DC converter to a directly connected state when the remaining capacity in the remaining capacity determination step is determined to be larger than the predetermined remaining capacity threshold value; and a switching control step which controls a switching operation of the first DC-DC converter when the remaining capacity in the remaining capacity determination step is determined to be larger than the predetermined remaining capacity threshold value.

According to the control method for a fuel cell vehicle, when the remaining capacity of the power storage device is determined to be larger than the predetermined remaining capacity threshold value, by connecting the fuel cell and the motor controller in a directly connected manner, it is possible to prevent switching losses produced at the second DC-DC converter. Furthermore, since the motor controller constructed from the inverter that applies voltage to the motor, and the like, is supplied with voltage obtained by switching operation to the output power of the power storage device by the first DC-DC converter, it is possible to secure the desired motor output power in response to the accelerator opening degree without excessively increasing the output power of the fuel cell (i.e., without excessively consuming reaction gasses supplied to the fuel cell).

The control method for a fuel cell vehicle may further include: a low-and-middle output power control step which controls operations of the first DC-DC converter and the second DC-DC converter such that a supply of an output electrical power from the fuel cell to the motor takes priority over a supply of an output electrical power from the power storage device to the motor, when the target motor output power is equal to or less than the predetermined output power threshold value.

According to the control method for a fuel cell vehicle, while in a low-and-middle output power state in which the target motor output power becomes equal to or less than the predetermined output power threshold value, by limiting or terminating the output power supplied from the power storage device, and by supplying, in first, the output electrical power of the fuel cell that is relatively lager than that of the power storage device, to the motor, it is possible to prevent increasing switching losses at first DC-DC converter, and thereby enabling efficiently securing the motor output power in response to the target motor output power.

The low-and-middle output power control step may include: a direct connecting step which sets the second DC-DC converter to a directly connected state; and a power storage device output power terminating step which controls an operation of the first DC-DC converter such that an output electrical power from the power storage device becomes zero.

According to the control method for a fuel cell vehicle, while in a low-and-middle output power state in which the target motor output power becomes equal to or less than the predetermined output power threshold value, by terminating the output power supplied from the power storage device, and by connecting the motor controller with the fuel cell that has relatively lager output power than that of the power storage device, in a directly connected manner, it is possible to prevent switching losses produced at the first DC-DC converter and the second DC-DC converter, and thereby enabling efficiently securing the motor output power in response to the target motor output power.

The low-and-middle output power control step may include: a direct connecting step which sets the second DC-DC converter to a directly connected state; and a switching control step which controls a switching operation of the first DC-DC converter when the target motor output power is larger than an output power of the motor that corresponds to an output electrical power of the fuel cell.

According to the control method for a fuel cell vehicle, while in a low-and-middle output power state in which the target motor output power becomes equal to or less than the predetermined output power threshold value, by connecting the motor controller with the fuel cell that has relatively lager output power than that of the power storage device, in a directly connected manner, it is possible to prevent switching losses produced at the second DC-DC converter. Furthermore, the deficiency with respect to the target motor output power (i.e., the difference between the target motor output power and the output power of the motor in response to the output electrical power of the fuel cell in the directly connected state) is appropriately secured by supplying the motor controller with voltage obtained by switching operation of the first DC-DC converter to the output voltage of the power storage device.

In addition, the present invention also provides a fuel cell vehicle including a motor being a driving source of the fuel cell vehicle, a motor controller for controlling an operation status of the motor, and a fuel cell system being a power source for the motor. The fuel cell system includes: a fuel cell which receives reaction gasses and performs electrochemical reactions to generate an electrical power; a power storage device which is charged with the generated electrical power from the fuel cell and a regeneration power from the motor; a first DC-DC converter provided between the power storage device and the motor controller; and a second DC-DC converter provided between the fuel cell and the motor controller. The fuel cell vehicle includes: a target motor output power obtaining device which obtains a target motor output power corresponding to an accelerator opening degree; and a high output power controller which controls operations of the first DC-DC converter and the second DC-DC converter, such that an output voltage of the power source becomes equal to or larger than a predetermined voltage that is required for securing a desired motor output power, when the target motor output power is larger than a predetermined output power threshold value.

According to the fuel cell vehicle, even when, for example, the motor output power decreases from the desired motor output power in accordance with reducing voltage to be applied to the motor in a range where the reducing voltage becomes equal to or less than the predetermined voltage, it is possible to prevent the motor output power from becoming less than the desired motor output power by controlling the first DC-DC converter and the second DC-DC converter such that the output power voltage of the hybrid-type power source constructed from the fuel cell and the power storage device (i.e., voltage to be supplied to the motor controller constructed from the inverter which applies voltage to the motor, and the like) becomes equal to or over the predetermined voltage. Accordingly, even in a high output power state in which the target motor output power becomes larger than the predetermined output power threshold value, it is possible to secure the motor output power corresponding to the target motor output power.

The high output power controller may include: a remaining capacity determination device which determines whether remaining capacity of the power storage device is equal to or less than a predetermined remaining capacity threshold value; a voltage-increasing device which controls a voltage-increasing operation of the second DC-DC converter when the remaining capacity is determined to be equal to or less than the predetermined remaining capacity threshold value by the remaining capacity determination device; a voltage-increasing device which controls a voltage-increasing operation of the second DC-DC converter when the remaining capacity is determined to be equal to or less than the predetermined remaining capacity threshold value by the remaining capacity determination device; and a power storage device output power limiting device which controls an operation of the first DC-DC converter such that an output electrical power of the power storage device becomes equal to or less than a predetermined electrical power threshold value when the remaining capacity is determined to be equal to or less than the predetermined remaining capacity threshold value by the remaining capacity determination device.

According to the fuel cell vehicle, when the remaining capacity of the power storage device is determined to be equal to or less than the predetermined remaining capacity threshold value, by controlling an operation of the first DC-DC converter such that the output electrical power of the power storage device becomes equal to or less than the predetermined electrical power threshold value, it is possible to prevent problems such as deterioration of the power storage device due to, for example, excessive reduction in the remaining capacity of the power storage device.

Furthermore, it is possible to secure the desired motor output power in response to the accelerator opening degree, since the motor controller constructed from an inverter that applies voltage to the motor, and the like, is supplied with the voltage obtained by the voltage-increasing operation to the output power of the fuel cell by the second DC-DC converter.

The high output power controller may include: a direct connecting device which sets the second DC-DC converter to a directly connected state when the remaining capacity is determined to be larger than the predetermined remaining capacity threshold value by the remaining capacity determination device; and a switching controller which controls a switching operation of the first DC-DC converter when the remaining capacity is determined to be larger than the predetermined remaining capacity threshold value by the remaining capacity determination device.

According to the fuel cell vehicle, when the remaining capacity of the power storage device is determined to be larger than the predetermined remaining capacity threshold value, by connecting the fuel cell and the motor controller in a directly connected manner, it is possible to prevent switching losses produced at the second DC-DC converter. Furthermore, since the motor controller constructed from inverter that applies voltage to the motor, and the like, is supplied with voltage obtained by switching operation to the output power of the power storage device by the first DC-DC converter, it is possible to secure the desired motor output power in response to the accelerator opening degree without excessively increasing the output power of the fuel cell (i.e., without excessively consuming reaction gasses supplied to the fuel cell).

The fuel cell vehicle may further include a low and middle output power controller which controls operations of the first DC-DC converter and the second DC-DC converter such that a supply of an output electrical power from the fuel cell to the motor takes priority over a supply of an output electrical power from the power storage device to the motor, when the target motor output power is equal to or less than the predetermined output power threshold value.

According to the fuel cell vehicle, while in a low-and-middle output power state in which the target motor output power becomes equal to or less than the predetermined output power threshold value, by limiting or terminating the output power supplied from the power storage device, and by supplying, in first, the output electrical power of the fuel cell that is relatively lager than that of the power storage device, to the motor, it is possible to prevent increasing switching losses at first DC-DC converter, and thereby enabling efficiently securing the motor output power in response to the target motor output power.

The low-and-middle output power controller may include: a direct connecting device which sets the second DC-DC converter to a directly connected state; and a power storage device output power terminating device which controls an operation of the first DC-DC converter such that an output electrical power from the power storage device becomes zero.

According to the fuel cell vehicle, while in a low-and-middle output power state in which the target motor output power becomes equal to or less than the predetermined output power threshold value, by terminating the output power supplied from the power storage device, and by connecting the motor controller with the fuel cell that has relatively lager output power than that of the power storage device, in a directly connected manner, it is possible to prevent switching losses produced at the first DC-DC converter and the second DC-DC converter, and thereby enabling efficiently securing the motor output power in response to the target motor output power.

The low-and-middle output power controller may include: a direct connecting device which sets the second DC-DC converter to a directly connected state; and a switching controller which controls a switching operation of the first DC-DC converter when the target motor output power is larger than an output power of the motor that corresponds to an output electrical power of the fuel cell.

According to the control method for a fuel cell vehicle, while in a low-and-middle output power state in which the target motor output power becomes equal to or less than the predetermined output power threshold value, by connecting the motor controller with the fuel cell that has relatively lager output power than that of the power storage device, in a directly connected manner, it is possible to prevent switching losses produced at the second DC-DC converter. Furthermore, the deficiency with respect to the target motor output power (i.e., the difference between the target motor output power and the output power of the motor in response to the output electrical power of the fuel cell in the directly connected state) is appropriately secured by supplying the motor controller with voltage obtained by switching operation of the first DC-DC converter to the output voltage of the power storage device.

DETAILED DESCRIPTION OF THE INVENTION

A fuel cell vehicle and a control method for a fuel cell vehicle, according to one embodiment of the present invention will be explained below with reference to the drawings.

As shown inFIG. 1for example, a fuel cell vehicle10of the present invention includes a power storage device11, a first DC-DC converter12, a fuel cell13, a second DC-DC converter14, a PDU (a Power Drive Unit)15, a motor16, an output power controller17, an air-supply device (A/P)18, a hydrogen tank19aand a hydrogen supply valve19b,a backpressure valve20, a purging valve21, a controller22, a system voltage sensor31, a first voltage sensor32, a first current sensor33, a second voltage sensor34, a second current sensor35, a motor rotation number sensor36, and an accelerator-opening degree sensor37.

The power storage device11is a capacitor or a battery or the like formed from, for example, an electric double layer condenser, an electrolytic condenser, or the like. The power storage device11is connected with the second DC-DC converter14and the PDU15in a parallel manner, via the interactive first DC-DC converter12.

The first DC-DC converter12is formed so as to include, for example, an interactive chopper-type power conversion circuit which can increase the terminal voltage VE and can decrease the system voltage VS of the of the power storage device11. The first DC-DC converter12controls the output current IE output from the power storage device11, by chopping operations for intermitting the voltage applied to the load and the current supplied to the load, that is, by ON and OFF operations (switching operations) of a switching element provided in the chopper-type power conversion circuit. The switching operations are controlled in accordance with a duty of a control pulse input from the controller22(i.e., the ratio of ON and OFF operations).

That is, the first DC-DC converter12can charge the power storage device11by decreasing the system voltage VS which relates to the generation of the fuel cell13or the regenerating operations of the motor16. In addition, the first DC-DC converter12can increase the terminal voltage VE of the power storage device11and apply it to the PDU15.

Furthermore, the first DC-DC converter12prohibits outputting the output current IE from the power storage device11in accordance with operating status of the fuel cell vehicle10. In this case, when, for example, the duty of the control pulse input from the controller22to the first DC-DC converter12is set to 0%, then the switching element provided in the first DC-DC converter12is fixed to OFF-state, and the power storage device12and the PDU15are thereby electrically disconnected. Furthermore, in this case, when, for example, the duty of the control pulse is set to a suitable value within a range between 0% and 100%, ON and OFF operations of the switching element provided in the first DC-DC converter12are controlled such that the output power of the first DC-DC converter12becomes zero.

Thus, each measurement signals from the first voltage sensor32which measures the terminal voltage VE of the power storage device11, and the first current sensor33which measures the charging current and discharging current of the power storage device11, is input to the controller22.

The fuel cell13includes a plurality of layers of fuel cells, each fuel cell being an electrolytic electrode structure formed from a solid high-polymer electrolytic membrane formed from a cation-exchanging membrane and the like, sandwiched between a fuel electrode (an anode) formed from an anode catalyst and a gas-diffusion layer and an oxygen electrode (a cathode) formed from a cathode catalyst and a gas-diffusion layer, wherein the electrolytic electrode structure is further sandwiched between a pair separators. And these stacked fuel cells are sandwiched between a pair of end plates from both sides in the stacking direction thereof.

Air being an oxidant gas (reaction gas) including oxygen is supplied from the air-supply device18having an air compressor and the like to the cathode of the fuel cell13, while fuel gas (reaction gas) including hydrogen is supplied from, for example, the highly pressurized hydrogen tank19avia the hydrogen-supply valve19bto the anode of the fuel cell13.

Then, hydrogen ionized by catalytic reactions on the anode catalyst of the anode migrates to the cathode via the suitably humidified solid high-polymer electrolytic membrane. In addition, electrons generated accompanied by this migration are extracted to an external circuit and used as direct current electrical energy. At the cathode at this time, hydrogen ions, electrons, and oxygen react and produce water.

Moreover, the hydrogen-supply valve19bis for example a pneumatic type of proportional pressure control valve which takes the pressure of air supplied from the air-supply device18as a signal pressure, and controls the pressure at the point of exit from the hydrogen-supply valve19bof the hydrogen gas passing through the hydrogen-supply valve19bso as to be within a predetermined range that corresponds to the signal pressure.

In addition, the air-supply device18having an air compressor and the like takes air from, for example, the outside of the fuel cell vehicle, compresses, and supplies the air as reaction gas to the cathode of the fuel cell13. In addition, the rotation number of the motor (not illustrated) which drives the air-supply device18is controlled by the output power controller17having, for example, a PWM inverter that operates in a pulse width modulation mode (PWM), based on control instruction sent from the controller22.

Then, the unreacted discharged gas discharged from the hydrogen discharging outlet13aof the fuel cell13is introduced into a dilution box (not illustrated) via a discharging control valve (not illustrated) which is openably and closably controlled by the controller22, and is discharged to the outside (atmosphere or the like) via the purging valve21after the hydrogen concentration thereof is reduced in the dilution box to a predetermined concentration.

Moreover, a part of the unreacted discharged gas discharged from the hydrogen discharging outlet13aof the fuel cell13is introduced into a circulation path (not illustrated) having, for example, a circulation pump (not illustrated), an ejector (not illustrated), and the like. Hydrogen supplied from the hydrogen tank19aand the discharged gas discharged from the fuel cell13are mixed, and are again supplied to the fuel cell13.

Then, the unreacted discharged gas discharged from an air-discharging outlet13bof the fuel cell13is discharged to the outside (atmosphere or the like) via the backpressure valve20of which a valve opening degree is controlled by the controller22.

The second DC-DC converter14is formed so as to include, for example, an interactive chopper-type power conversion circuit which can increase and decrease the output voltage VF of the fuel cell13. The second DC-DC converter14controls the output current IF output from the fuel cell13, by chopping operations for intermitting the voltage applied to the load and the current supplied to the load, that is, by ON and OFF operations (switching operations) of a switching element provided in the chopper-type power conversion circuit. The switching operations are controlled in accordance with a duty of a control pulse input from the controller22(i.e., the ratio of ON and OFF operations).

For example, the second DC-DC converter14increases the output voltage VF of the fuel cell13in accordance with the driving status of the fuel cell vehicle10. In this case, the duty of the control pulse is set to the suitable value within a range between 0% and 100%, the output current IF of the fuel cell13being a primary current is suitably limited in accordance with the duty of the control pulse, and the limited current is output as a secondary current.

Furthermore, the second DC-DC converter14sets a direct connection between the fuel cell13and the PDU15, in accordance with the driving state of the fuel cell vehicle10. In this case, if the duty of the control pulse is set to 100% and if the switching element is fixed to ON-state, then the output voltage VF of the fuel cell13and the system voltage VS which is an input voltage of the PDU15become the equivalent values with each other.

Each measurement signals output from the second voltage sensor34which measures the output voltage VF of the fuel cell13and the second current sensor35which measures the output current IF of the fuel cell13, are input to the controller22.

The fuel cell13and the power storage device11forming the fuel cell system work as batteries for the motor16.

The PDU15is provided with, for example, a PWM inverter that operates in a pulse width modulation mode (PWM), and controls the driving and the regenerating operation of the motor16based on control instruction sent from the controller22. This PWM inverter is provided with a bridge circuit which is formed by connecting a plurality of, for example, transistor switching elements so as to form a bridge. While, for example, driving the motor16, the PWM inverter transforms the direct current powers output from the first DC-DC converter12and the second DC-DC converter14to three-phase alternating current power based on the pulse width modulation signal input from the controller22, and then supplies it to the motor16. On the other hand, while the motor16is in a regenerating operation, the three-phase alternating current power output from the motor16is converted to the direct current power, and the direct current power is supplied to the power storage device11via the first DC-DC converter12to charge the power storage device11.

Moreover, the motor16is formed, for example, by a permanent magnet type three-phase alternating current synchronous motor that uses permanent magnets for the magnetic field, and is controlled so as to be driven by three-phase alternating current power supplied from the PDU15. While the fuel cell vehicle is in deceleration, if driving power is transmitted from the driving wheels WF to the motor16, the motor16also works as a generator, and produces so-called regenerative braking force to recover the kinetic energy of the fuel cell vehicle10as an electric energy.

The controller22controls the power-generating state of the fuel cell13by outputting instructions for the pressure and the flow rate of the reaction gas supplied from the air-supply device18to the fuel cell13, and an instruction for valve opening degree of the backpressure valve20based on, for example, the driving state of the fuel cell vehicle, the concentration of the hydrogen contained in the reaction gas supplied to the anode of the fuel cell13, the concentration of the hydrogen contained in the discharged gas discharged from the anode of the fuel cell13, and the power generating state of the fuel cell13(for example, the voltage between terminals of the plurality of fuel cells, the output voltage VF of the fuel cell13, the output current IF output from the fuel cell13, and the internal temperature of the fuel cell13).

Furthermore, the controller22controls an electrical power converting operation of the PWM inverter provided in the PDU15. While driving the motor16for example, the controller22calculates a torque instruction which is an instruction value for the torque output from the motor16, based on the measurement signal output from the accelerator-opening degree sensor37which measures an accelerator opening degree AC that corresponds to the accelerator-driving operation amount by the driver, and the measurement signal output from the motor rotation number sensor36, with reference to, for example, a torque instruction map or the like which was set in advance so as to indicate the predetermined relationship of the accelerator opening degree AC, the rotation number NM, and the torque instruction. Then, the controller22calculates the target motor output power which is necessary for making the motor16output the torque that corresponds to the torque instruction. Then, in accordance with the target motor output power, the controller22sets the switching instruction (i.e., the pulse width modulation signal) formed from pulses for driving ON and OFF of the switching element of the PWM inverter, by the pulse width modulation (PWM).

When the switching instruction is input from the controller22to the PDU15, the current sequentially flows through the stator loop windings (not illustrated) of each phases of the motor16. With this, the magnitude of the applied voltage (i.e., amplitude) and phases in U-phase, V-phase, and W-phase are controlled. Then, phase currents for U-phase, V-phase, and W-phase, which correspond to the torque instruction will be supplied to each phases of the motor16.

Therefore, the measurement signal output from the system voltage sensor31which measures the system voltage VS being an input voltage for, for example, the PDU15; the measurement signal output from the motor rotation number sensor36which measures the rotation number NM of the motor16(i.e., motor rotational number); and the measurement signal output from the accelerator-opening degree sensor37which measures the accelerator opening degree AC that corresponds to the accelerator operation amount by the driver, are input to the controller22.

In addition, the controller22calculates the remaining capacity SOC of the power storage device11by, for example, calculating an integrating charging amount and an integrating discharging amount by integrating the charging current and the discharging current of the power storage device11for each predetermined time interval, and by adding these integrating charging amount and integrating discharging amount to a remaining capacity at the initial state or the before of starting charging and discharging, or subtracting these integrating charging amount and integrating discharging amount from the remaining capacity at the initial state or the before of starting charging and discharging.

Then, the controller22outputs a control pulse for controlling the electrical power converting operations of the second DC-DC converter14in accordance with the target motor output power and the remaining capacity SOC of the power storage device11, controls the value of the output current IF output from the fuel cell13, outputs the control pulse for controlling the electrical power converting operations of the first DC-DC converter12, and thereby controls charging and discharging of the power storage device11.

Accordingly, each measurement signals output from the first voltage sensor32which measures the terminal voltage VE of the power storage device11and the first current sensor33which measures the charging current and the discharging current of the power storage device11, is input to the controller22.

The fuel cell vehicle10according to the present embodiment of the present invention has the above-mentioned construction, and the operations of the controller22, that is, the control method for a fuel cell vehicle10will be explained below with reference to drawings.

Firstly, an explanation will be made below for operations for controlling the first DC-DC converter12and the second DC-DC converter14such that, when the target motor output power exceeds the predetermined output power threshold value, the system voltage VS of the fuel cell system provided with the fuel cell13and the power storage device11which work as batteries for the motor16becomes equal to or over the predetermined voltage that is necessary for securing the desired motor output power.

As shown in for exampleFIG. 2and Table 1 shown below, at a duration C1from time t0to t1where applied voltage to the motor16reaches predetermined voltage V2, in a duration from t0to tm where the fuel cell vehicle10starts and accelerates, the first DC-DC converter12is set to an OFF-state in which an electrical connection is terminated or is set to execute a switching operation in which the output electrical power becomes zero, while the second DC-DC converter14is set to ON-state which is an electrically direct-connected state. In accordance with this, extraction of the output current IE from the power storage device11is prohibited, and the motor16is supplied with the output current IF from the fuel cell13, which is relatively large output comparing to that of the power storage device11. In addition, while the output electrical power from the power storage device11is maintained to zero, the output electrical power from the fuel cell13and the supply electrical power to the motor16gradually increase from zero to the suitable electrical power P2for example.

At this time, in a predetermined characteristics between the output current IF and the output voltage VF of the fuel cell13(i.e., an I-V characteristics), since the output voltage VF decreases in accordance with the increasing output current IF, the output voltage VF of the fuel cell13and the applied voltage to the motor16gradually decrease from the suitable voltage V3to the predetermined voltage V2(<V3) for example. In addition, the remaining capacity SOC of the power storage device11maintains the suitable remaining capacity SOC3.

Then, when the fuel cell vehicle10is in the acceleration state (i.e., in a state in which the output power of the motor16changes in a increasing tendency), the following operations are performed at a duration C2: from time t1where the supply electrical power to the motor16reaches the suitable electrical power P2to time t2where the output power of the motor16reaches the predetermined output power threshold value upon the supply electrical power to the motor16reaching to the predetermined electrical power threshold value Pa; and where the applied voltage to the motor16reaches the predetermined voltage V2. That is, in the duration C2, if, for example, power-assisting (assist) is executed by the power storage device11, then the first DC-DC converter12is set to execute a voltage-increasing operation (i.e., a switching operation) to the terminal voltage VE of the power storage device11, while the second DC-DC converter14is set to ON-state which is an electrically direct-connected state.

At this time, the power-generating state of the fuel cell13is controlled such that the output electrical power thereof maintains the suitable electrical power P2, and thereby maintaining the output voltage VF of the fuel cell13and the applied voltage to the motor16, to be the predetermined voltage V2. In accordance with this, extraction of the output current IE from the power storage device11is started, and the output current IE from the power storage device11and the output current IF from the fuel cell13are supplied to the motor16. As a result, the output electrical power from the power storage device11and the supply electrical power to the motor16gradually increase while the output electrical power from the fuel cell13maintains the suitable electrical power P2. Then, the remaining capacity SOC of the power storage device11changes so as to decrease from the suitable remaining capacity SOC3.

Here, as shown inFIG. 3for example, in a predetermined characteristics PM which indicates the relation between the applied voltage to the motor16and the maximum output power that can be output from the motor16, the following operations are performed. That is, in a region where the applied voltage to the motor16is equal to or larger than the predetermined voltage V2, the maximum output power that can be output from the motor16maintains the predetermined value P0(≧P3) regardless of the change in the applied voltage, while in a region where the applied voltage to the motor16is less than the predetermined voltage V2, the maximum output power of the motor16changes so as to decrease in accordance with the decreasing applied voltage. Accordingly, by prohibiting the applied voltage to the motor16to become, at least, less than the predetermined voltage V2, it is possible to prohibit the maximum output that can be output from the motor16decreasing to below the predetermined value P0.

In accordance with this, as shown inFIG. 3for example, in a duration from time t0to time t1where the applied voltage to the motor16changes so as to decrease from the suitable voltage V3to the predetermined voltage V2, the maximum output power PS of the fuel cell system equipped with the power storage device11and the fuel cell13which are the batteries of the motor16, changes along the output characteristics PS of the fuel cell13, that changes such that the maximum output power increases in accordance with the reducing output voltage VF. Then, after the time t1, and after the applied voltage to the motor16reaches the predetermined voltage V2, it changes along the output power characteristics PE of the power storage device11that can increase the maximum output power while maintaining the output voltage VE so as to be the suitable value.

Moreover, when the target motor output power at the suitable applied voltage is larger than the maximum output power of the fuel cell13, such as, for example, when the fuel cell vehicle10makes a jackrabbit start, output power-assisting (assist) by the power storage device11is executed. As a result, the maximum output power PS2of the fuel cell system changes along the output power characteristics which is the sum of the output power characteristics PF of the fuel cell13and the output power of the power storage device11.

Then, as shown inFIG. 2for example, such as when the fuel cell vehicle10moves from the acceleration state to the normal driving state, the following operations are performed in duration C3which includes: duration from time t2to time tm where the supply electrical power to the motor16increases from the predetermined electrical power threshold value Pa to the suitable electrical power P3; and duration from time tm to t3where the supply electrical power to the motor16is controlled so as to maintain the electrical power P3. That is, when execution of the output power-assisting (assist) by the power storage device11is instructed for example, the first DC-DC converter12is set so as to execute the voltage-increasing operation (i.e., the switching operation) to the terminal voltage VE of the power storage device11, while the second DC-DC converter14is set to ON-state which is an electrically direct-connected state.

At this time, the power-generating state of the fuel cell13is controlled such that the output electrical power thereof maintains the suitable electrical power P2, and it is set such that the output voltage VF of the fuel cell13and the applied voltage to the motor16maintain the predetermined voltage V2.

In addition, the switching operation of the first DC-DC converter12is controlled such that: the output electrical power of the power storage device11changes so as to increase to the suitable electrical power P1(<P2) in a duration from time t2to time tm; and the output electrical power of the power storage device11maintains the suitable electrical power P1in a duration from time tm to time t3.

In accordance with this, the motor16is supplied with the output current IE from the power storage device11and the output current IF from the fuel cell13; the supply electrical power to the motor16increases from the predetermined electrical power threshold value Pa to the suitable electrical power P3in a duration from time t2to time tm; and the supply electrical power to the motor16is maintained to be the suitable electrical power P3, while the remaining capacity SOC of the power storage device11changes so as to decrease to the predetermined remaining capacity SOC2, in a duration from time tm to time t3.

Then, when the output current IE from the power storage device11is supplied to the motor16(i.e., when the remaining capacity SOC of the power storage device11changes so as to decrease), if execution of the output power-assisting (assist) by the power storage device11is instructed in a duration C4from time t3where the remaining capacity SOC reaches the predetermined remaining capacity SOC2, to time t4where the remaining capacity SOC reaches the predetermined lower limit remaining capacity SOC1, the following operations are performed. That is, the first DC-DC converter12is set so as to execute the voltage-increasing operation (i.e., a switching operation) to the terminal voltage VE of the power storage device11, while the second DC-DC converter14is set so as to execute the voltage-increasing operation (i.e., a switching operation) to the output voltage VF of the fuel cell13.

At this time, the switching operation of the first DC-DC converter12is controlled such that the output electrical power from the power storage device11changes so as to decrease from, for example, the suitable electrical power P1to zero. In addition, the power-generating state of the fuel cell13is controlled such that the output electrical power increase from the suitable electrical power P2to the electrical power P3, to cancel the reduction in the output electrical power of the power storage device11. Then, the switching operation of the second DC-DC converter14is controlled such that the applied voltage to the motor16maintains the predetermined voltage V2by canceling the reduction in the output voltage VF that occurs in accordance with increasing output power from the fuel cell13. In accordance with this, the supply electrical power to the motor16is maintained to be the suitable electrical power P3. In addition, while the applied voltage to the motor16is maintained to be the predetermined voltage V2: the output electrical power of the fuel cell13changes in an increasing tendency; the output voltage of the fuel cell13changes in a decreasing tendency; the output electrical power of the power storage device11changes in a decreasing tendency; and the remaining capacity SOC of the power storage device11changes in a decreasing tendency.

Then, when the supply electrical power to the motor16is controlled so as to maintain the suitable electrical power P3, at duration CS from time t4to time t5where the remaining capacity SOC reaches the predetermined lower limit remaining capacity SOC1, if execution of an output power assisting (assist) by the power storage device11is prohibit, the first DC-DC converter12is set to OFF-state in which electrical connection is terminated, or to executing the switching operation in which the output electrical power becomes zero, while the second DC-DC converter14is set so as to execute the voltage-increasing operation (i.e., a switching operation) to the output voltage VF of the fuel cell13.

In accordance with this, extraction of the output current IE from the power storage device11is prohibited, and thereby the remaining capacity SOC of the power storage device11maintains the predetermined lower limit remaining capacity SOC1. Then, the output current IF from the fuel cell13is supplied to the motor16. And, when the output electrical power from the power storage device11is zero, the output electrical power of the fuel cell13and the supply electrical power to the motor16are set so as to maintain the suitable electrical power P3. In addition, it is set such that the output voltage VF of the fuel cell13maintains the suitable voltage V1, while the supply voltage to the motor16maintains the predetermined voltage V2.

Processes for controlling operations of the first DC-DC converter12and the second DC-DC converter14in accordance with the target motor output power and the remaining capacity SOC of the power storage device11will be explained below.

Firstly, in step S01shown inFIG. 4, for example, a torque instruction for the torque output from the motor16is calculated based on measurement signal of the accelerator opening degree AC output from the accelerator opening degree sensor37, measurement signal of the rotation number NM output from the motor rotation number sensor36, and the like. In addition, target motor output power is calculated that is necessary for making the motor16output the torque corresponding to the torque instruction.

Next, in step S02, it is determined whether the target motor output power is larger than the predetermined output power threshold value or not.

If the determination is “YES”, then the process proceeds to after-mentioned step S07.

On the other hand, if the determination is “NO”, then the process proceeds to step S03.

In step S03, the second DC-DC converter14is set to ON state which is an electrically direct-connected state, and it is also set such that the output current IF of the fuel cell13, that is a relatively larger output comparing to that of the power storage device11is supplied with high priority to the motor16.

Next, in step S04, it is determined whether, for example, execution of output power assisting (assist) by the power storage device11is instructed or not.

If the determination is “YES”, then the process proceeds to after-mentioned step S06.

On the other hand, if the determination is “NO”, then the process proceeds to step S05.

Next, in step S05, the first DC-DC converter12is set to OFF-state where an electrical connection between the power storage device11and an electrical load (i.e., the PDU15and the output controller17) is terminated, or to the switching operation where output electrical power from the first DC-DC converter12becomes zero. Then, like at the duration C1shown in the above-mentioned Table 1 for example, extraction of the output current IE from the power storage device11is prohibited, and a series of processes is terminated.

In addition, in step S06, in order to execute assisting to the output electrical power of the fuel cell vehicle10by the output electrical power from the power storage device11, the first DC-DC converter12is set to execute the voltage-increasing operation (i.e., a switching operation) to the terminal voltage VE of the power storage device11, like at the duration C2shown in the above-mentioned Table 1. Then, a series of processes is terminated.

In addition, in step S07, it is determined whether, for example, execution of the output power assisting (assist) by the power storage device11is instructed or not.

If the determination is “NO”, then the process proceeds to the after-mentioned step S13.

If the determination is “YES”, then the process proceeds to step S08.

In step S08, it is determined whether the remaining capacity SOC of the power storage device11is larger than the predetermined remaining capacity threshold value (for example, the predetermined remaining capacity SOC2shown inFIG. 2) or not.

If the determination is “NO”, then the process proceeds to the after-mentioned step S11.

On the other hand, If the determination is “YES”, then the process proceeds to step S09.

In step S09, like at duration C3shown in the above-mentioned Table 1 for example, the second DC-DC converter14is set to ON-state which is an electrically direct-connected state, and thereby controlling the power generating state of the fuel cell13such that the output voltage VF of the fuel cell13and the applied voltage to the motor16maintain the predetermined voltage V2.

Next, in step S10, while the output electrical power of the power storage device11changes in an increasing tendency, or is stable, the first DC-DC converter12is set so as to execute the voltage-increasing operation (i.e., a switching operation) to the terminal voltage VE of the power storage device11, such that the applied voltage to the motor16maintains the predetermined voltage V2. Then, the assisting to the target motor output power (output power assisting) by the output electrical power from the power storage device11is executed, and then a series of processes is terminated.

In addition, in step S11, like at duration C4shown in the above-mentioned Table 1 for example, the second DC-DC converter14is set so as to execute the voltage-increasing operation (i.e., a switching operation) to the output voltage VF of the fuel cell13, and thereby controlling such that the applied voltage to the motor16maintains the predetermined voltage V2.

Then, in step S12, the first DC-DC converter12is set so as to execute voltage-increasing operation (i.e., a switching operation) to the terminal voltage VE of the power storage device11, such that the applied voltage to the motor16maintains the predetermined voltage V2while the output electrical power of the power storage device11changes in a decreasing tendency, and thereby executing an assisting (output power assisting) by the output electrical power of the power storage device11to the target motor output power. Then, a series of processes is terminated.

In addition, in step S13, like at duration C5shown in the above-mentioned Table 1 for example, the second DC-DC converter14is set to execute a voltage-increasing operation (i.e., a switching operation) to the output voltage VF of the fuel cell13, and thereby controlling the applied voltage to the motor16to maintain the predetermined voltage V2.

Then, in step S14, the first DC-DC converter12is set so as to OFF-state where an electrical connection between the power storage device11and an electrical load (i.e., the PDU15and the output controller17) is terminated, or to the switching operation where output electrical power from the first DC-DC converter12becomes zero. Then, like at the duration C1shown in the above-mentioned Table 1 for example, extraction of the output current IE from the power storage device11is prohibited, and a series of processes is terminated.

As has been explained in the above, according to the fuel cell vehicle10and the control method for the fuel cell vehicle10, of the present embodiment, when the target motor output power is larger than the predetermined output power threshold value, by controlling operations of the first DC-DC converter12and the second DC-DC converter14such that the system voltage VS of the fuel cell system equipped with the power storage device11and the fuel cell13which are the batteries of the motor16, becomes equal to or larger than the predetermined voltage required for securing the desired motor output power, it is possible to prevent reducing the maximum output power that can be output from the motor16, and thereby enabling securing the desired acceleration performance of the fuel cell vehicle10.

Furthermore, while the applied voltage to the motor16is maintained to be equal to or larger than the predetermined voltage that is required for securing the desired motor output power (for example, the voltage V2shown inFIG. 3), by controlling so as to prevent the execution of the switching operations of the first DC-DC converter12and the second DC-DC converter14at the same time, and thereby executing only one of the switching operations in accordance with a driving state of the fuel cell vehicle10, it is possible to increase switching losses that is accompanied by the switching operations of the first DC-DC converter12and the second DC-DC converter14, and thereby enabling executing efficient electrical power converting operation as a whole fuel cell system.

Moreover, in the above-mentioned embodiment, in the durations C1and C5shown in the above-mentioned Table 1 for example, the first DC-DC converter12is set to the OFF-state in which the electrical connection is terminated or is set to execute a switching operation in which the output electrical power becomes zero; however, the present invention is not limited to this construction. For example, assisting (output power assisting) by the output electrical power of the power storage device11to the target motor output power may be executed by controlling the switching operation of the first DC-DC converter12such that the output voltage of the power storage device11becomes equal to or less than the predetermined electrical power threshold value.

While a preferred embodiment of the invention has been described and illustrated above, it should be understood that this is an exemplary of the invention and is not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims.

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