Electrically powered vehicle and method of controlling the same

1. An electrically powered vehicle comprising:

a motor generator configured to be capable of transmitting and receiving torque to and from a driving shaft coupled to a driving wheel;

a DC power supply including a power storage device;

an inverter configured to perform bidirectional DC/AC power conversion between said DC power supply and said motor generator;

a motor control unit configured to control a plurality of power semiconductor switching elements forming said inverter in accordance with a torque command value and a state value of said motor generator;

a charge/discharge monitoring unit configured to set a charge power upper limit value of said power storage device based on the state of charge of said power storage device; and

a vehicle control unit configured to set said torque command value based on a vehicle state and said charge power upper limit value set by said charge/discharge monitoring unit,

said motor control unit including a DC offset generation unit programmed to control said inverter to cause said motor generator to output a deceleration torque, by superimposing a DC current component on an AC current of each phase in said motor generator in accordance with a state of charge of said power storage device, during release of an accelerator pedal,

said vehicle control unit including a determination unit configured to determine whether or not a first power exceeds said charge power upper limit value, said first power being equivalent to regenerative power caused by said motor generator outputting deceleration torque required for ensuring prescribed deceleration during release of said accelerator pedal, and

when it is determined that said first power exceeds said charge power upper limit value during release of said accelerator pedal, said DC offset generation unit being configured to control said inverter to superimpose said DC current component on said AC current of each phase,

said vehicle control unit further including a torque command value setting unit configured to limit the regenerative power by said motor generator so as to fall within a range not exceeding said charge power upper limit value, to set said torque command value, and

said DC offset generation unit and said torque command value setting unit being configured to set a current amount of said DC current component and said torque command value, respectively, so as to ensure the required deceleration torque by a sum of dragging torque caused by said DC current component and said torque command value, during release of said accelerator pedal while charging is limited during which said first power exceeds said charge power upper limit value.

2. The electrically powered vehicle according to claim 1 , wherein

said torque command value setting unit sets said torque command value at zero when charging is inhibited during which said charge power upper limit value is set at zero, and

said DC offset generation unit sets the current amount of said DC current component at a prescribed value when said charging is inhibited.

3. The electrically powered vehicle according to claim 1 ,

wherein

said vehicle control unit sets said torque command value at zero when charging is inhibited during which said charge power upper limit value is set at zero, and

said DC offset generation unit sets a current amount of said DC current component at a prescribed value when said charging is inhibited.

4. The electrically powered vehicle according to claim 1 , wherein

said motor control unit includes

a control command generation unit for generating a voltage command value of a voltage applied to said motor generator based on said torque command value and said state value,

an addition unit for adding an offset voltage in accordance with said DC current component to said voltage command value when said DC current component is superimposed by said DC offset generation unit,

a carrier wave control unit for controlling a frequency of a carrier wave, and

a modulation unit for generating an on/off control signal of each of said plurality of power semiconductor switching elements based on comparison between said voltage command value processed by said addition unit and said carrier wave, and

when said DC current component is superimposed, said carrier wave control unit increases the frequency of said carrier wave as compared with a case where said DC current component is not superimposed.

5. The electrically powered vehicle according to claim 1 , wherein

said motor control unit further includes a demagnetizing factor estimation unit for estimating a demagnetizing factor of said motor generator, and

said DC offset generation unit limits a time period during which the DC current component is superimposed on said AC current of each phase in accordance with an estimate value of said demagnetizing factor.

6. The electrically powered vehicle according to claim 1 , wherein

said motor control unit further includes a demagnetizing factor estimation unit that estimates a demagnetizing factor of said motor generator, and

said DC offset generation unit variably sets a current amount of the DC current component superimposed on said AC current of each phase in accordance with an estimate value of said demagnetizing factor.

7. A method of controlling an electrically powered vehicle including a motor generator configured to be capable of transmitting and receiving torque to and from a driving shaft coupled to a driving wheel, a DC power supply including a power storage device, and an inverter for performing bidirectional DC/AC power conversion between said DC power supply and said motor generator, said method comprising:

the step of detecting that an accelerator pedal is released;

the step of calculating a first power equivalent to regenerative power caused by said motor generator outputting deceleration torque required for ensuring prescribed deceleration during release of said accelerator pedal;

the step of comparing said first power with a charge power upper limit value set based on the state of charge of said power storage device,

the step of, during release of said accelerator pedal, controlling said inverter to cause said motor generator to output a deceleration torque by superimposing a DC current component on an AC current of each phase in said motor generator when said first power exceeds said charge power upper limit value; and

the step of, during release of said accelerator pedal while charging is limited during which said first power exceeds said charge power upper limit value, limiting the regenerative power by said motor generator so as to fall within a range not exceeding said charge power upper limit value, to set a torque command value of said motor generator, and setting a current amount of said DC current component so as to ensure said required deceleration torque by a sum of dragging torque caused by said DC current component and said torque command value.

8. The method of controlling an electrically powered vehicle according to claim 7 , further comprising:

the step of, when said first power exceeds said charge power upper limit value, determining whether or not charging is inhibited during which said charge power upper limit value is set at zero;

the step of, when said charging is inhibited, setting a torque command value of said motor generator at zero and setting a current amount of said DC current component at a prescribed value; and

the step of, when said charge power upper limit value is not zero, limiting the regenerative power by said motor generator so as to fall within a range not exceeding said charge power upper limit value, to set said torque command value, and setting the current amount of said DC current component so as to ensure said required deceleration torque by a sum of dragging torque caused by said DC current component and said torque command value.

9. The method of controlling an electrically powered vehicle according to claim 7 , further comprising the step of setting a torque command value of said motor generator at zero and setting a current amount of said DC current component at a prescribed value, during release of said accelerator pedal while charging is inhibited during which a charge power upper limit value of said power storage device is set at zero.

10. The method of controlling an electrically powered vehicle according to claim 7 , wherein

a plurality of power semiconductor switching elements forming said inverter are controlled to be turned on/off in accordance with comparison between a voltage command value of a voltage applied to said motor generator and a carrier wave,

when said DC current component is superimposed in said controlling step, an offset voltage in accordance with said DC current component is added to said voltage command value, and

said controlling method further comprises:

the step of determining whether or not said DC current component is superimposed in said controlling step;

the step of setting a frequency of said carrier wave at a first frequency when said DC current component is not superimposed; and

the step of setting the frequency of said carrier wave at a second frequency higher than said first frequency when said DC current component is superimposed.

11. The method of controlling an electrically powered vehicle according to claim 7 , further comprising:

the step of estimating a demagnetizing factor of said motor generator; and

the step of limiting a time period during which said DC current component is superimposed on said AC current of each phase, in accordance with an estimate value of said demagnetizing factor.

12. The method of controlling an electrically powered vehicle according to claim 7 , further comprising:

the step of estimating a demagnetizing factor of said motor generator; and

the step of variably setting a magnitude of said DC current component superimposed on said AC current of each phase in accordance with an estimate value of said demagnetizing factor.