Apparatus and method for preventing overload on switching device in inverter circuit for motor applicable to electric vehicle

A control apparatus for a motor driven electric vehicle, comprising:

• a motor drive means, having a plurality of arms and each arm including a series-connected semiconductor switching device pair, for switching a voltage applied across each switching device of the corresponding one of the switching device pairs from a DC power supply so as to apply an AC power having a plurality of phases of the same number of the arms to the motor, the vehicle being driven by means of the motor;
• sensing means for detecting a rotation velocity of the motor;
• torque demand instruction value determining means for determining a value of a torque demand instruction that a vehicle driver has demanded;
• locked state determining means for determining whether the electric vehicle falls in a locked state on the basis of the detected rotation velocity of the motor and the determined torque demand instruction value;
• motor drive controlling means for controlling switching operations of the respective pairs of the switching devices in the motor drive for the respective switching pairs of the motor drive to supply respective phase currents to the motor so as to regulate an output torque of the motor according to the torque demand instruction value;
• and
• a torque reducing means for outputting a command to the motor drive controlling means to reduce the output torque of the motor so as to change a present phase domain of the motor to another phase domain when the locked state determining means determines that the electric vehicle has fallen in the locked state.

A control method for a motor driven electric vehicle, comprising:

• switching a voltage applied across each semiconductor switching device of a motor drive from a DC power supply so as to apply an AC power having a plurality of phases to the motor, through the motor drive having a plurality of arms of the same number of the phases of the AC power, each arm including a pair of the same series-connected semiconductor switching devices;
• detecting a rotation velocity of the motor;
• determining a value of a torque demand instruction that a vehicle driver has demanded;
• determining whether the electric vehicle falls in a locked state on the basis of the detected rotation velocity of the motor and the determined torque demand instruction value;
• controlling switching operations of the respective pairs of the switching devices in the motor drive for the respective switching pairs of the motor drive to supply respective phase currents to the motor through a motor drive controller so as to regulate an output torque of the motor according to the torque demand instruction value;
• and
• outputting a command to the motor drive controller to reduce the output torque of the motor so as to change a present phase domain of the motor to another phase domain when determining that the electric vehicle has fallen in the locked state.