Motor-driven compressor with switching element

A motor-driven compressor comprising:

• an electric motor that drives a compression unit;
• a motor driver that drives the electric motor, wherein the motor driver includes a switching element that converts DC voltage from a battery to AC voltage, the DC voltage to be applied to the switching element being in a certain applicable range between a highest voltage and a lowest voltage;
• a control unit that controls the switching operation of the switching element;
• a temperature detector that detects the temperature of the switching element;
• and
• a voltage detector that detects DC voltage applied to the switching element;
• wherein the control unit is configured to
• execute a suspension control that suspends the switching operation of the switching element when the temperature detected by the temperature detector rises to a temperature threshold,
• execute a field weakening control that reduces counter electromotive force generated by the electric motor when the voltage detected by the voltage detector is less than a low voltage threshold wherein when the field weakening control is executed, the electric motor that drives the compression unit is operated at a fixed torque, and
• change the temperature threshold in accordance with the DC voltage detected by the voltage detector,
• wherein the temperature threshold has a lowest value when the DC voltage detected by the voltage detector is the highest voltage in the applicable voltage range, and
• the temperature threshold gradually increases from the lowest value as the DC voltage detected by the voltage detector decreases in the applicable voltage range.