The present invention relates to a motor-driven compressor for a vehicle, more specifically, to a technique for detecting when a capacitor starts discharging.
Japanese Patent No. 4898964 discloses a motor-driven compressor including a capacitor, a current detection means, and a load resistor. The capacitor is connected to a power supply line and a ground line. The current detection means is arranged on the power supply line between the capacitor and a power source connection means. The current detection means detects whether the current flowing from a power source toward a power element is positive or negative. The load resistor is located between the current detection means and the power source connection means. The load resistor connects the power supply line to the ground line. When current flows from the power element toward the power source, disconnection of the power source from the power source connection means is detected. When the power source is disconnected, the power source stops supplying current to the capacitor. Thus, the capacitor starts discharging the accumulated electric charges so that the discharged electric charges flow to the load resistor.
A typical motor-driven compressor for a vehicle includes a housing, a compression unit, a motor, and an inverter device. The compression unit and the motor are arranged in the housing. The motor-driven compressor may include a resistor located between a connector, which is connected to a power source, and a capacitor across the power source and ground. The motor-driven compressor may further include a current sensor located between the resistor and the capacitor. In this case, disconnection of the connector from the power source is determined when current flows to the current sensor in a direction opposite to when the motor is operating. The resistor is connected in parallel to the capacitor. Thus, power is consumed even during normal operation of the motor. This may lower the efficiency of the motor-driven compressor and generate heat that damages elements.