MOTOR POWER CONVERSION DEVICE

Iron loss is one type of damage to a motor; when iron loss suddenly becomes large in the high-speed range of a motor, the motor cannot be protected by an electronic thermal relay for overload detection which operates at a fixed product of current squared and time calculated on the basis of current detection in the motor. This motor power conversion device accurately detects total loss, which includes copper loss, iron loss, mechanical loss, stray load loss, etc., without attaching a temperature detector on the motor winding, and provides overload detection protection to the motor. By calculating the total loss, which in addition to copper loss includes iron loss, quantitatively difficult-to-predict stray load loss and mechanical loss, as the total loss obtained by subtracting the output power from the input power of the motor, a motor power conversion device is realized with an overload protection electronic thermal relay which detects by constantly performing said calculation even with the motor in four-quadrant operation, including power running and regenerative operation, and operates at a fixed product of time and total loss.