Patent ID: 8541962

Claim:
A motor driving apparatus comprising: at least one motor driving unit comprising an inverter coupled between a positive direct current bus line and a negative direct current bus line of a direct current power source, the inverter being configured to convert direct current power into alternating current power to drive an alternating current motor; a low-voltage source coupled between a ground and at least one of the positive direct current bus line and the negative direct current bus line; a current detecting element configured to detect a closed circuit current flowing through a closed circuit of the low-voltage source, the alternating current motor, and a part of the inverter; and an insulation resistance degradation determinator configured to make a comparison between the closed circuit current detected by the current detecting element and a predetermined threshold, and configured to determine, based on the comparison, whether an insulation resistance of the alternating current motor is degraded, wherein the inverter includes a plurality of arm switching elements configured to switch between an open state and a closed state with respect to the alternating current motor, wherein the current detecting element is configured to detect: the closed circuit current flowing through the closed circuit of the low-voltage source, the alternating current motor, and the part of the inverter with at least one of the arm switching elements of the plurality of arm switching elements being in the open state; and an offset current flowing through the closed circuit with all of the arm switching elements of the plurality of arm switching elements being in the open state, wherein the motor driving apparatus further comprises an offset removal element configured to obtain a difference between the offset current and the closed circuit current which are detected by the current detecting element, and wherein the insulation resistance degradation determinator is configured to make a comparison between the difference and the predetermined threshold.