Motor driving apparatus

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 at least one motor driving unit comprises a plurality of motor driving units coupled to each other in parallel between the positive direct current bus line and the negative direct current bus line,
• wherein the plurality of motor driving units comprise respective inverters comprising axis switching elements,
• wherein the motor driving apparatus further comprises an axis selector configured to select at least one of the axis switching elements of the plurality of motor driving units to constitute the closed circuit,
• wherein the motor driving apparatus further comprises:
• an offset current detecting element configured to control the current detecting element to detect an offset current with all of the axis switching elements open;
• and
• an offset removal element configured to, with the at least one of the axis switching elements selected by the axis selector, obtain a difference between the offset current and the closed circuit current detected by the current detecting element, and
• wherein the insulation resistance degradation determinator is configured to make a comparison between a predetermined threshold and the difference associated with the closed circuit current, and configured to determine, based on the comparison, whether the insulation resistance of the alternating current motor is degraded.