Patent ID: 7977963

Claim:
A method for determining whether a first inverter sub-module of an inverter module is operating normally, the method comprising the steps of: defining a plurality of sectors of a first current command signal based on a phase angle of the first current command signal, the plurality of sectors including a first positive sector in which an amplitude of the first current command signal has positive values, and a first negative sector in which the amplitude of the first current command signal has negative values; maintaining a present value at a positive counter that counts a number of consecutive times the amplitude of a first current signal is determined to be less than the positive current threshold when the phase angle of the first current command signal is within the first positive sector; regularly measuring an amplitude of the first current signal; and after each measurement: determining, whether a present value maintained by the positive counter exceeds a first maximum count; determining that the first inverter sub-module is operating abnormally when the present value maintained by the positive counter exceeds the first maximum count; and determining that the first inverter sub-module is operating abnormally when the present value maintained by the positive counter is less than the first maximum count.