Patent ID: 7773396

Claim:
A method for synchronizing plural parallel-connected inverter units configured to supply current to a motor, wherein the motor includes either one winding, which is supplied by the plural parallel-connected inverter units connected in parallel, or the motor includes several parallel windings, in which each the several parallel windings is supplied by a corresponding one of the plural parallel-connected inverter units, wherein a first of the parallel connection inverter units functions as a master inverter unit and the other parallel connection inverter units function as slave inverter units, and wherein each of the parallel connection inverter units includes a corresponding modulation cycle counter, the method comprising: automatically storing, by each of the plural parallel-connected inverter units, a value based on an instantaneous value of a clock counter used for pulse width modulation; reading, by each of the plural parallel-connected inverter units, the corresponding stored inverter unit modulation counter value at a termination time of a first telecommunications message; sending a master inverter unit modulation counter value from the master inverter unit to the slave inverter units via a second message; and correcting, by each of the slave inverter units, a corresponding slave inverter unit modulation counter based on the master inverter unit modulation counter value.