Adjustable frequency drives using normalized modulation control signals to compensate for phase imbalance and methods of operating the same

A method of operating a motor drive comprising a plurality of DC buses and a plurality of inverter circuits, respective ones of which are coupled to respective ones of the plurality of DC buses, the method comprising:

• generating a representative DC voltage signal based on DC voltage signals for respective ones of the DC buses;
• generating a first modulation control signal from the representative DC voltage signal;
• generating second modulation control signals for respective ones of the inverter circuits from the representative DC voltage signal and the first modulation control signal that are normalized based on the DC voltage signals for the buses and the representative DC voltage signal;
• and
• modulating the inverter circuits responsive to respective ones of the second modulation control signals, wherein the first modulation control signal comprises a first modulation amplitude index signal and an angle signal, and wherein generating second modulation control signals comprises:
• applying an inverse Clarke transformation to the first modulation amplitude index signal and angle signal to generate respective second modulation amplitude index signals for the respective inverter circuits;
• generating respective gain factors for the respective inverter circuits based on the voltage signals for the DC buses and the representative DC voltage signal;
• and
• scaling respective ones of the second modulation amplitude index signals by the respective gain factors to generate respective ones of the second modulation control signals.