Controller and drive circuits for electric motors

An electric motor comprising:

• a drive circuit comprising a contactor, an inverter, and an H-bridge comprising at least two phases of the inverter, wherein the drive circuit is configured to supply variable frequency current and line frequency current;
• and
• a controller communicatively coupled to the drive circuit, wherein the controller is configured to:
• determine a polarity of a sensed alternating current (AC) voltage while the drive circuit is supplying variable frequency current;
• disable, based upon the determined polarity of the sensed AC voltage, at least two switches of the H-bridge;
• and
• control the contactor to close, thereby preventing the contactor and the inverter from energizing the electric motor at the same time.

A method of controlling a drive circuit, wherein the drive circuit comprises a contactor, an inverter, and an H-bridge comprising at least two phases of the inverter, wherein the drive circuit is configured to supply variable frequency current and line frequency current, the method comprising:

• determining a polarity of a sensed alternating current (AC) voltage while the drive circuit is supplying variable frequency current;
• disabling, based upon the determined polarity of the sensed AC voltage, at least two switches of the H-bridge;
• and
• controlling the contactor to close, thereby preventing the contactor and the inverter from energizing an electric motor at the same time.