Controller and drive circuits for electric motors

An electric motor comprising:

• a drive circuit configured to supply variable frequency current over a first duration and a contactor configured to supply line frequency current over a second duration, wherein the drive circuit includes a three-phase inverter and an H-bridge comprising two phases of the inverter;
• and
• a controller communicatively coupled to the drive circuit, wherein the controller configured to:
• control the inverter to supply variable frequency current to the electric motor over the first duration;
• determine to control the drive circuit to transition from supplying variable frequency current to supplying line frequency current;
• determine a polarity of a sensed alternating current (AC) voltage;
• 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 once the contactor is closed.

A method of operating an electric motor, wherein the electric motor is coupled to a drive circuit that is communicatively coupled to a controller, wherein the drive circuit is configured to supply variable frequency current over a first duration and a contactor configured to supply line frequency current over a second duration, wherein the drive circuit includes a three-phase inverter and an H-bridge comprising two phases of the inverter, said method comprising:

• controlling the inverter to supply variable frequency current to the electric motor over the first duration;
• determining to control the drive circuit to transition from supplying variable frequency current to supplying line frequency current;
• determining a polarity of a sensed alternating current (AC) voltage;
• 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 the electric motor at the same time once the contactor is closed.