Controller and drive circuit for electric motors

An electric motor comprising:

• a drive circuit including an inverter configured to supply variable frequency current over a first duration and a contactor configured to supply line frequency current over a second duration;
• and
• a controller communicatively coupled to the drive circuit and the electric motor, wherein the controller is configured to:
• control the inverter to supply variable frequency current to the electric motor over the first duration, thereby operating the electric motor at a variable motor speed;
• dynamically determine, based upon at least one input parameter indicating build up of at least one of pressure or temperature while the electric motor has operated at the variable motor speed, a maximum potential motor speed the inverter can achieve;
• determine to operate the electric motor at line frequency current, wherein the electric motor operates at a motor speed corresponding to line frequency when line frequency current is supplied, and wherein the motor speed corresponding to line frequency is greater than the variable motor speed and the maximum potential motor speed is between the variable motor speed and the motor speed corresponding to line frequency;
• and
• as speed of the motor transitions between the variable motor speed and the motor speed corresponding to line frequency, control the drive circuit to transition from supplying variable frequency current to supplying line frequency current before the maximum potential motor speed the inverter can achieve is reached.

A method of operating an electric motor, wherein the electric motor is communicatively coupled to a controller and coupled to a drive circuit including an inverter configured to supply variable frequency current over a first duration and a contactor configured to supply line frequency current over a second duration, said method comprising:

• controlling the inverter to supply variable frequency current to the electric motor over the first duration, thereby operating the electric motor at a variable motor speed;
• dynamically determining, based upon at least one input parameter indicating build up of at least one of pressure or temperature while the electric motor has operated at the variable motor speed, a maximum potential motor speed the inverter can achieve;
• receiving a command to operate the electric motor at line frequency current, wherein the electric motor operates at a motor speed corresponding to line frequency when line frequency current is supplied, and wherein the motor speed corresponding to line frequency is greater than the variable motor speed and the maximum potential motor speed is between the variable motor speed and the motor speed corresponding to line frequency;
• and
• as speed of the motor transitions between the variable motor speed and the motor speed corresponding to line frequency, controlling the drive circuit to transition from supplying variable frequency current to supplying line frequency current before the maximum potential motor speed the inverter can achieve is reached.