Controller and drive circuit for electric motors
A control system for an electric motor in a compressor system includes a processing system configured to control an inverter to supply variable frequency power to the electric motor from the inverter. The processing system is configured to determine when to transition from supplying variable frequency power to supplying line frequency power to the electric motor. The processing system is configured to engage a pressure equalization mechanism to at least partially reduce a pressure differential developed between a suction portion and a discharge portion of the compressor system. The processing system is configured to apply line frequency power to at least one winding of the electric motor.
1. A control system for an electric motor in a compressor system, the control system comprising:
a motor controller coupled directly in communication with an inverter of the electric motor, a pressure equalization mechanism, and one or more switches, the motor controller configured to:
control the inverter to supply variable frequency power to the electric motor from the inverter;
determine when to transition from supplying variable frequency power to supplying line frequency power to the electric motor;
estimate a maximum speed currently achievable by the electric motor based on at least one input parameter;
if the estimated maximum speed does not meet a threshold speed for transitioning to supplying line power, engage the pressure equalization mechanism to at least partially reduce a pressure differential developed between a suction portion and a discharge portion of the compressor system during the transition from supplying variable frequency power to supplying line frequency power; and
if the estimated maximum speed meets the threshold speed, control the one or more switches to apply line frequency power to at least one winding of the electric motor.
2. The control system of claim 1 , wherein the motor controller is further configured to synchronize variable frequency power supplied by the inverter with line frequency power after engaging the pressure equalization mechanism.
3. The control system of claim 1 , wherein the motor controller is further configured, in determining to transition, to receive a command to transition to line frequency power.
4. The control system of claim 1 , wherein the motor controller is further configured, in determining to transition, to determine a load on the inverter exceeds a threshold for the inverter.
5. The control system of claim 1 , wherein the motor controller is further configured to engage the pressure equalization mechanism until the electric motor completes acceleration to a desired speed or torque output for operating under line frequency power.
6. The control system of claim 1 , wherein the motor controller is further configured to engage the pressure equalization mechanism to reduce the pressure differential by up to 90 percent.
7. The control system of claim 1 , wherein the motor controller is further configured to compute a target reduction in the pressure differential to enable complete transition to line frequency power.
8. The control system of claim 1 , further comprising a system controller coupled in communication with the motor controller.
9. The control system of claim 1 , wherein the motor controller is further configured, in engaging the pressure equalization mechanism, to engage a pressure equalization valve.
10. A method for controlling an electric motor in a compressor system, the method performed by a motor controller coupled directly in communication with an inverter of the electric motor, a pressure equalization mechanism, and one or more switches, the method comprising:
controlling the inverter to supply variable frequency power to the electric motor from the inverter;
determining when to transition from supplying variable frequency power to supplying line frequency power to the electric motor;
estimating a maximum speed currently achievable by the electric motor based on at least one input parameter;
if the estimated maximum speed does not meet a threshold speed for transitioning to supplying line power, engaging the pressure equalization mechanism to at least partially reduce a pressure differential developed between a suction portion and a discharge portion of the compressor system during the transition from supplying variable frequency power to supplying line frequency power; and
if the estimated maximum speed meets the threshold speed, controlling the one or more switches to apply line frequency power to at least one winding of the electric motor.
11. The method of claim 10 , further comprising synchronizing variable frequency power supplied by the inverter with line frequency power after engaging the pressure equalization mechanism.
12. The method of claim 10 , wherein determining to transition comprises receiving a command to transition to line frequency power.
13. The method of claim 10 , wherein determining to transition comprises determining a load on the inverter exceeds a threshold for the inverter.
14. The method of claim 10 , further comprising engaging the pressure equalization mechanism until the electric motor completes acceleration to a desired speed or torque output for operating under line frequency power.
15. The method of claim 10 , further comprising engaging the pressure equalization mechanism to reduce the pressure differential by up to 90 percent.
16. The method of claim 10 , further comprising computing a target reduction in the pressure differential to enable complete transition to line frequency power.
17. A compressor system comprising:
an electric motor; and
control system comprising:
a motor controller coupled directly in communication with an inverter of the electric motor, a pressure equalization mechanism, and one or more switches, the motor controller configured to:
control the inverter to supply variable frequency power to the electric motor from the inverter;
determine when to transition from supplying variable frequency power to supplying line frequency power to the electric motor;
estimate a maximum speed currently achievable by the electric motor based on at least one input parameter;
if the estimated maximum speed does not meet a threshold speed for transitioning to supplying line power, engage the pressure equalization mechanism to at least partially reduce a pressure differential developed between a suction portion and a discharge portion of the compressor system during the transition from supplying variable frequency power to supplying line frequency power; and
if the estimated maximum speed meets the threshold speed, control the one or more switches to apply line frequency power to at least one winding of the electric motor.
18. The compressor system of claim 17 , wherein the control system further includes a system controller coupled in communication with the motor controller.