Systems and methods for improved motor drive power factor control
AssigneeRockwell Automation Technologies, Inc.
InventorsNavid Reza Zargari, Jason Cornelius Wiseman, Yuan Xiao
Life of this patent
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Abstract
Systems and methods are described for controlling power factor in motor drives having a switching rectifier providing a DC link current to an inverter in which the rectifier gain is increased to provide additional DC link current to correct the drive power factor based on current drawn by capacitors of the AC drive power input, and the inverter gain is decreased by introducing bypass states in the inverter switching control scheme or by reducing the motor flux to accommodate the increased DC link current.
Claims22
A motor drive system, comprising:
- a switching rectifier including a first set of switching devices coupled with an AC input and operable according to a first set of switch control signals to selectively couple the AC input with an intermediate DC link to provide a DC link current;
- an inverter including a second set of switching devices coupled with the DC link and operable according to a second set of switch control signals to provide an AC output current to a motor;
- and
- a controller operatively coupled with the switching rectifier and with the inverter to provide the first and second sets of switch control signals, the controller comprising:
- a motor control component determining a required motor control current value according to motor feedback and a setpoint or profile,
- a power factor control component determining a required power factor compensation current value corresponding to input capacitors associated with the AC input,
- a rectifier control component operative to provide the first set of switch control signals to the switching rectifier to provide an increased DC link current over at least a portion of a motor speed range according to the required motor control current value and the required power factor compensation current value to control the power factor of the motor drive system, and
- an inverter control component operative to provide the second set of switch control signals to the inverter to provide the AC output according to the required motor control current.
A control system for controlling power factor in a motor drive system having a switching rectifier providing a DC link current to an inverter, the control system comprising:
- a motor control component determining a required motor control current value according to motor feedback and a setpoint or profile;
- a power factor control component determining a required power factor compensation current value corresponding to input capacitors associated with an AC input of the rectifier;
- a rectifier control component operative to provide a first set of switch control signals to the switching rectifier to provide an increased DC link current over at least a portion of a motor speed range according to the required motor control current value and the required power factor compensation current value to control the power factor of the motor drive system;
- and
- an inverter control component operative to provide the second set of switch control signals to the inverter to provide the AC output according to the required motor control current.
A method for controlling an AC motor, comprising:
- rectifying an AC input to provide a DC link current using a switching rectifier;
- inverting the DC link current to provide an AC output current to a motor using an inverter;
- determining a required motor control current value according to motor feedback and a setpoint or profile;
- determining a required power factor compensation current value corresponding to input capacitors associated with the AC input;
- controlling the switching rectifier to provide an increased DC link current over at least a portion of a motor speed range according to the required motor control current value and the required power factor compensation current value;
- and
- controlling the inverter to provide the AC output according to the required motor control current.
Dependencies are inferred from the claim text.