Induction motor controller
AssigneeUnitrode Corporation
InventorPhilip Cooke
Life of this patent
Estimating the term…
Abstract
A controller for variable speed three-phase AC squirrel-cage induction motors in accordance with a volts-per-hertz control method is disclosed. Direct current ("DC") link current is employed to compensate for rotor slip. In particular, rotor slip is estimated and added to a speed reference command to compensate for changing loads. A direction input and speed reference command provide complete control over the induction motor.
Claims23
A controller for an induction motor having a rotor and a stator, the controller being operative in response to a first motor speed command signal, and comprising:
- a rotor slip estimator circuit that employs link current to generate a motor rotor slip estimate, the rotor slip estimate being calculated as I.sub.2 R.sub.2 /(V.sub..phi. /f.sub.e), where I.sub.2 is rotor current, R.sub.2 is per phase rotor resistance, V is per phase RMS voltage and f.sub.e is motor frequency, said rotor slip estimate being combined with the first motor speed signal to provide a second motor speed signal;
- and
- a drive circuit operative in response to the second motor speed signal to drive the induction motor.
A controller for an induction motor having a rotor and a stator, the controller being operative in response to a first motor speed command signal, and comprising:
- a rotor slip estimator circuit that employs link current to generate a motor rotor slip estimate, said rotor slip estimate being combined with the first motor speed signal to provide a second motor speed signal;
- a drive circuit operative in response to the second motor speed signal to drive the induction motor;
- and
- a speed rate limiter circuit that prevents the rate of change of the second motor speed signal from exceeding a predetermined maximum value such that the pull-out torque of the motor is not exceeded even when the rate of change of the rotor slip estimate exceeds the predetermined maximum value.
A method for controlling an induction motor that has a rotor and a stator in response to a first motor speed signal, comprising the steps of:
- employing motor link current in a rotor slip estimator circuit to generate a motor rotor slip estimate, the rotor slip estimate being calculated as I.sub.2 R.sub.2 /(V.sub..phi. /f.sub.e), where I.sub.2 is rotor current, R.sub.2 is per phase rotor resistance, V.sub..phi. is per phase RMS voltage and f.sub.e is motor frequency;
- combining the rotor slip estimate with the first motor speed signal to provide a second motor speed signal;
- and
- driving the induction motor with a drive circuit operative in response to the second motor speed signal.
A method for controlling an induction motor that has a rotor and a stator in response to a first motor speed signal, comprising the steps of:
- employing motor link current in a rotor slip estimator circuit to generate a motor rotor slip estimate;
- combining the rotor slip estimate with the first motor speed signal to provide a second motor speed signal;
- driving the induction motor with a drive circuit operative in response to the second motor speed signal;
- and
- preventing the rate of change of the second motor speed signal from exceeding a predetermined maximum value such that the pull-out torque of the motor is not exceeded even when the rate of change of the rotor slip estimate exceeds the predetermined maximum value.
A controller for operating an induction motor that has a rotor and a stator, the controller being operative in response to a first motor speed signal, and comprising:
- a circuit for providing link current from each stator, the link current being provided to a filter circuit to provide a rotor current output;
- a rotor slip estimator circuit that employs link current to generate a motor rotor slip estimate, the rotor slip estimate being calculated as I.sub.2 R.sub.2 /(V.sub..phi. /f.sub.e), where I.sub.2 is rotor current, R.sub.2 is per phase rotor resistance, V.sub..phi. is per phase RMS voltage and f.sub.e is motor frequency, where the rotor slip estimate is combined with the first motor speed signal to provide a second motor speed signal;
- and
- a drive circuit operative in response to the second motor speed signal to drive the induction motor, the drive circuit including a speed rate control circuit that controls rate of change of the second motor speed signal in a specified manner.
Dependencies are inferred from the claim text.