Induction motor controller

Claim 2

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 2 R 2 /(V.sub.φ /f e ), where I 2 is rotor current, R 2 is per phase rotor resistance, V is per phase RMS voltage and f 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.

Claim 3

The controller of claim 1 wherein link current is provided to a filter circuit to provide an estimated rotor current output.

Claim 4

The controller of claim 1 wherein link current is provided to a filter circuit to provide an estimated stator current output.

Claim 5

The controller of claim 1 wherein a frequency component of the second motor speed signal is produced by summing the first motor speed signal with the calculated rotor slip estimate.

Claim 6

The controller of claim 4 wherein a product of V/f and the frequency component of the second motor speed signal is employed to produce a voltage amplitude component of the second motor speed signal.

Claim 7

The controller of claim 1 wherein the drive circuit includes a pulse width modulator.

Claim 8

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.

Claim 9

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.

Claim 10

The controller of claim 7 further including a first auxiliary speed rate control circuit that reduces the maximum rate of change permitted by the speed rate limiter circuit by a predetermined factor when motor current exceeds a predetermined level.

Claim 11

The controller of claim 8 wherein the first auxiliary speed rate control circuit reduces the maximum rate of change permitted by the speed rate control circuit by 1/2 when measured motor current exceeds nominal motor current by 1.5 per unit.

Claim 12

The controller of claim 9 further including a second auxiliary speed rate control circuit that sets a negative rate specified by the first auxiliary speed rate control circuit to decrease motor speed when current exceeds nominal motor current by 2.0 per unit.

Claim 13

The controller of claim 10 further including a third auxiliary speed rate control circuit that latches off the controller when measured motor current exceeds nominal motor current by 3.0 per unit.

Claim 16

The method of claim 12 including the further step of inputting link current to a filter circuit to provide an estimated rotor current output.

Claim 17

The method of claim 12 including the further step of inputting link current to a filter circuit to provide an estimated stator current output.

Claim 18

The method of claim 12 including the further step of generating a frequency component for the second motor speed signal by summing the first motor speed signal with the calculated rotor slip estimate.

Claim 19

The method of claim 15 including the further step of employing a product of V/f and the frequency component of the second motor speed signal to produce a voltage amplitude component of the second motor speed signal.

Claim 20

The method of claim 12 including the further step of pulse width modulating wherein the drive circuit includes a pulse width modulator.

Claim 23

The method of claim 18 including the further step of reducing the maximum rate of change permitted by a predetermined factor when motor current exceeds a predetermined level.

Claim 24

The method of claim 19 including the further step of reducing the maximum rate of change permitted by 1/2 when measured motor current exceeds nominal motor current by 1.5 per unit.

Claim 25

The method of claim 20 including the further step of setting a negative rate to decrease motor speed when current exceeds nominal motor current by 2.0 per unit.

Claim 26

The method of claim 21 including the further step of latching off the drive to the motor when measured motor current exceeds nominal motor current by 3.0 per unit.

Claim 27

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 2 R 2 /(V.sub.φ /f e ), where I 2 is rotor current, R 2 is per phase rotor resistance, V.sub.φ is per phase RMS voltage and f 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.

Claim 28

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 2 R 2 /(V.sub.φ /f e ), where I 2 is rotor current, R 2 is per phase rotor resistance, V.sub.φ is per phase RMS voltage and f 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.