Method and apparatus for automatic IR compensation

Claim 2

A flux regulator for an a-c induction motor having a variable frequency, variable voltage power input comprising: a. means for providing a call signal representative of desired motor current; b. means coupled to said motor for deriving a feedback signal representative of sensed motor current; c. means for generating a slip frequency signal representative of the motor slip frequency at which said feedback signal tends substantially to equal said call signal over a given range of said variable frequency; d. means responsive to the relative values of said call signal and said slip frequency signal for deriving a signal representative of the motor flux which is desired to maintain a predetermineD substantially constant ratio of said call signal to said slip frequency signal; and e. means for varying motor voltage amplitude as a function of said desired motor flux signal, thereby maintaining a substantially constant motor flux.

Claim 3

A flux regulator as set forth in claim 1 wherein said last-mentioned means varies motor voltage in accordance with a voltage signal which is produced by multiplying said desired motor flux signal by a signal which varies with the value of said variable frequency, thereby maintaining substantially constant loop gain.

Claim 4

A flux regulator as set forth in claim 1 wherein said means for deriving the desired motor flux signal includes summing means for obtaining an error signal comprising the difference between signals corresponding to said slip frequency signal and to said call signal, respectively, and means for integrating said error signal, thereby to provide zero steady state error.

Claim 5

A flux regulator as set forth in claim 3 wherein said call signal has a magnitude proportional to the desired magnitude of motor current and a relative polarity indicative of whether a motoring or a braking mode of operation is desired and wherein said desired motor flux signal deriving means also includes means for inverting the polarity of said error signal during operation in the braking mode.

Claim 6

A flux regulator as set forth in claim 4 wherein said feedback signal is derived from the real component of motor current.

Claim 7

A flux regulator as set forth in claim 1 wherein said slip frequency signal generating means comprises means for comparing said feedback and call signals to obtain a current error signal equal to their difference and means for deriving said slip frequency signal from the time integral of said current error signal.

Claim 8

A flux regulator as set forth in claim 6 and including summing means having as inputs said slip frequency signal and a signal representative of the rotational speed of the induction motor shaft, and having as an output a frequency signal representative of the desired frequency of the variable frequency power input.

Claim 9

A flux regulator as set forth in claim 6 wherein said feedback signal is derived from the real component of motor current.

Claim 10

A flux regulator as set forth in claim 1 wherein said call signal comprises a variable d-c voltage.

Claim 11

A flux regulator as set forth in claim 1 and including summing means having as inputs said slip frequency signal and a signal representative of the rotational speed of the induction motor shaft, and having as an output a desired frequency signal representative of the desired frequency of the variable frequency power input.

Claim 12

A flux regulator as set forth in claim 4 wherein said voltage varying means includes a waveform generator having as inputs said desired frequency signal and said desired motor flux signal, and having as an output signal a waveform whose frequency corresponds to said desired frequency and whose amplitude varies with said flux signal.

Claim 13

A flux regulator as set forth in claim 11 and including an inverter circuit interconnected between said induction motor and a d-c power source and controlled by said waveform generator for applying to said motor alternating voltage whose frequency and amplitude correspond to said waveform.

Claim 14

A flux regulator as set forth in claim 12 and including means connected to said d-c power source for varying the amplitude of said waveform generator output signal as an inverse function of the magnitude of d-c line voltage so as to compensate for voltage changes in the d-c power source.

Claim 15

A power control system for an a-c induction comprising: a. an inverter for receiving a current from a d-c source and providing variable frequency, variable voltage a-c power to the induction motor; b. an inverter control circuit for controlling the frequency and voltage of the inverter output to the induction motor; c. a current control circuit having as representative input sIgnals a desired motor current signal and an actual motor current signal and having as an output signal responsive to the difference therebetween, a signal representative of the slip frequency desired to minimize said difference; d. a frequency control circuit having as representative input signals a motor shaft speed signal and said desired slip frequency signal and having as a summation output signal to said inverter control circuit a stator frequency signal; and e. a voltage control circuit having as input signals the desired motor current signal and the desired slip frequency signal and having as an output signal responsive to the ratio thereof, a signal representative of the motor flux which is desired to maintain said ratio substantially constant, said inverter control circuit being responsive to said desired motor flux signal for varying the inverter output voltage as a function thereof, thereby providing flux regulation and automatic IR compensation for the motor.

Claim 16

A power control system for an a-c induction comprising: a. an inverter for receiving a current from a d-c source and providing variable frequency, variable voltage a-c power to the induction motor; b. an inverter control circuit for controlling the frequency and voltage of the inverter output to the induction motor; c. a current control circuit having as representative input sIgnals a desired motor current signal and an actual motor current signal and having as an output signal responsive to the difference therebetween, a signal representative of the slip frequency desired to minimize said difference; d. a frequency control circuit having as representative input signals a motor shaft speed signal and said desired slip frequency signal and having as a summation output signal to said inverter control circuit a stator frequency signal; and e. a voltage control circuit having as input signals the desired motor current signal and the desired slip frequency signal and having as an output signal responsive to the ratio thereof, a signal representative of the motor flux which is desired to maintain said ratio substantially constant, said inverter control circuit being responsive to said desired motor flux signal for varying the inverter output voltage as a function thereof, thereby providing flux regulation and automatic IR compensation for the motor.

Claim 17

A power control system as set forth in claim 14 wherein said voltage control circuit further includes a multiplier circuit, said multiplier circuit being connected to and receiving stator frequency signals from said frequency control circuit whereby said desired motor flux signal is multiplied by said stator frequency signal to provide a voltage signal to said inverter control circuit and thereby maintain constant loop gain.

Claim 18

A power control circuit as set forth in claim 14 wherein said voltage control circuit further includes a divider circuit, said divider circuit being connected to said d-c source and receiving therefrom a d-c signal representative of the voltage magnitude of said source, whereby said desired motor flux signal is divided by said d-c signal so as to compensate for voltage changes in the d-c power source and thereby prevent corresponding changes in the a-c motor voltage.

Claim 19

A power control system as set forth in claim 14 and including in said voltage control circuit an integrator to obtain zero steady-state error.

Claim 20

A flux regulator as set forth in claim 14 wherein said actual motor current signal is derived from the real component of motor current.

Claim 23

A power control system for an a-c motor comprising: a. power conversion means for receiving current from a power source and for providing a-c power output of variable frequency and variable voltage to an alternating current motor; b. a control circuit for said power conversion means, comprising first and second inputs, for controlling the frequency of said a-c power output of the power conversion means responsive to signals applied to said first input and for controlling the voltage of said a-c power output of the power conversion means responsive to signals applied to said second input; c. means to produce a stator frequency signal the value of which is determined by the error between a feedback signal representative of a sensed motor parameter and a call signal representative of the desired value of said parameter; d. means for coupling said stator frequency signal to said first input of the control circuit; e. a source of motor flux signal representative of desired motoR flux; f. multiplier circuit means comprising a first input connected to receive said motor flux signal and a second input connected to receive said stator frequency signal to provide a voltage signal which varies with the product of said motor flux and stator frequency signals; and g. means for coupling said voltage signal to said second input of said control circuit.

Claim 24

A power control system for an a-c motor comprising: a. power conversion means for receiving current from a power source and for providing a-c power output of variable frequency and variable voltage to an alternating current motor; b. a control circuit for said power conversion means, comprising first and second inputs, for controlling the frequency of said a-c power output of the power conversion means responsive to signals applied to said first input and for controlling the voltage of said a-c power output of the power conversion means responsive to signals applied to said second input; c. means to produce a stator frequency signal the value of which is determined by the error between a feedback signal representative of a sensed motor parameter and a call signal representative of the desired value of said parameter; d. means for coupling said stator frequency signal to said first input of the control circuit; e. a source of motor flux signal representative of desired motoR flux; f. multiplier circuit means comprising a first input connected to receive said motor flux signal and a second input connected to receive said stator frequency signal to provide a voltage signal which varies with the product of said motor flux and stator frequency signals; and g. means for coupling said voltage signal to said second input of said control circuit.

Claim 25

A power control system for an a-c induction motor as set forth in claim 18 wherein said power conversion means comprises an inverter adapted to receive current from a d-c source and wherein said stator frequency signal producing means comprises summation means responsive to a motor shaft speed signal and to a desired slip frequency signal to produce said stator frequency signal.

Claim 26

A power control system as set forth in claim 20 wherein said motor flux signal source comprises means for integrating an error signal derived from the difference between a signal representative of the slip frequency of the motor and said call signal.

Claim 27

The power control system of claim 22 wherein said motor parameter is current.