System for controlling the torque output of an induction motor

Claim 2

A motor control system for an induction motor for causing the motor to operate with a predetermined torque-speed characteristic comprising, an induction motor having a winding, a variable output frequency control circuit comprised of a plurality of switching devices having an output connected with said winding and operable to provide said winding with a variable frequency alternating voltage, a source of voltage connected to the input of aid control circuit, means responsive to actual motor speed and coupled to said control circuit for causing said motor to operate with a predetermined constant slip frequency, a voltage control means for said system operative to control the magnitude of the voltage applied to said motor winding, means for developing an alternating voltage the frequency of which is a function of actual motor speed, function generator means having an output voltage-frequency characteristic which corresponds to a desired predetermined torque-speed characteristic for said motor, means for applying said alternating voltage representing actual motor speed to the input of said function generator means, means for developing a torque signal which is a function of the actual output torque of said motor, means for comparing said torque signal and a signal which is a function of the output of said function generator means to produce a control signal, and means applying said contrOl signal to said voltage control means to thereby control the magnitude of the voltage applied to said motor winding as a function of said voltage control signal.

Claim 3

An induction motor drive system having a predetermined torque-speed characteristic comprising, an induction motor having a winding, a source of alternating current, a controlled rectifier connected to said source of alternating current effective to rectify the voltage of said source and produce a direct voltage having a magnitude determined by the firing angle of said controlled rectifier, an inverter connected to said controlled rectifier and responsive to said direct voltage to produce an alternating voltage the magnitude of which is a function of the firing angle of said controlled rectifier, means coupling the output of said inverter to said winding of said induction motor, means responsive to actual motor speed to control the frequency of the inverter output voltage so as to provide a constant slip frequency for said induction motor, means responsive to actual motor speed to produce an alternating voltage the frequency of which is a function of actual motor speed, a filter having output voltage-frequency characteristic corresponding to a desired torque-speed characteristic for said motor, means for applying said alternating voltage representing actual motor speed to the input of said filter, means for developing a voltage which is a function of the torque output of said motor, and means responsive to a comparison of said torque related voltage and a voltage which is a function of the output voltage of said filter for controlling the firing angle of said controlled rectifier.

Claim 4

An induction motor drive system having a predetermined torque-speed characteristic comprising, an induction motor having a winding, a source of alternating current, a controlled rectifier connected to said source of alternating current effective to rectify the voltage of said source and produce a direct voltage having a magnitude determined by the firing angle of said controlled rectifier, an inverter connected to said controlled rectifier and responsive to said direct voltage to produce an alternating voltage the magnitude of which is a function of the firing angle of said controlled rectifier, means coupling the output of said inverter to said winding of said induction motor, means responsive to actual motor speed to control the frequency of the inverter output voltage so as to provide a constant slip frequency for said induction motor, means responsive to actual motor speed to produce an alternating voltage the frequency of which is a function of actual motor speed, a filter having output voltage-frequency characteristic corresponding to a desired torque-speed characteristic for said motor, means for applying said alternating voltage representing actual motor speed to the input of said filter, means for developing a voltage which is a function of the torque output of said motor, and means responsive to a comparison of said torque related voltage and a voltage which is a function of the output voltage of said filter for controlling the firing angle of said controlled rectifier.

Claim 5

A motor control system for an induction motor for causing the motor to operate with a predetermined torque-speed characteristic which simulates the torque-speed characteristic of an internal combustion engine comprising, an induction motor having a winding, a source of voltage, frequency control means connected between said source of voltage and said motor winding for determining the frequency of an alternating voltage applied to said motor winding from the output of said frequency control means, means responsive to actual motor speed coupled to said frequency control means for controlling the output frequency of said frequency control means to cause said motor to operate at a substantially constant slip frequency, a voltage control means for said system operative to control the magnitude of the voltage applied to said motor winding, means for developing an alternating voltage the frequency of which is a function of actual motor speed, function generator means having an output voltage-frequency characteristic simulating a torque-speed characteristic of an internal representing actual motor speed to the input of said function generator means, means for developing a torque signal which is a function of the actual output torque of said motor, means for comparing said torque signal and a signal which is a function of the output of said function generator means to produce an error signal that represents the difference between actual and desired torque, and means applying said error signal to said voltage control means to thereby control the voltage applied to said motor winding as a function of said error signal.

Claim 6

A motor control system for an induction motor for causing the motor to operate with a predetermined torque-speed characteristic which simulates the torque-speed characteristic of an internal combustion engine comprising, an induction motor having a winding, a source of voltage, frequency control means connected between said source of voltage and said motor winding for determining the frequency of an alternating voltage applied to said motor winding from the output of said frequency control means, means responsive to actual motor speed coupled to said frequency control means for controlling the output frequency of said frequency control means to cause said motor to operate at a substantially constant slip frequency, a voltage control means for said system operative to control the magnitude of the voltage applied to said motor winding, means for developing an alternating voltage the frequency of which is a function of actual motor speed, function generator means having an output voltage-frequency characteristic simulating a torque-speed characteristic of an internal representing actual motor speed to the input of said function generator means, means for developing a torque signal which is a function of the actual output torque of said motor, means for comparing said torque signal and a signal which is a function of the output of said function generator means to produce an error signal that represents the difference between actual and desired torque, and means applying said error signal to said voltage control means to thereby control the voltage applied to said motor winding as a function of said error signal.

Claim 7

A motor control system for an induction motor for causing the motor to operate with a predetermined torque-speed characteristic comprising, an induction motor having a polyphase winding, a source of polyphase alternating current, a three-phase full-wave bridge rectifier circuit having AC input terminals and direct current output terminals comprised of a plurality of controlled rectifiers and a plurality of diodes, means connecting said AC input terminals of said bridge circuit to said source of said polyphase alternating current, an inverter comprised of a plurality of switching devices having a pair of direct current input terminals and a plurality of AC output terminals, means connecting the direct current ouTput terminals of said bridge circuit with the direct current input terminals of said inverter, means connecting said polyphase winding of said induction motor with said AC output terminals of said inverter, means developing an electrical signal which is a function of actual induction motor speed, means adding said signal to a slip frequency signal to provide an output singal that controls the switching frequency of the inverter such that said motor is operated at a substantially constant slip frequency, means developing an alternating voltage the frequency of which is a function of actual motor speed, an active filter circuit having an output voltage-frequency characteristic corresponding to a desired torque-speed characteristic to be maintained by said motor, means applying said alternating voltage representing actual motor speed to the input of said filter, means developing an electrical signal which is a function of the actual output torque of said motor, means for comparing said torque signal with a signal which is a function of the output voltage of said filter circuit whereby the actual and desired torque are compared, said last named means developing an error voltage when there is a difference in the actual and desired output torque of said motor, and means for controlling the firing angle of said controlled rectifiers of said bridge circuit in response to said error signal when said error signal exists.

Claim 8

A motor control system for an induction motor for causing the motor to operate with a predetermined torque-speed characteristic comprising, an induction motor having a polyphase winding, a source of polyphase alternating current, a three-phase full-wave bridge rectifier circuit having AC input terminals and direct current output terminals comprised of a plurality of controlled rectifiers and a plurality of diodes, means connecting said AC input terminals of said bridge circuit to said source of said polyphase alternating current, an inverter comprised of a plurality of switching devices having a pair of direct current input terminals and a plurality of AC output terminals, means connecting the direct current ouTput terminals of said bridge circuit with the direct current input terminals of said inverter, means connecting said polyphase winding of said induction motor with said AC output terminals of said inverter, means developing an electrical signal which is a function of actual induction motor speed, means adding said signal to a slip frequency signal to provide an output singal that controls the switching frequency of the inverter such that said motor is operated at a substantially constant slip frequency, means developing an alternating voltage the frequency of which is a function of actual motor speed, an active filter circuit having an output voltage-frequency characteristic corresponding to a desired torque-speed characteristic to be maintained by said motor, means applying said alternating voltage representing actual motor speed to the input of said filter, means developing an electrical signal which is a function of the actual output torque of said motor, means for comparing said torque signal with a signal which is a function of the output voltage of said filter circuit whereby the actual and desired torque are compared, said last named means developing an error voltage when there is a difference in the actual and desired output torque of said motor, and means for controlling the firing angle of said controlled rectifiers of said bridge circuit in response to said error signal when said error signal exists.

Claim 9

A motor control system for an induction motor for causing the motor to operate with a predetermined torque-speed characteristic comprising, an induction motor having a polyphase winding, a source of polyphase alternating current, a three-phase full-wave bridge rectifier circuit having AC input terminals and direct current output terminals comprised of a plurality of controlled rectifiers and a plurality of diodes, means connecting the AC input terminals of said bridge circuit to said source of said polyphase alternating current, an inverter comprised of a plurality of switching devices having a pair of direct current input terminals and a plurality of AC output terminals, means connecting the direct current output terminals of said bridge circuit with the direct current input terminals of said inverter, means connecting said polyphase winding of said induction motor with said AC output terminals of said inverter, means developing an electrical signal which is a function of actual induction motor speed, means adding said signal to a slip frequency signal to provide an output signal that controls the switching frequency of the inverter such that said motor is operated at a substantially constant slip frequency, means developing an alternating voltage the frequency of which is a function of actual motor speed, an active filter circuit having an output voltage-frequency chracteristic corresponding to a desired torque-speed characteristic to be maintained by said motor, means applying said alternating voltage representing actual motor speed to the input of said filter, means developing an electrical signal which is a function of the actual output torque of said motor, means for comparing said torque signal with a signal which is a function of the output voltage of said filter circuit whereby the actual and desired torque are compared, said last named means developing an error voltage when there is a difference in the actual and desired output torque of said motor, means for controlling the firing angle of said controlled rectifiers of said bridge circuit in response to said error signal when said error signal exists, and means for at times operating said induction motor in a braking mode, said last named means including means for connecting the phase windings of said motor in series and to the output of said bridge rectifier.

Claim 10

A motor control system for an induction motor for causing the motor to operate with a predetermined torque-speed characteristic comprising, an induction motor having a polyphase winding, a source of polyphase alternating current, a three-phase full-wave bridge rectifier circuit having AC input terminals and direct current output terminals comprised of a plurality of controlled rectifiers and a plurality of diodes, means connecting the AC input terminals of said bridge circuit to said source of said polyphase alternating current, an inverter comprised of a plurality of switching devices having a pair of direct current input terminals and a plurality of AC output terminals, means connecting the direct current output terminals of said bridge circuit with the direct current input terminals of said inverter, means connecting said polyphase winding of said induction motor with said AC output terminals of said inverter, means developing an electrical signal which is a function of actual induction motor speed, means adding said signal to a slip frequency signal to provide an output signal that controls the switching frequency of the inverter such that said motor is operated at a substantially constant slip frequency, means developing an alternating voltage the frequency of which is a function of actual motor speed, an active filter circuit having an output voltage-frequency chracteristic corresponding to a desired torque-speed characteristic to be maintained by said motor, means applying said alternating voltage representing actual motor speed to the input of said filter, means developing an electrical signal which is a function of the actual output torque of said motor, means for comparing said torque signal with a signal which is a function of the output voltage of said filter circuit whereby the actual and desired torque are compared, said last named means developing an error voltage when there is a difference in the actual and desired output torque of said motor, means for controlling the firing angle of said controlled rectifiers of said bridge circuit in response to said error signal when said error signal exists, and means for at times operating said induction motor in a braking mode, said last named means including means for connecting the phase windings of said motor in series and to the output of said bridge rectifier.