Motor current control circuit utilizing real current component

Claim 2

A control circuit comprising in combination, a motor, a variable-frequency device connected between voltage source terminals and said motor to supply energy of a variable current to said motor, regulator means connected to regulate the output of said variable-frequency device, means connected to sense the current in said motor, phase-sensitive detector means connected to said sensing means to discriminate between the real and reactive components of the current, and control means connected to be responsive to the real component of current output of said detector means and connected to said regulator means to limit the current output of said variable-frequency device.

Claim 3

A circuit as set forth in claim 1, wherein the limited current output limits the torque applied by the motor.

Claim 4

A circuit as set forth in claim 1, wherein the real component of the motor current is limited.

Claim 5

A circuit as set forth in claim 1, including means to vary the voltage output of said variable-frequency device, and said control means controls the voltage output of said variable-frequency device.

Claim 6

A circuit as set forth in claim 4, wherein said control means controls the voltage and frequency output of said variable-frequency device.

Claim 7

A circuit as set forth in claim 1, wherein said variable-frequency device is an inverter.

Claim 8

A circuit as set forth in claim 1, including a reference source, and means comparing said real current component with said reference source to obtain an error signal, said error signal controlling said regulator means.

Claim 9

A circuit as set forth in claim 1, said control means controls the frequency of said variable-frequency device.

Claim 10

A circuit as set forth in claIm 1, wherein said current is controlled during both motoring and regenerative action of said motor.

Claim 11

A circuit as set forth in claim 1, wherein said motor is an induction motor.

Claim 12

A circuit as set forth in claim 1, including a current reference source, means comparing the real component of the motor current with said reference source, said control means being responsive to the excess of said real component over said reference source.

Claim 13

A circuit as set forth in claim 1, wherein said control means includes a reference source, an amplifier having an input and an output, an output resistor connected to the output of said amplifier, means connecting said reference source to said amplifier, and means connecting said real component of the motor current to said amplifier input, whereby when the input current to said amplifier exceeds a value preset by said reference source the amplifier is biased into conduction to develop a voltage across said output resistor for an output from said control means.

Claim 14

A circuit as set forth in claim 1, wherein said control means includes a current source, a transistor having an input and an output, an output resistor connected to the output of said transistor, a diode connected between said current source and said transistor input, an input resistor connected to said transistor input, and means connecting an input from said real component of the motor current to said input resistor, whereby when the input current through said input resistor exceeds a value preset by said current source the transistor is biased into conduction to develop a voltage across said output resistor for an output from said control means to said regulator means.

Claim 15

A circuit as set forth in claim 1, wherein said control means includes a current limit circuit having a constant current source, a diode connected across said constant current source output, a transistor having an input and an output, an output resistor connected to the output of said transistor, means connecting said input of said transistor to said diode to be normally biased thereby into a nonconducting state, an input resistor connected to said transistor input, and means connecting an input from said real component of the motor current to said input resistor, whereby when the input current through said input resistor exceeds a value preset by said constant current source the transistor is biased into conduction to develop a voltage across said output resistor for an output from said current limit circuit.

Claim 16

A circuit as set forth in claim 1, wherein said control means includes a current limit circuit having a constant current source having negative and positive current outputs, first and second diodes connected in series across said positive and negative constant current source outputs, the junction between said diodes being grounded, first and second transistors, first and second output resistors connected in series between said transistors, the junction between said output resistors being grounded, each of said transistors having an input connected across said series-connected diodes to be normally biased into a nonconducting state, first and second input resistors connected in series across said first and second diodes, an input from said real component of the motor current to the junction of said input resistors for current flow through said first or second input resistors dependent upon whether the real component of the current is positive or negative, whereby when the input current through one of said input resistors exceeds a value preset by said constant current source the respective transistor is biased into conduction to develop a voltage across the respective output resistor for an output from said current limit circuit.