Motor control system with volts/hertz regulation

Claim 2

A control system for regulating the volts/hertz ratio of the AC output voltage supplied from an inverter to an AC motor, comprising: a variable DC voltage supply circuit connected to pass an output DC voltage to the inverter, a combined oscillator-regulator circuit, including adjustable means for presetting the desired volts/hertz ratio of the inverter AC output voltage, comparator means for providing an error signal responsive to any deviation of the inverter AC output voltage from the preset volts/hertz ratio, means for supplying a first control signal to regulate the level of said output DC voltage, and means for supplying a second control signal to regulate the frequency of said inverter AC output voltage, thus maintaining a desired volts/hertz ratio of the inverter AC output voltage, and means for applying an input signal signifying the actual inverter AC output voltage to said oscillator-regulator circuit, for comparison with a preset volts/hertz ratio to provide said error signal.

Claim 3

A control system as claimed in claim 1 in which said variable DC voltage supply circuit includes a DC-to-DC converter, connected to vary the amplitude of the output DC voltage in accordance with variations in the first control signal.

Claim 4

A control system as claimed in claim 1 in which said comparator means includes a first transistor having a base, an emitter, and a collector, and in which said adjustable means includes a first potentiometer for presetting the desired volts/hertz ratio, which potentiometer is coupled between the base and the means for applying the input signal which signifies the actual inverter AC output voltage, such that the conduction level of said first transistor is a measure of the sense and direction of any deviation between the preset volts/hertz ratio as set by said first potentiometer and the actual volts/hertz ratio as signified by said input signal.

Claim 5

A control system as claimed in claim 3 in which a short circuit and current limit arrangement is connected to provide an output signal when an overcurrent condition is sensed at the output side of the variable DC voltage supply circuit, including a second transistor having a base, an emitter, and a collector, means for coupling the emitter-collector path of said second transistor in series with the emitter-collector path of said first transistor, and means for applying the output signal from the short circuit and current limit arrangement to the base of said second transistor to interrupt conduction of said first transistor when an overcurrent condition is sensed.

Claim 6

A control system as claimed in claim 1 in which said combined oscillator-regulator circuit comprises an operational amplifier connected as a constant current source for operation in accordance with a variable bias voltage input signal related to the error signal developed by said comparator means, and a multivibrator circuit coupled to said operational amplifier to provide said second control signal for regulating the frequency of the AC voltage in accordance with the conduction level of said operational amplifier.

Claim 7

A control system as claimed in claim 5 in which means, including a Zener diode and a voltage divider circuit, is connected to apply a fixed bias voltage to said operational amplifier in addition to said variable bias voltage, such that the addition of said fixed and variable bias voltages enhances the linearity of the operational amplifier circuit.

Claim 8

A control system for regulating the volts/hertz ratio of an AC output voltage passed from an inverter to an AC motor comprising: a DC-to-DC converter connected to supply a variable level DC voltage to energize the inverter; a converter control circuit connected to regulate the amplitude of the DC output voltage passed from said converter to the inverter in accordance with a first control signal; an inverter logic circuit connected to regulate the frequency of the inverter AC output voltage in accordance with a second control signal; an oscillator-regulator circuit, comprising adjustable means for presetting the desired volts/hertz ratio of the inverter AC output voltage, an input circuit for receiving an input signal related to the actual inverter AC output voltage, means for comparing said input signal against the setting of said adjustable means to provide said first and second control signals, said first control signal signifying the desired level of the converter DC output voltage and the second control signal signifying the desired frequency of the inverter AC output voltage to maintain the preset volts/hertz ratio; means for applying said input signal to the oscillator-regulator circuit to provide an indication of the actual AC output voltage of the inverter; means for applying said first control signal to the converter control circuit to regulate the level of the DC voltage supplied by the DC-to-DC converter, and thus regulate the amplitude of the inverter AC output voltage; and means for applying said second control signal to said inverter logic circuit to regulate the frequency of the inverter AC output voltage.

Claim 9

A control system for regulating the volts/hertz ratio of an AC output voltage passed from an inverter to an AC motor comprising: a DC-to-DC converter connected to supply a variable level DC voltage to energize the inverter; a converter control circuit connected to regulate the amplitude of the DC output voltage passed from said converter to the inverter in accordance with a first control signal; an inverter logic circuit connected to regulate the frequency of the inverter AC output voltage in accordance with a second control signal; an oscillator-regulator circuit, comprising adjustable means for presetting the desired volts/hertz ratio of the inverter AC output voltage, an input circuit for receiving an input signal related to the actual inverter AC output voltage, means for comparing said input signal against the setting of said adjustable means to provide said first and second control signals, said first control signal signifying the desired level of the converter DC output voltage and the second control signal signifying the desired frequency of the inverter AC output voltage to maintain the preset volts/hertz ratio; means for applying said input signal to the oscillator-regulator circuit to provide an indication of the actual AC output voltage of the inverter; means for applying said first control signal to the converter control circuit to regulate the level of the DC voltage supplied by the DC-to-DC converter, and thus regulate the amplitude of the inverter AC output voltage; and means for applying said second control signal to said inverter logic circuit to regulate the frequency of the inverter AC output voltage.

Claim 10

A control system as claimed in claim 3, in which the combined oscillator-regulator circuit further comprises a Zener diode and a speed control potentiometer having its end terminals respectively coupled to the opposite end connections of the Zener diode and having a movable arm, and means for passing a signal from the movable arm of the speed control potentiometer to the base of the first transistor, such that said comparator means continually receives both voltage amplitude and voltage frequency information.

Claim 11

A control system as claimed in claim 7, in which the oscillator-regulator circuit further comprises a second adjustable means including a movable portion for providing a signal related to the frequency of the AC output voltage, and means for passing a signal from the movable portion of the second adjustable means to the comparing means for combination with the signal denoting the inverter AC output voltage, such that the comparing means continually receives both voltage frequency and voltage amplitude information.