Motor variable frequency drive

Claim 2

Means for varying the speed of a motor powered through power conductors by a three phase AC power source, comprising in combination: rectifying means for converting the AC voltage supplied by the power source to positive DC voltage on a positive rail and negative DC voltage on a negative rail; three positive switches, each connecting the positive rail to one of the power conductors; oscillator means for supplying pulses of frequency which can be varied to select a desired motor speed; counter means for repeatedly counting the pulses to a selected number and providing a binary output for each pulse counted; memory means connected between the counter means and an interface circuit means of each of the switches for isolating voltages on the rails from the memory means, the memory means being programmed to directly control and determine entirely the state of each of the switches in a full waveform by providing a programmed output directly to each interface circuit means for each binary output received from the counter means; and means for varying the amplitude of the waveform produced in proportion to the frequency selected.

Claim 3

Means for varying the speed of a motor powered by a three phase AC power source, comprising in combination: rectifier means for converting AC voltage supplied by the power source to positive DC voltage on a positive rail and negative DC voltage on a negative rail; a pair of switches for each phase, one connecting the positive rail to a power conductor to the motor, the other connecting the negative rail to the power conductor; oscillator means for supplying pulses of a frequency which can be varied by changing the level of a DC input and for supplying a triangular wave; counter means for repeatedly counting the pulses to a selected number and providing a binary output for each pulse counted; differential amplifier means for comparing a triangular wave with a DC level proportional to the DC input applied to the oscillator means, and for producing enabling pulses of widths equal to the width of the triangular wave that exceeds the DC level; memory means, having an output for each switch, for providing in response to the binary outputs a repetitive series of pulses, the pulses in each series having differing widths programmed so that each synthesizes one-half of a sine wave; the memory means being enabled by the enabling pulses to produce a pulse only during the width of each enabling pulse; and integration means between the switches and the motor for integrating the pulses created by the opening and closing of the switches to produce a smooth waveform.

Claim 4

Means for varying the speed of a motor powered by a three phase AC power source, comprising in combination: rectifier means for converting AC voltage supplied by the power source to positive DC voltage on a positive rail and negative DC voltage on a negative rail; a pair of switches for each phase, one connecting the positive rail to a power conductor to the motor, the other connecting the negative rail to the power conductor; oscillator means for supplying pulses of a frequency which can be varied by changing the level of a DC input and for supplying a triangular wave; counter means for repeatedly counting the pulses to a selected number and providing a binary output for each pulse counted; differential amplifier means for comparing a triangular wave with a DC level proportional to the DC input applied to the oscillator means, and for producing enabling pulses of widths equal to the width of the triangular wave that exceeds the DC level; memory means, having an output for each switch, for providing in response to the binary outputs a repetitive series of pulses, the pulses in each series having differing widths programmed so that each synthesizes one-half of a sine wave; the memory means being enabled by the enabling pulses to produce a pulse only during the width of each enabling pulse; and integration means between the switches and the motor for integrating the pulses created by the opening and closing of the switches to produce a smooth waveform.

Claim 5

Means for varying the speed of a motor powered through power conductors by an AC power source, comprising in combination: rectifying means for converting AC voltage supplied by the power source to DC voltage with a negative rail and a positive rail; frequency switch means having a negative and a positive switch connecting the negative rail and the positive rail, respectively, with each conductor, for alternately supplying negative and positive voltage to the motor; oscillator means for supplying pulses of frequency which can be varied to select a desired motor speed; counter means for repeatedly counting the pulses to a selected number and providing a binary output for each pulse counted; memory means connected between the counter means and an interface circuit means of each of the switches for isolating voltages on the rails from the memory means, the memory means being programmed to directly control and determine entirely the state of each of the switches at any given point in a full waveform by providing a programmed output directly to each interface circuit means for each binary output received from the counter means; amplitude switch means connected into one of the rails for switching on and off the DC voltage; and pulse width means for providing amplitude pulses of duration proportional to the frequency of the oscillator means and for actuating the amplitude means with the amplitude pulses to vary the DC potential between the rails.

Claim 6

Means for varying the speed of a motor powered through power conductors by an AC power source, comprising in combination: rectifying means for converting AC voltage supplied by the power source to DC voltage with a negative rail and a positive rail; frequency switch means having a negative and a positive switch connecting the negative rail and the positive rail, respectively, with each conductor, for alternately supplying negative and positive voltage to the motor; oscillator means for supplying pulses of frequency which can be varied to select a desired motor speed; counter means for repeatedly counting the pulses to a selected number and providing a binary output for each pulse counted; memory means connected between the counter means and an interface circuit means of each of the switches for isolating voltages on the rails from the memory means, the memory means being programmed to directly control and determine entirely the state of each of the switches at any given point in a full waveform by providing a programmed output directly to each interface circuit means for each binary output received from the counter means; amplitude switch means connected into one of the rails for switching on and off the DC voltage; and pulse width means for providing amplitude pulses of duration proportional to the frequency of the oscillator means and for actuating the amplitude means with the amplitude pulses to vary the DC potential between the rails.