Speed controls for electric motors

Claim 1

An electronic control system for an induction motor, comprising: a speed setting circuit comprising i. means for varying the magnitude of a direct current signal in proportion to a desired motor speed; ii. a first oscillator connected to receive said direct current signal, the frequency of said first oscillator being determined by the magnitude of said motor speed signal; iii. pulse generating means, connected to be driven by said first oscillator, for generating a series of pulse train waveforms; and iv. an inverter, connected to the pulse generating means to receive said pulse train waveforms, for producing an output multi-phase induction motor power supply through selective switching of said inverter responsive to said pulse train waveforms; said control system further comprising a motor voltage control circuit, comprising v. an amplifier; vi. loop means connected between said output of said inverter and a first input to said amplifier for feeding back negative direct current signals respectively a function of motor supply voltage and of motor supply current; vii. a second, pulse width modulated oscillator connected to an output of said amplifier, the magnitUde of the amplifier output signal controlling the mark to space ratio of said second oscillator; viii. gate means connected between said pulse generating means and said inverter and to an output of said second oscillator, the mark to space ratio of the output pulses from said second oscillator modulating said pulse train waveforms; and ix. means, having an input connected to receive said direct current signal and an output connected to a second input of said amplifier, for producing an output signal which causes the setpoint of said amplifier to vary so as to increase the gain of said negative feedback loop means with an increase in said frequency and to decrease the gain of said current negative feedback loop with a said increase in said frequency.