Variable frequency control system for single phase induction motors

A variable frequency controller for an induction motor, comprising:

• (a) a voltage controlled oscillator having a square wave output and a sawtooth output;
• (b) a flip flop coupled to said square wave output and having a square wave output of 1/2 the frequency of said square wave output of said voltage controlled oscillator;
• (c) a source of variable voltage coupled to an input of said voltage controlled oscillator;
• (d) waveform shaping means for converting sawtooth pulses on said sawtooth output to approximate sinusoidal half waves;
• (e) a pulse width modulator controller (PWM) having an input coupled to an output of said waveform shaping means;
• (f) logic circuitry coupled to an output of said PWM and to an output of said flip flop;
• (g) a full wave inverter bridge driving an inductive load and connected across a DC source of voltage for producing two sets of sinusoidal half waves of pulse width modulated signals 180 degrees out of phase;
• and
• (h) means for coupling one of said sets of sinusoidal half waves of signals to one side of said bridge and another of said set to the other side of said bridge so as to trigger one side of said bridge on during one half cycle and the other side on during the other half cycle.