Sine wave inverter

A d.c. to a.c. sine wave inverter comprising:

• means for providing a sine wave control signal at the desired sine wave output frequency;
• means for providing a control signal at a frequency substantially higher than the desired sine wave frequency;
• a low pass filter having an input and an output;
• means for providing positive and negative supply voltages;
• high speed switching means for selectively connecting said filter input to either said positive or said negative supply voltage thereby to generate a filter input voltage;
• integrator means responsive to a composite of signals which includes a contribution from said higher frequency control signal for generating a waveform having a generally triangular configuration;
• comparator means responsive to said triangular waveform for operating said switching means at substantially the same frequency as said square wave control signal;
• means for combining said sine wave control signal with said triangular waveform thereby to vary the duty cycle of said comparator and said switching means;
• and
• means for attenuating and phase adjusting said filter input voltage thereby to generate a feedback signal having a high frequency component which is substantially in phase with said square wave signal, said feedback signal and said square wave control signal being combined for application to said integrator means thereby to cause the duty cycle of said filter input voltage to vary in correspondence with said sine wave signal and the loading of said filter output.

A d.c. to a.c. sine wave inverter comprising:

• means for providing a sine wave control signal at the desired sine wave output frequency;
• means for providing a square wave control signal at a frequency substantially higher than the desired output frequency;
• a low pass filter comprising a series inductor and a shunt capacitor;
• means for providing positive and negative supply voltages at levels greater then the peak values of the desired sine wave output from the inverter;
• first high speed semiconductor switching means for selectively connecting the input of said filter to said positive supply voltage thereby;
• second high speed semiconductor switching means for selectively connecting the input of said filter to said negative supply voltage;
• means for driving said first and second switching means alternately thereby to generate a filter input voltage;
• integrator means responsive to a composite of signals which includes a contribution from said square wave control signal thereby to generate a triangular waveform;
• comparator means controlled by said integrator means for operating said driving means at substantially the same frequency as said square wave control signal;
• means for combining said sine wave control signal and said triangular waveform thereby to vary the duty cycle of said comparator;
• and
• means for attenuating and phase adjusting said filter input voltage thereby to generate a feedback signal having a high frequency component which is substantially in phase with said square wave signal, said feedback signal and said square wave signal being combined for application to said integrator means thereby to cause the duty cycle of said filter input voltage to vary in correspondence with said sine wave signal and the loading of said filter output.