Sine wave inverter

• US 4,907,145 A
• Filed: 05/11/1989
• Issued: 03/06/1990
• Est. Priority Date: 05/11/1989
• Status: Expired due to Term

• Current Assignee: Belmont Instrument Corporation
• Original Assignee: Belmont Instrument Corporation
• Inventors: Cassidy, David E.
• Primary Examiner(s): Salce, Patrick R.
• Assistant Examiner(s): STERRETT, JEFFREY L
• Application Number:
  US07/350,313
• Time in Patent Office: 299 Days
• Field of Search: 363/41, 363/97, 363/134
• US Class Current: 363/41
• CPC Class Codes: H02M 7/538 in a push-pull configuration H02M7/5375 takes precedence ; with oscillating arrangements H02M7/53832, H02M7/53846

Abstract

In the sine wave inverter disclosed herein the input of a low pass filter is switched at high frequency between positive and negative supply voltages. The switching is controlled by a comparator which is responsive to a composite of signals which include contributions from a sine wave control signal at the same frequency desired for the output and a square wave control signal which is at a frequency substantially higher than the desired output frequency. The filter input voltage is attenuated and phase adjusted to generate a feedback signal having a high frequency component which is substantially in phase with the high frequency control signal. This feedback signal is combined with the sine wave and high frequency square wave control signals to generate the composite of signals which controls the comparator. Accordingly, the duty cycle of the filter input voltage is varied in correspondence with both the sine wave control signal and the loading of the inverter output.

Claims

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

means for providing a sine wave control signal at the desired 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;

means responsive to a composite of signals which includes contributions from said high frequency control signal and said sine wave control signal for operating said switching means at substantially the same frequency as said high frequency control signal with a duty cycle which varies as a function of the sine wave control signal;

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; and

means for combining said high frequency signal, said sine wave signal and said feedback signal to generate said composite of signals 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.

2. An inverter as set forth in claim 1 wherein said higher frequency control signal is a square wave and said means responsive to a composite of signals provides an integrating function.

3. 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.

4. 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.

5. An inverter as set forth in claim 4 wherein output frequency is in the order of 60 Hz and the frequency of said square wave is in the order of 40,000 Hz.