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An inverter producing an alternating current from a direct current source has a primary stage coupled to the direct current source having a step-up transformer, a first switching circuit coupling the direct current to the transformer primary and a rectifier coupled to a secondary of the transformer

An inverter producing an alternating current from a direct current source has a primary stage coupled to the direct current source having a step-up transformer, a first switching circuit coupling the direct current to the transformer primary and a rectifier coupled to a secondary of the transformer for producing a DC voltage; a controller for the first switching circuit providing pulse drive signals to control switches of the first switching circuit to cause current to flow in the transformer primary and induce an alternating current in the transformer secondary; a secondary stage receiving the DC voltage having a second switching circuit and a controller for the second switching circuit for generating control signals to cause current through the second switching circuit to flow in alternate directions thorough the load. In one embodiment the alternating current period is divided into time slices and the switches of the first switching circuit are duty cycle modulated at different duty cycles in each time slice. A second embodiment switches series-connected primary windings of a multi-tap transformer.

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1. An inverter producing an alternating current output of a defined frequency and period from a direct current comprising: a primary stage coupled to a source of the direct current and producing a higher voltage direct current, the primary stage comprising a step-up transformer having a primary wind

1. An inverter producing an alternating current output of a defined frequency and period from a direct current comprising: a primary stage coupled to a source of the direct current and producing a higher voltage direct current, the primary stage comprising a step-up transformer having a primary winding and a secondary winding, a first switching circuit coupling the direct current to the primary winding of the transformer and a rectifier coupled to the secondary winding of the transformer for producing a DC voltage;a controller for the first switching circuit providing drive signals to the first switching circuit to control switches of the first switching circuit to cause current to flow in the primary winding and induce an alternating current to flow in the secondary winding;further wherein the controller for the first switching circuit divides the period of the alternating current of the defined frequency and period into a preset number of time slices and, within each time slice, generates said drive signals for the first switching circuit as duty cycle modulated drive signals having a defined duty cycle within each time slice, the duty cycle being variable from one time slice to the next time slice whereby a stepped voltage waveform is generated at the secondary winding of the transformer;further comprising a secondary stage comprising a second switching circuit receiving the DC voltage from the rectifier, and converting the DC voltage into the alternating current output to power a load;further comprising a controller for the second switching circuit for providing control signals to control switches of the second switching circuit to cause current through the second switching circuit to flow in alternate directions thorough the load;the control signals for the second switching circuit being synchronized with the drive signals for the first switching circuit to generate the alternating current output of the defined frequency and period. 2. The inverter of claim 1, wherein the time slices are of unequal duration in each quarter cycle of the alternating current output. 3. The inverter of claim 1, wherein the rectifier comprises either a half-wave rectifier or a full-wave rectifier. 4. The inverter of claim 1, wherein the transformer comprises a multi-tap transformer having series-connected primary winding portions and a center-tap, said first switching circuit comprises a plurality of switches each coupled between one pole of the direct current source and a respective terminal of the multi-tap transformer, the center-tap of the primary winding being coupled to a second pole of the direct current source, respective pairs of said plurality of switches being driven by said controller for the first switching circuit alternately whereby current from the direct current source flows alternately through one or two of said series-connected primary winding portions to induce a stepped voltage in said secondary winding. 5. The inverter of claim 4, wherein said stepped voltage is caused by a change in turns ratio of the transformer in accordance with whether current flows through one or two of said series-connected primary winding portions. 6. An inverter producing an alternating current output of a defined frequency and period from a direct current comprising: a primary stage coupled to a source of the direct current and producing a higher voltage direct current, the primary stage comprising a step-up transformer having a primary winding and a secondary winding, a first switching circuit coupling the direct current to the primary winding of the transformer and a rectifier coupled to the secondary winding of the transformer for producing a DC voltage;a controller for the first switching circuit providing drive signals to the first switching circuit to control switches of the first switching circuit to cause current to flow in the primary winding and induce an alternating current to flow in the secondary winding;further wherein the controller for the first switching circuit divides the period of the alternating current of the defined frequency and period into a preset number of time slices and, within each time slice, generates said drive signals for the first switching circuit as duty cycle modulated drive signals having a defined duty cycle within each time slice, the duty cycle being variable from one time slice to the next time slice whereby a stepped voltage waveform is generated at the secondary winding of the transformer;further comprising a secondary stage comprising a second switching circuit receiving the DC voltage from the rectifier, and converting the DC voltage into the alternating current output to power a load;further comprising a controller for the second switching circuit for providing control signals to control switches of the second switching circuit to cause current through the second switching circuit to flow in alternate directions thorough the load;the control signals for the second switching circuit being synchronized with the drive signals for the first switching circuit to generate the alternating current output of the defined frequency and period;further wherein the primary stage comprises a push-pull converter, the first switching circuit comprises first and second switches each coupled between one pole of the direct current source and opposite terminals of the primary winding, the primary winding having a center-tap coupled to a second pole of the direct current source, the first and second switches being driven by said drive signals in a complementary manner whereby only one switch is on at the same time with a dead-band between on-times of the switches when both switches are off; the controller for the first switching circuit controlling the dead-band within each time slice whereby the dead-band is constant within each time slice thereby developing a defined voltage magnitude at the secondary of the transformer for each time slice. 7. The inverter of claim 6, wherein the dead-band varies between time slices. 8. The inverter of claim 6, further comprising a filter for removing a pulse frequency of the duty cycle modulated drive signals from the DC voltage from the rectifier. 9. The inverter of claim 6, wherein the second switching circuit comprises an H-Bridge. 10. The inverter of claim 9, wherein the control signals for the second switching circuit have a primary switching frequency at the defined frequency modulated onto a carrier frequency. 11. The inverter of claim 10, wherein the defined frequency is 50 or 60 Hz and the carrier frequency of the control signals for the second switching circuit is about 20 KHz. 12. The inverter of claim 6, wherein a pulse frequency of the duty cycle modulated control signals ranges from 33 to 150 KHz and the defined frequency is 50 or 60 Hz. 13. The inverter of claim 6, further comprising a first feedback signal provided to the controller for the first switching circuit from the alternating current output. 14. The inverter of claim 6, further comprising a second feedback signal provided to the controller for the first switching circuit from the source of direct current. 15. The inverter of claim 6, further comprising a third feedback signal provided to the controller for the first switching circuit from the DC voltage from the rectifier. 16. An inverter producing an alternating current output of a defined frequency from a direct current comprising: a primary stage coupled to a source of the direct current and producing a higher voltage direct current, the primary stage comprising a step-up transformer, a first switching circuit coupling the direct current to a primary winding of the transformer and a rectifier coupled to a secondary winding of the transformer for producing a DC voltage;a controller for the first switching circuit providing drive signals to the first switching circuit to control switches of the first switching circuit to cause current to flow in the primary winding and induce an alternating current to flow in the secondary winding;wherein said primary winding of said transformer comprises a multi-tap primary winding having respective series-connected primary winding portions, the first switching circuit comprising a plurality of switches each coupled between a first pole of the direct current source and a respective terminal of the multi-tap primary winding, a center-tap of the primary winding being coupled to a second pole of the direct current source, respective pairs of said plurality of switches being driven by said controller for the first switching circuit alternately whereby current from the direct current source flows alternately through one or two of said series-connected primary winding portions to induce a stepped voltage in said secondary winding, and wherein said stepped voltage is caused by a change in turns ratio of the transformer in accordance with whether current flows through one or two of said series-connected primary winding portions;further comprising a secondary stage comprising a second switching circuit receiving the DC voltage from the rectifier and converting the DC voltage into the alternating current output to power a load;further comprising a controller for the second switching circuit for providing control signals to control switches of the second switching circuit to cause current through the second switching circuit to flow in alternate directions thorough the load;the control signals for the second switching circuit being synchronized with the drive signals for the first witching circuit to generate the alternating current output of the defined frequency. 17. The inverter of claim 16, wherein said plurality of switches comprises four switches arranged in pairs whereby one pair of switches allows current to flow through one or two of said series-connected primary winding portions to generate a waveform corresponding to a positive half-cycle of said alternating current output and a second pair of switches allows current to flow through a different one or two of said series-connected primary winding portions to generate a waveform corresponding to a negative half-cycle of said alternating current output. 18. The inverter of claim 17, wherein a first of said four switches in a first pair of said switches is turned on to cause current to flow through two series-connected primary winding portions, then a second of said switches in the first pair is turned on while the first switch is turned off to cause current to flow only in one of said series-connected primary winding portions, then the first of said switches is turned on while the second switch is turned off to cause current to flow in two of said series-connected primary winding portions, followed by controlling first and second switches in a second pair of said switches connected to two different series-connected primary winding portions in a similar sequence as the switches in the first pair. 19. A method for producing an alternating current output of a defined frequency and period from a direct current comprising: switching the direct current through a primary winding of a step-up transformer with a first switching circuit and inducing an alternating current in a secondary winding of the transformer;controlling the switching of the direct current by dividing the period of the alternating current output of the defined frequency and period into a preset number of time slices and, within each time slice, generating duty cycle modulated drive signals having a defined duty cycle within each time slice, the duty cycle being variable from one time slice to the next time slice whereby a stepped voltage alternating current waveform is generated at the secondary winding of the transformer;rectifying the stepped voltage alternating current waveform from the secondary winding into a DC voltage;converting the DC voltage into the alternating current output to power a load by switching a second switching circuit to cause current through the second switching circuit to flow in alternate directions through the load;synchronizing the switching of the second switching circuit with the switching of the first switching circuit to generate the alternating current output of the defined frequency and period. 20. The method of claim 19, further comprising switching the second switching circuit with control signals having a primary switching frequency at the defined frequency modulated onto a higher frequency carrier frequency. 21. The method of claim 20, further comprising duty cycle modulating the carrier frequency. 22. The method of claim 19, further comprising providing the transformer as a multi-tap transformer having series-connected primary winding portions and a center-tap, providing said first switching circuit with at least four switches each coupled between one pole of the direct current source and a respective terminal of the multi-tap transformer, the center-tap of the primary winding being coupled to a second pole of the direct current source, controlling respective pairs of said at least four switches alternately whereby current from the direct current source flows alternately through one or two of said series-connected primary winding portions to induce a stepped voltage in said secondary winding. 23. A method for producing an alternating current output of a defined frequency and period from a direct current comprising: switching the direct current through a primary winding of a step-up transformer with a first switching circuit and inducing an alternating current in a secondary winding of the transformer;controlling the switching of the direct current by dividing the period of the alternating current output of the defined frequency and period into a preset number of time slices and, within each time slice, generating duty cycle modulated drive signals having a defined duty cycle within each time slice, the duty cycle being variable from one time slice to the next time slice whereby a stepped voltage alternating current waveform is generated at the secondary winding of the transformer;rectifying the stepped voltage alternating current waveform from the secondary winding into a DC voltage;converting the DC voltage into the alternating current output to power a load by switching a second switching circuit to cause current through the second switching circuit to flow in alternate directions through the load;synchronizing the switching of the second switching circuit with the switching of the first switching circuit to generate the alternating current output of the defined frequency and period;further comprising providing said duty cycle modulated drive signals as complementary duty cycle modulated drive signals with a dead-band between pulses of said complementary drive signals and changing the dead-band to vary said duty cycle. 24. The method of claim 23, further comprising varying the time duration of said time slices within the defined period. 25. A method for producing an alternating current output of a defined frequency from a direct current comprising: switching the direct current through a primary winding of a step-up transformer with a first switching circuit and inducing an alternating current in a secondary winding of the transformer;rectifying the alternating current from the secondary winding into a DC voltage;converting the DC voltage into the alternating current output to power a load by switching a second switching circuit to cause current through the second switching circuit to flow in alternate directions through the load;synchronizing the switching of the second switching current with the switching of the first switching circuit to generate the alternating current output of the defined frequency;wherein said step of switching the direct current through the primary winding comprises providing a transformer having a multi-tap primary winding having respective series-connected primary winding portions, connecting a plurality of switches each coupled between a first pole of a direct current source and a respective terminal of the multi-tap primary winding, coupling a center-tap of the primary winding to a second pole of the direct current source, driving respective pairs of said plurality of switches alternately whereby current from the direct current source flows alternately through one or two of said series-connected primary winding portions to induce a stepped voltage in said secondary winding, and wherein said stepped voltage is caused by a change in turns ratio of the transformer in accordance with whether current flows through one or two of said series-connected primary winding portions. 26. The method of claim 25, further comprising switching said plurality of switches in pairs whereby one pair of switches allows current to flow through one or two of said series-connected primary winding portions to generate a waveform corresponding to a positive half-cycle of said alternating current output and a second pair of switches allows current to flow through a different one or two of said series-connected primary winding portions to generate a waveform corresponding to a negative half-cycle of said alternating current output. 27. The method of claim 26, further comprising switching a first of said four switches in a first pair of said switches on to cause current to flow through two series-connected primary winding portions, then switching on a second of said switches in the first pair while turning off the first switch to cause current to flow only in one of said series-connected primary winding portions, then switching on the first of said switches while turning off the second switch to cause current to flow in two of said series-connected primary winding portions, followed by controlling first and second switches in a second pair of said switches connected to two different series-connected primary winding portions in a similar sequence as the switches in the first pair.