US 5,155,672 A · Switched multi-tapped transformer power conversion method and apparatus

Abstract

A switched multi-tapped transformer-based power conversion circuit is disclosed. A polarity alternator comprising dual switch devices controlled by a microprocessor selectively periodically impresses across a transformer's center-tapped primary winding a voltage from a battery to produce a modified square waveform. Each of the taps of the transformer's secondary winding synchronously selectively switched by the microprocessor to a common wired-OR junction where the discrete voltage levels combine to produce a stepped approximation of a stored sine waveform. The switching circuits for each of the taps comprises dual back-to-back series-connected FET switches with diodes shunting each FET's source and drain. The microprocessor periodically senses the voltage across the primary winding, calculates the voltage across the secondary winding based upon the predetermined turns ratio of the tap that is switched to the common junction and compares the calculated output voltage with a normalized memory-based sine wave representation, thereby to determine when to switch to another tap. The converter, which operates concurrently as an inverter and a charger, responds in real time to changing DC source and AC load conditions. A similar converter having a full-wave rectifier on the primary winding side of the transformer is connectable to an AC source and provides for the charging of a connected DC load.

Claims12

Dependent claims

For use with an AC element having a nominal operating frequency, power conversion apparatus comprising:

a transformer having a primary winding and a secondary winding including multiple tap leads and a common lead connectable with a first terminal of an AC element;
alternating means connectable with a DC source for impressing a periodically alternating-polarity voltage across said primary winding of said transformer to produce pairs of alternately positive-going and negative-going voltage pulses on said tap leads, wherein said pulse pairs occur at an alternation frequency that is equal to the nominal operating frequency of such AC element;
switching means interposed between said tap leads and a second terminal of such AC element, said switching means being switchable under the influence of control signals sequentially to select ones of said tap leads to be conductively connected with the second terminal of such AC element;
and
a switch controller generating control signals to said switching means in such manner that plural ones of said tap leads are conductively connected with the second terminal of such AC element during controllably brief periods of time and that only one of said tap leads at a time is so-connected during controllably relatively substantially longer periods of time within each AC cycle.

2 more elements

Power conversion apparatus comprising:

a transformer having a primary winding and a secondary winding connectable with an AC load and plural individual leads corresponding to plural taps having predefined graduated turns ratios relative to said primary winding;
alternating means for selectively operatively impressing a DC voltage of periodically alternating polarity across said primary winding of said transformer at a first nominal frequency;
plural switching circuits operatively connected with said secondary winding of said transformer and responsive to switch control signals, with one side of each of said switching circuits being operatively connected with a corresponding one of said plural leads of said secondary winding of said transformer and with the other side of each of said switching circuits being operatively connected with one another and being operatively connectable with such AC load, each of said switching circuits in a first non-conducting state operatively isolating said corresponding one of said plural leads from such AC load and in a second conducting state operatively connecting said one of said plural leads with such AC load;
a controller supplying said switch control signals at a second frequency that is of the same order of magnitude as said first nominal frequency to said plural switching circuits in a desirable timing sequence, thereby to supply an AC voltage of a desired waveform to such AC load.

1 more element

A power conversion circuit usable with a DC element having a pair of terminals and with an AC element comprising:

a transformer having a primary winding with a center tap connectable with one of such DC element terminals and a secondary winding with first and second end taps and plural taps intermediate said first and second end taps, said second end tap and said intermediate taps being selected to predefine a plurality of turns ratios of the secondary winding relative to the primary winding;
a polarity-alternating circuit, responsive to switch control signals, including diode means shunted across transistor means, said polarity-alternating circuit selectively, alternately connecting either of said primary winding end taps to such other DC element terminal;
plural switching circuits, responsive to switch control signals, each of said plural switching circuits having one side operatively connected to a corresponding one of said second end tap and said intermediate taps and having the other side operatively connected with one another at a wired-OR junction;
switch controller means capable of supplying said switch control signals to said polarity-alternating circuit to produce an alternating polarity square wave the positive-going and negative-going portions of which are interposed by lull periods of time during which the primary winding of said transformer is deenergized, said switch controller means including means for sensing the instantaneous voltage amplitude between said primary winding end taps of said transformer, said switch controller means further including means for calculating a corresponding instantaneous voltage amplitude between said first end tap and said wired-OR junction based upon the predefined plural turns ratios of said secondary winding, said switch controller means further including means for comparing such calculated instantaneous voltage amplitude with a corresponding instantaneous voltage amplitude of a stored sine waveform representation to produce a comparison result, said switch controller means further including means responsive to said comparison result for supplying said switch control signals to said plural switching circuits in such manner that said second end tap and said intermediate taps selectively sequentially are operatively connected with said wired-OR junction to produce across an AC element, when operatively connected between the first end tap and said wired-OR junction, an alternating polarity output voltage of a desired amplitude representing a stepped approximation of a sine waveform.