Switched multi-tapped transformer power conversion method and apparatus

• US 5,155,672 A
• Filed: 08/09/1990
• Issued: 10/13/1992
• Est. Priority Date: 08/09/1990
• Status: Expired due to Term

• Current Assignee: Xantrex Technology Incorporated (Mission Critical Electronics LLC)
• Original Assignee: Heart Interface Corporation
• Inventors: Brown, Craig W.
• Primary Examiner(s): Stephan, Steven L.
• Assistant Examiner(s): BERHANE, ADOLF D
• Application Number:
  US07/565,450
• Time in Patent Office: 796 Days
• Field of Search: 363/39, 363/40, 363/43, 363/133, 363/134, 363/26, 307/107, 323/255, 323/257, 323/258, 323/343
• US Class Current: 363/43
• CPC Class Codes: G05F 1/20 semiconductor devices only
• CPC Class Codes: H02J 2207/20 Charging or discharging characterised by the power electronics converter
• CPC Class Codes: H02J 7/02 for charging batteries from ac mains by converters
• CPC Class Codes: H02M 1/12 Arrangements for reducing harmonics from ac input or output
• CPC Class Codes: H02M 7/483 Converters with outputs that each can have more than two voltages levels
• CPC Class Codes: H02P 13/06 by tap-changing; by rearranging interconnections of windings

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.

Claims

1. 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. 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.

3. The apparatus of claim 2, wherein said controller operates in such manner that a AC voltage having a stepped approximation to a sine waveform is supplied.

4. The apparatus of claim 3, wherein said stepped approximation to a sine waveform is symmetric over each half cycle of the alternating polarity voltage.

5. The apparatus of claim 2, wherein at least one of said switching circuits operates bidirectionally and includes dual, back-to-back, series-connected, independently controllable switching devices

7. The apparatus of claim 2, wherein said alternating means operates selectively in such manner that said primary winding of said transformer is deenergized for an interval of time within which the alternating polarity voltage changes polarity.

6. 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; and

means operatively coupled with said controller for periodically sensing the voltage across said primary winding of said transformer, at a frequency substantially greater than the frequency with which said alternating means operates, comprising the sensed voltage level with a desired voltage level and determining the timing sequence in which said switch control signals are supplied responsive thereto.

8. For use in a DC-to-DC power conversion system including a DC source, a transformer having a primary winding impressed with an input voltage periodically alternating at a first frequency, and a multi-tapped secondary winding, with the taps of predefined turns ratios being selectively switchable by a controller to supply an alternating polarity sequence of discrete output voltage levels to an AC load in a stepped approximation to a sine waveform representation stored in memory, a method responsive to changing source or load conditions for generating such a waveform comprising:

sensing the instantaneous amplitude of the input voltage across the primary winding of the transformer;

calculating the instantaneous amplitude of the output voltage corresponding to such sensed input voltage based upon the predefined turns ratios of the multi-tapped secondary winding of the transformer;

comparing the calculated instantaneous amplitude of the output voltage to a stored sine waveform representation having a desired peak amplitude;

selectively switching the taps of the secondary winding of the transformer to supply an instantaneous output voltage level to the AC load that approximates such a stored sine waveform representation having the desired peak amplitude; and

repeating the above steps periodically at a second frequency substantially higher than the first frequency, thereby to supply to the AC load an alternating polarity stepped voltage waveform having characteristics which are responsive in real time to changing conditions of the DC source and the AC load.

9. 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.

10. 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 with 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,

wherein at least one of the plural switching circuits includes a pair of back-to-back series-connected switch devices, whereby said switching circuit including said pair when selected is capable of conducting current either from such DC element to such DC element or from such AC element to such DC element.

11. The circuit of claim 10, wherein each of said switch devices of said pair of switch devices of at least one of said switching circuits including said pair is responsive to corresponding dual switch control signals produced by said switch controller means to operate the switch devices of said pair independently from one another.

12. Power conversion apparatus comprising:

a transformer having a primary winding and a secondary winding, with the secondary winding having a common lead connectable with an AC source and plural individual leads corresponding to plural taps having predefined graduated turns ratios relative to said primary winding;

rectifier means operatively connectable with a DC load for rectifying an AC voltage appearing across said primary winding of said transformer;

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 source, each of said switching circuits in a first non-conducting state operatively isolating said corresponding one of said plural leads from such AC source and in a second conducting state operatively connecting said one of said plural leads with such AC source;

a controller synchronized with such AC source supplying said switch control signals to said plural switching circuits in a desirable timing sequence, thereby to supply a DC voltage having desired characteristics from such AC source to such DC load.