Lossless switching converter with DC transformer

A converter for providing power from a DC voltage source connected between an input terminal and a common input terminal to a DC load connected between an output terminal and a common output terminal, said converter comprising:

• an input inductor winding, an isolation transformer with primary and secondary windings, and an output inductor winding, placed on a common magnetic core to form an Isolated DC Transformer, and each winding having one dot-marked end and an other unmarked end whereby AC voltage applied to said primary winding of said isolation transformer induces AC voltages in said secondary winding of said isolation transformer and said input and output inductor windings so that said applied AC voltage and said induced AC voltages are in phase at said dot-marked ends of said input inductor winding, said output inductor winding and said primary and secondary windings of said isolation transformer;
• said input inductor winding connected at said dot-marked end thereof to said input terminal to form an input winding of said Isolated DC Transformer;
• said output inductor winding connected at said dot-marked end thereof to said output terminal to form an output winding of said Isolated DC Transformer;
• said primary winding of said isolation transformer connected at said dot-marked end thereof to said common input terminal to enable galvanic isolation in said Isolated DC Transformer;
• said secondary winding of said isolation transformer connected at said dot-marked end thereof to said common output terminal to enable galvanic isolation in said Isolated DC Transformer;
• an input capacitor connected between an unmarked end of said input inductor winding an unmarked end of said primary winding of said isolation transformer;
• an input switch with one end connected to said common input terminal and an other end connected to said unmarked end of said input inductor winding;
• an output switch with one end connected to said common output terminal and an other end connected to an unmarked end of said output inductor winding;
• a complementary output switch, having one end connected to said unmarked end of said output inductor winding and another end of said complementary output switch connected to an unmarked end of said secondary winding of said isolation transformer;
• a branch comprising a complementary input switch and an auxiliary capacitor, having one end of said complementary input switch connected to one end of said auxiliary capacitor, while an other end of said complementary input switch and an other end of said auxiliary capacitor comprise ends of said branch;
• means for connecting said ends of said branch to said converter preserving galvanic isolation of said isolation transformer;
• switching time control means for providing a precise sequence and timing of turning ON and turning OFF signals for said input switch, said complementary input switch, said output switch and said complementary output switch whereby during a State-1 interval no current flows through said branch and during a State-2 interval only AC current flows through said branch;
• wherein said input switch, said output switch, and said complementary output switch are semiconductor switching devices, capable of conducting the current in at least one direction while turned ON, and sustaining voltage in at least one direction while turned OFF;
• wherein said complementary input switch is a semiconductor current bidirectional switching device, capable of conducting the current in both directions while turned ON, and sustaining voltage in at least one direction, while turned OFF;
• wherein said semiconductor switching devices and said semiconductor current bidirectional switching device turn ON and OFF at high switching frequency;
• wherein said primary winding and said secondary winding are tightly coupled for reduced leakage between said primary winding and said secondary winding;
• wherein a DC-to-DC voltage conversion ratio of said converter depends linearly on a duty ratio D;
• wherein turns ratio of said secondary winding to said primary winding of said isolation transformer provides additional control of DC-to-DC voltage conversion ratio of said converter;
• wherein for said duty ratio D in a range from 0 to 1, DC currents in said input inductor winding and said primary and secondary windings of said isolation transformer flow into said dot-marked ends of respective windings, whereas DC current in said output inductor winding flows out of said dot-marked end of said output inductor winding;
• wherein said input inductor winding has the same number of turns as said primary winding of said isolation transformer, and said output inductor winding has the same number of turns as said secondary winding of said isolation transformer, whereby for said duty ratio D in a range from 0 to 1, net zero DC flux is obtained in said common magnetic core;
• wherein said common magnetic core has no air-gap, whereby said net zero DC flux in said common magnetic core enables increased inductances of said input and output inductor windings and said primary and secondary windings of said isolation transformer thereby providing said converter with increased overload capability, and
• whereby said Isolated DC Transformer combines said input inductor winding, said output inductor winding, and said primary and secondary windings of said isolation transformer to provide galvanic isolation between said input DC voltage source and said DC load and efficient DC-to-DC power transfer from said input inductor winding to said output inductor winding with reduced energy storage within said common magnetic core of said Isolated DC Transformer, thereby reducing size and weight of said converter by reducing said common magnetic core size and weight while simultaneously increasing efficiency and converter overload capability, and providing reduction of electromagnetic interference.

A method for power conversion comprising:

• providing an input switch, a complementary input switch, and an output switch being controllable semiconductor CBS (Current Bidirectional Switch) switches, each said controllable semiconductor CBS switch having a parasitic body-diode and a parasitic capacitance in parallel;
• providing a complementary output switch being a current rectifier having a parasitic capacitance in parallel;
• controlling a State-1 interval and a State-2 interval regulating an output load voltage, each said controllable semiconductor CBS switch being turned ON and OFF during an (1-2) transition and a (2-1) transition which are shorter than said State-1 interval and said State-2 interval;
• providing a positive current in a branch with said complementary input switch during said (1-2) transition and a negative current in said branch during said (2-1) transition;
• controlling sequence and timing of turn-ON and turn-OFF signals for said controllable semiconductor CBS switches during said (1-2) transition, recycling charge among said capacitances of said switches and turning ON said complementary input switch losslessly at substantially zero voltage;
• initiating said (2-1) transition by turning OFF said complementary input switch;
• providing a resonant circuit during said (2-1) transition by turning ON said output switch before said parasitic body-diode of said output switch starts to conduct;
• exchanging charge between said capacitances of said controllable semiconductor CBS switches losslessly facilitated by said negative current and a voltage across said input switch present when said output switch is turned ON;
• turning ON said input switch when voltage across said input switch is at minimum reducing switching losses;
• integrating an input inductor winding, a middle inductor winding, and an output inductor winding on a common magnetic core into a DC Transformer;
• subjecting said input, middle, and output inductor windings to AC voltages in phase at dot-marked ends of said input, middle, and output inductor windings;
• subjecting said input inductor winding and said middle inductor winding to DC currents flowing into said dot-marked ends thereof, thereby to generate a DC flux in one direction in said common magnetic core;
• subjecting said output inductor winding to DC current flowing out of said dot-marked end thereof, thereby to generate a DC flux in opposite direction in said common magnetic core, resulting in substration of said DC fluxes in said common magnetic core;
• providing a selected number of turns for said input, middle, and output inductor windings to produce equal volts-per-turn and zero total DC Ampere-turns resulting in substantially zero DC flux in said common magnetic core, whereby reducing DC energy storage in said DC Transformer.

A method for lossless switching comprising:

• providing an input switch, a complementary input switch, and an output switch being controllable semiconductor CBS (Current Bidirectional Switch) switches, each said controllable semiconductor CBS switch having a parasitic body-diode and a parasitic capacitance in parallel;
• providing a complementary output switch being a current rectifier switch having a parasitic capacitance in parallel;
• controlling a State-1 interval and a State-2 interval regulating an output load voltage, each said controllable semiconductor CBS switch being turned ON and OFF during an (1-2) transition and a (2-1) transition which are shorter than said State-1 interval and said State-2 interval;
• providing a positive current in a branch with said complementary input switch during said (1-2) transition and a negative current in said branch during said (2-1) transition;
• controlling sequence and timing of turn-ON and turn-OFF signals for said controllable semiconductor CBS switches during said (1-2) transition, recycling charge among said parasitic capacitances of said controllable semiconductor CBS switches and turning ON said complementary input switch losslessly at substantially zero voltage;
• initiating said (2-1) transition by turning OFF said complementary input switch;
• providing a resonant circuit during said (2-1) transition by turning ON said output switch before said parasitic body-diode of said output switch starts to conduct;
• exchanging charge between said parasitic capacitances of said controllable semiconductor CBS switches losslessly facilitated by said negative current and a voltage across said input switch present when said output switch is turned ON;
• turning ON said input switch when voltage across said input switch is substantially at minimum reducing switching losses.

A method for reducing DC energy storage in a common magnetic core resulting in a DC Transformer, comprising:

• integrating an input inductor winding, a middle inductor winding, and an output inductor winding on a common magnetic core;
• subjecting said input inductor, middle inductor, and output inductor windings to AC voltages in phase at dot-marked ends of said input inductor, middle inductor, and output inductor windings;
• subjecting said input and middle inductor windings to DC currents flowing into said dot-marked ends thereof, thereby to generate a DC flux in one direction in said common magnetic core;
• subjecting said output inductor winding to DC current flowing out of said dot-marked end thereof, thereby to generate a DC flux in opposite direction in said common magnetic core, resulting in subtraction of said DC fluxes in said common magnetic core;
• providing a selected number of turns for each of said input inductor, middle inductor, and output inductor windings to produce equal volts-per-turn and reduced total DC Ampere-turns resulting in reduced DC flux in said common magnetic core.