Lossless switching DC to DC converter with DC transformer

An isolated switching DC-to-DC 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 isolated switching DC-to-DC 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 an 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 a dot-marked end thereof to said input terminal to form an input winding of said Isolated DC Transformer;
• said output inductor winding connected at a 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 a 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 a 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 and 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 an other end of said complementary output switch connected to an unmarked end of said secondary winding of said isolation transformer;
• a branch comprised of a complementary input switch and an auxiliary capacitor connected in series, wherein one end of said branch is connected to dot-marked end of said primary winding of said isolation transformer and an other end of said branch is connected to said unmarked end of said input inductor winding;
• switching means for keeping both said input switch and said output switch closed for a duration of time interval DTS and, keeping both said complementary input switch and said complementary output switch closed for a duration of complementary time interval D′TS, where D is a duty ratio and D′ is a complementary duty ratio within one complete and controlled switch operating cycle TS;
• wherein said input switch, said output switch, and said complementary output switch are semiconductor switching devices, capable of conducting the current in one direction while in an ON state, and sustaining voltage in one direction while in an OFF state;
• wherein said complementary input switch is a semiconductor current bidirectional switching device, capable of conducting the current in both directions while in an ON state, and sustaining voltage in one direction, while in an OFF state;
• wherein said semiconductor devices 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 said 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 isolated switching DC-to-DC converter;
• wherein for said duty ratio D from 0 to 1, a DC current in said input inductor winding and DC currents in said primary and secondary windings flow into said dot-marked ends of their respective windings, whereas a 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 at said duty ratio D, 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 inductors and said isolation transformer thereby providing said isolated switching DC-to-DC 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 a 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 isolated switching DC-to-DC converter by reducing said common magnetic core size and weight while simultaneously increasing efficiency and overload capability of said isolated switching DC-to-DC converter, 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 CBS (Current Bidirectional Switch) switches, each side controllable CBS switch having an anti-parallel diode and a capacitance in parallel;
• providing a complementary output switch being a current recifier having a capacitance in parallel;
• controlling an ON-time and an OFF-time of said controllable CBS switches regulating an output load voltage, each said controllable CBS switch being turned ON and OFF during transition D to D′ and transition D′ to D which are shorter than said ON-time and OFF-time;
• providing a positive current in a branch with said complementary input switch during said transition D to D′ and a negative current in said branch with said complementary input switch during said transition D′ to D;
• controlling sequence and timing of turn-ON and turn-OFF signals for said controllable CBS switches during said transition D to D′, recycling charge among said capacitances of said switches and turning ON said complementary input switch substantially losslessly at substantially zero voltage;
• initiating said transition D′ to D by turning OFF said complementary input switch;
• providing a resonant circuit during said transition D′ to D interval by turning ON said output switch before said anti-parallel diode of said output switch starts to conduct;
• exchanging charge between said capacitances of said controllable CBS switches substantially 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 three inductor windings on said common magnetic core into a DC Transformer;
• subjecting said three inductor windings to AC voltages in phase at dot-marked ends of said inductor windings;
• subjecting two of said three 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 a third of said three inductor windings 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 three inductor windings to produce equal volts-per-turn and zero total DC Ampere turns resulting in substantially zero total DC flux in said common magnetic core.

A method for substantially lossless switching comprising:

• providing an input switch, a complementary input switch, and an output switch being controllable CBS (Current Bidirectional Switch) switches, each said controllable CBS switch having an anti-parallel diode and a capacitance in parallel;
• providing a complementary output switch being a current rectifier switch having a capacitance in parallel;
• controlling an ON-time and an OFF-time of said controllable CBS switches regulating an output load voltage, each said controllable CBS switch being turned ON and OFF during transition D to D′ and transition D′ to D which are shorter than said ON-time and OFF-time;
• providing a positive current in a branch with said complementary input switch during said transition D to D′ and a negative current in said branch with said complementary input switch during said transition D′ to D;
• controlling sequence and timing of turn-ON and turn-OFF signals for said controllable CBS switches during said transition D to D′, recycling charge among said capacitances of said switches and turning ON said complementary input switch substantially losslessly at substantially zero voltage;
• initiating said transition D′ to D by turning OFF said complementary input switch;
• providing a resonant circuit during said transition D′ to D by turning ON said output switch before said anti-parallel diode of said output switch starts to conduct;
• exchanging charge between said capacitances of said controllable CBS switches substantially 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.

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

• integrating three inductor windings on said common magnetic core;
• subjecting said three inductor windings to AC voltages in phase at dot-marked ends of said inductor windings;
• subjecting two of said three 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 a third of said three inductor windings 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 three inductor windings to produce equal volts-per-turn and reduced total DC Ampere turns resulting in reduced total DC flux in said common magnetic core.