Phase-shifted full-bridge topology with current injection

A method for operating a pulse-shifted full-bridge (PSFB) DC-DC Converter, the converter comprising

• a primary side and a secondary side;
• a transformer having at least one primary winding at the primary side and at least one secondary winding at the secondary side, wherein a leakage inductance is formed between the at least one primary winding and at least one secondary winding;
• a bridge formed by two legs connected in parallel at the primary side, one leg being a linear leg and another leg being a resonant leg,
• wherein each leg is formed by corresponding bottom primary switching element and upper switching element at the primary side configured in a totem pole arrangement,
• wherein common terminals of the two legs are connected to an input voltage source,
• wherein shared terminals of switching elements within one leg, from the two legs, are connected to one end of at least one primary winding and wherein shared terminals of the switching elements of another leg, from the two legs, are connected to another end of at least one primary winding,
• wherein primary switching elements of a given leg, from the two legs, are configured to be complementarity to each other during operation of the converter with a period of dead time that includes driving signals from one leg to be phase-shifted with respect to driving signals from another leg;
• first and second synchronous rectifiers at the secondary side;
• at least one output inductor at the secondary side, wherein a first terminal of said at least one output inductor is connected to a load of the converter, wherein a second terminal of said at least one output inductor is directly connected to a synchronized rectifier from the first and second synchronous rectifiers;
• a current-injection electronic circuit that includes:
• two current-injection switching elements, respectively corresponding to switching elements in the resonant leg;
• two current-injection windings disposed on the secondary side and coupled to the at least one secondary winding of the transformer;
• and
• two current-injection capacitors;
• two diodes;
• and
• a voltage-injection voltage source;
• wherein said two current-injection switching elements are connected to respectively-corresponding first terminals of two current-injection windings,
• wherein each of respectively-corresponding second terminals of the two current-injection windings is connected to a corresponding current-injection capacitor from the two current-injection capacitors;
• wherein a cathode of each of the two diodes is connected to said corresponding current-injection capacitor at the corresponding second terminal and an anode of each of the two diodes is connected to the voltage-injection voltage source;
• and
• a controlling electronic circuitry configured to generate control signals to the primary switching elements, the control signals having square waveforms;
• the method comprising:
• (i) Switching on an upper primary switching element of the resonant leg and a bottom primary switching element of the linear leg, said upper primary switching element of the resonant leg and the bottom primary switching element of the linear leg defining a first diagonal of the bridge and,
• while the first synchronous rectifier is on, transferring power from the primary side to the secondary side, wherein said transferring is characterized by linearly changing, with time, a first amplitude of first current flowing through the at least one output inductor and linearly increasing a second amplitude of magnetizing current of said transformer to a peak value of the second amplitude;
• (ii) After switching off the bottom primary switching element of the linear leg and turning on the upper primary switching element of the linear leg, continuing the transferring power to the load and continuing the linearly changing of the amplitude, of current flowing through the at least one output inductor, to a lowest value of said first amplitude while maintaining the second amplitude of the magnetizing current at the peak value;
• (iii) After switching off the upper switching element of the resonant leg, discharging a parasitic capacitance reflected across primary switching elements of the resonant leg, with the use of the leakage inductance;
• (iv) Before switching off the upper switching element of the resonant leg, turning on a current-injection switching element corresponding to a bottom switching element of the resonant leg with a time interval that is adjustable with respect to the moment of said switching off the upper switching element to reflect an injection current, flowing through said current-injection switching element, in a secondary winding;
• (v) Switching off the first synchronous rectifier after a sum of a magnetizing current, reflected in the secondary winding, and said injection current reflected into the secondary winding, exceeds the lowest value of the first amplitude by a predefined excess amount of current to cause the excess amount of current to flow into at least one primary winding while continuing said discharging the parasitic capacitance towards zero.