A new series resonant converter composed of two resonant circuits with the same converter leg is presented to achieve the zero-voltage switching (ZVS) turn-on of power switches at a wide range of input voltage and load conditions and zero-current switching (ZCS) turn-off of rectifier diodes in a low input voltage case. Thus, the switching losses of power switches and reverse recovery current on rectifier diodes are improved. If the minimum dc voltage gain of the proposed converter is properly selected, the output voltage can be regulated at no-load condition. Two resonant converters using the same power switches are operated by the phase shift half-switching cycle. Thus, the current ripple at the input terminal capacitor can be reduced. In order to reduce the current stresses of output diodes, the output sides of two resonant converters are connected in parallel. The root mean square currents on transformer secondary windings, transformer copper losses and thermal losses can be further reduced. The output voltage doubler topology is adopted in the output side such that the voltage stress of rectifier diodes is equal to the output voltage instead of two times the output voltage in the conventional centre-tapped rectifier topology. Based on the resonant behaviour, all switches are turned on at ZVS and rectifier diodes are turned off at ZCS if the switching frequency is less than the series resonant frequency. The laboratory experiments with a 1000 W prototype are provided to verify the effectiveness of the proposed converter.

A new zero voltage switching (ZVS) converter with a double-ended rectifier is presented to reduce switching losses on power semiconductors, decrease voltage stresses on rectifier diodes and achieve bidirectional power delivery to output load. A buck-boost type of active snubber is connected in parallel with the primary side of a transformer to recycle the energy stored in transformer leakage and magnetising inductors and to limit voltage stress on the main switch. During the transition interval, the transformer leakage inductor and the output capacitor of power MOSFET are resonant to realise the ZVS turn-on of the switch. Finally, the experimental results were given to demonstrate the circuit performance and to verify the feasibility of the proposed converter.

An integrated converter with active clamping technique to achieve zero voltage switching (ZVS) is presented. In the proposed converter, the flyback and zeta topologies are used in the input and output sides to achieve the following features: to share the power switches in the transformer primary side, to achieve the partial magnetising flux reset and to share the load current. The input power is delivered to the load by the interleaved operation. The active clamping circuit, besides contributing to reduce commutation losses, resets the energy stored in the leakage inductances of both converters and the magnetising inductance of the zeta converter. The magnetising inductance of the flyback converter is reset by the load. Based on the resonance with the resonant inductance and output capacitance of switches, switches can be turned on at ZVS during the transition interval. Experimental results, taken from a laboratory prototype rated at 360 W, input voltage of 200 V, output voltage of 12 V and switching frequency of 125 kHz, are presented to demonstrate the converter performance.

A soft switching bi-flyback converter is presented. Two identical flyback converters are used in the proposed circuit to share the load current. Thus, the transformer copper losses and the conduction losses on the output diodes are reduced. An active snubber is adopted to reduce the voltage spike and realise the ZVS turn-on of switches at the transition interval. Thus, the switching losses and thermal stresses of the semiconductors are reduced. Experiments are provided to verify the effectiveness of the proposed converter.

System analysis of a bidirectional DC–DC converter for a fuel cell electric vehicle driving system is presented. The proposed converter is based on a zero voltage switching (ZVS) half-bridge converter with centre-tapped rectifier at the secondary side of the transformer. The asymmetrical pulse-width modulation is used in the converter to achieve ZVS feature of power switches and to regulate the output voltage at the desired value. The proposed converter has the advantages of high efficiency, low circuit components and simple circuit configuration. The operating principle and the system analysis are described and discussed in detail. Finally, the experimental results for the proposed converter are provided to verify the theoretical analysis.

An isolated converter with boost voltage conversion ratio is presented. The active clamp circuit is used to achieve zero voltage switching, release the energy stored in the transformer leakage inductance and limit the voltage stresses on power switches. Compared with the conventional active clamp forward converter, the adopted circuit has no large output filter inductor. Thus, it has features of simpler structure, lower cost and no effective duty loss. Experimental results for a converter with an input voltage of 24 V, an output voltage of 200 V and operating at switching frequency of 73 kHz are provided to verify the effectiveness of the proposed converter.

A soft switching interleaved forward converter with current doubler rectifier is presented. Active clamp circuit is used in the primary winding of transformers to recycle the energy stored in the leakage inductor and the magnetising inductor so that the voltage stresses of switches are reduced. The leakage inductance of transformers, the magnetising inductance and the clamp capacitance are resonant to achieve zero-voltage switching (ZVS) of clamp switches. The resonance between the leakage inductance of transformers and output capacitance of switch will achieve ZVS operation for the main switches in the proposed converter. The interleaved operation can reduce the current ripple on the output capacitor. Two current doubler rectifiers with ripple current cancellation are connected in parallel at the output side to reduce the current stress of the secondary winding of the transformer. All these features make the proposed converter suitable for the DC–DC converter with high output current. The operation principle and system analysis of the proposed converter are provided in detail. Finally, experimental results, taken from a laboratory prototype rated at 125 W, are presented to verify the feasibility of the proposed converter.

A soft-switching converter with parallel-connected full-wave rectifiers is presented. In the proposed converter, the primary windings of two transformers are connected in series. Two full-wave rectifiers with ripple current cancellation are connected in parallel at the output side to reduce the current stress of the secondary winding of the transformer. The clamp circuit, based on an auxiliary switch and a clamp capacitor, is connected in parallel with the primary side of the transformer to recycle the energy stored in the leakage inductance. The leakage inductance of transformers, the magnetising inductance and the clamp capacitance are resonant to achieve zero-voltage switching (ZVS) of the auxiliary switch. The resonance between the leakage inductance of the transformer and the output capacitance of the switch will achieve ZVS operation for the main switch in the proposed converter. The pulse-width modulation technique is adopted to regulate the output voltage. The operation principle and system analysis of the proposed converter are provided. Some experimental results for a 200 W (5V/40 A) prototype are given to demonstrate the effectiveness of the proposed converter.

An eight-switch voltage source inverter for harmonic elimination and reactive power compensation is presented. The adopted inverter is based on a three-phase two-leg clamped capacitor circuit topology to reduce the voltage stress on the power semiconductors. Four active switches and one clamped capacitor are used in each inverter leg to achieve three-level pulse-width modulation. The adopted inverter is operated as a controllable current source to supply the necessary active power to compensate for the inverter losses, to eliminate current harmonics and to compensate the reactive power. Therefore, the sinusoidal line currents are drawn from the AC source. Three control loops are used in the control scheme to obtain the constant DC-link voltage, to track the line current command and to balance the neutral-point voltage. The redundant operating states in the adopted inverter can be selected to compensate the clamped capacitor voltage. A mathematical model of the proposed inverter for an active power filter is derived and the control scheme provided. Simulations and experiments based on a laboratory scale-down prototype are presented to verify the effectiveness of the proposed control scheme.

A zero voltage switching DC/DC converter is presented, which gives a stable output voltage and high circuit efficiency. In the adopted DC/DC converter, a full-bridge inverter with phase-shift PWM technique is used to achieve zero voltage switching for active power switches and to regulate the output voltage. To increase the converter efficiency at the transformer secondary side, a current doubler rectifier with the property of one diode conduction drop, frequency doubling in the output capacitor and low current rating in the transformer secondary winding are used in the adopted circuit. The detailed circuit operation, mathematical analysis and design example of the converter are presented. The measured full-load efficiency of a 100 kHz experimental prototype was higher than 92%. Experimental results are presented to verify the performance of the adopted circuit.