High-Step-Up and High-Efficiency Fuel-Cell Power-Generation System With Active-Clamp Flyback–Forward Converter



A high-efficiency fuel-cell power-generation system with an active-clamp flyback–forward converter is presented in this paper to boost a 12-V dc voltage into a 220-V 50-Hz ac voltage. The proposed system includes a high-efficiency high-step-up interleaved soft-switching flyback– forward converter and a full-bridge inverter. The front-end active-clamp flyback–forward converter has the advantages of zero-voltage-switching performance for all the primary switches, reverse-recovery-problem alleviation for the secondary output diodes, large voltage-conversion ratio, and small input-current ripple. Furthermore, there are two coupled inductors in the proposed converter. Each coupled inductor can work in the flyback mode when the corresponding main switch is in the turn-on state and in the forward mode when it is in the turnoff state, which takes full use of the magnetic core and improves the power density. In addition, the full-bridge inverter with an LC low-pass filter is adopted to provide low-total harmonic-distortion ac voltage to the load. Therefore, high-efficiency and high-power density conversion can be achieved in a wide input-voltage range by employing the proposed system. Finally, a 500-W prototype and another 1-kW converter are implemented and tested to verify the effectiveness of the proposed system.


  1. Active clamp
  2. Fly back–forward converter
  3. Fuel cell generation system.



 Fig. 1. Proposed high-efficiency fuel-cell power-generation system.



Fig. 2. Experimental results of proposed ZVS flyback–forward converter: (a) ZVS operation of main switch S1. (b) ZVS operation of clamp switch Sc1. (c) Voltage and current waveforms on clamp capacitors Cc1 and Cc2. (d) Current waveforms of primary side. (e) Voltage waveforms on output diodes Do1 and Do2. (f) Detailed turnoff current across output diode Do1.

Fig. 3. Experimental results of full-bridge inverter: (a) AC output-voltage and output-current waveforms at 500-W resistor load. (b) AC output-voltage and output-current waveforms at 180-W RCD load. (c) Dynamic response from 50- to 500-W resistor load.


In this paper, an interleaved high-step-up ZVS fly back–forward converter has been proposed for the fuel-cell power generation system. The voltage doubler rectifier structure is employed to provide a large voltage-conversion ratio and to remove the output-diode reverse-recovery problem. Furthermore, ZVS soft-switching operation is realized for all the primary active switches to minimize the switching losses. In addition, the input-current ripple is small due to the interleaved operation and the current-fed-type configuration. The steady state operation analysis and the main circuit performance are discussed to explore the advantages of the proposed converter in a high-efficiency high-step-up power-generation system. Finally, a 500-W 12-V dc to 220-V ac system is employed and another 1-kW prototype operated at 100 kHz is tested as examples to illustrate the important design guidelines of the proposed converter. Experimental results have demonstrated that the proposed system is an excellent power-converter system for fuel-cell applications, featuring high efficiency, high-step up ratio, and high power density.


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An Efficient High-Step-Up Interleaved DC–DC Converter with a Common Active Clamp



This paper presents a high-efficiency and high-step up non isolated interleaved dc–dc converter with a common active clamp circuit. In the presented converter, the coupled-inductor boost converters are interleaved. A boost converter is used to clamp the voltage stresses of all the switches in the interleaved converters, caused by the leakage inductances present in the practical coupled inductors, to a low voltage level. The leakage energies of the interleaved converters are collected in a clamp capacitor and recycled to the output by the clamp boost converter. The proposed converter achieves high efficiency because of the recycling of the leakage energies, reduction of the switch voltage stress, mitigation of the output diode’s reverse recovery problem, and interleaving of the converters. Detailed analysis and design of the proposed converter are carried out. A prototype of the proposed converter is developed, and its experimental results are presented for validation.


  1. Active-clamp
  2. Boost converter
  3. Coupled-inductor boost converter
  4. Dc–dc power converter
  5. High voltage gain
  6. Interleaving




 Fig. 1. (a) Parallel diode clamped coupled-inductor boost converter and (b) proposed interleaved coupled-inductor boost converter with single boost converter clamp (for n = 3).



Fig. 2. (a) Drain-to-source voltage of the switch in a coupled-inductor boost converter without any clamping and (b) output voltage, clamp voltage and drain to- source voltage of the switch in a coupled-inductor boost converter with the proposed active-clamp circuit.


Fig. 3. (a) From top to bottom: total input current of the converter, input currents of the interleaved coupled-inductor boost converters, and (b) primary current, secondary current, and leakage current in a phase of the interleaved coupled-inductor boost converters.


Fig. 4. (a) Gate pulses to the clamp boost converter and (b) inductor current of the clamp boost converter.


Fig. 5. Gate pulses to the interleaved coupled-inductor boost converters (10 V/div).


 Coupled-inductor boost converters can be interleaved to achieve high-step-up power conversion without extreme duty ratio operation while efficiently handling the high-input current. In a practical coupled-inductor boost converter, the switch is subjected to high voltage stress due to the leakage inductance present in the non ideal coupled inductor. The presented active clamp circuit, based on single boost converter, can successfully reduce the voltage stress of the switches close to the low-level voltage stress offered by an ideal coupled-inductor boost converter. The common clamp capacitor of this active-clamp circuit collects the leakage energies from all the coupled-inductor boost converters, and the boost converter recycles the leakage energies to the output. Detailed analysis of the operation and the performance of the proposed converter were presented in this paper. It has been found that with the switches of lower voltage rating, the recovered leakage energy, and the other benefits of an ideal coupled-inductor boost converter and interleaving, the converter can achieve high efficiency for high-step-up power conversion. A prototype of the converter was built and tested for validation of the operation and performance of the proposed converter. The experimental results agree with the analysis of the converter operation and the calculated efficiency of the converter.


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