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In order to meet the requirements of the fuel cell stack power interface converter applied in the fuel cell vehicles, a common ground wide voltage-gain range DC-DC converter is proposed. On the input voltage side, an interleaved structure is adopted in this converter to reduce the input current ripple. On the output voltage side, two series capacitors are combined with a diode-capacitor structure to improve the voltage gain and reduce the voltage stress of power semiconductors and capacitors. As a result, the efficiency and reliability of the proposed converter can be improved. The operating principle, steady-state characteristic, parameter design, efficiency calculation, and comparison with other converters are analysed. A 1.6 kW prototype of the proposed converter with the 400 V output voltage has been developed to validate the analytical results. Theoretical analysis and experimental results show that the proposed converter can meet the requirements of a fuel cell stack power interface converter and is suitable for use as a fuel cell stack power interface converter applied in fuel cell vehicles.

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In this paper, a bidirectional inductor-inductor-capacitor-inductor (LLCL) resonant dc-dc converter is presented. Compared with the conventional LLC, a parallel-connected inductors structure is employed into the resonant tank. By virtue of this unique resonant tank, LLCL exhibits the following desirable features: 1) good voltage gain regulation capability in bidirectional power flow applications; 2) zero-voltage-switching turn-on of the power switches in a wide load range; 3) compared with the other bidirectional LLC-type resonant converters, lower resonant tank currents and lower resonant capacitor voltage stress are achieved under the same working conditions. The topology derivation and operating principles of LLCL are shown, and the vital characteristics of LLCL are especially discussed. Moreover, based on battery applications in energy storage systems, in order to make the voltage gain range of LLCL meet the requirements while minimizing the resonant tank currents, a parameter design method is conducted. Finally, a 500-W prototype is established to verify the operating principles and design effects of the proposed converter. INDEX TERMS Bidirectional power transmission, energy storage system, isolated dc-dc converter, LLCtype resonant converter.

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Hybrid energy storage systems (HESS) play an important role in maintaining the power balance of a direct current (DC) micro-grid. A HESS is mainly composed of high power density super-capacitors (SCs) and high energy density batteries. According to the operational requirements of an SC, a bidirectional DC-DC converter with the characteristics of a good dynamic response and a wide voltage conversion ratio is needed to interface the SC and a high-voltage DC bus. In this paper, a novel common grounded H-type bidirectional converter characterized by a good dynamic response, a low inductor current ripple, and a wide voltage conversion ratio is proposed. In addition, it can avoid the narrow pulse of pulse width modulation (PWM) voltage waveforms when a high voltage conversion ratio is achieved. All of these features are beneficial to the operation of the SC connected to a DC bus. The operating principle and characteristics of the proposed converter are presented in this paper. A 320 W prototype with a wide voltage conversion ranging from 3.3 to 8 in step-up mode and 1/8 to 1/3 in step-down mode has been constructed to validate the feasibility and effectiveness of the proposed converter.

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