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The effects of the design and optimization of trapezoidal channels and baffles on the net power density of proton-exchange membrane fuel cells (PEMFCs) are studied. The significant effects of the length of upper and lower sides of the trapezoidal cross section and the number and position of baffles on the net power density of PEMFC have been investigated. It is found that at the same flow rate, changing the effective contact surface between the flow channel and the gas diffusion layer can tremendously improve the current density of fuel cells; moreover, the performance of a PEMFC based on the addition of a baffle can be further improved. The results show that the trapezoidal cross-sectional flow channel with baffles has higher efficiency and better overall performance compared with a basic straight flow channel. In addition, the response surface was used to optimize the trapezoidal crosssectional flow channel by considering the power loss of output power and the flow rate. The optimal result was obtained with an upper side length of 1.234 mm, a lower side length of 1.8 mm, and a baffle from the entrance at 9.5 mm, increasing the net power density by 4.347%.

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Abstract. Input current distortion in the vicinity of inputvoltage zero crossings is a major concern for conventional singlephase Boost PFC applications, especially under high ac line frequencies. This paper discusses the previously known causes for the input current distortion and points out that the multi-level power conversion technique can effectively reduce the zerocrossing distortion under high frequencies. A three-level (TL) Boost converter containing flying capacitors is then presented as the PFC topology. The system control method of the converter is also discussed. Experimental results are presented to validate the effectiveness of the proposed method.