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In this letter, the redundant circulating current is identified as the key factor leading to the degradation of the efficiency of current-fed series resonant converters at light loads, which limits their performance in fuel cell vehicles. To tackle this issue, a zero-voltage switching (ZVS) critical current tracing modulation is proposed for the current-fed series resonant converter. In the proposed method, the circulating current is adjusted to trace the critical circulating current for ZVS, and the excessive loss caused by the redundant circulating current can be suppressed. Finally, a 1-kW prototype is built to verify the effectiveness of the proposed modulation, and a maximal efficiency increase of 15.1% at light load is achieved.

The advent of third-generation semiconductors brings the switching frequency into a much higher level, which enables high-frequency transformer with a smaller footprint in power electronics. Due to its inherent ability of voltage amplification, the transformer-based voltage-multiplier becomes prevalent in step-up converters which are the inevitable parts in the usage of low-voltage renewable resources. Though its feasibility has been verified in many researches, an uncertain error in voltage conversion ratio exists between the reality and ideal, which leaves a theoretical gap. Accordingly, the key affecting characteristics, the reverse recovery process of the leakage inductance, is considered and analyzed in this paper. The power transmission mechanism is clarified, and the root-mean-square error of the gain can be reduced from 24.31% to 3.13%, and the maximum output power together with power effect on the gain are obtained. With the conclusion of this paper, parameters of power supply can be optimized at the beginning of design to satisfy the demand of maximum output power and gain over a wide power range, which can save the unnecessary trial-and-error during the case-by-case design.

This article investigates the effects of airgaps between different parts of magnetic cores on the parasitic capacitance of magnetic components, which was excluded by previous research. According to the physical mechanism of the electric field in airgaps, the single-perfect-electric-conductor assumption, which has been widely used in previous research, is improved to mutiperfect-electric-conductor assumption by considering the effects of airgaps on the voltage potential distribution of magnetic components. Furthermore, the improved physics-based analytical model is developed based on the proposed assumption for demonstrating the effects of airgaps on the parasitic capacitance of magnetic components. The analyses are verified by finite-element-method simulations and experimental verifications, which accurately predict the effects of airgaps on the voltage potential distribution and the parasitic capacitance in magnetic components.