Increasing switching frequency can greatly improve power density of dc–dc power converter, while meets challenges of significant high-frequency dc output ripple. The capacitor filter is a most cost-effective suppression for the output ripple. However, the capacitor parasitic parameters will deteriorate the suppression. The frequency characteristic of the capacitor filter was analyzed by considering the parasitic parameters. Then, a novel parallel dual capacitors filer is proposed, which creates the reverse coupling between the two adjacent capacitors of the filter by constructing opposite current flowing through the capacitors. Using the novel dual capacitors filer as a cell, a novel compact multicapacitors filer of V-shape is further extended. The insert gain test and the prototype with 20 MHz of switching frequency are constructed, and the experiments verified that the novel filters suppress the ripple by maximum about 50% comparing with the traditional capacitor without adding volume and cost.

Circulating current suppression can effectively improve the reliability and redundancy of parallel inverter systems. The mechanism and influencing factors of the low- and high-frequency zero-sequence circulating current (ZSCC) are analyzed in this study. Based on a mechanism analysis and the built mathematical model, the composite control strategy of zero-sequence voltage difference (ZSVD) compensation and virtual inductance is proposed to suppress the low- and high-frequency ZSCC. In the composite control strategy, the low-frequency ZCSS (LF-ZCSS) is suppressed by the ZSVD compensation method, and the HF-ZCSS is suppressed by the virtual inductance method. The ZSVD compensation is incorporated into the SVPWM as an input to regulate the modulation and suppress the LF-ZCSS, and virtual inductance is introduced into the current control loop to suppress the HF-ZCSS. A parallel system prototype composed of two 6 kW inverters is constructed. The experiments show that the ZSCC of the parallel system is reduced by 45%, which verifies the effectiveness of the proposed composite control strategy.