Owing to low voltage stresses, wide range of input voltage and the same polarity of output voltage and input voltage, double-switch buck-boost converter (DSBBC) is a popular choice to achieve dc/dc conversion in photovoltaic generations (PV), power factor correction (PFC), portable devices and so on. Combined control (CC) makes DSBBC operate efficiently, but large ripples of output voltage are unavoidable during mode transition. With two equal duties, interleaved modulation (IM) makes the inductor ripple current decrease remarkably compared with synchronous modulation (SM) while inductor average current is still high. By introducing duty offset, inductor average current declines and efficiency is enhanced obviously under interleaved modulation with duty cycle offset (IMDO). However, with 180degree phase-shifted angle, the ripple current is not low enough in some cases. Thus, to make further improvement on ripple current, an interleaved modulation scheme with optimized phase shifting (IMOPS) is proposed for DSBBC in this paper. Current features, optimal phase-shifted angle (OPSA) and operating region under IMOPS are described meticulously. Besides, theoretical and quantitative comparisons of different modulation schemes are presented, including inductor average current, inductor ripple current and ratio of direct power transfer (DPT). Based on a 150W prototype, the feasibility and effectiveness of IMOPS are demonstrated by experimental results.INDEX TERMS Double-switch buck-boost converter, optimal phase-shifted angle, inductor ripple current, efficiency promotion.

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