Optimal Switching Method Using Variable Additional On-Time Control for CRM-Operated Multicell Series-Parallel Converter

Unlike the conventional boost-derived power-factor-correction (PFC) converter, the cell series-parallel (MCSP) converter can step-up/step-down the output voltage. Its modular concept has a flexibility to select the voltage rating of switches depending on the number of cells. Based on its high degree-of-freedom (DOF) in combination of switching states, this article proposes an optimal switching method that can suppress the amplitudes of switch currents while improving converter efficiency by synthesizing pentagonal inductor current waveform in critical conduction mode (CRM) control. In addition, a total harmonic distortion of input current (iTHD) is improved with variable additional
on
-time control. Thanks to an inherent capacitor voltage balancing feature of the MCSP converter, it does not require additional balancing control. The feasibility of the proposed control is verified by experiments in the 300 W prototype.