A Soft-Switching Control for Cascaded Buck-Boost Converters Without Zero-Crossing Detection

This paper proposes a novel soft-switching control without zero-crossing detection for the cascaded buck-boost converters (CBBCs). The proposed soft-switching control consists of two parts: soft-switching modulation and closed-loop control. In the modulation, the employed PWM approach is constructed by introducing a small negative current into the conventional PWM, and the soft-switching modulation based on the negative-current-based PWM is presented by adding a new switching process controlled by a modulation variable in the CBBC. In the closed-loop control, the relationship between the models of the negative-current-based PWM and the soft-switching modulation is deduced, and by utilizing the deduced relationship, the closed-loop control is designed while the PWM is modified to achieve the soft-switching. Meanwhile, to further reduce the ripple current and device losses, the parameter of the proposed control is optimized by refining the restrictive conditions. While the zero-crossing point of the inductor current is calculated with a given algorithm based on a current measurement, the circuit of zero-crossing detection is avoided. The validity and feasibility of the proposed soft-switching control approach are confirmed by the simulations and experiments on a 200-W prototype.