Switched-Capacitor-Based Hybrid Clamped Converter for Wide Power Factor Applications

Abstract

The clamped multilevel converter generally adopts the zero-sequence voltage injection method to realize the voltage balancing of the DC link capacitors. However, the relationship between the reference modulation voltage and the duty ratio of phase neutral point current is often a triangle or trapezoidal function. When the power factor is low, the required optimal zero-sequence voltage will be out of bounds, which will lead the capacitor voltage ripples to become larger or even divergent. Therefore, a novel switched-capacitor-based hybrid clamped(SCB-HC) converter is proposed in this article. The new redundant switching states are obtained by introducing the boost characteristics of the switched-capacitor(SC) circuit. And a hybrid phase-shifted pulse width modulation(PS-PWM) is developed to extend its functional relationship. This ensures the peak current that flow out of the neutral points is fewer, then the capacitor voltage drift is reduced significantly. Moreover, the proposed hybrid PS-PWM method not only ensures that SC circuit switches series and parallel patter once during a carrier period, but also achieves the voltage balancing of SC and DC link midpoint capacitor naturally under ideal conditions. On top of that, the capacitor voltage balancing method is designed to ensure independent and decoupled control of all capacitor voltages. Simulations and experiments show that the proposed topology, modulation method and voltage control method are practical and feasible for wide power factor applications.