Self-Balanced Nine-Level Flying Capacitor Inverter With Double-Period Level-Shifted Control

Abstract

Voltage imbalance and peak charging current often occurs in capacitor-containing inverters. To solve this problem, a nine-level flying capacitor inverter and a double-period level-shifted pulse-width modulation (DPLS-PWM) strategy is proposed. The proposed topology has the advantage of reduced capacitor count and low total standing voltage (TSV). Owing to the special redundant states of proposed inverter, a DPLS-PWM is introduced. By applying DPLS-PWM strategy, the two capacitors in the proposed inverter can be balanced naturally. Meanwhile, unlike most switched-capacitor (SC) inverters whose self-balance scheme often generate large inrush current, the current stress of the proposed balance scheme is low. The working modes of proposed inverter and the principles of DPLS-PWM is analyzed in detail. And comparisons are made to highlight the merits of the topology and modulation method. Simulation and experimental results have verified the feasibility of the proposed topology and self-balance modulation. The experimental efficiency of this inverter can reach over 98%.