A Symmetric Carrier Technique of CRPWM for Voltage Balance Method of the Flying Capacitor Multi-level Iinverter

플라잉 커패시터 멀티-레벨 인버터의 커패시터 전압 균형을 이루기 위한 캐리어 비교방식을 이용한 캐리어 대칭 기법

This paper presents a simple carrier symmetric method for the voltage balance of flying capacitors in FCMLI(flying capacitor multi-level inverter). To achieve the voltage balance of flying capacitors, the utilization of each carrier must be balanced during a half-cycle of the switching period such as PSPWM(Phase-Shifted PWM). However, the CRPWM(Carrier Redistribution PWM) method causes the fluctuation of flying capacitor voltages because the balanced utilization of carriers is not achieved. Moreover, it does not consider that the load current change has an influence on flying capacitor voltages by assuming that the current flows Into the load. To overcome the drawbacks of CRPWM, it is modified by the technique that carriers of each band are disposed symmetrically at every fundamental period. Firstly, the CRPWN method is reviewed and the theory on voltage balance of flying capacitors is analyzed. The proposed method Is introduced and is verified through the experiment result.