ANPC-5L Inverter Floating Capacitor Pre-Charge Solution Design

Abstract

This paper proposes novel solutions addressing the pre-charge issue of floating capacitors in two ANPC five-level topologies. Floating capacitors play a crucial role in ANPC five-level topologies, where their pre-charge process directly impacts voltage stability during system startup. Traditional pre-charge methods often suffer from low safety, inefficient charging, and poor stability. Therefore, for the three-capacitor ANPC topology, this paper employs a pre-charge scheme utilizing the topology's inherent redundant state. For the single-capacitor ANPC topology, this paper designs a scheme that extracts energy from the control circuit and elevates the floating capacitor voltage to the required level via a push-pull boost circuit. Leveraging the high-efficiency energy conversion characteristics of the push-pull circuit, this approach achieves stable capacitor charging within a short timeframe while maintaining low circuit complexity. Experimental results demonstrate that both proposed approaches can reliably charge the floating capacitor to the target voltage. Compared to conventional methods, the three-capacitor pre-charge scheme reduces inverter size and simplifies control. The single-capacitor pre-charge approach significantly enhances charging safety while lowering system energy consumption. The proposed solutions show promising application prospects and can be widely adopted in power electronic systems demanding high efficiency and reliability.