A Modified Modulation Strategy for an Active Neutral-Point-Clamped Five-Level Converter in a 1500 V PV System

With the development of 1500 V photovoltaic (PV) systems in recent decades, multilevel inverters such as the five-level inverter have gained much attention for their higher equivalent output frequency and low semiconductor devices’ voltage stress. Among five-level inverters, the active neutral-point-clamped five-level (ANPC-5L) inverter is very competitive due to its simple structure and control methods. However, with its conventional commutation strategy, the topology of the ANPC five-level converter has the security risk of overvoltage in the power device when switching to dead time under special conditions, which affects the reliability and safety of the switch state switching process. In this paper, this issue is analyzed in detail and a modified commutation strategy is proposed. Meanwhile, a novel soft start-up method adopted to an ANPC-5L inverter is also proposed. A prototype is also set up to analyze the issue of traditional switching commutation strategies and to verify the effectiveness of the proposed commutation strategy and the soft start-up method.