An optimized neutral-point potential balancing algorithm for seven-level ANPC inverters

This paper decouples the floating capacitors voltage controlling and the neutral-point potential balancing of Seven-level Active Neutral-point-clamped (ANPC-7L) inverter by using the concept of average state, proposes a neutral-point potential balancing model based on zero-sequence voltage injection and derives the full controllable region of neutral-point potential. Based on this model, a testing-verification type real-time neutral-point potential balancing algorithm is proposed. This algorithm is further optimized for ANPC-7L inverter to ensure the series devices' operating frequency is the output frequency of the inverter and eliminate the multi-level jumping of phase output voltage. The algorithm is verified by results from a 380 V/5 kW ANPC-7L inverter.