Control of the Neutral Point Voltage Balance in the Hybrid Three-Level Active Neutral-Point Clamped Inverter

Hybrid three-level active neutral point clamped (3L-HANPC) inverters feature both high power densities and low costs, and have strong application potential in energy storage systems, electric vehicles, and other fields. Controlling the dc bus neutral point voltage (NPV) balance across the entire modulation index (m) and power factor (PF) range for 3L-HANPC inverters with unbalanced dc links is a significant challenge, particularly when aiming to minimize switching losses. To solve this problem, we propose a new integrated control method. The method includes gate drive signal distribution and a hybrid pulsewidth modulation (HPWM) strategy. The gate drive signal distribution extends the application of a hybrid modulation strategy from traditional three-level neutral point clamped inverters to 3L-HANPC inverters. A GaN/Si 3L-HANPC prototype was devised to validate this approach. Experimental results show that HPWM effectively controls NPV fluctuations within +/- 3 V across the entire m and PF range. Compared to space vector pulsewidth modulation, HPWM reduces switching losses by 15%-50% over 75% of the m and PF range, and by up to 25% in the remaining 25%.