A Space Vector PWM Strategy for Charging of Bootstrap Capacitor in Three-Level Neutral-Point-Clamped Inverter

This paper presents a space vector PWM method to achieve a high power density three-level inverter (3LI) with a bootstrapped gate drive circuit. The objective is to shift from a two-level inverter (2LI) to a 3LI but without a significant increase in the size and cost of the inverter board. The proposed method solves an inherent issue of the charging of the bootstrap capacitors during the inverter operation. The effectiveness of the method is demonstrated through experiments carried out on a 5 kW motor drive with an input voltage of 350 V and a switching frequency of 12 kHz. Stable and efficient performance is maintained across a wide modulation index range, with a bootstrapped 3LI board approximately half the size of a conventional 3LI. Furthermore, loss comparisons between the bootstrapped 3LI board and a 2LI board with reactive load show that the power output can be increased by 1.5 times due to reduced switching losses.