Bootstrap power supply for three-level neutral-point-clamped voltage source inverters

This paper presents a survey of floating power supplies based on bootstrap operation for three-level neutral-point-clamped (NPC) voltage source inverters (VSI). The floating power supply for upper switches is achieved by the bootstrap capacitor charged during on-time of the switch underneath. Hence, a large number of bulky isolated DC/DC power supplies for each gate driver are reduced. The PSPICE simulation results show the performance of the three-level VSI using bootstrap technique. Moreover, the effect of fundamental output frequency, the PWM frequency and the modulation index on the voltage of bootstrap capacitor is also investigated.