A Novel Hybrid PWM Method for DC-Link Voltage Balancing in a Three Level Neutral Point Clamped Inverter

A 3-Level Neutral Point Clamped inverter plays an imperative role in high power applications with medium voltage level. However, it possess a drawback of neutral point potential variation in the converters. This paper presents an algorithm to balance the DC-link voltage in a three level neutral point clamped inverter using a hybrid PWM technique. The advantage of both carrier based PWM and Space vector approaches are combined to get the desired voltage level without compromising on the quality of voltage being supplied by the inverter. A comparative analysis of the inverter performance with and without the proposed balancing scheme is provided. In addition, total harmonic distortion of current (% THD) and the DC-link voltage balancing capabilities are also compared. It is proven that by using this scheme the harmonic distortion is well below the permissible level, thereby reducing the losses on the drive system. Simulation studies are carried using MATLAB/Simulink on a 5HP induction motor and dc-link capacitor ratings of 100 mu F each.