Performance Analysis of Four Level NPC and NNPC Inverters using Capacitor Voltage Balancing Method

Mostly, the conventional neutral point clamped (NPC) multilevel inverters are implemented for odd number of levels in the output. In this paper, four level NPC inverter is implemented and compared with the nested neutral point clamped (NNPC) inverter. The NNPC inverter is a four level inverter for high power applications. This inverter is a combination of diode clampedand flying capacitor multilevel inverters which consists of two flying capacitors in each phase and uses the same voltage rating of diodes. This method is suitable for SPWM and SVM PWM schemes. The inverter is fed to an induction motor load for static and dynamic operations using capacitor voltage balancing method. The performance results of SPWM method of four level NNPC inverter is compared with the four level diode clamped inverter using MATLAB/Simulink. SVM method is also implemented for four level NNPC inverter using various modulation indices and observed that the NNPC inverter has better THD values.