Comparison between 3-level single phase NPC and SI-NPC Multilevel Inverter Based on PD PWM & POD PWM Techniques for Photovoltaic Applications

In recent years, photovoltaic (PV) power generation systems are employing single phase transformerless (TRL) multilevel inverters with low leakage current and voltage stress of switches to reduce the total harmonic distortion and improve system efficiency, such as three-level Neutral Point Clamped (3L-NPC) inverter. However, the shoot through problem in the converter leg can affect its reliability. Therefore, a three-level split Inductor Neutral Point Clamped (3L-SI-NPC) inverter is introduced. This paper compares between the behavior of single phase 3L-NPC and 3L-SI-NPC under different carrier-based pulse width modulation (CB-PWM) techniques for PV system application. In this work, both converters are controlled by level shifted PWM strategies including, phase disposition (PD-PWM), phase opposition disposition (POD-PWM) and alternative phase opposition disposition (APOD-PWM). The performance of both converters is investigated using Matlab/Simulink environment. By comparing the converters behavior under both control strategies, the results show a better performance of single phase 3L-SI-NPC under PD-PWM due to its ability to overcome the shoot through problem, and the current total harmonic distortion is reduced from 26.16 % to 14.22 %. Moreover, the comparison shows that by adopting POD-PWM approach, a significant improvement in both converter behavior is achieved in terms of the ripple content in the DC and AC side voltage/current waveforms. In addition, the 3L-SI-NPC with POD-PWM control, provides a substantial reduction in the percentage total harmonic distortion (THD) with a value of 1.21% only. Therefore, the 3L-SI-NPC controlled by POD-PWM can be considered as better candidate for transformerless PV system.