Selective Harmonics Mitigation Modulation Scheme Applied to CHB and NPC Multilevel Inverters

Abstract

Energy demand from renewable energy sources is increasing every day. Therefore, there is necessity to integrate large scale solar PV based systems in the grid in compliance with the specific grid codes. The inverter is the most important component of the Solar PV based system. Multilevel inverter (MLI) has various rewards such as less EMI issues, voltage stress and switching losses, it is a best choice for industrial bid.
In tradition inverters, Harmonics can be eliminated by using large size of filters due to the lower order harmonics. This leads to growth the overall size, volume and cost of an inverter. Nonetheless in MLI, the implementation of selective harmonic elimination (SHE) techniques eliminates lower order harmonics. The multilevel inverters (MLI) are capable of generating high quality waveforms of voltage (stepped in nature) with reduced distortion in harmonics (less THD), operates at less switching frequency and impress low current and voltage stress on the switching devices. MLI is preferred for large scale PV integration over conventional two-level inverter. Also for large power and high voltage application, the rating of the devices and switching frequency are limited. In MLI, Cascade H-Bridge (CHB) and Neutral Point clamped (NPC) is a best choice for PV and drives applications. In medium and high power applications, usage of high switching frequencies is not recommended because the thermal losses due to switching loss could damage the switching devices