Analysis of Harmonic Distortion Reduction through Modular Multi-Level Inverter using Nearest Level Modulation (NLM) Control Strategy

Abstract

The research paper presents the control strategy to reduce THD (Total Harmonic Distortions) losses by the implementation of the Nearest Level Modulation control technique in a Modular Multilevel Converter. Modular Multilevel Converter is found one of the leading technologies in Power Electronics & Control, its applications are very common in HVDC systems, FACTS (Flexible Alternating-current Transmission system), Variable frequency drives and Electric vehicles as well. The power quality of MMC is better and has lesser THD in comparison to conventional converters like 2-level converters with carrier-based modulation techniques. The MMC has been designed with high scalability and has high voltage and power capacity. Sub-module is an integral part of MMC which is built up as an identical and controllable part of it. This converter is also called a controllable voltage source (VSC). Researchers aim to come up with a detailed review of control methods and necessary operations applied to MMC-based systems for HVDC, particularly focusing to control the total harmonic distortions. Power converters use many modulation techniques, but the existing techniques contribute to a great part in switching losses. MMC up to 49 levels, by implementing the Nearest Level Modulation (NLM) technique, is robust and has less complexity for the systems like MMC-HVDC, and the levels control the total harmonic distortions. In this research paper, the reduction of THD by increasing the voltage levels in MMC is comprehensively evaluated. The simulation results in MATLAB/Simulink are used to examine and confirm the proposed control strategy for stable operation of MMC for HVDC application.