Various Control Strategies for Medium Voltage High Power Multilevel Converters: A Review

Multilevel converters have been emerged as powerful devices in the power industries. In the past, depending upon the topologies used numerous control strategies have been proposed for desired output waveform. This paper presents the review of various topologies and different types of control strategies used for multilevel converters. The existing control strategies are discussed and the suitability of the control strategies to various multilevel topologies are mentioned. Apart from classical methods, advanced control strategies are also mentioned. Objective of these control strategies is to reduce total harmonic distortions while maintaining the switching frequency within the permissible range as required for high power and medium voltage applications. This paper presents the idea of multilevel converters working at a lower switching frequency with the modified control strategies while maintaining the lower harmonics. As a preferred option for future scope, reduction of total harmonic distortion with the aid of hybrid modulation techniques to the five levels NPC/H bridge converters and further extension to seven levels converter is suggested.