Control of a Multilevel Modular Converter using a state observer

Modular Multilevel Converters (MMC) have been considered an attractive option for medium/high-power applications due to their reliability and power quality. The MMC operation relies on voltage balancing. Consequently, many researchers have addressed the issue of voltage balancing and developed several schemes and controlling methods for this issue. This paper presents two approaches to control the MMC by using a state observer. In one proposed approach, a voltage balancing based method is developed which takes advantage of a state observer to estimate the total voltage at each arm. In the second approach, the voltage balancing method is used with state estimation for each sub-module. First, each approach is used without the state observer in an open-loop configuration with different pulse width modulation (PWM) schemes. Then the state observer is added to show the performance improvement The simulation results for the proposed control are presented and a comparison between the proposed approaches and the open-loop control are shown to prove the effectiveness of using the proposed methods.