Lyapunov-Based Capacitor Voltage Observation of Modular Multilevel Converters

Modular multilevel converter (MMC) has achieved its popularity in wide range of voltage applications over other multilevel topologies due to its modularity, scalability, and ease of design. A typical MMC is composed of many capacitors and the voltages across them are required to be measured for the control of system variables like the circulating current and for capacitor voltage balancing. The number of capacitors and their associated measurement devices increase with higher voltage levels. Hence, to reduce the economical and design burden, several techniques for the observation of capacitor voltages have been presented till date. In this article, capacitor voltages of the submodules are observed using a simple Lyapunov-based observer (LBO) and the convergence proof of the observation error is established mathematically. The performance of the proposed LBO is studied in simulation using MATLAB/Simulink and also experimentally validated. The proposed observer is also compared in simulation with two other existing observation techniques from literature.