Submodule Capacitor Voltage Estimator for Modular Multilevel Converters Without Internal Measurements

In this article, a modular multilevel converter (MMC) sub-module (SM) capacitor voltage estimator which determine the state of the capacitors measuring the bus voltage, output voltage and current, is proven via simulation and experimentation. The estimator deals with the complete elimination of sensors for internal converter states in a MMC. This is achieved through a state observer based on an Extended Kalman Filter. Additionally, a dead-time compensator is included, which is not dimensioned within the state observer using converter equations. The steady-state behavior of the observer during startup with zero initial conditions and the dynamic behavior during a reference change are evaluated via experimentation, both cases are studied in open-loop configuration. To prove performance for various operating points, results are obtained for different modulation indexes.