Research on Sliding Mode Observer of MMC Capacitor Voltage

In the practical application of modular multilevel converters (MMC), with the improvement of voltage level and power, more submodules (SMs) need to be cascaded in order to obtain more levels with different amplitudes to approximate the sinusoidal output voltage. The acquisition of submodule capacitor voltage is the premise of MMC capacitor voltage control, which makes the MMC system need many sensors to monitor sub-module capacitor voltage. In order to reduce the number of sensors and weaken the system jitter, this paper collects the current signal of the MMC bridge arm combined with the switching signal of the submodule and uses the saturation function set as the switching function of the sliding mode observer (SMO) to estimate the capacitor voltage. The simulation results show that the sliding mode observer has good robustness and accuracy.