High reliability observers for modular multilevel converter capacitor voltage evaluation

This paper proposes to observe a set of capacitor voltages from modular multilevel converter using only one current and one voltage measurement for the ensemble. This is achieved by estimating the voltage values using the current and the gating signal. The estimation is then corrected using a sliding mode control on the voltage error of the whole half-arm. When compared with previously proposed observers, this one has the advantage of being simpler and expandable to any number of submodules. Furthermore, each half-arm can be treated independently, making it possible to solve them in parallel. Accuracy of the proposed observer is demonstrated through a real-time simulation of a 300 submodules three-phase modular multilevel converter during initialization, steady-state and AC-fault operation.