An Improved Submodule Capacitor Voltage Measuring Algorithm for MMC with Reduced Sensors

The nearest level modulation (NLM) based submodule capacitor voltage measuring technology for a modular multilevel converter (MMC) with reduced sensors can effectively reduce the costs of the data acquisition system of MMC and simplify the operation system. One of the technical challenges of this submodule capacitor voltage measuring technology is to reduce the measurement errors of submodule capacitor voltage. This paper proposes an improved submodule capacitor voltage measuring algorithm to overcome this challenge. In the proposed algorithm, by keeping the operation states of submodules unchanged during the continuous control period, the probability of obtaining the actual capacitor voltage is increased, and then the number of corrections of observed capacitor voltage is significantly increased. Thus, the proposed algorithm can effectively reduce the measuring errors. More significantly, the proposed algorithm can also improve the measurement accuracy even in the capacitance deviation situation. Finally, both simulation and experimental results are provided to verify the feasibility and effectiveness of the proposed voltage measuring algorithm.