Series-Connected MMC with capacitor arms and its small Signal Impedance Modeling

Due to the high construction cost of traditional MMC (Modular Multilevel Converter), a more economical MMC with capacitor arms is proposed. The proposed topology is a modified version of the SC-MMC (Series-Connected MMC). Firstly, the operating principle of the proposed MMC is given. The classical control loops are adopted to control the active power and reactive power of the proposed MMC. Then, multi-harmonic linearization method is utilized to establish its small signal AC-side impedance model, including phase locking loop (PLL), inner current controller and outer power controller. A compensation strategy for the impedance modeling is proposed, which reduces the modeling error in low frequency band and improves the whole modeling accuracy. Finally, the analytic model is compared with simulation measurements in Matlab/Simulink, which verifies the effectiveness of the proposed modeling method.