Impedance Model of MMC With CCSC and Sampling Delays

Due to the implementation of a large number of renewable energy systems, the oscillations related to the Modular Multilevel Converter (MMC) have caused serious damages to the HVDC systems. Therefore, in this paper the impedance model of the MMC in a wide frequency range has been proposed to identify the impedance characteristics of the MMC. The impedance model proposed not only takes into account the outer and inner control loops, but also considers the effects of the Circulating Current Suppressing Control (CCSC) and sampling delays in the control system. The consistency between the theoretical result and simulation result has also approved the efficiency and accuracy of the proposed impedance model of the MMC.