Impedance Modeling of Modular Multilevel Converter Based on Multi-Harmonic Linearization

Modular Multilevel Converter (MMC) has the advantages of modular design and low AC voltage distortion. Recent studies reported harmonic instability problems in MMC-connected grids. Impedance-based stability criterion has proven to be effective for analyzing harmonic instability, which requires the impedance model of MMC. Based on the review of converter modeling methods, this paper establishes an impedance model of MMC using multi-harmonic linearization method. The modeling focus on the positive sequence. The on-resistance of MMC submodule switches is considered in the modeling of power stage of MMC. The control modeling comprises the modeling of five controls including phase current control, circulating current control, phase-locked loop, active power control as well as reactive power control. Finally, the results obtained by PSCAD simulation confirms that the impedance model is correct in an excellent accuracy.