Harmonic State-Space Based DQ Impedance Model of a Modular Multilevel Converter

The impedance model of modular multilevel converters (MMCs) is the key to the stability analysis of MMC grid-tied system. However, MMC contains a large number of power electronic devices, and the components of MMC have significant steady state harmonics, resulting in strong coupling and nonlinear characteristics, which makes impedance modeling complicated. In this manuscript, harmonic state-space method is introduced to establish the impedance model of MMC, which contains all harmonics of internal components. Moreover, the proposed impedance model is established in dq frame, which offers advantages as follows: 1) the controller model is established in dq frame, which is convenient to analyze the influence of controller parameters; 2) the main devices in power system are modeled in dq frame, it’s easy to analyze the stability of system with proposed impedance model. Finally, the accuracy of the impedance model proposed in this manuscript is verified in MATLAB/Simulink environment.