DC Impedance Modeling of MMC with Passive Circulating Current Suppressing Circuit

This paper proposes a simple method to establish the dc impedance of MMC with passive circulating current suppressing circuit (PCCSC) by analyzing the flow path of common mode and differential mode components of arm currents small signal harmonics. It turns out that there exists two resonance points in magnitude-frequency characteristic curves of dc impedance, one resonance peak fixed at second-order frequency and one resonance valley whose frequency is related to the electrical parameters of PCCSC. There also exist two corresponding phase steps in phase-frequency characteristic curves, one phase drop and one phase jump. Effects of control parameters on dc impedance of MMC with PCCSC are also analyzed. Time-domain simulations are provided to verify the theoretical analysis.