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Although the impedance/admittance model of modular multilevel converter (MMC) considering internal harmonic is discussed extensively in the literature, few attentions have been focused on how to determine the number of harmonics to be included in the model. This article fills this gap by developing the MMC signal-flow graph (SFG), providing the analytical transfer function to quantitatively estimate the attenuation degree of MMC harmonics, so as to guide the model truncation. Besides, SFG offers an intuitive understanding on the mathematical characteristic of MMC, including the conjugate symmetry and the effect of phase reference on admittance, which helps to reduce the modeling calculation. Moreover, conversion formula of MMC multiple input multiple output and single input single output admittance is derived based on the truncated model to further simplify the stability analysis. The correctness of this article has been verified by simulation and experiment. [ABSTRACT FROM AUTHOR]

This paper introduces a node elimination method for analog circuit analysis. It is useful for manually deriving the transfer functions of small active circuit cells in analog integrated circuit design. This method is essentially a variant of Gaussian elimination and can be established based on the driving point impedance method. By successively reducing the circuit size, a circuit can be easily solved as soon as all internal nodes are eliminated. Examples are provided to illustrate the analysis steps. [ABSTRACT FROM AUTHOR]