Abstract
Modular multilevel converter (MMC) based multi-terminal direct current (MTDC) system has attracted much attentions. MMC-MTDC may contain many MMCs and has large amount of state variables. In order to establish the small-signal model for stability analysis of MMC-MTDC, the steady-state values of state variables of the whole MTDC must be obtained. The current method is to solve all nonlinear equations at one time. However, the large amount of state variables and diverse control strategies of MTDC lead to much programming work and difficulty in solving too many nonlinear equations of the whole MTDC at one time. To solve the above problems, this paper proposes a modular algorithm based on alternating iteration to obtain the steady-state values of the whole MTDC. Based on modularity idea, the algorithm takes single MMC in MTDC as the basic unit for solving the steady-state values of state variables. Each iteration only invokes the fsovle functions in Matlab for several typical control modes of MMC. The algorithm reduces the order of the equation group and computation burden, and meanwhile it makes it easy to modify state variables in single fsolve function. Finally, MMC-MTDC system under different control strategies is constructed in Simulink to validate the accuracy and correctness of the proposed algorithm.
Published Version
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