Modeling and Analysis of VSC-MTDC Transmission Systems

A small-signal model of voltage source converter based multi-terminal direct current (VSC-MTDC) systems is presented based on modular modeling for avoiding deducing the elements of the matrixes. The entire system is divided into three subsystems: AC system, VSC and DC system, where VSC is composed of AC electrical module, DC electrical module, and controller. The nonlinear state-space model and link equations of each subsystem are deduced based on equivalent circuit. The small-signal model for the whole system is automatically produced via the linearized state-space model and link equations, Finally, combined with the new energy generation in Gansu province, the small-signal model is validated via the comparison of the step response of the electromagnetic model based on a four-terminal system. The impact of converter control parameters on system stability under different control modes is analyzed via eigenvalues.