Modeling and Initialization of Modular Multilevel Converter Based High-voltage DC Transmission in Power System Dynamics Simulations

Dynamic phasor model of modular multilevel converter based high-voltage DC transmission (MMC-HVDC) and its initialization in power system dynamics simulations are presented in this paper. In order to study the influences of MMC-HVDC on the power system dynamic behaviors, the MMC-HVDC models need to be integrated into the power system dynamics simulation. Then the models must be initialized based on power flow data. Firstly, the dynamic phasor model of MMC-HVDC considering the internal dynamic characteristics of the MMC and suitable for dynamics simulation of power system is proposed, and then it is initialized based on AC-DC power flow data. Finally, the influences of auxiliary frequency control of MMC-HVDC on the angle stability of the system are studied through the four-machine two-area system. The correctness of the dynamic phasor model is verified by comparison with electromagnetic transient simulation. And the dynamics simulation results show that the auxiliary frequency control of MMC-HVDC can improve the angle stability of the system.

I. Introduction

Due to its many operational advantages for high voltage and high power applications, the modular multilevel converter has become a choice solution for dc/ac conversion in HVDC applications [1]. The widely used MMC-HVDC models can be divided into three categories: 1) the electromagnetic transient (EMT) model [2], which is highly accurate but unsuitable for large-scale systems because of the long simulation time. 2) the phasor model [3], which is convenient for power-flow and parameter studies but neglects all of the dynamics. 3) the dynamic phasor model, which has flexible accuracy and simulation time for various applications [1].