基于下垂控制的单台换流器-无穷大系统数学模型及直流系统稳定的解析条件

Mathematical model and analytical stabilizing condition of a droop-based single converter-infinite DC system

基于功率-电压下垂控制的换流器因其较好的控制灵活性在多端直流输电系统中的应用日益广泛,同时也为直流电网稳定运行带来了新的挑战。利用单输入单输出分析法研究了单台并网换流器直流系统的稳定性问题。首先,建立系统扰动后的直流电压变化量和直流电流变化量间的传递函数。其次,利用Routh判据得到不同控制模式下系统的稳定判据。然后,定义了一个评价系统稳定性的关键指标—直流功率传输极限。最后,数值仿真结果验证了稳定性分析的准确性,以及所提稳定判据的正确性。

The droop-based converter plays an important role in a multi-terminal DC(MTDC) system because of its control flexibility. However, this imposes a great challenge on the stability of the DC grid. The main purpose of the paper is to examine the DC side stability of a single grid-connected VSC with the single input single output(SISO) method. The transfer function between the small perturbation of DC-link voltage and DC current at the end of transmission line is first constructed. Based on the SISO model, the stability criteria for a single VSC converter in different control modes is proposed by using the classical Routh judgement. A critical operation index, namely the DC power transfer limit, is defined to assess system stability. Finally, numerical simulation results validate the accuracy of the proposed stability analysis and the criteria for the droop-based converter.