提出可用于大型电力系统暂态稳定分析的电网换相换流器-电压源换流器(line commutated converter -voltage source converter,LCC-VSC)混合直流电网机电暂态建模方法.首先,根据LCC、VSC换流器技术特点,建立混合直流电网的基本形态.其次,根据换流器基本数学模型和机电暂态仿真的特征,通过合理简化提出混合直流电网基本元件LCC、VSC、DC/DC 换流器的机电暂态建模方法.基于Dommel 算法,提出直流网络模型的求解方法.在 PSASP程序中实现了各元件的模块化设计,使用户可根据需要自由搭建仿真算例.最后,基于VSC-HVDC汇集分布式可再生能源和常规能源、LCC-HVDC 实现远距离大容量稳定输电的构想,设计四端混合直流电网的仿真算例,分析对比 3种不同工况下的运行特性.结果表明,所提LCC-VSC混合直流电网机电暂态模型准确、可靠,可用于大型电力系统暂态稳定性分析.
The paper aims to propose a method for modeling the electromechanical transient process of line commutated converter-voltage source converter (LCC-VSC) hybrid DC grid to be used for bulk power system transient stability analysis. Firstly, the basic structure of hybrid DC grid was constructed according to the different technology characteristics of LCC and VSC converters. Then, after analyzing electromechanical transient simulation features and performing rational simplification, the methods for modeling the electromechanical processes of LCC, VSC and DC/DC converter were proposed. Based on Dommel theory, the method for finding the electromechanical transient solution of DC grid was also presented. The modularization design of all elements are realized at PSASP, allowing users to freely build simulation cases. Finally, in view of the conception that renewable generation and conventional generation in energy bases were collected by VSC-HVDC and transmitted by long distance LCC-HVDC to load centers, a four-terminal hybrid DC grid simulation case was designed. The operation characteristics under three different operational modes were compared and analyzed. The simulation results show that the proposed LCC-VSC hybrid DC grid electromechanical transient model is accurate and reliable, which can be applied into bulk power system transient stability study.