突发不对称大扰动下LCC–HVDC直流输电系统实时单端暂态等值建模研究

LCC–HVDC高压直流输电在交直流混联电网中承担着端对端大容量输电的重要职能，其暂态响应直接影响着混联电网的整体特性。由于无法给出高阶非线性时变微分方程的解析解，目前分析直流系统只能采用电磁暂态数值扫描，或者对关键电气量做出低阶近似假设，求解动态相量等值模型。这种低阶近似及采用的频域算法，使得对故障暂态的仿真精度和速度都无法满足要求；特别是现有模型为双端电压受控电流源模型，无法与交流系统的单端等值模型相匹配。因此，本项目提出了逆变侧动态相量精细模型+整流侧准稳态模型相融合的单端实时等值方案；逆变侧以时域计算代替频域分析，提出大扰动下开关函数时域解析表达及修正方法，保证换相失败暂态特征仿真的高精度、实时性；整流侧保证外特性准确，理清各环节的等值误差及传递过程，提出抑制方法；最终实现不对称大扰动下直流系统的实时单端暂态等值建模，满足交直流混联电网控保系统整定校核、稳定分析等在线应用需求。

LCC-HVDC plays the important function of point-to-point power transmission in AC-DC hybrid power grid, and its transient response directly affects the overall characteristics of the hybrid power grid. Because the analytical solution of high-order nonlinear time-varying differential equation cannot be given, at present, only electromagnetic transient numerical scanning can be used to analyze the LCC-HVDC system, or the dynamic phasor equivalent model is used on the assumption of low-order approximation to the key electrical quantities. This low-order approximation and used frequency-domain calculation make the simulation accuracy and speed of the fault transient unable to meet the requirements; especially the existing LCC-HVDC transmission models are two terminal voltage controlled current source models, which cannot match the widely applied single terminal equivalent model in AC power grid. In order to solve this problem, a single terminal real-time equivalent scheme is proposed in this application which combines the improved dynamic phasor model at the inverter side with the quasi steady model at the rectifier side; the frequency-domain analysis is replaced with the time-domain calculation at the inverter side, the time-domain analytical expression and correction method of the switch function under the large disturbance will be put forward, so as to ensure the high accuracy and real-time performance of the transient characteristics simulation of the commutation failure; the external characteristics will be guaranteed in the simulation at the rectifier side with full consideration of the equivalent error suppression. Finally, the real-time single terminal transient equivalent modeling of LCC-HVDC system under asymmetric large disturbance is realized to meet the application requirements of online verification, analysis for AC-DC hybrid power grid control and protection system.