电网故障下多馈入直流输电系统相继换相失败机理与特性

在多馈入的电网换相换流器型高压直流(LCC-HVDC)输电系统中,交直流系统以及不同LCC-HVDC之间的复杂耦合作用造成换相失败形态产生变化,使得LCC-HVDC的控制保护系统面临挑战.目前,由电网故障直接引发的多回LCC-HVDC同时换相失败现象受到关注,但是换相失败过程中LCC-HVDC系统之间的相互影响却被忽视.LCC-HVDC换相失败后的状态和输出特性急剧变化,通过交流系统的耦合势必对相邻LCC-HVDC产生直接的影响.为此,文中研究了LCC-HVDC换相失败对相邻健全LCC-HVDC的影响,分析了受端弱电网故障下多馈入LCC-HVDC系统中相继换相失败的产生机理和换相失败期间控制系统作用下逆变站的动态无功特性;推导了计及控制系统响应的逆变站无功功率表达式,解析了相邻LCC-HVDC无功交换特性,分析了相继换相失败的特征和影响因素.最后,通过标准模型验证了理论分析的正确性.

Mechanism and Characteristics of Successive Commutation Failure of Multi-infeed HVDC Transmission System Under Power Grid Fault

In the multi-infeed line commutated converter based high-voltage direct current (LCC-HVDC) transmission system, the complex coupling between AC/DC systems and different LCC-HVDC causes the change of commutation failure modes, which makes the control and protection system of LCC-HVDC face challenges. At present, commutation failures of multi-circuit LCC-HVDC directly caused by power grid faults have attracted much attention, but the interaction between LCC-HVDC in the process of commutation failure has been ignored. The state and output characteristics of LCC-HVDC change sharply after commutation failure. Through the coupling of AC system, it is bound to have a direct impact on adjacent LCC-HVDC. Therefore, this paper studies the influence of LCC-HVDC commutation failure on adjacent normal LCC-HVDC, analyzes the generation mechanism of successive commutation failure in multi-infeed LCC-HVDC system under weak power grid fault at the receiving end, and the dynamic reactive power characteristics of inverter stations under the operation of control system during commutation failure. The reactive power expression of inverter station considering the response of control system is deduced; the reactive power exchange characteristics of adjacent LCC-HVDC are analyzed; and the characteristics and influencing factors of successive commutation failure are analyzed. Finally, the correctness of the theoretical analysis is verified through the standard model.