混合级联UHVDC系统换相失败抑制分析

Analysis of Commutation Failure Mitigation in Hybrid-cascaded UHVDC System

换相失败是基于电网换相换流器的特高压直流输电系统中最常见的故障类型之一。近年来新投运的混合级联特高压直流输电系统的逆变侧仍包含电网换相换流器,因此换相失败无法避免。首先,在分析电网换相换流器触发调节过程的基础上,明确了换相失败控制的投入时刻是影响换相失败抑制效果的关键因素;进一步地,结合白鹤滩—江苏混合级联特高压直流输电受端的结构特点和接入交流系统方式,分析了混合级联拓扑下的换相失败抑制新思路;最后,提出可充分利用逆变侧电压观测点增加、模块化多电平变换器所连接母线的电压响应更为灵敏的特点,来加快换相失败控制的投入速度,提升系统的换相失败抑制性能。基于PSCAD/EMTDC仿真平台验证了该分析的正确性。

Commutation failure is one of the most common types of failures in line commutated converter based ultra-high voltage direct current(LCC-UHVDC)system.In recent years,the inverter side of the newly installed hybrid-cascaded UHVDC system still contains LCC,so the commutation failure is unavoidable.Based on the analysis of trigger regulation process of LCC,it is clear that the input time of commutation failure control is the key factor affecting the effect of commutation failure suppression.Further,according to the structure characteristics of receiving end of Baihetan-Jiangsu hybrid-cascaded UHVDC and the access mode of AC system,a new idea of commutating failure suppression under hybrid-cascaded topology is analyzed.It is proposed to fully utilize the increased voltage observation points of inverter,and enhance the sensitivity of bus voltage response connected to modular multilevel converter(MMC),which can accelerate the startup speed of commutation failure control and the suppression performance of commutation failure.The correctness of analysis is verified by PSCAD/EMTDC simulation platform.