特高压混合直流输电系统中串联换流器的电压分配策略

Voltage Distribution Strategy of Series Converters in Hybrid UHVDC Power Transmission System

在常规直流(line commutated converter-high voltage direct current,LCC-HVDC)改造升级中,将受端换流站改造成柔性换流站是一种安全可行的技术方案。基于±800 kV特高压直流工程,将受端的双低端换流器置换为双柔性换流器(voltage source converter,VSC),形成特高压混合直流输电拓扑。针对LCC和VSC换流器串联时的电压比例问题,提出一种基于受端换流站无功配置的高低端换流器电压分配策略。该策略考虑VSC换流站和交流滤波器共同提供无功功率支撑的方案,通过建立VSC额定容量与LCC额定功率的函数关系式,优化得到LCC和VSC换流器的电压分配结果。基于电磁暂态模型,设计了系统的协调控制策略,并与改造前常规特高压直流系统的暂态响应特性进行了对比。结果表明柔性化改造方案能够提升特高压直流系统的换相失败抵御能力,并且电压分配策略下的系统具备良好的运行特性。

In the upgrading of line commutated converter-high voltage direct current(LCC-HVDC)projects,the flexible reconstruction scheme of receiving conventional converter station is safe and feasible.Based on±800 kV UHVDC project,a series hybrid UHVDC system is formed by replacing the double low-end converters on the inverter side with double VSC converters.In this paper,a voltage distribution strategy for high-end and low-end converters considering reactive power compensation is proposed to solve the voltage allocation problem of series converters in hybrid UHVDC system.This strategy considers the scheme that VSC and AC filter provide reactive power together.By establishing the functional relationship between rated capacity of VSC and rated power of LCC,the voltage distribution results of LCC and VSC are determined after optimization.Based on the electromagnetic transient model,coordinated control strategy is designed and compared with the transient response characteristics of conventional UHVDC system before reconstruction.The results show that the flexible transformation scheme improves the resistance ability to commutation failures of UHVDC system,and UHVDC system under voltage allocation strategy performs good operation characteristics.