海上风电接入多端柔性直流输电系统中换流站退出运行时直流功率再分配策略

Optimized Power Redistribution of VSC-MTDC Transmissions With Offshore Wind Farms Integrated After Onshore Converter Outage

大容量海上风电场通过多端柔性直流输电系统接入主网是未来极具前景的并网方式。研究了岸上换流站故障退出运行后,基于电压源型换流器的多端直流输电系统(voltage source converter based multi-terminal HVDC,VSC-MTDC)直流功率的优化再分配策略。岸上健全换流站间的功率再分配可分为自消纳情景与无法自消纳情景。首先,针对自消纳情景,以减小潮流重分配对交流电网频率稳定影响为优化目标,合理地重新配置各受端换流站的控制器,使转移功率完全被故障端换流站所在交流电网消纳;其次,针对无法自消纳情景,保持故障端换流站所在交流电网内的其余健全换流站满发,并利用源侧风电场的桨距角控制以及虚拟惯量控制减小换流站退出功率冲击对岸上电网频率稳定影响。最后,在PSCAD/EMTDC中搭建改造的39节点系统,所设计的直流功率再分配策略对系统频率稳定提升得到了验证。

Voltage source converter based multi-terminal HVDC（VSC-MTDC） transmission is prospective to integrate gigawatt offshore wind energy. This paper presents an optimized power redistribution method in VSC-MTDC system after onshore converter outage. Generally, there exist two scenarios of power redistribution after converter outage： self-redistribution and non-self-redistribution. For self-redistribution scenario, transferred power is redistributed among healthy onshore converters within disturbed AC system with better frequency performance as optimization objective. Outer controllers of the onshore converters are reset according to new DC power flow calculation. For non-self-redistribution scenario, an offshore wind farm control strategy combined with emulating inertia control and auxiliary pitch angle control is proposed to alleviate adverse effect of transferred surplus power on frequency stability of asynchronous grids. Simulation verifications are carried out in a modified New England 39-bus system in PSCAD/EMTDC.