适用于背靠背柔性直流输电的双环附加频率控制

Dual-loop supplementary frequency control for BTB-VSC-HVDC

通过背靠背柔性直流输电(BTB-VSC-HVDC)实现异步互联的2个交流系统之间缺乏相互支援的能力,使得各交流系统的频率响应特性下降。为了应对该问题,在理论分析柔性直流输电系统实施附加频率控制(SFC)的可行性的基础上,提出了一种适用于BTB-VSC-HVDC系统的双环SFC策略,使未受扰动端系统参与受扰动端系统的频率响应,实现两端交流系统的相互频率支撑。所提双环SFC策略中,通过在定有功功率控制环上增加频率-有功附加控制为受扰动系统提供频率支撑,改善频率响应的稳态特性;通过在定无功功率控制环上增加频率-无功附加控制以提供虚拟惯量支撑,改善频率响应的暂态特性。分别在含BTB-VSCHVDC的4机2区域系统和含有渝鄂BTB-VSC-HVDC的实际电网等值简化模型中进行仿真研究,仿真结果验证了所提双环SFC策略能有效地改善受扰动系统频率响应过程的暂态与稳态特性。

The two asynchronous AC systems interconnected by BTB-VSC-HVDC(Back-To-Back Voltage Source Converter based HVDC)cannot provide necessary frequency support for each other,which results in reduced frequency response characteristics of each AC system under faults. To address this issue,a dual-loop SFC(Supplementary Frequency Control)strategy for BTB-VSC-HVDC system is proposed with theoretical analysis of its feasibility. The proposed SFC,which includes both active and reactive power-loop(P-loop SFC and Q-loop SFC),ensures that the non-perturbed system can participate in the frequency response of the disturbed system and realizes mutual frequency support of the AC systems at both ends. The P-loop SFC can provide frequency support for the disturbed system during the primary frequency modulation,and hence improving the steady-state characteristics of the frequency response. The Q-loop SFC can provide virtual inertia support to improve the transient characteristics of the frequency response. Simulations are conducted in a 4-machine 2-area benchmark with BTB-VSC-HVDC and an equivalent simplified model of Southwest Power Grid with Hubei Power Grid connecting by Chongqing-Hubei BTB-VSC-HVDC. Results show that the proposed control strategy effectively improves the transient and steady-state characteristics of the frequency response of the perturbed system.