用于改善交流系统暂态稳定性的VSC-HVDC交流电压–频率协调控制策略

VSC-HVDC AC Voltage-Frequency Coordination Control Strategy for Improving AC System Transient Stability

小水电群富集的地区电网与主网的交流联络较弱时,容易引起系统低频振荡问题。用电压源换流器型直流输电系统(voltage source converter based high voltage direct current transmission,VSC-HVDC)异步联接小水电群电网与主网的方式可消除小水电群引起的低频振荡问题。但小水电群电网属于弱交流系统,此场景下VSC-HVDC有必要参与弱交流系统的电压和频率控制。该文设计了一种改善交流系统暂态稳定性的VSC-HVDC交流电压–频率协调控制策略,该策略的首要控制目标是保证VSC-HVDC设备的安全,第二控制目标是提高交流系统的电压稳定性,第三控制目标是提高交流系统的频率稳定性。设计的协调控制器结构能够确保暂态过程中多个控制目标按照优先级顺序实现。以云南电网的实例分析表明:VSC-HVDC异步联网方案能够有效提高系统的小扰动稳定性水平;VSC-HVDC交流电压–频率协调控制策略能够改善交流系统的暂态稳定性。

Low frequency oscillation may occur when the connection between regional grids containing many small hydropower stations and the backbone grid is weak. Connecting small hydropower girds to the backbone gird asynchronously by voltage source converter based high voltage direct current transmission （VSC-HVDC） can eliminate the low frequency oscillation. However, the small hydropower grids are weak AC systems, and it is necessary for VSC-HVDCs to participate in controlling the AC voltage and the frequency of the weak systems. A VSC-HVDC AC voltage-frequency coordination control strategy for improving AC system transient stability was proposed. In the strategy, the first objective is to ensure the safety of the VSC-HVDC equipment, the second objective is to improve the AC voltage stability, and the third objective is to improve the frequency stability. The designed controller structure can guarantee that the objectives are implemented in order of priority. A practical case analysis of Yunnan grid demonstrated that the VSC-HVDC connection scheme can improve the small-signal stability of the whole system and the proposed strategy can enhance the transient stability of the weak AC system.