弱交流/多端柔性直流混联的群岛电网有功/无功联合优化

Joint optimization of active/reactive power for hybrid island power grids with weak AC system and VSC-MTDC

传统群岛交流电网通常较为薄弱,面临着海底电缆充电功率较大、系统状态接近稳定极限、设备投切频繁且使用寿命较短等多项挑战。多端柔性直流输电(VSC-MTDC)技术较适用于群岛供电场景,弱交流/多端柔性直流混联逐步成为群岛供电的新模式。在群岛弱交流电网中,有功和无功功率的传输特性相互关联,电压幅值差不只与无功传送有关,相角差也不仅与有功传送相关。提出一种有功/无功联合优化策略,借助电压源换流器(VSC)调节有功功率和无功功率输出的能力,实现VSC-MTDC的可控输出与并列运行交流电网中措施之间的优化协调,建立了考虑网络损耗、设备投切成本和系统稳定裕度等的多目标优化模型,并采用遗传算法进行求解。结合群岛电网的实际运行需求,依托浙江舟山±200kV五端柔性直流示范工程的仿真案例,验证所提优化策略的有效性,并通过经济和稳定指标的比较,证实了有功/无功联合优化优于单一的优化策略。

The traditional island AC grids are usually weak and faced with some inherent challenges such as the large reactive power imposed by AC submarine cables,the small stability margin,the short device service-life due to frequent switching,and so on. As VSC-MTDC(Voltage Source Converter based MultiTerminal Direct Current) system fulfills the supply demands of islands in a better way,the AC/VSC-MTDC hybrid power grid tends to be the popular choice in island. Since the transmission characteristics of active and reactive power in the weak AC island power grids correlating with each other,the voltage amplitude difference is not only relevant to reactive power,while the phase angle difference is not only related to real power. An active/reactive power joint optimization strategy is proposed. It controls the VSC outputs to coordinate the controlled outputs from VSC-MTDC with the measures of AC networks in parallel. A multiobjective optimization model solvable by GA(Genetic Algorithm) is established,which considers the system loss,the switching costs of devices and the stability margin. In line with the concerned issues in island power grids,the proposed optimization strategy is validated by the simulation case of ±200 kV five-terminal flexible DC demonstration project in Zhoushan,Zhejiang. The results confirm the advantages of the joint optimization over the sole strategy based on either active or reactive power.