混合多馈入交直流混联系统中长期电压分级协调控制

随着高压直流输电的发展，柔性直流与常规直流接入同一或电气距离较近交流母线，形成混合多馈入交直流混联系统。为充分发挥柔性直流功率解耦及快速调节特性，减小常规直流换相失败概率，并保持交直流混联系统电压安全稳定，文中提出了一种混合多馈入交直流混联系统中长期电压分级协调控制方法。首先,对混合多馈入交直流系统进行建模，并分析柔性直流不同控制方式下控制量对交流母线电压灵敏度的求解方法。其次,构建两级协调电压控制，系统级控制以交流系统最低节点电压轨迹偏差和控制成本最小为目标；换流站级控制以保证常规直流馈入母线电压和换相裕度为目标。根据发电机无功裕度设计不同的控制方案，针对常规高压直流输电熄弧角和有功功率，避免其发生控制冲突，设计两级协调策略。最后，仿真结果表明所提控制方法能够明显提高交直流混联系统的中长期电压稳定性。

Hierarchical Coordinated Medium- and Long-term Voltage Control in Hybrid Multi-infeed AC/DC System

With the development of high voltage direct current (HVDC) transmission, flexible DC and conventional DC are connected to the same bus or relatively close AC bus to form a hybrid multi-feed AC/DC system. In order to take full advantage of the characteristics of flexible DC power decoupling and rapid adjustment, reduce the probability of conventional DC commutation failure, and maintain the safety and stability of voltage for the hybrid AC/DC system, a hierarchical coordinated medium- and long-term voltage control method in the hybrid multi-infeed AC/DC system is proposed. Firstly, the hybrid multi-feed AC/DC system is modeled, and the solving method of the sensitivity of the control variable to the AC bus voltage in different flexible DC control modes is analyzed. Secondly, a two-level coordinated voltage control is constructed. The system-level control aims at the lowest node voltage trajectory deviation of the AC system and the minimum control cost. The station-level converter control aims at ensuring the conventional DC infeed bus voltage and commutation margin. Different control schemes are designed according to the reactive power margin of the generator, and the two-level coordination strategy is designed for control of the arc extinguishing angle and active power of conventional HVDC transmission to avoid control conflicts. Finally, the simulation results show that the proposed control method can significantly improve the medium- and long-term voltage stability of the hybrid AC/DC system.