特高压直流分层接入下交直流系统中长期电压稳定协调控制

与传统特高压直流单层接入方式相比,分层接入方式从电网结构上改善了交流系统对多馈入直流系统的接纳能力和电压支撑能力,在潮流分布与控制上更加灵活、合理。为了充分利用分层接入直流系统快速功率调节能力,避免或减少中长期电压失稳过程中切负荷造成的经济损失,文中提出一种特高压直流分层接入下的交直流系统中长期电压稳定协调控制方法。首先,基于直流分层接入系统准稳态模型,推导了不同直流控制方式下换流母线电压对分层接入直流逆变器传输功率的灵敏度解析表达式,并建立交直流系统电压轨迹预测模型。综合考虑直流电流和高、低端逆变器熄弧角的调制,基于预测轨迹构建协调电压控制的滚动优化模型,对直流分层注入功率和交流系统各电压控制手段进行协调控制。对山东电网规划系统的仿真分析表明,所提方法能够有效协调直流传输功率在交流电网中的分配,提高了系统电压稳定性并减少了切负荷损失。

Coordinated Control for Medium- and Long-term Voltage Stability of AC/DC Power Systems with Hierarchical Connection Mode of UHVDC System

Compared with the conventional single-layer connection mode of ultra-high voltage direct current (UHVDC) system, the hierarchical connection mode improves the ability of AC system in acceptance and provides voltage support for multi-infeed UHVDC systems from the aspect of grid structure, and it makes power flow distribution and control more flexible and reasonable. In order to make full use of the fast power adjustment capability of UHVDC systems in the hierarchical connection mode, and avoid or reduce the economic loss caused by the load shedding during the medium- and long-term voltage instability process, this paper proposes a coordinated control method for AC/DC power systems with hierarchical connection mode of UHVDC systems. Firstly, based on the quasi-steady model of UHVDC system in the hierarchical connection mode, this paper deduces the analytical expressions of the sensitivities of converter bus voltages with different control modes of UHVDC systems to the inverter transmission power of UHVDC systems in hierarchical connection mode. Secondly, the voltage trajectory prediction model of AC/DC power systems is established based on the derived sensitivities. Finally, considering modulations of the DC current and the extinguishing angles of high and low ends of the inverter, a receding horizon optimization model of coordinated voltage control is constructed based on the predicted trajectory. The hierarchical DC injection power and the voltage control means of AC system are coordinately controlled. The simulation analysis of the planning system of Shandong power grid shows that the proposed method can effectively coordinate the distribution of DC transmission power in AC power grid, which enhances the system voltage stability and reduces the load shedding loss.