直流调制策略改善交直流混联系统的频率稳定性研究

Improving Frequency Stability of Parallel AC-DC Hybrid Systems by Power Modulation Strategy of HVDC Link

为了抑制交直流混联系统的负荷突变而引起交流系统的频率振荡,提出变结构的直流功率调制和快速汽门最优控制的协调控制策略。首先建立交直流系统的简化模型,通过交叠分解的方法将模型分解为2个独立的子系统,对子系统采用直流功率的变结构控制,切换函数采用最优控制设计。该控制策略实现简单,能显著减少频率偏差的首摆峰值,但稳态误差较大。因此采用发电机的快速汽门最优控制来协调控制频率,采用线性最优理论设计快速汽门综合控制器。对采用这2种控制器的输电系统,在负荷发生扰动的情况下进行仿真。结果表明,变结构的直流调制在扰动发生的初期能显著抑制频率振荡,汽轮发电机的调速器与直流功率调制器相结合,减少了稳态误差。

In order to suppress frequency oscillatory when an interconnected AC and DC system is subjected to a load shedding in one area of AC system, the coordination of variable structure control of DC power modulation and turbine-generator steam valve optimization was presented. At first, the simplified model of AC/DC hybrid system was established which was divided into two independent subsystem by adopting overlap decomposition, and then put forward a linear variable structure control of DC power modulation, switching function of variable structure control was establishedby applying optimal control theory. Although the controller decreases the peak of the first swing significantly and is easy to realize, the steady state error is large. To solve the problem, the concept of coordinated control of DC power modulation and fast steam valve optimal control of governor was established. The steam valve controller was studied with linear optimal control theory. Simulation experiments were conducted for the purpose of applying two kinds of control mode under the condition of load disturbance. The result shows the DC power modulation can affect frequency stability at the initial stage of disturbance, it can coordinate with the fast steam valve governor controller to suppress the frequency deviation of steady state error.