孤网下水轮机PID调速器抗速度饱和研究

水轮机调节系统稳定性对电网安全稳定运行具有重要意义,当电网容量较小或因事故处于孤网运行时,水轮机调节系统的作用显得尤为突出,但国内外多个水电站均出现了随负载扰动幅值增加系统调节品质迅速下降甚至发生频率发散振荡的现象。该文考虑调速器接力器速度限制等非线性因素,建立了水轮机调节系统仿真模型,在5%负载扰动下整定了调速器参数,当负载扰动幅值从5%增加至10%时衰减度从2.52%增加至8.84%,当负载扰动幅值增加至15%时系统调节过程发散,重现了孤网下水电机组随负载扰动幅值增加系统稳定性下降的现象,经过分析发现引起这一问题的主要原因是PID调速器的速度饱和,主要体现为接力器速度限制引起的比例项和积分项速度饱和。针对此问题,提出了1种抗速度饱和的微分优先型PID调节器,经改进后,负载扰动幅值分别为5%、10%以及15%时,衰减度分别为2.52%、2.19%以及1.79%,随负载扰动幅值增加系统稳定性无明显变化,表明改进调节器能够有效抑制调速器的速度饱和,大大降低了调节品质对负载扰动幅值的敏感性,并将该调节器应用在多布水电站的中,得到了满意的效果,该方法进一步完善了水轮机调速器的控制算法,具有重要的理论指导意义和工程应用价值。

Study on anti-speed saturation of PID governor for isolated hydraulic turbines

Abstract: The stability of hydraulic turbine control system plays an important role in the safety and stability of power grid, especially in the small capacity grid systems and the isolated grid systems. However, it repeatedly appears in some hydropower stations at home and abroad that with the load disturbance amplitude increasing, the system stability rapidly decreases and even the frequency divergent oscillation occurs in the process, such as Weituo power station, Manla power station and Majitang power station. In order to solve this problem, Weituo power station reduces the proportional gain and integral gain of governor, but this method will reduce the primary frequency regulation speed. Manla power station gradually reduces the guide vane opening limit and makes the unit output reduced to 0, and then gradually increases the unit output when the power grid is steady. This method can''t provide proper adjustment in the power grid disturbance, and the unit output decreases will inevitably cause new disturbance to the power grid. Majitang power station limits the variable quantity and the change rate of load, but this method can''t fully perform the adjustment ability of the unit, and the power grid has higher requirements to load. So, it doesn''t fundamentally solve the problem. In this paper, a simulation model of hydraulic turbine control system is built and the calculation method for the regulator is introduced which considers the nonlinear factors such as the limit of servomotor speed, the limit of servomotor displacement and the restraining measures for the limit of servomotor displacement. Decay rate of 5% rated load disturbance is 2.52%, the decay rate of 10% rated load disturbance is 8.84%, and in the 15% rated load disturbance process occurs divergent oscillation through the simulation. Those results reproduce the phenomena that with the load disturbance amplitude increasing, the system stability decreases. A step response of regulator is researched and the results show the PID (proportional, integral, derivative) regulator speed saturation is the main cause of this problem mainly reflected in the proportion and integral parts. That is the proportional output change rate is greater than the maximum of servomotor speed and the integral output is overmuch. Based on the results, an improved PID method is proposed which limits the rate of proportional output value, stops the integral change when proportional output is limited, and the differential output does not change considering the advance correction action of differential part. The step response results of improved PID regulator show the speed saturation is restrained. The decay rate of 5% rated load disturbance is 2.52%, the decay rate of 10% rated load disturbance is 2.19%, and the decay rate of 15% rated load disturbance is 1.79% by using the improved regulator. The simulation results show the improved regulator can effectively restrain the speed saturation of the regulator for ensuring the excellent regulation quality. Finally, an engineering example of load disturbance processing of Duobu power station is simulated. The system frequency divergent oscillation appears in 25% rated load disturbance process in isolated power grid by using original speed governor, but the decay rate of 25% rated load disturbance is 4.76% and the regulation quality is satisfactory by using improved governor. The conclusions obtained are as follows: 1) The main cause of the problem that with the load disturbance amplitude increasing, the system stability rapidly decreases and even the frequency divergent oscillation occurs in the process is regulator speed saturation, mainly reflected in the proportional and integral speed saturation. 2) The improved PID regulator can restrain the speed saturation, ensure the advance correction action of regulator and the high stability is proved by using simulation and engineering examples in the small capacity grid systems and the isolated grid systems. The method proposed in this paper improves the control algorithm of the hydraulic turbine regulator, and has important practical value in engineering application.