调速系统间隙特性引发的水电站过渡过程极限环振荡特性

Characteristic of limit cycle oscillation induced by backlash in transient process of hydropower plant

水轮发电机组的动态调节稳定性对电力系统至关重要,尤其是在考虑非线性引起的潜在不稳定性的情况下。为了探究间隙非线性对水力发电系统动力学特性的影响,重点研究了水力发电机组间隙可能引起的极限环振荡现象及系统动态响应特性。首先构建了适合小波动过渡过程的水轮发电机组单机系统传递函数数学模型,通过将间隙特性表示成描述函数,进而建立了考虑间隙环节的非线性数学模型。采用描述函数法对系统动态特性进行理论分析,并结合使用MATLAB进行时域仿真验证,研究四个重要的水力-机械时间常数对系统间隙引发极限环的影响机制,量化给出各时间常数的相对作用大小。结果表明:机组惯性时间常数Ta和接力器响应时间常数Ty是极限环幅值最重要的两个影响因素;极限环频率则主要受水流惯性时间常数Tw和机组惯性时间常数Ta的影响;而弹性水击系数Te则是极限环特性的一个次要影响因素。各水力-机械时间常数对系统极限环特性具有不同的作用机制,该结论可加深对间隙非线性与水力发电系统中不同物理量间耦合作用的理解。

Dynamic regulation stability of hydropower units is crucial for power systems, especially under the consideration of potential instability caused by nonlinearities. In order to investigate the influence of backlash nonlinearity on the dynamics of hydropower generating systems(HGSs), the possible backlash-induced limit cycle oscillation and the dynamic response characteristics of the hydropower units are focused on. Firstly, a transfer function mathematical model of the single-unit HGS suitable for the transient process in small fluctuations is constructed, and then a nonlinear model considering the backlash represented by describing function is established. The theoretical analysis of the dynamics of HGS is carried out using the describing function method, and combined with time-domain simulations using MATLAB for verification, the influence mechanism of four important hydraulic-mechanical time constants on backlash-induced limit cycles is investigated, and the relative magnitude of the effect of each time constant is quantified. The results show that the rotor inertia time constant Ta and the servo time constant Ty are the two most important factors on the limit cycle amplitude;while the limit cycle frequency is mainly influenced by the water starting time constant Tw and the rotor inertia time constant Ta;and the time constant of water column elasticity Te is a secondary factor of both characteristics. The hydraulic-mechanical time constants have different mechanisms on the backlash-induced limit cycle characteristics, and the results can deepen the understanding of the coupling between backlash nonlinearity and different physical quantities in the HGSs.