具有游隙非线性的大型风力机变桨距电液负载模拟系统的研究

Pitch control is one of the key technologies of improving the efficiency of mega-watt wind turbine and the quality of electric energy. Establishing an accurate load simulation system is the prerequisite of getting an optimal pitch control strategy. This project researchs electro-hydraulic load simulation system for the pitch control of mega-watt wind turbine. Aiming at system overshoot, loading precision reduced and even instability or self-oscillation which caused by clearance nonlinearity in the system, we will deeply reveal the formation mechanism and dynamic behavior of clearance in the system, and build the mathematical model of the electro-hydraulic load simulation system with clearance nonlinearity. A reasonable nonlinearity compensation approach is presented. Then the relations between clearance nonlinearity parameters and the system overshoot, the loading precision or the self-oscillation determines are obtained. In addition，considering the characteristics of the computer sampling control system, we will research how the sampling frequency and calculation delay reinforce the impact the clearance nonlinearity on the performance of system. At last electro-hydraulic load simulation system for the pitch control of mega-watt wind turbine will be developed. All of these provide the theoretical basis and the implementation for the design of control strategy of the mega-watt wind turbine pitch system.

变桨距控制是提高大型风力机发电效率和电能品质的关键技术之一。获得最佳变桨距控制策略的前提条件是建立准确的负载模拟系统。本项目以大型风力机变桨距电液负载模拟系统为研究对象。针对系统中游隙非线性导致的系统超调、加载精度降低，甚至诱发不稳定或自激振荡等问题，深入揭示系统中游隙的形成机理和动力学行为，建立具有游隙非线性的电液负载模拟系统的数学模型，提出合理的非线性补偿方法，确定游隙非线性参数与系统超调量、加载精度和自激振荡之间的关系。结合计算机采样控制系统的特点，研究采样频率和计算时延如何强化游隙非线性对系统性能的影响，研制大型风力机变桨距电液负载模拟系统，为大型风力机变桨距系统的控制策略设计提供理论依据和实现方法。

本项目以大型风力机变桨距电液负载模拟系统为研究对象，针对系统中游隙非线性导致的系统超调、加载精度降低，甚至诱发不稳定或自激振荡等问题，采用一个线性弹簧和线性阻尼形成的游隙子模型描述，建立了含有游隙非线性的电液负载模拟系统的数学模型，提出间隙的软、硬件补偿方法，研究了采样频率的选取对间隙非线性的强化作用；研究了釆用chirp（调频脉冲扫频）信号作为激励源进行系统频率特性测试时，测试数据在低信噪比（小于10dB）时的信号滤波问题；研究了反馈通道具有游隙非线性的电液控制系统的情况。研究结果表明：当间隙值从0.108 mm增大到0.811 mm时，系统稳态误差从0.2 mm增加到0.4 mm，超调量从20%增大到50%。当间隙值达到1 .10 mm左右时，系统出现极限环振荡现象，系统在越过间隙重新接触时，由于能量累积，产生较大冲击，其响应曲线相位产生明显的滞后，最大幅值处出现不光滑的尖点。采用双缸联动法的结构对间隙非线性进行补偿，其阶跃响应曲线没有超调量，能够有效补偿系统含游隙时的相位滞后现象；采用模糊自整定PID控制算法对间隙进行补偿，依据间隙的振－冲模型制定模糊推理规则，间隙为0. 8mm时使超调量从56. 7%降低至36. 9%，变桨冲击次数由4次降到2次；在间隙值为0.1mm时，当采样频率小于25 Hz会导致系统出现极限环振荡而失控；在位置系统启动与换向时，链间隙从0增大至0.8mm时，多余力矩峰值从18.2N.m上升至164.2N.m，当传动链间隙达到0.9mm时，加载系统出现极限环振荡；采用带通滤波和小波包变换对系统频率响应信号进行预处理，再由 FFT分析和处理获得系统频率特性曲线的方法，对于截止频率以下的频段，在信噪比低于10dB时，仍可以得到精度不低于1 dB的幅频特性曲线和不低于3°的相频特性曲线。