摘要
本文的研究目标是为大型并网风力发电机组建立一种以获取最大能量转换效率为目的的控制算法,该算法同时兼顾到控制过程良好的动态特性与稳定性,并将机组结构在风力作用下引起的动力学问题及其疲劳影响程度减到最低。
根据风力机的能量转换特性,风力机叶轮转速与风速必须保持在某个恒定的速比上,即风力机的转速必须跟随风速的变化,才能获得最大能量转换效率。要实现这一目标,必须解决两个问题,第一个问题是在作为原动力的风速随机变化的情况下,如何控制风力机转速使之能够跟随风速变化。第二个问题是如何实现发电机在变速运行时恒频输出。交-直-交全功率变频技术和交流励磁变速恒频技术的发展,为同步或异步发电机在变速运行时恒频输出提供了强有力的技术支撑,使大型并网运行的风力发电机组由定桨距恒速运行方式向变速恒频运行方式转变成为可能。但在解决风力发电机转速跟随风速变化的控制技术方面,尚有大量的理论与技术问题需要探索。
本文首先对风力机的基本工作原理及其能量转换特性进行详细的理论分析,对变速变桨风力发电机组各风速段的运行特性进行了实验研究与分析,提出了在低于额定风速时,通过对发电机转矩控制实现对最佳转速曲线跟踪的基本策略;提出了在高于额定风速时通过控制桨叶节距配合发电机转矩控制来稳定最大功率输出的策略;讨论了变速与变桨距两种控制策略的相互耦合关系;介绍了控制算法的实现过程及在该控制算法影响下风电机组主要部件包括叶轮、传动系统和塔架的各阶振动模态以及它们之间的相互影响力;在此基础上提出了转矩控制对传动系统扭转振动和桨距控制对塔架前后振动的影响力及控制方案;应用BLADED和MATLAB软件对主要控制环节进行设计及参数调整,并对完整的控制算法进行了仿真研究。
由于空气动力学的不确定性,常规PID控制方法所跟踪的理论最佳曲线有一定的局限性。本文在上述研究的基础上提出了基于模糊逻辑控制的智能方法:用模糊逻辑解决风力机叶轮转速在跟踪风速变化时的控制问题,并用类似的方法改善发电机在变速运行时的工作效率。通过仿真和模拟试验,证明了智能方法的可用性。
论文最后对基于观测器的风力机关键机械部件的故障监测进行了探讨,利用支持向量回归(SVR)模型辨识建立风力机整机及其关键机械部件的观测器。通过变桨距风力机半物理仿真试验表明,通过观测器可以判断出机组是否出现故障,并且由各个部件的观测器能进一步确定故障发生源。以完善控制系统功能,提高机组运行的可靠性。
The research objective of this paper is to find a control method which can obtain maximum energy conversion efficiency for a complicated non-linear time-varyingsystem------variable speed wind energy conversion system(WECs). According to theenergy conversion characteristic of WECs, the maximum wind energy conversion efficiency can be obtained if the ratio of rotor speed and wind speed is kept at a constant, namely the rotor speed of wind turbine can be continuously adapted to the wind speed. For achieving the aim, two problems must be resolved. The first problem is how to control rotor speed in order to track stochastic wind speed. The second one is how to realize constant frequency output of generator under variable speed operation. The development of the technique of A.C Excitation for variable speed constant frequency(VSCF) supplies strong technique support for constant frequency output of generator under variable speed operation, which make it is possible that operation manner of large-sized grid-connected WECs changes from constant pitch constant speed to VSCF. But, so far, theory analysis and experimental study about the control technique of rotor speed tracking wind speed haven't been carried out in china.
In this paper, basal operation principium and energy conversion characteristic of WECs are discussed in detail. Operation manner and control strategy of variable speed WECs is confirmed in theory, then a basal method for control rotational speed in order to track the wind turbine maximum power operation point are put forward. Research with PI control is implemented. The problem of wind speed measurement is resolved by using torque observer. The mathematic model of rotational speed control system is developed, and transfer function is deduced. Finally, correctness of the theory and validity of the method are validated through simulating and imitating.
But theoretical optimal curve is tracked using PID control method has high limitation because of uncertainty of aerodynamic behaviour and complexity of electricity-electron model for a VSCF WECs. For these reasons, intelligentmeans------fuzzy logic control is developed on the basis of the above research.Control problem of tracking maximum power operation point is resolved by fuzzy logic. By similar method generator efficiency under variable speed operation is also improved. Through testing of simulating and imitating, the correctness of WTGS variable speed operation control strategy is further testified, at the same time, superiority of intelligent means is also testified. Those pave the way for developing new type of control system for VSCF WECs.
Finally, the fault monitoring of key mechanical components of wind turbine based on observation is discussed, and the observers of the whole wind turbine and its key mechanical components through SVR model identification are established. The variable pitch semi-physical simulation experiments show that through observer the unit can be judged from failure, and failure source can be further comfirmed, so as to improve the control system and the reliability of unit operation.
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