Research On Model And Control Strategy Of Large Scale Pitch Regulated Direct-driven Wind Turbines

Direct-driven permanent-magnet synchronous generator (PMSG) wind turbines have higher reliability since the high speed rotating parts have been removed. Thus the research of direct-driven PMSG wind turbines has become a hotspot and has obtained fast development for the past few years. However, as the top wind power producing country in the world, China has not complete ability to research, design and develop large scale direct-driven PMSG wind turbines; some design and operation key technologies still depend on import. It is necessary to carry out systematic and deep study on direct-driven PMSG wind turbines. In this thesis, some key theories and technologies about direct-driven PMSG wind turbines, such as system model and pitch control, are studied, which is helpful for optimization design and control for large scale direct-direct PMSG wind turbines. The main research contents and achievements are as follows.The aerodynamic analysis theory and method are studied and an aerodynamic analysis model is constructed based on the blade element momentum (BEM) theory and dynamic stall (DS) model. In this model, the blade element momentum theory is employed as the aerodynamic analysis theory and some corrections, such as Prandtl and Buhl models, are carried out. Considering the influence of dynamic stall on the aerodynamic performance of airfoils, a new modified DS semiempirical model is proposed based on the B-L semiempirical dynamic stall model. Then, by combing BEM modified theory with DS semiempirical model, an aerodynamic analysis model and method for large scale wind turbines is constructed. The researches on loads calculation and analysis are carried out and loads calculation models including aerodynamic, centrifugal and gravity loads are established. A set of coordinate systems is established to describe large scale wind turbines and the coordinate transformation matrixes are deduced. Based on the above aerodynamic theories, the calculation model of aerodynamic loads for large scale wind turbines is constructed. Then the centrifugal and gravity loads calculation models for large scale wind turbines are proposed; the expressions on edgewise moment, flapwise moment, pitch moment, edgewise force and flapwise force, etc., are deduced in detail.The main energy flow system of large scale direct-driven wind turbines is researched; a new modelling method of main energy flow system is presented. The wind-rotor back propagation neural network (BPNN) is proposed which consists of a four-layer network and is used to describe the wind-rotor aerodynamic characteristics. Then, the coupling dynamic model of the wind-rotor and PMSG, AC-DC-AC converter model is established, respectively; the control strategies for the generator-side converter and grid-side converter are constructed, too. The mechanical model, electric model and control model are integrated into the whole simulation model, and the numerical simulation is carried out.Model and control of the individual pitch drive system of large scale wind turbines are studied. The nonlinear dynamical equations, including electromagnetic torque equation, electromechanical motion equation, drive shaft and planetary gear motion equations are built. A servo control structure is presented, in which rotor flux field-oriented vector control and three close-loop servo control with current, speed and position feedback are employed. Then, the response characteristics and servo control properties of the individual pitch drive system are analyzed.The pitch control for large scale directly-driven wind turbines with permanent magnet synchronous generator is studied. By analysing the pivotal pitch control targets, power and fatigue loads are selected as the control targets and the corresponding expressions are deduced. In succession, the power control strategy based on the collective pitch control (CPC) is constructed; the power and loads joint control strategy are constructed which is based on the individual pitch control (IPC), too. Then the system simulation model is established in which the aforementioned aerodynamics, loads, energy flow and pitch drive models are included. Based on the simulation model the pitch control simulation is carried out and the pitch control dynamic characteristics of different control strategies are obtained.