Research On The Technologies For Reliable Operation Of Island Small And Medium Scale Stand-alone Wind Turbine Generation System

Wind energy generation, which is an effective way to provide electric energy for theresidents live in the island, has received more and more attention. However, the relativelycomplex marine environments bring higher requirements for the safety and reliability of awind turbine generation system, in the aspects of both the structure design and the controltechnology. Most wind turbine generation systems applied on the islands and coastal areassimply adopt the structures and technologies of inland wind turbines with a process of surfaceanti-corrosion coating, while it is impossible to fundamentally solve the wind turbine’senvironmental adaptability. It is very common for these machines with the problems of shortlifetime and low reliability because of the environmental factors being overlooked, such aswet, salt spray, lightning, gusts, and so on. Especially, the likelihood of strong typhoons in theeastern continents makes most existing wind turbines unsuitable.This thesis, which depends on the project of “The key technology of a standalone windturbine generation system with high reliability applied on the islands and coastal areas”,focuses on the reliability of the operation and control system and the structural design ofsmall and medium scale stand-alone wind turbine generation system. Based on the structureand model of the wind turbine generation system, this thesis advances the correspondingcontrol strategies according to different operation areas of the wind turbine, and makes deepstudies on the optimal control below the rated wind speed and on the overspeed protectionand power regulation above the rated wind speed. Combined with the specific control targetsof the stand-alone wind turbine, the thesis designs intelligent controller and analyzes the mainparts of the controller. On the aspect of the structural reliability, this thesis makes specificdesigns of the stand-alone wind turbine which are suitable for developing the wind energy ofislands and coastal areas. In general, this thesis mainly investigates the following contents:Firstly, this thesis introduces the backgrounds and significances of the study, summarizesthe status of development and application of small and medium scale stand-alone windturbine generation systems at home and abroad, and discusses the status of the structuraldesigns and control technologies of the stand-alone wind turbines. Then, the main researchcontents of this thesis are introduced.Secondly, this thesis systematically analyzes the main structures of small and mediumscale horizontal-axis fixed-pitch wind turbine generation system, and establishes the wholemathematic and simulated model. Through analyzing the mathematic model, this thesisdeeply investigates the operating characteristics including the power characteristics and the torque characteristics of the variable-speed fixed-pitch wind turbine and the influence ofdifferent solidity and yaw angle of the wind turbine on the operating characteristics. Bydiscussing the matched problems about the turbine and the generator, this thesis indicates thatthe matched characteristics between the turbine and the generator have a significant effect onthe turbine’s efficience and operational reliability. Based on these studies, it is helpful for usto comprehensively and deeply comprehend the constructures and control principles of smalland medium scale horizontal-axis fixed-pitch wind turbine generation system, which establishtheoretical foundations for the following researches.Thirdly, this thesis discusses the basic control structures of the variable-speed fixed-pitchwind turbine. According to the different working status of the wind turbine, the operatingregion is divided to three small regions. Based on these regions, this thesis provides basiccontrol principles and analyzes the control strategies. This thesis makes comparative studieson several common algorithms that could achieve maxmuim power point tracking control ofvariable-speed wind turbine, introduces the optimal state feedback control algorithm to thecontrol of small and medium scale stand-alone wind tuebine, and advances LQG (LinearQuadratic Gaussian) optimal control strategy based on effective wind speed estimation tominimize the wind turbine’s fatigue loads and power fluctuation because of stochastic windso as to realize the multi-parameters optimal control of variable-speed fixed-pitch windturbine. To compensate for the shortage of LQG controller that results in the instability ofcontrol performance because of the less stability operation margin, this thesis introduces thecontrol method of LTR (Loop Transfer Recover) to the LQG optimal control. The simulatedresults indicate that the method not only realizes the control objects, but also dramaticallyimproves the control system’s robustness and stability in spite of the stochzstic disturbances.Fourthly, this thesis investigates the overspeed protection of the stand-alone wind turbine.This thesis analyzes the stall control characteristics of variable-speed fixed-speed windturbine, studies the furling system that achieves the overspeed protection of small andmedium scale wind turbine generation system, and establishes the dynamical equations of thetail fin in the noninertial system. Combined with the structural characteristics of wind turbinekeeping in line with wind automatically by the tail fin, this thesis introduces theelectric-driven control technology to the furling system of middle and small wind turbine, andadvances the control strategy of the wind turbine’s overspeed protection and power regulationbased on auto-furling. Meanwhile, this thesis establishes the simple mathematic model of theelectric-driven linear actuator that achieves auto-furling and the simulation model of thewhole wind turbine generation system in the software of Matlab/Simulink. By simulatedstudy combined with corresponding power control strategy, the auto-furling system achievesthe overspeed protection and power regulation of middle and small wind turbine generationsystem. Fifthly, this thesis analyzes and designs the intelligent controller of small and mediumscale stand-alone wind turbine generation syatem, including the main control circuit, thepower parameters measuring circuit, the main circuit of power, the data acquisition andremote monitoring, and the yaw controller. The controller adopts the ARM microprocessor asmain controller, and designs the software based on the operation system of Embed Linux, sothat it could adequately make use of the ARM’s strong expansibility and the Linux’s highstability and nice portability. Meanwhile, combined with the specific control targets, thisthesis designs corresponding control procedures of software.Finally, at the aspect of structural reliability of the island stand-alone wind turbine, wedesigns the seldom rotor with four blades that are suitable for the low wind speed applicationand the metals and nonmetals laminated hub with high fatigue strength. The blades adopt thestall airfoil. We design a direct-drive permanent-magnetic synchronous generator with lowstarted torque and high overloaded ability to improve the efficiency and reliability. Becausethe bolstering bearings of the wind turbine applied in the island are a little fragile, we design agroup of axial and radial non-metallic bearings with high strength. In order to ensure theoverspeed protection of the wind turbine in the severe marine environments, we adopt lightaerodynamic tail vane with electric-driven furling function. The prototype wind turbinegeneration system was applied in the realistic island environments. After monitoring theoperation status for a long time and analyzing the collected data, the results indicate that theperformances of the turbine are very stable and reliable.