Research On The Variable Pitch Based On Elecktro-hydraulic Proportional Control Technology For Wind Turbine

Energy and environment have been the chief issue facing humanity in the twenty-first century. Wind energy is being attached great importance to all over the world because of its advantages: renewable, non-polluting, low-cost etc. R&D of wind power system has been a hot and difficult point in energy technology field .Since wind energy has the characteristics of lower density, random, instability and so on, it is of great realistic significance to make a deep study in control technology of wind turbines especially in large scale sets. Compared with fix-pitch wind turbine, the variable-pitch wind turbine has the virtue: stable output power over rated power, high wind power coefficient, holding rated power at high wind speed, good starting and shut-off etc. In view of this, combining automation technology, this paper aims to design a variable pitch control system to meet the requirements of the large-scale wind turbine.Now, the variable pitch actuating mechanism popular at home and abroad for large scale wind turbine is divided into two types: One is the motor actuating mechanism, and the other is the hydraulic actuating mechanism. Hydraulic actuating mechanism promotes blades rotate through the hydraulic system and changes the pitch angle. At present, hydraulic actuating mechanism occupants main position with the advantages of fast frequency response, torque, easy layout, etc. Pitch-controlled system for big scale wind turbine set designed in this paper is driven by hydraulic and controlled by micro-computer, it's a typical electro-hydraulic control system. At present, electro-hydraulic switch control, electro-hydraulic proportional control and electro-hydraulic servo control are three kinds of electro-hydraulic control system in real application. And different system choose different component as its core. Proportional valve is a kind of hydraulic component between switch valve and servo valve. It's cheaper and more anti-polluting than servo valve. And its performances are as good as servo valve's except precision and response speed. Its static and dynamic characteristic can meet the needs of most of industrial control system. Compared with classic on-off valve, though proportional valve is more expensive, its good control performance made some compensation. So we use proportional valve in those occasion where high control qualities are needed in stead of switch valve. Besides, proportional valve has the function of hybrid control of flow, pressure and direction. All these factors make proportional valve control system has better control performance and more simple structure than classic switch valves.Considering the factors of synthesis performance requirement and cost and combining electronics technology, micro-computer technology and control technology, we choose the electro-hydraulic proportional valve system as the working device of pitch-controlled system for big scale wind turbine set.Firstly, This paper analyses the dynamic characteristics of wind turbine in accordance with the aerodynamic principle, and formulates the operating principle of wind generator and the theoretical source of variable pitch. Then, we develop a single chip microcomputer as bottom-computer to design the system controller. The system accepts the pitch signal from the main system controller and the feedback signal from the position sensor in the fuel tank. The controller outputs the control signal to control the electro-hydraulic proportional direction valve, Under the function of the valve controller, the voltage signal makes Electro- hydraulic proportional direction valve export a certain hydraulic oil , in order to control the position of the fuel tank and the pitch angle and finish the process of variable pitch. While designing the hardware electric circuit, this paper adopts the dependable and mature electric circuit as much as possible. The controller chooses 8 bit single chip AT89C52, AT89C52 do not need to expand program memorizer and data memorizer. A/D converter chooses ADC0809, D/A converter chooses DAC0832. We highlights the proportional controller, including the slope signal generator, the PID adjuster, power amplifier etc. For making the system have the good control result, this paper build up the mathematics model of the system each part, beg a square distance of mathematics and research the control algorithm. Finally, we experiment with the proportional controller, the experimental result shows that the controller has good linearity of the output, the output current range can be good to meet system requirements.