Research On Key Technologies For Megawatt Level Vertical-Axis Wind Turbine

The contradiction between keeping sustained and rapid economic development and maintenance of ecological balance and protecting environment is an urgent issue faced by all over the world. In order to protect our environmental resources on which we survived, China and the international community, particularly developed countries, have made their important commitments for reducing carbon emissions and improving energy efficiency. In the future industrial production, they will use clean energy to replace traditional energy, renewable energy technologies and new energy technologies to replace fossil fuels. Compared with traditional energy, utilization technology of wind energy is maturing. As a result, the superiority of wind energy is obvious in the construction cycle and the way of investment. Besides, wind energy has better social and economic benefits.There is a big disparity between China and developed countries in the research level of wind power theory and engineering applications. Under the current condition of the technology in our country, the cost of wind power, grid electricity quality and the level of equipment manufacturing and control technologies are all at a disadvantage. Many problems of wind power are waiting for being tackled, for example, urgent domestic demand for wind power product, weak research foundation of wind electricity technology, large scale and form diversification of electrical machinery. Various reasons urge our country to degenerate gradually into the trash product dumping market of international wind power manufactory giants and the new product experimental plot. Therefore, doing deep research on every aspect of wind power technology has vital practical significance for holding lasting development and efficient use of wind power, forming independent and innovative design, and obtaining absolute intellectual property rights of wind power products.Wind power technology is a comprehensive and systematic project involving aerodynamics, computational fluid dynamics, automatic control, electrical science and many other subjects. Nowadays, with the applications of new technologies and materials, the breakthrough of the traditional forms of wind turbine has gradually become the research focus in this field. Wind turbine is a complex multi-variable nonlinear hybrid system. and wind power has the qualities of variability and instability with time. Therefore. research on the key technologies of wind turbine with new form is the sticking point for the solution of security of generator operation and economical high efficiency.The current studv focuses the on key technologies for megawatt level vertical-axis wind turbine. The major research is summarized as the following points:1). Based on Betz theory, the momentum theory and other fundamental theories of wind turbine modeling, and the aerodynamic characteristics of low-speed airfoil, the current study established the non-linear theoretical model for wind wheel of vertical axis wind turbine with the effect of the Reynolds number and the correct value of calculated attack angle in aerodynamic characteristics of airfoil being considered. On the basis of this model, numerical analyses have been done on H-type vertical axis wind turbine, 34-meter diameter vertical axis wind turbine in U.S. Sandia National Laboratories and 40-meters vertical axis wind turbine in Zhejiang University. The wind energy utilization coefficient of the wind wheel, output torque of wind wheel, the blade aerodynamic loads and other major issues have been discussed. Besides, the current thesis has analyzed the influence of blade of different types on aerodynamics performance and output torque of wind wheel under the condition of different wind speeds and locations. As a result, the designed model of wind turbine has been further optimized.2). According to the analysis of vertical axis wind turbine model, the thesis summarized the plan solution method for calculation attack angle of all airfoils:"Vector-Circle" method. The method refers to when the remote wind speed vector is constant, for the blades in circular motion in space, we can draw a circle with the radius which is numerically equal to the value of tangential velocity of one blade and establish the system of rectangular coordinated with remote speed vector as one axis. In the model of "Vector-Circle", the vector of blade's location lags behind vector of blade's tangential velocity forπ/2. The vector of remote wind speed v, vector of blade's tangential velocity u and vector of relative wind speed w form triangular. In this vector triangle the angle of attack a is an acute angle between u and w or its supplementary angle. The thesis has completed the derivation of "vector-Circle" which is an innovative research. It has a guiding role in the further research work of mathematical models for wind turbine.3). According to megawatt-level electromagnetic design of permanent magnet synchronous generators and its geometrical characteristics, the current study established the model of equivalent thermal circuit diagram in generator based on the lumped parameter. This model has generaliability for the same type of generators with rotor in structure, which provides a theoretical basis for the calculation of temperature rising of generators.4). The current study composed the heat exchange equation of in generators based on the heat exchange law. Through adopting finite difference to approximately replace differential and using the results of calculation for equivalent thermal circuit diagram to determine the thermal contact within generator, the current study converted the partial differentia] equations and boundary conditions in the calculated temperature field to become applicable to the differential equations of various nodes in calculated region and on the calculated boundary. Based on method of iteration for solving equations, the temperature distribution of calculated field in generator could be obtained. The method of temperature rising calculation in generator provides a theoretical guidance for motor design and testing.5). According to the characteristics of permanent magnet synchronous generator, the thesis did a research on grid control strategies of permanent magnetism synchronization generator. The article also proposed double pulse-width modulation rectifier and double voltage source rectifier for wind turbine generators. Besides, the equivalent circuit model was established. In this model, voltage source PWM rectifier connected with the permanent magnet synchronous generator stator uses direct current control. Its control system structure is dual PWM rectifier or dual voltage source PWM rectifier circuit model which is composed of inner double loop cascade of outer DC voltage, AC input current and PWM inverter module based on three-phase voltage source. Its generaliability of typology is strong and has great advantages in the rectifier modeling, control algorithm and the ability of enhancing its operational capability failure. At the same time, both permanent magnet synchronous generator-side and network side of the rectifier adopt digital control based on digital signal processor. The vector control method possesses capabilities of four-quadrant operation and flexible control. It also could realize the speed governing of permanent magnet synchronous generators and grid power quality control. These grid-control strategies are beneficial to resolve the harmonic pollution, voltage fluctuations, current imbalance of power system caused by Wind Turbines. They also have important practical significance for the grid-control of large-scale wind turbine in China.