Study On Control Technology Of A Doubly Fed Generator

On the current tendency, wind energy is widely concerned by man, because it can't be used up forever. During the process of switching electrical energy, it doesn't produce any bad gas and waste and also doesn't pollute circumstance;it has the characteristics of using local materials and not requiring transportation.Wind is the world's fastest growing renewable energy and a beacon of hope for a future based on sustainable, pollution free electricity, of which utilization will ultimately resolve those problems such as energy shortage, environmental pollution and greenhouse effects etc. Therefore, it is a kind of ideal alternative energy source for conventional energies.In the field of wind power generation variable speed constant frequency (VSCF) operation is a new high efficient technology. It can make full use of wind energy, which is the main target every developed country is studying. In this paper, based on the widely applied doubly fed generator in wind energy application technology in the day, a controller in the core of 87C196MC is designed, where the control theory and technology with wind power generation is studied.In the paper, firstly, the advantages of VSCF are discussed compared to constant speed constant frequency and the mathematic model based on the structure of AC excitation doubly fed generator is built. The power characteristics of the doubly fed generator are analyzed based on the model, which set a foundation for the design of the control system and study of the experiments.Secondly, a mathematic model based on a doubly fed generator and its rotor excitation control system, which is related by the phase angle φ_rs between the stator and rotorvoltage, is established. Meanwhile, a unified vector control model in synchronous rotating reference frame is deduced. This model not only reflects doubly fed generator parameters, excitation control system hardware structure and rotor excitation control system parameters;but also indicates in theory that the doubly fed generator has common characteristic of the inductionmachine and synchronous machine, and the technical superiority for being used in VSCF generation system.Lastly, an experimental system of VSCF doubly fed power generation system based on 87C196MC as the central control unit has been built and the experimental study of the excitation control technique has been carried out. The VSCF control and the soft-connection of the generator to the grid are realized. The simulation and experiment results suggest that the model is reliable, which conduces to the study on doubly fed excitation control strategy and the design on the rotor excitation control system.