The Study Of Grid-connected Control Of Brushless Doubly-fed Wind Power Generator

With increasingly serious environmental problems, the wind power, Efficient and green, is one of the best choice for our sustainable development strategy. In wind power field, brushless doubly-fed generator(BDFG) has obvious advantages, compared with other generators, it has some of the advantages of double-fed brush generator, such as achieving Variable Speed Constant Frequency power generation; control capacity becomes small; At the same time, compared to ordinary double-fed machine, due to the cancellation of the brush and slip ring, its stability has also been greatly improved, which reduces the maintenance costs of the system.Firstly, This paper describes the development prospects and background of the brushless doubly-fed wind power system. It also introduces the present situation and the existing problem of the control algorithm on the BDFG.Secondly, Analyzing the working principle of BDFG, its mathematical model is derived under the three-phase static coordinate system. And the cascade model of BDFM is obtained, according to the characteristics of the rotor magnetic field modulation. With the use of the coordinate transformation, The mathematical model under the rotor mechanical speed rotating coordinate system is deduced, and then simplified this model.Thirdly, based on simplified mathematical model, amplitude and frequency control algorithm is obtained. And the phase shift control was also given to meet the requirement of the connected-grid. As the complex magnetic coupling between BDFG, this paper presents a constant current control, when generator connects to grid. A droop control strategy for this system is also proposed to provide voltage and frequency support, which improves the stability of the system voltage and frequency. And then the entire control system was simulated, using MATLAB / SIMULINK software.Finally, grid and off-grid experiment are took in the experiment platform of the brushless doubly-fed wind power generation system. And some relevant experiments are also took to simulinate the output power of wind power generation system. The waveforms of the experiment proves the validity of the control algorithms.