Research On Design And LVRT Control Of Permanent Magnet Synchronous Wind Power System

With the development of the society, energy has become an important factor that restricting the development of human society. The used of a large number of fossil energy, which has bring on serious impact on the environment and people’s daily life, so vigorously promote the renewable energy has became the important means to solve these problems. Permanent magnet synchronous wind power system is gradually becoming the mainstream direction in wind power zone. It has more advantages:high efficiency, low maintenance cost, easy to control, and more suitable for running in low wind speed, etc. In recent years, grid capacity of permanent magnet direct-drive wind power is increasing. Once the power grid appear voltage drop, it will cause the motor to take off the grid, and then will lead to the grid lost stability, more serious situation,will cause significant power accident. Therefore, it is great significance to study the ways of increasing the ability about low voltage ride through (LVRT) of PMSG on improving the stability of power grid and power quality.Studied and analyzed the history and development status of wind power about home and abroad, summarized a variety of methods that improving LVRT ability of permanent magnet wind power system.Through analyzing the design characteristics and method of the permanent magnet wind turbine, a 2MW direct drive permanent magnet wind generator was designed by equivalent magnetic circuit method. The simulation model of 2D Electromagnetic Field of generator was established by ANSYS software, the magnetic flux and the back EMF curve of the generator were analyzed and calculated under no load, rated load and short circuit conditions.By analyzing the working principle and the working characteristics of permanent magnet direct-drive wind power system, and operation characteristics of each component, a wind power machine, permanent magnetic synchronous generator, full power converter, and the mathematical model of dc link and other components were builded, which providing theoretical basis for the research of low voltage control strategy.Full power converter control strategies were studied:the machine side converter adopted the current inner ring and the power outer ring double closed loop control strategy; the network side converter adopted the voltage outer ring and current inner ring double closed-loop control structure. The theory of low voltage drop and permanent magnet direct-drive wind power system in the dynamic response process of voltage dropping were analyzed.The power tracking optimization control strategy to achieve LVRT was proposed:by switching power curve, the unbalanced voltage of DC side was transfer into the unbalance power between the mechanical power with the electromagnetic power, finally, reflects the change of the generator speed of the permanent magnet synchronous generator. An improved control strategy was proposed:to serve information for reflecting the instantaneous active power generator as feedforward compensation amount, stack to the network side d shaft given current. This method can rack the change of the generator output active power and steady DC voltage in real time, and comparative analyzed with the Crowbar protection circuit scheme. In Matlab/simulink simulation platform to verify the effectiveness of the proposed method.