Direct Drive Permanent Magnet Synchronous Wind Turbines Participate In The Research Of Grid Frequency Support

The current mainstream wind turbines are direct-driven permanent magnet synchronous units and doubly-fed asynchronous induction units.Compared with doubly-fed units,direct-driven units eliminate the gearbox,improving the reliability of the units,reducing mechanical losses,and improve the efficiency of power generation,so more and more attention has been paid.Since the converter in the direct-driven unit decouples the generator from the grid,the generator’s response to grid frequency changes is minimal.With the rapid development of wind power generation,the penetration of wind power generation in the power system has increased year by year,resulting in a reduction in the grid equivalent inertia and a reduction in frequency stability.Frequency is one of the important indicators of power quality.In order to improve the grid frequency stability,this paper takes direct-driven permanent magnet synchronous wind turbine as the research object.With the wind turbine participating in the grid frequency support control,the goal of increasing the grid equivalent inertia is achieved.The main studies are as follows:(1)The normal operation control strategy of the wind turbine is studied.The relationship between the output power and the speed of the wind turbine in the two modes of maximum power point tracking and power limitation is analyzed.The control of the generator-side converter and the grid-side converter is studied.A simulation model for normal operation of direct-driven permanent magnet synchronous wind turbine is built in Matlab/Simulink,and the effectiveness of the control strategy is verified by simulation.(2)The control strategy of conventional wind turbine participating in grid frequency support is studied.In the normal operation mode of the wind turbine,the inertia controller and the droop controller are added respectively to make the wind turbine participate in grid frequency support.Taking the grid frequency drop as an example,the simulation verification and semi-physical experiment verification are carried out.Both the simulation and experiment verify the effectiveness of the control strategy.(3)The control strategy of the wind turbine with the flywheel energy storage device to participate in the grid frequency support is studied.The flywheel energy storage device is connected to the DC bus of the wind turbine,so that the additional active power of the wind turbine to participate in the grid frequency support is from the flywheel energy storage device.It realizes that the wind turbine can more effectively improve grid frequency dynamic characteristic and can still effectively support the grid frequency in the low wind speed.The simulation analysis of the wind turbine in the middle wind speed and the low wind speed is carried out to verify the effectiveness of the control strategy.