Research On Low Voltage Ride Through Of Direct-Driven Permanent Magnet Synchronous Generation

With the increasing of capacity of wind power generator, mutual effect between the wind power generator set and the grid becomes stronger.lt is necessary designing new grid code requirements by considering the grid safety. The direct-driven permanent magnet wind power generation is selected as the research object in this thsis, aiming at which improving the LVRT capability of system in grid fault.Firstly, the current development of wind power technology and wind power LVRT technology around the world are introduced in this thesis. The mathematical model and the control model of PWM converter are also studied. The rotor flux-oriented vector by id = 0 control scheme is used in permanent magnet synchronous motor and the dual closed-loop control scheme is used in grid.Secondly, in order to solve problem of the escalating DC voltage, a control scheme is adopted in this thsis to stabilize the DC voltage, in which the Crowbar is introduced, the output power of motor-side is reduced and the reactive power supported by grid-side.In order to solve problem of the double frequency oscillations in active power and the reactive power of grid, the asymmetry of three-phase current by negative sequence component in gird asymmetry fault. According to the diffevent the grid control of griding current,there are three selective control targets in gird-side, there are the output of gird-side without reactive power fluctuation, the output of gird-side without active power fluctuations and no negative sequence current flowing into the grid. A dual closed-loop control scheme is used in grid to filter the double supply frequency oscillations in power and no negative sequence current.Finally, the control model is set up in Matlab/Simulink, simulation results show that the control model and the control scheme are correct. Therefore, the LVRT capability of the system can be improved.