Research On Coordinated Control Of All-DC Offshore Wind Farm Under Fault

With the increasing competition in the exploitation of fossil energy,clean energy such as wind energy has attracted more and more attention from all countries.Offshore wind energy resources have the advantages of high quality and high wind speed,so the research on offshore wind farms is gradually increasing.The main content of the existing research focuses on the operation of offshore wind farms,such as topology,fault operation control and a series of explorations and presents a deeper and broader research trend.For all DC offshore wind power structure,there is no widely recognized topology structure.Therefore,through comparing several kinds of existing topologies,this paper decided to adopt the series-parallel topology with high recognition as the research basis.This form adopts the way of one-stage boosting,so it can realize the energy transmission at the same time of high efficiency boosting.On this basis,the study of typical faults were carried out,which focused on the control strategy during the fault period and fault recovery and verified accuracy of the strategy.The main research contents are as follows.Firstly,In this paper,the components of series-parallel wind farm are analyzed,and the mathematical models of wind turbine,rectifier converter and isolated boost converter in abc three-phase static and dq coordinate system are built.On this basis,the basic control strategy of wind turbine and converter is given,and the controller parameters are calculated.The detailed model is also built and simulated in MATLAB.The accuracy of the model is confirmed by the simulation results.Secondly,the typical faults happened in series-parallel wind farm are studied.Based on the theoretical analysis of the fault situation,a new control strategy is put forward for the operation of the wind farm during the fault period,that is to adjust the speed of the generator with the help of unloading resistance when the fault occurs,so that it can run at a low speed.In this strategy,the stator current is controlled to increase under the coordination of unloading resistance,which makes the generator work in the state of heavy load,the rotor speed is reduced,and the rotating speed of fan blade is reduced.Therefore,as the wind speed is constant,the wind energy utilization coefficient of the wind turbine is reduced,and the mechanical power input to the generator is reduced,resulting in the reduction of its output power,which not only relieves the heat dissipation problem of the unloading resistance,but also avoids wind turbine from shutdown and restarting,and speeds up the fault recovery of the DC system.In this paper,the fault situation,the fault operation under the proposed control strategy and the fault recovery process are simulated and analyzed,and the results verified the effectiveness and feasibility of the control.