Study On Propagation Mechanism And Control Strategy Of Subsynchronous Oscillation In Direct Drive Wind Farm

In recent years,wind power generation has been fully developed with its unique advantages,and the penetration of wind power grid has been continuously improved.However,in order to realize the absorption and integration of wind power,a large number of power electronic devices are used in VSCF wind turbines.These power electronic devices interact with wind turbines,which weakens the anti-interference ability of wind turbines,easily induces sub-synchronous oscillation,and seriously threatens the safe and stable operation of the system.The dissemination mechanism and control strategy of sub-synchronous oscillation in direct-drive wind farm are studied in this paper.The main contents and achievements are as follows:Aiming at the problem that it is difficult to analyze the controller of wind turbine deeply in the analysis of sub-synchronous oscillation at present,this paper establishes the port energy function of direct-drive wind turbine based on port theory,ignores the dynamic energy potential energy transformed periodically in the port energy,extracts the non-periodic component,that is,the dissipated energy corresponding to the damping,and establishes the dissipated energy function of direct-drive wind farm output.The energy function takes into account the dissipated energy corresponding to active power and reactive power,which can better reflect the damping characteristics of wind farms.By calculating the positive and negative levels of dissipated energy of the wind farm during the oscillation process,the damp level of the wind farm at a specific sub-synchronous oscillation frequency can be assessed,and the effect of the wind farm on the divergence or suppression of the sub-synchronous oscillation can be judged.In view of the current research,the whole wind farm is often equated to a fan,so the interaction between the fans under different conditions in the wind farm can not be considered.Taking the multi-machine equivalent model as an example,this paper compares the dissipated energy of the oscillating fan under two conditions of simultaneous oscillation and one oscillation and one stable operation in the wind farm,and analyses the interaction between the two units.The influence of subsynchronous oscillation is analyzed by comparing the dissipated energy of two wind turbines at different locations and wind speeds,and the influence of unit interaction on subsynchronous oscillation is analyzed under different locations and wind speeds.In order to solve the problem of negative damp caused by many control parameters of fans and improper coordination,a parameter adjustment strategy based on energy function model is proposed in this paper.Firstly,the response process of direct-drive wind turbine control system to disturbance under grid disturbance is studied,and the divergence mechanism of sub-synchronous oscillation of direct-drive wind farm is presented.The divergence criterion of sub-synchronous oscillation of direct-drive wind farm under grid disturbance is given.Based on the divergence criterion,the influence of PI parameters of phase-locked loop and converter control system on the damping characteristics of wind turbine is quantitatively analyzed,and the adjustment strategy of single control parameter is obtained.The control parameters of all subsynchronous oscillating fans in direct-drive wind farms are coordinated adjusted,and a multi-constrained multi-objective minimum optimization model is established to optimize the phase-locked loop and converter control parameters of all subsynchronous oscillating fans in wind farms.