Research On SMES-VRB Coordinated Control And Mechanism Of Improving Wind Power Operation By Them

To solve the problem of intermittent and fluctuating power output of the renewable energy,large-capacity electrical energy storage technologies are researched in this thesis to realize large-scale grid connection of renewable energy.Firstly,the topology and coordinated control of Superconducting Magnetic Energy Storage(SMES)are explored.Based on the idea of multi-winding isolation transformer and modular topology,a new type of easy-to-expansion large-capacity SMES topology is proposed.The working principle and circulation characteristics are analyzed in detail.The modeling and analysis of circulation,feasibility and small-signal stability are carried out.The multi-level VSC power current control and multi-chopper vector switching coordinated control strategy are proposed.Combined with carrier phase shift modulation,the DC bus voltage can be stabilized and the multi-chopper current sharing problem can be solved.The simulation model under different working conditions is constructed in MATLAB/Simulink,and the current sharing effect of PI control and vector switching control and the power tracking performance of power and current control are compared.At the same time,the four-quadrant power adjustment experiment is carried out on the modular SMES experimental platform.The effectiveness of the power and current control strategies is verified.Secondly,the Vanadium Redox-flow Battery(VRB)topology and coordinated control are studied.The working principle,performance and equivalent model of VRB are analyzed.The architecture and control strategy of high-capacity VRB two-stage bidirectional converter are proposed.The VRB multiple bidirectional DC converter model is established.Based on the power average distribution strategy,the VRB intelligent charge and discharge optimization control strategy is proposed to control the charge and discharge of each VRB,reducing the number of VRB charge and discharge.The VRB simulation model and experimental platform are constructed to test the VRB current sharing and power tracking effects.The validity of the VRB converter topology and control strategies are verified by simulation and experimental results.Thirdly,for the problem of wind power fluctuation and bad smoothing effect of single type energy storage,the power type energy storage of SMES and the energy type of VRB are composed to form Hybrid Energy Storage(HES)to smooth wind power fluctuation,using Empirical Mode Decomposition(EMD)and sliding average method for power configuration.The HES optimization configuration model is established,and the optimal energy and capacity of energy storage is solved by the improved Particle Swarm Optimization(PSO)algorithm.The simulation compares the smoothing power fluctuations effects of single energy storage and HES.The results show that the smoothing power fluctuation effect of HES is better than that of single energy storage.When the HES is connected to the wind farm,combining with the EMD decomposition power optimization configuration,the wind power fluctuation can be effectively smoothed.The smooth and controllable power of the grid-connected wind farm is realized,and the grid-connecting capability of the wind farm is improved.The effectiveness of HES power distribution and smoothing wind power fluctuation strategies are further validated by experiments under different conditions.Finally,the Low-Voltage Ride Through(LVRT)strategy of the HES-assisted doubly-fed induction generator(DFIG)is studied for the problem of large-scale wind turbines off-grid and abandoned wind.The HES-assisted DFIG low-voltage ride through architecture is constructed,and the steady-state power relationship of DFIG and its transient characteristics during grid voltage drop are analyzed.Based on conventional unbalanced control,the voltage feedforward positive sequence current control strategy based on ?-? coordinate system is proposed to quickly compensate the reactive current to stabilize the DC bus voltage,and suppress the PCC point voltage and power oscillation by timely exchanging active power,and assist the DFIG to achieve low-voltage ride through quickly.The effectiveness of the HES-assisted DFIG low-voltage ride through strategies are verified by simulation and experimental results.The large-capacity power storage topology,coordinated control,power distribution and other technologies studied in this thesis can help solve the problems of volatility and intermittentness of renewable energy,make renewable energy coordinated and friendly,and access to large power grids to improve energy and environmental safety,and it is of great significance.