Research On Grid-connected Control Strategy Of Wind Energy System Based On Hybrid Storage Consisting Of SMES And Hydrogen As Well As Battery

At present,due to the fluctuation and unpredictability of wind power,it is difficult to make full use of such clean and efficient energy on a large scale.The energy storage with bidirectional power characteristics can just compensate or absorb energy to improve the utilization rate of wind energy.However,under the limitation of current technical conditions,only one kind of energy storage can not meet the above requirements at the same time,so hybrid energy storage system(HESS)has become the first choice to solve this problem.In addition,the energy storage system may be in overcharged and deep-discharged state when the power fluctuates greatly,which reduces the performance of the energy storage system and cannot guarantee the stability of the system.And the control difficulty of HESS increases accordingly.Above all,it is extremely important to choose the appropriate grid-connected structure of wind energy system with HESS,power allocation strategy of energy storage and grid-connected control strategy.In this thesis,the active grid-connected structure of HESS consisting of superconducting magnetic energy storage(SMES),hydrogen energy storage(HES)and battery energy storage(BES)is adopted.Based on the establishment of mathematical models of doubly-fed fan,PEM electrolyzed water to produce hydrogen and lead-acid battery,a two-layer fuzzy logic control strategy of energy storage power allocation considering State of Charge(SOC)is proposed:Firstly,the grid-connected power and power of HESS are obtained by first-order low-pass filtering the remaining wind power that meets the load demand.Secondly,the filter is used again to preliminarily obtain the high-frequency power assumed by SMES and the low-frequency power assumed by HES.Finally,according to the SOC and the initial power of energy storage,the final reference power is obtained by the fuzzy logic controller,so as to realize the optimal power allocation of HESS.The simulation results proves that this strategy of power allocation can not only improve the utilization rate of each energy storage,but also avoid the energy storage from frequently entering the overcharge and overdischarge area,and prolong the service life of the energy storage system.Furthermore,the grid-connected control method is that HES and BES are controlled by outer-loop virtual synchronous generator control and inner-loop PID control,and SMES are controlled by outer-loop constant power control and inner-loop PI control.The simulation results of HESS and single energy storage grid connection show that the control strategy can improve the anti-interference ability when wind power fluctuates,and realize the system from fast response to long-term power supply.The effectiveness of the proposed power allocation strategy is proved again by the simulation under different initial SOC of energy storage in three States:charging,discharging and overcharge and overdischarge.In addition,BES can not only replace the role of HES,but also avoid the frequent start and stop of SMES,thus prolonging its service life to some extent.