| Recently, the scale of grid-connected wind power generation is increasing continuously and the harmfulness of its fluctuation and uncontrollability to the stable operation of the grid is increasingly obvious. Battery energy storage device which acts as an energy storage equipment and a bidirectional power flow equipment can make contribution to the voltage stability,power quality,utilization rate of power equipment and the ability of peak load and frequency regulation of grid-connected wind power system. Based on the study of at home and abroad research status about grid-connected wind power system and battery energy storage system, this article studies the characteristics of forced power oscillation due to large-scale grid-connected wind power generation and determines to use energy storage devices to solve the problems of forced power oscillation caused by wind fluctuation. Therefore, the modeling and simulation of Lithium-ion battery is done to model battery energy storage system and design the charge-discharge control strategy of energy storage device. Thus establish the equivalent model of the wind power and energy storage system,then design the control algorithm to confirm the total output power of the wind power and energy storage system. Eventually, some experiments are carried to validate the effectiveness of the use of energy storage devices to solve the problems of forced power oscillation caused by wind fluctuation.The works and innovative achievements in the dissertation are as follows.(1)Stable operation of two-area four-machine system which connected wind power generation is studied. Based on the system construction and parameters, the system linearized differential equations are found by using small signal stability analysis. Characteristics of system oscillation,local and inter-area system oscillation mode are also analyzed. Forced power oscillation is analyzed through the research simulated with Matlab/Simulink. At last, this paper finds the characteristics of forced power oscillation caused by wind fluctuation.(2)Equivalent circuit of lithium ion battery is confirmed by electrochemical principle about LiFePO4 Li-ion battery and parameters of equivalent model are found through technical indicators given by manufacturer. A comparison of simulation and hardware testing results including the changing and discharging curves shows a high degree of accuracy with the selected lithium-ion battery model. Furthermore, series-parallel characteristics of single battery are studied and equivalent model of battery group is established.( 3) Bidirectional DC/DC converter is used to control charging and discharging of batteryenergy storage devices and the effectiveness is tested by simulation. Energy storage devices whose grid-connected inverters are operated by using PQ control method are connected with wind power system to act as cogeneration system of wind power and energy storage. Simulation results show that battery energy storage device can smooth fluctuation of wind power generation and that it is possible for energy storage device to solve forced power oscillation caused by wind fluctuation in multi-machine system because of the fast speed of energy storage device to deal with power fluctuation due to wind fluctuation.(4)Based on the prediction of wind speed and load forecasting, in order to give full play to the energy storage capacity, cost savings, and make wind power fluctuation to meet safety margin,design algorithm to optimize the total output power of the wind power and energy storage system.Damping forced power oscillation caused by wind fluctuation is realized by energy storage devices and the effectiveness of control method is also tested. |
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