| In the development process of power system,the degree of interconnectivity of regional power grid gets higher,this will not only bring economic and social benefits but also create more and more long-distance,weak-connection,heavy-load transmission lines.However,lines that own such features are very likely to arise power oscillation.In addition,the permeability of clean energy such as wind power and solar energy gets higher,the volatility and randomness of its power output will also shock the grid and lead to oscillation after its merging into system.And this will cause serious blackouts and bring huge loss and influence the stable operation of grid if not properly handled.Energy storage technology can realize fast and accurate power control bi-directionally,so it is equivalent to a controllable power source and can realize real-time compensation for power,suppress the power oscillation so that to improve the stability of power grid operation.This thesis introduces the composition and working principle of the battery energy storage device firstly,mainly includes battery system and its simplified model,the composition and working principle of power conversion system,the working mechanism of the battery management system and four control strategies,such as constant power control,commonly used in energy storage devices.Take a single-machine infinity system composed of H-P generator model as an example,and analyze influence of energy storage system on electromagnetic torque and the principle how the system stability is improved.Secondly,the operation principle of energy storage system under constant power control strategy is analyzed in detail.This part mainly analyzes the mathematical model of the converter,working principle of DC/DC bi-directional converter and control strategy of voltage source active inverter.The transfer function of energy storage system under constant power control strategy is deduced and simulation model of energy storage system under constant power control strategy is established in PSCAD on the basis of previous analysis and is used in single-machine infinity system to study the effect of improving the stability of power system through simulation.Thirdly,this thesis analyzed the principle of energy storage system under the control strategy of virtual synchronizer.Through the analysis of the working principle of the synchronous generator,the control strategy of the virtual synchronizer is obtained and the detailed introduction is made,the analysis contents mainly conclude ontology structure analysis of virtual synchronizer,inertia equation and outer power control of virtual synchronizer,double loop control of inner voltage and current,pre-synchronization control strategy for virtual synchronizer.The transfer function of energy storage system under the control strategy of virtual synchronizer is deduced and simulation model of energy storage system under control strategy of virtual synchronizer is established in PSCAD on the basis of previous analysis and is used in single-machine infinity system to study the effect of suppressing power oscillation through simulation.Lastly,the effect of the energy storage device under two different control strategies on suppressing power oscillation is analyzed qualitatively and quantitatively.Because the power response speed of the energy storage system under the constant power control strategy is faster than the response speed under the virtual synchronizer,the former has a better effect on the suppression of the power oscillation than the latter. |
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