Battery Energy Storage System And Its Operation And Control In The Isolated Grid Based On Wind-battery

As a device which can store the chemical energy and transmit thestored energy into the electrical power in bi-direction, battery energy storagesystem (BESS) not only can be widely regarded as an effective solution todeal with the large scale integration of renewable energy sources intoelectric network, but can improve the use ratio of the grid facilities and theability of load following and frequency regulation and reactive powersupporting to the grid. Furthmore, it also can enhance the stability, economyand flexibility of the gird. The capacity and reliability of BESS will beraised when the sub-BESSs operate in parallel. The domestic research onBESS is still in the stage of base theory and demonstration. This dissertationhas focused on the modeling and sate of charge (SOC) estimation of thebattery system and control of the islanded power system based on windpower and BESS. The works and innovative achievements in thedissertation are as follows.1. The operation principle and simpled model of large capacity batterysystem (LCBS) is analyzed in details. Considering the inconsistent qualityof the cells and the characteristics of the circuit in series and parallelconnection, an accurate equivalent circuit model of Li-ion LCBS isproposed, which is applicable for electrical circuit design and simulation.The accurate models of the battery system in series and/or parallelconnection are constructed under Matlab/Simulink conditions2. Considering the factors such as the structure form, SOC estimationaccuracy of battery system, the cost of battery management system and soon, a hierarchical SOC estimation scheme of LCBS is designed. A cell SOCestimation method based on voltage compensation is proposed for the problems such as the indeterminacy of SOC initial value and the erroraccumulation in current integration operation. Due to the LCBS is anonlinear system, a SOC estimation method which is based on extendedkalman filter is presented to estimate SOC of LCBS.3. The dynamic model of BESS is built. The structure and operationalprinciple of BESS dynamic model are introduced in details. Themathematical models and its control characteristics of power conversionsystem (PCS) and battery system are analysized thoroughly. The dynamicsimulation plat is constructed in PSCAD/EMTDC simulation conditions.Some simulations of charging and discharging characteristics of BESS areconducted and the simulational results are analysized extensively.4. The control strategy of the islanded system when the wind turbinesare out of operation for long time is proposed. Owing to the problem ofinconsistent SOC of battery system in application, which leading to the lifedecrease of the battery and power system instability, a modified droopcontrol strategy based on SOC of battery sytem is proposed to shareeffectively load active power and enhance the ability of battery managementsystem. Considering an inherent static error in droop control and theimpedance being not pure inductance in middle or low voltage grid, andouble loop control strategy based on linear compensating loop is presented,named volatage amplitude and frequency control.5. The system configuration and coordinate operation scheme isdesigned separately for the hybrid power system consisting of doubly-fedinduction generator (DFIG) and BESS. Cosidering the influence of loadlevel and wind energy average using hours per year and wind intermittenceon system investing cost, a system configuration scheme is designed and itseconomy is analyzed. Considering the different operation characteristics ofDFIG and BESS and the different operation restraint conditions of each unit,a coordinate operation scheme is illustrated for the islanded system.6. The control strategy of a islanded system consisting of DFIG andBESS is proposed. For the problems caused by the integration of DFIG, such as new reactive power balance and operation state control, the energybalance and a hierarchical control strategy are presented respectively for theislanded power systems. For the problem that the reactive power output ofBESS is limited using the traditional droop control, a modified droopcontrol based on SOC of battery system is raised to share effectively loadreactive power, which can improve the system ability of reactive poweroutput.7. The wind-battery hybrid system setup is built and some experimentsare carried. The system setup construction and the design of PCS areintroduced in details. Some experiments are carried to validate theeffectiveness of the presented control strategies, which consisting of theoperation and control of BESS when the wind turbines are out of runningand in operation in the islanded system based on wind-battery.