Modelling And Controlling Of Vanadium Redox Flow Battery To Smooth Wind Power Fluctuations

Since the random fluctuation of wind power, a large quantity of wind power integrated to the power grid has got much impact on the power grid. Therefore, the use of Energy Storage Systems(ESS) to stabilize power fluctuations of the wind power is becoming more and more important.The Vanadium Redox Flow Battery(VRFB) has the advantage of long life, which attracts many people to study it. In this paper, referring to the VRFB as wind power energy storage device to study the control strategy to smooth the fluctuation, it includes: Electrical modeling of the VRFB for power system simulation and Controlling to smooth fluctuations of wind power.Based on Electrochemical AC impedance equivalent circuit of VRFB, the parameters of the equivalent circuit of the VRFB have been analyzed and simplified to establish mathematical model for simulation.Comparing the simulation results with the experimental charge and discharge characteristics curves of VRFB, it shows that the established VRFB model is effective and accurate.Furthermore, a tested system including an Energy Storage System (ESS) and a single Double Fed Induction Generator (DFIG) has been established in a well-known PSCAD/EMTDC digital simulation package. The ESS is connected to the AC terminal side of the DFIG through an AC/DC converter. Based on the power decoupling control of the AC/DC converter, a control strategy to stabilize wind power fluctuation by VRFB Energy Storage Systems has been designed.Wind power fluctuations characteristics in the frequency domain and the range of the frequency to stabilize the wind power Energy Storage System have been analyzed. A control target of smoothing output wind power has been designed with a low-pass filter method. Then the energy storage capacity has been determined, correspondingly. As an example, the proposed smoothing control strategy has been studied with practical wind speed data and 1.5MW DFIG by PSCAD/EMTDC digital simulation software.In order to improve the dispatched ability of wind power and optimized control of battery, a new control method, which is based on short-term wind power prediction error envelope curve. Hysteresis voltage control is used in the proposed method to achieve conversion charge and discharge state of the ESS, which limits the number of the charging and discharging of storage batteries. Therefore, it extends the life of the storage batteries and improves the overall efficiency of energy storage batteries. Finally, the simulation results have showed that the proposed method is effective and feasible to improve the dispatched ability and optimized control of battery.