Control Strategy Of Battery Energy Storage System Participating In Frequency Regulation In The New Power System

With the deepening of the reformation of the electric power system,the transition of clean energy has entered a critical period.The electric power system presents new characteristics such as high new energy penetration rate and high electric power electronization.Although the large-scale application of new energy can effectively alleviate environmental problems and energy crisis,compared with the traditional power system with more controllable power sources,the new power system with high proportion of new energy penetration has poor controllability.The operational risk and the frequency fluctuation of the new system are high.It is difficult to guarantee the safety and stability of the power system.Battery energy storage technology,as a new technology,by virtue of its rapid power output,flexible regulation and other advantages in maintaining system frequency stability,is expected to become an important means to ensure the frequency safety of new power system.In order to promote the application of battery energy storage technology in the field of power system frequency modulation,this paper studies the control strategy of battery energy storage system participating in new power system frequency modulation.Firstly,the advantages of the battery energy storage system participating in the power system are briefly explained from the technical and economic aspects.This paper introduces the frequency regulation engineering and the construction of auxiliary service market of energy storage power system around the world.At the same time,this paper reviews the control strategy of energy storage power system participating in primary frequency regulation and secondary frequency regulation of power system,and summarizes the shortcomings of current research.Secondly,this paper proposes a control strategy for improving the performance of BESS participating in the primary frequency regulation（PFR）.First of all,the dead band of BESS is limited within the range of the conventional generators’,and the impact of changing the dead band of BESS is analysed by combining with the frequency characteristics of the grid.On the basis of this,the control strategy of BESS based on weight factors and optimization of the state of charge（SOC）in PFR is proposed in this paper.On the one hand,when the frequency fluctuation in the grid exceeds the dead zone of the BESS,a calculation method for the coefficient of BESS’s output power is proposed,which is used to avoid excessive charging and discharging of batteries.At the same time,two weigh factors of the virtual inertia control and the virtual droop control are introduced to adjust their output proportion with the change of frequency automatically.Then,the control method of frequency modulation based on the coefficient and weight factors is designed.On the other hand,a method of the SOC self-recovery,taking the need for energy storage self-recovery and the grid’s affordability into account,is established when the frequency fluctuation is within the dead band of BESS.Then,aiming at the problems in the power grid such as the difference in frequency modulation cost and residual FM capacity of different types of battery energy storage power stations,and the SOC of battery energy storage units（BESUs）in battery energy storage power stations could be too high or too low,a two-layer optimization strategy which takes FM cost and SOC recovery into account in multi-battery energy storage system was proposed.The strategy includes frequency modulation power optimization layer and SOC optimization layer.In the frequency modulation power optimization layer,the resistance coefficient related to the residual FM capacity of the battery energy storage power stations is introduced.The objective function of this layer is composed of resistance coefficient and frequency modulation cost,so that the optimal distribution of frequency modulation power between different BESPSs can be realized according to the frequency modulation cost and residual frequency modulation capacity of different battery energy storage power stations.The SOC weight is introduced in the SOC optimization layer which can reallocate the frequency modulation power of different battery energy storage power stations to recover the SOC of BESUs.A regional power grid with three different battery types is used to verify the effectiveness of the proposed strategy.Finally,this article taking day-ahead scheduling as an example constructs the formation method of the day-ahead scheduling plan（DASP）and the modulation frequency limitation of the power system.Based on this,a control strategy of energy storage is proposed which combined energy storage assisting wind farm tracking the DASP with participating in frequency modulation.Then,a wind-energy storage（WES）operation model is established under the electricity market environment to maximize the profit of the WES station.The combined output power constraint of WES station and the frequency security constraint which formed by the proposed strategy are considered in the model.This model can calculate the optimal output power of the energy storage which are used to tracking DASP and participating in frequency modulation.Simulation verification is carried out based on actual measurement data.