| Large-scale integration of wind power will put a great deal of pressure on frequency regulation since wind power generators do not have such inertia response features as conventional generators do and their outputs are volatile and uncertain, especially when an impact load disturbance occurs in a power grid with large-scale wind power, conventional generators may not respond fast enough to meet the frequency regulation requirements of the grid. This problem has become one of the main constraints to integrate large-scale wind power into grids. Therefore, in order to ease the bottleneck of integrating intermittent power sources and improve frequency indices, it is necessary to introduce new supplementary means of frequency regulation and battery energy storage system(BESS) has an advantage here because of its rapid response feature. In this paper, the method of involving BESS in frequency regulation is explored on the basis of traditional frequency regulation; the frequency regulation oriented simulation model, technical and economic evaluation model, optimal capacity allocation and action moments and depth of BESS are researched; simulation software for applying BESS to frequency regulation is developed. The main research contents are as follows:1, A frequency regulation oriented simulation model is constructed for BESS. By analyzing the amplitude and charge-discharge frequency characteristics of primary and secondary frequency regulation, the output characteristics of BESS are obtained; based on an electro-magnetic transient(EMT) model of BESS, a simulation model suitable for frequency regulation research is built; with experimental data of several Li Fe PO4 batteries, the model parameters are identified and the impacts of the batteries’ various initial states of charge and different constant current operation modes on the model parameters are analyzed; In certain circumstances, the simulation model is further simplified, and the applicability of the simplified models to frequency regulation research is verified through simulations of frequency regulation operating conditions..2, An optimal capacity allocation method of BESS is put forward for its participation in frequency regulation in power grids containing wind power. The universal way to allocate the power and capacity of BESS is introduced; by combining the simulation model of BESS with its method of participating in primary and secondary frequency regulation, and considering the power conversion efficiency of the power conversion system(PCS) and the efficiency of the energy storage battery device in BESS, a physical property model of BESS is obtained; through analyzing the costs and benefits of BESS during frequency regulation operation process, based on the whole life cycle theory, an economic evaluation model of BESS for frequency regulation is established by using the net present value(NPV) evaluation method; combining this model with the physical property model forms the corresponding technical and economic evaluation model; a charge-discharge strategy of BESS to participate in primary and secondary frequency regulation are designed, and with the charge-discharge strategy, considering the composite load affected by volatile wind power and from the corresponding fluctuation characteristics of grid frequency and area control error(ACE), the capacity allocation schemes of BESS with the optimal frequency regulation performance, the optimal economic benefits and the comprehensive optimum of both are respectively obtained under the constraints of grid frequency regulation and BESS operation requirements.3, A control strategy of BESS is proposed for primary frequency regulation(PFR). The frequency characteristics of regional power grids involving BESS are analyzed in the complex frequency domain with the sensitivity theory, and according to the analysis, a comprehensive control mode composed of virtual inertial control and virtual droop control is proposed for BESS; based on the sensitivity theory and frequency regulation evaluation indices, the frequency response characteristics of BESS in PFR are derived in the time domain, the conditions to determine the reasonable action moments of BESS are analyzed, and according to these conditions, the action moments and corresponding control modes are determined; then, based on the requirements of frequency regulation evaluation indices, the action depth is determined, its relationship with the rated power of BESS is derived, and the corresponding capacity requirements are analyzed. Thus the control strategy of BESS considering its action moments and depth is formed and the corresponding implementation process is designed. Finally, simulations are carried out with reference accidents of a typical grid as the initial conditions and the results verify the effectiveness and rationality of the proposed control strategy.4, A control strategy of BESS is proposed for secondary frequency regulation(SFR). Based on the presented area control error(ACE) and traditional area regulation requirement(ARR) signal distribution modes, the frequency characteristics of regional grids involving BESS are analyzed in complex frequency domain with the sensitivity theory, and according to the analysis, a method to determine the action moments and regulation modes of BESS is presented; taking into account the energy limitation of BESS and the ramping rate constraints of conventional generators in the time domain, based on the dynamic available AGC(DAA) indices, a method to determine the action depth of BESS is put forward. Thus the control strategy of BESS considering its action moments and depth is formed and the corresponding implementation process is designed. Finally, the effectiveness and rationality of the proposed control strategy is verified through simulations of step disturbance operating conditions of an actual power system.5, Simulation software for applying BESS to power grid frequency regulation is developed. It contains the following functions: wind power contained composite load characteristics analysis; frequency regulation oriented BESS simulation model construction; optimal capacity allocation of BESS for primary and secondary frequency regulation; control strategy design of BESS in primary and secondary frequency regulation considering its action moments and depth. Being open-source, extensible, and easy to operate, it provides a set of user-friendly analysis tools for assistant decision-making on applying BESS to frequency regulation.The direction and focus of further research on applying BESS to frequency regulation are pointed out in the end. |
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