| With the recent economic growth, rising demand for electricity, and global energy shortages and environmental deterioration, new energy sources represented by wind energy are rapidly growing. However, due to uncertainty and volatility of wind, and the inherent shortcomings of conventional units, the quality of the grid frequency becomes more prominent issue. In recent years, based on various new energy storage technologies thriving, and thus can meet the stability and reliability requirements of the grid when acted as a frequency regulation auxiliary means with "rapid response", "precision tracking" and other characteristics.First, considering the possibility of the units capacity increase for improving frequency regulation effect, the necessity of energy storage participating in frequency regulation is studied. Based on the current problems of the conventional unit and the advantages of energy storage on frequency regulation applications, analysis of the needs mechanism for energy storage is conducted. According to conventional'work processes and technical indicators on frequency regulation, as well as investment cost of storage and units, technical factors and economic factors of the demand scenarios were setting up respectively. Then, demand scenarios and evaluation methods are proposed, at the basis of these factors and existing reasons of the unsatisfactory regulation action of conventional units. On this basis, simulation analysis and comparison of demand scenarios for energy storage and units involved in a primary and secondary frequency regulation are carried out, and the final results of the necessary scenarios for storage participating in frequency regulation is acquired.Secondly, energy storage model applicable to frequency regulation is built aiming at the time scale for frequency regulation. Based on elaboration of the various energy storage technologies'characteristics, the applicability evaluation system is established. Further, energy storage type suitable for frequency regulation is selected by weight distribution via subjective weighting method. Then, an introduction to three kinds of domestic and foreign common battery energy storage model was offered. Based on analysis of the shortcomings of these models, the lithium-ion hybrid model is simplified for complex issues of model parameter identification. The key parameters are extracted from lithium-ion model under different time scales through sensitivity analysis to study the effects of the dominant characteristics parameters of the battery SOC (State of Charge), the gradual simplification of hybrid model and contrast of terminal voltage and output power. Eventually, simplified models of primary and secondary frequency regulation were proposed respectively.Finally, control strategies of the storage on the participation of frequency regulation based on the proposed models are presented. For primary frequency regulation, based on preferences between regulation effects and holding effect of SOC, this paper discussed three variable droop control strategies considering the state of charge (SOC) constraint, and thus summarized the applicable scenarios for these strategies. Aiming at defects of battery energy storage participating in AGC by distribution of ARR (Area Regulation Requirement) signal in fixed proportion, a control method of energy storage based on ACE (Area Control Error) signal was proposed. Dynamical adjust of energy storage output by tracking frequency deviation was available in this method by distributing ACE signal directly into energy storage and conventional units in proportion. Regulation effect, SOC and units output were analyzed by comparison of two control methods and sensitivity analysis of energy storage output factor a. The simulation results show that the proposed method has advantages in terms of reducing the frequency deviation and energy storage capacity, and significance for energy storage control strategy participating in AGC. |
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