Research On Integrated Collaborative Control Strategy Of Battery Energy Storage System Participating In Frequency Regulation

With the development of renewable energy sources(RESs),the inaccuracy and difficulty of predicting the output power of RESs h ave brought significant negative influence on power system frequency,which is reflected from the three aspects as follows: 1)The output power of RESs features the intermittency,randomness,and fluctuation,which will lead to severer imbalance between th e power supply and the load power;2)RESs replace the role of some conventional generator units(CGUs),which reduce the inertia of the power system and will cause more serious frequency deviation during the power fluctuation;3)Although RESs can provide droop and inertial response to some extent,the available power capacity of RESs for frequency regulation is far from enough to completely replace CGUs' role.Therefore,to relieve the power pressure of CGUs during frequency regulation,it is necessary to improve the control strategy of battery energy storage system(BESS)for frequency regulation,which is also beneficial to BESS for using its fast response to participate in frequency regulation.Based on the existing research,the thesis studies the impr oved primary and secondary frequency regulation methods with BESS,as well as the action limitation and depth of state of charge(S o C)reconstruction during frequency regulation.The main novelties and contributions are listed as follows:(1)To improve the performance of frequency regulation,the influences of various BESS output power characteristics on power system frequency are analyzed with the droop response(DR)and the inertial response(IR)respectively.Then,the coordinated control strategy of DR and IR is accordingly proposed.For the purpose of assessing the frequency regulation ability of BESS,the Logistic SoC maintaining strategy is proposed,which can also contribute to the S o C maintaining performance.To reduce the number of involving in t he primary frequency regulation of CGUs,the dead band classification and limitation of CGUs are analyzed in depth based on the power-frequency response characteristics,and the re sponse strategy using flexible dead band for BESS is proposed.Then,the ada ptive primary frequency regulation strategy for BESS consists of the above three strategies,which can use the BESS replace CGUs to suppress the small load power fluctuation,and accordingly reduce the pressure of CGUs during primary frequency regulation.(2)To improve the standby SoC of BESS for primary frequency regulation,the frequency regulation method considering adaptive SoC reconstruction is proposed for BESS.For the purpose of determining the range of frequency deviation in which SoC can be reconstructed,the relationship between power reserve and frequency deviation is quantitively analyzed.Further,the power demand of adaptive SoC reconstruction is determined by quantitively analyzing the range of SoC during normal operation.In order to prevent the pressure that the SoC reconstruction power may exert on CGUs,the constraint relationship between the adaptive reconstruction power and the power reserve of CGUs is established and limiting factor is accordingly determined.Finally,the adaptive SoC reconstruction method for BESS in primary frequency regulation is proposed with the above-mentioned reconstruction limits,power reserve and limiting factor.The proposed strategy is validated compared with conventional methods under different variation conditions.(3)To coordinate the secondary frequency regulation and SoC reconstruction,the secondary frequency regulation method considering SoC reconstruction is proposed,which takes good advantages of CGUs and BESS.First,the secondary frequency regulation strategy with BESS is designed based on the area control error(ACE)signal,the area regulation requirement(ARR)signal,and the power characteristics of CGUs in secondary frequency regulation.Then,in regard to SoC reconstruction,a SoC reconstruction strategy for BESS in secondary frequency regulation is proposed to meet the demands of both frequency regulation and SoC recovery.Finally,a secondary frequency regulation strategy considering SoC reconstruction is proposed based on the above-mentioned sub-strategy and validated using the simulation cases.(4)To reveal the mutual influence between the results of ultra-short-term load forecast and the future demand of frequency regulation,the characteristics of fixed-reference SoC reconstruction strategy is analyzed in depth.Then,a SoC reconstruction method for BESS in secondary frequency regulation is proposed based on the dynamic reference value,which can improve the utilization and the SoC maintaining performance of BESS during secondary frequen cy regulation.Finally,the proposed strategy is validated using the typical regional power grid cases.