| With the full utilization of renewable energy and fast development of smart grids, electricity energy storage(ES) technology is considered as a new promising and encouraging control and regulation mean in the recent years due to its features of flexible control and easy utilization. ES devices are usually divided into two types, i.e. energy-type ES(EES) and power-type ES(PES). EES has the features of large-capacity storage and short cycle life, whereas PES has the features of rapid response characteristic and long cycle life. Generally, the applicable range of a single type of ES is always more limited, but hybrid ES technology has been widely applied in power systems because it can take full advantage of the complementary technical characteristics between two types of ES to meet the demand of different customers. Currently, research on hybrid energy storage system(HESS) in the world is still in the stage of basic theory research and demonstration engineering projects. Therefore, studies on HESS models, control, and optimization and so on can provide a helpful guidiance and reference for the applications of HESS in practical engineering.Studies on multi-scale modeling, control strategy design, operation control optimization and integrated optimization have been done in this thesis, which was supported in part by the research projects, such as “Key technologies development of microgrid containing distributed power sources”(863 program, 2011AA05A107) and “Key technologies research and experimental platform construction of HESS with the access of distributed power sources”(major special project of State Grid Corporation, ZDK/GW003-2012). Acoording to the proposed new strategies, new indices and new models, the measures were proposed to improve the overall technical and economic performance of HESS, which are helpful to make decision for optimal operation of HESS, and is also of great significance to promote the application of HESS.The model of energy storage system(ESS) is the basis and prerequisite for microgrid’s design, planning and operation analysis. In order to meet the need of a variety of research on different occasions, the multi-scale models of HESS are necessary. Based on the consideration of technical and economic requirement, a model library is given for the typical HESS containing lithium batteries and supercapacitors. This model library can satisfy the need of transient analysis, steady-state analysis, technical analysis and economic analysis in multiple different applications. The ES devices have a variety of structure and operation, the single-stage device is used in lithium battery ESS(LB-ESS), and the two-stage device with multiple structures is used in supercapacitor ESS(SC-ESS). The transient simulation models of two ESSs which are the same with real devices are checked by PSCAD simulation and real devices’ operation. Considering the impact of self-discharge rate and charge-discharge efficiency, the common model for steady-state analysis is given based on the common characteristics of PES and EES in active power regulation of power system. According to the different service life characteristics of various components in HESS, the different life quantization models are given to meet different technical requirements. Considering the technical and economic impact of all components in HESS, the economic analysis models of each ESS are given respectively from the aspect of initial investment and loss equivalent cost.The existing research of HESS control mainly focused on the protection control of ESSs themselves and power allocation of HESS. A novel control strategy of HESS is proposed to take full advantage of the technical complementary between EES and PES. The coordination of various ESSs in HESS and overall performance optimization of HESS are considered in this strategy. On the basis of filtering power allocation, the overall adjustment ability optimization, over-charge protection coordination, over-discharge protection coordinaton and maximum power limit protection coordination are newly considered in this strategy. Considering the low energy density characteristic of PES, the state of charge(SOC) of PES is dynamically adjusted based on external demand and state of each ESS to optimize the overall regulation ability of HESS. The coordination between two ESSs is considered in over-charge protection, over-discharge protection and maximum power limit protection to meet the need of external demand more properly. At the same time, the specific process and the effect of HESS coordination are reflected by the change of filtering time constant, the real-time operational status and output spectrum analysis of various ESSs. The numerical examples show that, compared with the basic strategy which only considers power allocation, the proposed strategy is the effective way to enhance the overall performance of HESS because it can get better control effect in both storage limited configuration and storage redundant configuration.The parameters of HESS control strategy have certain impact on the control performance. To describe the degree of coordination, a new index, i.e. state of charge coordinated response margin of supercapacitor ESS, is presented. The multi-level optimization models of operation control parameters in HESS are established for extending the lithium battery life, enhancing the overall technical and economic characteristics, etc. The parameters optimized in the models are the main parameters of HESS control strategy such as the filtering time constant of power allocation and the proposed margin index. Taking into account the low-energy density feature of PES, the second-level data of field measurements is used in calculation and analysis to reflect the true work state of supercapacitor ESS. The numerical example indicates the necessity of operation control parameter optimization because it can significantly reduce the total loss equivalent cost of HESS. Sensitively analysis is present for the impact of control parameters’ changes on all influencing factors of lithium battery life loss.Consideirng the impacts of rated power and energy capacities of ESSs on the system technical and economic performance, a comprehensive optimization model is proposed to futher improve the overall system technical and economic perfoermance based on the optimization of operation control parameters. Based on the technical and economic constraints, a new index, i.e. effective rate of ESS, is proposed to reflect the common satisfaction of load demands and power output of renewable energies. An integrated optimization model is built to optimize the rated power and energy capacities of ESSs as well as the control parameters of HESS. The integrated model is used to enhance the overall system technical and economic performance, and is applied to the optimization of EES schemes of practical engineerings. In order to explore the optimal balance among the orderliness of control, the contributive range of frequency and the response ability to instantaneous variables, sensitivity analysis of the impacts of operation control parameters on the system technical and economic performance is presented detailedly. Case studies show that: compared with the optimization results of operation control parameters, integrated optimization can be used to not only further reduce the equivalent total cost of HESS, but also decrease more than half of its total capital cost. |
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