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Power Control Technique For Energy Storage Systems In DC Microgrid

Posted on:2018-07-31Degree:DoctorType:Dissertation
Country:ChinaCandidate:J YangFull Text:PDF
GTID:1312330512497562Subject:Electrical engineering
Abstract/Summary:PDF Full Text Request
Micro-grid is not only the trend of distributed energy resources distribution systems,but also the significant part of future power system.In micro-grid system,many distributed energy resources such as photovoltaic and fuel cell have dc output type,and dc type load is booming,so dc micro-grid improves the system efficiency because many conversion stages are eliminated.Meanwhile,there is no reactive power and harmonics in dc system,which means easier-controlled.In this paper,power electronics converter(hereafter referred to micro-grid converter)control is studied with energy storage system in dc microgrid as the object of the research,aiming at building a general primary control which can achieve three kinds of power control objectives,while enriching the primary control layer and simplifying systematic control layer.Firstly,the primary control of dc micro-grid is investigated.The model of dc micro-grid with multiple micro-grid converters is built,and based on this the relationship between line resistance and power sharing accuracy is analyzed.To reduce the effect of line reistance,an improved droop control is proposed where change rate of voltage is global indicator.Meanwhile,zero-resetting controller is also proposed to compensate the improved droop and make sure the stability of dc voltage.Small-signal model is built for system stability analysis.The proposed method is verified by experimental results.Secondly,distributed energy storage systems are analyzed to prolong the life of energy storage units.Based on the improved primary control,an adaptive SOC controller is proposed.The comprehensive principle of power sharing for distributed energy systems is given,and a unified control strategy is proposed based on this principle.Power sharing ability under different controllers is discussed,and experimental results show the effectiveness of proposed control.Thirdly,to improve the dynamic characteristics and power quality of dc micro-grid,hybrid energy storage systems are analyzed.Based on the improved primary control,a wireless hierarchical control strategy is proposed to realize power sharing between energy density storage unit and power density storage unit in reasonable fashion.First control introduces change rate of voltage as virtual information carrier,and urges supercapacitor unit to pick up major dynamic power immediately in the load switching moment,by setting sensitivity of different storage units.The steady state error produced in primary control is eliminated by secondary control,in which voltage magnitude is maintained and zero steady state current in supercapacitor is guaranteed.The feasibility and effectiveness of the proposed control strategy are validated by experimental results.Fourthly,systematic control of dc micro-grid is investigated.The model of dc micro-grid with multiple buses is build and based on this the improved primary control is also feasible in the complex structure.A virtual capacitor representation has been addressed to introduce the change rate of the dc output voltage.This global indicator has been employed to avoid negative effect on current sharing caused by mismatched networks.A complementary virtual resistance has been added for keeping output voltage at steady state.Consensus algorithm is transplanted into zero-resetting controller due to their similarity,and an improved droop with consensus mechanism is proposed.The feasibility and effectiveness of the proposed control strategy are validated by simulation results.
Keywords/Search Tags:Dc micro-grid, Micro-grid converter, Distributed energy storage systems, Hybrid energy storage systems, Change rate of voltage, State of charge, Virtual impedance, Consensus algorithm
PDF Full Text Request
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