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Research On Distributed Cooperative Control Of Microgrid

Posted on:2018-07-09Degree:MasterType:Thesis
Country:ChinaCandidate:W H YanFull Text:PDF
GTID:2382330572465825Subject:Control theory and control engineering
Abstract/Summary:PDF Full Text Request
As a systematic approach to integrate renewable energy into power grid,microgrid has gained widely attention since its advantages such as flexible structure and environmental friendly.Microgrid is considered as a small-scale low-and medium-voltage level power system which unifies transmission level and distribution level.Different from traditional power grid and its rigid network structure,microgrid contains a large amount of intermittent DGs with small capacity and the locations of DGs are widely distributed.Therefore,centralized control structure usually employed in traditional power grid encounters great challenges in microgrid systems.In order to address this problem,a distributed cooperative control structure for inverter based microgrid is proposed in this paper.Besides,photovoltaic DG and its energy storage system are analyzed.The local primary control of microgrid based on virtual synchronous generator(VSG)also is designed in this paper and the distributed cooperative control strategy is presented.Furthermore,the cooperative regulation of microgrid's voltage and frequency can be realized in this paper.First of all,this paper analyzes the distributed photovoltaic generation system.Extremum Seeking with variable gain algorithm is proposed in order to improve the efficiency of maximum power point tracking(MPPT).Besides,a Ternary Interleaved Boost Converter Topology is employed such that the output power of distributed photovoltaic generator becomes more stable and steady voltage output of DG can be achieved.Meanwhile,energy storage subsystem is implemented in DG so that more stable and reliable output of DG can be guaranteed.Simulations and experiments are able to verify the validity of proposed approach.Secondly,the local control structure of microgrid is established based on the analysis of droop control method.Moreover,VSG algorithm is developed as microgrid local power controller in order to make inverter of DG to further imitate the dynamic behavior of traditional synchronous generator.Meanwhile,the state-space model of VSG and its stability analysis are also presented in this paper elaborately.Based on the analysis of VSG,it can be summarized that VSG and droop control method are identical during their steady state.However,VSG is able to perform better anti-disturbance characteristic during its transient state comparing to droop control.Then,aim to the microgrid system which contains multiple DGs,feedback linearization method is used to linearize the mathematical model of each DG.Hence overall microgrid model can be obtained according to actual communication network of microgrid system.In order to restore the steady error caused by load disturbance which cannot be overcame through individual microgrid primary controller,this paper designs and performs the distributed cooperative secondary control strategy for microgrid system.Cooperative regulation of DGs can be achieved through proposed distributed cooperative secondary control strategy.It ensures the states such as the voltage and frequency of microgrid can be restored to nominal value effectively.Finally,simulation model of both DG and microgrid system is performed in Matlab/Simulink platform.Consider actual microgrid,modified IEEE 14 bus testbed is employed as microgrid model.In this paper,both DG system based on VSG algorithm and the distributed cooperative control system for inverter-based microgrid are performed.Simulation results demonstrate the validity and feasibility of proposed method.
Keywords/Search Tags:distributed generator, microgrids, droop control, virtual synchronous generator, distributed cooperative control
PDF Full Text Request
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