Research On Coordinated Control Method For Bidirectional Power Converters In AC/DC Hybrid Microgrid

Microgrid is an important way to solve the problem of large-scale renewable energy access to the distribution system,AC/DC hybrid microgrids take into account the advantages of AC microgrids and DC microgrids,which has become an inevitable trend in the development of microgrids.The power interface is formed by several bidirectional power converters(BPCs)in a AC/DC hybrid microgrid,the power interface is an important channel connecting the AC sub-microgrid and the DC sub-microgrid,It can support the direct power of the AC sub-microgrid and the DC sub-microgrid to support each other.It can realize the mutual support of the power of the AC sub-microgrid and the DC sub-microgrid,which plays an important role in maintaining the internal power balance of the AC/DC hybrid microgrid.Because a large number of intermittent random power supplies and AC/DC loads are connected to the AC/DC hybrid microgrid,when the AC/DC hybrid microgrid is in island operation mode,due to the loss of power support of the large grid,the internal power fluctuations of the AC/DC hybrid microgrid are more frequent,and the hybrid microgrid is always facing the problem of power balance.Therefore,it is necessary to study the coordinated control method of BPCs in AC/DC hybrid microgrid.This thesis first studies the operation modes of AC/DC hybrid microgrid,and focuses on the droop control mechanism of the BPCs in the power interface in island operation mode.Then,the control structure diagram of the bidirectional power converter under droop control is established.Second,aiming at the flexible control of a single BPC,based on the theory of adaptive inverse control,an adaptive inverse droop control method is studied.In order to improve the dynamic response and steady-state performance of the system,an adaptive inverse droop control method based on the optimal open-loop cutoff frequency is proposed.This method sets the droop coefficient by learning the optimal open-loop cut-off frequency,which further optimizes the system’s dynamic response and steady-state performance.Third,aiming at the problem of coordinated control of multiple BPCs in the power interface under island operation mode,based on the H_∞robust control theory and adaptive inverse droop control theory,combined with the idea of optimal decentralized coordinated control,this thesis proposes a decentralized coordinated control method for multiple parallel BPCs is proposed.This method takes a system composed of multiple BPCs operating in parallel as the research object,and on the basis of ensuring that the adaptive inverse droop control achieves no static difference adjustment,the output of each power converter is coordinated by a H_∞decentralized coordination controller.To a certain extent,the system instability caused by each adaptive inverse droop controller’s unnecessary adjustment of the droop coefficient is avoided,and the dynamic response and steady-state performance of the system are improved.Finally,this thesis verifies the correctness and effectiveness of the control strategy proposed by MATLAB simulation.