Research On Improvement Of Renewable Energy Access Capacity In Regional Microgrid With Harmonic Resonance Limits

China has clearly proposed the goal of carbon peaking and carbon neutrality to build the renewable energy dominated power system.However,with the increasingly prominent characteristics of high proportion of renewable energy and high proportion of power electronic devices,grid-connected inverters and the power grid may interact with each other.It will lead to the harmonic oscillation caused by the complex characteristic of the utility grid and load.Further,the improvement of renewable energy access capacity has been limited.In this thesis,the regional microgrid with renewable energy is taken as the research object.Considering the impact of the non-ideal weak grid working condition caused by the access of diversified local load and reactive power compensation capacitor,the improvement of renewable energy access capacity in regional microgrid with harmonic resonance limits is carried out in the following.Firstly,the basic structure and working principle of important devices,which include the utility grid,grid-connected inverter,diversified local load and reactive power compensation capacitor,are introduced.Then a small signal impedance model of three-phase inverter considering current feedback control and phase locked loop is established,and the impedance model of the regional microgrid is built based on the IEEE9-node grid.Based on the source side model and grid side model,the source-grid impedance model of the regional microgrid system is constructed.Secondly,the change of the grid side impedance after the access of diversified local load and reactive power compensation capacitor are analyzed.Then,an inverter impedance reshaping scheme for diversified local load and an inverter loop improvement scheme based on harmonic negative pseudo capacitance capacitor are proposed respectively.On this basis,a composite control scheme for inverter based on capacitive feature cancellation is proposed considering the simultaneous access of diversified local load and reactive power compensation capacitor under the non-ideal weak grid working condition.At the same time,based on the dual limitations of the system Nyquist curve and the open-loop amplitude-frequency characteristic of the single inverter,the engineering setting principles of the parameters in the proposed scheme are given.The improvement scheme effectively suppresses harmonic resonance problems and improves the renewable energy access capacity.Thirdly,the strategy of maximum renewable energy access capacity for single-node of the regional microgrid with harmonic resonance limits is explored,under the working condition of non-ideal weak grid.Through the verification of the conventional control scheme and the composite control scheme based on capacitive feature cancellation,the law of renewable energy access capacity caused by different line impedance of different nodes in regional microgrid is revealed.On this basis,the strategy of maximum renewable energy access capacity for multi-node of the regional microgrid with harmonic resonance limits is explored,and the maximum allocation strategy of renewable energy access capacity in multi-feed regional microgrid with harmonic resonance limits is proposed.These strategies provide guidance on the optimal renewable energy access node and capacity allocation for the installation and address selection of renewable energy power generation units.Finally,the correctness of the above research and the feasibility of the proposed scheme are verified by the multi-inverter experimental platform,which includes the harmonic resonance limits caused by diversified local load and reactive power compensation capacitor,the composite control scheme for inverter based on capacitive feature cancellation,and the strategy of maximum renewable energy access capacity for the regional microgrid with harmonic resonance limits.