| In today’s global context of decreasing traditional fossil fuels and increasing environmental pressure,countries around the world are actively developing clean,safe,efficient and sustainable modern energy sources,and microgrid technology,which can exploit clean energy such as wind and solar,has become one of the main means to develop renewable energy.Unlike traditional large grids,microgrid is a weak grid,the impedance on the grid side is not negligible and will change.The changing impedance of microgrid will cause the original control strategy of the system to fail,the robustness of the grid-connected inverter will be reduced,and the grid-connected current will be distorted under the influence of grid harmonics,which will cause the system to lose stability and cannot guarantee good power quality.Compared with the large grid inverter using voltage proportional feedforward to suppress grid voltage harmonics,the effect of microgrid impedance will reduce the effect of this strategy,and the inverter system will no longer be stable when the impedance changes too much.The study of inverter control strategy in microgrid has become a hot topic nowadays.In order to improve the robustness of the inverter and ensure the high quality of power output,a single-phase LCL-type grid-connected inverter is used as the research object.The circuit adopts the double closed-loop control of capacitor current inner loop and grid current outer loop to suppress the resonant spikes of the LCL filter and ensure the phase of the output current synchronized with the grid voltage phase.To address the problem that the traditional voltage proportional feedforward reduces the stability of the system under the microgrid,the traditional grid voltage proportional feedforward is improved by adding an integration link based on impedance identification to the proportional feedforward channel,which improves the phase margin of the system to a certain extent to ensure the stability of the system.When the grid impedance changes too much,a single improved voltage proportional feedforward with fixed controller parameters is not enough to achieve the desired operating state,and then gain scheduling adaptive control is used to dynamically modulate the controller parameters according to the grid impedance at this moment to ensure the system has good phase margin and improve the robustness of the inverter.After that,the simulation model is built and simulated in Matlab/Simulink,and the simulation results confirm the feasibility of the scheme.Finally,the experimental platform of single-phase grid-connected inverter with 2k W output power is designed and built from both hardware and software parts,and full-load/half-load switching experiments are conducted on the inverter under gain scheduling adaptive control to further verify the effectiveness of this control strategy. |
