Research On Stability Of Parallel Inverters Based On Adaptive Virtual Impedance Control In Harmonic Domain

With the tremendous progress of society and the rapid development of the economy,problems such as environmental pollution and the depletion of the earth’s resources have become increasingly prominent.Micro-grid technology has attracted widespread attention for the problem of reducing resource waste and rationally applying it.However,as a large number of distributed power generation units are connected,during the actual operation of the microgrid,even if a single inverter is stable,the interaction between multiple inverters will still cause series-parallel resonance,which will seriously affect stability.Therefore,research on the stability of the microgrid is very necessary.In this paper,multiple voltage-controlled inverters and multiple current-controlled inverters in parallel system in isolated microgrid are taken as research objects.First,the voltage-controlled inverter is modeled as the Thevenin equivalent circuit,and the current-controlled inverter is modeled as the Norton equivalent circuit.According to the Kirchhoff’s voltage law and Kirchhoff’s current law,the characteristic equation of AC microgrid can be obtained.Secondly,the Middlebrook criterion is used to judge the stability of the island microgrid system,and the effects of inverter control parameters,the number of inverters and line impedance on the system stability are analyzed.Finally,an adjustment strategy based on harmonic domain adaptive virtual impedance control is proposed for the current-controlled inverter.The output impedance of the voltage-controlled inverter and the current-controlled inverter are matched with each other,and the stability criterion is satisfied.Therefore,the stability of the island microgrid system is improved.In order to verify the correctness and feasibility of the method proposed in this paper,PSIM simulation software is used to build simulation models of multiple parallel inverters with different control types.At the same time,the hardware circuit of the system is designed Experimental platform for parallel connection of single-phase full-bridge inverters were built The simulation and experimental results both prove the rationality of the controller design of each inverter and the stability analysis of the multi-inverter parallel system,and also verify that the harmonic virtual adaptive impedance adjustment strategy designed in this paper can effectively improve the stability of the island microgrid system.