Research On Off-grid Inverter Based On Quasi Proportional Resonance Control And Parallel Control Strategy

The construction of off-grid regional microgrid can effectively solve the power transmission problem caused by the random distribution of micro source,improve the overall utilization rate,and promote the development and utilization of new energy sources.As the interface unit of micro source and microgrid,the output power quality and parallel characteristics of the inverter directly affect the performance of the microgrid.Therefore,based on the single-phase full bridge topology,this paper research on the output characteristics and parallel control strategy of the off-network inverter.In this paper,firstly the double loop control model that the inductance current proportion control and the capacitor voltage proportional-integral control is established.In order to reduce the effect of load on the output voltage,an output impedance reshaping strategy based on load current feedforward is proposed,which effectively inhibits the load effect.Aiming at the problem that low output voltage accuracy and large low order harmonic content of double loop control inverter,the voltage outer loop based on quasi PR control of is proposed.It realizes the closed loop tracking for the given signal without static error,and reduce the output impedance at the harmonic frequency,and reduce the corresponding frequency point output voltage harmonics.Secondly,in order to improve the flexibility and reliability of micro grid system,and realizing the micro source plug and play,wireless parallel control structure based on droop control is adopted in this paper.The active power loop model and the reactive power loop model is established by dynamic vector method.The effect of droop coefficient on the stability and dynamic performance of the parallel system is analyzed through the root locus diagram,and the range of the droop coefficient is derived.At the same time,the virtual impedance is designed to suppress the circulation of parallel inverters.Finally,the simulation model of the system is built by MATLAB/Simulink.The load current feedforward,quasi proportional resonant control and droop parallel control strategy are simulated and verified.The system hardware and software are designed,and two sets of 2.5kW parallel inverter experimental platform is established.The proportional integral dual loop control and quasi proportional resonant control was validated,and selecting appropriate droop coefficient to realize the two inverters wireless parallel control.