Research On The Optimization Method Of Equivalent Impedance Of The Grid-connected Interface Circuit

As the energy bridge which connects distributed generations to the public power grid,grid-connected interface circuit is critical for ensuring stable operation and high-quality operation of the microgrid.Its equivalent output impedance to Common DC Bus is a key criterion microgrid to evaluate its characteristics.This paper aims to improve the equivalent output impedance characteristics of grid-connected interface circuit by the optimization of its digital controller.Firstly,the equivalent mathematic model of grid-connected inverter system under cascade control is established.Based on which,the delaying characteristics of the digital controller is taken into account,the paper conducts both quantitative and qualitative analysis about the gains range voltage loop controller and current loop controller.Secondly,the Grid-connected control algorithm of Grid-connected interface circuit in the condition of without Phase Locked Loop according to Instantaneous Power Theory is studied,the functional features of active power and reactive power towards Common DC Bus voltage is decoupled,furthermore the equivalent output impedance model of grid-connected interface circuit towards Common DC Bus is established,and the comprehensive operational mechanism of systematic controller is concluded,controlling parameters and filter towards system equivalent output impedance is revealed as well.The paper also studies the optimization mechanism of disturbance current feedforward control towards system equivalent output impedance on the basis of equivalent output impedance model.Besides,by improving disturbance current feedforward,grid-connected interface circuit is able to realize distributed connection with DC microgrid.The paper also presents a delay compensation link that is applied to inductive current inner loop.The algorithm can be used to expand the value range of voltage loop controller gain and improve system stability margin.The paper also studies whether the algorithm can shape the system equivalent output impedance characteristics.Finally,the simulation experiment is carried out in Matlab/Simulink environment,and the back-to-back form of simulation DC microgrid disturbance experiment platform and grid interface circuit experiment platform are set up,The simulation and experimental results show that the analysis method and the impedance optimization strategy are effective.