Research On Control Strategy Of Three-Phase Stand-alone/Grid-connected Inverter

With environmental pollution and energy crisis, the research of new energy gains moreand more attention. In this paper, based on an inverter with dual mode, control strategies instand-alone and grid-connected mode and related technology are detailedly analyzed.First, main circuit structure of the inverter for battery discharge is given and theswitch of two modes is analyzed. Mathematical models of the inverter are established instand-alone mode and grid-connected mode.Secondly, giving priority to grid-connected mode, selecting inner current ripple,capacitor reactive power consumption as well as ratio of grid-connected current ripple toinner current ripple as starting point, a set of optimal LCL parameter values can be gotthrough the step-by-step method. Besides, LC filter which is obtained by switching LCLfilter can fulfill requirement of stand-alone mode.Then, based on mathematics models of two modes, control strategies are designed. Instand-alone mode, PI+repetitive control are selected as voltage controller and controllerparameters design steps and results are shown. In grid-connected mode, a two-loop controlstrategy under αβ coordinate is adopted which chooses the capacitor current as the innercontrol variable and grid-connected current as the outer loop variable. Moreover, adesigning method is given to get the parameters of the two-loop controller.Finally, a180kVA inverter system for battery discharge with dual mode is developedand selection and design of the key parts are introduced mainly. The inverter system modelis built in Matlab for simulation and experiments are carried out in the developed prototypeinverter. Simulation and experimental results are consistent with theoretical analysisconclusions, which verify the correctness of the analysis.