Modeling and Control of Grid-Connected Three Phase Inverters

This paper analyses the stability problem of grid connected inverter. Distributed generation (DG) systems are usually connected to the grid using power electronic converters. Power delivered from such DG sources depends on factors like energy availability and load demand. The converters used in power conversion do not operate with their full capacity all the time. The unused or remaining capacity of the converters could be used to provide some ancillary functions like harmonic and unbalance mitigation of the power distribution system. As some of these DG sources have wide operating ranges, they need special power converters for grid interfacing. Being a single-stage buck-boost inverter, recently proposed Z-source inverter (ZSI) is a good candidate for future DG systems. This paper presents a controller design for a ZSI-based DG system to improve power quality of distribution systems. Due to the variation of grid impedances, the system gets affected by stability problems. Since the grid impedance varies, the system tends to be unstable. In this control strategy, the inverter is controlled by means of robust H^∞ controller along with stability is analyzed. An inner inverter-output-current loop with high bandwidth is also designed to get better disturbance rejection capability. The selection of weighting functions, inner inverter-output-current loop design, and system disturbance rejection capability are discussed in detail in this paper. The proposed control method is tested with simulation results obtained using Matlab/Simulink. In this paper the performance of the grid model is compared when it is connected from renewable energy sources through traditional and Z-Source inverter.