Modeling and control of a grid connected VSI using a delta connected LCL filter

In order to connect an LCL filter in a three phase system, two methods are possible. The first one is a wye connection and the second one is a delta connection. To study the stability problems, a mathematical model should be known, but the model of a delta connected LCL filter is not formulated. In this paper, a model with transfer functions is proposed for that purpose. Furthermore, this paper describes the design of a proportional plus resonant controller who regulates grid currents. The design is based on the frequency response analysis. Controller design is respectively carried out for a system with a delta connected LCL filter and a system with a wye connected LCL filter. To verify the proposed model and the designed controller, simulation and experimental results for a system with a delta connected LCL filter are compared with results for a system with a wye connected LCL filter.