Dynamic model of a grid-connected three-phase inverter with slope voltage control

Three-phase inverters are the mostly used converters for connecting distributed generation sources to the main grid. Conventionally, these renewable sources must inject only its generated active power. Recently, reactive power injection has been included in some national grid codes. In voltage regulation, the conventional PI control can not be used. The whole system tends to instability when PI controllers work distributively for voltage regulation in different connection points along the grid. The slope voltage controller seems to be the best option to avoid these instabilities. The parameters design of the slope voltage controller is normally carried out by trial and error methodology due to lack of a small-signal model of the complete system. With this widely used methodology, the dynamic behavior can not be determined by the designer. This work develops a closed-loop small signal model of a grid-connected distributed generation source with voltage regulation capabilities. The derived mathematical model predicts accurately the system behavior in the frequency range of interest. This model can be used in future research for tuning the controller parameters with the aim of achieve predefined design objectives. The model has been validated through simulation results.