Modeling and control of three-phase grid-connected PV inverters in the presence of grid faults

A two-stage photovoltaic grid-connected microgrid modeling approach is presented in this work. The purpose of the modeling is the behavior study of the microgrid during the low-voltage event on the grid. A complete mathematical model is discussed for each component of the system. The MPPT of the photovoltaic system is integrated with the boost controller to inject the constant current in the DC-link. The boost converter and the inverter control is implemented using the cascaded PI control. A dual second-order generalized integrator (DSOGI) method is implemented for the sequence extraction. The inverter controller is designed to meet the grid-code requirement of low-voltage ride through (LVRT) and reactive power injection. The simulation model is designed in a MATLAB/PLECS environment, and the controller design is validated by running a low-voltage event on the grid. To observe the interaction of a multiple PV system with the grid, a nonlinear average model of the two-stage grid-connected PV system was designed and validated against the switching model. A low voltage event on the grid was simulated to observe the impact on the multiple PV system. A power quality event of voltage dip during the unbalance voltage on the grid is presented. The implication of the ungrounded system during the low-voltage event is explained. In addition, the importance of grounding and the effect of the line impedance for the why-connected system is described in detail --Abstract, page iii