DC Stage Modelling for LVRT Capability in Photovoltaic Systems

The design of control algorithms for power converters requires the modeling of different power stages. The selection of the appropriate models must consider the trade-off between accuracy and complexity according to the application to be analyzed. In grid-connected photovoltaic (PV) systems, the model for the PV panels array and the DC booster can be as simple as an ideal independent DC voltage source at the inverter DC side. However, this model does not correctly represent operational phenomena such as voltage oscillations on the DC-link during unbalanced faults. This paper compares some of the most common DC-stage models to characterize their performance to study low voltage ride-through (LVRT) capacities. Selected operational cases are simulated to discuss the advantages and limitations of the models under study. Results indicate that the best models to study oscillations at the DC-link include a variable current source with a PI control that calculates the injected power reference and the source reference as well as a constant current source with a chopper resistor.