Modeling and control of a single-phase grid-tied medium-frequency isolated converter for active and reactive power management in photovoltaic applications

A single-phase photovoltaic converter formed by the full-bridge dc-dc converter with a capacitive output filter and a grid-tied full-bridge inverter is studied in this paper. The switched model, the average model based on a modified-conventional approach, and the linear state-space model of the dc stage operating in discontinuous conduction mode are presented and compared with the behavior of the state variables obtained from a simulator. A duty-ratio constraint is obtained from the modified average model, which is eliminated by expressing its dependency on the control and the state variables. In addition, the modeling of the ac stage is carried out in the dq reference frame. Linear controllers are designed to guarantee the maximum power point tracking, the regulation of the dc-link voltage, the injection of the active power generated, and the reactive power management as an ancillary function. The controllers proposed, according to the transfer functions derived from the linear models, are validated via simulation for a 1.41 kVA converter.