Simplified feedback linearization control of a single-phase photovoltaic NPC converter in direct-quadrature rotating reference frame

Half-Bridge Neutral Point Clamped (NPC) converter topology is particularly proper for transformer-less grid-connected photovoltaic (PV) systems since it avoids leakage currents circulation. In case of single-phase applications, resonant controllers are successfully applied to PV converters due to the optimum tracking and harmonic rejection capability in spite of the poor performances of the PI controllers. Nonlinear control methods, such as controls based on the Feedback Linearization (FL), provide global stability compared to controllers based on small-signals linearized model. However conventional FL method, applied to a grid-connected converter, is very complex and its implementation involves a high computational burden. In this paper a Simplified Feedback Linearization (SFL) control is applied to a single-phase NPC converter for PV transformer-less applications. An imaginary orthogonal circuit has been introduced in order to develop the control system in a direct-quadrature (d-q) rotating reference frame. The proposed control scheme guarantees infinite gain at the fundamental frequency and consequently no steady-state error. It exhibits also high power quality and satisfactory dynamic performances. The advantage relies on taking into account every coupling term into the model of the considered system, hence it provides global stability.