Feedback linearisation oriented approach to Q–V control of grid connected photovoltaic units

This study proposes a new control scheme to manage active and reactive power injections into the distribution grids provided by photovoltaic (PV) generating units. Such scheme is derived by resorting to the so-called 'feedback linearisation' theory, which relies on the central concept to algebraically transform non-linear systems dynamics into fully or partly linear ones, so that linear control techniques can be applied. To do this, a suitable state transformation is required, in order to simplify the form of the power system to be controlled. The developed scheme receives as input the reference signal for the PV unit voltage (generated by a maximum power point tracker controller) and the one for the desired reactive power and produces as output the modulating signal of the grid interface pulse width modulation inverter. A detailed simulation campaign on a medium voltage grid connected PV power plant is performed in the PSCAD-EMTDC electromagnetic environment, in order to verify the effectiveness of the proposed control algorithm and to highlight its main advantages with respect to traditional regulation methodologies.