Grid-interfaced photovoltaic system with enhanced resilient control schemes for low-voltage ride-through

The fast-growing influence of grid-interfaced photovoltaic (PV) networks makes it necessary to adhere to grid-code (GC) regulations. These regulations mandate that PV systems inject active power both during and after the grid fault occurrence, as well as provide reactive current to the grid during voltage dips, in order to prevent power system stability concerns. In this context, two novel control schemes have been proposed in this paper for grid-connected photovoltaic networks that can support low-voltage ride-through (LVRT). The proposed control techniques have been demonstrated to be simple and efficient in the event of severe voltage dips, i.e., work up to a voltage drop of 90% of the nominal grid voltage. Our first approach involves an enhanced reactive current injection strategy that provides reactive power support to the power grid during voltage dips without any additional devices. The control structure is comprised of a voltage level estimator and a reactive current controller. The voltage level estimator obtains power grid voltage, while the reactive current controller computes active−reactive current commands. It is particularly noteworthy that the proposed scheme generates active current as much as possible according to the voltage dips and tracks the active current reference correctly, where conventional strategies fail to cope. The second control method for LVRT presented in this research work involves using hardware, specifically a crowbar. The use of a crowbar is the most straightforward method to provide support to the power system, bypassing over-current during voltage dips and keeping the current within the normal converter rating. The control strategies proposed in this paper are validated in MATLAB/Simulink under symmetrical and unsymmetrical severe voltage dips as well as grid voltage harmonics, and a detailed comparison study with a state-of-the-art PQ-based fault-ride-through controller has been conducted.