Photovoltaic generator modelling to improve numerical robustnessof EMT simulation

Numerical simulation is an indispensable tool for studying photovoltaic (PV) systems, to derive component ratings, optimise protections, design controllers as well as to evaluate the impact of embedded generation on distribution system operation. In EMT simulation, the non-linear equations representing the PV generators are separated from the linear equations of the rest of the power system. This technique presents high computational efficiency but introduces a one-step delay, which can cause problems of numerical instability. These problems are particularly evident when the PV generator is represented by multiple single-diode equivalent circuits, such as in the cases of PV generators composed of different types of arrays or subject to partial shading or interfaced by multilevel inverters. To overcome such problems, in this paper a new approach is proposed to include the PV generator model into EMT simulation. A convergence analysis gives proof of the obtained improvements, which are also confirmed by numerical results. The robustness of the proposed technique is tested by simulation of an IEEE benchmark system in the cases of partial shading and of electric faults.