The strong increase in the number of installed photovoltaic (PV) production plants has slowly changed the assets and the operating conditions of the electricity power system. In this context, the supply and control of the reactive power from the renewable generation plants are becoming an important issue to be exploited that can facilitate the integration of PV and wind power in electricity grids. The aim of this paper is to propose an optimized control strategy to manage the reactive power resource generated by PV plants in order to improve the quality of the low/medium voltage distribution network and meet the latest technical requirements listed by distribution system operators in their grid codes. A methodology to define the optimal reactive power references for each PV unit connected to a generic distribution network is presented for a specified goal (e.g., the achievement of suitable voltage levels at the grid nodes). Such reference signals are then provided to the PV plants regulation systems, which are designed in order to guarantee the decoupling between the active and reactive power channels, due to the use of the Feedback Linearization control technique. The problem is formulated in a generalized way, so that it can be extended to any possible grid configuration.

In this paper, the developed formulation, which we shall call the “reference” one, is used to assess the validity of the most popular simplified approach for the calculation of the lightning electromagnetic field over a conducting earth, namely, the Cooray‐Rubinstein (CR) approximation. This formula provides a simple method to evaluate the radial component of the electric field which is the component most affected by the finite ground conductivity and which plays an important role within the Agrawal et al. (1980) field‐to‐transmission line‐coupling model. Several configurations are examined, with different values for the ground conductivity and different field observation points. A thorough analysis of all the simulated field components is carried out and comparisons are also made with the “ideal” field, namely, the field that would be present under the assumption of perfectly conducting ground. It is shown that for channel base current typical of subsequent strokes and for very low conductivities, the CR formula exhibits some deviations from the reference one but it still represents a conservative estimation of the radial field component, since it behaves as un upper bound for the exact curve. The developed algorithm is characterized by fast performances in terms of CPU time, lending itself to be used for several applications, including a coupling code for lightning induced overvoltages calculations.

The paper addresses the important issue of evaluating the overvoltages produced on a power system by a lightning event. First, the theoretical formulation of the problem in the time domain is presented. Then its numerical solution together with its implementation is described. Finally, a PSCAD-EMTDC interface and platform is developed, which allows us to model a realistic network, automatically distinguish between direct and indirect strokes and account for power network precontingency conditions. The obtained results are compared with a frequency-domain solution for a simple case in order to validate the finite-difference time-domain method adopted to solve the coupling equations and the interface with PSCAD. The comparison with the well-known LIOV code for a more complex case is used as a general validation of the overall tool. In a companion paper, the developed platform will be used to evaluate the lightning performance of a portion of the Italian MV distribution network.