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.

The increasing penetration of Renewable Energy Sources (RES) and, more in general, of converter connected power generation is progressively reducing the overall inertia of the electricity system introducing new challenges in the network Frequency Support (FS). Therefore, FS strategies for RES are becoming an important aspect to be developed in order to ensure the secure operation of the electricity power grid. The aim of the present article is to propose an innovative approach for the inertial emulation of Wind Turbine Generators (WTGs) in order to ensure a positive effect on the system frequency avoiding unstable operations of the WTG and reducing the negative impact of the rotor speed recovery on the secondary frequency drop. Moreover, the paper provides a detailed definition of the triggering logics adopted to activate and deactivate the FS making it suitable for implementation in available industrial controllers. The proposed controller is firstly tested in a simplified configuration to show its enhanced performances with respect to previously developed approaches. Then, simulations are carried out in a more realistic network to assess the positive impact of the controller on the system frequency. Results highlighted a 40% reduction of the system Rate of Change of Frequency while the frequency deviation at the transient nadir is improved of 35%.

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.