In the modern scenario of smart-grids, the concept of Virtual Power Plant (VPP) is undoubtedly a cornerstone for the smooth integration of Renewable Energy Sources (RESs) into existing energy systems with an high penetration level. A Virtual Power Plant is the aggregation of decentralized medium-scale power sources, including photovoltaic and wind power plants, Combined Heat and Power units, as well as demand-responsive loads and storage systems, with a twofold objective. On the one hand, VPP relieves the stability and dispatchability problems on the external smart-grid since it can be operated on an individual basis, appearing as a single system on the whole. On the other hand, VPP improves flexibility coming from all the networked units and enable traders to enhance forecasting and trading programs of renewable energies. This paper proposes a novel distributed decentralized prediction method for the management of VPPs. The novelty of the proposed technique is to effectively combine the concepts of neural networks and machine learning with a distributed architecture that is suitable for the aggregation purposes of the VPP.

We present the evaluation of the induced voltages in a lossless single transmission line, located at a given height over an infinite conductivity ground plane, and exited by an external field due to a step current moving along a vertical channel. This is a classic topic of the theory of lightning-induced voltages on power lines. The technical literature related to this topic has performed a significant effort; however, only approximated formulas have been obtained so far. In this paper, we derive the exact closed-form solution. We also will discuss, evaluate, and compare the approximated formulas with reference to the proposed exact one, thus contributing to clarifying a matter that still is debated and sometimes misleading, as we will show in the paper. We furthermore recall that the examined lightning-induced voltages model is fundamental for the IEEE standard 1410, a guide for improving the lightning performance of power distribution line.

In this paper, we present a new tool for lightning-induced voltage calculations. The tool, a circuit model which can be integrated into power systems simulators, is based on the theory developed by Andreotti (2001, 2009, 2013). In Part II, the accuracy, stability, and efficiency of the new tool are demonstrated via comparison with other solutions/codes found in the literature and with experimental data.

Recently, Andreotti (2009) have presented an analytical solution for the evaluation of voltages induced on an infinitely long, lossless, single-conductor located at a given height above an infinite-conductivity ground plane, and excited by an external field due to a step current wave moving without attenuation and at a constant speed along a vertical lightning channel. The solution presented, in contrast to previously published solutions, was derived in an exact way, i.e., no approximations were introduced in its derivation. In this paper, this exact approach is extended to more practical line configurations. Specifically, still for the case of an external field due to a step current and perfectly conducting ground, the cases of terminated single-conductor line and multiconductor line (including grounded conductors) will be studied. Further, single- and multiconductor lines (including grounded conductors) excited by an external field due to a linearly rising current will be examined.

When concerning the installation and operation costs, it is always desirable to protect an overhead distribution network with a limited quantity of surge arresters (SAs). This paper presents a novel procedure for designing differentiated protection against lightning, by identifying appropriate positions for those SAs on the overhead line. Rather than the traditional flashover rate of a whole line, indices in terms of flashover numbers at individual poles and associated with possible stroke locations are introduced in this paper. Based on these flashover indices, a differentiated configuration of SAs can be identified using a selection strategy. After several rounds of selection, a differentiated SA protection scheme can be obtained, given by a pre-set quantity of SAs. In this procedure, a simplified probability-based approach is proposed to determine the flashover indices. By comparing the traditional Monte Carlo method, this approach can achieve a 10-fold increase in computational efficiency with reasonable accuracy. Two different selection strategies are introduced in this paper. Compared with the selection strategy using the flashover indices at individual poles, the selection strategy based on a group of poles is recommended because it yields a configuration with better lightning performance with the same quantity of SAs. This design procedure is applied to practical distribution networks with a shield wire and nearby structures. The influence of grounding impedance, a shield wire, and nearby structures is addressed. Finally, a generalized step-by-step procedure is provided to assist in a differentiated SA protection design.

The presence of the new liberalized markets has increased the interest in power-quality (PQ) disturbances due to their economic effect. In particular, in the case of disturbances caused by a single event (such as a capacitor switching or voltage sag), the waveform assessment can be difficult due to the rapid variations in waveform spectral component characteristics; these difficulties require a suitable choice of signal-processing techniques for spectral analysis and, in particular, the resort to time-frequency representations. In this paper, the adaptive Prony method is proposed to calculate PQ indices based on a time-frequency analysis of waveforms. Numerical applications on a simulated transient due to capacitor switching, a measured voltage sag, and a test waveform are also presented and discussed in order to investigate the validity of the proposed method.