Among the innovative contributions to electric distribution systems, one of the most promising and qualified is the possibility to manage and control distributed generation. Therefore, the latest distribution management systems tend to incorporate optimization functions for the short-term scheduling of the various energy and control resources available in the network (e.g., embedded generators, reactive power compensators and transformers equipped with on-load tap changers). The short-term scheduling procedure adopted in the paper is composed by two stages: a day-ahead scheduler for the optimization of distributed resources production during the following day, an intra-day scheduler that every 15 min adjusts the scheduling in order to take into account the operation requirements and constraints of the distribution network. The intra-day scheduler solves a non-linear multi-objective optimization problem by iteratively applying a mixed-integer linear programming (MILP) algorithm. The linearization of the optimization function and the constraints is achieved by the use of sensitivity coefficients obtained from the results of a three-phase power flow calculation. The paper shows the application of the proposed approach to a medium-voltage 120 buses network with five wind plants, one photovoltaic field, ten dispatchable generators, and two transformers equipped with on-load tap changers.

Energy storage has become a key issue for achieving goals connected with increasing the efficiency of both producers and users. In particular, supercapacitors currently seem to be interesting devices for many applications because they can supply high power for a significant amount of time and can be recharged more quickly than electrochemical batteries. In different applications, a combination of the two devices, batteries and supercapacitors, could be used to develop a high-efficiency storage system with a high dynamic performance. Because of the diffusion of supercapacitors, a good model is needed to represent their behavior in different applications. Some models have been proposed that characterize supercapacitors working at either low or high frequencies. In this paper, the authors present a full-frequency-range model that can be used to represent all of the phenomena that involve supercapacitors. Moreover, to realize a simple and useful tool, the authors present a simple procedure to identify the parameters of the model that can be used to characterize a supercapacitor before use.

The paper proposes the modeling and the optimal management of a hot-temperature (sodium nickel chloride) battery system coupled with wind generators connected to a medium voltage grid. A discrete-time model of the storage device reproducing the battery main dynamics (i.e., state of charge, temperature, current, protection, and limitation systems) has been developed. The model has been validated through some experimental tests. An optimal management strategy has been implemented based on a forward dynamic programming algorithm, specifically developed to exploit the energy price arbitrage along the optimization time horizon (“generation shifting”). Taking advantage of this strategy wind generation performances can be enhanced and adapted to load demand, obtaining an increased economic gain measured by the difference between the economic revenue obtained with and without the proposed generation shifting policy.

Currently, the quality of supplied power is important to several customers. Power quality (PQ) is a service and many customers are ready to pay for it. In the future, distribution system operators could decide, or could be obliged by authorities, to supply their customers with different PQ levels and at different prices. A new device that can fulfill this role is the OPEN unified power-quality conditioner (UPQC), composed of a power-electronic series steady-state performancemain unit installed in the medium-voltage/low-voltage (LV) substation, along with several power-electronic shunt units connected close to the end users. The series and parallel units do not have a common dc link, so their control strategies are different than traditional UPQC control techniques. This device can achieve general improvement in PQ, reducing the most common disturbances for all customers that are supplied by the mains (PQ) by using only the series unit. Additional increments in PQ (i.e., mains power interruptions), can be provided to the customers who need it (custom power) by the shunt units. Therefore, this new solution combines an improvement in PQ for all end users, with a cost reduction for those that need high quality power. The proposed solution has been analyzed and described, and a model of a 400-kVA LV grid is considered a test network to evaluate the steady-state performance and functioning limits. The results obtained under steady-state conditions justify the configuration chosen and good device performance.

During overloads in the mains, the load curtailment applied to interruptible loads is often the only solution to keep the network in operation. Normally, in contingencies, the difference between the power absorbed and the power produced is very low, often less than 1% of the latter. Therefore if all the loads participated in the load shedding program, the discomfort would be minimal, considering its usually short duration. According to this point of view, we present a new approach to the load shedding program to guarantee the correct electrical system operation by increasing the number of participants. This new load control strategy is named Distributed Interruptible Load Shedding (DILS). Indeed, it is possible to split every user's load into interruptible and uninterruptible parts, and to operate on the interruptible part only. The optimal load reduction request is found by minimizing the expected value of an appropriate cost function, thus taking the uncertainty about the power absorbed by each customer into account. Presently, several users such as hospitals, data centres, supermarkets, universities, industries, etc. might be very interested in typical shedding programs as a way to spare money in their electrical account. However, in the future, when the domotic power plants are likely to be used widely, the distributors could interest the end users in participating in DILS programs for either economic or social reasons. By adopting the DILS program, the distributors can resort to the interruptible loads not only in case of emergency conditions but also during normal and alert operations.

Inertia is a measure of a power system’s capability to counteract frequency disturbances: in conventional power networks, inertia is approximately constant over time, which contributes to network stability. However, as the share of renewable energy sources increases, the inertia associated to synchronous generators declines, which may pose a threat to the overall stability. Reliably estimating the inertia of power systems dominated by inverted-connected sources has therefore become of paramount importance. We develop a framework for the continuous estimation of the inertia in an electric power system, exploiting state-of-the-art artificial intelligence techniques. We perform an in-depth investigation based on power spectra analysis and input-output correlations to explain how the artificial neural network operates in this specific realm, thus shedding light on the input features necessary for proper neural-network training. We validate our approach on a heterogeneous power network comprising synchronous generators, static compensators and converter-interfaced generation: our results highlight how different devices are characterized by distinct spectral footprints - a feature that must be taken into account by transmission system operators when performing online network stability analyses.