Direct current (DC) microgrids (MG) constitute a research field that has gained great attention over the past few years, challenging the well-established dominance of their alternating current (AC) counterparts in Low Voltage (LV) (up to 1.5 kV) as well as Medium Voltage (MV) applications (up to 50 kV). The main reasons behind this change are: (i) the ascending amalgamation of Renewable Energy Sources (RES) and Battery Energy Storage Systems (BESS), which predominantly supply DC power to the energy mix that meets electrical power demand and (ii) the ascending use of electronic loads and other DC-powered devices by the end-users. In this sense, DC distribution provides a more efficient interface between the majority of Distributed Energy Resources (DER) and part of the total load of a MG. The early adopters of DC MGs include mostly buildings with high RES production, ships, data centers, electric vehicle (EV) charging stations and traction systems. However, the lack of expertise and the insufficient standards’ framework inhibit their wider spread. This review paper presents the state of the art of LV and MV DC MGs in terms of advantages/disadvantages over their AC counterparts, their interface with the AC main grid, topologies, control, applications, ancillary services and standardization issues. Overall, the aim of this review is to highlight the possibilities provided by DC MG architectures as well as the necessity for a solid/inclusive regulatory framework, which is their main weakness.

The integration of a variety of heterogeneous energy sources and different energy storage systems has led to complex infrastructures and made apparent the urgent need for efficient energy control and management. This work presents a non-linear model predictive controller (NMPC) that aims to coordinate the operation of interconnected multi-node microgrids with energy storage capabilities. This control strategy creates a superstructure of a smart-grid consisting of distributed interconnected microgrids, and has the ability to distribute energy among a pool of energy storage means in an optimal way, formulating a virtual central energy storage platform. The goal of this work is the optimal exploitation of energy produced and stored in multi-node microgrids, and the reduction of auxiliary energy sources. A small-scale multi-node microgrid was used as a basis for the mathematical modelling and real data were used for the model validation. A number of operation scenarios under different weather conditions and load requests, demonstrates the ability of the NMPC to supervise the multi-node microgrid resulting to optimal energy management and reduction of the auxiliary power devices operation.

In this paper, an interactive learning experience is proposed, aiming to involve museum visitors in a personalized experience of the transmittal of cultural knowledge in an active and creative way. The proposed system, called HapticSOUND, consists of three subsystems: (a) the Information, where visitors are informed about the traditional musical instruments; (b) the Entertainment, where visitors are entertained by playing serious games to virtually assemble traditional musical instruments by a set of 3D objects; and (c) the Interaction, where visitors interact with a digital musical instrument which is an exact 3D-printed replica of a traditional musical instrument, where cameras have been placed to capture user gestures and machine learning algorithms have been implemented for gesture recognition. The museum visitor can interact with the lifelike replica to tactilely and aurally explore the instrument’s abilities, producing sounds guided by the system and receiving real-time visual and audio feedback. Emphasis is given to the Interaction Subsystem, where a pilot study was conducted to evaluate the usability of the subsystem. Preliminary results were promising since the usability was satisfactory, indicating that it is an innovative approach that utilizes sensorimotor learning and machine learning techniques in the context of playing sounds based on real-time gesture and fingering recognition.

Premature ageing of lithium-ion battery energy storage systems (BESS) is a common problem in applications with or without renewable energy sources (RES) in the household sector. It can result to significant issues for such systems such as inability of the system to cover load demand for a long period of time. Consequently, the necessity of limiting the degradation effects at a BESS leads to the development and application of energy management strategies (EMS). In this work, EMSs are proposed in order to define optimal operation of a BESS without RES under time-of-use (ToU) tariff conditions. The objective of the developed EMSs is to reduce the capacity loss at the BESS in order to extend its lifetime expectancy and therefore increase the economic profit in the long-term. The EMSs utilize a widely used battery mathematical model which is experimentally validated for a specific BESS and a battery degradation mathematical model from the literature. Indicative simulation results of the proposed strategies are presented. The outcomes of these simulated scenarios illustrate that the objectives are achieved. The BESS operates efficiently by preventing premature ageing and ensuring higher economic profit at the long term.

The design of simple linear control laws via linear mathematical models is a standard part of every control systems laboratory in a standard undergraduate curriculum. A typical example is the design of PI control laws for the speed control problem of DC motors. Embedded control is taught nowadays using cheap take-home equipment based on low-cost microprocessors like Arduino and dc micro-motors. Although offering ease for the demonstration of simple PI control laws, these motors exhibit nonlinear characteristics, which can be dealt with the application of more advanced control laws. The paper's purpose is twofold: first, to explore the possibilities offered by low-cost equipment, as a test bed for the “proof of concept” of more sophisticated switching control laws; and secondly to unfold the possibilities offered by this new environment for teaching, demonstration, project work, as well as research purposes, in the current laboratory practice.