• Energy Research

Road transportation accounts for about 20% of the total GHG emissions in the EU. Nowadays, the substitution of conventional fossil fuel-based ICEs with electric engines, or their hybridization, operating along with Energy Storage Systems, seems to be the most appropriate measure to achieve reductions in both fuel consumption and GHGs. However, EVs encounter crucial challenges, such as long charging time and limited driving range. Hence, the transition to the mass adoption of EVs requires considerable effort and time. However, significant steps have been taken in the hybridization of road vehicles, with the aid of renewables and energy recovery/saving systems. In this context, this paper presents a comprehensive literature review of modern green technologies for GHG reduction that are applicable to road transportation, such as on-vehicle energy harvesting and recovery (e.g., thermal, kinetic, etc.) systems and the incorporation of RES into EV charging stations. The impact of road vehicles on the environment is discussed in detail, along with the EU roadmap towards the decarbonization of transportation. Next, methods and techniques for fuel consumption and GHG reduction are systematically presented and categorized into on-vehicle and off-vehicle ones. Finally, a future outlook on more environmentally friendly road transportation is presented.

The purpose of this study was to investigate the impact of voltage drop of a three-phase voltage source inverter on driving brushless motors. This study also proposes an enhanced field-oriented control scheme that accounts for inverter voltage drop, enabling efficient driving at very low motor speeds. Experimental results are provided to verify the theoretical study and the proposed control scheme.

This paper investigates the wireless power transfer (WPT) system incorporation into dc microgrids applications. Emphasis is given on the mathematical analysis of the series–series (SS) WPT system for constant voltage source loading conditions that cannot be effectively described by the equivalent constant resistance model. For this reason, the complete harmonic analysis is considered in this paper in order to study the real operational characteristics of SS-WPT systems that interface to a dc bus. The proposed system interconnects a dc bus with various distributed energy sources, while the ability of constant power generation behavior of the proposed system is revealed and examined for various SS-WPT system parameters’ values, highlighting its advantageous characteristics for distributed energy exploitation. Additionally, the incorporation of the SS-WPT system in distributed energy sources exploitation offers reduced wiring complexity and installation flexibility. Experimental and simulation results are presented, validating the theoretical analysis.

The upcoming adoption of low-voltage-ride-through requirements in low-voltage distribution systems is expected to raise significant challenges in the operation of grid-tied inverters. Typically, these inverters interconnect photovoltaic units, which are the predominant distributed energy resource in low-voltage distribution networks, under an umbrella of standards and protection schemes. As such, a challenging issue that should be considered in low-voltage distribution network applications, regards the coordination between the line protection scheme (typically consisting of a non-settable fuse) and the low-voltage-ride-through operation of photovoltaic generators. During a fault, the fuse protecting a low-voltage feeder may melt, letting the generator to continue its ride-through operation. Considering that the efficacy/speed of the anti-islanding detection is affected by ride-through requirements, this situation can lead to protracted energization of the isolated feeder after fuse melting (unintentional islanding). To address this issue, this paper proposes a fault-current-limitation based solution, which does not require any modification in the existing protection scheme. The operation principles, design, and implementation of this solution are presented, while, its effectiveness is supported by extensive simulations in a test-case low-voltage distribution system. A discussion on the presented results concludes the paper.

This paper investigates energy efficiency issues in modern lifts, based on the VDI 4707 guidelines, in the context of “KLEEMANN-LESS” research project, funded by national resources and the EU. The above analysis is applied to various lift types manufactured by the Greek multinational company ΚLEEMAN HELLAS. The obtained results indicate the relationship between critical technical parameters, such as the elevator driving system type and the standby energy consumption, according to the aforementioned standard. Furthermore, in the current work, new techniques for energy savings are proposed, employing realistic scenarios, which significantly enhance energy efficiency. Experimental work shows that an energy saving of up to 40% can be achieved. The outputs of the current work are not limited to lift models manufactured by KLEEMAN HELLAS, but concern the majority of lift manufacturers as well.

In this work, a novel performance analysis method for evaluating the robustness of emerging power distribution networks (PDNs), which involve deployable renewable energy sources, is proposed. This is realized with the aid of the outage probability (OP) criterion in the context of cooperative communications, which is widely considered in modern wireless communication systems. The main usefulness of this method is that it allows the involved components to communicate to each-other by means of a robust and flexible wireless sensor network architecture. In this context, any conventional medium voltage (MV) bus of the PDN is represented as a wireless relay node where data signals gathered from each MV bus can be forwarded reliably to a control station for the subsequent processing. The received signals at wireless nodes are decoded and then forwarded to ensure minimal errors and maximal robustness at the receiving site. The considered OP analysis denotes the probability that the power of a received information signal drops below a pre-defined threshold which satisfies the acceptable Quality of Service requirements of a reliable signal reception. To this end, simple closed-form expressions are proposed for the OP of a regenerative cooperative-based PDN in the presence of various multipath fading effects, which degrade information signals during wireless transmission. The offered results are rather simple and provide meaningful insights for the design and deployment of smart grid systems.

Nowadays, the imperative need for the reduction of Greenhouse Gas (GHG) emissions leads to the wider adoption of environmentally friendly transportation means. As a result, various policies underpinning the Electric Vehicle (EV) deployment are legislated globally, and several technical advances contributing to the electrification of the transportation sector are pursued. In this paper, a comprehensive overview of the current status of the infrastructure utilized for the realization of both conductive and contactless (wireless) charging of an EV battery is conducted. Furthermore, the issue of EV integration in conventional distribution networks, as well as in future power system architectures, is discussed in detail. Particular focus is given to wireless (i.e., inductive) charging. A detailed presentation of the respective standards and charging levels, as well as the magnetic couplers and the compensation network configurations, is carried out. Moreover, innovative concepts such as dynamic and quasi-dynamic wireless charging, as well as future challenges and opportunities, are presented and discussed. Finally, smart control and communication techniques applicable to EV charging are presented in the context of the future Internet of Energy (IoE) concept.