• Energy Research
• engineering and technology close

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.

The objective of this paper is to present a power conversion system, based on a bidirectional DC/DC converter, along with a supercapacitor bank, that mitigates the voltage transients that occur on the DC distribution network of More/All Electric Aircrafts. These transients, such as voltage sags and swells appear on the DC buses of on-board microgrids, mainly due to load variations and are classified according to the aircrafts electric power system standards. First, we shortly describe an aircraft distribution network, that is applicable to the most common actual aircraft architectures, then we present the proposed system, along with the bidirectional DC/DC converter design, the control technique and the supercapacitor bank sizing. Finally, we present simulation and experimental results that support the effectiveness of the proposed system to effectively compensate voltage transients, supporting the DC buses in dynamic conditions. Concluding, the proposed system provides high power quality and compliance with the respective power quality standards for aircraft microgrids.

Active anti-islanding schemes that are based on the injection of harmonic currents, such as the measurement of the impedance at a specific frequency or similar techniques, have been proposed for anti-islanding protection in photovoltaic (PV) systems due to their low impact on inverter active power, their fast detection response in island, and reduced non-detection zone (NDZ). Integer multiples of the fundamental frequency as well as sub/inter-harmonics have both been used for the implementation of those schemes. Although utilization of sub/inter-harmonics present significant advantages, they also present significant limitations. This work investigates those limitations, particularly the ones that are caused by the parallel operation of multiple inverters. In addition, the distortion effect that is caused in the output current of the widely used PV microinverters with pseudo dc-link (PV Pdc-MICs) is discussed and thoroughly analyzed. It is concluded that when the injection is performed asynchronously (without communication among the inverters) sub/inter-harmonics are unsuitable for utilization under the parallel operation of multiple inverters. It is worth noting that a strategy is proposed in the current work that retains the effectiveness of the harmonic injection scheme under the injection of integer multiples of fundamental frequency. On the other hand, the distortion effect that is caused by the sub/inter-harmonics on PV Pdc-MICs output current, has been evaluated as insignificant when harmonics are used for anti-islanding purposes. Finally, the theoretical/mathematical outcomes of this work are supported by simulation and experimental results.