Search

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. [ABSTRACT FROM AUTHOR]

Static waste heat recovery, by means of thermoelectric generator (TEG) modules, constitutes a fast-growing energy harvesting technology on the way towards greener transportation. Many commercial solutions are already available for small internal combustion engine (ICE) vehicles, whereas further development and cost reductions of TEG devices expand their applicability at higher-power transportation means (i.e., ships and aircrafts). In this light, the integration of waste heat recovery based on TEG modules in a shipboard distribution network is studied in this work. Several voltage step-up techniques are considered, whereas the most suitable ones are assessed via the LTspice simulation platform. The design procedure of the selected LLC resonant converter is presented and analyzed in detail. Furthermore, a flexible control strategy is proposed, capable of either output voltage regulation (constant voltage) or maximum power point tracking (MPPT), according to the application demands. Finally, both simulations and experiments (on a suitable laboratory testbench) are performed. The obtained measurements indicate the high efficiency that can be achieved with the LLC converter for a wide operating area as well as the functionality and adequate performance of the control scheme in both operating conditions. [ABSTRACT FROM AUTHOR]

The characterization of electric vehicles as environmentally friendly means of transportation hinges, on the one hand, upon the manner in which the energy for their charging is generated and, on the other hand, on the recyclability of the materials composing them, with primary emphasis on the recycling of batteries. Given that we are still in the early stages of electrification in road transportation, it can be argued that at least a decade is required for the development of a sustainable battery recycling industry. Conversely, the progressively increasing number of electric vehicles makes the necessity of charging them with clean, green energy imperative. In this context, this study examines the energy and economic aspects of replacing 50% of the public passenger vehicle fleet, which currently relies on internal combustion engines, with electric vehicles on the island of Zakynthos, Greece. Specifically, it calculates the energy needs of these vehicles and proposes methods for environmentally friendly electricity generation to meet the electrical demand. To assess the benefits for the owners of the charging stations and the electric vehicles, the Life-Cycle Cost Analysis (LCCA) method is employed for various scenarios regarding (a) the pricing of the supplied electrical energy for electric vehicle charging and (b) the evolution of fossil fuel prices. The study concludes by highlighting the environmental advantages of such an investment. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper presents a novel active power control scheme for SRMs that are used as S/G units at MEAs; the proposed method uses a vector-controlled SAF, facilitating the acceleration of the SRM during starter mode and the efficient power control of the SRG at various operational points during generator mode. Moreover, an energy storage unit is incorporated in the SAF, aiming at enhancing the SRM's starting torque production and taking full advantage of the SRG's energy generation capability, through the appropriate phases’ magnetization regulation that is imposed by the developed adaptive SAF vector control. In addition, the proposed scheme provides enhanced FRTC during both modes of operation. The mathematical analysis is verified through MATLAB/Simulink simulations, while the performance of the S/G concept under study is evaluated via real-time CHIL tests, with the use of the dSPACE 1202 (MicroLabBox) platform and the 16-bit dsPIC30F4011 microcontroller. [ABSTRACT FROM AUTHOR]

SRM is one of the most attractive electric machines to be used as a S/G in the future MEA thanks to its special physical characteristics that facilitate its direct coupling to the propulsive unit; however, the controllability of the SRG at different operational points, imposed by the specific application, is critical. In this article, a novel active power control scheme which uses a vector-controlled SAF is proposed, in order to efficiently drive the SRG in a wide set point range. Considering the highly non-linearity of the SRM operational behavior, an adaptive phases’ magnetization regulation is applied, aiming at taking full advantage of the SRG's energy production capability, in compliance with the MEA power system specifications and limitations. The mathematical analysis is verified through simulation results, while the SRG concept under study is validated via a RT CHIL implementation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper introduces a new cross-correlation anti-islanding detection scheme for module-integrated converters (MICs) with pseudo dc-link. The proposed scheme periodically injects a second-order harmonic current component of low magnitude (in open-loop mode) and evaluates grid response by means of correlation. The proposed scheme is highly reliable, providing nondetection-zone free operation, fast detection, and compliance with the relevant power quality and anti-islanding standards. Additionally, it excels in lower computational cost, reduced fault detection zone, and higher output power quality, compared to the referenced anti-islanding schemes that are compatible with MICs. Last but not least, it can be implemented in MIC platforms without requiring an output current sensor, being an easily upgradable solution in software level. A firm theoretical framework that considers both high penetration levels of PV systems and weak grid conditions is also included in this paper. The theoretical framework, as well as the effectiveness of the proposed scheme, is verified through extensive experimental results for various electrical-network parameters and nonlinear loading conditions. Finally, a comprehensive comparison between the proposed method and the most common anti-islanding techniques (compatible with MICs) is performed, leading to some valuable conclusions from MICs perspective. [ABSTRACT FROM AUTHOR]

This paper studies the significant impact of distributed-energy-resource (DER) inverters (which are connected to the same node) on anti-islanding protection of DER-installations. As it concerns the harmonic injection-based schemes, the induced harmonic voltage component that is provoked by each inverter is compromised, as synchronous injection (injection at the same time intervals) among the inverters cannot be reassured. Therefore, harmonic injection-based anti-islanding schemes will fail if the harmonic voltage component falls below a certain level. In this framework, a novel metric (i.e., the upgrade factor, UF) is introduced, indicating the supplementary power (of DERs) that can be installed in the same point of common coupling without compromising the effectiveness of the harmonic injection scheme. As this metric enables the evaluation of harmonic injection schemes prior to the future integration of DERs, it could be a substantial addendum into the relevant standards that evaluates the anti-islanding features of grid-tied DER-inverters. Finally, this paper proposes a technique (implemented in the software level), which maximizes UF and reassures the effectiveness of the harmonic injection schemes under the power variations of installed inverters. Extensive simulations and experimental tests have been conducted that verify the effectiveness of the proposed strategy under various penetration-levels and islanding-network conditions. [ABSTRACT FROM AUTHOR]

This work presents the first comprehensive study of active anti-islanding techniques suitable for module integrated converters (MICs), which considers the high penetration level of photovoltaics (or other distributed energy resources) at low-voltage distribution networks. As such, the state of the art in anti-islanding methods are presented and the most appealing solutions compatible with MICs are selected and experimentally evaluated, reaching to some valuable conclusions from the perspective of MICs. In order to compare these methods under the same operating conditions and specifications, a benchmark is set based on zero non-detection zone, reduced false-detection zone, and power-quality requirements compliance. Based on comparative results, the most suitable methods for wide MICs penetration in low-voltage distribution networks are suggested. [ABSTRACT FROM AUTHOR]

Over recent years, the output power of micro-inverters [module-incorporated inverter (MIC)] is progressively pushed to higher levels, following the current photovoltaic (PV) modules market trends. The interleaved Flyback inverter—under discontinuous conduction mode of operation (DCM)—is an appealing solution for PV applications which are based on MIC technology. This topology provides increased power level for distributed PV generation exploitation with simple control configuration, high efficiency, and reduced filter size. In this paper, the harmonic injection capability is incorporated into the interleaved Flyback inverter for the implementation of an active anti-islanding scheme. A suitable technical solution is proposed that bypasses the unfolding H-bridge, without affecting the active power generation of the inverter and without requiring any hardware modification. In addition, a mathematical model based on the instantaneous power balance theory is presented, being a powerful analysis tool for inverters operating under complete magnetic discharge such as the Flyback inverter (either conventional or interleaved) under DCM or boundary conduction mode of operation. The proposed model predicts accurately the steady-state operational behavior of the Flyback inverter under current harmonic injection, either in grid-tied or islanding operation. The proposed technical implementation method and mathematical model are verified through simulation and experimental results. Finally, an anti-islanding set-up based on the proposed harmonic injection technique is presented and implemented into the Flyback micro-inverter. The proposed set-up is verified through experimental results on various quality factor values, as well as for weak grid conditions. [ABSTRACT FROM AUTHOR]

The prescribed perspective of high accession of distributed generation photovoltaic (DG‐PV) units on low‐voltage distribution networks has brought up many issues regarding their performance in case of network transient phenomena. In this study, the design principles that DG‐PV units must incorporate in order to meet the requirements of low‐voltage ride through capability (LVRTC) are investigated through detailed theoretical analysis and calculations. The analysis shows that a realistic over‐sizing of interfaced inverters of DG‐PV as well as an appropriate selection of the equivalent interconnecting reactance XDG, in conjunction with high penetration levels, can lead to satisfaction of LVRTC demands without violating the protection limits of the network. Moreover, the scenario of uniform dispersion along the distribution lines is proved rather favourable concerning the demand of LVRTC for voltage selectivity. Finally, considering the derived outcomes, a methodology of optimum design about LVRTC is proposed within the framework of reasonable constraints, which can be applied to any low‐voltage distribution network. [ABSTRACT FROM AUTHOR]

During the last decade, autonomous residential photovoltaic (PV) systems have been widely installed, especially in remote areas (islands, rural territories, etc.), in an effort to produce electrical energy in a reliable and inexpensive manner. The appropriate design of a PV system and the compatibility of its power quality indices with national and international standards are crucial for efficient and economical autonomous operation of the system. To this direction, the critical parameters of a three-phase autonomous PV residential system are properly determined. Moreover, a new design methodology that meets the demanded standards and improves further the power quality is also introduced. Finally, an optimization algorithm is designed utilizing artificial intelligence techniques. The analytical results are corroborated by extensive simulation results and insightful discussions are provided demonstrating the efficiency of our proposed design. [ABSTRACT FROM PUBLISHER]

The flyback inverter-based alternating current-photovoltaic modules' behaviour under voltage rise/drop conditions is investigated. Specifically, the aim is to calculate the module steady-state operational characteristics of distributed generators, such us generation loss and root mean square current rise, based on the low-voltage ride-through capability requirements. The proposed analysis stands for the widely known discontinuous conduction mode of operation and it can also account for high power inverter topologies. Furthermore, the derived expressions are corroborated by means of PSPICE simulation along with the selected experimental results and insightful discussions. [ABSTRACT FROM AUTHOR]

OPEN-SME introduces an Open Software Component Reuse, which collectively provides two processes and three tools. COMPARE (Component Repository and Search Engine) is one of the three tools, the one that allows SME software re-users to search and discover the assets (software artefacts, technical documents, test suites, metamodels) produced by the Domain Engineering Process. COMPARE features an advanced search engine that can be used for searching among the components, according to specific needs and selection criteria. Also, COMPARE supports the effective communication of structured information flows between the software re-users (asset consumers) and the reuse engineers (asset producers). These information flows allow re-users to place orders/requests and provide their feedback to the reuse engineers. [ABSTRACT FROM AUTHOR]

The aim of the research is to analyse the energy transition in the Visegrad Group countries, because they depend on the production of energy from the burning of fossil fuels, and transition is a huge challenge for them. The diversity of the energy transformation in the V4 countries was examined by using two qualitative methods, including literature analysis and comparative analysis. The timeframe of the study was set for the period from 2020 to 2030, as these years are crucial for the implementation of the European Green Deal Programme. Four diagnostic features were taken into account in the analysis: the share of RES in final energy consumption, reduction of CO2 emissions in the non-Emissions Trading System (ETS) sector, date of withdrawal of coal from the economy, and energy efficiency. The analysis shows that the V4 countries have different approaches and levels of energy transformation in their economies. Poland is in the most difficult situation, being the most dependent on the production of electricity from coal, as well as having the largest number of employees in the coal and around coal sector. The other countries of the group can base their transformation on nuclear energy, as each of them has at least four such power units. The increased use of biomass for energy and heat production is the most important stimulus for Renewable Energy Sources (RES) growth in the analysed countries. The ambivalent attitude of the political elite to unconventional sources in the four analysed countries significantly hinders the development of certain forms of green energy. However, it has been observed that an increasing proportion of the population, especially those living in regions of the country where there is no fossil fuel mining industry, has a positive attitude towards energy transformation. The study is the first that shows the state of involvement in the process of systemic change of the Visegrad Group countries. The results can serve as a starting point for understanding the reticence of this group of European countries towards the transformation phenomenon, as well as contributing to further research on the implementation of closed-circuit economies in the Visegrad Group countries. [ABSTRACT FROM AUTHOR]

Fundamental shifts in the structure and generation profile of electrical grids are occurring amidst increased demand for resilience. These two simultaneous trends create the need for new planning and operational practices for modern grids that account for the compounding uncertainties inherent in both resilience assessment and increasing contribution of variable inverter-based renewable energy sources. This work reviews the research work addressing the changing generation profile, state-of-the-art practices to address resilience, and research works at the intersection of these two topics in regards to electrical grids. The contribution of this work is to highlight the ongoing research in power system resilience and integration of variable inverter-based renewable energy sources in electrical grids, and to identify areas of current and further study at this intersection. Areas of research identified at this intersection include cyber-physical analysis of solar, wind, and distributed energy resources, microgrids, network evolution and observability, substation automation and self-healing, and probabilistic planning and operation methods. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Cost-effective energy saving in the building sector is a high priority in Europe; The European Union has set ambitious targets for buildings' energy performance in order to convert old energy-intensive ones into nearly zero energy buildings (nZEBs). This study focuses on the implementation of a collective self-consumption nZEB concept in Mediterranean climate conditions, considering a typical multi-family building (or apartment block) in the urban environment. The aggregated use of PVs, geothermal and energy storage systems allow the self-production and self-consumption of energy, in a way that the independence from fossil fuels and the reliability of the electricity grid are enhanced. The proposed nZEB implementation scheme will be analyzed from techno-economical perspective, presenting detailed calculations regarding the components dimensioning and costs-giving emphasis on life cycle cost analysis (LCCA) indexes—as well as the energy transactions between the building and the electricity grid. The main outcomes of this work are that the proposed nZEB implementation is a sustainable solution for the Mediterranean area, whereas the incorporation of electrical energy storage units—though beneficial for the reliability of the grid—calls for the implementation of positive policies regarding the reduction of their payback period. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this work, the electromechanical system of the 8000-series of Athens trolleybuses, based on data provided by OSY S.A., is analyzed. Those data were used to develop a valid model in order to estimate the total energy consumption of the vehicle under any possible operating conditions. In addition, an effort is made to estimate the energy saving potential if the wasted energy—in the form of heat—during braking or downhill courses is recovered (regenerative braking) and retrofitted during normal operation. This process requires the installation of appropriate electrical apparatus to recover and temporarily store this energy amount. Moreover, due to the fact that the main engine of the system is an asynchronous electric machine, its driving scheme is also of interest. This study assumes the current driving scheme, that is the direct vector control (DVC), and proposes an alternative control method, the direct torque control (DTC). Energy consumption/saving calculations highlight the effectiveness of incorporating regenerative braking infrastructure in trolleybuses transportation systems. Finally, a sustainable hybrid energy storage unit that supports regenerative braking is proposed. [ABSTRACT FROM AUTHOR]