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Synchronization of single-phase inverters is a challenging task due to the difficulty of deriving a rotating voltage frame, in the absence of adequate information from the other two phases. Moreover, modern standards, such as the fault ride-through (FRT) directives, require inverter-based distributed generators (IBDGs) to respond as fast as possible to grid disturbances; thus, it is necessary to rely on accurate and fast synchronization algorithms. The scope of this paper is to propose a new synchronization technique, which satisfies three important requirements: a) fast dynamic response, b) adequate double frequency rejection, c) low computational complexity. Our synchronization technique is a flexible method relying on variable-length transfer delay, which calculates network frequency by analyzing voltage angle differentials. To enhance this differentiation process and address potential discontinuities, we introduce Heaviside-based functions. Both simulations conducted in MATLAB/Simulink and experimental trials demonstrate that our proposed synchronization method outperforms the most widely adopted existing techniques in terms of dynamic response and computational efficiency. Due to its excellent dynamic performance, the proposed method can offer a stable FRT capability, with fast detection of the voltage dips and seamless resynchronization following fault clearance, all while preventing DC-link overvoltage issues.

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 work introduces a compensation scheme that uses a genetic algorithm to mitigate the 2nd voltage harmonic component of hybrid microgrids. The foremost advantage of the proposed scheme, is its capability to effectively compensate the 2nd harmonic component regardless of the feeder impedance, the location of the equipment and without any need for real-time communications. A graphical representation of the genetic algorithm parameters is also presented, being a handily tool for designing it for any microgrid application and the mathematical analysis of hybrid microgrids under the prospect of harmonic compensation is given. Simulations and experimental tests verify the effectiveness of the proposed method, indicating that its efficiency is maintained at about 90%, while the efficiency of the other methods falls below 35% when the impedance of the connection line increases at $1+\,\,\text{j}0.16\,\,\Omega _{\mathrm {(\text{@}100 Hz)}}$ . Finally, a comparative analysis is also performed between the proposed method and existing ones.

In this work the harmonic injection active anti-islanding technique that has been recently proposed in reference Voglitsis et al. (2018) published in Trans. Power Electron. is generalized under the prospect of a high penetration level of distributed energy resource (DER) installations. Towards this direction, the theoretical limitation for the penetration level of such schemes is investigated and a firm theoretical background is presented that takes into account the installation parameters, as well as the penetration level at the installation common coupling point. Furthermore, a substantial feature which indicates the upgrade-ability of each installation is studied. Finally, extensive simulations and experiments verify the theoretical analysis.

This paper presents a transmitter side control scheme for a series-series compensated wireless power transfer (SS-WPT) system for electric vehicle (EV) charging applications. The proposed control scheme matches the reflected load impedance, by controlling accordingly the front-end dc-dc converter (FEC) of the SS-WPT system. The proposed control scheme drives the FEC, through an optimizer which takes into account the misalignment but also the operational conditions of the system to achieve high efficiency throughout the entire charging process - regardless the EV type, the misalignment conditions or the on-board charger. The novelty of the proposed optimizer lies upon its universal characteristic, which makes it compatible to various SS-WPT topologies. As such, the proposed charging concept is a universal solution, which optimizes the system efficiency regardless the receiver side on-board charger topology (single-stage or double-stage), technical characteristics or control scheme that implements the charging profile. Finally, for the necessary communication between the transmitter and the receiver sides, the Internet of Things (IoT) is employed, offering a low-cost and flexible solution that overcomes compatibility problems between wireless antennas. Simulation and experimental results validate the feasibility of the proposed control scheme, highlighting the efficacy of the proposed wireless charging process.

To increase the reliability of aerospace electronics and reduce their overall power consumption, we investigated the possibility of incorporating active thermoelectric cooling (TEC) solutions. The harsh avionic environment demands sophisticated active control schemes that enable the achievement of high coefficient of performance. The positive effect of active PWM control has been validated both in simulation and on a working laboratory prototype that allowed us to clarify the pros and cons of the incorporation of TEC techniques in avionics applications. This paper has been performed under the framework of CLEAN SKY-THERMICOOL project.

Standalone photovoltaic systems is a key technology for the increase of renewable energy sources share in electricity production worldwide. The power quality of those systems plays a fundamental role in avoiding volatile power supply. This calls for a concrete design in order to meet power quality specifications. In this context, a methodology has been developed in a previous work, in order to set the values of the parameters that optimize the power quality indices of the system. In this paper, an extensive sensitivity analysis is performed regarding the influence of the optimized parameters variation on the power quality indices. Throughout the outcomes of the sensitivity analysis a more insightful view of the system performance under the deviations of system parameters is revealed, which in combination with the aforementioned optimal design strategy becomes an essential tool that ensures high power quality level. The theoretical outcomes are validated by experimental results, highlighting the effectiveness of the proposed design strategy.

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.

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.

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.