This work 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 work proposes a technique (implemented in 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.

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.

This article introduces a compensation methodology that enables the coordination of multiple dc–dc converters to mitigate the second-order voltage harmonic component in hybrid microgrids. The proposed methodology utilizes metaheuristic algorithms to prohibit circulating currents and share harmonic currents among the compensating circuits. The proposed method can be easily implemented by any dc–dc converter while its efficacy is independent of the feeders’ impedances and the physical location of the compensating equipment. The elimination of circulating currents and the capability to share the total compensation current between the compensating circuits are not affected by the line impedances. In addition, the implementation of the proposed scheme does not require any expensive real-time communication. The mathematical analysis of hybrid microgrids seen from the perspective of harmonic compensation by coordinating multiple dc–dc converters is also presented, being a useful tool to design compensation methods. In addition, a qualitative and a quantitative comparison of the proposed methodology with prior-art methods in the literature are presented to further demonstrate the performance of the proposed solution. Finally, simulations and experimental tests verify the effectiveness of the proposed methodology.

This work introduces a compensation scheme that uses a genetic algorithm to mitigate the 2 ^nd voltage harmonic component of hybrid microgrids. The foremost advantage of the proposed scheme, is its capability to effectively compensate the 2 ^nd 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 development of an energy recovery control unit to be incorporated in the light-emitting diodes (LEDs) lighting systems of heavy-duty vehicles is presented. This innovative industrial product adopts modern power electronics technology to improve existing trucks’ LED lighting system by eliminating the so far inevitable power consumption by the conventional central control unit of the majority of these vehicles, which is obligatory for the uninterruptable operation of their lighting system. The main idea of this innovative product is its capability to virtually increase the lighting system power consumption without actually consuming this amount of energy, thus facilitating the central control unit requirements regarding these vehicles in an energy-conscious way. Under this light, a mature power converter’s topology is employed to draw the proper amounts of power from the vehicle’s batteries supply, to the level that the central control unit recognizes, and return this energy back to the batteries. The tests results of the developed industrial product highlight the energy saving potential of the proposed energy recovery scheme, while the Life Cycle Cost Analysis (LCCA) results confirm its techno-economical and environmental profit for the truck applications under study.

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.