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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.

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.

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.