The anticipated high penetration of distributed photovoltaic (PV) energy sources is expected to lead to significant changes in utility interconnection requirements for PV systems. These changes will include provisions for voltage and frequency regulation capability, as well as better voltage and frequency ride through requirements. For distributed energy resources (DER), in particular PV, to provide grid support, it must participate in frequency and voltage regulation. Frequency and voltage ride through allows inverters to remain connected to ensure robust recovery in the event of voltage and frequency disturbance. Implementing these advanced capabilities is essential to mitigating the negative impacts of high penetration PV, but their integration into a typical distribution system presents significant technical challenges, one of which is the increased risk of unintentional islanding. In this paper, an island detection method is presented that relies on a continuous subharmonic signal, a power line carrier permissive (PLCP), that is injected at the transmission level or at the substation and detected by any type of DERs in any combination. Absence of the signal indicates loss of utility and possible island condition. Laboratory and simulation experiments were done to investigate feasibility of the method. The PLC system discussed herein is novel in that it utilizes a power electronics based series voltage injection method. Advantages include the ability to use a smaller and less expensive transformer and enhanced flexibility in the amplitude, waveform and frequency of the injected signal.

As utility interconnected photovoltaic systems (PV) become integrated into the electrical power system (EPS) at an increasing rate, utilities and regulators have become concerned about the potential for increased voltage and frequency deviations as well as EPS reliability and resiliency. These concerns have initiated the need to amend the utility interconnection standard to allow advanced inverter control functionalities that provide: (1) reactive power control for voltage support, (2) real (active) power control for frequency support and (3) voltage and frequency ride- through for bulk system support. The new real and reactive power modulation are intended to reduce EPS voltage and frequency deviations by mimicking the droop and excitation controls of conventional generation. The new ride-through capabilities are needed to prevent a large quantity of generation from autonomously de-energizing or disconnecting in response to a voltage or frequency deviation. These changes, however, may have the potential to interfere with autonomous anti-islanding, especially when multiple inverters from different vendors are co-located on one bus. This report presents results from an investigation of multi-inverter autonomous anti- islanding with advanced functions, and the development of a means to mitigate adverse interaction between the two.

This paper describes and explores the effectiveness of a novel power line carrier-based islanding detection and prevention system in which a dynamic voltage restorer (DVR) is usedto transmit a low-frequency power line carrier permissive (PLCP) signal. The approach itself is briefly described, and then results are provided showing the effectiveness of this approach in detecting unintentional islands and single-phase opens (SPOs), or series faults. The results indicate that this method works extremely well in detecting islands, with low risk of false trips, and that propagation of the signal is not expected to be a limiting factor. Fast detection (in less than 400 ms) appears possible, and the means for achieving this are described. The SPO detection results were promising, but still less than desired; SPOs were readily detected as long as there were no delta transformers or phase-phase loads on the circuits, but in reality there usually are. The paper concludes with discussion of how to improve performance, andfuture work recommendations.