Islanding Detection

Abstract

A higher penetration of distributed power generation systems (DPGSs), involving both conventional and renewable technologies, is changing the power system face. There is a clear evolution towards active grids that could include a significant amount of storage systems, could work in island mode and could be connected through flexible transmission systems. This complex scenario will put different requirements on the DPGS units depending on their size and on their level of integration with the power system. Thus the monitoring of the grid condition will always be a crucial feature of the DPGS units at every level. The detection of a possible island condition will always be important in a power system with a significant amount of DPGS.Typically in a low-power DPGS like, for example, PV systems, this feature is defined as an 'anti-islanding requirement' in order to highlight the request of the utility operator, as pointed out in Chapter 2, that the DPGS should disconnect in case the main electric grid should cease to energize the distribution line. A higher power DPGS, typically wind plants, have completely different requirements and generally benefits of communication systems and a supervisory control that interact with the utility operator in view of making the DPGS contribute to the stability of the grid. Here the latest grid codes require low-voltage ride-through capability, meaning that they should stay connected during grid faults, which is quite opposite for the PV systems. Hence islanding detection can be considered a requirement only for low-power DPGSs. However, as already pointed out, the power system is evolving and the future scenario may consider the presence of a smart micro-grid (SMG) usually operated in connection to distribution grids but with the capability of automatically switching to a stand-alone operation if faults occur in the main distribution grid, and then reconnecting to the grid. Since it is not possible to predict the level of connection and the reliability of the information exchange among the different players of this future scenario, the detection of islanding can be considered as an important feature, requested in some cases and optional in others.In this chapter islanding detection will be treated with attention paid to the consequences of an uncontrolled islanding (amplitude and frequency variation of the grid voltage, which are usually the first signs of the island condition) and to the performances of the islanding detection methods: reliability, selectivity and minimum perturbation. Ideally, the methods should be able

Anti-Islanding Techniques for Integration of Inverter-Based Distributed Energy Resources to the Electric Power System

“…However, after an islanding event, the PCC voltage will be determined by the interaction between the DGS output current and the load impedance. In [47], the relationship between the PCC voltage before and after the grid interruption is derived and presented in equation (6). One can note that the voltage variation depends on the mismatch between the power supply from the DGS and the power demand of the load.…”

“…The main advantage of this strategy lies on its nondependency of the power unbalance of generated and consumed power [47]. However, its implementation is marked by the difficulty of the protection relay parametrization.…”

“…The Slip Mode Frequency Shift (SMS) is based on the insertion of the a small disturbance in the phase estimated by the PLL through a frequency positive feedback according to (33) [47].…”

“…Other popular names for this strategy are: harmonic component injection, impedance at specific frequency, harmonic amplitude jump or high frequency signal injection [37]. The main advantage of this approach lies on its non-dependence of the unbalance between the generated and the consumed power [47]. However, one of the main drawbacks is the chosen of a security threshold to detect the islanding.…”