Management of a multiple-set synchronous island

Abstract

The continuity of power supply can be improved by power system islanding. A possible solution, synchronous islanded operation, enables the islanded system to remain in phase with the main power system while not electrically connected, and so avoids out-of-synchronism re-closure. Specific consideration is required for the multiple-set scenario, and is the topic of this paper. A suitable island management system is proposed, with the emphasis being on maximum island flexibility by allowing passive islanding transitions to occur, facilitated by autonomous control. These transitions include: island detection, identification, fragmentation, merging and return-to-mains. It can be challenging to detect these transitions while maintaining synchronous islanded operation. A Mathworks SimPowerSystems simulation is used to investigate the performance of the island management system. However, return-to-mains is particularly difficult to detect, and so a method based on voltage phase angle variability is explored by using a laboratory demonstration and time stamped phasor measurements.

Techniques for Multiple-Set Synchronous Islanding Control

“…An island management scheme, in addition to providing stable steady-state control, must also be able to detect and cope with the various transitions and reconfigurations that may occur during islanding. These are as follows: island detection and identification, island fragmentation or DG loss, return-tomains detection, island merging, and island shut-down [19]. These islanding state transitions are shown in Fig.…”

“…A further method is proposed; based on the assumption that the grid connected phase difference is more stable than the islanded system phase difference. The variance of the phase difference is calculated from a set of phasor measurements taken over a specified period of time [19]. For example, 2 or 3 seconds of phasor measurements sampled at 25 Hz would be suitable.…”

“…The phase difference must be prefiltered if noise and erroneous values are not to affect the operation of this function. Laboratory results for this technique are given in [19].…”

Design criteria for a power management system for microgrids with renewable sources

“…1. In case of failures, the microgrid may switch from its normal operating mode (in parallel with the grid) [1,2] into an emergency mode (in parallel with some violation of operating limits for one or more equipment) or into islanded mode (not connected to the grid) [3]. The operator may intentionally command the transition into islanded mode.…”

Grid reconnection detection for synchronous distributed generators in stand-alone operation

“…However, implementation of such scheme or similar ones implies PMU installation for distribution systems which unlike transmission grids needs deploying special PMU designs . Furthermore, detection based on phase variance may fail in applications of constant loads, because power perturbation is a requisite for phase variance .…”