Coordinated operation of parallel-connected inverters for active islanding detection using high frequency signal injection

Abstract

The high frequency impedance measured at the terminals of inverters connected in a microgrid by means of the injection of a small magnitude, high frequency voltage, has been shown to be a reliable metric to detect islanding. While the implementation of this method is simple when only an inverter injects the high frequency signal, this case is of limited applicability. On the other hand, several concerns arise when multiple inverters work in parallel, primarily due to risk interference among inverters. Islanding detection using high frequency signal injection in microgrids with multiple parallelconnected inverters is studied in this paper. A strategy for the coordinated operation of the inverters, without the need of communications or pre-established roles is proposed. Simulation and experimental results will be provided to demonstrate the viability of the concept. 1Index Terms-Active islanding detection, grid impedance measurement, high frequency signal injection, distributed generation.

Islanding detection in three-phase and single-phase systems using pulsating high frequency signal injection

“…Passive and active methods are inverter resident [9,10], while communication based methods are remote [9,10]. Passive based methods are grid friendly, as they do not introduce any disturbance in the grid [10], but have the disadvantage of a large nondetection-zone (NDZ) [11].…”

“…Passive based methods are grid friendly, as they do not introduce any disturbance in the grid [10], but have the disadvantage of a large nondetection-zone (NDZ) [11]. Active methods are based on the injection of some disturbing signal in the grid [9,[11][12][13][14][15][16][17][18][19], therefore having a negative impact on the power quality. However, they have low NDZ [17,18], being easy and cheap to implement.…”

“…Three different scenarios can be considered for islanding detection: Single-inverter, Multi-inverter and Microgrid [9]. In the Single-inverter scenario only one DG exists and all the power is exported to the grid.…”

“…Islanding detection methods can be classified into three groups: passive [10,11], active [9,[11][12][13][14][15][16][17][18][19] and communication based [11] methods. Passive and active methods are inverter resident [9,10], while communication based methods are remote [9,10].…”

“…The Multi-inverter case could be considered as a particular case of the Microgrid scenario, but with a major portion of the energy being exported to the utility grid. In all cases, the system is required to have the ability to detect if it is connected or isolated from the utility grid [9,[17][18][19].…”