Introduction - Control of Power Inverters in Renewable Energy and Smart Grid Integration - page 61

Table 1.5 Some islanding detection methods

Passive methods Active methods Utility-based methods

Under-/over-voltage Impedance measurement Manual disconnection

Under-/over-frequency Impedance measurement at a

specific frequency

Automated disconnection

Phase jump detection Slip mode frequency shift Transfer-trip method

Harmonics detection Frequency bias Impedance insertion

1.6.3.6 Anti-islanding

Here, islanding refers to unexpected situations when renewable energy, distributed generation
or storage systems continue feeding power to a grid that has lost power. Islanding can be
dangerous for the utility workers, who may not realise that a circuit is still powered, and it
may prevent automatic re-connection of devices. 7 Hence, islanding must be detected and the
renewable energy, distributed generation and storage systems involved must be disconnected
from the grid. This is referred to as anti-islanding. However, intentional islanding is often used
by backup power systems to power the local circuit when it is disconnected from the grid.
As mentioned before, synchronisation is one of the most important requirements for smart
grid integration. A good synchronisation method could be utilised for fault ride-through
(Rodriguez et al . 2006b; Timbus et al . 2006b) and anti-islanding. Islanding detection is the
subject of considerable research and there are many methods available, which can be classified
into passive methods, active methods and utility-based methods. 8 Passive methods attempt to
detect transient changes on the grid caused by grid failures while active methods attempt to
detect grid failures by injecting small signals into the grid and then detecting whether or not
the signal changes. The utility can also apply a variety of methods to force systems offline in
the event of a failure. Some of these methods are listed in Table 1.5.
The first four problems are addressed in this topic in detail and the last two problems are
not discussed any further.

7 http://en.wikipedia.org/wiki/Islanding
8 http://en.wikipedia.org/wiki/Islanding