An Irregular Current Injection Islanding Detection Method Based on an Improved Impedance Measurement Scheme

Abstract

One class of islanding detection methods, known as impedance measurement-based methods and voltage change monitoring-based methods, are implemented through injecting irregular currents into the network, for which reason they are defined in this paper as irregular current injection methods. This paper indicates that such methods may be affected by distributed generation (DG) unit cut-in events. Although the network impedance change can still be used as a judgment basis for islanding detection, the general impedance measurement scheme cannot separate island events from DG unit cut-in events in multi-DG operation. In view of this, this paper proposes a new islanding detection method based on an improved impedance measurement scheme, i.e., dynamic impedance measurement, which will not be affected by DG unit cut-in events and can further assist some other equipment in islanding detection. The simulations and experiments verify the stated advantages of the new islanding detection method.

Synchronization Issues with Irregular Current Injection Islanding Detection Methods in Multi-DG Operation

“…The identification of an island is based on the changes of the irregular voltages excited by the injected irregular currents. By following this route, a second harmonic was injected in [1], [2] and [3]; even harmonics injection was proposed in [4]; a non-characteristic harmonic was used in both [5] and [6], while dual-frequency harmonics were introduced in [5] to cope with the unbalanced grid impedance; inter-harmonics were used in [7] and [8]; asymmetric sub-harmonics, which must contain a negative sequence low frequency component, were injected in [9]; a pulse current was adopted in [10]; and negative sequence currents were adopted in [11]- [13]. On the other hand, the observed objects in these references are also different, even though in some references the same irregular currents were injected.…”

“…On the other hand, the observed objects in these references are also different, even though in some references the same irregular currents were injected. Changes of irregular voltages were directly monitored in [1], [2], [4], [6] and [9]- [12], whereas network impedance was measured by means of the irregular currents and voltages in [3], [5], [7] and [8], and the voltage unbalance factor was measured in [13]. Moreover, irregular voltage injection for islanding detection was proposed in [14]- [20].…”

A Solution to the Parameter Selection and Current Static Error Issues With Frequency Shift Islanding Detection Methods

“…As current injection methods, [15] and [16] monitored the changes of voltage and network impedance, respectively, which were used as the indices for islanding detection. [17] pointed out a misjudgment problem with the irregular current injection methods and proposed a solution. [18] and [19] belonged to the passive methods, which measured the network impedance passively and employed the wavelet theory, respectively.…”

Compatibility Issues with Irregular Current Injection Islanding Detection Methods and a Solution

“…According to the irregular current injection method, a DG unit (seen as a current source) injects high/low frequency currents or negative sequence fundamental frequency currents into the network and observes the resultant voltages to detect an island [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. In practice, there are some special circuit topology and control algorithms, and then how to inject a harmonic under such conditions is an interesting topic [1,4].…”

“…Island misjudgment is a problem that must be faced in islanding detection. In [18], a scenario that may result in a misjudgment was discussed; the reason for the misjudgment was analyzed and a solution was proposed. On the contrary, in [13][14][15][16][17], irregular voltage injection was exploited for islanding detection, by which the DG units were presented as voltage sources, and the problems with multi-DG operation were addressed.…”