Detection and Classification of Islanding and Nonislanding Events in Distributed Generation Based on Fuzzy Decision Tree

Abstract

This paper presents a new approach for islanding detection of distributed generation systems (DGs), using the features obtained from a new time-frequency transform with the negative sequence voltage, negative sequence current and the 3-phase voltage and current signals as inputs. The well-known S-transform suffers from high computational complexity, for on-line applications and hence, a new time-frequency transform (frequency filtering S-transform or simply the FFST) similar to it but faster by almost 30 times is proposed here using the frequency sampling and band pass filtering only for neighborhood of significant frequency components, determined from FFT of the power disturbance signals at the DG terminals. Thus using only the important frequency components present in the signal, it results in a significant reduction of computational complexity of the discrete S-transform. A data mining approach using a certainty factor-based fuzzy decision tree is used to yield fuzzy rules with the extracted features from the FFST output to recognize disturbance events like islanding or non-islanding for a variety of operating conditions of both the DGs and the electric power system. The results achieved during testing using existing hybrid distribution systems show that the proposed method is very reliable, and fast even in the presence of large disturbances like faults and capacitor bank switching.

Appendix

The various parameters for the distribution system (Samui and Samantaray 2013), depicted in Fig. 3 are given below:

Sl. no.	Element	Specifications
Specification of elements used in test system 1
1	Utility	115 kV, $\hbox {V}_{\mathrm{base}} = 115$, f = 60 Hz, $\hbox {R}_{\mathrm{s}} = 0.377\,\Omega$, $\hbox {L}_{\mathrm{s}} = 16.58\,\hbox {mH}$, AC voltage source
2	TR1	42 MVA, 115 kV/12.47 kV, $\hbox {V}_{\mathrm{base}} = 12.47\,\hbox {kV}$, f = 60 Hz, D1Yg
3	TR2 and TR3	7 MVA, 12.47 kV/12.47 kV, $\hbox {V}_{\mathrm{base}} = 12.47\,\hbox {kV}$, f = 60 Hz, YgD1
4	TR4 and TR5	2 MVA, 12.47 kV/0.575 kV, $\hbox {V}_{\mathrm{base}} = 12.47\,\hbox {kV}$, f = 60 Hz, D1Yg
5	TR6 and TR7	120 kVA, 12.47 kV/0.44 kV, $\hbox {V}_{\mathrm{base}} = 12.47\,\hbox {kV}$, f = 60 Hz, D1Yg
6	TR8 and TR9	4 MVA, 12.47 kV/2.4 kV, $\hbox {V}_{\mathrm{base}} = 12.47\,\hbox {kV}$, f = 60 Hz, D1Yg
7	Total Load	12.47 kV, 60 Hz, 3- phase series RLC Load, a load connected at each bus
8	Transmission Lines	$\hbox {R}_{0} =0.1153\,\Omega , \hbox {L}_{0} = 1.05 \hbox {mH}, \hbox {C}_{0} = 11.33\times 10^{-9}\,\, \hbox {F,R}_{1} = 0.413\,\Omega , \hbox {L}_{1} = 3.32\,\hbox {mH}, \hbox {C}_{1} = 5.01\times 10^{-9}\, \hbox {F}$.
9	DG5 and DG6	575 V, 60 Hz, 2 MW WIND FARM (cluster of four units of D.F.I.G wind turbines), The parameters for each unit being as follows:[$\hbox {V}_{\mathrm{s}\_\mathrm{nom}} = 575\,\hbox {V}, \hbox {V}_{\mathrm{r}\_\mathrm{nom}} = 1975\,\hbox {V}, \hbox {R}_{\mathrm{s}} =0.023$ p.u., $\hbox {L}_{\mathrm{s}} = 0.18$ p.u., $\hbox {R'}_{\mathrm{r}} =0.016$ p.u., $\hbox {L'}_{\mathrm{r}} =0.16$ p.u., $\hbox {L}_{\mathrm{m}} = 2.9$ p.u., Inertia Constant H(s) = 0.685, Friction Factor=0.01, Pair of Poles = 3, Grid-side converter maximum current= 0.8 p.u., Grid-side coupling inductor [ L, R] (p.u.) = [ 0.3 0.003], Nominal DC bus voltage = 1150 V, DC bus capacitor = 10000 $\upmu \hbox {F}$, Line filter capacitor (var) = 120$\times 10^{3}$, Nominal mechanical output power 2 MW, DC Bus Voltage[Kp Ki] = [8 400], Grid-side converter current regulator gains [Kp Ki] = [0.83 5], Speed regulator gains[Kp, Ki] = [3 0.6], Grid-side converter current regulator gains [Kp Ki] = [0.6 8], Pitch compensation gains [Kp Ki] = [3 30], Pitch controller gain [Kp] = [150], Maximum pitch angle (deg) = [27], Maximum rate of change of pitch angle (deg/s) = 10 ].
10	DG3 and DG7	440 V, 60 Hz, 2 MVA SOLAR FARM comprising of (35$\times$30) Solarex MSX 60 modules, $\hbox {T}_{\mathrm{ref}}= 298\,\hbox {K}, \hbox {L}_{\mathrm{f}} = 0.5\,\hbox { mH}, \hbox {C}_{\mathrm{f}} =120\upmu \hbox {F}, \hbox {C}_{\mathrm{dc}} = 6,000\,\upmu \hbox {F}, \hbox {Kp} = 0.0035, \hbox {Ki} = 300$ for PI Controller.
11	DG1 and DG2	7 MW, 12.47 kV, 60 Hz synchronous generators, H = 3.6 s, $\hbox {R}_{\mathrm{s}} = 0.047$  p.u., $\hbox {X}_{\mathrm{s}} =0.19$  p.u., $\hbox {X}_{\mathrm{d}} = 1.325$  p.u., $\hbox {X'}_{\mathrm{d}} = 0.275$  p.u., $\hbox {X''}_{\mathrm{d}} = 0.275$  p.u., $\hbox {X}_{\mathrm{q}} = 0.568\,$ p.u., $\hbox {X''}_{\mathrm{q}} = 0.256\,$ p.u., $\hbox {T'}_{\mathrm{d}0} = 5.495\,\hbox {s}$, $\hbox {T''}_{\mathrm{d}0} = 0.069\,\hbox {s}$ and $\hbox {T''}_{\mathrm{q0}} = 0.1\,\hbox {s}$.
12	DG4 and DG8	2.4 kV, 4 MW, 60 Hz, diesel CHP plants.