IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 27, NO. 5, MAY 2012
2367
Improved Active Frequency Drift Anti-islanding
Detection Method for Grid Connected
Photovoltaic Systems
Ahmad Yafaoui, Student Member, IEEE, Bin Wu, Fellow, IEEE, and Samir Kouro, Member, IEEE
Abstract—As more distributed generators join the utility grid,
the concern of possible undetected islanding operation increases.
This concern is due to the safety hazards this phenomenon imposes
on the personnel and equipment. Passive anti-islanding detection
methods monitor grid parameters to detect islanding, whereas active methods inject a perturbation into the current waveform to
drive these parameters out of limit when islanding occurs. The
performance of active methods, such as conventional active frequency drift (AFD), is limited by the amount of total harmonic
distortion (THD) they inject into the grid, which defines its nondetection zone. In this paper, an improved AFD anti-islanding method
is presented based on a different current distortion injection waveform. The proposed method generates 30% less THD compared
to classic AFD, resulting in faster island detection and improved
nondetection zone. The performance of the proposed method is
derived analytically, simulated using Matlab and verified experimentally using a prototype setup. A single-phase grid-tied photovoltaic distributed generation system is used for the simulation and
experimental setup, and considered as potential application.
Index Terms—Active frequency drift, anti-islanding detection,
distributed generation, photovoltaic energy conversion.
I. INTRODUCTION
HE increase in penetration levels of distributed generation
(DG) into the grid, such as photovoltaic and wind energy
systems, has raised the concern about undetected islanding operation [1]–[3]. Islanding is a phenomenon in which the grid-tied
inverter of a distributed generation system and some of the local
loads are disconnected from the rest of the grid. If this condition
is not detected and the generation (e.g., from a photovoltaic or
wind energy source) remains operative, the isolated DG system will stay energized by the inverter [4]–[6]. This situation
is undesirable since it is a potentially dangerous condition for
the maintenance personnel and may cause damage to the inverter and loads in the case of unsynchronized reconnection of
the grid due to phase difference between the grid and inverter
voltage [7], [8].
T
Manuscript received April 28, 2011; revised July 22, 2011; accepted September 25, 2011 Date of current version February 27, 2012. Recommended for
publication by Associate Editor Pedro Rodriguez.
A. Yafaoui and B. Wu are with the Electrical and Computer Engineering Department, Ryerson University, Toronto, ON M5B2K3 Canada (e-mail:
yafaoui.ahmad@ryerson.ca; bwu@ee.ryerson.ca).
S. Kouro is with the Electronics Engineering Department, Universidad Tecnica Federico Santa Maria,Valparaiso 1680, Chile (e-mail:samir.
kouro@ieee.org.).
Digital Object Identifier 10.1109/TPEL.2011.2171997
The IEEE Standard 929 and Standard 1547 demand the use
of an anti-islanding detection feature by the grid connected
inverter [9], [10]. The standards also suggest test procedures
and set the limits for the grid parameters, as shown in Table I
[9]–[11]. Passive and active methods have been proposed to
detect the islanding of the system and force the inverter to cease
energizing the loads.
Passive methods are those methods which use the grid parameters and measurements (voltage, frequency, harmonic content,
etc.) in order to detect islanding operation . The boundary limits of these parameters define the nondetection zone (NDZ). If
the local loads have similar power capacity of the DG system,
i.e., all the generated power is consumed locally, then voltage
and current levels at the point of common coupling (PCC) will
only vary slightly when islanding occurs. The system variables
will be then within the boundary limits and the islanding condition will remain undetected. Passive methods have, therefore,
a large NDZ. Nevertheless, passive methods are conceptually
simple and easy to implement and do not introduce any change
to the power quality of the system.
In order to reduce the NDZ, particularly in cases where the local loads are close in capacity to the DG system, active detection
methods have been proposed. In active methods, a perturbation
is injected in the current waveform to drive one of the system
parameters out of its limits during islanding operation [12], [13].
Among the active methods the active frequency drift (AFD)
method has drawn increased attention in literature because of
its capability to effectively detect islanding with a smaller NDZ
[14]–[18]. In AFD, a perturbation is injected to the current
waveform that makes the inverter drift the frequency in case of
islanding operation, which does not happen when the grid is
available. The frequency drift can then be easily detected with
the boundary limits.
Unfortunately, the smaller NDZ obtained with AFD compared to passive methods comes at expense of increased THD
which degrades the power quality provided by the grid-tied converter [19]. The loss in power quality is inherent to AFD due
to the distortion injected to the current waveform. In order to
minimize the impact on power quality, several variations of the
AFD method had been suggested in literature like the AFD with
pulsation of chopping fraction [14]. However, these methods
introduce a design compromise or tradeoff between the amount
of distortion added to the system and the reduction of the NDZ.
In this work, a new distortion injection to the current waveform is presented and analyzed. The proposed perturbation introduces lower THD to the current waveform, while improving
0885-8993/$26.00 © 2011 IEEE
2368
IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 27, NO. 5, MAY 2012
TABLE I
GRID PARAMETER LIMITS STANDARDS
the NDZ compared to AFD. The performance of the proposed
method is derived analytically and simulated using MATLAB.
Validation of the analysis and simulation is obtained experimentally using a prototype setup. A single phase grid-tied photovoltaic distributed generation system with local RLC loads,
as suggested in the IEEE Standard 929 and IEEE Standard
1547.1, is considered as application for the simulation and
experimental setup.
II. ACTIVE FREQUENCY DRIFT METHOD OVERVIEW
In order to better understand the proposed method, first an
overview of the classic AFD method is presented. This analysis
is also necessary for comparison purposes in later sections of
the paper.
The AFD method is based on the injection of a current waveform distortion to the original reference current of the inverter,
to force a frequency drift in case of islanding operation. By
introducing a zero conduction time tz at the end of each half
cycle, as shown in Fig. 1, the phase angle of the fundamental
component of the current is shifted. During normal grid connected operation the inverter usually operates with unity power
factor and is synchronized to the grid voltage and will operate
at grid frequency. In islanding operation, the added distortion
to the current will produce a permanent drift in the operating
frequency toward the local load resonance frequency in order
to keep unity power factor. This drift will eventually reach the
frequency boundary limits set for islanding detection. The dead
Fig. 1. AFD method: (a) Original reference current and AFD reference current
waveforms. (b) Original reference current and injected current waveforms.
time tz in which zero current is forced and the period of the original signal T can be related to each other to define the chopping
factor Cf used to perturb the waveform as
Cf =
2tz
.
T
(1)
YAFAOUI et al.: IMPROVED ACTIVE FREQUENCY DRIFT ANTI-ISLANDING DETECTION METHOD
The AFD reference current waveform shown in Fig. 1(a) can
be defined as:
⎧
⎪
I sin(2π f´t)
→ 0 ≤ ωt < π − tz
⎪
⎪
⎪
⎨0
→ π − tz ≤ ωt < π
(2)
iaf d (t) =
´
⎪
I
sin(2π
f
t)
→
π
≤
ωt
<
2π
−
t
⎪
z
⎪
⎪
⎩
0
→ 2π − tz ≤ ωt ≤ 2π
1
where f´ = f ( 1−C
).
f
Basically, the chopping factor defines the amount of drift
introduced to the frequency f . Note that since the current waveform has a different frequency f´, the vertical axis is shifted to
facilitate the zero current period tz .
The distortion introduced by tz can be deducted from the
original reference current, as shown in Fig 1(b).
Note that, according to (1), the greater tz , the greater the
chopping factor; hence, a larger perturbation is introduced to
the current. In contrast, if tz = 0, from (1) Cf is also zero,
and replacing in (2) the AFD reference current waveform is
equal to the original reference current waveform (iaf d (t) =
I sin(2πf t)).
When this modified waveform is applied to an isolated DG
system with an RLC load, the frequency of the load will change
according to the following equation [20]–[22] :
−1
= 0.5πCf .
(3)
arg R−1 + (jωL)−1 + jωC
This method is effective for resistive loads but has a larger
NDZ for some RLC load combinations. To overcome this problem positive feedback AFD methods have been proposed [23].
These improve the NDZ for different load types, but still affect
the power quality introducing a higher THD.
A. Parameter Relations for Islanding Detection Analysis
Undetected islanding can happen when there is a balance
between the power (both active and reactive) delivered by the
inverters and consumed by the local loads of the DG system. A
mismatch would lead to a change in the amplitude, frequency,
or both of the load voltage, consequently resulting in islanding
detection. This mismatch can be forced by injecting reactive
power to the system by introducing a distortion to the current
waveform.
The relationship between the reactive power mismatch ∆Q
and the frequency threshold can be obtained by [24]
2
2
f
f
∆Q
< Qf · 1 −
<
(4)
Qf · 1 −
fm in
P
fm ax
where P is the active power, f the grid frequency, fm in , fm ax
under/over frequency threshold, and Qf is the quality factor.
The quality factor is defined as the reactive power stored in L
or C divided by the active power consumed in R.
In order to drive the load frequency out of limit faster and
with smaller NDZ, a larger ∆Q/P is needed. With the limit
values of the frequency specified in Table I, fm in = 59.3 Hz,
fm ax = 60.5, f = 60, and a quality factor of Qf = 2.5, (4) is in
2369
the range of
−5.95% ≤
∆Q
≤ 4.11%.
P
(5)
For nonsinusoidal waveforms the active power is defined in
IEEE Standard 1459-2010 [25] as
P = V · I1 · cos(φ1 )
(6)
where I1 and φ1 are the rms value and the phase angle of the
fundamental waveform, respectively. On the other hand, the
reactive power is defined as
Q = V · I1 · sin(φ1 )
(7)
Q
= tan(φ1 ).
P
(8)
from which
Equation (8) shows the relation between the reactive power
generated by the distortion of the current waveform and the
phase angle of the fundamental waveform. In the AFD method,
a distortion is added to the current, which forces the fundamental
component of the current to shift by angle φ1 . It is known from
[14] that Q/P = T HD for the AFD method. Consequently,
increasing the reactive power injected into the load to reduce
the NDZ will increase the THD of the current wave form.
B. THD Problem in AFD Method
For the AFD method to be effective, Cf needs to be fairly
large, which directly affects the THD of the current waveform
[12], [23]. The relationship between THD and Cf has been
reported to be linear [14], [23]. The maximum allowable Cf is
limited by the maximum THD (<5% according to Table I). It is
mentioned that a Cf of 0.046 results in a THD of 4.88% [17].
Hence, like most of the active methods, the AFD reduces the
quality of the power delivered to the grid. Generally speaking,
the larger the chopping factor, the smaller the NDZ and the
higher the THD for AFD based methods.
The injected current waveform used in AFD shown in
Fig. 1(b), introduces high low-order frequency harmonics to the
original current waveform. This can be seen from the fact that
the injected current waveform changes slowly over half cycle
of the original reference current. In other words, the phase shift
of the fundamental component (φ1 ) is achieved gradually over
half cycle, which in consequence translates to high low-order
harmonics. This has motivated the present work to find different
perturbations that lead to a reduced THD reference current but
with same or better NDZ features.
III. IMPROVED AFD ANTI-ISLANDING METHOD
Instead of introducing a gradual change in the current waveform over half cycle, a sudden change can also introduce the
necessary phase shift of the fundamental component (φ1 ) while
introducing less THD. The following section describes the proposed waveform, which is analyzed analytically and compared
to classic AFD.
2370
IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 27, NO. 5, MAY 2012
Fig. 3.
Fig. 2. Proposed improved AFD method: (a) Original reference current and
proposed injected current waveforms. (b) Original reference current and proposed reference current waveforms.
An effective way to shift the fundamental component phase
angle of a sine wave is by introducing a step change in the
amplitude in the 1st and 3rd or 2nd and 4th quarters of the
waveform. This perturbation injection and the resulting reference waveform are illustrated in Fig. 2(a) and (b), respectively,
for the case in which the 2nd and 4th quarter are considered.
The resulting reference current waveform is defined by
⎧
I sin(ωt)
→ 0 ≤ ωt < π/2
⎪
⎪
⎪
⎨ I sin(ωt) − KI → π/2 ≤ ωt < π
(9)
i(t) =
⎪
I sin(ωt)
→ π ≤ ωt < 3π/2
⎪
⎪
⎩
I sin(ωt) + KI → 3π/2 ≤ ωt ≤ 2π
where I is the current amplitude, ω the grid frequency, and K
the distortion factor. In order to analyze the harmonic contents
and the phase angle of proposed current waveform, the Fourier
series coefficients of the fundamental components are found
a1 =
∞
a0
+
[an cos(ωn t) + bn sin(ωn t)]
2
n=1
(10)
2KI
π
(11)
b1 = I 1 −
I1 = I
1+
φ1 = tan−1
2K
π
(12)
8K 2
4K
−
2
π
π
(13)
a1
b1
= tan−1
2K
π − 2K
The rms value of the current waveform is defined as
2π
1
i2 (t)dt
Irm s =
2π 0
(14)
where a1 and b1 are the cosine and sine components of the
series, and I1 and φ1 are the amplitude, and displacement angle
of the fundamental waveform, respectively.
(15)
then the rms value for the proposed current waveform can be
obtained replacing (9) in (15), which yields
1 2K
K2
−
+
.
2
π
2
Irm s = I ·
A. Proposed Current Waveform Distortion
F (t) =
THD versus Q/P for both methods.
(16)
In addition, the THD of the current waveform is defined as
2
2
Irm
I1
s − I1rm s
(17)
THD =
, with I1rm s = √ .
I1rm s
2
Replacing (16) and (13) in (17) yields
THD =
π2
K 2 (π 2 − 8)
.
− 4πK + 8K 2
(18)
In addition, by replacing in (8) the terms (11), (12), and (14),
the Q/P ratio of the proposed waveform can be computed as
2K
Q
=
.
P
π − 2K
(19)
Using (18) and (19) the THD and the Q/P ratio can be calculated for different distortion factors (K). For example, with
a distortion factor of K = 0.075 the THD of the current waveform is 3.42% and a Q/P ratio of 5%. When compared with
traditional AFD, in order to generate the same Q/P ratio of 5%,
the THD of the AFD current waveform increases to 5% (more
than 30% increase in distortion).
Fig. 3 shows the THD versus Q/P curve for both methods
at different values of their respective distortion factors K and
Cf . It is obvious that the proposed method always generates
less harmonic distortion at any given Q/P value. Based on the
above analysis, it can be concluded that:
i) The proposed method can achieve the same results of the
conventional AFD method with about 30% reduction in
THD.
ii) Alternatively, if the maximum allowed THD is considered to be 5%, which is obtained with K = 0.108 for a
Q/P = 7.4% in the proposed method, then compared to
the traditional AFD method which with Cf = 0.046 it will
generate Q/P = 4.8%, there is about a 50% increase in
YAFAOUI et al.: IMPROVED ACTIVE FREQUENCY DRIFT ANTI-ISLANDING DETECTION METHOD
Fig. 5.
2371
DG photovoltaic grid connected system with local RLC load.
TABLE 2
DG CIRCUIT PARAMETERS
Fig. 4. Practical proposed improved AFD method: (a) Original reference current and practical injected current waveform (b) Original reference current and
practical reference current waveform.
reactive power injected to the system resulting in better
islanding detection.
IV. IMPLEMENTED WAVEFORM
The proposed current waveform illustrated in Fig. 2 has one
drawback: The fast changes in current, when crossing zero,
are difficult to implement in practice. The current controller is
not able to follow this sudden change in reference accurately.
Therefore, a slight modification is introduced to the proposed
waveform which eliminates the fast change in current at zero
crossing. The proposed practical current injection and the resulting reference current waveform are shown in Fig. 4(a) and
(b), respectively. Note that the original motivation, which is to
concentrate the perturbation in the 2nd and 4th quarter of the
waveform still holds.
The resulting waveform can be defined by
⎧
I sin(ωt)
→ 0 ≤ ωt < π/2
⎪
⎪
⎪
⎪
⎪
I sin(ωt) − KI → π/2 ≤ ωt < π − α
⎪
⎪
⎪
⎪
⎨0
→ π − α ≤ ωt < π
(20)
í(t) =
⎪
I sin(ωt)
→ π ≤ ωt < 3π/2
⎪
⎪
⎪
⎪
⎪
I sin(ωt) + KI → 3π/2 ≤ ωt < 2π − α
⎪
⎪
⎪
⎩
0
→ 2π − α ≤ ωt ≤ 2π
where α = arcsin(K).
For this new current waveform, the Fourier coefficients and
the rms value can be computed following same steps as for
previous waveform, which yields
K2 I
2KI
−
π
π
√
arcsin(K)
K 1 − K2
′
b1 = I 1 −
−
π
π
a′1 =
′
Irm
s =
I·
√
3K 1 − K 2
arcsin(K) · (1 + 2K 2 )
1 K2
+
−
−
.
2
2
2π
2π
(23)
Since the values for the distortion factor are small (K ≤
0.1) the quadratic terms K 2 ≪ 1 can be neglected. In addition,
for small values of K the following holds: arcsin(K) ∼
= K.
Replacing both approximations in (21), (22), and (23) yields to
the same results obtained for the originally proposed waveform
from (11) to (19). In summary, the small modification introduced
to eliminate the fast change in current at zero crossing and make
the proposed waveform practical, does not affect the THD and
NDZ achieved with the originally proposed waveform.
V. SIMULATION RESULTS
In order to verify the proposed method, a single phase photo(21) voltaic distributed generation system with a local RLC load has
been considered. The power circuit of the system is shown in
(22) Fig. 5. The system parameters are listed in Table II. The simulations for both AFD and the proposed method were implemented
2372
IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 27, NO. 5, MAY 2012
Fig. 8.
Fig. 6. Inverter current: a) for AFD with C f = 0.046, b) for original proposed
method with K = 0.08, c) for practical proposed method with K = 0.08.
NDZ of both ADF and proposed methods for different C n o rm .
than with classic AFD. Again, these results are consistent with
the ones obtained analytically in previous section, thus verifying
the validity of (10)–(22). This also confirms that the approximation introduced by the practical implementation waveform of
the proposed method does not affect the power quality and is a
valid approach to overcome the drawback of the original current
injection waveform.
When the proposed waveform is applied to an RLC load,
the frequency at the PCC will change during islanding until
the load phase angle is equal to the displacement angle of the
fundamental waveform φ1 given in (14) as shown below
arg R−1 + (jωL)−1 + jωC = tan−1
Fig. 7. Inverter current spectrum: (a) for AFD with C f = 0.046, (b) for
original proposed method with K = 0.08, for practical proposed method with
K = 0.08.
in Matlab/Simulink platform together with over/under voltage
and over/under frequency relays.
The active frequency drift method was simulated with chopping factor of Cf = 0.046. The resulting current waveform is
shown in Fig. 6(a). The simulation of proposed method was
performed considering a distortion factor of K = 0.08. These
values were chosen since they generate the same Q/P as shown
before. The resulting current waveforms for both the original
and practical cases are shown in Fig. 6(b) and (c), respectively.
The spectra of the three current waveforms are compared in
Fig. 7 along with their THD values. Note that the fundamental component amplitude in Fig. 7 corresponds to 100% and
appears truncated to show in more detail the harmonic content.
The THD value obtained for classic AFD current waveform
is found to be 4.90% which coincides with the data given in [14]
and discussed in the above analysis.
The proposed methods resulted in current waveforms with
THD of 3.65% and 3.64%, respectively, around a 30% lower
2K
π − 2K
.
(24)
The NDZ of the proposed method can be obtained using
(24). Fig. 8 shows the NDZ of both AFD and the proposed
method mapped into the load space that is characterized by the
quality factor Qf and the normalized load capacitance Cnorm .
This mapping method relates the NDZ to the IEEE Standard
929-2000 requirements in an efficient way [21]. This graph is
obtained for AFD method with Cf = 0.046 and the proposed
method with K = 0.105 which both generate same THD =
4.9%. Although both methods have same NDZ shape in relation
to the quality factor, the proposed method has a higher NDZ,
making the islanding formation in the vicinity of balanced load
more unlikely. This holds particularly for Qf <5, which is the
usual case in practical applications.
The simulation of the islanding phenomena is performed with
load capacitor C = 139.2 µF whose normalized capacitance is
Cnorm = 1.01, and Qf = 2.5, which is one of the load combinations required by IEEE Standard 929-2000 to test against
islanding. This load combination is a point shown in Fig. 8 that
lies inside the NDZ of the AFD but outside the NDZ of the
proposed method. Here also AFD method with Cf = 0.046 and
proposed method with K = 0.105 were used. The utility breaker
was opened after four cycles to simulate the grid disconnection.
As expected, the AFD method fails to detect the islanding and
the inverter continues to energize the load beyond the 2 s limit,
as shown in Fig. 9(a). Whereas the proposed method forces the
frequency of the PCC to increase above the limit in nine cycles
which triggers the over frequency relay and causes the islanding
YAFAOUI et al.: IMPROVED ACTIVE FREQUENCY DRIFT ANTI-ISLANDING DETECTION METHOD
Fig. 11.
2373
Experimental setup power circuit diagram.
Fig. 9. Voltage and current at PCC: a) for AFD with C f = 0.046, b) for
proposed method with K = 0.105 .
Fig. 12. Experimental voltage and current waveforms together with frequency
spectrum for the AFD method with C f = 0.046.
Fig. 10. System frequency evolution for AFD with C f = 0.046 and proposed
method with K = 0.105.
operation to be detected, as shown in Fig. 9(b). This effect can
be more clearly appreciated in the evolution of the frequency of
the system for both methods shown together for comparison in
Fig. 10.
VI. EXPERIMENTAL RESULTS
An experimental prototype has been built in order to test the
proposed method. The corresponding power circuit of the setup
is shown in Fig. 11. The grid-tied inverter is constructed as a
MOSFET H-bridge followed by an LC filter (L = 1.3 mH and
C = 3 µF), and connected to an RLC load. A digital signal
processor board (TMS320F2812) is used to generate a 20 KHz
unipolar PWM gate signals and to implement a proportional
resonant current controller which is a typical controller for single
phase ac systems to ensure zero steady state error [26], [27] .
Fig. 12 shows the voltage and current waveform of the AFD
method with a chopping factor of Cf = 0.046, the THD in the
current was measured using the power analyzer YOKOGAWA
PZ4000 to be 5.16%. The measured active and reactive power
were P = 334 W and Q = 17.4 VAR, respectively. Also the
frequency spectrum of the current waveform is shown, the third
and fifth harmonics are the dominant harmonics in accordance
with the simulation results shown in Fig. 7
Fig. 13 shows the voltage and current waveform of the proposed method with K = 0.08. The THD of the current was
measured to be 3.91%. The measured active and reactive power
were P = 335 W and Q = 18.2 VAR, respectively. The experimental results shown in Figs. 12 and 13 match the simulated
results of Figs. 6 and 7 for the AFD and the proposed method,
respectively. Note that when both methods generate the same
amount of reactive power to shift the frequency in case of islanding, the proposed method features a lower THD than the
AFD method, as demonstrated analytically and the frequency
spectrum of the current waveform of the proposed method has
lower third and fifth harmonics as has been shown previously in
the simulation results shown in Fig. 7.
2374
IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 27, NO. 5, MAY 2012
Fig. 15.
Islanding test result for the proposed method with K = 0.105.
Fig. 16.
= 1.
Islanding test result for the AFD method with C f = 0.046 and Q f
Fig. 13. Experimental voltage and current waveforms together with frequency
spectrum for the proposed method with K = 0.08.
Fig. 14.
Islanding test result for the AFD method with C f = 0.046.
The islanding detection test is carried first in accordance with
IEEE 929-2000 standard with load quality factor Qf set to 2.5
and with the same parameters as the ones used for simulation
and listed in Table II. The AFD method chopping factor is
Cf = 0.046 . As can be seen from Fig. 14, the inverter fails to
detect the islanding after the grid is disconnected and continues
to energize the load beyond the 2 s limit.
The same test is repeated with the proposed method and
distortion factor is set to K = 0.105, which results the same
amount of harmonic distortion as the AFD method with Cf
= 0.046. The inverter detects islanding operation as the load
frequency increases beyond the limit (60.5 Hz) and discontinues
energizing the load, as can be seen from Fig. 15.
The second islanding test is carried with the load quality
factor Qf set to 1.0 and Cnorm = 1.02 as required by IEEE
1547.1 standard. Note that this operating point is outside the
NDZ of both methods, as can be seen from Fig. 8. The AFD
method chopping factor is set to Cf = 0.046 and the proposed
method distortion factor is set to K = 0.105. It is clear from
Figs. 16 and 17 that the proposed method is faster in detecting
the islanding due to the extra reactive power injected in the load
Fig. 17. Islanding test result for the proposed method with K = 0.105 and
Q f = 1.
during islanding. Note that there is a three cycle delay after the
frequency reaches the limit before the inverter stops, which is
necessary to eliminate false tripping.
VII. CONCLUSION
This paper presents an improved active anti-islanding detection method that can detect islanding with less total harmonic
distortion compared to the conventional AFD method. The rms
value and the Fourier series coefficients of the current waveform
of the proposed method are obtained and used to derive analytically some of the operational characteristics of the method.
Simulation and experimental results of proposed method
show a 30% reduction of THD in the current waveform. Considering the limits of THD set by IEEE Standard 929-2000
and IEEE Standard 1547.1, this method is able to detect the
islanding faster with better NDZ. The proposed method could
be enhanced further by adding a positive feedback such that the
distortion factor K becomes a function of the frequency drift,
YAFAOUI et al.: IMPROVED ACTIVE FREQUENCY DRIFT ANTI-ISLANDING DETECTION METHOD
as in the active frequency drift with positive feedback method
(AFDPF).
REFERENCES
[1] P. Du, Z. Ye, E. Aponte, J. Nelson, and L. Fan, “Positive-feedback-based
active anti-islanding schemes for inverter-based distributed generators:
Basic principle, design guideline, and performance analysis,” IEEE Trans.
Power Electron., vol. 25, no. 12, pp. 2941–2948, Dec. 2010.
[2] F.-S. Pai, J.-M. Lin, and S.-J. Huang, “Design of an inverter array for
distributed generations with flexible capacity operations,” IEEE Trans.
Ind. Electron., vol. 57, no. 12, pp. 3927–3934, Dec. 2010.
[3] J.-H. Kim, J.-G. Kim, Y.-H. Ji, Y.-C. Jung, and C.-Y. Won, “An islanding
detection method for a grid-connected system based on the goertzel algorithm,” IEEE Trans. Power Electron., vol. 26, no. 4, pp. 1049–1055, Apr.
2011.
[4] A. Pigazo, M. Liserre, R. Mastromauro, V. Moreno, and A. Dell’Aquila,
“Wavelet-based islanding detection in grid-connected pv systems,” IEEE
Trans. Ind. Electron., vol. 56, no. 11, pp. 4445–4455, Nov. 2009.
[5] I. Balaguer-Alvarez, Q. Lei, S. Yang, U. Supatti, and Z. Peng, “Control for
grid-connected and intentional islanding operations ofdistributed power
generation,” IEEE Trans. Ind. Electron., 2010.
[6] D. Velasco, C. Trujillo, G. Garcera and, and E. Figueres, “An active antiislanding method based on phase-pll perturbation,” IEEE Trans. Power
Electron., vol. 26, no. 4, pp. 1056–1066, Apr. 2011.
[7] H. Zeineldin, “A q-f droop curve for facilitating islanding detection of
inverter-based distributed generation,” IEEE Trans. Power Electron.,
vol. 24, no. 3, pp. 665–673, Mar. 2009.
[8] W. Bower and M. E. Ropp, “Evaluation of islanding detection methods for
photovoltaic utility-interactive photovoltaic systems,” International Energy Agency, Paris, France, Tech. Rep. IEA-PVPS T5-09, 2002.
[9] IEEE Recommended Practice for Utility Interface of Photovoltaic (pv)
Systems, IEEE Standard 929-2000.
[10] Ieee Standard for Interconnecting Distributed Resources With Electric
Power Systems, IEEE Standard 1547-2003.
[11] Ieee Standard Conformance Test Procedures for Equipment Interconnecting Distributed Resources With Electric Power Systems, IEEE Standard
1547.1-2005.
[12] T. T. Ma, “Novel voltage stability constrained positive feedback antiislanding algorithms for the inverter-based distributed generator systems,”
Renewable Power Generat., IET, vol. 4, no. 2, pp. 176–185, 2010.
[13] S.-K. Kim, J.-H. Jeon, J.-B. Ahn, B. Lee, and S.-H. Kwon, “Frequencyshift acceleration control for anti-islanding of a distributed-generation
inverter,” IEEE Trans. Ind. Electron., vol. 57, no. 2, pp. 494–504, Feb.
2010.
[14] Y. Jung, J. Choi, B. Yu, G. Yu, and J. So in A novel active frequency
drift method of islanding prevention for the grid-connected photovoltaic
inverter, Jun., 2005, pp. 1915–1921.
[15] V. John, Z. Ye, and A. Kolwalkar, “Investigation of anti-islanding protection of power converter based distributed generators using frequency
domain analysis,” IEEE Trans. Power Electron., vol. 19, no. 5, pp. 1177–
1183, Sep. 2004.
[16] Y. Jin, Q. Song, and W. Liu, “Anti-islanding protection for distributed
generation systems based on reactive power drift,” in Proc. 35th Annu.
Conf. IEEE Ind. Electron. (IECON) 2009, Porto, Portugal, Nov., pp. 3970–
3975.
[17] L. Lopes and H. Sun, “Performance assessment of active frequency drifting
islanding detection methods,” IEEE Trans. Energy Convers., vol. 21, no. 1,
pp. 171–180, Mar. 2006.
[18] P. Du, Z. Ye, E. Aponte, J. Nelson, and L. Fan, “Positive-feedback-based
active anti-islanding schemes for inverter-based distributed generators:
Basic principle, design guideline, and performance analysis,” IEEE Trans.
Power Electron., vol. 25, no. 12, pp. 2941–2948, Dec. 2010.
[19] M. Ciobotaru, V. Agelidis, R. Teodorescu, and F. Blaabjerg, “Accurate
and less-disturbing active anti-islanding method based on pll for gridconnected converters,” IEEE Trans. Power Electron., vol. 25, no. 6,
pp. 1576–1584, Jun. 2010.
[20] M. E. Ropp, M. Begovic, and A. Rohatgi, “Prevention of islanding in gridconnected photovoltaic systems,” Progr. Photovolt.: Res. Appl., vol. 7,
no. 1, pp. 39–59, Jan./Feb. 1999.
[21] F. Liu, Y. Kang, and S. Duan, “Analysis and optimization of active frequency drift islanding detection method,” in Proc. 22nd Annu. IEEE Appl.
Power Electron. Conf. (APEC) 2007, pp., 1379–1384.
[22] X. Zhu, G. Shen, and D. Xu, “Evaluation of afd islanding detection methods based on ndzs described in power mismatch space,” in Proc. IEEE
[23]
[24]
[25]
[26]
[27]
2375
Energy Conversion Congress and Exposition (ECCE) 2009, San Jose, CA,
Sep. 2009, pp. 2733–2739.
M. Ropp, M. Begovic, and A. Rohatgi, “Analysis and performance assessment of the active frequency drift method of islanding prevention,” IEEE
Trans. Energy Convers., vol. 14, no. 3, pp. 810–816, Sep. 1999.
Z. Ye, A. Kolwalkar, Y. Zhang, P. Du, and R. Walling, “Evaluation of antiislanding schemes based on nondetection zone concept,” IEEE Trans.
Power Electron., vol. 19, no. 5, pp. 1171–1176, Sep. 2004.
Ieee Standard Definitions for the Measurement of Electric Power Quantities Under Sinusoidal, Nonsinusoidal, Balanced, or Unbalanced Conditions, IEEE Standard 1459-2010.
R. Teodorescu, F. Blaabjerg, U. Borup, and M. Liserre, “A new control
structure for grid-connected lcl pv inverters with zero steady-state error
and selective harmonic compensation,” in Proc. 19th Annu. IEEE Appl.
Power Electron. Conf. Expo. (APEC), 2004, vol. 1, pp. 580–586.
M. Ciobotaru, R. Teodorescu, and F. Blaabjerg, “Control of single-stage
single-phase pv inverter,” in Proc. Eur. Conf. Power Electron. Appl. 2005,
Dresden, Germany, p. 10.
Ahmad Yafaoui (S’95) received the Bachelor and
Master degrees in electrical engineering from Middle
East Technical University, Ankara Turkey, in 1996
and 1998, respectively. He is currently a Ph.D. student
at Ryerson University, Toronto, Canada.
He worked as Senior Design Engineer from 1998
to 2006. His research interests include solar energy
conversion systems and DC/DC converter.
Bin Wu (S’89-M’92-SM’99-F’08) received the
Ph.D. degree in electrical and computer engineering
from the University of Toronto, Canada, in 1993.
After being with Rockwell Automation, Canada,
as a Senior Engineer, he joined Ryerson University,
Toronto, Canada, where he is currently a Professor
and NSERC/Rockwell Industrial Research Chair in
power electronics and electric drives. He has published more than 200 technical papers, authored/coauthored two Wiley-IEEE Press books, and holds
more than 20 awarded/pending patents in the area
of power conversion, advanced controls, adjustable-speed drives, and renewable energy systems.
Dr. Wu received the Gold Medal of the Governor General of Canada, the
Premier’s Research Excellence Award, Ryerson Distinguished Scholar Award,
Ryerson Research Chair Award, and the NSERC Synergy Award for Innovation.
He is a fellow of Engineering Institute of Canada (EIC) and Canadian Academy
of Engineering (CAE). He is an Associate Editor of the IEEE TRANSACTIONS
ON POWER ELECTRONICS and IEEE CANADIAN REVIEW.
Samir Kouro (S’04-M’08) was born in Valdivia,
Chile, in 1978. He received the M.Sc. and Ph.D. degrees in electronics engineering from the Universidad
Técnica Federico Santa Marı́a (UTFSM), Valparaı́so,
Chile, in 2004 and 2008, respectively.
In 2004, he joined the Electronics Engineering
Department, UTFSM, as a Research Assistant, and
became an Associated Researcher, in 2008, and Research Academic, in 2011. From 2009 to 2011 he was
on a Postdoctoral stay in the Department of Electrical and Computer Engineering, Ryerson University,
Toronto, Canada. His research interests include power converters, variable-speed
drives, and renewable energy conversion systems. He has coauthored one book,
two book chapters, and more than 50 refereed journal and conference papers.
Dr. Kouro has served as Guest Editor in one special section of the
IEEE TRANSACTION ON INDUSTRIAL ELECTRONICS and was recipient of
the Best Paper Award of 2008 of the IEEE INDUSTRIAL ELECTRONICS
magazine.