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IEECON.2017.8075791

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An Evaluation of Voltage Variation and Flicker
Severity in Micro Grid
Nuruddin Hama
Department of Electrical
Engineering
Kasetsart University
Bangkok, Thailand
nuruddin.h@ku.th
Weerawoot Kanokbannakorn
Department of Electrical
Engineering
Kasetsart University
Bangkok, Thailand
fengwwk@ku.ac.th
Siriroj Sirisukprasert
Department of Electrical
Engineering
Kasetsart University
Bangkok, Thailand
siriroj.s@ku.th
Abstract— This paper evaluates the effects of voltage
fluctuation in a micro grid. The micro grid is modeled and
simulated using the DIgSILENT software. The voltage flicker
due to the variation of power productions from renewable
sources in microgrid during off-grid and grid-connected mode
are presented. The results indicate that the main sources of
voltage fluctuation in the studied micro grid are PV and wind
generations. The situation becomes worse when the microgrid
is operated in off-grid mode. The renewable sources can
improve voltage profiles in some cases.
nominal voltage with frequencies range between 0.5 - 35 Hz.
Thus voltage changes can be described by Eq. 1 and 2 for
rectangular and sinusoidal variation respectively [8].
Keywords— Micro Grid, Voltage Flicker, Power Quality,
Distributed Generation (DG)
Where
I.
INTRODUCTION
A cluster of Distributed Energy Resources (DER) or a
system is called “Micro grid”. A Micro grid is a new concept
for modern power distributed systems to enhance their
stability, reliability and power quality. Micro grid system
helps down time reduction, cost of operation and
maintenances and power losses in the system [1]. The
penetration level of DGs to the micro grid network has a
significant impact on power quality, especially voltage
variation at the utility and their customer equipment. Voltage
flicker is one of the voltage variation which negatively
impacts on human eyes and makes sensitive equipment
malfunction [2]. The intermittent generation may create
flicker problems in the power system [3]-[6]. Particularly for
the weak system as a micro grid, the voltage flicker level can
exceed the limit [7].
This paper evaluates the effects of voltage fluctuation in
PEA micro grid at Mae Sariang. The main sources of voltage
fluctuation in the studied microgrid system are the
combinations between PV and wind generations. The power
produced from wind turbine fluctuates due to the variations
of wind speed. While the PV power fluctuations are come
from solar irradiation. The voltage flicker in microgrid
during off-grid and grid-connected mode are studied.
II.
VOLTAGE FLICKER ASSESSMENT
A. Voltage Flicker
Voltage flickers are described as variations envelope or a
random voltage changes in voltage waveform as show in Fig
1. Generally, the variations range from 0.1% to 10% of
978-1-5090-4666-9/17/$31.00 ©2017 IEEE
{
v (t ) = V sin(2π ft ) 1 +
{
1 ΔV
2 V
v (t ) = V sin(2π ft ) 1 +
}
signum[sin 2π f f t ]
1 ΔV
2 V
}
sin[sin 2π f f t ]
(1)
(2)
f is the fundamental frequency of system,
ΔV V is the relative voltage change,
f f is the frequency of flicker.
Fig. 1. Voltage flicker waveform.
B. Flicker Severity Index Evaluation using Flickermeter
IEC 61000-4-15 standard defines the severity of voltage
fluctuation by two indices i.e. short-term flicker severity
indices (Pst) and long-term flicker severity indices (Plt). The
standard flicker meter as show in Fig. 2 is used to calculate
the indices [9]-[10].
Short term flicker severity value (Pst) is calculated on the
basis of the probability distribution function of the
instantaneous flicker sensation in 10 minutes period as
equation below [11]:
Fig. 2. Functional diagram of IEC 61000-4-15 flickermeter.
III.
Pst = 0.0314 P0.1 + 0.0525 P1s + 0.0657 P3 s + 0.28 P10 s + 0.08 P50 s
(3)
Where the percentiles P0.1 , P1 , P3 , P10 and P50 are the
flicker levels exceeded for 0.1, 1, 3, 10 and 50 % of the time
during the observation period, respectively.
The suffix s in the formula indicates that the smooth
value should be used. These are obtained using the following
equations:
P10 s =
(P
30
+ P50 + P80 ) / 3
(4)
(P + P + P + P + P ) / 5
P = (P + P + P ) / 3
P = (P + P + P ) / 3
6
3s
8
10
2.2
13
3
17
4
(5)
(6)
(7)
Long term flicker severity value (Plt) is calculated for 120
minutes period on the 12 values of Pst, according to the
following:
1s
0.7
1
12
Plt =
¦ ( Psti )
1.5
A. Study System
The studied micro grid is illustrated in Fig. 3. The
microgrid is radially connected to 22 kV grid through a long
feeder (106 km). The microgrid comprises of 4 types of DG.
The 4x1 MVA PV plants are connected to the feeder 4 and
located 5 km from substation (PCC). A 5 MVA wind
generator is connected to the feeder 1. A 2x625 kVA mini
hydro plants are between main grid and PCC. The diesel
generator 4x1250 kVA are installed at PCC. The maximum
load in the system is 7.7 MW. During a day, the loads are
mainly supplied by PV and wind sources. The diesel
generator is started during peak load (6.00 – 8.00 p.m.)
due to the absence of power from PV. To investigate voltage
variation due to the renewable sources in microgrid, the daily
load consumption, wind speed profile and PV generation
profiles during a day in summer, rainy and winter season are
chosen and included in the model by PEA observation [13].
The profiles are illustrated in Fig. 4(a) – 4(c) respectively.
The voltage variations at PCC are observed. Pst and Plt are
calculated using flickermeter model as described in Section
II.
GRID
3
(8)
3 i =1
12
The Pst and Plt should not exceed the values specified in
Table I, in accordance with PRC - PQG - 02 / 1998 [12].
Mini Hydro
2x625 kVA
G
106 km
P50 s =
METHODOLOGY
PCC
TABLE I. DATA OF DISTRIBUTION TEST SYSTEM.
Voltage Level
Pst
Plt
115 kV or Below
1.0
0.8
Above 115 kV
0.8
0.6
G
Diesel Gen F1 Wind Farm F2
4x1250 kVA
5 MVA
F3
F4 Solar PV F5
4x1000kVA
Fig. 3. Single line diagram of Mae Sariang micro grid.
International Electrical Engineering Congress, Pattaya, Thailand, 8-10 March 2017
5th
B. Case Study
The studies are divided into 3 scenarios as follows:
Scenario I : The renewable resources are unavailable.
The loads in microgrid are supplied by only main grid. This
scenario is intended to investigate the voltage variations due
to long feeder.
Scenario II : The microgrid is in grid-connected mode.
The power can deliver to main grid if load consumption is
less than power production from the renewable sources.
Scenario III : The microgrid is in off-grid mode. The
loads are supplied by local renewable sources.
IV.
STUDY RESULTS
Fig. 5(a) – 5(c) show the voltage profiles at PCC from
the simulation results. The results show the voltage varies all
the time throughout a day. During peak load (6.00 – 8.00
p.m.), the voltage is decrease due to the absence of PV
generations for all cases. The voltage drop below 10% of
nominal voltage can be observed in the Scenario III (off-grid
mode). The worst case occurs in the summer day because the
highest evening peak load (7 MW) as shown in Fig 4(a).
The overvoltages can be observed during light load
periods (1.00-4.00 a.m.). The voltage reaches 1.1 p.u. in the
winter day as in Fig. 5(c). The excess power produced by
wind generator flows back to main grid. The energy storage
can mitigate the overvoltage impacts.
During daytime (8.00 a.m. - 4.00 p.m.), PV and wind
generations can meet the local load demands. The voltage at
PCC is improved during this time as can be observed in Fig.
5(b) and Fig. 5(c). Comparing the results of voltage profiles
between Scenario I and II, the voltage of the latter case
varies around 1 p.u.
(a)
(a)
(b)
(b)
(c)
Fig. 4. Selected power profile a) summer day b) rainy day and c) winter day.
5th
International Electrical Engineering Congress, Pattaya, Thailand, 8-10 March 2017
V.
CONCLUSION
Voltage (p.u.)
The impacts of renewable sources on the voltage profile
in micro grid were presented. Due to the nature of micro
grid, the system become weak during operating in off-grid
mode. The voltage flicker level can exceed the limit. Based
on the study results, the operation in grid-connected mode
were improved the voltage level at PCC. However, the
reverse power flow can occur during light load condition and
may lead to overvoltage problem.
ACKNOWLEDGMENT
The authors would like to thank Provincial Electricity
Authority (PEA) for the financial support and providing
technical data for this research under the joint project of PEA
and Kasetsart University.
(c)
Fig. 5. Voltage profile at PCC during a) summer b) rainy and c) winter day.
Fig. 6 and Fig. 7 present flicker severity indices Pst and
Plt are calculated from voltage profile in Fig. 5. Pst values are
less than 1.0 and within the limit specified by PRC - PQG 02 / 1998 for all study cases.
During off-grid mode (Scenario III), the values Pst and Plt
are rather high compared to other cases. Plt values exceed 0.8
in rainy and winter day as the consequence of cloud effect
and variations of wind speed. The fluctuations in PV and
wind generations output power are shown in Fig. 4(b) and
Fig. 4(c). Comparing flicker severity indices between
Scenario I and II, it is evident that the present of renewable
source create the voltage flicker in micro grid.
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
REFERENCES
[1]
[2]
[3]
[4]
[5]
[6]
[7]
Summer
Scenario I
Rainy
Scenario II
Winter
[8]
Scenario III
Fig. 6. Short-term flicker severity
[9]
1.2
1
[10]
0.8
0.6
0.4
[11]
0.2
0
Summer
Scenario I
Rainy
Scenario II
Winter
[12]
Scenario III
[13]
Fig. 7. Long-term flicker severity
P. R. Sujin,T. R. D. Prakash And L. P. Suresh, “Voltage Flicker
Estimation and Mitigation of Voltage Controlled DG Grid Interfacing
Converters with Wind Power Source.” International Journal of Current
Engineering and Technology, Vol.2, No.2, pp.239-243, June 2012.
M. Joorabian, D. Mirabbasi and A. Sina, “Voltage flicker compensation
using STATCOM.” In Proc. of ICIEA 2009 : 4th IEEE Conf. on Industrial
Electronics and Applications, pp.2273-2278, China, May 2009.
J. C. Hernandez, M. J. Ortega, J. D. Cruz and D. Vera, “Guideline for
the Technical Assessment of Harmonic, Flicker and Unbalance
Emission Limits for PV-Distributed Generation.” Elect. Power Syst.
Res., Vol.81, No.7, pp.1247-1257, July 2011.
F. Favuzza and F. Spertino, “Comparison of Power Quality Impact of
Different Photovotaic Inverters: The Viewpoint of the Grid.” In Proc.
2004 IEEE International conf. on Industrial Technology, pp.542-547,
Tunisia, December 2004.
I. El-Samahy and E. El-Saadany, “The Effect of DG on power Quality
in a Deregulated Eviroment.” In Proc. 2005 IEEE Power Engineering
Society General Meeting, pp.2969-2976, San Franscisco, USA, June
2005.
A. Woyte, R. Belmans and J. Nijs, “Fluctuation in Instantaneous
Clearness Index: Analysis and Statistics.” In Solar Energy, Vol.81,
pp.195-206, 2007.
J. M. Sexaver and S. Mohagheghi, “Voltage Quality Assessment in a
Distribution System With Distributed Generation- A Probabilistic Load
Flow Approach.” IEEE Transaction on Power Delivery, Vol.28, No.3,
pp.1652-1662, July 2013.
M. Silsüpür And B. E. Türkay, “Flicker Source Detection Methods
Based on IEC 61000-4-15 and signal Processing Techniques - A
review.” Balkan Journal of Electrical and Computer Engineering Vol.3,
No.2, pp.93-97, September 2015.
G. Petroviü, R. Malariü and I. Kardum, “Matlab based flickermeter.”
18th International Workshop on ADC Modelling and Testing
Research on Electric and Electronic Measurement for the Economic
Upturn, Italy, Semtember 2014.
International Electrotechnical Commission(IEC), “IEC 61000-4-15
Testing and measurement techniques-Flickermeter-Functional and
Design Specificatiion, Flectromagnetic Compatibility-Part 4-15 .”
Geneva, Switzerland, 2010.
The Institute of Electrical and Electronics Engineers (IEEE),
“1453TM IEEE Recommended Practice for Measurement and Limits
of Voltage Fluctuations and Associated Light Flicker on AC Power
Systems.” New York, United States of America, March 2005.
Provincial Electricity Authority (PEA), “PRC - PQG - 02 / 1998 The
voltage fluctuation regulation for the commercial and industrial.”
Thailand 1998.
Provincial Electricity Authority Area 1 (North) Chiang Mai Province,
“Power Quality Data in Mae Sariang Area.” Chiang Mai, Thailand,
2016.
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