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2012 IEEE Student Conference on Research and Development
Power Quality Impact of Grid-Connected
Photovoltaic Generation System in Distribution
Networks
Masoud Farhoodnea
Azah Mohamed
Hussain Shareef
Hadi Zayandehroodi
Department of Electrical,
Electronic and Systems
Engineering
Universiti Kebangsaan,
Department of Electrical,
Electronic and Systems
Engineering
Universiti Kebangsaan,
Department of Electrical,
Electronic and Systems
Engineering
Universiti Kebangsaan,
Department of Electrical,
Electronic and Systems
Engineering
Universiti Kebangsaan,
Malaysia
Malaysia
Malaysia
Malaysia
which can decrease the reliability of the system [5].
Therefore, accurately analysing the impacts of installing
such technology on the performance of the electric
network is quite necessary to provide feasible solutions
for potential operational problems that grid-connected PV
systems can make for distribution systems and their
components.
The aim of this paper is to accurately study the
influences of installed large grid-connected PV systems
on the dynamic performance of distribution networks. To
investigate the effects of different weather conditions on
the produced power of the PV modules, required
meteorological data related to Kuala Lumpur for one year
are collected from the Malaysian Meteorological
Department (MMD), and simulation is carried on a
modified radial 16 bus test system with an embedded 1.8
MW grid-connected PV system with SunPower SPR 305
and Sanio HIP 225 modules using Matlab/Simulink
software under sunny and cloudy weather conditions.
Abstract—In recent decades, the presence of photovoltaic
(PV) systems is increased to provide power for local or
remote loads. However, when a large PV system connects to
the distribution network under variable weather conditions,
it may cause severe problems for power system components.
This paper presents a dynamic power quality analysis on a
grid-connected PV system in a distribution system subjected
to different weather conditions. A 1.8 MW grid-connected
PV system in a radial 16 bus test system is modelled and
simulated under varying solar irradiations using the
Matlab/Simulink software. The simulation results proved
that the presence of high penetrated grid-connected PV
systems can cause power quality problems such as voltage
rise, voltage flicker and power factor reduction.
Keywords — Power Quality; Distributed Generation;
Renewable Energy; Photovoltaic Systems; Voltage
Fluctuation; Voltage Flicker
I. INTRODUCTION
The application of PV systems in power systems as a
safe and clean source of energy from the sun can be
divided into two main fields including stand-alone and
grid-connected applications. Stand-alone PV systems are
able to provide power for remote loads that do not have
any access to power grids, whereas grid-connected
applications can be used to provide energy for local loads
as well as to the exchange power with utility grids [1].
PV systems are able to improve the performance of the
electric network by reducing the energy losses of
distribution feeders, maintenance costs and loading of
transformer tap changers during peak hours [2].
Nonetheless, in comparison with other renewable energy
based power resources, PV systems may cause some
adverse effects to the system such as harmonic pollution,
high investment cost, low efficiency and reliability which
hinder their widespread use [3]. Moreover, variations in
solar irradiation can cause power fluctuations and voltage
flickers and resultantly undesirable effects of high
penetrated PV systems on the electric network [4]. In
addition, any unintentional islanding in the presence of
PV systems may increase the risk of safety problems or
damage to the other parts of the system components,
978-1-4673-5160-7/12/$26.00 ©2012 IEEE
II. PV SYSTEM MODELLING
The fundamental components of a grid-connected PV
systems consists of a series/parallel mixture of PV arrays
to directly convert the sunlight to DC power, and a
power-conditioning unit that converts the DC power to
AC power, and also keeps the PVs operating at the most
efficient point [6]. Fig. 1 shows a general diagram of the
grid-connected PV systems.
Fig.1. Simplified diagram of grid-connected PV system
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2012 IEEE Student Conference on Research and Development
Generally, the electric characteristics of a PV unit can
be expressed in terms of the current-voltage, or the
power-voltage relationships of the cell. The variations of
these characteristics directly depend on the received solar
irradiation and the cell temperature. Therefore, to analyse
the dynamic performance of PV systems under different
weather conditions, an accurate model is required to
convert the effect of irradiance and temperature
variations on the produced current and voltage of the PV
arrays.
Fig. 2 shows the equivalent electrical circuit of a
typical PV module, where I is the output terminal current,
IL is the light-generated current, Id is the diode current, Ish
is the shunt leakage current, Rs is the internal resistance,
and Rsh is the shunt resistance.
I sc −Tr
qVoc −Tr
I o − Tr =
e
nKTr
(5)
−1
In (4) and (5), Vg is the band gap voltage, Voc-Tr is the
open circuit voltage, and Isc-Tr is the short circuit current
at rated operating conditions.
The photocurrent IL in (3) is directly proportional to
solar radiation level, G (W/m2), and can be expressed as,
(
I L = I L −Tr 1 + α I sc (T − Tr )
)
(6)
where,
I L−Tr =
G × I sc−Tr
(7)
Gr
where, α Isc is the short circuit temperature coefficient.
The open circuit voltage Voc which is sensitive to
temperature can be also obtained as [9],
(
Fig.2. Equivalent circuit of PV module
Voc = Voc −Tr 1 − βVoc (T − Tr )
From Fig. 1, the output current, I of the PV module can
be express as,
I = IL − Id −
Vo
Rsh
where Vo is the voltage on the shunt resistance.
The diode current, Id can be obtain using classical
diode current expression as [7],
(2)
III. IMPACTS OF LARGE GRID-CONNECTED PV
SYSTEMS ON DISTRIBUTION SYSTEMS
where Io is the saturation current of the diode, q is
electron, n is curve fitting constant, K is Boltzmann
constant, Tr is temperature on absolute scale and n is the
ideality factor which its value is between 1 to 2.
By substituting (2) in (1) and ignoring the last term, the
output current, I can be rewritten as,
(
)
I = I L − I o e q (V + IR s ) / nKTr − 1
By increasing the applicability of PV systems, the risk
of operational problems for the distribution networks and
their components has been increased. The severity of
occurred problems directly depends on the PV
penetration level and geography of the installation. The
aim of this section is to introduce possible impacts which
PV systems may impose to the system.
(3)
A. Inrush Current
The small inevitable difference between the PV system
and the grid voltages may introduce an inrush current
which flows between the PV system and the utility grid at
the connection time and decays to zero at an exponential
rate. The produced inrush current may cause nuisance
trips, thermal over stresses, and other problems [10].
where, the saturation current I0 at different operating
temperatures can be calculated as [8],
⎛T
I o = I o −Tr × ⎜⎜
⎝ Tr
3
− qV g
⎞n
⎟⎟ × e nK × (1 / T −1 / Tr )
⎠
(8)
where, βVoc is the open circuit temperature coefficient.
Using the provided coefficient by manufacturers and
the mathematical equations (3-8), any PV module can be
modelled for dynamic analysis.
The produced DC voltage of PV module can be raised
to any desired level using a DC-DC boost converter and
MPPT technique can be used in the boost converter to
efficiently control the produced power of PV arrays. The
produced DC power is then converted to AC power using
a three-phase three-level Voltage Source Converter
(VSC) and injected to the system using a coupling
transformer.
(1)
⎡ qVoc
⎤
I d = I o ⎢e nKTr − 1⎥
⎢
⎥
⎣
⎦
)
(4)
B. Safety
One of the major concerns about the PV systems is the
safety problem due to the unintended islanding at the
and,
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2012 IEEE Student Conference on Research and Development
create different solar irradiance for sunny and different
cloudy weather conditions with slow and fast variations,
as shown in Fig. 4.
time of fault occurrence at the grid side. In this situation,
the PV systems continue to feed the load even after the
network is disconnected from the utility grid, which may
lead to electric shock of workers [11].
C. Overvoltage
Most of the times, PV systems are designed to operate
close to unity power factor to make full use of solar
energy. In this case, PV system only injects active power
into the utility grid which may change the reactive power
flow of the system. Therefore, voltages of nearby buses
can be increased due to the lack of reactive power [12].
The produced overvoltage can have negative impacts on
the stable operation of both utility and customer sides.
D. Output power fluctuation
The fluctuation of the output power of PV systems is
known as one of the main factor that may cause severe
operational problems for the utility network. The power
fluctuation phenomenon occurs due to the variations in
the solar irradiance caused by the movement of clouds
and may continue for few minutes to hours depending on
the wind speed, the type and size of passing clouds, and
the area covered by and topology of the PV system.
Power fluctuation may cause power swings in lines, over
and under loading, unacceptable voltage fluctuations and
voltage flickers [1].
Fig.3. Single-line diagram of the16 bus test system
E. Harmonic
Harmonic distortion is known as a serious power
quality problem, which may occur due to the use of
power inverters for converting DC current to AC current
in PV systems. The produced harmonics can cause
parallel and series resonances, overheating in capacitor
banks and transformers and false operation of protection
devices which may decrease the reliability of power
systems [13].
Fig.4. Solar irradiance pattern
The PV system starts to inject 600KW power, which is
equal to 6% of the total load demands for the first
penetration level at 350 milliseconds. In this situation,
PV continues to feed loads with produced power under
1000 W/m2 solar irradiance until 560 milliseconds. The
PV system then feed through solar irradiance with slow
and fast variation at 560 and 1000 milliseconds,
respectively. This scenario is repeated under medium and
high PV penetration levels by injecting power of
1200KW (12% of the total load demands) and 1800 KW
(18% of the total load demands), respectively. Fig. 5
shows the injected power by the PV system at bus 11
under three abovementioned penetration levels, where
Fig. 6 through 11 show the effect of injected power of the
PV system on active power, reactive power and power
factor of the utility grid1and grid2 at bus 1 and 2,
respectively.
IV. SIMULATION RESULTS
To investigate the various impacts of the gridconnected PV system on distribution systems, a modified
16 bus test system [14] shown in Fig. 3 is simulated using
the Matlab/Simulink software. The system, which is fed
through two 69 kV utility grids, consists of 8 loads with
total power of 10 MVA and 0.8 power factor, and three
inter-tie circuit breakers. In addition, a 1.8 MW gridconnected PV system, which consists of three 600 kW
units, have been placed in bus 11 to provide required
power for local loads and exchange the rest with the
system. Two types of commercial PV array named
SunPower SPR 305 [15] and Sanio HIP 225 [16] are
modelled using the company data sheets and described
equations in section 2. The produced DC voltage by each
PV array is raised using a 5-kHzDC-DC boost converter
and MPPT [17] is implemented in the boost converter to
efficiently control the photovoltaic energy conversion.
Furthermore, boosted DC voltage is converted to AC
voltage using a three-phase three-level VSC. In this
analysis, the required information related to solar
irradiance under different weather conditions during a
year are collected from the MMD [18] and mixed to
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2012 IEEE Student Conference on Research and Development
Fig.9. Utility grid2 reactive power at bus 2
Fig.5. Injected power by PV system at bus 11
As shown in Fig. 5 through 9, by increasing the
penetration level of the PV system, a portion of
consumed active power by the loads are covered by the
PV system, while the reactive power consumption has
still to be provided by utility grids. Therefore, the power
factors of the grids decrease up to 70% at 1000 W/m2
solar irradiance. It should be noted that when the
irradiance is low, the produced active power of the PV
unit is low. In this situation, PV unit has to draw a very
small amount of reactive power from the system due to
the occurrence of a small difference between the line
voltage and the reference voltage in PV controller.
As the penetration level of the PV system and
resultantly the produced active power increases, the
system voltage increases as shown in Fig. 10. From Figs.
5 and 10, by increasing the injected active power of the
PV unit at sunny weather condition and high penetration
level, the voltage magnitude at bus 6 increases over 1.06
pu which is considered as over voltage based on the IEEE
Std 1159-2009 [19]. Fig. 10 also demonstrated that
voltage flicker is occurred at 1000 milliseconds due to the
fast power fluctuation of PV unite under cloudy weather
condition, and Fig. 11 shows the measured flicker index
( ΔV / V ) at bus 6 which in worst condition exceeds over
6% that exceed the IEEE std 519 limits [20].
Fig.6. Utility grid1 active power at bus 1
Fig.7. Utility grid1 reactive power at bus 1
Fig.10. System voltage magnitude at bus 6
Fig.8. Utility grid2 active power at bus 2
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2012 IEEE Student Conference on Research and Development
TABLE I
CURRENT HARMONIC SPECTRUM AT PV TERMINAL
Frequency (Hz)
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
800
850
900
950
Fig.11. Measured flicker index at bus 6
The occurred power fluctuation and voltage variation
which are harmful for sensitive loads also caused a slight
variation in total active and reactive power demands from
loads as shown in Fig. 12 and 13, respectively, and these
variations may cause cables and transformers
overloading.
Magnitude (%)
100.0
0.60
0.83
0.33
1.40
0.56
1.48
0.48
0.24
0.25
0.46
0.47
0.82
0.39
0.28
0.51
0.29
0.59
0.62
Angle (degree)
0.0
-23.4
160.0
244.1
-40.3
44.4
11.6
-2.8
269.5
65.4
31.6
261.2
-41.9
179.2
-84.1
241.2
-33.1
183.5
253.1
V. CONCLUSION
This paper presents a study on the impacts of high
penetrated grid-connected PV systems on power quality
in distribution systems. All information related to
modelling of PV units and solar irradiances are collected
from different solar panel producers and the Malaysian
Meteorological Department (MMD), respectively. A 1.8
MW grid-connected PV system in a radial 16 bus test
system are simulated using the Matlab/Simulink software
under different solar irradiances and the results show that
the produced active power by PV system causes voltage
rise, voltage flicker and power factor reduction, which
may create severe problems for system components.
Fig.12. Total load active power
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Fig.13. Total load reactive power
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this value violates the THD limit of 5% as defined in
IEEE Std. 519 [20], due to the absence of proper
harmonic filter for PV inverter.
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