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International Electrical Engineering Journal (IEEJ) Vol. 4 (2013) No. 3, pp. 1087-1097 ISSN 2078-2365 http://www.ieejournal.com/
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Mehdi and Majid Voltage Control of Microgrid Systems Connected to Power Network System in Fault Condition
Voltage Control of Microgrid Systems
Connected to Power Network System in Fault
Condition
Abstract: In today's world, according as interest about renewable
energy source rises, many researches are progressing about
energy source development and power distribution system
configuration for improving renewable energy source's
efficiency. The microgrid is small power system that consists
of several consumers' loads and small size Distributed
resources and accomplishes one independent system. It is
operated by interconnecting with power distribution system
and could be islanding operation according to situation.
Therefore, the control of microgrid makes microgrid can be
connected to the power distribution system without
equipment correction of power distribution system, and can
compensate voltage quality and must satisfy dynamic
request of loads as active and reactive power are controlled
independently. Specially, when consumer's load includes
sensitive loads, consumer is going to expect very high
reliability from microgrid. In this paper, we studied about
effects that get to power distribution system relationship
fault condition this microgird using EMTP modeling and
simulation. And we proposed microsource's control
algorithm and simulated to improve voltage quality that is
supplied in microgird interior load in fault condition of
power distribution system. This shows that microgird can
provide local high quality power supply or voltage
compensation ability.
Keywords: Microgrid, Voltage control, power quality,
EMTP
I. INTRODUCTION The microgrid is defined as one independent grid
providing continuous power to loads on grid and
compromising two or more microsources with enough
capacity so as to operate independently, storage assets
and loads [5], [11].
Any energy sources should be connected on microgrid
and not affect operations of the existing grid including
protection coordination, reliability, power quality
problem, voltage control and so on correspond to
adding of new energy sources. And when microgrid are
separated from grid operating protection devices by
faults of the grid side, microsources should charge
electrical power needs of loads in microgrid and
operate maintaining power and voltage quality [5].
But in case of instantaneous fault or voltage or power quality deteriorations, not permanent faults of the grid
side, microgrid should operate economic and effective
compensation over a falling-off in quality maintaining
connection to grid.
It is similar to compensating voltage drop changes in
emergency conditions by interconnecting DVR
(Dynamic Voltage Restorer) which is custom power
device to the existing to distribution system. But in case
of microsources, unlike DVR, it has no limitation of
energy capacity on direct current side. So there is a
need of many studies over improvement of voltage
Mehdi Hadinezhad Islamic Azad University, Saveh Branch
Saveh, Iran
Majid Gandomkar
Department of Electrical Engineering
Islamic Azad University, Saveh Branch
Saveh, Iran
International Electrical Engineering Journal (IEEJ) Vol. 4 (2013) No. 3, pp. 1087-1097 ISSN 2078-2365 http://www.ieejournal.com/
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Mehdi and Majid Voltage Control of Microgrid Systems Connected to Power Network System in Fault Condition
quality controlling micro sources, not custom power
devices.
In this paper, we designed and simulated distribution
system interconnected to micro sources and microgrid
using Electro Magnetic Transient Program. And we
figured out dynamic characteristics of microgrid in
emergency conditions of distribution system and made
a comparative study between the proposed control
algorithm of microsources and the existing control
algorithm.
II. Voltage and Power Quality Lately, as the equipment using micro-processor and
semiconductor, high sensitive and large load etc.
increase, about high quality electric power is increasing. The reason is that voltage sag or distortion
influence quality of product, result in information
damage, and consequently these bring big economic
loss. Existent analog signal was not influenced by
voltage sag caused by successful open/close result for
instantaneous system fault.
However, control element, speed control appliances
and computer etc are influence easily by voltage sag.
Especially, in case of computer, power loss caused by
voltage sag can influence seriously to the computer
processing or information etc.
Fig. 1. IEEE Std. 1100-1992 The CBEMA curve [13].
Like above the CBEMA curve, the computer can
perform the normal operation within +6% ~ -13% of
normal voltage. And the permissible limitation of
voltage is big in condition of momentary voltage
variation within 0.5cycle. Therefore the compensation
for the magnitude of voltage variation according to
loads and time is necessary.
III. MICROSOURCE CONTROLLER The inverter converts DC into AC and this is the key
element of micro source operation. The inverter
controller should be designed to response effectively in
Microgrid loads variations. According to Microgrid
operation modes especially, as micro source operate by
voltage source, in order to be connected into microgrid,
it need inductor (XL) for interconnecting to the power
distribution system. [3].
International Electrical Engineering Journal (IEEJ) Vol. 4 (2013) No. 3, pp. 1087-1097 ISSN 2078-2365 http://www.ieejournal.com/
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Mehdi and Majid Voltage Control of Microgrid Systems Connected to Power Network System in Fault Condition
Fig. 2. Micro source control structure.
where P : power angle, V : output voltage of inverter, E
: Grid voltage Like (1) ~ (3) and active power in the
load angle, reactive power depend in magnitude of
output voltage V of the inverter.
Therefore output voltage magnitude of voltage source
inverters and phase control will lead and will be able to
control micro source outputs.
A. Active power control
Fig. 3. Active power versus Frequency droop controller.
Microgrid system with distribution system
interconnection in case is driven being done each Micro
source must do fixed output according to the Active
Power output direction amount, must decide the
readjustment amount of output automatically in
Islanding mode.
Fig. 3 is active power control block diagram that use power-frequency droop [3]. This block is that apply
power frequency droop control principle that is used to
existent synchronous generator to inverter control.
Equation (4), (5) describes input/output of power-
frequency droop controller.
Where Pm is Micro source active power output
reference, PL is calculated active power, θ0 is phase
angle of grid.
While microgrid is supplied active power in
distribution system, by islanding mode operation because microgrid gets into overload in case is done
frequency drop. Is proportional and increase fuel
International Electrical Engineering Journal (IEEJ) Vol. 4 (2013) No. 3, pp. 1087-1097 ISSN 2078-2365 http://www.ieejournal.com/
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Mehdi and Majid Voltage Control of Microgrid Systems Connected to Power Network System in Fault Condition
control standard signal in droop set point in control
system. Droop control has special quality that
frequency decreases about output increase.
B. Q versus E Droop and Voltage Control
Fig. 4. Q versus E droop and voltage controller.
Fig. 4. is voltage control block that use Q-E droop
control.
where Ereq is voltage reference of node. applying Q-E
droop control, make new voltage reference and voltage
control [3]. This can be possible to reduce large output
of reactive power by allowing some voltage changes (
ΔV/Qmax) from reference voltage. voltage controller
and Active power model in droop control using EMTP
is illustrated in Fig. 5.
Fig. 5. EMTP/RV module development for P and Voltage magnitude.
(Droop)
International Electrical Engineering Journal (IEEJ) Vol. 4 (2013) No. 3, pp. 1087-1097 ISSN 2078-2365 http://www.ieejournal.com/
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Mehdi and Majid Voltage Control of Microgrid Systems Connected to Power Network System in Fault Condition
Fig. 6. Proposed active power controller.
The Block diagram of the proposed active power
controller is illustrated in Fig. 6, This can be expressed the following equation:
The proposed controller, when many micro sources
within microgrid in islanding operation operate in
parallel, limits active power output of micro sources
which operate in exceeding rated active power output
of inverter and provides lack of active power from
other micro sources.
International Electrical Engineering Journal (IEEJ) Vol. 4 (2013) No. 3, pp. 1087-1097 ISSN 2078-2365 http://www.ieejournal.com/
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Mehdi and Majid Voltage Control of Microgrid Systems Connected to Power Network System in Fault Condition
Fig. 7. EMTP/RV module development for P and Voltage magnitude. (proposed)
IV. MICROGRID AND FAULT MODELING A kind of faults in distribution system can classify into
instantaneous fault, permanent fault as fault
maintenance time and line to ground fault, line to line
fault as fault conditions. Fault in distribution system the moment fault about 98% occupy and also, most of
distribution line fault appear by line to ground fault.
In this case, when recloser produces fault being
engaged to protect distribution system, because fault is
intercepted instantaneously, Causes a lot of short-cycle
voltage sag.
Therefore, the momentary voltage sag compensation
micro source through the control effectively, the fault will be reduced by the loss.
International Electrical Engineering Journal (IEEJ) Vol. 4 (2013) No. 3, pp. 1087-1097 ISSN 2078-2365 http://www.ieejournal.com/
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Mehdi and Majid Voltage Control of Microgrid Systems Connected to Power Network System in Fault Condition
Fig. 8. Model of a Microgrid.
Microgrid modeling is a 15kW, 11.25kVar capacity is
configured as three micro sources, and 10kW, 1kVar of
the load capacity of the three places are located. Fig. 9,
is active power output of proposed micro source
controller.
Fig. 9. Active power output of micro source controller.
V. CASE STUDY
Following Fig. 10. It shows the result of simulation that
the micro source existing in the microgrid does not
work. In this case, we simulated general distribution
International Electrical Engineering Journal (IEEJ) Vol. 4 (2013) No. 3, pp. 1087-1097 ISSN 2078-2365 http://www.ieejournal.com/
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Mehdi and Majid Voltage Control of Microgrid Systems Connected to Power Network System in Fault Condition
system existing only loads except micro sources. And
the condition of simulation is set to at 5 seconds from
grid and restore at 6 sec.
At this time, the internal voltage in microgrid is
influenced by voltage variation caused by distribution
system fault.. In this simulation, average voltage for
fault period is 180V (RMS) as following Fig. 10
Fig. 10. Voltage of the microgrid when micro source does not exist. (RMS)
A. Droop control In the internal microgrid, three micro-source based on
droop control is connected. At this time, voltage
variation caused by distribution system fault is
compensated partly. In simulation, average voltage for
the fault period is 255V (RMS) as following Fig. 11,
And when the system is recovered normally, voltage
increase is very large according to the micro-source
control.
International Electrical Engineering Journal (IEEJ) Vol. 4 (2013) No. 3, pp. 1087-1097 ISSN 2078-2365 http://www.ieejournal.com/
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Mehdi and Majid Voltage Control of Microgrid Systems Connected to Power Network System in Fault Condition
Fig. 11. Microgrid internal voltage that is consisted of droop controller base micro source.
B. Proposed control In the internal microgrid, three micro-source based on
the proposed control is connected. Fig. 12, shows that
the compensation for voltage variation of micro-source
caused by distribution system fault is more developed
than the compensation by micro-source based on droop
control.
In this simulation, average voltage for the fault period
is 261V(RMS) as like Fig. 12, And when the system is
recovered normally, voltage increase caused by the
micro source control is smaller than the increase caused by micro source based on droop control.
International Electrical Engineering Journal (IEEJ) Vol. 4 (2013) No. 3, pp. 1087-1097 ISSN 2078-2365 http://www.ieejournal.com/
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Mehdi and Majid Voltage Control of Microgrid Systems Connected to Power Network System in Fault Condition
Fig. 12. Microgrid internal voltage that is consisted of proposed controller base micro source.
VI. CONCLUSIONS If the fault of grid is not permanent but instantaneous or
reduction of power quality, micro source can
compensate voltage sag by similar principle that use to
distribution system or custom power equipment.
However, compensation rate is different from the control method of micro-source. The controller of
micro-source proposed by simulation is more efficient
than existent control method of micro-source for
voltage sag compensation ability.
And when micro-source based on the proposed
controller transfer to the islanding operation, or the
loads increase /decrease in islanding operation, it is
operated normally within rating output range.
This paper is the result of simulation in the ideal
inverter model supposing three phase balance system,
don't considered the economical operation of micro-
source. In the next research, switching model of
inverter including 3 phase unbalance system and
modeling of real source would be simulated.
VIII. REFERENCES
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[3] M.Shao, R. L. Dianjun Lv,‟‟ Control Strategy of
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