power quality improvement using upqc in distribution … · 2019-04-22 · power quality...
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VOL. 14, NO. 7, APRIL 2019 ISSN 1819-6608
ARPN Journal of Engineering and Applied Sciences ©2006-2019 Asian Research Publishing Network (ARPN). All rights reserved.
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POWER QUALITY IMPROVEMENT USING UPQC IN DISTRIBUTION
SYSTEM WITH HYBRID RENEWABLE RESOURCES
CONSIDERING DYNAMICS
J. P. Sridhar Department of Electrical and Electronics Engineering, SJB Institute of Technology, Bangalore, India
E-Mai: [email protected]
ABSTRACT
The DG placement algorithms perform the optimal placement and sizing in distribution system. But it only
considers the real and reactive power loss minimization. The analysis is static. The DGs are generally dynamic in nature as
they are renewable resources. But the loads connected in the DGs are not only linear loads. Many loads at the feeder are
non-linear. In this paper the unified power quality conditioner (UPQC) is interfaced with PV (Photo Voltaic) and wind
generators. The current reference generation technique is used for series converter and shunt converter by using this hybrid
combination. This takes care of all types of voltage sags and swells. The real and reactive power both is controlled from
PV and wind to grid. The system is considered as a standard distribution feeder system. The 230V feeder system is
considered here for testing these dynamics.
Keywords: unified power quality conditioner, photo voltaic, squirrel cage induction generator
INTRODUCTION
There are many papers published on this problem.
Some literatures study different impact of wind farms on
power system under symmetrical and asymmetrical grid
faults [2-5]. Some methods to compensate voltage sag
have been investigated in [6-7]. Flexible AC Transmission
System (FACTS) devices such as Static Var Compensator
(SVC) [8], STATic synchronous COMpensator
(STATCOM) [9], Dynamic Voltage Restorer (DVR) [10-
11] are effective solution for voltage sag compensation.
These devices absorb or inject reactive and active power to
the grid to overcome the fault problems. In the other hand,
FACTS devices can control the power between SCIG and
grid to avoid disconnection of wind turbine from grid [4-
5].
Unified power quality conditioner (UPQC) is one
of the versatile FACTS devices that consists of two parts
which are connected in series (SERC) and shunt (SHUC)
Voltage Source Inverters (VSI) [12-13]. Depending on the
type of control system, the UPQC represents a practical
solution to protect sensitive loads in the presence of grid
disturbances, such as voltage sags, swell, harmonics and
etc. Some methods have published to control of UPQC
such as UPQC-P [12-14], UPQC-Q [14]. UPQC-P can
compensate only the magnitude of voltage but it could not
compensate the phase jump recovery. This control scheme
can compensate the voltage sag by a minimum injection
voltage. UPQC-Q need a large voltage magnitude and this
can be increase the rating of UPQC. However, UPQC-Q
inject a minimum energy to the grid [14].
In this paper the hybrid PV and Wind dynamics
are added to the standard distribution system and the
performances are analyzed with UPQC and without
UPQC. By using the MATLAB 2017b/Simulink for
testing the proposed solution method.
METHODOLOGY
Block diagram
VOL. 14, NO. 7, APRIL 2019 ISSN 1819-6608
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Figure-1. Block diagram of proposed system.
Problem definition
The UPQC previously is analyzed only with the grid
connected system
The Renewable energy resources are having problem
of harmonics, sag and swell due to dynamics.
The real and reactive power control is not properly
done in renewable energy resources
Problem solution
The UPQC is analyzed with wind and grid
synchronization
The PV is used for supplying real and reactive power
at DC link, which make stability in the system
Here disturbances like Harmonics, Sag and swell can
be mitigated by using PV and wind-based grid
integrated with UPQC.
The current reference generation technique is used
here for doing all the above.
RESULTS AND DISCUSSIONS
VOL. 14, NO. 7, APRIL 2019 ISSN 1819-6608
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Figure-2. Simulation diagram of UPQC with PV and wind (SCIG).
The project is designed on the basis of working of
Unified Power Quality Conditioner (UPQC)
connected between the Grid and a Squirrel cage
Induction generator (SCIG) to eliminate the voltage
sag occurred during fault condition.
One side of system is connected with a three-phase
programmable voltage source which is considered as
source to the distribution system adjacent to it.
The other end is provided with a Squirrel cage
Induction generator to which it will operate as
generator when the Mechanical torque is negative.
The UPQC circuit is connected between the
distribution system and SCIG to compensate the
voltage sag, swell and harmonics during fault
condition. It also provided with a Photo voltaic
system as hybrid to wind generation.
UPQC (Unified power quality conditioning):
Unified power quality conditioning is the matter of
conditioning the components of the power i.e. Supply
voltage and Load current.
The conditions to satisfy the conditioning are as
follows:
a) If there is any fluctuations or harmonics occurs in the
supply voltage, which should not be affected to the
load. So, we need to take care of the voltage to be
sinusoidal and controlled at desired value.
b) If there is a non-linear load is working at the load
side, then it consumes non-linear current which leads
to non-linearity in the grid part and that affects to
other loads also. So, we need to take care of the
current to be sinusoidal and to make it like there
should have minimum amount of THD value.
c) And we need to take care of the reactive power to be
maintained at zero level at Grid point.
The UPQC part includes 3 points:
Voltage compensation (Series APF)
Current compensation (Shunt APF)
DC capacitor voltage controller
A. Voltage compensation (Series APF):
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Figure-3. Voltage Compensation block.
Voltage compensation will decide how much
voltage error is there in the grid and how much voltage has
to induce in the grid to make the voltage sinusoidal with
desired voltage magnitude and frequency.
Figure-4. Series converter controller block.
The supply voltage have to be subtracted by
Reference voltage (Vabc*), it calculates the error in
voltage which is then compared with error voltage
produced in 3 lines and then proceeded to Hysteresis
control to produce the pulses to minimize that error
produced by difference in calculated error voltage and
produced error voltage.
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Figure-5. PWM and reference voltage generation.
B. Current compensation (Shunt APF):
Current compensation will decide how much
current error is there in the grid and how much current
have to induce in the grid to make the current non-linearity
sinusoidal with desired current magnitude and frequency.
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Figure-6. Shunt converter active power filter block
The load current has to be subtracted by
Reference currents (Iabc*) which will be sinusoidal which
Id and Iq currents are purified by collecting load currents,
it calculates the error in current which is then compared
with error current produced in 3 lines and then proceeded
to Hysteresis control to produce the pulses to minimize
that error produced by difference in calculated error
current and produced error current.
Figure-7. Shunt controller of active power filter.
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Figure-8. Reference current generation blocks.
Figure-9. DC link capacitor voltage control:
The DC capacitor voltage has to be maintained at
some desired value. For that the controlling part has to be
designed. The reference value has to be subtracted by
measured DC voltage and the Error has to be minimized to
zero by a transfer function and the control signal have to
be added to Id current.
PI
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Figure-10. Photo voltaic system with boost converter for MPPT:
When PV works, the DC voltage may oscillate.
Boost converter also provided to boost up the voltage
from 500V from PV to 800V DC across capacitor
with MPPT capability.
RESULTS AND DISCUSSIONS
The entire system is built for 230 V, 50 Hz
system. There are four disturbances created in this system
as given in tabular column. Grid has the change in its
amplitude to 230 to 184 V at 0.1 secs, then 184 to 230V at
0.2 secs and 230V to 276 V at 0.5 secs. Then the UPQC is
turned on at 0.06 secs. Solar changes from 1000 w/m2 to
500 w/m2 at 0.75 secs. Wind speed is changed from 10 m/s
to 1m/s. Figure-11 shows the voltage without UPQC
during fault. Figure-12 shows the Injected Voltage and
current by UPFC, Figure-13 shows the Grid side voltage
and current. Figure-14 shows Grid side current before
compensation THD. Figure-15 shows the Grid current
after compensation. Figure-15 shows the DC capacitor
voltage. Figure-16 shows before and after compensation in
RMS voltage. So, from these figures the voltage sag and
swell are compensated very well even with solar and wind.
The THD is 28.68% without any compensation. After
compensation 1.97% of THD.
VOL. 14, NO. 7, APRIL 2019 ISSN 1819-6608
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Figure-11. Voltage and current without UPQC during fault.
Figure-12. Injected Voltage and current by UPFC.
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Figure-13. Grid side voltage and current after compensation by using UPQC.
Table-1. Dynamics applied to the simulation.
grid dynamics
Voltage in pu [1 0.8 1 1.2 1.2]
Time in secs [0 0.1 0.2 0.5 1]
UPQC dynamics
relay [off on on]
Time in secs [0 0.06 1]
solar dynamics
Irradiance (W/m2) [1000 500 500]
Time in secs [0 0.75 1]
Wind dynamics
wind speed 10
Time in secs 1
VOL. 14, NO. 7, APRIL 2019 ISSN 1819-6608
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Figure-14. Grid side current before compensation THD.
Figure-15. Grid current after compensation.
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Figure-16. DC capacitor voltage:
Figure-17. Before and after compensation in RMS.
CONCLUSIONS
The UPQC device is constructed for series and
shunt compensation. The grid produces sags and swell in
the system which can be overcome with using controller
gives better performance in transient switching conditions
is explained and the results shows the same performance is
achieved including PV and wind. The UPQC controller is
VOL. 14, NO. 7, APRIL 2019 ISSN 1819-6608
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performing better to rectify the problem of harmonics,
voltage sag and swell in distribution system.
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