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International Journal of Electrical and Computer Engineering (IJECE)
Vol. 8, No. 1, February 2018, pp. 530~537
ISSN: 2088-8708, DOI: 10.11591/ijece.v8i1.pp530-537 530
Journal homepage: http://iaescore.com/journals/index.php/IJECE
Moth Flame Optimization Method for Unified Power Quality
Conditioner Allocation
M. Laxmidevi Ramanaiah, M. Damodar Reddy
Department of Electrical and Electronics Engineering, S.V. University, India
Article Info
ABSTRACT
Article history:
Received Jun 6, 2017
Revised Dec 28, 2017
Accepted Jan 12, 2018
This paper introduces a new optimization method to determine the optimal
allocation of Unified Power Quality Conditioner (UPQC) in the distribution
systems. UPQC is a versatile Custom Power Device (CPD) to solve problems
related to voltage and current by the series and shunt compensator in the
distribution systems. The task of UPQC highlighted in this paper is the
required load reactive power is provided by both the series and shunt
compensators. The UPQC’s steady state compensation capability has given a
solution for providing reactive power compensation in large distribution
systems. The optimization method adopted is Moth Flame Optimization
(MFO). The best location and series compensator voltage are determined
using MFO. The voltage injected by the series compensator and reactive
power injected by the shunt compensator is incorporated in the load flow
method. The effectiveness of the proposed method is validated with standard
distribution systems.
Keyword:
Moth flame optimization
Unified power quality
conditioner
Reactive power compensation
distribution systems
Copyright © 2018 Institute of Advanced Engineering and Science.
All rights reserved.
Corresponding Author:
M. Laxmidevi Ramanaiah,
Departement of Electrical and Electronics Engineering,
Sri Venkateswara University,
Tirupati, Andhra Pradesh-517502, India.
Email: m.laxmidevi@yahoo.com
1. INTRODUCTION
For productive operation of the electric utility the necessary condition is to operate the system at its
maximum efficiency. The losses in the system can be curtailed by minimizing the total flow of reactive
power. Reactive power is essential to maintain the quality of supply. Some of the industrial load imposes on
the supply large demand for reactive power. Hence reactive power compensators assume a key part in
meeting the reactive power needs of the system. The compensators include shunt capacitors and series
voltage regulators. Shunt capacitors cannot create variable reactive power constantly. Series voltage
regulators drive the source to produce reactive power. Hence, to overcome these disadvantages the static
compensators utilizing power electronic devices are employed for effective operation of the system.
The static compensators include Distributed Flexible Alternating Current Transmission System
(DFACTS). These devices can provide continuously variable reactive power. The most generally used
DFACTS devices for reactive power compensation is DSTATCOM [1] and Unified Power Quality
Conditioner (UPQC).
UPQC [2] is a device which consists of a DVR and DSTATCOM. DVR is a series connected device
which handles all the voltage related problems in the system. Unified Power Quality Conditioner [2-4] has
the potential to inject the necessary amount of reactive power into the network when the network is in
shortage of the reactive power and vice versa. Another advantage of this device is, its output reactive power
can be continuously varied. Hence, the shortages of capacitors, which cannot meet the network demands as
required, are abolished. The application of UPQC for two bus systems and for sensitive loads to address the
problems of power quality is practical as detailed in [5-7].
Int J Elec & Comp Eng ISSN: 2088-8708
Moth Flame Optimization Method for Unified Power Quality Conditioner… (M. Laxmidevi Ramanaiah)
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The most common classification of UPQC is based on voltage compensation methods. These
include UPQC-P (active power injection), UPQC-Q (reactive power injection), UPQC-S (active and reactive
power injection) and UPQC-VAmin (minimum apparent power injection). Another classification is based on
the physical structure. These include UPQC-R (right shunt), UPQC-L (left shunt), UPQC-I (interline)
UPQC-MC (multi-converter), UPQC-MD (modular), UPQC-ML (multi-level), UPQC-D (distributed) and
UPQC-DG (distributed generator integration).
In this paper, the application of UPQC for improving the voltage is realized for large distribution
system by way of utilizing the series compensator i.e. DVR. The problem with UPQC placement has been
solved by numerous methods as detailed in [8-12].
Boutebel et al. [8] has used the hybrid optimization technique combining differential evolution and
PSO for determining the optimal sizing and location of the UPQC device in radial distribution systems.
Ganguly et al. [9] has introduced the phase angle control model of UPQC known as UPQC–PAC to validate
the concept of maximal utilization of series inverter. The series inverter also shares the load reactive power
along with the shunt inverter in steady state conditions, leading to a decrease in the rating of shunt inverter.
Atma Ram Gupta et al. [10] has modeled the shunt compensator as the source of 1 MVAr reactive power and
by assuming the voltage at the candidate bus as 1 p.u. The value of series reactive power compensation is
calculated in the steady state. The total power losses are calculated by placing the acquired size of UPQC at
the respective buses. The bus having the minimum value of losses is selected as candidate bus for UPQC
installation. M. Hosseini et.al [11] has demonstrated the effectiveness of UPQC to improve steady state
voltage. S. A. Taher et.al [12] has used Differential Evolution (DE) algorithm to decide the optimal location
of unified power quality conditioner for different loading conditions and also the savings with UPQC are
obtained. DE results are compared with Genetic Algorithm (GA) and Immune Algorithm (IA).
This paper also explores the capability of series and shunt compensator of UPQC to participate in
load reactive power compensation in steady state by a new Optimization method known as a Moth Flame
Optimization method. The losses and voltages for the network are obtained with the load flow method
described in the following section
2. RADIAL DISTRIBUTION SYSTEM LOAD FLOW
Load flow is an important tool to assess the performance of the distribution system. S. D. Chiang
et.al [13] has developed decoupled and fast decoupled load flow method. S. Ghosh et al. [14] has developed a
load flow method based on estimation of effective real and reactive power loads. J. H. Teng et.al [15] has
proposed two matrices Bus Injection to Branch Current (BIBC) and Branch Current to Bus Voltage (BCBV)
to solve the load flow equations.
Here the active power load and reactive power load at the mth bus is denoted by and
respectively.
: Voltage at the mth bus
: Branch current and : Load current
, are the receiving end node voltage and sending end node voltage respectively.
, and are the impedance, resistance and reactance for the ith branch respectively.
Calculation of load currents:
(1)
Formation of BIBC matrix:
By applying the Kirchhoff’s Current Law to the distribution network, BIBC matrix can be formed.
Consider a six bus network which is shown in Figure 1.
Figure 1. Six bus system network configuration
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532
The BIBC matrix, which gives the relation between load and branch currents, for Figure 1 is given
as
(2)
Bus voltage is obtained by Equation (4)
(3)
(4)
The error in voltage is calculated. If the error is less than tolerance then the load flow converges.
The power losses in a distribution system are given by (5) and (6)
(5)
(6)
Here n is the total number of branches.
3. UPQC STRUCTURE
A UPQC as the combination of series and shunt compensator is displayed in Figure 2 [3].
Figure 2. Equivalent circuit of UPQC
Here is the sending end voltage, is the source impedance, PCC is the pont of common
coupling, is the voltage injected by series compensator, is the shunt compensating current and is
the load bus voltage.
The series compensator generates a voltage and injects it in series with the line near to the receiving
end such that the voltage at the load side is always maintained at desired voltage magnitude.
The new load bus voltage
, after injecting voltage by the series compensator is calculated as
given in Equation (7)
(7)
The complex power obtained by the series compensator is obtained as follows:
(8)
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Here is the branch current in which series compensator is included.
The function of shunt compensator is to provide load VAr support.
Figure 3 shows the phasor diagram for series voltage injection.
Figure 3. Phasor diagram for series voltage injection
The UPQC series compensator is modeled as a source of real and reactive power whereas shunt
compensator is modeled as the source of reactive power.
With the injection of voltage by the series compensator, the receiving end voltage is changed to
.
The reactive power to be injected is calculated as given in Equation (9).
(9)
compensating current after series compensation which is calculated as given in [16].
4. MOTH FLAME OPTIMIZATION
The inspiration of this algorithm [17] is the navigation method of moths known as transverse
orientation. Moths fly at night using the moonlight. By keeping a constant angle concerning the moon, moths
fly in straight line to achieve the goal. The convergence of moths is towards the light. Similar to moths,
flames are the key elements of this optimization based on which the moths update their positions. Flames are
the best solutions. In each iteration the flames are sorted based on fitness. The moths update their positions
with respect to their corresponding flames. The principal moth dependably updates its position concerning
the best flame. The number of flames decreases adaptively over the course of iterations.
4.1. Algorithm for finding the Location and Series Compensator Voltage of UPQC
Step 1: Initialize the moth population size, maximum iterations, dimensions of the search space, minimum
and maximum limits of the moth positions.
Step 2: Run the load flow and find the real power loss before optimization.
Step 3: Generate randomly the moth positions of the order within the limits, where m denotes the
moth population size and n denotes the dimension. The dimensions are location, real and imaginary part of
series injected voltage, for one UPQC.Hence, n is assumed as 3.
Step 4: Set the iteration count to 1.
Step 5: Find the number of flames using Equation (10).
Number of flames
(10)
Here N is the maximum number of flames, m is the current iteration number and T is the maximum number
of iterations.
Step 6: Run the load flow by injecting the voltage at the corresponding location as given in Equation (7) and
by injecting the reactive power as given in Equation (9).
Step 7: Evaluate the fitness. Discard the moths which violate the constraint that the voltage at the
corresponding location should not exceed 1 p.u. Sort the moths based on fitness values.
Step 8: Initialize these moths as flames and fitness values as flame fitnesses. If current iteration number is
greater than 1 then sort the moths based on fitness values of the moths in the previous iteration and the
ISSN: 2088-8708
Int J Elec & Comp Eng, Vol. 8, No. 1, February 2018 : 530 – 537
534
current iteration and assign these to flames. Select the best flame fitness and its corresponding flame position
known as best flame position.
Step 9: Initialize given by Equation (11)
(11)
Step 10: Calculate the distance of the pth moth for the qth flame using Equation (12)
(12)
Step 11: Update the position of the moth using Equation (13)
(13)
Where S=Spiral function.The Spiral Function is given in Equation (14)
(14)
Where (15)
b is a constant which defines the shape of the spiral function (logarithmic spiral). It is assumed as 1
in this paper.
Step 12: Increase the iteration number.
Step 13: Reprise the steps from 5-12 until the iterations reach their maximum limit.
Step 14: Display the best flame fitness and the corresponding best flame position which gives the location of
UPQC and voltage injected by the series compensator.Print the results for real and reactive injected by the
series compensator and reactive power injected by the shunt compensator.
5. RESULTS
The test systems considered for checking the effectiveness of the proposed method are 10-bus,
34-bus and 33-bus systems. The losses, voltage profile, location and real and reactive power injected by
UPQC are determined.
5.1. Results of 10-bus System
10-bus system is a 23 kV system. The data of the system is taken from [20]. The real and reactive
load on the system is 12368 kW and 4186 kVAr respectively. 6 buses out of 10 buses have under voltage
problem.
From Table 1, it can be concluded that bus 7 has the least loss in real power which is 599.6457 kW.
The voltage to be injected by the series compensator is 0.0134 + 0.3929i p.u. The voltage improvement is
from 0.8375 p.u. @bus 10 to 0.9377 p.u. @bus 10 which is shown in Figure 4.
Table 1. Results of 10 bus System
Description
Without UPQC
With UPQC
Bus No
-
7
Total real power loss (kW)
783.7785
599.6457
Total reactive power loss (kVAr)
1036.5
793.8046
Complex Voltage injected by the series compensator (p.u.)
-
0.0134 + .3929i
Real power injected by the series compensator (kW)
-
607.50
Reactive power injected by the series compensator (kVAr)
-
1751.6
Reactive power injected by the shunt compensator (kVAr)
-
499.7686
Minimum voltage (p.u.)
0.8375@bus 10
0.9377@bus 10
Nodes with under voltage problem (<0.95)
6
2
Int J Elec & Comp Eng ISSN: 2088-8708
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535
Figure 4 Voltage Profile for 10 bus system without and with consideration of UPQC
5.2. Results of 34-bus System
34-bus system is a 11 kV system. The data of the system is taken from [18]. The real and reactive
load on the system is 4636.5 kW and 2873.5 kVAr respectively. 6 buses out of 34 buses have under voltage
problem.
Table 2. Results of 34 bus System
Description
Without UPQC
With UPQC
Bus No
-
26
Total real power loss (kW)
221.7235
149.5901
Total reactive power loss (kVAr)
65.1100
43.9272
Complex Voltage injected by the series compensator (p.u.)
-
0.3021i
Real power injected by the series compensator (kW)
-
302.75
Reactive power injected by the series compensator (kVAr)
-
23.412
Reactive power injected by the shunt compensator (kVAr)
-
1163.1
Minimum voltage (p.u.)
0.9417 @bus 27
0.9563@ bus 25
Nodes with under voltage problem (<0.95)
6
0
From Table 2, it can be concluded that bus 26 has the least loss in real power which is 149.5901kW.
The voltage to be injected by the series compensator is 0.0000 + 0.3021i p.u. The voltage improvement is
from 0.9417 p.u. @bus 27 to 0.9563 p.u. @bus 25 which is shown in Figure 5.
Figure 5. Voltage Profile for 34 bus system without and with consideration of UPQC
5.3. Results of 33-bus system
33-bus system is a 12.66 kV system. The data of the system is taken from [19]. The real and reactive
load on the system is 3715 kW and 2300 kVAr respectively. 21 buses out of 33 buses have under voltage
problem.
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536
Table 3. Results of 33 bus System
Description
Without UPQC
With UPQC
Bus No
-
31
Total real power loss (kW)
202.6771
123.4237
Total reactive power loss (kVAr)
135.141
83.6298
Complex Voltage injected by the series compensator (p.u.)
-
0.3080i
Real power injected by the series compensator (kW)
-
256.39
Reactive power injected by the series compensator (kVAr)
-
59.241
Reactive power injected by the shunt compensator (kVAr)
-
954.2685
Minimum voltage (p.u.)
0.9131@bus 18
0.9273 @bus 18
Nodes with under voltage problem (<0.95)
21
10
From Table 3, it can be concluded that bus 31 has the least loss in real power which is 123.4237
kW. The voltage to be injected by the series compensator is 0.0000 + 0.3080i p.u. The voltage improvement
is from 0.9131 p.u. @bus 18 to 0.9273 p.u. @bus 18 which is shown in Figure 6.
Figure 6. Voltage profile without and with consideration of UPQC in 33 bus system
Table 4 shows the comparison of UPQC placement results for 33-bus distribution system. The
method proposed in Reference [12] is Differential Evolution optimization method. The corresponding
reduction in real power loss is 25.84 %. The method proposed in Reference [10] is based on placement of
UPQC at each and every bus in the distribution system and obtaining the real power losses. The reduction in
real power losses is 27.99 %. The method proposed in this paper is placement of UPQC by using Moth Flame
Optimization method. The reduction in real power losses is 39.10%.
Table 4. Results of 33 bus System
Description
Ref [12]
Ref [10]
Proposed method
Optimal location
29
30
31
Real power loss (kW)
150.3
151.94
123.4237
Minimum voltage (p.u.)
-
0.9177
0.9273
Real Power Loss reduction (%)
25.84
27.99
39.10
Size of shunt compensator
Size of series compensator
914.1 kVAr
0.0015 kVAr
1000 kVAr
385.44 kVAr
954.2685 kVAr
256.39+j59.241 kVA
6. CONCLUSION
A new optimization method known as Moth Flame Optimization method is used to determine the
optimal allocation of Unified Power Quality Conditioner in the distribution system. UPQC’s series
compensator provides both real and reactive power and shunt compensator provides the required load
reactive power. This functionality of UPQC allows the series compensator to take part in reactive power
compensation. The best location and complex voltage injected by series compensator of UPQC is obtained by
using MFO. MFO has strong convergence characteristics for solving the problem of UPQC placement. The
Int J Elec & Comp Eng ISSN: 2088-8708
Moth Flame Optimization Method for Unified Power Quality Conditioner… (M. Laxmidevi Ramanaiah)
537
results prove the effectiveness of the proposed method to reduce real power losses and improve the voltage
profile. Comparative results demonstrate the effectiveness of the proposed method.
REFERENCES
[1] A. R. Gupta, et al., “Optimal D-STATCOM Placement in Radial Distribution System Based on Power Loss Index
Approach,” International Conference on Energy, Power and Environment: Towards Sustainable Growth (ICEPE)
2015, pp.1-5. doi:10.1155/2012/838629
[2] V. Khadkikar, et al., “Enhancing Electric Power Quality Using UPQC: A Comprehensive Overview,” IEEE
Transactions on Power Electronics, vol. 27, pp. 2284–2297, 2012.
[3] V. Khadkikar, et al., “Conceptual Study of Unified Power Quality Conditioner (UPQC),” 2006 IEEE International
Symposium on Industrial Electronics,Montreal, Quebec,2006
[4] V. Khadkikar, et al.,“UPQC-S: A novel concept of simultaneous voltage sag/swell and load reactive power
compensations utilizing series inverter of UPQC,” IEEE Transactions on Power Electronics, vol. 26, pp. 2414–
2425, 2011.
[5] K.Ramalingeswara Rao, et al., “Improvement of Power Quality using Fuzzy Logic Controller In Grid Connected
Photovoltaic Cell Using UPQC,” International Journal of Power Electronics and Drive System (IJPEDS), vol. 5,
no. 1, pp. 101-111, 2014.
[6] K. Sai Teja, et al., “Power Quality Improvement Using Custom Power Devices in Squirrel Cage Induction
Generator Wind Farm to Weak-Grid Connection by using Neuro-fuzzy Control”, International Journal of Power
Electronics and Drive System (IJPEDS), vol. 5, no. 4, pp. 477-485, 2015.
[7] R. Saravanan, et al., “Neuro Fuzzy Based Unified Power Quality Conditioner for Power Quality Improvement Fed
Induction Motor Drive,” IAES International Journal of Artificial Intelligence (IJ-AI) , vol. 4, no. 1,pp. 1-7, 2015.
[8] M.Boutebel, et al., “Optimal Steady State Operation of Unified Power Quality Conditioner for Power Losses
Reduction and Voltage Regulation Improvement,” Journal of Electrical Engineering, vol. 14, pp.114-121, 2014.
[9] S. Ganguly, et al., “Unified power quality conditioner allocation for reactive power compensation of radial
distribution networks,” IET Generation, Transmission and Distribution, vol. 8, pp. 1418–1429, 2014.
[10] A. R. Gupta, et al., “Performance Analysis of Radial Distribution Systems with UPQC and D-STATCOM,”
Journal of Institution of Engineers, India Ser. B, pp.1-8, 2016.
[11] M. Hosseini, et al., “Modeling of unified power quality conditioner (UPQC) in distribution systems load flow,”
Energy Conversion and Management, vol. 50, pp. 1578–1585, 2009.
[12] S. A. Taher, et al., “Optimal Location and Sizing of UPQC in Distribution Networks Using Differential Evolution
Algorithm,” Mathematical Problems in engineering, vol.2012, pp.1-20, 2012.
[13] H. D. Chiang, et al., “A decoupled load flow-method for distribution power networks: Algorithms, analysis and
convergence study,” Electric Power and Energy Systems, vol. 13, pp. 130–138, 1991.
[14] S. Ghosh, et al., “Method for load solution of radial distribution networks,” IEE Proceedings on Generation,
Transmission and Distribution, vol. 146, pp. 641–648, 1999.
[15] J. H. Teng, et al., “A direct approach for distribution system load flow solutions,” IEEE Transactions on Power
Delivery, vol. 18, pp. 882–887, 2003.
[16] M.H.Haque, et al., “Capacitor placement in radial distribution systems for loss reduction,” IEE Proceedings-
Generation Transmission, Distribution, vol. 146, pp.501-505, 1999.
[17] S. Mirjalili, et al., “Moth-flame optimization algorithm: A novel nature-inspired heuristic paradigm,” Knowledge-
Based Systems, vol. 89, pp. 228–249, 2015.
[18] M. Chis, et al., “Capacitor placement in distribution systems using heuristic search strategies,” IEE proceedings
on Generation, Transmission and Distribution, vol. 144, pp. 225-230, May 1997.
[19] M.E. Baran , et al., “Network reconfiguration in distribution systems for loss reduction and load balancing,” IEEE
Transactions on Power Delivery, vol 4 no.1, pp. 1401-1407, 1989.
[20] C.T. Su, et al., “Optimal Capacitor Placement in Distribution Systems Employing Ant Colony Search Algorithm,”
Electric Power Components and Systems, vol. 33, pp. 931-946, 2005.
