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Due to urbanization, utilization of electricity has been enhanced which increasing the construction of new lines and usages of more inductive loads. Due to this the losses in the transmission system increased and voltage profile values deviated from the specified value which causes to increase the cost of the real power generation. So, for avoiding these problems, proper reactive Power compensation should be done in transmission systems. Reactive power is controlled properly by installing Flexible AC Transmission System devices (FACTS). Unified Power Flow Controller (UPFC) is Voltage source converter type FACTS device which increase the voltage profile and reduce the losses. The parameter setting of UPFC is a challenging task, in this paper it is achieved by using resent metaheuristic optimization algorithm called firefly algorithm (FA). In this optimization process, a multiobjective function is considered. This consists of four objectives those are total transmission line loss, voltage deviation, the cost of true power generation & the branch loading. To validate the proposed approach IEEE 14bus & IEEE 30bus systems have been measured in MATLAB environment. Genetic Algorithm (GA) has been used for comparison purpose. The results indicate that FA gives better results in both the cases compared to GA.
firefly algorithm, FACTS, optimal parameter setting, optimization, UPFC
Voltage collapse & voltage instability have been measured as a foremost hazard to the current power system networks because of their heavily loaded operation. Due to increasing usages of inductive loads, losses in the transmission system enhanced and voltage profile values deviated from the prescribed value which also causes to increase the cost of the real power generation [14]. So, for avoiding these problems, proper reactive Power compensation should be done in transmission systems. Reactive power compensation in transmission lines recovers the stability of the system. It helps to maintain a significantly uniform voltage profile at all points of power transmission, which increase transmission efficiency and avoid voltage collapse [56].
Conservative power systems are structured with mechanical devices but control with these devices is not as trustworthy as static devices because machinedriven devices incline to wear out speedily. This compels that to use the static controllers in power system. Recently developed power electronic based FACTS providing an extremely efficient & costeffective way to regulator the power flow in organized AC transmission system [79]. Instead of constructing new transmission lines utilize the existing lines in a better way by using FACTS devices. There are so many FACTS devices out of which UPFC is the best voltage source converter type device. It can control all the Power flow control variables like phase angles, bus voltages, and line impedance. UPFC built by grouping of static synchronous compensator (STATCOM) & Static Synchronous Series Compensator (SSSC) [10]. It was familiarized by Gyugiy in 1991. The advantages achieved from UPFC consist of stability improvement of power system networks, enhancement of power transfer capability of lines and reduction of power losses in the system [1112].
This broadsheet describes the usage of firefly algorithm to find optimal parameter setting of UPFC device by considering multiobjective function. This function consists of four objectives those are transmission line losses, voltage deviation, the true power generation cost and the branch loading. The true power generation and PV bus voltages are taken as variables and their limits along with UPFC converter limits are chosen as constraints throughout the optimization processes [1314]. The attained results illustrate that UPFC is the best reactive power compensation device which escalates the voltage stability of the system. For simulations purpose, MATLAB 2009 version has been used and IEEE 14 bus system & IEEE 30 bus system is taken as test cases. UPFC device consists of voltage source converters which provide more suppleness to handle all power flow control & transmission line reimbursement problems [1516]. The preliminary amounts of UPFC device voltage sources converter are selected as VCR = 0.04 p.u, δCR = 87.130, VVR = 1 p.u. δVR = 00.
The remainder of this paper is organized as follows: Section 2 Problem origination, Section 3 describes Firefly algorithm, Section 4 results & analysis and Section 5 conclusion with future scope.
Optimal parameter values of UPFC device is obtained by minimizing the multiobjective function with adequate equality & inequality limitations. The objective function consists of overall transmission line loss, complete voltage deviation, the entire cost of true power generation & branch loading.
2.1 Objective function
$\mathrm{F}=\mathrm{V}_{1} * \mathrm{TTPC}+\mathrm{V}_{2} * \mathrm{TTL}_{loss}+\mathrm{V}_{3} * \mathrm{VD}+\mathrm{V}_{4} * \mathrm{BL}$ (1)
$\mathrm{V}_{1}+\mathrm{V}_{2}+\mathrm{V}_{3}+\mathrm{V}_{4}=1$ (2)
where, V_{1}, V_{2}, V_{3}, V_{4} are the weighting factors in this work equal importance is given to all the objectives so V_{1}+V_{2}+V_{3}+V_{4 }= 0.25.
2.1.1 Total true power generation cost (TTPC):
This objective considering the quadratic function, the function follows as
TTPC=$ \sum_{i=1}^{n g}\left[a_{i}+b_{i} P_{G_{i}}+c_{i} P_{\mathrm{Gi}}^{2}\right]$ (3)
where, Ng is the number of PV buses.
a, b & c are cost quantities of a true power generation plants.
2.1.2 Total transmission line loss (TTL):
It can be conveyed as:
$\mathrm{TTL}=\left(\sum_{i=1}^{n t l} \operatorname{real}\left(S_{i j}^{\mathrm{k}}+S_{\mathrm{ji}}^{\mathrm{k}}\right)\right)$ (4)
where, ntl is number of inter linked lines, $S_{j i}^{k}$ is compound power flow in line k, from bus j.
2.1.3 Voltage deviation (VD):
The Voltage Deviation (VD) is one of the main intents to improve the power system performance, it can be shown as:
$V D=\left(\sum_{k=1}^{N b u s}\leftV_{k}V_{k}^{\mathrm{ref}}\right^{2}\right)$ (5)
Vk is voltage at bus k, Vk^{ref} is specified voltage at bus k.
2.1.4 Branch loading (BL):
It can be given as:
$B L=\sum_{\mathrm{k}=1}^{\mathrm{nl}}\left(\frac{\mathrm{S}_{\mathrm{k}}}{\mathrm{S}_{\mathrm{k}}^{\mathrm{max}}}\right)^{2}$ (6)
S_{k} is complex power in line k & Sk^{max} is maximum compound power in line k.
2.2 Constraints
$\sum_{i=1}^{N} P_{G i}=\sum_{i=1}^{N} P_{D i}+P_{L}$ (7)
$\sum_{i=1}^{N} Q_{G i}=\sum_{i=1}^{N} Q_{D i}+Q_{L}$ (8)
$V_{G i} \min _{\leq} V_{G i} \leq V_{G i} \max$ (9)
$P_{G i} \min _{\leq} P_{G i} \leq P_{G i} \max$ (10)
i=1, 2, 3... N & N is number of true power generation buses
$Q_{G i} \min \leq Q_{G i} \leq Q_{G i} \max$ (11)
2.2.1 UPFC limits
$V_{v r}^{\min } \leq V_{v r} \leq V_{v r}^{\max }$ (12)
$V_{c r}^{\min } \leq V_{c r} \leq V_{c r}^{\max }$ (13)
In this work, the main objective is to identify the best parameter settings for UPFC device.
Dr. XinShe Yang develops the firefly algorithm. It works on the usual behavior of Firefly and mainly used for resolving the multiobjective optimization problem [1718]. Fireflies are charming creatures and they produce light. These are unisex & produce unique flashes. For easiness, the following 3 basic rules are used in FA growth those are I) All the fireflies are unisex & every firefly will fascinate the other firefly II) Based on the brightness they will attract each other. Brighter one is trying to attract the less sunny one, III) the background of objective function moves the firefly illumination. In this paper, the uninterrupted inhibited optimization problem is used to minimize the multiobjective function f(x). Convergence achieved in less no. of iterations in firefly algorithm & its result based on the number of fireflies, desirability value, the fascination coefficient value & iteration limit. The solution procedure is given in [1920].
To identify the usefulness of the planned firefly Algorithm optimal parameter setting of UPFC, IEEE 14 & IEEE 30 bus system are engaged as case studies. MATLAB R2009 environment with Windows 7 Home Basic operating system consists of an i3 processor and 4 GB RAM laptop has been used to do the simulation. Simulation results of firefly algorithm established OPF without& with UPFC have been tabulated. In these study, 50 fireflies with 20 generations have been considered.
4.1 For 14 bus system
IEEE 14 bus system involves of five generator buses out of that first bus is considered as a swing bus and second, third, sixth and eighth buses are taken as generator buses & remaining all buses are PQ buses. All these buses are interconnected with twenty transmission lines. Simulations were done on MATLAB environment and the obtained results are presented in Tables. Table 1 indicates the input parameters of FA. Table 2 specifies the generator characteristics of IEEE 14 bus system. Table 3 specifies the UPFC parameters for different conditions. Table 4 designates various objectives in objective function consisting without and with UPFC using Firefly Algorithm. Table 5 presents the voltage profile comparison with GA & FA. Table 6 shows the optimized generator values of the generator using GA & FA. From these results, it is witnessed that FA is superior to GA. Figure 1 and Figure 2 presents the voltage magnitude and phase angles comparison with and without UPFC.
Figure 1. Comparison of bus voltages for 14bus system using FAOPF without and with UPFC
Figure 2. Comparison of phase angles for 14 bus system using FAOPF without and with UPFC
Table 1. Input parameters of Firefly Algorithm
S.No 
Parameters 
Quantity 
1 
No.of. fireflies 
20 
2 
Maximum Generation 
50 
3 
Random movement factor (a) 
0.5 
4 
Attractiveness parameter (b) 
0.5 
5 
Absorption parameter (g) 
1 
Table 2. Generator characteristics of IEEE 14 bus system
Generator Bus No 
a 
b 
c 
$P_{G}^{\min }$ 
$P_{G}^{\max }$ 
1 
0.005 
2.45 
105 
10 
400 
2 
0.005 
3.51 
44.1 
20 
180 
3 
0.005 
3.89 
40.6 
20 
150 
6 
0.005 
3.25 
0 
10 
135 
8 
0.005 
3 
0 
10 
130 
Table 3. Comparison of UPFC parameters in IEEE 14 bus system

location of UPFC (starting bus ending bus) 
Parameters of UPFC 

Optimal Power Flow with GA 
1314 
V_{cr} 
0.04 
θ_{cr} 
87.1236 

V_{vr} 
1.0183 

θ_{vr} 
14.6897 

49 
V_{cr} 
0.0440 

θ_{cr} 
87.1236 

V_{vr} 
1.0191 

θ_{vr} 
8.1057 

Optimal Power Flow With FA 
1314 
V_{cr} 
0.038 
θ_{cr} 
87.1236 

V_{vr} 
1.02 

θ_{vr} 
4.6116 

49 
V_{cr} 
0.0394 

θ_{cr} 
87.1236 

V_{vr} 
0.9975 

θ_{vr} 
2.8626 
Table 4. Comparison of different objectives using FA OPF in IEEE 14 bus system
IEEE 14 Bus System 
FA OPF 

Parameter 
Without UPFC 
With UPFC 
Voltage deviation 
0.8940 
0.5286 
System loadability 
2.5967 
2.3016 
Active power losses 
4.8234 
3.1207 
Fuel cost 
1824.2853 
1719.5398 
Fitness function value 
549.4832 
517.2688 
Table 5. Comparison of voltage profile of IEEE 14 bus system
GA OPF & FAOPF 
No UPFC 
Non Optimal location of UPFC 
Optimal location of UPFC 

Genetic Algorithm based Optimal Power Flow 
UPFC connected between bus no’s 
 
49 
1314 
Net voltage deviation (p.u) 
0.9296 
0.6106 
0.5396 

Firefly Algorithm based Optimal Power Flow 
UPFC connected between bus no’s 
 
49 
1314 
Net voltage deviation (p.u) 
0.8940 
0.5637 
0.5286 
Table 6. Comparison of the real power generation of generator busses in various methods
PV bus N0 
Generation limits 
GAOPF 
FAOPF 


Min 
Max 
Without UPFC 
With UPFC 
Without UPFC 
With UPFC 
1 
10 
400 
134.32 
132.11 
34.54 
32.84 
2 
20 
180 
43.82 
43.82 
74.53 
74.53 
3 
20 
150 
44.84 
44.84 
146.07 
146.07 
6 
10 
135 
76.61 
76.61 
55.986 
55.983 
8 
10 
130 
98.91 
98.91 
82.62 
82.629 
4.2 For 30 bus system
IEEE 30 bus system has six generator buses, in which first is slack bus and second, fifth, eighth, eleventh and thirteen buses are PV buses, remaining buses are PQ buses. These buses are connected by fortyone lines. Simulations are performed on MATLAB environment and the results have been tabulated. Table 7 represents the generator characteristics of 30 bus system. Table 8 shows the size of the UPFC for different conditions. Table 9 indicates various objectives of the minimization function. It shows the without and with UPFC objectives using Firefly Algorithm.
Table 7. Generator characteristics of IEEE 30 bus system
Generator Bus No 
a 
b 
c 
$P_{G}^{\min }$ 
$P_{G}^{\max }$ 
1 
0.00375 
2 
0 
50 
300 
2 
0.0175 
1.75 
0 
20 
80 
5 
0.0625 
1 
0 
15 
50 
8 
0.00834 
3.25 
0 
10 
35 
11 
0.025 
3 
0 
10 
30 
13 
0.025 
3 
0 
12 
40 
Table 8. Comparison of UPFC parameters in IEEE 30 bus system
OPF Methods 
location of UPFC (starting bus ending bus) 
Parameters of UPFC 

Optimal Power Flow with GA 
2122 
Vcr 
0.1100 
θcr 
92.4571 

Vvr 
1.0176 

θvr 
14.3387 

Optimal Power Flow with FA 
2122 
Vcr 
0.0945 
θcr 
87.5156 

Vvr 
1.0176 

θvr 
11.6496 
Table 9. Comparison of different objectives using FA OPF in IEEE 30 BUSSYSTEM
IEEE 30 bus system 
FA OPF 

Parameter 
Without  upfc 
With  upfc 
Voltage deviation 
0.9260 
0.6589 
System loadability 
3.4415 
3.2376 
Active power losses 
5.0034 
4.4574 
Fuel cost 
1002.4771 
901.0301 
Fitness function value 
302.7129 
272.0536 
Table 10. Comparison of Voltage deviation of IEEE 30 bus system
OPF Methods 
No UPFC 
Non Optimal location of UPFC 
Optimal location of UPFC 

Genetic Algorithm based Optimal Power Flow 
UPFC connected between bus no’s 
 
2526 
2122 
Net voltage deviation (p.u) 
0.9361 
0.722 
0.6854 

Firefly Algorithm based Optimal Power Flow 
UPFC connected between bus no’s 
 
2526 
2122 
Net voltage deviation (p.u) 
0.9260 
0.6911 
0.6589 
Table 11. Comparison of the Real power generation of Generator busses in various methods
PV bus NO 
Generation limits 
GAOPF 
FAOPF 


Min 
Max 
Without UPFC 
With UPFC 
Without UPFC 
With UPFC 

1 
50 
300 
173.82 
173.24 
86.95 
86.41 

2 
20 
80 
49.104 
49.1041 
55.44 
55.44 

5 
15 
50 
21.729 
21.7296 
44.58 
44.58 

8 
10 
35 
23.854 
23.8543 
34.03 
34.03 

11 
10 
30 
12.848 
12.8483 
28.42 
28.42 

13 
12 
40 
12.009 
12.0098 
38.94 
38.94 
Figure 3. Voltage profile comparison for IEEE 30 bus system without and with UPFC
Table 10 presents the comparison of Voltage deviation considering FA & GA. Table 11 shows power generation of generator buses using GA & FA. From these tables, it is observed that FA is superior to GA. Figure 3 shows that after incorporating UPFC in FAOPF voltage, profile has been enhanced.
In this paper, a flock optimization method termed Firefly Algorithm applied to categorize the finest parameter tuning values of UPFC device. The effectiveness of Firefly Algorithm was proved and tested on two systems. Firefly Algorithm finds the best values for UPFC within a given limit by considering multiobjective function. The results indicate that after placing the UPFC in the IEEE14 bus & IEEE30 bus system, total transmission line losses are condensed, voltage profile boosted & loading capacity enlarged. The results attained with Firefly algorithm were accorded with genetic algorithm & it is witnessed that firefly algorithm superior to the genetic algorithm. Firefly algorithm will be implemented for optimization of real power generation and size of the multi type FACTS devices. Further to improve the system performance renewable energy sources will be incorporated in the power system.
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