A Comparative Study of BAT and Firefly Algorithms for Optimal Placement and Sizing of Static VAR Compensator for Enhancement of Voltage Stability

A Comparative Study of BAT and Firefly Algorithms for Optimal Placement and Sizing of Static VAR Compensator for Enhancement of Voltage Stability

B. Venkateswara Rao (Department of Electrical and Electronics Engineering, Gandhi Institute of Technology and Management (GITAM), Visakhapatnam, India) and G.V. Nagesh Kumar (Department of Electrical and Electronics Engineering, Gandhi Institute of Technology and Management (GITAM), Visakhapatnam, India)
Copyright: © 2015 |Pages: 17
DOI: 10.4018/ijeoe.2015010105
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Abstract

Modern electric power utilities are facing many challenges due to increasing power demand but the growth of power generation and transmission has been limited due to limited resources, environmental restrictions and right-of-way problems. These problems can be minimized by installing Flexible Alternating Current Transmission System (FACTS) devices in modern electric utilities to optimize the existing transmission system. Most effective use of the FACTS devices depend on the fact, how these devices are placed in the power system, i.e. the location and size. An optimal location and size of FACTS devices allows controlling its power flows and thus enhances the stability and reliability of the power systems. In this paper, Firefly Algorithm (FA) and BAT Algorithm (BAT) have been applied and compared to determine the optimal location and size of Static VAR Compensator (SVC) in a power system to improve voltage stability subjected to minimize the active power losses, fuel cost, branching loading and voltage deviation. The effectiveness of the proposed algorithms and improvement of power system stability has been demonstrated on IEEE 57 bus system using fast voltage stability index. The results obtained with variation of parameters of Firefly and BAT Algorithms has been studied and compared with Genetic Algorithm. The results are presented and analyzed.
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1. Introduction

Modern electric power utilities are facing many problems due to increasing complexity in their operation and structure. In recent years, the transmission lines are operated under the heavily stressed condition, hence there is a risk of consequent voltage instability in the power network. Conventional power systems are controlled mechanically (Kundur, 1993; Hingorani and Gyugyi, 2000). However control, through mechanical devices is not as reliable as they tend to wear out quickly compared to the static devices. This necessitates power flow control to shift from mechanical devices to static devices. Static devices called the Flexible Alternating Current Transmission System (FACTS) device (Acha et al., 2004) were developed, capable of effectively controlling the load flow distribution and the power transfer capability. The FACTS device performance depends upon its location and parameter setting. The power electronic based FACTS introduced in 1980’s, provided a highly efficient and economical means to control the power transfer in interconnected AC transmission systems (Roy and Mandal, 2013). Power flow through an AC line is a function of phase angles, bus voltages and line impedance. Using FACTS devices, these variables can be effectively and efficiently controlled. A FACTS device in a power system improves voltage stability, reduces the power loss and also improves the stability of the system. However, controlling power flow is the main function of FACTS device (Chung and Li, 2001; Cherkaoui and Germond, 2001).

The Static VAR Compensator (SVC) is most commonly used shunt connected FACTS device capable of providing simultaneous control of voltage magnitude and reactive power flows. The SVC, constructed by the combination of the fixed capacitor and thyristor controlled reactor can inject or absorb the capacitive or inductive reactive power to the system to control power flow in transmission lines and its parameters, like the voltage magnitude and the phase angle (Sun et al., 1984).

In this paper, a Multi Objective function containing active power losses, fuel cost, branch loading and voltage deviation with constraints of real and reactive power generation, voltage of generator buses and susceptance of SVC are taken for optimal placement and sizing of SVC using BAT and Firefly Algorithms to improve voltage stability. In this paper voltage stability has been determined with line based voltage stability index called Fast Voltage Stability Index (FVSI). The system becomes unstable if FVSI is equal to or greater than unity. The results obtained using Firefly and BAT Algorithms were compared with Genetic Algorithm. The proposed methods have been tested on IEEE 57 bus system and the results have been presented and analysed.

1.1. Nomenclature Used

  • : Complex voltage at bus i;

  • : Difference between and

  • : Susceptance of SVC

  • : Objective function

  • : Total fuel cost of all the generators in $/hr

  • : Total real power losses in MW

  • : Net voltage deviation in p.u

  • : Total loading capacity of transmission lines in p.u

  • : Active Power transmission line losses, MW

  • : The svc reactive power in MVAR

  • : Bus voltage at ith bus, V

  • : Minimum voltage at bus i, V

  • : Maximum voltage at bus i, V

  • : Minimum real power generation, MW

  • : Maximum real power generation, MW

  • : Minimum reactive power generation, MVAR

  • : Maximum reactive power generation, MVAR

  • : Apparent power flow from bus i to j, MVA

  • : Active power flow from bus i to j, MW

  • : Reactive power flow from bus i to j, MVAR

  • : Admittance of the element between bus i and j

  • Z : the line impedance (p.u)

  • X : the line reactance (p.u)

  • Qj : the reactive power at bus j (receiving end bus)

  • Vi : the voltage magnitude at bus i (sending end bus)

  • FVSIij: FVSI for line connected between bus i and bus j (p.u)

  • PL : total active power losses (MW)

  • QL : total reactive power losses (MVAR)

  • PGi : the active power generation at bus i (MW)

  • PDi : the power demand at bus i (MW)

  • Sk : the apparent power in line k (MVA)

  • Skmax: the maximum apparent power in line k. (MVA)

  • Vk : the voltage magnitude at bus k, V

  • Vkref : the reference voltage magnitude at bus k, V

  • ntl :no. Of transmission lines

  • ng : no of generator buses

  • N : no. Of buses

  • α : random movement factor

  • β : attractiveness parameter

  • γ : absorption parameter

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