An Analysis of Two Area Load Frequency Control with Different Types of Feedback Controllers

An Analysis of Two Area Load Frequency Control with Different Types of Feedback Controllers

Debirupa Hore1 Assistant Professor

Department of Electrical Engineering

K J Educational Institutes, KJCOEMR, Pune

Abstract: This paper deals with the classical method of reducing transients of load frequency of a two area power system. The load frequency of a two area power system is studied with and without Controllers. The model is compared in terms of its uncontrolled response obtained earlier.. A new model is represented in this paper where an advance PID Controller is used compared to Integral Control . For a practical two area power system the change in frequency response is studied for different change in load condition with both types of controllers. The PID controller is properly tuned in such a way that it proved to be a more better controller in comparison to Integral Controller for change in frequency response. With PID Controller applied to two area power Systems the frequency transients are quenched at much faster rates without oscillations.

Key words: Two area frequency power system, PI controller, PID controller

1. INTRODUCTION

   The modern power systems with industrial and commercial loads need to operate at constant frequency with reliable power. The load frequency control of an interconnected power system is being improved over the last few years. The goals of the LFC are to maintain zero steady state errors in a multi area interconnected power system [1], [2]. Studies on two area interconnected power system networks were presented based on conventional techniques. Recently many researchers are applying different advance Controllers to improve the dynamic performance of the system by damping the oscillations resulted from load perturbations faster. Subsequently a robust load frequency control for uncertain non linear power systems using fuzzy logic approach to quench the transients in frequency deviations and tie line power deviations is presented [7]. In all these works the basic dynamic model representation of a two area power system given in the reference [2] is considered and the responses of two area power systems are evaluated. These studies using different conventional and fuzzy control methods show that the frequency deviations are oscillatory and the total time to reach final steady state is more. After a sudden load change in area 1

   or in area 2 or in both the areas the frequency deviations are oscillatory without any control method. With integral controller in the feedback of the system the steady state frequency error finally reaches Zero. But there are transient present in the change in Frequency response. The behaviour of the two area power system for different load changes to predict the variations is a major study with and without the application of the fuzzy controller. With this aim an attempt is made to improve the transient behavior of the two area power system. The first part of the study is concentrated on the transient behaviour of the uncontrolled system for a range of step load changes for the dynamic model considered here.. The system frequency deviations are zero before any disturbance in the power system. Assuming a step load change in area 1 if the fuzzy controller is incorporated in area 1 the system behaviour is observed. Studies are also conducted to find the response of the system by placing the fuzzy controller in area 2. Studies are also performed to load changes in both areas with fuzzy controllers. The behaviour of the interconnected power system for different load changes are also obtained in all these cases.

2. TWO AREA SYSTEM

   A two area system consists of two single area systems, connected through a power line called tie-line, is shown in the Figure 1. Each area feeds its user pool, and the tie line allows electric power to flow between the areas. Information about the local area is found in the tie line power fluctuations. Therefore, the tie-line power is sensed, and the resulting tie-line power is fed back into both areas. It is conveniently assumed that each control area can be represented by and equivalent turbine, generator and governor system. Figure1 shows the block diagram representing the two area power system . This model includes the conventional integral controller gains (K1 , K2) and the two auxiliary (stabilizing) signals( u1, u2). The stabilizing signals will be generated by the proposed fuzzy logic load frequency controller (FLFC). Each power area has a number of generators which are closely coupled together so as to form a coherent group, i.e. all the generators respond in unison to changes in the load. Such a

   coherent area is called a control area in which the frequency is assumed to be the same throughout in static as well as dynamic situation

   2() = , 2 + 22 (s)

3. INTEGRAL CONTROL

   The integral control composed of a frequency sensor and an integrator. The frequency sensor measures the frequency error f and this error signal is fed into the integrator The input to the integrator is called the Area Control Error (ACE). The ACE is the change in area frequency , which when used in an integral-control loop, forces the s steady- state frequency error to zero. The integrator produces a real-power command signal Pc and is given by-

   = =

   = input of speed changer Ki = integral gain constant.

   PID Controller

   In place of Integral controller PID controller is placed to reduce the transients in tie line Power

   Figure 1

   = . + +

   Power transported out of area 1 is given by-

   , 1 = |1 ||2| ( – )

   = . + +

4. SIMULATION AND RESULTS

12 1 2

1, 2 is power angles of equivalent machine of the two areas

For incremental changes in 1, 2 the incremental tie line power can be expressed as-

, 1() = 12 (1 2)

Where,

= |1 ||2| cos( – )=Synchronizing Co-efficient

12 112 1 2

Since incremental power angles are integrals of incremental frequencies we can write-

Ptie,1=212 ( 1 dt- 2 )

Where 1 2 are incremental frequency changes of area1 and area2 respectively.

Similarly incremental tie power out of area 2 is given by

Ptie, 2=221 ( 2 dt- 1 )

The following simulations were performed in order to investigate the performance of PID controller over the conventional integral controller with 1%, 3% and 5% change in load of each area.

Simulation is carried out of two area system as per following systems for response of f1,

1. With PI controller

2. With PID Controller

Simulation is carried out of two area system as per following systems for response of f2,

1. With PI controller

2. with PID Controller

Where, = |1 ||2| cos( – ) =( 1 )

=

the

221

2 1 2 12

12 12

incremental power balance equation for area1 can be

written as-

=21 1 +

+Ptie, 1

1

1

1

1 1

Taking Laplace transform we get-

= [

]* ,1

1 1

,1=1/1

1

1

1+ 1()

1 ()=21 /1

Similarly,

Ptie, 1(s) = 212[ [ ]

1 2

Ptie, 2(s) =- 212[ [ ]

1 2

Area Control Error (ACE) for two areas are

1 = ,1 + 1 1

1 is called frequency bias

1() = , 1 + 11 (s)

Figure-1:Simulation of a Two Area Load frequency System V. CONCLUSION

0.01

0

Change in Frequency

-0.01

-0.02

-0.03

-0.04

-0.05

Change in Frequency Response for Two Area Control with Integral and PID controller

ith Integral C

With PID Co

ntroller

ontroller

W

0 10 20 30 40 50 60 70 80 90 100

Time

In this study an approach of PID controller has been investigated for two area frequency control of power system. Results have been compared for step load change against PI controller technique for different change in load conditions. The result shows the PID controller is having more improved dynamic response. With the aid of PID controller the transients in the frequency response reduced to A great extend.

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   Figure-2: Change in frequency response for integral & PID Controller for 1% change in Load

   Change in frequency response for Two area Control for 3% change in Load (Del Pd)

3. Jawat, T. and Fadel, A, B. Adaptive Fuzzy Gain Scheduling for Load frequency control, IEEE Trans. on PAS, vol. 14, No 1, February 1999.

   ontroller

   ith Integral C

4. Nanda, J. and Kaul, B.L, Automatic Generation

   0.02

   0

   -0.02

   Change in Frequency

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   ntroller

   -0.06

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   -0.1

   -0.12

   -0.14

   W

   With PID Co

   0 10 20 30 40 50 60 70 80 90 100

   Time

   Figure-3: Change in frequency response for integral & PID Controller for 3% change in Load

   Change in Frequency Response for Two Area Load Frequency Control for 5% change in Load

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   0.1

   0.05

   ontroller

   W

   0

   Change in Frequency

   -0.05

   -0.1

   -0.15

   -0.2

   -0.25

   ith Integral C

   With PID Co

   ntroller

   0 10 20 30 40 50 60 70 80 90 100

   Time

   Methods in Engineering, MME-06, Cankaya University\ Ankara, Turkey, April 27 – 29 , 2006.pp:

10. Nilay.N.Shah, Aditya.D.Chafekar, Dwij.N.Mehta, Anant.R.Suthar Automatic Load Frequency Control Of Two Area Power System with Conventional and Fuzzy Logic Control IJRET NOV 2012, ISSN: 2319

    – 1163 Volume: 1 Issue: 3 pp.343 – 347

11. B. Venkata Prasanth, Dr. S. V. Jayaram Kumar New Control Strategy for Load Frequency Problem of a Single Area Power System Using Fuzzy Logic Control Journal of Theoretical and Applied Information Technology 2008 pp 253-260

Figure-3: Change in frequency response for integral & PID Controller for 3% change in Load

APPENDIX

Bibliography:

Debirupa Hore was born in Guwahati Assam India on April 19th 1983.She received her B.E Degree in Electrical Engineering. from Assam Engineering College Guwahati in 2006 and M.Tech in Energy and Power Systems in 2010 from NIT Silchar. She worked in GIMT Guwahati for 5 years as Assistant Professor. Currently she is working as an Assistant Professor in Electrical Engineering Department in KJ Educational Institutes, KJCOEMR, Pune (Maharashtra).Her research areas of interest includes Power Systems, AI Techniques, Power Electronics and Drives etc