Load Frequency Control for A Multi Area Power
System Involving Wind, Hydro and Thermal
Plants

N. Kiran Kumar; I.E.S. Naidu

Load Frequency Control for A Multi Area Power System Involving Wind, Hydro and Thermal Plants

N. Kiran Kumar, I.E.S. Naidu
Department Electrical & Electronics Engineering, GITAM University, Visakhapatnam, India

Related article at Pubmed, Scholar Google

Visit for more related articles at International Journal of Innovative Research in Science, Engineering and Technology

Abstract

In an interconnected power system, as a power load demand varies randomly both area frequency and tie-line power interchange also vary. The objectives of load frequency control (LFC) are to minimize the deviations in these variables (area frequency and tie-line power interchange) and to ensure their steady state errors to be zero. In this area of energy crisis, renewable energy is the most promising solution to man’s ever increasing energy needs. But the power production by these resources cannot be controlled unlike in thermal plants. As a result, standalone operation of renewable energy is not reliable. Hence grid-connection of these along with conventional plants is preferred due to the improved performance in response to dynamic load. It is observed that fluctuations in frequency caused due to load variations are low with increase in penetration of renewable resources. Load frequency control (LFC) including PID controller is proposed in order to suppress frequency deviations for a power system involving wind, hydro and thermal plants owing to load and generating power fluctuations caused by penetration of renewable resources. A system involving two thermal plants, a wind farm and a hydro plant will be modelled using MATLAB.

Index Terms

Distributed power generation, load frequency, Control (LFC), wind power, hydro power, and thermal power plants.

NOMENCLATURE

ΔPC Command signal

ΔF Change in Frequency

ΔYE Changes in steam valve opening

R Speed regulation of the governor

Ksg Gain of speed governor

Tsg Time constant of speed governor

Rp Permanent droop

Rt Temporary droop

Tg Main servo time constant

D Change in load with respect to frequency

Tw Water starting time

Tr Reset time

INTRODUCTION

The high Indian population coupled with increase in industrial growth has resulted in an urgent need to increase the installed power capacity. In India, majority of power production, around 65 per cent is from thermal power stations. Due to problems related to uncertainty in pricing and supply of fossil fuels, renewable resources have been identified as a suitable alternative like solar, wind, and biogas plants are using in recent days. However, standalone operation of renewable resources is not reliable as they are intermittent in nature. The intermittent nature of resource increases the frequency deviations which further add to the deviation caused by load variation. This necessitates the grid connection of renewable resources wind and solar.

Frequency deviation is undesirable because most of the AC motors run at speeds that are directly related to frequency. Also the generator turbines are designed to operate at a very precise speed. Microcontrollers are dependent on frequency for their timely operation. Thus it is imperative to maintain system frequency constant. This is done by implementing Load Frequency Control (LFC). There are many LFC methods developed for controlling frequency. They include flat frequency control (FFC), tieline bias control (TBC) and flat tie-line control (FTC). In FFC, Some areas act as load change absorbers and others as base load.

The advantage is the higher operating efficiencies of the base load as they run at their maximum rated value at all times. But the drawback here is the reduced number of areas absorbing load changes which makes the system more transient prone. In FTC load changes in each area are controlled within the area, thereby maintaining tie line frequency constant. The most commonly used method is the tie-line load bias control in which all power systems in the interconnection aid in regulating frequency regardless of where the frequency change originates. In this project, the power system considered has a Thermal system with four thermal areas, a Hydro plant and a wind farm.

MODELING OF THERMAL AREAS

The thermal areas have been modelled using transfer function. Speed governor, turbine and generator constitute the various parts namely the speed governing system, turbine model, generator load model [7].

References

R. Oba, G. Shirai, R. Yokoyama, T. Niimura, and G. Fujita,“Suppression of Short Term Disturbances from Renewable Resources by Load Frequency Control Considering Different Characteristics of Power Plants”, IEEE Power & Energy Society General Meeting, pp.1 – 7, Jul.2009.
N. R. Ullah, T. Thiringer, and Daniel Karlsson,“Temporary Primary Frequency Control Support by Variable Speed Wind urbines— Potential and Applications”, IEEE Transactions n Power Systems, vol.23, No.2, May 2008.
P. Kundur, Power System Stability and Control, 1st ed., New ork: McGraw-Hill, 1993.
L. Freris and D. Infield, Renewable Energy in Power Systems, 1st ed., J.Wiley Sons Ltd., 2008.
H. Saadat, Power System Analysis, 1st ed., Tata McGraw- Hill, 2002.
O. Anaya-Lara, N. Jenkins, J. Ekanayake, P. Cartwright, M. Hughes,Wind Energy generation Modelling and Control, 1st ed., J. Wiley Sons Ltd., 2009.
O. Elgerd, Electric Energy Systems Theory An Introduction, 2nd ed., Tata McGraw-Hill, 1983
Juan Manuel Mauricio, Alejandro Marano, Antonio Gomez- Exposito,and Jose Luis Martinez Ramos, “Frequency regulation contributionthrough variable- speed wind energy conversion system,” IEEE Trans. Power. Syst., vol. 24, no. 1, pp. 173-180, Feb. 2009.
G. Lalor, A. Mullane, and M. O’Malley, “Frequency control and wind turbine technologies,” IEEE Trans. Power Syst., vol. 20, no. 4, pp. 1905–1913, Nov. 2005.
J. de Almeida and R. G. Lopes, “Participation of doubly fed induction wind generators in system frequency regulation,” IEEE Trans. Power Syst., vol. 22, no. 3, pp. 944–950, Aug. 2007.
M. Iulian and N.A.Cutululis , Optical control of wind energy systems, Ist ed., springer –erlag,London,pp. 93- 145.
L.R. Chang-Chien, W.T. Lin and Y.C. Yin, “Enhancing frequency response control by DFIGs in the high wind penetrated power systems,” IEEE Transactions on power systems, 2010.