Journal of Theoretical and Applied Information Technology

Topics: Neural network, Artificial neural network, Control theory Pages: 8 (2307 words) Published: December 22, 2009
Journal of Theoretical and Applied Information Technology
© 2007 JATIT. All rights reserved.




G. Tulasi Ram Das

Department of Electrical and Electronics Engineering, Chaitanya Bharathi Institute of Technology, Hyderabad, India. 2 Department of Electrical and Electronics Engineering, J.N.T.U. College of Engineering Hyderabad, India. Email:

ABSTRACT The continuous growth in the demand for electric power necessitates the flexibility of operation in power system. Of different power electronics-based Flexible AC Transmission System (FACTS) devices, which enhance the power transmission capabilities, Unified Power Flow Controller (UPFC) provides an emerging and promising solution for the power flow problems in the system, as it simultaneously and/or selectively controls the transmission parameters. In this context, the paper proposes the power flow control in a simple system by injecting the series compensating voltage, which is an important function of UPFC. For this purpose, ANN controller based UPFC is used. Control patterns are generated for obtaining the adjustable series voltage from the second converter that, in turn, controls the power flow in the system. With the proposed model, by varying control coefficient the series injected voltage can be adjusted. MATLAB Simulation is used to test the proposed model. The control horizon is identified and presented for various values of existing active and reactive powers. Key words: FACTS, UPFC, ANN, Power Flow Control.

1. INTRODUCTION The UPFC is conceptually a Synchronous Voltage Source (SVS) [1, 2] which generates the adjustable voltage on the ac side. The voltage source exchanges both active power and reactive power with the transmission system. The UPFC consists of two-voltage source converters, one in series and one in shunt in a transmission line. Both using switching elements and operated from a common dc storage element as shown in Fig.1.1. This configuration facilitates free flow of real power between ac terminals of two converters in either direction while enabling each converter to independently generate or absorb reactive power at its own ac terminals. The series converter referred as converter 2 shown in Fig. 1.2 injects a

Fig. 1.1 Two-converter model of UPFC voltage with controllable magnitude vi and phase angle ρ in series with the line via an insertion transformer, there by providing main function of UPFC. Electric power flow through an alternating current transmission line depends on the line parameters and complex voltages at the sending end and receiving end of the line. The adjustable voltage at one end of the line would allow us to control the power flow through the line [3]. A voltage magnitude and phase angle at a particular point in a transmission system can also be adjusted by using more advanced device like UPFC. This paper presents the use of twoconverter model of UPFC with ANN controller for power flow problem.


Journal of Theoretical and Applied Information Technology
© 2007 JATIT. All rights reserved.

system as shown in figure 2. Some other lines also may be connected parallel in with the above line. Assuming that receiving end voltage Vr of the line maintained constant. When the line is represented by a two-port network with generalized ABCD constants, The active power Pr and reactive power Qr at the receiving end of the line can be written as [4] Fig.1.2. Conceptual representation of UPFC with two-machine system Basically, the UPFC control system can be divided functionally into two units concerning internal and external controls [1]. The internal control unit operates the two inverters so as to produce the commanded series injected voltage, and simultaneously draws the desired shunt real and reactive currents from the shunt inverter by controlling a proper output voltage at its...

References: [1] Hingorani, N. G. and Gyugyi, L. Understanding of FACTS. IEEE Press, New York. 1999.
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