The use of Facts devices in disturbed Power Systems-Modeling, Interface, and Case Study

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1 nternational Journal of Computer an Electrical Engineering, ol., No., April The use of Facts evices in isturbe Power Systems-Moeling, nterface, an Case Stuy Salim. Haa, A. Haouche, an H. ouyea Abstract This paper escribes the theory an simulation by matlab of flexible Alternative Current Transmission Systems (FACTS) evices use in the isturbe power systems. One of these evices, Unifie Power Flow Controller (UPFC) will be chosen for a specific application, etaile in this paper. Simulation investigate the effect of UPFC on the voltage of the relate bus, it s also consiers the effect on the amount active an reactive power flowing through the transmission system. Finally simulation results have been presente to inicate the improvement in the performance of the UPFC to control voltage in isturbe power systems. nex Terms Facts, UPFC, Power Systems, isturbances, nterface, Moelling, Controls.. NTRODUCTON The power electronic base flexible AC transmission systems (FACTS) have been evelope an use as economical an efficient means to control the power transfer in the interconnecte AC transmission systems []. This allows forcing the power transit in the lines with higher transmission capacity [], [3]. Among the FACTS components, Unifie Power Flow Controller (UPFC), is the most complete. t is able to control inepenently the throughput active an reactive powers. The UPFC is capable to act over three basic electrical system parameters [4]: line voltage, line impeance, an phase angle, which etermine the transmitte power. Power Flow through an alternative current line is a function of the line impeance, the magnitue of the sening-en an receiving-en voltage an the phase angle between these voltages [4]. The power flow can be increase, firstly by ecreasing the line impeance with a capacitive reactance, seconly by increasing the voltages an finally by increasing the phase angle between these voltages. n our work, the power flow is controlle by controlling the sening an receiving bus voltage. Also, the control of the shunt an series element of the UPFC will be stuie in this paper. an reactive line flows (P, Q). The phase angle regulator type can be use to control active power flow. Table () lists the several types of existing an propose FACTS evices. These types are terme A,, an C here for convenience. [5] TALE : TYPES OF FACTS DECE MODELS Type Parameter esignation controlle FACTS evices Type A Series P an Q UPFC Type Series P TCSC, phase angle regulator Type C Series Q SC, STATCON These figures show types (a), (b), an (c) FACTS evices (a) (b). TYPES OF FACTS DECES The types of FACTS evices currently available can be categorize into evices that control certain electrical parameters. For example the UPFC can use to control active Mechanic s Department Skika University Electro mechanic s Department Annaba University Electronics Department Annaba University

2 nternational Journal of Computer an Electrical Engineering, ol., No., April real/reactive power flows by injecting a series voltage of ajustable magnitue an phase angle. The UPFC can provie multiple power flow control functions by aing the injecte voltage phasor with appropriate magnitue se an phase angle Ө to the sening-en-voltage phasor [8]. (c) Fig. Moels of a Type (a), (b), an (c) FACTS evices. UNFED POWER FLOW (UPFC) CONCEPT The UPFC configuration is shown in fig. Fig. asic Structure of an UPFC t can be seen. That the UPFC consists of a series an a shunt converter is connecte back-to-back through a common c link. The shunt converter is connecte also in parallel with the line transmission by transformer, allows controls the UPFC bus oltage/shunt reactive power an the c capacitor voltage [6]. Fig. 4 Series oltage njecte Phasor iagrams. As illustrate in figure 4, by the appropriate choice (control) of phasor se, the three customary power flow control functions: ) oltage regulation ) Series reactive compensation. 3) Phase Shift. Simultaneous control of terminal voltage, line impeance an phase angle allows the UPFC to perform multifunctional power flow control.. UPFC MATHEMATCAL MODEL n orer to simulate a power system that contains a UPFC, the UPFC nees to be moelle. Fig shows a iagram for UPFC; all the variables use in UPFC moel are enote in fig with bol fonts representing phasors [9]. Per unit system an MKS units are jointly use in moelling. The ac system uses par unit system with its variables calculate base on the system-sie S an, while the c variables are expresse in MKS units. We first consier the UPFC c link capacitor charging ynamics. The current, (see fig.5.) an the capacitor voltage an current have the following relation with harmonics neglecte [0]: = C = + () Fig.3. Power exchange of the Shunt Converter Figure 3a shows the exchange of the reactive power between the UPFC an the electrical system. The shunt converter generates a voltage s in phase with A but with variable magnitue. f s=s. The UPFC injects some reactive power, if s=s the UPFC absorbs some reactive power an no reactive power is exchange for s=a. [7]. n orer to compensate the series converter losses, figure 3b shows very clearly. That the active power is exchange between UPFC an the electrical system. The oltage generate by shunt converter is no it in phase with the voltage of the system but of the same magnitue [7]. Whereas the series converter of the UPFC controls the transmission line Fig. 5 Transmission line with UPFC installe f we assume the inverters are ieal, the real power exchange with the ac system will be (P an P are in p.u.): P = S

3 nternational Journal of Computer an Electrical Engineering, ol., No., April () P = S From equation () an (), we have: (3) CC = ( P P ) S From ac system, we know that P an P calculate by: (4) P=R = R n s e e t + S pq R P=R pq L = R e e pq Applying moern PWM control technique [0] two the two voltage source converters, the relations between the inverter c-an ac-sie voltages can be expresse by: = m (5) = m Where coefficient m an m represent the PWM control effects in orer to maintain esire inverter ac-sie voltages an respectively. The esire m an m are UPFC main control outputs. an are in p.u. an is the ac system base voltage. The phase angle of ( ) an ( ) are enote as (Ө ) an (Ө ) respectively. They are controlle through firing angle (φ ) an (φ ) of two converters: S (6) S The esire φ an φ are UPFC main control outputs. Finally, taking series transformer ratio into consieration, an rewriting equations () to (6), the UPFC power frequency moel use in ynamic stuy will be: (7) C = ( P P ) S P=R e P=R e n t pq s + = m S S pq R (8) (9) = m pq /n pq s The esire m, φ, m an φ can be obtaine from UPFC main control system, therefore base on equation (9) together with UPFC control system equations an ac network interface equation.. NTERFACE OF UPFC TO THE AC NETWORK The interface calculation of UPFC to ac network will have significant impacts on transient stability [0]. Fig. 6 The nterface of the UPFC to the network n the interface calculation we assume that the bus amittance matrix has been reuce to generator internal buses with UPFC ac terminal buses remaine. The corresponing reuce bus amittance matrix takes the form: (0) Y E Y G G G G G U = Y Y U G U U U U E G : Generator internal voltage. G : Generator internal voltage. U : ac terminal bus voltages of the UPFC. The UPFC currents injecting to the ac network can be expresse by: n + pq = n S S R U t S pq R () + U = t t is clear that in equation (), though the UPFC output voltage magnitues an pq can be known from control output an equation (3), (4), an (9). The phase angles of an pq are unknown since they epen on the phase angle of s. the phase angle of s is unknown that shoul be obtaine from the network solution. Therefore an iteration approach is require to obtain the network solution. Substituting equation () into equation (0), an rearranging the secon equation of equation (0), we finally have:

4 nternational Journal of Computer an Electrical Engineering, ol., No., April n Y Y Y Y ( ) G+ G+ R + + SS RS + + S SR RR t n = t = G Y Y R RS S RR pq Y SS YSR G Y an Y EG UU UG YY = = G RS RR f we efine a constant matrix: n Y + Y + Y + Y RS SR RR SS t Y = UU Y Y + RS RR We have: G G ( ) n + t = U pq G () (3) Y = (4) UU U U The equations from (3) to (4) are use for iteration of UPFC network interface as follows: A. STEP : Estimates the initials voltages of sening an receiving buses an calculate current base in equations (3) an (9).. CASE STUDY Fig.7 the Algerian ELHajar s Complex Power System. A. Disturbances Simulation The simulate system is an M Electrical Network of EL-Hajar Steel-making complex in Algeria. The system is shown in Fig.7. This latter functions with a lot such problems: Flicker, Harmonics an Asymmetric currents. These latters are ue to the presence of furnaces in the complex. To simulate the effect of the UPFC on power system, we have use Matlab. The UPFC was installe between buses (S) an (Y), an the shunt branch was connecte to the bus S. the effect of the series branch of the UPFC on the transmission power between buses (S) an (Y). First of all, we have to choose the references: oltage in buses (S) an (Y): = p.u. Real an reactive Power in furnace bus: P=0.8 p.u./q=0.6 p.u. To the instant t=s, we change the references in furnace us, so that they become: P=0. p.u./q=. p.u. Then, to the instant t=3s we put back the initial references.. SMULATON RESULTS.STEP : Solve equation (4) for ifference of the initials voltages values. f the ifference is less than the given tolerance for new value of sening an receiving voltages are consiere as the solution of equation (). Otherwise go to step 3. C. STEP 3: Upate initial voltages an repeat steps an till convergence is reache. Fig. 8 Disturbances simulation results

5 nternational Journal of Computer an Electrical Engineering, ol., No., April We notice that the voltages at buses (Y) an (S) follow their orer even the isturbances that happene at furnace buses.. CONCLUSON n this paper, the compensation of an electrical system by using UPFC-FACTS evice has been stuie. Two important coorination problems have been aresse in this paper relate to UPFC control. One, the problem of real power coorination between the series an the shunt converter control system. Secon, the problem of excessive UPFC bus voltage excursions uring reactive power transfers requiring reactive power coorination. The simulation results, obtaine by Matlab show the efficiency of UPFC, in controlling line both active an reactive power flow. REFERENCES [9] Le DU A., Pour un réseau électrique plus performant: l e projet FACTS RGE n 6/9, juin 99, pp [30] Saeghazaeh S.M., Ehsan M., Hajsai N., Application of FACTS evices for the maximum lauability improvement in transmission line, EPE 97, Tronheim, 8-0 sept, vol.3, pp [3] elcheheb K., Saaate S., utilization of the UPFC for optimal exploitation of costly centrals in the electrical systems, PEMC 98, Prague Czech Republic, September 98. [3] L. Gyugyi, Unifie power flow control concept for flexible AC transmission systems generation, in proc. Transmission istribution conf. vol 39, July 003, pp [33] Douglas J., Hey G.T., Power flow control an power flow stuies for systems with FACTS evices, in EEE transactions on power systems,vol.3,n,february 998, pp [34] J. F. Keri, Unifie Power Flow Controller (UPFC): Moeling an analysis. EEE. Trans. Power Delivery, vol. 4. pp , apr [35] S. Saaate, K. elacheheb, Comparison of three basic control methos of mains compensation by means of unifie power flow controller (UPFC), in EPE 00-Graz. [36] L. Gyugyi, Converter-ase FACTS Controllers, in the institution of electrical engineers (EE), Savoy place, Lonon 998. [37] Z. Huang, Y. Ni, C. Shen, F.F. Wu, S. Chen, an. Zhang, Application of Unifie Power Flow Controller in nterconnecte Power Systems-Moelling, nterfacing, Control Strategy an Case Stuy, in EEE transaction on power system, vol 5, May 000, pp [38] Y. Ni, Z. Hang, S. Chen, an. Zhang, ncorporating UPFC moel into power system toolbox of the Matlab for transient stability stuy, in EEE, 998, pp Salim Haa was born in Roknia, Algeria in 975. He receive his Engineer an Magister egree from Annaba University, Algeria respectively in 998 an 006. Currently; he is an assistant professor at the electromechanical epartment of Skika University, Algeria. His main research interests are focuse on power quality an especially on voltage sags, power system harmonics an flickers. Ali Haouche was born in oue zenati, Algeria in 959. He receive his Ph egree from mines institute University, Moscou URSS in 988 an. currently; he is a professor at the electromechanical epartment of Annaba University, Algeria. His main research interests are focuse on power quality an power systems protection. Hocine ouyea was born in Roknia, Algeria in 97. He receive his Engineer an Magister egree from Guelma University, Algeria respectively in 998 an 007. Currently; he is a PhD Stuent at the electronics epartment of Annaba University, Algeria. His main research interests are focuse on communication, interfacing systems