Improvement of power factor of a grid connected load system using a static compensator

Transcription

1 Science Front Publiher Journal for Foundation and Application of Phyic, ol. 1, No. 1 (2014) (ciencefront.org) ISSN Improement of power factor of a grid connected load ytem uing a tatic compenator Manoj Kumar Kar, Bidyadhar Rout and J K Moharana a Department of Electrical Engineering, Veer Surendra Sai Unierity of Technology, Burla, Odiha, India a Department of Electrical & Electronic Engineering, GITA, Bhubanewar, Odiha, India Correponding author rout.bdr@gmail.com (Receied 10 June 2014, Publihed 28 July 2014) Abtract The power factor deteriorate due to non-linear load, interconnected grid ytem, amplitude diturbance and wae hape diturbance. A low power factor ytem draw high internal current cauing exceie heat. It require heaier equipment to aborb internal energy requirement. Alo large penalty i impoed on low power factor conumer. So power factor hould be improed in order to get rid of the aboe problem. In thi paper, a hunt connected Flexible AC Tranmiion Sytem (FACTS) deice uch a Static Compenator (STATCOM) i ued to improe the power factor by compenating the reactie power required by the load Science Front Publiher Keyword: FACTS, Static Compenator (STATCOM), VSC, Sytem Meling 1. Intruction Power factor i the pruct of ditortion factor and diplacement factor. So in order to improe power factor we need to improe both. Ditortion factor can be improed by filtering out the harmonic where a diplacement factor can be improed by uing compenating deice. Preiouly the claical meth like ynchronou condener, capacitor bank were ued for compenating reactie power but haing a number of diadantage [1]. The reactie power (VAR) compenation and control hae been recognized [2-6] a an efficient and economic mean of increaing power ytem tranmiion capability and tability. The FACTS (Flexible AC Tranmiion Sytem) deice uch a STATCOM (Static Compenator) hae been intruced [6-8] more recently which employ a VSC (oltage ource conerter) with a fixed DC link capacitor that proide the required VAR control [9-11], with a rapid control of bu oltage and improement of utility power factor[12-16]. 2. Meling and Analyi Operating Principle The STATCOM i a hunt-connected deice in which output current i controlled independent of ariation of ac ytem oltage. The STATCOM i a oltage-ource conerter (VSC)- baed deice which maintain the bu oltage by injecting a ariable ac current through a tranformer and generate real (when power torage deice i aailable) and reactie power at it ac terminal. Thi enable more robut oltage upport. Thi deice need to be intalled a cloe to the enitie load a poible to maximize the compenating capability. Figure-1 STATCOM mel In mot cae, the DC oltage upport for the VSC will be proided by the DC capacitor of relatiely mall energy torage purpoe. Therefore, in teady tate condition, the actie power exchanged with the line ha to be maintained at zero a hown in figure 1. The angle between the 3-phae ytem oltage and STATCOM output oltage V o i. When the STATCOM operate with =0, the actie power ent to the ytem deice become zero while the reactie power will mainly depend on the oltage mule. If V o >, the reactie power will be ent to the 3-phae ytem from STATCOM (capacitie operation), cauing a current flow in thi direction. In the reere cae, the reactie power will be aborbed from the ytem through the STATCOM (inductie operation) and the current will flow in the oppoite direction. Finally if the mule of and V o are 5

2 Kar et al. Journal for Foundation and Application of Phyic, ol. 1, No. 1 (2014) equal, there won t be either current or reactie flow in the ytem. Sytem Mel The meling of the STATCOM i carried out under the following aumption: All witche are ideal The ource oltage are balanced The harmonic content pruced by witching action are negligible The mathematical mel of the STATCOM in d-q frame i obtained a gien below. = co in (4) 0 Steady State Analyi In the teady tate operation, all the d-q ariable are denoted a teady tate ariable. The teady tate repone of actie I cd and reactie I cq, current component of the STATCOM and DC-link oltage are obtained on ariation of in the interal of -5 to +5. The detailed teady tate repone with the Table.1 are gien below and repone ugget the tatic and dynamic condition of the STATCOM. SI No. TABLE.1 STATCOM PARAMETERS Parameter Value 1 Frequency 50 Hz 2 Angular Frequency 314 rad/ec Figure 2: Main circuit diagram of tatcom The 3-phae ytem oltage lagging with the phae angle to the STATCOM output oltage and differential form of the STATCOM current are defined in (1) and (2). inωt α = = inωt α (1) inωt α The STATCOM current i goerned by the following equation. V = - + -V (2) V The witching function S of the STATCOM i defined a in S = = in (3) in Where i the mulation index. 3 RMS Line to Line oltage 415 V 4 Coupling Reitance 1.0 ohm 5 Coupling Inductance 5.0 mh 6 DC-Link Capacitor 500 uf 7 Mulation Index Phae Angle 5 9 Load Reitance 52 ohm 10 Load Inductance 126 mh 11 Load Power Factor Deign of Controller The oltage and current gien in the equation (1) and (2) are tranformed in to d-q frame a follow d L ( icq ) = Ricq ωlicd + q (5a) dt d L ( icd ) = ωlicq Ricd + d (5b) dt The equation (5) can be mified a gien in equation (6) R ω d i cq L icq 1 q = + (6) dt i R cd ω icd L d L 6

3 Kar et al. Journal for Foundation and Application of Phyic, ol. 1, No. 1 (2014) So the equation (6) i a Multiple Input and Multiple Output (MIMO) ytem and it input and output are gien in equation (7) icq [ u ] =, [ y] = (7) icd The actie and reactie current are coupled with each other through the reactance of the coupled inductor. So it i ery eential to decouple the actie and reactie current from each other and deign the controller for getting the required alue. Deign of current controller Thi trategy attempt to decouple the d and q axe equation, o that the MIMO ytem reduce to two independent Single Input Single Output (SISO) ytem. Hence, the control input and are configured a, Licd + = ω = + ωlicq + The equation (9) gien below can be obtained by replacing (6) by (8) which i independent of each other and thu define an independent SISO ytem. R 0 icq L icq 1 = + R icd icd L 0 L (9) G I I V cq cd i = = V q d 1 = R + L (10) The tranfer function of a PI controller i, 1 Ki Gpi = K(1 + ) = K p + τ (11) K = K, K K τ = p i = L R τ = 0.3m econd K p = 5.44Ω, Ki = 10 3 Ω. rad / Deign of oltage controller Relation between dc oltage dc and dc current i dc i, 1 dc = idcdt C (8) (12) The tranfer function can be written a Vdc 1 G = = (13) I C dc Neglecting the power lo in the ource reitance and power loe in the witche, balancing the power on both ide, i = i (14) d cd dc dc idc 415 = d = = 0.52 (15) icd dc 800 The alue of K can be determined from root locu a follow 2 K 0.15, K = p = i 4. Simulation Reult The control cheme for DC link oltage, capacitor current, conerter oltage, STATCOM current and teady tate repone are obtained with MATLAB/SIMULINK with the parameter gien in Table 1. A. DC Link Voltage The ource current i regulated by the DC link oltage in the grid ytem. So the DC link oltage i kept contant acro the capacitor. On increaing the magnitude of DC link oltage, the oerhoot of all ignal decreae. Figure-3 DC Link Voltage B. Capacitor Current The current through the DC link capacitor indicate the charging and dicharging operation. The DC link capacitor contain the input ripple current of the conerter and act a the main reactie energy torage element. From the aboe equation we hae, 7

4 Kar et al. Journal for Foundation and Application of Phyic, ol. 1, No. 1 (2014) C. STATCOM Current Figure-4 Capacitor current When STATCOM controller i made ON, without changing any other load parameter, it tart to diminih for reactie demand a well a harmonic current. If the STATCOM deice are able to witch fat enough, it can alo be ued to inject harmonic current in to the main and operated a an actie harmonic filter. Steady tate Analyi Figure-6 Conerter oltage On ariation of in the interal of -5 to + 5, the following teady tate repone are obtained and gien in Figure- 7(a),7(b) and 7(c). Varie linearly according to. The teady tate alue of the decreae a the alue of mulation index increae. The reactie power ha a linear ariation according to. The actie power alway exit to coer the loe in the ytem and to maintain the DC-link oltage at the operating leel. Conerter Voltage Figure-5 STATCOM current By increaing the amplitude of the STATCOM terminal oltage,, aboe the amplitude of the utility oltage caue leading (capacitie) current to be injected to the ytem. Figure 7(a) Actie and reactie component of current 8

5 Kar et al. Journal for Foundation and Application of Phyic, ol. 1, No. 1 (2014) Grid Phae A Voltage and STATCOM Phae A current:- Figure 9 how the grid phae A oltage and STATCOM phae A current. By injecting the STATCOM current to the load improe the power factor. Figure 7(b) DC link oltage Figure 9 Grid phae A oltage and STATCOM phae A current Grid Phae A Voltage and Phae A current:- Figure 10 how the grid phae A oltage and phae A current with unity power factor. Figure 7(c) Actie and reactie component of power Grid Phae A Voltage and load Phae A current Fig. 8 how phae A load current lag behind the grid phae A oltage due to nonlinearity nature of load. The power factor in thi cae i Figure 10 Grid phae A oltage and phae A current. Figure 8 Grid phae A oltage and load phae A current 5. Concluion Thi paper preent the deign, meling and analyi of STATCOM baed control meth for improing power factor. It ue PWM technique for witching trategy. Root locu meth i ued to find the controller parameter in DC oltage controller. The operation of the control ytem for the STATCOM i performed in MATLAB/SIMULINK. STATCOM cancel out the harmonic part of the load current. It i een that the STATCOM act a a controlled reactie current ource while compenating for internal loe and maintaining the dc bu oltage to a reference alue. Thu it can improe power ytem performance. 9

6 Kar et al. Journal for Foundation and Application of Phyic, ol. 1, No. 1 (2014) REFERENCES [1] C.W.Taylor and A.L.V.Leuen Improing Power ytem tability Uing the Time-Oer oltage Capability of Large hunt Capacitor Bank, IEEE Tranaction on Power Deliery, 11(2), 783 (1996) [2] N.G.Hingorani and L. Gyugyi, Undertanding FACTS tandard publiher Ditributor New Delhi, (1999) [3] R.M.Mathur and R.K.Varma, Thyritor baed FACTS controller for Electrical Tranmiion ytem, IEEE power Engineering ociety, Wiley-Intercience Publication, (2002). [4] Y.H.Song and A.T. John Flexible AC Tranmiion Sytem(FACTS) IEE power and Energy erie Inc.(1999) [5] A.T.John, A.Ter-Gazarian and D.F.Wame, Flexible ac tranmiion ytem (FACTS), IEE power and Energy Serie, London [6] A.M.Kulkarni and K.R.Padiyar, Deign of Reactie current and oltage controller of tatic condener Electrical power and energy ytem,19(6), 397 (1997) [7] P.enarma, K.R.padiyar and V.Ramnarayanam Analyi and performance Ealuation of a DSTATCOM for compenating oltage fluctuation IEEE Tranaction on power deliery, 16(2), 259 (2001) [8] Joica V. Milanoic and Yan Zhang Meling of FACT Deice for oltage ag mitigation tudie in large power ytem IEEE Tranaction on power deliery, 25(4), 3044 ( 2010) [9] C.Hochgraf and R.H.Laeter, STATCOM control for operation with unbalanced oltage IEEE Tranaction on power deliery,13(2), 538, (1998) [10] Sharad W.Moh, Mohan V.Aware A STATCOM control cheme for Grid connected wind Energy ytem for power Quality Improement, IEEE ytem Journal,4(3), 346 (2010) [11] D.Maand, S.Jain and G.Agnihotri Control trategie for Ditribution tatic compenator for power quality improement IETE Journal of Reearch, 54(6), 421, (2008) [12] Amit Jain, Karan Johi, Aman Behal and Ned Mohan Voltage regulation with STATCOM: Meling, control and reult IEEE Tranaction on power deliery, 21(2), 726 (2006) [13] P.W.Lehn and M.R.Iraant Experimental Ealuation of STATCOM cloed loop Dynamic IEEE Tranaction on power deliery, 13(4), 1378 (1998) [14] B.Lin and Y.C.Lee, Three-phae power Quality compenator under the unbalance ource and nonlinear load, IEEE Tranaction on Indutrial Electronic,51(5), 1009 (2004) [15] B.S.Chen and Y.Y.Hu A minimal harmonic controller for a STACOM IEEE Tranaction on Indutrial Electronic,55(2), 655 (2008) [16] H.Karhena, H.Korjic and S.Dewan Generalied technique of electie harmonic elimination and current control in current ource inerter/conerter IEEE Tranaction on power Electronic,10(5), 566 (1995) 10