Enhancement of Power Quality by Using Shunt Hybrid Power Filter With TCR D. Srikanth1, V. Sreepriya2 1

Transcription

1 IJSEAT, ol 2, Isse 12, December Enhancement of Power Qality by Using Shnt Hybrid Power Filter With TCR D. Srikanth1,. Sreepriya2 1 M. Tech scholar, Department of EEE, S.R Engineering College, Warangal, T.S, Ina Assistant Professor, Department of EEE, S.R Engineering College, Warangal, T.S, Ina 2 Abstract:- This paper presents a thyristor-controlled reactor (TCR) in combination with a fifth-tned C passive filter and active power filter (APF) in order to compensate the reactive power and to redce harmonics.in adtion, it redces significantly the voltampere rating of the APF part. The shnt hybrid power filter (SHPF) is the combined system of a small-rating APF connected in series with a fifth-tned C passive filter. A control scheme based on proportional-integral controller has been sed to mitigate the harmonics and reactive power.the proposed system also helps in achieving a low cost highly effective control. Keywords- Power Qality, harmonics, shnt hybrid power filter, thyristor-controlled reactor, reactive power. I. INTRODUCTION Now a day s power electronic eqipment s are mostly sed in indstrial and domestic prpose. This eqipment s have major impact on the qality of spply voltage and have increased the harmonic crrent content of stribtion systems. They have many negative effects on stribtion system side eqipment s and cstomer, sch as adtional losses in overhead and ndergrond cables, transformers and rotating electric machines, problem in the operation of the protection systems, over voltage and shnt capacitor, error of measring instrments, and malfnction of low efficiency of cstomer sensitive loads.the most important power qality problems are harmonics and high netral crrent.the definition of power qality given in the IEEE ctionary originates in IEEE Std1100: Power qality is the concept of powering and gronng sensitive eqipment in a manner that is sitable to the operation of that eqipment. Power qality problems are common in most of commercial and indstrial networks. Natral phenomena, sch as lightning are the most freqent case of power qality problems.also, the connection of high power non-linear loads contribtes to the generation of crrent and voltage harmonic content the major and critical power qality problems are voltage sags de to the high economical losses that can be generated [1]. For all these reasons, from the consmer point of view, power qality isses will become an increasingly important factor to consider in order satisfying good prodctivity. On the other hand, for the electrical spply indstry, the qality of power delivered will be one of the stingishing factors for ensring cstomer loyalty in this very competitive and dereglated market. Reactive power, Power factor, Harmonic stortion and oltage nbalance in power spply are the major problems of power qality. Accorng to IEEE-519, total harmonics stortion is defined as the smmation of the effective vale of the harmonics components in the storted waveform relative to the fndamental component. Passive filter have been sed trationally for minimizing the stortion de to harmonic crrent in indstrial power systems. Bt they have many drawbacks sch as resonance problem, dependency of their performance on the system impedance, absorption of harmonic crrent of nonlinear load, which cold lead to frther harmonic propagation throgh the power system [2].To overcome those problems active power filters is introdced. It has no sch drawbacks like passive filter. They inject harmonic voltage or crrent with appropriate magnitdes and phase angle into the system and cancel harmonics of nonlinear loads [9]. Bt it has also some drawbacks like high initial cost and high power losses de to which it limits there wide application, especially with high power rating system [3]. To minimize these limitations, hybrid power filter have been presented and implemented in practical system applications[4] - [8]. Shnt hybrid filter consists of an active power filter which is connected in series with the passive filter and with a three phase PWM inverter. This filter effectively mitigates the problem of a passive and active filter when sed alone. It provides cost effective harmonic compensation, particlarly for high power nonlinear load [5]. Several filter topologies for compensating harmonics and reactive power have been proposed in the literatre [9] [12]. In [9], a mlticonverter contioner topology formed by an activecontioner operating in parallel with a hybrid contioner hasbeen proposed. The hybrid contioner is a combination of one or morepassive filters in series with a low-rated active power filter(apf). The contioner compensates harmonic stortion, imbalance,and reactive power in three-phase for-wire systems.this topology constittes an effective soltion Page 936

2 IJSEAT, ol 2, Isse 12, December at high-powerlevels, which is cost-effective becase of the kilovoltampererating redction of the inverters. A hybrid consists of a three-phase three-level netral pointclamped (NPC) inverter and a series connection of a three-levelh-bridge inverter with a novel control scheme to control thefloating voltage sorce of the Hbridge stage has been introdced in [10]. In this topology, the NPC inverter is sed to spplythe total active power while the H-bridges operate as seriesactive filters for the harmoniccompensation of the NPC otptvoltage. The rating of the series active filter is redced becaseit provides only the reactive power for the operationof the floating capacitor.different control techniqes are present for extracting harmonic components of the sorce crrent. Some of them are synchronos reference frame (SRF) transformation, instantaneos power (p-q) theory, etc. where high pass filters (HPF) are sed or extracting harmonic components of the sorce crrent from the fndamental components [6]. The proposed combination of SHPF and TCR is as shown Fig. 1 which compensates the reactive power and redces harmonic crrents. In adtion, it redces significantly the volt-ampere rating of the APF part. The SHPF consists of a small-rating APF connected in series with a fifth-tned Cpassive filter. The APF consists of a three-phase fll-bridge voltagesorce plse wih modlation (PWM) inverter with an indctor (,R ) and a dc bs capacitor (C ). The APF sstains very low fndamental voltages and crrents of the power grid, and ths, its rated capacity is greatly redced.considering the above mentioned merits, the presented combined topology is very appropriate in compensating reactive power and eliminating harmonic crrents in power system. The tned passive filter in parallel with TCR forms a shnt passive filter (SPF). This latter is mainly for fifth harmonic compensation and power factor correction. The small-rating APF is sed to mitigate the harmonics generated by the load and the TCR by enhancing the compensation characteristics of the SPF aside from eliminating the risk of resonance between the grid and the SPF. The TCR goal is to obtain a reglation of reactive power.the simlation reslts are listed in comparison of fferent control strategies and for the verification of reslts. II. MODEING AND CONTRO OF SHPF A. Modeling of SHPF The system eqations are first elaborated in 123 reference frame. Using Kirchhoff s voltage law, one can write d C d C d d C 1 i The switching fnction C of the k (for k 1, 2, 3) is defined as C (1) leg of the converter 1 if s is on and s is off 0 if s is off and s is on A switching state fnctiond { 1 3 (2) is defined as ( )} (3) Moreover, the absence of the zero seqence in the ac crrents and voltages and in the [d ] fnctions leads to the following transformed model in the three-phase coornates R i d v v v R i d v v v R i d v v v C d i d i cos cos d i (4) However, the model is time invariant dring a given switching state. Frthermore, the principle of operation of the SHPF reqires that the three state variables have to be controlled independently. The interaction between the inner crrent loop and the oter dc bs voltage loop can be avoided by adeqately separating their respective dynamics. Since the steady state fndamental components are sinsoidal, the system is transformed into the d-q reference frame at constant spply freqency. The conversion matrix is cos sin sin sin (5) Page 937

3 IJSEAT, ol 2, Isse 12, December Fig. 1 Basic Circit of SHPF-TCR Compensator Where θ ωt and the following eqalities hold: Cdq123 (C123dq)1 (C123dq)T. Then, by applying dqtransformation, the state space model of the system in the synchronos reference frame is obtained. B. Controlling of Harmonic Crrent A nonlinear control of SHPF is developed for crrent tracking and voltage reglation prposes. It is based on a decopled control strategy, which considers that the controlled system may be vided into an inner fast loop and an oter slow dc voltage loop, is adopted. Note that the first and the second time derivative TCR capacitor voltages have no significant negative impact on the performance of the proposed control techniqe becase their coefficients are too low. Conseqently, they can practically be ignored. By sing the d-q transformation, the decopled dynamics of the crrent tracking is obtained. The crrents idand i can be controlled independently. Frthermore, by sing proportional integral compensation, a fast dynamic response and zero steady- state errors can be achieved. The expressions of the tracking controllers are 1C ω R 1C ω i k i k k i k 1C ω R i i 1C ω i (6) Where i i*d idand i i*q i are crrent errors and i*dand i*qdenote the reference signals of idand i respectively. The transfer fnction of the proportional integral controllers is given as U (s) k G (s) k s i (s) U (s) k G (s) k (7) s i (s) Page 938

4 IJSEAT, ol 2, Isse 12, December C Fig. 2 Inner Control oop of the Crrent id The inner control loop of the crrent is shown in Fig. 2. The closed-loop transfer fnctions of the crrent loops are k I (s) I (s) A s k I (s) (s) I A s k k (8) Where A (1 CPFT ω2) Tand B R (1 CPFT ω2). The closed-loop transfer fnctions of the crrent loops have the following form I (s) 2ζω I (s) s 2ζω s ω (9) whereω is the oter loop natral anglar freqency and ζ isthe damping factor. For the optimal vale of the damping factor ζ 2/2, the theoretical overshoot is 20.79%. The following design relations can be derived k k 2ζ 1C ω R 1C ω k k 1C ω ω (10) Note that the inpts q and q consist of a nonlinearity cancellation part and a linear decopling compensation part. C. DC Bs oltage Reglation The active filter prodces a fndamental voltage which is in-phase with fndamental leang crrent of the passive filter. A small amont of active power is formed de to the leang crrent and fndamental voltage of the passive filter and it delivers to the dc capacitor. Therefore, the electrical qantity adjsted by the dc-voltage controller is conseqently. The oter control loop of dc bs voltage is as shown in Fig. 3. To maintain eqal to its reference vale, the losses throgh the active filters resistive-indctive branches will be compensated by acting on the spply crrent eqation(4) can be rewritten as d R d i (11) The three-phase filter crrents are given by sin 2 2 sin (12) sin 3 The fndamental filter r.m.s crrent I is i I (13) 3 Fig. 3 oter control loop of the dc bs voltage The q-axis active filter voltage q Z is expressed as i (14) Where ZPF1 is the impedance of the passive filter at 60 Hz and i*q1 is a dc component. q i (15) The control effort of the dc voltage loop is dedced i Z i (16) The dc component will force the SHPF-TCR compensator to generate or to draw a crrent at the fndamental freqency. To reglate the dc voltage the error *dc ispassed throgh a PI-type controller given by k k (17) The response of the dc bs voltage loop is a second-order transfer fnction and has the following form: (s) 2ζω (s) s 2ζω s ω (18) The closed-loop transfer fnction of dc bs voltage reglation is given as follows: Page 939

5 IJSEAT, ol 2, Isse 12, December (s) (s) s (19) Where is the average vale of dc voltage which iseqal to 50volts.The proportional k and k integral gains are then obtained as follows: k 2ζ ( C / 3ZPF1Ic), k ω2nv ( C / 3ZPF1Ic). III. MODEING AND EXTRACTION OF FIRING ANGE OF TCR TCR eqivalent circit is as shown in Fig. 5. Using Kirchhoff s voltage law, the following eqations in 123 reference frame are obtained d d d d d (20) Fig. 5 TCR eqivalent circit Applying Park s transformation to above eqation we get ( ) ( )ωi ωi R i d Fig. 4 Schematic agram of SHPF and TCR controller By designing the dc bs voltage loop mch slower than the crrent one, there wold not be any interaction between the two loops. The controller of the proposed SHPF and TCR system is as shown in Fig. 4. The system parameters are given in Table I. TABE I: SYSTEM PARAMETERS ine to ine sorce voltage and freqency ine impedance Nonlinear load inear load Passive filter parameters Active filter parameters DC bs voltage of APF of SHPF Switching freqency Inner controller parameters Oter controller parameter Ct off freqency of the low pass filters TCR indctance C 208,f 60 Hz 0.5 mh, R 10 mh, R 20 mh, R 1.2 mh,c 3000 μf,r 0.1 Ω 27 Ω 27 Ω 240 μf 1 kω Hz K K K K K 0.26, K 42 F 70 Hz 25 mh ( ) ( )ωi R i d (21) ωi The reactive part is chosen to control the reactive crrent so that 0 and T(α)ωi 0 B( )ω ωi dnqdc(22) R i Where B (α) 1/ ( )ω is the ssceptance. An eqivalent inpt is defined as (23) Accorng to this expression, one dedces B(α) ω ωi R i d (24) π 2π 2 sin(2 ) The ssceptance is given by (25) On the other hand, the eqivalent indctance is given by ( ) B( ) B Where B 1/PFω0. 2π 2 sin(2 ) π (26) Page 940

6 IJSEAT, ol 2, Isse 12, December Fig.8 TCR controller Fig.6. Ssceptance verss firing angle. Fig.6. illstrates the ssceptance verss firing angle. A PI controller is sed to force the reactive crrent of the SHPF-TCR compensator to follow exactly the reactive crrent consmed by the load. I. SIMUATION MODE AND RESUTS Simlations were performed nmerically sing the Power System Block set simlator operating nder MATAB/Simlink environment, in order to verify the operation of the proposed SHPF-TCR compensator sing the nonlinear control scheme. Fig.9 Hybrid power filter controller Fig.7, Fig.8, Fig.9, are the Simlink model of SHPF TCR compensator, TCR controller and controller of hybrid power filter respectively.here simlation is carried ot in several cases, in that 1). Proposed Hybrid Power Filter with Steady State Harmonic Generated oad. 2) Transient State Harmonic oad and 3) Transient State Harmonic and Reactive Power Generated oad. 1) Steady State Response of the System for Harmonic Generated oad Fig.7 Simlink model of proposed SHPF and TCR combination for power qality enhancement Page 941

7 IJSEAT, ol 2, Isse 12, December Fig.10Sorce oltage, Sorce Crrent, oad Crrent, Compensation Crrent, DC ink oltage. Fig.12 Sorce oltage, Sorce Crrent, oad Crrent, Compensation Crrent, DC ink oltage Fig.10 shows the Steady State Response of Sorce oltage, Sorce Crrent, oad Crrent, Compensation Crrent and DC ink oltage of the SHPF-TCR Compensator on Harmonic Generation oad. Fig.12 shows the Transient Response of Sorce oltage, Sorce Crrent, oad Crrent, Compensation Crrent and DC ink oltage of the SHPF-TCR Compensator on Harmonic Generation oad. 3) Transient State Response of the System for Harmonic and Reactive Power Generated oad Fig.11FFT Analysis of Sorce Crrent Fig.11shows FFT Analysis of Sorce Crrent of the SHPF-TCR Compensator on Harmonic Generation oad, attains THD as 0.90%. 2) Transient State Response of the System for Harmonic Generated oad Fig.13 Sorce oltage, Sorce Crrent, Harmonic oad Crrent, Compensation Crrent, DC ink oltage and Reactive oad Crrent Fig.13 shows the Sorce oltage, Sorce Crrent, Harmonic oad Crrent, Compensation Crrent, DC ink oltage and Reactive oad Crrent of the Dynamic response of SHPF-TCR compensator nder the harmonic and reactive power type of loads. Fig.14 FFT Analysis of Sorce Crrent of the SHPFTCR Compensator on Harmonic and Reactive Power Generation oad attains THD as 0.88%. Page 942

8 IJSEAT, ol 2, Isse 12, December Fig.14FFT Analysis of Sorce Crrent. CONCUSION In this paper a SHPF TCR compensator is proposed in order to sppress the crrent harmonics and reactive power compensation generated by the load. In adtion, it redces significantly the volt-ampere rating of the APF part. The control circit for the SHPF and the TCR are also explained. A control techniqe is proposed to improve the dynamic response and decrease the steady-state error of the TCR. The otpt of the system for varios contions had been explained with the help of the simlation reslts. The performances of the SHPF TCR compensator for steady state and transient state of varios harmonic and reactive loads are fond to be effectively eliminated the crrent harmonics and reactive power compensation. It has been shown that the system has a fast dynamic response, has good performance in both steady-state and transient operations, and is able to redce the THD of spply crrents. REFERENCES [1] E. F. Fchs and M. A. S. Masom, "Power Qality in Electrical Machines and PowerSystems," Academic Press, USA, [2] J. C. Das, "Passive filters; potentialities and limitations, IEEE Trans. on IndstryApplications, ol. 40, pp , [3] B. Singh, K. Al-Haddad, and A. Chandra, A review of active filters for power qalityimprovement, IEEE Trans. Ind. Electron., vol. 46, no. 5,pp , Oct [4]. Asiminoaei, E. Aeloiza, P. N. Enjeti, and F. B laabjerg, Shnt active-power- filtertopology based on parallel interleved inverters, IEEE Trans.Ind. Electron. vol. 55, no.3, pp , Mar [5] H. Fjita, H. Akagi, "A practical approach to harmonic compensation in power systems;series connection of passive and active filters," IEEE Trans. on Indstry Applications,ol. 27, pp , [6]. Asiminoaei, E. Aeloiza, P. N. Enjeti, and F. B laabjerg, Shnt active-power- filtertopology based on parallel interleaved inverters, IEEE Trans.Ind. Electron. vol. 55, no.3, pp , Mar [7]B. Singh,. erma, A. Chandra, K. Al-Haddad, "Hybrid filters for power qalityimprovement," IEEE Proc. on Generation, Transmission and Distribtion, ol. 152,pp , [8] Salem Rahmani, AbdelhamidHama, NassarMendalek, and Kamal Al-Haddad, A New Control Techniqe for Three-Phase Shnt Hybrid Power Filter, IEEETransactions on indstrial electronics, vol. 56, no. 8,pp , agst [9] M. I. Milanés-Montero, E. Romero-Cadaval, and F. Barrero-González, Hybrid mlticonverter contioner topology for high-power applications, IEEE Trans. Ind. Electron., vol. 58, no. 6, pp ,Jn [10] C. A. Silva,. A. Cordova, P. ezana, and. Empringham, Implementationand control of a hybrid mltilevel converter with floating dc linksfor crrent waveform improvement, IEEE Trans. Ind. Electron., vol. 58,no. 6, pp , Jn [11] A. o, S. Peng, C. W, J. W, and Z. Shai, Power electronic hybridsystem for load balancing compensation and freqency-selective harmonicsppression, IEEE Trans. Ind. Electron., vol. 59, no. 2, pp , Feb [12] A. o, Z. Shai, W. Zh, and Z. John Shen, Combined system forharmonic sppression and reactive power compensation, IEEE Trans.Ind. Electron., vol. 56, no. 2, pp , Feb DADI SRIKANTH crrently prsing his M.Tech in Power Electronics from S.R Engineering College (Atonomos), Warangal, Telangana, Ina, affiliated to JNTU, Hyderabad. He has done his B.Tech degree from S..S Institte of Technology, affiliated to JNTU, Hyderabad, Telangana, Ina and his fields of interest inclde Power Systems.. SREEPRIYA received her B.Tech degree in Electrical and Electronics Engineering from JNTU, Hyderabad, the M.Tech degree in Power Electronics from JNTU, Hyderabad, Telangana state and she is crrently working as Assistant Professor, EEE department at S.R Engineering College (Atonomos), Affiliated to JNTU, Hyderabad, Telangana, Ina. Page 943