HARMONIC ANALYSIS USING SHUNT ACTIVE FILTER

Transcription

1 HARMONIC ANALYSIS USING SHUNT ACTIVE FILTER 1 MS. POORVI M. PARMAR, PROF. M.V. MAKWANA 1 M.E.[Power Electroncs] Student, Power Electro. Dept., L.E College, Morb, Gujarat Asso. Professor, Power Electroncs Engneerng, L.E College, Morb, Gujarat. poorv_el@yahoo.com, shafmakwana@gmal.com ABSTRACT: Power system harmoncs are a menace to electrc power systems wth dsastrous consequences. The lne current harmoncs cause ncrease n losses, nstablty, and also voltage dstorton. Wth the prolferaton of the power electroncs converters and ncreased use of magnetc, power lnes have become hghly polluted. Actve flters have been used near harmonc producng loads or at the pont of common couplng to block current harmoncs. Shunt flters stll domnate the harmonc compensaton at medum/hgh voltage level, whereas actve flters have been proclamed for low/medum voltage ratngs. Wth dverse applcatons nvolvng reactve power together wth harmonc compensaton, passve flters are found sutable.the necessary modellng and smulatons are carred out n MATLAB usng SIMULINK and power system block set toolboxes. Installng a flter for nonlnear loads connected n power system would help n reducng the harmonc effect. The flters are wdely used for reducton of harmoncs. Wth the ncrease of nonlnear loads n the power system, more and more flters are requred. actve flter are desgned and analyzed to mprove the power qualty at ac mans. Keywords harmoncs, flter, actve flter I: INTRODUCTION The growng use of non-lnear and tme-varyng loads has led to dstorton of voltage and current waveforms and ncreased reactve power demand n ac mans. Harmonc dstorton s known to be source of several problems, such as ncreased power losses, excessve heatng n rotatng machnery, sgnfcant nterference wth communcaton crcuts and audble nose, ncorrect operaton of senstve loads. Passve flters are tradtonal method to elmnate harmoncs, but wth recent developments n power semconductor swtches and converters, coupled wth developments n control technques and analog and dgtal mplementatons, actve flters are becomng an effectve and commercally vable alternatve to passve flters. Actve flter offer the followng advantages: able to cover a wde range of harmonc frequences; do not contrbute resonant frequences to the network; harmonc attenuaton s network mpedance dependent. Among the varous topologes the shunt actve power flter based on voltage source nverter (VSI) s the most common one because of ts effcency. The performance of actve power flters depends on the adoptve control approaches. Varous current detecton methods, such as nstantaneous reactve power theory, synchronous reference frame method. The commonness of these methods s the request for generatng reference current of APF, ether wth the load current or the mans current. The commonness of these methods s to control VSI wth the dfference between real current and reference current. II: ACTIVE POWER FILTER A flexble and versatle soluton to voltage qualty problems s offered by actve power flters. The basc prncple of APF s to utlze power electroncs technologes to produce specfc currents components that cancel the harmonc currents components caused by the nonlnear load. Currently they are based on PWM converters and connect to low and medum voltage dstrbuton system n shunt or n seres. Seres actve power flters must operate n conjuncton wth shunt passve flters n order to compensate load current harmoncs. Shunt actve power flters operate as a controllable current source and seres actve power flters operates as a controllable voltage source. Both schemes are mplemented preferable wth voltage source PWM nverters, wth a dc bus havng a reactve element such as a capactor. Actve power flters can perform one or more of the functons requred to compensate power systems and mprovng power qualty.[11] III: Types of Actve Power flter Manly there are three types of actve power flter: Based on the converter type VSI Inverter CSI Inverter Based on topology Actve Shunt Flter ISSN: NOV 1 TO OCT 13 VOLUME 0, ISSUE - 0 Page 34

2 Actve seres Flter Hybrd flter Based on supply system AC Source S Vf L Nonlnear load 1-Phase- wre system 3-Phase -3 wre system 3-Phase-4 wre system 3.1 SHUNT ACTIVE POWER FILTERS Cf Shunt actve power flter compensate current harmoncs by njectng equal-but-opposte harmonc compensatng current. In ths case the shunt actve power flter operates as a current source njectng the harmonc components generated by the load but phase shfted by 180o. Ths prncple s applcable to any type of load consdered a harmonc source. Moreover, wth an approprate control scheme, the actve power flter can also compensate the load power factor. In ths way, the power dstrbuton system sees the non lnear load and the actve power flter as an deal resstor. [11] A C S o rc e S L f L N o n ln e a r lo a d F Fg 3.1 shunt actve power flter [1] V S I 3. SERIES ACTIVE POWER FILTER C f Seres APF s connected n seres wth the dstrbuton lne through a matchng transformer. VSI s used as the controlled source, thus the prncple confguraton of seres APF s smlar to shunt APF, except that the nterfacng nductor of shunt APF s replaced wth the nterfacng transformer. Here operaton prncple of seres APF s based on solaton of the harmoncs n between the nonlnear load and the source. Ths s obtaned by the njecton of harmonc voltages across the nterfacng transformer Seres APFs are less. Here resultng hgh capacty of load currents wll ncrease ther current ratng consderably compared wth shunt APF, especally n the secondary sde of the nterfacng transformer. Ths wll ncrease the IR losses. Here advantage of seres APFs over shunt one s that they are deal for voltage harmoncs elmnaton.[1] VSI Fg 3. seres actve power flter [1] It provdes the load wth a pure snusodal waveform, whch s mportant for voltage senstve devces (such as power system protecton devces). Wth ths feature, seres APF s sutable for mprovng the qualty of the dstrbuton source voltage [1] IV. CONTROL STRATERGIES 4.1 SRF CONTROLLER IMPLEMENTATION The synchronous reference frame theory or d-q theory s based on tme-doman reference sgnal estmaton technques. It performs the operaton n steady-state or transent state as well as for generc voltage and current waveforms. It allows controllng the actve power flters n real tme system. Another mportant characterstc of ths theory s the smplcty of the calculatons, whch nvolves only algebrac calculaton. The basc structure of SRF controller conssts of drect (d-q) and nverse (d-q)-1 park transformatons as shown n fg. These can useful for the evaluaton of a specfc harmonc component of the nput sgnals. Fg 4.1 Synchronous d-q reference frame based compensaton algorthm[6] These three phase space vectors statonary coordnates are easly transformed nto two axs d- q rotatng reference frame transformaton. Ths algorthm facltates dervng d-q(rotatng current coordnate) from three phase statonary coordnate load current La.Lb Lc, as shown n equaton[6] ISSN: NOV 1 TO OCT 13 VOLUME 0, ISSUE - 0 Page 343

3 The d-q transformaton output sgnals depend on the load current (fundamental and harmonc components) and the performance of the Phase Locked Loop (PLL). The PLL crcut provdes the rotaton speed (rad/sec) of the rotatng reference frame, where ωt s set as fundamental frequency component. The PLL crcut provdes snѳ and cosѳ. The d-q current are sent through low pass flter (LPF) for flterng the harmonc components of the load current, whch allows only the fundamental frequency components. The LPF s a second order Butterworth flter, whose cut off frequency s selected to be 50 Hz for elmnatng the hgher order harmoncs. Sfa Sfb sfc Sha Sa Shb Sb Shc Sc Sfα Sfβ Sfa Sfb Sfc In the synchronously rotatng D-Q reference frame, the components at the fundamental frequency are transformed to DC quanttes and all the harmoncs are transformed to non DC quanttes. SRF controller extracts the DC quanttes by a low pass flter and hence t s nsenstve to phase error. The seres actve flter s current controlled wth the 3 phase fundamental supply current references sa, sb, sc. The SRF controller realzes the seres actve flter nverter as a current controlled harmonc voltage source whch njects only harmonc voltage and zero fundamental frequency voltage nto the supply lne and consequently does not handle any fundamental VA. [5][6] Equaton used for converson: Convertng 3 phase to phase (abc-alpha beta) 1 1 Sα Sβ Convertng alpha beta to DQ SD SQ cos sn 1 3 ( wt ) sn( wt ) ( wt ) cos ( wt ) Sa Sb Sc Sα Sβ v v v Ths voltage s used to produce PWM sgnal. 4. P-Q THEORY af bf cf K Sha Shb Shc The p-q theory s tme doman method often called nstantaneous reactve power theory. Ths theory s vald for steady state and transent operaton as well as generc operaton current and voltage waveform. The actve power flter s expected to generate the approprate compensatng voltage/current sgnals that cancel the harmonc and reactve power components n the voltage/currents from the mans. The reference compensaton sgnals are generated by makng use of a control algorthm. The p-q theory s based on a set of nstantaneous powers defned n the tme doman. No restrctons are mposed on current or voltage wave forms and t can be appled to three phase system wth or wthout a neutral wre. Ths theory s advantageous due to easy algebrac calculaton.[3] Convertng DQ to alpha beta Sfα Sfβ cos sn ( wt ) sn ( wt ) SdcD ( ) ( ) wt cos wt SdcQ Convertng phase to 3phase (alpha beta-abc) Fg 4. p q theory Instantaneous reactve power theory (IRPT) uses the park transform, to generate two orthogonal rotatng vectors (α and β) from the three phase vectors (a, b and c). Ths transform s appled to the voltage and current and s gven by eqn 1.[3] ISSN: NOV 1 TO OCT 13 VOLUME 0, ISSUE - 0 Page 344

4 The system parameters consdered for the study of actve shunt flter o AC Source Vs415v, f50 Hz o Nonlnear Load 3-Φ Thyrstor Rectfer o R10 (Ω) Matlab model and results of actve shunt flter By lookng at nstantaneous powers, the harmonc content can be vsualzed as a rpple upon a DC offset representng the fundamental power. By removng the DC offset and performng the nverse park transform the harmonc current can be determned The supply voltage and load current are transformed nto αβ quanttes. The nstantaneous actve and reactve powers p and q are calculated from the transformed voltage and current as gven n Eq. (). [3] Fg 5.1 matlab model of shunt APF Whch gves, ( Eqn.) [4] Po vo.o nstantaneous zero sequence power p vα.α + vβ.β, nstantaneous real power q -vβ.α+vα.β, nstantaneous magnary power The nstantaneous actve and reactve powers are fltered to leave the AC components. The compensatng currents are determned by takng the nverse and s gven by Eq. (3) [3] Fg 5. smulaton result of APF Table1.FFT Analyss for Actve Flter alpha 5th 7th 9th 11th Overall THD VI. CONCLUSION (Eqn. 3) Ths current s then multpled by gan (k) to produce PWM sgnal. V. SIMULATION RESULT To demonstrate the performance of these actve flters feedng a three-phase converter wth R load s used, these actve flters are modelled n MATLAB along wth SIMULINK and power system block set toolboxes. SYSTEM PARAMETERS The MATLAB smulaton has verfed the effectveness of the proposed control scheme of actve flter. The dstorton of power supply current s dmnshed to a satsfactorly level. Usng actve flter the total harmonc dstorton s reduced from to1.9 (for alpha30) VII. REFERENCES 1. Budwal Amrnder Sngh, Chnmaya R. Chute, Shva Gourshett, Harmoncs Effect on Power Qualty and ts Mtgaton Technques usng Actve Power Flter, NCNTE- 01, Feb 4-5 ISSN: NOV 1 TO OCT 13 VOLUME 0, ISSUE - 0 Page 345

5 . Smrut Ranjan Prusty, FPGA Based Actve Power Flter for Harmoncs Mtgaton, Natonal Insttute of Technology Rourkela,June Kaushalchandra n. Barot, R.N.Rathod, three phase shunt actve power flter based on p-q theory for harmonc mtgaton and power qualty mprovement 4. Book by: hrofum akag,edsn hrokazu watanabe, nstantaneous power theory and applcaton to power condtonng. 5. Subhashsh bhattacharya, Deepak dvan, Synchronous frame based controller mplementaton for a hybrd seres actve flter system, unversty of Wsconsn-madson. 6. Manjulata Bad, Power qualty mprovement usng passve shunt flter, tcr and tsc combnaton, department of electrcal engneerng,natonal nsttute of technology, Rourkela, may N.Srnvasa Rao, H.J.Jayatheertha, Modelng and smulaton of varous srf methods for shunt actve power flter and applcaton to bldc drve, Internatonal Journal of Advanced Engneerng Research and Studes E- ISSN Rajn Patel, Naresh Kumar and Amt Patel, A matlab model of hybrd actve flter based on svpwm technque, nternatonal journal of electrcal engneerng. ISSN Volume 5, Number 5 (01), pp Engn Özdemr, Murat Kale, Şule Özdemr, Actve Power Flter for Power Compensaton Under Non-Ideal Mans Voltages,Member IEEE 10. L.r. cmong,m.c. cavacant,fas neves,gms azevedo, Implementaton of dsp controlled shunt actve flter,electrc power qualty and utlzaton journal 006,brasl 11. Lus A. Morán(1) Juan W. Dxon() José R. Espnoza(1) Rogel R. Wallace, usng actve power flters to mprove power qualty ISSN: NOV 1 TO OCT 13 VOLUME 0, ISSUE - 0 Page 346