Harmonic Filter Design for Hvdc Lines Using Matlab

Transcription

1 Iteratioal Joural of Computatioal Egieerig Research Vol, 3 Issue, 11 Harmoic Filter Desig for Hvdc Lies Usig Matlab 1, P.Kumar, 2, P.Prakash 1, Power Systems Divisio Assistat Professor DEEE, P.A. College of Egieerig ad Techology, Pollachi 2 VLSI Desig,, Assistat Professor DEEE, P.A. College of Egieerig ad Techology, Pollachi ABSTRACT: This paper presets harmoic filter desig for HVDC lies usig MATLAB versio R29a.No-liear devices such as power electroics coverters ca iject harmoics alteratig currets (AC) i the electrical power system. The umber of sesitive loads that require ideal siusoidal supply voltage for their proper operatio has bee icreasig. To maitai the quality limits proposed by stadards to protect the sesitive loads, it is ecessary to iclude some form of the filterig device to the power system. Harmoics also icreases overall reactive power demaded equivalet load. This paper deals with the desig of three phase filter baks coected i parallel to achieve optimal cotrol for harmoic elevatio problems. KEYWORDS: harmoic filter, sesitive loads, reactive power, three phase filter baks, optimal cotrol, harmoic elevatio problems. I INTRODUCTION Advacemet i techology of semicoductor devices has led to a revolutio i electroic techology over the past decade. However rise i the power quality (PQ) problem is due to power equipmets which iclude adjustable-speed motor drives (ASDs), electroic power supplies, direct curret (DC) motor drives, battery chargers, electroic ballasts. The distortio i curret is due to the oliearity of the resistor. The oliear loads are costructed by oliear devices, i which the curret is ot proportioal to the applied voltage. The cocept of curret distortio is illustrated i the figure 1.I figure 1 a siusoidal voltage is applied to a simple oliear resistor i which the voltage ad curret vary accordig to the curve show. From figure 1 we observe, the voltage is perfectly siusoidal, the resultig curret is distorted. Figure.1 Curret distortio caused by oliear resistace The No-liear loads seem to be the mai source of harmoic distortio i a power distributio system. The No-liear loads produce harmoic currets ad iject it ito the power distributio etwork at the poit of commo couplig (PCC).These harmoic curret ca iteract egatively with a broad rage of power systems equipmet such as trasformers, motors ad produce more losses, overheatig ad overloadig. II SOLUTIONS FOR HARMONIC DISTORTION PROBLEMS There are set of covetioal solutios to the harmoic distortios which have existed for a log time. Some of them are as follows 1) The passive filterig is the simplest covetioal solutio to mitigate the harmoic distortio. The passive filterig mechaisms do ot deped upo a exteral power supply. Although simple, the use of passive elemets does ot respod correctly to the dyamics of the power distributio systems. Also the use of passive elemets at high power level makes the filter heavy ad bulky. The passive filters are kow to cause resoace, thus affectig the stability of the power distributio systems. 2) The active power filter (APF) provides solutio for harmoic distortio mitigatio. The active filters are made of passive ad active compoets ad require a exteral power source. The APF utilize power electroics techologies to produce curret compoets that Iss November 213 Page 12

2 Harmoic Filter Desig For cacel the harmoic currets from the o-liear loads. With the APF the switchig frequecy oise requires additioal filterig to prevet with other sesitive equipmets. 3) The passive high-pass filter (HPF) used i additio to the covetioal APF for mitigatig harmoics. This combiatio is kow to be hybrid APF.The mai objective of hybrid APF is to improve the filterig performace of high-order harmoics while providig a cost-effective low order harmoic mitigatio. III MATHEMATICAL ANALYSIS OF HARMONICS 3.1 TOTAL HARMONIC DISTORTION The basic parameter that is used for the harmoic aalysis is the total harmoic distortio (THD).The total harmoic distortio (THD) gives the commo measuremet idices of harmoic distortio.thd applies to both curret ad voltage ad is defied as the root-mea-square (rms) value of the harmoics divided by the rms value of the fudametal ad the multiplied by 1%.The THD is give by the followig equatio. Where THD h max h 1 M M 1 2 h 1 M is the rms value of harmoic compoet h of the quatity M. h THD of the curret varies from a few percet to more tha 1%.THD of the voltage is usually less tha 5%.Voltage THDs below 5% are widely cosidered to be acceptable, while values above 1% are defiitely uacceptable ad will cause problems for sesitive equipmet ad loads.the biggest problem with harmoics is voltage waveform distortio. We ca calculate a relatio betwee the fudametal ad distorted waveforms by fidig the sum of the squares of all harmoics geerated by a sigle load, ad the dividig this umber by the omial 5/6 Hz waveform value. We do this by a mathematical calculatio kow as Fast Fourier Trasform (FFT) Theorem. This calculatio method determies the total harmoics distortio (THD) cotaied withi a oliear curret or voltage waveform. 3.2 FOURIER SERIES Fourier series are used i the aalysis of periodic fuctios or periodic sigals ito the sum of oscillatig fuctio called sies ad cosies. May of the pheomea studied i egieerig ad sciece are periodic i ature eg. the curret ad voltage i a alteratig curret circuit. These periodic fuctios ca be aalyzed ito their costituet compoets (fudametals ad harmoics) by a process called Fourier aalysis. By defiitio, a periodic fuctio, f(t) is that where f(t) = f(t+t). This fuctio ca be represeted by a trigoometric series of elemets cosistig of a DC compoet ad other elemets with frequecies comprisig the fudametal compoet ad its iteger multiple frequecies. This applies if the followig so-called Dirichlet coditios are met: If a discotiuous fuctio, f(t) has a fiite umber of discotiuities over the period T If f(t) has a fiite mea value over the period T If f(t) has a fiite umber of positive ad egative maximum values The expressio for Fourier series expasio is give as follows, a ft ) [ a cos 2 Where 2 1 / T t b si t ] We ca further simplify equatio (1), we get Where c si 1 (1) (2) f ( t ) c t (3) a 2 2 c, c a b, ta 2 1 b a Iss November 213 Page 13

3 th order harmoic of the periodic fuctio c magitude of the DC compoet ad c magitude ad phase agle of the th harmoic compoet Harmoic Filter Desig For The compoet with =1 is the fudametal compoet. Magitude ad phase agle of each harmoic determie the resultat waveform f (t). The equatio (3) ca be writte i complex form as, Where =, 1, 2 1 j o t f ( t ) c e (4) c 1 T T / 2 f T / 2 ( t ) e j t dt (5) The mai source of harmoics i power system is the static power coverter. Uder ideal operatio coditio, harmoics geerated by a p pulse power coverter are characterized by, I 1 I, ad pl 1 (6) where stad for the characteristic harmoics of the load; l=1, 2 ad p is a iteger multiple of six. The figure below gives the example of harmoic spectrum Figure 2. Example of harmoics spectrum IV SIMULATION AND RESULTS The figure 3 represets the simulik model of proposed system created i MATLAB.The three phase harmoic filters are coected betwee the buses B1 ad B2 through breaker. For aalysis of the harmoics two cases were take. Case 1 with the three phase harmoics filters coected to the lies ad the case 2 with the harmoic filters ot coected to the lies. Iss November 213 Page 14

4 Harmoic Filter Desig For Figure 3. Simulik model of the proposed system Three-phase harmoic filters are shut elemets that are used i power systems for decreasig voltage distortio ad for power factor correctio. Noliear elemets such as power electroic coverters geerate harmoic currets or harmoic voltages, which are ijected ito power system. The resultig distorted currets flowig through system impedace produce harmoic voltage distortio. Harmoic filters reduce distortio by divertig harmoic currets i low impedace paths. Harmoic filters are desiged to be capacitive at fudametal frequecy, so that they are used for producig reactive power required by coverters ad for power factor correctio.the HVDC (High Voltage Direct Curret) rectifier is built up from two 6-pulse thyristor bridges coected i series. The coverter is coected to the system with a 12-MVA three phase trasformer (three widigs).a 1-MW resistive load is coected to the DC side through a.5 H smoothig reactor. The filters are made of the followig four compoets of the powerlib/elemets library: 1. Oe capacitor baks (C1) of 15 Mvar modeled by a Three-Phase Harmoic Filters are used i HVDC lie. (i).oe C-type high-pass filter to the 3 rd (F1) of 15 Mvar (ii).oe double-tued filter 11 th /13 th (F2) of 15 Mvar (iii).oe high-pass filter tued to the 24 th (F3) of 15 Mvar. I order to achieve a acceptable distortio, several baks of filters of differet types are usually coected i parallel. The combiatios of differet baks are derived from basic filters Butterworth Chebyshev ad Cauer filters. The most commoly used filter types are 1. Bad-pass filters, which are used to filter lowest order harmoics such as 5 th,7 th,11 th,13 th etc.bad-pass filters ca be tued at a sigle frequecy(sigle tued filter) or at two frequecies(double-tued filter) 2. High-pass filters, which are used to filter high-order harmoics ad cover a wide rage of frequecies. A special type of high-pass filter, the C-type high-pass filter, is used to provide reactive power ad avoid parallel resoaces. It also allows filterig low order harmoics (such as 3 rd ), while keepig zero losses at fudametal frequecy. The figure below shows the differet types of three-phase RLC harmoic filter. Figure 4. Differet types of three-phase RLC harmoic filter Iss November 213 Page 15

5 Harmoic Filter Desig For The simulik model of the proposed system is give i figure 2.The power coverter usually act as oliear source ijectig harmoics ito the system. The three phase harmoic filter is istalled betwee the buses B1 ad B2. Figure 5. Three phase voltage at the bus B1 without harmoic filter Figure 6. Three phase voltage at the bus B1 with harmoic filter Figures 4 ad 5 gives the simulatio results of the three phase voltage at the bus B1 with ad without harmoic filters. From figure 4 we observe that i the absece of three phase harmoic filters the three phase voltage at the bus B1 gettig distorted due to the harmoics ijected by the rectifier, which is the o-liear load i this case. Figure 7. Three phase curret at the bus B1 without harmoic filter Figure 8. Three phase curret at the bus B2 without harmoic filter Iss November 213 Page 16

6 Harmoic Filter Desig For Figure 9. Three phase curret at the bus B1 with harmoic filter Figure 1. Three phase curret at the bus B2 with harmoic filter Figures 6 ad 7 gives the simulatio results of three phase currets at the buses B1 ad B2 without harmoic filters. Figures 8 ad 9 gives the simulatio results of three phase currets at the buses B1 ad B2 with harmoic filters. O compariso of figures 6,7 ad 8,9 we observe that i the absece of three phase harmoic filters the three phase currets at the bus B1 ad B2 gettig distorted due to the harmoics ijected by the oliear load. Figure 11. Harmoic spectrum of three-phase currets at bus B2 without harmoic filter Figure 12. Harmoic order of three-phase currets at bus B2 without harmoic filter Iss November 213 Page 17

7 Harmoic Filter Desig For Figure 13. Harmoic spectrum of three-phase currets at bus B2 with harmoic filter Figure 14. Harmoic order of three-phase currets at bus B2 with harmoic filter O compariso o figures 1, 11 with figures 11, 12 we observe that the total harmoic reductio (THD) was cosiderably reduced from 12.59% for the case without harmoic filters to.7% for the case with harmoic filters. The simulatio is performed for the test case with alpha 19 degree.simulatios ca be performed for various values of alpha ad the impact o the DC level ad o geerated harmoics ca be oted. V CONCLUSION There will be a icreasig ecoomical impact o the operatio of electrical power system due to losses i the system.i this study the HVDC model i MATLAB/SIMULINK is used with differet three phase filter baks to reduce the distortio ad to icrease the power quality of the system. Three phase harmoic filter used i this work for decreasig the voltage distortio ad for power factor correctio. The focus of this work is to have ecoomical impact of the electrical power system through harmoics, distortio reductio ad to icrease the power quality of the system. VI SCOPE OF FUTURE WORK This is work ca be exteded i future with differet filter combiatios for decreasig the harmoics. Advaced modificatios ca be imparted to this filter desig to address various power quality issues ad to provide the ed users with reliable source of power. REFERENCES [1] Himabidu. T, Jayaprakash, Performace of sigle phase shut active filter based o P-Q techique usig matlab/simulik, Iteratioal Joural of Egieerig Research ad Techology, vol.1, Issue 9, November 212. [2] P.Thirumoorthi, Jyothis Fracis ad N.Yadaiah, Power coditioig i battery chargers usig shut active power filter through eural etwork, Iteratioal Joural of Advaces i Egieerig & Techology, March 212. [3] R.Srirajai ad S.Jayalalitha, Ivestigatio the performace of the various types of harmoic filters, World Applied Scieces Joural 17(5): [4] C. Nalii Kira, Subhrasu Sekhar Dash, ad S. Prema Latha, A Few Aspects of Power Quality Improvemet Usig Shut Active Power Filter, Iteratioal Joural of Scietific & Egieerig Research,vol.2, Issue 5, May 211. Iss November 213 Page 18

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