A Novel Harmonic Elimination Approach in Three-Phase Multi-Motor Drives

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1 Dowloaded from vb.aau.dk o: marts 7, 019 Aalborg Uiversitet A Novel Harmoic Elimiatio Approach i Three-Phase Multi-Motor Drives Davari, Pooya; Yag, Yogheg; Zare, Firuz; Blaabjerg, Frede Published i: Proceedigs of the 015 IEEE Eergy Coversio Cogress ad Expositio (ECCE) DOI (lik to publicatio from Publisher): /ECCE Publicatio date: 015 Documet Versio Early versio, also kow as pre-prit Lik to publicatio from Aalborg Uiversity Citatio for published versio (APA): Davari, P., Yag, Y., Zare, F., & Blaabjerg, F. (015). A Novel Harmoic Elimiatio Approach i Three-Phase Multi-Motor Drives. I Proceedigs of the 015 IEEE Eergy Coversio Cogress ad Expositio (ECCE) (pp ). IEEE Press. Geeral rights Copyright ad moral rights for the publicatios made accessible i the public portal are retaied by the authors ad/or other copyright owers ad it is a coditio of accessig publicatios that users recogise ad abide by the legal requiremets associated with these rights.? Users may dowload ad prit oe copy of ay publicatio from the public portal for the purpose of private study or research.? You may ot further distribute the material or use it for ay profit-makig activity or commercial gai? You may freely distribute the URL idetifyig the publicatio i the public portal? Take dow policy If you believe that this documet breaches copyright please cotact us at vb@aub.aau.dk providig details, ad we will remove access to the work immediately ad ivestigate your claim.

2 A Novel Harmoic Elimiatio Approach i Three- Phase Multi-Motor Drives Pooya Davari, Yogheg Yag, Firuz Zare, Frede Blaabjerg Departmet of Eergy Techology Aalborg Uiversity, 90 Aalborg, Demark pda@et.aau.dk, yoy@et.aau.dk, fbl@et.aau.dk Dafoss Power Electroics A/S 6300 Gråste, Demark fza@dafoss.com Abstract Power electroics techology has bee widely used for decades i the moder motor drive systems. Beyod the cotrol flexibility, the power electroics devices (e.g., diode rectifiers) are also the mai harmoic source to the grid due to their oliearity, which deteriorate the power grid quality ad may cause uecessary losses i power system trasformers. Both degradatios are apt to occur i motor drive applicatios. As a cosequece, it calls for advaced ad itelliget cotrol strategies for the power electroics based drive systems like adjustable speed drives i idustry. At preset, may idustrial drives are still equipped with three-phase diode rectifiers. Thus, it is difficult to implemet the prior-art harmoic cotrol strategies for active frot-eds. Moreover, the total cost ad complexity has become a obstacle for these harmoic elimiatio approaches i multiple drive systems. Therefore, i this paper, a ew cost-effective harmoic mitigatio approach has bee proposed for multiple drives. The proposed approach ca cotrol the geerated curret harmoics by beefitig of the oliearity of the drive uits ad through a ovel curret modulatio scheme. Simulatio ad experimetal results have validated the effectiveess of the proposed approach i terms of harmoic elimiatio i three-phase multi-drive systems. Keywords adjustable speed drives; harmoic elimiatio; multiple drives; three-phase rectifiers; I. INTRODUCTION Electrical motor drive systems cosume a cosiderable amout of global electrical eergy. As the electricity demad is growig faster worldwide, idustry has bee pushed towards a era of developig more eergy-efficiet drives. Employig itelliget cotrol techiques for the power electroics based drive systems ca improve the efficiecy to some extet [1]. However, geerated harmoics as a cosequece of employig power electroics devices deteriorates the power grid quality []-[4]. The high level imposed harmoic iput currets may cause uecessary losses ad heat i power system trasformers ad uisace trippig of circuit breakers ad overstressig of power factor correctio capacitors. This highlights the ecessity for the drive systems to comply with iteratioal stadards such as IEC61000 stadard [5], ad it calls for more smart harmoic elimiatio strategies for the drive systems. Typically, a stadard motor drive system comprises of three mai sectios: the frot-ed power coverter that coverts AC power from the mais to DC power, a eergy storage uit called the DC-lik, ad fially a iverter as the rear-ed power coverter which coverts the DC back to AC at the voltage ad frequecy demaded by the motor. A three-phase diode bridge rectifier is usually employed at the frot-ed stage, thus beig the mai harmoic source. A vast array of methods have bee itroduced to improve the iput curret quality by shapig it as close as possible to a siusoidal waveform [3], [4], [6]-[8] as well as usig active dampig methods [9]-[14]. However, the complexity ad cost are sigificatly icreased. Therefore, diode rectifiers (ucotrolled) or thyristor-based rectifiers (phase-cotrolled) of less complexity ad cost are still widely used i Adjustable Speed Drives (ASD). I additio, the udesirable oliearity of the covetioal AC-DC coversio stage may become sigificat, whe a large umber of idustrial coverters ad ASDs are coected to the Poit of Commo Couplig (PCC). It has bee foud that a proper arragemet of these oliear loads ca cotribute to a effective harmoic mitigatio, where some of the harmoics from oe uit (e.g., diode rectifier) ca be cacelled out by the other/s uits [15]. The feasibility of this solutio is attaied oly whe suitable ad accessible commuicatio amog the oliear uits ca be performed. For istace, it ca be observed i some practical applicatios, where may ASD based idustrial pumps, fas or compressors are operated all together. I fact, improvig the iput curret quality by combiig the oliear loads was first itroduced i multipulse rectifiers [16]. I this method, by employig phaseshiftig trasformers, the harmoics of each uit ca be phasedisplaced with respect to each other, ad thus they ca cacel out each other. Depedig o the umber of coected uits a rage of harmoics ca be elimiated. Takig a 4-pulse rectifier [16] as a example, the curret Total Harmoic Distortio (THD i ) ca sigificatly be improved (< 5 %) by usig this method. Despite the effectiveess i harmoic mitigatio, the volume, associated losses, ad also the cost of the phase-shifted trasformer are the mai cocers. I this paper, a ovel harmoic elimiatio approach is proposed to tackle the aforemetioed challeges. The proposed method does ot require ay phase-shiftig trasformers like what have bee used i multi-pulse rectifiers. Istead, as depicted i Fig. 1, it combies a three-phase diode rectifier with a three-phase Silico Cotrolled Rectifier (SCR) uit to cacel out the harmoics. Additioally, i order to improve the performace ad flexibility of the system, each /15/$ IEEE

3 Fig. 1. Typical cofiguratio for a multi-drive applicatio with the proposed harmoic mitigatio method. uit is equipped with a ovel curret modulatio techique, which ca idividually mitigate a certai umber of curret harmoics. Obtaied simulatio ad experimetal results have verified the effectiveess of the proposed method. The rest of this paper is orgaized as follows. Sectio II presets the detailed aalysis of the proposed harmoic elimiatio method alog with the optimum harmoic solutios. I Sectio III, implemetatio details ad hardware setup are poited out. The performace of the proposed method is validated through simulatio ad experimetatio i Sectio IV. Fially, cocludig remarks are give i Sectio V. II. PROPOSED HARMONIC ELIMINATION METHOD A. Noliear Loads Comibiato for Harmoic Cacellatio I order to demostrate ad evaluate the proposed method a multi-drive system of two three-phase rectifier uits is built up as show i Fig. 1. The details of system operatio are illustrated i Fig., where it is assumed that the curret source at the DC-lik side of the rectifier draws a costat curret (i.e., I dc ). I practice, the curret source ca be implemeted i a DC-DC coverter (e.g., a boost coverter), which ca emulate a ideal iductor behavior [17]-[0]. Therefore, for both rectifiers as show i Fig., the iput currets (i.e., i s ad i d ) will be a square-wave with the coductio agle of 10 o, sice at each istat of time iterval oly two phases coduct ad circulate the DC-lik curret through the grid. For the rectifier system show i Fig., Fourier series aalysis has bee adopted to idetify the harmoic cotet of the iput currets. Accordig to Fig. (a), i a cotrolled rectifier (SCR), the harmoics (i.e., i s ()) of the square-wave iput curret with the 10 o coductio agle ad a adjustable phase agle of α 0 (α 0 = α f + 30 o ) ca be idetified as: with ( ) = ( ) + ( ) s i a b I dc ( ) π a = si α + si α π 3 I π dc b = cos( α ) cos α π 3 i which is the harmoic order. As for the three-phase diode rectifier, it ca be take as a special case of the SCR with a fixed phase agle of α 0 = 30 o (α f = 0 o ). I that case, a =0 accordig to (1), ad thus the harmoics of the iput curret iduced by the diode rectifier ca be calculated as: i d ( ) 4I dc π = cos π 6 Accordig to Fig., the harmoics appearig i the lie curret (i g = i s + i d ) ca be expressed as, ( ) ( ) ( ( ) ) (1) () i = a + i + b (3) g d (a) (b) Fig.. Curret distributio at the PCC of a multi-drive system with oe diode rectifier ad oe SCR uit: (a) ideal currets ad (b) system schematic.

4 Fig. 3. Illustratio of the proposed curret modulatio waveform with selected harmoic cacellatio for a sigle rectifier uit (α f = 0 i the case of a diode rectifier). I order to cacel out ay -th harmoics ad maitai the desired fudametal cotet of the grid curret as the modulatio idex, the trascedetal equatios give i (4) should be solved. () 1 i = M g a a = 0 b + i ( ) = 0 d where M a is the desired modulatio idex. B. Novel Curret Modulatio Techique Although a appropriate adjustmet of the phase agle of the SCR uit ca cotribute to a improvemet of the curret quality, a ew curret modulatio techique is further applied to each DC-DC coverter i order to improve the curret quality. I the ew curret modulatio approach, certai low frequecy harmoics i the three-phase iput lie currets ca be elimiated by addig (or subtractig) phase-displaced curret levels, thus leadig to a better overall grid power quality. This techique is based o a pre-programmed switchig patter for the DC-lik curret to obtai iput currets with zero cotet at those specific harmoics [7]. The basic idea of the proposed curret modulatio method for oly oe rectifier uit (SCR) is demostrated i Fig. 3. For simplicity, the waveforms have bee cetralized i respect to the grid voltage to aalyze the harmoic characteristics. I order to mitigate the triple harmoics, ew added curret levels should be repeated every 1/6 of the fudametal period. For istace, i the two sectors of 1 ad show i Fig. 3, where i each sector i sa is circulated through oe of the other phase currets, if the ew curret level is added ito sector 1, it should be exactly repeated i sector. This meas that the frequecy of the added pulses at the DC-lik should be six times of the fudametal frequecy. As it is show i Fig. 3, the proposed curret waveform cosists of three square-wave sigals with differet magitudes ad agles. The first curret waveform has the magitude of I dc1 with the coductio phase agle of α 0 (α 0 = α f + 30 ο ). Notably, for a three-phase diode rectifier this coductio phase agle is costat, α 0 =30 o. The (4) secod curret waveform has the magitude of I dc with the coductio phase agle of α 1. The third curret waveform has the magitude of I dc but with a coductio phase agle of α. Accordig to (1) the iput curret harmoics ca be calculated. i ( ) = ( a + a ) + ( b + b ) s with j+ 1 I ( 1) π dc a = si( ) si α + j α α + 0 j j 1 π = 3 j+ 1 I ( 1) π dc b = cos( α ) cos α α + j 0 j j = 1 π 3 (5) where i a is the phase A curret of the grid, a' ad b' are the Fourier coefficiets of the ew added curret levels that coduct at α 1 ad α, ad α 0 < α 1 <α < α Hece, i order to idividually cacel out up to two low order harmoics, e.g., i a (m) ad i a (k), the followig coditio holds, + = or ( α α ) ( α α ) β θ 60 + = 60 (6) As for the three-phase diode rectifier α 0 =30 o (α f = 0 o ) ad i that case a = a' = 0. Therefore, the harmoics of the iput curret represeted i (5) ca be simplified as: 4 ( ) π cos cos( ) π = + α cos α π 6 3 i I I I d dc dc dc Hece, applyig the proposed curret modulatio techique to both of the rectifier uits ca sigificatly improve the iput curret quality. Notably, the harmoics appearig i the supply lie (i.e., i g ) ca be calculated as, ( ) ( ) ( ( ) ) (7) = (8) g d i a a i b b

5 C. Optimum Harmoic Solutio The above illustrates the impact o the harmoics by selectig proper modulatio parameters (amplitudes ad switchig agles) for the proposed curret modulatio scheme. However, a optimizatio for these parameters may result i a more suitable solutio ad also higher flexibility to elimiate the harmoics of iterest. The followig demostrates the harmoic optimizatio solutio cosiderig the maximum allowable harmoic level defied by the applicatio or the grid code. I other words, istead of fully ullifyig the distortios, the harmoics could be reduced to acceptable levels by addig suitable costraits (L ). The, a optimizatio problem (Obj ) that searches a set of α ad I dc values over the allowable itervals ca be defied as, Obj = M i (1) L 1 a g 1 i () g Obj = L i (1) g (9) Based o (9) a objective fuctio F obj has to be formed to miimize the error. The objective fuctio plays a importat role i leadig the optimizatio algorithm to the suitable solutio set. Here, F obj is formed based o a squared error with more flexibility by addig costat weight values (w ) to each squared error fuctio [1]: ( ) (10) F = w Obj L obj Moreover, the THD i restrictio could also be the objective fuctio or icluded i (10) ad prioritized with a suitable weight value. I additio to the optimizatio costrait L, the followig coditio eeds to be icluded as well: π α < α < α < < α < α + (11) 0 1 m 0 3 III. SINGLE SWITCH THREE-PHASE BOOST RECTIFIER SYSTEM I order to cotrol the DC-lik curret shape ad magitude followig the waveforms show i Fig., a boost coverter topology based o the electroic iductor [17]-[0] cocept is employed. Usig the covetioal boost topology has the advatage of boostig the output DC voltage to a suitable level whe it is fed to a iverter. Moreover, as the DC-lik curret is cotrolled based o the load power, it has the advatage of keepig the THD i idepedet of the load profile. Fig. 4 depicts the block diagram of the overall cotrol structure for the multi-rectifier uits, where a hysteresis cotroller is adopted as the curret cotrollers for the boost coverters. The referece trackig performace of the curret cotroller has a importat role i the harmoic mitigatio, thus fast curret cotrol methods such as hysteresis or deadbeat cotrol should be employed. I order to sychroize the curret cotrollers with the grid, for each rectifier uit a Secod-Order Geeralized Itegrator (SOGI) based Phase Fig. 4. Block diagram of the overall cotrol structure implemeted for the multi-rectifier system. Locked Loop (PLL) system is adopted []. For simplicity, assumig a balaced system, oly oe lie-to-lie voltage is fed to the PLL. Therefore, the result will have a phase shift of 30 o i respect to the phase voltage, which should be corrected withi the referece curret geerator algorithm. I order to obtai a discretizatio for the PLL ad the Proportioal Itegrator (PI) cotroller, a trapezoidal method is used. Moreover, as it ca be see from the system schematics show i Fig. 4, the firig agle of the thyristor based rectifier (SCR) should be applied accordig to the phase detected by the PLL. Fig. 5 shows the developed prototypes for the three-phase rectifier systems, where Fig. 5(a) depicts a photograph of the three-phase diode rectifier uit ad Fig. 5(b) shows the threephase SCR uit icludig the boost coverter for each uit. Table I summarizes the employed modules i the implemeted prototypes. IV. RESULTS Simulatios have firstly bee doe to verify the effectiveess of the proposed method. A compariso with other systems (see Fig. 6) i terms of harmoic mitigatio has bee carried out. For the first two systems show i Fig. 6, a costat curret source (implemeted by a boost coverter) at the DC-lik side has bee cosidered. Actually, the SCR without ay curret modulatio i the secod system has a fixed 30 o phase-shift i respect to the other uit. The grid impedace L g ad R g (Z g ) as show i Figs. ad 4 are set to 0.1 mh ad 0.01 Ω, respectively. For the 1-pulse phaseshiftig trasformer impedace compoets are selected to be 160 µh ad 5 mω. The grid phase voltage is 0 V RMS ad the grid frequecy is 50 Hz. The output voltage of the boost coverter is maitaied at 700 V DC by employig a proportioal itegrator cotroller ad a hysteresis cotroller is adopted as the curret cotroller. A MATLAB fuctio fmico has bee used for optimizatio. The results are show i Figs. 7 ad 8. Sice oly the low-order harmoics are of much iterest, the proposed method has bee optimized accordig to (9)-(11) i order to atteuate the 5 th, 7 th ad 11 th harmoics to be less tha 1 % of the fudametal compoet (i.e., selected optimizatio costraits). I additio, THD i is also icluded i the objective fuctio (THD i < 1.5 %). Fig. 7 (a) presets the

6 TABLE I EMPLOYED MODULES IN THE IMPLEMENTED PROTOTYPE (FIG. 5) Module Part-Number Qty Three-phase diode rectifier SKD30 1 Three-phase SCR SKKT 106/16 3 IGBT-diode SK60GAL15 IGBT gate drive Skyper 3-pro SCR triggerig circuit RT380T 1 Curret measuremet HX-15 Voltage measuremet LV5-P SCR subber brach R sub = 100 Ω, C sub = 0.1 µf 6 Cotroller TMS30F8335 (a) (b) Fig. 5. Photograph of implemeted sigle switch three-phase boost rectifier for (a) diode rectifier ad (b) SCR system. results of the multi-drive system show i Fig. (b) with the proposed modulatio strategy, which cofirms that a multilevel iput curret is achieved by the phase-shift based modulatio scheme, cotributig to a lower THD i. This beefit is further verified by the compariso with other cofiguratios (see Fig. 6), where the low-order harmoics (5 th, 7 th, ad 11 th ) have bee cotrolled (optimized) to a relatively low level by the proposed method, as it is show i Fig. 7(b). However, the 7 th ad the 11 th harmoics are slightly higher tha the optimizatio target (less tha 1 %) due to the effect of the grid impedace. I additio, the flexibility of the proposed method is demostrated i aother case study, where the THD i is selected as the optimizatio objective fuctio. It ca be observed i Fig. 8(a) that a THD i of 10.5 % is attaied i the multi-drive system with the proposed method regardless of output power levels (load profiles) i cotrast to the 1-pulse based drive system. Although some idividual harmoics are higher whe compared to the 1-pulse rectifier as show i Fig. 8(b), the THD i is miimized i cotrast to that i Fig. 6(b). Table II summarizes the detailed harmoic cotet of the rectifier systems at a costat output power level of 5.5 kw. It should be oted that the optimizatio was performed based o a assumptio that each rectifier uit draws equal amout of curret from the grid; otherwise, the rectified voltages V rec_s ad V rec_d (see Fig. 4) are differet due to the phase-shift ad thus leadig to differet boost coversio gai ratio ad may complicate the harmoic distributios. I additio to the effect of the phase-shift, i real-world applicatios the two rectifier uits do ot ecessarily operate at the same power level. Sice the system is ot depedet o the load profile, the power level itself is ot the cocer, ad the ratio betwee output-power levels of the rectifier uits are of importace. Therefore, as log as the followig equatio holds true, the rectifiers draw equal amout of curret from the grid; otherwise it should be reflected i the optimizatio process i oe of the objective fuctios. (a) (b) (c) Fig. 6. Differet rectifier uits: (a) two diode rectifiers, (b) oe diode rectifier ad oe SCR with a fixed phase shift of 30 o ad (c) 1-pulse rectifier.

7 (a) (a) ig()/ig(1) (b) Fig. 7. Performace of a multi-drive system show i Fig. (b) with the proposed method: (a) curret waveforms ad (b) compariso of the loworder harmoics with other cofiguratios (see Fig. 4) at the total output power level of 5.5 kw. (b) Fig. 8. Performace of the multi-drive system with the proposed method ad the 1-pulse rectifier based system: (a) total iput curret THDi at varied power levels ad (b) iput curret spectrums of the two systems at the total output power level of 5.5 kw. P P o_ d o_ s cos( α ) = 1 (1) where P o_d ad P o_s are the output power of the diode rectifier ad SCR uit, respectively. Notably, to save computatio complexity differet pre-calculated curret modulatio parameters with their correspodig power ratios should be icluded as a look-up table i the cotroller. Therefore, by icludig a commuicatio betwee each rectifier uits suitable combiatio of the iput currets at the PCC ca be made uder varied situatio. I order to verify the effectiveess of the proposed method, experimetal tests have bee carried out o a 5.5-kW multirectifier system (Fig. 5). Firstly, the cotrol objective is to lower the THD i ad also to reduce the 5 th, 7 th, ad 11 th harmoics. It ca be see i Fig. 9 that the 5 th, 7 th, ad 11 th order harmoics are almost completely elimiated, sice they are cosidered i the optimizatio fuctio as show i (10). I additio, a THD i of 11.5 % of the grid curret is also obtaied, f TABLE II. HARMONIC DISTRIBUTION OF DIFFERENT SIMULATED RECTIFIER SYSTEMS AT A TOTAL OUTPUT POWER LEVEL OF 5.5 KW. System Harmoic Distributio ad THD i (%) Cofiguratio i g(5) /i g(1) i g(7) /i g(1) i g(11) /i g(1) i g(13) /i g(1) THD i Two Diode Rectifiers (Fig. 6(a)) SCR + Diode Rectifier (Fig. 6(b)) 1-Pulse Rectifier (Fig. 6(c)) 1 Proposed Method Proposed Method Optimizatio objective is to miimize the low order harmoics icludig the THD i (see Fig. 7). Optimizatio objective is to achieve a lower THD i (see Fig. 8(b))

8 TABLE III. HARMONIC DISTRIBUTION OF DIFFERENT EXPERIMENTAL CASES FOR RECTIFIER SYSTEMS AT A TOTAL OUTPUT POWER LEVEL OF 5.5 KW. Optimizatio Harmoic Distributio ad THD i (%) Objective i g(5) /i g(1) i g(7) /i g(1) i g(11) /i g(1) i g(13) /i g(1) THD i 1 Proposed method Proposed method Optimizatio objective is to miimize the low order harmoics icludig the THD i (see Fig. 9). Optimizatio objective is to achieve a lower THD i (see Fig. 10) Fig. 9. Experimetal results (phase A) of the multi-drive system with the ovel curret modulatio scheme at P o 5.5 kw, V o = 700 V DC, targetig at reducig the low order harmoics ad also a lower THD i: grid curret i g [10 A/div], grid phase voltage v a [00 V/div], diode rectifier iput curret i d [10 A/div], SCR uit iput curret i s [10 A/div], ad Fast Fourier Trasform (FFT) aalysis of the grid curret [500 ma/div]. TABLE IV. OPTIMIZED CALCUALTED MODULATION PARAMETERS (WITH M a = 1). Normalized Parameters Optimizatio Objective I dc1 I dc α 1 α f 1 Proposed method o 36 o Proposed method o 38.7 o 1. Optimizatio objective is to miimize the low order harmoics icludig the THD i (see Fig. 9). Optimizatio objective is to achieve a lower THD i (see Fig. 10) summarizes the harmoic distributio of the coducted experimetal cases. As stated before, the pre-calculated switchig parameters for the modulatio strategy uder differet situatios should be icluded as a look-up table i the cotroller. Table IV illustrates the estimated curret modulatio parameters for the two optimized cases with ormalized amplitudes. Notably, the same parameters are applied to both rectifier uits with a phase-shift of α f. Fig. 10. Experimetal results (phase A) of the multi-drive system with the ovel curret modulatio scheme at P o 5.5 kw, V o = 700 V DC, targetig at a miimized THD i: grid curret i g [10 A/div], grid phase voltage v a [00 V/div], diode rectifier iput curret i d [10 A/div], SCR uit iput curret i s [10 A/div], ad Fast Fourier Trasform (FFT) aalysis of the grid curret [500 ma/div]. whe applyig the ovel modulatio scheme to both rectifier uits. The occurrece of the curret spikes i the SCR curret (e.g. i s ) at the poit of commutatio is due to presece of the subber braches i the SCR uit. I practice, to avoid SCR uit failures ad to reduce the overvoltage to a reasoable limit a RC subber brach is coected across each thyristor. I order to damp the curret spikes, small AC-side iductors ca be placed i series prior to the SCR uit. To further validate the performace of the proposed method miimizig the THD i was oly cosidered as the optimizatio target. Fig. 10 presets the performace of the multi-rectifier system where a THD i of aroud 10 % is achieved. At the same time, the low order harmoics are at relatively low levels. The results are quite i agreemet with the simulatios. Table III To sum up, both the experimetal tests ad the simulatios have demostrated the effectiveess of curret harmoic mitigatios i multi-rectifier systems by meas of: a) phaseshiftig the currets draw by SCR uit ad b) a ovel curret modulatio scheme at the boost iductor. Those ca sigificatly cotribute to a good power quality i both the sigle-drive ad the multi-drive systems. V. CONCLUSIONS I this paper, a ew harmoic elimiatio approach by combiig differet o-liear loads has bee proposed for three-phase multi-drive systems, where also a Silico Cotrolled Rectifier (SCR) is adopted. The proposed method ca eable the selected harmoic cacellatio by adjustig the phase agle of the SCR, ad thus it ca cotribute to a improved power quality of the mai grid. Moreover, i order to further reduce the harmoics, a ovel modulatio scheme has bee applied to the DC-DC coverter i the drive systems. The modulatio scheme is able to elimiate the harmoics of iterest by addig or subtractig specific curret levels with respect to the covetioal modulatio approach. As a cosequece, the combiatio of multiple o-liear loads with the ew modulatio scheme offers much flexibility as well as

9 cost-effectiveess for the multi-drive systems i terms of harmoic elimiatio. A mai advatage of the proposed method is that the harmoic distributio remais the same regardless of load profile variatios. Simulatio ad experimetal results have verified the effectiveess of the proposed harmoic elimiatio approach. REFERENCES [1] B.K. Bose, B.K., "Power electroics ad motor drives recet progress ad perspective," IEEE Tras. Id. Electro., vol. 56, o., pp , 009. [] J.W. Gray ad F. J. Haydock, "Idustrial power quality cosideratios whe istallig adjustable speed drive systems," IEEE Tras. Id. Appl., vol. 3, o. 3, pp , May/Ju [3] D. Kumar ad F. Zare, "Aalysis of harmoic mitigatios usig hybrid passive filters," i Proc. of PEMC, 014, pp , 1-4 Sept [4] F. Zare, "Harmoics issues of three-phase diode rectifiers with a small DC lik capacitor," i Proc. of PEMC, 014, pp , 1-4 Sept [5] G.K. Aderse ad F. Blaabjerg, "Curret programmed cotrol of a sigle-phase two-switch buck-boost power factor correctio circuit," IEEE Tras. Id. Electro., vol. 53, o. 1, pp , Feb [6] J. W. Kolar ad T. Friedli, "The Essece of Three-Phase PFC Rectifier Systems - Part I," IEEE Tras. Power Electro., vol. 8, o. 1, pp , Ja [7] F. Zare, "A ovel harmoic elimiatio method for a three-phase diode rectifier with cotrolled DC lik curret," i Proc. of PEMC, 014, pp , 014. [8] C. Klumper, F. Blaabjerg, ad P. Thogerse, "Coverter topologies with low passive compoets usage for the ext geeratio of itegrated motor drives," i Proc. of PESC, vol., pp , 003. [9] H. Akagi ad K. Isozaki, "A hybrid active filter for a three-phase 1- pulse diode rectifier used as the frot ed of a medium-voltage motor drive," IEEE Tras. Power Electro., vol. 7, o. 1, pp , Ja. 01. [10] M. Liserre, A. Dell'Aquila, ad F. Blaabjerg, "A overview of threephase voltage source active rectifiers iterfacig the utility," i Proc. of Power Tech Cof., pp. 1-8, vol. 3, 003. [11] M. Liserre, F. Blaabjerg, ad S. Hase, "Desig ad cotrol of a LCLfilter-based three-phase active rectifier," IEEE Tras. Id. Appl., vol. 41, o. 5, pp , 005. [1] H. Akagi, "Moder active filters ad traditioal passive filter," Bulleti of the polish academy of scieces techical scieces, vol. 54, 006. [13] J. W. Kolar ad H. Ertl, "Status of the techiques of three-phase rectifier systems with low effects o the mais," i Proc. of Telecommuicatio Eergy Cof., pp. 1-16, [14] S. Hase, P. N. Ejeti, H. Jae Hog, ad F. Blaabjerg, "A itegrated sigle-switch approach to improve harmoic performace of stadard PWM adjustable speed drives," i Proc. of IAS Aual Meetig, vol., pp , [15] S. Hase, P. Nielse, ad F. Blaabjerg, "Harmoic cacellatio by mixig oliear sigle-phase ad three-phase loads," IEEE Tras. Id. Appl., vol. 36, o. 1, pp , Ja/Feb 000. [16] S. Choi, B.S. Lee, ad P.N. Ejeti, "New 4-pulse diode rectifier systems for utility iterface of high-power AC motor drives," IEEE Tras. Id. Appl. vol. 33, o., pp , Mar./Apr [17] K. Mio, M. L. Heldwei, ad J. W. Kolar, "Ultra compact three-phase rectifier with electroic smoothig iductor," i Proc. of APEC, 005, pp. 5-58, 005. [18] J. Salmo ad D. Koval, "Improvig the operatio of 3-phase diode rectifiers usig a asymmetrical half-bridge DC-lik active filter," i Proc. of IAS Aual Meetig, vol. 4, pp , 000. [19] P. J. Grbovic, P. Delarue, ad P. Le Moige, "A Novel Three-Phase Diode Boost Rectifier Usig Hybrid Half-DC-Bus-Voltage Rated Boost Coverter," IEEE Tras. Id. Electro., vol. 58, o. 4, pp , 011. [0] C. Galea ad L. Asimioaei, "New topology of electroic smoothig iductor used i three phase electric drives," i Proc. of EPQU, pp. 1-6, 011. [1] L. G. Fraquelo, J. Napoles, R. C. P. Guisado, J. I. Leo, ad M. A. Aguirre, "A Flexible Selective Harmoic Mitigatio Techique to Meet Grid Codes i Three-Level PWM Coverters," IEEE Tras. Id. Electro., vol. 54, o. 6, pp , 007. [] M. Ciobotaru, R. Teodorescu, ad F. Blaabjerg, "A New Sigle-Phase PLL Structure Based o Secod Order Geeralized Itegrator," i Proc. of PESC, 006, pp. 1-6, 18- Jue 006.