A higher level of efficiency

Transcription

1 Product innovtion A higher level of efficiency Five-level frequency converter for medium voltge Pieder Jörg, Gerld Scheuer, Per Wiktröm The depletion of energy reource nd the relee of greenhoue ge into the tmophere i of growing concern to mnkind. ABB i reponding to the chllenge y promoting energy efficiency. One re with huge potentil for ving i in motor tht operte fn, pump nd compreor. Thee re uully driven y fixed-peed motor, with the flow eing controlled y energy-wting throttling method. Frequency converter cut out thi wte y dpting the peed of the motor to directly mtch the required preure or flow. So i the prolem olved? Not totlly. There re two ic prolem to e overcome in deigning frequency converter for medium voltge: Thee re reching the voltge of the motor nd getting cloer to n idel inuoidl voltge. ABB innovtive olution lie in the re-comintion of exiting olution to olve oth of thee prolem. A five-level rrngement men there re five output level inted of the uul two or three. Thi tep deliver coniderle improvement in the wveform, while t the me time chieving higher output voltge. And to crown the ucce, the innovtion w relized y drwing lrgely on proven concept, reducing rik nd oltering reliility. 6 ABB Review 4007

2 Product innovtion Trditionl control trtegie for flow control uully rely on wteful throttling method. To ue imple nlogy, thi i like driving cr y plcing rick on the g pedl (fixed upply) nd uing the rke pedl for peed control (friction-ed throttle). Frequency converter re the vrile g pedl of motor control, nd repreent huge potentil for energy ving. Motor conume round 30 percent of ll the electric energy produced in the world. Aout three-qurter of ll motor power pump, fn or compreor ued in ppliction where energy conumption cn e reduced through peed control. An ABB etimte how tht the worldwide doption of uch frequency converter in medium voltge drive cn deliver ving of 7 TWh in other word, the output of 44 foil fuel power plnt or the totl energy conumption of country uch Spin ). At preent, le thn ten percent of ll motor old every yer re equipped with the mot efficient peed control tht exit: the frequency converter. Depite lo eing the let mintennce-intenive men of motor control ville, cutomer re till opting for other men of control in the mjority of ce. Why? The mot frequently mentioned rrier for dopting the technology re: ) reliility ) hrmonic c) cot nd/or very hort pyck requirement ABB innovtive five-level witche ddre ll of thee chllenge. Better wveform, higher voltge Electricity generted in the trditionl mnner uing ynchronou genertor h inuoidl output voltge. Electric motor tht re connected directly to the min grid (direct-online connection) nd hence operted t fixed peed re optimized for thi type of wveform. If the me motor Footnote ) See lo Wiktroem, P., Tolvnen, J., Svolinen, A., Bro, P., Sving energy through drive efficiency, ABB Review 007, (epecilly pge 74 76). A motor connected direct-on-line nd with frequency converter inerted etween the min grid nd the motor deign i to e ued for vrile peed ppliction, the frequency converter hould deliver wveform tht i cloe to the idel inuoidl hpe needed. Devition from the idel wveform led to dditionl heting of the motor. Thi in turn men the motor cnnot e ued to it full power nd mut e de-rted. Another negtive impliction i tht uperimpoed torque ripple cn cue torionl ocilltion in the drivechin nd mchinery. Motor conume round 30 percent of ll the electric energy produced in the world. Aout threequrter of ll motor power pump, fn or compreor ued in ppliction where energy conumption cn e reduced through peed control. Furthermore, motor come in tndrdized voltge cle. For the medium voltge (MV) rnge of motor for power of up to out 7000 kw, the mot frequent voltge found on indutril ite re 6 kv/50 Hz nd 4 kv/60 Hz. Thi men tht, in order to ue the me rnge of motor in oth direct-on-line connection nd with frequency converter, the output of the frequency converter h to e le to ttin imilr voltge vlue. 50 Hz / 60 Hz 50 Hz / 60 Hz 0 Hz 00 Hz Such output voltge re not ey to ttin with trditionl two- nd threelevel converter the mximum output voltge i determined y the voltge rting of the power emiconductor. Inide frequency converter circuit The energy converion in converter i relized in two tep: In the firt, the energy upply in the form of inuoidl voltge t fixed frequency nd contnt mplitude i rectified into D-voltge or D-current. Thi D-quntity i then, in econd tep, inverted into n A-voltge or current whoe frequency nd mplitude re vrile. Both the rectifier prt nd the inverter prt of thi converion re relized y electronic circuit uilt up of electronic witche. Thi rticle i primrily out the Phe repreenttion of two-level voltge ource inverter y men of n idel witch, fed y D-voltge ource +D/-D : D connection point : cpcitor D voltge ource S : electronic olid tte witch U : output voltge U D U D + D - D U ABB Review

3 Product innovtion 3 Two-level inverter with plit cpcitor nd three-level inverter (conceptul drwing) 4 Although the witche in converter re often repreented imple contct (left), they do in fct integrte lrger numer of emiconductor component (right). how two-level phe leg nd it three-level equivlent U D U D U D U D + D - D + D - D = i i u u U D U D U D U D + D - D + D - D c c c c = u,,c u,,c i i i c i i i c M M technology of thi econd tep, the inverter. Mot ABB converter re o-clled Voltge Source Inverter (VSI). how the implet topology of VSI: A ingle output phe of the frequency inverter i lterntively connected to one or the other pole of lrge D-cpcitor. It i the purpoe of the rectifier circuit (not hown) to enure tht thi cpcitor i kept chrged to fixed D-voltge. If n A-voltge i to e generted, the witch in the inverter circuit need to chnge poition (ie, chnge the output voltge) t let once every hlf cycle. If n output of 50 Hz i required, for exmple, the witch hould chnge to ech of it two poition t let 50 time per econd. In prctice, the witch i uully flipped much fter thn thi. A digitl controller i ued to direct it witching ttu. The witching trtegy of thi controller determine not only the frequency ut lo the verge voltge cro the lod. Thee level re modified y djuting the input vlue of thi unit deired. Thi control trtegy i known Pule Width Modultion (PWM). In relity, the witch i not moving contct the digrm ugget, ut i Fctox Semiconductor: 50 yer of development in witching In the pt 50 yer, ABB h etlihed nd mintined leding poition in the field of power electronic. Frequency converter for motor re n eentil prt of thi uine. Electronic witche re t the hert of every frequency converter. The tory of the emergence of five-level witching, i et introduced y rief tour of the evolution of thee device. Reder who hve een following the development of thee device long enough will rememer tht the firt high-power electric drive were ed on line-commutted thyritor. Thee thyritor cn e deigned for high current nd high locking-voltge (preent-dy verion rech vlue of 8 0 kv). Their mjor drwck i tht they cn e witched on t ny given point ut cnnot e witched off (they remin on until n externl effect cue the current to top flowing). Thi feture limit the ville witching trtegie, nd y conequence the uitility of uch circuit from power qulity point of view (ee two-level witching in 7 ). onverter uing thee witche crete hrmonic of high mgnitude nd reltively low frequency. Such hrmonic cue prolem oth on the upply nd the motor ide. Moreover, the power fctor on the network ide vrie over the operting rnge of the frequency converter. Line ide prolem hve een ddreed y uing filter. The motor ide prolem re delt with y dimenioning the motor to cope with the dditionl heting nd to deign the hft nd coupling ccording to the requirement clled for y torionl ocilltion. At the time, thi w conidered cceptle ecue there w no other olution tht could compete. In fct, it i till the preferred olution for very high power ppliction (0 MW nd ove) ecue of it reliility. However, with the rrivl of new witching component, new topologie tht provide voltge wveform much cloer to the idel inuoidl hpe cn e implemented. The new component, ll of them differently optimized trnitor uch IGBT (Inulted Gte Bipolr Trnitor) nd IGT (Integrted Gte ommutted Thyritor), re chrcterized y the fct tht they cn e witched off ritrrily. 8 ABB Review 4007

4 Product innovtion uilt up from power emiconductor device 4. The development nd cpilitie of uch witche h, ince the firt emergence of uch converter, een dependent on progre in power emiconductor Fctox. Redy for the next level Although the two-level VSI voltge wveform hown in 7 cn e vried in mplitude nd frequency y men of PWM, the hpe of the output i fr from inuoidl. A reult, the hrmonic current ditortion, nd hence dditionl loe nd the reulting het genertion in the motor, re high. One wy to render the voltge wveform more deirle i to introduce more voltge level. To introduce nother imple nlogy, thi i imilr to increing the reolution on computer monitor to mke the grphic hrper. VSI topology nd modern power emiconductor i.3 kv. Thi i not enough for the tndrd rnge of medium voltge motor. 5 oncept of the new innovtive five-level inverter phe (left) nd the complete three-phe motor drive with nine-level phe-to-phe voltge ' U D U D +D -D i u ' ' U D U D U D U D The topology with two cpcitor nd n electronic three-poition witch, which i lo referred to the threelevel inverter ecue of the numer of output voltge comintion per +D -D +D -D u u i i M ABB AS 5000 converter ue five-level technology c' U D +D c c i c A further reon for wihing to move wy from the two-level rrngement i tht the highet output voltge tht cn e chieved with the two-level U D -D u c 6 ABB AS 5000 converter ue five-level technology, delivering nine-level phe-to-phe voltge to the motor ABB Review

5 Product innovtion phe, h een known for ome time. 3 how conceptul chemtic with three-poition witch. Thi circuit h to witch ny of the three connection point of the cpcitor to the output for oth current direction ). For pecific voltge nd current rting, ABB h tndrdized thi electronic three-poition witch 4 Power Electronic Building Block (PEBB). Thi tndrdiztion provide the dvntge tht the me uilding lock re ued in different ppliction, permitting ABB to collect field experience much more quickly nd o fine-tune the deign, providing higher reliility for the cutomer. Increing the numer of level drticlly improve the wveform. 7 Increing the numer of level from two, through three to five c drticlly improve the wveform, even for the miniml witching frequency hown U, U (P.U.) I (P.U.) Inverter output voltge u, u t (mec.) Motor current i U K (P.U.) I K (P.U.) Spectrum of inv. output voltge u hrmonic order k Spectrum of the motor current i - For out decde, thee uilding lock hve een ued for different product nd ytem, including converter for vrile peed drive (eg, in the AS 000 nd AS 6000 drive unit), energy torge ytem nd power qulity ytem t (mec.) inverter output voltge u, u hrmonic order k pectrum of Inv. output voltge u The five-level evolution omintion of higher numer of cpcitor nd increingly complex electronic circuit hve een dicued in cdemi for ome time. Uully, however, uch uggetion did not fit etlihed technologie for cpcitor energy torge, nor were they comptile with the propertie of the emiconductor witche the mrket hd to offer. Furthermore, uch u, u t (mec.) motor current i u k hrmonic order k pectrum of the motor current i Fctox ABB drive product rnge i i k ABB, the leding upplier of drive, offer the complete rnge of vrile peed drive for ppliction in the power rnge of kw to over 00 MW t (mec.) hrmonic order k The compny erve utilitie nd indutril cutomer in the cement, mining & minerl, chemicl, oil & g, mrine, metl nd pulp & pper indutrie. For further informtion, viit olution llowed little re-ue of exiting uilding lock, nd their reliility figure were quetionle due to high prt count. For the ltet ddition to it fmily of medium voltge drive, the AS 5000, ABB engineer looked ck t trditionl thyritor-ed product uch cycloconverter nd with the ville three-level uilding lock of 4 in mind cme up with n tonihingly imple olution for product with five output voltge level (nd 30 ABB Review 4007

6 Product innovtion 7c Inverter output voltge u, u Spectrum of Inv. output voltge u A 5-level power electronic uilding lock eily lide into the drive on ril u, u - u k t (mec.) hrmonic order k Motor current i Spectrum of the motor current i i i k t (mec.) hrmonic order k hence nine level phe-to-phe) 8. Thi w chieved y pplying the proven three-level technology in reltion to the tr point of the electricl ytem independently for ech phe. The conceptul circuit 5 i derived from identicl exiting uilding lock S nd S repectively. The well-etlihed technology of the three-level inverter i re-ued in n innovtive configurtion. Why five level? The phe-to-phe voltge wveform of two-level inverter nd three-level inverter re compred with tht of the new five-level converter 7c. The five-level inverter ued in the AS deliver nine-level phe-tophe voltge to the motor 8. Jut from looking t the wveform, it lredy ecome oviou tht the new five-level inverter produce n output tht i much cloer to the idel ine wve. In fct, the reult i o convincing tht it i now poile to ue motor deigned for direct-on-line connection without needing to de-rte them. Thi preent the optiml olution for 6 kv converter tody. Would dding further witching level e gol to further improve wveform? Such ttempt would ignificntly dd to complexity without delivering proportionl enefit. In prticulr, the reliility of the drive would get wore due to the higher prt count. 8 Uing five-level converter, the output voltge reche nine level phe-to-phe Volt Motor current Motor voltge 50 Hz opertion point Proven olution ABB h found urpriingly imple wy of creting ner-inuoidl voltge wveform with frequency converter lrgely ed on proven, exiting component. The well etlihed technology of the three-level inverter i re-ued in n innovtive configurtion, providing five-voltge level per phe, or even nine-voltge level phe-to-phe. The full re-ue of ic power electronic uilding lock llow thee excellent output wveform to e chieved with proven r eliility. The gol to ue tndrd motor i reched while mintining high efficiency with low prt count Amp Pieder Jörg Gerld Scheuer Per Wiktröm ABB Switzerlnd Ltd. Turgi, Switzerlnd [email protected] [email protected] [email protected] Footnote ) Mot high-power emiconductor device cn conduct current in only one direction. ABB Review