AUTOMATIC ON-LINE OPTIMIZATION OF AC WOUND MOTOR'S ROTOR RESISTORS IN ADVANCED INDUSTRIAL CRANE CONTROLLER

Transcription

1 AUTOMATIC ON-LINE OPTIMIZATION OF AC WOUN MOTOR'S ROTOR RESISTORS IN AVANCE INUSTRIAL CRANE CONTROLLER 16 th Int. Conference on Electrcal rves and Power Electroncs Slovaka September 4 6, 007 Fetah Kolonc 1, Alojz Slutej, Alen Poljugan 1 1 Faculty of Electrcal Engneerng and Computng, HR Zagreb, Croata* tel./fax / , e-mal: fetah.kolonc@fer.hr, alen.poljugan@fer.hr ABB Industral Systems AB, S Västerås, Sweden** / 40 90, e-mal: alojz.slutej@se.abb.com Abstract. gtal ntegrated ndustral controller s a specally desgned speed control system for the cranes and another heavy duty materal handlng systems. It s ntended for wound (slp-rng) motors and fully supports stator voltage control, rotor step swtchng, postonng, brake control and another applcaton functons. Bascally, the controller performs stator and rotor control functons. Stator control s related to the stator voltage control (motor torque control), usng phase controlled AC/AC converter. The rotor control ncludes rotor resstor optmzaton logc, whch changes the amount of the external added resstors n the rotor crcut by means of the rotor contactors. In ths paper specal attenton s pad to the automatc rotor resstor optmzaton logc, realzed n the crane applcaton program n separate software module. All the applcaton functons are runnng on the MC6833 mcrocontroller. Usng process I/O dgtal outputs, man control board drectly drve rotor contactors whch optmze rotor addtonal resstors. The control system also ncludes protectve functons, necessary for crane motor drves applcaton. Keywords: AC/AC converters, Industral applcatons, Speed control, Torque control, AC wound machne, rotor resstors swtchng 1. INTROUCTION Of the drve systems sutable for the sze between kw, the stator voltage controlled systems wth wound motors (ncludng rotor resstor control) snce long tme has been and stll s very sutable soluton. There are a lot ndustral applcatons based on the system mentoned, such as materal handlng systems, ppe and paper mlls, steel and rollng mlls, contaner loadng/unloadng cranes, power plants, engneerng workshops, etc. For the crane drve that most of ts tme s run n full speed up or full speed down, the losses except motors and cables are about 4% of the motor power. The fgure s smlar to the descrbed stator voltage controlled system for wound motors and a regeneratve frequency nverter drve system as well as a regeneratve C-drve system, [1]. However, the stator voltage controlled system has the mportant feature that the mayor part of the losses occurs n an external resstor(s), not nsde the electrcal equpment. Also, the regeneraton of the full speed lowerng energy s based on drect connecton by fully conductng phase control thyrstors of the oversynchronously runnng motor to the mans. In ths mode, wth a slghtly hgher speed then the motors synchronous, the motor wll regenerate the energy back to the lne n the most robust manner. When the lowerng speed s approachng the synchronous, the rotor resstor s mnmzed and the drecton of torque changes electroncally. The new ntegrated drve controller mnmzes the stator current and senstvty to lne voltage fluctuatons consderng the requred torque, [-5]. The controller wth wound motor s more robust for the nstantaneous qualty of the lne voltage than another type of the AC or C drve. Of ths reason t has been meanngful to desgn the advanced ntegrated controller capable to perform desred tasks at a lne voltage as low as 75% of the nomnal voltage In ths paper a specal attenton wll be pad to the automatc rotor resstor optmzaton logc. By means of the rotor contactors, ths logc uses specal automatc procedure to choose the optmal motor characterstc, takng nto account maxmal motor torque and stator current lmt, rotor resstor heatng, supply voltage and number of resstor steps. The optmzaton of the rotor resstance, changng the addtonal (external) added resstors, s realzed n a fully automatc way gvng to the motor the rght characterstcs.. CONTROLLER STRUCTURE Speed control systems for crane and heavy duty materal handlng purposes are well establshed systems usng AC/AC phase angle controlled thyrstor converters, [-5]. The crane controller performs stator and rotor control functons. By means of a par of thyrstors n each phase, stator voltage can be contnuously controlled. Usng fve thyrstors pars (three pars n each phase and two pars for reversng) four quadrant operaton s realzed. Because the avalable motor torque of nducton motor s proportonal for each speed to the square of the stator voltage, the speed control s obtaned by varyng the stator voltage so that the desred speed s obtaned for a gven load. Rotor control gves to the motor the rght characterstcs optmzng the external rotor resstance. When lowerng wth a slghtly hgher speed than the motors synchronous (potental load n 1

2 host drves), the motor wll regenerate the energy back to the lne n the most robust manner. Ths regon of operaton wth oversynchronous regeneratve brakng s often used. Fg.1 Structure of the ndustral crane controller Ths s because n the reverse current brakng, as another soluton, lowerng close to synchronous speed would result n slp close to two, and consequently overheatng addtonal external rotor resstors. It can be seen from the Fg.1. that the core of the systems s man control board (control module) realzed on the MC6833 mcrocontroller, runnng the crane applcaton program Control module generates the frng pulses to the thyrstor module by means of a conventonal wre, whch lmts the dstance between these unts to a few meters. Rotor voltage frequency estmaton unt estmates speed (slp) based on the rotor voltage frequency measurement and sends ths nformaton va the process unt to the man control board, [3]. Torque estmaton unt estmates the machne torque based on the stator voltage and current measurement, [4]. Estmated torque sgnal s also sent to the man control board. Estmator unts are based on the AMC300 SP board and ncluded n the control system modular structure as a separate module. The man control board performs the speed control task and communcates wth all other unts n the drve controller, [5]. All control system connectons to Master/Follower communcaton, Overrdng control and Process control (ncludng cabn I/O communcaton) are made by optcal fber, Fg.1. a). The communcaton s realzed wth two communcaton mcrocontrollers SAB853. etals can be found n [5]. Speed or torque (selected va parameter) control loop wth nner current control loop s presented n Fg.. Controllers are generally PI type, wth parameters and structure dependent on the specfc applcatons. Control algorthm s runnng on the control board whle the controller parameters settngs, program downloadng, montorng and data recordng are performed on the PC, Fg.1. It s possble to use mechancal speed feedback sensors (tachogenerator and ncremental encoder) as well as speed estmator based on the rotor voltage frequency measurement, [3]. Fg.. The speed control structure of the AC wound motor based ndustral controller

3 3. ROTOR RESISTOR CONTACTOR SWITCHING LOGIC Once upon a tme, n the begnnng of the AC machne control era, manly one effcent speed control of AC machnes for ndustral applcaton was used. That control was appled on the AC wound motor. It was focused manly on the rotor motor sde usng speed-based rotor contactor swtchng for dscontnuous addtonal external rotor resstor change. Statonary 'world' (stator) and rotatonal 'world' (rotor) were connected wth smple nterface; rotatng rngs and statonary brushes. Thanks to that, AC wound motor was surely unque electrcal AC machnes capable to start wth maxmal avalable torque and at the same tme drawng mnmal stator current from the mans. In those years t was very pragmatc soluton to use AC wound motors for those tasks, because of ts hgh robustness and very smple and effectve speed/torque control from the rotor sde. Nowadays, thanks to the refurbshment requrements assocated to the wound motor, conventonal rotor resstor swtchng logc s replaced by the advanced one. Heren, the new developed rotor resstor swtchng logc s presented. As mentoned earler, the new method s based n the on-lne automatc optmzaton of the rotor resstors by means of rotor contactors. For any sampled motor speed, defned stator current lmt, maxmal torque avalable, resstor temperature and supply voltage, the man task s to fnd the optmal resstor to be swtched n the rotor crcut n order to fulfll some optmal crteron. Ths crteron can be, e.g. maxmal developed motor torque at ths sample tme, calculated for each addtonal external resstor. Among the all of calculated torques avalable for each addtonal rotor resstor, one resstor (the best n optmalty sense) wll be chosen and connected to the rotor by means of contactor. All contactors are handlng by dgtal outputs (O) of the process I/O board, Fg.1. Fg.3. Schematcs of the rotor resstor swtchng The schematcs of the 5 steps rotor resstors (R1-R5) wth 4 contactors (K0-K3) drven by process I/O dgtal (O1- O4) respectvely s presented on Fg.3. The resstor value ΣR has to be chosen accordng to specfc ndustral applcaton. For dfferent types of movements (e.g. hostng, plug mode lowerng, oversynchronous regeneratve mode Fg.4. Flowchart dagram of the rotor resstor swtchng logc 3

4 lowerng, travelng, etc), the values suggested n [] gve trouble-free performance n most stuatons. Resstor value ΣR s calculated as Rm + Rc + R1 + R + + R Σ R = 100%, R where R s ohmc value of the external rotor resstor R and R 100 s unty resstance defned as 100 P R100 =. () 3 I r n ( ) [ Ω] 1 s n Unty resstance s defned as resstance that wll hold the motor at zero speed wth nomnal load and nomnal voltage. The values ΣR used n ndustral applcatons are usually 8, 18, 38, 65, and 100% of the unty resstance R 100. The values ΣR4 and ΣR5 are only used for lowerng, where the load requrement s lower than n the hostng drecton. The resstors R m and R c are defned as [ Ω], R 0, R [ Ω] Rm = R100 sn c Here R m s the rotor resstor value whch gves nomnal slp at nomnal load and nomnal voltage supply (n other words ths s nomnal slp part of the motors unty resstance) and R c s ohmc value of the cable between motor and resstors. Now all elements for R calculaton, based on, are noun. Influence of the resstor change n dependence of the temperature, s consdered throe the followng equatons R R C W = R ( K /100)) (4) ( R = R ( K /100)), (5) ( R where R C and R W are rotor resstors n cold and warm state and K R s percent change n resstor value caused by the temperature. For the other ntal calculaton n Fg.4, t s needed to make a basc calculaton. Stator voltage and rotor speed measurement are nherent n each wound nducton motor controller based on the stator voltage and rotor resstor control, [1-5]. Before the maxmal torques calculaton logc starts (see Fg.4), mode of operaton should be determned. Ths s because the rotor contactor logc s workng n a dfferent way for a dfferent mode of operaton. Wth the frst decson block n flowchart dagram n Fg.4, t s assgned whether the drve s n subsynchronous or n oversynchronous (pluggng or regeneratve) regon. For subsynchronous regon of operaton, operaton mode s tested. rve mode s defned on the base of drecton of the moton requested, drecton of the feld (converter state), type of the moton (hostng potental loads, travelng reactve loads) and actual motor speed. Motor must be able to produce requested torque (TREQ); LIMP requested torque for postve and LIMN for negatve mode. Then the possble motor torques for each R resstor at each speed for cold and warm state are calculated accordng to equatons T T C W TM s = MIN s + scm TM s = MIN s + swm CM WM s I ; s I ; lm lm s s R R C W (6).(7) Here T C and T W are possble torques n cold and warm state for -th rotor resstors at slp s (as a multple of nomnal torque) and U and I lm are supply voltage and current lmt. At maxmal (breakdown) torque T M, slp n cold and warm state s WM and s CM s defned as s R ( T + T 1) (8) = CM C M M s R ( T + T 1). (9) = CW W M M What s the basc strategy? Check n order possble motor torques T 5, T 4,..,T 1 to fnd a T that s bgger than TREQ, Fg.4. As soon as the T s found, the rght external resstor (.e. rght contactor swtchng accordng to Table 1.) s defned. Table 1. Contactor swtchng logc TREQ K 0 K 1 K K 3 TPOSS1> TPOSS> TPOSS3> TPOSS4> TPOSS5> It should be emphaszed here that the rotor contactors should never be addtonally controlled by any PLC or smlar. It s mportant that the Os of the controller drectly handle the rotor contactors. It means that the rotor control s an ntegrated part of the real tme moton control wth 3 ms samplng tme. In order to help the user to calculate the resstor values and to study the result of the voltage fluctuatons and current lmts, the resstor checker applcaton tool s desgned. The applcaton tool has two worksheets n Mcrosoft EXCEL envronment. Based on the data of motor, voltage supply and resstor value ΣR selected, frst sheet returns the nomnal torque of the motor and the Ohm values of the resstor steps n the same sheet. The torque speed dagram s another tab of the worksheet, Fg.5. It s based on the data of the nput sheet. The torque speed dagram s shown and by varyng the nput data, advanced smulatons can be done 4

5 and help to get good engneerng solutons for the specfed moton control, []. M1 AC wound motor (380V, 18,5kW, 1450rpm) M C separately excted motor (0V, 17kW, 1500rpm) TG tachogenerator Fg.6. Laboratory test bench for expermental verfcaton of automatc rotor contactor swtchng logc Fg.5. Rotor resstors checker worksheet 4. EXPERIMENTAL RESULTS Comparson between conventonal (manual, speed base rotor contactor swtchng logc) and proposed automatc rotor contactor swtchng logc has been performed on the laboratory test bench, Fg. 6. (etaled descrpton n [3-5]). Target AC wound motor drven wth developed controller ASTAT s mechancally coupled wth C motor. The latter s drven by the SIMOREG controller n torque mode loadng target AC motor. In Fg.7.and 8. the comparson between automatc and manual rotor contactor handler for no load a) and cca 80% rated torque b) s presented. Practcally, there s no dfference n responses. The steady state speed error n hostng drecton s a consequence of the nherent AC saturaton characterstc (Fg.7b and 8b). The good performance of the automatc rotor contactor () () a) s b) s Fg. 7. Performance of the AUTOMATIC rotor contactor handler n one workng cycle; hostng mode wth pluggng subsynchronous brakng wth no load a) and cca 80% rated torque load b). Scale =50% for ref.speed and actual speed (), 100% for motor torque. () () a) s b) s Fg..8. Performance of the MANUAL rotor contactor handler n one workng cycle; hostng mode wth pluggng subsynchronous brakng wth no load a) and cca 80% rated torque load b). Scale =50% for ref.speed and actual speed (), 100% for motor torque. 5

6 () s a) () b) s Fg. 9. Performance of the AUTOMATIC rotor contactor handler n one workng cycle; hostng wth regeneratve oversynchronous lowerng brakng, load 0% a) and 80% rated torque b). Scale =50% for ref. speed and actual speed (), 100% for motor torque. () a) s () b) s Fg.10. Performance of the MANUAL rotor contactor handler n one workng cycle; hostng wth regeneratve oversynchronous lowerng brakng, load 0% a) and 80%of rated torque b). Scale =50% for ref. speed and actual speed (), 100% for motor torque. handler s confrmed also n representatve demand task oversynchronous regeneratve brakng, (Fg.9.). It s obvous n comparson wth manual rotor contactor (Fg.10.) that usng automatc rotor contactor handler extra tme and money for the commssonng wll be avoded wth the same control performances preserved. 5. CONCLUSION Ths automatc procedure developed for the optmal rotor resstor swtchng s a part of the complex crane applcaton program realzed on the MC6833 mcrocontroller. However, electromagnetc motor torque needed for calculaton, s runnng on the SP AMC300 and owng to modular controller desgn, the actual torque nformaton s transferred to the man board thru fast RS4 lnk. Here s expermentally approved that algorthm for ON-LINE rotor resstor calculaton has excellent features n all requested modes of operaton and can replace successfully standard speed-based rotor contactor handler where contactor swtchng ponts has to be calculated n advance, each tme for the new ndustral applcaton. From ndustral pont of vew, ths means no extra cost for addtonal commssonng caused by speed-based swtchng ponts determnaton. 6. REFERENCES [1].., ASTAT, economy and precson for safe heavy duty crane applcatons, ABB Industral Systems AB, Crane & Harbour Systems, ReklamCenter AB (603), Västerås, Sweden, 05/1996. [].., ASTAT Crane Moton Control, (C-ROM), Manual, ABB Automaton System, 000. [3] F. Kolonć, T. Idžotć, A. Slutej. Sensorless speed control of slp-rng AC motor based on rotor voltage frequency estmaton, Proceedngs of the EPE 001, Graz, Austra, 7-9 August, pp 01163, 001. [4] F. Kolonć, A. Slutej, A. Poljugan. Torque estmaton n ndustral control system wth AC slp - rng motors, Proceedngs of the 10 th EPE-PEMC 00 (C ROM), ubrovnk, Croata, September, 00. [5] A. Slutej, F. Kolonć. Control network as a backbone of the crane moton control system, Proceedngs of the EPE-PEMC 00 (C ROM), ubrovnk, Croata, September, 00. ACKNOWLEGEMENT The project of ndustral controller (wth commercal name ASTAT ) s result of mutual cooperaton between Faculty of Electrcal Engneerng and Computng (Zagreb, Croata) and Swedsh company ABB, and t s fnancally supported by ABB. As a result of cooperaton, over 000 ndustral applcatons, especally n the crane and another heavy duty materal handlng systems are nstalled all over the world. 6

7 THE AUTHOR(S) Fetah Kolonć (1956) receved hs Ph..E.E. n 1997, M.S.E.E. n 1990 and B.S.E.E. n 1980 at the Unversty of Zagreb, Croata. He s currently assocate professor at the Faculty of Electrcal Engneerng and Computng, Unversty of Zagreb. Hs areas of nterest are control of electrcal drves and power converters, optmal and robust control of ndustral systems and ntegraton structure n complex mechatronc systems. As a prncpal nvestgator and project leader he has been conductng several projects funded by nternatonal and Croatan ndustry as well as by the Croatan government. Hs teachng and research nclude applcaton of advanced control technques n ndustral systems. He has been coauthor of many papers publshed n journals and presented at the natonal and nternatonal conferences. He s the member of KOREMA, Croatan Natonal Commttee CIGRE and IEEE (Robotcs and Automaton Socety). Alojz Slutej (1950) receved hs Ph..E.E. n 1986, M.S.E.E. n 1981 and B.S.E.E. n 1980 at the Unversty of Zagreb, Croata. He s employed as Senor System Engneer and works as techncal expert n ABB Crane & Harbour dvson n Sweden. Hs nterest s mostly n hardware and software development regardng automated contaner cranes actvtes. Partly, he s engaged as assocate professor at the Faculty of Electrcal Engneerng and Computng, Unversty of Zagreb. He has been co-author of many papers publshed n journals and presented at the natonal and nternatonal conferences. He s the member of IFAC CC Techncal commttee for dstrbuted control systems, AISE (USA Assocaton of Iron and Steel Engneers) and KoREMA (Croatan Socety for Communcatons, Computng, Electroncs, Measurement and Control). Alen Poljugan (1977) receved hs M.S.E.E. n 005 and B.S.E.E. n 001 at the Unversty of Zagreb, Croata. From 001 he works as assstant at the Faculty of electrcal engneerng and computng (epartment of electrcal machnes, drves and automaton). Hs fled of nterests are control of electrcal drves and power converters, optmal and robust control of ndustral systems and ntegraton structure n complex mechatronc systems. He has been co-author of several papers publshed at the natonal and nternatonal conferences. 7