Managing Transients Generated by the Reconfiguration Process at the Tandem Inverter Fed Induction Motor

Transcription

1 IEEE 7 th Internatonal Conference on Intellgent Engneerng Systems March 46, 3 Managng Transents Generated by the Reconfguraton Process at the Tandem Inverter Fed Inducton Motor József Vásárhely * Mára Imecs ** Csaba Szabó ** Ioan Iov Incze ** Ádám Thamér * *Department of Automaton, Department of Electrcal Drves and Robots Unversty of Mskolc Techncal Unversty of ClujNapoca H355 Mskolc Egyetemváros, Hungary RO34 Cluj str. Dacovcu 5, Hungary Romana {vajo, adam@mazsola.t.unmskolc.hu} {mecs, csaba.szabo,oan.ncze@edr.utcluj.ro} Abstract The paper focuses on the reconfguraton process of vector control systems of the nducton motor suppled from the tandem (hybrd) statcfrequency converter. Reconfgurable control structure ensures dfferent strateges for operatng modes wth nonfaled and partalfaled converter. The reconfguraton process ntroduces perturbatons n the vector controlled AC drves. The paper analyses the perturbaton effects of the control system reconfguraton and presents smulaton results. The paper tres to gve some solutons for the transent management. Problems related to hardware and software mplementaton of the transton from a control structure to another are dscussed. Smulaton results are presented for both basc topologes of the feldorented control system The smulaton results were obtaned wth the help of a module lbrary created n Matlab Smulnk specal for mplementaton n Feld Programmable Gate Arrays (FPGA) of vector control structures for AC drves. I. INTRODUCTION Reconfgurable hardware was used n vector control n the last years for control system mplementatons [.], [3.], [5.]. In vector control systems, the reconfgurablty was ntroduced by Imecs et all n [4.]. When reconfguraton condton occurs, the system wll start reconfguraton process n whch t swtches the current confguraton to the next correspondng one. Ths type of confguraton s the context swtchng and was developed by Scalera n [.]. Whle context swtchng s a reconfguraton technology for Feld Programmable Gate Arrays (FPGA), the logc state machne (wth dfferent control system structure n each state) s a reconfguraton method for vector control systems. Reconfguraton of vector control systems was treated n [4.]. For each vector control scheme one have to assocate a state of the confguraton state machne supervsed by the confguraton manager. Shraz et al n [.] treated the runtme management of dynamcally reconfgurable devces. The confguraton state machne assocated to the reconfguraton of the tandem converter system was treated n [5.] (Fg ). The perturbatons ntroduced by the reconfguraton process were treated n [6.]. Ths paper tres to analyse and gve a soluton for the transent management durng the reconfguraton process. II. RECONFIGURATION OF TANDEM CONVERTER CONTROL SYSTEM The term tandem converter denotes a soluton of DC lnk Statc Frequency Converters (SFC), used n medum and hghpower AC drves [3.], [4.]. It combnes the advantages of the two component nverters, wth dfferent source character (current and voltage) and dfferent modulaton method. The larger CurrentSource Inverter (CSI) s operatng n Pulse Ampltude Modulaton (PAM) and converts the actve power, whle the smaller VoltageSource Inverter (VSI) s workng n Pulse Wdth Modulaton (PWM) and supples the reactve power requred for mprovng the qualty of the motor currents [5.], [3.] and [4.]. If one of the two converters s not workng (.e. t fals) the control system structure needs to be reconfg.d n order to be able to mantan the control of the drve. The vector control system should be reconfg.d f one of the converters fals. The most senstve stuaton for the tandem converter s when the VSI fals, because the control structure looses ts voltagesource character [5.]. In such a stuaton, the motor s fed only by the CSI and the current control concept wll be appled. Under these crcumstances the control structure does not correspondng any more for the new demands and ths justfes the need for reconfguraton. Poweron Int STATE Tandem Converter STATE 3 VSI Converter STATE CSI Converter Fg. Reconfgurable state machne wth dfferent vector control structures n each state 388

2 IEEE 7 th Internatonal Conference on Intellgent Engneerng Systems March 46, 3 Several reconfguraton methods were treated by Luk [8.], but the most sutable method for the vector control systems s to so called context swtchng method mentoned n [.], where the confguraton manager swtch between the confguraton contexts. One has to allocate for each context a control structure of the vector control system. There are three possble precomputed structures as presented n Fg and the frst two control structures are descrbed n detal n [4.], [5.]. These control structures are as follows: tandem converter (the VSI + CSI s workng together), voltage source nverter (CSI fals) and currentsource nverter structure (when VSI fals). The reconfguraton of a control system ntroduces perturbatons n the control system, whch actually are transents generated by the changes of the control structure. The man problem of the reconfguraton s that, whle the transents generated n the control system are low power transents, the perturbatons, whch appear n the nducton motor and converter, have hgh power character. In order to make possble the reconfguraton and analyse the perturbatons ntroduced by the reconfguraton process n the AC drve let us present wo control schemes on whch the reconfguraton was studed. Fg. present the vector control system correspondng to the reconfguraton state machne presented n Fg, for the state and. The thrd possblty reconfguraton to state 3 was not studed yet. The multplexers from Fg. are a possble representaton of the transton from one state to the other. But one should note that, whle these components may be ndeed possble mplementatons, they are ntended to be abstract enttes dd not need any mplementaton as was presented by Luk n [8.] Fg. represent the schemes for the control structures of the nducton motor n two dfferent stuatons, as follows [5.]. Tandemconverterfed nducton motor operates wth statorfeld orentaton (Fg. state ). Usng two parallel nverters to supply the motor s no more necessary to apply PWM procedure to control the whole energy of the load, because a large value of the energy s transferred through the PAMCSI converter. Consequently, n comparson wth an equvalent PWM VSI, the tandem nverter swtchng losses wll be consderable reduced. The currents of the AC machne should acheve the snewave pattern. The output currents of the tandem converter (.e. the load currents) n each phase are to be equal to the fundamental currents of the prmary CSI nverter. The current n a phase of the secondary VSI can be expressed as the output fundamental current of the prmary nverter mnus the squarewave CSI current n the same phase. In Fg. 3 are shown the motor, CSI and VSI currents, and the currents n the AC drve are: s_a,b,c = CSI_a,b,c + VSI_a,b,c. DClnk current () AC lne ω r+ ω r Ψ s r + m e Speed Identfed Torque Flux + m e m e C Ψ s Identfed Feld Mechancal Angular Speed Torque sdλs sqλs Torque Computaton StatorVoltage Computaton V S C ω λs Ψ s,r v sd, qλs VA Coordnate Transformaton sdλs,r sqλs,r CooT [D(λ s )] cosλ CooT [D(λ s )] Ψ sd,q snλ sd,q x sd,q sd,q Coordnate Transformaton Ψ r Co sd,q Ψ rd,q RotorFlux Compensaton Ψ md,q s π 3 VA CSI Current Vector Analyser v sd,q ω λs DC ε s v sd,q VA 3 Ψ S C + Statorflux Ψ m Co Computaton Argapflux Compensaton Synchronsaton v sd,q v s γ s sd,q α PWM logc SVM PhT DC PhT f s ε CSI Phase Transformaton Phase Controlled Rectfer V d [v s ] [ s ] PAM CSI L d Dode Rectfer C d PWM VSI Inducton Motor 3xC Fg.. Statorfeldorented vector control system for the tandem converterfed nducton motor 389

3 IEEE 7 th Internatonal Conference on Intellgent Engneerng Systems March 46, 3 s Durng ths tme the motor change ts workng parameters compared to the reference CSI VSI Tme[sec] Fg. 3. Current waveforms at the output of the tandem converter. CSIfed nducton motor. If the VSI fals, t s decoupled from the motor termnals and the CSI wll supply alone the motor. Due to the currentsourcecharacter of the CSI the motor control need to be reconfg.d to rotor feld orentaton (see Fg. correspondng to state ) or stator feld orentaton. Fg. 4. Current waveforms before and after reconfguraton. It can be observed that the reconfguraton ntroduces perturbatons n every observed parameter of the drve (Fg. 5 and Fg. 6). III. PERTURBATIONS INTRODUCED BY THE RECONFIGURATION PROCESS In the case of the tandem nverter when the VSI fals control system wll start a self reconfguraton process conform to the reconfguraton dagram presented n Fg. To vsualse the reconfguraton process, the control structure from Fg. was smulated usng MATLABSmulnk envronment. The motor was started wth the tandem converter and the reconfguraton was made after.5s. The smulaton structure used the module lbrary created wth the Xlnx System Generator and presented n [6.]. The nducton motor data used for smulaton are: 5.5 kw, 5 Hz, V rms, 4 A rms, cosφ =.735 and 7 rpm (4 polepars). As mentoned the reconfguraton of a vector control system s necessary n certan crcumstances, so the effects ntroduced by the transents are unavodable. For ths reason one have to pay attenton to the transent management durng the reconfguraton process. The transents appear usually as damped oscllatory motons, whch persst for relatvely short tme after the reconfguraton has occurred as was treated for the transents n dgtal sgnal processng for lnear systems [9.]. For vector control systems, whch are nonlnear systems, the perturbatons ntroduced n the AC drve appear manly because of the transton from voltagecontrolled character (tandem converter fed CSI+VSI) to the current or/and voltage controlled character (current nverter fed CSI or/and voltage fed CSI) of the AC drve. In Fg. 4 can be observed the perturbatons ntroduced n the stator currents. The transent effects on the AC drve whle the stator current waveforms became snusodal agan can be observed for.s. Fg. 5. Statorcurrent spacephasor. Fg. 6. Rotor and stator resultant flux. The smulaton results were compared wth [5.], and they show that the reconfguraton fulfls the expectatons, and nfluences the motor performances, too. IV. Implementaton The algorthms of the computng blocks were decomposed n elementary mathematcal operatons, 39

4 IEEE 7 th Internatonal Conference on Intellgent Engneerng Systems March 46, 3 and a module lbrary was ssued for the reconfguraton, usng Matlab n order to mplement t n FPGA structure. From the analyss of vector control schemes results that vector control schemes presents modularty [.], [.], [3.] and [6.]. The modules used at one vector control scheme are reusable to another one. One can conclude that the modularty s ndependent of the used vector control schemes. Also the modules can be reduced to a common form represented by the equatons: g d = a d x d + b d y d ; (a) g q = a q x q + b q y q,, (b) where g d and g q are the output varables of the actual workng block, a d,q and b d,q may be parameters or nput varables resultng from a prevous block, x d,q and y d,q are also nput varables of the same block resultng from another prevous block [6.]. The module lbrary allows a rapd prototypng and fast mplementaton of the vector control structures n FPGAs [6.]. As presented n equaton () the modules have a general form, whch s also presented n [5.]. Usng ths generalsed module to mplement each module of the module lbrary wll result n smlar hardware resource consumpton for each module. a d x d b d y d ; a q x q g d The hardware resources occuped n the FPGA by each module The quantsaton error of the module All these crtera nfluence the mplementaton of the vector control system n one FPGA or n a dstrbuted FPGA array. To show the hardware resources consumed by one module wth the mathematcal form of equatons (), n Table. The smulaton of the control structure shown that the quantsaton error s smaller then.6 * 3, and s presented n Fg. 8 Release 4..3 Map E.33 Xlnx Mappng Report Fle for Desgn Desgn Informaton Number of Slces: 5 out of 3,7 % Number of Slces contanng Unrelated logc: out of 65 % Total Number 4 nput LUTs:, out of 6,44 9% Number used as LUTs:,8 Number used as a routethru: 4 Total equvalent gate count for desgn: 5,579 The Delay Summary Report The Score for ths desgn s: 534 The Average Connecton Delay for ths desgn s:.969 ns The Maxmum Pn Delay s:.56 ns The Average Connecton Delay on the Worst Nets s: 7.36 ns Lstng Pn Delays by value: (ns) d<.<d<4.<d<6.<d<8.<d<. d >= b q y q g q Table. Hardware resources consumed and tme delay ntroduced by the module CooT[D(λ)] Fg. 7. Unversal computaton module of vector control systems Naturally where constants are one of the nputs the modules became much smple. Usually the mplementatons of control systems for AC drves make use of the mentoned general form of the equatons. And they are sequental ones as presented by [.], [3.]. As the tandem nverter has to be confg.d and there are varable value transfer problems, for the control structure presented n Fg., t was chosen the parallel mplementaton method. In the mean tme some modules present exceptons from the generalsed form. These modules are the PI controllers and the Vector Analyser (VA) module. When analysng the performances of the modules of the parallel mplementatons one should consder the followngs: The tme delay ntroduced by each module, The maxmum workng frequency of the FPGA, Fg. 8. Quantsaton error of block CooT[D(λ)] V. Transent Management Because of the reconfguraton from one control structure to another (.e. from tandem CSI+VSI to CSI structure), may appear some unavodable and undesred transents n the controlled varables of the drve. The transents appear usually as damped oscllatory sgnals, whch persst for relatvely short tme after the 39

5 IEEE 7 th Internatonal Conference on Intellgent Engneerng Systems March 46, 3 reconfguraton has occurred. The transents were treated for reconfgurable control loops also n [9.], [.]. There are several solutons for the reducton of reconfguraton transents. Pécel presented the transent reducton methods and treated for flterng problems n [9.] The transents n the reconfgurable vector control system appear at the drve as hgh power perturbatons, and nfluence the dynamc performance of the drve system. The perturbatons are generated due to the changes of the control structure,.e. of the hardware structure. The reconfguraton transents for the AC drve act as dsturbances and reduce the qualty of the drve performances (Fg. 9). s CSI VSI / C stablty of the control system but the acton have to be done n all the controllers. Takng the flux controller functon for example one should consder the control functon contnuty at the reconfguraton tme t r, whch means: (t ) = sdλr k = k p p ( Ψr ) + k ( Ψr ) ( Ψr ) + k ( Ψr ) dt for t t dt for t < t () where the sdλ r s the d component stator reference current, Ψr s the reference rotor flux, Ψ r s the calculated actual rotor flux and t rec s the tme when the reconfguraton s done. The transent flterng t would be successful, when the controlled d component stator current functon conform equaton () s contnue at t rec. Ths means: sd λ r ( trec ) = sd λr ( trec + ); (3) To show the partal results acheved by the transent management n Fg., Fg. are presented some smulaton results. tec tec ; ; tme[s] Fg. 9. Smulated current waveforms before and after reconfguraton. For ths reason t s mportant to reduce the reconfguraton transents. Let us take the case of the reconfguraton from State to State, the case when the VSI fals. The source of perturbaton s also the swtchng process from the faled VSI to the capactors. Ths swtchng s also part of the reconfguraton but ths has drectly nfluences on the stator currents. The overall nfluence of the reconfguraton,.e. the ntroduced perturbatons, can be observed n Fg. 9. In ths case, the perturbatons ntroduced n the AC drve appear manly because of the reconfguraton from a structure, whch has voltagecontrolled character (.e. for the tandem converterfed motor) to another structure wth currentcontrolled character (.e. for the CSIfedmotor) of the drve. The transents ampltude and duratons also depends on the controlled character of the state n whch t wll be reconfg.d the tandem converter. If both control structures, have the same control character (.e. voltage or current), then the transent maxmal ampltude wll be smaller and the duraton shorter. If one has a look on the possbltes to manage the transents then on Fg., may be observed that are very few modules where the transent flterng can be solved. There are the PI controllers of flux, torque, and speed, and there s the DC lnk PI controller. One may found that f the DC lnk wll have PID character there s possble to flter the transents, but ths nfluence the controller actons on the controlled reference flux and speed. So the transent management should act n concordance wth the Fg.. Motor current stator space phasor Fg.. Statorflux space phasor. There can be observed n the smulaton results that the transent nfluences were dmnshed. VI. CONCLUSIONS The transents of the reconfguratonreconfguraton process generate perturbatons n the AC. Each varable reacts n partcular way to the reconfguraton. The stator flux controlled before reconfguraton s senstve to the transents for about.5s, whle the rotor flux, whch s controlled after reconfguraton, wll reach the controlled level n about.s. The transent management should flter completely the perturbaton n the drve. The obtaned 39

6 IEEE 7 th Internatonal Conference on Intellgent Engneerng Systems March 46, 3 partal results are promsng, but stll not gve the expected flterng level. Further research should be made to fnd solutons for the compensaton of these negatve effects. ACKNOWLEDGEMENT The tandem nverter the subject of a research project supported by Danfoss Drves A/S was realzed at the Insttute of Energy Technology, Aalborg Unversty, Denmark. Specal thanks to Prof. A. Trzynadlowsk from Nevada Unversty, Reno, USA for the collaboraton n ths theme, to Prof. F. Blaabjerg from the Aalborg Unversty and to the Danfoss Drve A/S, Denmark for ther generous support. The authors are grateful to Xlnx Inc. and Trscend Inc. and specal thanks for Mr. Chrs Balough for donatons, whch made possble the research on some aspects of reconfgurable vectror control framework. REFERENCES [.] AUBÉPART F., POURE P., BRAUN F., Contrbuton to SystemonChp n moton control: VLSI desgn of a dgtal controller for an nducton machne, PCIM Power Electroncs Intellgent Moton Power Qualty, June 9, Nuremberg, Germany, pp. 6 [.] BELMIMOUN M. H., MONMASSON E., SAMBUIS E., Modularty n Code Development for DTSFC Algorthms Implementaton on a FxedPont DSP, PCIM Power Electroncs Intellgent Moton Power Qualty, May 6, Nuremberg, Germany, pp.935 [3.] CIRSTEA M., AOUNIS A., MCCORMICK M., Rapd Prototypng of Inducton Motor Vector Control System Based on Reusable VHDL Dgtal Archtectures and FPGA Implementaton, PCIM Power Electroncs Intellgent Moton Power Qualty, May 46, Nuremberg, Germany, pp [4.] IMECS Mara, BIKFALVI P., NEDEVSCHI S., VÁSÁRHELYI J.: Implementaton of a Confgurable for an AC Drve Control a Case Study, Proceedngs of the Conference on Feld Programmable Custom Computng Machnes FCCM Conference, Napa Valley, USA, 69 Aprl. pp [5.] IMECS Mára, INCZE J. J., VÁSÁRHELYI J., SZABÓ Cs.: Tandem Converter Fed Inducton Motor Drve Controlled Wth ReConfgurable Vector Control System, PCIM Power Electroncs Intellgent Moton Power Qualty, June 9, Nuremberg, Germany, pp [6.] IMECS Mára, VÁSÁRHELYI J., INCZE J. J., SZABÓ Cs.: Vector Control Of Tandem Converter Fed Inducton Motor Drve Usng Confgurable System On A Chp, INES IEEE Internatonal Conference on Intellgent Engneerng Systems, Sept. 68,, HelsnkStockholm, FnlandSweden, pp [7.] KELEMEN Á., IMECS Mara: Vector Control of AC Drves. Volume : Vector Control of Inducton Machne Drves. OMIKK Publsher Budapest, 99, ISBN [8.] LUK W., SHIRAZI N., CHEUNG P., Modelng and Optmzng Runtme Reconfgurable Systems, Proceedngs FCCM96, IEEE Computer Socety Press, 996, pp [9.] PÉCELI G., KOVÁCSHÁZY T., Transents n Reconfgurable Dgtal Sgnal Processng Systems, IEEE Transactons on Instrumentaton and Measurement, Vol. 48, No.5, Oct. 999, pp [.] SIMON GY, KOVÁCSHÁZY T., PÉCELI G.: Transents n Reconfgurable Control Loops, IEEE Instrumentaton and Measurement Technology Conference IMTC, Baltmore, Maryland, USA, May 4,, Vol 3, pp [.] SCALERA M. S., VÁZQUEZ R. J. The Desgn and Implementaton of Context Swtchng FPGA, IEEE Symposum on FPGAs for Custom Computng Machnes FCCM 998, Los Alamtos Calforna, USA, Aprl 57, 998, pp [.] SHIRAZI N., LUK W., CHEUNG P. Y. K.: Run Tme Management of dynamcally reconfgurable Desgns, Proceedngs of Feld Programmable Logc and Applcatons 8 th Internatonal Workshop, FPL 98, Tallnn, Estona, Aug. 3 Sept. 3, 998, Edtors Hartensten R. W and Keevallk A., Sprnger, ISBN , pp [3.] TRZYNADLOWSKI A. M., BLAABJERG F., PEDERSEN J. K., PATRICIU Nculna: The Tandem Inverter: Combnng the Advantages of Voltage Source and CurrentSource Inverters, Appled Power Electroncs Conference, APEC 98, Anahem, USA, pp [4.] TRZYNADLOWSKI A. M., IMECS Mara, PATRICIU Nculna: Modellng and Smulaton of nverter Topologes Used n AC Drves: Comparson and Valdaton of Models, ELECTRIMACS 99, Volume I/3, Lsboa, Portugal, 999, pp [5.] VÁSÁRHELYI J., IMECS Mara, INCZE J. J., SZABÓ Cs.: Reconfguraton Generated Perturbatons In The Vector Controlled AC Drves, Power Electroncs Intellgent Moton Power Qualty PCIM, May 6, Nuremberg, Germany, pp. 95. [6.] VÁSÁRHELYI J., IMECS Mara, INCZE J.J., SZABÓ Cs: Module Lbrary for Rapd Prototypng and Hardware Implementaton of Vector Control Systems, INES IEEE Internatonal Conference on Intellgent Engneerng Systems, May 68,, Opatja, Croata, ISBN , pp