Inverter topology comparison for remedial solution in transistor faulty case

Transcription

1 Inverter topology comparson for remeal soluton n transstor faulty case LANFRANCHI Vncent Inverter topology comparson for remeal soluton n transstor faulty case Keywors: DOC Carolne, LANFRANCHI Vncent, FRIEDRICH Guy Laboratore Electromécanue e Compègne U.T.C. (E.A. 16 B.P Compègne Ceex, FRANCE Tel.: /.( Fax: / ( E-Mal: carolne.oc@utc.fr ; vncent.lanfranch@utc.fr ; guy.frerch@utc.fr «Converter crcut», «fault hanlng strategy», «mechatroncs», «permanent magnet motor», «relablty», «smulaton», «three phase system» Abstract Electrc actuators are more an more use for applcaton reurng hgh relablty. A stuy of fferent nverter topologes to ncrease relablty an avo an expensve reunancy s presente. To llustrate our wors, remeal operatons are apple to the case of short-crcute transstor of the nverter. Introucton Nowaays, electrc actuators are more an more use for applcatons reurng hgh relablty, lke X-by-wre or plane actuators. In aeronautc, several actuators are use for the same functon. Thus, when a fault occurs, the motor an the nverter are sconnecte. Ths kn of reunancy s not acceptable n car nustry because of reure compactness an low cost. That s why n a faulty case, the actuator has to stll be operatng, even wth lower performance n orer to park the car or to reach home. Fg. 1: Topology of -leg half brge nverter Fg. : Topology of -leg full-brge nverter To mprove the relablty of the nverter-machne system, the commonly amtte ea s to ncrease the reunancy, for example, n ncreasng the number of motor phases or the complexty of the nverter. An other soluton s to esgn the system to lmt the effects of a fault. In [1], Mecrow avses to separate the phases. Mechancal separaton, realze by havng one slot per wnng, prevents from havng nter-phase short crcut. Electrcal separaton allows controllng phases nepenently, whch s possble wth a full brge snce phases are electrcally separate. The relablty conseratons can be taken nto account from the motor concepton, by nstance, to have the lowest short-crcut current [1]. A full brge creates a reunancy by usng twce as many components as a half brge nverter but allows sconnectng easly the faulty phase wthout any conseuences on the remanng phases. However, f we can rve the motor wth only two phases of the half brge nverter too, there wll be no more avantages n usng a full brge nverter. The man avantage of half brge nverter s that t nees fewer components. EPE 7 - Aalborg ISBN : P.1

2 Inverter topology comparson for remeal soluton n transstor faulty case LANFRANCHI Vncent Beses, n usual motor moels, we suppose that the system s balance. In ths case, the sum of the currents s null that s why the zero-seuence component s not calculate an fxe to. In case of fault, whatever the type or the locaton, the system s not balance anymore. The zero seuence components s fferent from zero but f we use classcal moel for motor, t wll stll be fxe to an results wll be wrong. The real value of zero seuence component s neee to compute the phase currents n orer to control the system n faulty case. In the case of ths stuy, we use a permanent magnet synchronous motor that has a low falure rate because of the absence of mechancal commutator. Moreover, accorng to [6], most of the falures are ue to a ysfuncton of a swtchng component. The weak part of the system s efntely the nverter. That s why ths stuy s focuse on nverter. Ths artcle presents a comparson between full brge nverter (or H-brge, -leg an 4-leg half brge nverter for supplyng a -phase motor when a fault occurs. A smplfe moel base on electrcal representaton, nclung computaton of zero seuence components, s use to test fferent strateges n the occurrence of a short crcut fault on a transstor, whch occurs 8% of the whole falure rate [6]. The smulaton results allow us to foresee an compare ther behavour but also to mprove them by usng a remeal strategy of control. In a frst part, we escrbe the stue system an the moelsaton use. Then, we smulate the effects of efault on a -leg half brge nverter. In a thr part, we stuy how the use of a full-brge nverter coul mprove the system behavour n case of fault. An fnally, we test the case of a 4-leg half brge nverter, whch presents a goo compromse. Descrpton of system an moelsaton The system we smulate s a smplfe electrc moel of a -phase permanent magnet synchronous motor an ts nverter. Each phase of the motor s moelze as a resstor, an nuctance an a voltage source, whch represents the e.m.f., n seres. Ths electrcal crcut s moelse thanks to Matlab Smulnk toolbox Power BlockSet. We measure (I a, I b, I c, whch pass through the moelse phases, then, calculate (I, I, I wth Park transformaton (Euatons (1, (, n orer to compute the prouce torue accorng to the Euaton ( an, later, to control the motor. In case of sconnecton of a faulty phase, the Euaton ( coul be mofe. Inee, L an L, rect an uaratc nuctances, coul change because of the mofcaton of the mutual nuctance. Ia Ib C Ic 1 I I I (1 cos sn 1 1 C cos( sn( 1 where s the electrc angle ( cos( sn( 1 Te p( F ( L L ( The motor wll be star-mounte when a -leg nverter s use. When a H-brge nverter wll be use, each wnng connecton wll be plugge to a leg of the H-brge. The wnng connectons wll thus have to be avalable. To use the 4-leg nverter, the motor wll be star mounte an the neutral pont wll be plugge to the forth leg. EPE 7 - Aalborg ISBN : P.

3 Inverter topology comparson for remeal soluton n transstor faulty case LANFRANCHI Vncent For all the legs, the swtchng components of the same leg are force to be n opposton. In the faulty case, f a transstor s n short-crcut, then the other stay opene an the source coul not be shortcrcute. All the transstors plus free-wheel oes are moelze by an eal swtch block of the Power BlockSet toolbox but coul, as well, been moelze wth the Mosfet block. Mosfet block smulates both transstor an oe. Both solutons have been teste an lea to a fferent results only n open-crcut fault ue to the fact that current coul not return through the open swtch as t coul through the free-wheel oe. In the case of short-crcute transstor, whch s the one stue here, results of both smulatons are the same. That s why the eal swtch coul be use to reuce smulaton tme. a Ieal swtch b Mosfet Fg. : Power BlockSet Block The targete reference s the motor spee. For all the smulaton, a PID controls the system. A resstve torue s apple. Ths torue s proportonal to the spee. From ms to 18 ms, the motor runs n a transent moe. Durng ths transent moe, the spee s rsng untl reachng the target spee (here rpm. After t18 ms, the system s n establshe moe an the spee s then constant an eual to the target. The Fgure (4 shows the results of smulaton n the unfaulty case (whatever the use nverter. The nstantaneous torue, spee an effectve currents are presente. a Torue (Nm b Spee (rpm c Currents Ia Ib Ic (A Fg. 4: Smulaton results for unfaulty case -leg nverter We pont out that, for the -leg nverter, the motor s star-mounte an thus, the sum of currents has to be null. The smulate fault s a short crcut on the upper transstor, whch means that the eal swtch, moelsng t, s always n close poston. As mentone before, ths fault s the most freuent one. As the lower transstor s n opposte poston, t s always opene. The fault occurs at t ms. Ths stuy s lmte to the sfunctonment take place after the transent ens. If the pont was about reachng a poston wthn a gven tme, even n faulty case, a fault coul as well been trggere at t ms. The Fgure (5 shows the conseuences on torue, spee an currents of a short crcut on upper transstor of half brge nverter f no remeal soluton woul be apple. We can notce frst that I c s always bgger than zero. Inee, the C-leg of the nverter coul only be lnke wth the postve connecton of the battery. Moreover, we can see that torue an spee oscllatons are not neglgble. In a current applcaton, ths woul lea to harmful vbratons, whch coul lea from smple scomfort to mechancal sfunctonment. Our goal was then to fn a soluton to reuce these oscllatons an reach the spee reference. EPE 7 - Aalborg ISBN : P.

4 Inverter topology comparson for remeal soluton n transstor faulty case LANFRANCHI Vncent a Torue (Nm b Spee (rpm c Currents Ia Ib Ic (A Fg. 5 : Smulaton results for short-crcute upper transstor of -leg half brge nverter The frst ea was to sconnect the faulty phase snce ths phase s out of control. However, the motor s star-mounte, so I a -I b. The results of such a soluton are shown n Fgure (6. We can notce that the ampltue of oscllatng spee s smaller than the case wthout any mofcaton but the coggng torue reman mportant. Furthermore, the zero seuence component s then null whch reuce the losses. a Torue (Nm b Spee (rpm c Currents Ia Ib Ic (A Fg. 6: Smulaton results for faulty phase sconnecte of -leg half brge nverter H- brge Thus, the -leg nverter oesn t offer a satsfyng soluton, the soluton that comes mmeately, s to ncrease reunancy n orer to ncrease relablty. However, the H-brge s the nverter that offers the maxmum of reunancy. That s why H-brge coul be use n applcaton reurng a hgh rate of relablty, n spte of the over cost t mples. Full brges are use for three man reasons: - When a transstor breaks, there s no change on the healthy phases because current path are nepenent [1] - It s stll exstng a way for current to crculate n the faulty phase because when a transstor s short-crcute, t freezes only one half of the H-brge. Two values of tenson are stll accessble (for a upper short crcute transstor, tenson of wnng can be V or Vc - It s easer to sconnect the faulty phase thus openng all the transstors, whch reman uner control, sconnect the faulty phase. We can compare the prouce torue wth the torue create by a -leg half brge nverter wth a short crcut on the upper transstor. When a fault occurs, we open the complementary transstor to avo havng a short crcut on the power supply. Then we coul ether open the two remanng transstors to sconnect the faulty phase, or contnue to rve them for havng a less effectve but stll operatve phase. The faulty phase has to be sconnecte n orer to prevent from unforeseeable behavour [1]. In ths case, we obtan torue an spee oscllatons (Fgure (7 whose ampltues are eual to those of the -leg brge nverter case. So, espte the reunancy, results are not better. Nevertheless, the EPE 7 - Aalborg ISBN : P.4

5 case showe n the Fgure (6 oesn t nuce an over-cost because the mofcaton s carre out by a mofcaton of the control laws. In ths case, there woul be no avantages to use a H-brge. Fg. 7: Smulaton of a fault H-brge (faulte phases stll connecte At ths moment, we have only mofe the topogy of the nverter, but not ts control laws. The system s controle n orer to get the control laws shown n Euaton (4, whch are the classcal laws. sn( cos( sn( cos( sn cos c b a (4 The obtane results are not as satsfyng as expecte compare to the over cost lnke to the reunancy. But a better torue coul be obtane by mofyng the control laws to take nto account efault [], [], [9]. Inee, snce we sconnect the faulty phase (we assume the faulty phase s the phase C, no current coul pass through t anymore. Accorng to [4], we can use Euaton (5: c b a (5 So, we can fx I c as a reference an then make sappear component. c b a (6 In orer to keep constant torue, I an I must stll be the same. That s why we have: cos sn sn cos (7 Puttng Euaton (7 n Euaton (6 leas to the followng aapte control laws: cos sn cos( sn( c b a (8 We can notce n Fgure (8 that, n ths case, the only remanng oscllatons have hgh freuency an are ue to the smulaton step sze. The spee s eual to ts reference. The torue waveform s almost the same as the unfaulty case. To succee reachng the reference, we nee tmes hgher current I a an I b. Ths leas to an over szng of the global system because the nverter woul have to supply ths a Torue (Nm b Spee (rpm c Currents Ia Ib Ic (A Inverter topology comparson for remeal soluton n transstor faulty case LANFRANCHI Vncent EPE 7 - Aalborg ISBN : P.5

6 Inverter topology comparson for remeal soluton n transstor faulty case LANFRANCHI Vncent hgher current, the wnngs not to melt because of t, an the motor yoke not to saturate. Ths results to an ncrease of the total sze of the motor an of ts costs. But a compromse coul be foun between havng the full torue but tmes hgher current an havng a / tmes lower torue but nomnal currents, epenng of the targete applcaton. a Torue (Nm b Spee (rpm c Currents Ia Ib Ic (A Fg. 8: Smulaton of a faulty H-brge wth new control law Reucng the number of transstor: 4-leg nverter As sa before, for cost lmtatons, the number of transstor has to be as lower as possble. That s why the -leg half brge nverter s nterestng an the H brge s use only when hgh relablty s neee. We suppose we have a star mounte motor wth an avalable neutral pont. In case of fault, the only possble acton to control the system s to sconnect the faulty phase, for example by usng fast fuses or TRIACs ([5]. The problem wth star-mounte motor s that, n unbalance case, the zero seuence components s not null any longer an the I current has to reach the source. To allow ths, we coul lnk the neutral pont to a mle pont of the supply source or lnk t to the source through a forth leg of nverter ([4], [5] an [7], as shown n Fgure (9. The forth leg s Fg. 9 : Topology of 4-leg half brge rven followng the euaton: In Ia Ib Ic. Ths gve In eual to the zero seuence component whch then coul reach the source. We can notce that the current passng through the forth leg s the same than the one passng through a wre lnke to a DC m pont. However a contnuous battery wthout mle pont supples the nverter. A battery wth a mle pont s not always avalable. That s why the forth leg of a 4-leg nvert wll be lnke to the groun of the battery. Then no mle pont wll be reure. The create torue an spee are shown n Fgure (1, below. a Torue (Nm b Spee (rpm c Currents Ia Ib Ic (A Fg. 1: Smulaton of a faulty 4-leg nverter wth control laws of Euaton (4 EPE 7 - Aalborg ISBN : P.6

7 Inverter topology comparson for remeal soluton n transstor faulty case LANFRANCHI Vncent We can notce that, even wth classcal laws (not aapte to the efault, the spee varatons become almost null. Ths s ue to the forth leg whch allows the I current to be fferent from zero an Ia coul be fferent from I b. Torue rpple are stll generate, even f the ampltue of the torue oscllatons are 4 tmes smaller than those generate by a -leg nverter. However, snce now, we can have the sum of currents fferent from zero, we can use the aapte control laws as seen for the H-brge (Euaton (8, we are able to obtan the same torue performance as wth a H-brge nverter an aapte control laws (Fgure (11 but usng 4 transstors less. The torue after the efault occurs can be eual to the torue before sfunctonment (here. Nm. Once more, the hgh freuency onulatons are ue to the smulaton an wll not beng takng nto account. No more spee oscllatons are prouce. But, here agan, the nverter an the wnngs must be able to carry current tmes hgher. a Torue (Nm b Spee (rpm c Currents Ia Ib Ic (A Fg. 11: Smulaton of a faulty 4-leg nverter wth aapte control law Concluson Snce, we have stue the behavour of the system for fferent remeal strateges n the case of the short-crcute upper transstor, we are now able to have some wors about the best soluton to choose. Frst, the efnton of the acceptable behavour of the system s an mportant pont. As mentone before, f the torue level s what matters, currents wll have to be tmes hgher than n the unfaulty case, whch reures that the whole actuator as to be sze n orer to work wth these currents. On the other han, f we amt that / of the full torue s enough to reach the reure performances n faulty case, currents woul stay eual to those n normal functonment an no over-szng woul be neee. In aton, 4-leg nverter uses 4 transstors less than H-brge an so, offers a better use rate by component [8]. Beses, the most mportant beneft of 4-leg brge s the possblty to use aapte control laws. Inee, mofyng control laws oesn t lea to an over cost but, as we have seen, can mprove the ualty of the prouce torue. That s why the 4-leg nverter wth aapte control laws appears to be a valuable soluton for system reurng a goo relablty. Nevertheless, when a fault occurs, t has to be etecte then analyse n orer to know what kn of fault t s an on what phase. Although we ha only stue short crcut case, an open crcut coul be possble. The fference between those two cases has to be mae. Ths agnostc can cost tme. Durng the agnostc tme, the system s stll beng runnng wthout any mofcaton, because as long as the fault s not entfe, forth leg cannot be actvate an control laws cannot be change. We can notce that f agnostc plus reacton tme were greater than 1 ms, n our case, a more mportant torue rpple woul be felt. If we conser Fgure (5, after the efault occurs, torue reaches ts frst 1 Nm hgh peak wthn 1 ms. other ways of conserng ths agnostc tme lmtaton coul be efne. Fnally, we can remark that, when we are usng the aapte control laws, zero seuence current exsts. These currents on t prouce any torue an coul then be consere as losses. New control laws coul be calculate n orer to reuce I. EPE 7 - Aalborg ISBN : P.7

8 Inverter topology comparson for remeal soluton n transstor faulty case LANFRANCHI Vncent To conclue, we can say that a fault proof nverter can be foun. To efne what kn of nverter as to be use, some aspects have to be consere: over cost, relablty, torue ualty, agnostc an remeal tme an yel. A way to stuy the mportance of these factors on the fnal movement s to smulate the whole system actuator an mechansm so as to uantfy the effect of a efault of a swtchng component on the global behavour. In ths way, the relablty of the whole system can be teste an faulty behavour can be foreseen to esgn safe an relable electrcally controlle mechansm. References [1] : Mecrow B.C., Jack A.G., Haylock J.A. an Coles J., Fault Tolerant Permanent Magnet Machne Drves, IEE Proceengs Electrc Power Applcaton; Vol 14, No. 6, pp [] : A.Krautstrunk, P. Mutschler, Remeal Strategy for a Permanent Magnet Synchronous Motor Drve, 8th European Conference on Power Electroncs an Applcatons, Lausanne, Swtzerlan [] : Bran A. Welchko, Thomas M. Jahns, Wen L. Soong, James M. Nagashma, IPM Synchronous Machne Drve Response to Symmetrcal an Asymmetrcal Short Crcut Faults, IEEE Transactons on energy converson, Vol. 18, No.,pp [4] : N. Banch, S. Bolognan, M. Zglotto an M. Zoran, Innovatve Remeal Strateges for Inverter Faults n IPM Synchronous Motor Drve, IEEE Transactons on energy converson, Vol. 18, No., pp 6-14 [5] : Bran A. Welchko, Thomas M. Janhs, Thomas A. Lpo, Fault Interruptng Methos an Topologes for Interor PM Machne rves, EPE Power Electroncs an Moton Control Conference, EPE-PEMC 4, Rga, Latva [6] : H. Schwab, A. Klönne, S. Reck, I. Ramesohl, Relablty Evaluaton of a Permanent Magnet Synchronous Motor Drve for an Automotve Applcaton, 1th European Conference on Power Electroncs an Applcatons, Toulouse, France [7] : Tham ELCH-HEB, Strateges e commane un ensemble onuleur-machne asynchrone fonctonnant en moe egrae, Thess, Unverté es scences et technologes e Llle, 199 [8] : Bran A. Welchko, Thomas A. Lpo Thomas M. Jahns Steven E. Schulz, Fault Tolerant Three-Phase AC motor Drve Topologes : A Comparson of Features, Cost an Lmtatons, IEEE Internatonal Electrc Machnes an Drves Conference, June [9] : Byoung-Kuk Lee, Tae-Hyung Km, Mehra Ehsan, On the Feasblty of 4 Swtch Phase BLDC Motor Drves for Low Cost Commercal Applcatons : Topology an Control, IEEE Transactons On Power Electroncs, Vol.18, No. 1, pp EPE 7 - Aalborg ISBN : P.8