Dynamics of the Drives Used in Modern Railway Vehicles

Transcription

1 Dynamics of the Drives Used in Modern Railway Vehicles Tomáš Fridrichovský 1,* 1 ČVUT v Praze, Faklta strojní, Ústav atomobilů, spalovacích motorů a kolejových vozidel, Technická 4, Praha 6, Česká repblika, Vedocí práce: doc. Ing. Josef Kolář, CSc. Abstract This text deals with a research, which is focsed on the torsional oscillations in drives of modern railway vehicles. The oscillations have become a sbject of varios researches and discssions in technical society over last years. Therefore the athor of the text deals with this topic as well in the frame of his PhD stdies. The aim of the research was a possible mtal inflence between mechanical and electrical vales in the drive. The research has been done via simlation methods with a help of Simpack and Simlink software. This text describes a methodology of the research, obtained reslts and its main otcomes. Some of the simlations reslts have been sed for a proposal of a way how to redce or sppress the oscillations. Keywords: railway vehicles; drives; dynamics; torsional oscillations 1. Introdction In 29 a slight rotation of the wheel and the axle on the powered wheelset has been discovered dring maintenance on one of the DB locomotive. The same problem has been fond conseqently on other vehicles of the same type. Althogh the occrrence was jst a matter of a small nmber of the total cont of the vehicles, this isse showed to be a serios safety risk [1]. Fig. 1. Relative rotation of the wheel and the axle [1]. The main problem is a fact that the relative rotation of the wheel and the axle means a short term loss of the friction between them. This means a failre of a press fitted joint that garantees the right position of the wheels on the axle. This may be very problematic, especially in the sitation when the vehicle passes throgh a crve and it is plled on the oter rail de to the centrifgal force. Reslting transversal force may lead to a movement of the wheel along the axle and decrease of the wheelset gage nder a permissible vale. This may lead to a derailment with critical conseqences in the extreme sitation. 2. State of Art This isse has been given a great attention in Germany and worldwide since its discovery. It is a generally known fact that the wheelset and whole drive may torsionaly oscillate. [2]. The axle is a torsional spring with given stiffness and both wheels may be considered as two masses. This makes mechanical oscillator. Among the first, who described a wheelset as a mechanical oscillator, were Benker and Weber [3]. Except Germany there was other topic from athors Yao, Zhang and Lo [4]. These articles were focsed mainly on analysis of the phenomena, others were focsed on possibilities of detection and redction. A method of detection has been described in an article from Markovic, Kostic and Bojovic [5]. They made a mathematical model of a wheelset that was powered via a direct crrent (DC) motor. The reslts showed that the stator voltage increases and starts to oscillate when adhesion is lost and the wheelset oscillates. Both the oscillations of the voltage and the oscillations of the wheelset had the same freqency (eqal to the natral freqency of the wheelset). This means there had to be a connection between both oscillations. A method of redction of the oscillations has been described in an article by Biker and collective [6]. Athors dealt with an idea of sing of brake discs elastically connected to the wheels which may serve as torsional dampers. 3. Presented Otpts of the Research Transversal force Fig. 2. A standard wheelset composed from one axle and two wheels. * Kontakt na atora: Tomas.Fridrichovsky@fs.cvt.cz A comptational model of a driving vehicle has been made in the frame of a stdent grant SGS No. SGS14/184/OHK2/3T/12. The vehicles parameters correspond to parameters of crrently operated locomotives that are sed via state or private companies throghot Erope.

2 F [kn] P [kw] The model is composed of two main parts mechanical and electrical. The first one calclates dynamics of the vehicle (general dynamics, drive dynamics, contact between the wheel and the rail), the second one contains sperior control strctre (simplified model of a traction motor, stick slip protection). The otpts of the model have been time corses of wheelsets oscillations. These corses have verified that the oscillations may emerge in the sitation, when a vehicle operates with higher amont of the torqe and the adhesion between the wheel and rail mst be rapidly decreased. More detailed description can be fond in the article Analysis of occrrence of torsion oscillations in wheelset drives sed in modern railway vehicles [7]. Another important otpt was a fact that the higher oscillations may appear within higher velocities of the vehicle. It is a sitation when the vehicle operates with almost maximm vale of the torqe and the otpt power. These oscillations are responsible for higher twisting of the axle and may lead to defects on press fitted joint according to high inertia forces Parameters of Simlation As an object of interest has been chosen a modern Tars type locomotive. The analysed vehicle has a tractive power P max=64 kw (temporary 72 kw), tractive effort F max=274 kn and operates with maximm velocity v max=23 km/h. The aim of the simlations was to bring on the loss of adhesion and emerge torsional oscillations of the wheelset. The vehicle was tested in the velocity range between 36 and 72 km/h. This had to ensre higher vales of the torqe and power of the traction motor. operated with a maximm amont of a friction between the wheel and the rail. Ad b. redction of the wheel forces lowers a maximm transmissible tractive effort. The wheelset will be more ssceptible to a slippage, when the adhesion is sddenly decreased. The vehicle operated with a high amont of the adhesion dring the simlations. The adhesion was sddenly rapidly decreased. The adhesion was nderstood as an inpt with a major inflence in the frame of research Simlation Otpts Different time corses of velocities and adhesion lead to different oscillations of the wheelset. Generally, it is possible to state that higher velocities are bond with higher amplitdes of oscillations. One of these time corses is in fig. 4. The figre displays twist of the axle dring velocity v=72 km/h (2 m.s -1 ). The axle is slightly twisted in the left part of the image de to the torqe that is transmitted and divided between both wheels. In the mid part of the image the adhesion is lost and the wheelset starts to oscillate. The oscillations and the axle twist disappear in the right part of the image, when the stick slip protection makes an intervention and decreases the torqe Ft(v) P(v) 1 2 v [km/h] Fig. 4. Time corse of the oscillation. Fig. 5 displays analysis of the time corse. It shows amont of the torqe in the axle and anglar acceleration of oscillating wheels. Fig. 3. Traction characteristics showing plling force Ft and otpt power P. The vehicle was loaded with a resist force O(v). The prpose of this force was to simlate real operating conditions. This force was approximately eqal to the tractive effort of the vehicle. Reasons were following: a. the vehicle had approximately constant velocity with a small amont of acceleration b. wheel forces on the front wheelset have been redced de to the interacting forces Ad a. this sitation simlates acceleration of the vehicle which plls a heavy freight train. The locomotive Fig. 5. Analysis of the oscillation

3 The time corses reveal a very high spremm vales of the torqe in the axle according to the eq. (1). Vales of the axle torqe may be several times higher than maximm nominal vales. Analogically to this, the anglar accelerations have very high amplitdes according to the eq. (2). Mt k t (1) y (2) 2 y Presented maximms may be a sorce of mentioned problems and may lead to failres described in chapter 1 (Introdction). This leads to a tendency to redce these oscillations and protect the wheelset against hazardos conseqences. 4. Relation Between Electrics and Mechanics Fig. 6 Vector control of the torqe [9] t t t t R i 1 1 R i 1 1 R i 2 2 R i 2 2 t t t t d1 d1 d d t t 2 2 t t p p p p m m t 2 t t t 2 t L1i1 t Lhi2 t t L1i1 t Lhi2 t t L2i2 t Lhi1 t t L i t L i t 2 2 The torqe is described via eq. (5) h 1 t p i t t i t t M p (3) (4) 3 (5) Extension of the Simlation Model Detailed description of the asynchronos motor was the main focs of the last year of the research. The motor was p to then done as simplified sbstittion via the second order transfer fnction. Althogh this allowed to cont with a base inertia of the mechanical events, the electrical vales were not described at all. This is the reason why new model blocks have been added into the model asynchronos motor and its control strctre. The model of the motor is based on a description of an asynchronos machine. The model is described via voltage (3) and flx eqations (4), see [8]. The model spposes that all of the parameters are constant dring the operation (mainly resistances and indctance). The three-phase machine has been simplified into the two-phase machine. Alternating vales has been converted into direct vales via Park s transformation [9]. This allows to control the alternating crrent motor as a direct crrent motor. i 1d i 1q i 1 i cos i 1 1 sin i 1 sin cos (6) The torqe of the motor is then described via following eqation M m k i (7) This allows simple control of the torqe and it is also sitable for observation of its dynamics. The motor is controlled via an indirect torqe control method [1]. This allows to control the amont of the

4 prodced torqe and a field weakening, which is necessary to increase the speed of the motor above the nominal vale. The scheme of the control is shown in fig Oscillations in the Drive The simlations have been done with the se of the newly made control strctre. The aim was to determine if the oscillations are transmitted via the drive chain and how their conseqences can be. The attention has been focsed on the anglar speed of the rotor ω m that is an inpt of the voltage eqations. The speed is shown in fig 7, which represents a sitation when the adhesion is decreased and the wheelset starts to oscillate. drive chain to the rotor. These oscillations affect dynamics of the motor. Their inflence shows the time corse of the control crrent i 1q. The crrent starts to wave when the wheelsets oscillations emerge. The sperposed crrent oscillations are clearly visible after few moments. These oscillations have the same freqency as the wheelsets oscillations. It is therefore clear that both oscillations are interlinked. Fig. 7. Anglar speed of the rotor. The graph shows that the rotor oscillates similarly to the wheelset with the same freqency. This means the oscillations are transmitted from the wheelset via the Fig. 8. Anglar velocity of the rotor and the stator crrent. The corrgation of the crrent can be detected and it allows to detect the origin and the development of the oscillations. This kind of detection may be a few hndrehs or tenths of the second faster than the standard stick slip protection. This detection may be sed as an additional implse for redction of the torqe, which Fig. 9. Time corses of the oscillations

5 may be helpfl as a prevention of high oscillations The fig. 9 compares two time corses of the wheelsets oscillations. The black line is the original time corse, the red line is the time corse with improved control. The comparisons reslt is a notable redction of the amplitde and time dration of the oscillations. The oscillation has been redced approximately to one third of the original time corse. 5. Smmary This text describes a method of detection and redction of the torsional oscillations in the powered wheelsets that are sed in modern railway vehicle. According to the simlation reslts the mechanical oscillations of the wheelset may be transmitted throgh the drive chain into the motor. This affects time corses of its electrical vales, which may be sed as a way of detection and an implse to intervention. The research presented was focsed on the se of the flly sspended drive. The other types of drives were not considered in the research. Conseqences of the dynamics of the partially sspended drive will be investigated in the frame of a grant No. SGS17/77/OHK2/1T/12. The grant shold also have an experimental part that shold be made on an experimental testing device. This will be sed as a basis for athor s PhD thesis. Acknowledgement The paper was created with the financial spport SGS grant No. SGS14/184/OHK2/3T/12. List of Used Symbols µ coefficient of the friction (1) i jk crrent (A) γ angle (rad) F i force (N) J i inertia momentm (kg.m 2 ) k coefficient(1) k t torsional stiffness of the axle (Nm.rad -1 ) L indctance (H) M i torqe (Nm) M * reqired torqe (Nm) P i power (kw) p p nmber of pole pairs (1) R resistance (Ω) t time (s) voltage (V) v velocity (m.s -1, km/h) y amplitde (m) φ twist of the axle (rad) Ψ jk magnetic flx (Wb) ω anglar velocity (rad.s -1 ) List of Literatre Used [1] KADEŘÁVEK, Petr a Jaromír PERNIČKA. Torsion oscillations of powered wheelsets. Railvoltion. 213, 213(2), ISSN [2] FREIBAUER, Ladislav, Ladislav RUS a Josef ZAHRÁDKA, Dynamika kolejových vozidel. Praha: Nadas. Knižnice nové techniky a technologie. ISBN X. [3] BENKER, T. a T. WEBER, 215. Torsionsschwingngen von Radsätzen - eine Herasforderng. Eisenbahningenier. (April), [4] YAO, YY., H. ZHANG a S. LUO, 211. An analysis of resonance effects in locomotive drive systems experiencing wheel/rail satration adhesion. International Jornal of Vehicle Mechanics and Mobility. 49(8), [5] MARKOVIC, P., D. KOSTIC a N. BOJOVIC, 215. One Method for Detection of Torsional Oscillations of Drving Axles of Electrical Locomotives. In: PRORAIL XXII. Medzinárodná konferencia Súčasné problémy v koľajových vozidlách. 2. Žilina: Žilinská niversita, Strojnícka faklta, s ISBN [6] BIKER, G., J. DEDE, D. DÖRNER, H. KLEIN a A. PUSNIK, 214. Bremsscheibe als Tilger für Radsatztosionsschwingngen. ZEV Rail. (138), [7] FRIDRICHOVSKÝ, T. Analysis of occrrence of torsion oscillations in wheelset drives sed in modern railway vehicles. In: MORAVEC, J., ed. Stdentská tvůrčí činnost sborník konference. Konference stdentské tvůrčí činnosti 216, Praha, Praha: České vysoké čení technické v Praze, Faklta strojní, 216. ISBN [8] KAZ MIERKOWSKI, Marian P. a Henryk. TUNIA, Atomatic control of converter-fed drives. Warszawa: PWN-Polish Scientific Pblishers. ISBN X. [9] KRAUSE, Pal C., Oleg. WASYNCZUK a Scott D. SUDHOFF. Analysis of electric machinery and drive systems. 2nd ed. New York: IEEE Press, c22. ISBN X. [1] HOLTZ, J., 22. Sensorless control of indction motor drives. In: Proceedings of the IEEE. 9(8), s DOI: 1.119/JPROC ISSN Available online: