Macel Ionel, Mihail-Floin Stan, Coneliu Ioan Salisteanu, Octavian Macel Ionel Contol systems fo high powe Induction machines MARCEL IONEL, MIHAIL-FLORIN STAN, CORNELIU IOAN SĂLIŞTEANU, OCTAVIAN MARCEL IONEL Electonic, Telecommunications and Enegetically Engineeing Depatment Automatics, Infomatics and Electical Engineeing Depatment Student Valahia Univesity Tagoviste, Electical Engineeing Faculty 18-24 Uniii Blvd., 130082 Tagoviste ROMANIA ionel.macell@yahoo.com, flo.stan@gmail.com, salisteanu@valahia.o, ionel.octavian@yahoo.com www.valahia.o Abstact: - Issues odes in a powe dives should be viewed in a moe complex and diffeent fom how do Electonics enginees of contol systems. It is best to look at the contol system as a set of black boxes cascading with mathematical models defined on a system of altenating cuent application. Even if it takes a vecto contol stategy and obtain a simila behavio to that of a DC moto, many poblems emain unesolved because of the paticula stuctues of the convete and the moto due to thei inteaction with load and souce. This pape ecommends to the expets and to the uses of command systems with fequency convetes the usage of speed command and position command to the vaiable fequency dives. Thee ae analyzed also the commands without position tansduces, speed tansduces o flux tansduces based on appoximately esults. Thee ae included also logic elements and it s poves how the velocity evolution of the technology command of electical machines in diffeent banches of the wold economy finds a specific field in moden electical applications [10]. Poweful micopocessos and DSP (Digital Signal Pocesso) ae able not only to diectly calculate the time of ignition of a powe semiconducto cicuit such as the bidge phase, opeating on fequency of feed, but also pefom othe impotant tasks in applications industial automation as well as statup and shutdown sequencing, self monitoing and diagnosing faults. The most impotant contibution is that powe chips have opened new fonties in implementing sophisticated contol systems fo electic dives. Key-Wods: - Electical commands, scala contol, vecto contol, mechanical chaacteistics, tansduces contol, diect contol appoach, indiect contol appoach, hamonic unit, test signal injection method. 1 Intoduction The commands of AC motos has a geat impact in many technical applications like tanspotations, home devices o industial automations, and ecently even in echeché studies. The fequency egulation advantages can t be full exploited without an appopiate contol stategy. Toque pulsations, the fequency hamonic content, optimize efficiency, change paametes, esponse times etc. ae just some of the many issues to be esolved by an application enginee and contol stategies that can help solve. Anothe majo facto that helped shaeholdes AC technology dive to gow apidly and is closely connected to issues of contol epesents the development of micopocessos [12]. The evolution of powe electonic semiconducto devices to the default static fequency convete is a key point in the evolution of advanced applications [4], [5]. The existence of a system capable of geneating enegy with a fequency adjustable machine allowed AC to each a new hoizon in the field fo eseach and technical applications, a hoizon pobably completely unexploited today [3]. The inheent advantages in the opeation of adjusting the fequency can not be fully exploited without the adoption of an appopiate contol stategy, which is essential in chaacteizing the oveall pefomance of a system [6], [7]. In Fig.1 ae pesented specific stategies [9] fo contol of induction machines. Command stategies ensue a coect and efficient opeation to dives [13]. Duing nomal ISSN: 1790-5060 232 Issue 7, Volume 4, July 2009
Macel Ionel, Mihail-Floin Stan, Coneliu Ioan Salisteanu, Octavian Macel Ionel opeation the nominal values of the motos and invete must be met by ensuing that moto opeation is limited in opeation domain. Fig.1 Command specific stategies fo induction machines. The vaiations of voltage, cuent, fequency sliding and toque accoding to induction moto speed. Contol poblems to an electic machine should be egaded in a diffeent way to eseach how to make contol systems specialists [9]. Pefeably be consideed as a set of black boxes cascade having defined mathematical models. The command system in AC is complex and multivaiate nonlinea paametes, which can hadly be descibed on a single analytical model. Even if it adopts a vecto contol stategy and it obtains a simila behavio to that of a DC moto, many poblems emain unsolved due to stuctues of pivate AC machine and convete and inteaction with the souce and load with diffeent chaactes and behavio [12]. The toque pulsations, the hamonic fequency, vaiation of paametes, the esponse time is only few of the many issues that must solve a specialist and that contol stategies can help solve. Anothe majo facto which contibuted to the technological advance commands in altenating cuent and is closely elated to contol issues is the evolution micopocessos of computes and specialized softwae. Poweful micopocessos such as DSP (Digital Signal Pocesso) ae able not only to diectly calculate the time of ignition of powe semiconducto in a cicuit of a thee phase bidge opeating fequency on powe supply fequency, but also to fulfill othe impotant tasks in automation applications industial as well sequential statup and shutdown, auto tests, deficiencies in monitoing and diagnosis duing the opeation. The most impotant contibution of powe micopocessos is that it has opened new fonties in the application of sophisticated contol stategies in tems of electical systems commands [4]. In the supply lines and electic dive, electic induction machines of metallugy stat fom a few kw up to seveal hunded kw. This ange of powe makes induction moto is used pimaily. Fo the eel, and means olle o olling mill but also fo electic dives of the utility of metallugy, powe ange can extend even up to 9 MW. Fo applications in metallugy, moto chaacteistics must be such so that they can avoid the lage ated cuent values equie lage the invete and inceased costs of investment. Figue 2 shows an example of application type eel (envelopes) with chaacteistic of load figue with ed line. Basic speed of this application is 300 pm. Fo these types of loads it is compaed two moto options, consideing the impact of oveload equiement to maximum moto speed. The mechanical chaacteistics of the moto epesented in blue ae the standad moto. Both options ae fo a moto with eight (8) pole, with a toque epesented on the same axis. Special Option Blue is the most ecommended combining bette toque load equied. As toque deceases vey apidly, this could be maintained only if the maximum speed of the mechanism involved does not exceed 900 pm, taking into account the limit appopiate oveload. Fig. 2 Output chaacteistics of the actuato of a envelopes ISSN: 1790-5060 233 Issue 7, Volume 4, July 2009
Macel Ionel, Mihail-Floin Stan, Coneliu Ioan Salisteanu, Octavian Macel Ionel Geat advantage fo this choice is the classification of moto ated cuent that occus due to load and achieves nominal voltage of 480 V at a slowe speed than synchonous. This standad option should be selected if maximum moto speed o pump equied moe than 1500 pm. Vey impotant to potect the moto and unit sizing of invetes is the choice and sizing of the eactance [8]. Invetes supplying units feed a voltage with voltage amplitude of the intemediate cicuit. Consideing that it is used high fequency and type IGBT semiconducto devices, when voltage will incease to values of appoximately 10 kv high, causing the insulation and compatibility moto convesion. This equest is moe obvious when the distance between the invete units and electical machines is significant and the powe cables default length is lage and small sections. Geat length cables ae high capacitive loads and lead to wosening of commutation and theefoe it is necessay to incease the invete. Cables also incease the enegy stoed in Coona effect which is vey hamful to the moto installation and pompted us to take measues to intoduce filte du / dt accoding to Figue 3. Cable length 20 m can geneate a significant voltage peak fo moto teminals, leading to a phenomenon eflecting the blood by about 65% highe than the voltage of intemediate cicuit. The lengths of ove 50 m, maximum voltage inceases slowly accoding to cable length and easy to appoach the theoetical maximum, twice the voltage of intemediate cicuit (2Ud). As cable lengths incease, the eflection wave powe geneated (between moto and contol unit) esults in a longe tansition peiod until the moto teminals will each a voltage equal to that of the intemediate DC cicuit. All motos manufactues have taken steps to pevent effects due to tansition Coona which is an exponential incease and the length powe cod with significant consequences dielectic insulation beakthough poduction engine (Figue 4). AC motos fed by invetes wee analyzed taking into account that the insulation should be able to withstand shocks caused by IGBT contols and cable lengths up to 300m without filtes du / dt. If output eactances ae designed in accodance with the lengths of wie, invetes can function popely without futhe guidance. Output eactance offset capacitive load existing supply netwok and the existing capacitive output cuent limiting, educing voltages and thus indiectly helping the moto. Switching fequency IGBT odes out advantages and disadvantages they offe pesents. Fig.3 Voltage at moto teminals, depending on cable length Fig.4 Coona effect tansition by cable enegy ISSN: 1790-5060 234 Issue 7, Volume 4, July 2009
Macel Ionel, Mihail-Floin Stan, Coneliu Ioan Salisteanu, Octavian Macel Ionel Output voltage pulse shaped blocks and geneates a high fequency cuent is in the fom of pulses. In situations whee thee is high capacity it will leak at the table between the cable, moto and belt gound. As a esult cicuit inteuption and voltage dop can intefee with contol signals fom blocks of small signals. The most effective way to avoid this intefeence can be achieved by sepaating the contol signals and signals poduced by the additional capacity of cable. This equies that in ode cabinets to meet a minimum distance of 20 cm between the contol and powe blocks and 60 cm between powe blocs. 2 Basic techniques fo contol of AC machines Positive esponse that the maket gave shaeholdes the application of vaiable fequency in many aeas is due mainly guaantee that electic dive is the best solution in at least two classes of application. The fist class is equied with a fai and efficient management of electicity and that can achieve high conveting applications fo enegy, nomally at constant speed in vaiable speed systems diven by electic motos contolled by AC fequency (olling mills o lage machine tools) [16], [17]. Inceased efficiency can be 20-30% highe compaed with the constant speed systems, meaning a majo economic powe ove a shot peiod, which take into account additional costs due to electic powe equipment. The enegy savings wee so convincing that the dives fo vaiable speed pumps and fans ae now the most popula electic dives and thee ae easily puchased. A second class of applications includes industial automation. Hee, the need fo easy integation and eliable pefomance of the execution element (powe command) in the automatically pocess find an appopiate esponse to shaeholdes vey dynamic pefomance of vaiable fequency [20]. The esult is that an inceasing numbe of hydaulic and pneumatic automatic systems ae eplaced today by the dive which povides speed and highe pecision contol and a bette powe / weight atio, obustness and ease in maintenance. The two classes of electical dives have contol diagams vey diffeent. Vaiable speed dives fo enegy saving enegy consuming ae equipped with a constant voltage / fequency contol of open loop, while dives of high dynamic pefomance ae made with a moe complex contol, usually involving a vecto contol fo independent egulation of toque and flux, including field weakening mode fo high speed commands [4], [5]. The simple and cheap method of contolling the speed of induction moto, obtained by keeping constant the atio U / f, has been extensively studied and applied [18]. Thee ae intoduced seveal impovements in the contol scheme to ovecome some of its significant disadvantages. Offsetting the fall in voltage stato esistance can be achieved by implementing a chaacteistic voltage / fequency in which the tension is inceased above its nominal value out of the popotionality of the fequency at lowe values. Voltage egulation may be popotional to the magnitude of stato cuent o (in altenative) to the phase component of stato cuent [19]. Cuent contol in closed loop duing the tansfe opeation has been intoduced to solve the poblem ovecuent value tigge, while slip adjusting is usually added to compensate fo the fall speed due to load. Although dive pefomance is impoved by the pevious opeations, the value of the constant voltage / fequency atio emains still a difficult poblem because it can not be held the ai-gap flux to a constant value coesponding to a fixed point of opeation. Fig.5 Toque contol of induction moto using decoupled scala flux method ISSN: 1790-5060 235 Issue 7, Volume 4, July 2009
Macel Ionel, Mihail-Floin Stan, Coneliu Ioan Salisteanu, Octavian Macel Ionel In the pesence of vaiations of this epot (due to tempeatue and / o satuation) the esponse can disupts in a diffeent opeation point. Scala decoupled contol was intoduced to enable a contol scheme to povide an acceptable pefomance when good dynamic pefomances of the application ae demanded. Such a scheme (such as in Fig.5) is based on a sepaate flux and toque contol of the moto, but the tensions and cuents must be pevious measued to calculate the flux and toque sizes. Vecto contol system is the stuctue of any dive system opeating in AC high pefomance. Fo now, it suffices to ecall that the vecto contol may allow the moto toque and flux ae contolled independently, in accodance with the eal vaiations, designing in two stato cuent eactive components in a field of efeence that otates with the synchonous otos flux. In this way, moto toque is diectly contolled by the q cuent component and flux though the d component. To implement the vecto contol is necessay to measue and to calculate both the magnitude and position of the oto s flux [15]. These poblems ae specific to both induction machines and synchonous machines [19]. Howeve, while the synchonous machines flow angle otos can be detected as a size mechanical pecision, because the oto s flux is in synchonism with the moto axis, it becomes impossible fo an induction moto (asynchonous), since the fequency of diffeent otos fequency of ai-gap (slipping occus) [1], [14]. We adopt two stategies that will define two diffeent types of vecto contol: 1. In the diect contol appoach, the vecto of oto s flux is poduced diectly using detectos such as flux coils o Hall sensos located in the stato slots fo the measuement of ai-gap flux. Thee ae also measued stato voltages and stato cuents to obtain the voltage change ove time due to stato flux. To the diect methods we have known dispesion inductances to calculate oto s flux. The main shotcomings of this method occus at low fequency, whee both need to assess the fall voltage stato esistance and difficulties elated to the tension - to get the flux signal conducts to a vey difficult definition of flux vecto. As a ecommendation, diect method does not apply to low speeds; 2. Indiect method. It detemines the position of oto s flux by adding to the oto position the position coesponding to the slip, calculated as an integal function of fequency sliding. In tun, this value is econstituted fom the values that belong to the ode of the two components of cuent using a mathematical model of the electic machine. Although most high pefomance dives is based on indiect vecto contol ae ecoded and some dawbacks. The econstitution of efeence values of cuents and sliding fequency is not a complex action. These values ae deteminate fom the chaacteistics of the motos. The accuacy is much affected by the paametes of the moto used in the calculations, and if the oto time constant is diffeent to the value used in the calculation of the efeence slip fequency, the coect oientation of the field can not be obtained because the dynamic esponse of the dive is coupt. The calculations ae influenced by vaiation of oto esistance with tempeatue [2] and magnetic satuation influence. Fig.6 The scheme of oiented diectly contol of the field ISSN: 1790-5060 236 Issue 7, Volume 4, July 2009
Macel Ionel, Mihail-Floin Stan, Coneliu Ioan Salisteanu, Octavian Macel Ionel Fig.7 The scheme of oiented indiectly contol of the field. Vecto contol accentuates the fact that will be esolved at least two poblems, especially fo indiect vaiant, fo induction moto dives [8], (whicheve has been applied successfully in high pefomance dive): 1. Simplifying o even eliminating any mechanical device used to detect speed tangential o angula. 2. Identifying electical and mechanical paametes of the dive to set the contolle paametes (fo the initial dive fo an abitay machine, and the ganting of the contol system fo sophisticated applications). 3 Adjust AC vecto contolled dives paametes Study on induction machine contol simulation shows that the indiect vecto contols applications, is an essential equiement and detemination of oto esistance machine (o oto time constant) [11]. Although so fa have been conducted many studies, the question of continue accoding has not been esolved satisfactoily because of shotcomings in contol systems due to thei complexity. Once the indiect vecto contol has been a wide use only high pefomance and the sevo dives fo special puposes, but also in a numbe of low-cost applications, linea estimation of paametes fo the gant is still a cucial issue, having seveal impotant featues to satisfy. A pope awad should be inexpensive and non time consumption, and not equie additional sensos compaed to those equied unde the oiginal scheme of indiect vecto contol, avoiding thus, complexity and costs inceased. Also, the functions should be self - ganted that they ensue automatic and accuate detemination of amplification and sliding both duing nomal opeation - including a low speed, - and befoe the stat opeation. To achieve full automation, awad system would equie a moto o contolle thee estictive extenal mechanical means such as locking the moto. Finally, nomal moto opeating functions should be distubed by the pocedue of testing and adjusting the amplification and sliding (when injected into the moto test signals to identify time constant oto). Gant by injecting the test signal. Unfotunately, all methods consideed fo the awad of vecto contolled dives can meet only some of the above pefomance equiements, because they ely on the use of appopiate test signals. Howeve, futhe impovements wee possible by adjusting the popeties of PWM invete step by step and on-line. Next we pesent in detail one of these possibilities. Unde this method the diect and indiect ganting of a vecto contolled dives can be obtained by using eo ate effects due to a test signal injected on the baseline oto fluxe value. i qs 3 2 p T e Lm L = (1) 3 2 λ d L T ω s = (2) τ pλ e 2 d Fom the above equations can be deduced that if a supeimpose pulsation (ipple) on low fequency sinusoidal efeence oto fluxe shaft toque poduced will not change, which shows that the time constant oto slip fequency contolle is chosen ISSN: 1790-5060 237 Issue 7, Volume 4, July 2009
Macel Ionel, Mihail-Floin Stan, Coneliu Ioan Salisteanu, Octavian Macel Ionel coectly. Othewise, if is not coect, the couple will be diffeent and will show oscillations. A simple and effective way to detect any conditions fo ganting poo obsevation eo is speed o - even bette - its integal, given espectively: e ω = ω ω (3) I eω = e ω dt (4) Because the system woks with a PI speed egulato, the above sizes ae available and hence the two signals T T can be detected and is ep, el popotional to e ω and espectively I. If the oto time constant τ used in the amplification of slipping, toque pulsation will occu at the same fequency as the pulse flow will lead to impaied unne speed eo and its integal (o signals coesponding enty egulatos). Pulse amplitude is the integal of speed eo eω T el by τ being loaded sinusoidal test signal as eo signal fom: τ : e = τ τ. If this eo is negative, the pulsation T el of the signal is delayed to the test and if eo is positive, the pulsation T el is advanced to the test signal. In conclusion, by calculating the amplitude and phase shift pulse T becomes possible to deduct el an appopiate coection within the oto time constant. The ganting automatic time constant adjustment is shown in Fig. 8. Figue 8. Adjusting the oto time constant by injecting the test signal. This system only equies the speed tansduce (Tahogeneato) usually included in shaeholdes fo indiect vecto contolled induction motos, speed contol and field oientation. Ganting pocess may be made independently of the value of speed, including zeo speed, and not affect the nomal ode of opeation. Gant by injecting a voltage of thid hamonic. It can be made a hamonic analysis of altenatives study, based on injecting thid hamonic voltages. Both machines and as induction, synchonous, fo easons of efficiency ae designed to wok in the aea of satuation chaacteistics B - H. Theefoe, as the fluxe of ai-gap is distoted and flattened. In this case, the fluxe wavefoms can be viewed as the sum of a fundamental hamonic and a numbe of hamonics with a pedominant tiple that of fundamental netwok. A pecise technical flow detection and flow assessment ai-gap position can be obtained taking into account (instead fundamental hamonic) thid hamonic stato voltage. In a sta connected thee phase moto thid hamonic stato cuents can not exist, and the thid hamonic voltage is not affected by load o stato esistance vaiations. Futhemoe, the thid ISSN: 1790-5060 238 Issue 7, Volume 4, July 2009
Macel Ionel, Mihail-Floin Stan, Coneliu Ioan Salisteanu, Octavian Macel Ionel hamonic is a fequency, which is thee times the fundamental hamonic fequency and to obtain a bette signal low-speed wok. By measuing the ai-gap fluxe using thid hamonic stato voltage, it is possible to ovecome a majo shotcoming of conventional flow measuing techniques based on integation fundamental voltage is dependent esistive voltage dop. Moeove, it is possible to measue flow and vey low speeds. Analysis of the thid hamonic was used diectly to measue the cuent position of ai-gap fluxe, o to induction motos contolled by field oientation fo ganting indiect oto time constant. In the fist case, stictly equies continuous measuement of oto flux position coectly align the stato cuent vecto. An accuate assessment aigap fluxe position can be obtained by obseving the zeo cossings of the flow fo thid hamonic, which is not affected by machine paametes o place of functioning. With such an appoach is not possible to obtain continuous infomation fluxe position because each spin can be detected only 6 positions. Continuous infomation fluxe about the oto position can be deived fom assessing the fluxe of thid hamonic amplitude, which in an induction machine is depending on the magnitude of fundamental hamonic. Diect measuement of the thid hamonic voltage can be easily obtained summing the thee stato voltages obtained in the common point of connection between the sta o by measuing cente of the sta and the midpoint of the filte capacitance of the powe convete. Using the method of the thid hamonic is possible also the calculation fluxe position unne as a function of the fluxe of ai-gap and stato cuent components. Moeove, thee must be a suveillance system to close loop speed contol speed. It tuned out that by this method can dive the ca even up to 0.1 Hz and evese diection of otation without poblems. So, as stated ealie, in induction motos with field oientation indiect oto time constant compensation can continuously and easily on each pass though zeo fo the thid hamonic fluxe. Gant though the filtes. To ovecome the shotcomings associated with the injection method of test signals in the machine, estimate oto time constant and othe paametes of the machine can be used conventional identification methods such as Kalman filte. Although the stoy fist appeaed 15 yeas ago and today is done attention to this matte. Kalman filte method is based on the consideation that the supply voltage fom invete moto have a boadband hamonic spectum can be consideed as a noise (distubance) of the amount equied invete moto itself. Such a motive dive system can be seen as an ideal set fo the application of extended Kalman filte that is natually available to identify andom input paametes and all elements ae pesent fo diect estimation of oto time constant. Recent studies on the chaacteistics of convegence, paamete sensitivity and accuacy of measuements of speed (when adopting schemes extended Kalman filte) showed that the pactical implementation of an extended Kalman filte identifie may be inefficient at low speeds and sensitivity to changes in othe paametes that may be noticeable. Clealy futhe eseach is needed on this method befoe to obtaining a final decision on its pactical efficiency. 4 Concussions The vey fast developing of the dives with asynchonous motos and vaiable speed and of systems fo the convesion of electical enegy made also technical innovation to be an unpecedented level [5], [20]. Shae inceasingly lage asynchonous motos in industial pocesses, in dives with vaiable speed, in pocesses of high fidelity and pecision electonics boosted the development of powe electonics and egulation and contol electonics (at a ate compaable I would say with the compute and consume goods), so that the news in this maket began to appea in vey shot peiods of time [13]. Thus, the electical adjustable dives with asynchonous motos led to significant enegy savings, inceasing poduct quality, incease system eliability, etc. Majo facto which has helped the technology of altenating cuent dives to incease apidly the maket is the evolution of seveal closely elated fields like this: powe semiconducto devices, fequency convetes, micopocessos, techniques of contol and simulation though mathematical models. The impact of advanced and unconventional contol stategies in electical dives development was examined in this aticle with a geat attention diected on non-sensoy stategies and issues foecasts in ode to identify the size of electical machines and paametes of mechanical tansmission. Techniques based on obsevation shows a bette pecision, but suffe fom machine load (loading) and the sophisticated methods of calculation, needed, obviously, the fastest micopocessos. It should be noted that, cuently, most adopted non-sensos scheme ae ISSN: 1790-5060 239 Issue 7, Volume 4, July 2009
Macel Ionel, Mihail-Floin Stan, Coneliu Ioan Salisteanu, Octavian Macel Ionel based on appoximate data (such as satuation neglect and the effects of time and tempeatue vaiation on inductance, inductance pefect symmety about the position shaped tooth of poles, stato and oto), which in pactice, obviously, ae not tue, and that affects the accuacy of the algoithm fo calculation and analysis. Finally, it should be taken into account the influence of ion losses in position detection algoithms etc. Compaed with unifom hamonic cuent shaeholdes, AC dives geneate additional nonunitay hamonic hamonic band called maginal (edge band). Compaed with othe commonly used AC dives, fequency convetes geneate significant levels of highe ode hamonics. To assess whethe a convete disupt thei command o othe tasks must be fulfilled befoe a tial installation of a system such convete. The geate the powe, the study is the impotance. Refeences: [1] CARDOLERTI, L., Commande et eglage de moteus synehones auto-commutes pa des capteus indiects de position, Thesis No 1118, EPFL, Lausanne, 1993. [2] ENESCU, D., COANDA H.G., VIRJOGHE E.,O. and CACIULA, I., Numeical investigation by means of polynomial egession method fo detemining the tempeatue fields in a medium with phase tansition, The 8 th WSEAS Intenational Confeence Systems Theoy and Scientific Computation (ISTASC 08), Rhodos, Gecia, August 20-22, 2008, pg.88-93, ISSN: 1790-2769, ISBN: 978-960-6766-96-1 [3] IONEL, M., STAN, M.F., DOGARU, V., IONEL, M.O. Posibilities of Diminishing the Distotions Intoduced by Supeio Hamonics of Electic Cuent, Poceedings of 6th WSEAS Intenational Confeence on Simulation, Modelling and Optimization, Lisbon, Potugal, Septembe 22-24, 2006, pp. 689-692, ISSN 1790-5117; [4] IONEL, M., STAN, M.F., Electical Engineeing Teaty, vol. II, Bibliotheca Publishing House, Tâgovişte, 2006, ISBN 978-973-712-191-2. [5] IONEL, M., STAN, M.F., Electical machines and electical dive system. Electonic convetes commands, Bibliotheca Publishing House, Tâgovişte, 2005, ISBN 973-8413-648. [6] IONEL, M., STAN, M.F., IVANOVICI, T., The integation of the a.c. machines command system, Scientific Bulletin of the Electical Engineeing Faculty, no. 1 / 2009, Bibliotheca Publishing House, Tâgovişte, June 2009, pp. 23-27, ISSN 1843-6188. [7] IONEL, M., STAN, M.F., The complete dive system, Poceedings of Intenational Symposium on Electical Engineeing, ISEE 2005, 17-19 oct. 2005, Tâgovişte, DâmboviŃa, pp. 93-96, ISBN 973-712-101-5. [8] IONEL, M., STAN, M.F., The invetes noise caused by electomagnetic induction of the asynchonous cages motos, The Scientific Bulletin of the Electical Engineeing Faculty, no.1, novembe, 2006, pp.13-16, ISSN 1843-6188; [9] IONEL, M., STAN, M.F., VÎRJOGHE, E.O., New methods fo the command of the electical induction machines, The Scientific Bulletin of the Electical Engineeing Faculty, no.2, octobe, 2007, pp.45-47, ISSN 1843-6188; [10] IONEL, M., STAN, M.F., SĂLIŞTEANU I.C., IONEL, M.O. Advanced command techniques of electical induction machines, Poceedings of the 9th WSEAS Intenational Confeence on Powe Systems (PS '09), Budapest, Hungay, Septembe 3-5, 2009, pp.176-180, ISSN 1790-5117; [11] IONEL, M., Adjustable electic dives with induction motos fo ion and steel industy, Bibliotheca Publishing House, Tagoviste, 2004, ISBN: 973-8413-81-8 [12] JUFER, M., Electical dives. Classification, stuctues and applications. Symposium on Electical Dives, Cagliai, 1987, pp. 255-266. [13] JUFER, M., Entainements electiques pou tansfet de position. Evolution et compaaison, Compte-endu des 4es jounees d'etudes su les moteus pas a pas, Lausanne, Ecole Polytechnique Fedeals, pp. 1-10, 1986. [14] OSSENI, R., Modelisation et auto-commutation de moteus synehones, Thesis No 767. EPFL, Lausanne, 1988, [15] STAN, M.F., IONEL, M., Double-fed induction machines, Poceedings of Intenational Symposium on Electical Engineeing, ISEE 2005, 17-19 oct. 2005, Tâgovişte, DâmboviŃa, pp. 89-92, ISBN 973-712-101-5. [16] STAN, M.F., IONEL, M., IONEL, O.M., Contibution to the Optimization of the Electical Dives of the Ponounced Dynamic Regime Woking Machines, WSEAS Tansactions on Powe System, Issue 9, volume 1, Septembe 2006, pp.1654-1658, ISSN 1790-5060; [17] STAN, M.F., IONEL, M., IONEL, O.M., Moden automatic system fo the optimization of the electical dives fo woking machines with mechanical banches, Poceedings of 8th WSEAS ISSN: 1790-5060 240 Issue 7, Volume 4, July 2009
Macel Ionel, Mihail-Floin Stan, Coneliu Ioan Salisteanu, Octavian Macel Ionel Intenational Confeence on Mathematical Methods and Computational Techniques in Electical Engineeing, Buchaest, Romania, Octobe 16-17, 2006, pp. 5-8, ISSN 1790-5117; [18] STAN, M.F., IONEL, M., VRĂBIESCU, L., New stuctues of synchonous motos with two statos and single oto, adial flux, The Scientific Bulletin of the Electical Engineeing Faculty, no.1, novembe, 2006, pp.7-11, ISSN 1843-6188. [19] STAN, M.F., VÎRJOGHE, E.L., IONEL, M., Electical Engineeing Teaty, vol. I, Bibliotheca Publishing House, Tâgovişte, 2005, ISBN 973-712-099-X. [20] VLĂDESCU, C., STAN, M.F., IONEL, M., Supple electical dives optimization fo metallugical industy, Bibliotheca Publishing House, Tâgovişte, 2007, ISBN 978-973-712-300-8. ISSN: 1790-5060 241 Issue 7, Volume 4, July 2009