Detuning Minimization of Induction Motor Drive System for Alternative Energy Vehicles

Transcription

1 Enegies 2015, 8, ; doi: /en Aticle OPEN ACCESS enegies ISSN Detuning Minimization of Induction Moto Dive System fo Altenative Enegy Vehicles Habibu Rehman Depatment of Electical Engineeing, College of Engineeing, Ameican Univesity of Shajah, Shajah 2666, UAE; Tel.: ; Fax: Academic Edito: Joei Van Mielo Received: 9 Apil 2015 / Accepted: 18 August 2015 / Published: 26 August 2015 Abstact: This pape evaluates diffeent types of AC machines and vaious contol techniques fo thei suitability fo the dive system of Altenative Enegy Vehicles (AEV). An Indiect Field Oiented (IFO) dive system fo the AEV application is chosen and its majo poblem of detuning is addessed by designing an offline and an online oto esistance adaptation technique. The offline scheme sets the slip gain at vaious opeating conditions based on the fact that if the oto esistance is set coectly and field oientation is achieved, then thee should be a linea elationship between the toque cuent and the output toque. The online technique is designed using Model Refeence Adaptive System (MRAS) fo the oto esistance adaptation. Fo an ideal field oiented machine, the oto flux along the q-axis should be zeo. This condition acts as a efeence model fo the poposed MRAS scheme. The cuent model flux obseve in the synchonous fame of efeence is selected as an adjustable model and its oto esistance is tuned so that the flux along the q-axis becomes zeo. The effectiveness of the offline tuning scheme is evident though pefomance validation of the dive system, which is implemented in a eal Fod vehicle. The expeimental esults obtained while diving the test vehicle ae included in the pape while the poposed online scheme is validated on a 3.75 kw pototype induction moto. Keywods: induction moto; detuning; field oiented contol; hybid electic vehicle; integated state altenato

2 Enegies 2015, Intoduction DC machines ae not a viable option fo the Altenative Enegy Vehicles (AEV) because they have low levels of efficiency, loweed powe to weight atio, a high-cost maintenance, and have limited high-speed opeation capabilities. AC machines ae a bette altenative fo Battey-poweed Electic Vehicles (BEV), Hybid Electic Vehicles (HEV), and Integated State Altenato (ISA) dive systems. The induction moto, the switched eluctance moto, and the pemanent magnet moto ae thee competito machines that ae being examined fo thei efficacy. Although the switched eluctance moto has a simple stato winding and ugged oto stuctue, it has poblems of toque ipple, noise, and vibations. The Pemanent Magnet Synchonous (PMS) moto, on the othe hand, is moe efficient but elatively moe expensive. Moeove, its magnets ae sensitive to high tempeatues. Nevetheless, advancements in the pemanent magnet technology and ongoing eduction in the pemanent magnet s cost demonstate that the futue of PMS machines is pomising. The induction moto, on the othe hand, is well known and accepted because of its wide-speed ange, complete de-enegization, uggedness, and loweed cost. The 48-volt ISA system is cuently exploed as a potential powe net by the automotive industy. Fo an ISA application, a PMS moto faes bette than the AC induction moto because of its highe efficiency, especially when an ISA is poweed by a smalle-sized battey than a BEV. Thus, an AC induction moto is eithe bette, o at least a compaable, altenative fo BEV and HEV applications because of the associated advantages mentioned above. Inteestingly, anothe deciding facto is the expeience and technology that the majo automotive companies have developed. Fod and Geneal Motos ae moe inclined towads the induction machine, while Toyota and Honda ae choosing the PMS machine fo almost all of thei AEV applications. The Field Oiented Contol (FOC) includes the Indiect Field Oientation (IFO) and Diect Field Oientation (DFO) contol [1] and the Diect Toque Contol (DTC) [2] ae the two main contol techniques fo AEV dive systems. Figues 1 3 shows block diagams fo IFO, DFO, and DTC dive systems, espectively [3]. Fo speed contol, the toque contol loop will be eplaced with the speed contol loop fo the FOC. Since the DTC egulates toque diectly, anothe block fo speed egulation needs to be added so that the output is the toque command. The DTC, shown in Figue 3, has the following featues: a fast dynamic esponse, simplicity of design since it does not equie stato cuent and flux egulation loops equied by the FOC, and obustness against the paametes vaiation. The basic DTC dive system also has a sensoless stuctue and applies a bang-bang toque and flux contol. Despite its featues, the DTC dive system is lacking because it has low speed flux, and toque estimation and contol, high cuent, and toque ipples. The toque ipples ceate vibations, which make the DTC less appealing fo automotive applications. Despite its negative attibutes, the DTC is a wothy candidate fo the ISA application because the ISA mostly opeates in the canking mode with a moto equiing only a good dynamic pefomance. The toque ipples of the DTC dive system in the steady state opeation ae not a majo poblem because, as a state, the ISA opeation time is shot; in the steady state, it mostly opeates as an altenato. Fo BEVs, it is only the AC moto dive that popels the vehicle both in the dynamic and steady state opeations. Thus, the DTC is not an ideal choice because of its toque ipples, which makes the FOC moe suitable fo BEVs. The HEV has geneally thee basic configuations: seies hybid, paallel hybid, and seies paallel hybid. The AC

3 Enegies 2015, machine opeation fo HEV vaies based on its achitectue and the designed hybid featues in the dynamic and steady state opeations. The FOC is a bette choice only if the machine opeation in the steady state condition inceases significantly. Othewise, the DTC can be selected fo an ISA type of opeation. * T e * + _ + - e Flux Reg. * i ds + - PI v ds e i * qs + v qs KT PI - Te 2 - to T 1 v s v s 3 Va V b V c PWM Invete Kslip. s * + i ds i qs T 3 to 2 i a i b 1/s e + Te Flux, and Toque Estimato Figue 1. Indiect Field Oiented (IFO) dive system. Figue 2. Diect Field Oiented (DFO) dive system.

4 Enegies 2015, Figue 3. Diect Toque Contolled (DTC) dive system. Taking into consideation the two field oiented contol techniques, DFO contol is pefeed ove the IFO contol because IFO is a feed-fowad open loop based contol system while DFO is a feedback closed loop contol. Howeve, DFO is sensitive to stato esistance, which is the coe of the flux and its angle estimation. The IFO contolle, as shown in Figue 1, is ealized by an accuate slip fequency contol, a necessay and sufficient condition fo keeping the machine field oiented. Accuate speed infomation is a must fo an IFO dive system, which potentially comes fom the speed senso o by designing a speed estimato. The IFO dive system is advantageous because it does not equie explicit stato o oto flux estimation since the optimal flux setting can be ealized by setting the flux cuent ids and, thus, omitting the flux egulation block. The oto flux oiented IFO contolle, shown in Figue 1, still emains one of the most attactive choices [4,5] and is a widely used contol technique fo AEV dive systems [3,6,7]. Theefoe, this wok focuses on an IFO dive system and pesents its pefomance enhancement. The IFO contol, ealized by an accuate slip fequency contol, equies the paametes of oto inductance and esistance fo the slip calculation. The IFO is inheently paamete sensitive because the oto inductance is a function of cuent and speed, while the oto esistance and, hence, the oto time constant (T) vay substantially with tempeatue changes. The atio of command T to actual T can ange fom 0.5 to 1.5 in pactice. This pocess of deviation of T fom its actual value to the command value is known as detuning of the machine. Detuning is a long standing poblem. Although it has been widely studied ove the last thee decades, an effot to make the tuning of oto time constant simple and accuate is still being eseached. The thee diffeent appoaches adopted fo ovecoming the detuning poblem ae: (i) designing an intelligent contolle, which can wok effectively even when the machine paametes ae inaccuate [8 11]; (ii) designing an offline oto esistance adaptation technique [6]; and (iii) designing an online oto esistance identification mechanism [7,12 23]. The intelligent contolles [8 11], although able to ovecome the contolle pefomance degadation due to detuning, do not coect the oto esistance, which esults in lesse toque pe amps. The offline scheme [6] has been widely adopted by the industy but it cannot incopoate all the opeating conditions.

5 Enegies 2015, Moeove, it also equies intensive contolle chaacteization befoe the machine can be put into opeation. Finally, the online esistance adaptation [12 23] is most appopiate choice because it can adjust the oto time constant unde all of the opeating conditions. This pape poposes and compaes an off-line tuning method [6] and anothe Model Refeence Adaptive System (MRAS) based online tuning scheme [14] fo the oto esistance adaptation and analyzes thei effectiveness though expeimental study. The off-line scheme popounded in this pape is a pactical one and its pefomance is validated fo the ISA application. The online oto esistance adaptation techniques [12 23] ae designed based on the neual netwok, o using sliding mode obseve, o ae ealized by the Model Refeence Adaptive Scheme (MRAS). Fo example, the online oto esistance adaptation technique pesented in [17] is based on an atificial neual netwok in which the eo between the oto flux linkages, based on a neual netwok model and a voltage model, is back popagated to adjust the weights of the neual netwok model fo the oto esistance estimation. A Luenbege-sliding mode obseve with paamete adaptation algoithm is poposed in [18] to compensate fo the oto esistance vaiation effects. An adaptive vaiable stuctue identifie that povides finite time convegent estimate of the induction moto oto esistance unde feasible pesistent of excitation condition is pesented in [20]. A compaison between vaious model efeence adaptive schemes (MRAS) has been pesented in [21] and it has been documented that an MRAS based technique can effectively wok fo the oto esistance adaptation. This pape also poposes an MRAS based online oto esistance adaptation scheme [14]. The poposed technique is simple than the ones pesented in the past [16 23], does not equie igoous tuning like neual net, and poved to effectively adjust the oto esistance on a pototype 3.75 kw induction machine. 2. Roto Flux Oiented IFO Contol with Off-Line Tuning The Cuent Model Flux Obseve (CMFO) of the induction machine in the stationay fame of efeence is epesented by the following set of equations [24]: 1 ω piαs T L λ m α i m αs i s αs 1 v L R αs pi βs σll λ s 1 β T i βs σl i s βs σl v s βs ω T 1 ω pλ α λ α i T Lm αs pλ β 1 λβ T i βs ω T The esultant oto flux and the flux angle ae calculated as: (1) (2) λ λ λ (3) 2 2 α β θ e tan 1 λ λ β α (4)

6 Enegies 2015, The oto flux oiented indiect field oientation is ealized by locking the esultant flux λ with the synchonously otating d-axis vecto. The q-axis is pependicula to the d-axis and theefoe the flux along the q-axis should be zeo. In doing so, the cuent applied along the d-axis will independently contol the flux, while the cuent along the q-axis will contol the toque. In the oto flux oiented IFO, the condition of locking the d-axis with the esultant flux vecto, o alignment of the esultant flux vecto with the d-axis, is guaanteed assuming that the entie flux is aligned along the d-axis of synchonous fame of efeence, which imposes the following condition on the machine slip: ω L i 1 i qs qs sl R i ds T i (5) ds Fo the IFO contol, an accuate command slip is the deciding facto fo maintaining the field oientation, which equies pecise oto time constant infomation. The IFO contol is ealized by imposing the slip condition specified by Equation (5). The mechanical motion, and toque equation in the synchonous fame of efeence, can be witten as follows [24]: B 1 pω ω ( Te TL) J J (6) 3P L T ( λ i λ i ) (7) m e dqs qds 2 L The oto flux oientation contol scheme is simple and esults in decoupling of the flux and toque components focing the flux along q-axis to zeo. This decouples the flux contol fom the toque contol, simplifying the toque equation [5] to: T 3P L m e λdiqs 2 L (8) In pactice, the moto paametes, specifically the oto esistance, ae sensitive to tempeatue and elative speed of the machine. Consequently, if the esistance in the slip equation is not set popely, the decoupled contol of the flux and the toque is lost. To ovecome this poblem, an off-line gain schedule is designed and implemented. The gain schedule, poposed in this wok, tunes the machine s paametes in a simple and efficient manne, and is ealized by designing a slip gain (Kslip) which modifies Equation (5) as [6]: ω i qs sl Kslip (9) i ds Slip gain Kslip is a key contol paamete in the implementation of indiect oto flux oientation contol. If the slip gain is set popely, the highly complicated induction machine model becomes decoupled and contolle design is significantly simplified. One citeion designed to detect the pope setting of Kslip is based on the following definition: Assuming that the gain is set coectly and oto flux oientation is achieved, then the toque Equation (7) can be expessed as [6]: 3P L 3P L T i i i K i i (10) 2 e 2 m m (λ d qs) L 2 L qs ds T qs ds

7 Enegies 2015, If ids is maintained constant, then the output toque would be a linea function of iqs. Theefoe, one way to tune Kslip is to adjust Kslip so that a linea elationship between the output toque and iqs is achieved. The paamete KT in Equation (10) seves as a scaling facto between the command cuent i and the toque command T *, as indicated in Figue 1. Theefoe, KT and Kslip can be tuned * qs e simultaneously using the poposed methodology. This offline paamete tuning scheme is applied on an 8 kw induction which has been deployed in a eal vehicle fo the ISA opeation. The moto paametes and toque speed chaacteistics ae shown in Table 1 and Figue 4, espectively. The moto has a limited constant toque egion while its field weakening egion has been extended up to 5000 pm. This is because a constant toque is equied only fo the engine stating up to about 800 pm while most of the time the machine is opeating in the geneation mode. The expeimental setup includes an 8 kw induction moto, an IGBT invete, and a flexible high pefomance advanced contolle (ACE) [25] fo electic machine. The DSP on the CPU boad pefoms all eal time contol functions, while a micopocesso pefoms downloading, data logging, and data communication functions. Figue 5 [25] shows the eal time contol panel Gaphical Use Inteface (GUI) built fo testing an induction machine. By using this GUI, it is vey convenient to change contol paametes and immediately see the effects of that change. Any contol input o contol paamete can be set up to be diven fom the GUI and hence can be changed in eal time. Likewise, any system measued o calculated output can be displayed on the GUI. Many diffeent types of contol and display widgets ae povided, including stip chats, switches, and numeic displays. These featues make the ACE development system vey flexible and efficient. Fo example, PI cuent egulato contol gains (shown at the bottom ight of the contol panel in Figue 5 fo an induction machine can be changed while the system is unning. The built-in datalogge can be easily used to see the exact effects of that change in gain on the commanded phase voltages and measued phase cuents. The datalogge is designed so that all of the data is coheent that is, sampled fom the same contol loop iteation and thus pefectly synchonized and guaanteed to be valid [25]. Figue 4. Toque speed chaacteistics of an ISA machine.

8 Enegies 2015, Table 1. Specifications of the induction moto. Moto Paametes Values Design Voltage 300 V Rated Powe 8 kw Poles 12 Base Speed 300 pm Peak Toque 280 Nm Figue 5. Contol panel fo induction moto testing. The moto is put on the dynamomete as shown in Figue 6 and opeated at diffeent speeds and loads both in motoing and geneating modes of opeation fo tuning the KT and Kslip. The oto flux oiented dive system has two independent inputs: toque command and flux command. Nomally the opeating conditions, e.g., speed and toque, ae govened by the moto application. The flux setting povides a degee of feedom; i.e., ids can be selected to achieve additional objectives such as maximizing the system efficiency while meeting the toque demand. In Figue 7, the flux optimization is demonstated at speeds of 2000, 3000, 4000 and 4500 pm. The optimum flux cuent and efficiency ae plotted in each tace fo each speed [3]. The Figue 7a1 a4 show the optimal flux cuent setting fo speed of 2000, 3000, 4000 and 4500 pm espectively at diffeent powe levels while Figue 7b1 b4 show the optimal efficiency measued at the coesponding points. Expeimental esults eveal that KT and Kslip depend upon the opeating mode of the machine (motoing/geneating), opeating speed, and flux cuent setting i.e., ids. Afte a caeful study of the test data, based on the citeia outlined above, a gain schedule fo KT and Kslip is developed and implemented in the induction moto contolle. As an example, one such gain schedule designed fo the state altenato application both fo the motoing and geneating modes of opeation fo a speed ange of 600 pm is shown in the Figue 8. This gain schedule is integated fo an IFO dive system of ISA and is implemented in the Fod Euopean Mendo. The oveall system shown in

9 Enegies 2015, Figue 9 [6] includes a thee-phase IGBT invete, induction moto as a state altenato, two dc/dc convetes, a 42 volt lead acid battey and thee 1-F ultacapacitos. The expeimental esults while diving the vehicle on oad ae demonstated in Figue 10. In this figue, Figue 10a shows the engine speed, Figue 10b shows the toque command cuent in the synchonous fame of efeence set by the contolle to attain the desied speed. The actual moto phase a and b cuents ae plotted in Figue 10c,d espectively while the DC bus voltage is shown in Figue 10e. Figue 10a shows that the designed contolle can stat the engine and bing it to a speed of about 800 pm in less than 0.3 s and aftewads, at about 0.37 s, it woks as a geneato to chage the battey by applying a negative iqs as shown in Figue 10b. Thus, the gain schedule designed in Figue 8 woks effectively to keep the machine field oiented and get an instantaneous toque esponse fo opeating the vehicle. Thee ae othe such gain schedules designed fo diffeent anges of speed and pogamed in the moto s contolle. Futhemoe, the state and altenato actions of the ISA can be obseved fom the subplot (e) in which the invete DC bus voltage initially deceases duing the motoing action fom 0.1 to about 0.3 s and then it stats inceasing because of the geneato action ealized by a negative iqs. Figue 6. Off line tuning of Induction moto fo gain schedule.

10 Enegies 2015, (a1) I ds VS Powe at 2000 pm (a2) I VS Powe at 3000 pm ds (a3) I ds VS Powe at 4000 pm (a4) I VS Powe at 4500 pm ds (b1) Efficiency VS Powe at 2000 pm (b2) Efficiency VS powe at 3000 pm (b3) Efficiency VS Powe at 4000 pm (b4) Efficiency VS Powe at 4500 pm Figue 7. Expeimental esults fo efficiency and flux cuent. a1 a4: optimal flux cuent vesus powe at 2000, 3000, 4000 and 4500 pm espectively; b1 b4: Efficiency calculation with optimal flux level at 2000, 3000, 4000 and 4500 pm espectively. Figue 8. Off line tuning of gain schedule.

11 Enegies 2015, Figue 9. The ISA system design. Figue 10. In vehicle testing esult fo the ISA with the poposed gain schedule. (a) Engine speed in pm; (b) Toque command cuent; (c) Moto phase a cuent; (d) Moto phase b cuent; (e) DC bus voltage.

12 Enegies 2015, Online Roto Resistance Adaptation The online oto esistance adaptation method analyzes vaious flux obseve stuctues to exploe thei suitability fo the oto esistance adaptation. An obseve o estimato has an integation pocess model that estimates the desied state. This integation pocess model can be implemented with o without a feedback loop. The feedback loop coects the eo and hence impoves the estimation s accuacy. An obseve without a feedback loop is called an open loop obseve wheeas one with the feedback loop is called a closed loop obseve. Theefoe, the open loop obseve is essentially a eal-time simulation of the physical pocess. The cuent model open loop flux obseve and voltage model open loop flux obseve ae the two most commonly used open loop flux obseves. The cuent model flux obseve in the stationay fame of efeence, given by Equation (2), can be tansfomed in the synchonous fame of efeence as [24]: p p L m λd ids λd ωsl λq T T L m 1 λq iqs λq ωsl λd T T The model epesented in Figue 11 [14] can estimate the oto flux diectly fom the stato cuent, slip speed ωsl, oto inductance L, and oto esistance R. Fo an ideal oto flux, egulated indiect field oiented machine the oto flux along the q axis is zeo, which educes the block diagam given in Figue 11 to the one shown in Figue 12. The voltage and cuent model flux obseves ae commonly used in the stationay fame of efeence fo diect field oientation contol, fo sensoless contol, o fo the flux estimation and egulation of an indiect field oiented dive system. Howeve, this wok adopts a unique appoach fo using the cuent model flux obseve. Fo an IFO dive system, the obseve stuctue is designed in the synchonous fame of efeence instead of the stationay fame of efeence. Magnetizing inductance, oto inductance, and oto esistance ae machine paametes in the cuent model flux obseve pesented in Equation (11). The magnetizing inductance (Lm) and oto inductance (L) of the machine do not equie an online adaptation because they don t change with tempeatue vaiations. The leakage inductance of an induction machine is sensitive to the opeating conditions of the machine; howeve, in contast to the voltage model obseve, no explicit knowledge of leakage inductance is equied fo the cuent model obseve. The oto esistance is the only paamete which changes with the machine s tempeatue in the cuent model flux obseve. This discussion leads to the poposed MRAS scheme, which is used fo online oto esistance adaptation. The idea to tune the oto esistance is poposed as: The fact that the oto flux along the q-axis is zeo, i.e., L m 1 the equation pλq iqs λq ωsl λd T T 1 (11) λ q 0 is used as a efeence model. Then is used as an adjustable model. The adaptation mechanism adjusts the oto esistance in the adjustable model such that it follows the efeence model. As a esult the oto esistance is tuned to its coect value and λ q is diven to zeo. The poposed contol algoithm is shown in Figue 13 [14]. The only unknown paamete in the adjustable model is R. If R is coect, then the flux calculated fom the adjustable model will be equal to

13 Enegies 2015, the efeence model. When the tempeatue changes, R deviates fom the oiginal value, which then dives q λ away fom zeo. This eo in the flux will be foced back to zeo by adjusting R, which will bing the oto esistance to its actual value. The flux eo equation can be witten as whee λ q(ef) 0. A PI stuctue is used fo the oto esistance adaptation [14]. whee q(ef) q e λ λ R( k) R( k 1) R( k) (12) R ( k) K e( k) K e( k) T (13) p i T is the sampling time of the adaptation mechanism. Figue 11. Cuent model oto flux obseve. Figue 12. A tuned cuent model oto flux obseve.

14 Enegies 2015, Figue 13. MRAS stuctue fo oto esistance adaptation. 4. Simulation and Expeimental Results fo Online Roto Resistance Adaptation A simulation study was pefomed to validate the poposed algoithm. Afte intensive, multiple simulations testing, the poposed algoithm was validated on a 3.75 kw induction machine using the same test setup that was deployed fo offline tuning. The machine paametes ae shown in Table 2. The moto was stated at an ambient tempeatue unde the most pactical applications. The nominal oto esistance given in Table 2 is used as the initial value to stat the contolle. When the machine opeates, its tempeatue vaies which also changes the oto esistance. The oto esistance needs to be adjusted in the contolle to keep the machine field oiented. The inductance pogammed in the contolle, based on the cuent and speed of the machine, does not change with tempeatue. If the oto inductance is inaccuate, the algoithm will keep adjusting the oto esistance until the oto flux along q-axis becomes zeo. Thus, the poposed technique also indiectly has the advantage of ovecoming any poblems that esult fom the inaccuate value of the oto s inductance. Table 2. Pototype induction moto paametes. Machine Voltage Cuent Powe Stato and Roto Inductance Magnetizing Inductance Rated Speed Stato Resistance Roto Resistance Pole Values 220 V 14.8 A 3.75 kw L ls = L l = 1.9 mh L m = 41.2 mh 1670 pm R s = 0.6 Ω R = Ω 4 poles Simulation esults fo a command speed of 1500 pm ae shown in Figue 14. The command and actual speeds ae plotted in Figue 14a while the Figue 14b,c espectively show the toque command cuent and coesponding toque command set by the field oiented contolle to attain the desied speed.

15 Enegies 2015, The oto esistance is plotted in Figue 14d while the flux in the synchonous fame of efeence along d and q axis ae given in Figue 14e,f espectively. Additionally, at 0.5 s, a load of 10 Nm is applied on the machine. Initially, as can be obseved in Figue 14b, moto applies the maximum allowable toque command cuent of 50 amp to bing the moto to the desied speed. Once the moto speed eaches the command speed the toque command cuent is educed to a minimal value to keep the moto unning at 1500 pm. At 0.5 s, when the machine is loaded with a toque of 10 Nm, it can be seen that the contolle can effectively espond to this extenal load and keep the machine unning at 1500 pm by applying a toque command cuent of 30 amps. The Figue 14d shows the poposed algoithm can tune the oto esistance to its accuate value of Ω while diving the flux d-axis to its steady state value as shown in Figue 14e, and flux along q-axis to zeo as shown in Figue 14f. Figue 14. Simulation Results with command speed of 1500 pm and 10 Nm load. (a) Moto speed; (b) Toque command cuent; (c)toque command; (d) Roto esistance; (e) Flux in the synchonous fame of efeence along d-axis; (f) Flux in the synchonous fame of efeence along q-axis. Finally, two types of expeiments wee pefomed to (i) investigate the effect of detuning on the machine s pefomance; and to (ii) validate the effectiveness of the poposed algoithm fo adjusting the

16 Enegies 2015, oto s esistance to its accuate value. In these expeiments, a step command of 250 pm was applied and a PI contolle was used to egulate speed. The flux level was kept fixed in all thee cases with a fixed ids command input of 6 amps. The gains of the PI contolle wee kept the same to validate the effectiveness of the poposed scheme. The data unde all thee opeating conditions wee collected though the data acquisition capability of the Advanced Contolle fo Electic machines (ACE) [25]. The same hadwae platfom is used both in the vehicle testing and fo the validation of online oto esistance adaptation algoithm. The contolle is fed with a wong value of oto esistance and no adaptation mechanism is applied to investigate the detuning effect. The contolle is pogammed with one fouth and one half of its actual value, which is Ω at the ambient tempeatue. The esults of these opeating conditions ae epoted in Figues 15 and 16 espectively. Finally, the oto esistance is set to one fouth of its ambient value (0.412) and the poposed adaptation algoithm is applied to check its effectiveness. This scenaio effectively ensues that the contolle is commanded with a oto esistance at a tempeatue much lowe than the ambient tempeatue. The expected esult is that the poposed MRAS scheme will tune the oto esistance and adjust T to its coect value and keep the machine field oiented. The online oto esistance adaptation technique is insensitive to tempeatue, when the tempeatue changes the oto esistance will change, which will cause the oto flux along q-axis to deviate fom the efeence value of zeo. The poposed MRAS will then adjust the oto esistance such that the flux along q-axis becomes zeo. This has been poven by expeimental esult shown in Figue 17 whee oto esistance is fed by one fouth of its actual value (0.412) at the ambient tempeatue, meaning esistance of anothe tempeatue and the poposed MRAS did adjust the oto esistance to its accuate value of The expeimental esults fo this case ae plotted in Figue 17. In all the thee Figues 15 17, Figue a shows the moto actual speed, Figue b pesents the toque command cuent set by the field oiented contolle to attain the desied efeence speed of 250 pm. The Figues 15 17c,d espectively show the flux along q and d axis in the synchonous fame of efeence while the oto esistance is given in Figues 15 17e. Following ae obsevations made fom the expeimental esults: Figues tace (b) shows the actual cuent iqs fo thee diffeent opeating conditions. The cuent level of iqs is at a maximum in Figue 15; it deceases slightly in Figue 16 while it is at a minimum level in Figue 17. As stated above, Figue 15 pesents the case in which the oto esistance is set to one fouth of its value, and Figue 16 shows the esults with oto esistance set at one half of its value and when no adaptation is applied in eithe scenaio. Figue 17 pesents the case whee, despite the oto esistance being initialized with one fouth of its value, the MRAS adjusted the esistance to its accuate value, thus putting the machine into field oientation and equiing a minimal level of cuent fo the same opeating conditions as pesented in Figues 15 and 16. This poves that the poposed algoithm woks effectively and inceases the toque pe amps output of the machine. The speed esponse unde thee diffeent conditions is plotted in tace (a) of Figues It shows that the esponse is faste with adaptation, poving that the contolle with the adaptation adjusts the esistance to its accuate value and hence keeps the machine field oiented, poviding an instantaneous toque/speed esponse. Tace (c) and (d) of Figues show the estimated oto fluxes, λ d and λ q, in the synchonous fame. λ d and λ q each thei steady state values faste with adaptation compaed to when no adaptation is applied.

17 Enegies 2015, The oto esistance is plotted in tace (e) of Figues In Figues 15 and 16, the oto esistance emains at its pe-set value while tace (e) of Figue 17 demonstates that the poposed adaptation mechanism has the ability to tune the oto esistance to its actual value of Ω. Figue 15. Expeimental esults with R/4 and no adaptation. (a) Moto speed in pm; (b) Toque command cuent in synchonous fame of efeence; (c) Flux along q-axis in synchonous fame of efeence; (d) Flux along d-axis in synchonous fame of efeence; (e) Roto esistance. Figue 16. Expeimental esults with R/2 and no adaptation. (a) Moto speed in pm; (b) Toque command cuent in synchonous fame of efeence; (c) Flux along q-axis in synchonous fame of efeence; (d) Flux along d-axis in synchonous fame of efeence; (e) Roto esistance.

18 Enegies 2015, Figue 17. Expeimental esults with R/4 and adaptation. (a) Moto speed in pm; (b) Toque command cuent in synchonous fame of efeence; (c) Flux along q-axis in synchonous fame of efeence; (d) Flux along d-axis in synchonous fame of efeence; (e) Roto esistance. 5. Conclusions This pape poposes an off-line and anothe online technique to ovecome the detuning fo impoving the pefomance of vehicula dive system. The pefomance of off-line scheme is validated fo the dive system of a test vehicle while the online scheme is tested on a pototype induction moto in the lab. Both techniques can effectively tune the oto esistance to its coect value, and keep the machine field-oiented. The following ae majo conclusions dawn fom this wok: The off-line technique pe-sets the oto esistance fo diffeent opeating conditions. It needs intensive testing to pogam the contolle with the coect value of the oto esistance at vaious opeating conditions. Theefoe, it becomes moto-specific and cannot be used fo an off-the-shelf machine. The online technique pefoms bette because it does not equie the machine to be pe-tested and can wok fo any machine unde any opeating condition. The poposed online oto esistance adaptation technique is simple compaed to the ones pesented in the past and is bette than using techniques that incopoate intelligent contolles fo ovecoming the detuning poblem. Even though intelligent contolles povide a bette toque esponse, they do not fix the oto esistance to its accuate value esulting into lesse toque pe amps. Conflicts of Inteest The authos declaes no conflict of inteest.

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