Self-sensing Control of the Externally-Excited Synchronous Machine for Electric Vehicle Traction Application

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1 Self-ening Control of the Externally-Excited Synchronou Machine for Electric Vehicle Traction Application Mohamad Koteich, Amir Meali, Simon Daurelle To cite thi verion: Mohamad Koteich, Amir Meali, Simon Daurelle. Self-ening Control of the Externally-Excited Synchronou Machine for Electric Vehicle Traction Application. SLED 27 8th IEEE International Sympoium on Senorle Control for Electrical Drive, Sep 27, Catania, Italy. SLED proceeding, < <hal-5736> HAL Id: hal Submitted on 8 Aug 27 HAL i a multi-diciplinary open acce archive for the depoit and diemination of cientific reearch document, whether they are publihed or not. The document may come from teaching and reearch intitution in France or abroad, or from public or private reearch center. L archive ouverte pluridiciplinaire HAL, et detinée au dépôt et à la diffuion de document cientifique de niveau recherche, publié ou non, émanant de établiement d eneignement et de recherche françai ou étranger, de laboratoire public ou privé.

2 Self-ening Control of the Externally-Excited Synchronou Machine for Electric Vehicle Traction Application Mohamad Koteich, IEEE Member, Amir Meali 2, Student Member, Simon Daurelle 2, Student Member Abtract Thi paper tudie the poibility of removing the poition enor from electric vehicle EV) powertrain that employ the externally-excited ynchronou machine EESM) for traction. Three poition etimation approache are tudied: back-electromotive-force integration, tate-oberver and highfrequency voltage injection approache. Theoretical background i preented, a comparative performance analyi i performed, and experimental reult on a 65-kW EESM drive tet bench are hown. Some requirement for EV powertrain are emphaized. I. INTRODUCTION The electric vehicle EV) market i expected to grow increaingly in the next decade. Mot of nowaday EV ue inet permanent-magnet ynchronou machine IPMSM) drive for traction. The main challenge of the IPMSM in the automotive indutry i the dependence on the rare-earth market. Several alternative olution have been tudied in order to remove magnet from EV drive without increaing their volume and their ma []. One potential alternative i the externally-excited ynchronou machine EESM) which i being uccefully ued in Renault Zoé, Fluence and Kangoo EV. The preent paper tudie the poibility of removing the poition enor from the EESM drive ytem, uing elfening control technique [2], in order to reduce the cot and increae both the reliability and the mechanical robutne of the drive. Compared to the IPMSM, very few paper have tudied the elf-ening capabilitie of the EESM [3] [7], epecially that everal deign of the latter have been propoed: if the Zoé traction drive i taken a example, there exit at leat 3 different EESM powertrain, the firt two generation are manufactured by Continental, and the latter one are Renault in-houe manufactured machine. Thi paper i aimed at preenting a primary tudy of the feaibility of elf-ening control for EESM traction drive. Three broad approache for poition etimation are teted and compared: ) back-electromotive force EMF) integration approach [8], preented in Section III, 2) tate-oberver approach [6], in Section IV, and 3) high-frequency HF) injection approach [9], in Section V. The performance of the firt approach are preented for medium and high peed. The limitation of the econd approach are analyzed. The third approach ha two major advantage over the firt two one: ) it work tably at low peed and tandtill and 2) it doe not require the knowledge of any machine parameter. Experimental tet have been performed on a 4-pole, 65- kw EESM, the reult are preented in Section VI. Groupe Renault, Technocentre, Guyancourt, France 2 Ecole Centrale Nante, LS2N Laboratory, Nante, France II. EESM MATHEMATICAL MODEL The chematic repreentation of the EESM i hown on Fig. : a three-phae tator, with an externally DC-excited winding in the rotor [6]. A. Notation The complex pace vector notation i ued to model the revolving electromagnetic tator quantitie []. Let x r be a tator quantity in the rotor reference frame, it can be expreed a x r = x e jθ or equivalently x d + jx q = x α + jx β )co θ j in θ) Subcript and f tand for tator and rotor field) quantitie repectively, wherea upercript and r tell whether the quantity i expreed in the tator αβ) or the rotor dq) reference frame. θ i the angle between the tator and the rotor reference frame. The fluxe, current, voltage and back EMF are denoted by ψ, i, v and e, repectively. The inductance and the reitance of a given circuit are denoted by L and R repectively, and M denote the mutual inductance between the tator and rotor circuit. B. Stator equation The tator voltage equation in the tator coordinate can be written a: v = R i + dψ ) dt In the rotor reference frame, the previou equation become: v r = R i r + dψr + jωψ r 2) dt Neglecting the cro-aturation inductance, the tator flux can be expreed in the rotor coordinate a: ψ r = L d + L q i r + L d L q i r + M f i f 3) 2 2 = L i r + L 2 i r + M f i f 4) where i r denote the complex conjugate of i r. C. Rotor equation The rotor calar equation are expreed in the rotor reference frame. The voltage equation i: with v f = R f i f + dψ f dt 5) ψ f = L f i f + M f i d 6)

3 b q the filter by the following function, in order to bring the LPF repone cloer to the pure integrator repone []: c v b v c v f v a Fig. : The EESM chematic repreentation III. EQUIVALENT-FLUX BASED ESTIMATION Thi ection decribe a unified poition etimator for AC machine. It i deigned by merging of the contribution of everal paper including [8], [] [5]. The following etimator conit of two part: tator flux etimation baed on a programmable tatically-compenated PSC) low-pa filter LPF), and rotor flux poition etimation baed on the Equivalent Flux, or Active Flux, concept decribed below. A. Stator flux etimation The tator flux vector can be etimated by integrating the back-emf e ): ψ = v R i )dt = e dt 7) where v i the command voltage etimated uing an inverter model, R i conidered to be fairly accurately known, and i i the meaured tator current. The implementation of a pure integrator i prone to drift problem due to inverter nonlinearitie, current meaurement noie, unbalanced gain and DC offet. Furthermore, an initial condition error would reult in a DC-offet in the integrator output. To overcome thee problem, variou algorithm have been reported in the literature, including adaptive flux oberver [3], which require the knowledge of the machine inductance. Neverthele, it can be argued that if the openloop) integration function i optimized, the ue of adaptive cloed-loop) etimation tructure would not be eaily jutifiable. Thu, an optimized modified integration algorithm i deigned for tator flux etimation. To remove the error due to the DC-offet at the input of the integrator, a high-pa filter, with a corner frequency, i implemented in erie with the input of the pure integrator. Thi reult in a low-pa filter LPF) approximated integrator: Ψ ) e ) =. = 8) + + The filter generate both magnitude ditortion and phae lag, which can be compenated for, in teady-tate, by multiplying θ d a jω + jω = j ω 9) Furthermore, the tunning of the filter cut-off frequency i a trade-off between the offet rejection dynamic and the teadytate accuracy: for example, higher corner frequency enure fater DC-offet rejection, however, it introduce higher ditortion in the output ignal due to increaing attenuation and phae lag. Therefore, an adaptive corner frequency tuning hould be adopted: i choen in a way to be dependent on the tator angular frequency ω a follow [8]: = λ ω ) where λ i a poitive real number maller than one. At low peed, λ can be tuned to a low value, e.g.., wherea for higher peed, it can take higher value. In thi cae, the timecontant of the LPF, /λ ω ), i decreaed with the increae of the tator frequency. The time-domain expreion of uch a PSC-LPF i [8]: ˆψ = λ ω ˆψ ) + [ jλignω )] e dt ) The performance of the PSC-LPF depend on the tator reitance, the accuracy of the inverter model, and the choice of λ. Furthermore, it heavily relie on the accuracy of the tator flux angular frequency ω ) etimate. A PLL-baed etimation cheme, applied to the command voltage, i implemented to etimate the tator angular frequency [2], a hown in Fig. 2. B. Equivalent-flux concept and poition etimation The tator back-emf integration i valid for all AC machine, ince they all have the ame voltage tructure. The rotor poition etimation baed on the tator flux relie on the interaction between the tator and the rotor field, which i dependent on the rotor tructure. Neverthele, a unified flux model can be developed in view of rotor field-oriented control of AC drive, by introducing the Equivalent Flux concept ψ eq and an equivalent tator inductance L eq [4]: ψ ψ eq = L eq i + ψ eq 2) = ψ eq e jθ 3) with L eq = L q for ynchronou machine and L eq = σl for induction machine IM), and the equivalent flux ψ eq i expreed for the EESM, IPMSM and the IM a the following: EESM : ψ eq = L d L q )i d + M f i f IPMSM : ψ eq = L d L q )i d + ψ r IM : ψ eq = k r ψ rd 4) The rotor poition of the EESM can be etimated from the tator flux by evaluating the phae angle of the equivalent flux vector uing the arctangent function for example. The complex ignal flow of the equivalent-flux-baed poition etimator i hown on Fig. 2.

4 i v R e Compenation jλ e jθ v q ign K i K p Low-pa filter ω λ PLL Fig. 2: Equivalent-flux baed Etimator θ v ˆψ L q IV. STATE-OBSERVER BASED ESTIMATION The tate-pace model of the EESM can be deduced from Section II, by incorporating the mechanical model equation [6]. A tate-oberver, uch a the extended Kalman filter EKF) can be deigned to etimate the rotor poition and peed baed on the tator and rotor current meaurement. Neverthele, a tate oberver require the ytem to atify the o-called obervability condition, in order to enure table and accurate etimation. The obervability of the EESM i tudied in [6], where it i hown that at tandtill, the obervability i not guaranteed, unle ome varying high-frequency) voltage i injected in the machine. According to the author experience, a full-order oberver, uch a the EKF, i not a practical olution for EV EESM elf-ening control, for the following reaon: Oberver-baed etimation fail at very low-peed, unle an HF voltage i injected. In the cae of the tudied EESM, the injection in the rotor winding i not helpful becaue of the low bandwidth of the rotor circuit. A low amplitude HF ignal will be filtered if injected to the rotor, and lower frequency ignal would generate torque ripple. On the other hand, if the HF ignal i to be injected in the tator, then HFI technique would be preferred thank to their robutne and implicity. The model doe not only rely on the knowledge of L d and L q, but alo on L f and M f. Thee inductance cannot be accurately known due to nonlinear aturation phenomenon that occur in the machine. Therefore, apart from obervability problem at low peed, a tate-oberver, uch a the EKF, would fail to accurately etimate the poition over the whole operating range, due to the abence of an accurate linearized model. the EKF implementation require high computational burden. A a concluion, tate oberver that rely on the knowledge of the inductance are le likely to work on the EESM, where ˆψ eq ˆθ ˆω j ˆq jq v ˆqc jβ θ ˆθ d v ˆdc ˆd α Injected Voltage v ˆdc = V c co t v ˆqc = ˆω V c in t Reulting Flux ψ ˆdc = V c in t ψ ˆqc = Fig. 3: HF voltage injection principle. magnetic aturation phenomena are more complex than the IPMSM. More robut method are to be ought. V. PULSATING HF INJECTION BASED ESTIMATION The pulating HF injection HFI) poition etimation ha been propoed for the IPMSM by Corley and Lorenz [9]. It i baed on the property of the d- and q- axe flux being decoupled: if the following HF voltage vector, at angular frequency >> ω ) vˆr c = V c co t) + jv c ˆω in t) 5) i injected to the drive, in the etimated rotor reference frame Fig. 3), it i expected to induce HF current only on the etimated d-axi. The meaured HF current through the etimated q-axi i driven to zero via a PI mechanim in order to make the etimated poition track the actual poition. The HF reitive drop voltage can be neglected. The induced HF flux in the etimated poition coordinate i ψˆr c = V c in t) 6) it can be expreed in the tationary coordinate a follow: ψ = V c inω c c t)e j ˆθ 7) The induced HF current in the tationary coordinate can be written a by inverting equation 4 and tranforming it into the tator reference frame): i c = L 2 L2 2 L ψ c L 2ψ c ej2θ) 8) = I cp e j ˆθ in t) I cn e j2θ ˆθ) inωc t) 9) I cp and I cn denote the maximum magnitude poitive- and negative-equence component of the HF current repectively: I cp = V c L L 2 = V c L 2) L2 2 L d L q I cn = V c L 2 L 2 = V c L 2 2) L2 2 L d L q The HF q-axi current component i extracted uing a firt order high-pa filter HPF), and the following poition etimation error ignal, ε, i evaluated by low-pa filtering thi HF component multiplied by in t): ε = LP F [ in t)im i ce j ˆθ )] 22)

5 i α Carrier Extraction i ˆq HPF i ˆqc Demodulation LPF ε K i PLL ˆω i β in ˆθ co ˆθ in t K p ˆθ Fig. 4: Demodulation ignal proceing for HFI enorle control which finally yield: ε = I cn 2 in 2θ ˆθ) I cn θ ˆθ) 23) Thi ignal i then fed to a PLL tracking mechanim that output the poition. The demodulation proce i illutrated in Fig. 4. For more detail about the PLL tuning refer to [6]. The Pulating HFI i alo a generic etimation technique that can be applied to AC drive. It only required a magnetic aniotropy in the flux path. In the cae of the EESM, the tator HF current can generate a rotor HF current due to the coupling between the two circuit. Neverthele, a mentioned earlier, the rotor bandwidth i much lower than the tator one for the tudied EESM, and the HF ignal i choen in a way to be filtered by the rotor circuit. VI. EXPERIMENTAL RESULTS Thi ection preent the reult of the experimental tet that have been performed on the 4-pole 65-kW Renault manufactured EESM drive that i ued on the Zoé electric car. The drive i operated in enorle configuration, the poition enor i ued for comparion. A khz witching frequency PWM voltage ource inverter i ued, with a 4 Volt DC bu. A. Flux-baed poition etimation The Equivalent-flux-baed poition etimator preented in Section III ha been teted under elf-ening control configuration, for a peed ramp, from to 9 rpm, with no- and full-load. The reult are hown on Fig. 7. The value of L q i generated baed on a look-up table with two input for implicity): the etimated peed and etimated torque. The look-up table i filled baed on experimental tet. Other technique can be ued for L q identification, uch a polynomial identification uing the tator current a input. To the bet of the knowledge of the author, the adaptive, robut etimation of L q i till an open problem, and no promiing olution have been propoed yet. The poition etimation error depend mainly on the value of L q. Higher accuracy and higher preciion look-up table i needed to enure better etimation quality. Poition etimation baed on flux etimation i not table at low peed, due to the low amplitude range of the back-emf. The peed etimation uing the tator voltage PLL eem to be fairly accurate. It dynamical performance can be further improved by fine tuning the PLL or by incorporating the mechanical model and the torque requet. B. Kalman Filter baed poition etimation The extended Kalman filter EKF) algorithm hown in Fig. 5 ha been teted, uing the tationary αβ electromechanical model of the EESM [6]. Sytem linearization matrice and matrix inverion calculation had been done analytically, off-line, in order to reduce computational burden. The HF injection in the rotor winding propoed in [6] ha been implemented. Fig. 6 how that at very low peed, when a HF current i injected to the rotor winding, the poition etimation error i around zero, which i not the cae when no HF current i injected. Thi i conitent with the obervability analyi reult preented in [6]. On the other hand, the EKF performance depend on the accuracy of the machine model; due to magnetic aturation phenomena, which are ignificant in traction drive, the poition etimation error varie ignificantly depending on the operating point. The tet how that an EKF with a imple EESM model cannot provide an accurate etimation for different operating point. C. HFI-baed poition etimation HFI-baed poition etimation i teted for peed lower than rpm. The injected voltage amplitude i 3 V, at.5 khz. A very challenging torque-peed profile i ued for the tet ee Fig. 8); it include ituation that are not likely to happen in practice. The pulating HFI-baed elf-ening control eem to be robut enough, epecially that no parameter are needed for etimation. It hould be noted that the teady tate etimation error increae a the peed increae. A for the peed etimation, it eem to be accurate enough. The dynamical performance of thi etimation technique can be improved by fine-tuning the filter and the PLL bandwidth. The EESM under tudy eem to have advantageou aliency characteritic. VII. CONCLUDING REMARKS The electric vehicle traction drive i a very challenging application for the elf-ening control, becaue it require

6 ˆx P ˆx Linearization fx,u) A k = x Prediction / Etimation ˆx k+/k = ˆx k/k + T f ˆx ) k/k, u k Correction / Innovation ˆx k+/k+ = ˆx k+/k + K k yk hˆx k+/k ) ) P k+/k+ = P k+/k K k C k P k+/k Oberver Gain ˆxk/k,u k ; hx) C k = x ˆxk/k P k+/k = P k/k + T Ak P k/k + P k/k A T k ) + Q K k = P k+/k C T k Ck P k+/k C T k + R) Fig. 5: Extended Kalman Filter etimation algorithm Rotor current i f Meaured and Etimated Electrical Poition Degree) Time ec) Fig. 6: EKF experimental reult. very accurate poition etimation with high dynamical performance, including critical ituation uch a high-torque zero-peed operation. In addition, the AC machine ued in traction have high power-to-volume ratio, with a complex magnetic aturation) behavior. Throughout thi paper, three poition etimation approache have been tudied and teted on an EESM traction drive: the equivalent-flux, the tateoberver and the high-frequency injection approache. The firt approach can be applied to all AC machine. It main limitation are the tability at low peed and the dependence on the accuracy of the inductance L q etimation. The econd approach highly relie on the machine inductance, and require higher computation complexity. The latter approach i accurate and robut enough at low peed, and can be applied for all alient AC machine. However, it uffer from limited dynamical performance at higher peed. Combining the firt or econd) and the latter approache i a viable etimation trategy that i well known and often ued [7]. Further invetigation of the rotor winding injection characteritic and benefit [4] [6] are to be carried out in the future. REFERENCES [] T. Jahn, Getting rare-earth magnet out of ev traction machine: A review of the many approache being purued to minimize or eliminate rare-earth magnet from future ev drivetrain, IEEE Electrification Magazine, vol. 5, pp. 6 8, March 27. [2] J. Holtz, Senorle control of induction machine with or without ignal injection?, IEEE Tranaction on Indutrial Electronic, vol. 53, pp. 7 3, [3] A. Griffo, D. Drury, T. Sawata, and P. H. Mellor, Senorle tarting of a wound-field ynchronou tarter/generator for aeropace application, IEEE Tranaction on Indutrial Electronic, vol. 59, pp , Sept 22. [4] J. Choi, I. Jeong, K. Nam, and S. Jung, Senorle control for electrically energized ynchronou motor baed on ignal injection to field winding, in IECON 23-39th Annual Conference of the IEEE Indutrial Electronic Society, pp , Nov 23. [5] A. Rambetiu and B. Piepenbreier, Carrier ignal baed enorle control of wound field ynchronou machine uing the rotor winding a the receiver: Rotating v. alternating carrier, in Proceeding of PCIM Europe 25; International Exhibition and Conference for Power Electronic, Intelligent Motion, Renewable Energy and Energy Management, pp. 8, May 25. [6] M. Koteich, A. Maloum, G. Duc, and G. Sandou, Obervability analyi of enorle ynchronou machine drive, in 25 European Control Conference ECC), pp , IEEE, [7] A. Beciu, E. Godoy, P. Rodriguez-Ayerbe, I. Bahri, and A. Maalouf, High frequency impedance analyi for enorle tarting of wound rotor ynchronou machine, in IFAC 27, Touloue, July 27. [8] M. Hinkkanen and J. Luomi, Modified integrator for voltage model flux etimation of induction motor, IEEE Tranaction on Indutrial Electronic, vol. 5, no. 4, pp , 23. [9] M. Corley and R. Lorenz, Rotor poition and velocity etimation for a alient-pole permanent magnet ynchronou machine at tandtill and high peed, Indutry Application, IEEE Tranaction on, vol. 34, no. 4, pp , 998. [] J. Holtz, The repreentation of ac machine dynamic by complex ignal flow graph, IEEE Tranaction on Indutrial Electronic, vol. 42, pp , [] N. Idri and A. Yatim, An improved tator flux etimation in teadytate operation for direct torque control of induction machine, IEEE Tranaction on Indutry Application, vol. 38, no., pp. 6, 22. [2] M. Comanecu, L. Xu, and S. Member, An improved flux oberver baed on pll frequency etimator for enorle vector control of induction motor, Indutrial Electronic, IEEE Tranaction on, vol. 53, no., pp. 5 56, 25. [3] I. Boldea, G. D. Andreecu, C. Roi, A. Pilati, and D. Caadei, Active flux baed motion-enorle vector control of dc-excited ynchronou machine, in Energy Converion Congre and Expoition, 29. ECCE 29. IEEE, pp , 29. [4] M. Koteich, G. Duc, A. Maloum, and G. Sandou, A unified model for low-cot high-performance ac drive: the equivalent flux concept, in The Third International Conference on Electrical, Electronic, Computer Engineering and their Application EECEA), Apr. 26. [5] M. 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7 Meaured and Etimated Mechanical Speed RPM) Meaured and Etimated Mechanical Speed RPM) Mechanical Speed etimation error RPM) 4 Mechanical Speed etimation error RPM) Electrical poition etimation error Degree) 5 Electrical poition etimation error Degree) Time ec) Time ec) Fig. 7: Flux-baed enorle experimental reult: no-load left) and full-load right) peed ramp from to 9 rpm. pu Torque N.m.) Meaured and Etimated Mechanical Speed RPM) Mechanical Speed etimation error RPM) Meaured and Etimated Electrical Poition Degree) Electrical poition etimation error Degree) Time ec) Fig. 8: HFI enorle experimental reult.