The accuracy of rotor position estimation in the conventional signal injection based sensorless control of permanent magnet brushless AC drives depends on the load current. This paper proposes an improved method, which significantly reduces the estimation error by accounting for the cross-coupling effect between the d-and q-axes. The conventional and proposed methods are described and their performance is compared by both simulation and experiment

Bingham, Chris

Howe, D.

Li, Y.

Zhu, Z .Q.

English

Crossref

Improved Signal Injection Based Sensorless Technique for PM Brushless AC Drives

University of Lincoln Institutional Repository

Proceedings of the 2007 IEEE International Conference on TuesA03Networking, Sensing and Control, London, UK, 15-17 April 2007Improved Signal Injection Based Sensorless Technique for PMBrushless AC DrivesY. Li, Z. Q. Zhu, C. M. Bingham, and D. HoweAbstract- The accuracy of rotor position estimation in the (several kHz), and its amplitude cannot be changed as it isconventional signal injection based sensorless control of determined by the DC-link voltage and the PWM duty cycle,permanent magnet brushless AC drives depends on the load the amplitude of high frequency current will be too small forcurrent. This paper proposes an improved method, which the motor having a large stator inductance. Thus, the PWMsignificantly reduces the estimation error by accounting for the signal injection method may fail ifthe AD converter has a lowcross-coupling effect between the d- and q-axes. The accuracy and the high frequency current signal of the driveconventional and proposed methods are described and their has a low signal-to-noise ratio. Specially designed high speedperformance is compared by both simulation and experiment. AD converter, trigger circuit and data buffers are required inI. INTRODUCTION order to sample the critical points on the high frequencyor permanent magnet (PM) brushless AC (BLAC) drives, current waveform which, as mentioned above, is usuallyaccurate rotor position is required in order to provide several kHz, identical to the PWM frequency. This will3-phase current references for torque control. It is usually significantly increase the cost and complexity of the driveobtained directly from an encoder or a resolver, which is system. In addition, since the method is based on the detectionobtamehanicallyfixed anthenodrrshaf. Hwesver, the rotor of winding inductances and its accuracy is influenced by themechanically fixed on the motor aft However, the rotor magnetic saturation.position sensor not only increases the hardware and The INFORM pulse [6] [7] is used to avoid the problemsmaintenance cost, as well as the system complexity, but also in PWM injection method. In the INFORM pulse injectionreduces the reliability ofthe system. It is desirable to estimate method, the amplitude of injected signal is large, but it is anthe rotor position indirectly from the voltage and current of intermittent signal in order to reduce the average injectedthe BLAC motor. power. The pulse width, amplitude, duty cycle of theMany back-EMF-based rotor position estimation methods INFORM injected signal can be set to a reasonable value, andhave been developed for PM BLAC motors [1] [2] [3]. In all it can avoid using high accuracy and specially designedof these methods, the rotor position is estimated from the current sampling hardware. As the injected signal isvoltage equation, and their differences are the rotor position intermittent, the estimation values of rotor position areand speed estimation methods, such as flux-linkage observer, discrete and cannot be corrected continuously. This mayfuzzy logic, EKF, etc. The back-EMF-based rotor position deteriorate the dynamic performance of the INFORM pulseestimation method can precisely predict the actual rotor injection sensorless method.position if accurate stator inductances and resistances are The most popular high frequency signal is usingknown. However, since the back-EMF is proportional to the sinusoidal carrier voltage signal. This method was originallyrotor speed, it is very small at low speed and does not exist at developed for induction motors and recently extended to PMzero speed. Therefore, the back-EMF-based sensorless BLAC motor with saliency [8] [9]. However, themethods cannot start the motor and may fail at low speeds. identification ofthe initial rotor polarity was not reported in [8]Signal injection based sensorless method is developed to [9] and was subsequently addressed in [10] [11], in which sineestimate the rotor position at low speed or zero speed for and cosine terms of the 2nd harmonic in d-axis current weremachines which exhibit rotor magnetic saliency. The injected compared to identify the rotor polarity. In the above papers,signal is usually of high frequency, and the rotor position is the BLAC motors under consideration have salient rotor poles.estimated from the high frequency voltage equation. Three It was extended in [12] to a non-salient BLAC motor withtypes of injected signals, i.e., sinusoidal carrier, PWM, and surface-mounted PM rotor by utilizing the saliency which wasINFORM pulse, are reported in literature [4]-[12]. induced by magnetic saturation. The high frequency signal inTo avoid introducing extra injected harmonic current, the this type of sensorless method is simple to analyze and itsPWM signals which are inherent in the inverter output are current amplitude is controllable. However, as an extraconsidered to be the injected signal in [4] [5]. As the harmonic current signal is introduced into the motor stator, itfundamental frequency of PWM voltage signal is very high will cause undesirable acoustic noise, torque ripple and loss.This paper firstly describes the conventional signalinjection based sensorless control method in section II. Then,Y. Li, Z. Q. Zhu, C. M. Bingham, and D. Howe are with Department of an improved method, which accounts for the influence ofElectronic and Electrical Engineering, University of Sheffield, MappinQ+--+l 'TTNTIV t'-" a I %,; 1 r",- I,-f' ,- I1'- cross-coup ling effect between the d- and cq-axes, iS developedStreet, SheffieldSi 3JD, UK. (email: yi.li@shef.ac.uk, in section III. Simulated and measured results are compared in,.h@hfa.k cXiga@hfa.k d.oe@hf section IV to illustrate the advantages ofthe proposed method.ac.uk).1-4244-1076-2/07/$25.00 ©2007 IEEE 734II. CONVENTIONAL HIGH FREQUENCY SIGNAL INJECTION VMETHOD [12] ie = Sig 2 [L +L cos(2A0)]For a 3-phase BLAC motor, when the cross-coupling gP avg /(7)between d- and q-axes is neglected, the d- and q-axis voltage e= - sig if sin(2A0)equations for the high frequency components are given by L p(Lvg - L4f )vch1 cLh 0 i If the estimation error of rotor positionAO is sufficiently=.p/. (1) small, it can be simplified as:Vqh _ L Lqh LIdqwhere Vdh, Vqh, idh, iqh are the high frequency components ofd- AO avg-Fqf )pij = k ie (8)and q-axis voltages and currents, and Ldh and Lqh are the d- - 2vsigLdifand q-axis incremental inductances, respectively. p=d/dt. 2 2Since the actual rotor position 0r is unavailable, the where k AO -_ _Vg- _dif)Pestimated rotor position Oe iS obtained from the observer. The HF - 2v Lbdq-axis voltages and currents in (1) are required to be Sig d/factual t As the error in the estimated rotor position is proportionaltransformed from the actual rotor position reference frame to to the q-axis high frequency current in estimated rotorthe estimated rotor position reference frame, i.e. reference frame, iqhe it can be controlled to zero by controllingevr i e1ir iqh=O [12].V =h T(O)Vh /h= T()h (2)Veh v r ie ir 11I. IMPROVED HIGH FREQUENCY SIGNAL INJECTIONqh~~qh- 'qh- qh- METHODwhere AOO=e-Or iS the difference between the estimated rotorpoiio- n th acua roo poiton an T(AO) is th For a 3-phase BLAC motor, when the cross-couplingcosornate rotating matrix andnisTgivensby: between d- and q-axes is considered, the d- and q-axisvoltage equations for the high frequency components arecos(AO) sin(AO) given by:\ S) L- sin(AO) cos(AO) (3 g FVdh L1FLdh Ldcqh 1 Fcdh] (9)Therefore, the high frequency voltage equation in the Vqh Lqdh Lqh iLdqjestimated rotor reference frame is obtained by multiplying therotating matrix T(AO) on both sides of (1). where Ldqh and Lqdh are the incremental mutual-inductancesbetween d- and q-axis.Vdh (AO) dh By way of example, Fig. 1 shows typical finite elementvqe Lv predicted variation of incremental self- andrldh o 1 rt 1 mutual-inductances with the load current, iq, due to magnetic= T(A)dLh 0 i'dh saturation. For the interior permanent magnet (IPM) BLACL Lqh LPqh j motor under consideration, Table I, Ldh Lqh and Ldqh are 25mH,Lch e 32mH and -7mH, respectively, when id-OA and iq=4A.= T(AO)I dh T-1(AO)pcdh/| Clearly, since the magnitude of Ldqh is comparable with thatTLo Lqh j ihj of Ldh and Lqh, its influence cannot be neglected in the high~Lavg~L/fcos(A0) Lc/ sin(2A) iFe 1frequency voltage equations.=Lag-Ldif cos(2A+)Ldif sin(2A) idh (4) Equation (9) can be transformed to its estimated rotorLLdif sin(2A0) Lavg +Ldif cos(2A0) L'qh j reference frame by multiplying T(AO) on both sides.where Lag and Ldf are defined as: FveD1 Lavg-LcOs(2AO+Om) Ldcfsin(2AO+Om) l eF5h{Lavg = (Lqh + Ldh)/2 LVhj L df/Jsin(2A0+Om) Lavg+Ldc/fcos(2AO+O7) jiqhcL =(L -Ldh)/2 (5) (10)dif qh dWhen the high frequency sinusoidal voltage, vs,g, is where m arctan(Ldqh/dc/) (11)applied to the estimated d-axis, i.e., Vdh=Vsig, Vqqh O, (4) 1L = L2+L2becomes:F 1 FL lbcos(2AO~ lb sin(2AO~ 1Since the high frequency sinusoidal voltage is applied toSVig_ avg c/sdif /dif d) c/h (6) the estimated d-axis, (10) becomes:0 L sin(2A0) Lb +L cos(2A0) iqeL I L c/~~if avg c/f iL hiThe dq-axis high frequency currents in estimated rotor ILav ^ C A Inp 1reference frame are obtained by solving (6): L °J L Lfsin(2AO+Om) La,g+Lc/in 9OS(2AO+O_)jA i](12)735The resulting d- and q-axis high frequency currents in the ie =- (Ldh / Lqh )i3h (16)estimated reference frame are obtained by solving (12): q qje Vsig Clearly from (16), the accuracy of rotor positiondh 2 [ avg+Ldifcos(2A+Om)] (1 3a) estimation depends on the ratio of LdqhlLqh in the improvedP(Lavg Lf signal injection based sensorless control. Ldqh/Lqh varies withv d- and q-axis currents due to the variation of Ldqh and Lqh. Theqhe 2 1dif sin(2A0+Om) (13b) incremental dq-axis self- and mutual-inductances may beP(L-,vgLdif ) predicted by the finite element method or measured byapplying various id and iq.Thus, if the high frequency component in the q-axis In the proposed improved signal injection basedcurrent is controlled to be zero, i.e. iqhe 0, as was in the sensorless control method, iqhe=_(Ldqh/Lqh)idhe control strategyconventional signal injection based sensorless scheme [12], is used to make the error in the estimated rotor position to bean error exists in the estimated rotor position as a result ofthe zero. When the cross-coupling effect is sufficiently smallincremental mutual inductance, Ldqh, which exists between d- compared with Lqh, i.e. Ldqh O, the control strategy becomesand q-axes. The error iS given by: iqh e=0- which is identical to the conventional signal injection0. I2Ldqh based sensorless method in section II.AO=_m =- arctan (14) 602 2 Ldh Lqh )o 4060 a ; |6 0 ~ ~~~ ~ ~ ~ ~ ~ ~~~~.Eo. < o=>2() 0 qr~~~~~~~~~~~~~~-20-20c |(L) i.UJL _§-_ 20 -4 -34 -2 -1 0 1 2 3 4- ~~~~~~~~~~~~~~~~~~~~~~q-axiscurrent (A)-20~~~~~~~~~~~~-20~~~~~~~~~~~~~~~~Fig.2. Estimation error of conventional signal injection based sensorless-40 -3 -2--1-0-1 2-3---controlq-axis current (A)Fig 1 Finite element predicted incremental d- and q-axis self-and IV. COMPARISON OF RESULTS OBTAINED BY PROPOSEDmutual-inductances at various q-axis current (i~0A). AND CONVENTIONAL METHODSFig.2 shows the error in estimated rotor position of The experimental system setup is shown in Fig.3, while theconventional signal injection based sensorless control of the signal injection based sensorless control system is shown inprototype 1PM BLAC motor under 1dhe=0 control, which is Fig. 4. The parameters of the interior permanent magnetpredicted by using the incremental self- and brushless AC motor, whose incremental inductancemutual-inductances in Fig. 1 and (14). characteristics were shown in Figs. 1, are given in Table I.Clearly, the error in the estimated rotor position will only The control strategy is implemented on a TMS320C3 1 DSP,be zero when Ldqh=O. The stronger the cross-coupling effect together with a PIC18F443 1 MCU, which serves as thebetween the d- and q-axes, the larger will be the error in the PWM generator and the encoder interface. The frequenciesestimated rotor position. Thus, iqhe=0 sensorless estimation ofthe AD sampling, the speed control loop, and the PWM arestrategy in [12] is not suitable for the 1PM BLAC motor with all set to 5kHz, and the injected signal is 35V, 330H4z. Thelarge Ldqh at heavy load condition. It iS necessary to consider acua roo .oiin r sotie rm a12the cross-coupling effect to reduce the error in estimated us-e-eouinecdr,wihi sda eeecrotor position. In this case , n order to control the rotor fothesiadrtrpstonO.position estimation error AOS to be zero, the high frequencyrcomponent in the q-axis current should not be controlled tobe zero but should be controlled according to ( E3) by letting TAL I S O B MOTOAO0=0, viz.: Number ofpole-pairs 3Rated speed 1000rpmV.~~~~~~~~~~~~~~~~~~~~~~c'qh sig-L2) Ld,sinO (d1 5) Rated torque 4.0NmP(Lavg dfifi Rated phase voltage (peak) 158VOr more conveniently, it can be controlled according to Rated phaseqcurrenti(peak) 4.0A(16) which is obtained from (13a) and (13b) whenpoi0: Phase resistanceRx 6.0Q736As in Fig. 4, there are 3 PID controllers in the experiment C Csystem: one is used to control the motor rotational speed, i.e.speed loop, and the other two controllers are used to control I o m;rthe d- and q-axis currents, i.e. current loops. The PID-6b mkcontroller of the speed loop is set as: Kp=0.2A/Hz, cK1=0.5A/(Hz-S), and KD=OA/(Hz-S-). The parameters of d-and q-axis current loop controllers are: Kp=OV/A,KI=5000V/(A-S), and KD=OA/(A-S-). ROW. M11A IX niFig. 3 Experimental test setup.r - - - - -- - -- -- ---- - -- - -- - -- - -- -- - -- - - -- - -- - - -- - -- Vdc1 5 I _ ,^j,i~~~q r ,,:,, qI_I! v IaI - I I d1D-IDtIr1.imator4 PWM isIIFig. 4. SensorIess BLAC mo todi Gevsm I.reFigs. 5 and 6 compare theestimatedandactual rotor|effectivenessofthep oABCe m|awaretpositionwhe the estimatd roo.osto is used fo~~~~~~~~~~~~~~~~~IdIbe see in Fis 5(a an 6() whe th covninl sga neto sdvlpdt eueteerrInI:<511 <'1'"'' 11 1~~~~~~~~~~~~~~d,i I | ~~~~~~~~~~~~~~ABCADI|CI. IIISimilar improvement canbe seen from sim| Hateanda~~~~~~~~ ~ ~ ~~ ~ ~ ~~~~~~~~~~~~~-----------i- -l---measured results, whichclRotor rld otn e thIPosition7-3EstimatorE E.IElstfiud I 3IDSP ControllerlFig. 4. Sensorless BLAC motor drive system.Figs. 5 and 6 compare the estimated and actual rotor effectiveness ofthe proposed method.position when the estimated rotor position is used forV OCUINposition feedback and the rotor speed command is changed V OCUINfrom -lOHz to +lOHz, i.e., -200rpm to +200rpm. AS will In this paper, an improved sensorless method based onbe seen in Figs. 5(a) and 6(a), when the conventional signal injection is developed to reduce the error insignal injection based sensorless scheme is employed, the estimated rotor position due to the neglect of cross-couplingestimated rotor position error increases significantly with effect in the conventional method. Significant improvementthe load current, and is -25° when iq=4A. By applying the in the estimation accuracy of rotor position has beenproposed method, this reduces to -5°,Figs. 5(b) and 6(b). achieved, as confirmed by both simulation and experiment.Similar improvement can be seen from simulated andmeasured results, which clearly demonstrates thesl1 d 1(t )Uii 4)Jff|yR0a~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .B ...AC" Elt 411j i/._.B~~~~~~~~~~~~~~~~-2(A)=._......_;E.T_ _ _._._.4)1E',l-i*''1*N.Rbiot~~~~~~~~~~~~~~~~rL..2..4gil~~(a Covntoa metho10(liz)e< f1hF6it 6E1§t -J4e>;1 1zOid~~~~~4ft f6t ., .........................4m-!....E'A) ~ A(a) Conventional method200~~~ 1 1b~tiu; IL d)I1~' I \~fV j~ l/V I11i I~II(616bDog IEmII8tli mate(ol&~~VXvwD mD 2 3(b) Proposed methodFig. 5. Simulated step speed response of signal injection based sensorless operation (speed command: 101Hz, and idO).permanent-magnet synchronous motors," IEEE Trans. IndustrialVI. REFERENCES Electronics, vol.50, no.2, pp. 288-295, 2003.[1] K. R. Shouse, D. G. Taylor, "Sensorless velocity control of [4] S. Ogasawara, and H. Akagi, "Implementation and position controlpenmanent-mag,net synchronous motors," IEEE Trans. Control System performance of a position-sensorless IPM motor drive system based onTechnology, vo 67neo. 3, pp. 3t13-324 1998. magnetic saliency," IEEE Trans. Industry Applications, vol.34, no. 4,[2] S. Morimoto, K. Kawamoto, M. Sanada, and Y. Takeda, "Sensorless pp.806-812,1998.control strategy for salient-pole PMSM based on extended EMF in [5] C. Wang, and L. Xu, "A novel approach for sensorless control of PMrotating reference frame," IEEE Trans. Industry Application, vol.38 machines down to zero speed without signal injection or special PWMno.4, pp. 1054-1061,2002. technique," IEEE Trans. Power Electronics, vol. 19, no. 6, pp.no 4. DD. 1054-106L 2002.~~161-107 004[3] Z. Chen, M. Tomita, S. Koki, and S. Okuma, "An extended 10-67 04electromotive force model for sensorless control of interior738[6] M. Schrodl, and M.Lambeck, "Statistic properties of the INFORM operation," IEEE Trans. Power Electronics, vol. 14,no. 1, pp.202-208,method for highly dynamic sensorless control of PM motor down to 1999.standstill," Proc. IECON.2003, vol. 2, pp. 1479-1486, 2003 [10] J.I. Ha, K. Ide, T. Sawa, and S.K. Sul, "Sensorless rotor position[7] E. Robeischl, and M. Schroedl, "Optimized INFORM measurement estimation of an interior permanent-magnet motor from initial states",sequence for sensorless PM synchronous motor drives with respect to IEEE Trans. Industry Applications, vol. 39, no. 3, pp.761-767, 2003.minimum current distortion," IEEE Trans. Industry Applications, vol. [11] H. Kim, K.K. Huh, and R.D.Lorenz, "A novel method for initial rotor40, no. 2, pp. 591-598, 2004. position estimation for IPM synchronous machine drives," IEEE Trans.[8] M. J. Corley, and R. D. Lorenz, "Rotor position and velocity estimation Industry Applications, vol. 40, no. 5, pp. 1369-1378, 2004.for a salient-pole permanent magnet synchronous machine at standstill [12] J.H. Jang, S.K. Sul, J.I. Ha, K. Ide, and M. Sawamura, "Sensorless driveand high speed," IEEE Trans. Industry Application, vol.34, no. 4, pp. of surface-mounted permanent-magnet motor by high-frequency signal784-789, 1998. injection based on magnetic saliency," IEEE Trans. Industry[9] T. Aihara, A. Toba, T. Yanase, A. Mashimo, and K. Endo, "Sensorless Applications, vol. 39, no. 4, pp. 1031-1039, 2003.torque control of salient-pole synchronous motor at zero-speed_-20~~~~~~~~~~~~~2(A) ~~~~~~~~~~~~~~50'I 11 H .jI..~~~~~~~~~~~~~~~~~~~~~~~~~~r......RI f' EZ1. eII~i(i C t methodEstV, iu t XII~~~~~ soEstiiwit['v ' II,W DKEaxa50ii J 1.. ..4 1Ji n(b) Proposed methodFig. 6. Measured step speed response of signal inj'ection based sensorless operation (speed command: ± 10H-z, and id0O|{739

Improved signal injection based sensorless technique for PM brushless AC drives

Abstract

Similar works

Full text

Available Versions

Crossref

University of Lincoln Institutional Repository