DSP-Based Brushless DC Motor Sensorless Drivers with Sine PWM

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1 DSPBsed Brushless DC Motor Sensorless Drivers with Sine PWM Tzuenih Chern ihsing iu ChinWen Tien ChunYu Chen Deprtent of Electricl Engineering Deprtent of Electricl Engineering Deprtent of Electricl Engineering Deprtent of Electricl Engineering Ntionl Sun YtSen University Ntionl Sun YtSen University Ntionl Sun YtSen University Ntionl Sun YtSen University ohsiung, Tiwn R.O.C ohsiung, Tiwn R.O.C ohsiung, Tiwn R.O.C ohsiung, Tiwn R.O.C Abstrct This pper presents brushless DC otor sensorless driver with sine pulse width odultion signl. For speed control, the current feedbck is included to the closed loop control strtegy to decrese the power consuption nd increse the otor perfornce. In ddition, the sine wve phsechnging signl is closed with set of specific electricl ngles in the zero crossing point to detect the bck electrootive force nd observe the output perfornce. A siple theticl odel of brushless DC otor is derived, nd the control strtegy is ipleented by digitl signl processing (DSP) pltfor. The vlidity of the ethod is verified by the experients. eywordsbrushless DC Motor; Sensorless; Digitl Signl Processing. I. INTRODUCTION Brushless DC (BDC) otors incresingly re being used in coputer, utootive, ir conditioner, industril nd household products becuse of its high power density, copctness, relibility, high efficiency, low intennce nd ese of control. Generlly, the rotor position infortion is required for proper couttion of currents [1]. There re ny ethods to generte the couttion signls for driving BDC otor [2]. Especilly, the Hll effect sensor is the ost populr sensor for phsechnging detection since it is uch ore econoic thn the other encoders or resolvers. However, there re liittions on the instlltion of Hll effect sensors in soe pplictions [35]. Firstly, the Hll effect sensors re very sensitive to het. They becoe ineffective if the working teperture is higher thn ºC. The other liittion of the Hll effect sensors is its size, the instlltion of the Hll effect sensors will substntilly increse the volue of the syste. In soe devices which internl spce is too nrrow to plce the Hll sensor. Soe other devices which internl pressure is higher nd contining refrigernt oil like ir conditioner copressor. In these situtions, the Hll effect sensors re not suitble for these reltive pplictions. Figure 1. Brushless DC Motor Equivlent Circuit. wheel current ethod nd so on. Fro ny references, the bck EMFbsed detection is the coon ethod to hve the rotor position infortion. However, in this ethod, the perfornce of BDC otor is ffected by the position phse error cused by the phse shift of the filter, the inccurcy of clcultion nd the rture rection. Therefore, this pper presents the sensorless BDC otor speed control strtegy with bck EMF detection nd current feedbck control to iprove the rotting torque nd reduced the output power consuption. The siple theticl odel of BDC otor is derived in section III. Section IV shows the closed loop speed control with current feedbck strtegy nd the experientl results re shown in section V. II. BRUSHESS DC MOTOR MATHEMATICA MODE Brushless DC otor uses the sensor coponents to insted of the brush nd couttor of the conventionl DC otor. Nevertheless, the syste dynic odel of BDC is the se s the conventionl one. Therefore, the BDC otor theticl odel cn be derived s the conventionl DC otor. The brushless DC otor driving circuit is siplified s Fig. 1 nd the sybols of equtions re listed in tble 1. Therefore, the sensorless rotor position control technology hs otivted reserch in the re of BDC otor drives. There re ny ethods for detecting the rotor position of sensorless BDC otors. Such s, the bck EMFbsed ethod [68], the flux linkge estition ethod [9], the free s Fro Fig. 1, the syste chrcteristic eqution is derived V R i e di b, (1) dt 1349

2 TABE I. THE SYMBOS AND DESCRIPTIONS OF EQUATIONS T V 1 I T 1 W 1 θ R T s B sj s E b b Figure 2. Brushless DC Motor Trnsfer Function Block Digr. Sine Wve of UPhse(V) where (1) is the rture circuit eqution. The bck EMF e b nd the otor torque T re in proportion to the rotor ngulr velocity ω nd the rture current i respectively. The equtions re given by eb b ω (2) T t i t. (3) () () T The lod torque eqution of dc otor s dω () T t J T B ω. (4) dt Assuing the otor initil stte is sttic, nd ll initil vlues re zero, the chrcteristic eqution of (1), (2), (3), nd (4) cn therefore be written s V R I Eb s I (5) Eb b W (6) T T I (7) T s J s W s T s B W s. (8) () () () () Substituting (5), (6), nd (7) into (8), the otor ngulr velocity W yields T V () ( R s ) T W s. (9) ( R s )( s J B) T b Fro (9), the brushless otor trnsfer function block digr is drwn s Fig. 2. In this syste, there is only slight viscous friction nd no lod in the output stge, the viscous friction coefficient B nd the lod torque T re neglect here. Therefore, the trnsfer function of rotor ngulr velocity W with supply voltge V cn be derived s W G() s V T s J ( R s ) T b 1. (10) 2 J R J 1 b s s T b T b Sine Wve of VPhse(V) Sine Wve of WPhse(V) III. Figure 3. The 3Phse Stndrd Sine Wve Driving Signl. COSED OOP SPEED CONTRO WITH CURRENT FEEDBAC STRATEGY Electricl Electricl Electricl Generlly, in threephse otor, the bck EMF is detected fro the phse which is floting. The other two phses re conducting with current. But if the driving signl is sine wve s shown in Fig. 3, there is no floting phse existing nd the bck EMF is difficult to detect. Therefore, in this pper, the bck EMF detection strtegy is to close sll durtion t zero crossing point () of the sine wve s shown in Fig. 4. If the control object is to stbilize the BDC otor nd high perfornce output in speed control, the speed infortion ust be feedbck nd copred with the speed cond. In this pper, the speed error signl is trnsfer to the reference current fter the PI controller. Three reference phse currents re de nd ech one copres with ech corresponding phse current feedbck signls. After ultiplying the gin, the sine wve driving signls re odulted into the pulse width odultion signl nd sent it to the inverter to turn the six power switches on nd off. The control block digr s shown in Fig. 5. In this control strtegy, the otor speed cn be control precisely nd iproving the stedy stte speed ripple fter cobined the speed control closed loop with current feedbck. Besides, strting ethod is needed before the brushless DC otor rottes. There re ny strting ethods proposed by other reserchers [10]. Here, the fixedphse strting strtegy is choosing. The first step is to send signl to the specific phse. After tht, the rotor would be fixed t prticulr position. Then, the control signl drives the sttors phse by phse nd ccelertes it. Until the rotor speed reches bout 200 rp, the 1350

Figure 4. The 3Phse Sine Wvefor Driving Signl with Closed Durtion t Zero Crossing Point. Coputtion sin( θ Γ ) Phse Chngi ng Si gnl Bck EMF Detect i on 3 Phse Di vi di ng Vol t ge IV.

3 Figure 4. The 3Phse Sine Wvefor Driving Signl with Closed Durtion t Zero Crossing Point. Coputtion sin( θ Γ ) Phse Chngi ng Si gnl Bck EMF Detect i on 3 Phse Di vi di ng Vol t ge IV. EXPERIMENTA RESUTS Developing the sensorless speed control strtegy hs been ipleented vi DSP controller TMS320F2407A [11]. The core progr is running by DSP chip to reduce developing tie nd debug siply. Fig. 6 shows the control strtegy progr flowchrt. The dt processing, cond trnsitting, theticl coputtion, output estition, nd interfce couniction re integrted in the DSP responsibility. In this wy, the controller hs higher flexibility with coplicted control lgorith. The test otor specifiction of the drught blower ws shown in tble 2. In the experientl setting, the input voltge is 156 DCV, nd the rotor speed is set bout 900 rp under drught blower condition. The PWM switching frequency is 15 khz. Testing sensorless BDC otor nd the drught blower re shown in Fig. 7 nd Fig. 8 respectively. Cond Error DSP control stge PI Iref 2π sin θγ 3 2π sin θ Γ 3 Iw Iv Iu PWM Controller Si x Swi t ches 3 Phse Inverter Cur r ent f eedbck Figure 5. Brushless DC Motor Control Syste Block Digr. Motor bck EMF is detected nd the speed control closed loop strtegy tkes off the open loop control. In the control stge, the control strtegy is ipleented by digitl signl processing (DSP) pltfor. DSP tool cn del with the huge coputtion circustnces like the speed estition, bck EMF detection, current feedbck, PWM control, nd power MOS switching. The function block in the syste digr is detiled s below: 1. Bck EMF Detection: Fro ech phse dividing circuit, the bck EMF is detected nd the rotor position infortion is obtined. 2. Rotor Coputtion: The rotor speed is estited by the bck EMF phsechnging signl. Then, the speed error signls re obtined fter copring the speed cond with the rel speed infortion. 3. Controller: It is used for ccelerting or decelerting the rotor speed by referring the speed error signls. 4. 3Phse Sine Wve Genertor: After converting the speed error signl into the reference current signls, the 3phsechnging signls re de nd differ with 120 degree of ech other. 5. PWM Controller: After ultiplying the gin, the current error signls input to the PWM genertor to generte the phsechnging signls. 6. Inverter: After the duty cycle is clculted, the inverter outputs the supply voltge of 3phses nd controls six power MOS switching sequences. Figure 6. The Sensorless Brushless DC Motor DSP Control Flowchrt. TABE II. PARAMETERS OF THE TEST MOTOR 3phse Sensorless Brushless DC Motor Type Yconnection, 8 poles, 12 slots Rted voltge 300 DCV Output power 120 Wtt Rted speed 1200 RPM Sttor resistnce 27.5 Ω Sttor inductnce 91.6 H 1351

Figure 7. Sensorless Brushless DC Motor. (b) The Phse Current with 900 rp Figure 9. The Phse Current Wvefors of Rotor in 500 nd 900 rp. Figure 8. Drught Blower with The Testing BDC Motor.

Ech tie the cond incresing 100 rp, the syste current, power consuption, phse voltge, nd phse current re recorded. Closing 10º electricl degree t phse current wvefors re shown in Fig.

Fro the result curve in highspeed prt, it deonstrtes the perfornce of sine wve driving signl with current feedbck is better thn the sixstep squre wvefor.

Tht is becuse when the current feedbck phse switches on nd off properly nd the current provides to the output lod torque in the right tie.

In ddition, the perfornce is higher when the closed durtion of electricl ngle is sller.

4 Figure 7. Sensorless Brushless DC Motor. (b) The Phse Current with 900 rp Figure 9. The Phse Current Wvefors of Rotor in 500 nd 900 rp. Figure 8. Drught Blower with The Testing BDC Motor. In the experient, the driving signl closed durtion t the zerocrossing point re setting 10º, 15º, nd 30º electricl degree respectively. The speed cond is setting fro 100 to 900 rp. Ech tie the cond incresing 100 rp, the syste current, power consuption, phse voltge, nd phse current re recorded. Closing 10º electricl degree t phse current wvefors re shown in Fig. 9 with 500 rp nd 900 rp. The experientl results tht copre with conventionl sixstep squre driving signl without current feedbck control re shown in Fig. 10. Fro the result curve in highspeed prt, it deonstrtes the perfornce of sine wve driving signl with current feedbck is better thn the sixstep squre wvefor. The syste power consuption of proposed ethod is less thn () The Phse Current with 500 rp Figure 10. The Output Power Consuption Coprison Results. the sixstep PWM. Tht is becuse when the current feedbck phse switches on nd off properly nd the current provides to the output lod torque in the right tie. Therefore, the output is including in the control strtegy, the driving signl turns 3 current is decresing nd the syste perfornce is iproving in the drught blower circustnce. In ddition, the perfornce is higher when the closed durtion of electricl ngle is sller. The bck EMF cn be detected esily with wilder closed durtion of electricl ngle, but tht lso cuses the driving signl integrity getting worse. Consequently, the closed width t should be decided properly which kes syste perfornce output better. V. CONCUSIONS This pper presents new control strtegy for sensorless brushless DC otor. The current feedbck is including in the closed loop controller. In ddition, by closing short durtion t zerocrossing point of the driving signl, the sine wve bck EMF cn be detected clerly nd the rotor position lso cn be obtined esily. The whole control ide is ipleented by DSP pltfor voids the noise signl interferences when the signls feedbck to the controller nd decreses the developing tie. In the loding condition, the perfornce is higher when the closed durtion t zerocrossing point is sller. The output torque is ore scrificed if the electricl ngle is closed too uch. In the experientl setting, the sensorless brushless DC 1352

5 otor without loding nd the drught blower were tested. By including the current feedbck with sine wve driving signls, the experientl results show tht the proposed closed loop speed control technique is better thn the conventionl sixstep squre wve driving signl control ethod without current feedbck. Fro the experientl results, sine wve driving signl with current feedbck in speed control technique produces high syste perfornce nd reduces the output power consuption effectively. ACNOWEDGMENT This work ws supported by Ntionl Science Council, through grnt nuber NSC962622E110013CC3. The uthors would like to thnk Tiwn DEI Building Autotion Technology Co., td. Specil thnks re dedicted to Chris in for his ssistnces with this work. REFERENCES [1] Wu Xiojing, Zhou Bo, Song Fei, Chen Fngshun, Wei Jidn, closed loop control ethod to correct position phse for sensorless Brushless DC otor, ICEMS, Pge: , Oct [2] Nisr, A.H. Moghbelli, H. Vhedi, A., A lowcost sensorless control for reducedprts, brushless DC otor drives, ISIE, Pge: , July [3] ChengHu Chen, MingYng Cheng, A New Sensorless Control Schee for Brushless DC Motors without Phse Shift Circuit, PEDS, Volue 2, Pge: , [4] J. P. Jhnson, M. Ehsni, nd Y. Guzelunler, Review of Sensorless Methods for Brushless DC, in Proc. of IEEE IAS Annu. Meeting Conf., Phoenix, USA, pp , [5] J. Sho, D. Noln, M. Teissier, nd D. Swnson, A Novel MicrocontrollerBsed Sensorless Brushless DC (BDC) Motor Drive for Autootive Fuel Pups, IEEE Trns. on Ind. Applict., Vol. 39, No. 6, pp , Nov./Dec [6] G. H. Jng, M. G. i, Optil Couttion of BDC Motor by Utilizing the Syetric Terinl Voltge,. IEEE TRANSACTIONS ON MAGNETICS, 2006, 42(10): [7] Wei Chen, Chngling Xi, Sensorless Control of Brushless DC Motor Bsed on Fuzzy ogic,.wcica 2006, Volue2: , 21 23June 2006,. [8] ChengHu Chen, MingYng Cheng, A New Sensorless Couttion Drive for Brushless DC Motors nd Alterntors. IEEE ISIE 2006, volue3: , July912, [9] FRENCH C, ACARNEY P, Control of pernent gnet otor drives using new position estition technique,. IEEE Trns on Ind,32(5): , Appl, [10] YenChun Chng, YingYu Tzou, New Sensorless Strting Method for Brushless DC Motors without Reversing Rottion, PESC 2007, Pge: , June [11] A. Hlvei Nisr, H. Moghbelli, A. Vhedi; High Perfornce Torque Control of Brushless DC Motor Drive bsed on TMS320F2407 DSP Controller, Interntionl Review of Electricl Engineering (IREE) Journl, Vol. 2, No. 3, pp , MyJune

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