A Novel Back EMF Zero Crossing Detection of Brushless DC Motor Based on PWM

Transcription

1 A ovel Bck EMF Zero Crossing Detection of Brushless DC Motor Bsed on PWM Zhu Bo-peng Wei Hi-feng School of Electricl nd Informtion, Jingsu niversity of Science nd Technology, Zhenjing 1003 Chin) Abstrct: In order to solve the problem of the phse dely of the filter cpcitor in the trditionl bck EMF zero crossing detection technology, In this pper, through the PWM pulse regultion of the new bck-emf zero-crossing detection method ccurte nd relible commuttion. The Brushless DC motor rotor positioning ccurcy nd commuttion smooth hs been chieved. The experimentl results verify the vlidity of the new bck-emf zero-crossing detection method. Key words: Brushless DC motor; ew counter electromotive force zero - crossing detection; Phse dely; PWM pulse regultion; CLC number: TP17 Literture identifiction code: A 1. Introduction Brushless DC motor using electronic switch device to replce the brush motor mechnicl commuttion, to void the crbon brush mechnicl commuttion to bring the sprks, noise, with good speed chrcteristics, dynmic performnce, nd smll size, simple structure, High power density [1].Especilly brushless DC motor using Hll element position sensor, becuse of its no chnge in sprks, relible opertion, esy mintennce, simple structure, no loss nd mny other dvntges, hs been more nd more extensive Appliction []. However, brushless DC motors require n dditionl position sensor to provide the necessry commuttion signl to the inverter bridge, nd its presence brings lot of flws nd inconveniences to the ppliction of the brushless DC motor: 1) The position sensor Increse the size nd cost of the motor; ) The position sensor will reduce the relibility of motor opertion, even now widely used Hll sensor lso hs certin degree of mgnetic non-sensitive re; 3) Sensor instlltion ccurcy will ffect the motor running Performnce, incresing the difficulty of the production process. In recent yers, the control of brushless DC motor without position sensor hs been more populr reserch topic t home nd brod. In this pper, phse control method bsed on rel-time PWM pulse control to control the C time constnt in the filter circuit t the terminl voltge is proposed for the phse dely of the filter cpcitor in the trditionl bck-emf zero-crossing detection technique. The experimentl results show tht the zero - crossing detection of the brushless DC motor bsed on PWM regultion cn effectively solve the phse dely problem of the filter cpcitor. 7

2 . Bck EMF Zero-Crossing Detection Technology Three-phse six-str strter brushless motor, the bck-emf zero-crossing detection method of the bsic principle: ech phse winding single-phse positive nd negtive were 10 conduction, nd t ny time t ny time three phses only two simultneous, By mesuring the potentil of the three-phse winding terminl nd the neutrl point, when the other phse terminl potentil nd the neutrl point potentil is equl, tht is, the non-conduction of the opposite electromotive force zero crossing, nd then 30 electricl ngle dely for electronic switching Phse [8]. Therefore, s long s the detection of ech winding bck electromotive force zero crossing, you cn determine the motor rotor position nd the next commuttion time. As the bck EMF is difficult to directly mesure, usully through the detection of terminl voltge to obtin nti-bcklsh zero. Therefore, this method is lso known s the terminl voltge detection method [9-10]. With trpezoidl bck electromotive force wveform brushless DC motor min circuit schemtic, bck EMF wveform shown in Figure -1,- + s - 3 V1 V V 3 5 A VD 1 B VD VD5 C V V 4 V VD4 VD VD i i b i c L L L e e b e c Figure -1 Equivlent model of brushless DC motor nd three-phse full-bridge min circuit In the figure, s is the DC bus voltge nd V -V 1 re the power switching devices. Currently, IGBT or MOSFET is used. VD 1 - VD re the freewheeling diode nd for the motor neutrl point voltge. Tht is, the motor neutrl point corresponds to the DC bus negtive voltge, the three-phse current direction of the motor nd the polrity of the three-phse bck electromotive force re shown in Fig -. e e b e c Figure - Three-phse bck electromotive force wveform, b, c re the negtive terminl voltges of the input terminls of ech phse with respect to the power supply s respectively. Assuming the system uses two-two wy of conduction, three-phse nd six-stte 10 conduction mode, the djustment of the bridge on the tube with PWM modultion, the other tube hving been conduction. The three-phse voltge blnce eqution of the motor is: 8

3 di = i + L + e + (-1) dt dib b = ib + L + eb + (-) dt dic c = ic + L + ec + (-3) dt In this conduction mode, only two tubes re turned on for every 0 electricl ngle. In the rnge of 0 ~ 10 in Fig. 1-, the A nd B phses re conducting nd A positive B negtive, this is, the A phse current flows into the neutrl point of the motor, nd the B phse current flows out of the motor neutrl point. At this time A, B two-phse current equl size, the opposite direction, C phse current is zero, so the formul (-3) cn be simplified s: c = ec + (-4) e b + c = b (-9) Through the bck-emf zero-crossing detection method, in the compenstion of the bck-emf to the motor commuttion time 30 phse shift. According to the clculted motor speed, rel-time djustment PWM pulse control terminl voltge filter circuit C time constnt, in order to chieve ccurte nd relible 30 phse shift 3. ew Zero Crossing Detection Method nd Its Implementtion 3.1Phse Compenstion of The Filter Cpcitor or ec = c (-5) As i = i b, e eb =, the formul (-1) nd (-)re dded to obtin neutrl point voltge + b = (-) Substituting formul (-) into formul (-5) yields: When the bck-emf of the power-off phse winding fter zero, nd then fter 30 electricl ngle, nlysis of the bck EMF wveform shows tht the plce is the phse of the commuttion point. However, in the prcticl ppliction of the motor bck EMF detection circuit, s shown in Figure 3-1, the filter cpcitor on the one hnd to filter the role of filtering, on the other hnd the detection voltge hs certin phse shift [11-1].According to Figure 3-1, it is esy to clculte the phse shift of the detection circuit. Tke the A phse s n e c + b = c (-7) exmple, where A is the A-phse voltge, Similrly, the A-phse nd the B-phse bck-emf zero-crossing detection eqution re: e b + c = (-8) o is the filtered output voltge, nd f is the bck-electromotive force frequency. Clculted by bse wve: 9

4 o = + + jπ f C Phse ngle dely is (3-1) resistnce 3 does not work. Chnging the PWM pulse width cn be equivlent to chnge π C 1 1f = rctn + 1 (3-) It cn be seen from the bove formul, the phse ngle dely of the filter cpcitor nd the function of the motor speed need to be detected or clculted in rel time. In this pper, solution is dopted so tht the controller cn be compensted better when the motor speed is high or the speed is very low. The bsic principles re s follows: the resistnce, nd then chnge the C time constnt, tht is, chnge the phse shift of the filter circuit. As the PWM pulse width djustment is simple nd convenient nd cn be continuous, it cn chieve 0 ~ 90 phse shift. In this scheme, constnt 30 phse shift is required in the full speed rnge of the low speed to high speed motor, nd the pulse width of the PWM cn be djusted in rel time ccording to the motor speed clculted by the CP detection. When the resistnce > 1 (in the ctul ppliction circuit, tke >> 1, the purpose is to increse the PWM regultion effect), djust the PWM pulse width, so tht it is proportionl to the motor speed, so the motor speed rnge to constnt 30 phse shift. At the sme time, When the motor in the quiescent stte, n increse of three resistors 5,, 7 nd 15V Figure 3-1 Phse shift compenstion circuit To A phse, for exmple, s shown in Figure 3-1, Terminl voltge by the resistnce 1, prtil pressure, nd then by the cpcitor C1 filter, PWM pulse control trnsistor Q 1 off. When the PWM pulse is high, the trnsistor sturtion open, the resistnce 3 equivlent ground, nd the resistnce in prllel; when the PWM pulse is low, the trnsistor cut-off, the power supply, so tht the bck electromotive force is zero nd the position signl detection circuit comprtor hs stble output. 5,, 7 selection principle is: 5 1 >>. 5 7 >>, 7 >>, 3. ew Bck EMF Zero-Crossing Detection of The Hrdwre Circuit At present, the counter-electromotive force zero-crossing detection uses hrdwre circuit to chieve [13-14]. The bsic structure of the 10

5 hrdwre detection circuit is shown in Figure 3-. In this circuit, the comprtor forwrd input nd three-phse detection voltge is connected nd the reverse input nd three-phse detection e b voltge of the neutrl point voltge 1 e c connected. H H b H c Figure 3-3 Counter electromotive force nd the corresponding comprtor output wveform Figure 3- Counter-electromotive force zero-crossing detection hrdwre circuit 4. Experimentl esults nd Anlysis signl The following shows the comprtor output H, H b, Hc nd the motor bck electromotive force digrm (which hs been 30 phse shift processing). As shown in Figure 3-3. The signl output of the bck-emf zero-crossing detection circuit is shown in Figure 4-1 when the motor is t rest. Figure, 3, 4 chnnel wveforms corresponding to A, B, C phse, -chnnel wveform for the high nd low levels of 50ms ech squre wve, 4-chnnel wveform mplitude constnt 0,3 chnnel wveform mplitude constnt 5V. This is consistent with the design of this progrm. In the cse where the motor counter electromotive force is zero, in order to stbilize the bck electromotive force detection circuit, in the C phse detection circuit superimposed on smll signl, the smll signl mkes the detection circuit output stble, which is esy to determine the motor to run the motor sttus. In order to 11

6 mke the bove judgment more relible, in the A phse to increse high nd low levels of 50ms ech squre wve signl, The progrm on the bck EMF detection circuit output signl within 50ms to determine whether the motor running to ensure tht the motor cn be relible strt. Figure 4- Phse compenstion wveform Figure 4-1 output wveform of the counter electromotive force detection circuit when the motor is t rest The phse compenstion wveform for the filter cpcitor is shown in Figure 4-. -chnnel wveform is the detection circuit output wveform nd 3-chnnel for the corresponding phse of the terminl voltge wveform. It cn be seen tht the rising nd flling edges of the signl output wveform of the detection circuit correspond to the commuttion point of the terminl voltge wveform, nd the 30 phse shift of the bcklsh point to the commuttion point is ccurtely relized. This fully proves the vlidity of the method used to control the phse shift of the C constnts of the PWM control filter circuit used in this pper. The shrp pulse on the slope of the midpoint voltge wveform is due to the sudden chnge in voltge cused by the freewheeling diode. By controlling the PWM for phse compenstion, over-compenstion cn lso be chieved, s shown in Figure 4-3. Figure -chnnel wveform for the detection circuit output wveform nd 3-chnnel for the corresponding phse of the terminl voltge wveform. In the process of over-compenstion, the motor noise is very lrge, serious het nd lmost no norml opertion, we cn see the importnce of phse compenstion. Figure 4-3phse over compenstion wveform 5. Conclusion In this pper, new bck EMF zero - crossing detection circuit is designed for the phse dely of the filter cpcitor in the trditionl bck EMF crossing zero detection 1

7 locomotive electric drive, 004 (1): technology. When compensting the bcklsh of [14]Wikr S P.A,A Low Cost Low Loss Brushless the bck electromotive force, the C time Permnent Mgnet Motor Drive : [The office of grdute studies of Texs A&M niversity],s,texs constnt of the filter circuit t the control A&M niversity,001 terminl voltge is djusted by rel-time djustment of the PWM pulse to chieve n ccurte nd relible 30 phse shift. eferences [1] Xu Dzhong, He Yikng. Motor Control [M]. edition. Hngzhou: Zhejing niversity Press, 00. [] Zhng Chen. Principle nd ppliction of brushless DC motor [M]. Beijing: Mechnicl Industry Press, October 001. [3] en Junjun, Zhng Zhongcho.o sensorless control method for new DC motor [J]. Power Electronics Technology. 004,4 (3): 1 ~ 15. [4]Zhng Ho, Design of Brushless DC Motor Controller Bsed on DSP [J].008. [5] Zou Jibin, Xu Yongxing, Yu Chenglong. ew otor Position Detection Method for Sine Wve Brushless DC Motor [J]. Proceeding of the CSEE, 00, (1): [] CAO Sho-yong, CHEG Xio-hu.Study on otor Position Detection Method of Brushless DC Motor without Position Sensor [J]. Explosion-proof Motor, 007 (l): [7] Liu Yi, He Yikng, Qin Feng et l.study on vector control of permnent mgnet synchronous motor without position sensor bsed on rotor slient pole trcking [J] Proceedings of the CSEE, 005,5 (17): [8] Lin Xio, Pn Shungxi, Hu Xiokng, etc. A non-position sensor BLDC zero-strt pure hrdwre implementtion method [J]. Journl of Zhejing niversity, 008,4 (9), [9] Bi Ho, Cui Jinhu, Xu Xiohui et l. eserch nd Prospect of Permnent Mgnet Brushless DC Motor Controller, Mechnicl nd Electricl Engineering, 004,1 (4): [10]Jufer M,Osseni,Bck EMF Indirect Detection for Self-Commuttion of Synchronous Motors,Proceedings of the 1987 Europen Conference on Power Electronics nd Applictions,EPE Assocition,Grenoble,Frnce,1987: [11] Shen Jinxin, Luo Ji, Chen Yong school. Anlysis nd compenstion of position error of sensorless brushless DC motor [J]. Micro Motor, 1999 (5): 3-7. [1] Lin Mingyo, Li Qing, Yng Peiqi. Sensorless brushless DC motor rotor position detection error nlysis nd its compenstion [J]. Micro Motor, 003 (): 8-9. [13] Ho Su-ping, Luo Longfu. DSP-bsed brushless DC motor without position sensor control technology, 13