IJCTA, 9(33), 2016, pp. 01-10 Interntionl Science Press Closed Loop Control of Soft Switched Forwrd Converter Using Intelligent Controller 1 A Cost Effective Speed Control Method for BLDC Motor Drive M. Arun Noyl Doss* V. Klynsundrm* V. Gnpthy** nd K. Krthik*** Abstrct : This pper presents cost effective speed control method for brushless dc (BLDC) motor drive using PI controller. Pulse width modultion (PWM) technique is used which is the most widely used speed control technique. The switches in voltge source inverter (VSI) re electroniclly commutted using PI controller feedbck signl. The switches re operted t low frequency to minimize the switching losses. Simultion of the proposed topology is performed using Mtlb nd the obtined results vlidte the efficiency of the system. Keywords : Brushless DC(BLDC) motor, Pulse width modultion (PWM) technique, Voltge source inverter (VSI), PI controller, electronic commuttion, hll-effect, Mtlb. 1. NOMENCLATURE 2. INTRODUCTION BLDC Brushless DC motor PWM Pulse width modultion VSI Voltge source inverter G(s) System trnsfer function k p Propotionl gin k i Integrl gin J moment of inerti B Coefficient of friction The speed control techniques for vrible speed drives hve chnged rpidly nowdys when compred to the conventionl prototypes. With the dvncement in the power electronics field dvnced controllers nd converters re designed for both AC nd DC drives. Some of the populr controllers like PI, PID, Fuzzy logic, Genetic lgorithm etc re being used in industril pplictions for controlling power converters. Further severl PWM techniques were lso developed to improve the switching performnce nd reduce switching loss in power electronic converters. Since the conventionl speed control methods re not highly efficient, designing suitble speed controller for prticulr motor hs been primry concern for the present dy reserches. Among ll the motors vilble, BLDC motor hs been chosen for this pper for their dvnced sophisticted fetures. * Assistnt Professor, Deprtment of Electricl nd Electronics Engineering, SRM University, Kttnkulthur, 603203, Indi, runnoyl@gmil.com, klynsrm@gmil.com. ** Professor, Deprtment of Informtion Technology, SRM University, Kttnkulthur, 603203, Indi, dr.vgee@gmil.com. *** PG Scholr, Deprtment of Electricl nd Electronics Engineering, SRM University, Kttnkulthur, 603203, Indi krthikkumr654@gmil.com.
2 M. Arun Noyl Doss, V. Klynsundrm, V. Gnpthy nd K. Krthik Brushless dc (BLDC) motor is type of permnent mgnet synchronous motor which is widely used nowdys due to the dvntges like high power density, high efficiency, low mintennce requirement, nd their tolernce to electromgnetic interference (EMI) problems. These motors cn be operted t wide rnge of speed. Fig.1 shows the conventionl BLDC drive topology. (Figure.1) Figure 1: Conventionl BLDC drive topology The min difference between BLDC motor nd permnent mgnet synchronous motor is tht BLDC motor hve trpezoidl bck emf. Unlike synchronous motors BLDC motors re self strting in nture nd speed cn be vried smoothly. The BLDC motor hs torque speed chrcteristics similr to DC motor. BLDC motor looks similr to tht of DC motor. In DC motors, the sttor my contin permnent mgnet if it is Permnent Mgnet dc (PMDC) motor. The rotor will hve windings nd windings will get excited using commuttor nd brushes rrngement. On the other hnd the BLDC motor will hve windings in the sttor nd the permnent mgnets re present in the rotor. The term brushless is mentioned becuse here the brushes nd current crrying coils re replced by permnent mgnets nd the permnent mgnets perform the rottor opertion. Trditionlly Ferrite mgnets re used for mking permnent mgnets in rotor nd nowdys rre erth mgnets re gining populrity becuse of their high mgnetic field density per volume. Normlly BLDC motors re not directly connected to three phse AC supply system. The phse windings of the BLDC motor re energized using three phse inverter. Since BLDC motors re inverter driven the speed of the motor is controlled by vrying the DC link cpcitor voltge on the source side of the inverter or by vrying the pulse width of the inverter switching pulses. But the speed cnnot be controlled over wide rnge using PWM technique. Further the inverter switches re subjected to lrge voltge stress which will decrese the life time of power electronic components. Prior reserches hve been mde in estblishing speed control nd toque control for BLDC motor. Anlysis on brushless mchines nd their pplictions hve been stted in 1. Torque control of BLDC drives using direct torque control method is explined in 2. The method for minimizing commuttion torque ripple during the implementtion of direct torque control is explined in 3. 4 explin the indirect flux control method in BLDC motor. Self control of BLDC motor using three dimensionl co-ordinte system is explined in 5. Direct torque control of BLDC motor using self controlled flux linkge is explined in 6 nd in 7 direct torque control long with long with non idel bck emf is explined. An pproch to torque ripple reduction using direct torque control is explined in [8]. But the speed nd torque control pproch bsed on direct torque control pproch mentioned o in 6,7,8 requires complicted control lgorithms nd thus incresed the cost nd size of the system. Anlysis on sensor bsed speed control method for BLDC motor is explined in 9. Performnce nlysis of PI controller bsed BLDC motors is explined in 10.
A cost effective speed control method for BLDC Motor Drive The method to minimize cogging torque by reducing the sttor tooth width is presented in 11. In this pper the cogging torque is minimized using bifurcted sttor teeth nd the modifiction of sttor teeth is mde using finite element nlysis. In 12 mthemticl model of BLDC motor hs been proposed to minimize cogging torque, hrmonics nd torque ripples. 13 explins speed control model for BLDC motor designed nd nlyzed using PSIM. A comprtive nlysis on vrious controllers used to improve the trnsient response in speed nd torque ripple minimiztion in BLDC motor. 15,16,17 explins the bsic principle of BLDC motor, operting principle of vrious power electronic converters nd drive systems. This pper proposes PI controller bsed pproch for controlling the switching pulses of the inverter nd thereby controlling the speed of the motor. The prmeters considered for nlyzing the BLDC motor is mentioned in tble.1 Tble 1 Specifictions of BLDC motor Prmeters Connection type Rted Current Rted Voltge Rted Speed Vlue Str 4.52 A 310 Vdc 4600 rpm Electromechnicl torque 2.2 Nm To employ cost effective speed control mechnism PI controller is used. In the PI controller two control strtegies re implemented nmely, proportionl control nd the integrl control. The proportionl control produces n error signl tht is proportionl to the current error vlue. The vlue of the error cn be djusted by multiplying with the proportionl gin vlue (k p ). The integrl control produces n error vlue which is proportionl to the mgnitude of the error nd durtion of the error. The vlue of the corresponding error cn be djusted by multiplying with the integrl gin vlue (k i ). The theoreticl nlysis is performed by considering the prmeters mentioned in Tble.1. 3. MATHEMATICAL MODELLING OF BLDC MOTOR The voltge eqution of the BLDC motor is given s, di dib dic V = ir + L + Mb + Mc + e (1) dt dt dt dib di dic V b = ibrb+ Lb + Mb + Mbc + eb (2) dt dt dt dic di dib V c = icrc + Lc + Mc + Mcb + ec (3) dt dt dt Here e, e b, e c re the bck emf of BLDC motor.1 The mthemticl model of BLDC motor cn be expressed in mtrix form s, é L M M ù é b c i ù é V ù ér 0 0 ùé i ù é e ù d úê Mb Lb M bc i b dt = V b - 0 Rb 0 úêi b - e úê b (4) êmc Mcb L ú ê c i ú ê ë û ë c û V ú ê c 0 0 R úê c i ú ê c e ú ë û ë ûë û ë cû Where L, L b nd L re self inductnce nd M, M, M, M, M nd M c re mutul inductnce. b b bc cb c c For simplifiction ll self inductnce re ssumed s Lnd ll mutul inductnce re ssumed s M. Since it is blnced three phse system ll resistnce re equl nd therefore, R = R b = R c = R (5) 3
4 M. Arun Noyl Doss, V. Klynsundrm, V. Gnpthy nd K. Krthik Replcing the vlue of self inductnce, mutul inductnce nd three phse resistnce, eq.4 cn be written s, é L M M ù éi ù é V ù ér 0 0 ùé i ù é e ù d úê M L M i b dt = V b 0 R 0 úêi b e úê b (6) êm M L ú ê i ú ê ë û ë c û V ú ê c 0 0 R úêi ú ê c e ú ë û ë ûë û ë cû The electromgnetic torque of the BLDC motor is expressed s, d T e = J +B +T l dt (7) In terms of ngulr velocity, the electromgnetic torque of BLDC motor is expressed s, 1 T e = ( ei + ei b b+ ei c c) (8) The trnsfer function of BLDC motor is, G(s) = 1 ke 2 TT m es +T ms +1 (9) Where T nd T m re the mechnicl time constnt nd electricl time constnt respectively. e 4. PROPOSED PI CONTROLLER BASED SPEED CONTROL SYSTEM The proposed drive system hs three phse inverter driven BLDC motor powered by Single phse AC supply connected to single phse bridge rectifier. The speed of the BLDC motor is sensed using rotor position sensor nd the using comprtor the mesured speed is compred with reference speed. The error signl is given s input to the PI controller by compring ctul speed nd reference speed. The output of PI controller is fed s input to current limiter nd this signl will be considered s the reference current signl. This reference current signl is compred with ctul current signl which is obtined from line current feedbck. A current sensor is used to mesure the line current. The output of the P controller is compred with tringulr wve nd by vrying the duty cycle corresponding switching pulse is given to the inverter. Fig. 2 shows the schemtic lyout of the proposed closed loop speed control system. (Figure.2) BLCD Motor Figure 2: Schemtic lyout of proposed topology The clcultion of proportionl gin (k p ) nd integrl gin (k i ) is done using Ziegler-Nichols method.
5. PI CONTROLLER DESIGN A cost effective speed control method for BLDC Motor Drive 5 PI controller is the most widely used feedbck control system in industries. Bsiclly the control method hs two feedbck components nmely proportionl gin (k p ) nd integrl gin (k i ). The PI tuning method is performed for the speed control nd corresponding prmeters re obtined. Since the mthemticl model of the system is complicted the control prmeters re tuned using Ziegler-Nichols method. The controller prmeters re obtined from the output response using the following response grph. (Figure 3) ct () Tngent line t infection point K 0 t L T Figure 3: Ziegler-Nichols rules for tuning P, PI nd PID controller The response of the system is obtined nd the point of infltion is noted. A tngent line is drwn on the point nd the vlues of L nd T re clculted. The vlue of K is tken from the point when the system reches stble condition. Tble.2 shows the formuls for clculting K p, K i nd K d for P, PI nd PID controller. The PI controller bsiclly works in two modes nmely the proportionl mode nd the integrl mode. The proportionl mode controls the instnt speed error nd the integrl mode determines the rection bsed on the recent error. The output of the PI controller is given by, Output(t) = t ket p ()+ kiò e() d (10) Where e(t) is the error signl. The error signl e(t) Is clculted by, e(t) = ref m (t) (11) Where is the reference speed nd ref (t) is the mesured speed. m Tble 2 Result of PI tuning method 0 Type of Controller k p k i k d P T/L 0 PI 0.9T/L L/0.3 0 PID 1.2T/L 2L 0.5L
6 M. Arun Noyl Doss, V. Klynsundrm, V. Gnpthy nd K. Krthik Tble.3 shows the clculted vlues of k nd k p obtined for the proposed system. i Tble 3 Result of PI tuning method Method k i k p Overshoot(%) Drop in speed (rd/sec) Settling time (Sec) Ziegler-Nichols method 16.61 0.013 2.7 6.5 0.20 The simultion is performed by considering reference speed s 3000 rpm. The PI controller bsed speed control model is given by ki G(s) = + k p (12) s Where, G(s) = Controller trnsfer function, k p = Proportionl gin, k i = Integrl gin. These prmeters re clculted using Ziegler-Nichols method. The closed loop trnsfer function of the system is shown in Figure. 4. The system trnsfer function eqution is, T(s) = Figure 4: Closed loop trnsfer function of PI controller ( ks+ k)/j p i 2 s + k s k { p } (B + ) + /J (13) p i k p = 2ξ n J B (14) k i = J n (15) 6. SIMULATION RESULTS A. Dynmic Performnce of the proposed Drive Tble 4 Comprison of Speed nd Torque t different Voltge levels. Voltge Speed Torque 12 205 3.63 24 405 1.84 36 618 1.20. 48 859 0.868 60 1048 0.711 72 1208 0.617
A cost effective speed control method for BLDC Motor Drive Test simultions prove the efficiency of the proposed drive system. The BLDC motor is cpble of operting in between 12V to 310V. The speed nd torque of the motor recorded t different voltges re mentioned in tble.4. By choosing the vlues of k nd k p s mentioned in tble.3 the peek overshoot % ws 2.7. The motor i ws ble to rech 1400 rpm t 80V. Fig.5 shows the speed torque response of the proposed drive system. (Figure.5) 4 Speed Vs Torque 7 3.5 3 Torque(N-m ) 2.5 2 1.5 1 0.5 200 400 600 800 Speed (RPM) 100 1200 1400 Figure 5: Speed vs Torque response of BLDC motor The motor ws ble to chieve mximum speed of 3000 rpm during test simultion. Figure.6 shows output speed of the BLDC motor. (Figure.6) Figure 6: Speed of BLDC motor Figure.7 shows the line currents of the voltge source inverter. (Figure.7)
8 M. Arun Noyl Doss, V. Klynsundrm, V. Gnpthy nd K. Krthik Voltge (V) 500 400 300 200 100 0 100 200 300 Figure 7: Line current of voltge source inverter Vb 400 500 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05 Time( s) Voltge (V) 500 400 300 200 100 0 100 200 Vbc 300 400 500 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05 Time( s) Voltge (V) Vc 500 400 300 200 100 0 100 200 300 400 500 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05 Time( s) Figure 8: Line voltge of voltge source inverter
A cost effective speed control method for BLDC Motor Drive The motor consumed line current of 1.2A nd the line voltge ws 265V. Figure.8 shows the line to line voltges of voltge source inverter. (Figure.8) B. Hrdwre Implementtion of the proposed topology The PI control lgorithm is progrmmed using dspic30f2010 digitl signl controller. The BLDC motor with the specifictions mentioned in tble.1 is considered for the evlution of the hrdwre prototype. Figure.9 shows the hrdwre prototype of the proposed topology. (Figure.9) 9 Figure 9: Hrdwre Prototype of the proposed topology The performnce of the BLDC motor ws smooth nd the motor ws operted t 1508 rpm. Figure.10 shows the speed of the BLDC motor. (Figure.10) 7. CONCLUSION Figure 10: Speed of the BLDC motor t 1508 rpm This pper hs proposed cost effective speed control method for BLDC motor drive using PI controller. The motor is operted in wide rnge of speed. The results obtined from mtlb/simulink simultion hve proved the effectiveness of the implementtion of PI controller. But even though PI controller finds good ppliction in industril drives speed control is less ccurte. Becuse during strting oscilltions occur in speed which dmps out in time. PI controller holds good only for liner systems nd smll vritions in speed cn be observed. The effectiveness of the proposed topology cn be further improved by using neurl-fuzzy logic technique. 8. REFERENCES 1. Tkshi Kenjo nd Shigenobu Ngmori.Brushless motors: dvnced theory nd modern pplictions,tokyo, Jpn: Sogo Electronics Press, 2003. 2. Liu Yong, Zhu Z Q nd Howe D. Direct Torque control of brushless DC drives with reduced torque ripple. IEEE Trns. On Industry Applictions, vol.41, no. 2, pp. 599-608, 2005.
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