Modelling and Simulation of Closed Loop Controlled Buck Converter Fed Pmbldc Drive System

Transcription

1 Researh Journal of Applied Sienes, Engineering and Tehnology 3(4): , 2011 ISSN: Maxwell Sientifi Organization, 2011 Reeived: Feruary 14, 2011 Aepted: Marh 15, 2011 Pulished: April 20, 2011 Modelling and Simulation of Closed Loop Controlled Buk Converter Fed Pmld Drive System 1 S. Prakash and 2 R. Dhanasekaran 1 Researh Sholar, E.E.E Department, SathyaamaUniveristy, Chennai, Tamilnadu, India 2 Syed Ammal Engineering College, Ramanathapuram, Tamilnadu, India Astrat: Permanent Magnet Brushless DC Motor (PMBLDC) is one of the est eletrial drives that has inreasing popularity, due to their high effiieny, reliaility, good dynami response and very low maintenane. This makes the interest of modeling an ideal PMBLDC motor and it s assoiated Drive System in simple and luid manner. In this paper the drive system is proposed with a uk onverter topology. It has the advantages of redued swithing losses, low indutor power loss, redued ripple y using a pi-filter, whih in turn makes the DC link voltage to e stale. The modeling and simulation of the PMBLDC motor is done using the software pakage MATLAB/SIMULINK. The operation priniple of the uk onverter is analyzed and the simulation results are presented in this paper to verify the theoretial analysis. Key words: Converter, drive, filters, Permanent Magnet Brushless DC Motor (PMBLDC) INTRODUCTION Permanent magnet rushless DC (BLDC) motor is inreasingly used in automotive, industrial, and household produts eause of its high effiieny, high torque, ease of ontrol, and lower maintenane (Krishnan, 2003; Krishnan and Shiyoung, 1997). A BLDC motor is designed to utilize the trapezoidal ak EMF with square wave urrents to generate the onstant torque. A onventional BLDC motor drive is generally implemented via a six-swith, three phase inverter (Rahul et al., 2003) and three Hall-effet position sensors that provide six ommutation points for eah eletrial yle. Cost minimization is the key fator in an espeially frational horse-power BLDC motor drive for Home appliations. It is usually ahieved y elimination of the drive omponents suh as power swithes and sensors. Therefore effetive algorithms should e designed for the desired performane and the relevant drive system whih in turn ontrols the motor for all its defined appliations with high effiieny, as well as good in maintaining the speed for variale torque. The mathematial modeling of DC to DC onverter is given y (Luo, and Ye, 2005; Muo, 2004). The ojetive of the preset work is to model and simulate uk onverter fed PMBLDC drive. PMBLDC motor: The rushless DC motor is atually a permanent magnet AC motor whose torque-urrent harateristis mimi the DC motor. Instead of ommutating the armature urrent using rushes, eletroni ommutation is used. Having the armature on the stator makes it easy to ondut heat away from the windings, and if desired, having ooling arrangement for the armature windings is muh easier as ompared to a DC motor. A BLDC is a modified PMSM with the modifiation eing that the ak-emf is trapezoidal instead of eing sinusoidal as in the ase of PMSM (Luk and Lee, 1994). The position of the rotor an e sensed y hall effet position sensors, namely Hall_A, Hall_B, and Hall_C, eah having a lag of 120º w.r.t the earlier one. Three Hall position sensors are used to determine the position of the rotor field. Model of a BLDC motor Sine a BLDC motor is easy to ontrol, it is the motor of hoie in many appliations requiring preise ontrol of speed (AtefSalehOthman and Al-Mashakeh, 2009), (Byoung- KukLee et al., 2001). The BLDC motor model is explained as, the eletromagneti torque, T em is linearly proportional to the armature urrent i a. i.e., T em = K T i a, where K T is the torque onstant. The ak-emf in a BLDC motor is linearly proportional to the rotational speed of the shaft. The akemf is proportional to the speed of the motor and its diretion is given y Flemings right hand rule. Considering that in a magneti field of intensity B, a ondutor of length l on the edge of rotor of radius r is rotating at an angular veloity of radians per seond. Then the speed of the ondutor is given y: vel = T x r Corresponding Author: S. Prakash, Researh Sholar, E.E.E Department, SathyaamaUniveristy, Chennai, Tamilnadu, India 284

2 Res. J. Appl. Si. Eng. Tehnol., 3(4): , 2011 The emf e generated in that ondutor is given y: e = T rbl Conventionally the numer of ondutors in an eletrial mahine is given y Z, and if the numer of ondutors in series is Z/2, the series ak-emf is given y e as: e = T m rbl (Z/2) In terms of the magneti flux: e = K e T m where, K E is the ak emf onstant. The model of a BLDC onsisting of three phases is explained y means of equations, sine there is no neutral used, the sum of the three phase urrents must add upto zero, i.e., i a +i +i = 0 i a +i = - i Considering all the three phases following equations are used to model the two pole three phase BLDC motor. va Ra 0 0 ia v R i = v 0 0 R i La La La ia ea d L L L i e dt a + La L L i e If the permanent magnet induing the rotor field ios in the shape of an ar, it requires that the indutanes e independent of the rotor position, hene: L a = L = L = L p Considering the symmetry of the aove matrix in addition to independene w.r.t the rotor position: L a = L a = L = L = L a = L a = M Aove equation redues to: v v v Ra 0 0 ia R i = R i Lp M M ia ea d M Lp M i e dt + M M Lp i e a From aove two equations we get: v v v Ra 0 0 ia R i = R i Lp M Lp M Lp M a d dt i i i ea e e Rearranging the equations, we have otained equations in a form suitale for simulation. PMBLDC motor with new power onverter topology is given y Krishnan and Shiyoung (1997). Four swith three phase rushless motor for low ost ommerial appliations is given y Lee (2003). The aove literature does not deal with Modelling and Simulation of Buk Converter fed PMBLDC drive. This study proposes uk onverter for PMBLDC Drive. SIMULATION RESULTS Closed loop system is simulated using Matla Simulink. The Simulink model of losed loop ontrolled uk onverter inverter fed PMBLDC drive whih shown in Fig. 1a. Here 48V DC is stepped down to 24V DC using a uk onverter. The output of uk onverter is filtered using pi-filter. The output of the pi-filter is applied to the three phase inverter, the inverter produes three phase voltage required y the PMBLDC motor. The tehnial speifiations of the drive systems are as follows: Input voltage: 48 V DC Buk output voltage: 24 V DC Pulse width to Buk MOSFET: 0.5 duty yle (50%) T off : 50% Pulse width (33%) to Inverter MOSFET: 120 mode of operation. a 285

3 Res. J. Appl. Si. Eng. Tehnol., 3(4): , 2011 Fig. 1a: Simulink diagram of losed loop system Fig. 1: Triggering pulses Parameters of BLDC motor: The inverter is a MOSFET ridge: Stator resistane R s : ohms Stator Indutane L s : 8.5e-3 Henrys Flux indued y magnets : Weer's Bak EMF Flat area : 120 degrees Inertia : 0.8x10G 3 Frition fator : 1x10G 3 Pole pairs : 4 Stator windings are onneted in star to an internal neutral point. The atual speed is measured and it is ompared with the referene speed, the error is given to the PI Controller, the output of the PI ontroller is one of the inputs to the omparator. The other input is high frequeny triangular wave. The output of the omparator ontrols the pulse width applied to the uk MOSFET. The pulses given to the MOSFETS 1, 3 and 5 are shown in Fig

4 Res. J. Appl. Si. Eng. Tehnol., 3(4): , 2011 Fig. 1: DC input voltage Fig. 1d: Phase voltages of inverter Current Fig. 1e: Output urrents of inverter 287

5 Res. J. Appl. Si. Eng. Tehnol., 3(4): , 2011 Fig. 1f: Bak EMF waveforms Speed Fig. 1g: Rotor speed in rpm D.C. input voltage is shown in Fig. 1 and its value is 48 volts. Phase voltages of the three phase inverter are shown in Fig. 1d. The voltages are displaed y 120º. Three phase urrents drawn y the motor are shown in Fig. 1e. The ak emfs in the three phases are shown in Fig. 1f. The response of speed is shown in Fig. 1g. The speed settles at 130 rpm, whih is equal to the set value. Fig. 1: DC input voltage CONCLUSION Closed loop ontrolled PMBLDC drive system is modeled and simulated using MATLAB/SIMULINK and the results are presented. Buk onverter is proposed to redue the input voltage to the required value. Pi-filter is proposed at the output of the uk onverter to redue the ripple. This drive system has advantages like redued numer of swithes and improved response. The sope of this paper is modeling and simulation of losed loop ontrolled PMBLDC drive system. The hardware implementation is yet to e done. The ontriution of authors is the development of new simulink model for uk onverter fed PMBLDC motor drive. ACKNOWLEDGMENT The experiment was onduted in power eletronis laoratory, Sathyaama University. The authors would 288

6 Res. J. Appl. Si. Eng. Tehnol., 3(4): , 2011 like to thank Head of the Department, Eletrial Department, Sathyaama University for providing the failities. REFERENCES Atef, S.O. and Al-Mashakeh, Proportional Integral and derivative ontrol of rushless DC motor. Eur. J. Si. Res., 35(2): Byoung-Kuk, L., K. Tae-Hyung and J. Mehrdad Ehsani, On the feasiility of four-swith three phase BLDC motor drives for low ost ommerial appliations topology and ontrol. IEEE Tran. Power Eletron., APEC, 18(1): Krishnan, R., A Text Book on Eletri Motor Drives, Modelling, Analysis and Control. Prentie Hall of india Pvt Ltd., New Delhi. Krishnan, R. and L. Shiyoung, PM rushless DC motor drive with a new power-onverter topology. IEEE Tran. Indus. Appl., 33(4): Luk, P.C.K. and C.K. Lee, Effiient modeling for a rushless DC motor Drive. 20 th International onferene on Industrial Eletronis, Control and Instrumentation, IECON'94, 1: Luo, F.L. and H. Ye, Energy Fator and Mathematial modeling for power d-d onverters. Pro. Inst. Elet. Eng., 152(2): Muo, E.L., Mathematial modelling for power dd onverters. IEEE International Conferene. Poweron 04, Singapore, pp: Rahul, K., S.M. Madani, H. Masoud and A.T. Hamid, A low ost BLDC motor drive using ukoost onverter for residential and ommerial Appliations. IEEE International Conferene on Eletri Mahines and Drives, IEMDC 03, 2: