International Journal of Research and Reviews in Electrical and Computer Engineering (IJRRECE) Vol. 1, No. 3, September 2011, ISSN: 2046-5149 © Science Academy Publisher, United Kingdom www.sciacademypublisher.com

1009

Speed control of Four-Switch BLDC Motor Drive P. Devendra1, K. Vinodkumar2, K. AliceMary3, and Ch. Saibabu3 1

EEE dept ,GMR Institute of Technology, Rajam, AP, India GMR Institute of Technology/EEE department, Rajam, AP, India 3 EEE department, Vignan‘s Institute of Information Technology, Visakhapatnam, AP, India 4 Jawaharlal Nehru Technological University, Kakinada, AP, India 2

Email: [email protected], [email protected]

Abstract – The main work of this paper is to control speed of a four switch three phase Brushless DC motor drive based on the concept of switching functions. A Direct Phase Current (DPC) control method is implemented so as to overcome the problems caused due to the elimination of the two power switches. The working principle of the Four switch BLDC motor drive and the developed control scheme are th analysed and the performance is demonstrated through MATLAB/Simulink. Keywords – Switching functions, Direct Phase control, and four switch BLDC

1.

Introduction

Brushless DC Motors (BLDC) drives are nowadays widely used for various purposes in consumer products and industrial applications. Hence researchers are exploring the possibility of cost reduction. The cost reduction of variablespeed drives is accomplished by the two approaches [1],[2]. One is the topological approach and the other is control approach. In topological approach, minimum numbers of switches are being used to compose the power conversion circuit. In control approach, control algorithms are designed and implemented in conjunction with the reduced parts converter to produce the desired dynamics. As a result, many different topologies have been developed and various PWM control strategies have been proposed to improve the performance of the developed system. However, these days, the BLDC motor is attracting much interest, due to its high efficiency, high power factor, high torque, simple control, and lower maintenance. Therefore the proposed work investigated the possibility of the reduced converter for BLDC motor drives with advanced control techniques. As a result, it was observed that one switch leg in the conventional six-switch converter is redundant to drive the three-phase BLDC motor. It results in the possibility of the four-switch configuration instead of the six switches. The present work proposes the direct phase current control technique for current control and technique is based on the concept of Switching functions..The developed method generates robust speed and torque responses. Therefore, based on the Switching function the four-switch three-phase BLDC motor drive could be a better alternative to the conventional sixswitch counterpart with respect to low-cost and high performance. The operation of the four switch three-phase BLDC motor drive and the proposed DPC, Switching Function control schemes are explained in following sections

2.

Analysis of four-switch Inverter fed three-phase BLDC Drive

The configuration of four-switch Inverter fed BLDC Motor drive is shown in the Fig. 1 and modelling is done based on following assumptions[3].  Stator resistance of all the windings are equal, self and mutual inductances are constant.  The motor is not saturated.

Figure 1.Four switch BLDC motor drive equivalent circuit.

From the above assumptions, a BLDC motor can be modeled as follows va  1 0 0 ia   L  M v   R 0 1 0 i    0 s   b  b   vc  0 0 1 ic   0

0 LM 0

0  ia  ea  0  p ib   eb  L  M  ic  ec 

(1)

Where, Va , Vb and Vc are three phase terminal voltages, ea, eb and ec are trapezoidal back-EMF voltages and ia,ib and ic are the current s of each Phase . L and M are the self inductance and mutual inductance of each phase.

P. Devendra et al. / IRRECE, Vol. 1, No. 3, pp. 1009-1015, September 2011

Fig. 2 shows the trapezoidal back-EMF, current waveforms and position of Hall Effect sensor signals of a three-phase BLDC motor.

Figure 2. Back-EMF, current and position Hall Effect Sensors waveforms of a three-phase BLDC motor.

To drive the motor effectively with maximum and constant torque, the generated phase currents must be synchronised with the back EMF voltages. The Fig .3 shows current conduction directions based on the six different modes of operation of BLDC Motor. The modes are generated based on the Hall effect signals generated while the rotation of the motor. In out of all the six modes, in modes 2,5 the currents are controlled independently. Therefore the back EMF voltage of phase C does not disturb the phase currents. 2

1 A

2

1

C

B 3

Modeling of Four switches three phase BLDC Motor can be done by using the switching function concept. By using switching function concept power conversion circuit can be modeled according to their functions, rather than circuit topology. The model can be implemented using the functional block of the MATLAB/simulink software. The overall it consisting of five different functional blocks namely: BLDC motor, power inverter, current controller, speed control and the switch current block. 3.1. BLDC Motor This block consisting of four inputs i.e., input phase voltages and the load torque and the output of this block is speed ωr, phase currents back EMF voltages and the Mode of operation. This block consists of current calculator, back EMF voltage generator, torque, speed calculator, theta and mode of operation generator. The phase currents of the BLDC motor can be obtained by using the following model equations[5].

dia 1  (Va  ea  R.ia ) dt LM

dib 1  (Vb  eb  R.ib ) dt L M

(2)

The electromagnetic torque obtained is given by

B

4

Modeling of Four Switch three phase BLDC Drive

dic 1  (Vc  ec  R.ic ) dt L M

A

C

3.

1010

3

4

(3) (a) Mode-1

2

1

2

1

Te  TL  J

A

A

C

C

B

B 3

3

4

(c) Mode 3

4

(d) Mode 4

A

A

C

C

B

B

(d) Mode 5

2

1

2

1

3

Where Zp is the number of pole pairs. ωr is the electrical speed derived from the following equation

(b) Mode 2

4

3

(e) Mode 6

Figure 3 switching operation for six operating modes.

4

d r  B r dt

(4)

Where TL, J, B are the load torque, moment of inertia and the frictional coefficient respectively. Hence BLDC Motor block consisting of four inputs i.e., input phase voltages and the load torque and the output of this block is speed ωr, phase currents back EMF voltages and the Mode of operation. The overall block implementation of BLDC motor is as shown in fig 4 The BLDC Motor block also consists of various subblocks like current calculator, back EMF voltage generator, torque, speed calculator, theta and mode of operation generator. The various sub-blocks of total drive system is shown below from Fig.5 to Fig.7.

P. Devendra et al. / IRRECE, Vol. 1, No. 3, pp. 1009-1015, September 2011

1

[van ]

[van ]

1/(L-M)

2

[vbn ]

[ea ]

-K-

3

[vcn ]

1 s

[da ]

[ia ] ia

R [tload ]

5 Tload

1011

4 ia

-K[vbn ]

1/(L-M)

1 [eb ]

ea

[theta ]

1 s

-K-

[ea ]

[ib ] ib

[eb ]

eb

5 ib

R

2 eb ec 3 ec

[vcn ]

1/(L-M)

[ec]

-K-

[vbn ]

[ec]

1 s

[ic] ic

E

-K-

[eb ]

-K-

[ec]

wm _rpm ]

[van ]

[db ]

ea

[ea ]

mode ]

[vcn ]

R -K-

ke(v/rpm )

60 0

inverter

t

Clock

wm

Ta -K-

[wr]

Tb

[eb ]

1/Wr

60 /(2*pi )

te

[ib ] 1

Figure 8 Inverter block.

[te]

[ia ] [ea ]

-K-K1/j

u

1 s

floor

-K-

[wm _rpm ]

1/Zp

6 wm _rpm

theta 1 s

[ic] Tc

Rotor position in electrical degrees can be calculated from the integration of the speed as follows:

[wr] [theta ]

[ec] Ha mod

mode

f(u) Hb f(u)

[tload ]

f(u)

[ea ] [eb ] [ec] [vb ]

[mode ]

Mode Determinator

mode

Hc

2*pi

[va ]

f(u)

[ia ]

7

 r   r dt   0

(5)

ϴ0 is the initial position of the rotor. Hall effect signals can be generated based on the below functions designed in the Simulink as follows: Ha = (u[1]>pi/6).(u[1]5*pi/6)*(u[1]3*pi/6)*(u[1]u[3].0.95)(u[1]u[2]) (u[1]>u[3].0.95).(u[1]u[3].0.95).(u[1]0 ) Db_S3 = ( ia > 0 ).( Db >0 ) = ( ia > 0).( Da 0 ).( Db 0 3 ia

[id 2]

0

-u

[id 1]

-5

-u

[is2]

-10

0 4 da

-15

0

Figure 14. Generated Back EMF‘s ea,eb,ec at an load torque of 5N. 15

[id 4] 1 ib

10

-u

[id 3] 5

< 0 -u

[is4]

0

> 0 2 db

-5

< 0 -10

Figure 13. Simulink model of Switch Current calculator. -15

4.

Simulation The speed control of four switch BLDC Motor is

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

P. Devendra et al. / IRRECE, Vol. 1, No. 3, pp. 1009-1015, September 2011

1014

15

7 10

6 5

5 0

4 -5

3 -10

2 -15

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

1

0 0

20

0.05

0.1

0.15

0.2

0.25

0.3

0.35

15

Figure 18. rotor position of the BLDC motor.

10 5

180

0

160

-5

140

-10

120

-15

100 -20

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

80 60

Figure 15. Phase currents ia, ib, ic at 180 rpm reference speed.

40

2

20

1.5

0

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1

Figure 19. Speed Vs Time at an reference speed

0.5 0

5.

-0.5 -1 -1.5 -2

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

2 1.5 1 0.5 0

Conclusion

In this paper, the speed control of four switch BLDC Motor is investigated to provide a possibility for the realization of low cost and high performance BLDC Motor drive and from the simulation results of the proposed method it is observed that it requires proper PWM technique .As a solution, the proposed method implemented a Direct Phase Current (DPC) control method so as to overcome the problems caused due to the elimination of the two power switches. Hence the proposed driving system for BLDC motor can be applicable for low cost applications.

-0.5

Appendix

-1

Table 1. Parameters of BLDC Motor

-1.5 -2

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Pn

425 [W]

Zn

16 [pole]

In

10 [A]

ωn

350 [rpm]

R

0.64 [Ω]

VDC-bus

60 [v]

Ls

1.0 [mH]

M

0.25 [mH]

Kt

1.194[N.m/A]

Ke

0.0667[V/rpm]

Figure 16. Duty cycles Da,Db of the two different phases. 6 5.5 5 4.5

References

4

[1]

3.5 3 2.5

[2]

2 1.5 1

0

0.05

0.1

0.15

0.2

0.25

0.3

Figure 17. the modes of operation of the motor.

0.35

[3]

P. Pillay, R. Krishnan; ―Analysis of permanent-magnet motor drives. I: The permanent-magnet synchronous Motor Drive‖,IEEE Transactions on Industry Applications, vol. 25, No. 2,March 1989, pp. 265-273. B.K. Lee, T.H. Kim, M. Ehsani; ―On the feasibility of fourswitch three-phase BLDC motor drives for low cost commercial applications: topology and control‖, IEEE Transactions on Power Electronics, Vol. 18, No. 1, pp. 164-172, January 2003. P. Pillay, R. Krishnan; ―Modeling, simulation, and analysis of permanent-magnet motor drives. II: The Brushless DC MotorDrive‖, IEEE Transactions on Industry Applications, vol. 25,No. 2, March/April 1989, pp. 274-279.

P. Devendra et al. / IRRECE, Vol. 1, No. 3, pp. 1009-1015, September 2011 [4]

[5]

[6]

[7]

[8]

[9]

[10]

[11]

[12]

[13]

[14]

[15]

[16]

B. K. Lee and M. Ehsani; ―A simplified functional model for 3-phase voltage-source inverter using switching function concept‖, in Conf. Rec. IEEE-IECON, pp. 462-467, 1999. A. Halvaei Niasar, H. Moghbeli, A. Vahedi; "Modeling and Simulation Methods for Brushless DC Motor Drives",Proceeding of the First International Conference on Modeling,Simulation and Applied Optimization (ICMSAO'05), pp.05-6/05-6, February 2005, Sharjah, U.A.E. B.K. Lee and M. Ehsani; ―Advanced BLDC Motor Drive for Low Cost and High Performance Propulsion System in Electric and Hybrid Vehicles‖, 2001 IEEE International Electric Machines and Drives Conference, 2001, Cambridge, MA, June 2001, pp. 246-251. L. Salazar, G. Joos; ―PSPICE Simulation of Three-Phase inverters by Means of switching Functions‖, IEEE Trans. OnPower Electronics, Vol. 9, No. 1,pp. 35-42 January 1994. E. P. Wiechmann, P. D. Ziogas, V. R. Stefanovic;―Generalized Functional Model for Three Phase PWM Inverter/Rectifier Converters‖, in Proc. IEEE IAS’85, 1985,pp. 984-993. A. Halvaei Niasar, A. Vahedi, H. Moghbelli; ―Analysis andControl of Commutation Torque Ripple in Four-Switch,Three-Phase Brushless DC Motor Drive‖, Proceeding of the 2006 IEEE International Conference on Industrial Technology (ICIT06), pp.239-246, India. T.-H. Kim and M. Ehsani, ―Sensorless control of the BLDC motor from near-zero to high speeds,‖ IEEE Power Electron., vol. 19, no. 5, pp.1635–1645, Nov. 2004. J. P. Johnson, M. Ehsani, and Y. Guzelgunler, ―Review of sensorless methods for brushless DC,‖ in Proc. IEEE Ind. Appl., 1999, vol. 1, pp. 143–150. I. Barbi, R. Gules, R. Redl, and N. O. Sokal, ―DC-DC converter: Four switch Vpk = Vin=2, capacitive turn-off snubbing, ZV turn-on,‖IEEE Trans. Power Electron., vol. 19, no. 4, pp. 918–927, Jul. 2004. K. Iizuka et al., ―Microcomputer control for sensorless brushless motor,‖IEEE Trans. Ind. Applicat., vol. 27, pp. 595–601, May/June 1985. R. C. Becerra, T. M. Jahns, and M. Ehsani, ―Four-quadrant sensorless brushless ECM drive,‖ in Proc. IEEE APEC’91 Conf., 1991, pp.202– 209. T. M. Jahns, R. C. Becerra, and M. Ehsani, ―Integrated current regulation for a brushless ECM drive,‖ IEEE Trans. Power Electron., vol. 6, pp.118–126, Jan. 1991 W. Brown, ―Brushless DC control made easy,‖ Application Notes— Microchip. AN857.

1015