Speed control of brushed DC motor for low cost electric ... - IEEE Xplore

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control the speed of low cost brushed D.C. motor by combining a IC. 555 Timer with a High Boost Converter. The main purpose of using. High Boost Converter ...
Speed Control of Brushed DC Motor For Low Cost Electric Cars Vikas Gupta and Anindya Deb Center for Product Design and Manufacturing Indian Institute of Science Bangalore, India [email protected]

Abstract- As petrol prices are going up in developing countries in upcoming decades low cost electric cars will become more and more popular in developing world. One of the main deciding factors for success of electric cars specially in developing world in upcoming decades will be its cost. This paper shows a cost effective method to control the speed of low cost brushed D.C. motor by combining a IC 555 Timer with a High Boost Converter. The main purpose of using High Boost Converter since electric cars needs high voltage and current which a High Boost Converter can provide even with low battery supply. Keywords- Brushed DC Motor,Duty cycle, High Boost converter, 555 Timer.

I. INTRODUCTION One of the ways of varying speed of a DC Motor is to control the armature voltage [1][3]; this can be done with an IC 555 Timer and High Boost converter. The output voltage which goes to motor through High Boost converter depends on duty ratio and duty ratio can be varied through IC 555 Timer circuit by varying one of the resistances which connected to the brakes of the electric car. Entire method is explained in detail. The main reason of using IC 555 Timer is its stability, cheap cost and easy availability. This method of controlling DC Motor speed is cost affective as compared to other methods which use either costly Brushless DC Motor [9] or quite complex technique to control the speed of Brushed DC Motor [2][7].

II. IC 555TIMER Refer Fig 1555 Timer is used as an astable circuit. Astable 555 Timer produces a square wave output with transitions between low (0 V) and high (+ V1) as shown in Fig 2. The output is continuously changing between low and high. During TON the capacitor will charge through Ra and a high pulse with amplitude (V1) is generated, during TOFF the capacitor discharges through Rb generating low pulse.

Fig. 1 555 Timer circuit

TON = 0.69 *Ra*C4

(1)

TOFF = 0 .69*Rb*C4

(2)

TS = TON + TOFF

(3)

TON = DTs

(4)

TOFF = (1-D) Ts

(5)

Duty Ratio (D) = TON / (TON + TOFF)

(6)

Duty Ratio (D) = Ra/(Ra+Rb)

(7)

Fig. 2 Output through IC 555 Timers

TOFF is fixed while TON can be varied by varying resistance of potentiometer Ra.To achieve variable duty cycle a diode is added in parallel with Rb as shown in the Fig 1. This bypasses Rb during the charging part of the cycle so that TON depends only on Ra and C4.

III. HIGH BOOST CONVERTER

During time DTsor TON Here S1 and S4 are ON and S3 and S2 are OFF. The voltage across L1 is given as (8)

The inductor stores energy during this time. During this time, the capacitor C1 reverses bias diode D2 and forward bias D1.The voltage across L2 is given as VL2 = VC1 – Voutput

(VC1– Voutput) TON + (-Voutput) TOFF= 0

(14)

Voutput = VC1D

(15)

The following input- output relationship results:

Fig 3 shows a High Boost converter [6], its working is as follows.

VL1 = Vinput + Vc1

Fig. 3 High Boost Converter

(9)

During time (1-D) Ts or TOFF In this case S1 and S4 are turned OFF and S3 and S2 are ON. The energy in the inductor L1 charges up the capacitor C1 through the diodes S3 and S2. The voltage across L1 is given as

Voutput = VinputD/1-2D

(16)

The above relation clearly shows that we can get high amplification in input voltage using a High Boost converter. Both circuits Fig 1 and Fig 3 circuits are combined to form the final circuit shown in Fig 4. The IC 555 Timer output is fed to switches S1 and S4 of High Boost Converter. During TON when a high pulse from IC 555 Timer is giving to S1and S4, S1 and S4 will be in ON state while during TOFF a low pulse from IC 555 Timer is giving to S1 and S4, S1and S3 will be in ON state while S1 and S4 will be in OFF state. In the given circuit the Duty Ratio can be varied by varying TON and TON can be varied by varying resistance of potentiometer Ra which is connected to brake of electric car. Thus resistance of Potentiometer can be varied by movement of brake.

IV.RESULTS VL1 = Vinput – VC1

(10) TABLE I

During the time, the current in L2 through D2 transferring energy from L2 to C2. The diode D1 is reverse-biased during this time and is therefore OFF. The voltage across L2 is given as VL2 = -Voutput

(11)

Applying the volt-second balance rule for L1 (Vinput + VC1) TON+ (Vinput – VC1) TOFF= 0

(12)

VC1= Vinput/1-2D

(13)

Applying the volt-second balance rule for L2,

Vinput (VOLT)

DUTY RATIO (D)

Voutput(VOLT)

30

0.46

172.5

30

0.47

235

30

0.48

360

30

0.49

735

30

0.50



Fig. 4 Speed Control System for Brushed DC Motor

From the results as shown in Table I it is clear that this method can give very high output voltage (Voutput) with small input voltage (Vinput) supply which is very useful in case of electric cars and since this method is cost effective so it is very useful in designing low cost electric cars.

ACKNOWLEDGMENT Author like to acknowledge the center for product design and manufacturing of IISc in providing all necessary facilities for conducting design and testing this circuit on a actual electric car platform.

(17)

ω α Voutput

In Brushed DC Motor the angular velocity (ω) is directly proportional to armature voltage(Voutput) [4][5], as armature voltage increases angular velocity will increase. So by changing Duty ratio (D) we can change the angular speed (ω) of Brushed DC Motor, if R of motor is kept small value, or when the motor is lightly loaded [8][10], Ia is small, and if the field current is kept constant, the motor speed (ω) depends only on the supply voltage.

V. CONCLUSION The speed controller has been successfully tested on Brushed DC motor and electric car platform to control motor speed. The detail explanations of the circuit have been also presented. This method provides a cost effective way to control the speed of a Brushed DC Motor.

REFERENCES [1]. Microchip, application notes on brushed Dc motors, AN905, 2004,pp.1-7. [2]. Chan CC and Chau K T, “Modem Electric Vehicle Technology”, oxford University press, 2001. [3]. P. C. Sen, “Electric Motor Drives and Control”: Past, Present and Future”, IEEE Transaction on Industrial Electronics, Vol. IE37, No. 6, 1990,pp-562-575. [4]. G.K. Dubey, Power Semiconductor controlled Drives, Englewood, Cliffs, N.J: Prentice Hall, 1989 [5]. STMicroelectronics, application notes on brushed Dc motors, AN380, 2003,pp.1-14. [6]. L. Umanand, “Power Electronics: Essentials & Application”, Wiley India,2009pp.263-265. [7]. Muhammad H. Rashid,”Power Electronics Circuits, Devices, And Applications”, Pearson Education, 2004,pp.190-191. [8]. P. S. Bimbhra, “Generalized Theory of Electrical Machines”, Khanna Publishers, Delhi, India, 2001, pp. 93-98. [9]. E. Afjei, M.A. Saati, M.M. Nezamabadi, S. Ataei, “ New Converter Topology for a Hybrid Brushless dc Motor Without Permanent Magnet”, ICEM Conf., Greece, pp. 20-25 ,2006. [10]. B.C. KUO and J. TAL, “Incremental Motion Control, Vol. 1, DC Motors and Control Systems”, SRL Publishing Co., Champaign, IL, 1979.