PI Control of Boost Converter Controlled DC Motor

PI Control of Boost Converter Controlled DC Motor RESHMA JAYAKUMAR 1 AND CHAMA R. CHANDRAN 2 1,2 Electrical and Electronics Engineering Department, SBCE, Pattoor, Kerala Abstract- With the development of technology, the demand for automation in industries have increased. Thus, DC motor control implementation is required. In this paper, PI controller is employed along with boost converter is used to control the motor. DC motor, boost converter and PI controller have been modelled in MATLAB Simulink. Keywords DC Motor, dc/dc boost converter, PI controller. I. INTRODUCTION The development of industrial systems is recognized by the role played by the electrical machines. DC motor drives are studied frequently because the structure and operation of the DC drives are reflected in almost all other drives, and lessons learned from the study of the DC drive therefore have close parallels to other types. The DC drive tends to remain the yardstick by which other drives are judged. Under constant flux conditions the behavior is governed by a relatively simple set of linear equations, so predicting both steady state and transient behavior is not difficult [1]. When we turn to the successors of the DC drive, notably the induction motor drive, we will find that things are much more complex, and that in order to overcome the poor transient behavior, the strategies adopted are based on emulating the DC drives. DC motors are used for high control requirements. DC motor can provide a high starting torque and it is also possible to obtain wide range speed control. Some of the most common problems with DC motor include its inefficiency to start immediately. There are many reasons for its incapability to start such as low voltage supply, wrong connections, excessive load, frozen bearing, ground fault and so on. Earlier to control the DC motor, pulse width modulation (PWM) signals where used. These signals where applied with respect to the motor input voltage. Hard switching strategy of the PWM method, created abrupt variations in the voltage and current of the motor [2]. These problems can be addressed by using dc/dc power converters, which allow smooth start of dc motor by applying required voltage in accordance with one demanded for the performed task. II. OVERVIEW 2.1 DC Motor Electric motors are used to drive loads of varying characteristics. Precise speed control of electric motors in either direction or their constant speed operation under varying load conditions is required in different applications in industries, electric traction and machine tool etc to attain a high rate of production, high quality of products and at same time to achieve economy in production [3]. For example, the speed control of motors in steel mills is required to a high degree of accuracy inorder to avoid sag between stands. In metal cutting machine tools, speed of drive is set and adjusted depending upon quality of metal to be cut and tool to be used. In paper mill, weight per unit area of paper is determined by speed of machine. Speed of a DC motor is given by Va IaR a Kt where, V a = armature voltage I a = armature current R a = armature resistance K t = torque constant @IJMTER-2016, All rights Reserved 320

Φ = field flux From the above equation we can say that speed is dependent on armature voltage V a, armature resistance R a and field flux Φ. If R a is small (which is usual) or when motor is lightly loaded, i.e., I a is small, then Va Kt Thus, speed of the motor can be controlled in two ways: i. By varying armature voltage for below rated speed (armature control) ii. By varying field flux to achieve speed above rated speed (field control) 2.2 Boost Converter Fig. 1. Circuit diagram of Boost converter Boost converters are being used extensively in regulating switch mode DC power supplies. As the name implies, output voltage is always greater than input voltage [4]. When switch is ON, inductor L is connected to supply E and inductor stores energy during T ON period. Hence, diode D is reverse biased and isolates output stage. When switch is OFF, output stage receives energy from inductor as well as from input. Current flows through L, D F, C and load. Thus, output voltage has been boosted. 2.3 PI Controller The Proportional Integral (PI) controller is one of the conventional controller which is used for the speed control of DC motor drives. These are widely used in industries because of its ability to maintain a zero steady state error to a step change in reference [5]. Proportional controller (K p ) will have the effect of reducing the rise time and will reduce, but never eliminate the steady state error or offset. By including the integral action, the offset will be eliminated. Integral action gives the controller a large gain at low frequencies that results in eliminating offset and beating down load disturbances. Mathematical expression of the PI controller is where, u(t) = actuating signal K p = proportional gain constant e(t) = error signal K i = integral gain constant Laplace transform of above equation is t u t K e t K e t d t p i 0 Es U s KpE s Ki s Fig. 2. shows the block diagram of PI controller where error signal E(s) is fed into two controllers, i.e. proportional block and integral block, called PI controller. The output of PI controller, U(s) is fed to plant. The output of plant, C(s) may be speed or position is feedback to reference input R(s). As long as error is present the controller keeps changing its output and once the error is zero the controller does not change its output. @IJMTER-2016, All rights Reserved 321

Fig. 2. Block diagram of PI controller with DC motor system Table 1. Effect of K p and K i Controller Response Rise time Overshoot Settling Time Steady State error K p Decrease Increase Small Decrease change K i Decrease Increase Increase Eliminate III. MODELLING EQUATIONS OF DC MOTOR A DC motor system can be represented by an electromechanical schematic that equates electrical losses and mechanical forces to finite, measurable values. Mathematical model of a DC motor is expressed as LasI a (s) RaI a (s) V(s) Kes (s) where, L a = armature inductance K e = back emf constant J = moment of inertia of motor and load b = frictional coefficient of motor and load K m = motortorque constant 2 Js (s) bs (s) KmI a(s) Table 2. List of parameters for DC motor PARAMETER K e K m R a L a NOMINAL VALUE 120.1 10-3 Nm/A 120.1 10-3 Nm/A 0.965 Ω 2.22 10-3 H J 118.2 10-3 kgm 2 B 129.6 10-3 N ms IV. SIMULATION RESULTS Fig. 3. DC motor simulated block diagram @IJMTER-2016, All rights Reserved 322

Fig. 7. Simulation result of boost converter output voltage Fig. 8. Simulink model of speed control of DC motor with boost converter Fig. 9. Simulation result of armature current of motor converter combination @IJMTER-2016, All rights Reserved 324

Fig. 10. Simulation result of motor torque of motor converter combination Fig. 11. Simulation result of speed control of DC motor along with converter Fig. 12. Simulink model of speed control DC motor along with boost converter using PI controller @IJMTER-2016, All rights Reserved 325

Fig. 13. Simulation result of speed control DC motor along with boost converter using PI controller V. ACKNOWLEGDEMENT If words are considered as symbol of approval and token of acknowledgement then let the words play the heralding role of expressing my gratitude. I am deeply indebted to my guide Ms. Chama R. Chandran, Assistant Professor, Electrical and Electronics Department, SBCE, Pattoor, for guiding me through the difficult phases of my thesis and inspiring me during each stage of the work. REFERENCES [1] Austin Hughes, Electric Motors and Drives, Elsevier Publications, New Delhi, 2001. [2] F. Antritter, P. Maurer, and J. Reger, Flatness based control of a buck converter driven DC motor, in Proc. 4th IFAC Symp. Mechatron. Syst., Heidelberg, Germany, Sep. 12 14, 2006, pp. 36 41. [3] N. K. De, P. K. Sen, Electric Drives, Prentice Hall of India Pvt. Ltd., New Delhi, 1999. [4] Ned Mohan, et al., Power Electronics: Converters, Design and Applications, Wiley. [5] Shashi Bhushan Kumar, Mohammed Hasmat Ali and Anshu Sinha, Design and Simulation of Speed Control of DCMotor by Fuzzy Logic Technique with Matlab/Simulink, International Journal of Scientific and Research Publications, Volume 4, Issue 7, July 2014. @IJMTER-2016, All rights Reserved 326