Sliding Mode Control of Boost Converter Controlled DC Motor

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1 Sliding Mode Control of Boost Converter Controlled DC Motor Reshma Jayakumar 1 and Chama R. Chandran 2 1,2 Member, IEEE Abstract Nowadays automation of industries are increasing, with the rapid development of technology. Thus, with the increase in automation, the operational characteristics of the motors must be improved. In order to increase these characteristics, efficient controllers must be designed for the motors. This paper introduces a robust controller known as Sliding Mode Controller. Here Sliding Mode Controller (SMC) along with boost converter is used to control the speed of the DC motor. Simulation of DC motor, boost converter and SMC were all carried out in MATLAB SIMULINK. Keywords DC Motor, dc/dc boost converter, SMC, MATLAB SIMULINK. I. INTRODUCTION DC drives are widely used in applications requiring adjustable speed, good speed regulation and frequent starting, braking and reversing. Some important applications are rolling mills, paper mills, mine winders, hoists, machine tools, traction, printing presses, textile mills, excavators and cranes. Although, since late sixties, it is being predicted that AC drives will replace DC drives, however, even today the variable speed applications are dominated by DC drives because of lower cost, reliability and simple control [1]. Conventionally, DC motors were driven by Pulse Width Modulation (PWM) technique where the PWM signals are given to the motor input voltage. But, due to the hard switching strategy of the PWM causes variations in voltage and current. Thus DC/DC power converters are used to control the DC motor. Based on the applications, these converters are of various types. Here DC/DC boost converter is employed. DC/DC power converters are non linear due to the presence of non linear elements (such as R, L C) and time variant systems [2]. These converters produces disturbance during large parameter variations, operating point variations and load variations. Also control of boost converter is difficult as compared to a buck converter. Thus in order to achieve the required speed, sliding mode control can be used. SMC is a non linear control technique so as to improve the performance of the drive as required. In SMC, the load is always kept constant irrespective of change in line voltages and parameters. Good dynamic response, simple implementation, stability, robustness, disturbance rejection and insensitive to parameter variations are some of the merits of SMC [3]. II. OVERVIEW A. DC Motor The principle of speed control for DC motors is developed from the basic emf equation of the motor V e ia Ra (1) where, V = applied armature voltage e = induced emf i a = armature current R a = armature All rights Reserved 309

2 Torque, flux, current, induced emf and speed are normalized to present the motor characteristics [4]. Relation of flux and speed on induced voltage is given by e K e e V iara Speed, m f if if Thus, there are two types of control available for DC motor. They are namely armature control and field control. These methods are combined to yield a wide range of speed control. Here, armature control is used in order to vary the speed which are below the rated speed. In armature control field current is maintained constant. Then, equation (1) becomes m (V iar a ) Hence, varying applied voltage changes speed. Armature control has advantage of controlling the armature current swiftly, by adjusting the applied voltage. B. Boost Converter f m Fig. 1. Circuit diagram of Boost converter Boost converter is basically a switch mode DC/DC power supply in which output voltage is greater than the input voltage. In the ON state, the switch S (from fig. 1) is closed, resulting in an increase in the inductor current. Then, by KVL E e L And by KCL, di E L dt i c i o dv v C dt R In the OFF state, the switch is open and output side will have the source voltage as well as the discharging inductor voltage. Hence in OFF state, the two voltages aids giving an increase in output voltage. C. Sliding Mode Control A sliding mode control is non linear and can be applied to a linear or non linear plant. As the name indicates, the drive response is forced to tract or slide along a predefined trajectory or reference model irrespective of plant s parameter variation and load disturbance [5]. SMC is a variable structure control system (VSS) where structure or topology of control is intentional varied to stabilize the control and make its response robust. The motion of the system trajectory along a closed path in state space All rights Reserved 310

3 called the sliding mode and the controller designed with the aim to achieve the sliding motion is called sliding mode controller. The path which is chosen for the system to slide is called the sliding surface [6]. Fig. 2. Sliding regime Design of sliding mode controllers consist of two parts namely, first one is to design a sliding surface so that the sliding motion satisfies the design specifications. Second one is the selection of control law. Switching line is represented as x2 cx1 0 The important property of the phase trajectory is that once the system is close to the switching line, the control law ensures that system does not divert from the switching line as shown in fig. 2. At this stage the system becomes a stable system. From fig. 1there are zig zag paths on the switching line. These are due to a phenomenon known as chattering. In ideal situation, it is a straight line along the switching line. Chattering occurs due to no idealities of the switching devices which causes high frequency oscillations in the output. In practical situation, chattering cannot be eliminated. D. Simulation Results Fig. 3. Simulink model of DC motor boost converter All rights Reserved 311

5 Fig. 7. Simulation result of voltage of fig. 6. Fig. 8.Simulink model of speed of motor in fig. 6. From fig. 4 and 7 it is clearly seen that the voltage has been controlled and thus the speed alsoas shown in fig. 5 and 8. III. CONCLUSION Unlike the traditional controllers where the dynamic performance is limited, the sliding mode control is one of the best method for the analysis of non linear systems. SMC is robust, stable for even very large line and load variations, good dynamic response and simple implementation. IV. ACKNOWLEDGMENT If words are considered as symbol of approval and token of acknowledgement then let the words play the heralding role of expressing my gratitude. First of all I would thank almighty for giving me the strength to carry out my work. 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 All rights Reserved 313

6 REFERENCES [1] Gopal K. Dubey, Fundamentals of Electrical Drives, Narosa Publishing House Pvt. Ltd., New Delhi, [2] F. Antritter, P. Maurer, and J. Reger, Flatness based control of a buckconverterdriven DC motor, in Proc. 4th IFAC Symp.Mechatron. Syst.,Heidelberg, Germany, Sep , 2006, pp [3] Z. Chen, J. Hu, and W. Gao, Closed-loop analysis and control of anon-inverting buck-boost converter, Int. J. Control, vol. 83. no. 11, pp , Nov [4] R. Krishnan, Electric Motor Drives: Modelling, Analysis and Control, PHI Learning Pvt. Ltd., New Delhi, [5] Bimal K. Bose, Modern Power Electronics and AC Drives, Prentice Hall, USA, [6] G. Spiazzi, P. Mattavelli, L. Rossetto, L. Malesani, Application of Sliding Mode Control to Switch Mode Power Supplies, Journal of Circuits, Systems and Computers (JCSC), Vol. 5, No. 3, September 1995, All rights Reserved 314

INTERNATIONAL JOURNAL OF ENGINEERING SCIENCES & RESEARCH TECHNOLOGY

[Sarvi, 1(9): Nov., 2012] ISSN: 2277-9655 IJESRT INTERNATIONAL JOURNAL OF ENGINEERING SCIENCES & RESEARCH TECHNOLOGY A Sliding Mode Controller for DC/DC Converters. Mohammad Sarvi 2, Iman Soltani *1, NafisehNamazypour