1 CHAPTER 1 1.1 Motivation INTRODUCTION Permanent Magnet Brushless DC (PMBLDC) motor is increasingly used in automotive, industrial, and household products because of its high efficiency, high torque, ease of control, and lower maintenance. The Brushless DC (BLDC) motor is designed to utilize the trapezoidal back Electro Magnetic Force (EMF) with square wave currents to generate the constant torque. The conventional BLDC motor drive is generally implemented via a six-switch, three phase inverter and three Hall-effect position sensors that provide six commutation points for each electrical cycle. Cost minimization is the key factor especially in a fractional horse-power BLDC motor drive for home applications. It is usually achieved by the elimination of the drive components such as power switches and sensors. Converters are designed for high efficiency, and they are good in maintaining the speed for variable torque. The switching losses are to be reduced and the power dissipation towards the switching techniques is analyzed and so a snubber circuit is implemented. Snubbers are used in electrical systems to reduce the transient across the device while switching ON/OFF the device. Voltage provided to the motor is fed by high side switch, so that its average value may be altered by changing the switch on period. To keep the average voltage across the motor constant, whatever may be the load condition it is affected by correcting the duty cycle. Efficient modelling of PMBLDC is given Lee et al (2001). PID control of brushless motor is given by Othman et al (2009), and four switch / reduced switch converters are given by Lee et al (2001). By using Interleaved Buck Converter (IBC) high power factor can be maintained, as given by Marcos Alonso et al (2008). Interleaved
2 Buck Converter having low switching losses and improved step down conversion ratio is discussed by Il-Oun Lee et al (2011). The above literature does not deal with IBC fed PMBLDC drive system. This thesis proposes IBC for the control of PMBLDC drive systems. 1.2 Problem Statement The aim of this research work is to propose an ideal converter for Permanent Magnet Brushless DC Motor. The analysis of PMBLDC motors are made with buck converter, buck converter with snubber circuit, interleaved buck converter with PI, PID and fuzzy logic control circuit. Whatever may be the load condition, the PMBLDC motor has to run in constant speed to achieve better performance. The fuzzy logic controlled interleaved buck converter maintains the speed of the PMBLDC in line. The proposed converter should be robust, stable, fault tolerant and should be able to exhibit transient and steady state response. 1.3 Solution to the Problem In this research work, analysis of converters for PMBLDC drive system is done with buck converter. The buck converter fed PMBLDC drive system is compared with and without snubber, similarly an interleaved buck converter fed PMBLDC motor drive is analyzed with PI, PID and Fuzzy logic controller. This work explores the possibility of using best, a more appropriate converter for PMBLDC motor drive system whatever may be the load condition, and the speed is maintained constant. Also the converter is made to focus on stability, fault tolerant and robustness.
3 1.4 Objectives of the Thesis The objectives of the research work are as follows: 1. To improve the efficiency of PMBLDC motor drive system using buck converter. 2. To simulate and compare the closed loop buck converter fed PMBLDC motor drive system with and without snubber. 3. To simulate interleaved buck converter fed PMBLDC motor drive system with and without input disturbance. 4. To simulate and compare the results of PI, PID and Fuzzy controlled interleaved buck converter fed PMBLDC motor drive system. 1.5 Methodology for Solving the Problem The effects of the conventional PMBLDC drive system are studied. Whenever there is a change in the load, the motor speed is varied. But most of the applications need to be run in constant speed, so whatever may be the change in the load condition. Whenever there is change in the load the converters are intended to maintain a constant voltage across the motor which is done by varying the duty cycle. For this purpose a buck converter is used for analysis. Then the analysis is extended with Buck converter following snubber circuits, interleaved buck converter with PI, PID and Fuzzy logic control circuit. Out of all the best performance is achieved by using fuzzy logic control circuit where the variation in the speed due to change in load is very less. The observations are verified by Matlab/Simulink based simulation.
4 1.6 Merits of the Proposed Work Depending upon the motor load, the motor input voltage should be maintained constant whatever may be the load condition. So a buck converter fed PMBLDC motor drive system is used. Now to have more advancement and efficient drive system, we are going to use interleaved buck converter system fed PMBLDC drive system. Mainly the PMBLDC drive system requires non-isolation and a good step down conversion ratio at high output current with low ripples. This necessitates the importance of IBC fed PMBLDC drive system. Now IBC with active clamp circuits is introduced; here all active switches are turned on with Zero Voltage Switching (ZVS). This creates high conversion ratio and the voltage stress across the freewheeling diodes can be reduced. When an IBC with two winding coupled inductors is introduced, it has the following advantages, since it operates at Continuous Conduction Mode (CCM), the current stress is lower than that of DCM IBC. The voltage stress is reduced in the semiconductor devices, maintains high power factor is maintained and switching losses are reduced and a high step down conversion ratio is attained. Based on the above discussion, the interleaved buck converter with PI, PID and Fuzzy logic control circuit are analyzed. Out of all the best performance is achieved by using IBC fed PMBLDC drive system with fuzzy logic control circuit where the variation in the speed due to change in load is very less. The observations are verified by Matlab/Simulink based simulation. Moreover, the proposed scheme is very easy to implement.
5 1.7 Thesis Organization The thesis is organized as follows: Chapter 1: INTRODUCTION. In this chapter, motivation of the research work, Problem Statement and Solution, Methodology for solving the Problem, Objectives and organization of the Thesis are presented. Chapter 2: LITERATURE REVIEW. In this chapter, the literature review conducted for the research work is presented. The literature reviews include surveys on PMBLDC motor drive system, buck converters, interleaved buck converters and fuzzy controlled PMBLDC drive systems. Chapter 3: PMBLDC MOTOR DRIVE SYSTEM. In this chapter, it deals with a review of PMBLDC motor, various power converter topologies and sensorless techniques are discussed. Chapter 4: BUCK CONVERTER FED PMBLDC DRIVE SYSTEM WITH AND WITHOUT SNUBBER. In this chapter, the basic principles of buck converter and the Matlab/Simulink based simulation of buck converter fed PMBLDC drive system are presented. Also the effect of the snubbers is introduced to the converter circuit. The Matlab/Simulink based simulation of Buck converter fed PMBLDC drive system with and without snubber is presented. The results of the drive system are compared with and without snubber. The simulation results are confirming the effect of the drive system with snubber are better and is presented. Chapter 5: INTERLEAVED BUCK CONVERTER FED PMBLDC DRIVE SYSTEM. This chapter deals with the details of interleaved buck converter fed PMBLDC drive system. Similarly interleaved buck converter fed
6 PMBLDC drive system with change in the input value is analyzed. The features, operation and simulation results of the interleaved buck converter fed PMBLDC drive system with variation in input results are presented in this chapter. The Matlab/Simulink based simulation of interleaved buck converter fed PMBLDC drive system with input disturbance is presented. Chapter 6: INTERLEAVED BUCK CONVERTER FED PMBLDC DRIVE SYSTEM WITH PI, PID AND FUZZY LOGIC CONTROL. Details of closed loop controlled interleaved buck converter fed PMBLDC drives system with PI, PID and Fuzzy Logic Control are discussed in this chapter. The basic theory of PI, PID and fuzzy logic control and the basic components of fuzzy logic based control system are presented. The Matlab/Simulink based simulation of interleaved buck converter fed PMBLDC drive system with PI, PID and Fuzzy logic Control are presented. The stability and robustness of the proposed control scheme are discussed. Chapter 7: CONCLUSION & FUTURE SCOPE. In this chapter, the conclusion of the research work and scope for the future work are presented.