CHAPTER 1INTRODUCTION 1.1 IntroductionRecently, controlled AC drives have been extensively employed in various high performance industrial applications. This has been conventionally achieved by using DC drives with their simple control structure. AC machines are generally inexpensive, compact and robust with low maintenance requirements compared to DC machines but require complex control. However, recent advances in power electronics, control techniques and signal processing have led to significant developments in AC drives. Permanent Magnet Synchronous Motors (PMSM) are increasingly replacing traditional DC motors in a wide range of applications where a fast dynamic response is required. A Permanent Magnet Synchronous Motor (PMSM) is a synchronous motor that uses permanent magnets to produce the air gap magnetic field rather than using electromagnets. By the replacement of electromagnets with permanent magnets the permanent magnet synchronous motors had many advantages such as high efficiency, high torque to inertia ratio and efficient heat dissipation. The replacement of the rotor winding with PM in PMSM makes it compact structure or smaller in size that results a high power density. The heat loss in the rotor of PMSM that affects the machine operation is also negligible. Because of the above mentioned advantages this motor is extensively used in many applications such as electric vehicles, robotics, automation, hard disk drives etc. In PMSMs, the magnets can be placed in different ways on the rotor. Depending on the placement they are called either as Surface mounted Permanent Magnet Motor or Interior Permanent Magnet Synchronous Motor.As the shape of the induced E.M.F in permanent magnet synchronous motor is sinusoidal it has less torque ripples. The speed control of the PMSM can be achieved by using the scalar and vector control techniques or field oriented control technique (FOC). The problem with scalar control is that motor flux and torque in general are coupled. This inherent coupling affects the response and makes the system prone to instability if it is not considered. By using the vector control technique, separately excited DC motor like characteristics can be obtained from the PMSM which are most desirable for some specific applications. That means we can control the flux and torque of the PMSM independently. Vector control offers attractive benefits including wide range of speed control, precise speed regulation fast dynamic response, lesser torque ripples, and operation above speed etc.

1.2 Literature SurveyR.Krishnan[1] introduced the permanent magnet materials, characteristics and applications of permanent magnet materials in motors. The properties of the permanent magnet material affects directly the performance of the motor and proper knowledge is required for the selection of the materials and for understanding PM motors. Based on the location of the permanent magnets, two types of PMSM motors are available, they are Surface mounted Permanent Magnet Synchronous Motor and Interior Permanent Magnet Synchronous Motor. P. Pillay and R. Krishnan [2] discussed the working principle of PMSM and their torque, e.m.f equations. The applications of PMSM in various fields are given. Pragasen Pillay and R. Krishnan [3] discussed modeling of PMSM. The modeling of PMSM includes both state-space modeling and Transfer function modeling.Erwan Simon [4] presented the control techniques of PMSM. The implementation of Scalar control and Vector control techniques for PMSM are discussed. The idea of Field Oriented Control method is to control the current of the machine in space quadrature with the magnetic flux created by the permanent magnets as in the case of DC motors.Zheng-Guang Wang, Jian-Xun Jin, You-Guang Guo, and Jian-Guo Zhu [5] described the implementation of space vector pulse width modulation (SVPWM) technique for PMSM. Space Vector Modulation (SVM) was originally developed as vector approach to Pulse Width Modulation (PWM) for three phase inverters. It is a more sophisticated technique for generating sine wave that provides a higher voltage to the motor with lower total harmonic distortion.Bon-Ho Bae,Seung-Ki Sul, Jeong-Hyeck Kwon,Ji-Seob Byeon[6] discussed the sensorless control of PMSM. The advantages and disadvantages with the Sensorless control are discussed in detail.Yuchao Shi, Kai Sun, Lipei Huang, and Yongdong Li [7] given various types of Sensorless control techniques. Back- EMF based and signal injection based methods of state estimation techniques are discussed in detail. The problems with the estimation and the procedure to overcome the problems are also discussed. Ambarisha Mishra, Vasundhara Mahajan, Pramod Agarwal and S.P.Srivastava[8] discussed the MRAS based state estimation technique for the PMSM. MRAS computes the desired state using two different models. (i.e. reference and adjustable models). The error between the two models is used to estimate unknown parameters. The stability of closed loop estimator is achieved through popovs hyperstability criterion.Sakorn Po-ngam[9] presented the designing of speed controller for PMSM. The designing of proportional-integral (PI) and fuzzy logic controller are given in detail. Various types of tuning procedures for the PI controller are given. Ziegler and Nichols tuning method for the PI controllers is discussed in detail.

1.3 Problem formulationTo implement the vector control technique for PMSM drives, the speed and position information of the rotor are required. Hall Effect sensors, optical encoders and resolvers are used to detect the rotor speed. However, these sensors impair the ruggedness, reliability and simplicity of the PMSM. Moreover, they require careful mounting and alignment and special attention is required with electrical noises. Speed sensor needs additional space for mounting and maintenance and hence increases the cost and the size of the drive system. Moreover, using a speed sensor in a hostile environment like chemical industries is not practical. To overcome the above difficulties, it is always encouraged to eliminate the mechanical sensors in electrical drive applications through alternate approaches, namely estimation techniques. In sensorless PMSM drive the speed and rotor position of the rotor are estimated rather than measured. Such control reduces the drive's cost, size and maintenance requirements while increasing the system's reliability, robustness and noise immunity. Model Reference Adaptive System based state estimation technique is proposed to use to estimate the speed and rotor position.

1.4 Objective of the thesisThe main objective of this thesis is to estimate the speed and rotor position of the PMSM using the model reference adaptive system (MRAS) technique. The basic ideas of the work are summarized as follows:1. Designing the mathematical model of the PMSM.2. Implementing space vector pulse width modulation (SVPWM) technique for a three phase bridge inverter.3. Designing of the speed controller for PMSM drive.4. Implementing the MRAS technique to estimate the speed and rotor position of PMSM drive.5. Implementing the model in Real time environment.

1.5 Organization of the thesisThe organization of this project is set to five chapters as followsChapter -1 includes introduction about the project, problem formulation and the objective of the thesis.The detailed mathematical modeling of the PMSM is explained in Chapter-2. The operation of the PMSM and the vector control of the PMSM are also explained in Chapter-2. The complete transfer function of the PMSM drive is also derived in this chapter. Various types of PWM techniques are given and mainly focused on the space vector pulse width modulation technique. The advantages of SVPWM technique compared to the other PWM techniques such as SPWM are also summarized. The major subject treated in this thesis is described in the Chapter-3, i.e. the Model reference adaptive system based state estimation. Different types of estimation techniques are listed and the problems associated with the estimation techniques are discussed. The mathematical equations of the reference model, adjustable model and adaption mechanism are given. Development of control strategy for PMSM drive is also discussed in this Chapter. Designing of the PI controller and Ziegler & Nichols tuning methods are explained. The MATLAB simulation results and discussions are given in Chapter-3. Chapter-4 deals with the real time simulation. The advantages with the real time simulation are given. The procedure to convert the model from MATLAB to real time is explained. Real time simulation results & discussions are given in Chapter-4. The simulation results are observed for constant load, step change in load and during speed reversal conditions. The final concluding comments of the thesis are given in the Chapter- 5 and it also gives some suggetions for further work which would be possible due to the knowledge acquired during this study. 4