Torque Ripples Minimization In A Permanent Magnet Brushless DC Motor Using SVPWM Technique‎

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Overview

ABSTRACT

Permanent magnet brushless DC motors have the large applications because of its easiest control system and the highest efficiency. Industrial BLDC motor drives suffers from the ripples in the torque, due to which motor has more noise, vibrations and less efficient. To reduce the ripple, the Space Vector PWM (SVPWM) is implemented in BLDC drive. Space Vector PWM control method is implemented and it overcomes the disadvantages in PWM such as losses in switching of the converter, output harmonic content& provides better DC-bus voltages. In this paper BLDC motor with a PI controller fed by a PWM controlling (closed loop controller) converter and with SVPWM technique is presented. The SVPWM makes the drive less ripple in torque& more efficient. SVPWM technique enjoy an assortment of advantages such as high output quality and less THD. The Matlab/Simulink model of SVPWM method of the BLDC motor also presented.

 TABLE OF CONTENTS

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWLEDGEMENT

ABSTRACT

CHAPTER ONE

  • INTRODUCTION
  • BACKGROUND OF THE STUDY
  • PROBLEM STATEMENT
  • AIM AND OBJECTIVES OF THE STUDY
  • SIGNIFICANCE OF THE STUDY
  • RESEARCH QUESTION
  • SCOPE OF THE STUDY

CHAPTER TWO

LITERATURE REVIEW

  • REVIEW OF THE STUDY
  • ELECTRIC MOTOR
  • OVERVIEW OF DC MOTOR
  • PRINCIPLE OF DC MOTOR
  • TYPES OF ELECTRIC MOTORS

2.5.1  Construction of PMDC Motor

2.5.2  Operation of PMDC Motor

2.5.3  Circuit Diagram of PMDC Motor

2.5.4  Characteristics of PMDC Motor

2.5.5  Advantages and Disadvantages of the PMDC Motor

2.5.6  Applications of the PMDC Motor

  • THEORY OF OPERATION
  • PROPERTIES OF A DC MOTOR
  • WORKING PRINCIPLE OF A DC MOTOR
  • BRUSHLESS DC ELECTRIC MOTOR
  • CONSTRUCTION OF BLDC MOTOR
    • WORKING PRINCIPLE AND OPERATION OF BLDC MOTOR

2.10.2                       ADVANTAGES OF BLDC MOTOR

  • DISADVANTAGES OF BRUSHLESS MOTOR
  • APPLICATIONS OF BRUSHLESS DC MOTORS (BLDC)
  • Variations in construction of Brushless DC Motors (BLDC)
  • CONTROLLING A BLDC MOTOR
  • PARTS OF A DC MOTOR
  • HISTORICAL BACKGROUND OF AN ELECTRIC MOTOR
  • REVIEW OF RELATED STUDIES
  • CONTROL APPROACHES OF AN ELECTRIC MOTOR
  • REVIEW OF VARIOUS METHODS OF CONTROLLING THE SPEED OF ELECTRIC MOTOR
  • REVIEW OF BLDC MOTORS
  • PULSE WIDTH MODULATION

CHAPTER THREE

METHODOLOGY

  • INTRODUCTION
  • BLDC MOTOR MODELING
  • PI SPEED CONTROLLER
  • BLDCM WITH SVPWM SIMULINK MODEL

CHAPTER FOUR

4.0  SIMULATION RESULTS

CHAPTER FIVE

  • CONCLUSION
  • RECOMMENDATION
  • REFERENCES

CHAPTER ONE

  • INTRODUCTION

BLDC motor is supplied from the inverter in 120 degree mode. Due to the electronically Commutation in BLDC motor, the effective speed control is possible and it makes the BLDC is more superior in performance compared to DC brush motors and AC motors. Brushless DC motor (BLDC) has permanent magnet poles on the rotor. Brushless DC Motors have high efficiency, high power to torque ratio, low noise and better operating performances. BLDC motor is supplied from the converter to control of stator voltage and currents. Due to the electronically Commutation in BLDC motor, the effective speed control is possible and it makes the BLDC is more superior in performance compared to DC brush motors and AC motors. BLDC motors are widely used in hybrid electric vehicles (Yoon, 2005). The BLDC motor does not have brushes and commutator so losses are less and has a long lifetime. The control in supply voltage to the BLDC motors,3 phase bridge converters (Mondal et al., 2002) are used. Two phases of stator windings are provided supply and the third phase of the stator winding is isolated. The position of the rotor is decided by the two phases which are active. By knowing the rotor position, converter switching devices is turned on. Each switching device is turned on for every 60 degrees. Electronic commutation is happening with this process, So the Back-emf is induced in the stator. BLDC motors have better regulation because of their linear speed and torque characteristics compared to induction motors. So BLDC motors are more suitable for variable frequency drives, electrical vehicle and actuators for industrial robots applications etc.

Brushless DC motors have the large applications because of its easiest control system and the highest efficiency. The position of rotor is observed for every 60 degree interval. As the speed of the motor increases, then ripple frequency of torque ripple is also increases, which is undesirable. With ideal trapezoidal back EMF and rectangular currents, motor produces the constant torque. For one cycle of rotor position, there are six intervals each one having 60 degrees. In any one interval, two switches in ON position, i.e. two phases are in conduction. In consecutive interval also two phases are in conduction but only one phase is changing compared to first interval. So for every two consecutive commutation interval the conduction of current is changing from one phase to another phase. Due to the motor inductance, the motor current will take some finite time to rise and fall. During the commutation interval; all the three thyristers are in conduction, so commutation occurs. The conduction of current is changing from one phase to another phase six times. Six torque ripples are producing for every 3600. Torque ripples are existing due to the commutation. Due to the stator and rotor slots interaction, the motor has ripples in the torque. The Industrial BLDC motor drives suffers from the ripples in the torque, due to which motor has more noise, vibrations and less efficient. Modulation techniques will give the variable voltages by making the continuous signal into pulses. This will reduce the magnitude of harmonics and make the output waveform into a pure sinusoidal.

To reduce the ripple, the Space Vector PWM (SVPWM) is implemented in BLDC drive. Space Vector PWM control method is implemented and it overcomes the disadvantages in PWM such as losses in switching of the converter, output harmonic content& provides better DC-bus voltages. In this paper BLDC motor with a PI controller fed by a PWM controlling (closed loop controller) converter using SVPWM method is presented. The SVPWM makes the drive less ripple in torque& more efficient. The MATLAB/Simulink models of SVPWM method of the BLDC motor also presented. The space vector control method is best suitable for BLDC motor for reducing the torque ripple.

1.1                                             BACKGROUND OF THE STUDY

An electric motor plays a vital role in every sector of the industry, and also in a wide range of applications. There are a variety of types of electric motors are available in the market. The selection of these motors can be done based on the operation and voltage and applications. Every motor has two essential parts namely the field winding & the armature winding. The main function of field winding is to produce the fixed magnetic field, whereas the armature winding looks like a conductor which is arranged within the magnetic field. Because of the magnetic field, the armature winding uses energy to generate an adequate torque to make the motor shaft turn. Currently, the classification of the DC motor can be done based on the winding connections, which means how the two coils in the motor are connected with each other.

Motors are used in a wide range of applications, such as fans, power tools, appliances, electric vehicles, and hybrid cars.

Motors have many different working parts in order for them to continually rotate, providing power as needed. Motors can run off of direct current (DC) or alternating current (AC). For the purpose of this work, a permanent magnet brushless type of DC motor will be analyzed.

Brushless Direct Current (BLDC) motors are one of the motor types rapidly gaining popularity.  BLDC motors are used in industries such as Appliances, Automotive, Aerospace, Consumer, Medical, Industrial Automation Equipment and Instrumentation. As the name implies, BLDC motors do not use brushes for commutation; instead, they are electronically commutated. BLDC motors have many advantages over brushed DC motors and induction motors (Ki-Yong et al., 2016). A few of these are:

  1. Better speed versus torque characteristics;
  2. High dynamic response;
  3. Higher speed ranges;
  4. Long operating life;
  5. High efficiency;
  6. Noiseless

However, in a practical BLDC drive, since machine has both inductance and resistance, the stator currents are different from the ideal case and the currents reach to their final values with delay. In other words, circuit has a time constant. Therefore, the current ripple is produced by influence of the inductance and the torque ripple is affected by current ripple directly (Viswanathan et al., 2018).

The torque ripple generated in commutation period is the main drawback of BLDC motor which deteriorates the precision of BLDC motor (Viswanathan et al., 2018).Therefore, the torque ripple minimization or elimination is a considerable issue in BLDC motor drives.

Torque ripple is one of the most prevalent problems in BLDCM applications. The three primary sources of torque ripple generation in BLDCMs are cogging, reluctance, and mutual torques (Li et al., 2016). These torque ripples can be decreased by (a) choosing the suitable motor, (b) using the proper control techniques, or (c) doing both. If either the rotor magnets or the stator slots in a BLDCM have skewed one slot pitch, the impact of the first two torque components is considerably decreased. The torque ripple is reduced when the phase back-EMF waveform and phase current wave- form are entirely matched. However, when uneven magnetization and improper windings are considered, the exact matching of phase back EMF and phase current is problematic (Lin et al., 2011). A three-phase inverter is required to power the motor, and the commutation is done electronically.

Torque ripple is the major disadvantage of BLDC motor used in industrial applications. The inverter control contains the harmonics and its cause to have torque ripple (Viswanathan and Jeevananthan, 2015). By using with hysteresis current control, non-ideal Back emf sensing, magnet segmentation, stator and rotor shape designs of Interior Permanent Magnet (Sun-Kwon et al., 2012) etc. methods are used to reduce the torque ripple content for the BLDC motor drive. Modulation techniques will give the variable voltages by making the continuous signal into pulses. This will reduce the magnitude of harmonics and make the output waveform into a pure sinusoidal. The space vector Pulse width modulation makes the motor less torque ripple compared to Sinusoidal pulse width modulation (Bech et al., 2011; Narayanan et al., 2008). The PWM & SVPWM methods are given improved performance for permanent magnet synchronous motors (Ting et al., 2015).

This paper presents the Matlab/simulation of SVPWM controlled BLDC motor models. The torque ripple analysis is made on this method. This method is reducing the torque ripple and total harmonic distortion in the output. The torque ripple reduction due to Sinusoidal pulse width modulation is presented.

1.2 STATEMENT OF THE PROBLEM

An electric motor is a device used to convert electricity into mechanical energy.. They operate using principles of electromagnetism, which shows that a force is applied when an electric current is present in a magnetic field. This force creates a torque on a loop of wire present in the magnetic field, which causes the motor to spin and perform useful work.

Torque ripple is a critical concern in many applications where low acoustic noise, high efficiency, or friendly human-machine interactions are highly demanded. In the automotive industry, electrical power steering systems are being developed to replace the traditional hydraulic systems, where an electric motor is used as the actuator. In such a system, the motor shaft is connected to the steering wheel through a gearbox. Therefore, the motor torque pulsation must be small enough so that the driver would not be able to feel it.

Permanent magnet (PM) brushless dc motors have been widely used for their ease of control. However, a drawback of this type of machine, which limits their applications, is the characteristic torque ripple caused by the commutation of current from one phase to another, nontrapezoidal back-emf, and cogging. Therefore, as a candidate for electrical power steering actuator, this type of motors cannot be practically applied until the torque ripple problem is solved. Much research has been performed to analyze and reduce the torque ripple of PM brushless dc motors. Some have considered the torque ripple problem mainly from a design aspect, such as (Waikar et al., 2018), while others have emphasized drive and control aspects, such as (Caricchi et al., 2019 and Krishnan et al., 2018). However, a phenomenon observed from experimental test data of a PM brushless dc motor, which is believed design related, has not been addressed by existing research. Experimental measurement of the torque of the motor (Sunil et al., 2019) at low speed showed unexpected dips on the ripple of the torque waveform as a function of rotor position. The cause of such unexpected behavior is a serious concern for machine designers, especially in applications where torque ripple is critical. Recognition of the formation mechanism of the dips is undoubtedly the first step in determining whether anything, such as to control the magnitude or the position of the dip by changing design parameters either in geometry or materials, can be done in the machine design to reduce net torque ripple.

SVPWM is a powerful and economical approach to characterize the torque ripple of a given design without hardware prototyping, and makes it easy to change parameters to run different design scenarios.

1.3 AIM AND OBJECTIVES OF THE STUDY

The aim of this work is to carry out a study on torque ripples minimization in a permanent magnet brushless dc motor using SVPWM technique‎. The objectives of the study are:

  1. To determine how torque ripple in brushless DC motors can the reduced
  2. To study the causes torque ripple in BLDC motor
  • To generate torque and EMF equation of permanent magnet brushless DC motor
  1. To carry out a simulation approach using MATLAB/ SIMULINK for torque ripple minimization of BLDC motor that led to effective reduction of the torque ripple using SVPWM

1.4 SIGNIFICANCE OF THE STUDY

This study will expose the student involved to the operation of a permanent magnet brushless dc motor, its working principle, applications and the meaning of torque ripples in a permanent magnet brushless dc motor

This study will serve as a means of learning how torque ripple can be minimize in a permanent magnet brushless dc motor thereby improving the system performance thus making it suitable for various application.

This control method used in this study improves the system performance thus making it suitable for immense applications employing electromechanical actuators.

1.5 RESEARCH QUESTIONS

  1. How can we reduce torque ripple in brushless DC motors?
  2. How can we reduce torque ripple in motor?
  • What causes torque ripple in BLDC motor?

1.6      SCOPE OF THE STUDY

The scope of this work covers the study of a permanent magnet Brushless DC motor and  the analysis of SVPWM control technique by employing two phase connection mode applied to Brushless DC motor (BLDC) drive with a view to reduce torque ripple. The work includes MATLAB/ SIMULINK results of conventional hysteresis current PWM and the proposed SVPWM approach. The simulation results reveals that the SVPWM technique is effective in reducing the torque ripple and THD of current.

CHAPTER FIVE

5.0                          CONCLUSION AND RECOMMENDATION

5.1      CONCLUSION

BLDC motor torque pulsations are generated by unnecessary torque pulsations in the drive, which causes oscillations in the motor speed and resonances in the motor, resulting in noise and vibration. There is a ripple in the torque produced by brushless DC motors (BLDCM) when switching-in and switching-out occurs in different phases. It would be possible to reduce ripple in the communication torque if the slew rates were the same.

Torque ripple minimization of BLDC motor using direct torque control has been implemented successfully and it is compared with ordinary speed control technique.

The performances of BLDC motor are observed by MATLAB/ simulation. With the help of modulation techniques, the torque ripple reduces to some extent. With the proposed SVPWM, the torque ripple still reduced to 14%. The SVPWM is taking less current during speed control and the utilization of DC supply effectively. The speed curve is taking less time to settle and has low oscillations in SVPWM. This result SVPWM is the best suited method to control the converter supply to the BLDC motor.

5.2 RECOMMENDATION

The study has been carried out successfully and the obtained results show the good dynamic performance and reduced torque ripples in BLDC motor. The above results depict that the direct torque control is capable of controlling the torque instantaneously by using SVPWM technique. I hereby recommend that different method of torques ripples minimization should be used and compare the result with the result obtained in this study in the future research.

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