ABSTRACT
Sensorless speed
estimation of induction motors
using parameter and non-parameter based
approaches and themerits and demerits of different techniques have been presented.
This formed thebasis for the work on improved observer based speed estimation
developed. The earlier work by Pradhyumnan was helpful in developing a rotor eccentricity
harmonic based speed estimation that hasbeen established as a reliable method
for speed estimation. However due to advances in both digital
technology andpower semiconductor devices, ac drives have become more economical
and popular. For accurate torque controland precise operating speeds, more
sophisticated techniques are necessary in the control of ac motors. These
techniques
CHAPTER 1
CHAPTER 1
1.
INTRODUCTION
1.1Sensor less speed estimation of induction motor
Electric
motors for variable speed drives have been widely used in many industrial
applications. In the early years dc motors were widely used for adjustable speed
drives because of their ease of control.However, due to advances in both
digital technology andpower semiconductor devices, ac drives have become
moreeconomical and popular. For accurate torque controland precise operating
speeds, more sophisticated techniques are necessary in the control of ac motors.
These techniques employ high speed Digital Signal Processors and control
techniques based on estimation or identification of speed and other machine
states.Speed estimation is an issue of particular interestwith respect to
induction motor drives as the rotorspeed is generally different from the speed
of theirevolving magnetic field.Commercially available speed measurement devices
require direct contact with the shaft of the motor and are often inaccurate and
unreliable after prolonged use. The induction motor is controlled through field
orientation techniques that require knowledge of the rotor speed .Since speed
sensors decrease the reliability of a drive system (and increase its price), a
common trend in motor control is to use an observer to estimate speed.
1.2 SCOPE OF THE DISSERTATION
This research dissertation only
considers:
· Ac induction motors
· Three phase supply
· The application of Motor Current
Signature
Analysis
is limited to speed estimation only.
CHAPTER 2
APPLICATIONS
2.1 APPLICATION
·
Investigate
speed estimation using techniques that are dependant and those that are
independent on machine parameters Correction of one technique using the other
for greater accuracy
·
A torque
control system for induction motors is developed. The system allows for fast
and precise torque tracking over a wide range of speed.
·
The paper also
presents the identification and parameter estimation of an induction motor
model with parameters varying as functions of the operating conditions
encountered in hybrid electric vehicles applications.
·
An adaptive
sliding mode speed-flux observer is developed and a cascade of discrete time
sliding mode controllers is used for flux and current control.
·
The goal of
this research is the development of a sensor less torque control system for
hybrid electric vehicle applications.
·
2.2 OBSERVER BASED SPEED ESTIMATION
In this chapter the method adopted in
the design and development of the speed estimator is presented. The simulations
were done in SIMULINKusing a
model based on the stationary and synchronous reference frame equations of the
induction motor. The derivation of the observer equations is based onthe
coupled circuit dq equations of the motor. It is convenient to express the
machine equations in the stationary reference frame, as real-time measurements
of motor voltages as input and the rotor flux as state variables in the
calculation of the output. The equations are modified and expressed in the form
required for the observer, as
CHAPTER 3
RECENT SENARIO
3.1 IMPLEMENTATION OF SENSORLESS SPEED
ESTIMATION
The implementation of speed estimation
using the speed observer and fine-tuning it using MCSA is dealt with in this
chapter. This includes the experimental set-up and results. The experiments
were carried out on a 250W, 4pole, 3ph induction motor. The parameters of the
machine were determined from the no-load, blocked rotor and dc resistance
tests, which are given in Appendix
3.1.1 Experimental Set-up for Speed
Estimation
The experimental set-up for the speed
estimation is The quantities measured are used as inputs to
the observer and the MCSA algorithm for speed estimation. As shown in the block
diagram in Fig 4.1, the speed estimates were compared and the induction motor
parameters of the observer were tuned to follow the speed estimated using MCSA.
CHAPTER 4
CONCLUSION AND FUTURE
SCOPE
4.1 CONCLUSION
Sensor less speed estimation of
induction motors using parameter and non-parameter based approaches and the
merits and demerits of different techniques have been presented in the
literature survey. This formed the basis for the work on improved observer
based speed
Estimation developed in this thesis. The
earlier work by Pradhyumnan R.[8] was helpful in developing a rotor
eccentricity harmonic based speed estimation that has been established as a
reliable method for speed estimation.
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