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
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.
· 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
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.
CONCLUSION AND FUTURE SCOPE
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. was helpful in developing a rotor eccentricity harmonic based speed estimation that has been established as a reliable method for speed estimation.