# Speed sensor-less control of induction machine based on carrier signal injection and smooth-air-gap induction machine model

Abstract (Summary)

iii
The standard induction machine model will lose its observability at DC excitation,
so the rotor speed can not be estimated if only based on the fundamental frequency
variables. Many speed estimation methods that are still effective at DC excitation either
use second order effects or require modification of the rotor structure of the induction
machine. This thesis presents one speed estimation scheme that can work at fundamental
DC excitation based on the standard smooth-air-gap induction machine model and
carrier signal injection.
The carrier signals used for speed estimation are selected to rotate in the opposite
direction of the fundamental frequency signals at a sufficiently high frequency, so even if
the fundamental exciting frequency is zero, the rotor speed can still be estimated based
on the injected carrier signals.
In the stator flux reference frame, the locus of steady-state stator currents as
a function of rotor speed is a circle. Using the difference between the stator current
and the center of this locus as an auxiliary vector, we can define a correction term for
the rotor speed as the cross product of the vector based on measured stator current,
which is related with the actual rotor speed, and the estimated stator current vector,
which is related to the estimated rotor speed. The stability of the scheme is analyzed
using the two-time-scale method and classic control stability theory. This estimation is
implemented in the stator flux reference frame of the carrier frequency. The estimated
rotor speed is then used in the torque controller, which is at fundamental frequency.
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Simulation and experiments are carried out on a 3-phase, 4-pole induction machine
rated at 1.5 HP, 60 Hz, 230 V line-line, and 4.7 A to verify the feasibility of the scheme.
The carrier signal will tend to cause torque ripple. The magnitude of the carrier
signal can be selected relatively small compared to the fundamental frequency signals
to minimize the ratio of the torque ripple to the rated torque. However, one can use
different methods to reduce or even eliminate this torque ripple. Experimental results
are given to illustrate these ideas.
Bibliographical Information:

Advisor:

School:Pennsylvania State University

School Location:USA - Pennsylvania

Source Type:Master's Thesis

Keywords:

ISBN:

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