SPEED SENSOR-LESS CONTROL OF INDUCTION MACHINE BASED ON CARRIER SIGNAL INJECTION AND SMOOTH-AIR-GAP INDUCTION MACHINE

Open Access
Author:
Wang, Guanghui
Graduate Program:
Electrical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
October 22, 2004
Committee Members:
  • Heath Hofmann, Committee Chair
  • Jeffrey Scott Mayer, Committee Member
  • Constantino Manuel Lagoa, Committee Member
  • Christopher Rahn, Committee Member
Keywords:
  • Induction machine
  • Speed Sensor-less
  • Control
Abstract:
This thesis presents a speed sensor-less control scheme of induction machine based on carrier signal injection and standard smooth-air-gap induction machine model. 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. Speed estimation methods that are still effective at DC excitation either use second order effect or require modification of the rotor structure of the induction machine. This thesis will propose one speed estimation scheme that can work at DC excitation based on carrier signal injection. There are different ways to inject the carrier signals, but the carrier signals used for speed estimation are selected rotating at the opposite direction of the fundamental frequency signals at a non-trivial frequency, so even 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 stator currents is a circle. Using the difference between the stator current with the center of the locus as an auxiliary vector, we can define the derivative of the rotor speed as the cross product of the measured vector which is explicitly related with the rotor speed and the estimated vector which is not explicitly related with the rotor speed. The stability of the scheme is analyzed with two-time-scale method and classic control stability theory. This estimation is implemented in the carrier frequency stator flux reference frame. The estimated rotor speed is then used in the torque controller which is at fundamental frequency. Simulation is carried out to verify the validity of the scheme. Experiments are implemented on a 3-phase 4-pole induction machine rated at 1.5 HP, 60 Hz, 230 V line-line and 4.7 A. It is shown that the proposed scheme can estimate the rotor speed even at DC excitation. In the experiment for basic rotor speed estimation and torque control, the carrier signals are injected directly to the fundamental frequency voltage commands and this will cause torque ripples. The magnitude of the carrier signals can be selected relatively small compared to the fundamental frequency signals to minimize the ratio of the torque ripple with the rated torque. Or we can use different carrier signal injection method to reduce or even eliminate the torque ripples. Experimental results are given to illustrate these ideas.