Position Tracking of the Induction Motor without
Rotor Velocity or Rotor Flux Measurements

Background:

Due to its simplistic construction, low cost, and high reliability, the induction motor has long been industry's premiere workhorse for constant speed applications. However, as advances in nonlinear control techniques progress, the induction motor is slowly evolving into a high precision actuator. Precise control of the motor is complicated due to the following: i) the model dynamics are highly coupled and nonlinear in nature, ii) rotor flux measurements cannot be obtained in a cost effective manner, iii) and rotor velocity measurements are inherently noisy in nature thereby affecting the performance of a full-state feeback controller. Hence, extensive research is conducted to combat these difficulties.

Research Objective:

Our objective is to design a partial-state feedback, singularity free controller for the full-order, nonlinear dynamic model of an induction motor to obtain rotor position/rotor flux tracking. That is, we wish to obtain rotor position/ rotor flux tracking without measurement of rotor flux or rotor velocity (i.e., we only can measure stator current and rotor position).

Approach:

In the control development, we construct three nonlinear observers for stator current, rotor flux, and rotor velocity. We then develop a desired torque trajectory to achieve rotor position tracking that is based on the observed mechanical system. Desired rotor flux and stator current trajectories are then designed to ensure that i) the desired torque signal is conveyed to the mechanical subsystem, ii) the controller does not exhibit any control singularities, and iii) the square of the desired rotor flux magnitude tracks a strictly positive, smooth function. Finally, voltage control inputs are constructed to guarantee stator current tracking.

The Setup:

An experiment was conducted on a three phase induction motor (Baldor Electric Co., Model M3541) powered by three linear amplifiers (Techron, Model 7570-60) to test the performance of the proposed controller. The rotor position was measured using a 6,000 line shaft-mounted encoder (Gurley Inc.). A QNX based real time X-windows environment developed in-house serves as the user-interface required to implement the control algorithm. The control algorithm is computed on a Pentium processor thus eliminating the need for a separate DSP board. The sampling frequency was selected to be 1000 Hz. The MultiQ board (8 A/D, 8 D/A, and 6 encoder channels) manufactured by Quanser Consulting was used to output the three phase voltages to the induction motor.

The Mechatronics Workstation - Union Camp Laboratory

Some Experimental Results:

Select and click to view some of the experimental plots:



Publication:

M. Feemster, D. M. Dawson, P. Aquino, and D. Haste, "Position Tracking of the Induction Motor without Rotor Velocity or Rotor Flux Measurements," Proceedings of the Conference on Control Applications, Trieste, Italy, September 1998, pp. 36-40.