Partial State Feedback Control of Induction Motors with Magnetic
Saturation: Elimination of Flux Measurements

Abstract

In this paper, we present a singularity-free, rotor position tracking controller for the full order, nonlinear dynamic model of the induction motor that includes the effects of magnetic saturation. By utilizing the pi-equivalent saturation model, we design a observer/controller strategy that achieves semi-global exponential rotor position tracking and only requires stator current, rotor velocity, and rotor position measurements. Experimental results are included to demonstrate the efficacy of the proposed algorithm.

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, which includes saturaion effects, to obtain rotor position tracking.The control algorithm requires measurement of rotor position, rotor velocity, and stator currents.

Approach:

In order to account for the lack of stator/rotor flux measurements in the control development, we first design closed-loop observers for the stator and rotor flux signals utilizing rotor position, rotor velocity, and stator current measurements. A preliminary Lyapunov analysis is then utilized to analyze the stability of the observers while also providing motivation for the structure of the observers. We then design the desired stator and rotor flux trajectory signals in order to promote rotor position tracking and rotor flux tracking despite the lack of stator and rotor flux measurements. The voltage input signal is then designed to promote stator flux tracking. Finally, a composite Lyapunov-type stability analysis is performed to examine the stability of the overall closed-loop observer/controller system.

The Experimental Setup:

An experiment was conducted on a 0.25 hp, three phase, wound rotor induction motor (Lab-Volt, Serial JR) equipped with three slip-rings on the rotor shaft, which allowed for rotor current measurements. Six Hall effect sensors (Microswitch, Model CSLB1AD) were used to measure the stator and rotor phase currents. Three linear voltage amplifiers (Techron, Model 7570-60) were used to apply the stator voltage inputs to the induction motor. The rotor position was measured using a 10,240 line shaft-mounted encoder (BEI Inc.). To obtain the rotor velocity signal, a backwards difference algorithm was applied to the rotor position signal with the resulting signal being passed through a second-order digital filter. A QNX based real-time Photon-windows environment developed in-house serves as the user-interface required to implement the control algorithm. The control algorithm was written in the C++ programming language, compiled, and executed on a Pentium II processor thus eliminating the need for a separate DSP board. The sampling frequency was selected to be 1500 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 and read in the three phase currents and the rotor position. We note that the rotor current measurements were used only for determining the saturation characteristics of the induction motor and are not required for implementation of the proposed control algorithm.

The Mechatronics Workstation - Union Camp Laboratory

Some Experimental Results:

Select and click to view some of the experimental plots:



Publication:

For more information concerning this research, please refer to the following publication:

A. Behal, M. Feemster, D. M. Dawson, and A. Mangal, "Partial State Feedback Control of Induction Motors with Magnetic Saturation: Elimination of Flux Measurements,'' Proc. of the American Control Conference, Chicago, IL, pp. 1582-1586, June 2000.