An Improved Indirect Field Oriented Controller for the Induction Motor
With regard to the use of a given control strategy, industrial firms are primarily concerned with the controller's: i) reliability, ii) performance, iii) cost of implementation, iv) and practicality. As evidenced by its extensive industrial use, the indirect field oriented control (IFOC) scheme for the induction motor provides a solid standard by which many other algorithms are compared. Over the last ten years, a large amount of induction motor research, many schemes with an IFOC-like control strategy at the core of the controller, have been developed to examine the induction motor control problem from a nonlinear control perspective as opposed to a more classical motor control perspective.
In this research, we illustrate how the standard indirect field oriented controller (IFOC) commonly used in current-fed induction motor drives can be modified to achieve global exponential rotor velocity/rotor flux tracking. In spite of the controller's popularity, the indirect field oriented control scheme has, until recently, lacked a clear, mathematical analysis of closed-loop system stability. Hence, we wish to illustrate the global exponential rotor velocity/rotor flux tracking result through a structured Lyapunov stability analysis.
The modifications to the IFOC scheme, which involve the injection of nonlinear terms into the current control input and the so-called desired rotor flux angle dynamics, facilitate the construction of a standard Lyapunov stability argument. The construction of a standard Lyapunov exponential stability argument allows one to easily design adaptive controllers to compensate for parametric uncertainty associated with the mechanical load.
The Experimental Setup:
Experiments were conducted on a three phase induction motor (Baldor Electric Co., Model M3541) powered by three linear amplifiers (Techron, Model 7570-60) to compare the performance of the standard IFOC scheme to that of the improved IFOC scheme in a simple rotor velocity tracking application. The rotor position was measured using a 10,240 line shaft-mounted encoder (BEI Inc.). The rotor velocity was obtained using a backwards difference algorithm applied to the rotor position signal with the resulting signal being passed through a second-order digital filter. The control algorithm was computed on a Pentium processor running under the QNX operating system at a sampling frequency of $2000 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.
Some Experimental Results:
Select and click to view some of the experimental plots:
Publication:For more information on this research, please refer to the following publication:
A Behal, M. Feemster, D. M. Dawson, and D. Haste, "An Improved Indirect Field Oriented Controller for the Induction Motor," Proceedings of the IEEE Conference on Control Applications, Kohala, HI, August 1999, pp. 1084-1089.