Real-Time Implementation of a Wavelet Based Speed Controller for Induction Motor Drives

This paper presents a real-time implementation of a wavelet-based multiresolution proportional-integral-derivate (PID) controller for accurate speed control of an induction motor drive under system uncertainties. A field oriented induction motor drive model is used to decouple the flux and torque components of the motor dynamics. The discrete wavelet transform is used to decompose the error signal between the actual and estimated speed into different frequency components at various scales. The wavelet-transformed coefficients of different scales, which represent many underlying phenomena such as process dynamics, measurement noise, and effects of external disturbances, are scaled by its respective gain and then added together to generate the control signal. The performance of this newly devised wavelet controller is evaluated by simulation results as well as by experimental results. The complete vector control scheme incorporating the proposed controller is successfully implemented in real-time using the DS1102 digital signal processor board for the laboratory 1-hp induction motor. In order to prove the superiority of the proposed controller over the conventional controllers, a comparison between the proposed and the conventional proportional-integral (PI) controller based systems is made at different dynamic operating conditions.

I. INTRODUCTION

Induction motor (1M) drives are used in a multitude of industrial and process applications requiring high performances. The indirect field-oriented control methods have been widely used in industry for high performance control of 1M drives. The field-oriented technique is easy to implement and is independent of machine terminal conditions [1]–[2]. The control performance of the 1M drives can be influenced by the system uncertainties such as mechanical parameter variations, external load disturbance, unstructured uncertainty due to non-ideal field orientation in transient state, and unmodeled dynamics in practical applications. Much research has been done in recent years to apply various approaches in order to avoid the effect of system uncertainties in closed loop controlled 1M drives. The PI and PID controllers have been widely used in industry due to their simple control structure, ease of design, and inexpensive cost [3]. However, the fixed-gain PI and PID controllers are very sensitive to step change of command speed, parameter variations, load disturbance, etc. Thus, the controller parameters have to be continually adapted before being transferred to the process under control [4]. Researchers have tried to solve the problem by several adaptive control techniques such as intelligent control [5], model reference adaptive control (MRAC) [6], sliding mode control (SMC) [7], variable structure control (VSC) [8], and self-tuning PI controllers [9].