Fuzzy Logic Versus PI Speed Control in High-Performance AC Drives: A Comparison

Abstract

A frequently discussed application of artificial intelligence inmotion control is the replacement of a standard Proportional Plus Integral (PI)speed controller with a fuzzy logic (FL) speed controller. A common conclusionthat emerges from such studies is that the FL control provides superior performance. However, such a conclusion usually is based on a limited simulation and/or experimental study. It appears that a thorough comparison of the drive behavior under PI and FL speed control, using simulations and an experimental rig, is still missing. This paper attempts to provide such an in-depthcomparison of the operation of a vector-controlled permanent magnet synchronous motor. Speed responses under PI and FL speed control are at first simulated and then measured on the experimental rig for a variety of operating conditions. Twodifferent machines are used in simulation and experimentation, enabling a better generalization of the results. The transients studied include response to a large step speed command from standstill with nominal inertia and an increased inertia, response to a small step speed reference change, response to a step load torque application, and a reversing transient. The transient behavior is examined for various initial speed settings, so that a thorough comparison is enabled. It is shown that superiority of the FL speed control is much less pronounced than it is often portrayed in literature on the basis of limited comparisons. Indeed, in a number of cases PI speed control provided a superior speed response. Predictions obtained by simulations and experimental results are found to be in reasonable agreement, considering all the differences between the simulation and experimental study.