Nonlinear Dynamics 23: 87–102, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands. Comparison of Quasi Bang-Bang and Sliding Mode Controls for a DC Shunt Motor with Time Delay * M. BIKDASH, V. KUNCHITHAPADAM, K. RAGUNATHAN, and A. HOMAIFAR NASA Autonomous Control Engineering Center, Department of Electrical Engineering, North Carolina A&T State University, Greensboro, NC 27411, U.S.A. (Received: 9 July 1999; accepted: 16 November 1999) Abstract. We propose a hybrid fuzzy-linear controller for a nonlinear terminal voltage-controlled DC motor. The nonlinearity includes the effect of magnetization saturation and a nonlinear fan load. The input to the proposed Fuzzy Logic Controller (FLC) is an ‘aggregate’ error between the required and the actual rpm and its time deriv- atives. The FLC is designed to approximate a bang-bang controller and its coefficients are chosen as a tradeoff between short rise time, small steady-state errors, and control chattering. The FLC performance was compared to that of a well-known design; namely a sliding mode controller with a boundary layer. Although the FLC design procedure is easier, the performance of the two controllers are quite similar. Unfortunately, the FLC design was not robust enough to counter the effect of large time delays introduced by the power electronics interface. Keywords: Fuzzy logic control, quasi bang-bang, sliding mode, hybrid fuzzy PID. 1. Introduction DC motors are easily controllable and have dominated the adjustable speed drive field. AC motors are more expensive to control and are used in drive systems where special features of AC motors, such as the absence of commutators and brushes are desirable [1]. Moreover, DC motors respond quickly to changes in control signals due to their high ratio of torque to inertia. Shunt motors are suitable whenever constant speed is needed at any pre-selected value or where an appreciable speed range is required. Most shunt motors operate from adjustable voltage supplies and do not need auxiliary starting equipment. A stabilizing winding helps prevent the speed from increasing as the load increases at weak field settings [2]. There are many methods of controlling the speed of a DC motor; one of them is using a thyristor. The armature voltage is adjusted by controlling the electrical angle within the AC wave at which the gate signal is applied to each thyristor or other power-electronics based voltage regulators. DC motors are competitive whenever a wide speed control range is needed. They are often used where they momentarily deliver three or more times their rated torque without stalling and also respond quickly because of their high torque-to-inertia ratio. The advent of Silicon Controlled Rectifiers (SCRs) has enlarged the scope of the technology for speed control of DC motors. SCR units for power control have made modern speed control units cheaper and more compact. Fetih et al. [3] investigated and analyzed the method of controlling the speed of a DC series motor using an integral-cycle controlled single triac and a bridge rectifier. Ramamoorthy and Illango [4] studied the transient response of the thyristor controlled DC series motor. * Contributed by Professor D. T. Mook.