A computer program is written in the PC environment to simulate a position control system using a brushless DC motor drive. This program features user friendly interfaces to set the simulation parameters and an online display of the controlled variables. A collection of statistical data is also provided. The calculation and graphical plots are developed with the MATLAB environment. The practical approach of using a discrete controller to control a continuous plant is adopted in the simulation. This program will be valuable for off-line system design and can be considered as a reference model for online tuning of the controller parameters for a host computer where this program is running. INTRODUCTION Brushless DC motors find more applications as motion actuators nowadays. However, simulation packages for them are quite scarce. Here, we describe a simulation package based on the MATLAB platform. For a position control system, in practical case, the system consists of a discrete controller and a continuous plant, as shown in Fig. 1. The controller may be a general purpose microprocessor or a high-performance digital signal processing chip. Both devices are operated in discrete time or in sampled-data domain. However, for the plant which consists of a brushless DC motor and the mechanical system, as well as a disturbance acting on the plant dynamics, are operated in the continuous time domain. Thus, this simulation package aims to investigate the effect of a discrete controller in controlling a continuous plant, where the sample delay is included. With digital controller implementation, computational delays cannot be avoided Transactions on Engineering Sciences vol 3, © 1993 WIT Press, www.witpress.com, ISSN 1743-3533