Numerical simulation of the sensorless control for an electrical drive system with brushless DC servomotor

Within the appliance servomotor control industry there is an increasing trend to move towards using brushless DC servomotors. Brushless DC servomotors require in every moment the rotor position information in order to select the appropriate commutation sequence. Therefore, these servomotors are equipped with a rotor position transducer device to detect the rotor position and command the static switching devices by adequate signals (sensored control). These position transducer devices bring a number of disavantages, which is way it aims to achieve the information about rotor position using no position sensing devices (sensorless control). The authors present in this paper a sensorless control technique which consists of sensing the zero crossing points of Back-Electromotive Force in the unpowered phase. Therefore, are presented the results obtained by numerical simulation in Matlab/Simulink.