Design of a Sensorless Field Oriented Control Drive for Brushless DC Motors

Field Oriented Control (FOC) is a widely employed motor control methodology for Brushless DC (BLDC) motors. FOC requires an accurate measure of the rotor angular position for proper operation. Depending on how this rotor position is obtained, FOC can be implemented in either sensored mode or sensorless mode. Typically, sensored FOC employs position sensors to measure rotor angular position, whereas sensorless FOC estimates the rotor position using state observers based on currents, voltages and back electro motive forces (BEMF). This paper presents the first stage of a research aimed to identify an optimum observer type for a sensorless FOC, and it focuses in particular on the implementation of a Luenberger BEMF observer (LBO) based sensorless FOC system. Based on the mathematical formulation of the problem, the LBO was constructed to be a timevarying system, which introduced additional complexities when implementing the system in MATLAB. All simulations were carried out in the MATLAB Simulink environment according to predefined test criteria. The simulation results of the sensored FOC show accurate tracking of the reference speed and smooth transition dynamics, whereas the sensorless FOC simulations also indicate similar performance to the sensored case in general. However, a steady state speed ripple was noticed in the sensorless mode compared to sensored mode, along with increased settling times.