Sensorless control of 3-phase BLDC motors using DC current model

This paper proposes a new sensorless control algorithm for 3-phase BLDC (Brushless DC) motors with the 120° conduction mode. This algorithm uses the mathematical DC current model of the BLDC motor to estimate the rotor´s speed and angle. The principle is similar to the conventional current model-based control of 3-phase PMSM (Permanent Magnet Synchronous Motor) with sinusoidal current waveform. The rotor speed and the angle can be obtained using the error between the measured and estimated currents. According to the proposed solution, the 3-phase BLDC is simplify modeled as a DC motor. Due to the non-ideal characteristics such as electrical commutation phenomenon and actual back-EMF shape, the estimated rotor speed and angle will deviate from the actual values. To overcome this problem, the change of the current through the feedback loop of the PI current regulator is used to correct the estimation of the rotor´s speed and angle. The validity of the proposed sensorless algorithm is verified through simulations and experiments.