Adaptive soft starting method with current limit strategy for sensorless BLDC motors

This paper proposes an adaptive soft start-up strategy for sensorless control of three-phase BLDC motors in applications to consumer electronics and high efficiency cooling fans. The proposed start-up control scheme combines a closed-loop I/Hz control with adaptive ramping current profile in accordance to different load torque-speed characteristic. The proposed start-up scheme can reduce the start-up current while at the same time provides a robust and smooth start-up for different applications. A synchronous current sampling control scheme based on the dc-link current is developed for the regulation of motor phase current. A start-up current limit profile is calculated based on assumed load torque-speed characteristics. The controller will switch to sensorless control mode once a verified sensorless commutation signal is detected. Simulation and experimental results have been given to show the robustness of the proposed sensorless start-up control scheme.