Novel Architecture of a Mixed-Mode Sensorless Control IC for BLDC Motors with Wide Speed Ranges

This paper presents a novel sensorless control architecture, which is dedicated for mixed-mode IC implementation, for many low-cost applications of brushless DC (BLDC) motors over wide speed ranges. In order to measure the back-EMFs over a whole PWM switching cycle from low to full duty ratio, a hybrid back-EMF zero-crossing detection circuit is presented to sense and compare the back-EMFs without heavy filtering during both the PWM-on and PWM-off states. And the detected zero-crossings can be synchronously sampled with an internal high-frequency signal, which considers the turn-on and turn-off delays of the power transistors, for reducing the latency between the real zero-crossings and the detected ones to achieve wide speed operations. Besides, an auto-detection technique with an adjustable level detector is also proposed to improve the robustness of detecting the free-wheeling diode conducting period at high speeds with heave-load operations. Furthermore, to achieve a smooth startup operation, an initial rotor position estimation strategy is presented by measuring the rise time of the dc-link current instead of measuring its peak current. Lower sensitivity to motor parameters can be obtained with the proposed method, and the maximum current can be limited during the initial angle detection. Neither a micro control unit (MCU) nor analog-to-digital converters (ADCs) are required with the proposed sensorless architecture to achieve the low-cost but high-performance sensorless solutions. The whole architecture is evaluated with a FPGA-based system.