Brushless Dc Motor Position Sensor Control System

Sensor-less control strategy for BLDCM is becoming a research hotspot in both domestic and abroad from 1990s. Using the certain method without hall sensors, BLDC Motor can not only work well in both high-temperature & high-pressure, save space, but also cut your cost in those expensive hall sensors.Nowadays, most of the senseless control methods are based on the B-EMF, and this theory is proved right almost in all circumstance. But as you know when the motor is at standstill or at a low speed, it is ridiculous to get the position information that can let the motor go well from B-EMF, because at that time, B-EMF is little to detect. So how to let the motor start well becomes another hotspot in senseless research.Based on the principle and the mathematical model of the BLDC Motor drives, the theory of Back-EMF method and the zero-crossing detecting circuit are introduced and analyzed. At the same time, determining the initial position of the permanent magnet by the time periods of discharge of stator windings which are excited before discharge let the motor start from standstill, and when at a certain speed, the whole system transfers to the B-EMF method. Rotor position detection error and interruption is also investigated in this paper, then compensation and restraination methos are also proposed.Based on quantities of circuit design and the actual situation, the hardware system of BLDCM sensorless control using HC08MR8 is built, at the same time,an E-BIKE controller is designed. Experimental results shows that the whole system can meet the required need, and also prove the accuracy of the theory.