| 摘要 |
<p>A sensorless control system for determining the position of the rotor 5 of a brushless motor 3 comprises a back EMF sensor 12 and a controller 13. The back EMF sensor generates a digital signal BEMF that is output to the controller, where certain edges of the BEMF signal correspond to zero-crossing in the back EMF. The controller then commutates the phase winding 7 at times relative to these edges. The back EMF sensor comprises a voltage sensor, an amplifier, a differentiator, a low pass filter and a comparator. The back EMF sensor generates a first signal having a voltage that is proportional to a voltage across a winding of the motor, and a second signal having a voltage that is proportional to a current in the winding. The second signal is then differentiated to generate a third signal, and the voltages of the first signal and the third signal are compared. The output signal BEMF is generated in response to the comparison, the output signal having an edge whenever the voltages of the first signal and the third signal correspond.</p> |
