Method for starting and commutating a permanent-magnet direct current

Abstract

Starting of single phase permanent magnet direct current motors in the desired direction of rotation is accomplished by providing a look up table stored in memory giving the correct sign or polarity of current for the angular position of the permanent magnet rotor of the motor. This stored look up table is developed by initially injecting current pulses of opposite polarity at different angular positions of the rotor, determining the difference between the rise times, and mapping the sign and the magnitude of the differences versus angular position. Thereafter, to start the motor in the correct direction, it is only necessary to inject current pulses of opposite polarity to know the angular position of the rotor and the polarity of the current required to start the motor in the correct direction. After the motor has been started, it is commutated by blanking the drive current at the zero crossings of the back emf. The current is turned off prior to a back emf crossing, and turned back on after the back emf crossing. The stored look up table tells how long to apply drive current before blanking because the table indicates how far away the zero crossing is, which is convened into the time remaining before blanking the drive current. Several embodiments of single phase motors are disclosed, as well as circuits useful for starting a motor and sensing back emf.