Dynamic rate feedback pm motor starting technique

Abstract

A two-phase motor includes two orthogonally disposed stator windings and a permanent magnet rotor. One of the stator windings is energized with a maximum energizing input for a narrow time period, whereupon the rotor is driven to a position intermediate the two stator windings. At the end of the narrow time period, the other of the stator windings remains energized whereupon the rotor is driven to align with the magnetic flux generated by the other winding. A switching arrangement is actuated to prevent loading on the one phase winding while the back EMF from the one winding is conditioned and interrogated for magnitude and for rotor direction. When the proper magnitude and direction are sensed the switching arrangement renders the motor in a run mode while closing the drive loop for the one phase winding which is now driven with a maximum input. As the rotor accelerates toward the one phase winding the back EMF from the undriven phase winding is converted from an angular rotor rate signal to an angular rotor position feedback signal, and which back EMF is used to determine if the motor is actually running so as to prevent restart, or to repeat the starting sequence, as the case may be.