Switched reluctance motor position by resonant signal injection

A system for controlling a switching frequency F.sub.s of a power signal to each winding of a brushless commutated motor having a plurality of poles on a rotor and a plurality of phase windings on a stator, the system comprising:

• at least one tank circuit incorporating one of the phase windings of the motor and having a resonant frequency F.sub.0 that varies over a band of frequencies in response to cyclic changes in the effective value of the inductance of the phase winding between maximum and minimum values as the poles of the rotor change position with respect to the one phase winding;
• a switch in series connection with the phase winding and responsive to a drive signal for providing the power signal to the one phase winding at the switching frequency F.sub.s ;
• means for injecting into an input of the tank circuit a low-energy signal having a frequency F.sub.1 that is substantially greater than the switching frequency F.sub.s ;
• a detector responsive to an output of the tank circuit for detecting when the difference between the resonant frequency F.sub.0 and the frequency F.sub.1 of the injected low-energy signal is at a minimum and generating a signal indicative thereof;
• and
• a motor controller responsive to the signal from the detector for generating the drive signals to maintain a predetermined relationship between the switching frequency F.sub.s and the signal from the detector.

A circuit for sensing the position of the poles of a rotor for a brushless commutated motor relative to the position of the poles of a stator for the motor, wherein the stator has a plurality of phase windings, the circuit comprising in combination:

• at least one tank circuit incorporating one of the phase windings and having a resonant frequency F.sub.0 that cyclically varies over a band of frequencies in response to cyclical changes in the effective value of the inductance of the one winding between maximum and minimum values caused by the poles of the rotor changing position with respect to the one phase winding;
• means for injecting into an input of the tank circuit a low-energy signal having a frequency F.sub.1 ;
• and
• a detector responsive to an output of the tank circuit for detecting when the difference between the resonant frequency F.sub.0 and the frequency F.sub.1 of the injected low-energy signal is at a minimum and generating a signal in response thereto that is indicative of the position of the rotor.