Hunting suppressor for polyphase electric motors

A controller for an n-phase electric motor, said motor including a stator having n windings and a rotor, comprising:

• (A) variable frequency oscillator for generating n periodic drive signals, each of said drive signals being at a frequency f.sub.o and having a phase .phi..sub.o, and being mutually shifted in phase by 180/n degrees,
• (B) means for coupling each of said drive signals to a respective one of said n windings, and
• (C) PLL means for phase locking said frequency f.sub.o to an applied clock reference signal, said clock signal having a frequency f.sub.c and phase .phi..sub.c, whereby said rotor rotates substantially at frequency f.sub.c ;
• said PLL means including:
• (i) means for generating a feedback signal representative of the drive signal coupled to one of said n windings,
• (ii) control signal means for generating a control signal proportional to the difference in phase of said feedback signal and said clock reference signal;
• said control signal means including phase compensator means responsive to said feedback signal and said clock reference signal for generating an error signal having a baseband component and a double frequency component and low pass filter means for rejecting said double frequency component and passing said baseband component to generate said control signal,
• (iii) means for applying said control signal to said oscillator whereby said frequency f.sub.o varies in response to said control signal so that said drive signal applied to said one winding is phase locked to said clock reference signal.

A controller for an n-phase electric motor, said motor including a stator having n windings and a rotor, comprising:

• a variable frequency oscillator for generating n periodic drive signals, each of said drive signals having a frequency f.sub.o, and being mutually shifted in phase by 180/n degrees, each of said drive signals being applied to a respective one of said n windings;
• a sensor for sensing a drive signal phase .phi..sub.o comprising one of a current phase and a voltage phase of said drive signals;
• a reference signal generator for generating a reference signal having a reference frequency f.sub.c and reference phase .phi..sub.c ;
• and
• a circuit for generating a difference phase .phi..sub.d proportional to the difference between the drive signal phase .phi..sub.o and the reference phase .phi..sub.c and for adjusting the other of the current phase or the voltage phase of said drive signals generated by the variable frequency oscillator based on the difference phase .phi..sub.d, such that said rotor rotates substantially at frequency f.sub.c.