> Thanks - have an idea to use PWM & H bridge, by following the zero 
> cross
> input from mains I can time the switching of the H bridge 
> transistors
> starting with a narrow pulse followed by increasing wider pulses up 
> to
> the peak of the AC wave an then decreasing pulse widths coming back 
> down
> to the zero cross point.
>
> By adjusting the PWM pulses I may get control on the motor speed.

No, alas.
The motor tracks the frequency less a "slip" frequency of a few Hz. 
you MUSt alter the basic frequency to get speed control. locking to 
mains frequency won't work.

        RM


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