Raghu,

You got some great comments from Michael and Steve!

Around 1982 I did a PWM drive for a brush motor, position servo with tach and current feedback. I found the servo performance did not change with PWM frequency until I got to some frequency above ~5kHz. Above that frequency motor torque decreased rapidly(!) as PWM frequency was increased - the motor got hot, too. I assumed eddy current losses in the motor iron (no, it didn't use laminations)were stealing air gap flux, thereby decreasing torque and increasing operating temperature.

The only reason at the time to increase PWM frequency was to reduce audble noise. As it turned out, the motor and its load was placed in a (nearly) sound proof environment for operational purposes to which I was not privy.

Good Luck,

Bruce