Originally Posted by
kreutz
The PWM frequency for the UHU board is 23.5 KHz, some old servo drives used from 5 to 15 KHz, the older technology, or higher power, the lower the switching frequency they use. So I expect a little more magnetic losses than usual on those motors.
The filters I use are designed to control DV/dt on the motor. Depending on the turn-on time of the power Mosfets used in the H bridge, and the size of the motor; cable lengths as short as eight feet can result in motor peak voltages that exceed the rating of the motor's insulation system. However, the longer the cable the greater the problem. Dampening the rate of voltage increase will minimize the peak voltage that occurs at the motor terminals.
When using low power/voltage motors the dv/dt could be effectively controlled using lower switching times, like in the original UHU design. When handling high voltages and currents, it is better controlled with external Snubbers, since slowing down the switching times could destroy the switching semiconductors.