[SOLVED] Best PWM frequency for DC motor driver

Hi
I am designing a DC motor dirver. I use IRFP150 power mosfet. what is the best PWM frequency to reduce dissipation in my device?

This depends a lot on the power switch element and the
DC motor attributes. Your armature inductance will be one
concern, you need ripple current to be sensible (maybe
10% of full load amps) and you can get that from worst
case max line voltage and motor inductance (though I'd
guess maybe this is modal too, what's the worst case
minimum inductance found at?).

Then you have the tradeoff between conduction losses
and switching losses which for any DC load and device
type (IGBT, MOSFET, bipolar, GaN) have a "sweet spot".
IGBTs like to run slow but are the winner at very high
bus voltage and current (less so at low voltage where
their saturation voltage eats up efficiency). MOSFETs
as you indicate just have a fairly fixed Qgg per cycle,
and a fairly fixed conduction loss per cycle (Iavg*V*ton)
and you can play with that.

I recommend making an -in-efficiency oriented spreadsheet
where each of the loss terms is individually figured. This
is a useful design tool, unlike rollup efficiency numbers.

Hi,

I've heared that high frequencies may increase wear out of the brushes inside the motor.
The company slowed down switching frequency in the audible range. Some kHz.
I don't have exact or more reliable informations.

Klaus

Back when inverter drives were the New New Thing there
was some hoopla about "inverter duty" motors. Supposedly
the HF components of the drive waveforms were too much
for standard winding insulation (varnish) and the capacitive
currents could cause damage. Now I'm told all of the main
motor mfrs are just doing better construction because they
have to assume someone will use inverter drive even on
"dumb ol' 60Hz 3-phase motors".

But I think this is less about fSW and more about the
switching edge rates, where the real high harmonic content
is.

If you can it might be a good idea to add some filtering to remove the PWM components if it is an old motor to remove the effects that have been highlighted.