Hi All,

I would like to seek opinions from other users as to problems with impedance matching on low inductance nmotors.

Most high performance servomotors are built with a very low inductance. Since the magnetic force is proportional to the current flow through the coils, and the current rise time is proportional to the coil inductance, it can easily be seen that the lower the motors inductance the faster the motor can react. The problem here is though that a low inductance is close to a short circuit condition, and if the current rises too fast it can reach an overcurrent situation before the end of the normal PWM cycle.

We often use Maxon motors in our projects, their power to size ratio is really good, but with an inductance only 300uH we usually have to add inductance to the circuit to get good control. We recently modified one of our TEK10 drives and found that by doubling the PWM frequency (hence halving the PWM cycle) we could get good control and eliminated the need for in-circuit inductors.

We have now also modified the firmware on some of our TEK10s to allow for user selectable PWM frequencies to be preset for inductance matching between motors and drives.

I am putting this up to the forum to seek opinions, is this a common problem people have when setting up drives? And should we make this a standard feature of the drives, or just an option?

Any remarks, thoughts or ideas would be appreciated.

Cheers

Pete