I am struggling with the design of a LC- low-pass filter for my inverter.

Above the N-MOSFET you find my approach. R1 and L1 is one motor phase, therefore the load.

L2 and C1 are supposed to be a low-pass filter. I am not even sure if the cap should be above or underneath the inductor.

At the MOSFET gate will be a 62,5 kHz PWM modulated with a 1-100 Hz sine wave.

My intention of course is to filter the PWM and have my motor phase commutated with a clean sine wave.

I can't seem to find the right values and general setup in the simulation; it never looks like a sine. In real life on my table I was able to obtain a nice sine but only with a load resistance of 1000 kΩ, at least that tells me that my modulated gate signal is correct.

How do I approach this? The motor values are my input impedance, and my output impedance is the shunt (0.1 Ω), correct? Can anyone please suggest tips? enter image description here


1 Answer 1


How do I approach this? Can anyone please suggest tips?

I don't think your present approach is going to prove very satisfactory. Personally, I would create a "power square wave" with a half-bridge formed by two MOSFETs and an appropriate driver chip. Then I would use an LC low pass filter on the output of the half-bridge before connecting the motor winding.

There are plenty of options when choosing a half-bridge: -

enter image description here

And, there's nothing problematic about fitting an LC filter into the above circuit. Image from here.


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