# Filter design for DC PWM supply

#### salute2vishal1

Joined Jul 10, 2021
3
I am using a DC PWM supply which has ripple voltage of 300 Vrms and peak to peak noise of 1.5 V. This ripple voltage is at 38 kHz (inverter) and 400 Hz (chopper) frequency. The vendor doesnt know at the both frequency what is the individual contribution of the ripple.

The rated power of the DC PWM supply is 750 VDC and it will be used to power a motor controller (this motor controller will control PMAC motor). The rated power is 60 kW and peak power is 120 kW (for 10 seconds). I would like to design a filter which can reduce the ripple Vrms to less than 50 Vrms and peak to peak voltage to less than 250 mV. Can somebody help me please.

#### Papabravo

Joined Feb 24, 2006
20,600
1. "ripple voltage of 300 Vrms" -- that is almost half the output voltage!
2. "peak to peak noise of 1.5 V" -- not sure how this relates to ripple voltage.
3. "the rated power of the DC PWM supply is 750 VDC" -- that's great except that power is measured in watts, not volts.
4. Do the power ratings of 60kW and 120 kW (for 10 seconds) refer to the motor?
I'm curious about why you think a filter is what you need.

#### BobTPH

Joined Jun 5, 2013
8,088
You do realize that a PWM controller does not produce a constant voltage, right? How are you measuring the “ripple ?”

Bob

#### salute2vishal1

Joined Jul 10, 2021
3
1. "ripple voltage of 300 Vrms" -- that is almost half the output voltage!
2. "peak to peak noise of 1.5 V" -- not sure how this relates to ripple voltage.
3. "the rated power of the DC PWM supply is 750 VDC" -- that's great except that power is measured in watts, not volts.
4. Do the power ratings of 60kW and 120 kW (for 10 seconds) refer to the motor?
I'm curious about why you think a filter is what you need.
I was too fast in typing and made some mistakes in my post , apologizes for that. The current info is as below

ripple voltage of 300 mVrms
peak to peak ripple voltage is 1.5 V
The rated voltage of DC PWM is 750 VDC.
This PWM DC supplies power to a motor controller which inturn controls a PMAC motor. Yes the 60 kW and 120 kW refers to the motor. The maximum ripple voltage motor controller can accept is 50 mVrms and pp voltage of 250 mV , hence cause of that I think a filter is needed to reduce the ripple Vrms and peak voltage

#### salute2vishal1

Joined Jul 10, 2021
3
You do realize that a PWM controller does not produce a constant voltage, right? How are you measuring the “ripple ?”

Bob
Hi Bob,

The PWM DC supply is can supply output voltage 0 to 750 VDC. We are going to operate the PWM DC supply at max output voltage. Based on the measurements of the ripple by the manufacturer at max output voltage , he has shared the ripple and noise data.

#### Papabravo

Joined Feb 24, 2006
20,600
It will be easier to find a power supply with better specifications, than it will to make a filter at such power levels.

#### BobTPH

Joined Jun 5, 2013
8,088
Draw a waveform of what you understand the ouput to be, including the ripple and noise. I still can’t make sense of it.

Bob

#### ElectricSpidey

Joined Dec 2, 2017
2,628
Why in the world would you supply a motor controller with PWM?

Sounds like the PWM supply is actually a SMPS.

#### BobTPH

Joined Jun 5, 2013
8,088
Why in the world would you supply a motor controller with PWM?

Sounds like the PWM supply is actually a SMPS.
That would explain the confusion. Seems like there are a lot of people who use the term PWM wrongly.

Bob

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