Re: inductor sizing

Harry Dellamano wrote:

"Jamie Morken" <jmorken@xxxxxxx> wrote in message news:__2Dj.89735$w94.80971@xxxxxxxxxxxx
Harry Dellamano wrote:

"Jamie Morken" <jmorken@xxxxxxx> wrote in message news:vB3Aj.53407$w94.15226@xxxxxxxxxxxx
Harry Dellamano wrote:
Ok Jamie,
You sound like a nice person so here is a filter design that will meet your needs with a bottle of tequila to be sent upon the design's approval. This is the first LC section for one phase and will survive the 200KHz/440VDC stress and present a nice 60Hz sine wave to the second LC section input which you can design using high flux 60Hz material to meet you unspecified output requirements. As stated earlier the THD depends on the control loop and not the HF output filter.
For the 25uH/30Apk inductor use a Ferroxcube or similar EC-70 (3F3 material) core set and bobbin with 21 turns of #10 AWG LITZ wire wound in 3 layers of 7turns/layer. Insulate all for 3500VDC. The LITZ wire should be made up with 256/#34 AWG wires. This will require a 0.21" gap across all three legs of the core. Do not grind the center leg for a 0.42" gap because this will cause increased Rac losses. The total dissipation will be <7.0W so be aware.
For the shunt caps use 5X EPCOS 2.2uF/400VDC MetalPoly at DigiKey for $1USD/100 PN B32594C6225J008. Irms in each cap is ~=1A at 200KHz which MetalPoly types of this size can handle.

Hi Harry,

Sorry for the late reply I was out of province for the last week.

For the feedback of an LCLC filter like this, are only one of the
inductor currents and capacitor voltages required, or are both
currents and voltage required?

*The second LC stage is not required in the feedback loop and may be detrimental due to added lag. It is only needed to meet your output high frequency attenuation requirements which you have not yet revealed.

The output has to remain below 2.5% THD + noise.


For the LC filter version I use this algorithm for the feedback loop:

if inductor current > current_limit, pulse off

Duty cycle = ((desired voltage - current voltage) * gain) - (Inductor current * gain2)

I am not sure if I can use this for the LCLC filter as well.

*As we have stated before, the LCLC filter is a separate issue from the feedback loop. To simplify the feedback you may chose to feedback the output of the first LC and let the second LC run open loop. The FB loop must operate with the first LC but you can close the loop in any way your heart's desire as long as it stable.

I tried this in the simulator but never got the LCLC to regulate as well
as a simple LC does.


Also do you have part#'s for the high flux inductor for this LCLC filter
and the output capacitor? The output is 120VAC 60Hz at 3.6kW by the
way.

* So, asked but never answered, what is your output noise requirement? Are you trying to meet FCC, DO-160, MS-461, CE....? How much must the 100KHz and harmonics be attenuated? Notice I said 100KHz because at 200KHz the AC resistance of the first inductor will eat you up unless you know of a way to reduce it. The best I could do was using a single layer winding, at 100KHz, and got a Q of 475. Earlier in this thread I reported a Q of 150 to PH but cleaned up my measurement methods and attained a true 475. The AC resistance was still 5X the Rdc and the biggest obstacle. The second LC will see little 100KHz current and can be any high flux core. I like the MPP-HF or a gapped MET-GLAS. Size, cost, availability and familiarity come into play here so there is no simple answer.

I plan on using planar inductors instead of E cores and Litz wire, but

*Sounds interesting, are these planar inductors something you will purchase from the boys in Florida or your in house design? What kind of Rac at 100KHz and 200KHz is attainable?

Payton (http://www.paytongroup.com/) or Himag (http://www.himag.co.uk/)
both make these planar inductors. I got a quote for a 25uH 82Amp
inductor from Payton for the 200kHz filter with 15Amp peak to peak
ripple rating, and it has a specified 30watts loss. Its dimensions are
116mm by 66mm by 26mm high (big rectangular block).

I was way off with the original 250uH inductor, that would be huge at
these currents and frequency, 25uH seems to be more than enough
inductance (I think 15uH would work actually)

cheers,
Jamie


I will still send you the tequila for the design :D

*Tequila is only necessary for the closing ceremony.

cheers,
Jamie

Cheers,
Harry


.

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