Electronics > Power/Renewable Energy/EV's

need help to compute Irms of this topology

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ISO- I never thought the inductors wouldn't affect the result.  I just thought we could start without and iterate.  This does create an outer bound.  I guess I'm not too surprised that its linear either with the inductors in place- buck converters generally follow this rule.  We would have gotten to the same result as we went back and forth.

One thing that might simplify things is a control system like the following.  Put a current transformer over the main input and measure it.  Control the heater based on how close this gets to 30 amps, cut back the heater output based on the total current.  All analog and pretty simple.  I would use the Triac type of control probably with a zero crossing opto (MOC2011), etc.  Could do it without any micros or computation.

Have fun- nice problem.

Can't EVs adjust their load from the system software?

...so you want to reduce  current to your heater, so the combined power draw of your electric car, and the heater, is less then 30A.

...So really, do symetrical mains phase cutting with triac.....it will give good harmonics because it is  symetrical....cuts on the leading and lagging edge.

If you are going to do a switcher though.......just remember you are getting an overall sinusoidal input current (when filtered)......so you know what the peak current will be......so do your buck or bridge, or whatever....do the design for it at the case of mains peak......the rest will follow in  good order, as long as your topology makes imains follow vmains.

Easiest way for you is to  do a full bridge, with the resistor in the bridge, and just duty cycle it at HF, with only small capacitance after the bridge (like you are doing)...then your power througput will be according to the duty cycle....OR TRY THE SyMETRICAL TRIAC METHOD I PREVIOUSLY DESCRIBED. (woops sorry about capitals).

Do you want me to send you a ltspice sim of the bridge and the sym triac?

the EV charger cannot be modulated.
I don't want to use a triac : not EMC friendly

I always have fun and learn from another people's spice , yes publish it here.

So to get back on the math, based on the average voltage value of an inductor overall a _full_ cycle in CCM (I mean, the sinus envelope) =0
 I derive the average voltage across the resistor.
If , as I guess, there is a coefficient K between average current in resistance and rms current, then indeed, the power is linear with D.C.

I don't give up trying to find an algebra for Irms ... but until know I don't catch it.


--- Quote from: iso14000 on June 04, 2023, 10:33:47 pm ---I don't want to use a triac : not EMC friendly

--- End quote ---

There is nothing EMC unfriendly about triac, they are used everywhere no problem.

Your problem is apparently that you have to cut power off quickly per the ridiculously strict requirements ("few ms") from the power company.

I don't see what you think you are gaining by rectifying and working on the DC domain; it's only going to make things worse, much worse, by worsening power factor because of inherently small conduction angle. You could do active PFC (or, if the power company really applies a fixed current threshold and not some kind of RMS measurement over a full cycle, even constant-current type anti-PFC circuit just for this case) of course...

I think what you should really do is re-evaluate the exact conditions given by the power company, I don't buy the "few ms" story as is. You need to define the problem very exactly in engineering terms before you can find the right solution to it.


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