I'm not seeing what this could accomplish aside from a measurement of HF ripple. Just observing the summed ripple can't tell you which boost phase needs to be adjusted in order to keep it low.the solution: one low value resistor, sized such that the average dc current flowing out of the bridge rectifier produces a voltage approximately equal to 10% of the individual phase's current sense resistor. in this way the triangle wave of the boost inductor current is riding on top of the dc +ac current flowing through the sum of n phases. said resistor can be made of any number of small discrete .25 or .5 watt resistors for nearly zero inductance.
Whenever two or three phases start riding together, the voltage across this resistor will have lower frequency harmonics of greater ac amplitude than the ideal case, in which were there say to be 5 converters in parallel, the voltage across this resistor would consist of triangle waves with a peak to peak ripple of 20% of the dc component, at a frequency of 5 times the individual boost switching frequencies.
this is almost worth patenting...
btw, these additional current sense resistors can be paralleled with an inductor to provide greater sensitivity, however the resistors need to be sized such that the Q is rather low, and the harmonics must not be able to excite any parasitic LC resonances in the range of the switching frequency, or its going to wreak havoc.
Dithering will always keep peak spectral power lower, both with single and multiphase converters. However it won't be effective as having all phases frequency locked and phase interleaved, and then applying global dithering to all phases.Since this is a brainstorming session, and thinking out-of-the-box is acceptable, I'm proposing a wild idea that may (or not) have any merit:
How about if you apply some very small amount of dithering to the voltage fed to each error amp?
I think I get the idea, though a schematic would be helpful. I still don't see how this approach would result in feedback that forces interleaving, rather than some chaotic oscillation.All of the L6562 chips or equivalent are grounded to the common point ground, the extra dc bias with ac ripple is thus added to all of the current sense resistors, and this voltage is not low pass filtered, in fact we can put an inductor across this resistor to cause increased sensitivity. (provided the Q is rather low such that the instantaneous negative transient is not much more than say a few tens of millivolts)
because the ac ripple across this master current sense resistor is in phase and is not filtered, whenever two phases get close to each other, one of them will be forced to turn off sooner than it would have without it. (the ac ripple being a function of how close they are all to each other)
Here is a scenario:
10 phases in parallel, each with a .1 ohm current sense resistor, and on average they trip at 5 peak amps.
If they are all in phase, they would sum to form a triangle wave with 50 amps peak to peak.
so we put a .001 ohm resistor between all 10 phases and ground.
Ideally, they all space themselves out properly and across this resistor we get 25 millivolts of dc (corresponding to 10 x 5 amp peak triangle waves thus 25 average amps if my math is right) (25 average amps at 250vac is ~6 KW)
and on top of this 25mv dc is about 2.5 mv of ac ripple at 10 times the nominal switching frequency.
whenever two or three phases start creeping into each other, this 2.5mV of ac ripple is going to increase quickly, and decrease in frequency, depending on how you look at it. this ac ripple is what causes the individual phases to turn off sooner, because its added on top of all of the current sense resistors, we don't need to know which one is drawing too much current or running faster or slower than the other.
in fact we can add this voltage to the current sense trip comparator differently as well, we can capacitively couple it into the current sense pin as well, fed from a current transformer. thus we would be adding only the ac component.
does this make sense? i can draw the schematic if you want.
keep in mind that the inductor sense coil turnsthe switch on, the resistive current sense trurns it off.Another thing is that in interleaved converters their source and loads must be connected directly to each other, so using a resistive shunt in the ground paths wouldn't work. Using a current sense winding on each inductor would though.
turns out heatsinkable resistors are more expensive than mosfets.
I'm using 22mOhm p50no6 mosfets as current sense resistors.
**broken link removed**
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