Phase interleaving hysteretic current converters - Page 1
Forum section: electronics / general

author: uer166
author_rank: Super Contributor
timestamp: July 29, 2022, 11:49:02 pm
content: I'm thinking of implementing a thing called synthetic meter test bench, which basically circulates a large current (say 80A) thought a power meter in a loop from input to output, and also applies a voltage to the terminals, thereby tricking the meter that it's measuring high power. Commercial systems are 50-100k$, so thought it would be cool to homebuild a version.For the output current source stage the likely candidate is a multi-phase bidirectional buck stage, say 4 phases for each leg (one sources the other sinks, and vice versa, at 50Hz). I've had success with this topology in a hysteretic current mode, but only with one set of half-bridges. My question is: is it possible to interleave a hysteretic controller to enforce some phase relationship between the half-bridge outputs? For example, I can imagine you can do something by measuring the phase relationship timing, and doing a control loop to perform minute adjustments of the current reference to keep them all at 90 degrees or whatever.Another idea might be just average current mode control, but since it's a bidirectional stage, I don't quite understand how would one do peak current cycle by cycle limiting. It's a sync output/input stage and so there ought to be 2 current limits, and it basically becomes a hysteretic controller at that point regardless.

author: Faringdon
author_rank: Super Contributor
timestamp: July 30, 2022, 10:27:21 am
content: AYS, this is an AC mains power meter...as such, the attached gives a 32Arms 50Hz sinusoidal current for putting into meters to high current test them....(without dissipating the high power that you otherwise would if you used a dummy load)Was this along the lines of what you wanted? Sorry if it isnt.LTspice and PDF scm attachedOn the subject of hysteretic bucks intereaved....i think you just have to force switch them interleaved, and go from there.You basically do a hysteretic converter, and have some extra logic, which tells each of the interleaved fets, "you can switch on, but only when your allocated interleaved switch-on time slot comes round".....so basically send the fet switch on signal to an AND gate first, and the other input to that AND gate is from the interleaved_time_slot_allocator thingy....so basically , you end up being interleaved."constant off time hysteretic converters" are good for current sources, as the off time lets your inductor have some free wheel time......so the added bit of logic for interleaving,, just says, ok, you want to switch your fet on now?....wait till your allocated "interleaved" time slot comes round.I'm pretty certain that most BLDCs just use constant off time "hysteretic converters" to high frequency switch the coils to get a certain current in them.......this is done within the coil to coil switching envelope, (commutation envelope) which of course, is managed by software.

author: johansen
author_rank: Super Contributor
timestamp: August 29, 2022, 03:36:48 am
content: i discovered a way to interleave transition mode boost converters, it may work for interleaving hysteresis control.basically what you do is take 10% of the total current flowing through all the phases and you add it to each individual current sense error amplifier.the first switch to reach its limit and turn off reduces the amps measured by all the other current sense amplifiers.. which means they stay on longer, within a few cycles they will all cycle in step one after the other.its not chaotic, i was able to get a 4 phase transition mode boost converter to switch very nicely in step with each other, regardless of duty cycle.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 29, 2022, 04:14:31 am
content: Quote from: uer166 on July 29, 2022, 11:49:02 pmIf it's AC, wouldn't it be as simple as a toroidal transformer on a variac with the current test loop going through it? Then use a second variac for the voltage.

author: Faringdon
author_rank: Super Contributor
timestamp: August 29, 2022, 07:42:24 pm
content: QuoteThanks, this sounds interesting. May i ask which chip you used, since all the ones i know of dont have a current sense error amplifier...eg L6564 etcL6564https://www.st.com/en/power-management/l6564.html

author: johansen
author_rank: Super Contributor
timestamp: November 01, 2022, 06:47:49 pm
content: Quote from: Faringdon on August 29, 2022, 07:42:24 pmso you see pin 4? in the application examples, they typically use a 47pF capacitor to ground, and a 220 ohm resistor to the current sense resistors that are between the source of the mosfet and the ground of the entire circuit.what i did, was build a 4 phase boost converter that had two current sense resistors in series, all connected together. at the mid point.later i realized you can short out the common resistor with a lossy powdered iron core inductor. each pfc chip has its own current sense resistor, on top of the common current sense resistor.in order to make all the individual converters work properly, you parallel all the multiplier inputs rather than give each one its own voltage divider source. (*or tweak it slightly to make them share current equally)you then take pins 1 and 2 and connect them together. now the internal error amp is a -1 inverter.you then build your own error amp, invert the output, and drive all the pfc chips in parallel.now there is a way but i never finished it. you don't need to actually parallel the current sense resistors (very low inductance required. i built a board with the current sense resistor in the corner so i could put 4 of them together) . you can use a resistor divider by inserting another resistor in series with pin 4 and use more resistors to mix part of the current together from all n number of converters together.