How to generate 675Vdc with 25V Maximum Ripple from 50Hz 220Vrms? - Page 1
Forum section: electronics / projects

author: KerimF
author_rank: Frequent Contributor
timestamp: June 20, 2023, 03:59:53 pm
content: Hi,I guess, in theory, there are many topologies for generating 675Vdc (+/- 25V max) from 50Hz 220Vrms.But I wonder what a practical topology could be.Any ideas? Thank you.KerimEdited:It is a power converter since the load is 35 Ohm only.IMPORTANT:To me, the topic is closed. But this doesn't prevent adding more interesting ideas for others.

author: hussamaldean
author_rank: Unknown
timestamp: June 20, 2023, 04:04:14 pm
content: Check voltage multiplier.

author: KerimF
author_rank: Frequent Contributor
timestamp: June 20, 2023, 04:08:23 pm
content: Quote from: hussamaldean on June 20, 2023, 04:04:14 pmYou are right.I am sorry. I forgot to add that the load is 35 Ohm only.

author: TimFox
author_rank: Super Contributor
timestamp: June 20, 2023, 04:11:40 pm
content: Unfortunately, that input voltage (311 V peak from 220 V rms) is a bit low to give you 675 V DC from a simple voltage doubler.With small load current and large filter capacitors, you will get 620 V or less.A voltage tripler will give you too much.https://www.allaboutcircuits.com/textbook/semiconductors/chpt-3/voltage-multipliers/How much current do you need at 675 V DC?

author: TimFox
author_rank: Super Contributor
timestamp: June 20, 2023, 04:13:22 pm
content: 35 ohms at 625 V is 13 kW, and with perfect efficiency would draw 60 A from your 220 V rms AC input.

author: KerimF
author_rank: Frequent Contributor
timestamp: June 20, 2023, 04:14:59 pm
content: Quote from: TimFox on June 20, 2023, 04:11:40 pmIt is a relatively high current about 20 A

author: Siwastaja
author_rank: Super Contributor
timestamp: June 20, 2023, 04:15:54 pm
content: Quite obviously, a boost converter. Something similar to boost PFC stage, with SiC diode and high-voltage MOSFET or IGBT. PFC controller can be used to drive it and regulate the output.13.5kW converter is quite a beast. You want multi-phase boost, i.e. multiple converters in parallel syncronized and phases interleaved.The project is quite challenging due to sheer power, voltages and currents involved, and very dangerous too. I'm wondering if you can handle this safely, given you have to ask for such simple advice.

author: KerimF
author_rank: Frequent Contributor
timestamp: June 20, 2023, 04:34:09 pm
content: Quote from: TimFox on June 20, 2023, 04:13:22 pmYes, it seems who asked me to design it has an imported powerful inverter working directly from solar panels. The typical voltage of his set of panels is about 675V and sources up to about 20 A. He thought if it is possible for him to use this inverter, at night, by supplying its high DC power from his 220Vac (likely industrial). The 35 Ohm load is just the equivalent DC load as seen at the input of the inverter.OT: Connecting in series too many solar panels is risky since they are current sources and a partial faulty panel or the illumination is not equal on all panels in series, the power will degrade appreciably.

author: KerimF
author_rank: Frequent Contributor
timestamp: June 20, 2023, 04:48:28 pm
content: Quote from: Siwastaja on June 20, 2023, 04:15:54 pmYou are right indeed. The project is quite challenging.I am not familiar yet with "multi-phase boost, i.e. multiple converters in parallel synchronized and phases interleaved".I just need its general idea only.Would you please direct me to a source talking about it or perhaps give me the magic wordsto search it on the internet.Thank you.

author: KerimF
author_rank: Frequent Contributor
timestamp: June 20, 2023, 05:00:27 pm
content: Quote from: Siwastaja on June 20, 2023, 04:15:54 pmWould please confirm (or not) that these converters need a DC supply.Thank you.

author: KerimF
author_rank: Frequent Contributor
timestamp: June 20, 2023, 05:08:38 pm
content: To generate a high voltage from an AC source just needs a transformer (or transformers).But knowing how to get, speaking practically, a relatively small voltage ripple at a high current as 20A needs, I guess, thinking out of the box

author: wraper
author_rank: Unknown
timestamp: June 20, 2023, 05:20:59 pm
content: Quote from: KerimF on June 20, 2023, 04:34:09 pmAnd what's the point of converting 230V into 675V just to convert it again? As minimum it's inefficient.

author: Terry Bites
author_rank: Super Contributor
timestamp: June 20, 2023, 05:33:04 pm
content: Whatever way you go Linear or Switched you need a transformer or group of transformers that can deliver the full rated load.A big HF xfmr will lead you on painful design journey.You could knife and fork it with a nice 3 phase transformer, some fat diodes a a cap bank (a deadly bomb if ever).3 single phase transformers can do the job if a 3ph one is not avaiable.You'd need a six pulse rectifier- six big diodes. the peak output voltage will be about 1.35 Vphase. So you need a transformer near to 2.1:1That will get you a DC waveform with about 14% rippple superimposed.C = Iload / (2 x f x Vrip) . Note that f is 3x mains frequencyBut yes that evil ripple current in your caps- as a first guess, about 2xI Load.You can repalce the didoes with SCRs for regualation purposes- that's whole other kettle of fish.

author: Kim Christensen
author_rank: Super Contributor
timestamp: June 20, 2023, 05:45:37 pm
content: Quote from: KerimF on June 20, 2023, 04:34:09 pmJust have him buy/install an automatic solar power changeover switch. His idea makes no sense.

author: KerimF
author_rank: Frequent Contributor
timestamp: June 21, 2023, 04:09:09 am
content: Quote from: Kim Christensen on June 20, 2023, 05:45:37 pmI agree with you.And since I learnt now that this special request is just for one unit, I decided to drop it.After all, it is better for me to keep focusing on designing products which could be sold in quantities to the local consumers.

author: ArdWar
author_rank: Frequent Contributor
timestamp: June 21, 2023, 07:39:48 am
content: 675VDC sounds a lot like the output from 3-phase PFC. Are you sure it wasn't what they want in the first place?

author: KerimF
author_rank: Frequent Contributor
timestamp: June 21, 2023, 11:28:20 am
content: Quote from: ArdWar on June 21, 2023, 07:39:48 amYour remark is right.I didn't forget to ask if the requested converter will be connected to one, two or three phases. The answer was clear; just one phase!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 21, 2023, 12:16:55 pm
content: Then make it a 120A circuit, unless one uses a PFC stage instead. Voltage multipliers have ridiculously poor PF.Cost of developing such a solution, as one-off, is in the 5-6 digits USD (maybe less in your area, but I'm guessing the budget is proportionate).Tim

author: KerimF
author_rank: Frequent Contributor
timestamp: June 22, 2023, 11:47:19 am
content: Quote from: T3sl4co1l on June 21, 2023, 12:16:55 pmOn my side, I also realized while studying it in depth that its cost will be relatively very high, mainly because one phase only is available, and this is not practical for such power AC to DC converter, for many reasons.And I have another problem to solve. I can't get special controller ICs to drive the MOSFETs (or IGBTs), I have to design their fast drivers (if not isolated too) using discrete components only and controlled by a rather old MCU, ATmega8.Before having a clear idea about the project difficulty, I asked $1000 only for it. So, I was fortunate that my offer was refused as being high. Now, I won't do it even if they accept to pay $10,000Anyway, as I said earlier, this project is not a practical one in the first place. Such power converter should be supplied by three phases to make things much better on both sides: AC and DC.

author: Kim Christensen
author_rank: Super Contributor
timestamp: June 23, 2023, 01:00:29 am
content: It's funny that the guy never went and looked for anoff the shelf solution.Seems to be lots of high power AC to DC power supplies out there. Maybe he saw the price...

author: trobbins
author_rank: Frequent Contributor
timestamp: June 23, 2023, 01:35:56 am
content: What concerns me is that your first post had no insight or detail on the application and what the 675Vdc 20A was interfacing to. It seems that you were either hiding information, or had no good appreciation.I'd have interpreted the 675Vdc 20A rating as the nominal max output from a solar array, or the nominal max input of a PV inverter - which is typically a special inverter that wants to see a PV array and can't be fooled by just providing a 675Vdc 20A rated power supply. Perhaps that aspect should have stopped any 'design' thoughts straight away.

author: ArdWar
author_rank: Frequent Contributor
timestamp: June 23, 2023, 01:40:13 am
content: That makes me wonder. If the inverter have some sort of MPPT it would become quite interesting experiment 😅

author: trobbins
author_rank: Frequent Contributor
timestamp: June 23, 2023, 01:58:50 am
content: It's likely that safety functions would stop the PV inverter from starting - in particular any requirement for pv string isolation from protective earth - which would require a fully floating power supply. Then there could well be baked-in V-I assessment such that the power supply has to emulate the V-I curve, with appear to present a valid OCV and ISC, and a definable mpp that can be stepped to and dither around (rather than just a CV-CI control).

author: KerimF
author_rank: Frequent Contributor
timestamp: June 23, 2023, 04:20:24 pm
content: Quote from: trobbins on June 23, 2023, 01:35:56 amYour remarks are logical.Me too, I was informed about the project detail in steps. So, my bad is that I started this topic somehow in a hurry. Soon later, I realized it is not a project for me to do at any price.Should I delete this topic?

author: KerimF
author_rank: Frequent Contributor
timestamp: June 23, 2023, 04:49:25 pm
content: Quote from: Kim Christensen on June 23, 2023, 01:00:29 amIf you mean by 'the guy' me, I am an ordinary independent engineer who has no more the privilege to order and buy anything from abroad (due to the World's Regulations, not applied on Canadians).If you mean by 'the guy' the person who requested the unit, he was likely a technician. I hardly knew from him the reason for which he was looking for such a power converter. He first told me that the load is somehow resistive, and the output regulation is not that important. So, he had likely no clear idea on how power from solar panels could be transferred efficiently to their DC to AC inverters (DC current to AC voltage, likely 3 phases for high power motors). Anyway, I don't think I will see him again.

author: Kim Christensen
author_rank: Super Contributor
timestamp: June 23, 2023, 11:12:48 pm
content: Quote from: KerimF on June 23, 2023, 04:49:25 pmI meant the guy who made the request to you. But now I understand how your country's import restrictions would motivate someone find an unconventional solution.I still think that a change over switch, especially if operated manually, would be the simplest low tech solution for the guy and could probably be procured locally or be unrestricted.

author: KerimF
author_rank: Frequent Contributor
timestamp: June 23, 2023, 11:49:43 pm
content: Quote from: Kim Christensen on June 23, 2023, 11:12:48 pmI agree with you.But perhaps, I say perhaps because I am not sure of his situation, his load (as a power motor for example) has to work on 3 phases and his AC source is of one phase only. Even if this is the case, it is better for him to look for a 1-phase to 3-phase converter and a manual 3-phase changeover switch.