Design recommendation pfc 5kw - Page 1
Forum section: electronics / projects

author: yelstor
author_rank: Contributor
timestamp: February 13, 2018, 08:03:01 pm
content: HelloI need to design a pfc with an output of 5kw. The drawback is that I need a 110Vdc output, with an input of 120vrms. Having an output voltage lower than the input voltage, I can not use a boost converter as in the vast majority of cases. I can not use a buck converter either because its thd is higher than 5%. Could you give me some recommendation?I have thought to raise the voltage to 400vdc with a boost converter, and then rerduce it with a 110vdc with a buck converter, but it could be expensive. I also thought about the possibility of using a sepic, but I have never used this type of converter, and I do not know if it is recommended for the power of 5kw. One person told me that flyback was also possible, but according to the literature flyback is not recommended for powers greater than 100W. It may be possible to use flyback for a power of 5kw?Thank you for your recommendations

author: fourtytwo42
author_rank: Super Contributor
timestamp: February 13, 2018, 08:08:15 pm
content: Given you are cost sensative a bit more information about the application would be helpfull in particular the nature of the load and why it requires 110Vdc and cannot apparently accomodate something higher. Forget flyback at 5Kw, never seen them used for pfc anycase. Boost/Buck is my natural answer. 5Kw is a lot of power so the pfc inductor is going to be expensive anyway, no way around that one.

author: jbb
author_rank: Super Contributor
timestamp: February 14, 2018, 12:14:07 am
content: Some scoping questions:- isolation needed?- single or 3 phase?- what production quantity?- are you comfortable with microprocessor control?- what output ripple is acceptable?- how do you feel about large capacitor banks?The most likely to succeed (in my opinion) is a boost PFC stage to approx 190V DC, followed by a buck stage. This has 2 advantages: output voltage will have very low 120 Hz ripple, and output short circuit / overload protection is possible.An off-the-wall solution: buck PFC with a (parallel connected) Active Power Filter to clean up the waveform. Advantages: output short protection, probably more efficient (most power only goes through 1 conversion stage) and fun. Disadvantages: output voltage will have 120 V ripple, more complex.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 14, 2018, 03:28:25 am
content: Where are you getting 42A of 120VAC from??!Tim

author: jbb
author_rank: Super Contributor
timestamp: February 14, 2018, 04:43:18 am
content: ... 120 Hz ripple, sorry.(But that improves to 360 Hz if a three phase supply is used.)

author: yelstor
author_rank: Contributor
timestamp: February 14, 2018, 02:51:16 pm
content: QuoteIsolation is not necessary, but it would be the best.QuotesingleQuotethe production will be about 20 in principle.Quotethe bidding forces me to use digital control with a DSP.QuoteThe ripple voltage should be 200mv (I'm not sure if this is very easy to achieve)QuoteWell, as long as the circuit works, there's no problem. There is no size limitation.the efficiency as much as possible must be greater than 95%, and a THD less than 5% at full load.I read that the pfc buck has a higher THD than I need, besides there is not enough literature.I think it's best to use the most widely used thing that is boost pfc + buck.Now my question is whether the buck will have a good efficiency? , or is it better to use fullbridge LLC ?.

author: jbb
author_rank: Super Contributor
timestamp: February 15, 2018, 03:11:34 am
content: OK, no we’re getting somewhere.First up, what’s your power E experience like? Have you dealt with mains and large capacitors before? Have you done real time DSP control before? Do the phrases ‘soft charge’ or ‘inrush current limiting’ ring a bell?Second, what resources do you have? Sufficient time and budget? Mechanical engineering support? Scopes, differential probes, current probes, dummy loads?Third, that 200 mV voltage ripple spec is going to be hard.A single phase input will only give you bursts of power (at twice the line frequency, probably 2*60=120Hz). Capacitors are used to smooth out the bumps.Straight away you can throw out a single stage Buck PFC, because it would need horrifying amounts of capacitor to get that level of smoothing.I would tend to favour boost type bridgless PFC to approx 200V DC. (120V AC plus 10% high line condition times 1.41 plus 5% control margin, then round up.) Power devices should probably be 300V rated or higher. You may find the best devices around 650 V as this is used for ‘worldwide’ applications.Thereafter a dual phase synchronous buck converter can step down to 110V DC. However, you need to find out more about the expected usage: will high common mode voltages be a problem? (Warning signs are tight ripple specifications, long cables, battery banks, solar arrays and similar items with large surface area).If you need low common mode voltage, isolation is required and an LLC is perhaps a good option.

author: Phoenix
author_rank: Frequent Contributor
timestamp: February 15, 2018, 05:15:29 am
content: Realistically how much power electronics experience do you have - a 5kW supply is no easy feat? Selling 20 units doesn't really cut it to spend years making your own supply unless you have incredibly specific requirements.Is it possible to use an off the shelf power supply?Try MagnaPower but it would only if connected line-line to get 220V input:http://www.magna-power.com/products/programmable-dc-power-supplies/ts-series#modelsPowerBox looks to fit the bill:http://www.powerbox.com.au/euro-cassette-schaefer-c4800aReach out to the manufacturers, see what they offer.