Benchtop 3 Phase Generator? - Page 1
Forum section: electronics / projects

author: envisionelec
author_rank: Frequent Contributor
timestamp: December 05, 2015, 08:03:23 pm
content: Hi, I am developing a 3PH input SMPS and would like to know of any alternatives to the rotary converter for generating a benchtop 480V power source up to about 1kW. I understand I could use a VFD, but I would not be able to increase the voltage unless...I used a step up transformer. The variable frequency control would be helpful.Am I overthinking this? Has anyone tried this sort of thing?

author: TimFox
author_rank: Super Contributor
timestamp: December 05, 2015, 08:55:40 pm
content: There are many electronic (non-rotary) 3-phase generators. For example, seehttp://www.phaseperfect.com/

author: Jeroen3
author_rank: Super Contributor
timestamp: December 05, 2015, 08:58:47 pm
content: In most vfd's you can adjust the voltage at nominal speed. (since it's for motors)Only some can actually do this on the fly. I am also looking for a 3 phase "benchtop" power source / simulator, but so far all I found were 19" racks with more zeros in the price than is affordable.Note that the distortion and noise is significantly higher than with a rotary converter. Even with several transformers. (vfd's can't handle capacitive load, so a filter won't work)

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 05, 2015, 09:09:16 pm
content: VFD into a 3-pahse variac?

author: johansen
author_rank: Super Contributor
timestamp: December 05, 2015, 09:27:04 pm
content: just put an LC filter on the output of a 480 volt vfd, which ebay has lots of.You will need about 1mH per phase and 10uF at 8khz pwm frequency, then another stage in another box to clean up the noise.1 pound of 16 awg wire coiled up in a coil the shape of a donut should be enough inductance per phase.A 2 hp 480 volt VFD is pretty marginal to drive a 1KW smps downstream, but i think it can be done.You might try using a line reactor as a three phase choke but at the prices you pay for them, you can buy more than enough copper to make an air core inductor of the same millihenries.you may need a transformer anyways if you want 480 volts of three phase sinewave plus neutral because the modulation schemes used in those inverters fill the output with harmonics to get the voltage up.the cheapest way to get a sine wave out of them is increase the dc bus voltage till you do, or lower the output volts and boost it back up with a transformer..my 480v vfd shuts down at 760vdc on the dc bus if i recall correctly.. nominal dc bus voltage is only 676 or 480*1.41.another thing you can do is feed the VFD whatever it needs, 240, 480vac but feed the IGBT bus a different voltage to get the output voltage up while still maintaining a clean sinewave output.here's an example of an older mitsubishi freqrol inverter trying to deliver more volts than it can...

author: envisionelec
author_rank: Frequent Contributor
timestamp: December 05, 2015, 10:31:35 pm
content: Quote from: mikeselectricstuff on December 05, 2015, 09:09:16 pmMike, that's a great seed for an idea. Now, I have only 1 240V single phase mains input. It seems I could buy a 240V to 480V transformer and use that to drive the VFD and then the VFD to a variac. That way I could have variable voltage and frequency (50/60Hz only).This isn't a budget build. If I can do it for under $2k, that would be great. I would even entertain one of those benchtop converters but I'm having trouble finding them. As you can imagine, trying to Google "480V 3 Phase Power Supply or Generator" gets me lots of unusable results.

author: envisionelec
author_rank: Frequent Contributor
timestamp: December 05, 2015, 10:37:02 pm
content: Quote from: TimFox on December 05, 2015, 08:55:40 pmGreat Scott. That's huge. I'm looking for something a little smaller.But thanks for leading me in the right direction.

author: envisionelec
author_rank: Frequent Contributor
timestamp: December 05, 2015, 10:40:13 pm
content: Quote from: johansen on December 05, 2015, 09:27:04 pmI like this idea and it's cheap enough to try. So Mains -> 240 to Isolation 480V transformer -> VFD -> Filter -> VariacI like the versatility in this arrangement. It can be broken down and reused for other purposes.Thank you, all.

author: Pjotr
author_rank: Frequent Contributor
timestamp: December 05, 2015, 11:40:30 pm
content: Quote from: envisionelec on December 05, 2015, 10:31:35 pmThen you will probably need a full protected one as well. Look here:http://www.programmablepower.com/ac-power-source/Ls-Lx/Overview.htmBut be prepared, those are pricey (around 10K$) and noisy! An option is to rent oneDon't full you self, building something a like yourself takes a multiple amount of salary (I guess) and a lot of time.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 05, 2015, 11:45:41 pm
content: Quote from: envisionelec on December 05, 2015, 08:03:23 pmWhy benchtop? If it's big/noisy, put it in another room

author: envisionelec
author_rank: Frequent Contributor
timestamp: December 06, 2015, 12:08:19 am
content: Quote from: mikeselectricstuff on December 05, 2015, 11:45:41 pmIt was more of a description than requirement.

author: johansen
author_rank: Super Contributor
timestamp: December 06, 2015, 07:37:40 am
content: you don't even need a transformer to drive the vfd, you can do it with a voltage doubling dc rectifier.if you use the capacitors in the 480v inverter (most likely there are two 400v caps in series) as part of the voltage doubler... you will need to derate the VFD due to excess ripple current.