Three Phase Voltage Multiplier - Page 1
Forum section: electronics / projects

author: Unknown
author_rank: Unknown
timestamp: February 11, 2014, 06:10:31 pm
content: I do not know if anyone has asked this previously, so I apologize in advance.I am looking for the schematic for a three phase Y or three phase Delta driven Capacitor / Diode voltage multiplier. I'm familiar with the many documented designs for Cockcroft Walton, Greinacher, Villard multiplier geometries with both half wave and full wave rectified implementations, but I have not been able to locate a design based on a three phase AC source.My application is to boost the voltage produced by multiple vertical axis wind turbines employing three phase permanent magnet generators with a typical output of 12VAC so that the power transmission can span the distances across my 67 acre property. The DC output from the voltage multipliers can buss onto a single low loss kilo-volt transmission line which can then be down converted into usable power at the load.By the way, Inverter designs employing kilo-volt DC input would also be appreciated.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 11, 2014, 06:26:49 pm
content: How much multiplication were you hoping for?Intuitively, it should be the same thing, except the chain of capacitors coming up from ground becomes neutral rather than ground, and instead of a ladder of diodes and caps joined onto that, you have one such ladder for each phase. This is wye; there should be a delta form that's very similar. A full wave device can easily be made by stacking two end-to-end and driving the middle. (Adding a delta-wye phase shift transformer, and doubling the circuit again, could get you a "12 pulse" multiplier, but that would be massive for so little value.)But really, use a 240:12V iron cored transformer backwards. Can't get much better than that. Fairly cheap, much more efficient, and can be transformed up and down again just as easily. To do three phase, you'll need at least two ('open delta'), or a proper three phase unit (which should be available, but may not be as cheap as a pair of commodity transformers). If you want to rectify afterwards for distribution (saves on synchronizing them all, or using individual "grid" tie converters of some sort), it'll be far more efficient to do it here rather than at 12V, especially compared to a multiplier.Tim

author: woodchips
author_rank: Frequent Contributor
timestamp: February 11, 2014, 10:04:18 pm
content: A toroidal transformer seems to be the answer.If you want a bit of reading try thishttp://www.thebackshed.com/forum/forum_posts.asp?TID=1138fascinating.

author: kaindub
author_rank: Regular Contributor
timestamp: February 12, 2014, 09:08:49 am
content: Your problem is not at the transmission end but at the receiving endAt the transmission end, just use a three phase transformer, boosting the voltage to whatever level you want to transmit at. Rectify the output with a simple three phase rectifier and away you transmitAt the receiving end, you have to convert it down to some useful voltage.I assume you need AC.The usual way is with a self commutated converter. It's a three phase SCR rectifier connected to the DC. The rectifier outputs, in this case what you would normally call the input lines to a rectifier, connect to a transformer.This is neither new nor tricky.But not something that's cheap or commonly available.Sorry I can't recommend any modules.Robert

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: February 12, 2014, 12:58:59 pm
content: Quote from: Steaphany on February 11, 2014, 06:10:31 pmHow much power do the turbines generate?I assume that the frequency of the AC varies proportional to the wind speed? What is the range of frequencies that you have to deal with?Are the turbines close together?Jay_Diddy_B

author: AlfBaz
author_rank: Super Contributor
timestamp: February 12, 2014, 01:34:06 pm
content: Hi SteaphanyI'm curious to know if you have done some research into this and it's the reason you want to transmit the generated power how you have mentioned.To me it seems counter-intuitive and unnecessarily expensive but if this is something you have looked up I would be interested to read upon the why'sI'd also like to see Jay_Diddy_B's questions answered but would also like to know if the 12VAC output is straight out of the alternator or does it come out of some module. If it's the latter is it an alternator or a generator?

author: tszaboo
author_rank: Super Contributor
timestamp: February 12, 2014, 03:33:31 pm
content: Quote from: Steaphany on February 11, 2014, 06:10:31 pmThis thing does not exist. It cannot be done effectively. The frequency changes with the wind. the frequency is to low, so you need too big capacitors. The capacitors have to be rated for too high currents. Even if you make one, it is not regulated.The practical limits for switched capacitor is 0.1A and few stages.For this application, you have to use switching power electronics. Coils, transformers, mosfets, IGBTs and stuff.

author: ConKbot
author_rank: Super Contributor
timestamp: February 12, 2014, 05:21:18 pm
content: Quote from: NANDBlog on February 12, 2014, 03:33:31 pm+1 to a voltage multiplier not being practical hereIf you have 50 to say 500 Hz, use an off the shelf transformer to get the voltage up, send it across your property (3 phase AC, or HVDC) If youre charging/running a battery bank, see if your charger will run happily off of ~200-400VDC (you could use a variac + rectifier to test) If it does, I'd just do HVDC, and send your HVDC right into your battery charger. If it has an active PFC input(90-250VAC, 50,60 Hz on the input is usually a clue that is has APFC) , there is a decent chance it will run from DC.

author: C
author_rank: Super Contributor
timestamp: February 12, 2014, 09:23:03 pm
content: Hi Steaphany,Have you thought of what a load connected to the generator will do to your vertical axis wind turbines?No load = no power produced.Too much load = generator burning up or vertical axis wind turbine stopping.The wind determines the best spot between these two extremes.Add to this what a diode will do when converting the AC output to DC. With Three phase you would be going from no load to peak load many times for each AC cycle. You have some mass in your generator that will try to smooth the shocks from the load back to the wind blades, but some amount of the shock will get to the wind blades. Shocks like these will change the life of the vertical axis wind turbine.A lot of things can and will try to make the load on the wind turbine more constant and by doing this removing some of the above stress on the wind turbine.To get the most from the wind turbine you need a load that lets the wind turbine spin at it's max power point for that wind that is causing the spin.To get the most from the generator you need a load that lets the generator work at it's max power point for that wind that is causing the spin.With many wind turbines all working at a different frequency due to the wind at some point you will have a need to combine the outputs.As others have suggested a transformer could be a good first step if you can find or build one that will cover the frequency range of the wind turbine generator. But you still have the different frequency problem.I would suggest that a circuit like a power factor correction circuit could be used to supply the max power point load to the generator while also converting the AC output of the generator to a high DC value. Most of these types of circuits use inductive kick to create this DC value so the actual DC output voltage could change a lot. This would allow you to combine many generators at this point.The EMI filter on the input to the PFC would hide the high current spikes that the PFC would create while allowing you to create a close to ideal load for the generator.A MPU based PFC would give you the most options. You may want to look at some of the examples that ST has for their STM32. I am thinking of the solar collector example, the PFC example & the inverter example.Quote from: Steaphany on February 11, 2014, 06:10:31 pmFrom what little I have looked at high voltage DC transmission lines, the conversion from the high voltage is done with a stack of lower voltage inverters that are operated in a balanced mode to keep the input to each with in limits. Part of each inverter is floating.C