12kW power supply from 880-1000v input? - Page 1
Forum section: electronics / general

author: ocset
author_rank: Super Contributor
timestamp: April 03, 2020, 07:26:25 am
content: HiA way of doing this Power supply spec?…..Vin = 1000v to 880v (source is 1000V but cable resistance between source and Power supply is 7.5 Ohms so actual vin drops with load)Vout = 48VPout total = 12kWEfficiency 0.85Pin total = 14100WChosen Topology = In blocks of three Two Transistor forward converters with inputs stacked and fed from three “totem pole” series capacitors.7 totem poles altogether. (ie 21 x 670W two transistor forwards).All outputs paralleled.12 Amp Current clamps on output of each two transistor forward so none hog the current.Do you see any problems with this?

author: geggi1
author_rank: Frequent Contributor
timestamp: April 03, 2020, 07:50:31 am
content: If you can use of the shelf units one way to do this is how we done similar things on ROVs.Put a transformer in first to drop the voltage down to a reasonable level 4-500V at the maximum voltageUse of the shelfe switching power supply with a wide voltage range. In this example you can probaly use supplies that will work from 350V to 600VRemember that the drop will be less if you transform further down and at 230v the drop will be in the range of about 30V something that most of the shelf equipment can handle.But!This solution is heavy and bulky and is normaly not done at these power levles.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 03, 2020, 08:35:57 am
content: 1) Change the design of your drone motor BLDC controllers to accept a higher voltage than 48V, say 150V. This shouldn't be a problem if the motors are somewhere around 40-50V nominal. The motor controller works like a buck, and you likely don't need very low rpm, very low power in a drone, so the minimum pulse width won't become a problem even if your DC link is significantly higher than the voltage rating of the motor.2) Drop the 1000V supply to that chosen BLDC DC link value, say 150V, with a multiphase synchronous buck. Likely doable with off-the-shelf magnetics. Running in CCM, the inductor utilization is good and you don't need to think about winding transformers and snubbing their leakage inductances and whatnot. 96-97% efficiency easily achievable.So now you have a cascade of two power converters say 7:1 then 3:1, instead of 21:1 then 1:1. One of the power converters, the motor inverter with a large inductance (motor windings), is there anyway, utilize it to do part of the voltage dropping task, that's my point.

author: fcb
author_rank: Super Contributor
timestamp: April 03, 2020, 10:42:33 am
content: Treez, can you lump all your future posts about the same project into one - it's getting hard to follow.So just to understand - you want to drive 12,000W of brushless motors over a long cable, so you are jacking up the DC to 1000V. How much of an issue is weight? Is it a one-off proof-of-concept? Do you have a decent budget to solve the problem?If you don't have the time/budget to develop a high voltage motor and high voltage BLDC driver (the lightest way) - then I'd build simple 1000V to 48V bucks, one per motor drive amplifier.Assuming at least 8 motors, thats 1500W per buck converter. There are plenty of 1200V+ IGBT/MOSFET's about. The maths is straightforward, the only two areas that need careful selection are the isolated driver for the transistor and main inductor design.

author: ocset
author_rank: Super Contributor
timestamp: April 03, 2020, 03:40:58 pm
content: QuoteWeight is a very significant issue yesIt is one off.Budget is small.thanks but we cant do eight separate bucks, ie one for each motor....there is one single power rail of 48V...and it feeds all the motors...we're stuck with that.We could do 1000v to 48v bucks in parallel, with output current clamps on each...plus output drooping by iout sense and reduce reference to error amplifier....but prefer to stack two transistor forwards...since the switching losses with a 1000v to 48v buck will be quite something...even if we do it with a cascaded buck.Also, the two transistor forward as you know has leakage L in the txformer, so this makes the turn-on spike slightly less….so slightly less switching losses…..along with the lower vin due to the stacking which is a nicety.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 03, 2020, 08:55:17 pm
content: Don't forget that the BLDC drivers are bucks that switch at fairly low frequency (some 20kHz maybe) and have a lot of inductance. Use their ability to convert the voltage down for "free" (up to some limit).Even trying to source higher-voltage motors would help? I know Chinese motor factories are very willing to custom wind you motors. For the one-off, you might be able to DIY one set of motor windings, just remember the insulation at higher voltages. Like, reduce the wire thickness (or the number of paralleled strands) and increase the number of turns.This would allow you to get rid of the conversion stepcompletely, directly powering the BLDC bridges.

author: mzzj
author_rank: Super Contributor
timestamp: April 03, 2020, 09:08:57 pm
content: Quote from: treez on April 03, 2020, 03:40:58 pmWhy do you get all the fun projects?

author: Gyro
author_rank: Super Contributor
timestamp: April 03, 2020, 09:26:02 pm
content: I'm beginning to think that all of this drone's power is going to be devoted to lifting its own 250A umbilical (or some small portion of it!).I'm not sure I'd want to be anywhere in the vicinity when it's up and running.