# High-power, high-voltage DC/DC bidirectional converter?



## iruraz (Sep 4, 2012)

FriedChip said:


> I was looking for something like 48 V one side and 600 V in the other side. Power about 2,5kW. I can't find nothing in the market. I guess it's something too specifical.  Thank you.


@FriedChip,

As fas as I see the specs it is not adequate for you. But you should view it.

http://delphi.com/manufacturers/auto/hevevproducts/converter/dc-to-dc-converter/


----------



## FriedChip (Apr 29, 2013)

iruraz said:


> @FriedChip,
> 
> As fas as I see the specs it is not adequate for you. But you should view it.
> 
> http://delphi.com/manufacturers/auto/hevevproducts/converter/dc-to-dc-converter/


Thanks a lot iruraz, as you say it's not adequate for me. My converter hast to transfer power from low voltage to high voltage 2.5kW and from high voltage to low voltage 1.5kW. Anyway I will take a deeper look on it, thanks again!


----------



## Jan (Oct 5, 2009)

Maybe Brusa has an option.

http://www.metricmind.com/category/ev-dcdc-converters/page/1/


----------



## FriedChip (Apr 29, 2013)

Jan said:


> Maybe Brusa has an option.
> 
> http://www.metricmind.com/category/ev-dcdc-converters/page/1/


Wow, that's really close to what I need. I haven't been able to find anything like this. ¡Thank your very much Jan!


----------



## FriedChip (Apr 29, 2013)

Jan said:


> Maybe Brusa has an option.
> 
> http://www.metricmind.com/category/ev-dcdc-converters/page/1/


I have found this by following your advice: http://www.brusa.biz/index.php?id=144&L=1

The thing is I have heard that they are really high priced.


----------



## PStechPaul (May 1, 2012)

That's a really good idea. I'd be very interested to find out just how it works. Here is a user's manual that goes into some detail:

http://www.metricmind.com/wp-content/uploads/2011/09/BSC624-12V_User_Manual_080815.pdf

Actually, I just sketched up a block diagram and it seems that you just need a bridge circuit on both the primary and secondary windings of a transformer. If you drive the gates of the primary, the diodes of the MOSFETs or IGBTs of the secondary function as a full wave bridge rectifier, so it functions in the forward direction. Thus, a 72V battery pack could be used to provide 288 VDC with a 4:1 ratio. A sensor could determine when the motor operates in a regenerative mode, where current is injected into the high voltage link bus, which raises the voltage on the link capacitors. This could shut down the primary drive and operate the secondary bridge elements to produce AC on the transformer secondary, which will create a voltage on the primary that will be rectified and used to charge the 72V battery. 

Cool!


----------



## PStechPaul (May 1, 2012)

Here's a simulation of a 48V to 320V bidirectional DC-DC converter operating at 25 kHz:










As shown, the bridge circuit on the primary side are converting 48 volts from the battery to about 300V on the secondary, into a 100 ohm load, for about 900 watts. The secondary bridge circuit is inactive, so it just performs rectification through the MOSFET body diodes.

It can be run in reverse siply by deactivating the primary switching and activating it on the secondary. Thus the DC bus link voltage from the VFD will be transferred to the primary side batteries. There will need to be some sensing and control circuits as well as the actual PWM drive, but those are well-known concepts and should not be difficult to implement.

This will be especially useful for my smaller tractor projects so that I might use 4 12V 100Ah deep cycle batteries instead of 20+ smaller (8-12 Ah) SLAs.


----------



## Tesseract (Sep 27, 2008)

PStechPaul said:


> ...It can be run in reverse siply by deactivating the primary switching and activating it on the secondary. ...


Nope. There needs to be inductance in series with the transformer. If the inductance is on the secondary side then the topology is the traditional full-bridge converter, which can also be described as an isolated buck converter.

If the inductance is on the primary side then this is a boost-derived topology. There is a serious issue with startup in the boost full-bridge because the output voltage (reflected through the transformer turns ratio) must always be larger than the input voltage, but at startup this condition is not true and so the switch duty cycle is "undefined". A great many kludges have been contrived to get around this problem, but they always result in either higher stress on the switches, or a much higher component count (and usually both).

tl;dr version: bidirectional converters are not practical.


----------



## PStechPaul (May 1, 2012)

Well, all transformers have some effective inductance in series with the primary or the secondary. The one I have characterized has a coupling factor K of 0.998, which is very little, but I have also run the simulation with 0.995 or less, and it works acceptably well. There is a problem at start-up which I also encountered with my 12/24 VDC to 320 VDC booster that I built and used on my little tractor project. 

The problem is, as you state, that the secondary load and capacitance will be reflected to the primary and present as a very low impedance approaching a short circuit, and some inductance is needed to limit the peak current of a PWM square wave. So I found that I could start the circuit with a PWM duty cycle of about 5% or 1 uSec pulses at 20 uSec intervals alternating polarity of drive. Once the output starts rising, the PWM can be increased by monitoring the peak current, and when the output voltage reaches its target value of about 300V, I find that the efficiency is about 95%. Here are the waveforms near start-up:










I think it will be worthwhile to do further work on this design and put together a working prototype, perhaps at first only 100 watts or so. Then I might expand that to 1000W modules that can be connected in parallel for higher power. For my own immediate purposes 2-3 kW will be plenty.


----------



## iruraz (Sep 4, 2012)

@PStechPaul,

Could you please upload your LTspice file? I would like to analyze it.

Regards.


----------



## FriedChip (Apr 29, 2013)

I'm more interested in buying one. But all information is appreciatted, thank you.


----------



## PStechPaul (May 1, 2012)

Here is the LTSpice file:

http://enginuitysystems.com/pix/48V-320V_DCDC_Bidirectional.asc

The design is not really optimized and there may be some mistakes, but it's close enough to get an idea of how it works.


----------



## NewEagle (May 20, 2013)

The Delphi dc-dc did not meet your specs at this time, but if you have any questions please reach out to us here at New Eagle. We have the Delphi Dc-Dc's in stock and are a preferred distributor. [email protected]


----------



## PStechPaul (May 1, 2012)

More information on the Delphi DC-DC is at:
http://www.neweagle.net/support/wiki/index.php?title=Delphi

It's designed for maintaining the vehicle 12V accessory power from the traction pack, so bidirectionality is not needed or desired, but it looks like a solid design.

Here is a good detailed article on the design of a 2.5 kW DC-DC converter using a full bridge circuit as I propose:
http://webfiles.portal.chalmers.se/et/MSc/Christian%20Andersson.pdf

This also seems pretty good:
http://www.wpi.edu/Pubs/E-project/A...44/unrestricted/High_Voltage_DC_Converter.pdf

And this:
http://www.pes.ee.ethz.ch/uploads/t...ng_Capacitor_Banks_of_Power_Modulators_02.pdf


----------



## iruraz (Sep 4, 2012)

PStechPaul said:


> Here is the LTSpice file:
> 
> http://enginuitysystems.com/pix/48V-320V_DCDC_Bidirectional.asc
> 
> The design is not really optimized and there may be some mistakes, but it's close enough to get an idea of how it works.


@PStechPaul,

Thanks. Optimization is not important for now. I only want to analyze it.

Regards.


----------

