# DIY High Power Boost Converter



## nulluser (Mar 4, 2012)

I'm curious too see some math worked out for the required inductor size.

Here is some reference: http://www.ti.com/lit/an/slva061/slva061.pdf

http://www.stevehv.4hv.org/boost_converter.htm


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## piotrsko (Dec 9, 2007)

Does it need an inductor? we did voltage doublers and triplers way back in the tube days with capacitors. down side would be finding caps that could handle the current.


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## meanderingthemaze (Jan 25, 2010)

I'm no expert on this which is why I am posting here to get feedback. But you can see the basic circuit here:
http://en.wikipedia.org/wiki/Boost_converter

Looks like modern design dictates the use of an inductor and probably some serious IGBTs for the switching. 

Not sure what -let's say- the Soliton controller design is like inside, but my guess is that it would require a hardware redesign to build something like this into an existing controller. Tesseract?


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## SandRailEV (May 11, 2012)

I am, not understanding why you would want or need one...


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## bjfreeman (Dec 7, 2011)

This is done in high powered (10KW) inverters.
two stage boost the DC, then create the wave form.
The DC boost uses Multiple Boost circuits in parallel.
Each circuit can handle about 70 amps.
Realestate is important since each Boost Coil need not be coupled to the next one.
A scheme of turning each coil 90 degrees helps with this.
The can be a high frequency Circuit (about 10KHz) since the power stage produces the wave form for AC.
however if you get to 765 volts for the DC, you only need 300 amps for the output to achieve over 200KW.

the DC can be made with standard chips. if the output wave form is to be varied, then a micro should produce this, other wise it can be done with standard chips also.

That said, using such a scheme for a controller brings in the surges. so if you have hardware give a constant voltage, you need a capacitor bank to absorb the surges. They do this in the HEV Buses.


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## SandRailEV (May 11, 2012)

bjfreeman said:


> This is done in high powered (10KW) inverters.
> two stage boost the DC, then create the wave form.
> The DC boost uses Multiple Boost circuits in parallel.
> Each circuit can handle about 70 amps.
> ...


 
Well, if you built your battery pack for the final voltage you want going into the controller, you eliminate a companent of loss as well as weight...

Why would you not just design your pack for the voltage you want instead??


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## bjfreeman (Dec 7, 2011)

SandRailEV said:


> Well, if you built your battery pack for the final voltage you want going into the controller, you eliminate a companent of loss as well as weight...
> 
> Why would you not just design your pack for the voltage you want instead??


Cost of batteries.
I have 398V that I used with a expermental 100KW motor.
the 200KW motors, i had built, are higher voltage to keep the Current to about 300 amps.
to have 765 volts would just about double my cost, which at the time was about $600 a cell. A capacitor bank is 1/7 the cost.
I am not concern about wieght so much, since it is a motor coach and Water, Waste, Propane, Generator are other weights as well. I am more concern about Drag from a flat front end @60 mph.


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## SandRailEV (May 11, 2012)

bjfreeman said:


> Cost of batteries.
> I have 398V that I used with a expermental 100KW motor.
> the 200KW motors, i had built, are higher voltage to keep the Current to about 300 amps.
> to have 765 volts would just about double my cost, which at the time was about $600 a cell. A capacitor bank is 1/7 the cost.
> I am not concern about wieght so much, since it is a motor coach and Water, Waste, Propane, Generator are other weights as well. I am more concern about Drag from a flat front end @60 mph.


 
Ok, I see what you're doing there. It doesn't seem to me like it would be a common item in an EV though... I have used small(er) boosters in other applications but quite honestly wasn't impressed with their performance. Of course these were manufactured items designed specifically to boost sagging SLA voltages up to usable voltage for voltage-sensitive electronics.


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## bjfreeman (Dec 7, 2011)

The other consideration for me is I really want to become a Fuel cell power vehicle.
My target is the Ballard 150KW PEM cells output 465-730 Volts @300 amp (900lbs). estimated cost is $450K per unit, not counting the tanks and hardware.


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## PStechPaul (May 1, 2012)

If you do not need isolation, you can just add a 72V to 72V converter in series with the 72V battery pack. This is similar to an AC autotransformer or boost transformer. So the converter itself will draw 300 amps while the batteries will supply 600 amps total. Thus the converter would need to be only rated at 72*300 = 21.6 kVA.

The type of converter I have in mind is essentially the same as what I have built, but just ten times larger. Or you could build six of them with 12V input and output at 300A, and connect them in series. 3600W each.

If you go with the 12V modules, you would probably do best with MOSFETs, which should be rated at about 50V. Here is an automotive MOSFET rated at 55V and 89A and RdsOn of 10 mOhm. In a push-pull configuration you could have four of these in each leg which will handle 350A at 50% duty cycle, and power dissipation of 306 watts for both legs. For a 3600 watt module that's better than 90% efficiency. And these MOSFETs are only about $2 each, so you could add even more.

http://www.newark.com/international-rectifier/auirl3705n/n-ch-mosfet-automotive-55v-89a/dp/54T9027

You will need multiple conductors to share the load. The heat sinks can be solid aluminum so the drain tabs can be bolted directly, but the source pins need to be terminated to a PCB with wide tracks and several layers, or as I did with my design, I soldered the drain pin to a piece of #12 solid copper wire which was connected to a terminal block. It should handle 30-40 amps RMS in free air or with forced air cooling.

Or you can go with higher rated transistors in bigger packages, such as this 60V 293A beast which is still only $6. 
http://www.newark.com/international...f/n-channel-mosfet-60v-293a-d2-pak/dp/27P5260

Here are some larger modules rated at 75V and 480A, for just $24 each:
http://www.digikey.com/product-detail/en/IXFN520N075T2/IXFN520N075T2-ND/2217438

For the transformer, you just need something that can handle the power as well as the wire sizes you will need. With MOSFETs you can go up to 100kHz or so and use ferrite cores. But you need lots of heavy copper turns, probably best accomplished with copper foil. Alternately, you may be able to use a toroid with silicon steel tape wound core, and run it at up to 10kHz or so. You can probably get 5 volts per turn at that frequency, so you won't need many turns. For a 12 volt unit you can probably use bus bar for the primary. A 3600 watt toroid will probably be only about 4"x6" or so, and cost under $100. They are much more rugged than ferrite, too.

Since the drive is a square wave, the full wave rectified output will be almost pure DC, so very little capacitance will be required. You should not worry about regulation and adjustment, so basically the output will be a fixed multiple of the input.

Using the same circuitry as the one I have built, the square wave can be generated by a PIC, or you could use something like an SG3526, which has gate drivers built in. Otherwise, use some good gate drivers to reduce switching losses. In general, you will get less switching losses if you keep the voltage swings low, so the 12V to 12V units might be very efficient. Or maybe they should be 12V to 72V and be wired in parallel.

Of course the devil is in the details, and my experience has been only in lower power circuits like my 1.5 kVA module. But it's usually not too difficult to scale up, especially if you use multiple modules in series and parallel. And if there's a failure, you can probably disconnect the bad unit and still get enough power to limp along, and not be totally stranded. 

If there is enough interest I can devote more time and effort into a more detailed plan. Let me know


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## steven4601 (Nov 11, 2010)

A lightweight, small form factor Boost topology allowing to pass through many kilowatts may be very problematic!

Storing high amounts of energy in inductors is lossy. Better is to design an (auto)transformer or something along those lines. Make the operating frequency as low as you can go while keeping within the sat.limits of the iron(ferrite).

Expect a 100kw dc-dc to weigh somewhere between 50 to 100lbs.

It may be cheaper both financial as weight-wise to start off with a high voltage pack


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## psron (Jun 19, 2012)

I know it's an olllllld topic, but Toyota does this in every Hybrid.

The battery pack in my Highlander Hybrid is only 288V, whereas the Motors are 650V AC 3-phase.

Their Boost inverter is bi-directional... so that regen still works... SMART FOLKS!

Electric motors (especially AC) are much more efficient as their operating voltage increases... due in large part to the reduction of I*R losses (high currents result in higher resistive losses).

Higher voltage motors are substantially lighter/smaller than low voltage motors. All HV wiring is also much lighter and cheaper. 

The Highlander boost inverter is capable of driving both front & rear traction motors, for a combined total of 173kW (235HP), which comes out to around 266 Amps at 650V output.

THAT'S BIG... but it's small.

See the Prius version in this video:
https://www.youtube.com/watch?v=UxuqHcUbSQ0

See the boost converter in the lower-left corner of the inverter/converter assy here:
https://www.youtube.com/watch?feature=player_detailpage&v=UxuqHcUbSQ0#t=486

He describes the system here:
https://www.youtube.com/watch?feature=player_detailpage&v=UxuqHcUbSQ0#t=629

It's comprised of:
Reactor (Inductor)
Capacitor Module
IGBT Switching module


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