# Bi-directional buck-boost converter, battery simulator



## kennybobby (Aug 10, 2012)

Sounds interesting, definitely want to follow...opcorn:


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## bigmotherwhale (Apr 15, 2011)

WolfTronix said:


> Hello,
> I am not sure if anyone is interested in this, but I am in the process of building a 10kW Bi-directional buck-boost converter (48V - 500V).
> 
> This will be used as a battery pack simulator (replacing my large stack of AGM batteries, which are retired from my truck)... I repair motor controllers and battery chargers ( http://www.wolftronix.com/EV.htm ), so a large variable voltage bi-directional buck-boost converter is useful to me.
> ...


I like your idea of a polyphase converter, would you isolate the motor windings from each other? If so would you really need THE Inductors?  
I did some experiments on a similar topology and quite few others involving capacitors but it became difficult mainly due to lack of equipment and (lack of) programming skills. 
I did find that PWM was one of the least efficient ways to control a motor, but the easiest under varying torque load and rpm conditions.

I will keep an eye on what you are up to with great interest.

also if your batteries internal resistances are climbing use a capacitor discharge or inductive kickback circuit, you may be surprised how well these can restore lead acids and nicads and they are easy to make from spare parts. My preference for lead was with discharging a decent size capacitor charged to about twice the battery voltage or slightly under across the battery using a mosfet and a comparator - works great with a solar panel even under moonlight! there are lots of circuits available from the pseudoscience crowd.


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## WolfTronix (Feb 8, 2016)

Well, I am actually upgrading to Lithium-Ion:
http://www.diyelectriccar.com/forum...nginnering-nissan-leaf-bms-serial-169225.html

Getting the lead out.


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## bigmotherwhale (Apr 15, 2011)

I did exactly the same thing  good riddens.

Just watched some of your videos they are good to watch.


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## WolfTronix (Feb 8, 2016)

bigmotherwhale said:


> I like your idea of a polyphase converter, would you isolate the motor windings from each other? If so would you really need THE Inductors?


The poly phase was because the Prius inductor can only handle around 85kW peak, so with 2 or more inductors you can increase the peak and continuous power. 

Ideally the power converter should be able to provide peak power for 30 seconds (or how ever long it takes to get up to highway speed), and receive regen power to go from highway speed to a stop.

Then the battery pack only ever sees the 15kW or so it takes to maintain highway speed. 

Same with the stop and go city driving, ideally, the super/ultra caps provide a buffer for the battery pack.

This is the type of capacitor module I am thinking of:
http://www.maxwell.com/images/documents/hq_48v_ds10162013.pdf
They show up on eBay every once in a while, sometimes inside large UPS systems that have been pulled from service, (you have to look at the pics, most salvage sellers assume they are a battery).


However what you are proposing is what the Solectria (Brusa) AMC2XX motor controllers did:
http://www.wolftronix.com/amc230_514/images/IMG_2825.jpg

Note the 6 inductors (3 in front, 3 in back), split between the motor phases, they implemented the bi-directional buck-boost converter in the motor controller.

The battery stack voltage is 216V and the motor runs around 150V... So they would run in buck mode while accelerating, and then boost mode during regen.

That AMC230 was in sad shape, here is the repair log (I have been told it is a good read), for those that are interested:
http://www.wolftronix.com/amc230_514/index.html

Thanks, 
Wolf


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## bigmotherwhale (Apr 15, 2011)

I was actually suggesting that you could use the inductance of the winding in the motor, instead of using a separate one.


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## WolfTronix (Feb 8, 2016)

bigmotherwhale said:


> I was actually suggesting that you could use the inductance of the winding in the motor, instead of using a separate one.


A bi-directional buck-boost converter is not a motor controller...

It just converts one voltage to another, and allows boost in one direction and buck in the other direction.

i.e. in the Prius it is used to take 200V battery stack and boost it to the 600V that the motor controller works at, and during regen it takes in the 600V and bucks it down to 200V to charge the battery pack.

A motor controller (inverter) still drives the motor.

[Battery] <--> [bi-directional buck-boost] <--> [Motor Controller] <--> [Motor]

Hope that helps,
Wolf


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## bigmotherwhale (Apr 15, 2011)

I know a boost converter is not a controller, 

I was suggesting that if you were connecting the two together why make it a separate system? use the inductances already in the motor. 

a boost converter controller

do you comprehend what im getting at?


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## WolfTronix (Feb 8, 2016)

bigmotherwhale said:


> I know a boost converter is not a controller,
> 
> I was suggesting that if you were connecting the two together why make it a separate system? use the inductances already in the motor.
> 
> ...


No, I don't think I comprehend what you are suggesting...

Perhaps a schematic would help me understand your concept.

Thanks, 
Wolf


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## bigmotherwhale (Apr 15, 2011)

Sure, this is one of them, there are many ways to do the same thing that achieve different current or voltage on the inductor (read that as time to discharge time to charge in motor applications)

The difficulty is that it only works at one speed, at least without switching capacitors around, and also it does not give true 3 phase as you are driving each coil separately not as a pair. so the torque it provides is not like the norm. which is good in some respects and not others as you can quite easily see. 

Also the circuit is single sided.


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## AntronX (Feb 23, 2009)

WolfTronix said:


> The poly phase was because the Prius inductor can only handle around 85kW peak...


Is that max dc-dc power at inductor saturation? Prius boost converter is rated at about 22KW max. I am also looking at Prius inductors to build 100KWp 150V to 400V buck-boost converter using maybe 3 coils and half bridges with common cap bank. But those inductors are kind of hard to find.


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## WolfTronix (Feb 8, 2016)

AntronX said:


> Is that max dc-dc power at inductor saturation? Prius boost converter is rated at about 22KW max. I am also looking at Prius inductors to build 100KWp 150V to 400V buck-boost converter using maybe 3 coils and half bridges with common cap bank. But those inductors are kind of hard to find.


The inductor I used is from a 2nd generation Prius, it should be able to run 250A RMS peak... How I came up with the numbers at the 21 minute mark:
http://youtu.be/O8CSRCnCm3M

Power density will depend on what your lower voltage is...
i.e. 340V to 500V boost, would be 85kW...

So assuming 250A * 150V = 37.5kW Then three inductors would be able to operate 100kW peak.

Finding the saturation current is a bit more tricky...
In this video I measured the inductance to be 371uH:
http://youtu.be/CKiQwzH4n-E

Given the inductance, resistance of the coil, battery and IGBT Vsat, and knowing max conduction time is 600uS (60% at 1khz), you could calculate the peak inductor current in the Prius... And then assume saturation is a few percent above that.

Or you could measure it... But you would need to find a resistive load that can handle 300+ amps... And then hope that it does not fail, cause of all that energy stored in the inductor will make some serious high voltage arcs. 

Or, you could be like me and guess Saturation current is probably around 300A. 

Either way, three inductors looks fine... Two inductors would probably saturate... Unless you upped to 200V on the input.

Hope that helps,
Wolf


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## wernerc (Oct 28, 2014)

Any tips or hints where to find such Prius inductors for a project here.
I just found your interesting thread regarding the converter.

Some time before a company which I knew cleared their stock and I reserved several inductors (more than 20 pieces) for 100kW+ which should go to waste.
Unfortunately some employee there didn't recognize the reservation and all the parts were recycled before I could pick them up :-((

As I don't know the Prius hardware in detail, perhaps some details where those parts are included would be fine.
I assume its a combined inverter DC boost unit ?


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## WolfTronix (Feb 8, 2016)

wernerc said:


> Any tips or hints where to find such Prius inductors for a project here.


You can get the inductor for around $200 on eBay.
Search "Prius Inverter".

Inside you will find the inductor... Comes with free inverter.


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## wernerc (Oct 28, 2014)

So I can assume that ALL Prius inverters include such coil ?
As I said I am not familiar with the Prius hardware and if there are different models which might be with or without the boost converter due to different battery configs or whatever.


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## WolfTronix (Feb 8, 2016)

wernerc said:


> So I can assume that ALL Prius inverters include such coil ?
> As I said I am not familiar with the Prius hardware and if there are different models which might be with or without the boost converter due to different battery configs or whatever.


I know the Gen2 2003–2009 Prius have one, because that is how I got mine...

If you search for "prius inverter teardown"

You can find some internal pics of the inverter:
http://techno-fandom.org/~hobbit/cars/ginv/561unit.jpg
The inductor is in the upper right, next to the three phase motor connection.

Hope that helps,
Wolf


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## wernerc (Oct 28, 2014)

Thank you very much for your information.
Maybe I will have a look at the market and find such an inverter.
But first I will calculate if the inductor fits.
I already build such an buck/boost for battery testing but with much lower voltages.
It was able to test the very old SAFT NiCads on 4 parallel channels with charging and discharging.


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## WolfTronix (Feb 8, 2016)

wernerc said:


> Thank you very much for your information.
> Maybe I will have a look at the market and find such an inverter.
> But first I will calculate if the inductor fits.
> I already build such an buck/boost for battery testing but with much lower voltages.
> It was able to test the very old SAFT NiCads on 4 parallel channels with charging and discharging.


No problem. 

I will finish mine, after I get my truck running on Lithium, Spring is almost here!


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## bigmotherwhale (Apr 15, 2011)

so what do you think about using the inductance in the motor? any thoughts good or bad?


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## wernerc (Oct 28, 2014)

I assume there is a missunderstanding here.
Wolftronix seems to build some testinh equipment without an connected EV right ?
And so no motor inductance is in action.

Yes you can use motor inductances for charging.
The Renault Zoe does this for example.
So they succeeded in integarting an 43KW charger in the car by using the inverter and the motor in reverse mode savin parts, weight and...

Werner


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## bigmotherwhale (Apr 15, 2011)

There is no confusion, I was suggesting an alternative topology where the motor controller and voltage gain are in one circuit instead of two separate ones linked together.


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## WolfTronix (Feb 8, 2016)

bigmotherwhale said:


> There is no confusion, I was suggesting an alternative topology where the motor controller and voltage gain are in one circuit instead of two separate ones linked together.


The bi-directional buck-boost converter I am working on is for bench testing motor controllers, battery chargers, and simulating a battery.

It is not intended to go into a vehicle.

Honestly, I looked at the schematic you posted... but the circuit did not make sense to me... If you turn on the lower right switch, energy is stored in the inductor from the battery, then when the switch opens the upper right diode steers the current into the capacitor...

Then the other switch closes... and there is no path for current to flow... unless I am missing something....


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## bigmotherwhale (Apr 15, 2011)

you missed something  - both switches can close simultaneously to discharge the cap in series with the battery


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## prensel (Feb 21, 2010)

Would this buck-booster work in an EV with for example a 96V pack and a 320V controller and motor ?


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## dcb (Dec 5, 2009)

bigmotherwhale said:


> you missed something  - both switches can close simultaneously to discharge the cap in series with the battery


I think you are high.


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## WolfTronix (Feb 8, 2016)

prensel said:


> Would this buck-booster work in an EV with for example a 96V pack and a 320V controller and motor ?


Yes... It would work...

But it would be more efficient to find a motor and controller that ran at 96V.
Or up the pack voltage to 320V.


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## arber333 (Dec 13, 2010)

WolfTronix said:


> Yes... It would work...
> 
> But it would be more efficient to find a motor and controller that ran at 96V.
> Or up the pack voltage to 320V.


Hi WolfTronix

I am trying to make charge pump from Prius parts, similar to your idea.
Do you have any info on Prius boost bridge from Mitsubishi PM400DJA120. I can see that documents exist, but i cant get any online. 
I need IGBT control interface schematic/wiring. I have the module and connector, i just need to know which pin gets which signal.

Can you help me?

tnx


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## kennybobby (Aug 10, 2012)

@arber
Use a meter with diode and continuity settings to check if your PM400 igbt device is wired up like this:


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## arber333 (Dec 13, 2010)

kennybobby said:


> @arber
> Use a meter with diode and continuity settings to check if your PM400 igbt device is wired up like this:


Nice  but is it really that simple? I see 12 pins out the back. Hm...
I will try. Tnx.


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## kennybobby (Aug 10, 2012)

Is it really 12 pins, or just 10? My diagram was for an earlier generation, yours is newer and has integrated smarts for driving the gates.


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