big batteries and step up DC converters

AC, DC, amps, volts and kilowatt. It's all discussed in here
User avatar
weber
Site Admin
Posts: 2624
Joined: Fri, 23 Jan 2009, 17:27
Real Name: Dave Keenan
Location: Brisbane
Contact:

big batteries and step up DC converters

Post by weber » Wed, 25 Nov 2009, 16:31

HeadsUp wrote: Thanks weber
What kind of values would the components need to be ?
At least i can get a rough idea of parts costs for something like that
Will let you know when i find a prius one to strip down

Sorry HeadsUp, but it isn't at all practical to do it that way when you're considering a voltage ratio of around 10:1. Even at 2:1 it probably isn't practical. The reason is that the switching devices have to deal with the high input current and the high output voltage.

I've added the word "theoretical" to the caption of my schematic above (and added the integral diodes I should have included the first time).

Here's a topology that's suitable for DC DC conversion at high power levels and high voltage ratios.

Image

The voltage ratio is fixed by the transformer turns ratio. Here the MOSFETs only have to deal with the high input current and low input voltage, while the IGBT's only have to deal with the high output voltage and low output current. But it still won't be cheap at EV power levels. Possibly more than a 3 phase VF drive (3 phase inverter) of the same power level, which you will still need.

It's one thing to look at schematics of the power-stage topology of a switchmode converter or inverter, and quite another to design one that actually works and isn't just a complicated device for blowing up expensive lumps of silicon.

At first it looks like straightforward digital design, but in fact most of the hard design work is analog design involving "parasitic components" that don't even appear on the schematic but depend on the geometry of how it's all put together.
One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

User avatar
Johny
Senior Member
Posts: 3729
Joined: Mon, 23 Jun 2008, 16:26
Real Name: John Wright
Location: Melbourne
Contact:

big batteries and step up DC converters

Post by Johny » Wed, 25 Nov 2009, 16:57

I found the article I referred to a few posts ago. This is a buck-boost system designed to utilise ultra-capacitors (in addition to the batteries) in an EV.

Initial article

Testing and more details

And here is their design document:
Design of high power buck-boost

Edit: Simplified links and added design link
Last edited by Johny on Wed, 25 Nov 2009, 06:22, edited 1 time in total.

bga
Senior Member
Posts: 492
Joined: Mon, 01 Sep 2008, 19:27
Real Name: Bruce Armstrong
Location: Perth WA

big batteries and step up DC converters

Post by bga » Wed, 25 Nov 2009, 17:15

acmotor wrote:
A lot of the time the DC bus can be a lot less than 600V, maybe 300V or so.

Prius Gen3 is 650V so they must consider they are on to something with this boost system.

A 100V VFD has 6 times the silicon and higher switching loss (if IGBT) than a 600V unit. All the wiring is 6 times the CSA etc. There might be 20kg or so extra copper in the system. I guess these are factors that Toyota must have considered. Maybe it makes up for the booster efficiency ? Image
I think that the 'not all the time' bit is the important part.

When I originally started thinking about this, one factor that I was considering was how a boost (and reverse buck) coverter would interact with the 3PIM motor to allow a better match to the motor low speeds for drive and regen. (low speed regen is a bit pointless because there isn't much kinetic energy left to recover)

I think that it buys a lot less battery for Toyota. This is probably less of an issue for an EV where there is a lot of battery.

Further to my earlier Prius drivetrain comment. I should have added that the mechanical energy through the shafts is important, meaning that only a smaller part is actually being electrically converted. We should see that the Prius tries to make the gear ratios so that, at the most important road speeds, the MG1-MG2 converter isn't doing very much work at all.

Another thought is electronic series-parallel switching of the battery string to achieve the same result without any buzzing bits in the middle. A problem being that another motor controller's worth of big power semiconductors are needed for this and they lose a couple of percent all the time.   

User avatar
coulomb
Site Admin
Posts: 3779
Joined: Thu, 22 Jan 2009, 20:32
Real Name: Mike Van Emmerik
Location: Brisbane
Contact:

big batteries and step up DC converters

Post by coulomb » Wed, 25 Nov 2009, 18:45

weber wrote: Here's my attempt:

Image

Um, isn't this a standard half bridge per phase, as used in an AC controller, with input and output swapped? (Ok, plus actual inductors, since the motor's inductance can't be used).

So this circuit can't have the output voltage drop below the input voltage. So you can't do the low parts of the sine wave. This would be like adding DC to the motor, and extreme distortion to the motor current, which would surely result in poor performance and excess heat dissipation. Remember you need to synthesise the sine wave, it's not just limiting the minimum AC output voltage.

My circuit's complexity is mostly about allowing the output voltage to be less than the input.

I expect to be shot down in flames if I'm wrong here   Image

Edit: added "per phase"
Last edited by coulomb on Wed, 25 Nov 2009, 07:54, edited 1 time in total.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.

User avatar
Johny
Senior Member
Posts: 3729
Joined: Mon, 23 Jun 2008, 16:26
Real Name: John Wright
Location: Melbourne
Contact:

big batteries and step up DC converters

Post by Johny » Wed, 25 Nov 2009, 18:49

I think the resonance of motor inductance with those snubber caps is going to be the killer.

User avatar
coulomb
Site Admin
Posts: 3779
Joined: Thu, 22 Jan 2009, 20:32
Real Name: Mike Van Emmerik
Location: Brisbane
Contact:

big batteries and step up DC converters

Post by coulomb » Wed, 25 Nov 2009, 18:59

weber wrote: Here's a topology that's suitable for DC DC conversion at high power levels and high voltage ratios.

Image

Wouldn't it be simpler to just rectify the output of the transformer? it's going to be square waves in the transformer anyway, right?

Diodes are about as efficient as IGBTs, aren't they? And a fair bit cheaper, even though they need to be high speed, high voltage, and rated for moderate (output load) current?
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.

User avatar
Electrocycle
Senior Member
Posts: 985
Joined: Sun, 19 Oct 2008, 20:23
Real Name: Andrew
Location: Sydney
MSN: dumhed@dumhed.com
Contact:

big batteries and step up DC converters

Post by Electrocycle » Wed, 25 Nov 2009, 20:25

you can't regen back through a transformer without some choppers :)
The Engine Whisperer - fixer of things

User avatar
weber
Site Admin
Posts: 2624
Joined: Fri, 23 Jan 2009, 17:27
Real Name: Dave Keenan
Location: Brisbane
Contact:

big batteries and step up DC converters

Post by weber » Wed, 25 Nov 2009, 23:16

coulomb wrote:Um, isn't this a standard half bridge per phase, as used in an AC controller, with input and output swapped? (Ok, plus actual inductors, since the motor's inductance can't be used).
You couldn't have asked a better question if I'd primed you to ask one. Image

Yes Virginia, there is a Santa Claus. (plus the former DC bus caps have been split up into 3 groups).

All single-inductor-single-capacitor type converters, when made reversible, are exactly the same circuit. The only thing that changes is which of the 3 terminals is treated as common.
So this circuit can't have the output voltage drop below the input voltage. So you can't do the low parts of the sine wave. This would be like adding DC to the motor, and extreme distortion to the motor current, which would surely result in poor performance and excess heat dissipation. Remember you need to synthesise the sine wave, it's not just limiting the minimum AC output voltage.

My circuit's complexity is mostly about allowing the output voltage to be less than the input.

I expect to be shot down in flames if I'm wrong here   Image

Image

There are at least two ways of looking at this:

1. Consider it as three voltage-inverting boost-buck converters by treating DC+ as the common terminal. Then the outputs can go all the way to zero. That's how I derived it.

2. Consider it as three boost converters by treating DC- as common, and realise that with a 3 phase output, having no neutral connection, the common-mode voltage is irrelevant and so it doesn't matter if the outputs never go less than the input. The 3 sinewaves can be stacked on top of the input-voltage DC-offsets without the motor windings ever seeing any DC.

I expect this circuit would be difficult to control in a stable manner, as well as being impractical except for low power or low voltage boost due to the voltage and current stresses on the switching devices.
One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

User avatar
coulomb
Site Admin
Posts: 3779
Joined: Thu, 22 Jan 2009, 20:32
Real Name: Mike Van Emmerik
Location: Brisbane
Contact:

big batteries and step up DC converters

Post by coulomb » Thu, 26 Nov 2009, 00:02

Electrocycle wrote: you can't regen back through a transformer without some choppers :)

Oh yes, regen, right. Your diodes aren't bidirectional for power? Image Damn! Neither are mine!   Image
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.

User avatar
coulomb
Site Admin
Posts: 3779
Joined: Thu, 22 Jan 2009, 20:32
Real Name: Mike Van Emmerik
Location: Brisbane
Contact:

big batteries and step up DC converters

Post by coulomb » Thu, 26 Nov 2009, 00:06

weber wrote: 1. Consider it as three voltage-inverting boost-buck converters by treating DC+ as the common terminal. Then the outputs can go all the way to zero. That's how I derived it.
Um, right down to zero, with respect to the positive rail! So it can't go lower than the input, which is what I said.
2. ...The 3 sinewaves can be stacked on top of the input-voltage DC-offsets without the motor windings ever seeing any DC.

Ah, right. Image   Well spotted. Carry on!

Though it might stress the motor insulation a little more.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.

Mr. Mik
Groupie
Posts: 66
Joined: Fri, 08 May 2009, 04:41
Location: Gold Coast, Aus

big batteries and step up DC converters

Post by Mr. Mik » Thu, 26 Nov 2009, 02:58

Is it physically impossible to convert 3.5V DC to DC of (several)hundred V?

Or is it just not possible with the components available today?

Or is there some physical law that makes this impossible without severe losses?

The heavy conductor (required to carry very high currents) is not an issue IMHO.
It could be a sturdy metal frame that supports the cells structurally against movement, vibration and impact damage. If the converter was directly connected to this cell-frame, then not a single piece of heavy duty copper cable would be required!

Even if this converter caused 20% loss, it might be worth it, because you would never need more than a rudimentary BMS and all cells would remain perfectly balanced for their entire life! You could fully charge and fully discharge if needed, without any risk of individual cell damage.

Any idiot could drive it - just like an ICE vehicle, when the tank is empty, it would just suddenly stop running without any severe damage done.
Last edited by Mr. Mik on Wed, 25 Nov 2009, 16:00, edited 1 time in total.
There is always a way if there is no other way!

Mr. Mik
Groupie
Posts: 66
Joined: Fri, 08 May 2009, 04:41
Location: Gold Coast, Aus

big batteries and step up DC converters

Post by Mr. Mik » Thu, 26 Nov 2009, 03:03

Electrocycle wrote: we have talked about that before (I think it was me who jokingly suggested it :P) but the efficiency would be far too low for it to be practical.

Even charging would be very inefficient with that much voltage step down.


Can you point me to that discussion? You might remember in which thread it developed...
There is always a way if there is no other way!

User avatar
coulomb
Site Admin
Posts: 3779
Joined: Thu, 22 Jan 2009, 20:32
Real Name: Mike Van Emmerik
Location: Brisbane
Contact:

big batteries and step up DC converters

Post by coulomb » Thu, 26 Nov 2009, 03:15

Mr. Mik wrote: Can you point me to that discussion? You might remember in which thread it developed...

Could it be this one?

BMS free zone battery management

Edit: towards the end
Last edited by coulomb on Wed, 25 Nov 2009, 16:17, edited 1 time in total.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.

User avatar
Electrocycle
Senior Member
Posts: 985
Joined: Sun, 19 Oct 2008, 20:23
Real Name: Andrew
Location: Sydney
MSN: dumhed@dumhed.com
Contact:

big batteries and step up DC converters

Post by Electrocycle » Thu, 26 Nov 2009, 04:26

it's completely possible to step 3.5v up to whatever you want.

I have a battery powered gas lighter that generates several kilovolts from a 1.5v battery - but as soon as you want high power levels you're talking massive currents on the low voltage side - which means lots of silicon and huge cables, etc.
The Engine Whisperer - fixer of things

User avatar
Richo
Senior Member
Posts: 3737
Joined: Mon, 16 Jun 2008, 00:19
Real Name: Richard
Location: Perth, WA

big batteries and step up DC converters

Post by Richo » Thu, 26 Nov 2009, 07:09

Not so much the silicon or cables but the magnetics moreso.
It's not everyday you come across a toroid or similar to transfer 100kW or so in the 10+kHz region.
And it won't be cheap.
Or efficient.

And don't think you can do it at 100kHz with a smaller toroid because the silicon will then be the limit.

To put it in perspective start small.
Do a 2kW DC-DC design see how much it costs then multiply by 50...
So the short answer is NO but the long answer is YES.
Help prevent road rage - get outta my way!

bga
Senior Member
Posts: 492
Joined: Mon, 01 Sep 2008, 19:27
Real Name: Bruce Armstrong
Location: Perth WA

big batteries and step up DC converters

Post by bga » Tue, 01 Dec 2009, 02:03

If you stop at the 2kW size, you will have the battery charger!

User avatar
coulomb
Site Admin
Posts: 3779
Joined: Thu, 22 Jan 2009, 20:32
Real Name: Mike Van Emmerik
Location: Brisbane
Contact:

big batteries and step up DC converters

Post by coulomb » Sat, 19 Dec 2009, 19:11

Here is an interesting alternative boosting AC inverter:

Image

I haven't figured out how it works yet; basically I guess that as the IGBTs conduct, they supply energy to the inductors as well as to the motor stator. Or more likely, one or 2 or all 3 of the pairs of IGBTs is turned on together (forbidden in a conventional inverter) during the part of the cycle that energises the inductor.

The report that this figure comes from claims almost 1% higher efficiency than the conventional two stage design. This information seem to come in turn from this report:

10. F. Z. Peng, Z-Source Inverter for Hybrid Electric and Fuel Cell Vehicles, Michigan State University, March 2004.

Which may be the same as this:

Fang Zheng Peng, “Z-Source Inverter for Motor Drives” IEEE
Transactions on Power Electronics, Vol.20, No.4, July 2005,
pp.857-862.

Anyone find a PDF? This one may be helpful: http://fie-conference.org/fie2007/papers/1730.pdf

Anyone care to guess how it works?

Edit: boosing -> boosting   Image
Last edited by coulomb on Sat, 19 Dec 2009, 13:38, edited 1 time in total.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.

User avatar
weber
Site Admin
Posts: 2624
Joined: Fri, 23 Jan 2009, 17:27
Real Name: Dave Keenan
Location: Brisbane
Contact:

big batteries and step up DC converters

Post by weber » Sat, 19 Dec 2009, 20:06

That's fascinating, Coulomb. It does indeed use shoot-through for voltage boost, as you can read here
Z-Source Inverter for Power Conditioning and Utility Interface
Z-Source Inverter for Fuel Cell Vehicles
Z-Source Inverter
One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

Squiggles
Senior Member
Posts: 742
Joined: Wed, 22 Apr 2009, 03:19
Real Name: Neil
Location: Newcastle NSW

big batteries and step up DC converters

Post by Squiggles » Sat, 19 Dec 2009, 23:12

coulomb wrote: Here is an interesting alternative boosing AC inverter:


How much boose can one of these inverters consume before it affects operation?

User avatar
coulomb
Site Admin
Posts: 3779
Joined: Thu, 22 Jan 2009, 20:32
Real Name: Mike Van Emmerik
Location: Brisbane
Contact:

big batteries and step up DC converters

Post by coulomb » Sun, 20 Dec 2009, 00:41

Hic. I'd say about 1.5 litres, which suspiciously is exactly 2 wine bottles Image

Thanks for pointing out the festive season typo (now edited).   Image
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.

User avatar
coulomb
Site Admin
Posts: 3779
Joined: Thu, 22 Jan 2009, 20:32
Real Name: Mike Van Emmerik
Location: Brisbane
Contact:

big batteries and step up DC converters

Post by coulomb » Sun, 20 Dec 2009, 02:37

Alas, that pesky diode, which would appear to be necessary to operation, precludes regeneration back to the low voltage pack.

About the best that can be done for regeneration would be to replace one of the Z-source capacitors with an ultra capacitor bank or auxiliary battery (with much lower capacity than the main pack) rated at high-side voltage. None of those options is terribly appealing to me.

I wonder how many solar or wind grid interactive inverters use this topology as yet.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.

HeadsUp
Groupie
Posts: 265
Joined: Sat, 28 Feb 2009, 09:13
Real Name: Mark W
Location: Sydney

big batteries and step up DC converters

Post by HeadsUp » Thu, 24 Dec 2009, 14:14

some of you are already members over at Home Grown Power Forum

there has been some developments there with guys getting increased power efficiencies through incorporating DC capacitors into AC circuits ( yes ) on wind turbines

possibly of more interest might be the voltage doubler and tripler circuits where AC is paralleled , put through bridge rectifiers and then combined to give higher DC voltages , thats not quite the power sector we were looking at , but maybe some of you will see uses for that topology applied in other ways



voltage doubler tripler quadrupler circuits

Tritium_James
Senior Member
Posts: 683
Joined: Wed, 04 Mar 2009, 17:15
Real Name: James Kennedy
Contact:

big batteries and step up DC converters

Post by Tritium_James » Thu, 24 Dec 2009, 15:11

Man, that windmill stuff, what a lot of mucking around! Why not put in a proper MPPT boost or buck circuit and be done with it?

HeadsUp
Groupie
Posts: 265
Joined: Sat, 28 Feb 2009, 09:13
Real Name: Mark W
Location: Sydney

big batteries and step up DC converters

Post by HeadsUp » Thu, 31 Dec 2009, 05:56


T2
Groupie
Posts: 121
Joined: Sat, 08 May 2010, 04:51
Location: ON,CANADA

big batteries and step up DC converters

Post by T2 » Tue, 01 Jun 2010, 10:37

-HeadsUp

In the process of building, I've been looking at an Upconverter in the event that my system input voltage may need some boosting as well. I have been getting a Plan B going for this eventuality as adding batteries is not an option in my case.

Er, 64v --> 500 vDC. Like everything else moderation is the key. A 1:2 step up or even 1:3 looks to be feasible. While my suggestion would be that you start with a 128v chain, and try for 64v later if things work out.

The major component will be the transistor switch which must be rated for 200/300% above the average current supplied to the inverter bus.
Fortunately these large currents are accompanied with short duty cycles that will never exceed 50% so chance of switch overheat will be somewhat lessened.

I have to comment that when you're accustomed to large current draws at the battery it's interesting how small currents mean a lot, at 500vDC even a paltry 50A represents 25Kw.

Nevertheless the Upconverter switch will be dumping the power out in 200 amp chunks. Which means you need a second capacitor bank at the inductor supply.

A scrap 2000/300A DC controller will contain all the major parts you need here with a bit of reconfiguring.

I don't know your level of confidence and skill but if you haven't built a step-up before you need to choose a Maxim chip, like I did, and go build their reference cct which is just the chip + half a dozen components to step 5v to 24v @100mA. You need to do this just so you can get a handle on the waveforms and feedback cct. Maxim is quite well documented and have bulletins on all their chips in case you weren't aware.

The "choke" specified for this tiny project is a commodity priced off-the-shelf molded component the size of a 1/4W resistor btw. At full load the chip gets quite warm. It peaks at 500mA input when delivering just 100mA on the output.

I would then try an amplified version adding an external 10A 200v mosfet and a ferrite rod antenna wrapped with 100 turns of enamel wire. Or perhaps a CRT ferrite yoke (it has four wires) the horizontal scan winding is of course the lower resistance of the pair. It is designed for 15Khz and will not saturate until 10 amps, the waveform on the scope will change when it does. By simply adjusting the feedback resistor chain it should be possible to step the output above 100 volts. At this stage we have accumulated enough to be dangerous !

The next step is to get the inductor from a DC controller, mine comes from such a source [90 microhenry @300A]. They have a gapped iron cct so they don't saturate, the energy is actually stored in that air gap so it's important that you don't choose any transformer or AC wound device instead. These have contiguous magnetic ccts and will saturate easily.

A fast power diode is also needed. Generally these parts are in any DC armature controller. Anyway that's my next step.

A favourable aspect to this topology is in its having a built in failsafe. Should the upconverter switch suffer a BP moment, and be shut down for whatever reason, current will continue to flow uninterrupted from the source through the inductor and power diode and out to the load.

I examined the Z transform converter in passing. It's way more sophisticated than anybody needs here. Another problem is that it would be near impossible to fix, if it ever developed a fault much later. In the same way I tend to avoid some older electronics which can present harder faults than the original designer ever had to surmount when he was designing it in the first place with brand new parts.
T2

Post Reply