Boost Converter for high voltage electric vehicles

[cts_casemod]

This topic is meant for discussion of a high power boost converter for electric vehicle use.

Right now two instances are proposed:
Achieve power factor correction of an AC supply, with the intent to charge high voltage DC Battery packs at high power levels and with great efficiency. At a later stage I plan to ramify this to a power factor buck converter for 144V battery packs.

Boost a given battery voltage to allow 144-400V Battery packs to power standard 415VAC insdustrial motors, with Paul's 3 phase motor controller. Such motors typically require a DC-LINK voltage in excess of 600V, which requires a very large battery pack and reduces reliability.

Things to discuss:

• Topology: Single phase, interleaved, continuous or discontinuous modes, frequency of operation
• Semiconductors: IGBT, mosfet SIC diodes
• Inductors: Anything suitable goes here!
• Power Hardware: DC-LINK design, pre-charging, IGBT drivers
• Software: related to microcontroller based devices

[cts_casemod]

Just to get started on this thread Ill share some of the work I've been doing:

Disclosure: My work is primarilly concerning a single stage PFC controller, as such topology is slightly different from a boost converter that operates directly from a DC supply.

Aim:
Charge at up to 6KW from a 230VAC supply or 48-350VDC, such as a solar array or a portable battery pack. Output voltage: 440VDC, current: Adjustable from 0 to 13ADC at 440VDC.

The output power will be proportional to the input voltage (6KW at 240, 3KW at 120, 1KW at 48VDC)

So far I am using an interleaved aproach consisting of two UC3842 current controllers. These receive the clock pulse from a microcontroller and a modified feedback signal to draw line current in phase with the line voltage.
So far i am aiming at 1.5KW per module, so a complete interleaved pair would supply 3KW in a relativelly small footprint at 60-100Khz

The microcontroller takes care of current regulation, pre-charging, J1772 communication

I'm looking at suitable inductors that could be used for a 50 or 60KW version. I should have a working prototype finsihed by december. The system is able to operate from DC with increased output power by 33%.

[UFO]

"At a later stage I plan to ramify this to a power factor buck converter for 144V battery packs."
Can you explain this a bit more? Is this just another way of stating a simple PFC to high voltage DC, or are you bucking down the PFC voltage? If you are generating a high voltage simply to buck it back down, why? It seems to me a PFC can regulate a DC voltage well enough to directly run the motor controllers.

It looks like you are aiming very high, and I respect that, but targeting your 6kW charger to operate from both 230 AC and 48-350 DC sounds difficult without a significant efficiency loss at lower DC. I guess that is why you are limiting power at lower voltage inputs.

"So far I am using an interleaved aproach consisting of two UC3842 current controllers. These receive the clock pulse from a microcontroller and a modified feedback signal to draw line current in phase with the line voltage."
Are you synchronizing your UC3842s 180* out of phase? Is this simply to lessen the current ripple on your PFC? I'm not sure why this would require synchronization with line frequency since the PFC should be regulating this directly.

"I'm looking at suitable inductors that could be used for a 50 or 60KW version."
That is a huge step up. You are going to use the control scheme and scale up the magnetics. Presumably you are scaling up the switches too, and the drivers and the current sense circuits too, but what about your input source - do you still have use of 48VDC input? That is a massive scaling of current from 100A to 1000A at least.

What use do you see for this kind of power? Is this a very quick charger? What battery banks can take this kind of potential charge rate?

Lots of questions, love the ideas.

[cts_casemod]

For 144V I plan to use buck PFC. This only works from a 230VAC supply, basically were aiming at a reduction of the peaks on a normal rectifier to the whole portion of the sine wave where the voltage is greater than 144V. This can typically achieve PFC of about 0.9, with current proportional to voltage (resistive behaviour). A Google search will reveal solutions from Texas instruments and others.

The PFC converter can regulate to a DC voltage very well. Its just overcomplicated because the easiest approach, discontinuous mode, results on high harmonic content and that would likely not pass IEC certification ( USA must have something similar) On a DC supply this does not apply, so assuming there are no sensitive equipments on board one can be more relaxed with the design.

The charger does not provide 6KW at 48V. But it does work down to some 10V. That's a requirement of the PFC.

Operating from DC the supply voltage will set the current limit. If the limit is 10A, then 10*48= 480W, for example. The switches are not being overdriven.

The one currently on my vehicle charges at 1.5KW from a 250V supply, 1350W from a 220V supply and 1KW from a 150VDC supply, but it can operate at lower voltages.

Interleaved is just a way to make sure when one converter is 'charging' the other is supplying the load. With this logic the input and output power is more or less constant rather than pulsating. There is no line synchronization with the AC Mains. AC line synchronization is only used for the outer loop that regulates voltage, but that's a bit of a long subject to describe here.

I can easily charge my LIFEPO4 at 1C up to 70% capacity. Most EVSE's here are rated for at least 7KW (Some for 22). So for a quick 30 minute stop at the grocery shop with an empty battery I could potentionally put 3KW on the battery (15 miles).

[e*clipse]

Cool! Thanks for doing this and starting this thread.

My interests would be almost exactly what you've posted:

Battery voltage: 250V > 400V (based on Nissan Leaf battery packs)
Motor link voltage: 650V (based on Toyota hybrid motors)

For a charger, something that could deal with both 120AC minimum and 360DC from my solar system would be incredible!

If this could be pulled off in some svelt unit, or even combined with Paul's controller, that would be, um, orga....

For this to work out, I'm looking for power capabilities of about 50kW to 70kW. This would be only for boosting at high motor speeds, where a pack voltage of 400V would be inadequate. I don't have any interest in high speed charging, but the capability might be there anyway.

Oh, and running this at high switching speeds with SiC switches has my vote. Anything I can do to reduce weight is good. (by reducing inductor size) From my perspective, this part needs to be lighter than the batteries that could supply the difference between 650V and 350V, and put out a net 200kW. (multiple converters) So if the inductor is a huge, heavy part the net value may be negated.

- E*clipse

[cts_casemod]

The boost converter for the charger is not the same as the one used for the inverter. But the development efforts should be similar and many parts could be reused.

I'm looking at using the motor as the inductor for example. This would allow low frequency IGBTs, huge power output and continuous conduction mode, given the inductance.

For the Boost converter I'm looking to order some of these inductors.

High Power Inductor E Series : CWS Coil Winding Specialist, manufacturer of transformers, inductors, coils and chokes

As to charging directly from DC perfectly possible. Any active power factor charger has this capability from 150VDC to 410VDC

[cts_casemod]

Had to byte the wallet and order two inductors from coilws. Was hopping to get them this week, but the order is still pending. Maybe they are out of stock...

Last week I made a small prototype, feeding from a 12VDC transformer and boosting into a 100W 30V LED. This worked as expected with a unity power factor. Even bumping two series LED's to 60V resulted in very good PF.

Now, the switches to use. Fast mosfets would be desirable, but I'm a bit skeptical about their long term reliability. A brick IGBT such as a infineon FF450R12ME4 would be virtually indestructible and would allow buck as well.

These are pricey, at $200 each, but its easy enough to spot them on fleebay for $50-80.

I've been having a chat with some members, specially regarding this other design 10kW / 60A DIY charger open source design - DIY Electric Car Forums PStechPaul found that the boost stage for the last units produced actually uses a similar inductor. So, 12KW is realistic, which is great news.

Lastly I'm pondering if a PCB or a DC-LINK setup composed of aluminum links similar to that on the inverter for the power connections. What do you guys think?

[e*clipse]

Excellent news - thanks for the update.

I think this is a great way to supply a charger. I made a small demo boost converter charger that relied heavily on the batteries to smooth the output. It was based on an Infineon boost controller. When the cells (measured individually with the BMS) reached the constant voltage stage of charging, the BMS would ultimately control the charging. It did this by measuring the cells' voltage and calculating the voltage drop slope curve over time. The BMS would turn off the charger when the cells reached a pre-determined voltage, then turn on again when the voltage drop curve reached a pre-determined slope. Charging was complete when the voltage drop curve slope was low enough to consider the charge complete.

Do you have any #'s regarding boosting for 50kW or 60kW?

Or were you thinking of doing this differently than 'Yota (boosting to 650V, then creating 3ph)

For example were you planning *somehow* to boost to 3 ph directly??

Sorry if you've covered this already, I guess I'm a few steps back.

Thanks a bunch,

E*clipse

[cts_casemod]

Originally Posted by e*clipse

Excellent news - thanks for the update.

I think this is a great way to supply a charger. I made a small demo boost converter charger that relied heavily on the batteries to smooth the output. It was based on an Infineon boost controller. When the cells (measured individually with the BMS) reached the constant voltage stage of charging, the BMS would ultimately control the charging. It did this by measuring the cells' voltage and calculating the voltage drop slope curve over time. The BMS would turn off the charger when the cells reached a pre-determined voltage, then turn on again when the voltage drop curve reached a pre-determined slope. Charging was complete when the voltage drop curve slope was low enough to consider the charge complete.

Do you have any #'s regarding boosting for 50kW or 60kW?

Or were you thinking of doing this differently than 'Yota (boosting to 650V, then creating 3ph)

For example were you planning *somehow* to boost to 3 ph directly??

Sorry if you've covered this already, I guess I'm a few steps back.

Thanks a bunch,

E*clipse

That's pretty much what I do as well. The charger output is variable and reaches a peak at 444VDC. Once one cell reaches 3.45V the charge is stopped, otherwise they are allowed to 'float charge'. I don't do balance charging.

The output is pulsating DC so it needs some good capacitance to smooth before going to the battery.

At the moment I'm not particularly targeting the inverter boost converter, (I think Paul is working on that) but of course the work done may be used with little modifications. My personal idea is to boost on demand as more/less torque is required, rather than having a fixed voltage. This allows the converter to operate only while under heavy load (current mode) where the inductor current remains continuous. Discontinuous mode would possible generate far too many losses on the switches

I received my inductors yesterday and I'm waiting for some samples from on-semi and some fast MOSFET/diodes I got from the USA... I might eventually consider moving there to speed up the process

[cts_casemod]

Got the inductors and some intelligent power modules for PFC pre-converters.

One is for bridgeless and the other is standard topology, with inbuilt bridge rectifier, both interleaved. I'm going to start some simulations and see how this thing behaves under varying loads