CCS charging using Prius buck-boost converter

[MoonUnit]

Hello all, I have been following the amazing work done here on CCS rapid charging (Foccci and Clara), and with the Prius Gen 2/3 inverter with regards to using it as an AC charger. 

My battery pack voltage is too low for CCS, but I am wondering if perhaps I could boost it with the Prius converter to something that a CCS EVSE could deal with. I note that @clanger9 suggested exactly this:

Another crazy option I've been thinking about is DC charging via the buck/boost converter. This would ultimately allow me to add CCS to my bike (which by necessity will have a battery pack voltage below the minimum CCS level).

... but I have not seen any follow up posts.

I realise the power output from the EVSE would have to be limited to what the converter can handle but it would allow me to use the CCS chargers when there are no type 2 ones around, and likely at a faster rate than my onboard 6.6kW charger.

So the question is, is this the way of madness or could it work in theory? Thanks in advance for your thoughts.

[uhi22]

Let's collect the key points of this approach.
1. CCS side: The CCS EVSE is able to work in "constant-voltage" mode, and we can choose the voltage between 200V and 450V (or 150V to 500V at some chargers (Edit) Or above 230V at Tesla Supercharger V3). We can send a current limit to the charger, but this would not be effective in this case, I would set it to a value higher than needed, to avoid instabilities due to reaching the current limit.
2. The battery pack voltage range and current requirements.
3. The Prius buck-boost converter: What is the voltage range of both sides? Does it fit to the ranges of (1) and (2)? Is it possible to control the current?

[MoonUnit]

Hi Uhi, many thanks for replying.

I believe the buck-boost converter can happily accommodate the ranges of 1 and 2 in your reply. In my case low side would be about 90V, and I'd assume the EVSE would like to operate at 400V which the converter can handle as well.

I also believe it's possible to set a constant current, Johu has shown this in lab update 45, but I am not sure how yet. If the EVSE can be instructed to supply a specified current, even better.

Very naively, I was thinking it would be possible to set a constant voltage and a current required from the EVSE using Clara. I would get CANbus from my BMS sent to something intermediate, maybe a teensy, to take the pack voltage and charge current limit that my BMS wants, translate it to the 'high side' values that the EVSE should supply, and send this to Clara.

I would determine the amount of boosting that the converter is doing as my pack voltage rises. That is controlled via PWM, from what I understand, so as my pack charges from a constant voltage from the EVSE, I would need to reduce the boosting, and communicate with Clara to keep the current into my pack in line with what I want.

The teensy (or whatever) should be able to set the charging parameters for charging lithium batters (constant current phase, constant voltage phase) by adjusting the boost PWM and ideally communicating current required through Clara.

Or something like that!

[uhi22]

Sounds like a plan. Just two additional things:
"Boosting" is the wrong word. It would mean to create a high output voltage from a lower input voltage, at least this is my understanding. We need the other way around.
And: It is not clear how much intelligence the prius converter has. If it tries to regulate voltage or current, there is the risk for instabilities if the regulators in the evse and prius work against each other. So more details needed to refine the concept.

[johu]

I think I'd let the charger do the hard work (i.e. the current control). Set the converter to a fixed duty cycle, say 45%. This would translate 200V to 90V. Then send the current * 45% to the charger (and a voltage limit that doesn't get in the way). 20A on the CCS charger side will result in 44.4A on the battery side. I think you shouldn't got past 100A on the battery side because that is supposedly the inductor limit. So 9 kW is the maximum you can expect from the setup.

I think all 800V cars have a similar setup to be able to charge on older 500V chargers.

[MoonUnit]

"Boosting" is the wrong word. It would mean to create a high output voltage from a lower input voltage, at least this is my understanding. We need the other way around.

Yes, precisely - I believe the sequence needs to be something like:
Battery pack voltage (low side) used to precharge the converter.
Once converter pre-charged, boost it to (say) 400V at high side.
EVSE plugs into car and we request 400V ('high side'). It 'sees' 400V, no massive inrush as voltages equal.
Hence we boost from low voltage to high, rather than buck down from high to low pack voltage.

At least that's what I think, please don't throw stones at me if I am wrong. Or only small ones if you have to.

I think I'd let the charger do the hard work (i.e. the current control).

That's my thinking. If Clara can instruct the EVSE to provide a specific voltage and current, then I control the duty cycle to feed my battery pack.

So 3 questions:

1. Can Clara instruct an EVSE to provide a specific voltage and current (within sensible reason)? e.g. 400V, 20A? Does it have a low current limit at 400V (for tapering end of charging)?
2. Does the Gen 3 inverter/converter offer any advantages to the Gen 2 for this use case e.g., higher current limit, more / safer controllability?
3. I am not clear on how to get the low side to 'draw' current from the high, I presume I must reduce the boosting of the low side to a value below 400V to get the current to flow, hopefully subject to the maximum current one has set the EVSE to supply?

9kW is not brilliant. I was hoping for nearer 20. However, any charge is better than no charge!

Thanks both.

[uhi22]

1. Can Clara instruct an EVSE to provide a specific voltage and current (within sensible reason)? e.g. 400V, 20A? Does it have a low current limit at 400V (for tapering end of charging)?

Yes, the voltage and current limit can be adjusted during the charge process. So you are free to select a fix max voltage and fix max current at the beginning, or, more usual, adjust the limits dynamically, depending on the BMS wish.

3. I am not clear on how to get the low side to 'draw' current from the high, I presume I must reduce the boosting of the low side to a value below 400V to get the current to flow, hopefully subject to the maximum current one has set the EVSE to supply?

As I understand johus comment above, the converter is just feed with a certain PWM ratio, and exactly this ratio will be the ratio of input current to output current and also input voltage to output voltage. The current draw to the low side will just appear automatically as soon as on the high side there is a source which tries to increase the voltage above the "boosted" voltage.
Example: We boost the 90V to 200V. Instruct the charger to precharge to 200V, and close the contactors. Now instruct the charger the limits 300V and 10A. This will lead to transfer of the energy backwards, with 10A/0.45 on the battery side, and if the battery reaches 300V*0.45, the voltage will not further increase.

9kW is not brilliant. I was hoping for nearer 20. However, any charge is better than no charge!

Maybe two in parallel. The control effort does not increase.

BTW: Is there somewhere a block schematic of this converter? Does it really transfer energy in both directions? How does this work?

[johu]

BTW: Is there somewhere a block schematic of this converter? Does it really transfer energy in both directions? How does this work?

It's just a synchronous converter with IGBTs on low side and high side. Seen from one direction it is a boost converter, seen from the other direction it is a buck converter.
The Gen2 Prius has just one control signal for both plus an enable signal. The Gen3 has separate high and lowside signals with deadtime requirement.

[uhi22]

Got it

U2 is the lower side and can be adjusted between zero (if PWM is zero) and full U1 (if 100% PWM)
And if voltage is applied to U2, it will be stepped-up to U1=U2/PWM.

[MoonUnit]

Thanks both for replying.

It's just a synchronous converter with IGBTs on low side and high side. Seen from one direction it is a boost converter, seen from the other direction it is a buck converter.

I read in the Gen 2 Inverter wiki page it says:

"The gen 2 can only charge in buck mode. So maximum charge voltage is limited to the rectified AC input."

I think this statement is intended to say that the charger can only charge if one side is higher voltage than the lower one? As I understand the Gen 2, it is both buck and boost at the same time (synchronous), so it's not in buck or boost 'mode', it just has one side higher than the other, the amount set by the duty cycle? I want to make sure I am thinking about it the right way.

[Jacobsmess]

This is something I've also been interested in to reduce bulk, I believe the GS450H is similar to the prius Gen3 inverter but I'm not sure. Good luck with your quest, I'll be watching for your outcome

[MattsAwesomeStuff]

I'm very interested in the results of this on the Gen2 or Gen3 side. All I can do is help document if it gets dumbed down enough for me to understand, and spread the word afterwards.

One of the frustrations from the open-source-freeloader perspective is that no design seems to ever be taken to conclusion. The Prius inverter has all these things it can do, but all that you can get it to do is be an inverter and DC/DC. No A/C, no charging, no buck/boost.

Can't complain, beggars & choosers and all that, the amount I'm entitled to is strictly 0%, but in terms of effectiveness of the group effort it seems every year or so there's new effort in a new platform, it gets 30% done, and then the excitement moves onto the next platform.

[MoonUnit]

@MattsAwesomeStuff - I tend to agree, but it's the nature of open source stuff and frustrating to everyone I think. Those that do the creating get pestered and frustrated, those seeking answers find it hard to get them and few people write up their work fully. Let's face it, the write up's not the exciting bit.

This particular project has been rattling around my head for a while but I wasn't sure if it was feasible and I was a bit unsure about asking, in case I was shot down in flames for being too dumb to know, with the inevitable accompanying warning that HV kills dumb people. But Johannes and Uhi were kind enough to provide me with confirmation it should be do-able.

So from here, I think I'll get hold of a gen 2 inverter and try to master its control with some low voltages. If I can, I am very happy to write it up / you are welcome to help me! After that, there are many more stages - get my BMS to communicate its voltage and current requirements to an intermediary device that can control the converter accordingly, and then communicate with Uhi's Clara and Foccci for the actual CCS bit. So quite a lot to do and it will take me a while as I don't have much free time.

[johu]

Maybe this is somewhat interesting as it shows that the DC/DC part can be extracted and used separately from the inverter:


Of course this shows an AC/DC variant. Yours would be less complex electrically because there is no current control if you choose so and more complex logically as it needs a foccci

[MattsAwesomeStuff]

I tend to agree, but it's the nature of open source stuff

Sure is.

Even trying to put aside a selfish perspective, 6 options that are each 2/3 complete have zero value to a beginner. I'd rather 1 option that was 4x as thorough, for the same effort.

I think tons more people would be converting vehicles if it was simple and well documented and required a minimum of all the systems integration hell that we all know projects wander to their deaths in.

If I can, I am very happy to write it up / you are welcome to help me!

A second part of what's frustrating as a volunteer is that, frankly, it's often more effort to explain to me what to help with, than it is for the person who knows it to do it themselves. I'd be happy to trade 10 hours of my time for 1 hour of theirs, but it's more like, it takes 2 hours of their time to help me take 10 hours of mine to save them 1 hour of theirs.

It's part of what I keep saying "I'm going to rearrange the whole wiki so it's more intuitive to use!" once a year and then run into a brick wall each time.

So I relegate myself to idiotproof things like taking pictures and putting labels on them and expanding short sentences into longer ones.

In any case, sure, offer's there if I can be a useful shortcut on your time.

[uhi22]

Also asking questions and reminding the community about the needs of a beginner is a very important thing. Because it will lead to better documentation (hopefully). Not immediately, but over the time. For Prius buck boost, I'm beginner-level. And was not able to find a wiki page which explains it. I would like to improve this, by putting "silly questions", and this steals time of the experts. It seems to be difficult to distribute the knowledge and the workload to many shoulders.

Technical question: I still did not get the point, whether my picture above is correct. It has high voltage left and low voltage right, and a single PWM. It is buck from left to right, and boost from right to left. On the other hand, I read "buck mode" and "boost mode", and I read about two (Independent?) PWM inputs. This sounds like there would be two additional switches on the right side of the inductor, controlled by a separate PWM. This would allow buck and boost in any direction. Not sure if this is just a misunderstanding or reality. So the point is: Does the converter have two switches on one side of the L, or four switches, two on both sides of the L?

[johu]

As some know I used to work at a solar inverter company. When the handbook for a product was to be written the lady from tech doc called me regularly and had me explain how things work. I'd we more than willing to do something similar here, like have a (video) chat with Matt or whoever wants to take it on and talk about assorted topics. I think making the existing stuff more accessible is equally important as developing new stuff.

Does the converter have two switches on one side of the L, or four switches, two on both sides of the L?

Your drawing contains all elements. Only thing missing is the diodes in parallel to them. Lets call the upper switch "Q1" and the lower switch "Q2" and the parallel diodes "D1" and "D2". Here is what it can do:
- Only Q2 switches -> U2 is boosted and flows via the diode D1 to U1. U1 = 1/(100% - x) * U2 . No current can flow from U1 to U2 because diode
- Only Q1 switches -> U1 is bucked and flows via D2 to U2. U2 = x * U1 . No current can flow from U2 to U1 because diode
- Both Q1 and Q2 switch were the signal for Q2 = !Q1 (plus deadtime). Now both equations apply at the same time so it depends on the existing voltage U1 an U2 in which direction current flows. E.g. x=50%, U1=101V and U2=50V then current flows from U1 to U2 because the U1 bucked to 50.5V is greater than 50V (neglecting various voltage drops)

[MoonUnit]

So I relegate myself to idiotproof things like taking pictures and putting labels on them and expanding short sentences into longer ones.

These things are super useful. Don't underestimate them.

@Johu and the Lab Update 55, thanks for posting, I had watched it few times already. Very good work, and a useful reference for me. I won't be attempting that initially, but ultimately breaking the boost module and inductors out separately from the inverter might make sense, as I don't need the rest of the inverter, and as Uhi suggested I could parallel a pair to get better than 9kW charge rate. However, I am getting ahead of myself!

[uhi22]

Improved version of the overview drawing. (Swapped the sides, to have the same orientation as the (original?) Toyota drawing, which was shown in a video linked by Gregg in an other thread, viewtopic.php?p=66375#p66375)

Prius buck boost block diagram

So my lesson learnt is: Even if is called "buck boost converter", it can NOT do buck and boost in the same direction. It is boosting in the one direction, and bucking in the other direction.
For the original use in the car this means, the accu voltage is always less or equal the inverters bus bar voltage.

[Edit] The U1 and U2 are also swapped between my two pictures, to add a little bit more confusion So the formulas above are not valid for the new picture.

[MoonUnit]

I have a Gen 2 inverter/controller on the way, and some contactors and a precharge resister I got cheaply from Fleabay.

I am going to run the CPWM signal from a Teensy to start with so I've adopted @Cathphish's suggestion to run a low side then high side switch to make sure that if my Teensy crashes, the PWM output going to the boost control module will fail to low, meaning the upper IGBT is on, and the battery voltage will be passed through to the high side without shorting out the battery.

A couple of questions if anyone knows - what's the ideal frequeny to run the PWM at? I've seen Damien run it at 2kHz, and elsewhere it's been suggested that 5-8kHz is good.

Secondly, how much current does the boost module need to see on the CPWM pin?

[MoonUnit]

So I have finally got hold of a gen 2 inverter and I've jerry rigged a Teensy to control it. My intention is to only run the buck-boost part of the controller, so I will disconnect the DC inputs to the DCDC converter and I will power the boost module and control it directly through its 16 pin plug, not via the inverter's power plug and main 32 pin white plug.

This means, I think, that the rest of the inverter will not be switched on.

I am not passing AC through MG1, I will be eventually taking DC in from an EVSE and passing it through to my lower voltage battery so I don't need to use the rectifier circuitry, but I assume I need the "smoothing" capacitor buried in the black slab for the boost circuitry to work. So a few questions please before I start:

Where, in the inverter/controller, do I need to connect my EVSE DC in to match the below schematic posted by @Cathphish? I have circled the points in red. I believe these are the bolts circled in red again from the wiki picture?

and

Thanks in advance.

[MoonUnit]

I have managed to get very basic low voltage DC charging working using the buck/boost converter. As per previous post, I powered the boost control module directly through its input plug and bypassed the rest of the prius inverter/controller. I grounded CSDN, and held CPWM at 0 duty cycle. I enabled the converter with the 5V OVH (?) line, and then by increasing the duty cycle I could boost simulated car battery voltage onto the DC bus to match a simulated EVSE voltage. Then, by reducing the boosting, current will flow from the simulated EVSE side to the simulated car side.

I've got some very basic boards ordered from JLPCB to save myself the shonky breadboard pain. These will have CANbus and should mean I can get info from my BMS, and converse with Clara. I plan to try to set up the EVSE simulator working that Uhi22 cooked up so I can try to bridge my BMS (Orion) with his CCS controller and push this forward.

@MattsAwesomeStuff - I promised to update wikis / share what I've been doing so I'm ready to that, such as it is. I don't want to go editing the wiki without some hand holding, I don't want to screw anything up ...

[MattsAwesomeStuff]

@MattsAwesomeStuff - I promised to update wikis / share what I've been doing so I'm ready to that, such as it is. I don't want to go editing the wiki without some hand holding, I don't want to screw anything up ...

1 - Every edit is tracked and reversible. So no worries.

2 - You can "preview" your changes to sandbox it, so you're not making a mess of the edit history to just play around.

3 - Wiki syntax is easy enough a 5-year old can do it. Nothing that capable, but nothing that intimidating.

...

A few choices, once you've decided how you want to frame your knowledge, you can either add it in-line, or create a whole new page about your board and your project that repurposes it. The latter is probably what you want to do?

...

What would you like for hand-holding? How can I help?

[MoonUnit]

What would you like for hand-holding? How can I help?

I am not clear on 'where' I should document this. The wiki has a bunch of pages that are not linked to from the main page https://openinverter.org/wiki/Main_Page - for instance https://openinverter.org/wiki/CCS_EVCC_using_AR7420 is not accessible from the main page.

That sort of page would be ideal I think for me to document what I've got so far, so if you could help me by creating the empty page, I can fill it in.

[MattsAwesomeStuff]

I am not clear on 'where' I should document this.

Well like many open source projects, the Wiki is a Do-Ocracy. Those willing to do the work decide how it should be done.

I would create a... nevermind... Do-ocracy, I'll just do it rather than tell you how you should do it...

This page...

https://openinverter.org/wiki/Toyota_Pr ... 2_Inverter

Now has a "boost converter" section, which has a one sentence summary, and otherwise links to:

https://openinverter.org/wiki/Prius_Gen ... _Converter

Which is naked and ready for you to fill in however you please.

The wiki has a bunch of pages that are not linked to from the main page https://openinverter.org/wiki/Main_Page - for instance https://openinverter.org/wiki/CCS_EVCC_using_AR7420 is not accessible from the main page.

Yeah, it's not the best. At least once a year I look at the main page with fresh eyes and say "This is awful, I'm going to fix all this so it's more intuitive" and then get overwhelmed, lack knowledge to actually do it, and give up before I start. I'm not alone in this.

It's a wiki, it's a do-ocratic method. If you see something that can be fixed or better, fix it or make it better.

That sort of page would be ideal I think for me to document what I've got so far, so if you could help me by creating the empty page, I can fill it in.

Done.

You create an empty page by linking whatever you want it to be, with double square brackets. You can note this if you edit source on the main Prius Gen 2 inverter page above. Then it'll be in red (linked but doesn't exist yet), and then when you click on it, you'll be the first one to edit it.