Cost effective, low volume, Electric car charger?

Hello,
The company I work for want to have on-board, mains powered, 3.8kw electric chargers in their electric cars. The spec is 230VAC input, and 300-410VDC output.
They only need 6 chargers for 6 cars. The number may rise to 100, but not likely any more than that. Electric cars, as you know, are not experiencing that much buyer interest globally.
Anyway, the company have bought in off-the-shelf 3kW chargers to do the job. (about £1000 each) These chargers are very small which is favourable, as the electric cars are quite small. However, these bought in chargers are unfortunately, occasionally tripping out for quite long periods, and then suddenly start working again, for unknown reasons. (Also, the bought in chargers are only 3kw instead of 3.8kw, but I guess our bosses were willing to put up with that because of the off-the-shelf convenience).

This “tripping out” makes the chargers unfavourable, and so we decided to open them up and see if we could see what was going wrong. We found that the off-the-shelf chargers are Half bridge LLC converters supplied by a dual PFC stage. The LLC converter, and both PFC stages are all controlled by a single microprocessor.

The design is very small, and this has been possible because they are very tightly controlling the output voltage of the PFC stage so as to provide an optimum input voltage for the LLC converter. That is, the microprocessor very tightly adjusts the output voltage of the PFC stage so as to allow the LLC converter to operate at its resonant frequency over all battery voltage levels. We saw the PFC output voltage varying right up to the 450V level of the PFC output capacitors, and right down to 330VDC, depending on the battery voltage level. (well, it actually only went up to 440VDC, not 450VDC).

We could not see what was causing the chargers to trip out, therefore, I was tasked to come up with a design so we could make the charger ourselves, -one that would not trip out repeatedly. I chose a dual PFC stage, followed by a Full Bridge LLC converter. I do not have great software capability, so I would not be able to quickly do a PFC control algorithm in software (at least not at all quickly). Therefore, I chose a FAN9672 dual PFC controller to control the PFC stages. The problem with this is that though the output voltage of the FAN9672 can be varied, it is not possible to vary it to the wide extent that our bought-in charger does. Therefore, the design that I did does not always operate the LLC converter at its resonant frequency….indeed, when near the extremes of battery voltage, I rely on frequency change of the LLC switching frequency in order to correctly set the output of the LLC controller. This is OK, but it does mean that our design is not going to be as efficient as the bought-in charger modules that we have. This in turn means that my design will not be as small as our bought-in charger modules.
…This in turn is making the bosses reluctant and hesitant about going ahead with the design. As a side effect, the general staff of this company, (ie people not directly associated with doing this charger project) are extremeley anxious that they will loose their jobs. They see the swift acquisition of a suitable battery charger to be crucial for the company survival, and thus the survival of their jobs. They are thus very keen to see me depart this company as soon as possible, “with or without a parachute”.

I find in many UK electronics companies, non-electronics staff are neurotic about the acquisition of what they think is a fully competent electronics engineer. They (quite understandably) see the lack of (what they think is) a fully competent engineer as a threat to their jobs. –You can sympathise. In one particular company, I openly and honestly stated that I was not a software engineer, and that it would take me about a month to write some control software for them. (the engineer who had just left them would have taken just a day to do it). I was also doing hardware work for them, in fact, that was actually my main job. The general staff of that company overheard that I could not write the software quickly and decided to set about getting rid of me themselves. They believed, like many non-engineers do, that a modern electronics engineer cannot possibly be a “real” electronics engineer if he/she isn’t a software wizard. Therefore, they repeatedly offered me cups of coffee. I gladly accepted all these coffees. After a few days, I began to notice a very mild burning sensation in the back of my throat whilst drinking these coffees. I passed it off as my imagination, and in fact wondered if I was developing some kind of allergy to coffee. (heaven forbid).
Then one day, the usual complementary cup of coffee was again delivered to my desk…I thanked the chap politely, and took a sip. It was only one sip, as the “coffee” immediately burned the back of my throat quite harshly….i could then feel the burning sensation travelling down my gullet, and then into the top of my stomach. This was on a Friday, and the throat pain lasted the day, and prevented me from sleeping for virtually the entire weekend.
Everybody at this company was always very pleasant, though I regularly over-heard often angry discussions that they wanted a “real” engineer who could write software quickly like their previous guy. The bosses would not listen to them, (or just couldn’t find a software engineer) and so I guess they thought their only option was to hammer me with “firey” cups of coffee.

At a different company, (fuel pumps place), I was asked to get a 600W buckboost current source PCB that they had designed running. They had forgotten to add open-load overvoltage protection to it, so whenever it was powered up on no load, or the load removed, it would just blow itself up. Also, despite a 40Amps input current , the PCB trace for this was a long winding 1mm wide track. Also, they had not “Kelvin connected” the source current sense resistor, and in fact the connecting PCB trace was connecting to a thin copper track some 2.5 inches away from the actual current sense resistor pad. Also, they had strangely placed a common mode choke between the source sense resistor and the buckboost controller’s current sense input. Also, they had general analog monitoring circuitry liberally intermingled within the power switching loops of the buckboost converter, and no attempt whatsoever to manage the high di/dt power switch and rectifier current loops. There were also multiple other circuit errors. I informed them that a new PCB would be needed, but it took the bosses 3 weeks to sanction this. During this three weeks, the general staffing of this company decided that I was just making it up that a new PCB was needed, in excuse for not being able to do my job, and so decided to drain the brake fluid out of my back brakes whilst my car was in the company car park. The following day, I could hear a cackle of laughter, and jokes about brakes not working. The strange thing was, I eventually re-layed the PCB myself, got it working, and the chap who almost certainly had arranged for my brakes to be “done” came up and said he hoped I would be staying there now.

Anyway, back to the Electric car company of the present….
Another point about the 3.8kw charger that I have designed for them is that it obviously will use components sourced from Farnell or Digikey. As you will appreciate, for making just six chargers it simply isn’t possible to involve a big component distributor and get volume price reductions. The bosses actually have stated that the total materials and production cost of the units that I am tasked to make must be no more than the bought-in chargers. The bought-in chargers , however, are mass produced items, obviously attracting large volume cost reductions. The demand for my six chargers to be able to compete on price with the bought-in modules is obviously totally absurd.

Another point about the charger that I have designed for them is that I have used off-the-shelf Epcos TDK ferrite cores and off-the-shelf formers to go with them. However, the bought-in charger saves space by not using formers for the LLC power ferrites……they either wind the coils directly to the ferrite cores, or they have some custom made ‘coil-holder’. Either way, it would cost me far more to get the ferrites wound without using formers. The bosses have prohibited any extra ferrite production costs, and yet are insisting that the chargers that I am designing must be no bigger than the bought-in charger modules. This just isn’t possible.

Are there any magicians out there who fancy a job?

Are there any magicians out there who fancy a job?

Click to expand...

Not me. But if someone asked me to make a low quantity, low cost 300V-410V DC supply from 230V AC at ~16.5A for a stationary load, my first thoughts would be a big bridge rectifier. :shock:

Brian.

Thanks, this charger is mounted in the car, and so it needs to be as small as possible. We looked into a big rectifier and it cant do the job.

Wow, that's quite a story....

Thanks, here is another true story....

*****************************

In one UK based electronics company, I worked in a “closed lab” with three electronics engineers and one assembly girl. One of the engineers continually distracted the other two younger engineers, engaging them daily in hours & hours of non-work-related chat about just about anything. Very often, he would get them to join him in foul jokes directed at the assembly girl. The two younger engineers were of a disposition to 'get-on-with-their-work', however, the older engineer continuously distracted them, making them feel ‘anitsocial’ or ‘geekish’ if they did not join him in messing about instead of working. The manager of that site new that the work was going too slowly, however, that manager was seated in an office in a building across the road, and he simply could not see or hear what was going on in the lab…..and indeed, no other staff could see inside there either. Every month or so, the manager would insist that these engineers, due to their slow progress, should come and work a whole weekend, full-time, unpayed, to try and catch-up….the engineers would agree to this, but come the Monday, the larking about would just start all over again.

(I was in this lab as a contractor, I reported the foul language directed at the girl to her friend in the upstairs offices, but this girl told me not to report it further, as the girl might then be taken off her soldering exams, which would be useful to her in her imminent job application to a different company.)

One interesting point about this company, was that the older engineer discussed above was quite close to the Chief Design Engineer. The Chief Design Engineer gave me the impression of not wanting the body of engineers to become too technically adept, as indeed, perhaps this would simply act as a ‘threat’ to his technical superiority within the company. On one occasion, a bright new engineer had joined the company, and I overheard the Chief Design Engineer telling the older engineer “if he gets too keen, punch him one!”.

*****************************

Things are quite different in the Antipodies - except that senior design engineers still get jumpy when a truly bright junior engineer comes along....there is a lot of "protecting one's position" out there....

Sounds better down under..
Here's another true story, for anyone whose not too bored with it yet..

There was one company that I worked at where I was requested to design a 600W Buckboost converter on a certain sized PCB so as to demo that that size profile could handle the power.
Having done that, the company requested that I evaluate a novel BLDC drive method..

(It’s a current output regulated buckboost converter, attempting to regulate the speed of a BLDC motor by regulating the output current of the buckboost converter, the BLDC is switched by a three phase inverter, which is controlled by a Sensorless BLDC Motor control IC (ML4425), -the Sensorless BLDC Motor control IC is commutating the BLDC coils, but not high frequency PWM’ing the coils within the commutations. The Sensorless BLDC Motor control IC is a standard Voltage source inverter controller IC. The speed regulation circuitry inside the inverter control IC has been bypassed)

As such, regarding this job, my job whilst there was to evaluate the work of an Engineer showing a novel way to drive a BLDC. I advised that the project was not worth going forward with, since it involved driving a BLDC/Inverter from the current regulated output of a Buckboost converter. (In other words, the output current of the buckboost was to be regulated so as to control the speed of the BLDC.) The Inverter controller's speed control circuitry had been bypassed, and lots of external circuitry had been added in to achieve this. The inverter IGBT's were being commutation switched, as you'd expect, but were not being high frequency PWM'd within the commutations....the motor coil current regulation being entirely left to the 'upstream' buckboost converter.
This project was not worth them paying me to do it. Aside from being non-advantageous, it was using a large amount of unnecessary external circuitry.
I informed them that this project was not worthwhile and wrote a full report for them, explaining why.
I then left.
That dept has now closed down.
The engineer who came up with the novel drive method that’s explained here was the accepted department “guru”, everybody was too scared to challenge him, and he would use his “influence” within the company to put pressure on anyone who did challenge him. If you challenged him, you would quickly find yourself outnumbered by a large “squad” of cronies.
This “guru” actually left the company before the prototype came out, (his linkedin account did not show he’d gone to a new job) –It’s thought he left because he finally realised what a mess it was. However, lots of engineer time had been spent on it and so it was a big waste of money
The company's chief engineer (who was based in a different country) had seen what we were up to, and next thing the whole Power Electronics section was closed down. About 15 Engineers/Managers loosing jobs.

Another one: working in a very large assembly plant with a PA system covering the whole building. The microphone was at the reception desk in another building and the young lady at the desk was prone to 'giggles'. She was very good otherwise and every few minutes there would be an announcement "telephone call for Mr xxxx on line 24" or "Mr xxxx please go to flow solder line 10", you know the general pattern. What she absolutely could not say was "hand assembly line", she always burst out laughing because she visualized a line of people fitting fingers and thumbs to an otherwise bare hand! So if anyone asked her to page someone to that line, the message would come over the PA system "Mr xxxx please go the the place where the girls fit the bits the machines can't manage"!

Brian.

The best one was a (non-UK) company who were designing some kit for the British MOD.
The company hit big problems, needing mega-research, but refused to tell the MOD. Instead they just tried to rubbish talk the MOD that it was a small problem, and would soon be solved, telling the MOD that they should keep the funding coming forward.

Anyway, because they didn’t want the MOD to know about it, they started doing the testing on that particular problem during the small hours only, because the MOD staff weren’t on site then……but some one grassed this up and the MOD tipped up on site at 3am and caught them red-handed. (there was a rule that no work was to be carried out unless the MOD were present). The MOD read them the riot act, but then agreed to the testing to continue as long as they provided the MOD with a full report on the testing. Anyway, the report on the tests subsequently came out, and confirmed that the problem was indeed a big , “deep” problem, needing mega research, and not really something that the MOD would want to fund.
The company didn’t want to send this report to the MOD, because they thought the MOD would stop the funding. Therefore, this report was sent to yours truly in an email….this email showed all the previous threads showing all the gaffers panicing to each other about what would happen if the MOD saw this report……then the final email was a mail telling them to send the report to me, and get me to write an “alternative version of the truth”.
Indeed a senior engineer came up to me, and he had printed the report out, and he started telling me which (large) sections of the report that I should miss out, for the version that was to be presented to the MOD.
I don’t know if he knew that the report had actually been emailed to me.

Anyway, I printed out the report myself , and sent it anonymously to the MOD in Whitehall. I then left that company.
I don’t think the gaffer was happy that I was leaving. (especially when he knew I had seen that report). He started “barrel rolling” me in his office. –But as a leaving gift, I had bought £20 worth of donuts for the engineers, and one of the mech guys heard the gaffer going through me, and barged in and told this gaffer to shut it, and I then left the office, leaving them to speak with each other.

I actually sent the report to a number of MOD addresses, as I had visions of my report coming through the letterbox at Whitehall, and some tea-lady picking it up and shoving it in the bin.