European 3ø Inverter Interface

[tom5698]

Hi,

My i-miev is in a good condition and I did not have problems with the charging unit but now I face another challenge.
I have installed photovoltaic panels recently, around 13kWp with inverter capable of 11kW and it works great. I live in Europe so I have 3 phase 400V at home.
I would like to balance my phase load between phases when charging my car during the day. This is because I observe power export on two phases and only one phase is used to charge a car. This is not beneficial because each exported kWh costs me 20-30% and it would be better to consume the whole power immediately rather then exporting it and importing with 20-30% “penalty”. This situation is even worse when the sun is behind clouds and there is limited power available on the solar inverter.
The charger in the car is a single a phase, 230V, the same as we all possess but I made a mind experiment to power this imiev’s AC cable from 3 phases, 400VAC rectified by a half bridge composed of just 3 diodes into a direct current.
I know that the weakest point would be a “left quadrant” rectifier bridge of the “waffle plate”. The only one pair of diodes would be constantly loaded.
Have someone thought about powering this charging cable from a DC source like I described above?

 

[coulomb]

The charger in the car is a single a phase, 230V, the same as we all possess but I made a mind experiment to power this imiev’s AC cable from 3 phases, 400VAC rectified by a half bridge composed of just 3 diodes into a direct current.

I see two problems with this idea, neither of which may be fatal.

Firstly, the On Board Charger will see not a sine wave but three humps that never go zero or negative. The Power Factor Correction stage of the OBC tries to present a unity factor by changing the PWM of the boost converter to make the current match the voltage. It's used to seeing a double hump that goes to zero. I don't know how it will handle the extra abrupt changes in voltage direction. Possibly it will be fine, but it may get confused. I don't know how this would manifest, possibly causing the bus voltage (output of the PFC stage) to be less than smooth.

The second problem I see is that the inverters (DC-AC converters inside your 3-phase inverter) supplying AC to the car will see very poor power factor. The current drawn by each phase will be two thirds of one half-cycle (one third of a full cycle), and none during the other half-cycle. So these inverters will see peak current equivalent to the total charge power when it's their turn, and zero power (to the OBC) for the rest of the cycle. So if you're charging at 3.6 kW, then that counts as a 3.6 kW load on each phase as far as the inverter is concerned, even though you are only supplying 1.2 kW on average, and using only 1.2 kW (plus losses) from PV/battery. You have an 11 kW inverter, but that only leaves 11 - (3 × 3.6) = 0.2 kW for other loads! You have plenty of available power, but because of the power factor, it all comes in bursts that leave effectively nothing left for ordinary loads.

You can look at this another way: your 11 kW inverter is really three 3.7 kW phase inverters in one box. With the three diode arrangement, you will be powering the OBC (at up to 3.6 of your 3.7 kW) completely from one of those phase inverters at any one time. They time share the load, but never power the OBC together, so they never current share the load. So you aren't really sharing the load at all.

My initial thought was why not a standard 6-diode rectifier, but then of course you'd have 560 V peak to peak, which is way too much for the OBC, which probably uses 400 V capacitors and silicon rated for about 375 V DC max on the DC bus. I think it also doesn't share the current any better, just chopping it up into two periods of one sixth of a cycle, instead of one period of a third of a cycle.

 

[tom5698]

Hi, thanks for your reply.
You described what exactly I was thinking. Maybe there is somebody who tried it before.
I am simply not brave enough to make a test

 

[LilliLoret]

Hi...For what they cost these days, you should simply purchase a drive from somebody like automationdirect.com and afterward do the control interface to the outside world with the stamp. On the off chance that you likewise design the circuit appropriately, you can make the variable speed drive fill in as a stage converter to make three stage from single stage power.
The other methodology is to take existing ASIC's that can produce the PWM calculation in addition to give the interlocking between the inverter IGBT's and connection them to some other ASIC's with the goal that you can simply utilize the stamp for things like outside control interfacing. There is a lot of fulfillment in moving your own drive yet it tends to be very tedious.

 

[GregFordyce]

Another option would be to upgrade the car to 3ø. Muxsan.com offers this upgrade for the Leaf and from what I can tell they add 2x 3.6kW chargers that work in parallel with the existing charger. Each charger works off of one of the phases.

Obviously this would be a technically challenging project, both in time and money, but being able to charge in just over an hour at 11 or 22kW public charging points is a very attractive proposition.

 

[Sandrosan]

I am not sure but what do you think to use a single phase transformer 3.5kVA 400V / 230V?

Or using 3 Phase transformer 3.5kVA 400V / 230V and connecting only 2 wires in the secondary?

In both these ways you will charge 2 phases on your 3 phase inverter. Maybe better than charging 1 phase only.

Or somebody sees other problems?

Probably on second hand markets you can find such trafo for a very reasonable price. In my case I find out one but just 2kVA at 30 Euro

I would not care about low efficiency because the sun energy is free and green.