New design for EV chargers - Skip the transformer

[mspohr]

Radically smaller, more efficient and perhaps faster EV charger may be on its way

Interesting research project redesigns EV chargers.
It skips the utility transformer and converts utility "medium voltage" distribution lines (1kv to 35kv) AC directly to 480v DC.
"Made possible by the use of wide bandgap semiconductor devices, this design results in a charger that juices vehicles up just as quickly as a regular model, but is only one tenth the size – it weighs about 100 kg (220 lb), and can simply be mounted on a wall or pole. "
Research project is now 50 kW and could lead to cheaper, more ubiquitous charging stations.

 

[Uncle Paul]

Tesla Superchargers have done this since the beginning. They supply DC power directly to the batteries. No inverter necessary.

Inverters are only currently necessary for home charging and destination chargers.

 

[mspohr]

Tesla Superchargers have done this since the beginning. They supply DC power directly to the batteries. No inverter necessary.

Inverters are only currently necessary for home charging and destination chargers.

Actually, this device is a bit different. Tesla SuperChargers all have a transformer to take the "medium voltage" power company voltage from usually about 16,000 volts to less than 1kV AC and then rectify it to DC for the batteries.
This project takes the higher voltage power company supplied 16,000 V AC and converts it directly to 480 V DC. It doesn't use a transformer at all.

 

[tjkessler]

It appears that this would be lower cost and potentially lower loss than the super charger way (transformer plus AC to DC conversion)

 

[ItsNotAboutTheMoney]

What could possibly go wrong?

I'm not sure it would help Supercharger sites as much, but for single installs, maybe?

 

[swaltner]

Neat concept!

Since getting these 500-1,000 kVA transformers installed can be one of the major delays in a project, it should also speed up the process. The local Electrify America site waited on the utility transformer for a couple weeks. I drove by today. It finally had the transformer mounted, but was still missing the electric meter to power everything up.

 

[eprosenx]

Tesla Superchargers have done this since the beginning. They supply DC power directly to the batteries. No inverter necessary.

Inverters are only currently necessary for home charging and destination chargers.

I think you are confusing inverters (DC to AC) with rectifiers (AC to DC).

All commercial EV’s have rectifiers onboard (aka “chargers”)

Home and destination EVSE’s are not “inverters”, “rectifiers”, or “chargers”. They are just smart switches with GFCI in them.

So this is just a level 3 fast charger like a ChaDeMo station or a supercharger which has the rectifiers off the vehicle and supplies high voltage DC direct to the battery.

The novel bit here is that they can take “medium voltage” from the utility and convert it directly to DC at the right voltage for level 3 fast charging an EV without first needing an AC transformer to step it down.

My guess is they are feeding this thing from a single 7200v phase (or something similar). That would be part of a 12,470 phase to phase system. I suspect this as I find it unlikely that they ran three medium voltage phases in that small conduit to the device. 50kw is probably close to the upper bound of what you would want to put on a single phase, but I think the reality is that they will deploy three or more at a time, each on a single phase in order to balance the load.

It sounds like they are using some new fangled semiconductor technology to do this.

FWIW, all the Tesla supercharging stations I have seen have a three phase 500kVA transformer that takes medium voltage (say 12,470) down to 480v. Then all the supercharger cabinets have modules in them that connect line to neutral at 277v. Each module is good for about 12kw. I am told that each (non urban) supercharger cabinet has twelve modules in them (usually shared between two stalls). So if these new magic devices are each 50kw, you could put three of them together to get a similar amount of power as Twelve Tesla modules in that cabinet. Though if it needed to feed two stalls I am not sure how it would switch between them (I have been told the Tesla modules switch between the two cars in 36kw chunks - aka 3 modules at a time).

 

[yuhong]

This should be much cheaper than your normal DCFC charger, right? Hopefully it does not require three-phase too.

 

[mspohr]

This should be much cheaper than your normal DCFC charger, right? Hopefully it does not require three-phase too.

Should be much cheaper since don't have a transformer. Should work on single phase and three phase.

 

[Sealander]

It could be done with a series regulator but imagine that solid state device failing and shorting which would put the line voltage of 16kv AC into your car while you are charging. The transformer is there for isolation and so I guess they will have some form of rapid shutdown, but I still like the idea of stepdown/isolation for safety.

 

[mongo]

Huh...
With 480V, you can boost the voltage for power factor correction (PFC) to make the utility happy. With a higher voltage, you are either creating a crazy high internal DC bus, or inducing harmonics by bucking the voltage to a lower DC value. Unless they use a buck boost topology...

 

[yuhong]

There is a presentation describing how it works: https://www.poweramericainstitute.o...Xinyu-Liang-Graduate-Student-Presentation.pdf

I wonder if this is what "wide bandgap" semiconductor devices are referring too.

 

[mspohr]

Huh...
With 480V, you can boost the voltage for power factor correction (PFC) to make the utility happy. With a higher voltage, you are either creating a crazy high internal DC bus, or inducing harmonics by bucking the voltage to a lower DC value. Unless they use a buck boost topology...

From the presentation, it looks like they have a high frequency transformer similar to a switching power supply. High voltage is all internal to isolate the output.

 

[mongo]

From the presentation, it looks like they have a high frequency transformer similar to a switching power supply. High voltage is all internal to isolate the output.

Yah, it's an interesting topology. They are running at 2.4kV input, which is the low end of primary distribution. So, for many places, there will still likely be a dedicated upstream transformer.

The Model 3 SiCs are (reportedly) 650V wide band gap parts. StMirco also makes 1700V versions. Perhaps Supercharger 3.0 (or is it 2.0?) will use something similar....

 

[yuhong]

AFAIK this mentioned they already have higher voltage versions in the works:
https://curent.utk.edu/files/9014/6098/8200/srdjan_lukic_DOE_April_1.pdf

 

[mspohr]

More details on the new "transformerless" charger from NC State U.
New fast charger is more efficient, smaller, and half the cost
Says the cost will be $35,000 instead of $75,000 for 50kW version. Says it's easy to scale up voltage and power.