Fast E.V. Charging.

It's a great concept, but unless the DNOs start upgrading the cables and provide more subs to handle this as well as the effect of harmonics that the chargers add to the system, we are going to be stuck with 22kW and the occasional 50kW chargers for a fair while.

Tesla announced their 250kW chargers which can provide 1000 miles of charge in an hour, but unless you live near a power station, I doubt that there is going to be additional 1MW Tx popping up all over the place.

Indeed they'd need to be fed by their own substation, and probably their own feeder from the 33kv-11/6.6kv sub, as the switching on and off of a 1/4 megawatt load every time someone stops to refuel would cause disco lighting in many areas!

Indeed, the use of chargers this fast will require a dedicated supply and possibly at a voltage higher than 11Kv.

Possibly more applicable to a motorway services area.

Providing a 10Mw supply to such premises would be easy if already near a high voltage distribution circuit. That would allow for perhaps two dozen 250Kw chargers, several dozen 22Kw chargers, and lots of domestic 7Kw chargers. Charging points with a total demand of say 15Mw could reasonably be connected to a 10Mw supply since not every space will draw full load at the same time, several spaces could be taken by vehicles that have completed charging but not yet been driven away. Load management controls would either throttle back the charging rates, or delay the start of charging by a minute or two if needed so as not to overload the 10Mw supply. In most circumstances this would not be needed, but is clearly prudent for "just in case" Adding one megawatt of PV modules would allow extra charging in fine weather, and monitoring the actual transformer temperature might allow  a nominal 10Mw transformer to supply 11 or 12 Mw in cold weather.


250Kw charging might be a bit extreme for private cars, but could become the norm for electric trucks.

400-450kW charging systems already exist and are being trialed in Germany and the US:
https://www.hubersuhner.com/en/recent-pages/cooled-cable-radox-high-power-charging-system
https://www.hubersuhner.com/en/solutions/automotive/applications/high-power-charging/radox-hpc-high-power-charging-system
https://innovation-destination.com/2019/01/23/bmw-porsche-demo-ev-charger-that-gives-100-kilomter-range-in-3-minutes/

A motorway service area with 6 stations each side would require a dedicated 11 or 33kV supply. 800kW systems are being suggested for trucks but I am not aware of any viable systems. I previously posted this link about low emision comercial vehicles in Europe:
https://www.commercialfleet.org/news/truck-news/2019/04/02/lack-of-infrastructure-holding-back-cleaner-trucks

A key quote:

"ACEA estimates show there will need to be 20,000 DC 150-500kW charging points installed over the next six years in Europe.

Furthermore, it says there needs to be at least 6,000 high power 500kW+ chargers, 500 CH2 (compressed hydrogen) and LH2 (liquefied hydrogen) stations, 500 CNG (compressed natural gas) stations and at least 1,000 LNG (liquefied natural gas) stations."

That's several power stations worth of charging points.


Best regards


Roger

A significant infrastructure rethink will be needed to meet the current targets using electric lorries  - as is obvious from looking at the same consideration the other way - the rate of delivery of chemical potential energy at a conventional  fuel station at a motorway services compares with a small power station. (assume the calorific value of diesel or petrol is 45 Mega joules per litre,and then ask how many seconds to pump a litre of fuel, and how many pumps are running.)  There is an advantage that electric vehicles convert less of their fuel into waste heat, but it is only a factor of 2 or 3, not tens or hundreds.


The obvious short term solution is to put the electricity generation locally to the refueling point if at all possible. A regulatory rethink to permit higher voltages may be in order. Designs using 1000V cables with 400A/pin  and pumped liquid cooling down the cable to the connectors are interesting, but I sense desperation pushing at the arbitrary 1000V limit, and the connectors are always going to be a fire risk.


Allowing  few kV in shielded cables with sensible interlocking would be far safer, after all the death from a 1kV shock is not much different from a 2 or 3 kV shock - the key is not to make it possible to have the accident in the first place.


It is going to be worth getting this right, as the numbers are mind boggling.


There are roughly quarter of a million HGVs (i.e. over 7.5 tonnes) registered in the UK, or which about half are articulated lorries, and it is a fair bet the economics means they are mostly worked pretty hard and fuel up daily, we could  assume they may burn 250 litres per day each. The miles got estimated per gallon are interesting https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/749248/env0104.ods .I know of a few SUVs that appear to do worse than the average 'Artic' in that official list. I also think a lot of the heavy vehicles are a lot worse - as in more like 1 or 2 miles to the gallon for  recovery truck.

I am not sure where the nominal 1000V comes from. It may be technology dependant. When the current EV generation (Lithium batteries, a few hundred volts, inverter with 3 phase motor) was being developed there were no standards. Milk float, FLTs, etc with lead acid batteries, generally less than 100V, brushed DC motors were not appropriate. Full size electric rail with a few thousand volts and over 1000kW in a single drive package was again not appropriate. I believe that tram and trolly bus technology was used, so a few hundred volts and drive packeges of a few hundred kW. Under 1000V single semiconductors can be used for swithching and DC fuses are reasonably practical. Moving above this brings a new set of problems.

Current EVs operate at around 400V so even 800-1000V charging is a problem. Porsche have used a DC-DC converter (cost and weight). Splitting the battery pack and using series-parallel switching would be another solution but that depends on how the modules are configured. I am not sure how charging at a few kV would work? A DC-DC converter could be used however a HF supply and just the transformer and rectifier on board may be lighter and cheaper.

Lots to think about.


Best regards


Roger

Certainly (following a rather odd conversation) at least one of the makers of the electric racing cars (formula E) find themselves limited by a 1000V upper bound that they think is determined by the fact that any more would not be LV, and that would limit who can work on the car, and how, and in turn this affects how they are able to design, and the overall efficiency.  So for now they try and design right up close to 999..9V at the start of the race, and falling fast as they go round. However from a power and torque perspective they would love to hit the motors with less ampy slices of something higher pressure.


The  Silicon Carbide semiconductor devices for 3.3kV DC are readily available, and technology to scale up for making devices good for quite  a bit more is not really an issue, yes they are quite expensive, but nothing compared to a battery, and mainly because they only sell in small numbers to folk doing specialist things.


While I appreciate the rules of the racetrack are quite different, for lorries at least, I can see a similar need for a lot of horse power at the wheels, and a good electric efficiency, so a similar voltage shortage, may drive towards higher voltage batteries too.

Even if it does not, one can imagine, series charging as you suggest, much as HGVs often have double tanks, I can imagine that they will also have double batteries. In any case the LV HV threshold  is an entirely man made limit that may be an awkward one for high power vehicles - for any other load, let alone one that needs a 'flex' to plug it in, by the time we are looking at hundreds of kW, we don't normally design for an LV supply, and an article about 1000V charging cables needing liquid cooling suggests that they are already up against it, and these are the early prototypes, longer term we can expect more to be needed not less.

Putting the regs to one side, it may be nicer as we already allow and use 3 phase supplies  at 230/400  and 400/690  to extend the rule of 3 concepts to permit  690/1200 or even 1200/2060, and keep the 'fuel pumps' as simple transformers, and allow the vehicle to sort out the specifics of charging best to suit its on board batteries.

I think that we can agree that the technology is not yet mature: (1) how to deliver the power required to recharge quickly; and (2) how to do it safely (thinking of that dratted lost neutral/PME business). I don't think that voltage is really an issue - do what you like inside a vehicle.

Well - if you charge with 3 phase, there is no need to even give it a neutral for load carrying, the 3ph. load is then obliged to be in balance.

Also, unless there is a lot more standardisation of motor voltages, battery chemistry and cell-stack build up,  for now at least the vehicle itself has to have the charger on board configured to be specific to it's batteries, so there is little point in having too much extra electronics on the forecourt, apart from some interlocking so contacts are dead and to tell the vehicle not to be too greedy if local supply capacity is limited. This is after all already how the domestic charge points work, for exactly the same reasons.

The only problem is that somewhere between 60A phase and 100A plus, the whole plug/socket and flexible cable thing  starts to get very tricky very quickly. In showland we'd stay at 230/400 and switch to running singles at that sort of power level,until we needed another genet, but that is not really a quick and safe approach for a lorry to be hooked up and un-hooked rapidly by unskilled persons, hence the experiments with 1000v DC.


3 phase also rectifies nicely (on a 6 diode bridge the un-smoothed DC has a 4.5% ripple factor ) so mains frequency smoothing before an SMPS  can be quite light.




edit PS - a link to some blurb about those high voltage silicon carbide transistors
https://www.wolfspeed.com/downloads/dl/file/id/860/product/0/simplifying_power_conversion_with_medium_voltage_sic_mosfets.pdf  

scary current density mind you in the new ones

For comparison, now more or less run of the mill these days 1700V 72A
https://www.wolfspeed.com/power/products/sic-mosfets/c2m0045170p

A significant infrastructure rethink will be needed to meet the current targets using electric lorries  - as is obvious from looking at the same consideration the other way - the rate of delivery of chemical potential energy at a conventional  fuel station at a motorway services compares with a small power station. (assume the calorific value of diesel or petrol is 45 Mega joules per litre,and then ask how many seconds to pump a litre of fuel, and how many pumps are running.)  There is an advantage that electric vehicles convert less of their fuel into waste heat, but it is only a factor of 2 or 3, not tens or hundreds.

A bit of lateral thinking might suggest a couple of other possibilities....

1. Charge the batteries away from the vehicle - i.e. filling stations just swap battery modules rather than charging the battery while the vehicle waits. Batteries could then be charged more slowly (usually better for battery chemistry, especially for full charges) and at a time more convenient for the national grid. If the battery module included charging circuitry - then it could have a standardized 230V or 400V a.c. interface regardless of battery chemistry and perhaps a bit of logic to oversee performance and communication with the vehicle and charging system. Battery fade then becomes the responsibility of the "fuel" supplier, rather than the vehicle owner. In time an automated system (I'm imagining something between a car-wash and a juke box) could replace several modules probably faster than a liquid fuel fill up.

• Or do like I'm told the Swiss have done - ban long distance goods movement by HGV and move the goods by rail instead. The power is then picked up direct from overhead cables and all this messing about with batteries is completely avoided.

   - Andy.