In China 50% of the new vehicles sold are either full EV or
Plug-in hybrids. In US, the growth is slower around 15% of new vehicles sold.
The growth continues to increase as with more advances in EV technology and
cost reductions through economics of scale in battery technology. With the technological
breakthrough of battery technology, the range of the EV cars will likely
continue to increase, which will lead to increase in adoption of EVs. All the
EVs means it will require the electric grid to be able to handle the charging.
Battle of the Charging Connectors- The most common
one charging type is the CCS1 type charging port which includes both low
voltage AC level 1), high voltage AC (level 2), and DC charging. In US, we use
the model SAE J1772 charging. Tesla has its own charging standard called the
NACS (North America Charging Standard). There was a competition between the standardization
of the chargers between CCS1 and NACS. The Tesla’s NACS eventually won out,
with all the EVs starting to use NACS charging port regardless of which company
makes the EV. The NACS standard will change the J172 standard to SAE standard
of J3400. For older models, there are adaptors that can be use vice versa. With
the transition, all the charging stations in the US will eventually will have
the NACS.
Levels of charging- There are three types of charging
levels- Level 1 that is single phase AC either 120 V or 240 V. The utility source
is connected to the EVSE. These EVSE does not include any power electronics,
its only job is interface, communication, and protection. The EV itself
includes a AC to DC inverter that the EV uses to charge the battery. Level 3 or
the DC Fast Charging puts out the DC directly into the EV, and skips the AC to
DC conversion. DC fast chargers can
charge at 400V to 800 V. The DCFC usually are connected to 3 Phase AC utility
source. The Tesla super chargers have liquid colling, sensors, and connectors.
Charging limits- The latest version of the Tesla DC
fast charges can charge at 800V+ upto 350kW
maximum charging. This charging capacity is anticipated to increase to make the
charging faster. In real charging scenarios, the EVs cannot be charged at the
high power 250KW level the whole time. The fast charging works best for depleted
batteries. The new ChargePoint chargers can charge upto 500KW. Tesla envisions
that their charging go upto 1 MW. Tesla is using these 1MW charger (Mega
charger) to charge their tesla semi trucks. There are other companies that are
building DC lower chargers at 20-50kW chargers. These could be used at
businesses, hotels, car dealerships instead of AC charging for fasting charging
to electric cars.
Installing chargers- The NEC limits that the maximum
output can be only upto 80% of the circuit breaker rating, i.e. if you have a
100 amp circuit breaker, then at 80% limit, you can only power at 19.2kW at 240Volts.
For level 1, and cars can charge at 1.5kW at 120Vs. Unlike DC charging curves,
the level 2 charging stays flat for most of the time when it is charging. Because
if it is a continuous flat load, the distribution planners have to think about
how to meet these types of load. For homes that don’t have a 200Amp panel, the
chargers can be connected directly to the electric service utility meter. This
is upstream from the service panel, and reduces the need to change the electric
upgrades to install level 2 system.
Utility upgrades- As a power utility, all these EV
charging will impact the distribution grid. The primary feeders for the
distribution utilities have limits to how much they can power.
Feeders- These feeders have thermal
limit on how much power than transmit. Considering the thermal limits- if we
put 10 fast chargers charging at 175 kW we get 1750 kW that already limits to
the how much the power line can provide. Also in mind that these EV are new loads,
the feeders are designed for the prior load. If we had Level 2 load charging at
10kW, we can get up to 1000kW with 100 level 2 chargers on the feeders.
Distribution Transformers- In upstream,
these distribution transformers will be overloaded as well. The common transfomers are rated at 25 to 50 kVA.
These transformer limit will quickly overloaded.
What’s next- As EVs are essentially a huge power pack,
the EV can provide Vehicle to Home Power that allows the home to be isolated as
a microgrid and power the home during an outage. In the future, the EV could
even be bi-directional Vehicle to Grid and sell power back to grid.
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