NHP Technical News
Electrical Load Management
The most basic way to do load management for an application
of this nature would be to place energy metering with low-level
communication capabilities (Modbus over RS485, for example)
on the main incomer to the switchboard and on the moulded
case breakers upstream of the EV chargers, and contactors
upstream of the EV chargers. A simple program in a low-end
PLC would then be able to figure out in real-time what electrical
energy the building is consuming, and how much headroom
there is to support EV charging. The PLC would then open
contactors upstream of the EV chargers as required to keep the
total building load within acceptable limits.
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This approach is simple to implement and would work perfectly
from a pure load management perspective, but it will not meet
the expectations of electric vehicle owners. Turning the power
off mid charge with no warning is not great for the battery in
the vehicle and will in some cases result in the vehicle setting
off an alert or alarm. This may take the form of a message on
the in-vehicle display, or it may be more like a car alarm or an
automated notification to the driver’s phone.
There is also the issue that depending on the specific vehicle
charger and the specific vehicle, closing the contactor again may
not automatically restart the charging process. The car owner
may be required to manually press a reset button physically
located on the charger, for example, which will not
be convenient overnight.