How to start charging in under 1 second and the unresolved #ISO15118 AC charging interoperability issue! 😥💥
How fast an EV can start charging, meaning when current actually begins flowing, is crucial for customers. No one wants to stand by the charger for half a minute waiting. Personally, I wait until the charger or HMI shows a power flow before leaving to avoid unpleasant surprises.
It would be ideal to plug in and have the #EV charging within 1 second. For this, “PWM charging” can help. This #EVcharging OG lets the AC charger set PWM signal with a nominal duty cycle (e.g., 53%), indicating the grid can supply 32A. Simple! But this “PWM charging” also called "Basic Charging" (BC) is rudimentary, leaving no room for advanced ISO15118 features like #smartcharging, and #V2G (note ISO15118-20 also builds on the ISO15118-3 specification).
More AC Wallboxes are now implementing high-level communication (HLC) via ISO15118, which was rare in the past but is becoming more common. We have already certified several (aixACCT Systems GmbH, Bender, Switch ISO Stack) with more coming. (Our certification was focused on HLC for #pnc).
Combining fast time to charge and ISO15118 features would be ideal. ISO15118-3 aims to enable this (for AC) by starting with PWM charging with a nominal duty cycle (≠ 5%) and then initiating SLAC while already charging.
Spoiler alert: this doesn’t work. Most EVs, except some new BMW Group models, stop HLC charging when duty cycle ≠ 5%. But why? ISO-3 specifies this as fine. (See image)
My (personal) take: OEMs often buy the ISO stack from large SW vendors. When they enabled AC HLC via ISO15118, they bought the “extension” for AC too, but the Low Level Communication (LLC) controller (which manages duty cycle and CP voltage) was from another vendor or built in-house and never updated. This controller now creates the 5% duty cycle “lockdown” issue. However LLC and HLC must work together.
Why does this matter? Simply using 5% all the time isn’t feasible!
Plug-in hybrids, which often only support PWM charging, need a nominal duty cycle to start charging. But if the AC Wallbox always uses 5% for ISO functions, hybrids won’t charge. To work around this, most vendors start with 5% duty cycle and use a “fallback” to nominal duty cycle after an adjustable timeout if no SLAC request is received.
This is a prime example of a workaround for an interoperability issue. Enforcing proper ISO-3 implementation from OEMs would be ideal, but this will take time. Meanwhile, we’re stuck with the workaround.
To sum up this post: EV's should try SLAC even with an nominal duty cycle if implementing AC HLC.
Have you faced this issue? How did you handle it? Any other IOP workaround examples?
#electricvehicles #emobility
image source:
Figure 4 — Connection coordination Seq 2: AC EVSE with PnC and EIM and matching process not started before EIM, control pilot state X1 after plug-in
