Session limit question

[nagyrobi]

How does the Session Limit (Under power, Charging time, Consumption) feature stop the charhing, when power decrease under threshold, or charging time / consumption limit pass is detected?

• cuts the AC relay simply?
• changes to state B(2) first then cuts AC relay?
• is it indifferent from the actual current, or does it rather gradually decrease the max current to 6A (min possible) first and only cuts relay after that?

[dzurikmiroslav]

When limit is reached during D2/C2 state. Go to state C1/D1 (this stop CP pwm). In C1/D1 EV has 6sec to stop charging (CP go to 9V). After 6sec if EV not stop charging, EVSE disconnect AC contactor.

[nagyrobi]

Before going to state C1/D1, we should have an option to gradually ramp down the current to the lowest 6A, to add further protection of the charger module in the EV, also prolonge lifespan of contactors.
Some cars don't do this by themselves.

Something by decrease by 2A in 5 or 10 seconds steps until 6A is reached or past.

Eg. when limit reached, while still in C2/D2, round actual measured current value to integer, extract 6, divide by 2 = number of steps required to ramp down by 2. Adjust PWM to decrease by 2A before each 5s step, and only enter C1/D1 when around 6A, after last step. And let the flow go forward as usual from here.

Could name this intermediate step C3/D3 or C2e/D2e or similar so we can see the state in HMI.

[nagyrobi]

Fyi this is how some cars ramp down the charging power when they reach target value.
We could implement something alike, by adjusting the pilot PWM when limit reached.

It appears to take 10 minutes but I think any would be better than cutting instantly for the ones that don't have this feature.
And we dont necessarily need the curve to be so hi-res.

[dzurikmiroslav]

Yes charging power start falling between 80-90% SOC. My previous EV car haven't ability to set target charging percentage.
So I implemented underpower limit, for ex. when charging power fall under 4kW I know SOC is about 80% and stop charging.

I don't know that some EVs don't respond to PWM being turned off and still charging...
Maybe don't you think it would help to increase the time limit for break charging after PWM is turned off? (now it is 6 seconds)