Hi guys,
After so much time spent to find a way to give access to my Home Assistant outside my private network, I finally find a way 
First of all, yes… I’ve read all the topics, watch all the videos… and nope… nothing works with the TP-Link router !
Yes, you have to do all the steps about DuckDNS with your home assistant (there is lots of topics about that, and Youtube videos).
After that, you have to go to your TP-Link configuration board, and reserve your HA IP address :
Go on Network -> DHCP -> Add (search your HA IP and MAC)
After that you have to be sure that IP address is open to the world :
NAT Server -> Virtual Server -> HTTP for the service, 8123 for the interne and externe port and TCP Protocol (if you are really struggle after all this post try to add too the 443 port (SSL access).
And now as all the topics on the web you should have access to your HA ???
NOPE…
You can spend hour and hour to try to reach your IP Address and the 8123 port… and nothing happen… so no DuckDNS access too.
Why ?
Because of your internet provider and his box of course 
So… you have to go directly to your internet provider box settings :
- As above for your router settings, in the NAT Server section add your router IP address (not your HA IP -> you can’t anyway, they are not on the same network)
- Do not forget to add you HA port internal and external (8123)
Et voilà !
Now you can finish all the settings with DuckDNS, and control you HA anywhere in the world 