He's not, Kharn is only toughness 4.
no one runs a ic,hq,warlord alone and not in a squad,
Well if he isn't alone then he better be with a squad
Shoot out all that power amour, then get to him and take off all his wounds, then he jumps into another squad with new body guards.
Then if shooting won't work then turn his biggest strength into a weakness, challenge him with a unit that has a lash whip and bone sword.
Kharn is a terrible enemy to fight in close combat; without that charge your facing off against five strength six attacks (seven at strength seven if he charges) that go through everything that isn't an invulnerable save.
He has the champion of chaos rule, meaning he cannot refuse a challenge. And hitting him with a lash whip takes away his character level initiative, while the bonesword lets you ignore his armour. With no invulnerable save to speak of, every wound counts.
A hive tyrant should be able to kill him with the charge, and stands a good chance of killing him if he gets the charge (remember you can issue a challenge in his turn if he does not issue it to you.)
Something to keep note of when you fight Kharn in close combat: every failed to hit of 1 hits his allies. Thats one of his rules and is the risk you take when giving him any bodyguard.