Is there a way to get 100% connection for my PS3?

May be...

I have a Dlink DIR 628 and my PS3 is about 20 feet away from the router. It has 75% connection sometimes 77% but is there any way to get 90% or above?

your ps3 isnt based on distance from the router, its based on what the router gives off... so if you lose connection or its low, its the routers fault not the PS3... you just need a stronger internet connection in the house and thatll fix the problem... dont do anything to the PS3 though

I think it depends if the router is close to the ps3.

Because mine is and the signal is 97%