GRID TIE INVERTER

| Can someone help me to design a circuit for grid tie inverter for three | phase supply output for 10-20 KW load.

Is this just a classrom assignment or are you planning to make one that can really be hooked up? In the former case, you should be doing that all for yourself. In the latter case, these things have to go through a lot of rigorous testing to get certification before they can be hooked to the grid. For example, it has to be able to detect when the grid loses power, even if there are several of these connected to the line on your street, so it can instantly disconnect for reasons of safety.