Hi Caio, welcome to the forum. The Ben Peterson is the probably the best option if you want to use pellets. Here is some links for some charcoal gasifiers you may find helpful.
Gary Gilmore has designed a real nice and simple charcoal gasifier. The design is so simple it can be made from almost anything you have available.
Matt Ryder has made some really nice gasifiers made specifically for a generator setup. Most of those are charcoal also.
Let me just say I have no hands on experience with charcoal gasifier. Hope you find something useful in those threads.