Patent ID: 8228695

Claim:
A method of operating a neutral point clamped three level converter comprising at least two legs, each leg comprising first and second top switches connected in series at a first mid point, first and second bottom switches connected in series at a second mid point, and first and second middle switches connected in series at a third mid point therebetween, wherein the first top and second bottom switches are connected in series at a DC link, the first and second middle switches are connected between the first and second mid points, and each of the top, bottom and middle switches has an antiparallel diode thereacross, the method comprising: alternately switching the first and second top switches to ON state when the first middle switch is in ON state and the second middle switch is in OFF state; and alternately switching the first and second bottom switches to ON state when the first middle switch is in OFF state and the second middle switch is in ON state.