An 'American fantasy' alternate history series by Orson Scott Card. In this timeline of the early days of America, North America is a land of small magics called "knacks". Most people have at least one minor knack. There is no United States as we know it, but instead several smaller nations including Camelot, home to the deposed English monarchy. Into this world is born Alvin Miller, the seventh son of a seventh son, with all the special powers that often protends. Alvin is a good man with the significant knack of "making", who must quest for the meaning and purpose of his powerful ability. Racial tension and strife underly many of the novels.
Appropriately enough, there are (or will be, depending on when you read this) seven books in the series:
Note that while OSC's own website states that Le Grand Prix de l'Imaginaire was for Heartfire, the actual awards website says "Roman étranger : Orson Scott CARD pour Le septième fils (The Tales of Alvin Maker - Seventh Son)" so it seems more likely that the award was for the first book, and perhaps also for the series.
Award details from http://www.hatrack.com/osc/bibliography/index.shtml