The characteristics of a double-star synchronous generator with rectifier load have been studied from the fundamental machine equations. The generator has two stator windings shifted by 30 or 0 electrical degrees, which with their bridges can be connected either in series or in parallel. Therefore, the double-star synchronous generator with rectifier load can form four operating modes. From the fundamental machine equations, expressions of displacement angles and commutation angles are derived under these operating modes. The characteristics of a double-star synchronous generator with rectifier load can be predicted from given load current, field current generator speed, bridge delay angle and parameters. Theoretical results are compared with experimental results.