New magnetic isolation winding for modular multiple three-phase permanent-magnet machine with mixed-layer

In large scale permanent magnet (PM) machines, such as direct drive wind power generators, stator modularity is widely used for easy manufacturing and to protect the winding from mechanical damage due to being exposed to air. Multiple three-phase systems that use commercial inverters provide not only a fault-tolerant operation but also price competitiveness. Although the conventional modular structure of a concentrated single-layer or distributed winding shows good performance, a large magnetic mutual interference between coils is inevitable. Consequently, if conventional windings are applied to multiple three-phase systems, complexity and difficulty for controlling the machine can arise. This study proposes a new magnetic isolation winding scheme for modular multiple three-phase PM machines with a mixed layer to deal with the abovementioned limitation. For comparison, five different modular multiple-three phase PM machines with a mixed-layer winding (MMPM) are presented and three conventional modular types are selected. Then, several simulation results and experimental data confirm the validity of the proposed structure.