Design and analysis of permanent magnet induction generator for grid-connected direct-driven wind power application

Without power electronics and mechanical gearbox, the permanent magnet induction generator (PMIG), a new grid-connected direct-driven wind generator concept, is considered to be a highly efficient, low maintenance solution for high capacity offshore wind power generation system. In this paper, the characteristics and optimal design method of this generator for wind power application are investigated. The working principle and the dynamic model are deduced. Two kinds of permanent magnet rotors as well as the magnetic characteristics are analyzed and compared by the magnetic circuit. The size equation is analytically derived and the initial calculation of machine dimensions and parameters, namely, the core diameter, stack length, and permanent magnet size, are also discussed. Moreover, finite element analysis (FEA) is carried out for design optimization, in which the machine overload capability and demagnetization protection under grid short circuit fault are investigated. Finally, a design guideline form the PMIG is developed. A 10 kW prototype machine is built in the laboratory and the experimental results are given to verify the design and analysis.