Design and Analysis of a 2.5 MW Hybrid Excited Synchronous Wind Turbine Generator With Two Separate Rotors

In this paper, a 2.5 MW 16 rpm hybrid excited synchronous generator (HESG) is designed for direct drive wind turbine applications where two separate rotors for permanent magnet (PM) and DC excited field windings are utilized simultaneously. As a result, output voltage of the generator is due to the combination of the fixed field from the PM rotor and a variable field from wound field (WF) rotor. A model is constructed using a cost optimized 2.5 MW Permanent Magnet Synchronous Generator and it is simulated by using finite element method (FEM). The feasibility of the topology and the controllability range determined by the dominance of the excitation types are discussed. Finally, the design is compared with synchronous generators with single excitation type at the same ratings. The designed HESG yields 26% reduction in PM magnet amount compared to a PMSG at the cost of slightly reduced efficiency and power factor.