Multiple-airgap iron-cored direct-driven permanent magnet wind generators

Multiple-air-gap permanent magnet (PM) generators with iron cores are analysed for application in wind turbines. Electromagnetic analysis of a double-stator, radial-flux, low-speed PM generator with concentrated windings using time-stepping finite element analysis is presented. Two design variants - with magnetic and non-magnetic rotor yokes - are considered. Magnetic flux density, output electrical characteristics and electromagnetic torque are compared for the two variants. Generator structure (one vs. two level machines), winding topology (single vs. double layer windings) are discussed for the machine with magnetic rotor yoke. Finally, optimal number of air gaps is proposed based on predictions of generator´s power density and cost.