Slotless-PM Machine Design for an Integrated Generator-Rectifier Architecture for Off-Shore Wind Turbines

Integrated generator-rectifier architecture has been shown to substantially improve power density, efficiency and reliability of the electric drivetrains in wind turbines. From a power-electronic perspective, the architecture processes a majority share of the incoming power through passive diodes operating at the generator’s fundamental frequency. This paper presents a design methodology of a 10 MW generator, which involves a specific low-reactance generator to minimize the commutation voltage drop at the passive rectifiers as well as prevent power imbalance between different generator ports. Appropriate phase shifts between the multiple passive ports to eliminate the need for a dc-link capacitor improve the drivetrain reliability. The proposed design adopts a slotless permanent magnet (PM) generator, where the reactance is greatly constrained by eliminating the stator slots. In addition, a Halbach PM-array structure reduces the reactance by removing the rotor back iron. The design methodology uses these features along with a multi-objective optimization framework to maximize power density and efficiency while retaining a low reactance. Co-simulation of the generator and integrated power electronics shows that the proposed architecture is suitable for off-shore wind generators. Finally, a subscale generator is tested to verify the low-reactance design of the proposed generator.