Medium-Speed Synchronous Reluctance Generator as Efficient, Reliabile and Low-Cost Solution for Power Generation in Modern Wind Turbines

This paper proposes a medium-speed synchronous reluctance generator as an efficient, reliable and low-cost solution for modern wind turbines. An optimized 2.0 MW synchronous reluctance generator is presented with the help of a finite element simulation in order to analyze the performance characteristics of the machine concerning the efficiency, as the synchronous reluctance machine doesn't require magnets or copper winding in the rotor. Furthermore, the machine performance is investigated for the medium-speed range for wind turbines. The medium speed allows using a single-stage gearbox instead of a multi-stage gearbox which increases the reliability of the wind turbine powertrain, as gearbox failures are very crucial concerning time and operating costs in wind turbines. Moreover, the reliability is increased by avoiding the slip rings that are used for induction generators. The elimination of the permanent magnets and the copper winding reduces the investment costs while the increased efficiency and the improved reliability lead to reducing the operating costs and therefore the cost of energy. The full-scale three-level neutral-point-clamped converter is selected due to the medium voltage of the generator and due to the regulation standards, which became difficult to fulfill using the partial-scale converter solutions. The control of the proposed synchronous reluctance powertrain is also studied with the focus on the voltage stability of the DC-link voltage, as required for the wind turbine application.