Superconducting machines are promising candidates for direct-drive multimegawatt offshore wind turbines. Here, we designed a 20-MW fully superconducting synchronous wind turbine generator using magnesium diboride (MgB ₂ ) superconductors for both rotor and stator windings. MgB ² tapes operating at 10 K are used for the rotor windings in order to improve the packing factor. A Rutherford cable made of 91-filament MgB ₂ wires operating at 20 K is used for the stator windings in order to limit the ac losses. Two separate cryostats are considered for the stator and the rotor to increase the system reliability. Besides, to reduce the machine's weight and to simplify the cryogenic system, a toothless magnetic circuit is adopted. The goal of the two-dimensional finite element method based optimization was to minimize the levelized cost of energy (LCOE). Numerical results show that the adopted topology is lightweight enabling to reduce the cost of the nacelle, tower, and foundation, and therefore, the LCOE in comparison to a conventional generator. But the ac losses are significant, requiring at this stage of the study an impractical number of cryocoolers.

The levelized cost of energy (LCOE) of offshore wind energy conversion systems using permanent magnet and fully superconducting generators is compared. Scaling laws are used to calculate the masses and the costs of all the components, to the exception of the generators that are designed and optimized by using the finite element method. The comparisons are done for various turbine’s nominal power, ranging from 2 to 23 MW. The results show that for each generator type, there exists an optimal nominal power that minimizes the LCOE. In addition, the use of a superconducting generator could significantly lower (about 7% at 20 MW) the LCOE compared with using a permanent magnet generator.

This paper presents performance improvements of a double excitation synchronous motor by using a reluctance network (RN). The distinguishing feature of the double excitation principle is to use permanent magnets with high energy, while air-gap flux is flexibly controlled by field windings. Therefore, the first contribution of this paper focuses on maximizing air-gap flux range control. Second, an approach for torque ripple reduction is proposed by directly modifying air-gap flux according to the instantaneous torque profile. The achieved resultant torque stays almost constant for a case study. The validity of the RN method is examined by comparisons with 3-D finite element and experimental results for several machines.

This article investigates the comparison between two configurations of 20 MW offshore synchronous wind generators using ferrite and rare-earth permanent magnets. The optimization-based comparison concerns the torque ripple and active mass, which are two crucial criteria for offshore wind generators. Both generators adopt surface-mounted permanent magnet type with direct-drive technology to avoid problems associated with the gearboxes. The result shows that at the full-load condition, the ferrite permanent magnet generator can reduce the torque ripple to as much as 0.12%, while the rare-earth counterpart can be about 2.5 times lighter than the former one.

This article aims at reducing the cost of energy by targeting the optimal power of the wind generator of offshore wind farms in a region in Vietnam. The research employs various scaling laws for mass and cost calculations. The calculations are implemented using wind data of a specific region on the South-Central Coast. The permanent magnet synchronous generator with high efficiency, light-weight, and compact design will be used for the wind generator. The levelized cost of energy as a function of the generator’s nominal power is then built to figure out the optimal power of the wind generator. Results show that future offshore wind farms with monopile foundations having a mean wind speed of about 6.5 m/s should be installed with a turbine's nominal power of 7 MW.