Comparison of Electromagnetic Performance of 10-MW Superconducting Generators With Different Topologies for Offshore Direct-Drive Wind Turbines

This paper compares the electromagnetic performance of 10MW superconducting (SC) generators with three different topologies, i.e., iron-cored stator and rotor (ISIRT), iron-cored stator and air-cored rotor (ISART), and air-cored stator and rotor (ASART). The objective is to provide a powerful insight into the advantages and disadvantages of the different topologies, and to establish some design guidelines for selecting an appropriate direct drive SC generator for offshore wind turbine applications. Firstly, the structures of the three SC generator topologies are introduced. Then, the influence of the SC coil cross sectional area on torque capability is compared. After that, three SC generators with different topologies are optimized respectively for further comparison, including the active material cost, weight, harmonics in the electromotive force (EMF), torque ripple, field harmonics in the SC coil, and forces on the rotor and stator components, etc. It is found that, with the same SC quantity, the torque capability of the iron-cored stator and rotor topology is much better than that of the other two topologies. However, the advantage becomes less significant when a larger area of the SC coil is employed. The air gap flux density waveform of the ASART is much smoother than those of the ISIRT and ISART. The torque ripples of the ISIRT and the ISART are much higher than that of the ASART. The field harmonics (both amplitude and frequency) in the SC coil of the ASART are the lowest. For the ISIRT, most of the force on the rotor is acting on the rotor iron, and thus, the SC coil is more likely to be safe from a mechanical performance point of view and the design of the corresponding supporting structure is simple. However, for the air-cored rotor topologies, nearly all the force is acting on the SC coil. For the air-cored stator, the force mainly acts on the armature winding, while for the iron-cored stator, it is mainly on the stator teeth. Due to the excellent mechanical performance of iron, the iron-cored stator is therefore more robust

Influence of pole number and stator outer diameter on volume, weight and cost of superconducting generator with iron-cored rotor topology for wind turbines.

This paper investigates the influence of pole number and stator outer diameter on the performance of superconducting (SC) generators. The SC generator has an iron-cored rotor topology. Firstly, the generator structure is introduced and the optimization procedure is described. Then the influence of design parameters on performance, in terms of generator volume, weight, SC wire utilization, and active material cost, etc., is presented. Some relationships for the optimal combinations for different performance attributes are established. In addition, the influence of SC material price on the determination of optimal stator outer diameter and pole number is discussed. Finally, the influence of SC coil area per pole on performance is also investigated

Comparison of Peak Armature and Field Winding Currents for Different Topologies of 10-MW Superconducting Generators Under Short-Circuit Conditions

This paper studies the peak armature and peak field winding currents for three different topologies of 10 MW partial High Temperature Superconducting Generators (HTSGs) under Short-Circuit Conditions (SCC) by simulation. The investigated partial HTSGs employ copper armature windings and superconducting field windings with different armature and rotor topologies, i.e. iron cored armature and rotor, air cored armature and rotor, and iron cored armature and air cored rotor. For each HTSG topology, the investigation includes: (i) the field winding current control strategies, (ii) the influence of operating field current, and (iii) the ratings of circuit breakers for limiting the peak armature and peak field winding currents. The results can provide guidelines for determining the peak armature and peak field currents of HTSGs and also the possibility of limiting them by employing circuit breakers under SCC

Investigation of scaling effect on power factor of permanent magnet Vernier machines for wind power application

This study investigates the scaling effect on power factor of surface mounted permanent magnet Vernier (SPM-V) machines with power ratings ranging from 3 kW, 500 kW, 3 MW to 10 MW. For each power rating, different slot/pole number combinations have been considered to study the influence of key parameters including inter-pole magnet leakage and stator slot leakage on power factor. A detailed analytical modelling, incorporating these key parameters, is presented and validated with two-dimensional finite-element analysis for different power ratings and slot/pole number combinations. The study has revealed that with scaling (increasing power level), significant increase in electrical loading combined with the increased leakage fluxes, i.e. (i) magnet leakage flux due to large coil pitch to rotor pole pitch ratio, (ii) magnet inter-pole leakage flux and (iii) stator slot leakage flux, reduces the ratio of armature flux linkage to permanent magnet flux linkage and thereby has a detrimental effect on the power factor. Therefore, unlike conventional SPM machines, the power factor of SPM-V machines is found to be significantly reduced at high power ratings