Abstract
Surface mounted permanent magnet Vernier (SPM-V) machines are known for their high torque density but relatively poor power factor compared to conventional SPM machines. The high torque density feature of the SPM-V machines is desirable for direct-drive offshore wind power applications as it leads to reduced generator size, mass and cost. However, their poor power factor can negatively affect the converter cost and efficiency. This paper compares the system-level performance, including generator active and structural components and converter, between the SPM-V and the conventional SPM generator systems. Four different power ratings, i.e. 0.5MW, 3MW, 5MW and 10MW, have been considered to study the trend of system-level performance with increasing power rating. The study shows that the SPM-V generators can be lighter and cheaper than their conventional SPM counterparts. However, after the consideration of converter cost and efficiency, the conventional SPM generator exhibited slightly better overall performance. Nonetheless, with the development of novel Vernier topologies and reduction in converter costs in the future due to emerging technologies, the Vernier generators can still be competitive for direct-drive offshore wind power applications.
Highlights
Direct-drive generators are a preferred choice for offshore wind power applications as they do not have the reliability and maintenance issues resulting from geared systems
Vernier permanent magnet (PM) machines have a drawback of relatively low power factor compared to the conventional surface mounted PM (SPM) machines [4], [5]
The power factor becomes significantly lower (~0.4-0.5) for SPM Vernier (SPM-V) machines at high electrical loading, which is unavoidable for high power offshore direct-drive generators [4]
Summary
Direct-drive generators are a preferred choice for offshore wind power applications as they do not have the reliability and maintenance issues resulting from geared systems. The power factor becomes significantly lower (~0.4-0.5) for SPM Vernier (SPM-V) machines at high electrical loading, which is unavoidable for high power (multiMW) offshore direct-drive generators [4]. This will result in a significant increase in converter rating and cost. It would be interesting and valuable to study the impact of high torque density but low power factor features of the Vernier machines on the overall system-level performance at multi-MW power level for offshore wind applications. This is because, in the existing offshore wind market, the direct-drive generators often have multi-MW power ratings Such large generators will have significantly higher electrical loadings and magnetic saturation levels. The SPM-V machine with is shown in FIGURE 1 (b)
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