Abstract
Generators are a key technological element of the wind energy generation system. Currently, there is an increasing interest in adopting non-conventional stator-mounted permanent magnet generators, e.g., flux reversal generators (FRGs), which is a good alternative to conventional synchronous generators for medium-speed wind turbine generator applications. The usage of FRG with rare-earth (RE) permanent magnets (PMs) is increasing due to their high efficiency and high power density factors. However, RE PMs are unattractive to wind generators in terms of their cost and unpredictable market supply. In this paper, an attempt is made to study the potential of FRG with non-rare earths (ferrite PMs) for wind generators. The three-phase, 6/8 pole FRG is designed and compared with RE and NRE PMs for wind generator application at 375 r/min, 10 kW. Using 2D FEA, both the generators are compared in terms of their power generating performance with excellent overload capability. It shows that the average efficiency of the generators is approximately similar, but the torque density of NRE-FRG is only 51% that of RE-FRG. The NRE-FRG design is heavier, with the total active mass being 2.6 times higher than the RE-FRG, but with the estimated total active material cost of both generators almost the same. Moreover, the toque ripple for RE-FRG is 64% higher than for NRE-FRG. The demagnetization risk analysis was performed, and it is found that at higher temperatures, RE-FRG structures are prone to higher demagnetization risks, while it is much lower in NRE-FRGs. In summary, it is found that NRE-FRG is a suitable alternative to RE-FRG for medium-speed wind turbine generator applications in the 10-kW power range.
Highlights
Generators are a key technological element of the wind energy generation system.Recently, there has been an increasing growth and prominence of wind energy generation development, which has dominated the overall renewable power generating capacity and is considered one of the fastest growing renewable energy sources with an installed capacity of 651 GW by the end of 2020 [1]
Permanent magnet synchronous generators (PMSG) with permanent magnets on the rotor are attractive for high power wind energy generation applications because of their high energy yield compared to other induction and electrical-electrical synchronous generators [3]
The findings from the study revealed that the active mass of the soft magnetic composite (SMC) flux reversal machine (FRM) is reduced by 21% compared to the one whose rotor is purely contrived by steel laminations
Summary
Generators are a key technological element of the wind energy generation system. Recently, there has been an increasing growth and prominence of wind energy generation development, which has dominated the overall renewable power generating capacity and is considered one of the fastest growing renewable energy sources with an installed capacity of 651 GW by the end of 2020 [1]. Ferrites (NRE) materials are appearing as suitable replacements for RE-type machines To this end, the main motivation of this study is to expose the potential of NRE over RE PM material in FRG for geared medium-speed wind power generator applications. The proposed 10 kW power range being investigated is clearly a niche power level of lower power limit small wind turbines, the so-called micro wind power generation units [2,21,22] Both machines, NRE and RE FRGs, are compared in terms of their electromagnetic operating performance such as output voltage, torque density, power factor, torque ripple, as well as efficiency at either no-load or rated conditions. Thereafter, mass and cost estimates, as well as demagnetization risk analysis of the associated PM FRG variants are studied and compared in FEA for medium-speed wind power generation
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