Determining demagnetisation risk for two PM wind power generators with different PM material and identical stators

Abstract

Ways to utilise ferrite permanent magnets (PMs), in a better way has been in focus the last couple of years since the use of neodymium-iron-boron (NdFeB) PMs has been debated. While ferrite PMs offer a low-cost alternative to rareearth PMs, it is a trade-off for lower energy density. Depending on the type of PM and if the PMs are surface mounted or buried, the risk of demagnetisation during a fault condition can vary significantly between machines. In this study, the demagnetisation risk of two electrically similar generators with identical stators has been studied during several shortcircuit faults at different temperatures. The study is simulation-based, and the results show that the generator with the ferrite rotor will suffer from a small but not significant amount of demagnetisation in the worst, three-phase-neutral, short-circuit case at a temperature of 5°C, whereas the NdFeB PMs will suffer from partial demagnetisation if a fault occurs at 120°C. For operational temperatures between 20 and 60°C both generators will sustain a short-circuit event.

The Influence of Permanent Magnet Material Properties on Generator Rotor Design

“…The demagnetisation parameter C B min PM gives a minimum value of magnetic flux density along the magnetisation allowed in the PM as fraction B r . Considering demagnetisation is important since the different topologies can be expected to provide different levels of protection against demagnetisation [21]. The figure of merit used in comparison is torque per unit machine length and pole pair, with a fixed electrical loading of the stator and a fixed amount of magnetic energy in the rotor.…”

“…A spoke-type rotor with ferrites is compared to a rotor with surface mounted Nd-Fe-B magnets for a wind power generator in [19,20]. A comparison of demagnetization risk for the same generator types is presented in [21].The aim of this paper is to study how the magnetic properties of PM materials affect the machine design in low-speed radial flux PM generators. To our knowledge, there has not been any previous study combining material properties with rotor design and rotor topology choice.…”

“…A spoke-type rotor with ferrites is compared to a rotor with surface mounted Nd-Fe-B magnets for a wind power generator in [19,20]. A comparison of demagnetization risk for the same generator types is presented in [21].…”

A Review of Research on Large Scale Modern Vertical Axis Wind Turbines at Uppsala University

“…A simulation model studying partial demagnetizing of permanent magnet has been developed and experimentally verified [52]. The risk for partial demagnetization for the ferrite 12 kW generator has been investigated and compared to the risk for the NdFeB generator, showing that both generators have a reliable design if operated as intended [53].…”

Winding Design Independent Calculation Method for Short Circuit Currents in Permanent Magnet Synchronous Machines

“…To be able to determine these is therefore a necessary part of PM machine design [1]- [4]. This is usually done by either transient finite element (FE) simulation coupled with a circuit model, as in [5], or some combination of static FE calculation for parameter estimation and a parametric transient model. In [6] it is discussed how the theory commonly used for short circuit calculations in wound rotors can be adapted for use with PM machines.…”