Rotor Eddy Current Loss Reduction With Permeable Retaining Sleeve for Permanent Magnet Synchronous Machine

Abstract

This paper presents a new rotor design to reduce rotor eddy current loss of a high-speed permanent magnet synchronous machine for flywheel energy storage system. Instead of using common nonmagnetic sleeves, the new rotor incorporates permeable retaining sleeves (PRSs) to fix permanent magnets on the rotor hub. The PRSs are made of permalloy that features high permeability and high electrical conductivity. Thus, skin depths for asynchronous harmonics are extremely small. On the other hand, the PRSs are electrically insulated along the circumferential direction. Owing to these two reasons, rotor eddy current loss at open circuit decreases by 64.2% without sacrificing torque output, compared with an original rotor with nonmagnetic retaining sleeve. In addition, thermal and structural finite element analyses are performed to calculate rotor temperature distribution and evaluate the structural integrity of the new rotor. Rotor eddy current loss reduction benefits lowering rotor temperature rise. Prototype machine with the new rotor is fabricated, and preliminary tests are carried out to confirm the analysis results.

Improved Semi-Analytical Magnetic Field Solution for High-Speed Permanent-Magnet Machines With Permeable Retaining Sleeve Including Diffusion Effect

“…Other works propose alternative solutions to obtain a permeable RS, such as cold-worked stainless steel [50] and RS made of permalloy [49]. This is justified for its advantages, including the use of thinner PM with unchanged back-EMF and mean torque.…”

“…For conduction material, such as stainless steel or Incomel 718, eddy-current reaction fields affect rotor losses [15,[42][43][44] and machine produced torque [45][46][47]. Also, there are works evaluating the advantages of using permeable RS, which includes reduced PM usage and increased inductance [45,48,49]. These permeable RSs present nonlinear B(H) characteristics and affects the machine performance [50,51].…”

Design and Performance Investigation of 3-Slot/2-Pole High Speed Permanent Magnet Machine

“…1. A highly strengthened and resistive materials enclosure, such as carbon fiber composite (CFC), stainless steel, and titanium, can reduce the eddy current loss with PM safety provision [20]. Moreover, for the rated working condition, the enclosure width can be kept minimum so that the amplitude of airgap flux density affect slightly.…”

Rotor electrical conductivity and eddy current loss analysis of high‐speed permanent magnet machine with a novel composite rotor

“…Due to the limitation of rotor temperature rise, it is difficult to further improve the power, speed, efficiency, and power factor of the surface-mounted rotor HSPMM [5]. There are many ways to reduce the rotor eddy current loss, such as changing the sleeve or PM structure, but this method will reduce the output torque or PM utilization, and the strength cannot be guaranteed [6][7][8][9]. A more direct method is to reduce the electrical conductivity of PM materials, such as using other heavy metals to replace neodymium in PM materials to increase the Curie temperature of PM materials [10,11].…”