Reducing Rotor Temperature Rise in Concentrated Winding Motor by Using Magnetic Powder Mixed Resin Ring

Abstract

The demand for high-speed servomotors is increasing, and minimal losses in both high-speed and high-torque regions are required. Copper loss reduction in permanent magnet motors can be achieved by configuring concentrated winding, but there are more spatial harmonics compared with distributed winding. At high-speed rotation, the eddy current loss of the rotor increases, and efficiency tends to decrease. Therefore, we propose a motor in which a composite ring made from resin material mixed with magnetic powder is mounted on the stator to suppress spatial harmonics. This paper describes three characteristic motor types, namely, open-slot motors, composite-ring motors, and closed-slot motors. Spatial harmonics are reduced significantly in composite-ring motors, and rotor eddy current loss is reduced by more than 50% compared with open-slot motors. Thermal analysis suggests that the saturation temperature rise value is reduced by more than 30 K. The use of a composite ring is effective in reducing magnet eddy current loss during high-speed rotation. Conversely, the torque characteristics in the closed-slot motor are greatly reduced as well as the efficiency. Magnetic circuits and simulations show that on electrical steel sheets with high relative permeability, the ring significantly reduces the torque flux passing through the stator, thus reducing the torque constant. To achieve reduced eddy current loss during high-speed rotation while ensuring torque characteristics with the composite ring, it is necessary to set the relative permeability and thickness of the composite ring according to motor specifications.

Magnetic Material Modelling of Electrical Machines

“…M. Sato et al [9] propose a motor in which a composite ring made from a resin material mixed with magnetic powder is mounted on the stator to suppress spatial harmonics. This is a significant method to improve the efficiency of the motor at high speed.…”

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

“…U d is the cumulative content when the particle size is d, and U d0 and n are the fitting parameters. Bring in Equations (25) and (24) gives…”

“…Due to the powder state of the magnetic powder, the stress concentration of the rotor is eliminated, and the discontinuous state of the magnetic powder greatly weakens the eddy current loss on the rotor surface [21][22][23]. The advantages of the composites have been reported to include their capability to form three-dimensional shapes and their loss under high frequency conditions is relatively low [24].…”

Expansion of Motor High-Efficiency Area by Inserting Magnetic Composite Material into Rotor

“…The loss of a high-speed rotary motor is primarily affected by spatial harmonics caused by the magnetic flux's large time fluctuation. The use of magnetic composite material with precisely controlled permeability in the stator is effective in lowering the spatial harmonics of high-speed rotary motors [41,42].…”