• Energy Research

A bridgeless rotor of a synchronous reluctance machine is proposed to enhance the performance of high-power and -speed synchronous reluctance machines (SynRMs). Unlike traditional transversally laminated designs that rely on radial and tangential ribs or bridges to provide mechanical integrity for the rotor, the suggested rotor incorporates separate flux guides attached to non-magnetic back plates to form SynRM rotor modules that are stacked on the shaft of the machine. This innovative structure eliminates the need for radial and tangential bridges which form a performance-deteriorating bottleneck in the design of high-power SynRMs. The paper presents a detailed analysis of the electromagnetic and mechanical aspects of the proposed bridgeless rotor synchronous reluctance machine (BLRSynRM). Furthermore, a comprehensive optimization method is implemented to demonstrate the capabilities of the proposed BLRSynRM along with comparison with conventional transversally laminated SynRM. The results show a significant increase in torque and power factor compared with conventional structure rotor. However, the proposed bridgeless structure introduces new electromagnetic and mechanical challenges to machine design and they are explained and overcome in this research.

The performance capabilities of an axially laminated anisotropic rotor (ALA) in a high-speed synchronous reluctance motor (SynRM) were studied. A 12 kW ALASynRM was designed as an alternative to a high-speed induction motor (IM) with a solid rotor. The electromagnetic design was implemented taking into account possible issues related to the new manufacturing methods, which require thicker rotor layers than in a typical ALA. The ALASynRM shows a higher efficiency than the corresponding IM with a smooth or slitted solid rotor equipped with copper end rings. To verify the design method, a prototype IM with a smooth solid rotor was built and tested. In the analysis, it was found that, similar to IMs, in an ALASynRM a considerable part of losses takes place in the rotor despite the absence of slip-related losses in the SynRM. The distribution of eddy current losses in the ALA rotor is significantly uneven. The torque ripple in the ALASynRM is considerably larger than the corresponding ripple in IMs.

In this paper, a direct liquid cooling method is proposed for a radial-flux permanent-magnet motor. To demonstrate the feasibility of the cooling method, a test motor with a rated output of 205 kW was designed, constructed, and tested in an actual vehicle application, an electric city bus. The energy consumption tests were conducted by applying a heavy-duty chassis dynamometer capable of simulating the inertia, weight, and road loads that the buses are subjected to in the normal on-road operation. The electricity consumption on the real bus route of the Espoo line 11 in Finland was 0.61 kWh/km. The test results of the cooling solution show that the motor is capable of meeting the most challenging requirements of the load cycle even with a full payload. The highest winding temperature rise in the test driving cycles was only 26 °C, which proves the effectiveness of direct-liquid-cooled coils in a vehicle motor.