Due to the trade-off between rotor mechanical strength and magnetic leakage, the high-speed capability of interior permanent magnet machines (IPMSM) is severely limited. This paper proposes a novel rotor topology capable of delivering 5 kW at 100,000 rpm using commercialized electrical steel laminations. By implementing the mechanical analysis in an iterative evolution process, two promising new topologies were developed. The first topology uses smooth compound curves (CC) to minimize the stress concentration and will be referred to as CC-type; the second topology is developed based on the CC-type with the aim to strengthen the structure further using the concept of a double-tied arch bridge (DAB) and referred as the DAB-type henceforward. After comparing the designs obtained from a detailed multiphysics optimization process, the DAB-type design was found to outperform the CC-type in all aspects, especially the mechanical robustness. This design was selected for experimental verification and a prototype was constructed. The mechanical and electromagnetic performances of the design were fully verified experimentally. The DAB-type prototype has achieved 2.31 × 10 ⁵ rpm√kW, which is 1.5 times higher than other laminated rotor high-speed IPMSM designs found in the literature.

The open-winding permanent magnet synchronous machines (OW-PMSMs) have recently been gaining more attention because of their fault-tolerant capability and power quality comparable to a 3-level converter-driven system. This paper reviews the common configurations of OW-PMSM when used as a generator, highlighting its shortcomings and benefits. The OW-PMSM with a common DC bus was found to be a promising direct-drive generator solution for wind energy conversion (WEC) systems considering fault tolerance, DC bus utilization, and power quality when appropriate control algorithms are in place. The presence of the zero-sequence current is the key disadvantage of the common DC bus configuration. The review highlights the algorithms that have been proposed to suppress the zero-sequence current of the OW-PMSM under healthy and various fault conditions, especially the open-circuit fault of semiconductor switch. Shutting down remotely located wind turbines because of faults, until they can be repaired, may not make economic sense. The OW-PMSM can offer the opportunity, to run a WEC system even under fault conditions albeit with low output power. This paper will assess the literature gaps in the existing control techniques that prevent the extension via a comprehensive review.

This paper investigates the theoretical reasons behind the low torque ripple of a fractional-slot concentrated-winding (FSCW) spoke-type interior permanent-magnet (IPM) machine obtained via a genetic algorithm-based optimization. To better understand the torque performance of the IPMM, this paper uses the frozen permeability method to segregate the overall torque into four components—magnet torque, reluctance torque, cogging torque, and the torque caused by cross-magnetization. Equations and detailed procedures of the torque separation method are discussed in the paper. Analysis of the separated torque components reveals that the counteraction between ripples of different torques leads to the low torque ripple. At high-load conditions, the magnetic saturation alters the torque ripples caused by cross-magnetization to offset ripples of other components resulting in minimization of the overall torque ripple. A detailed parametric analysis of the geometric parameters was carried out to understand their effect in producing minimum torque ripple in the optimized design. In the end, a prototype was built and used for the verification of the torque separation method and the analytical findings based on it.

This paper proposes an improvement for the loss minimization control (LMC) of an interior permanent magnet synchronous machine (IPMSM). The LMC is also referred to as the maximum efficiency (ME) control because the maximum efficiency is obtained by minimizing both the core and copper losses. In conventional LMC methods, core loss is represented by a constant equivalent resistance. However, several recent studies showed that the core loss resistance can vary significantly with both load current and speed. If these variations are not included in the LMC, the true maximum efficiency of the motor cannot be achieved. The proposed method of this paper represents the equivalent core loss resistance as a function of load current and speed. It was observed that, by considering the derivative of core loss resistance with respect to current in the LMC trajectory calculation, the total electrical loss of the controlled IPMSM can be reduced. The proposed LMC was experimentally tested on a high-speed IPMSM and compared to the existing LMC and conventional maximum torque per ampere (MTPA) control. A detailed analysis was carried out to identify the operating conditions where the loss minimization control can outperform MTPA in high-speed IPMSMs.

The open-winding permanent magnet synchronous machines (OWPMSMs) with a common DC bus have a simple structure, low cost, enhanced fault tolerance, and power quality of a 3-level converter system. They have been proposed for many high-performance and safety-critical applications. The common DC bus topology leads to zero sequence current (ZSC) circulation in the stator windings. However, several different control techniques exist to reduce the ZSC to an acceptable level in practical applications. Like any other permanent magnet machine, the OWPMSM is susceptible to irreversible demagnetization when subjected to harsh thermal and electromechanical conditions. The localized partial demagnetization induces additional harmonics in the ZSC, resulting in a higher torque ripple. The demagnetization fault-tolerant control can only be developed once a theoretical framework for the zero-sequence current and torque ripple under demagnetization becomes available. This paper aims to develop such a framework, focusing on fractional-slot concentratedwinding OWPMSMs. The paper analyzes how magnet faults induce lower-order harmonics in ZSC and torque and shows that the slot/pole combinations primarily govern the orders of induced harmonics. These analytical findings have been verified through finite element analysis (FEA) and experimentation on prototype OWPMSMs.