This paper reviews the current technologies used in high-speed electrical machines through an extensive survey of different topologies developed and built in the industry and academia for several applications. Developments in materials and components, including electrical steels and copper alloys, are discussed, and their impact on the machines' operating physical boundaries is investigated. The main application areas pulling the development of high-speed machines are also reviewed to better understand the typical performance requirements.

Hairpin windings are gaining increasing popularity in recent years due to their advantages in improving electrical machine performance while reducing manufacturing time and costs. Their geometrical features introduce new challenges and opportunities on thermal management. In particular, spray cooling is increasingly being used, since hairpin windings open up regular and accurately defined gaps in the end-windings compared to the traditional random windings. To date, technical literature on the effectiveness of spray cooling with hairpin windings is lacking, with no practical guidelines available to researchers. In this article, taking an existing hairpin-wound stator, a test rig is developed to investigate the cooling ability of different spray cooling setups on the end-windings. Three types of commercial spray nozzles are chosen to carry out a series of experiments, varying the oil flow rate, pressure, outlet velocity, and number of nozzles. The winding temperature and heat transfer coefficients are presented and discussed. Furthermore, the efficiency of spray cooling is reviewed based on the experimental results. Finally, suggestions on designing similar cooling setups and increasing the cooling efficiency are also provided.

For the propose of increasing the reliability in hostile environment, techniques of fault diagnosis have been reported for three-phase voltage source inverter (VSI). Based on the average current Park's Vector method, this paper proposes a fuzzy-based fault diagnosis method for the VSI in the three-phase permanent-magnet synchronous motor drive. By utilizing the phase current information, the fault symptom variables are calculated by using the average current Park's Vector method. The fuzzy logic approach is applied to process the fault symptom variables and get the faulty information of power switches. Compared with other fuzzy logic methods, the fuzzy logic design, fuzzy inputs and fuzzy rules are different. The proposed fault diagnosis method can detect and locate not only the single or multiple open-circuit faults but also the intermittent faults in power switches, which can improve the reliability of the motor drive system. The effectiveness of the proposed method is validated by both simulation and experiments.

In the last decade, the trend toward higher efficiency and higher torque density electrical machines (EMs) without permanent magnets (PMs) for the industrial sector has rapidly increased. This work discusses the latest research and industrial advancements in synchronous reluctance machines (SynRMs), being the emergent motor topology gaining wide acceptance by many industries. This article presents an extensive literature review covering the background and evolvement of SynRM, including the most recent developments. Nowadays, SynRM has found its niche in the EM market, and the reasons for that are highlighted in this work together with its advantages and disadvantages. The key journal publications in SynRM topics are discussed presenting the biggest challenges and the latest advancements with particular regards to the design methodology. This article aims to provide a thorough overview to the research community and industry about SynRM. There is a clear potential for SynRM to take over a significant portion of the EM market in the near future to meet efficiency standards in industrial applications without the use of rare-Earth PM technology.

This paper introduces an innovative thermal modeling technique which accurately predicts the winding temperature of electrical machines, both at transient and steady state conditions, for applications where the stator Joule losses are the dominant heat source. The model is an advanced variation of the classical lumped-parameter thermal network approach, with the expected degree of accuracy but at a much lower computational cost. A seven-node thermal network is first implemented and an empirical procedure to fine-tuning the critical parameters is proposed. The derivation of the low computational cost model from the thermal network is thoroughly explained. A simplification of the seven-node thermal network with an equivalent three-node thermal network is then implemented, and the same procedure is applied to the new network for deriving an even faster low computational cost model. The proposed model is then validated against experimental results carried on a permanent magnet synchronous machine which is part of an electro-mechanical actuator designed for an aerospace application. A comparison between the performance of the classical lumped-parameter thermal network and the proposed model is carried out, both in terms of accuracy of the stator temperature prediction and of the computational time required.

This paper presents innovative research toward the development of a 45-kW high-speed switched reluctance drive as an alternative starter-generator for future aeroengines. To perform such a function, the machine had to be designed with a very wide constant power-speed range. During engine-start/motoring mode, a peak torque demand of 54 N · m at 8 kr/min was met, while in generating mode, 19.2-32 kr/min, the machine was designed to deliver a constant power of 45 kW. The key enabling feature of the design lies in the novel rotor structure developed so as to allow for such a wide speed range. The results presented are those measured during the initial testing phase and validate the system design and performance in the low-speed region with the machine operated in starting mode. The measured machine power density is at 9.8 kW/L, while the global system efficiency is at 82%.