Electric motors play a crucial role in modern industrial and domestic applications. With the trend of more and more electric drives, such as electric vehicles (EVs), the requirements for electric motors become higher and higher, e.g., high power density with good thermal dissipation and high reliability in harsh environments. Many efforts have been made to develop high performance electric motors, such as the application of advanced novel electromagnetic materials, modern control algorithms, advanced mathematical modeling, numerical computation, and artificial intelligence based optimization design techniques. Among many advanced magnetic materials, soft magnetic composite (SMC) appears very promising for developing novel electric motors, thanks to its many unique properties, such as magnetic and thermal isotropies, very low eddy current loss, and the prospect of low-cost mass production. This paper aims to present a comprehensive review about the application of SMC for developing various electric motors for electric drives, with emphasis on those with three-dimensional (3D) magnetic flux paths. The major techniques developed for designing the 3D flux SMC motors are also summarized, such as vectorial magnetic property characterization and system-level multi-discipline robust design optimization. Major challenges and possible future work in this area are also discussed.

In this paper, a hybrid transmission system equipped with a speed regulating differential mechanism (SRDM) is proposed for grid-connected wind turbines (WTs) to generate constant-frequency electricity. However, the transmission system is subject to pulsating torque from disturbances in the power grid. Coupled with parameter uncertainties, the speed control accuracy of SRDM and the system stability can hardly be warranted by conventional adaptive or robust controllers. Aiming at the proposed WT, this paper presents a discontinuous projection-based adaptive robust backstepping controller (ARBC) with an extended state observer (ESO) for high-accuracy speed control of permanent magnet synchronous motor (PMSM) in SRDM. The designed control approach, whose global robustness is guaranteed by a feedback robust law, can effectively handle parametric uncertainties and external disturbances together without using the large nonlinear feedback gain and violating any constraints during transient period. Then, the desired tracking performances of ARBC with ESO are verified through comparative experiments in a built platform of the wind turbine with SRDM. Comparative experimental results show that SRDM equipped with the integrated control method can accurately regulate the power frequency to constant under operating conditions of parametric uncertainties, varying wind speeds, sub-synchronous resonance (SSR) and sudden load fluctuation in the power grid.

One of the keys to the success of the fourth industrial revolution (Industry 4.0) is to empower machinery with cyber–physical systems connectivity. The digital twin (DT) offers a promising solution to tackle the challenges for realizing digital and smart manufacturing which has been successfully projected in many scenes. Electrical machines and drive systems, as the core power providers in many appliances and industrial equipment, are supposed to be reinforced on the verge of Industry 4.0 in the fields of design optimization, fault prognostic and coordinated control. Therefore, this paper aims to investigate the DT modelling method and the applications in electrical drive systems. Firstly, taking the high-speed permanent-magnet machine drive system as an example, multi-disciplinary design fundamentals and technologies, aiming at building initial mechanism and simulation models, are reviewed. The state-of-the-art of DT technologies is figured out to serve for high-precision and multi-scale dynamic modelling, by which a framework for DT models of electrical drive systems is presented. More importantly, fault diagnosis and optimization strategies of electrical drive systems in the decision and application layer are also discussed for the DT models, followed by the conclusions presenting open questions and possible directions.

As we face issues of fossil fuel depletion and environmental pollution, it is becoming increasingly important to transition towards clean renewable energies and electric vehicles (EVs). However, designing electric motors with high power density for EVs can be challenging due to space and weight constraints, as well as issues related to power loss and temperature rise. In order to overcome these challenges, a significant amount of research has been conducted on designing high-power-density electric motors with advanced materials, improved physical and mathematical modeling of materials and the motor system, and system-level multidisciplinary optimization of the entire drive system. These technologies aim to achieve high reliability and optimal performance at the system level. This paper provides an overview of the key technologies for designing high-power-density electric motors for EVs with high reliability and system-level optimal performance, with the focus on advanced magnetic materials and the proper modeling of core losses under two-dimensional or three-dimensional vectorial magnetizations. This paper will also discuss the major challenges associated with designing these motors and the possible future research directions in the field.

Hybrid drive wind power generation system, equipped with the speed regulating differential mechanism (SRDM), is able to be friendly connected to power grid without the need of partly- or fully-rated converters. The novel transmission schemes can promote not only the output power quality but also the low voltage ride through (LVRT) capability of the existing wind turbines (WTs). For the purpose of further improving the grid-connected operating performances of SRDM-based WT, this paper aims to develop a hybrid power production unit, in which the hydrogen storage system (HSS), comprising an electrolyzer, a hydrogen fuel cell and a supercapacitor, is integrated into SRDM-based WT. The basic architecture and numerical modelling methods of key subsystems in SRDM-based WT as well as in HSS are analyzed. After determining the eight different operating modes, a power supervision approach is synthesized for the proposed SRDM-based WT with HSS, by which the power flow management between energy sources and storage elements can be realized. Case studies are carried out in the presence of different randomly varying wind speeds and grid voltage faults. The satisfactory operating performances of the proposed wind-hydrogen hybrid system in terms of maximizing wind energy utilization, suppressing output power fluctuation and improving system continuous operating stability are verified.