Series Elastic Actuator-based exoskeleton can offer precise torque control and transparency when interacting with human wearers. Accurate control of SEA-produced torques ensures the wearer’s voluntary motion and supports the implementation of multiple assistive paradigms. In this paper, a novel variable transmission series elastic actuator (VTSEA) is developed to meet torque-speed requirements in different exoskeleton-assisted locomotion modes, such as running, walking, sit-to-stand, and stand-to-sit. The VTSEA features a SEA-coupled variable transmission ratio adjusting mechanism and works between three discrete levels of transmission ratio depending on the user’s initiative. The proposed prototype can also improve transparency in human-robot interaction. Also, an accurate torque controller with inertial compensation is developed for the VTSEA via the singular perturbation theory, and its stability is proved. The feasibility of the proposed VTSEA prototype and the precise output torque performance of VTSEA are verified by experiments.

Precision in multi-torque-speed characteristics, disturbance resistance, transparency, and back-drivability are expected in exoskeleton actuators' design and control. The introduction of series elastic actuators (SEA) for lower-extremity exoskeletons has recently attracted more attention owing to their special merits compared to traditional actuators in high torque control accuracy, favorable output compliance, and unique shock tolerance. In this work, a SEA with a variable transmission ratio for the hip exoskeleton is developed for different working conditions requiring variable torque-speed characteristics. A crank-slide mechanism that actively changes the torque transmission path based on different tasks to meet the torque-speed requirements for the low-extremity exoskeleton. The high-precision torque delivery is the main concern in SEA control. Also, the crank-slider mechanism added in SEA will bring a new control difficulty with the frequent switching of the transmission ratio which may cause severe mechanical vibration and unsafe factors to users. Thus, a novel torque control architecture, based on disturbance observer integrated with a three-mass modeling method for VTSEA is proposed. Simulations are carried out to validate that the developed controller can restrain disturbance and provide accurate assistive torque tracking effectively. This work serves as a fundamental for employing and developing hip exoskeleton for locomotion assistance.

In recent years, transverse flux permanent magnet motors (TFPMMs) have had a promising application in electric propulsion systems due to their modularity, simple winding distribution, and high reliability. However, the low motor space utilization, low average output torque, and complex manufacturing and assembly constraints have limited the further development of TFPMMs. Therefore, this paper proposes a novel double-stator transverse flux reversal permanent magnet machine (DS-TFRPMM). This new motor has no permanent magnets on the rotor and can achieve higher operating speeds. In addition, the permanent magnets are on the outer stator to improve motor space utilization. Firstly, this paper describes the structure and operating principle of the DS-TFRPMM. A 3D model of the DS-TFRPMM is then constructed, and a 3D-finite element analysis (FEA) is carried out to obtain the magnetic field distribution and the critical performance data. The simulation results show that the proposed motor has the average output torque of 11.70Nm, the torque density of 10.9Nm/L, and the 1.19Nm peak-peak value of cogging torque. Finally, the paper optimizes some critical parameters of the DS-TFRPMM and provides the dimensions of the vital motor components for optimum output performance.

Axial flux permanent magnet (AFPM) machines are welcomed in industries due to the compactness. In order to improve the fault-tolerant capability and decrease phase voltage level, a dual three-phase dual stator AFPM machine with mechanical offset is proposed. In this paper, a theoretical analysis is conducted for the harmonics of the proposed machine. The mechanical offset mainly affects the amplitudes of harmonics. Then, a 3D finite element analysis is performed to verify the theoretical analysis. The orders of main air-gap flux density harmonics are related to the number of rotor pole pairs and teeth, but the harmonics have little influence in the back electromotive force. As for the axial force density, the orders of main harmonic components are the two times number of stator pole pairs, rotor pole pairs, and teeth. The results are consistent with the theoretical analysis and in-depth discussion.

This paper proposes a new multi-port flux-modulated permanent-magnet (FMPM) composite machine. The combination of the multi-port and flux-modulated configurations leads to the large torque capacity, high efficiency and fault-tolerant capability. Firstly, the composite flux modulation principle is specifically illustrated, as a general design principle of FMPM composite machines. Specific performance analysis is carried out to demonstrate the electromagnetic characteristics of the proposed machine, with auxiliary of the harmonic analysis. The composite flux modulation effect is proven for effective contribution to the higher torque density of the proposed FMPM machine. As a result, the proposed machine serves as a promising candidate in electric transportation applications.

Transportation electrification has attracted much attention in modern society. Among all electrified transportation tools, electric vehicle (EV) is absolutely the one that has great potential to compete with and further take the place of traditional fossil fuel vehicles. This article is to outline and investigate advanced electric machines and their control strategies for EV applications. The key is not only to reveal new design ideas, topologies, structures, methodologies, control strategies, pros and cons, and foresight for advanced electric machines but also to fully integrate these ideas into practical EV applications. This critical review will clarify the development trends of electric machines and their controls.

This paper is to present an unmanned aerial vehicle (UAV)-oriented wireless power transfer (WPT) system which accommodates with an energy-efficient receiver. Actually, the key is to use a buck converter to greatly reduce the current through the receiving coil and the rectifying diodes. As a result, the total power loss on the receiver is effectively reduced. First, to realize the proposed design, the whole system is modeled to analyze its system-level performance. Then, the loss on the receiver is modeled to instruct the parameter design of the buck converter, namely the duty ratio and switching frequency. After that, an experimental prototype is developed to validate the effectiveness of the proposed system. Results show that the proposed WPT system can achieve a dc-to-load efficiency of 82%, which is 9% higher than the case without the buck. Moreover, when the charging current is 6 A, the total loss on the receiver is reduced up to 14.4 W by properly configuring the buck converter.

Researchers have recently attached more attention on permanent magnet brushless AC motors for electrified propulsion. Considering the further improvement of torque density, this paper proposes a novel pulse width modulation (PWM) magnet array and quantitatively analyzes the magnetic field with different magnet configurations. It is a good potential for reducing the magnet volume. Based on a slotless motor design which eliminates the influence of additional harmonic sources except for that from magnets, investigations on motor performance with proposed magnet array are made. Also, the improvement of torque density is discussed and verified.

Outer loop PI controllers have been widely applied before the inner model predictive torque control (MPTC) to determine the torque reference, which could increase the number of tuning parameters for the total control scheme. In this paper, to simplify the structure of total control scheme and improve the performance of MPTC in dual three-phase permanent-magnet synchronous motor (DTP-PMSM), the conventional PI controller is replaced by a nonlinear function to determine the output torque reference, which has only one adjustable parameter. Then, the additional offset is necessary to compensate the speed residual error. Furthermore, a torque load observer is designed to observe the torque and determine the value of offset. Finally, the simulation is given, which demonstrates the effectiveness of the proposed method.

This paper studies the spatial distribution laws of rotor deformation of interior permanent magnet synchronous motors (IPMSMs) with V-shaped rotor structures. The structural-electromagnetic finite element models of IPMSMs with deformed and undeformed rotors are developed to investigate the effect of different rotor deformation types on the magnetic radial forces at no-load and on-load conditions. The change laws between rotor deformation and radial force density are obtained and the result is helpful in solving problems of mutual influence between electromagnetic and mechanical characteristics during the engineering design of in-wheel motor.