Milestones, hotspots and trends in the development of electric machines

As one of the greatest inventions of human beings, the electric machine (EM) has realized the mutual conversion between electrical energy and mechanical energy, which has essentially led humanity into the age of electrification and greatly promoted the progress and development of human society. This paper will briefly review the development of EMs in the past two centuries, highlighting the historical milestones and investigating the driving force behind it. With the innovation of theory, the progress of materials and the breakthrough of computer science and power electronic devices, the mainstream EM types has been continuously changing since its appearance. This paper will not only summarize the basic operation principle and performance characteristics of traditional EMs, but also that of the emerging types of EMs. Meanwhile, control and drive system, as a non-negligible part of EM system, will be complementarily introduced. Finally, due to the background of global emission reduction, industrial intelligentization and transportation electrification, EM industry will usher again in a golden period of development. Accordingly, several foreseeable future developing trends will be analyzed and summarized

A Brushless Dual-Mechanical-Port Dual-Electrical-Port Machine With Spoke Array Magnets in Flux Modulator

Brushless dual-mechanical-port dual-electrical-port (BLDD) permanent magnet (PM) machines have been gaining more and more attentions in recent years, with the merits of two decoupled rotors and contactless torque transmission. However, existing BLDD machines tend to suffer from low torque density due to low working flux density. In this paper, a BLDD machine with spoke array permanent magnets (PMs) in flux modular is proposed, which improves the torque density significantly. The structure and operation principle of the proposed machine are introduced. Detailed performance comparison between three different BLDD machine topologies, i.e., surface-mounted PM (SPM) BLDD machine, flux-bidirectional modulation (FBM) BLDD machine, and the proposed BLDD machine, is presented through finite element analysis (FEA). The analyzing results show that although the modulated magnetic field coupled with the modulation winding is slightly reduced, the torque transmission capability of the regular winding in the proposed BLDD machine is significantly enhanced when compared with that of its two counterparts. Index Terms-Brushless dual-mechanical-port dual-electrical-port (BLDD) machine, flux modulation effect, magnetic geared machine (MGM), spoke array permanent magne

Dual-Segment Three-Phase PMSM With Dual Inverters for Leakage Current and Common-Mode EMI Reduction

In a motor drive system, the inverter working in discrete and impulse states generates a common-mode voltage (CMV) at the terminal of the stator winding neutral point. The high-frequency CMV can induce a leakage current and a common-mode (CM) electromagnetic interference (EMI), which are potential threats to personal safety and system stability. The conventional single three-phase inverter is found to be powerless in eliminating the CMV, while the two paralleled inverters can effectively eliminate the CMV theoretically, but the three coupled inductors (CIs) should be added to the motor drive system which reduces the power density and efficiency of the system. A novel method, which associates a specially designed dual-segment three-phase motor with the CMV elimination modulation algorithm, can be utilized to cancel the extra CIs without degrading the function of the leakage current and the CM EMI suppression. The design of the dual-segment three-phase permanent magnet synchronous machine is introduced, with identical back electromotive forces for two groups of windings but with little magnetic coupling between them. Simulation and experimental results are provided to verify the validity of the proposed method in CM-related reduction and CI cancellation. Compared with the zero-CM pulsewidth modulation for paralleled inverters proposed in a previous work, the proposed dual-segment three-phase motor drive can achieve a better power density by removing the CIs

Torque Capacity Improvement of Flux-Switching PM Machines Based on Directional Stator Permeance Design

As one type of flux modulation machines, flux-switching permanent magnet (FSPM) machines present high sensitivity to airgap structures. Therefore, both stator/rotor teeth and slot/pole combinations have significant influences on machine performance. However, the relationships between the optimal stator structure and maximum torque capability of the FSPM machine are barely investigated. Therefore, this paper is devoted to proposing a directional stator permeance design approach to achieve the maximum torque of the FSPM machines under a given rotor, and reveal the corresponding stator structure. First, the relations between torque and air-gap permeance are presented based on a constructed torque contribution equation, where amplitudes and phase angles of the stator permeance harmonics are determined. Then, main permeance harmonics are directionally optimized to enlarge positive torque, while negative contributions are inversed to be positive. Especially, two FSPMs with 6-slot/19-pole and 6-slot/13-pole are chosen as design examples, and their optimal design processes and torque performances have been deeply analyzed, which verifies the effectiveness of the proposed design approach

Performance Comparison of Surface and Spoke-Type Flux-Modulation Machines With Different Pole Ratios

In this paper, performance comparison between surface and spoke-type flux modulation (FM) permanent magnet (PM) machines is presented. Generally, spoke-array magnet arrangement is capable of increasing the torque density of PM machines due to its flux-focusing effect. Nevertheless, a flux-barrier effect is found when this magnet topology is applied in FM machines, which may offset the advantage in torque capability when the pole ratio is high. By flux distribution comparison of these two-machine topologies, the flux-barrier effect is visually explained. Through numerical FEA, this effect is further investigated in spoke-type vernier PM machines with a series of pole ratios. Finally, compared with surface-type FM machines, considerable reduction in modulated magnetic field as well as output torque capability is verified in high pole ratio, spoke-type FM machines

Inductance Evaluation and Sensorless Control of a Concentrated Winding PM Vernier Machine

Due to the advantages of high torque density and simple mechanical structure, permanent magnet vernier (PMV) machines have attracted more and more research interests. In this paper, the inductance nonlinearity of an advanced concentrated winding PMV machine is investigated with consideration of both magnetic saturation and cross-coupling saturation under different d-axis and q-axis current loading. Then, the mathematical model with a variable inductance matrix of the PMV machine is established through incorporation of the finite-element analysis and the surface fitting method. Further, a back electromotive force based sensorless control method is developed for this PMV machine model with design of a current-dependent state observer. Based on the sensorless algorithm, the influence of inductance variation on rotor position estimation performance is then quantitatively evaluated. Simulation results show that the PMV machine can be well controlled for steady- and dynamic-state operation, and the position estimation error is effectively decreased. Finally, the proposed sensorless control algorithm is validated through experimental tests of the PMV prototype machine

Torque Performance Enhancement of Flux-Switching Permanent Magnet Machines With Dual Sets of Magnet Arrangements

Torque performance, especially torque density, is a critical performance index for the flux-switching permanent magnet (FSPM) machine that is attractive for the propulsion system. In this article, a novel FSPM machine with dual sets of magnet arrangements is proposed. With the novel topology, the torque density of the proposed machine is significantly improved due to much increased working harmonic contents of magnetomotive force (MMF). Moreover, the cogging torque is also inherently reduced, which makes the proposed machine a promising candidate in the FSPM machine family. The operating principle of the proposed FSPM machine is revealed based on the MMF-permeance model and the numerical finite element analysis (FEA). The effect of geometric parameters, such as magnet thickness, auxiliary tooth width, and rotor tooth width on the average torque and cogging torque, is also investigated. Finally, a prototype has been manufactured to validate the analysis conclusion. With experimental test results, it is demonstrated that the proposed topology can achieve 30.8% higher torque density, 79.4% lower cogging torque, and 15.6% higher power factor than the conventional counterpart

A Novel Zero-Sequence Current Elimination PWM Scheme for an Open-Winding PMSM With Common DC Bus

This paper introduces a novel pulse width modulation (PWM) scheme for an OW-PMSM driven by dual two-level three-phase inverter with common dc bus which can effectively deal with the inherent zero-sequence current (ZSC) problem. Based on conventional symmetrical unipolar double frequency SPWM scheme with appropriate phase-shift, the common mode voltage (CMV) of two inverters can keep the same and cancel out each other to eliminate the modulated zero sequence voltage (ZSV) disturbance source. In this case, the double frequency effect can be retained to reduce the ac side current ripple and suppress both the corresponding motor vibration and acoustic noise which is advantageous to improve the synthetic performance of motor. The DC bus voltage utilization of the novel PWM scheme is proved to reach the maximum value as same as the conventional modulated ZSV elimination scheme. Meanwhile, a zero-sequence controller is designed to suppress ZSC by further adjusting the two CMVs to counteract other zero-sequence disturbance sources. To verify the analysis, the proposed PWM technique associated with the control method is implemented in an OW-PMSM experimental setup to validate the superiority of proposed method

Additively Manufactured Winding Design for Thermal Improvement of an Oil-cooled Axial Flux Permanent Magnet Machine

This article proposes a new additively manufactured winding with integrated heat sinks to improve thermal performance of an oil-cooled yokeless and segmented armature (YASA) axial flux permanent magnet machines. The heat sinks featuring pin-fin structure are integrated to the two sides and top of the winding to increase the heat transfer area and convective heat transfer coefficient, thus improving the thermal performance. Computational fluid dynamics is employed to evaluate the thermal performance of the proposed winding, which is further compared with that of the state-of-the-art rectangular winding. Besides, the influence of pin spacing in streamwise direction, tilt angle, flow rate and resistances on the thermal performance and pressure drops of the proposed winding are investigated. Finally, prototypes of the proposed winding and the counterpart rectangular winding are manufactured to verify the numerical analyses. The experimental results show that the winding temperature of the proposed winding can be reduced by 27.6 °C compared with that of rectangular winding