Yuting Gao

Influence of Pole Ratio and Winding Pole Numbers on Performance and Optimal Design Parameters of Surface Permanent-Magnet Vernier Machines

In recent years, surface permanent-magnet vernier machines (SPMVM) have been attracting more and more attention for several advantages, including a high torque density and a simple mechanical structure. However, the influence of the pole ratio, which is defined as the ratio of rotor pole pair numbers to winding pole pair numbers, and the winding pole pair numbers on the performance of SPMVMs has not been investigated in literature. This paper mainly focuses on the effects of the pole ratio and the winding pole pair numbers on the torque capacity, power factor, torque ripple, and cogging torque of an SPMVM. The variations of optimal design parameters for maximum torque, such as the split ratio (the ratio of the stator inner diameter to the outer diameter), the slot opening width, and the permanent-magnet thickness, with the pole ratio and the winding pole pair numbers are also investigated by finite-element analysis. The analysis results reveal that the pole ratio and the winding pole pair numbers significantly influence the performance and optimal design parameters of the SPMVM. Finally, an SPMVM prototype is built, and experiments are conducted to validate the aforementioned results.

Consequent-Pole Flux-Reversal Permanent-Magnet Machine for Electric Vehicle Propulsion

Conventional flux-reversal permanent-magnet (FRPM) machines suffer from large pole leakage flux, which leads to the poor utilization of PMs and reduction of main flux. This paper proposes a consequent-pole FRPM machine, whose magnet usage is halved compared with that of a conventional FRPM machine. Nevertheless, due to the reduction of the pole leakage flux, the proposed machine exhibits larger back EMF and torque than that of the conventional one. In this paper, the operation principles and mechanism of reduced pole leakage flux of the proposed machine are introduced. Moreover, with the employment of finite-element analysis, the electromagnetic performances of the proposed machine are evaluated and quantitatively compared with a conventional FRPM machine in terms of airgap flux density, flux linkage, back EMF, pulsating torque, rated torque, losses, and flux-weakening and overload capabilities.

HTS Vernier Machine for Direct-Drive Wind Power Generation

A high-temperature superconducting (HTS) vernier machine is proposed for direct-drive wind power generation. The rotor adopts conventional configuration where high-temperature superconductors are used for field winding, while the stator has toothed-pole structure, which is composed of copper drum windings and iron core, thus combining advantages of both HTS and vernier machines. With the employment of finite-element analysis, the electromagnetic performances of the proposed machine are evaluated and quantitatively compared with a conventional HTS generator. It is found that the HTS vernier machine can provide higher average torque, lower pulsation torque, higher efficiency and smaller short circuit current, among which the last one is rather large in conventional HTS machines.

Design of Three-Phase Flux-Reversal Machines With Fractional-Slot Windings

This paper proposes several slot-pole combinations of flux-reversal machines (FRMs) with fractional-slot windings (FSWs) to achieve a larger torque density and a lower pulsating torque. First, the general rules for the determinations of the winding pole pair and slot per pole per phase (SPP) are introduced, and then the feasible slot–pole combinations of three-phase FRMs with FSWs are given. Second, the analytical expressions for the back electromotive force (EMF) and torque of fractional-slot FRMs are derived and expressed in terms of machine dimensions. Based on the analytical equations, the effects of rotor pole number, split ratio, slot opening ratio, permanent magnet (PM) thickness, and rotor pole arc on back EMF are investigated and analyzed, which gives a prediction for maximal achievable back EMF and power density of the FRM with FSWs. Third, the proposed 12-slot/14-pole FRM is compared to a conventional 12-slot/16-pole FRM in terms of cogging torque, flux linkage, back EMF, average torque, torque ripple, and efficiency. It is found that the cogging torque and torque ripple of the proposed FRM are 55% and 48% lower than that of the conventional one, respectively. Moreover, the rated torque of the former is also 4% higher than the latter. Finally, the analysis results are verified by the experiments on a 12-slot/14-pole FRM prototype with FSWs.

Torque performance analysis of three-phase flux reversal machines for electric vehicle propulsion

Flux reversal machines (FRMs) have a great potential in the field of electric vehicle (EV) propulsion due to their high torque density, robust structure, fast response, etc. This paper focuses on the analysis of the torque performances including average torque, cogging torque and ripple torque of three-phase FRMs. First, the general expressions of instantaneous torque and pulsating torque are analytically derived based on flux harmonic theory. Then, using the proposed equations, the effects of stator/rotor slot combination, split ratio, PM thickness, stator and rotor slot opening ratio on the torque performances are investigated and analyzed, which give a prediction for maximum achievable torque density and minimum possible pulsating torque of a FRM. Finally, the theoretical analyses are validated on a 12-stator-slot /17-rotor-slot FRM prototype.

Design of three-phase flux reversal machines with fractional-slot windings

The conventional three-phase flux reversal machines (FRMs) are with integer slot windings (ISWs) and the most significant drawback is large cogging torque. This paper proposes several slot-pole combinations of FRMs with fractional slot windings (FSWs), taking advantage of the FSW with low cogging torque. First, the general rules for the determination of the FSW pole pair are introduced, and the feasible slot-pole combinations of three-phase FRMs with FSWs are predicted and analyzed. Second, the winding connections of the proposed combinations are obtained with the employment of star of slots method. Third, based on finite element analyses (FEA), the effects of rotor pole number, split ratio, slot opening ratio, PM thickness and rotor pole arc on cogging torque and rated torque are investigated and analyzed, which gives a prediction for optimum achievable torque waveforms of FRM with FSWs. Finally, a proposed 12-slot/14-pole FRM with FSWs is compared with a conventional 12-slot/16-pole FRM with ISWs in terms of cogging torque, flux linkage, back-EMF, average torque, torque ripple and efficiency. It is found that the cogging torque and torque ripple of the proposed FRM are 55% and 48% lower than that of the conventional one, respectively.

Review of off-line synchronous inductance measurement method for permanent magnet synchronous machines

In permanent magnet synchronous machines (PMSMs), the synchronous inductances have important influences on both steady state and dynamic performances, such as designing control strategies, predicting torque and flux-weakening capabilities. However, standard procedures for the inductance measurement have not been established yet. This paper presents a comprehensive analysis and comparative study of the various off-line methods that can be used to measure the inductances based on their accuracy, experimental setup and complexity. These approaches can be classified into three main categories: load test, DC standstill test and AC standstill test. Moreover, with the employment of finite element analysis (FEA), qualitative comparisons are done among these methods.

A Novel Permanent Magnet Vernier Machine with Halbach Array Magnets in Stator Slot Opening

Permanent-magnet vernier (PMV) machines are attracting more and more attention due to their high torque density and simple mechanical structure. In this paper, a novel PMV machine with an improved permanent-magnet circuit is proposed. Compared with the regular PMV machine, half of the permanent magnets (PMs) in the rotor are moved to the stator slot opening, and Halbach array PMs are employed in the stator while the consequent pole is employed in the rotor. The analysis of this machine indicates that the back electromotive-force amplitude of the proposed PMV machine could be two times that of the regular PMV machine with similar magnet usage, and for the same torque density, viz., 23.1 kNm/m3, the power factor of the proposed machine can reach 0.89, while this value is only 0.65 in the regular PMV machine.

Design procedure of flux reversal permanent magnet machines

Flux reversal permanent magnet machines (FRPMMs) exhibit many advantages such as simple rotor configuration, high torque density, fast transient response, etc. However, the general analytical design procedure of FRPMMs has not been established. Thus, this paper mainly focuses on developing an analytical design methodology of three-phase FRPMMs. First, the sizing equations are derived based on a magneto motive force-permeance model. Then, the influences of several key parameters in the sizing equation, including slot–pole combination, airgap radius, electric loading, and equivalent magnetic loading on the torque density, are analyzed. Moreover, the feasible slot–pole combinations are summarized and the corresponding winding type of each combination is recommended in order to maximize the output torque. Additionaly, the detailed geometric design of stator and rotor is presented. Finally, the proposed analytical design procedure is verified by finite element analysis and experiments on a 12-stator-slot/17-rotor-slot FRPMM prototype.

Performance Analysis of Interior Permanent Magnet Motor Using Overlapping Windings With Fractional Ratio of Slot to Pole Pair

Conventional concentrated windings with fractional-slot per-pole per-phase (SPP) are widely used to reduce the cogging torque and ripple torque of interior permanent magnet (IPM) machines. However, the rich magnetic motive force (MMF) harmonics of the fractional SPP concentrated winding (FSCW) will result in high rotor losses. This paper proposes a new overlapping winding with fractional slot per-pole-pair (SP), which can greatly reduce the pulsating torque with lower winding harmonics. First, the principle of the proposed winding configuration is analyzed with respect to the cogging effect and the stator MMF. Then, the electromagnetic performances of the new fractional SP windings are compared to that of integer SPP windings, FSCWs and odd SP windings in terms of airgap flux density, back electromotive force, cogging torque, average torque, torque ripple, and losses. It is found that the IPM machine with the proposed winding configuration has the lowest cogging torque and ripple torque, and its winding MMF harmonics are significantly smaller than that of the IPM machine with FSCWs.