Field Modulation Theory Research Articles

Mechanism and Characteristics of Cogging Torque in Surface-Mounted PMSM: A General Airgap Field Modulation Theory Approach

Mechanism and Characteristics of Cogging Torque in Surface-Mounted PMSM: A General Airgap Field Modulation Theory Approach

Reduction of losses in dual‐permanent‐magnet‐excited Vernier machine by segmented stator for electric aircraft

AbstractThe authors present a low‐loss dual‐permanent‐magnet‐excited vernier (DPMEV) machine with segmented stator design to meet the requirements of low iron loss of electric aircraft based on the field modulation theory. The stator topology features and losses of both the original and segmented DPMEV machines are comparatively investigated. Then, the armature air‐gap flux density is deduced by the magnetic motive force‐permeance model, and the influence of each harmonic on the losses are analysed. It is found that the harmonic which produces losses in the original machine reduced greatly after introducing the segmented structure. Furthermore, the electromagnetic performances of two DPMEV machines are comparatively analysed by finite element analysis. Finally, two prototypes of the original and segmented DPMEV machines are built and tested to verify the theoretical analysis.

Design and Analysis of Surface-Mounted Permanent-Magnet Field-Modulation Machine for Achieving High Power Factor

Along with the establishment of general air-gap field modulation theory, a new type of field-modulation machine has attracted increasing attention. However, the low power factor always plagued its popularization. This paper is to focus on the simplest structure surface-mounted permanent-magnet field-modulation (SMPMFM) machine, aiming at exploring the implementation of high power-factor design. The key is that the power factor calculation formula is derived parametrically, hence the originally vague causal relationship between the structural parameters and power factor become clear, guided by which the initial structure design for high power factor achievement is determined, meanwhile the power factor adjustment evaluation and the electromagnetic performance comparison with the help of finite element analysis (FEA) are conducted to verify the validity of the proposed power factor calculation formula. Finally, a feasible high-power-factor SMPMFM prototype is fabricated and the experimental testing is performed, which has a good agreement with the formular calculation and FEA results. Hence, the validity of the proposed analysis for achieving high power-factor design of field-modulation machines is verified.

Decoupling Analysis of Brushless Dual-Mechanical-Port Dual- Electrical-Port Machines

The brushless dual-mechanical-port dual-electrical-port (BLDD) machine has emerged as a promising alternative to the traditional mechanical continuously variable transmission (CVT), due to its gearless and brushless design. In BLDD machines, two sets of windings are placed in the same stator, and care must be taken to avoid strong coupling that may deteriorate the machine performance and reliability. This paper categorizes the topologies of existing BLDD machines into five types and presents a systematic decoupling analysis from the perspective of field-modulation theory. Using the presented method, the conditions to achieve decoupled designs are concluded and the decoupling characteristics of each type of BLDD machine are identified. Besides, a simple indicator is developed to fast identify the coupling type, i.e., decoupled, low or high coupling design, of BLDD machines, enabling an efficient selection of slot-pole combinations. With the aid of finite-element analysis (FEA), the coupling degree of BLDD machines with various slot-pole combinations has been analyzed for verification. Other performances, such as torque density and PM utilization, are also compared among the five types of BLDD machines to provide a more comprehensive view of their characteristics. Finally, a prototype of a BLDD machine is manufactured and tested to validate the analysis.

A pole-changing flux reversal permanent magnet motor

In this paper, a pole-changing (PC) flux reversal permanent magnet (FRPM) motor is proposed for obtaining a wide speed range. According to the general air-gap field modulation theory, the permanent magnet (PM) magnetic field is modulated into a series of harmonics with different pole numbers by rotor teeth. By introducing an especial PM arrangement, two groups of working harmonics with different pole-pair numbers are generated in the proposed 12-7 PC-FRPM motor due to the modulation of rotor teeth. Based on the calculated slot pitch angles of these harmonics, two winding connections can be obtained for PC operation to achieve two operating modes. The electromagnetic performance of PC-FRPM motor before and after PC are analyzed using finite element analysis and verified by the experimental test results.

Core Loss Analysis of Flux Switching PM Machines with Toroidal Winding and Concentrated Winding by Field Modulation Theory

Core Loss Analysis of Flux Switching PM Machines with Toroidal Winding and Concentrated Winding by Field Modulation Theory

Investigation of Five-Phase Flux-Switching Permanent Magnet Machines for EV and HEV Applications

As a member of stator permanent magnet (PM) brushless machines, flux-switching (FS) PM machine features outstanding advantages, e.g., robust rotor structure, easy temperature management, high torque density, etc. In this paper, the five-phase FSPM machines for electric vehicle (EV) and hybrid electric vehicle (HEV) applications are investigated. Firstly, the working principle of such machine is analyzed by air-gap field modulation theory. Then, the feasible slot/pole combination is discussed, considering flux leakage, back electro-magnetic force (EMF) quality and unbalanced magnetic force (UMF). Besides, in order to further choose the recommendable slot/pole combination, the torque performances are studied and compared by taking the 20-stators-slot FSPM machines as examples, such as rated torque, overload capability, flux weakening capability and fault tolerance capability. Further, in order to optimize the slot/pole combination which suffers from severe UMF, two different techniques for UMF reduction are proposed, including chamfering both in stator and rotor side. Finally, finite element analysis is employed to verify the analytical analyses. Meanwhile, a 20/18 prototyped machine is manufactured and tested. It is found that the experimental results verify the effectiveness of the analytical analyses.

Basic Elements Acting Mechanism of Electrical Machines from the Perspective of the Airgap Field Modulation Theory

Basic Elements Acting Mechanism of Electrical Machines from the Perspective of the Airgap Field Modulation Theory

Design and Optimization of a Pole Changing Flux Switching Permanent Magnet Motor

A flux switching permanent magnet (FSPM) motor is designed and optimized in this paper to achieve high torque density and expanded speed regulation range from a design viewpoint of pole-changing (PC). Based on the field modulation theory, the PM field in the FSPM motor is modulated by the stator and rotor teeth, generating rich harmonics with different pole-pair numbers in the air-gap flux density. By adopting an appropriate slot pole combination, working harmonics with different slot pitch angles are obtained to establish a basis of the PC-FSPM motor. Then, different working harmonics can be used to achieve different energy conversions with different winding configurations, so the PC operation can be performed to realize the high torque and wide speed regulation range by switching the working modes. Based on the field modulation theory, the operation principle of conventional and PC-FSPM motors are analyzed and compared. Then, according to the design principle of the PC-FSPM motor, a 24/22-pole PC-FSPM motor with the E-core is designed and optimized by a multi-level optimization method. Finally, the electromagnetic performances are analyzed by finite element analysis and the test results of the prototype have verified the feasibility of the motor.

A Brushless Hybrid Excited Motor Based on Field Modulation Theory

This paper proposes a novel brushless hybrid excited (HE) motor, in which both armature and field windings are located on the stator, and PMs are housed on the rotor. The key difference is that a special consequent-pole rotor structure is adopted, in which each two PMs is separated by a rotor tooth. So, when DC current is fed into the field winding, the produced stationary wound field can be modulated by the rotor teeth to generate rotary wound field harmonics. Thus, an effective HE operation can be achieved due to the interaction between the synchronous rotating PM field and the wound field harmonics. The motor configuration is introduced firstly. Then the operating principle is discussed by the magnetic field modulation theory. By finite element analysis, the electromagnetic performances are calculated and analyzed. The results verify the validity of theoretical analysis.

Design of a Wound Rotor Brushless Doubly-Fed Machine With 1/5 Pole-Pair Combination

The brushless doubly-fed machine (BDFM) can be used in the variable speed constant frequency field. For BDFM, the choice of the pole-pair combination and the design of the rotor are significant. The output factor of the BDFM with 1/5 pole-pair combination is higher than that of the 2/4 pole-pair counterpart. However, the rotor of the BDFM with 1/5 pole-pair combination is hard to design for its wide pole-pair ratio. This paper presents a 1/5 pole-pair combination BDFM used in hydro power with a three-phase symmetrical wound rotor to solve the design challenge. First, the magnetic field modulation theory of the BDFM and the optimal output power in terms of different pole-pair combinations are introduced. Then, the slot-number phase diagram and the ampere-conductor wave method are applied to design windings of a BDFM with 1/5 pole-pair combination. Finally, the finite element (FE) models of the 1/5 and the 2/4 pole-pair combination BDFMs are established for comparison. A prototype of the 1/5 pole-pair combination is manufactured based on the proposed design scheme. Simulated and experimental results verified the feasibility of the design scheme.

Suspension Flux Internal Model Control of Single-Winding Bearingless Flux-Switching Permanent Magnet Motor

A suspension flux internal model control method is proposed to address the problem of the strong coupling of a single-winding bearingless flux-switching permanent magnet motor leading to a significant ripple of the rotor radial displacement. Firstly, based on air-gap magnetic field modulation theory, the stator flux equation considering rotor dynamic eccentricity is established to reveal the relationship between the eccentric rotor and the magnetic field. Secondly, according to the dynamic characteristics of the motor and the variation law of the air-gap magnetic field, the suspension-plane flux is substituted into the rotor dynamic model, and the suspension flux-dynamics internal model and corresponding output are constructed, respectively. Finally, a complete control strategy is established, and the rotor is stably suspended by PWM control. The simulation and experimental results show that the proposed method has better steady-state and dynamic performance than traditional PID control, and the maximum radial displacement ripples of the rotor are reduced by 53% and 50% in steady-state and dynamic operation.

Investigation of a Flux-Switching Machine With U-V-Array Permanent Magnet Arrangement for Traction Applications

This paper investigates a flux-switching (FS) machine with U-V-array permanent magnet (PM) arrangement, termed UV-FSPM. The key design is to construct parallel magnetic circuit by adopting U-V-array PMs. Based on the parallel magnetic circuit, the operating principle of the UV-FSPM is illustrated. To provide a deeper insight into the torque enhancement mechanism, the analytical model of the UV-FSPM is built by using the general air-gap field modulation theory. It is found that the U-V-array PMs can significantly enhance the dominant working harmonic which effectively contributes to torque enhancement of the investigated UV-FSPM. To reveal the impact of key parameters on torque performances, the parametric optimization of the UV-FSPM is conducted. The electromagnetic performances of three FSPMs are comparatively studied by finite element analysis (FEA). It is proved that the investigated UV-FSPM exhibits the highest torque density and highest PM utilization ratio within the pool. Finally, a prototype of the UV-FSPM is fabricated and tested for verification of the investigated concepts.

Torque Generation Mechanism of Dual-Permanent-Magnet-Excited Vernier Machine by Air-Gap Field Modulation Theory

The dual-permanent-magnet-excited vernier (DPMEV) machine has attracted increasing interest for its high torque density. However, it is difficult to analyze due to the complex structure. In this article, the torque generation mechanism of DPMEV machines is analyzed from the perspective of magnetic field modulation. First, based on air-gap field modulation theory, the stator and rotor modulation factor models as well as armature and permanent magnet magnetomotive force (MMF) models are established, respectively. Considering the bidirectional field modulation effect of the DPMEV machine, the modulation process of MMF is derived. Then, by analyzing the modulated armature and permanent magnetic field, the torque generation mechanism is investigated. In addition, a machine with stator flux gap structure is proposed and the reasons for its torque increase are explained. Finally, a prototype of DPMEV machine is manufactured and tested to verify the effectiveness of the analytical results.

Design and Analysis of Axial-Modular Flux-Switching Permanent Magnet Machine

This paper proposes a novel axial-modular-flux switching permanent magnet (AM-FSPM) machine, which contains two modular parts and integrated toroidal windings. After investigating the operation principle of the AM-FSPM machine, the modular PM field complementarity and integrated armature reaction field complementarity principles of two axial modular parts are revealed based on the field modulation theory. Then, a comprehensive comparison of the modulation principle between the AM-FSPM and conventional FSPM machines is conducted from perspectives of PM field, armature reaction field, cogging torque and electromagnetic torque production mechanism. It can be found that the modulation principle reveals the difference between the operation principles of two flux switching machines. In addition, the cogging torque reduction capability of AM-FSPM machine is investigated, which provides guidance on stator-slot and rotor-pole combinations in the design stage of industrial applications. Moreover, compared with conventional FSPM machines, the AM-FSPM machine exhibits high torque capability and flux weakening capability, meanwhile maintains high efficiency at high speed. Further, its characteristics are verified by the experiments.

Performance Improvement in a Linear Primary Permanent Magnet Vernier Machine by Modular Unit Shift Effect

This article investigates the effects of modular unit shift on the detent force and mutual to self-inductance ratio in the modular linear primary permanent magnet vernier (MLPPMV) machine. First, the winding connection and slot/pole combinations for the modular design is discussed. Then, the relationship of the phase shift and modular unit spacing is given. The operation principle of the MLPPMV machine is analyzed from the perspective of the air-gap field modulation theory. Moreover, the analytical expressions of the modular unit shift and phase shift angle for the MLPPMV machine are derived. Afterwards, the back EMFs, detent forces and inductances are comparatively analyzed. The investigation reveals that the reasonable modular unit shift has significance to improve the electromagnetic performances. Furthermore, the finite element method is adopted to evaluate. Finally, a prototype of MLPPMV machine is built. Experiments are carried out on a linear test bench, verifying the theoretical analysis.

Incorporating Harmonic-Analysis-Based Loss Minimization Into MPTC for Efficiency Improvement of FCFMPM Motor

According to air-gap field-modulation theory, multiple field harmonics are responsible for high torque density of field modulation (FM) motors. However, abundant field harmonics will undoubtedly increase motor losses, especially iron loss and PM eddy-current loss. Therefore, a harmonic-analysis-based loss minimization (HLM) method incorporated into model predictive torque control (MPTC) for efficiency improvement of FM motors is proposed in this article. First, by analyzing the loss generation mechanism, a harmonic-based online loss calculation model is built to serve for loss minimization control. Then, the reference flux for MPTC can be derived from the proposed HLM method, which avoids complexity of equivalent resistance tuning and improves accuracy of loss calculation compared to the conventional model-based loss minimization method which lacks attention on the harmonic-based loss analysis. Consequently, the HLM-MPTC strategy is finally determined and then applied in a flux-concentrating field-modulation permanent-magnet prototype to verify its validity. The experimental results evidence that the proposed HLM-MPTC can effectively achieve loss reduction and efficiency improvement.

Analysis of Torque Ripple in V-Shape Interior Permanent Magnet Machine Based on General Airgap Field Modulation Theory

This paper proposes a novel torque ripple model of V-Shape interior permanent magnet (IPM) synchronous machine based on the general field modulation theory (GAFMT). Firstly, the magnetic field modulation behavior of a 12-stator-slot/8-rotor-pole (12/8) IPM machine is discussed, where the expressions of permanent-magnet-excited (PM-excited) and armature fields are derived. Secondly, the total torque ripple is divided into three components, namely, the PM-excited cogging torque, the armature cogging torque, and the modulation torque ripple. Additionally, the relationship between the field harmonics and the torque ripple is discussed based on the GAFMT. Then, a finite element analysis (FEA)-assisted dual fast Fourier transformation (FFT) method is proposed to obtain the accurate value of the field amplitude for torque ripple calculation. The field analysis results based on the GAFMT and the proposed torque ripple are then validated by comparing their results with those obtained from the FEA simulations, and a good agreement is observed, demonstrating the effectiveness of the field analysis and the proposed torque ripple model. Finally, experiments on a prototype 12/8 IPM machine demonstrate the validity of the torque ripple model, providing an effective method for torque ripple suppression of IPM machines.

Novel Memory Motor Drive with Integrated Winding Concept for Traction Applications

This article presents a novel memory motor drive with integrated winding concept for traction applications. The key feature of the proposed idea is to integrate the excitation winding with armature winding, and hence eliminating additional magnetization winding to achieve online magnetization-state regulations. Hence, the spatial confliction of conventional memory motors can be solved. Upon implantation of the proposed design, the winding utilization, torque/power density and fault tolerant capability are significantly improved. Based on the field modulation theory, the air-gap flux densities under different magnetization states are derived quantitatively to provide design guideline in initial stage. The integrated memory motor drive is presented systematically to consolidate the field and armature windings. To illustrate the effectiveness of the proposed design, two other conventional memory motors are included for comparisons. It is revealed the presented memory motor with integrated winding concept exhibits 28% higher winding utilization, 43% higher torque/power density and 218% higher flux regulation capability than its counterpart with conventional separate windings. In addition, fault tolerant capability can be significantly improved by eliminating mutual coupling between two winding sets. Finally, a prototype is fabricated, and the experimental measurements are carried out to verify the presented concepts.

Radial Displacement Sensorless Control in Full Speed Range of Single-Winding Bearingless Flux-Switching Permanent Magnet Motor

It is a key to realizing stable suspension operation of bearingless motor that the rotor radial displacement information is acquired accurately. Sensor applications are sensitive to environments, limiting to scenarios, and increasing costs. Herein, a radial displacement sensorless control method in the full speed range for single-winding bearingless flux-switching permanent magnet motor is proposed. First, an eccentric modulation function is presented, and the flux linkage equation of each winding with rotor eccentricity is derived based on the air-gap magnetic field modulation theory. Therein, the phase inductance and flux are functions of the rotor displacement. Second, the bias-flux equations of the symmetric windings are deduced, and the rotor displacement observer of the medium-high speed is established based on the bias-flux amplitude. Due to flux information being difficult to extract at low speed, the high-frequency current signal is injected into the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d_T</i> -axis of the torque plane. The rotor displacement observer of the zero-low speed is established based on the high-frequency bias-induced EMF amplitude. Besides, a novel smooth switching process is designed. Finally, the observers are analyzed, and the radial displacement sensorless control strategy is built. The experimental results verified the validity of the proposed method.