Outer Stator Research Articles

A High Torque Density Dual-Stator Flux-Reversal-Machine with Multiple Poles Halbach Excitation on Outer Stator

This paper proposes a high torque density dual-stator flux-reversal-machine with multiple poles Halbach excitation (MPHE-DSFRM), which uses two pole pairs’ numbers (PPNs) of PM excitation on one outer stator tooth, and one PPN of PM excitation on one inner stator tooth. The introduction of different PPNs of PM excitation on the outer and the inner stators can optimize magnetic circuit and airgap flux density. A Halbach array is formed by inserting three pieces of circumferentially magnetized PMs into four pieces of radially magnetized permanent magnets (PMs) on the outer stator, which aims to further enhance torque density, and reduce torque ripple. Based on the flux modulation effect, the analytical modeling of the proposed MPHE-DSFRM is established, together with the evolution process, and the working principle is presented. Then, the key design parameters of MPHE-DSFRM are optimized to achieve high torque density and low torque ripple for high torque quality. Three representative DSFRMs and a conventional FRM are designed and analyzed, and they share the same design key parameters, including PM usage, outer radius of the outer stator, and active airgap length. The electromagnetic performances, including airgap flux density, back electromotive force (back-EMF), and torque characteristics, are analyzed and compared by finite element analysis (FEA). The calculated results show that the proposed MPHE-DSFRM can provide high torque density and high PM utilization.

Maximum torque per ampere control of permanent magnet/reluctance hybrid rotor dual stator synchronous motor

AbstractCompared with a traditional low‐speed high‐torque permanent magnet synchronous motor (PMSM), a permanent magnet (PM)/reluctance hybrid rotor dual‐stator synchronous motor (PM/RHRDSSM) has the advantages of high torque density and high space utilization. This type of motor is composed of a "back‐to‐back" PM + reluctance hybrid rotor and an inner and outer double stator. The number of poles of the inner and outer unit motors is the same, and the inner and outer stator windings are connected in series, driven by a single inverter. Due to the special mechanical structure and electromagnetic relationship of PM/RHRDSSM, traditional PMSM and synchronous reluctance motor maximum torque per ampere (MTPA) control strategies are no longer applicable. In response to this issue, the authors establishe a PM/RHRDSSM mathematical model of stator winding series structure and propose a MTPA control strategy suitable for this new type of motor. This strategy is aimed at the special mathematical model of PM/RHRDSSM and derives the analytical expression of MTPA trajectory, which minimises the required stator current amplitude of PM/RHRDSSM at various load torques, thereby minimising the motor copper loss. Finally, the effectiveness and practicality of the proposed control strategy were verified through simulation and experiments.

Multi-mode operations of double-stator switched reluctance machine for electric vehicle

PurposeThe purpose of this paper is to introduce a double-stator switched reluctance machine (DS-SRM) for electric vehicles (EVs) and to propose multi-mode operations for this machine.Design/methodology/approachAnalysis of flux linkage distributions and torque characteristics using finite element method (FEM). Building a dynamic simulation model based on electromagnetic characteristics, mathematical equations and mechanical motion equations of the DS-SRM drive system. The paper proposes multi-mode operations (inner-stator excitation mode, outer-stator excitation mode and double-stator excitation mode) based on motor working regions. It also conducts simulation and experimental results to verify the effectiveness of the proposed multi-mode operations strategies and control schemes.FindingsThere is almost no electromagnetic coupling between the inner and outer stators due to the specially designed rotor structure and optimized windings polarity configuration. Analysis of flux linkage distributions and torque characteristics verified the independence of inner and outer stators. Proposal of multi-mode operations and corresponding control rules achieved the smooth switching between different modes.Originality/valueThe paper introduced the DS-SRM for EVs and proposed multi-mode operations, along with control rules, to optimize its performance. The specially designed rotor structure, optimized winding polarity configuration, and the proposed multi-mode operations contribute to the originality of the research.

Design and Analysis of a New Dual-Stator Hybrid Magnet Flux Modulation Machine

This paper proposes a new dual-stator hybrid-magnet flux modulation machine (DS-FMHMM) for direct-drive applications, which employs NdFeB magnet excitation and Ferrite magnet excitation on the rotor and outer stator sides, respectively. With this design, the proposed DS-FMHMM can not only fully use the bidirectional flux modulation effect, but also effectively alleviate the magnetic saturation issue. The machine configuration is described, together with the operating principle. Then, the design parameters of DS-FMHMM are globally optimized for obtaining high torque quality, and the influence of magnet dimensions on torque is analyzed. To evaluate the merits of the proposed DS-FMHMM, the electromagnetic performances of machines under different magnet excitation sources are analyzed, and a comprehensive electromagnetic performance comparison of DS-FMHMM and two existing dual-stator flux modulation machines (DSFMMs) is developed.

Development and comparison of double-stator memory machines with parallel hybrid magnets

PurposeThis paper aims to further develop stator permanent magnet (PM) type memory machines by providing generalized design guidelines for double-stator memory machines (DSMMs) with hybrid PMs. This paper discusses the design experience of DSMMs and presents a comparative study of radial magnetization (RM) and circumferential magnetization (CM) types.Design/methodology/approachIt begins with an introduction to RM and CM operating principles and magnetization mechanisms. Then, a comparative study is conducted for one of the RM-DSMM rotor pole pairs, inner and outer stator clamping angles and low coercive force PMs thickness. Finally, the two machines’ finite element simulation performance is compared. The validity of the proposed machine structure is demonstrated.FindingsIn this paper, the double-stator structure is extended to parallel hybrid PM memory machines, and two novel DSMMs with RM and CM configurations are proposed. Two types of DSMMs have PMs and magnetizing windings on the inner stator and armature windings on the outer stator. The main difference between the two is the arrangement of PMs on the inner stator.Originality/valueConventional stator PM memory machines have geometrical space conflicts between the PM and armature windings. The proposed double-stator structure can alleviate these conflicts and increase the torque density accordingly. In addition, this paper contributes to comparing the arrangement of hybrid PMs for DSMMs.

Two-Dimensional FEA-Based Iron Loss Calculation Method for Linear Oscillating Actuator Considering the Circumferential Segmented Structure

Linear compressors have a simpler mechanical structure and higher efficiency than the rotary compressors because they have lower frictional loss. Therefore, the linear oscillating actuator (LOA) is an attractive option for compressors owing to its high power density and efficiency. However, the complex structure of LOA such as segmented outer stator and mover leads to conduct 3-D finite element analysis (FEA) for calculating accurate iron loss, but it requires high computation cost. Thus, we proposes a method to calculate iron loss only using 2-D axisymmetric FEA considering the permeance in stator core. To compensate for the alterations in the magnetic flux density resulting from the structure of the mover and outer stator of the LOA, two equivalent coefficients are applied in permanent magnets in mover to correct the induced voltage and outer stator to correct the magnetic flux density. Through the utilization of these two equalization methods, iron loss can be accurately calculated using only 2-D axisymmetric FEA. The proposed method can be used to accurately determine the efficiency of the LOA without 3-D FEA, thus, making the LOA design process more efficient.

A Built-In Integrated Magnetorheological Fluid Brake Permanent Magnet Synchronous Motor

In this paper, a built-in integrated magnetorheological (MR) fluid brake permanent magnet synchronous motor is presented, which can switch between rotation and brake operation states in a relatively simple structure by integrating the MR fluid brake inside the rotor of the PMSM. Benefiting from the different flux paths design corresponding to the armature winding in the outer stator and the braking winding in the inner stator, the proposed machine can provide adequate brake torque and improve space utilization. This paper illustrates machine topology, operation principles, and design considerations. After proceeding flux leakage reduction, magnetic pole layout optimization of the braking winding, and balance optimization between brake torque and electromagnetic torque, successively, the optimal machine is obtained. Finally, the finite element analysis is devoted to the electromagnetic performance analysis of the proposed machine, and torque capabilities between rotation and brake states are compared, verifying the feasibility of the integration design.

Dynamic numerical simulation method and flow characteristic analysis on the mode transition in variable cycle compression system

Studying the dynamic aerodynamic characteristics and flow field characteristics for the dynamic mode transition in the variable cycle compression system (VCCS) can guarantee that the variable cycle engine (VCE) achieves high performance and stable mode transition. The common quasi-steady state analysis method cannot reflect the transient performance of the dynamic mode transition. Moreover, the dynamic simulation based on the dynamic grid technology will encounter the problem of negative volume grids because the adjustment range of variable components for VCCS is usually very large. To solve the problem, a dynamic simulation method based on real-time variation for geometry and aerodynamic boundaries of the dynamic mode transition in VCCS is first established in this paper. Using this method, the dynamic simulation was completed for the couple adjustment process of the outer bypass valve and variable stators of the dynamic mode transition in VCCS. The results of the dynamic simulation are compared with the quasi-steady state results. The results show that the rotor work ability and stator separation degree are affected by the stator variable angle degree and the mass flow rate (MFR) during the dynamic opening process of the outer bypass valve. For the MFR variation of 14.8%, when the stator variable angle is small (less than 3.3° in this study example), the flow separation on the variable stator blade pressure surface is increased during the dynamic opening process of the outer bypass valve. And the work ability of the downstream rotor is weakened. Therefore, in order to reduce the flow separation of stator blades with a small variable angle during the dynamic opening process of the outer bypass valve, a larger positive incidence angle can be adopted for stators at a small bypass ratio. For the whole dynamic process, the variation trend of the rotor work ability and stator separation state is opposite in the opening and closing process of the outer bypass valve. However, there is a dynamic effect of the flow field variation lagging behind the geometry variation in the opening and closing process. Therefore, the transient flow field in the opening and closing process is different from the quasi-steady state results, and the difference is more significant in the case of a small valve opening. Under a small valve opening, the work ability of the stage before the outer bypass entrance in the open process is significantly smaller than that in the closing process. And the difference in the flow field is mainly that the stator separation state of the stage before the outer bypass entrance in the open process is significantly weaker than that in the closing process. Therefore, the dynamic effect of the opening and closing process is more significant under a small valve opening, and the flow stability problem is more likely to occur during the dynamic mode transition in VCCS.

Design, Analysis, and Comparison of Permanent Magnet Claw Pole Motor with Concentrated Winding and Double Stator

Permanent magnet motors have become an important component of industrial production, transportation, and aerospace due to their advantages of high torque density, high power density, high reliability, low losses, and high efficiency. Permanent magnet claw pole motor (PMCPM) is a special type of transverse flux motor which has a higher torque density compared to traditional permanent magnet motors. Due to the absence of winding ends, its axial space utilization is high, and the usage of windings is greatly reduced, reducing the cost and weight of the motor. PMCPM has the advantages of small space, a light weight, a high torque density, a high efficiency, and simple production, which have potential for use in the field of electric vehicles. The double-stator structure design can improve the torque density, efficiency, and radial space utilization of PMCPM, which helps to expand their applications in the field of electric vehicles. This article designs two PMCPM with concentrated winding while different rotor structures (PMCPM1 and PMCPM2) and a three-dimensional finite element method is employed to compare and analyze the performance of PMCPM1 and PMCPM2 and the traditional PMCPM (TPMCPM). Multiphysics analysis is carried out for PMCPM1 and PMCPM2. The stress of the inner and outer stators during interference assembly are analyzed. In this paper, a hybrid material core design is proposed, in which the stator yoke is rolled by silicon steel material and the stator claw pole is pressed by the SMC die method. The multiphysics simulation performance of the PMCPM1 and PMCPM2 with hybrid cores is analyzed.

Thermal Loss Analysis, Design, and Test of a Novel HTS Magnet System for the Double-Stator Field-Modulation HTS Electrical Machine

A novel double-stator field-modulation high temperature superconducting electrical machine (DSFM-HTSM) has been proposed, in which the armature windings and the HTS magnets are mounted on the outer and inner stator respectively, realizing stationary seal of the coolant and brushless transfer of the excitation current. The HTS magnet system is the core component of the DSFM-HTSM, consisting of the HTS magnets and the cryogenic refrigeration system, the design and safe operation of which are a key issue. Therefore, this paper focuses on the thermal loss analysis, design and test methods of the new HTS magnet system for the DSFM-HTSM. An atypical HTS magnet with small dimensions is proposed to suit the topology of the DSFM-HTSM. The different thermal loss sources are carefully analyzed and theoretically calculated, considering the characteristics of each source. The detailed design process of the HTS magnet system is presented. Moreover, an experimental platform is built and tested to verify the validity of the thermal loss analysis and design method. The corresponding research results can lay the foundation for the development and application of the large scale DSFM-HTSM, and can provide some reference for the analysis and design of similar HTS magnet systems.

Electromagnetic Characteristics of Dual-Air-Gap Surface Permanent Magnet Synchronous Motor

This paper introduces a novel dual-air-gap surface permanent magnet synchronous motor (DAG-SPMSM) and investigates its electromagnetic characteristics. The motor comprises two stators (inner and outer) and a single rotor with permanent magnets on both sides (inner and outer). The magnets are arranged in a zig-zag configuration to isolate the inner and outer stator and rotor magnets. Additionally, a magnetic shield is incorporated into the rotor to further isolate the rotor magnetic flux, which results in a localized short flux path that can reduce core loss. The insertion of the magnetic shield also affects the flux path, reducing torque ripple. The electromagnetic characteristics, such as flux path, flux density, and torque, are analyzed using finite element analysis. The effectiveness of using a magnetic screen is also evaluated, and simple experiments are conducted to validate the observed characteristics of the proposed motor.

Power Circuit Design and Analysis of Controller For High-Power Axial Flux PMSM

Designing a high-power controller having high efficiency for permanent magnet motors is a challenge for developers in recent times and very few techniques are available. Design and analysis of power electronic drive for a high-power axial flux permanent magnet synchronous motor is presented in this paper. The motor under consideration here is having two outer stators and single permanent magnet rotor to drive the shaft. Control schemes and methodologies are the major concentration for research. Present paper explains a method to estimate the operational drive parameters and loss calculation according the selected power switches. In addition to this, thermal modelling is also important for designing a controller for high power machines. The hardware selection for high current switching operations is very critical for reliable and robust operation. Parts like IGBT module, gate driver, DC link capacitor, snubbers, current sensor sensitivities and estimation of losses are also critical along with control logic and processor. The importance of thermal analysis for high current switching drives is discussed and methodology for thermal analysis of power electronic devices is explained. The current work focuses on hardware level design of high-power drive for 150kW axial flux PMS motor.

Effects of Mechanical Offset Between Inner and Outer Stators in a Double Stator Switched Reluctance Machine

Effects of Mechanical Offset Between Inner and Outer Stators in a Double Stator Switched Reluctance Machine

PEDS13: Systemic force evaluation of Magnetic Bearings Design for a Pediatric LVAD Study

Study: A miniature magnetic levitation bearing system (maglev) was proposed for an implantable pediatric LVAD. The maglev bearing system is comprised passive radial bearings made of permanent magnet (PM) rings, and an active axial bearing. The study evaluates the passive bearing’s ability to radially stabilize the rotor within a moveable range of radial and axial displacements, and characterizes the axial forces produced. Methods: A stacked pair of concentric PM rings was placed on each side of the rotor and stator for the radial bearings. The PM rings were placed with like poles facing each other. The outer PM rings and stator were mounted on a six-axis force sensor attached to an xyz micrometer driven stage to set the position, and a rotational stage for alignment. The rotor and inner PM rings were inserted in the stator and held in place by both ends. The forces produced were measured at a combination of radial (0mm to 0.35mm with 0.05mm steps) and axial (0mm to 0.25mm with 0.05mm steps) displacements away from the center for a combination of 48 points. The measurements were taken three times and the average was taken. A finite element simulation was conducted by combining previously validated models of the motor, and the PM ring bearings to calculate radial and axial displacement forces. Results: As radial displacement increases, bearing force towards the center increases. Axial displacement decreases the force magnitude, but the direction towards the center remains. This shows the bearing’s ability to radially stabilize the rotor at a range of different radial and axial displacement combinations. As you increase axial displacement, the axial force away from the center increases. The radial position has little effect on axial force. This study quantifies the passive bearing’s axial forces to use in future work of developing the active axial bearing. The simulation results are in accordance with the experimental results. Variation is likely due to rotor-stator alignment error, holder manufacturing tolerances, and rotor rod flexing.Figure 1. Experimental Force Test SetupFigure 2. Axial and radial forces produced. Points are experimental results, dashed lines are simulation results.

Design and analysis of underwater power generation characteristics of deflected double-stator switched reluctance generator

The Deflectable double-stator Switched Reluctance Generator (DSRG) has the advantages of simple structure, small volume and multi-dimensional operation. The DSRG and propeller are combined into the application of underwater power generation. With the help of the deflect ability of the generator, the efficiency is improved. Due to the uncertainty of ocean current direction and the structure of switched reluctance generator, the torque ripple is one of the important factors damaging the underwater generator. In order to effectively suppress the influence of torque ripple caused by generator operation, a method of adding pole shoes on the pole side of outer stator is proposed, so as to reduce the torque ripple. The propulsion structure running at different deflection angles is simulated. The torque and speed obtained before and after pole shoe optimization are input into the propeller model. The pressure and speed characteristics of the corresponding blade structure are simulated to verify the effect of optimization and the effectiveness of the power generation system.

Structural Design of Hub Motor Based on Bidirectional Excitation

It is analyzed that the hub motor of new energy vehicles.Two kinds of hub motors,the inner rotor and outer rotor are designed. Their stators adopt the radial and axial bidirectional excitation.The rotor’s permanent magnets adopt Halbach distribution, and the magnetic circuit adopts composite magnetic conduction structure.The hub motor of the inner rotor is designed which includes its left stator,right stator and outer stator.The left and right stators are arranged on both sides of the axial direction of the rotor, the outer stator is arranged on the radial top side of the rotor,the three stators are fixedly sealed together,which are composed of composite iron core and coil.The rotor is composed of a yoke and permanent magnets.The permanent magnets of the rotor are pasted on the left and right side of the yoke and the outside of the top ring. The excitation magnetic flux of the three stators are distributed sinusoidally to form a three-way closed circuit.The outer rotor of the hub motor is designed,which T-shaped stator forms the radial and axial bidirectional excitation structure,which is fixedly sealed into an armature by excitation winding, composite material iron core and resin.The composite material iron core is composed of steel fiber reinforced epoxy resin.The rotor is arranged on the outside of the T-shaped stator to form an outer rotor.The T-shaped stator is fixed on the shaft, and the rotor is installed on the shaft by use of bearings. The above two hub motors have high output torque/power density, low heating effect, light weight and simple assembly.They are suitable for electric car series.

Feasibility study and performance analysis of external slotting of submersible motor stator

In view of the problem that the slot full rate of submersible motor is low due to the limitation of structure and manufacturing technology, a design scheme of stator slotting is proposed. In this scheme, a slot of a certain width is opened at the outer edge of the stator to facilitate the winding to adopt the press-in downline mode and fill it with magnetic epoxy resin. Using magnetic epoxy resin to meet the requirements of stator yoke magnetic circuit can effectively increase the full rate of stator slot, improve the motor efficiency and shorten the offline time. Through the structure design, the process design process based on the original manufacturing is put forward, and the feasibility analysis is carried out from the aspects of internal magnetic field, temperature, strength and performance of the motor. The results show that the scheme can effectively improve the motor performance and meet the design requirements under the premise of satisfying the magnetic field, temperature and strength. Finally, the electromagnetic design process of outer stator slotting for submersible motor is deduced, and verified by a 31 kW submersible motor. The results show that the scheme can improve the stator slot full rate by 10%, the efficiency by 1%, and the maximum torque multiple by more than 6% under the premise of keeping the original motor size unchanged. This technology can effectively reduce the power consumption of oil production, save the cost, and provide a research direction for the future research of high efficiency and energy saving submersible motor.

A New Dual Stator Permanent Magnet Machine Based on Field Modulation Theory

Increasing industrial development puts forward high requirements for the performances of stator permanent magnet (PM) machines, such as torque density and efficiency. The paper proposes a new dual stator PM machine based on field modulation theory (DSPMM), which employs the intermediate rotor participating in the electromechanical energy conversion of the internal and external machine. The proposed machine has the advantages of high torque density and high efficiency and solves the problem of insufficient space utilization of a single stator machine. The evolution process and working principle of the proposed DSPMM are studied. The flux-switching-type PM (FSPM) and the flux-reversal-type PM (FRPM) are employed in the proposed DSPMM, which forms four representative machines. For a fair comparison, the proposed machines employ identical key parameters, i.e., PM volume, the outer radius of the outer stator, and active airgap length. Based on finite element analysis (FEA), the electromagnetic performances of the four representative DSPMM under no-load and rated load, and different copper consumption conditions are analyzed and compared. The calculated results show that the proposed DSPMM with inner FSPM stator and outer FRPM stator can provide high output torque, low torque ripple, high power factor, and high efficiency.

Design of high power density double‐stator permanent magnet synchronous motor

AbstractCompared with the traditional permanent magnet synchronous motor (PMSM), the double‐stator permanent magnet synchronous motor (DS‐PMSM) can utilise the internal space adequately and has high power density. In this study, the design method of this kind of motor will be researched. Different rotor magnetic circuit topologies are analysed while keeping the outer diameter of outer stator unchanged, and the rotor magnetic circuit topologies with higher power density are selected. Furthermore, the effects of pole‐arc coefficient and stator split ratio on the power density of the motor are analysed, so a high power density DS‐PMSM can be designed. On this basis, a kind of magnetic pole structure with unequal pole‐arc coefficient is proposed to solve the problem of large torque ripple in DS‐PMSM. Finally, the DS‐PMSM is investigated by the FEA, compared with the traditional single stator PMSM, the average torque of the DS‐PMSM is increased by 62.2%, and the torque ripple is only 3.2%.

Performance Improvement for double-stator permanent magnet synchronous machine using analytical subdomain model

An analytical subdomain model is employed in this paper for predicting the magnetic field distributions in a three-phase double-stator permanent magnet synchronous machine (DS-PMSM) during open-circuit and onload conditions. Due to the stator cores are located in the outer and inner parts of the motor, the DS-PMSM construction is quite complex. The rotor magnets are positioned between these two stators. The stator inner radius, stator outer radius, slot opening, magnet arc, magnet thickness, inner and outer air-gap thickness and number of windings turns will directly influence the motor performance in DS-PMSM. The analytical subdomain model employed in this paper has a significant advantage as a rapid design tool since it is capable of precisely predicting the performance of DS-PMSM while requiring less computational effort. The analytical model was initially created using the separation of variables technique in four subdomains based on the Poisson’s and Laplace’s equations: inner air-gap, inner magnet, outer magnet and outer air-gap. Applying the appropriate boundary and interface conditions yields the field solutions in each subdomain. Besides, the fractional DS-PMSM with different number of slots between outer and inner stators to rotor poles can result in low cogging torque and non-overlapping winding configuration. The analytical results are validated by Finite Element Analysis (FEA). The slotted air-gap flux density, back-emf, and output torque have all been evaluated as electromagnetic performances. The results demonstrate that the suggested analytical model is capable of accurately predicting the DS-PMSM performance.