Stator Modules Research Articles

Study on the weakening of stator cogging torque of modular motors by gap offsets

Two schemes have been developed to reduce the cogging torque generated by the gap between the stator modules of the modular permanent magnet synchronous motor. These schemes involve shifting the gap position to change the phase of the cogging torque, thereby eliminating some of its components and reducing its magnitude. Finite element simulation was used to verify the cogging torque of E and C type modular motors using two different schemes. The effect of the offset gap on electromagnetic performance and motor vibration noise was also analysed. The results indicate that both schemes weaken the cogging torque without significantly affecting the electromagnetic performance of the motor or increasing vibration noise.

Modeling and Analysis of Axial Flux Permanent Magnet Machines with Stator Module Misalignment

Modeling and Analysis of Axial Flux Permanent Magnet Machines with Stator Module Misalignment

Modeling of Current-Driven End-Effect Force Ripple in Air-Cored Linear Synchronous Motor With Multiple Modular Stators

This paper presents a segmented layer model (SLM) for the air-cored linear permanent-magnet synchronous motors (LPMSMs) with multiple modular stators. In the LPMSM with modular stators, the significant current-driven ripples (CDRs) are observed as the PM mover moves across the stator modules, due to the magnetic end effects. Such CDRs become more severe as the current excitation level increases. In order to correctly model the overall motor forces in the LPMSM, the analytic motor model needs to be able to capture the magnetic end effects from both the stator and mover, and also include the current-driven effects. The SLM method presented in this paper divides the analytical region into several segmented layers to be able to accurately capture both the geometric-saliency- and current-driven force ripples by using layers with different fundamental spatial frequencies. The fidelity of the proposed SLM is validated both by the finite element method (FEM) and the experiments. The SLM achieves an accuracy of more than 97 % and 87 % compared to the FEM and experimental results, respectively, while reducing the computation time by two orders of magnitude as compared to the FEM.

Performance Analysis of Outer Rotor Multi-Tooth Biased Flux Permanent Magnet Motors

This paper proposes two biased flux permanent magnet (BFPM) motors in which the torque ripple issue of conventional doubly salient permanent magnet (DSPM) motor, as its predecessor, is greatly suppressed and the torque density of the BFPM structures has been improved. The permanent magnets (PMs) are positioned where they are easily accessible for an even better temperature management compared to other stator-PM structures. The second structure utilizes the available space between stator poles in which two sets of PMs are embedded between stator modules. This increases the torque density even more. The operation principles of these two structures are deeply discussed by identifying working harmonics of each flux source and then evaluated by the finite element method (FEM). An analytical procedure by deriving sizing equations of the structures is introduced and the effect of different design parameters on the electromagnetic performance is comprehensively studied. The performances of the structures are analysed by FEM. To better evaluate the superiority of the proposed structures, a demagnetization analysis is conducted and it is shown that even in high temperatures, the performance degradation of the proposed structures is much lower compared to other stator-PM structures. Finally, the proposed structures are prototyped to verify the simulation results.

Static and Dynamic Magnetic Pull in Modular Spoke-Type Permanent Magnet Motors

This work studied the static magnetic pull of a modular spoke-type permanent magnet motor (MSTPMM) with no rotor eccentricity during the motor’s final assembly process and its dynamic magnetic pull during different motor operating states. A new final assembly scheme was proposed to significantly reduce the static magnetic pull during the final assembly process of the motor. The methods required to reduce the unbalanced radial magnetic pull of the whole stator, which is caused by partial stator module operation, were also studied. Firstly, the structure of the MSTPMM was examined. The static magnetic pull that occurred with the implementation of the two motor final assembly methods was studied in order to prove the effectiveness of reducing the maximum static magnetic pull. Moreover, the maximum magnetic pull during the assembly process was also observed. Then, the dynamic magnetic pull was studied with different motor operating states: no load, on load, and partial stator module operation. To solve the unbalanced radial magnetic pull of the whole stator, which is caused by partial stator module operation, methods of changing the angle between the stator current vector and the q axis (Ψ) or the d axis current (id) were also studied.

Two‐phase switched reluctance motor with hybrid excitation: Modeling and evaluation

AbstractSwitched reluctance machines offer a robust structure, inexpensive maintenance, and a low‐cost drive. However, they can suffer from low mean torque, low torque density, and high noise. Techniques such as offering the stator poles at each phase in the shape of a C core, adding several teeth to the two poles of each C‐core, and embedding permanent magnets to overcome these deficiencies are presented. Permanent magnets are embedded into the structure to create a hybrid excitation that provides a higher torque density. The C‐core stator modules of the stator are toothed to improve the torque. The radial forces on the shaft are balanced. The design procedure, operating principles, and performance trade‐offs are explained. Also, a magnetic equivalent circuit model is introduced. The model provides continuous relationships over the operating regions and incorporates core saturation and accurate flux tubes to attain high precision. Finite element models are also employed in the analysis and design process. The motor is prototyped, and experimental results are extracted, closely matching those obtained with the model and finite‐element analysis.

Thermal Analysis of a Modular Permanent Magnet Machine under Open-Circuit Fault with Asymmetric Temperature Distribution

A modular permanent magnet machine is composed of several stator modules, and the three-phase winding of each module can be controlled independently. The novel modular permanent magnet machine has good abilities in terms of fault tolerance when the machine is exposed to fault conditions. The current of each phase is different and will result in uneven loss distribution in each phase. Heat transfer occurs in the circumferential direction and temperature distribution will be asymmetric in the circumferential direction. This paper proposes a 3D finite element thermal model to accurately calculate the rise in temperature under open-circuit conditions for modular permanent magnet machines. When two modules are in operation, the machine can output rated torque. When one module is in operation and the temperature is 150 °C, the output torque is 0.76 times the rated torque. The temperature of the machine under the one-phase open-circuit condition with a zero-temperature-difference control strategy will be 0.8 °C lower than that with a minimum copper loss control strategy. Finally, a prototype with three stator modules is manufactured and the calculation results are validated by experimental test. It holds great significance for the accurate calculation of a machine with asymmetric temperature distribution in the circumferential direction.

Design and analysis of a new bearingless switched reluctance motor

A bearingless switched motor with permanent magnets in the stator yoke (BSRM-PMSY) with two sets of windings on each stator tooth pole is studied. The current in one set of windings mainly controls the motor torque, and rotor suspension can be realised by adjusting the current in the other set of windings. Each stator module unit of the motor is composed of a permanent magnet and two U-shaped iron cores. Finally, a BSRM-PMSY finite element simulation model is established to explore the static characteristics of the motor, including magnetic field distribution, permanent magnet flux linkage and harmonic analysis, back electromotive force (EMF) and harmonic analysis, suspension performance, and so on. The analysis of the simulated results lays a foundation for the establishment of a BSRM-PMSY mathematical model and control system.

Comparative Analysis of AC Copper Loss With Round Copper Wire and Flat Copper Wire of High-Speed Stator-PM Flux-Switching Machine

In the high-speed flux-switching permanent magnet (FSPM) machine, the ac copper loss issue in the armature winding conductor is very prominent, due to the high-frequency leakage magnetic field in stator slot, which seriously affects the machine performance. To model and calculate ac copper loss more accurately, a coupled electric circuit-magnetic field model is constructed based on 2D-finite element method, and consequently the influence of modeling methods and winding types on ac copper loss calculation of a 12-slot/10-pole (12/10) 54.7 kW/10 kr/min FSPM machine is investigated. First, ten simplified ac copper loss calculation models are established to deal with the problem of large consumption of calculation time and computer resources caused by the excessive number of wires, small size of winding conductors, high precision modeling, and mesh refinement. Second, the influences of voltage-/current-source and steady/rotating rotor are considered, and the ten models are evaluated in terms of computing time and accuracy. Third, based on the preferred model from the ten models, the effects of frequency, round/flat wires, and wire sizes on ac copper loss are further studied. Fourth, to investigate the influence of flux leakage at the end of winding on ac copper loss, a 3-D ac copper loss calculation model with different axial lengths of winding end space is established. Fifth, the change process of ac copper loss and transient temperature of winding under short time overload condition are obtained combined with the bidirectional coupling model between electromagnetic and thermal field method through multiple iterations of electromagnetic loss and temperature. Finally, the stator modules of round and flat copper wires are manufactured, respectively, and an experimental modular device is built to measure the ac copper loss, which confirms the improved accuracy of the predictions by the proposed model.

Dynamic strain measurement of propeller shaft vibrations

The paper proposes an approach to the registration of vibrations parameters to increase the reliability and predict the durability of technical systems with a continuously rotating shaft. For systems with stochastic loads, such as a ship’s shaft line, the actual measurement of shaft stresses and deformations is an actual way to prevent failures and non-destructive testing under operating conditions. The adaptation of the dynamic strain measurement method made it possible to develop a software and hardware complex for recording and analysing transverse, torsional and longitudinal vibrations of shafts. The design of a hardware complex consisting of a measuring mobile and stator modules connected by a wireless network that allows dynamic strain measurement is proposed. The connection diagram and the main metrological and technical characteristics of the modules are given. To test the operability of the hardware complex, an experimental installation was built that allows carrying out investigation of the shaft line vibrations in real operation conditions. Experimental data are presented, the analysis of which allows us to predict the durability of the system.

Research on efficiency optimal torque distribution of stator module combined permanent magnet synchronous machine

The large permanent magnet synchronous machine (PMSM) usually adopts a modular technique to facilitate manufacture and maintenance. The rated power of large mechanical equipment is selected according to the limit capacity, and the motor efficiency is low at a low load. A kind of unwinding stator module combined permanent magnet synchronous machine (SMCPMSM) is proposed. Each module is mechanically and electrically decoupled. It can operate independently. The number of input modules can be flexibly selected according to the torque requirements in direct drive SMCPMSM to realise the optimum efficiency control of the ball mill. The work presents the loss model of the SMCPMSM and analyzes the torque distribution ratio of the modules. The mathematical model of torque distribution with optimum efficiency is established by using the genetic algorithm. The optimum efficiency control under different loads is determined. The motor performance of four operation modes is simulated by the finite element. An 80 kW prototype is developed, and its experiments are carried out. The experimental results verify the validity of the proposed method.

Optimal mixed control of Axial Flux Permanent Magnet Synchronous generator wind turbines with modular stator structure

Wind turbine systems are constructed using different types of generators, aero-mechanical components and control systems. Due to their ability to work in low speed, Axial Flux Permanent Magnet (AFPM) generators are becoming widespread in wind energy systems which contributes to eliminating the gearbox from the system, noticeable increase in efficiency and decrease in system weight. Due to the modular nature of the stator in AFPM generators, it is possible to control each module independently. In this paper, in addition to obtain the dynamic model of the turbine and AFPM generator, a control strategy is designed based on Mixed Integer Nonlinear Programming (MINLP) to incorporate both pitch angle and the number of active stator modules as control input signals. These control signals are used in order to maximize system efficiency and regulate output voltage in different wind speeds and electrical loads. Simulation results for a typical generator shows the effectiveness of the proposed method in speed control of the generator.

Magnetic Field Prediction of Module-Combined Stator Permanent Magnet Synchronous Motor Based on a Nonlinear Hybrid Analytical Model

Module-combined stator permanent-magnet machines have several independent stator modules and each module can be controlled independently. To predict the magnetic field distribution of module-combined stator permanent-magnet machines accurately under asymmetric conditions, this paper proposes a novel nonlinear subdomain and magnetic equivalent circuit hybrid analytical model. The main novelty of the proposed nonlinear hybrid analytical model is representing nonlinear effect by equivalent current sheets on the edges of slots. Equivalent current densities are calculated from magnetic equivalent circuit and used as boundary conditions in the improved subdomain model. The values of the equivalent current sheets are obtained in an iterative algorithm. The nonlinear hybrid analytical model considering saturation effect can accurately calculate magnetic field distribution and electromagnetic performance even under overload conditions. The finite element analysis is performed to validate the accuracy of the proposed hybrid analytical model. A prototype with three stator modules is manufactured and the experimental results verified these predictions.

3D Characteristic Analysis of 3-Leg Linear Permanent Magnet Motor With Magnet Skew and Overhang Structure

This paper presents the 3-leg linear permanent magnet motor (TLPMM), which has a novel structure. It has an advantage of reducing the entire volume due to the attraction force cancellation. The TLPMM consists of stator and mover modules, simplifying the manufacturing process and maintenance. The TLPMM has a permanent magnet skew and overhang structure to improve motor performance. Therefore, the consideration of three dimension (3D) effects is required in the characteristic analysis. The proposed method is based on a field reconstruction method that provides a reduction in computational burden with high accuracy in analyzing 3D characteristics. For the evaluation of magnetic fields in non-uniform and complex air-gap in the TLPMM, the virtual air-gap section method is introduced. Using these proposed methods, the TLPMM with the magnet skew and overhang structure are effectively analyzed. This approach was verified by comparison with finite element analysis and experimental results.

Study on modal characteristics and vibration reduction of an aircraft rotor–stator brake-induced squeal system

Based on the modal coupling theory, the rotor and stator contact stiffness and axial relative velocity are considered to build an electric aircraft brake dynamic system model in this study. Both the complex modal analysis and transient dynamic analysis methods are used to study the aircraft brake squeal performance and vibratory mechanism. The unstable vibration modes indicate that the out-of-plane vibration plays an important role and the feed-in energy is larger than the output energy in the brake rotor–stator module so that brake squeal takes place. Then the influences of the contact stiffness, friction damping and frictional coefficient on the brake squeal system are carried out, laying the foundation for the three proposed vibration suppression methods. Results show that the coefficient negative-slope condition will intensify the vibration. Also, a linear relationship between the squeal factor and the frictional coefficient is obtained to provide a guidance to predict squeal stability under more conditions. Vibration reduction design shows that adding a damping layer to the brake mechanism and chamfering the edge of braking stators both can reduce brake squeal effectively, while slotting braking stators is invalid in aircraft braking system.

Design and Experimental Investigation of a Hybrid Rotor Permanent Magnet Modular Machine with 3D Flux Paths Accounting for Recyclability of Permanent Magnet Material

Rare-earth metals used for manufacturing Permanent Magnets (PMs) remain classified as critical raw materials by the European Commission. In order to secure the supply of electrical machines due to the increasing demand of Hybrid and Full Electrical Vehicles ((H)EVs), recycling has emerged as a valuable alternative. Hence, this paper presents the concept of a modular PM machine with a hybrid rotor and 3D flux paths, for application in ((H)EVs). The proposed machine topology is intended to facilitate the extraction of PM material towards a recycling process. The selection of a machine for prototyping is carried out by investigating the effect of the variation of the number of rotor teeth and stator modules on various parameters, with models developed in Finite Element (FE). Finally, the models developed of the selected combination were validated with a detailed experimental evaluation of the prototype.

Analysis of Unwinding Stator Module Combined Permanent Magnet Synchronous Machine

The large permanent magnet synchronous machine(PMSM) usually adopts modularity technique to facilitate the manufacture and maintenance. In order to avoid the contact of adjacent coils between modules, a novel unwinding stator module combined permanent magnet synchronous machine (SMCPMSM) is proposed, in which each modular can operate independently. The number of input modules can be flexibly selected according to the torque requirement in the SMCPMSM of mill wrapping around to realize the optimal control of mill system efficiency. In this paper, the unwinding block method and its mathematical model of the SMCPMSM are described. The electromagnetic performance of the SMCPMSM and the operation performance of different power supply modules (PSMs) are analyzed, the radial force and electromagnetic vibration of the PSM in asymmetric operation is studied, which provides a reasonable basis for the part of PSM operation of the SMCPMSM in accordance with torque requirements.

The presence and absence of periplasmic rings in bacterial flagellar motors correlates with stator type.

The bacterial flagellar motor, a cell-envelope-embedded macromolecular machine that functions as a cellular propeller, exhibits significant structural variability between species. Different torque-generating stator modules allow motors to operate in different pH, salt or viscosity levels. How such diversity evolved is unknown. Here, we use electron cryo-tomography to determine the in situ macromolecular structures of three Gammaproteobacteria motors: Legionella pneumophila, Pseudomonas aeruginosa, and Shewanella oneidensis, providing the first views of intact motors with dual stator systems. Complementing our imaging with bioinformatics analysis, we find a correlation between the motor's stator system and its structural elaboration. Motors with a single H+-driven stator have only the core periplasmic P- and L-rings; those with dual H+-driven stators have an elaborated P-ring; and motors with Na+ or Na+/H+-driven stators have both their P- and L-rings embellished. Our results suggest an evolution of structural elaboration that may have enabled pathogenic bacteria to colonize higher-viscosity environments in animal hosts.

Analysis and evaluation of modular E‐shaped stator switched reluctance machines employing segmented and conventional rotor topologies

Switched reluctance machines (SRMs) with modular or segmented structures normally have light weight, low cost, easily manufactured and improved fault-tolerance capability. In this study, two novel three-phase modular SRMs (MSRMs) with the same E-shaped stator modules and different rotor topologies, namely, segmented rotor and conventional rotor are evaluated and compared. The basic machine topologies and simplified magnetic equivalent circuit (MEC) are presented first. The static electromagnetic characteristics of two MSRMs such as flux distribution, phase flux linkage and inductance, electromagnetic torque, and so on, are computed and compared by three-dimensional finite-element analysis. Then, the dynamic performances including steady state and transient operations of two MSRM drives are evaluated and compared. The corresponding predictions and comparisons indicate that the segmented rotor topology has less iron consumption, higher torque density and power density and lower torque ripple, which is preferred for the three-phase MSRMs. Finally, two MSRM prototypes with segmented rotor and conventional rotor are manufactured and tested for experimental verification and comparison. The experimental results of static flux linkage, steady state and transient performances of two MSRM drives are presented and compared, which verify the analytical MEC model, finite element analysis and the corresponding predictions.

A High Torque Density Axial Flux SRM with Modular Stator

A novel structure of Switched Reluctance Motors (SRMs) is proposed. The proposed structure uses the benefits of the axial flux path, short flux path, segmental rotor, and flux reversal free stator motors all together to improve the torque density of the SRMs. The main geometrical, electrical and physical specifications are presented. In addition, some features of the proposed structure are compared with those of a state-of-the-art radial flux SRM, considered as a reference motor. Then, the proposed structure is modified by employing a higher number of rotor segments than the stator modules and at the same time, reshaped stator modules tips. Achieved results reveal that, compared with the reference motor, the proposed and the modified proposed motors deliver about the same torque with 36.5% and 46.7% lower active material mass, respectively. The efficiency and torque production capability for the extended current densities are also retained. These make the proposed structures a potentially proper candidate for the Electric Vehicles (EVs) and Hybrid Electric Vehicles (HEVs) as an in-wheel motor.