Salient Permanent Magnet Motor Research Articles

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.

Electromagnetic Characteristics Analysis and Torque Ripple Reduction for Doubly Salient PM Machine

In this paper, the air-gap field modulation analysis and torque ripple reduction method for doubly salient permanent magnet motor (DSPMM) are presented. Based on the flux linkage distributions in the motor, the equivalent magnetic circuit models for permanent magnet (PM) and armature winding excitations are built, respectively. The air-gap magnetomotive forces (MMFs) caused by PM MMF and armature MMF can be obtained by combining the air-gap permeance and equivalent magnetic circuit models. The electromagnetic properties of the DSPMM are investigated from the perspective of air-gap field modulation principle. It is revealed that multiple field harmonics contribute to torque generation, and the torque ripples of the DSPMM are mainly caused by the cogging torque. To reduce the torque ripples, the 5th or 7th harmonic currents can be injected into the armature winding to compensate the cogging torque, and their analytical formulas will also be given. The finite element simulations and experiments are carried out to verify the results of theoretical analysis and the effectiveness of the proposed control method.

A Pole-Changing Doubly Salient Permanent Magnet Motor

This article presents a new pole-changing (PC) doubly salient permanent magnet (DSPM) motor. According to the general air-gap field modulation theory (GAFMT), the permanent magnet excitation field can be modulated by the stator and rotor teeth to a series of harmonics with different pole-pair numbers and different slot pitch angles. Thus, when the armature winding is connected and reconnected according to the different excitation field harmonics, the PC operation can be realized to obtain a high torque density at the low-speed region and a widened speed regulation range with a simple motor structure. According to the GAFMT, the operating principle of the proposed motor is introduced, and the winding connection is discussed. Then, to verify the validity, the electromagnetic performance of the proposed motor is analyzed by the finite element analysis. Finally, a prototype is built and tested.

Principle and Analysis of Doubly Salient PM Motor With Π-Shaped Stator Iron Core Segments

This paper investigates a novel three-phase doubly salient permanent magnet (DSPM) motor. Because of the adoption of Π-shaped stator iron core segments, the asymmetrical magnetic circuit among different phases occurring in conventional DSPM motors with E-shaped stator iron core segments can be avoided, so that balanced and sinusoidal three-phase PM flux linkage and no-load electromotive force (EMF) can be achieved. First, based on a 12/7 stator/rotor pole combination, the operation principle of Π-core DSPM motor is discussed using the least magnetic reluctance principle. Then, the general airgap field modulation theory is extended to the Π-core DSPM motor for explaining its operation principle further and armature winding connection. The finite element analysis is used to validate theoretical analysis, as well as to calculate its electromagnetic performances. The results show that the 12/7-pole Π-core DSPM motor possesses higher average torque output capability and lower torque ripple compared with the 12/8-pole E-core counterpart. Finally, a 12/7-pole Π-core DSPM motor is built and tested so as to experimentally verify the theoretical analysis.

Investigation of Novel Doubly Salient PM Variable Reluctance Resolvers

As rotor position sensors, the variable reluctance (VR) resolvers are playing critical roles in the industrial electric machine drivers. The VR resolvers have a simple structure, therefore, they are reliable and durable under rough operation scenarios. However, the dedicated decoding system requires the voltage signal injection with high-frequency (HF), which must be much higher than the machine operation frequency. The HF injection increases the decoding computation and system cost, especially for the high-speed applications. To avoid applying the HF injection, this paper proposes a new category of VR resolvers by adopting the concept of the doubly salient permanent magnet (PM) motor. The doubly salient PM machines have the magnets and windings on the stator side, thus, they can keep simple and reliable rotors as the VR resolvers. A significant benefit is that the stator-PM can produce back-EMF, which provides the rotor position information. By this way, the HF injection-based VR resolver solution is only serving for low-speeds and can be shut down as long as the PM back-EMF can be detected by the analog circuit. Besides, the proposed linear counterpart is also a novel option for the mover position sensor in the high speed and long distance linear drive system. The modeled examples are analyzed by finite-element analysis (FEA).

A Novel Initial Rotor Position Estimation Method at Standstill for Doubly Salient Permanent Magnet Motor

In order to receive ground signals efficiently, doubly salient permanent magnet (DSPM) motor which is applied in communication satellites as a drive needs to be activated frequently to adjust the attitude of communication satellites. Then, the initial rotor position of the motor must be estimated accurately at standstill for producing a steady and sufficient starting torque. If the rotor rotates during the estimation process, the pointing accuracy of the satellite pointing mechanism will be affected. To solve this problem, this paper proposes a novel rotor initial position estimation scheme based on the principle that different initial rotor positions can cause the variations of stator winding inductances. The identification signals, which do not cause the rotor to rotate during the identification process, are injected into the motor windings to identify the stator inductances. Thus, the variations of the winding inductances can be detected, and the initial rotor position can be estimated accurately by these variations. The proposed method is verified through experimental platform. The experimental results show that the initial rotor position is accurately estimated, and the starting performance of the DSPM is improved.

Design and analysis of doubly salient permanent magnet dual-mechanical port motor for offshore ships

To meet the requirements of the energy power transmission of the hybrid propulsion system, this paper proposes a new type of the doubly salient permanent magnet dual-mechanical port motor. The structure, electromagnetic properties and temperature field analysis are investigated by means of the finite element analysis method. Besides, it studies the output characteristic by establishing a co-simulation model based on the field-circuit coupled method. The simulation results prove that the motor has inherited the advantages of the doubly salient permanent magnet motor, has high reliability and high power density. Meanwhile, the dual-mechanical port can realize the synthesis and distribution of the motor’s energy flow under different operating conditions.

Analysis of a Novel Linear Doubly Salient Slot Permanent Magnet Motor

A novel linear doubly salient slot permanent magnet motor (LDSSPMM) is proposed in this paper. First, the topology and geometric parameters of the LDSSPMM with 12 slots (12s) are proposed and the basic operating principle is investigated. By analyzing the feasible slot/pole combinations and harmonic winding factors, 11 poles and 13 poles (11p/13p) are proved to have higher winding factor for working harmonic. In addition, the LDSSPMMs with 12s/11p and 12s/13p are optimized by global optimization with genetic algorithm. It is shown that 12s/13p is the optimal slot/pole combination. Finally, the electromagnetic performance of the 12s/13p LDSSPMM is investigated by 2-D finite-element analysis (FEA) and validated by 3-D FEA.

Cogging force mitigation techniques in a modular linear permanent magnet motor

Modular linear doubly salient permanent magnet motors are well adapted to linear propulsion systems because of their distinct characteristics, such as high efficiency and power density, reduced maintenance and initial cost, low noise and permanent magnet (PM) leakage flux, and fault tolerance capability. However, such motors suffer from high cogging thrust. In this study, various techniques based on previously proposed methods for PM machines are applied on the studied motor and evaluated by using non-linear three-dimensional time-stepping finite element analysis; three novel, optimised techniques are then presented. The techniques presented are based on the minimisation of the variation in air-gap reluctance relative to the displacement. The PM volume and average air-gap length are kept constant in all optimisations. Since the average thrust and thrust ripples under load condition may be affected by cogging reduction techniques, these values are presented for all given techniques. The results show that the proposed techniques not only maintained the average thrust under various loads but also significantly suppressed the thrust ripples for different average thrusts and cogging forces.

Research and design of doubly salient permanent magnet motor for hybrid electric vehicle based on the NdFeB permanent magnet material

The performance of hybrid electric vehicle motor directly affects its power performance and fuel economy. The high performance sintered NdFeB permanent magnet material is chosen as the core material of the hybrid vehicle motor for the design of the permanent magnet in this paper, and its size is also determined. A doubly salient permanent magnet motor is proposed here on the basis of the selected NdFeB permanent magnet material, and its structure size is designed. The finite element numerical calculation is carried out for the motor in particular rotor position angle on the basis of the field quantity to obtain the magnetic field distribution law in several typical rotor positions and the static characterise parameters of the motor are further obtained. Final, inspect the performance of the prototype objectively based on the bench experiment of the designed physical prototype, and the prototype experiment and finite element results both proved that the designed doubly salient permanent magnet motor could meet the requirements of hybrid electric vehicle, so as to achieve the purpose of the research and design of the doubly salient permanent magnet motor used in hybrid electric vehicle.

Novel Stator Design of Double Salient Permanent Magnet Motor

This paper presents a novel double salient motor design in which the permanent magnets are implanted in the stator to provide additional magnetic flux sources for enhancing its performance and reducing the inherent cogging torque. The feasible cones method is adopted to calculate the dimensional sizes of the proposed short flux path motor. The assembled stators concept is employed to design the magnetic flux paths of the double salient permanent magnet (DSPM) motor and also transfer the heat generated by the windings outside the motor. Due to the nonlinear properties of the doubly salient structure, this paper utilizes both magnetic circuit analysis and finite element analysis to evaluate different operating characteristics of the designed DSPM motor. Experimental data are provided to verify the proposed design.

A New Linear Double Salient Permanent Magnet Motor with Complementary Winding

In this paper, two novel structures of linear double salient permanent magnet (LDSPM) motor having magnets and armature windings in primary are proposed and compared. Firstly, the design principles of both motors are presented. Then, for a fair comparison, two motors are designed based on the same primary dimensions including the slot area, teeth number, pole pitch, permanent magnet volumes and coils number per phase, while the stator pole pitch and the primary structure are different. Finally, the configurations and static characteristics of both motors are critically compared based on finite element (FE) analysis. The results indicate that the proposed topology can avoid the asymmetry of back-EMF waveforms and reduce cogging force and thrust force ripple. Also, the proposed primary permanent magnet linear motors are suitable for the longer stator application such as urban rail transit (URT).

Effects of Structure Parameters on Performance of DSPM Motor

A novel flux switching external rotor doubly salient permanent magnet (DSPM) motor was researched. The two-dimensional model of the motor was established by Ansoft motor design software and the effects of air gap length and rotor pole arc on motor performance were discussed. The simulation results show that larger or smaller air gap length and rotor pole arc improve the torque ripple rate, but the increase of air gap length is helpful to enhance the overload capacity. The conclusions of this article have positive significance for improving the motor performance.

Optimization Analysis of Structure Parameters for External Rotor DSPM Motor

The external rotor doubly salient permanent magnet (DSPM) motor which included permanent magnet in the rotor tooth was designed. The two-dimensional model of the motor was established and several structure parameters were analyzed by Ansoft electromagnetic analysis software. The relationship of the structure parameters and the average electromagnetic torque and winding induction potential was obtained. The simulation results show that smaller or bigger stator yoke depth and the pole thickness is not good for the motor efficient operation.

A Linear Doubly Salient Permanent-Magnet Motor With Modular and Complementary Structure

A linear doubly salient permanent magnet (LDSPM) motor is particularly suitable for long stator applications due to its simple and low cost stator, which consists of only iron. This paper proposes a new LDSPM motor design with complementary and modular structure. The key of this structure is that the primary mover is composed of two modules whose positions are mutually four and one half of the stator pole pitch apart and there is a flux barrier between them. Hence, the back electromotive force (EMF) waveform and cogging force of the two modules have 180 electrical degree differences. This design results in the total cogging force being significantly reduced and the back-EMF of each phase becoming symmetrical because the even harmonics are canceled. For fair comparison, an existing linear LDSPM motor is designed based on the same electromagnetic parameters and compared by the means of finite element analysis (FEA). The results reveal that the proposed LDSPM motor can offer symmetrical back-EMF waveforms, smaller cogging force, lower force ripple, and higher magnet utilization factor than the existing one.

Design, analysis and control of hybrid excited doubly salient stator-permanent-magnet motor

In this paper, a new hybrid excited doubly salient stator-permanent-magnet motor is proposed, where both permanent magnets and DC field windings are located in the stator. In theory, the mathematical model and design method of the motor are developed. The corresponding output power equation and the relationship between the flux control capability and the extended speed range are deduced in details. By using an efficient “one-step” three-dimensional (3D) finite element method, the electromagnetic performances are analyzed, in which the leakage flux outside the stator circumference and end-effect are taken into account. Based on the operation principle of the motor, the control strategy and scheme are developed and implemented experimentally. Both experimental results and finite element analysis show that the proposed motor not only maintains the advantages of doubly salient permanent magnet motors, but also offers high energy efficiency over a wide speed range, which makes the motor an interesting candidate for electric vehicles.

Design of Doubly Salient Permanent Magnet Motors With Minimum Torque Ripple

This paper presents a design approach for doubly salient permanent magnet (DSPM) motors, aiming to minimize the torque ripple. The key is to propose the design criteria that the reluctance of all magnetic paths is the same, and the armature windings can be artfully connected to compensate the variation of self-inductance. Based on these criteria, the magnetic characteristics become symmetric, and the variation of self inductance is suppressed. Thus, the resulting torque ripple can be minimized. By using the time-stepping finite element method, the proposed DSPM motor and the existing DSPM motor are quantitatively compared in terms of their back-EMFs, self-inductances, and torque ripples, hence confirming the validity of the proposed design approach.

A flux-mnemonic permanent magnet brushless motor for electric vehicles

In this paper, a new permanent magnet (PM) brushless motor is proposed for electric vehicles. The key is to incorporate the concept of memory motors, namely, the online tunable flux-mnemonic PMs, into the stator doubly fed doubly salient PM motor, hence achieving effective air-gap flux control. By further employing the outer-rotor and double-layer-stator topology, the proposed motor takes the definite advantages of compact structure, low armature reaction, and direct-drive capability. Increasingly, this motor can offer the unique features of pole dropping and pole reversing. Finite element analysis and, hence, computer simulation are given to verify the validity of the proposed motor.

Performance Prediction of Multiphase Doubly Salient Permanent Magnet Motor Having Nonuniform Air Gap

This paper presents the effects of nonuniformity of the air gap on various performance characteristics of a multiphase doubly salient permanent magnet motor (DSPM). A 6/4 DSPM configuration is analyzed with the help of two-dimensional finite element analysis to predict the effects of three important air gap nonuniformities viz. 1) relative eccentricity between the stator and rotor axes; 2) concentricity error on one half of the rotor; and 3) an elliptical rotor. It is observed that a relative eccentricity up to 20% of air gap has no appreciable effect on the static torque characteristics of the DSPM, above which the permanent magnet torque increases due to reduced air gap, thereby increasing the unbalanced magnetic pull. Therefore, about 20% tolerance in air gap can be allowed for relative eccentricity errors. In case of the concentricity error on one half of the rotor, this tolerance is from -10% to plusmn15% of the air gap, whereas the corresponding limits in the elliptical rotor case are plusmn15% of the air gap

Effect of skewing the rotor teeth on the performance of doubly salient permanent magnet motors

This paper presents the effects of skewing the rotor teeth on the performance characteristics such as flux linkage, back emf, phase inductance, and reluctance torque of an 8∕6 doubly salient permanent magnet motor using a simple method, which utilizes the results obtained from the two-dimensional finite element analysis. The optimum skewing angle is obtained as 12°–15° for the least ripple torque without much reduction in the back emf. Skewing the rotor teeth of an 8∕6 doubly salient permanent magnet motor by 12°–15° will reduce the total harmonic distortion of the back emf profile to 29.69% from the original value of 44.69%. The reduction in the amplitude of the back emf in this case will be 18.79% only.