Doubly Salient Permanent Magnet Research Articles

Operational Analysis of an Axial and Solid Double-Pole Configuration in a Permanent Magnet Flux-Switching Generator

There are two main beneficial characteristics that doubly salient permanent magnet (PM) electrical machines present for aircraft applications: armature windings and PMs excitation sources placed on the stator side (maintenance and thermal management), and having a clear-cut rotor without PMs or excitation windings (vulnerable at high speeds due to associated centripetal mechanical stresses). Within this framework, a doubly salient permanent magnet (DSPM) generator was conceived by optimizing the stator size and rotor structure to minimize the torque ripple and maximize the root-mean-square (RMS) voltage value per turn of each generator phase. Firstly, a comparison between the 2D and 3D finite element method (FEM) models is made considering the results of 3D finite element analysis (FEA) as our benchmark in order to understand the accuracy of the 2D results against our benchmark model, the 3D one. A multi-objective design strategy based on a 2D FEA is made, it is set to have characteristics closest to optimal for a Boeing 767 turbine, that is, the necessary electromotive force for a required power of 90 kW at 3000 rpm, feeding a simplified Boeing 767 electrical power distribution system. The results show that the machine could not deliver the required power at 3000 rpm since the 2D FEA demonstrates that the 2D model gives optimistic results when compared with the 3D FEM model. However, with a 3D FEA of the machine feeding the aircraft load, it was seen that the machine’s efficiency is 92%, suggesting that this machine can be a plausible solution.

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.

A Novel Slot-PM Assisted Complementary-Rotor Doubly Salient Machine With Enhanced Torque Performance

This article presents a novel doubly salient permanent magnet (DSPM) machine with enhanced torque performance. The key is that an assistive magnetic flux is produced by using two sets of slot PMs inserted into the slot openings, which can effectively improve the torque production. Besides, a complementary magnetic path is built by dual rotors with 180° angle shift to reduce leakage flux, which can effectively suppress the torque ripple. In this article, the proposed machine design is presented, including working principle, winding configuration, magnetic path analysis. Then, the Genetic Algorithm is used to find the optimal designs for the proposed machine. Further, to verify the effectiveness of the proposed machine, three doubly salient machines are compared, including the proposed machine, a DSPM machine without assistive slot PM design, and a dual-rotor DSPM machine without complementary rotor structure. Finally, a prototype of the proposed machine is built and tested to verify the validity of the proposed machine design.

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.

Electromagnetic Performance Comparison of Doubly Salient PM Machines With Different Stator Iron Core Segments

This article compares the electromagnetic performances of doubly salient permanent magnet (DSPM) machines with different stator iron core segments. Since the permanent magnets (PMs) of the DSPM machines studied in this article exist in pairs, the feasible numbers of PMs in the 12/8-pole DSPM machine are 12, 6, 4, and 2, and thus, the corresponding stator tooth number between two adjacent PMs is 1, 2, 3, and 6, respectively. Therefore, the stator iron core segments of the four DSPM machines have different shapes. Furthermore, to improve the average torque, PMs are inserted into the slots, and flux focusing teeth are adopted. All four machines are designed to achieve larger average torque under the fixed copper loss and envelope size. The comparison shows that the DSPM machine with two stator teeth between adjacent PMs exhibits the largest average torque and the smallest torque ripple. Moreover, the DSPM machine with six stator teeth between two adjacent PMs has the optimal PM utilization. To verify the predicted results, a 12/8-pole DSPM prototype with two stator teeth between adjacent PMs is manufactured and tested.

Design Optimization of Outer Rotor Toothed Doubly Salient Permanent Magnet Generator Using Symbiotic Organisms Search Algorithm

Wind turbine (WT) technology becomes more and more important due to the serious environmental and energy issues. The toothed poles outer rotor doubly salient permanent magnet (DSPM) generator with simple and durable design, high torque and high-power density has a great prospect in wind turbines application. The large diameter makes the construction of such a machine more convenient due to the installation of the turbine blades directly to the outer rotor generator surface. Nevertheless, the size of the generator must be increased to provide larger output power. This increases the generator’s mass. Thus, larger massive DSPM generators are undesirable in wind turbine design. In this paper, an optimization design procedure of the outer rotor doubly salient permanent magnet generator ORDSPMG is proposed for 10 kW WT application. The reduction of the generator weight is demonstrated and proofed. The considered machine version is characterized by having the same effective axial length and output torque imposed by the specifications relative to the 10 kW direct drive WT. An optimization procedure using a fast and effective method, namely the symbiotic organism search (SOS) algorithm coupled to a parametric two dimensional finite elements analysis (2D-FEA), is employed to optimize the machine parameters. The main parameters affecting the generator design are also analyzed. The results obtained reveal that the proposed generator topology presents low weight and thus high torque density among other satisfactory characteristics.

Investigation of Novel Doubly Salient Hybrid Excited Machine With Non-Overlapped Field Winding

Hybrid excited machines, with synergies of permanent magnet (PM) and wound field (WF) excitations, exhibit high torque density as well as controllable flux and are perceived as promising candidate for variable speed application. A novel doubly salient hybrid excited (DSHE) machine with non-overlapped field winding is presented in this paper. It inherits simple structure of conventional doubly salient PM (DSPM) machine and facilitates the regulation of magnetic field by field winding. The electromagnetic performances of the proposed machine with different stator and rotor pole number combinations are investigated by finite element method (FEM), confirming these advantages. Furthermore, the effect of iron bridge on the hybridization between PM and WF excitations is analyzed to obtain a trade-off between high torque density and wide flux regulation range with the frozen permeability method (FPM). It is revealed that the proposed DSHE machine possesses higher power and fault tolerance at flux weakening region compared with the DSPM machine, albeit with sacrificed torque density and efficiency with introduction of field winding. Finally, a prototype is fabricated and tested to validate the theoretical analyses.

Improved Stator/Rotor-Pole Number Combinations for Torque Ripple Reduction in Doubly Salient PM Machines

Doubly salient permanent magnet (DSPM) machines suffer from a large torque ripple due to unbalanced three phases, nonsinusoidal-phase back electromotive force, large cogging torque, etc. To suppress the torque ripple, this article proposes a new type of stator/rotor-pole number combinations. The number of stator poles is 18, while the number of rotor poles differs from the conventional counterpart (i.e., 12) by one. The DSPM machines with different stator/rotor-pole number combinations are globally optimized under the fixed copper loss and machine envelope. It shows that compared with the 18/12 stator/rotor-pole DSPM machine, the torque ripples of 18/11 and 18/13 stator/rotor-pole DSPM machines are reduced significantly, while their torque densities remain almost the same. An 18/13 stator/rotor-pole DSPM machine is built and tested so as to experimentally verify such improvement.

An Improvement of Output Power in Doubly Salient Permanent Magnet Generator Using Pole Configuration Adjustment

The doubly salient permanent magnet (DSPM) machines are very attractive for low-speed power generation. In this work, we propose a design technique to improve the output power of the DSPM generator by an adjustment of pole configuration. The number of stator and rotor poles, split ratio, as well as the stator pole arc of the generator, were proposedly adjusted and optimized. The output characteristics of the generator including the magnetic flux linkage, electromotive force, harmonic, cogging torque, electromagnetic torque, output voltage and output power were analyzed through finite element analysis. The symmetrical magnetic field distribution of all generators was firstly verified. Then, the results indicated that this particular generator was optimized at 18 stator poles and 12 rotor poles, while the split ratio and the stator pole arc should be set as 0.78 and 6.15 degrees, respectively. The proposed optimal generator could provide a significant improvement in the output voltage and the output power compared to the conventional structure. The output power of 1.28 kW can be reached by the optimal structure, which was two times higher than that of the conventional structure. The physical explanation regarding to the structural modification was also given. The proposed design technique can be applied for improving the output power of the DSPM machines.

Optimal Stator Design to Improve the Output Voltage of the Novel Three-Phase Doubly Salient Permanent Magnet Generator

Since in many studies it has been widely indicated that the doubly salient permanent magnet (DSPM) generator could provide a high electromotive force (EMF), this paper proposes an optimal structural design of the DSPM generator for improving the output profile of the generator. The finite element method has been performed in the simulations and analysis. The effects of stator structural parameters, including the thickness of permanent magnet (PM) and the inner stator depth, on the output characteristics of the generator have been investigated. The generator outputs including the magnetic flux-linkage, the magnetic field distribution, the EMF, and the voltage regulation have been analyzed and discussed. The results have showed that the magnetic flux-linkage and the EMF of the proposed optimal structure could be significantly improved by an optimum modification of the PM thickness and the stator depth. Then, the optimal thickness of PM and inner stator depth of this particular generator has been proposedly selected. The flux-linkage and the EMF produced by the optimal structure have been 15.88 % and 6 % improved than the one of the conventional structure. The magnetic field distribution analysis has been also carried out in order to confirm the symmetrical property of simulation results. Furthermore, the optimal structure has also provided a greater voltage regulation profile than the conventional structure. This design technique can be also utilized to improve the generator output profile of other DSPM machines.

Equivalent Magnetic Circuit Analysis of Doubly Salient PM Machine With Π-Shaped Stator Iron Core Segments

An equivalent magnetic circuit (EMC) analytical method for a 3-phase doubly salient permanent magnet (DSPM) machine with Π-shaped stator iron core segments (Π-core DSPM machine) is presented in this paper. This method is based on the airgap field modulation theory. First, the airgap permeance of the doubly salient machine is calculated, based on which the influence of slotting on modulation effect is analyzed. Then, an EMC model of this machine is established according to its main magnetic field distribution. Considering the slotting effect on the average airgap flux density, Carter's coefficient is used to calculate the equivalent airgap length and the airgap magnetomotive force (MMF). Subsequently, the flux density is calculated, which allows the calculation of no-load electromotive force (EMF) and also on-load torque. In addition, the relationship between machine performances and key dimensions can be obtained by analytical expressions without complicated finite element analysis (FEA). Analytical results are validated by both the 2-dimension FEA and experimental results.

One special current waveform of toothed pole doubly salient permanent magnet machine for marine current energy conversion system

Marine current energy becomes more and more attractive because of its remarkable advantages. In this paper, one toothed pole doubly salient permanent magnet (DSPM) machine is proposed for marine current energy conversion system. This kind of machine has a simple structure, good fault tolerance, reliable operation, and high power density, which make it very suitable for marine tidal current applications. However, DSPM machine is conventionally operated by means of current chopping control and angle position control in a different region due to the trapezoidal back electromotive force (EMF) waveform. While for this toothed pole DSPM machine, the PM flux-linkage, inductance, and back EMF have more sinusoidal waveforms, which make the sinusoidal current be possible. Unfortunately, the classic sinusoidal current generates a relatively large torque ripple owing to the special inductance. Consequently, the primary purpose of this paper was to design one special current waveform to further reduce the torque ripple. Firstly, the model of the toothed pole DSPM machine is presented. Secondly, the torque distribution theory is proposed without taking into account mutual inductance effect. The mathematic expressions of the currents are deduced subsequently. Thirdly, several fitting currents are analyzed and compared based on the theoretical currents. Moreover, the simulation results verify the torque distribution theory and allow proposing the optimal current waveform (fundamental and second harmonic) in comprehensive consideration of the voltage, powers, and torque ripple. Finally, some robustness analysis is also presented to show the good performances of this current.

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.

Design and Analysis of a New Bipolar-Flux DSPM Linear Machine

In this paper, a new permanent magnet (PM) linear machine, termed the bipolar-flux (BF) doubly salient PM (DSPM) linear machine, is proposed and implemented. This BF-DSPM machine incorporates the stator-PM structure and the mover-PM structure into the DSPM machine topology. It consists of a mover with fault-tolerant teeth (FTT) and a stator with consequent poles. The FTT structure can provide the feature of phase-to-phase independence, thus offering the fault-tolerant capability. By using finite element analysis, the electromagnetic performances of the proposed machine are analyzed and then quantitatively compared with that of the flux-reversal PM machine, PM brushless DC (BLDC) machine and dual-PM machine. It confirms that the proposed machine can offer the advantages of high power density, high force density, and fault-tolerant capability. Experimental results are also given to verify the feasibility of the proposed machine.

Current waveforms analysis of toothed pole Doubly Salient Permanent Magnet (DSPM) machine for marine tidal current applications

This paper deals with the current supply waveforms and the effect of the mutual inductance on toothed pole Doubly Salient Permanent Magnet (DSPM) machine (10 kW, 50 tr/min). This DSPM machine is a low speed non-conventional stator – Permanent Magnet (PM) electrical machine, which is dedicated to marine tidal current applications. It has many significant advantages, such as simple and robust structure, good fault tolerance performance, high-power density, easy to control and cooling, reduce the winding mass and the resistance, etc., which make it very suitable for marine tidal current system. However, this machine generates a relative big torque ripple which will reduce the stability of the system and lead to maintenance problem. To increase the machine performances, several current waveforms (square and sinusoidal-based current waveforms) are proposed and compared. Moreover, the effect of the stator mutual inductance is analyzed based on these different current waveforms. Mathematical analysis and simulation results are presented to summarize the most suitable current waveform and the influence of DSPM machine mutual inductance, and indicate the optimization direction of the toothed pole DSPM machine.

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.

Core Loss Analysis and Calculation of Stator Permanent-Magnet Machine Considering DC-Biased Magnetic Induction

In this paper, core loss characteristics of stator permanent-magnet (PM) machines are analyzed and calculated, in which the unique dc-biased magnetic induction is taken into account. The flux density variation patterns in some key points in a doubly salient PM (DSPM) machine are analyzed by the two-dimensional time-stepping finite-element method. To calculate the core loss of stator and other minor hysteresis loops under dc magnetic bias, core loss characteristics of silicon steel sheet under dc-biased induction condition are first tested by a simple test system based on traditional Epstein frame and a functional relationship between the change of dc-biased induction and hysteresis loss is proposed. Two core loss calculation methods considering rotational magnetization based on flux density waveform are improved to take the influence of dc-biased magnetic induction into consideration. The calculation results are verified by experiments on a prototype DSPM machine. The conclusions are also applicable to other kinds of stator PM machines.

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.

Study on Torque Characteristic of Novel External Rotor DSPM Generator

The external rotor doubly salient permanent magnet (DSPM) generator with PM rotor tooth is designed. The two-dimensional model of the generator is analyzed by finite element method. Without changing the structure of generator, the magnet circuit is kept in the saturated state as soon as possible by paralleling capacitor besides the windings. By comparing the two kinds of rectifier topology structure, the results show that the average electromagnetic torque and the output voltage is significantly enhanced in series multiple rectifier circuit. The torque ripple of generator can be effectively suppressed in the case of load, which has a certain guiding significance for improving the output performance of the generator.

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).