Spoke-type Permanent Magnet Motor Research Articles

Torque Improvement of Spoke-type Permanent Magnet Motor with Auxiliary Stator Using Harmonic Current Control Strategy

The spoke-type permanent magnet motor with auxiliary stator exhibits high torque performance owing to the flux focus effects. To further improve its torque density, this paper proposes a control method by using harmonic current strategy. Based on the theoretical analysis, a 3-D torque look-up table by dq-axis current and electrical angle is established with the aid of the finite element method (FEM). The maximum torque per ampere curve at each rotor position is identified and summarized to adequately indicate the relationship between torque and current amplitude of the motor. Through theoretical derivation, it is concluded that the minimum torque cost curve is the contour line of ∂Te/∂i <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , which can be employed to identify the harmonic current for torque density improvement. Compared to traditional strategies, the proposed control strategy can increase torque density of forward and reverse torque by 1.22% and 1.40%, respectively. The experimental results verify the analysis and simulation results, as well as prove the effectiveness of the proposed strategy.

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.

Maximization of High-Efficiency Operating Range of Spoke-Type PM E-Bike Motor by Optimization Through New Motor Constant

This work focuses on maximizing the high-efficiency operating range of a spoke-type permanent magnet (PM) motor by minimizing losses with a proposed motor constant to extend the cruise range for E-bikes. Multiple factors are usually involved in reducing copper and iron losses, and the efficiency may not be easily manipulated in the design processes for high-performance motors. The motor efficiency may directly be obtained through simulations upon completion of designs, resulting in a long product development period. Therefore, this paper proposes a simple optimization method covering copper and iron losses to expand motor high-efficiency ranges. A 300 W spoke-type PM motor for E-bikes is used as the target. The torque density is enhanced and the power losses are minimized based on the proposed new motor constant, which is developed to comprehensively evaluate motor performance and efficiency. The Genetic Algorithm is used in conjunction with the new motor constant to maximize the high-efficiency operating range. The analysis results reveal that the optimized spoke-type PM motors can achieve a higher torque density and broader high-efficiency range than that without being optimized. A prototype is fabricated, and experiments are conducted to validate the analysis.

Effect of rotor magnetic isolation dimensions on no‐load performance of ultra‐low speed high torque spoke type permanent magnet motor

AbstractThis study investigates the effects of rotor magnetic isolation dimensions on the no‐load performance of ultra‐low speed high torque spoke type permanent magnet motor. The studied spoke type permanent magnet motor structures are shown, where the rotor magnetic isolation parts include a magnetic barrier near the air gap (MB‐NAG), a magnetic barrier near the magnetic isolation sleeve (MB‐NMIS), a magnetic isolation sleeve (MIS). The magnetic circuit model is performed and the finite element analysis method is used to analyse the no‐load performance. Through analysing no‐load performance with three MB‐NAG shapes, the way to narrow the optimise dimension range considering reducing the cogging torque and increasing the back‐EMF synchronously is concluded. The results with different MB‐NMIS and MIS dimensions show that: (a) the optimised MB‐NMIS dimensions can increase the back‐EMF with a thin MIS in a certain dimension range of MB‐NMIS, and (b) the increasing proportion of back‐EMF influenced by the MB‐NMIS is inversely proportional to the thickness of MIS. The feasibility and effectiveness of the proposed motor structure and conclusion are experimentally verified.

Multi-objective optimization of a spoke-type permanent magnet motor with fractional-slot concentrated windings for EVs

PurposeThis paper aims to propose a spoke-type fractional-slot concentrated windings (FSCW) PM machine for EVs driving system to improve torque density. To further improve electromagnetic performance, the multi-objective optimization design is processed based on response surface (RS) model and simulated annealing cuckoo search (SA-CS) algorithm.Design/methodology/approachThe spoke-type FSCW PM machine is designed and optimized to meet the requirement of EVs driving system. First, a spoke-type FSCW PM machine is designed and some of key parameters are obtained based on equivalent magnetic circuit (EMC) method. Then, the RS model and modified SA-CS algorithm are proposed to obtain higher torque, lower torque ripple and higher efficiency.FindingsAfter verification by finite element method for no-load and load performance, the optimal machine has higher torque density, lower torque ripple and higher efficiency compared with initial machine. Finally, a 20 kW prototype is manufactured and tested to verify the validity of the proposed optimization design method.Originality/valueThis paper designs a high torque density spoke-type FSCW PM machine, which is superior for EVs driving system. Meanwhile, a novel modified SA-CS algorithm is applied to the field of electrical machine multi-objective optimal design.

Robust optimization design of low-cost spoke-type permanent magnet motors with auxiliary salient poles

Applying ferrite to spoke-type permanent magnet motors with flux-focusing ability is a low-cost process and can yield torque density comparable to that of rare-earth permanent magnet motors. To overcome the drawback of the high torque ripple associated with traditional spoke-type permanent magnet motors, a new rotor with auxiliary salient poles is proposed. These poles enhance the plasticity of the rotor and increase the number of optimized parameters. The multiobjective optimization method, which combines response surface analysis and multiobjective backbone particle swarm optimization algorithm, is used to improve the torque performance of the motor. The motor will inevitably be affected by uncertainties, such as errors and tolerances, during motor mass production. Therefore, the six sigma design method and Monte Carlo analysis method are combined for optimizing the robustness of the motor. A comparison of the pre- and post-optimization electromagnetic performance revealed that the proposed motor can effectively reduce torque ripple while increasing the output torque and significantly reducing the mass production failure rate of the motor. Finally, experimental results verify the accuracy and feasibility of the proposed new motor structure and its robust optimization design.

Influence of Introducing the Rotor MMF Harmonic on Torque Performance of Spoke Type Permanent Magnet Motor With FSCW

This article proposes a torque optimization method that introduces the rotor magnetomotive force (MMF) harmonics, aiming to increase the average torque without increasing the cogging torque and torque ripple. A spoke type permanent magnet direct drive motor with fractional slot concentrated winding (FSCW) is designed. The FSCW can improve the utilization rate of the winding, but at the same time, it brings a wealth of MMF harmonics. First, the electromagnetic torque expression is derived using the principles of magnetic energy and virtual power. It means that the constant electromagnetic torque is generated when the stator and rotor MMF harmonics with the same space and time order are the same as the main wave speed. The analytical method is then used to analyze the influence of the stator and rotor MMF harmonics on the electromagnetic torque of the three-phase FSCW permanent magnet motor. On this basis, a rotor shape that introduces the third rotor MMF harmonics is proposed. Finally, the finite element software is used to compare and analyze the torque performance of motor before and after optimization. The finite element simulation and experiment results prove the correctness and effectiveness of the method.

A Novel Spoke-Type PM Motor With Auxiliary Salient Poles for Low Torque Pulsation

This paper proposes a novel spoke-type permanent-magnet (PM) motor with auxiliary salient poles (ASPs). With these ASPs, unequal ASPs and shifted ASPs in the circumferential direction can be realized and combined to reduce the torque pulsation, while their functions are different. Unequal ASPs are employed to eliminate the second-order torque pulsation. Nevertheless, the shifted ASPs are selected to reduce the first-order torque pulsation. Additionally, the relationship between the unequal angle or shifted angle of the ASPs and the order of the torque pulsation is revealed. Furthermore, the revealed principle of the torque pulsation reduction can be extended to other slot–pole combinations. Finally, a prototype is manufactured for experiments to evaluate the low torque pulsation spoke-type PM motor. Through theoretical analysis and experimental testing, it is verified that the proposed motor offers low torque pulsation and that the revealed principle for torque pulsation reduction of different orders is feasible and effective.

Design Optimization of a High Torque Density Spoke-Type PM Motor for a Formula E Race Drive Cycle

Performance trade offs for achieving high torque density and high drive-cycle efficiency in spoke-type permanent magnet (PM) motors are investigated. Unlike the traditional method, which relies on analytical equations, this trade-off study is conducted through a statistical analysis of the Pareto-optimal design candidates resulting from a large-scale design optimization of an example traction machine over a Le Mans-based drive cycle. In the design optimization process, both low-speed and extended-speed/field-weakening operating regions are evaluated using high-fidelity electromagnetic finite element (FE) simulations with an objective to simultaneously increase the torque density and decrease the power losses over the high energy-throughput-zones of the machine torque–speed plane. The resultant 3400 design candidates are utilized to investigate the impact of increasing power density on other important performance metrics such as power losses, PM demagnetization, and torque ripple. This analysis is supplemented by multiphysics simulation of three counterpart optimized designs and successful experimental verification of a prototype of one of those three designs which represents a record high power density motor in traction applications.

Process capability control procedure for electrical machines by using a six‐sigma process for achieving six‐sigma quality level

An overall six-sigma process (SSP) that includes a novel process capability control (PCC) procedure is presented for satisfying a six-sigma level for a Z -value as well as a mean value of target performance. An example of this process is present for the efficiency and torque ripple in a spoke-type permanent magnet motor considering the manufacturing tolerances of five rotor dimensions. In this context, six-sigma means that the probability of failure of the product or system is 0.00034%. A novel SSP with a PCC procedure is suggested for designing electrical machines. In this procedure, three possible PCC methods were determined based on the definition of the Z -value. Next, each method was carried out to achieve the target Z -value and to illustrate the advantages and possible issues associated with each method. Finally, the authors showed that the suggested PCC procedure effectively achieves the target Z -value of the motor and can be widely used for the design of electrical machines.

Optimal Design of a Spoke-type Permanent Magnet Motor with Phase-group Concentrated-coil Windings to Minimize Torque Pulsations

This paper proposes a novel multistep design and optimization strategy to minimize torque pulsations in a spoke-type permanent magnet motor with phase-group concentrated-coil windings. Different from the conventional techniques that work on the motor itself, in the first step, an auxiliary inner stator is designed to suppress torque pulsations with the aid of a finite-element method (FEM). In the second step, the optimization by using the Kriging method and genetic algorithm, is then applied to the auxiliary inner stator to further reduce torque pulsations. In the third step, the harmonic injected current is utilized to suppress torque ripple by maintaining the required power, while the optimal input current waveform is optimized by the aforementioned algorithms based on the harmonic analysis of back electromotive force. Through the analysis results by the FEM, it shows that the cogging torque and torque ripple of the final model are significantly reduced by 95.7% and 70.0%, respectively, when compared with those of the initial model.

Computational Method of Effective Remanence Flux Density to Consider PM Overhang Effect for Spoke-Type PM Motor With 2-D Analysis Using Magnetic Energy

According to the conventional study, it is possible to perform 2-D finite-element analysis (FEA) to consider rotor overhang effect through the adjusted remanence flux density by employing an overhang parameter. The latest study addressed that the overhang parameter can be obtained using the variation of operating point of permanent magnet (PM). In this paper, we propose the novel computational method to calculate the effective remanence flux density directly to consider PM overhang effect making use of magnetic energy, which is applied for a spoke-type PM synchronous motor. The proposed method is validated through a comparison with the results of 3-D FEA.

Analytical Prediction of Cogging Torque for Spoke Type Permanent Magnet Machines

A generalized analytical field solution by conformal transformation is presented for calculation of no-load magnetic field distribution in the slot-less and slotted air gap of spoke-type permanent magnet (PM) machines. These analytical field solutions are used to predict the cogging torque of spoke-type PM motors. The computed cogging torque using the proposed method is compared with the results from 2D finite element analysis (FEA) in three application examples.

Optimal rotor design for reducing the partial demagnetization effect and cogging torque in spoke type PM motor

This paper proposes an optimized rotor pole shape that can effectively reduce the partial demagnetization effect and cogging torque. First, for reducing the peak amplitude of the external field that directly affects the partial demagnetization on the permanent magnets in spoke-type permanent magnet motor, we conduct a variation of core shape and insertion of a barrier. Second, with the rotor shape obtained by the first processes for reducing the partial demagnetization effect, another part of the rotor pole is varied to make better sinusoidal distributed air gap flux density to reduce the cogging torque. In the process of designing the rotor pole shape, a steepest descent method and a response surface method are applied for improving convergence. By using the finite element method, we show that the optimized rotor pole shape drastically reduces the effect of the partial demagnetization and cogging torque.