Low Torque Ripple Research Articles

Permanent Magnet Synchronous Machines With Nonuniformly Distributed Teeth

An increasing interest for permanent magnet synchronous machines with low torque ripple and low vibration is observed. The purpose of this paper is to investigate the topology of non-uniformly distributed teeth and its influence of on cogging torque, tooth ripple harmonics and torque ripple of permanent magnet synchronous machines. The topologies with different number of non-uniformly distributed teeth are investigated. Analytical procedure is developed to illustrate the impacts of non-uniformly distributed teeth on cogging torque and unbalanced magnetic pull (UMP), and then identify the appropriate non-uniformly distributed teeth. A commercial 10kW 8-pole 48-slot V-shaped IPM machine is taken as the reference base machine. The machines with 2- and 6 non-uniformly distributed teeth are chosen to make an overall comparison to that with the well-known skewing slots. The machine with 2 non-uniformly distributed teeth is finally chosen to be fabricated. Intensive experiments including cogging torque, back-EMF, load current, efficiency and instantaneous torque are done.

Multiobjective Optimization of a Dual Stator Brushless Hybrid Excitation Motor Based on Response Surface Model and NSGA 2

This article proposes a multiobjective optimization design framework for a double stator brushless hybrid excitation motor (DSBHEM) to provide high torque, wide flux regulation ability and low torque ripple. The design variables are divided into sensitive level and insensitive level by sensitivity analysis. The response surface model (RSM) and nondominated sorting genetic algorithm 2 (NSGA2) are organically combined to generate a set of Pareto solutions for the sensitive level variables, from which the optimal values of the sensitive level variables are obtained. In addition, the optimal values of insensitive variables are obtained through single parameter scanning optimization, and a set of final optimal design variables are obtained. The electromagnetic performance of the initial design and the optimal design are compared with finite element analysis. Finally, a prototype is manufactured to verify the proposed concepts.

Design of Adjustable Cogging Torque Permanent Magnet Machine With High Contrast Ratio

This article presents a new adjustable cogging torque permanent magnet (ACT-PM) machine, which can provide two distinct operating states: the low cogging torque (LCT) state and the high cogging torque (HCT) state. The contrast ratio is defined as the ratio of the cogging torques between HCT and LCT states. The LCT state of this machine is designed to have similar performance as a conventional permanent magnet machine, with high average torque and low torque ripple that offer smoothness and control precision. For the HCT state, on the other hand, the machine generates HCT that can provide passive self-lock ability under power-OFF condition, serving as a parking brake that prevents the driveshaft from rolling. Consequently, a conventional mechanical parking brake that has corrosion and wearing-out concerns can be removed. The potential applications of this machine include auto-guided vehicles and other types of electric vehicles. This article illustrates the design flowchart and the proposed candidate structure, followed by the investigation and comparison of electromagnetic performances between different stator/rotor combinations. Then, multiobjective optimization and single parameter optimization are applied to the candidate structure to further improve the contrast ratio for cogging torque. A prototype machine with the optimal design parameters is fabricated and experimentally verified, where a mechanical switch is designed to adjust the machine between LCT and HCT states. The test result shows a good agreement with the finite-element analysis, and this confirms the feasibility of the proposed ACT-PM machine.

Four-Quadrant Model Following Sliding Mode Cruise Control for SRM With DITC Applied to Transportation Electrification

The ability of the four-quadrant operation is essential for transportation electrification applications. Switched reluctance machines (SRMs) have been increasingly considered an option for electric vehicles’ traction. However, achieving higher efficiency and low torque ripple may be a challenge for this type of machine, especially at low speeds. This article proposes a cruise control for SRM with the four-quadrant operation for extended autonomy. The cruise control is realized with a model following sliding mode speed controller and direct instantaneous torque control (DITC) for direct torque control. The proposed generating mode DITC aims for higher efficiency. An asymptotic stable model is developed for mode transition. The developed control system is Lyapunov stable in motoring, generating, and transition modes. Furthermore, an online multiobjective optimum point tracker (OPTPT) based on the steepest descent method is proposed aiming for efficiency maximization and torque ripple minimization. The experimental results show that the OPTPT convergence time is 1.25 s for a speed step and 1.2 s for a load step. The proposed control was submitted to an EUDC driving schedule, showing good speed regulation. The speed MAE of the cruise controller was 1.1344%. The transition between operation modes (motor–generator) occurs smoothly, which substantiates the proposed system for four-quadrant transportation electrification applications.

Synchronous reluctance machines with new type of fractional‐slot concentrated‐windings based on the concept of stator slot shifting

Fractional-slot concentrated-windings are appreciated for their simple construction, short end-winding length, high copper fill factor, low cogging torque, good field-weakening capability and fault-tolerant ability. However, in comparison to the conventional distributed windings, the fractional-slot concentrated-windings are characterised with high space magnetomotive force (MMF) harmonics, which results in undesirable effects on the machine performance, such as localised core saturation, eddy current loss in the rotor and noise and vibration. In order to improve winding characteristics, several techniques have been developed recently. This manuscript introduces the 5 new winding topologies by using the general concept of stator slot shifting. It means that, in order to cancel undesirable MMF harmonics, by doubling (or tripling or even multiplying) the slot number and dividing the winding and then relatively shifting the winding by one (or more) slots, the undesirable harmonics have been eliminated effectively. The best choice is chosen according to the lowest amount of the MMF harmonic, highest value of winding factor and torque desirable characteristics. At the end, comprehensive comparisons for the designed synchronous reluctance motor (SynRel) equipped with proposed windings and also distributed winding are presented. The analytical study and 2D FEM analysis results show that it is possible to get an ideal low space-harmonic winding topology, and consequently, a low torque ripple for these motors.

Design Optimization of a Switched Reluctance Machine with an Improved Segmental Rotor for Electric Vehicle Applications

In this article, a switched reluctance machine (SRM) with six phases and a misaligned segmental rotor is proposed. The segmental rotor has an internal 15-degree misalignment, allowing the SRM structure to be a one-layer 2D structure with a short flux path structure. The proposed SRM produces a relatively low torque ripple by exciting two phases simultaneously. Additionally, an optimization method is applied, allowing for the maximum torque position of one phase to be aligned with the zero-torque position of the adjacent phase. The finite element method (FEM) is used to analyze and design the proposed SRM and to simulate the proposed liquid cooling system. The static torque waveforms are analyzed, and the dynamic torque waveforms are simulated with a drive using SiC MOSFETs. Finally, a prototype is manufactured, and the experiment is performed to validate the design and simulation results.

A New Partitioned Stator Field Modulation Machine With H-Shape Permanent Magnet Excitation

A new partitioned stator field modulation machine (PSFMM) with H-shape permanent magnet (HPM) excitation (HPM-PSFMM) is proposed, which is evolved from the conventional flux-switching machine (FSM) and flux-reversal machine (FRM). The proposed HPM-PSFMM combines the merits of high reliability and good heat dissipation characteristic. In addition, it exhibits high torque production with low torque ripple. Based on the theory of electrical machine operation, the FSM and FRM can be transformed into PSFMM with interior permanent magnet (IPM) and surface-mounted PM (SPM) excitation by changing the position of PM excitation, respectively. It benefits to improve space utilization and increase slot area for a large number of armature windings. For reducing the flux leakage and enhancing the flux density in air gaps, the IPM and SPM excitation are combined into HPM excitation. The iron-pole rotor between the inner and outer stators acts the role of modulator to modulate the magnetic field excited by HPM excitation to couple with the armature reaction for converting electromechanical energy. The evolution process, operating principle, and key design parameters of the proposed HPM-PSFMM are presented. Finally, using the finite element analysis (FEA), it can be proven that the proposed HPM-PSFMM has the merits of high torque production, low flux leakage, low total harmonic distortion (THD), and low torque ripple when compared to other stator-PM machines, which is a desirable choice for high stability applications.

Suppression of Torque Ripple in a New Consequent-Pole Permanent Magnet Machine by Segmented Structure

A new consequent-pole permanent magnet (CPM) machine with segmented structure/unequal teeth (CPM-SU machine) is proposed in this article. The segmented structure is adopted to decrease the torque ripple. To improve the torque density, the structure of unequal teeth is used in this proposed machine. The five-phase winding located in the stator is composed of three fractional-slot concentrated windings (FSCWs), which are helpful to improve the fault-tolerant capability. Permanent magnets (PMs) are placed in the rotor. To decrease the PM cost, V-type PMs and iron cores are arranged with the sequence of S-iron-S-N-iron-N. The magnetic field generated by PMs is investigated, which is helpful to demonstrate the working mechanism of this proposed CPM-SU machine. To verify the superiority of the proposed CPM-SU machine, a conventional CPM machine with unsegmented structure/equal teeth (CPM-UE machine) is proposed. The electromagnetic properties of these two machines, including the electromagnetic torque, the cogging torque, and the back electromotive force (back EMF), are analyzed by the finite element (FE) method. The simulating results show that the CPM-SU machine can exhibit excellent performances, such as low torque ripple and high torque density.

Analysis of the operating principle of a dual-armature consequent-pole bearingless flux reversal permanent magnet machine

This paper proposes a new type of dual-armature alternating pole bearingless magnetic flux reverse permanent magnet machine, which combines the advantages of the alternating pole structure and the dual-armature structure. This machine shows the advantages of high torque density and good fault tolerance, which can not only reduce the number of permanent magnets but also further improve the machine’s torque. It is suitable for use in wind power, aerospace, and other applications. The dual-armature alternating pole bearingless magnetic flux reverse permanent magnet machine is used to improve the torque performance and suspension force. Based on the dual-armature alternating pole magnetic flux reverse machine, by adding an additional set of stator teeth to suspended windings, a new type of dual-armature alternating pole bearingless magnetic flux reverse permanent magnet machine is obtained. The number of permanent magnets is halved, and each permanent magnet has the same polarity. The ferromagnetic pole piece next to the permanent magnet automatically acts as the other pole. Based on the introduction of its related structure, the stator flux, rotor flux, stator back electromotive force, cogging torque, electromagnetic torque, etc., are analyzed. This new machine can reduce the number of permanent magnets and has a higher torque conferring advantages of output capacity and low torque ripple.

Robust Flux and Speed State Observer Design for Sensorless Control of a Double Star Induction Motor

In this paper, a robust flux and speed observer for sensorless control of a double star induction motor is presented. Proper operation of vector control of the double star induction motor requires reliable information from the process to be controlled. This information can come from mechanical sensors (rotational speed, angular position). Furthermore, mechanical flux and speed sensors are generally expensive and fragile and affect the reliability of the system. However, the control without sensors must-have performance that does not deviate too much from that which we would have had with a mechanical sensor. In this framework, this work mainly deals with the estimation of the flux and speed using a robust state observer in view of sensorless vector control of the double star induction motor. The evaluation criteria are the static and dynamic performances of the system as well as the errors between the reference values and those estimated. Extensive simulation results and robustness tests are presented to evaluate the performance of the proposed sensorless control scheme. Furthermore, under the same test conditions, a detailed comparison between the proposed state observer and the sliding mode-MRAS technique is carried out where the results of its evaluation are investigated in terms of their speed and flux tracking capability during load and speed transients and also with parameter variation. It is worth mentioning that the proposed state observer can obtain both high current quality and low torque ripples, which show better performance than that in the MRAS system.

Performance Analysis of DC-DC converters for Solar PV fed Switched Reluctance motor for Electric Vehicle Applications

This paper describes the performance of a Solar PV-powered switched reluctance motor with low torque ripple in electric vehicle applications. The prominence of switched reluctance motors has become significant in the electric vehicle industry, because of its ineradicable characteristics like simple structure, absence of rotor windings, less maintenance and its self-starting capability. However, the limitation of SRM is its high torque ripple because of its nonlinear characteristics. The performance of a switched reluctance motor with various DC –DC converters is analysed in this work and the results are compared in terms of the speed of the motor and its torque ripple percentage. The switching time of the converter is controlled by the MPPT controller, which uses incremental conductance and the Integrator method. The converters presented in this work are the Boost converter and the Cuk converter. These two types of converters are designed in MATLAB software and their characteristics are analysed while supplying the switched reluctance motor. The suitability of the proposed system with the motor is analysed by simulation results. From the results, it is confirmed that the performance of the Solar PV fed Switched reluctance motor is improved in terms of speed and torque ripple by implementing this type of converter. Hence, it is suitable for electric vehicle applications, which require less torque ripple and mechanical vibrations.

Multi-Objective Optimization Design of a Stator Coreless Multidisc Axial Flux Permanent Magnet Motor

The stator coreless axial flux permanent magnet (AFPM) motor with a compact structure, low torque ripple, and high efficiency is particularly suitable as a motor for electric propulsion systems. However, it still requires great effort to design an AFPM motor with higher torque density and lower torque ripple. In this paper, a stator coreless multidisc AFPM (SCM-AFPM) motor with a three-rotor and two-stator topology is proposed. To reduce rotor mass and increase torque density, the proposed SCM-AFPM motor adopts the hybrid permanent magnets (PMs) array with Halbach PMs in the two-terminal rotor and the conventional PMs array in the middle rotor. In addition, a multi-objective optimization model combining response surface method (RSM) and genetic algorithm (GA) is proposed and applied to the proposed SCM-AFPM motor. With the help of the three-dimensional finite-element analysis (3-D FEA), it is found that the torque ripple of the optimized SCM-AFPM motor is 4.73%, while it is 6.21% for the initial motor. Its torque ripple is reduced by 23.8%. Therefore, the proposed multi-objective optimization design method can quickly and reliably obtain the optimal design of the SCM-AFPM motor.

A novel integrated design of switched reluctance motors with planetary gear trains

This paper proposes a design process based on the aspects of structure, configuration, and function. A mechatronic integrated design combining a switched reluctance motor with a planetary gear train (PGT) reducer is developed systematically. First, feasible design concepts are generated from the identified design requirements and constraints by considering existing SRMs and PGT reducers. The integration elements are selected to fit the design requirements. Then, detailed design and analysis are performed regarding the performance of the PGTS as well as the electromagnetic characteristics and output performance of the motor. In addition, the Taguchi method is employed to identify the optimal electrical parameters and geometric configuration of the motor. Finally, the output characteristics of the integrated device and existing design are compared. The integrated design has a 12.94% higher average torque, 40.74% lower torque ripple, and 9.10% smaller axial space.

Design and optimization of yokeless magnetic gear with asymmetric Halbach permanent magnet array for electric vehicle powertrain

In this paper, a novel 3/27/24 (pole pairs of inner rotor permanent magnet [PM]s/modulator/outer rotor PMs) high torque density yokeless magnetic gear with asymmetric Halbach PM array is presented and optimized for electric vehicle powertrain. The key is to improve the torque performance by replacing the magnetic steel with the light nonmagnetic material as the rotor core and employing the embedded magnetic steel bar as well as trapezoidal PM structure to form a low magnetic resistance in the magnetic circuit. The proposed machine has significant performance improvements in two aspects. Firstly, it has high torque density and low iron loss with the yokeless structure. Secondly, it has a high anti-saturation capability and low torque ripple with the asymmetric Halbach PM array and the embedded magnetic steel bar. The proposed structure is optimized by the co-simulation of the finite-element method and C++ optimization software. For a clear evaluation, the proposed structure is compared with generalized solutions in terms of performance and cost. Comparison results indicate that the proposed solution has the highest output torque, torque density, and torque per PM weight among solutions, reaching 214.1 N·m, 58.2 N·m/kg, and 95.6 N·m/kg, which greatly enhances the performance of the magnetic gear.

Brushless Wound Rotor Synchronous Machine Based on a Consequent-Pole Rotor Structure with Better Torque Attributes

This paper presents a subharmonic-based brushless wound rotor synchronous machine (BL-WRSM) topology with permanent magnet-assisted (PMA) and consequent-pole (CP) rotor structures to achieve better torque characteristics as compared to the conventional subharmonic-based brushless WRSM. The proposed topologies use the conventional high-efficient subharmonic field excitation technique to achieve a brushless operation and a lower volume of permanent magnet (PM) to achieve better average, starting, maximum, and minimum torques and lower torque ripple. A four-pole, twenty-four-slot (4-pole/24-slot) machine with conventional, PM-assisted (PMA), and consequent-pole (CP) rotor structures are developed in a JMAG-Designer 20.1 environment to carry out two-dimensional finite element analysis (2D-FEA). The developed machines are used to validate the operation and achieve electromagnetic and electromechanical performances of the proposed subharmonic-based BL-WRSM topologies with better torque attributes.

Electromagnetic performance analysis of the umbrella shaping inner rotor coaxial magnetic gear with dual modulation rings

The coaxial magnetic gear is a new type of noncontact transmission mechanism, which avoids the inherent defects of the mechanical gearbox due to gear meshing transmission. To study a coaxial magnetic gear (CMG) with high torque density and low torque ripple to replace the mechanical gear in the semidirect drive wind turbine, a novel umbrella shaping inner rotor CMG (US-CMG) with an auxiliary modulation ring is proposed in this paper. The novel structure adopts a CMG with a dual modulated ring to increase the electromagnetic torque. In addition, the magnetic block of the poled inner rotor is divided into three pieces magnetized by Halbach arrays, and the middle piece is umbrella-shaped to reduce torque ripple. Based on the topology of the US-CMG and the principle of the magnetic field modulation, the operation mechanism of the US-CMG is analyzed. A contrastive analysis among the US-CMG, Halbach magnetized dual-modulator CMG (HM-CMG), and surface-mounted CMG (SM-CMG) is established to identify the performance of the US-CMG. Compared with the SM-CMG, the results show that the electromagnetic torque of the US-CMG has increased by 65.46%, and the torque ripple of the US-CMG is 57.6% of that of the SM-CMG.

Torque Ripple Suppression Based on Optimal Harmonic Current Injection in Dual Three-Phase PMSMs Under Magnetic Saturation

Dual three-phase permanent magnet synchronous machines (DTP-PMSMs) have received increasing attention from the industry and academia due to their advantages in lower burden on power inverters when operating in high power applications compared to the three-phase counterparts and low torque ripples. In this article, it reveals that the favorable low torque ripple characteristic of DTP-PMSM is undermined in the high power and overload operating mode. To solve this problem, this article proposes a novel torque ripple suppression strategy based on optimal harmonic current injection. A mathematical torque ripple model of DTP-PMSM considering the cross-coupling effects between <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d–q</i> axis and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> - <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> axis is built. And based on this model, a detailed analysis is carried out to obtain the optimal harmonic current. The theoretical analysis also guarantees that the induced machine loss is minimum. Moreover, the proposed strategy has good dynamic performance since the algorithm involves no iterative computation and is computationally effective, which is proved on a laboratory DTP-PMSM system. The effect of parameter variation is also discussed and tested. The experiment results prove that the influence of magnetic saturation on torque ripple can be effectively suppressed.

Direct Torque Control With Variable Flux for an SRM Based on Hybrid Optimization Algorithm

This article presents an optimal direct torque control (DTC) strategy with variable flux for a switched reluctance motor using the improved linear active disturbance rejection control (LADRC) plus the hybrid optimization algorithm (HOA). First, the constant flux amplitude is substituted by the variable flux DTC (VF-DTC) to reduce the torque ripple. Then, the LADRC with the improved extended state observer applied in speed controller is utilized instead of the conventional PI control to improve the speed of the observer, antidisturbance ability, and robustness. Moreover, the HOA is employed to search for the optimal control parameters and acquire satisfactory dynamic performances. Finally, the optimal VF-DTC system is implemented on a 12/8 SRM. Simulation and experimental results are carried out to compare the performances of the conventional DTC, the VF-DTC with LADRC, the VF-DTC with PI using HOA, and the proposed optimal VF-DTC using HOA. The results show that the proposed control method has a faster speed response, superior antidisturbance ability, and lower torque ripples.

A Novel Permanent Magnet Vernier Machine With Coding-Shaped Tooth

It is well known that permanent magnet Vernier machine (PMVM) has multiple flux field harmonics, which can produce stable torque. However, some flux field harmonics would create torque that undermines the total torque output. Such as the 6 slots 26 poles split-tooth PMVM here, of which modulated flux field outputs torque while fundamental flux field undermines torque output. In this article, a 26 pole PMVM with coding-shaped tooth is proposed. The coding-shaped tooth can introduce permeance harmonics with specific phase and amplitude, thus modulating flux fields that all output torque. Air-gap permeance harmonics of the proposed and the regular split-tooth PMVM are obtained via FEA. Based on MMF-permeance model, flux fields of two machines and their contributions to average torque are investigated, proving that the proposed machine has multiple flux fields that all output torque. Moreover, by optimizing geometric parameters of coding-shaped tooth, the proposed machine could obtain largest average torque and smallest torque ripple simultaneously. Electromagnetic performances of the optimized machines are studied comparatively in semianalytical way and FEA. It is proved that with same overall size, PM usage, and copper loss, the proposed machine could achieve 30% larger torque density, 86% smaller cogging torque, and 62% lower torque ripple than its counterpart. Finally, a 16-N·m (rated) prototype is built and tested.

Model Predictive Direct Torque Control of Switched Reluctance Motors for Low-Speed Operation

In this paper, a finite-control-set model predictive direct torque control (FCS-MPDTC) method is proposed to reduce the torque ripple of a segmented switched reluctance motor (SSRM) at the low-speed stage. Firstly, the prediction dynamic model is established, and the phase torque can be predicted by detecting phase current and rotor position signals. Then, the principle of power converter and selection of voltage vectors are introduced and presented. Considering torque ripple reduction, flux tracking performance and copper losses reduction, the cost function with phase torque, the amplitude of flux linkage and phase current, is established to select optimal voltage vector to control the power converter. In addition, the torque sharing function (TSF) is employed to distribute total torque to phase torque for further torque ripple reduction. Finally, the direct torque control (DTC) is selected as the comparison method, performance of MPDTC is verified by simulation and experiment results. It can be found that the proposed MPDTC can achieve lower torque ripple and copper losses, and high robustness.