Small Torque Ripple Research Articles

Effect of Parameter Modification on Torque Ripple in Interior Permanent Magnet Synchronous Motor

Electric motors are electromechanical machines commonly used in industry and automotive products. Interior Permanent Magnet Synchronous Motor (IPMSM) is a synchronous electric motor with a permanent magnet that is often used on electric vehicle engines. However, one of the characteristics of an electric motor with permanent magnet is the existence of torque ripples. The presence of torque ripples in electric motors can cause vibrations in the machine which affect efficiency, structural durability and operating speed. Therefore, it is necessary to make improvements or changes to the motor design to overcome this problem. This study was conducted to analyze the effect of a modification of the electric motor parameter on the torque value in the existing design. Modifications are applied to the existing design with an initial condition of torque ripples of 42.58%. This study modified the air gap, magnet angles, magnet thickness, and opening slot width. Modifications are carried out through a finite element method-based software simulation with the Taguchi method to reduce experimental configurations of design factors from 625 to 25 experiments. Through this research on parameter modification, the results of the analysis show that each modification of the design factor has an influence on the value of torque ripples. From the process of Analysis of Mean (ANOM), it can be seen that wider air gap and slot opening, the smaller torque ripples. Then, the greater magnet rib and thicker magnet cause the greater torque ripples.

Double star permanent magnet synchronous machine: modified direct torque control

In the area of high power drives, double star synchronous machines are an interesting choice compared to conventional synchronous machines, due to the relatively low torque ripple created. In this paper, direct torque control (DTC) of double star permanent magnet synchronous machine (DS-PMSM) using artificial neural networks (ANN) is proposed. MATLAB/Simulink results show the comparison between direct torque control (DTC) and direct torque control using artificial neural networks (ANN). The analysis of the results shows good performance for speed, small torque and flow ripple when using the artificial neural network (ANN) strategy.

Design and Analysis of Wide Speed Regulation of Variable Leakage Flux Reverse Salient-Pole Motor

In this article, a new variable leakage flux reverse salient-pole motor (VLF-RSPM) is raised to widen the speed range. The innovation is to realize both reverse salient-pole characteristics and variable leakage flux characteristics by using a method of adding magnetic bridges and magnetic barriers. Firstly, the evolution of the topological structure and working principle of the motor are introduced. Secondly, based on 2D Finite Element Analysis (FEA), the electromagnetic properties and noise of the motor are analyzed in detail, and the electromagnetic properties are contrasted with that of the conventional V-type synchronous motor (CVTSM). The results show that VLF-RSPM has the advantages of small torque ripple, strong magnetic weakening ability, low noise, high efficiency, and low risk of permanent magnet demagnetization under different conditions. In addition, it is verified that the proposed motor extends the speed range.

Optimization design of stepped rotor type bearingless switched reluctance motor

In order to solve the problems of small starting torque and large torque ripple existing in traditional 12/14 hybrid stator pole bearingless switched reluctance motor (BSRM), a stepped rotor type BSRM is proposed. The proposed motor not only inherits the advantages of traditional 12/14 hybrid stator pole BSRM, but also can start at any rotor position and has relatively small torque ripple. To obtain better electromagnetic characteristics, simulated annealing particle swarm optimization (SAPSO) algorithm is proposed to optimize the structure of the stepped rotor type BSRM. Then, the torque, inductance and suspension force characteristics of the stepped rotor type BSRM before and after optimization are analyzed and compared. Finally, the effectiveness of the proposed optimization algorithm is verified by analysis results.

Sequential Subspace Optimization Design of a Dual Three-Phase Permanent Magnet Synchronous Hub Motor Based on NSGA III

The multiobjective optimization design of dual three-phase permanent magnet synchronous hub motors (PMSHMs) is challenging due to the high dimension and huge computation cost of finite-element analysis (FEA). A new multiobjective optimization strategy is proposed for dual three-phase PMSHMs in this article. All design parameters are divided into two subspaces according to the Pearson sensitivity analysis results to improve optimization efficiency. A new training method is adopted to improve the accuracy of the approximate model. By improving a multiobjective intelligent optimization algorithm, nondominated sorting genetic algorithm (NSGA) III, a new algorithm is proposed, which will greatly shorten optimization time. It is found that the proposed optimization method can significantly improve the performance, such as smaller torque ripple and higher maximum torque for the investigated PMSHM, while the computation resources are reduced. A prototype based on the optimization results is manufactured, and experiments are conducted on the platform to verify the accuracy of the optimization results and the FEA. The effectiveness of optimization and the accuracy of the simulation are verified by the experimental results.

Fault operation analysis of a novel dual-three-phase dual-rotor flux-switching permanent magnet machine

In this paper, based on the conventional flux-switching permanent magnet (PM) (FSPM) machine, a novel dual-three-phase dual-rotor FSPM machine with PMs of NS layout (NS-DRFSPM) is proposed. The stator of the proposed NS-DRFSPM machine is equipped with dual PMs and dual armature windings to operate in a variety of operating modes and to handle the case of PMs or armature windings failure. Firstly, the topological structure and eight fault operating states of the NS-DRFSPM machine are introduced, and the key design parameters of the NS-DRFSPM machine are optimized by genetic algorithm (GA) optimization and finite element analysis (FEA). Then, the operation principle of the NS-DRFSPM machine is analyzed in detail. Finally, the finite element method is used to analyze the performances of the NS-DRFSPM machine under eight fault operating states, which is mainly analyzed from two aspects: no-load performance and torque performance. The results show that the NS-DRFSPM machine has good electromagnetic performance under different fault conditions, including large back-electromotive force (EMF) amplitude, sinusoidal EMF waveform, high average torque, small torque ripple, and strong anti-saturation ability.

Multi-Objective Optimization Framework of a Radial-Axial Hybrid Excitation Machine for Electric Vehicles

This paper proposes a multi-objective optimization framework for a radial-axial hybrid excitation machine (RAHEM) to provide higher average torque, better flux regulation ability and smaller torque ripple, which are applied to electric vehicles (EVs). The design variables related to multiple-objective are analyzed by sensitivity stratification. Non-dominated sorting genetic algorithm II (NSGA-II) based on response surface model (RSM) is adopted for the high sensitivity layer variable. The advantages are selected with the pareto optimal solutions (POS), while the low sensitivity layer variables are optimized by sensitivity ranking for single parameter scanning. The optimization function compares the two sensitive layers results to obtain the optimal design. Three-dimensional (3-D) finite element analysis (FEA) is used to compare the electromagnetic performance of initial and optimal designs. Finally, a prototype is manufactured to verify the effectiveness of the proposed framework.

Multi Objective Optimization of Permanent Magnet Synchronous Motor Based on Taguchi Method and PSO Algorithm

To solve the optimization issues of interior permanent magnet synchronous motors (IPMSMs) and ensure a large output torque while minimizing torque ripple and core loss, the multi-objective optimization strategy should be employed. In this study, we took an 8-pole, 48-slot IPMSM as a specimen. First, the width and thickness of the permanent magnet (PM) and the rotor bridge structures were pre-selected as optimization parameters, while torque ripple and core loss were taken as optimization targets. Then, the Taguchi method to perform orthogonal experiments was employed to select the multi-parameter combinations that make the experimental results stable and with little fluctuation. To ensure the optimal results, the function equations were obtained by multivariate nonlinear fitting, while the parameters were optimized by particle swarm optimization (PSO). Finally, the optimal results were verified by the Finite Element Method (FEM). The results show that our proposed hybrid method can provide an optimal design strategy with better performance such as smaller torque ripple and core loss while maintaining a larger output torque.

A Comprehensive Performance Comparison between Segmental and Conventional Switched Reluctance Machines with Boost and Standard Converters

This paper presents the comparisons between two types of switched reluctance machines (SRMs) and SRM converters. An SRM with a segmental rotor is compared with a conventional SRM (CSRM), and an SRM converter containing a passive boost circuit is compared with a conventional asymmetric half-bridge (AHB) converter. The segmental SRM has an asymmetric rotor with a segmented structure. The four rotor segments are made of steel laminations. Two segments are misaligned with the other two by 15 degrees. The torque ripple of the SRM with this structure is decreased, and the static torque is increased compared to a conventional SRM. The boost converter comprises a front-end circuit and a conventional AHB converter. The front-end circuit boosts the voltage level. The boosted voltage accelerates the rising and falling progress of the phase current. In this way, the SRM can obtain a greater speed and a smaller torque ripple. The comparison is conducted in simulation and validated through the experimental results. The experiment results have demonstrated that the segmental SRM obtains a maximum 7% torque ripple reduction at a low-speed range, compared to the CSRM. With the boost converter, both the CSRM and the segmental SRM can achieve a lower torque ripple and a higher maximum speed.

A Hybrid Control Strategy for Multimode Switched Reluctance Motors

A hybrid control strategy based on the principle of dynamic coordination control is proposed for switched reluctance motors (SRMs) in this article. The proposed controller can obtain a small torque ripple in a wide speed range. An SRM with 12/10 poles is considered as a multimode SRM as it can be used as a six-phase or a three-phase motor. In the three-phase mode, direct instantaneous torque control based on the torque sharing function is applied, which can achieve a small torque ripple and a large instantaneous torque. In the six-phase mode, the torque ripple of the multiphase SRM is small, but the system stability is insufficient. Angle position control based on active disturbance rejection control is applied to improve the stability of torque output. In order to reduce the energy loss and torque ripple caused by the switching process of the two modes, an improved dynamic coordination principle is designed to control the switching between different modes. The effectiveness of the control method is confirmed by both experiment and simulation results.

Comparative Analysis and Optimization of Novel Pulse Injection Sensorless Drive Methods for Fault-Tolerant DC Vernier Reluctance Machine

Multiphase dc-excited Vernier reluctance machine (DC-VRM) exhibits the merits of robust structure, small torque ripple, and good fault-tolerant ability. Developing advanced sensorless drive methods can further promote its application in the safety-critical system. In this article, pulse injection sensorless drive methods are optimized in a six-phase DC-VRM parallel H-bridge drive system to strengthen their acceleration performance and fault-tolerant ability. The acceleration performance studied in this article corresponds to the acceleration speed during the startup stage. By the full-phase alternative pulse injection method (APIM), each phase can be excited independently to avoid mutual-inductance influence on position estimation, but this method suffers from a long communication delay and relatively poor acceleration performance. A reduced-phase APIM can reduce detection time, but the lack of detected phase may influence position estimation accuracy and fault-tolerant ability. To solve these problems, a novel vertical-axis synchronous pulse injection method is proposed and compared with previous methods in this article. The key is to inject detection pulses into vertical-axis phases simultaneously, thus reducing the detection time and improving the torque generation. It is proved that the influence of mutual inductance on position estimation can be ignored, and the detection accuracy and acceleration performance can be improved without deterioration of fault-tolerant ability.

A Sensorless Control Strategy of Injecting HF Voltage Into d-Axis for IPMSM in Full Speed Range

This article presents a sensorless control strategy by injecting high-frequency (HF) voltage into the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis for the interior permanent magnet synchronous motor (IPMSM) in the full speed range. The defined quadratic virtual back electromotive force model can be adopted in the full speed range, and thus, there is no need to design a transition algorithm from the zero–low speed to the medium–high speed. Besides, the accurate model of IPMSM is applied to eliminate the error caused by ignoring the stator resistance. Furthermore, the estimation error caused by the filter and system delay during demodulating the HF current in the conventional HF voltage injection method is avoided. Compared with the method of injecting HF voltage into the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis, the proposed method has smaller torque ripple and smaller injected voltage. The effectiveness of the proposed method is verified by experimental results.

Design of a Chamfered Structure on Consequent-Pole Vernier Permanent-Magnet Machine

The consequent-pole (CP) Vernier permanent-magnet (VPM) machine has been developed over the last decade. In VPM machine, the CP structure can produce considerable torque with a half volumn of the PMs compared with the regular structure, so the cost is reduced and the mechanical strength is increased. In this paper, an improvement of chamfering structure on a CPVPM machine is proposed to alleviate the flux leakage and increase the torque density. The chamfered structure is easily machined and will not influence the robustness of the rotor. The comparison results show that under the same volume and copper loss constraint, the proposed structure has smaller cogging torque, smaller torque ripple, larger torque density and larger power factor.

Investigation of Surface-inset Machines with Mixed Grade Magnets Considering Magnet Thickness

This paper presents a mixed grade magnet model for surface-inset machines considering the magnet thickness. In the polar coordinates, on the basis of the Laplace/quas i-Poisson equations and boundary conditions, the constructed matrix equations are solved and the air gap magnetic field in the machine is derived. Taking an 8-pole/12-slot surface-inset motor as an example, through the presented optimization process, the air gap field is optimized considering the magnet thickness, remanence and magnetization angle. In addition, the back-EMF and electromagnetic torque are analytically obtained. The optimized results show that the proposed mixed grade magnet model has larger electromagnetic torque and smaller torque ripple than the conventional one. Finally, the analytical predictions are evaluated by finite element analysis (FEA).

Low–Harmonic Control Strategy of a Dual Three–Phase Synchronous Reluctance Motor Based on Three–Vector Synthesis

Dual three–phase synchronous reluctance motors (DTP–SynRM) have the advantages of simple structure, high power density, fast dynamic response, and small torque ripple, and have broad application prospects in flywheel batteries. However, the synchronous reluctance motor has no permanent magnet, and the inductance value will change with the current change in actual operation. Direct torque control (DTC) is more suitable for the control strategy of dual three–phase synchronous reluctance motors because of its low dependence on motor parameters. However, traditional direct torque control uses a large vector control motor within one control period, which can not suppress the inherent 5th and 7th current harmonics in the motor. A new harmonic suppression method is proposed in this paper: that is, using a low harmonic vector to replace a large vector in traditional direct torque control, which can be synthesized by adjusting the action time and order of three adjacent large vectors within one control period. Through this improvement, torque control can have a harmonic suppression effect. The three vector synthesis method can make full use of the existing space voltage vector, and to adapt to different working conditions, two synthesis methods of switching frequency reduction and constant torque response are proposed. An improved direct torque control strategy is obtained by optimizing the design of the switch table using a new vector synthesis method. Finally, the suppression effect of traditional DTC and improved DTC on current harmonics is compared and analyzed. The results show that the direct torque control with low harmonic vector can suppress the harmonic current in x–y subspace, and the current harmonic content is greatly reduced.

Predictive-Pulse-Injection-Based Dual-Inverter Complementary Sensorless Drive for 12/10 DC Vernier Reluctance Machine

A dc-excited Vernier reluctance machine (DC-VRM) using a 12-slot/10-pole-pair design exhibits the advantages of small torque ripple and a robust structure, which has good potential to be applied as an aerospace integrated starter/generator. By eliminating vulnerable position sensors, system reliability can be further improved by sensorless startup. However, driven by the traditional three-phase inverter, the phase inductance of the 12/10 DC-VRM becomes constant due to its complementary characteristic, which means the saliency effect in DC-VRM is obliterated, and thereby a sensorless operation using self-inductance detection cannot be applied. To release the machine saliency effect and further improve sensorless drive performance, a dual-inverter sensorless drive structure is introduced to reconstruct the machine saliency by using separated dual three-phase inverters. The released series inductance model with mutual inductance coupling is established through a piecewise function, and an accurate position estimation method without finite-element analysis or complex measurements is introduced. Moreover, by further analyzing the linearity of series inductance, the full-cycle inductance high-linearity range is composed of dual-inverter complementary features, and thus position estimation accuracy can be guaranteed. Through this feature, a predictive-position-based pulse injection sensorless drive method is proposed to improve acceleration performance with detection time reduction. Based on the predictive position, the detection pulses are only injected into one inverter whose corresponding phases are located at the inductance high-linearity range, thus decreasing the detection time and improving acceleration performance.

Investigation of Torque Ripple in an Induction Motor with Respect to Slot Number Combinations

In this study, the harmonic orders of varying magnetic flux density with respect to slot combinations are scrutinized through a spatial and temporal fast Fourier transform. A three-phase four-pole induction motor is selected, and, as its base model, 36 and 28 slots are set up in the stator and rotor, respectively. Eleven models with different numbers of rotor slots were designed to study torque ripples with respect to slot combinations. The correlation between torque ripple and slot harmonics in a stator and rotor is described thoroughly by comparing the tangential and radial magnetic flux densities in the air gap, tangential force density, and harmonic orders in torque. Some models having deteriorated torque ripples have one or more slot harmonic orders in common in the stator and rotor. The other models exhibit the same commonalities, but a small torque ripple occurs because of the high harmonic orders. Models with 24 stator slots are investigated through the same procedure to generalize the relationship between torque ripple and slot harmonics in 36 stator slots.

Cascade Model Predictive Current Control for Five-Phase Permanent Magnet Synchronous Motor

As to the model predictive control for five-phase permanent magnet synchronous motor (PMSM), it is difficult to ensure the optimal control performance by using calculation method to obtain the weighting factor. To solve this problem, a cascade model predictive current control based on the idea of sequential model predictive control is proposed for five-phase PMSM for the first time. Firstly, the principle of selecting the optimal voltage vector by the proposed method is analyzed in detail. Then, combined with the characteristics of five-phase PMSM, the control priority of controlled variables is set for designing two cost function schemes without weight factor. The maximum torque scheme can generate a trapezoidal stator voltage, improving the DC bus voltage utilization rate and the system loading capacity. The minimum harmonic current scheme can reduce the harmonic of stator current, obtaining small system noise and vibration. The experimental results indicate that the proposed method can ensure the optimality of the voltage vector applied. Therefore, the five-phase PMSM obtains good performance under different working operation, such as small torque ripple, fast dynamic response, and small harmonic current.

A New Rotor Dislocation Permanent Magnet Assisted High Speed Reluctance Motor for Improving Power Density and Reducing Torque Ripple

Switched reluctance motor has been widely used in various fields because of its simple, solid structure and high reliability. However, the disadvantage of large torque ripple limits its application in high-speed occasions. In this paper, a new type of rotor dislocation permanent magnet assisted high-speed reluctance motor (RDPMA-HSRM) is proposed, which realizes the axial magnetic flux through the structure of two groups of stator and rotor, and a permanent magnet is connected in series for auxiliary excitation. On this basis, the rotor dislocation is developed and a unique structural design is developed. The working principle of the motor is explained, the magnetic circuit model of the motor is analyzed, the mathematical model of the motor is given, and the contribution of permanent magnet assistance to torque is discussed. The magnetic characteristics of the motor in terms of flux density, flux linkage, inductance and torque are obtained by finite element simulation, and compared with the characteristics of the improved motor. The effects of rotor misalignment and permanent magnet auxiliary excitation on the performance of the motor are analyzed. Finally, the prototype is tested and the experimental results are obtained. Simulation and experimental results show the RDPMA-HSRM has smaller torque ripple and higher torque density.

Reconstructing Saliency Effect in 12/10 DC Vernier Reluctance Machine for Position-Sensorless Drive Aerospace Starter Generator Application

DC-Excited vernier reluctance machine (DC-VRM) using a 12-slot/10-pole-pair design, exhibits the advantages of small torque ripple and low cogging torque due to the inherent commentary characteristic. However, the inherent saliency is canceled out by a 12/10 pole combination of machine design driven by a traditional three-phase inverter. As a result, the sensorless operation in zero/low-speed regions becomes difficult because the position estimation methods using self-inductance detection cannot be applied. To tackle this problem, we first analyzed the saliency annihilation phenomenon through Fourier analysis that the odd-order harmonics in self-inductance are canceled. Moreover, reconstructing saliency method is proposed by splitting a phase winding into two sub-phase coils and using parallel H-bridge converters to supply sub-phase coils and achieve sensorless drive. Through this method, the saliency effect is recovered in self-inductance, thereby pulse injection sensorless drive can be applied. The constructed 12/10 DC-VRM sensorless drive shows good fault-tolerant ability and can be applied in safety-critical industry applications such as aerospace propulsion. Analysis and experiments are performed in the initial position detection, start-up and free-running stages to verify the feasibility of the proposed solution. A sector estimation accurate to 6° can be achieved.