High Torque Ripple Research Articles

Comprehensive Analysis and Optimized Control of Torque Ripple and Power Factor in a Three-Phase Mutually Coupled Switched Reluctance Motor With Sinusoidal Current Excitation

This article presents a comprehensive analysis of torque ripple and power factor for three-phase mutually coupled switched reluctance motors (MCSRMs) with sinusoidal current excitation. MCSRMs controlled by sinusoidal currents have the advantage of using the conventional voltage source inverter and the conventional vector control. However, MCSRMs are characterized by high torque ripple and low power factor. The torque harmonics due to the sinusoidal current excitation are investigated, and the effect of the current excitation angle on the motor saturation level and the power factor is analyzed. These analyses are then used in the development of an optimized control method to reduce torque ripple and to increase power factor and average torque. In the proposed control method, the power factor and phase voltage are calculated by the knowledge of the phase flux linkage and phase current. The phase flux linkage is represented in terms of Fourier coefficients, where these coefficients are functions of direct- and quadrature-axis currents. Hence, they are estimated from 2-D lookup tables (LUTs), which are independent of rotor position. Similarly, the Fourier coefficients of the torque harmonics are also estimated from the 2-D LUTs. The independence of the LUTs from rotor position reduces the size of the LUTs significantly. The proposed control method is validated by experiments on a 2-kW 12/8 MCSRM.

Analysis of cogging torque in dual-stage magnetically geared devices considering magnetic flux coupling

The dual-stage magnetically geared machine (DSMGM) has a high gear ratio. The first stage is a Vernier machine (VM), and the second stage is a coaxial magnetic gear (CMG). These two components share a common rotor (CR), and they are partially flux coupled. Two DSMGMs with different PM arrangements are fabricated and tested. The DSMGM-I with gear ratio 34 can work smoothly, while the DSMGM-II with gear ratio 14.875 is hard to be started up. The purpose of this paper is to reveal the failure of the DSMGM-II. Due to the magnetic flux coupling, there is a recessive CMG in DSMGM structure. The recessive CMG in DSMGM-II prototype is activated and results in high cogging torque and high torque ripple. The thickness of CR yoke controls the portion of flux penetrating through stator. When the thickness of CR yoke is large enough, the cogging torque of the DSMGM-II can be improved. Moreover, another effective method to improve the cogging torque is designing a flux barrier to magnetically decouple the VM and CMG components. For direct-drive robotic application, a DSMGM with Halbach-PM-array is presented. It has a high gear ratio, high torque capability and low cogging torque.

Torque Performance Enhancement in Consequent Pole PMSM Based on Magnet Pole Shape Optimization for Direct-Drive EV

Developing a permanent magnet synchronous machine (PMSM) for direct-drive electric vehicle (EV) has challenges such as obtaining high torque density and low torque ripple. The PMSM should have high pole numbers owing to low-speed operation, thereby increasing the use of rare earth magnets and cost. Therefore, in this article a consequent pole (CP) rotor topology is proposed in which the permanent magnet (PM) volume is reduced when compared with conventional surface PMSM (SPMSM). However, replacing south poles in an SPMSM with induced steel poles can increase torque ripple and reduce torque density. In order to improve torque density in a CP PMSM, structural modifications such as multilayer windings and non-ferromagnetic barriers have been proposed in the literature. These modifications increased the torque density while increasing the torque ripple. Therefore, this article proposes a novel two-level optimization method based on gradient descent algorithm, to address the challenges of improving torque density and reducing torque ripple simultaneously in a CP PMSM. Initially, an expression for the magnet pole arc angle is derived for CP PMSM based on magnetic equivalent circuit. A two-level optimization is performed on a baseline CP PMSM to determine the optimal magnet pole arc. The torque production and torque ripples of the optimized design are validated by simulation and experimental results.

New Sensorless Speed Control of a Hybrid Stepper Motor Based on Fuzzy Sliding Mode Observer

Stepper motors are widely used in industrial and consumer applications due to low-cost, high reliability, and open-loop control capability. Though open-loop features a simple structure, it bears low step resolution, high torque ripple, and low energy efficiency. To improve the performance without increasing hardware cost, a fuzzy sliding mode observer (SMO)-based new sensorless speed control structure is proposed. Unlike the conventional sensorless speed control, it does not use Park and inverse Park transformations to transform currents between a-b and d-q coordinates. Instead, it uses a new current transformation method to generate reference currents of stator windings, which not only reduces the calculation burden of the controller, but also improves the stability of the system. To reduce the chattering, a fuzzy logic controller (FLC) embedded into the SMO is designed to adjust the observer gain adaptively, without using the conventional method that replaces the discontinuous sign function with the continuous, such as sigmoid or saturation function. The effectiveness of the proposed controller is verified using MATLAB/Simulink simulation (R2018b, MathWorks, Natick, MA, USA) and experiment by assessing the speed and position tracking abilities.

Torque Ripple Reduction of SRM Drive Using Improved Direct Torque Control With Sliding Mode Controller and Observer

The industrial application of the switched reluctance motor (SRM) is limited by its high torque ripples caused by the doubly salient structure. In this article, an improved direct torque control (DTC) with sliding mode controller and observer is developed to reduce the torque ripples of a four-phase SRM. First, a sliding mode controller based on a new reaching law is developed for designing a sliding mode speed controller (SMSC) for the DTC system. An antidisturbance sliding mode observer (ADSMO) is then proposed and combined with the SMSC to build a composite antidisturbance speed control strategy. Moreover, detailed simulation validations are carried out to reveal the effectiveness of the new reaching law, SMSC and ADSMO. Finally, experiments are conducted to verify the performance of the proposed SMSC–ADSMO in a DTC system with a four-phase SRM prototype.

Buried PM inner rotor magnetic gear evaluation

Inner rotor SFPMR glued on the rotor surface with material of high compressive strength but low tensile strength cannot sustain the centrifugal force in the high-speed operation, thus require retaining sleeve. Electrical motor employ the retaining sleeve to increase the rotor strength, but so far in MG, there are limited design that employ this technique. Another method to avoid PM from displaced is by buried into the rotor yoke. However, this method may result in lower torque and noise. In this paper, new MG structure is designed. The inner rotor surface mount PM of magnetic gear is rearrange as buried PM. First, the torque analysis of the MG is simulated without counting any loses. Then, gear efficiency is simulated over high speed range and compared to the original topology to identify the amount of reduction of the torque. The result agrees that the buried rotor reduced the torque output 3 times lower than the surface mount PM and disturb the torque which result in high torque ripple over 240%.

Torque Improvement in Dual M-Phase Permanent-Magnet Machines by Phase Shift for Electric Ship Applications

This paper proposes a design technique for electric ship traction machines to achieve high torque density and low torque ripple by adopting dual <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> -phase windings with an appropriate phase shift. Firstly, the general relationship between the slot number and the phase number for dual <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> -phase windings is investigated. Secondly, the uniform analytical expressions of torque with different phase shifts are derived. Also, the optimal phase shift angle is summarized from the perspective of improving torque performance. Then, the 48-slot and 22-pole permanent-magnet machines for electric ship with different windings configurations are designed. The finite-element method is used to calculate their electromagnetic performances, such as back electromotive force, torque capability, stator magnetic motive force and radial force. Finally, some experiments on the prototype machine for electric ship are carried out for validation.

Torque Ripple and Efficiency Online Optimization of Switched Reluctance Machine Based on Torque per Ampere Characteristics

Relatively high torque ripple limits the further development of the switched reluctance machine, and the application of the ripple suppression method will reduce the efficiency of the system. To simultaneously improve the efficiency and torque ripple of the switched reluctance machine, a new commutation and online optimization strategy is proposed. According to the torque per ampere characteristics of the machine, two rotor position angles are defined, which are the boundaries for the high and low torque per ampere operation modes of the two adjacent phases, respectively, and for different operating modes, specific torque hysteresis control schemes are performed. Furthermore, an objective function is constructed with the efficiency and torque ripple coefficient, and during the operation of the machine, the defined boundary angles are online optimized by the genetic algorithm to maximize the value of the objective function. The effectiveness of the method is verified by detailed simulation and experiment under different operating conditions.

Investigation of an Inset Micro Permanent Magnet Synchronous Motor Using Soft Magnetic Composite Material

This paper presents the world’s smallest inset permanent magnet synchronous motor (PMSM) with a soft magnetic composite (SMC) core, providing ease of manufacturing for micromachine applications without silicon steel laminations. The inset motor can offer an additional reluctance torque and higher torque density with a lower usage amount of permanent magnet. A 15 mm diameter inset motor was developed with the thickness of a tile-type permanent magnet which is limited to 1 mm by the manufacturer. The motor was designed with high torque density and low torque ripple by varying the interpole iron width for the rotor. Two inset motors were made using both SMC and silicon steel materials for comparison. The performance of the SMC motor was inferior to the silicon steel motor, but it still meets the specifications of the commercial market. If the thickness of the tile-type permanent magnet is further reduced, the micro inset motor with a SMC core can be easily mass-manufactured using powder sintering.

Design of Neuro-Fuzzy Based Torque Controller for Torque Ripple Reduction of Asynchronous Motor

Among all the control methods developed for Induction Motor (IM) drivers, the hysteresis controller based Direct Torque Control (DTC) method has an important place. This control method does not require other rotor and stator parameters except the stator resistance and does not require position or velocity sensors. However, there are some disadvantages of the DTC method, such as high torque, flux and current ripples. In this study, in order to reduce the high torque ripples occurring in an induction motor that is controlled by the hysteresis controller based conventional DTC method, a simple and effective Sugeno type Neuro-Fuzzy Torque Controller (NFTC) is proposed. This proposed controller is used instead of hysteresis controller. An experimental setup consisting of 1.1 kW induction motor, current and voltage measurement, DS1103 control card and two-level voltage source inverter was installed. To evaluate the performance of the proposed controller structure, various experimental studies were performed. Results obtained from the proposed NFTC based structure and conventional hysteresis controller based DTC structures are given comparatively. By the obtained experimental results, it was confirmed that the proposed NFTC-based controller structure considerably reduced flux and torque ripples in the motor.

The Modified Model of Third-Harmonic Shaping for a Surface-Mounted Permanent-Magnet Synchronous Motor Under Parallel Magnetization

This article establishes an optimized third-harmonic shaping model in order to reach the goals of high power density and low torque ripple of the surface-mounted permanent magnet motor. The establishment of the model takes the nonideal factors into consideration, including PM relative permeability, stator slotting, pole leakage, pole edge effect, and magnetic circuit saturation. The formula of third-harmonic shaping and the optimal third-harmonic injection factor a m ( m ) are derived from the model. Then, a finite-element model was established to compare the electromagnetic performance of different magnetic poles. It is found that the average torque of the modified third-harmonic motor is 3.5% higher than that of the simplified third-harmonic motor, and the torque ripple is 47% lower than that of the simplified third-harmonic motor. This proves the superiority of the modified model. And experiments demonstrate that the modified model is feasible and effective.

A nonlinear time–frequency control based FOC for permanent magnet synchronous motors

PI control based field oriented control (FOC) scheme is the predominant method for the control of permanent magnet synchronous motors (PMSMs) in applications requiring high performance. A novel nonlinear time–frequency control based FOC design for the fast, accurate, and robust control of PMSMs is presented. Featuring a single nonlinear time–frequency controller and a PI controller as the 2 primary components in the control configuration, the new scheme is evaluated against a classic PI control based FOC design for performances in response to rapid speed-switching and abrupt external torque variation. The scheme displays significantly smaller steady-state tracking errors undergoing speed shifting and no high frequency current oscillations or electromagnetic torque ripple in the motor, as does the PI based scheme. The tracking errors corresponding to changes in torque are free of distortion and oscillation that would otherwise indicate instability and inaccuracy. Precision positioning control is also realized through incorporating a P controller into the controller configuration. When the motor reference position is briskly flipped between 360° and 1°, the novel controller design is shown to perform well with a rotor position error that is less than 0.13°.

An Improved Direct Torque Control for a Single-Winding Bearingless Switched Reluctance Motor

The direct torque control (DTC) and direct force control (DFC) method were introduced to reduce the torque and levitation force ripple in single-winding bearingless switched reluctance motors (SWBSRMs). However, it still has some disadvantages. Firstly, the flux-linkage control is not suitable for the DTC method in SWBSRMs. On the one hand, it can increase the torque ripple. On the other hand, the RMS current can be increased and then the torque-ampere ratio is decreased. Secondly, the vectors selection is also unreasonable, which can increase the torque ripple further. In order to solve these problems, an improved control method based on DTC and DFC method for SWBSRMs is proposed in this paper, which can obtain high torque-ampere ratio and low torque ripple simultaneously. In the proposed method, the flux-linkage loop control is not needed and the space voltage vector table is improved. The experimental results show that the torque ripple is reduced by 66.7%, the torque-ampere ratio is increased by 200% and the switching times in one electrical period are reduced by 47.3%.

Investigation of Unbalanced Magnetic Force in Fractional-Slot Permanent Magnet Machines Having an Odd Number of Stator Slots

Fractional-slot permanent magnet (PM) machines with an odd number of stator slots are attractive candidates for industrial applications due to their high torque density and low torque ripple. However, the unbalanced magnetic force is detrimental to the bearing and yields noise and vibration. This paper determines the existence criterion of UMF on both open-circuit and on-load conditions by analysis of air gap field and magnetic force waves. Only when the machine periodicity is one, will the open-circuit UMF be generated due to the mutual interaction between the modulated PM harmonics and the original PM harmonics. In addition, the existence of on-load UMF in machines with a periodicity of one is confirmed even when the slotting effect is ignored. Furthermore, among the five investigated machines with a given odd slot number of 9 but different pole numbers, the UMF in a machine with two poles is the smallest since the magnitude of the 2nd harmonic in the armature reaction is the smallest compared with other contributing harmonics. Meanwhile, the UMF in a machine with pole number 2p = Ns-1 is the largest due to the relatively larger magnitude of the (p + 1) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> armature reaction harmonic and the additive effect between the first order radial and tangential stresses.

A Novel Structure of Switched Reluctance Machine With Higher Mean Torque and Lower Torque Ripple

Switched reluctance motors (SRMs) have a robust and simple structure, high reliability because of the absence of magnetic field source on rotor, low cost and simple cooling system. However, conventional SRMs confront with some challenges such as low mean torque, low torque density and high torque ripples. For wider applications of SRM, the above-mentioned drawbacks must be mitigated. One possible method is changing the structure of SRMs. In this article, a novel 12/14 three-phase SRM with connected C-core structure is introduced which has a short path for the main flux of stator teeth. This brings about core loss reduction. On the other hand, both teeth of the stator phase in C-core develop a positive torque during the movement of the rotor from the unaligned position to the aligned position; this enhances the torque, the mean torque and torque density of the proposed SRM, keeping the volume fixed. Finally, the proposed SRM was prototyped and tested and its torque/rotor angular position characteristic was measured. To verify the novelty and merits of the proposed SRM, its mean and peak torque, torque density, core losses and torque ripples were compared with those of an optimized 12/8 three-phase conventional SRM and a significant match was achieved.

FLC-DTC METHOD FOR TORQUE RIPPLES MINIMIZATION OF 8/6 SWITCHED RELUCTANCE MOTORS DRIVE

The switched reluctance motor gains a significant response in industries in the past decade because of its ruggedness, high torque to inertia ratio, simple structure, high reliability and inexpensive manufacturing capability. These features make it a suitable candidate for various applications and electric drives. However, In the field of electric drives a switched reluctance motor drive is having doubly salient structure thus it inherently produces high torque ripples and acoustic noise problems and its controlling difficulties that is an undesirable effect for vehicle applications, especially at low speed. The main objective of this paper is to minimize the torque ripples and to control its speed. In this paper a fuzzy logic controller based direct torque control method is used for speed controlling and for controlling of torque ripples of the 8/6 SRM drive. It’s modelling and application of fuzzy logic controller based direct torque control method is done in MATLAB/SIMULINK environment.

Analytical validation of novel consequent pole E‐core stator permanent magnet flux switching machine

Flux switching machines (FSMs) encompass unique features of conventional direct current machine, permanent magnet (PM) synchronous machine and switch reluctance machine. Permanent magnet FSM (PMFSM) is capable of high torque density and applicable for high-speed application, however conventional PMFSM exhibits demerits of high PM volume, high torque ripples and significant stator flux leakage. In this paper, a novel consequent pole E-core stator PMFSM is proposed and compared with conventional topology utilising 2D finite-element analysis (2D-FEA). Finite-element analysis revealed that proposed design enhanced flux modulation effects by introducing flux bridges and flux barriers as a result reduced cogging torque by reducing 46.53% of the total PM volume, reduce torque ripples by reducing PM slot effects and reduce flux leakage utilising flux bridges in the stator. Furthermore, analytical model for flux linkages, cogging torque, mechanical torque, no load and on-load magnetic flux density (MFD) is developed for initial design of conventional and proposed model. 2D analytical methodologies resolve equivalent magnetic circuits for open-circuit flux linkages, Fourier analysis for cogging torque, Laplace equations for MFD and Maxwell stress tensor for mechanical torque. Finally, results obtained from 2D-FEA and analytical methodologies are validated and compared.

An Improved Model Predictive Current Control for PMSM Drives Based on Current Track Circle

Model predictive current control (MPCC) is a high-performance control strategy for permanent-magnet synchronous motor (PMSM) drives, with the features of quick response and simple computation. However, the conventional MPCC results in high torque and current ripples. This article proposes an improved MPCC scheme for PMSM drives. In the proposed scheme, the back electromotive force is estimated from the previous stator voltage and current, and it is used to predict the stator current for the next period. To further improve the steady state and dynamic performance, the proposed MPCC selects the optimal voltage vector based on a current track circle instead of a cost function. Compared with the calculation of cost function, the prediction of the current track circle is simple and quick. The proposed MPCC is compared with conventional MPCC and a duty-circle based MPCC by simulation and experiment in the aspect of converter output voltage and sensitivity analysis. Results prove the superiority of the proposed MPCC and its effectiveness in reducing the torque and current ripples of PMSM drives.

Permanent Magnet Parameter Design and Performance Analysis of Bearingless Flux Switching Permanent Magnet Motor

Since the bearingless flux switching permanent magnet motor has a doubly salient pole structure of conventional flux switching permanent magnet motor, there are many problems, such as high cogging torque, high torque ripple, and the magnetic flux leakage produced by PMs, which affect the characteristics of the electromagnetic torque and suspension force. To overcome the shortcomings above, a novel method-right angle chamfering scheme, is investigated to reduce the cogging torque. Firstly, based on the given rated speed and rated power, the parameter ranges of the angle variables at both ends of the permanent magnets are designed by the empirical formulas. Then, under the condition that the torque and the power are reduced in allowable ranges, the electromagnetic characteristics, such as cogging torque, harmonic, electromagnetic torque, radial suspension force, and decoupling, are simulated and analyzed in detail. Based on the proposed design method, the compromise design of the above design objectives is considered and realized. Finally, the scheme of stator and rotor component is built, and the experimental results show that the effectiveness and feasibility of the scheme are verified.

Induction motor harmonic reduction using space vector modulation algorithm

The vector control was proposed as an alternative to the scalar control for AC machines control. Vector control provide high operation performance in steady state and transient operation. However, the variable switching frequency of vector control causes high flux and torque ripples which lead to an acoustical noise and degrade the performance of the control scheme. The insertion of the space vector modulation was a very useful solution to reduce the high ripples level inspite of its complexity. Numerical simulation results obtained in MATLAB/Simulink show the good dynamic performance of the proposed vector control technique and the effectiveness of the proposed sensorless strategy in the presence of the sudden load torque basing on the integral backstepping approach capabilities on instant perturbation rejection.