Large Torque Ripple Research Articles

Torque Performance Improvement for Slotted Limited-Angle Torque Motors by Combined SMA Application and GA Optimization

Due to stator magnetic saturation and inherent cogging torque, the slotted limited angle torque motor (LATM) performs large torque ripple within its operation range, resulting in vibration noise and complex control problem. The novelty of this article is to not only first to apply 1J22 soft magnetic alloy (SMA) in the LATM but also to propose a multiobjective optimization method to improve the torque performances including torque ripple, cogging torque, and output torque, based on genetic algorithm (GA). First, 1J22 SMA is applied to the LATM to reduce the torque ripple caused by magnetic field saturation. Then, through the sensitivity analysis, weight coefficients of the related parameters of stator tooth for the optimization process are obtained. Besides, in order to optimize torque performances, the multiobjective optimization process is carried out and the GA is used to obtain the desired objective. Finally, the finite-element analysis (FEA) is used to validate the optimization design.

An Improved Direct Instantaneous Torque Control of Doubly Salient Electromagnetic Machine for Torque Ripple Reduction

The doubly salient electromagnetic machine (DSEM) is a suitable candidate in many industrial applications due to its simple construction and low manufacture cost. However, the doubly salient structure and the conventional square-wave control method lead to the large torque ripple in the DSEM. In this article, an improved direct instantaneous torque control (DITC) method is proposed to suppress the inherent torque ripple and enhance the torque capability of the DSEM. The maximum torque characteristics of the DSEM are obtained and analyzed with the finite-element method. Besides, the ideal phase current waveform to realize the low torque ripple is constructed according to the maximum torque characteristics. Then, the operation principle of the proposed DITC method is derived from the maximum torque characteristics. The proposed DITC method is implemented on a prototype of 12/8-pole DSEM drive system. The influence of the commutation angle parameters on the proposed DITC method is analyzed through simulation and experimental results. The simulation and experimental results indicate that the proposed DITC method can realize the smooth torque operation and high torque-ampere ratio simultaneously. Finally, the simulation and experiment under the step reference torque condition are performed to test the dynamic performance of the proposed DITC method.

A general closed-loop power-decoupling control for reduced-switch converter-fed IM drives

Twice ripple power exists in single-phase to three-phase reduced-switch induction motor drives, which degrades the performance of the drive system, such as larger total harmonic distortion of the grid current, the larger ripple voltage in the dc link and the larger torque ripple. Most existing power decoupling schemes are open-loop decoupling methods. However, the open-loop decoupling method has the disadvantages of heavy computation and strong dependency of parameters. This paper analyzes all steady state solutions of the decoupling capacitor voltage from the point of view of solving differential equations and presents a unified multi-proportional-resonant closed-loop decoupling method to suppress the ripple voltage on the dc bus. The whole drive system adopts a hybrid predictive control strategy with dual loops to coordinate the operation of each part. Comprehensive experimental results are presented to verify the effectiveness of the presented method.

Direct Torque Control for Induction Motors Based on Minimum Voltage Vector Error

The traditional direct toque control (TDTC) for induction motors (IM) is afflicted by large torque ripple, high current total harmonic distortion (THD), and variable switching frequency. Recently, some improved direct torque control (DTC) methods have been proposed to address the above problems, but they often suffer from obscure concept, intensive computation, and poor robustness. To further improve the performance, this article proposes a DTC method based on minimum voltage vector (VV) error. The proposed strategy effectively optimizes the duty ratio of fundamental VV to minimize the error between reference VV and final VV imposed on motor terminals. The optimization algorithm dose not increase the system's complexity much and can be intuitively understood by a graphical interpretation. Experiment comparisons between the proposed strategy and some existing DTC methods are conducted on a 0.55-kW IM platform. The proposed DTC method has proven to achieve better steady-state performance, while retaining fast dynamic response of TDTC. Furthermore, the proposed method can obtain almost constant average switching frequency in the entire speed range, especially with rated load, due to the utilization of proportional-integral type torque regulator.

High Precision Low-Speed Control for Permanent Magnet Synchronous Motor.

Due to the process defects and imperfection of drivers, permanent magnet synchronous motors (PMSM) are problematic to control. There is still a lack of effective high-performance control methods for inertial stabilized platforms based on PMSM currently. At present, the most frequently used method is sliding mode control (SMC), but traditional sliding mode control cannot overcome the contradiction between high performance and system chattering. In order to solve this problem and improve the system reliability and pointing accuracy, a new approach law for the sliding mode controller is proposed in this paper. In view of the large periodic torque ripple in PMSM, an iterative learning controller (ILC) is introduced to compensate for the disturbance. Based on these, aimed at suppressing all kinds of real-time disturbances in the working environment of the system, the extended state observer (ESO) is brought into the servo system to observe the lumped disturbance of the system, and the total disturbance observed is compensated into the sliding mode controller, so as to better suppress the system chattering and enhance the system’s ability of resisting external disturbance. Experiments are carried out on an inertial stabilization platform based on DSP + CPLD. The final experiments verify that the SMC with the new approach, combined with ILC and ESO, is of outstanding performance when compared with the traditional proportional integral (PI) + disturbance observer (DOB) control scheme.

Torque Ripple Suppression of Building-Block Transverse Flux Permanent Magnet Motor by Current Compensation and Variable Parameter Control Based on Real-Time Inductance

Building-block transverse flux permanent magnet motor (B-TFPMM) has the advantage of electromagnetic decoupling and high torque density, but it has the strong nonlinearity and the large torque ripple. To solve the problem, the nonlinear characteristics of B-TFPMM stator back electromotive force (EMF) $e_{\mathrm {pm}}$ , winding inductance $L$ and single-phase torque $T_{\mathrm {sp}} $ are analyzed firstly, and the nonlinear dynamic models involving $e_{\mathrm {pm}}$ , $L$ , $T_{\mathrm {sp}}$ , stator current and rotor position are established by three-dimensional finite element method (3DFEM). Secondly, apply the square wave current and sinusoidal current to stator windings respectively, and the result shows that using sinusoidal current would acquire smaller torque ripple rate when the load torque is more than 30 N $\cdot $ m. Furthermore, the variation rule of five-phase current utilization is obtained and the maximum current utilization model is established. Based on these, the current compensation method is developed and then the torque ripple rate could be reduced by 10% approximately. After that, combining with 7 nonlinear dynamic models of B-TFPMM, a closed-loop control system based on the compensation method and variable parameter PID algorithm is built. The ratio of the real-time winding inductance to sampling period is chosen as the proportional coefficient of controller. The results indicate that compared with the control mode which combining uncompensated current and traditional constant parameter PID algorithm, the control mode of using compensated current and variable parameter PID algorithm would reduce the torque ripple rate by 57% to 65% and increase the average torque by 13% to 33% in the meantime.

Technique of control PMSM powered by PV panel using predictive controller of DTC-SVM

The present paper is a part of the study of Direct Torque Control based (DTC) on space vector modulation using predictive controller (Predictive SVM) of a permanent magnet synchronous motor (PMSM) powered by a photovoltaic (PV) source. In the conventional direct torque control (DTC) of a permanent magnet synchronous motor (PMSM), hysteresis controllers are used to choose the proper voltage vector resulting in large torque ripples. The direct torque control can accelerate the torque responses but increases the torque ripple at same time. Nowadays, exist some other alternative approaches to reduce the torque ripples based on (Predictive SVM) technique. This method is based on the replacement of hysteresis comparators (used in conventional DTC) by Proportional Integral (PI) regulators and the selection table by space vector modulation (SVM). The simulation results confirm that this proposed method where the control of the switching frequency is well controlled, allows us to reduce the oscillations of the electromagnetic torque and flux by 20 % and 30%, respectively with a good dynamic response compared with conventional DTC.

Novel Current Profile of Switched Reluctance Machines for Torque Density Enhancement in Low-Speed Applications

In this article, a current profiling technique is proposed for the torque density enhancement in switched reluctance machines (SRMs). The novel current profile is initially developed from the harmonic current injection method and is then modified into a unipolar waveform to allow the application of an asymmetric bridge inverter. It is found that, neglecting the magnetic saturation, the optimal current profile for the maximum torque per ampere operation in an SRM is close to a pulse with high-order harmonics. However, an optimized current with relatively low-order harmonics can provide better performance in the practical situation. Based on the analytical and the finite element results, the proposed method is proved to be able to enhance the torque density by 20% at the light load condition and by 15% at the rated condition compared with the conventional SRM excitation. Also, the large torque ripple and core loss in SRMs are suppressed and the efficiency is improved. More importantly, unlike many other current profiling techniques, the proposed current profile has fixed parameters and is easily adaptable to different machine specifications. The effectiveness of the proposed method is verified by both the finite-element analyses and the experiments.

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

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

Improved Duty-Ratio-Based Direct Torque Control for Dual Three-Phase Permanent Magnet Synchronous Machine Drives

This article investigates the duty-ratio-based direct torque control strategies for dual three-phase permanent magnet synchronous machine (PMSM) drives. The classical switching-table-based direct torque control (ST-DTC) for the dual three-phase drives usually suffers from significant harmonic currents and a large torque ripple. To reduce the harmonic currents, 12 combined voltage vectors are generated and employed as active vectors. Then, the duty-ratio-based ST-DTC is introduced to reduce the torque ripple. Considering that the typical duty-ratio-based ST-DTC exhibits the drawbacks of machine parameter dependent and a certain degree of failure rate in the duty ratio regulation, a simple and effective method taking into account the effect of the machine speed is employed to obtain the duty ratio. Afterward, to prevent the issue of the inverter thermal imbalance caused by using only one type of zero vectors, two types of zero vectors are employed in the switching sequences. With the proposed method, not only the harmonic currents have been suppressed, but also the torque ripple can be considerably reduced, while the merits of the classical ST-DTC such as simple structure and excellent dynamic performance are preserved. The experimental results validate the effectiveness of the proposed strategy.

Comparative Study of Modular Dual 3-Phase Permanent Magnet Machines With Overlapping/Non-overlapping Windings

For modular permanent magnet (PM) machines with overlapping (OLP) windings widely employed in wind power generation, the large torque ripple and long end winding are major issues. In order to solve these problems, PM machines with non-overlapping (NOLP) windings and redundant teeth for easy modularity are proposed in this paper. The comparative study between modular machines with these two kinds of windings is necessary and is the major focus of this paper. For the sake of clarity, two modular dual 3-phase machines with 42-slots/32-poles (42S/32P) and 192S/32P combinations are chosen as examples to show the differences in terms of machine performance. The proposed 42S/32P modular machine adopts NOLP winding, while the conventional 192S/32P one uses the OLP type. Based on the results, it is found that the modular machine with NOLP winding has comparable average torque and efficiency. In the meantime, much lower torque ripple exists for the proposed modular machine regardless of the current value. The shorter and simpler end windings are beneficial to manufacturability. Moreover, the proposed modular machine with NOLP winding will be more fault tolerant due to smaller mutual inductances between phases and larger d -axis inductance. Finally, the proposed 42S/32P modular machine is prototyped and the experiments validate the correctness of the analyses in this paper. Despite two specific examples being used, the conclusion should be generic and can be employed to modular machines with other slot and pole number combinations.

Minimising torque ripple of SRM by applying DB‐DTFC

Since the traditional direct torque control (DTC) of switched reluctance motors (SRMs) has the shortcomings of large torque ripple and non-constant switching frequency, this study proposes the deadbeat-direct torque and flux-linkage control (DB-DTFC) method for SRM. By analysing the basic principles of SRM, a discrete-time model is established to predict the future states of the SRM drive system. With DB-DTFC, the stator flux and torque can be manipulated during each pulse-width modulation cycle to minimise torque ripple during operation. As a result, the proposed DB-DTFC can minimise the torque ripple as well as apply space-vector modulation with a constant switching frequency. Finally, to verify its effectiveness, DB-DTFC was applied to the 15 kW three-phase 12/8-pole SRM test bench in real time and the results are compared with conventional DTC.

Evaluation of Torque Ripple of an Optimal Designed 3-Phase Induction Motor Using Uncertainty

Background/ Objectives: This paper aims to reliably evaluate the torque ripple of an optimal designed 3-phase induction motor using the measurement uncertainty theory. Methods/ Statistical analysis: The measurement uncertainty theory is statistically applied to the actual test. To apply the measurement uncertainty theory to the simulation result such as torque ripple, the type-A standard uncertainty can be calculated through the periodical calculation of torque ripple and the type-B standard uncertainty expressing non-statistical factors such as measurement environment, instrument or method is regarded as 0 in the uncertainty evaluation process. Findings: The general expression of torque ripple of an optimal designed 3-phase induction motor is not dependable because of the fluctuating torque at steady state. Therefore, in this paper, the uncertainty of the torque ripple is evaluated by using the type-A and the type-B standard uncertainty which is regarded as 0. As a result, the torque ripples before and after the optimal design are reliably evaluated in a specific confidence level. Also, it is known that the uncertainty can be easily applied to the torque ripple as well as other motor parameters such as power loss, output power density and so on. Improvements/ Applications: Since this paper deals with evaluation method of torque ripple of a 3-phase induction motor with respectively low torque ripple, it could be applied to motors with large torque ripple.

3상 유도전동기 운전중 한상의 결상에 따른 운전 특성 해석

Induction motors are failing due to various causes. The biggest factor in electrical failure is due to overheating. Single phase loss in which one phase of the three phases is suddenly opened is included in the occurrence of a major failure in an electrical failure. The generation of a single phase loss can overheat the stator winding due to an increase in current, which can lead to burnout. It also affects torque, so it can deliver large torque ripple to the shaft. Therefore, it is very important to clarify what kind of problem exists when a single phase loss of the induction motor occurs. In order to compare the change of operation of induction motor during normal operation and single-phase loss operation, the rotational coordinate system theory was introduced. In this paper, changes in current, electric power, and torque were analyzed when single phase loss occurred due to the power source side of the induction motor being operated normally. It was found that the existence or absence of current and the pulsation of the magnetic flux at any phase specified during one-phase loss operation greatly affects the torque and affects the electric power.

Flux linkage optimization for direct torque control of switched reluctance motor based on model predictive control

In this paper, to solve the problem of large torque ripple in a switched reluctance motor (SRM), a new control strategy based on model predictive flux control is proposed in the direct torque control (DTC) algorithm. First, the flux linkage value in the next period is calculated from the discrete time model of the SRM. Second, to reduce the computation burden and increase the dynamic response, a torque hysteresis controller is embedded in the system to select three candidate voltage vectors for the cost function. Finally, based on flux linkage minimization, the best voltage vector is selected and applied to the system. The proposed direct torque and predictive flux control (DTPFC) method perfectly suits the nonlinear magnetic characteristics of SRM, and shows better steady‐state and dynamic‐state performances compared to DTC. Furthermore, since DTPFC has only one variable in the cost function, the huge task of obtaining the best weighting factor is eliminated. Simulation and experiments are carried out on a three‐phase 12/8 SRM with the proposed control algorithm and DTC. The results demonstrate the validity of the new control approach. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Analysis of Stator/Rotor Pole Combinations in Variable Flux Reluctance Machines Using Magnetic Gearing Effect

The torque production of variable flux reluctance machines (VFRMs) is explained by the “magnetic gearing effect” in recent research. Based on this theory, this paper concludes the general principles for feasible stator/rotor pole selection and corresponding winding configuration for VFRMs. The influence of stator/rotor pole combination on torque performance is comprehensively investigated not only in terms of average torque and torque ripple, but also in terms of each single torque component. It is found that the synchronous torque is proportional to the fundamental rotor radial permeance component and has the dominant contribution in average torque for all the VFRMs. The stator slot number and rotor pole number should be close to each other to achieve the highest output torque. Meanwhile, the 6-stator-slot/(6 i ± 2)-rotor-pole (6s/(6 i ± 2)r) and their multiples are large torque ripple origins for VFRMs due to the large reluctance torque ripple. Also, it is proved that a lower stator slot number is preferable choice to obtain higher torque/copper loss ratio, whereas a higher stator slot number is more suitable for large machine scale scenario. Finally, the analyses and conclusions are verified by finite element analysis on the 6-, 12-, 18-, and 24-stator-slot VFRMs and by experimental tests on a 6s/7r and 6s/8r VFRMs.

Study on a Novel Predictive Torque Control Strategy Based on the Finite Control Set for PMSM

In this paper, a novel predictive torque control (PTC) strategy based on the finite control set for the permanent magnet synchronous motor (PMSM) was proposed to overcome the large flux and torque ripples of the traditional direct torque control (TDTC). First, in the PTC, the complete decoupling of the stator flux and torque in the stator flux coordinate system enables a simpler PTC. Second, compared with the traditional predictive torque control (TPTC), using the magnitude comparison of the flux and torque errors, the selected voltage vector for each control cycle was reduced from eight to one, which greatly reduces the computation and complexity. What is more, the duty cycle modulation was used to fix the switching frequency to solve the problem that the switching frequencies of TDTC and TPTC are not fixed. Finally, the simulation results verified the superiority of PTC in reducing the torque and flux ripples.

Torque Ripple Reduction and Flux-Droop Minimization of DTC With Improved Interleaving CSFTC of IM Fed by Three-Level NPC Inverter

Direct torque control (DTC) is known for its fast control in AC motor drives due to its simple control structure that directly controls the torque without the need for modulation blocks or frame transformations. However, when used in induction motor (IM) drives it has three main drawbacks: large torque ripples, variable switching frequency, and sector flux-droop at the low-speed region due to the employment of the torque hysteresis controller (THC). Torque ripple minimization can be achieved in DTC drives by replacing the originally proposed two-level inverter with a three-level neutral-point clamped (3L-NPC) inverter. Nevertheless, the switching frequency remains variable and low, which produces an elevated torque ripple and asymmetrical switching signals for the inverter. In addition, sector flux-droop resulting from driving the IM at the low-speed region produces a high current distortion that consequently eliminates the robustness of DTC. To alleviate these problems, an interleaving constant switching frequency torque controller-based DTC (CSFTC-DTC) was implemented. It improves the operation of the IM at the low-speed region by increasing the duty-cycle of the applied active voltage vector and reducing the duration of the applied zero vectors. Although the conventional CSFTC-DTC regulates the stator flux of the IM at the low-speed region and minimizes the total harmonic distortion (THD) of the stator current, it produces a high torque ripple-one of the main disadvantages of classical DTC. In this paper, an interleaving CSFTC-DTC is proposed to subdivide the duty cycle of the applied vectors of the 3L-NPC inverter to limit the influence of the large duty-cycle of the applied vectors on flux-regulation and torque ripples. The simulation and experimental results presented validate the effectiveness of the proposed method over the conventional method.

Comparison between Modified MPC and DTC Control Method for Permanent Magnet Synchronous Motor

Direct torque control (DTC) and model predictive control (MPC) are widely used in the control of permanent magnet synchronous motor (PMSM). However, DTC for PMSM can cause large torque ripples and flux ripples, high harmonic distortion of the stator current, and high acoustic noises. Compared to DTC, MPC considers all possible switching states which can reduce the ripples of torque and flux. MPC with one-step delay compensation for PMSM and DTC with one-step delay compensation and two hysteresis comparators for PMSM have been proposed to solve some drawbacks of these two controllers. This paper makes a detailed comparison between these two improved control methods through Simulink and hardware experiments results to analyse the four indicators-torque ripple, flux ripple, transient time and THD of inverter current.

An Overview of Fault-Diagnosis and Fault-Tolerance Techniques for Switched Reluctance Machine Systems

This paper presents a technical overview for fault diagnosis and fault-tolerant strategies of switched reluctance machine (SRM) systems. With the widespread utilization of electrical motors, stability and reliability become the most important considerations for safety. SRMs are famous for their great robustness, wide speed range, and high fault-tolerant capability, which are much suitable for high-speed and safety-critical applications. Although the SRM drive have some fault tolerance ability, the fault still seriously affects the system performance. The faults happening in different parts, such as converter, motor winding, sensors, and rotor, may lead to low torque, large torque ripple, overcurrent, insulation damage, and even system broken-down, without any fault-tolerant consideration. Therefore, it is important and urgent to improve the motor system reliability and robustness for SRM drives. Aiming at offering novel solutions to the faults in SRM drives, this paper begins with mathematical modeling of the SRM, and then concentrates on the state-of-art fault diagnosis and fault tolerance techniques to enhance the fault ride-through ability. Two categories, containing fault diagnosis and fault tolerance technologies are emphasized for fast faults locating and stable post-fault operation. Advanced technologies are reviewed, classified, and compared comprehensively. Besides, several fault diagnosis and tolerance schemes that have been developed by authors are presented and discussed as well. Finally, the research status and outlooks on this topic are put forward. It is our target to offer a global vision on fault-related strategies and bring out promising ideas about fault-related techniques in SRM drives.