Electromagnetic Torque Ripple Research Articles

Behavior of a Pentacle Connected Five-Phase IM Supplied by a Rectangular Voltage

The presented article deals with the steady-state analysis of five-phase Induction Motor (IM), which is supplied by rectangular voltage from a five-leg Voltage Source Inverter (VSI). The new proposed approach is derived from complex Fourier-series using to express inverter terminal voltages. Based on mathematically described inverter output voltages, a formula for VSI output space phasor was derived. Assuming sinusoidal motor winding distribution and on the basis of motor parameters, stator and rotor current space phasors for defined motor load were determined. Finally, the electromagnetic torque ripple waveforms for different IM operation states were investigated.

Design, Analysis, and Realization of a Hybrid-Excited Magnetic Gear During Overload

This article proposes a novel hybrid-excited magnetic gear (HEMG) with eccentric magnet structure. The novel HEMG has a higher electromagnetic torque when compared to its conventional counterpart. This study looks into the magnetic field of coaxial magnetic gear during overload, and investigates the cause of demagnetization of permanent magnets (PMs) on rotor. The PMs are attached to the inner and outer rotor; PMs of inner rotor are eccentric structure and magnetized along the radial direction, PMs of outer rotor are the radial magnetized, and the outer rotor yoke is slotted and injected with current. The proposed HEMG topology with 4 inner and 23 outer pole pairs is established; the corresponding magnetic flux density distributions, electromagnetic torque, and torque ripples are assessed and verified by finite element analysis. Finally, the HEMG is built and tested; the test results show that its transmission efficiency is up to 92.6%, and the effective length of the prototype corresponds to the torque density that is 135.15 kN·m/m3.

Guaranteeing the fault transient performance of aerospace multiphase permanent magnet motor system: An adaptive robust speed control approach

To enhance the fault transient performance of aerospace multiphase permanent magnet synchronous motor (PMSM) system, an adaptive robust speed control is proposed regardless of the phase open-circuit (OC) and short-circuit (SC) fault in this paper, which can be applied for both the redundant motor system and fault tolerant motor system. For aerospace multiphase PMSM system, besides external load disturbance and system parameter perturbation, there inevitably exists the electromagnetic torque ripple in fault transient process, which can degrade the system performance and even cause the system instability. To cope with this issue, the electromagnet torque ripple of the multiphase PMSM system in fault transient process is first analyzed. Then, by considering the electromagnet torque fluctuation caused by fault transient as a system uncertainty, a novel adaptive robust speed control scheme is proposed, while the adaptive law is constructed to emulate the total system uncertainty bound, which include the load disturbance, the parameter variation, and the electromagnetic torque fluctuation due to fault transient. The resulting control can ensure the speed control performance even in fault transient process regardless of the uncertainty, in which no prior estimation of the uncertainty bound is required. In addition, the proposed adaptive robust speed control is demonstrated by a six-phase PMSM experimental platform. The novelty of this research is to explore a novel adaptive robust speed control to strengthen the fault tolerance performance of multiphase PMSM system even in fault transient process, which requires no prior estimation of the uncertainty bound.

Design techniques for cogging torque reduction in a fractional-slot PMBLDC motor

PurposeThis paper presents the design techniques applied to a novel fractional-slot 6/4 pole permanent magnet brushless direct current (PMBLDC) motor, for cogging torque reduction. The notable feature of this motor is the simplicity of the design and low production cost. The purpose of this paper is to reduce the peak cogging torque of the motor. The focus is put on the stator topology tuning, and a new design for the stator poles is proposed. By determining the optimum stator pole arc length and the best pole shoe thickness, the cogging torque is significantly reduced. This new optimised motor design has been analysed in detail. The validation of the results is documented with respective figures and charts.Design/methodology/approachAt the beginning, the design data for the 6/4 pole PMBLDC motor with concentrated three phase windings and asymmetric stator pole arcs is presented. In the study, this motor is taken as a reference model (A0, T0). A full performance finite element analysis of the reference motor has been carried out, and the weak points in the motor design have been identified. By simple design techniques, tuning the stator pole geometry, a two-stage design optimisation for cogging torque minimisation has been performed and the solution array has been derived. The optimised model is selected and proposed (Aopt, Topt). The comparative analysis of the reference and optimised motors show the advantages of the proposed novel design and prove the methodology.FindingsThe results of the work demonstrate how simple design techniques can minimise the peak of the cogging torque profile, while maintaining the specified electromagnetic torque value. The sensitivity of the cogging torque profile because of changes of the stator pole design inside the prescribed constraints is apparent. The stator poles of the reference motor have an arc length of 85° and pole shoe thickness of 6 mm. The newly shaped stator poles have an arc length of 78.5° and pole shoe thickness 4.8 mm. The peak-cogging torque has been reduced from 0.158 Nm to a respectable value of 0.066 Nm. However, to reduce electromagnetic torque ripple and pulsations, further investigations are required.Originality/valueThe paper presents an approach to cogging torque reduction for a 6/4 PMBLDC motor. A two-step original design procedure is introduced and an optimised stator pole geometry is defined. The minimised cogging torque has been demonstrated with improved usage of the active materials. This work could serve as a good basis for further optimisation of the motor design.

Optimization method for calculating the geometrical dimensions of the tooth zone of the switched reluctance motor

Background: Switched reluctance motor (SRM) is a promising type of electromechanical energy converter. It is used in both motor and generator modes. SRM can be used not only in mechanisms with rotational motion, but also as linear motors, including maglev transport systems.
 A lot of publications are devoted to SRM design issues. In development of this direction, further improvement of the SRM design process is proposed using the optimization method of forming the geometrical dimensions of the tooth zone.
 Aim: Reducing of electromagnetic torque ripple SRM by optimizing the geometrical dimensions of the tooth zone.
 Materials and Methods: To simulate magnetic fields, the FEMM 4.2 program was used. The implementation of the optimization algorithm and the processing of the results of field calculations, was carried out in the MATLAB program. The Monte Carlo optimization methods (they rely on random sampling) was taken as the basis for developing the optimization algorithm, and its improvement was achieved using mathematical methods based on probability theory.
 Results: As a result of the optimization calculations, the tooth zone geometry was obtained, which provides a reduction in the pulsation of the SRM electromagnetic torque ripple from 122% to 40%.
 Conclusion: The studies presented in the paper indicate the effectiveness of using the optimization algorithm in designing SRM, as well as the feasibility of removing restrictions on the shape of the tooth SRM and the use of a curved tooth shape, which is determined in the process of solving the optimization problem by a determined criterion.

Impact of Single and Combined Faults Composed of Rotor Eccentricity and Stator Interturn Short Circuit on Electromagnetic Torque Ripples in Synchronous Generator

In order to comprehensively study and identify the electromagnetic torque (EMT) difference among the single static air-gap eccentricity (SAGE) fault, the single stator interturn short circuit fault (SISC), and the combined fault composed of these two, this article investigates the EMT ripple properties due to the mentioned three faults. Different from other studies, this paper considers not only the effect of the single fault types but also the impact of the single fault combinations on the EMT ripple characteristics. Detailed EMT expressions for each fault are firstly derived on the basis of the magnetic flux density (MFD) analysis. Then, finite element calculation and experimental study on a CS-5 prototype generator with two poles at 3000 rpm, which is specifically designed and manufactured ourselves, are carried out to validate the analysis result. It is found that the three faults will induce different ripple components in EMT. The combined faults have the most intensive impact sensitivity on the EMT ripples, while the single SAGE fault ranks the last in the impact effect.

Sensorless speed control of 6/4-pole switched reluctance motor with ANFIS and fuzzy-PID-based hybrid observer

This paper presents the sensorless speed control of 6/4 pole SRM drive based on hybrid observer (HO). It consists of two modes, i.e., current sliding mode observer is for high speed and flux linkage sliding mode observer is for low speed control. A nonlinear model of SRM is simulated in MATLAB/Simulink. HO is simulated from low to high speed level, and also estimated position and speed errors are optimized with ANFIS and fuzzy-PID methods. Experimental validation is taken for three set speeds, and measured results are compared with the simulated results. Overall speed and position estimated error, electromagnetic torque ripple output results are compared, and its values are tabulated at the end. This observer has the advantages of high-precision speed control without any additional hardware, and also performance has improved.

New Eighteen-sector Direct Torque Control Based on Duty Ratio Modulation

In the traditional direct torque control (DTC) of permanent magnet synchronous motor (PMSM) system, the ripple of stator flux linkage amplitude and electromagnetic torque at the steady state is large. The unbalanced effect of active voltage vectors on stator flux linkage and torque control is analysed. Based on the idea of sector subdivision, combined with the six new active voltage vectors added by the three-level inverter, a new eighteen-sector DTC method is proposed to improve the control effect of voltage vectors. For the overcompensation problem caused by the voltage vector acting in a whole sampling period in DTC, the duty ratio modulation (DRM) method is used to reduce the torque ripple. Compared with the traditional DTC, the effectiveness of the proposed new control strategy for reducing the ripple of stator flux linkage and electromagnetic torque is verified.

ANFIS-based hysteresis comparators with intelligent dual observer and speed controller of a direct torque control

This article presents the adaptive-network-based fuzzy inference system (ANFIS)-based direct torque control (DTC) for induction motor (IM). DTC is distinguished by merging a simple structure with a good dynamic behavior. Despite these cited advantages, some disadvantages are also present. For this aim, which consists of reducing the ripples in electromagnetic torque, flux and current; and to improve the IM response characteristics, the conventional hysteresis comparators of the torque, flux and the proportional integral (PI) speed controller are replaced by others based on ANFIS technique. Furthermore, an intelligent dual observer is implemented to achieve sensorless control; merging a Luenberger observer (LO) based on ANFIS to insure the adaptation mechanism in order to estimate the rotor speed, and a Kalman filter (KF) to insure the flux components estimation. The proposed sensorless ANFIS-DTC shows a robust performance; reduced ripples, decreased overshoots, short time of rising and settling, and high resistance to perturbations.

ANFIS-based hysteresis comparators with intelligent dual observer and speed controller of a direct torque control

This article presents the adaptive-network-based fuzzy inference system (ANFIS)-based direct torque control (DTC) for induction motor (IM). DTC is distinguished by merging a simple structure with a good dynamic behavior. Despite these cited advantages, some disadvantages are also present. For this aim, which consists of reducing the ripples in electromagnetic torque, flux and current; and to improve the IM response characteristics, the conventional hysteresis comparators of the torque, flux and the proportional integral (PI) speed controller are replaced by others based on ANFIS technique. Furthermore, an intelligent dual observer is implemented to achieve sensorless control; merging a Luenberger observer (LO) based on ANFIS to insure the adaptation mechanism in order to estimate the rotor speed, and a Kalman filter (KF) to insure the flux components estimation. The proposed sensorless ANFIS-DTC shows a robust performance; reduced ripples, decreased overshoots, short time of rising and settling, and high resistance to perturbations.

Research on modeling and fault diagnosis of inter-turn short fault of permanent magnet synchronous motor

The stator winding inter-turn short fault of permanent magnet synchronous motor (PMSM) is a common motor fault with high probability. If this fault is not detected and handled in time, small initial fault will rapidly develop into other faults such as grounding short, inter-phase short, winding short et al., and even the motor damage. In order to diagnose the inter-turn short fault of PMSM, this paper firstly builds the model of the inter-turn short fault of PMSM, and then proposes a fast and simple fault diagnosis method for extracting the features of the inter-turn short fault under noise. For the first time, by introducing the full-short-circuit resistance Rf that relates with the fault severity factor δ and by estimating the inductance of inter-turn short fault motor on-line according to the three principles of the inductance calculation, which is used in the inter-turn short fault of transformer winding, the inter-turn short analysis model of PMSM is deduced. The model can be used to simulate the performance not only the health of PMSM but also the fault of inter-turn short fault of PMSM in one phase winding. This paper analyses the transient and steady state performance of 3-phase unbalanced current, speed and electromagnetic torque ripple and the relationship between full-short-circuit resistance and short current under fault condition. Finally, a fast and simple on-line fault diagnosis method of PMSM with inter-turn short fault is proposed based on phase sensitive detection (PSD) algorithm. The method uses the fundamental and third harmonic features of inter-turn short fault current. The simulation results show that the model can be well suited for the simulation of PMSM with inter-turn short fault, and the method can effectively extract the features and diagnose the fault.

Dual-Vector Model Predictive Current Control of Permanent Magnet Synchronous Motor Drives With the Segment Golden Search Method

Dual vector model predictive current control (DVMPCC) has been receiving plenty of concern due to its excellent static and dynamic performance. However, the application time of the selected voltage vector may be a wrong value because the calculation of duty cycle for each voltage vector is independent of the cost function. Here, to overcome the drawbacks of the current calculation methods, the paper introduces a novel approach to calculate the duty cycles for the two voltage vectors in one sampling time by combining the duty cycle calculation into the cost function. In this algorithm, the segment golden search method is used to find the optimal duty cycles for any pair of two voltage vectors. The cost function compares the available pairs of voltage vectors based on the obtained optimal duty cycles of each pair of voltage vectors to select the optimal pair of voltage vectors and duty cycles. In addition, to reduce the complexity of the algorithm, the redundant pairs of voltage vectors are eliminated and the available pairs of the voltage vectors is limit to five. Furthermore, a novel switching pattern is introduced to reduce the average switching frequency. When the inverter adopts the proposed MPCC, the optimal switching time and optimal voltage vector pair are both obtained at the same time, and the result duty cycle is always a reasonable number within the sampling interval. Comparative studies between the proposed method and a recently introduced duty cycle-based MPCC are carried out. The performance of a permanent magnet synchronous motor drive under the proposed MPCC confirms superiority in terms of average switching frequency, better quality currents, and electromagnetic torque ripple.

Utilization of an ANFIS-STSM Algorithm to Minimize Total Harmonic Distortion

Recently applications of second order super-twisting sliding mode (STSM) algorithm become more convenient in control of AC machines. The conventional technique, the capability of creating a high value of current or voltage. On the other hand, the STSMC algorithm popular in more applications. There are several types of intelligent techniques such as neural networks (NNs), adaptive network-based fuzzy inference system (ANFIS) and fuzzy logic controller (FLC). The ANFIS controller is very popular than other controllers because its control is very simple in comparison with others. The new technique of STSMC is utilized to reduce the harmonic distortion in direct torque control (DTC). Cat ANFIS-STSM algorithm is introduced as a new STSM algorithm to minimize harmonic distortion and electromagnetic torque ripples. The simulation results have been carried out using Matlab/Simulink software.

Optimal Selection of Rotor Bar Number for Minimizing Torque and Current Pulsations Due to Rotor Slot Harmonics in Three-Phase Cage Induction Motors

The paper develops a method to choose the number of rotor bars in order to eliminate rotor slot harmonics in stator current spectrum and pulsation torques that are their consequence. Mains-fed, three-phase cage induction motors with the most common number of pole pairs and number of stator slots, that result in integer slot winding, are analyzed. The analysis is based on the recently derived general rule for optimal selection of rotor bars, valid for symmetrical multiphase machine with prime number of phases and integer slot stator winding. As a tool for validation of analytically predicted results, parameterized winding function (PWF) model is used. Electromagnetic torque ripple factor is used as a measure of goodness of the number of rotor bar selection. The practical motivation of the study is an attempt to supersede the many existing rules for rotor bar number selection that, depending on the source, may be different, and provide a unified general approach to the problem. One of the main findings derived in the paper is ascertainment that increasing the number of pole pairs increases the degree of freedom in choosing the proper number of rotor bars. The same applies when the number of motor phases increases.

Study and design of dual stator permanent magnet machine with spoke-type configurations using phase-group concentrated-coil windings

In this paper, a novel dual-stator permanent magnet machine (DsPmSynM) with low cost and high torque density is designed. The winding part of the DsPmSynM adopts phase-group concentrated-coil windings, and the permanent magnets are arranged by spoke-type. Firstly, the winding structure reduces the amount of copper at the end of the winding. Secondly, the electromagnetic torque ripple of DsPmSynM is suppressed by reducing the cogging torque. Furthermore, the dynamic performance of DsPmSynM is studied. Finally, the experimental results are compared with the simulation results.

Impact of Number of Phases on Electromagnetic Torque Characteristics of Transverse Flux Permanent Magnet Machines

This paper presents an investigation on the influences of number of phases of Transverse Flux Permanent Magnet (TFPM) machines on the characteristics of developed electromagnetic torque. Electromagnetic torque is expressed in terms of the Fourier series of phase currents and internal voltages. After some algebraic and trigonometric calculations, a general equation is obtained that establishes a relationship between the electromagnetic torque ripples, number of phases and harmonic contents of both internal voltages and phase currents. This result is significant when it is required to design a few specific number of identical single-phase TFPM machines which finally they will be assembled such that to build a multi-phase machine with a minimum torque ripple. The design parameters of a case study Claw Pole TFPM machine are introduced with some details and a few FE based simulation results are given as the validations of the analytical approach of the present paper. The simulation results show clearly the impact of each harmonic of the internal voltages and phase currents on the torque ripple for various numbers of phases leading the designer to find out which number of single-phase machine combinations is the optimum one regarding the torque ripple.

Towards the optimal ‘slot combination’ for steady-state torque ripple minimization: an eight-pole cage rotor induction motor case study

This paper analyses the impact of the number of stator slots to rotor bars, i.e. the slot combination, in a cage rotor induction motor (IM) on its electromagnetic torque ripple during steady-state conditions. The study is focused on a conventional low voltage, eight-pole, three-phase, mains-fed IM design. To adequately evaluate the torque ripple magnitude, a ‘torque ripple factor’ is introduced and numerically calculated. To this end, IM behaviour in two common eight-pole stator slot number geometries is examined using numerical models, where, for each examined stator geometry, operation with a range of different rotor bar numbers used in practical IM designs is evaluated. For the sake of completeness and cross-validation, two different modelling approaches are used: a recently reported low-computational intensity winding function-based model and a commercial finite element analysis electromagnetic modelling software package. The paper findings deliver a detailed insight into the impact of rotor bar number, whether skewed or otherwise, on the motor steady-state torque ripple level. The presented results are indicative of the fact that the number of rotor bars only, and not the slot combination, is the dominant factor that influences the electromagnetic torque ripple in IMs with skewed rotor bars.

Optimal DTC Control Strategy of DFIG Using Variable Gain PI and Hysteresis Controllers Adjusted by PSO Algorithm

This paper presents an optimal Direct Torque Control (DTC) strategy for Doubly Fed Induction Generator based wind turbine. The proposed strategy is considered based on Particle Swarm Optimization (PSO) Algorithm. The PSO is found to be robust and fast in solving nonlinear problems. Motivation for application of PSO approach is to overcome the limitation of the conventional controllers design, which cannot guarantee satisfactory control performance when designed by trial and error. In this work PSO algorithm was used to adjust the hysteresis torque and flux comparators bandwidths and to tune the parameters of Variable Gain PI (VGPI) controller designed for Maximum Power Point Tracking (MPPT) speed control of wind turbine to ensure high performance torque control. The optimal control strategy is considered in detail and it is shown that the use of the optimized controllers reduces rotor flux and electromagnetic torque ripples and improves the system dynamic performances. The effectiveness of the proposed direct torque control based on PSO algorithm (optimal DTC) method is illustrated through simulations on 1.5 MW DFIG based wind turbine. Simulation results illustrate the improved performances of optimal DTC compared with the conventional DTC.

Deadbeat Direct Torque and Flux Control for Permanent Magnet Synchronous Motor Based on Stator Flux Oriented

Direct torque control (DTC) has become a widely acceptable alternative to field-oriented control in permanent magnet synchronous motor (PMSM) drives. Deadbeat direct torque and flux control (DB-DTFC) is a significant improvement over the classical DTC. However, there are some aspects that can be improved, such as insufficiently small electromagnetic torque ripple, unsmooth dynamic response, heavy computation burden, and relatively weak robustness to motor parameters variation. To improve the operation performance, an advanced DB-DTFC strategy is proposed in this article. First, the algorithm model based on stator flux oriented coordinate system is deduced. On this basis, the basic principle of proposed DB-DTFC is presented. Second, a novel graphical analysis method is proposed to help illustrate the proposed strategy. Third, a general solution method is proposed to solve the reference stator voltage, which is a key variable for the DB-DTFC. Finally, the stability of system is analyzed. Theoretical and experimental comparisons between the proposed DB-DTFC and the conventional DB-DTFC are done. The results show that the performance in the aspects of electromagnetic torque and stator current ripples reduction, dynamic response, computation burden, and robustness to motor parameters variation are all improved in the proposed DB-DTFC.

Adaptive-Gain Second-Order Sliding Mode Direct Power Control for Wind-Turbine-Driven DFIG under Balanced and Unbalanced Grid Voltage

In a wind turbine system, a doubly-fed induction generator (DFIG), with nonlinear and high-dimensional dynamics, is generally subjected to unbalanced grid voltage and unknown uncertainty. This paper proposes a novel adaptive-gain second-order sliding mode direct power control (AGSOSM-DPC) strategy for a wind-turbine-driven DFIG, valid for both balanced and unbalanced grid voltage. The AGSOSM-DPC control scheme is presented in detail to restrain rotor voltage chattering and deal with the scenario of unknown uncertainty upper bound. Stator current harmonics and electromagnetic torque ripples can be simultaneously restrained without phase-locked loop (PLL) and phase sequence decomposition using new active power expression. Adaptive control gains are deduced based on the Lyapunov stability method. Comparative simulations under three DPC schemes are executed on a 2-MW DFIG under both balanced and unbalanced grid voltage. The proposed strategy achieved active and reactive power regulation under a two-phase stationary reference frame for both balanced and unbalanced grid voltage. An uncertainty upper bound is not needed in advance, and the sliding mode control chattering is greatly restrained. The simulation results verify the effectiveness, robustness, and superiority of the AGSOSM-DPC strategy.