Electromagnetic Torque Pulsations Research Articles

Minimization of electromagnetic torque pulsations in a five-phase asynchronous electric drive

Minimization of electromagnetic torque pulsations in a five-phase asynchronous electric drive

Analysis of Wind Driven Doubly Fed Induction Generator under Transient Conditions

The Doubly-fed induction generator is one of the most effective and frequently used wind power generation systems in the wind power industry. It offers several enticing benefits, including consistent output voltage, low cost, independent control of active and reactive power, and improved power quality. Despite any of the aforementioned advantages of DFIGs, it is precisely impacted by grid interruption. Any sudden appearance of a fault, such as symmetrical or asymmetrical faults, can cause a reduction in stator voltage, oscillations in stator and rotor currents, DC-link overvoltage, and electromagnetic torque pulsations. Such a phenomenon can considerably affect the performance of the DFIG under a transient state if an appropriate protection system is not considered. Thus, in this thesis work, the crowbar protection system is employed for the enhancement of the FRT capability of the wind turbine. The performance of the machine with the existing capacitor bank and crowbar protection is analyzed and compared. Moreover, the MATLAB/Simulink 2015a software is used for modeling and simulation and all system parameters are obtained from ADAMA-II Wind Farm.

Characteristic Analysis and Experimental Verification of Electromagnetic and Vibration/Noise Aspects of Fractional-Slot Concentrated Winding IPMSMs of e-Bike

In this study, we performed the electromagnetic and mechanical characteristic analyses of an 8-pole 12-slot interior permanent magnet synchronous motor (IPMSM). Permanent magnet synchronous motors are classified into surface permanent magnet synchronous motor and interior permanent magnet synchronous motors according to the type of rotor. The IPM type is advantageous for high-speed operation because of the structure where the permanent magnet is embedded inside the rotor, and it has the advantage of having a high output density by generating not only the magnetic torque of the permanent magnet, but also the reluctance torque. However, such a motor has more vibration/noise sources than other types, owing to changes in reluctance. The sources of motor noise/vibration can be broadly classified into electromagnetic, mechanical, and aerodynamic sources. Electromagnetic noise sources are classified into electromagnetic excitation sources, torque pulsations, and unbalanced magnetic forces (UMFs). Vibration and noise cause machine malfunctions and affect the entire system. Therefore, it is important to analyze the electromagnetic vibration source. In this study, the electromagnetic characteristics of an IPMSM were analyzed through the finite element method to derive the UMF. Vibration and noise analyses were performed by electromagnetic–mechanical coupling analysis, and vibration and noise characteristics based on electromagnetic noise sources were analyzed.

Бесконтактные двигатели постоянного тока с трехсекционной обмоткой и двумя индукторами

Two brushless DC motors (BLDC) with a three-section armature windiщ and two cylindrical inductors-magnets are considered. One motor has an ordinary drum-type armature windiщ, and numbers of radial poles in its two inductors differ from each other by a factor of three. The other motor has a toroidal armature winding, and the numbers of radial poles in its two inductors differ from each other by a factor of two. An expression for the distribution of the resulting armature winding magnetic induction over the air gap circumference is given. The optimal relationships between the parameters of two inductors are determined. Expressions are obtained for the ratios of the electromagnetic torques of the considered motors and for the known BLDC motor with a conventional three-section armature winding and a composite inductor consisting of an inner magnetically soft bushing and external poles formed by magnets. The compared machines have the same number of power transistors and are made with the same dimensions of their electromechanical parts, and their armature windings consume the same power from the power source. It has been found that the electromagnetic torque in the considered motor with the ordinary armature winding is approximately a factor of 1.37 greater than in the known motor with a three-section armature winding, whereas in the motor with a toroidal armature winding it is smaller by about a factor of 1.1, i.e., insignificantly. However, the electromagnetic torque pulsation in the motor with a toroidal winding and three power transistors is approximately 3%, whereas in the known motor with three and six power transistors its values are approximately equal to 8 and 4.5%, respectively. The considered motors with simpler cylindrical inductors can compete with the known BLDC motors.

Бесконтактные двигатели постоянного тока с дискретным управлением и модуляцией тока по положению ротора

The article considers contactless DC motors with discrete control of the current in the three- and two-section armature winding using the rotor position feedback signal by means of a converter containing six and four power transistors, respectively. The motors are additionally equipped with a pulse width modulator (PWM) and a rectifier of the rotor position sensor signals. In the PWM, the periodic line-to-line voltage is compared with the rectified sensor signals to produce periodic rectangular pulses with the duration depending on the rotor position, which close the power transistors. Since the motor torque without PWM and the rectified sensor signals vary in a sine wave manner with turning the rotor (i.e., in the same way), a lower motor torque pulsation is obtained. The sensor and PWM designs and operation are described, and the requirements for their output voltages are formulated. Expressions for the contactless DC motor electromagnetic torque and its limit values are obtained. It is established that the electromagnetic torque pulsation levels in the contactless DC motors with three- and two-section armature windings do not exceed 1 and 1.5%, respectively, which is significantly lower than the pulsation level in the well-known contactless motors (4%).

A Reduced Switch Five-Level VSI for High-Performance Vector Controlled PMSM Drive

This work presents the strategy for vector control of permanent magnet synchronous motor (PMSM) drive fed with a three-phase multi-level voltage source inverter for high performance. In the present work, the traditional 2-level inverter is replaced with a novel reduced switch 5-level inverter, and comparative analysis is done. The implementation of the five-level inverter improves the torque, stator current, and mechanical dynamics of the drive. Here PWM technique is employed to generate the gate pulses for switching devices in a planned sequence to obtain five-level output voltage. The 12 operating modes are defined for reduced switch 5-level inverter that produces voltages as 0, ±2Vdc/3, ±Vdc, ±4Vdc/3 with reduced total harmonics distortion (THD). The close-loop vector control of PMSM with developed five-level inverter is implemented to improve the performance of drive in terms of rise time, settling time, stator current harmonics. The overall system is developed in MATLAB/Simulink and investigations are done in different input command and loading conditions. An extensive simulation study and analysis of results reveal the potential of the present work. This work mainly focuses on the reduction of motor electromagnetic torque pulsations along with improved speed response.

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.

Improved Voltage Harmonics Compensation Strategy for a Stand-Alone DFIG Operating under Unbalanced and Nonlinear Load Conditions

The study presents an improved control and operation for a stand-alone Doubly-Fed Induction Generator (DFIG) energy system under unbalanced and nonlinear load conditions. This type of loads results in unbalance and distorted stator voltage and current at the Point of Common Coupling (PCC), with subsequent power quality degradation and electromagnetic torque pulsations of DFIG. A new and simple control strategy based Proportional-Resonant Controllers (PRCs) in the stationary reference frame is applied in the Load-Side Converter (LSC) for fully compensate the unbalance and harmonic distortion in the PCC and avoid the torque pulsations of DFIG. As a result, symmetrical and sinusoidal AC voltage is applied to the PCC, which indicates that the Rotor-Side Converter (RSC) can be still controlled with the traditional vector control strategy, to adjust the generator torque and to balance active power. This strategy is conceptually simple, it does not require for rotating coordinate transformation and the sequence decomposition process, in addition no current sensors need to be installed at load or stator side, so that the number of current sensors employed is reduced. Simulation results using MatLab/Simulink are given and show the effectiveness and validity of the proposed control scheme to eliminate the harmonics in the PCC and torque pulsations of DFIG.

Multi-Resonant-Based Sliding Mode Control of DFIG-Based Wind System under Unbalanced and Harmonic Network Conditions

In general, the integral sliding mode control (ISMC) with an integral sliding surface would lead to tracking errors under unbalanced and harmonic grid voltage conditions. In order to eliminate tracking errors under these conditions, multi-resonant items are added to the conventional integral sliding surface in the proposed strategy, which can be called multi-resonant-based sliding mode control (MRSMC). A comparison of tracking precision on the ISMC and MRSMC is analyzed. In order to regulate the system powers directly, the errors of instantaneous active and reactive powers are selected as the state variables. Finally, the output current harmonics and a majority of the doubly-fed induction generator’s (DFIG) electromagnetic torque pulsations can be removed under unbalanced and harmonic grid voltage conditions. Simulation and experimental results are presented to verify the correctness and effectiveness of the proposed strategy.

Modeling and simulation of charging and braking regimes of AC/AC powertrain of HEV vehicle

The paper deals with modeling and simulation of chosen operational modes of HEV vehicle with direct AC/AC transfer and five-phase IM traction motors. Such configuration yields smaller voltage drops com-pared with the serial AC/DC/AC converter and five-phase machines offer some inherent advantages over their three-phase counterparts. The advantages include reduced electromagnetic torque pulsation and also noise characteristics of the five-phase drives are better when compared with the three-phase ones. Charging and braking regimes were chosen as possible operational modes for modeling and analyses. The result of the simulation. carried out with using of Matlab/Simulink are given in the paper.

Исследование пульсаций электромагнитного момента синхронных машин с постоянными магнитами с целым и дробным значениями q

Исследование пульсаций электромагнитного момента синхронных машин с постоянными магнитами с целым и дробным значениями q

Эксцентриситет ротора синхронных машин с постоянными магнитами

The article presents the results from studying the eccentricity in permanent magnet synchronous machines having different numbers of slots per pole and phase (q). The advantages and drawbacks of using winding arrangements with different values of qareshown. An expression describing the physical processes of interaction between spatial induction harmonic components in the air gap under eccentricity conditionsisanalyticallyobtained. The electromagnetic torque pulsations arising with different kinds of eccentricity—static, dynamic, and mixed—are determined with the aid of field models and using the Maxwell magnetic tension forces. Differences between the obtained characteristics are pointed out. Aprocedurefor calculating the electromagnetic torque pulsations in the no-load and on-load operation modes using the Femm finite-element computer program is presented. Recommendations on selecting the qvalue for reducing the negative effect of different eccentricity kinds aregiven.

Using of four-switch three-phase converter in the structure DPC of DFIG under unbalanced grid voltage condition

This paper proposes a novel direct power control (DPC) strategy for doubly fed induction generator (DFIG) drives fed by a four-switch three-phase converters (FSTPCs). In this method, two FSTPCs in rotor and grid side have been used instead of two six-switch three-phase converters (SSTPC). Reduction in the number of active switches will lead to improvement in reliability, reduction in costs and less conduction losses. The FSTPC will generate four unbalanced voltage vectors. A strategy used in order to balance these four voltage vectors. The introduced strategy is based on the emulation of the operation of the conventional SSTPC. In this method, four unbalanced voltage vectors that were generated by FSTPC somehow combined together which produced six balanced voltage vectors of the SSTPC. Then, the new switching table is written for new DPC method for DFIG. Also, during the unbalanced grid voltage condition, three selectable targets are provided for compensating active and reactive power, electromagnetic torque and stator current. These targets are added to power references and are caused decreasing the active and reactive power ripples, mitigation electromagnetic torque pulsations and sinusoidal and balanced stator currents. In the end, an economic comparison between two FSTPC and SSTPC is done. Also, the novel DPC method, i.e., use of FSTPC in rotor and grid side, is compared with prior DPC method, i.e., use of SSTPC in rotor and grid side, and its effectiveness is confirmed by simulation results from a 1-MW DFIG system.

Comparison of Starting Current Characteristics for Three-Phase Induction Motor Due to Phase-control Soft Starter and Asynchronous PWM AC Chopper

This paper presents the comparison of starting current characteristics of a three-phase induction motor fed by two types of soft starters. The first soft starter under investigation is a conventional AC voltage controller on the basis of a phase-control technique. The other is the proposed asynchronous PWM AC chopper which is developed from the conventional synchronous PWM AC chopper. In this paper, the proposed asynchronous PWM AC chopper control scheme is developed by generating only two asynchronous PWM signals for a three-phase main power circuit (6 switching devices) from a single voltage control signal which is compared with a single sawtooth carrier signal. By this approach, the PWM signals are independent and easy to implement since the PWM signals do not need to be synchronized with a three-phase voltage source. Details of both soft starters are discussed. The experimental and simulation results of the starting currents are shown. It is found that the asynchronous PWM AC chopper efficiently works as a suitable soft starter for the three-phase induction motor due to that the starting currents are reduced and are sinusoidal with less harmonic contents, when being compared with the starting current waveforms using the conventional phase-control starting technique. Also the proposed soft starter offers low starting electromagnetic torque pulsation.

Vector control of unbalanced 3-phase IM using forward and backward components

In some industries, continuous operation of 3-phase induction motors (IMs) even under faults until the scheduled maintenance time is essential. Conventional control techniques such as field-oriented control (FOC) cannot be used to control faulty IMs since this will result in significant oscillations in the speed and torque. Consequently, a new control approach must be developed for improving IM performance during fault conditions. This paper presents a method for vector control of 3-phase IMs under open-phase faults. The main advantage of this control scheme is its ability to handle not only one phase but also two phases of open-phase fault conditions. When applying this control technique to a faulty machine, only minor changes to the parameters used in the equations are needed and the conventional FOC algorithm used for healthy 3-phase IMs can still be used. In this paper, simulation and experimental results are presented to study the effectiveness of the proposed technique to control both healthy and faulty 3-phase IMs. The results show that the proposed technique reduces electromagnetic torque pulsations during open-phase fault conditions.

Комбинированная обмотка «славянка»

The magnetomotive force (MMF) of a usiual symmetrical three-phase winding contains higher harmonic components of the orders v= 6k ±1, k= 1,2,3,... The MMF of the combined winding does not contain harmonic components with the odd numbers k= 2n- 1, n= 1,2,3,..., which make half of the above-mentioned harmonic components. This MMF contains the remaining higher harmonics of the same orders v= 6k ±1, but only with the even numbers k= 2n, n= 1,2,3,.... The amplitudes of these harmonic components are almost identical with the amplitudes of similar harmonic components generated by a conventional winding that produces the combined one. Therefore, the MMF curve of the combined winding is closer to a sinusoidal waveform as compared with the MMF waveform generated by the classic winding. Electrical machines fitted with a combined winding will have a lower level of additional losses in the active materials of rotor and stator. Switched machines fitted with a combined stator winding will produce lower levels of vibration and noise due to more than half as high amplitude of electromagnetic torque pulsations, which also have twice as high frequency.

Modularized Control Strategy and Performance Analysis of DFIG System Under Unbalanced and Harmonic Grid Voltage

The paper presents a modularized control strategy of doubly fed induction generator (DFIG) system, including the grid-side converter (GSC) and rotor-side converter (RSC), under unbalanced and harmonic grid voltage. The sequence decomposition process and complicated control reference calculation can be avoided in the proposed control strategy. From the perspective of power grid friendly operation, the control targets of DFIG system in this paper are chosen as: 1) smooth active and reactive power injected into the power grid; 2) balanced and sinusoidal current injected into the power grid. The RSC and GSC can work as two independent modules and the communication between RSC and GSC can be removed. Furthermore, the third harmonic current component, dc-link voltage fluctuation, and electromagnetic torque pulsation under the different control targets are theoretically analyzed. Finally, the availability of the proposed modularized control strategy of DFIG system under unbalanced and distorted grid voltage is verified by experiment results.

IJIREEICE - Electrical, Electronics, Instrumentation and Control

3 Abstract: This paper presents greater value to control a doubly fed induction generator (DFIG) - based wind power complete persons living time system with series grid side changer (SGSC) under unbalanced network conditions. The behaviours of the DFIG system with SGSC during voltage unbalance are described by injecting a series control voltage Produced from the SGSC. To balance the stator voltage against effects of voltage unbalance upon the DFIG such as stator and rotor current unbalances electromagnetic torque and power pulsations can be removed , and then the Conventional vector control strategy for the rotor-side converter remains in full force under unbalanced conditions. Mean while, three control targets for the parallel grid-side converter (PGSC) are identified, including eliminating the oscillations in the total active power or reactive power, or eliminating negative-sequence current injected to the grid. Furthermore, a precise current reference Generation strategy for the PGSC has been proposed for The PGSC to further improve the operation performance of the whole system. The simulation results of a mw DFIG based wind turbine 12with SGSC and testing results on a laboratory13scale based on experience trick prices under small unchanging state grid voltage unbalance.

Fault-Tolerant Control of Brushless DC Motors Under Static Rotor Eccentricity

In some industries, continuous operation of motors even under faults until scheduled maintenance time is necessary. However, conventional control methods are inefficient for eccentricity faults. In a conventional brushless direct current (BLDC) motor control method, stator current commands are similar in shape and delayed by corresponding phase differences in each phase. However, if the actual shape of the back electromotive force (EMF) waveform of an eccentric motor and phase inductance variations due to eccentricity are not considered, undesirable torque ripples may occur. Hence, a new control strategy must be developed for improving motor performance. In this paper, a method for controlling BLDC motors under static rotor eccentricity is proposed. The proposed control method is based on online estimation of phase inductances and back-EMFs of the BLDC motor under eccentricity faults. Therefore, in contrast to conventional methods, stator currents are injected considering the estimated back-EMFs of the conducting phases. The experimental results verify that the proposed method reduces electromagnetic torque pulsations under static rotor eccentricity.

Rotor eccentricity fault compensation by voltage control of brushless DC motor

Rotor eccentricity is one of the common failures that can happen to a motor. In recent years, considerable amount of researches for rotor eccentricity fault diagnosis have been presented. However, no attention is given to the case of ‘eccentricity fault tolerant control’. The necessity of ‘eccentricity fault tolerant control’ is the importance of motor continuous operation during fault in sensitive industries with the best possible performance. Applying conventional control methods during eccentricity fault is not efficient. Since, these methods do not consider eccentricity fault effects such as distortion in flux linkage distribution and motor back-electro-motive force (EMF) waveform, as well as phase inductances changes which may lead to undesirable torque ripples. Hence, a new control strategy for improving motor performance is advantageous. In this study, a control method for brushless direct current (BLDC) motor in presence of static rotor eccentricity is proposed. On-line estimation of phase inductances and phase-to-phase flux linkages during eccentricity is the basis of the proposed control method. In the proposed strategy, the controller adjusts motor terminal voltages considering changes in motor specifications because of eccentricity, without using phase current control loop. Experimental results verify performance of the proposed method in reducing electromagnetic torque pulsations during fault.