Torque Pulsations Research Articles

Postfault Control and Harmonic Current Suppression for a Symmetrical Dual Three-Phase SPMSM Drive Under Single-Phase Open-Circuit Fault

Multiphase machines have been attracting more and more attentions in high-reliability-required applications due to their inherent fault-tolerant capability. Postfault control strategies with-standing open-circuit faults (OCFs) for several multiphase machine types, like five-phase, symmetrical six-phase (S6) and asymmetrical six-phase (A6) machines, have been widely investigated in recent literatures. However, fault-tolerant control for symmetrical dual three-phase (D3) machines have rarely been studied so far. To fill the gap, this paper addresses key issues in postfault decoupling modeling and field orient control (FOC) for the dual three-phase surface-mounted permanent magnet synchronous machine (SPMSM) with isolated neutrals under single-phase OCF. To do so, a postfault decoupling model with reduced-order transformation is established for D3 machines. Postfault current references are reconfigured with two main-stream criteria: minimum-loss (ML) and maximum-torque (MT). Furthermore, third harmonic flux linkage/back-EMF are taken into account in modeling and control, since it causes third harmonic currents and hence torque ripples under single-phase OCF. Proportional-resonant controllers are employed to decrease the third harmonic currents and torque pulsations. The validity of the postfault control strategies is proved by experiments.

Minimization of Cogging Torque in Axial Field Flux Switching Machine Using Arc Shaped Triangular Magnets

Axial flux permanent magnet machine (AFPMM) provides high torque characteristics at low speeds without any mechanical gears. AFPMMs have numerous applications in wind energy, electric cars, and direct drive elevator applications. These machines have low cost and improved power to weight ratio. However, single sided AFPM suffers from torque ripples because of its non-sinusoidal back emf, cogging torque, and rotor eccentricity. There are two major components of pulsating torque, namely torque ripples and cogging torque. In PM machine design, the cogging torque is a serious concern because it adds unwanted harmonics to the pulsating torque. Whereas the torque ripples cause noise and vibrations. In order to gain high efficiency, torque ripples should be minimum. The aim of this research is to design “Slotted axial field flux switching permanent magnet machine”. Mathematical models are used to design the machine and Finite element method (FEM) has been used to analyze the machine. In addition, Latin hypercube sampling (LHS) has been used to create the samples. Finally, Kriging Method is used for approximating the model and genetic algorithm has been applied to get the optimum machine. The results showed 61.8 % reduction of the cogging torque in the proposed machine model as compared to the conventional one. Moreover, the optimized model further provided 6.15 % reduction in the cogging torque as compared to the proposed one.

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.

Application of Concentrated Windings for High-Power Synchronous Wind Generators

The article analyzes the parameters of various configurations concentrated windings for application in high-power geared and direct drive wind generators. It is specified that the concentrated windings advantages over distributed ones can be fully realized by choosing the right values of pole pairs and the slots number. It is shown that the choice of the winding should take into account not only the highest winding factor, but also to the star of slots for the analysis of the harmonic contents of the magnetomotive force (MMF) and electromotive force (EMF), cogging torque and load torque pulsation. Windings with performance conditions Z=12+6k, 2p=Z ±2, k=0,1,2,3,…having an odd number of pole pairs are recommended for high-power wind generators.

Design and analysis of a high-performance surface inset permanent magnet motor with asymmetrical rotor

This paper presents a novel design strategy for surface inset permanent magnet (SIPM) motors to suppress torque pulsations and maintain the high output torque by integrating the magnet skewing and asymmetrical rotor configurations. The magnet skewing is implemented within one magnet pole pitch to reduce cogging torque by avoiding excessive torque degradation, and the asymmetrical rotor is designed to improve the utilization of the torque components, thus to compensate the decreased torque due to the magnet skewing. To highlight the advantages of the proposed motor, a conventional SIPM motor is adopted for performance comparison with the aid of the finite element method. As a result, the proposed SIPM motor highly reduced the cogging torque (−79.7%) and torque ripple (−54.7%) while maintaining a high average torque when compared to the conventional SIPM motor.

Development of a high-quality brushless dc electric drive systems model

When designing electric drives based on brushless DC motors with permanent magnets (BLDC), which have low level torque pulsations, the problem of modelling non-standard topological solutions appears. The known models of BLDC motors are either based on the assumptions about the symmetry of the stator pa-rameters of the electric motor and/or the ideal form of the phase back-EMF waveform, which reduce the accuracy of evaluating the effectiveness of the proposed solutions or prove unusable for modelling an operation of the electric motor with a non-standard semiconductor converter. It is necessary to develop a mathematical model of the BLDC motor-based electric drive that takes into account the structural features of the electric motor and allows for semiconductor converter configuration variability. The model is designed in the Matlab Simulink environment. The verification is carried out by comparing the modelling results with experimental data obtained previously by other researchers. The proposed method for generating phase back-EMF in the BLDC motor model provides the possibility for the user to set the EMF form templates independent for each phase. The proposed method for stator circuit simulating provides the user with access to each of the stator windings leads as well as with the possibility of asymmetric determination of each parameter of the electric motor. Upon verification, it has been shown that the difference in the control points between the simulated and experimental speed-torque curves does not exceed 3,5 %. The developed model allows analyzing the static and dynamic characteristics of operation modes of non-standard topology BLDC motor-based electric drives taking into account the stator pa-rameters asymmetry and the real phase back-EMF waveform. The specified features of the model allow exploring the operation of the designed electric drive, taking into account the BLDC motor and converter design. The model can be applied when checking atypical design decisions and when changing the set parameters of the electric drive and restrictions on working conditions and target functions to refine the control system algorithms and automate the search for optimal parameters of the motor and the semiconductor converter.

A New Structure for PMG-Based WECSs With Battery Storage Systems

This paper develops and tests the performance of a new structure for grid-connected permanent magnet generator (PMG)-based wind energy conversion systems (WECSs) that have battery storage units (BSUs). The new structure is called the split dc-bus, and it is designed to reduce the pulsations in PMG developed torque and fluctuations in the power delivered to the grid. The reduction in PMG torque pulsations is achieved by employing a 5-level ac-dc power electronic converter (PEC) as the generator-PEC, whose dc outputs are processed by a two-port active dc-link. This active dc-link charges the BSUs and supplies the discharging PEC. The reduction of fluctuations in the delivered power is achieved by discharging the BSUs at point-of-common-coupling (PCC). The generator-side PEC, dc-link, grid-side PEC, and discharging PEC, are operated by a supervisor droop controller. The split-dc bus PMG-based WECS is implemented for performance testing under different wind speeds and levels of power delivery. Test results demonstrate reductions in PMG torque pulsations, along with reductions in the power delivered to the grid. These features of the split-dc bus PMG-based WECS are found to be complimented with a minor sensitivity to the changes in wind speed and changes in the power delivered to the grid.

Performance Improvement of Sensorless Vector Controlled Induction Motor Drive for Medium Power Applications

This paper deals with sensorless vector controlled induction motor in which torque pulsations are reduced with improved input of induction motor. In proposed technique two multi winding transformers are used for generation of 18 sinusoidal signals given to rectifier unit and the rectifier output given as input to 9 level multi level inverter. In this proposed technique gating signals to the inverter switches will be provided through space vector pulse width modulation which considers speed as reference. This configuration was simulated in MATLAB/Simulink.and the simulation results are presented here with improvement in reduction of THD.

Sensorless Based Torque Ripple Reduction in Brushless DC Motor

Abstract— Brushless Direct Current Motor (BLDCM) has been commonly utilised in fields that necessitate high fidelity and specific control, owing to its simple structure, high power density, high efficiency, high starting torque, long operating life, and prolonged ranges of speed. While considering of the drive part of the motor, the most significant part is commutation control. During commutation, they generate some high torque ripples which is caused by non-ideal commutation currents in the stator windings which confines its application, exclusively at low-voltage fields. Some of the techniques for the mitigation of commutation torque ripples are reviewed here. A complete knowledge of commutation torque ripple was done by proposed phase advancing method for commutation control for diminishing torque pulsations for the complete ranges of speed. An analysis was made in order to design and implement an optimal current vector trajectory for reducing the torque pulsations for the complete speed range. This method utilises terminal voltage sensing technique and the terminal voltages are converted into d-q reference frame and hence those values are compared with specified values in order to generate the commutation signals. Initially the proposed system is simulated with Proportional Integral controller and then with Fuzzy Logic Controller. Simulation of the proposed system was done in MATLAB version 2013a and the results of comparison was made for both PI controller and fuzzy logic controller.

Theoretical and Experimental Investigation of the Supply Voltage Unbalance Effects on Squirrel Cage Induction Motors

Voltage unbalance is one of the power quality problems causing a lot of ill effects on induction motors. These are namely: Overheating, line-current unbalance, derating, torque pulsation, and inefficiency. The objective of the present work is to assess and quantify the effects of voltage unbalance on induction motors using both theory and experimentation. The analytical study is performed using the complex voltage unbalance factor model of this problem. The work deals specifically with the influence of the variations in the complex angle of the voltage unbalance factor on the stator and rotor currents, stator and rotor copper losses and total losses. The experimental investigation is carried out using an apparatus that measures currents, torque and power losses.

Torque Pulsation Reduction in Fractional-Slot Concentrated-Windings IPM Motors by Lowering Sub-Harmonics

This paper proposes a method to reduce the torque pulsation of the three-phase fractional-slot concentrated-winding (FSCW) interior permanent magnet (IPM) motor by lowering sub-harmonics. The key principle of this method is the selection of an optimized six-layer winding with different numbers of conductors. Firstly, the interaction of stator-rotor magnetomotive force (MMF) which contributes to the torque pulsation is analyzed. Additionally, the relationship between sub-harmonics (1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> sub-harmonic and 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> sub-harmonic) and torque pulsation orders is revealed. Then, different numbers of conductors are adopted in coils to eliminate the 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> sub-harmonic. Nevertheless, the 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> sub-harmonic increases in the two-layer and four-layer windings. Therefore, the optimized six-layer winding is employed to suppress the 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> sub-harmonic and ensure that the 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> sub-harmonic is zero. Besides, there are almost no other harmonics except the main harmonic and slot harmonics in the proposed IPM motor. Hence, the torque pulsation can be greatly reduced even under different current angles. Furthermore, the principle for torque pulsation reduction by lowering sub-harmonics is revealed. The effectiveness of the proposed method is verified through the comparisons with finite element analysis and experimental test.

Performance Improvement of Semicontrolled Open-Winding PMSGs Based on Virtual Zero-Crossing Detection and Segment Injection of Third-Order Harmonic Current

The semicontrolled open-winding permanent magnet synchronous generators (OW-PMSGs) with a common dc bus system have received more attention in recent years due to its advantages of reduced cost and simpler power supply. Good control performances could be achieved under the zero power factor angle (PFA). However, current clamping problem is normally presented under non-zero PFA condition, resulting in unexpected torque pulsations and voltage pulse disturbances. Meanwhile, misjudgment of voltage vectors and subsequent deteriorations in steady-state performances can be observed at current zero-crossing points. In order to improve the control performances of semicontrolled OW-PMSGs, a virtual zero-crossing detection method is proposed in this paper to effectively suppress the oscillation of voltage vectors at current zero-crossing points. In addition, a segment injection strategy of third-order harmonic current is proposed. With the proposed strategy adopted, the current clamping problem can be successfully solved, and more importantly, the torque ripple and third-order harmonic current could be simultaneously suppressed. Relevant experimental validations and performance comparisons based on a 2.3-kW semicontrolled OW-PMSG system are presented to verify the proposed control strategies.

Research on Improved Speed Identification Technology Based on MRAS

In order to accurately realize the asynchronous motor speed recognition, an improved speed recognition method based on MRAS is proposed, the motor body is used as the reference model and the stator current is used as the adjustable model. Based on MRAS, Considering the problems such as the poor output torque pulsation and high current harmonic content due to the influence of pure integral link, the low-pass filter plus compensation link is used to replace the pure integrator, the full range of stability is introduced on the basis of popov super-stability, and a new method of dead zone compensation is proposed. Finally, finally, in the simulation and experiment, the whole asynchronous motor speed sensorless MRAS is tested. Through the observation and comparison of the actual rotor speed and estimated speed curve, and the analysis of the speed error curve, the system can be accurately estimating the rotor speed and have a good static performance.

Modulation Effects in an Inverter Fed Nine-Phase Induction Motor Drive

Using electric motors with a number of phases greater than three present some advantages over conventional three-phase machines: higher reliability, reduced power per phase, increased torque density, and reduced torque pulsations. As the number of phases increases, the complexity of the modulation also increases due to a larger number of switching vectors and harmonic planes. A nine-phase inverter implies 512 switching vectors in each one of its four harmonic planes. In this article, a modulation technique for a nine-phase inverter based on a subset of the voltage vectors that yields a reduced number of on/off transitions in a switching period is shown. The resulting harmonics and their effects in multiphase machines are analyzed. Third harmonic injection is considered from the perspective of both torque improvement and dc bus voltage utilization. Simulation, finite element, and experimental results are presented to support the authors’ conclusions.

SPEED CONTROL OF SENSORLESS BRUSHLESS DC MOTOR BY COMPUTING BACK EMF FROM LINE VOLTAGE DIFFERENCE

Sensorless operation of permanent magnet brushless direct current (BLDC) motor drive controls the rotating speed with different applied voltage. No phase lagging is produced which leads to increase the efficiency and minimize the torque pulsation of the BLDC motor. Initially, motor can be started by following the v/f method then allows the sensorless mode after reaching the minimum speed of 500-1000rpm. The Sensorless BLDC motors are highly used due to higher efficiency, reliability power, acoustic noise, smaller, lighter, greater dynamic response, better speed versus torque characteristics, higher speed range and longer life. Thus the source voltage spikes and switching losses are reduced. This method can be demonstrated through MATLAB stimulation and DSP TMS 320LF2407A is used in the experimental setup to get the output.

Fuzzy Control of Spacecraft Reaction Wheel

The paper considers modification of a reaction wheel current control loop based on a fuzzy controller trained by a genetic algorithm. The control logic maintains the motor current which can be represented as a sum of two components, one of which is proportional to the input signal, and the other one corresponds to the error of control moment implementation. It is shown that the system with a fuzzy controller, which implements the variable gain on the error channel, eliminates the torque pulsation and reduces the time of transient processes while adjusting the control actions. The system operation has been simulated by means of MatLab Simulink software to confirm viability of the proposed control loop. The results of the work can be used in developing the advanced systems of spacecraft attitude control.

Simulation of Three Phase Voltage Controlled Soft Switching Start of Induction Motor Drive

In this paper a three phase voltage regulator (thyristor based) with RL load and induction motor load is simulated for fixed firing angle first. As was seen from the results obtained that the induction motor response is highly impaired with this fixed firing angle starting. The transient response as well as the steady state response is highly oscillatory in nature. Then a suitable firing scheme was developed to vary the firing angles of each thyristor in reference to the zero crossing of the respective phase voltages. The control circuit was studied for R-L load first and then the induction motor was simulated with this firing angle control scheme. The basic objective of this work is to improve the transient response of the voltage regulator fed induction motor. One basic requirement for the induction motor to have an improved transient response is that the applied voltage to the motor must gradually increase. The same was achieved with the proposed control logic. Next the fault mode (short circuit and open circuit switch fault) analysis of the induction motor was taken up. Till now not much work has been done on this fault tolerant induction motor drive. Here a 2-phase close loop control was adopted to improve response of the induction motor in fault mode. We used both the voltage control loop as well as the current control loop to do so. Unfortunately not much can be done on this fault tolerant operation as the time was very short. Till the speed and torque pulsation during a short circuited switch fault was greatly improved by adopting this two phase control strategy.

Adaptive steering‐based HDTC algorithm for PMSM

AbstractThis paper introduces sensorless hysteresis direct torque control for permanent magnet synchronous motors to provide a reduced torque pulsation profile, which leads to a smaller mechanical vibration. The suggested algorithm utilizes the principle of vehicle steering, which continuously fixes the direction of the vehicle in the track. Moreover, the algorithm efficiently employs the output of torque and the output of flux error controllers used in basic hysteresis direct torque control to select two nonzero adjacent vectors. The initial switching time for the selected vectors is determined by a function that considers the absolute magnitude of the torque error and the magnitude of the flux error in addition to the space angle position of the stator flux. To reduce the processing time in the control signal flow, a suggested structure for switching the initial time of the selected vectors is developed. The final switching time of the vectors is adaptively adjusted according to the minimum required stator voltage to drive the load and according to the stored rotor energy that arises due to the inertia of the mechanical load connected to the motor shaft. The simulation results along with the experimental results show a fast dynamic response of torque, relatively reduced torque ripples, and reduced current harmonics compared to the basic hysteresis direct torque control.

Analysis of Radial Vibration Caused by Magnetic Force and Torque Pulsation in Interior Permanent Magnet Synchronous Motors Considering Air-Gap Deformations

This paper mainly studies the influences of air-gap deformations on the electromagnetic performances and radial vibration characteristics of an interior permanent magnet synchronous motor (IPMSM) at peak rotating speed with rated power. Considering different air-gap states in the electromagnetic finite-element models of investigated IPMSMs, the effects of stator oval deformation, rotor centrifugal distortion, and both deformations on the air-gap magnetic flux field, radial and tangential magnetic force, and electromagnetic torque are analyzed and compared. Then, based on the accurate structural model of the stator system, the motor vibration characteristics are investigated with loading different electromagnetic force excitations on the stator inner face. Finally, the vibration experiments of the investigated IPMSM prototype are carried out to verify the results obtained by the simulations at a high-speed load condition. It is found that the air-gap deformations give a large increase in the particular vibration level. In order to improve the prediction accuracy of motor vibration characteristics, the air-gap deformations under all electromagnetic excitations, including magnetic force and torque pulsation, should be taken into consideration.

Modelling and comparative dynamic analysis due to demagnetization of a torque controlled permanent magnet synchronous motor drive for energy-efficient electric vehicle

In this paper modelling and comparative dynamic analysis of a field oriented controlled permanent magnet synchronous motor (PMSM) torque drive employing a hysteresis current controller and a PWM (Pulse Width Modulation) operated current controller is presented. To illustrate the proposed concept in this torque controlled drive, torque and mutual flux linkages are applied as external inputs and speed of the machine is kept fixed. Moreover the magnitude of torque angle as well as stator current reference is controlled through the proposed machine dynamics. In fact a computation based on demagnetization of direct axis current to achieve the flux weakening in this proposed drive for current compensation is also introduced. To achieve the faster computation and accuracy Euler’s integration technique is used to solve the proposed complex dynamics of the permanent magnet synchronous machine. In a hysteresis current, controllers with a large hysteresis band current ripple and the torque pulsations are prominent at higher carrier frequency of the inverter. Additionally, a relationship with the magnitude of torque pulsations, PWM carrier frequency and the hysteresis window size is also achieved through various case-studies. Furthermore, the presence of current ripple and the pulsations generate some noise as well as vibration in a typical electric propulsion system. Afterwards a PWM current controller with identical operating conditions is proposed for such reduction of torque pulsation as well as ripples in the current waveform. Finally various feasible results are presented through MATLAB simulation and necessary hardware implementation to justify the comparative assessment of the proposed controllers for dynamic performance analysis in energy-efficient electric vehicles.