back-EMF Waveform Research Articles

Influence of inner/outer stator pole ratio and relative position on electromagnetic performance of partitioned stator switched flux permanent magnet machines

Based on the 6-pole outer stator (armature winding-stator), the influence of inner (permanent magnet-stator)/outer stator pole ratio n (n=NIS/NOS), stator relative positions and rotor pole number combinations on electromagnetic performance of partitioned stator switched flux permanent magnet (PM) machines (PS-SFPMMs) is investigated in this paper. Since the armature windings and PMs are located in two separated stators and PMs are stationary, PS-SFPMMs have high fault tolerance capabilities. To maximize the torque performance, the PM of inner stator pole should be aligned with outer stator pole when n is odd while the iron rib of inner stator pole should be aligned with outer stator pole when n is even. No matter what n is selected, the rotor pole number NR can be any integers except the phase number and its multiples. The analysis results indicate that the optimal NR is closed to (N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IS</sub> +N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OS</sub> )/2 and it is odd when n is odd while it is even when n is even. Meanwhile, symmetrical phase back-EMF waveform will be obtained when the ratio of Min(N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OS</sub> , N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IS</sub> ) to the greatest common divisor of Min(NOS, NIS) and NR is even. Based on the optimal rotor pole numbers for 6-pole outer stator with different n and corresponding optimal relative position together with same rated copper loss, the average torque is improved by 18.4%, 25.1% and 25.7% respectively in PS-SFPMMs with n equal to 2, 3 and 4 when compared with PS-SFPMM with n equal to 1. The analyses are validated by experiment results of the prototype machine.

On-load Back-EMF Optimization Based on the Back-EMF MST Method and Parametric Optimization

This paper proposes an optimal design for a surface mounted permanent magnet synchronous machine (SM-PMSM) based on parametric optimization process to reduce the on-load Back-EMF distortions caused by an increase in the electromagnetic load and in the saturation. Unlike conventional methods described in the literature, the optimization approach proposed here accounts for the saturation effects, air gap flux density distribution and the evaluation of the on-load Back-EMF by means of finite element analysis, allied to the most recent on-load Back-EMF evaluation method, known as the Back-EMF MST (Maxwell stress tensor) method. Furthermore, the optimization process is performed considering either the machine's physical symmetry (based on pole numbers) and its nonevident symmetry (based on saturation effects and on the relevance of each tooth in the Back-EMF waveform), which is identified using the Back-EMF MST method. The proposed optimization process also analyzes different sets of variables based on symmetric and asymmetric tooth dimensions. The result is a machine with a reasonably improved design, higher average torque, lower torque ripple and smaller volume. In addition, the on-load Back-EMF is almost identical to the no-load one. Hence, the on-load cogging torque is almost identical to the no-load cogging torque.

Design of Variable Magnetization Pattern Machines for Dynamic Changes in the Back EMF Waveform

Variable magnetization pattern permanent magnet synchronous machines (VMP-PMSMs) capable of dynamic changes in the magnetization spatial distribution are discussed in this paper. VMP-PMSMs are able to change the harmonic components in the air gap magnetic flux density due to the magnet by intentional demagnetization; hence, they can effectively manipulate the torque ripples and losses according to the required operating points. The objective of this paper is to provide a procedure to design VMP-PMSMs that can have both the sinusoidal and the trapezoidal back EMF waveforms by switching magnetization pattern. The performance of the designed VMP-PMSM following the reported procedure is confirmed through experiments as well as finite element analysis (FEA) simulations in terms of the back EMF shaping, torque ripple reduction, and loss reduction. Loss analysis of VMP-PMSMs is also given as contrasting with variable flux permanent magnet machines (VF-PMSMs), showing that VMP-PMSMs can reduce more losses than VF-PMSMs with the same torque density.

Optimization Design of a New Type of Interior Permanent Magnet Generator for Electric Vehicle Range Extender

Aiming at the disadvantages of large leakage flux and low magnetic flux density of radial magnetic circuit and tangential magnetic circuit, a new type of permanent magnet (PM) rotor with parallel tangential and radial magnetic circuits is proposed. Based on Ohm’s law and Kirchhoff’s law of magnetic circuits, equivalent magnetic circuits for rotor poles are developed. The structure parameters of the generator are preliminarily determined. At the same time, by means of the Taguchi method and employing finite element analysis, the rotor poles of generator are optimized to improve air gap magnetic density, the cogging torque, and the distortion of back-EMF waveform. Finally, the validity of proposed design methods is validated by the analytical and experimental results.

Rotor design for line start AF‐PMSM

This study presents design and performance analyses for a new line start axial flux permanent magnet synchronous motors (AF-PMSMs). The innovative part of this study is that AF-PMSM can start directly from the line and operate with high efficiency and power factor after synchronisation. Prototype manufacturing was carried out after completing the analytical and electromagnetic designs for the targeted motor. The synchronisation capacity, power capacity, power–speed characteristic, power-efficiency relationship along with the total harmonic distortion and back-emf waveform of the induced voltage have been examined for the prototype motor. Simulation studies have been verified experimentally. The results obtained were compared with an induction motor with the same power. It was observed as a result of the work carried out and a line start AF-PMSM is obtained that is 4–10% more efficient in comparison with an induction motor having the same power.

Development and Analysis of a Novel Transverse Flux Permanent Magnet Linear Motor With the Concentrated Flux Mover

The magnetic field computation and performance characteristics analysis for a novel transverse flux permanent-magnet linear motor with the concentrated flux mover have been discussed. The following issues have been emphasized as: the construction of the transverse flux linear motor, magnetic flux distribution, winding flux linkage, and thrust force characteristic. The force ripple coefficient is theoretically derived from the mechanism of production of a force ripple, i.e., improving the waveform of back-EMF. The influence of structure parameters on the thrust force and cogging force characteristics is analyzed in detail. A special attention is paid to the pole pitch ratio between stator and mover, the ratio between slot width and pole pitch of stator. Finally, a prototype of transverse flux permanent magnet linear motor has been developed.

Investigation of a Stator-Ironless Brushless DC Motor With Non-Ideal Back-EMF

This paper deals with the effects of permanent magnets (PMs) shapes and segmentation types on the trapezoidal degrees of the back electromagnetic force (EMF) and torque characteristics and rotor losses. The back-EMF waveforms with different PMs shapes and segmentation types are calculated through transient finite element method (FEM). It is found that the effects of PMs inward eccentricity and curvature have no influence on the shape of the back-EMF waveforms. The PMs asymmetrical segmentation with the middle sub-PMs applied with low magnetic energy product sintered ferrite magnet can obtain better trapezoidal back-EMF waveforms. Then, the torque characteristics and rotor losses of PMs' symmetrical and asymmetrical segmentations are investigated and evaluated. The results show that the PMs segmentation and applying low magnet energy product PMs of the middle sub-PMs can further improve the torque characteristics. Moreover, the outer PMs eddy current loss and rotor iron loss exhibit a great extent of decrement. Finally, a stator-ironless PM BLDC motor without the outer rotor PMs segmentation is manufactured and tested. The experimental results show good agreement with the FEM ones.

Sources of torque ripple and their influence in BLDC motor drives

Abstract In automotive applications brushed DC motor is often used because of its simplicity and low price. It is very quiet motor, easy to control and serves as actuators with an overall short operating time. Brushless DC (BLDC) motors have less wear and probability of failure, higher efficiency, but need a more complex control algorithm than a DC motor drive. So brushless DC motor is most suitable for applications demanding long-term continuous duty like fuel pumps. Brushed DC motor is often used also in seat ventilation and in some HVAC (heating, ventilation, and air conditioning) compressors and blowers where low noise operation is required. There is an effort to replace this brushed DC motor with low-cost BLDC motor. But problem of these low-cost BLDC motors is in produced torque ripple, vibrations and acoustic noise. Therefore, sources of torque ripple and their suppression has to be identified. This article will be focused on identification of main sources of torque ripple caused by construction and control of BLDC motor. Sources such as cogging torque, waveform of Back-EMF in combination with waveform of phase currents (type of control technique), dead-time and commutation of currents will be investigated. Impact of these sources will be identified on real BLDC motor and also torque ripple, vibrations and acoustic noise will be evaluated in this article.

Chaotic inertia weight and constriction factor-based PSO algorithm for BLDC motor drive control

The population algorithms have a number of advantages over classical methods for solving complex optimisation problems such as tuning of controller parameters of motor drives These algorithms for solving various problems of global optimisation is often called as methods inspired by nature, methods in this class are based on the modelling of intelligent behaviour of organised members of the population. Particle swarm optimisation (PSO) algorithm is population-based algorithm which has ability to fine tune the controller parameters. In this paper, chaotic inertia weight and constriction factor-based PSO algorithms are proposed for tuning of proportional-integral-derivative (PID) controller parameters to control brushless direct current (BLDC) motor drive. The BLDC is modelled in MATLAB/Simulink and trapezoidal back emf waveforms are modelled as a function of rotor position using MATLAB code. The simulation results of PSO algorithms are compared and results shown the effectiveness of C-inertia weight and C-factor in tuning PID controller parameters.

Chaotic inertia weight and constriction factor-based PSO algorithm for BLDC motor drive control

The population algorithms have a number of advantages over classical methods for solving complex optimisation problems such as tuning of controller parameters of motor drives These algorithms for solving various problems of global optimisation is often called as methods inspired by nature, methods in this class are based on the modelling of intelligent behaviour of organised members of the population. Particle swarm optimisation (PSO) algorithm is population-based algorithm which has ability to fine tune the controller parameters. In this paper, chaotic inertia weight and constriction factor-based PSO algorithms are proposed for tuning of proportional-integral-derivative (PID) controller parameters to control brushless direct current (BLDC) motor drive. The BLDC is modelled in MATLAB/Simulink and trapezoidal back emf waveforms are modelled as a function of rotor position using MATLAB code. The simulation results of PSO algorithms are compared and results shown the effectiveness of C-inertia weight and C-factor in tuning PID controller parameters.

Impact of C-factor on PSO for solar PV-based BLDC motor drive control

The constriction factor (C-factor)-based particle swarm optimisation algorithm is proposed for the solar photovoltaic array powered brushless direct current (BLDC) motor drive control. The rotor position sensors are completely eliminated. Instead, it is determined by measuring the changes in back-emf. The CPSO algorithm is used for the tuning of proportional-integral-derivative (PID) controller parameters for the speed control of the drive. The BLDC motor drive is modelled in MATLAB/Simulink and trapezoidal back-emf waveforms are modelled as a function of rotor position using MATLAB code. This paper deals with rise time, settling time, peak overshoot and steady-state error under varying conditions and examines the effectiveness of the BLDC motor drive with the proposed algorithm. The comparison of simulation results of proposed algorithm with other PSO algorithms demonstrates the prominence of the constriction factor for the drive controller.

Winding Arrangement of A New Type Hollow Rotor BLDC Motor

This paper discusses about winding arrangement of fractional slot of a new type hollow rotor Brushless Direct Current (BLDC) motor. Hollow rotor has higher performance compared to other BLDC motor because it minimizes the unused flux below permanent magnet and maximize torque produce by the motor. It’s also known that 8 pole motor is favorite used in industrial because it has an optimum space of permanent magnet for a smaller motor size. The number of pole will affect the maximum speed of the rotor. Thus, the objective of this research is to investigate the best winding arrangement for 8 pole of hollow rotor that could produce the highest electromagnetic performance. At starts, four combinations of slot number and coil sizes had been selected. Structural comparison in term of coil vector and winding arrangement is studied. Finite Element Method (FEM) had been used to simulate the parameters such as backemf and torque waveforms. It was convinced that 9 slot 8 pole with 0.6 size of coil produces the best performance. The confirmed model had been fabricated and measured. Both results from FEM and measurement are compared in term of backemf and torque where percentage differences are 7.4 % and 8 %, respectively. As conclusion, this research shows the fundamental of winding arrangement of fractional slot of motor especially 8 pole motor.

Influence of magnetization pattern in three-phase permanent magnet synchronous machines

This paper investigates the influence of different magnetization patterns in the performance of three-phase permanent magnet synchronous motors (PMSMs). Three magnetization patterns widely used in surface-mounted PMSMs are radial magnetization, parallel magnetization and Halbach magnetization. In this paper, these magnetization patterns are applied to 9-slot/10-pole and 12-slot/10-pole surface-mounted PMSMs. The electromagnetic characteristics and performance of the motors such as air gap flux density distributions, phase back-emf, cogging torque, unbalance magnetic force and output torque are intensively evaluated in 2D finite element method. Important findings indicate that PMSMs with ideal Halbach magnetization exhibit almost zero cogging torque and sinusoidal phase back-emf waveform. Parallel magnetization and radial magnetization yield more trapezoidal phase back-emf waveform which results in higher torque ripples. One way to minimize the torque ripples is by reducing the higher-order harmonic components in the phase back-emf waveform which can be achieved with the best value of magnet pole arc. Additionally, a potential cost saving can be realized since the motor has smaller magnet volume as being demonstrated in the case of 9-slot/10-pole, three-phase surface-mounted PMSM in this paper.

Novel hybrid excited machine with flux barriers in rotor structure

PurposePermanent magnet (PM) electrical machines are becoming one of the most popular type of the machines used in electrical vehicle drive applications. The main drawback of permanent magnet machines, despite obvious advantages, is associated with the flux control capability, which is limited at high rotor speeds of the machine. This paper aims to present a new arrangement of permanent magnets and flux barriers in the rotor structure to improve the field weakening control of hybrid excited machines. The field weakening characteristics, back-emf waveforms and efficiency maps of this novel machine have been reported.Design/methodology/approachIn the study, finite element analysis was used to perform simulation research. Then, based on the simulation studies, an experimental model was built. The paper also presents selected experimental results.FindingsObtained results show that the proposed machine topology and novel control strategy can offer an effective flux control method allowing to extend the maximal rotational speed of the machine at constant power range.Practical implicationsThe proposed solution can be used in electric vehicles drive to extend its torque and speed range.Originality/valueThe paper presents original design and results of research on a new solution of a hybrid excited machine with magnetic barriers in a rotor.

Design Considerations of a Transverse Flux Machine for Direct-Drive Wind Turbine Applications

This paper presents the design considerations and analysis of a double-sided transverse flux machine (TFM) for direct-drive wind turbine applications. The proposed TFM has a modular structure with quasi U-core stators and toroidal ring windings. The rotor is designed with ferrite magnets in a flux-concentrating setup to achieve high air gap flux density. This paper presents the different aspects of the TFM, taking into consideration the critical geometric parameters affecting the back-EMF waveform, phase inductance, torque density, and power factor. Three-dimensional finite element analysis (3D-FEA) was used to analyze and optimize the critical TFM design parameters to meet the performance specification. A proof-of-concept prototype was developed based on the proposed design considerations. The prototype was experimentally tested at different operating points and the results showed good correlation with the 3D-FEA results.

On-Load Back EMF of PMSM Using Maxwell Stress Tensor

This paper is focused on the on-load back-electromotive force (EMF) assessment in a permanent magnet synchronous machine (PMSM) using Maxwell stress tensor along with the frozen permeability method (FPM). Although the back EMF is only measured at open-circuit condition, it is known that the on-load back EMF is heavily affected by electric loading and magnetic saturation. Since the main torque component of the PMSM is the mutual torque and it is based on the interaction between the back EMF and stator current, any distortion in the on-load back EMF will affect the electromagnetic torque and increase the torque ripple. A misleading on-load back-EMF waveform with some spikes around the commutation points is found if the on-load back EMF is assessed by means of differentiating the on-load PM flux linkage. This way, this paper proposes a new numerical method to assess the on-load back EMF in order to avoid all the shortcomings of the existing method. First of all, a quick review on the results achieved by other researchers is shown. Next, a review on the FPM is done in order to clarify the points where this method will be changed to overcome the drawbacks highlighted previously. Furthermore, a new method is introduced and explained in small details. Finally, the results for different rotor configurations and different electrical loads are presented in order to validate the proposed method’s accuracy against experiments and other numerical techniques.

Design of Doubly Complementary Stator-PM Machine With High Magnet Utilization Factor for Low-Cost Applications

Aiming to improve permanent magnet (PM) utilization factor, suppress cogging torque, and reduce back-EMF harmonics in stator-PM machines, a new type of stator-PM doubly complementary machines (DCMs) are proposed in this paper. These machines employ two complementarities in the structure, as one exists in double rotors and the other exists in the units belonging to same phases. The first complementary characteristic supplies a consecutive switching path for PM exciting flux, so that shorted or open magnetic path could be avoided to reduce cogging torque and improve PM utilization. The second one is designed to reduce back electromotive force (EMF) harmonics and improve the torque density. The topology, operation principle, characteristics, and design methodology for DCMs are presented. Simulation and experiments are conducted for a 12/11(stator teeth/rotor teeth) DCM to evaluate its performance and verify this design methodology. It is revealed that this machine could obtain good sinusoidal back-EMF waveform, small torque ripple, and high PM utilization factor due to the doubly complementary characteristic.

Analytical Modeling and Optimization for Electromagnetic Performances of Fractional-Slot PM Brushless Machines

This paper presents a closed-form solution to optimize surface permanent magnet (PM) machines using concentrated windings. An analytical model is developed to predict the electromagnetic performances of fractional-slot PM machines. The model can be used to evaluate open-circuit magnetic field distribution with stator slotting effects, armature reaction field distributions, back-EMF waveform, winding inductance, cogging torque, electromagnetic ripple torque, efficiency, specific power, radial force density, and vibration mode order. Particle swarm optimization technique is applied to the proposed model in order to search for solutions that are a good compromise between conflicting objectives. The performances of the optimized machine are verified using finite element analysis. Finally, the analytical and finite element results have been validated with the experimental data, demonstrating a strong correlation between key machine parameters.

An analytical method of calculating back-emf in dual consequent hybrid excitation synchronous machine

In order to solve the problem of asymmetric bidirectional flux control capability in hybrid excitation machine, a novel structure called dual consequent hybrid excitation synchronous (DCHES) machine is presented in this paper. Generally, the analysis of back-EMF for the machine with complex electromagnetic structure such as DCHES machine should utilize 3-D finite element analysis (FEA), which will require huge resources and computing time. In order to avoid using 3-D FEA to analyze the back-EMF of complex structure, an analytical method of calculating back-EMF is presented in this paper. The electromagnetic field in 3-D space can be simplified as a 2-D field by dividing the 3-D field into several simple zones, the resultant effect equals to the summation of every single 2-D field's effect. According to electromagnetic theory, the analytical formula of back-EMF is obtained on the basis of Fourier series. The influence of main parameters on back-EMF waveform under sine and trapezoidal flux distribution is discussed respectively. The theoretical result shows that the trapezoidal air-gap flux distribution would generate a sine back-EMF. Finally, the presented analytical method is verified and evaluated with experimental results.

Unbalanced distributed and balanced concentrated winding comparison in servo motor applications

A comparison between unbalanced distributed winding and balanced concentrated winding is presented in this paper. The application is a torque motor where low speed and high torque are main requirements. Concentrated winding slot/pole combination is selected so that winding factor is maximum and as well as it is equal to the winding factor of the unbalanced winding motor. Stator and rotor Magneto-Motive Force (MMF) functions are obtained for both motor types to model torque ripple components in the frequency spectrum. Finite element analysis (FEA) and experimental results are presented to compare back EMF waveforms, magnetic loading, torque constant and thermal performance of two motors.Two designs have identical stator outer diameter (OD) and active axial length. The detailed comparison shows that two motors have similar torque constant. The behavior of two motors under heavy load differs and concentrated winding design performs better. Thermal performance of the designs is also compared and it is observed that concentrated winding design has also less winding temperature rise.