Harmonic Flux Research Articles

Robust Control for Torque Minimization in Wind Hybrid Generators: An H∞ Approach

This study focuses on implementing a wind turbine emulator based on a permanent magnet synchronous machine with excitation auxiliary windings and thoroughly investigates the space harmonics created by this innovative topology in MATLAB/Simulink. A Hybrid Generator (HG) is a robust generator that does not have slip rings or brushes in its structure. Furthermore, the flux of the hybrid generator HG may be easily adjusted as it is created by direct current excitation coils and permanent magnets. Unfortunately, the space harmonic rate in the HG is relatively high. In other words, the mechanical vibrations caused by the electromagnetic torque ripple threaten the drive train’s behaviour and, ultimately, the wind turbine’s lifespan. This study describes two methods for decreasing the ripple in electromagnetic torque. Both circuit architecture and robust H∞ control techniques are considered. After simulating the two approaches, a list of requirements is provided for the maximum allowable amplitude of the inductance and the flux harmonics.

Concentric-Coil Distributed Winding Design for Large Direct-Drive Fully Superconducting Machines

Fully superconducting generators (FSCGs) use superconducting wires for both the field and armature windings to reach a high torque density for wind turbine applications. The AC armature winding of an FSCG design mostly employed racetrack tooth-coils to form fractional-slot concentrated windings. This winding type has high leakage flux and excessive harmonics, especially when used in superconducting machines. Other attempts like applying full-pitch racetrack coils can only be with one slot per pole per phase which also has significant slotting harmonics. This paper proposes an innovative concept of double-layer concentric coils to enable distributed windings with a larger integral number of slots per pole per phase. The concept successfully breaks the limitation that racetrack coils cannot be built with such integral slots. This paper then assesses the performance of the proposed winding concept within a context 20 MW FSCG design. The assessment finds out that the proposed concept has balanced three phases but reduces inductance compared to single-layer windings. The force on each concentric coil can significantly be different, thereby complicating the mechanical design of these superconducting coils.

Current Harmonics Minimization of Permanent Magnet Synchronous Machine Based on Iterative Learning Control and Neural Networks

Electrical machines generate unwanted flux and current harmonics. Harmonics can be suppressed using various methods. In this paper, the harmonics are significantly reduced using Iterative Learning Control (ILC) and Neural Networks (NNs). The ILC can compensate for the harmonics well for operation at constant speed and current reference values. The NNs are trained with the data from the ILC and help to suppress the harmonics well even in transient operation. The simulation model is based on flux and torque maps, depending on dq-currents and the electrical angle. The maps are generated from FEM simulation of an interior permanent magnet synchronous machine (IPM) and are published with the paper. They are intended to serve other researchers for direct comparison with their own methods. Simulation results in this paper verify that by using ILC and NNs together, current harmonics in transient operation can be eliminated better than without NNs.

Harmonic Injection Strategy Considering Multiplane Iron Loss Impact With Optimal Magnetizing Flux Distribution for Multiphase Induction Machines

Lagging orientation error detuning induced by iron losses for multi-planes of multiphase IM under non-sinusoidal supply control triggers error in determination of calculated harmonic, fundamental air-gap flux advance angles and harmonic slip frequency. This in-turn leads to inaccurate harmonic injected currents, which are dependent on harmonic multiple of frequency for the corresponding plane with respect to fundamental plane frequency. This paper proposes the novel harmonic injection strategy considering the detuned impact of iron losses by keeping in view the complete iron loss modeling for both harmonic magnetizing flux orientation control (MFOC) and fundamental rotor flux orientation control (RFOC) planes. Furthermore, satisfaction of complete optimal flux distribution constraints for multiphase IM are taken into account which results in preserving optimal flux patterns throughout the mechanical loading particularly at low and medium load conditions. Contrary to other traditional orientation schemes, this paper adopts the MFOC and RFOC for harmonic and fundamental plane respectively for acquiring the aligned and synchronized control of harmonic and fundamental air-gap flux distribution. Detailed experimental results incorporating seven phase induction machine as prototype are utilized to evaluate the harmonic injected currents, advance angles, slip frequencies and induced EMF waveforms which validate the effectiveness of proposed scheme.

An Improved Modulation Strategy With Torque Ripple Suppression Method for OEW-PMSM Drives With Common DC Bus

The open-end winding permanent magnet synchronous machine drive with common dc bus has zero sequence loop, which inevitably generates the zero sequence current (ZSC). Due to the existence of the third harmonic flux linkage, ZSC causes the zero sequence torque and augments the torque ripple. In this paper, an improved modulation strategy with torque ripple suppression method is presented. Firstly, to reduce the computation burden, a modified alternate sub-hexagonal center pulsewidth modulation (ASHCPWM) strategy is designed. The switching duration time of two inverters can be obtained by the projection of voltage vector on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">abc</i> coordinate frame. Secondly, a ZSC suppression method based on the time compensation coefficient is adopted for the modified modulation strategy, which can restrain ZSC and reduce torque ripple. Thirdly, to further reduce torque ripple, a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current injection method is employed in the control scheme. Finally, three methods are presented in simulation and experiments for comparison, namely the deadbeat predictive current control (DPCC) method with conventional ASHCPWM, the DPCC method with sample-averaged zero-sequence current elimination PWM, and the proposed DPCC method with modified ASHCPWM and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current injection. The results test the effectiveness of the proposed method.

High-Performance Vernier Machines with Halbach Array Permanent Magnets for Direct Drive Applications

This paper investigates the performance enhancements of permanent magnet Vernier machines (PMVMs) that can be achieved using a new structure of Halbach array permanent magnets (HAPMs) for a direct-drive motorcycle application. To start with, size and design specifications of the electric machine are determined based on the assumed acceleration and drive cycle performance of a motorcycle. Then, five-segment Halbach array permanent magnet Vernier machines (HAPMVMs) with two different slot/pole combinations (24 s/44 p and 12 s/20 p) are suggested and optimized to achieve a high torque density with an acceptable power factor while maintaining a low torque ripple. Two selected designs from optimizations are investigated in the full speed range considering power factor and efficiency maps. Consequently, in order to demonstrate the effectiveness of the proposed five-HAPM structure, the same optimization methods are repeated with three-segment HAPMs as well as with single-piece PMs. The comparisons show a great enhancement in torque and power factor achieved with the use of five HAPMs. For instance, for 22 s/44 p topology, generated torque doubles with the use of five-segment PMs compared to single-segment PMs. Finally, the harmonics of magnetic flux density in the airgap of PMVMs and HAPMVMs are compared and investigated to reveal the reasons behind the superiority of VMs with HAPMs.

A Novel Parallel-Excited Dual-PM Reluctance Machine With Enhanced Torque and Efficiency Performance

This paper presents a novel parallel-excited dual-PM reluctance machine (DPM-RM) with enhanced torque and efficiency performance. The key is to build an integrated magnetic field with two sets of PM excitation sources in both stator yoke and slot openings. Two excitation sources produce a parallel magnetic field, which contributes to a superimposed magnetic flux in the airgap, thus leading to strengthened flux variation, improved back-EMF and torque. Additionally, with a special slot&#x002F;pole combination, biased component and even order harmonics in the phase magnetic flux are eliminated to make the phase flux linkage more sinusoidal. In the meantime, self-inductance variation is greatly suppressed with odd order harmonics of self-inductance removed, resulting in suppressed torque ripple. The prototype is manufactured, and experiments are carried out to verify the effectiveness of the machine design.

Model Predictive Torque Control for Permanent- Magnet Synchronous Motors Using a Stator- Fixed Harmonic Flux Reference Generator in the Entire Modulation Range

To increase torque and power conversion of permanent-magnet synchronous motors (PMSMs) at high-speed operation, the dc-link voltage of the inverter must be fully utilized during steady-state and transient operations. This article proposes the incorporation of a harmonic reference generator (HRG) with a pulse clipping (PC) scheme into a model predictive control framework to achieve highest power output. The HRG calculates flux references in the stator-fixed coordinate system for an underlying continuous-control-set model-predictive flux control (CCS-MPFC). These reference trajectories contain the harmonic flux component induced by the voltage hexagon in the overmodulation range and specific switching states (e.g., six-step operation) of the inverter are ensured by the proposed PC scheme. This enables a seamless transition to the overmodulation range including six-step operation and increases the drive's power conversion to its maximum extent. Since the flux differential equation in the stator-fixed coordinate system, used as motor model for the HRG and CCS-MPFC, is able to represent PMSMs with linear and nonlinear magnetization, the proposed approach is well suited for the control of PMSMs with nonlinear magnetization. Extensive transient and steady-state experimental investigations on a highly utilized PMSM in the entire modulation and speed range prove the performance of the proposed approach.

Teamwork optimization based DTC for enhanced performance of IM based electric vehicle

The tailpipe emissions caused by vehicles using internal combustion engines are a significant source of air pollution. To reduce the health hazards caused by air pollution, advanced countries are now adopting the use of electric vehicles (EVs). Due to the advancement of electric vehicles, research and development efforts are being made to improve the performance of EV motors. With a nominal reference stator flux, the classical induction motor drive generates significant flux, torque ripple, and current harmonics. In this work, a teamwork optimization algorithm (TOA)-based optimal stator flux strategy is suggested for torque ripple reduction applied in a classical direct torque-controlled induction motor drive. The suggested algorithm's responsiveness is investigated under various steady-state and dynamic operating conditions. The proposed DTC-IM drive's simulation results are compared to those of the classical and fuzzy DTC-IM drives. The proposed system has been evaluated and found to reduce torque ripple, flux ripple, current harmonics, and total energy consumption by the motor. Further, a comparative simulation study of the above methods at different standard drive cycles is presented. Experimental verification of the proposed algorithm using OPAL-RT is presented. The results represent the superiority of the proposed algorithm compared to the classical DTC and fuzzy DTC IM drives. The torque ripple reduction approach described in this study can also be applied to all induction motors, not only those for electric vehicles or hybrid electric vehicles (HEVs).

Investigation of Air-Gap Field Modulation Effect in Spoke-Type PM Machines

In this article, the air-gap field modulation effects (AFMEs) in spoke-type permanent magnet (STPM) machines with concentrated winding are investigated and revealed by quantifying the torque contributions of the various air-gap flux density harmonics. Due to the relatively stronger flux concentrated effect, the STPM structure exhibits greater resulting air-gap field harmonics for torque generation. In order to provide an in-depth understanding of their torque generation mechanism, the contributed torque components of the various air-gap field working harmonics are quantified by employing the Maxwell stress tensor (MST) approach. It identifies a fact that the abundant air-gap flux density harmonics have participated in torque production in the STPM machine. As a consequence, the field-modulated harmonics contributed a nonnegligible torque component, and hence, a pronounced AFME can be obtained in the STPM machine. Besides, the influences of the key dimension parameters, including split ratio, stator slot opening ratio, rotor PM thickness, and length, on AFEM for torque performance of the STPM machines are evaluated by the finite-element (FE) method. Finally, the reliability and effectiveness of theoretical analysis and FE simulation are verified by experiments on an STPM machine prototype.

Design and Optimization a New Spoke-Type Flux-Modulation Machine With Inverted T-Shape Permanent Magnets

This paper takes a new spoke-type flux-modulation (STFM) machine with inverted T-shape permanent magnets as the research object and proposes a multi-objective optimization design method based on air-gap flux density harmonics to improve the torque and torque ripple. The key of the proposed method is to optimize the overall torque performance by improving the contribution of main air-gap harmonics to torque and torque ripple. The working harmonic expression of the machine is firstly obtained based on the magnetomotive force (MMF) -permeance model due to the new rotor structure make the working harmonics are different from the existing flux-modulation PM machine. Then, the torques generated by the 11th and 31st air-gap harmonics and the torque ripple generated by the 29th air-gap harmonics are taken as sub-objectives. Furthermore, the response surface analysis (RSM) and the barebones multi-objective particle swarm optimization (BB_MOPSO) algorithm are combined to optimize three sub-objectives. The overall torque and torque ripple are improved due to the optimization of three sub-objectives. Moreover, the 20-slot/11-pole pair traditional model is used as a benchmark to verify the performance of the investigated machine. Finally, a prototype is manufactured and tested to verify the correctness of the theoretical analysis.

Torque Quality Improvement in Induction Motor for Electric Vehicle Application Based on Teamwork Optimization

The tailpipe emission caused by the vehicles using internal combustion engines is a significant source of air pollution. To reduce the health hazards caused by air pollution, advanced countries are now adopting the use of Electric Vehicles (EVs). Due to the advancement of electric vehicles, research and development efforts are being made to improve the performance of EV motors. With a nominal reference stator flux, the classical induction motor drive generates significant flux, torque ripple, and current harmonics. In this work, a Teamwork Optimization Algorithm (TOA)-based optimal stator flux strategy is suggested for torque ripple reduction applied in a Classical Direct Torque Controlled Induction Motor (CDTC-IM) drive. The suggested algorithm's responsiveness is investigated under various steady-state and dynamic operating conditions. The proposed Direct Torque Controlled Induction Motor (DTC-IM) drive's simulation results are compared to those of the CDTC-IM and Fuzzy Direct Torque Controlled Induction Motor (FDTC-IM) drives. The proposed system has been evaluated and shown to have reduced torque ripple, flux ripple, current harmonics, and total energy consumption by the motor. Further, a comparative simulation study of the above methods at different standard drive cycles is presented. Experimental verification of the proposed algorithm using OPAL-RT is presented. The results represent the superiority of the proposed algorithm compared to the CDTC- and FDTC-IM drive. The torque ripple reduction approach described in this study can also be applied to all types of induction motors, not only those for electric vehicles or Hybrid Electric Vehicles (HEVs).

Quantitative Analysis of Electromagnetic Forces by Decoupling Air-Gap Field Modulation and Force Modulation in Rotor-Permanent-Magnet Machines

This article proposes a quantitative analysis model for the electromagnetic forces in rotor-permanent-magnet (rotor-PM) machines, decoupling the air-gap field modulation and the force modulation. First, a unified analytical model of the equivalent concentrated forces (ECFs) is deduced based on the air-gap flux density (AFD) harmonics. Second, the air-gap field modulation and the force modulation are decoupled by the ECF coefficient. Then, to determine the contributions of the modulated AFD harmonics, a quantitative analytical method is proposed. On this basis, the vibration performance of a 12-slot/10-pole (12s/10p) interior PM machine is investigated considering the modulation effect. The results reveal that the influences of rotation speed, PM-excited field, and armature field on the vibration can be clearly represented by the proposed method. Finally, the modal test and the acceleration measurement are conducted to validate the analysis.

Development of a Comprehensive Analytical Model of Induction Motor Under Stator Interturn Faults Incorporating Rotor Slot Harmonics

The objective of this article isto developa comprehensive mathematical model of a three-phase induction motor to facilitate stator interturn (SIT) fault related study. A detailed analytical model that includes accurate inductance modeling considering rotor slot harmonics (RSH) under healthy as well as SIT faults is described. The proposed model is developed analytically in a step-by-step manner incorporating the features of RSH. A detailed but simplified analysis considering both magnetomotive force harmonics and air-gap flux harmonics has been presented. An asymmetric model is proposed, including SIT faults, in a single phase of the induction motor in the next stage of the modeling. The effect of saturation has also been considered in the model. The proposed model is validated by comparing the simulation results in transient, steady state, and frequency domain with the experimental results. Comparison shows a high degree of correlation with the results of the actual motor. The contributions of this work are justified by comparing the proposed model with the existing models. This article also shows that a frequency signature related to RSH present in the line current is capable of characterizing the SIT faults.

Deep Learning Based Design Methodology for Electric Machines: Data Acquisition, Training and Optimization

This paper presents an automated deep learning-based design methodology to facilitate the design and optimization processes in electro-mechanical energy conversion devices. To validate the generality of the model, a complex machine structure with hybrid Permanent Magnets (PMs) is selected as the case study. First, the machine’s geometrical topology and the respective design variables are described in the cylindrical coordinate system and programmed into a Finite Element (FE) software package. Next, the program sweeps through the predefined ranges of selected design variables and captures corresponding air-gap flux distribution through an automated FE-based parametric analysis. The air-gap flux density data is post-processed and fed into a deep neural network (DNN) training algorithm. In particular, 10,000 data sets are utilized for training the DNN model. The trained model successfully predicts the machine’s performance for any random set of parameters, as confirmed via FE. Finally, by leveraging the trained model, the structural parameters of the machine are optimized to limit higher-order spatial flux harmonics and the cogging torque.

Iron Loss Calculation for FSPM Machine With the PWM Inverter Supply Based on General Airgap Field Modulation Theory

In this article, an iron loss for the flux switching permanent magnet machine with the pulsewidth modulation (PWM) inverter supply is calculated based on the general airgap field modulation theory (GAFMT). First, the amplitudes and rotation speeds of the main space harmonics of the airgap magnetic flux density with the supply of PWM harmonics are calculated based on the GAFMT. When calculating the source magnetizing magnetomotive force based on the GAFMT, the equivalent magnetic circuit is applied to calculate the working point of the permanent magnet. Second, each spatial harmonic in the airgap magnetic field is synthesized by an equivalent current layer in the airgap and then is substituted into the 2-D finite element analysis models to calculate the iron losses. Finally, the iron losses calculated by the proposed method with different speeds, loads, and control strategies are compared with the experimental results.

Modeling and Optimal Configuration Design of Flux-Barrier for Torque Improvement of Rotor Flux Switching Permanent Magnet Machine

The rotor permanent magnet flux-switching (RPM-FS) machine is a promising candidate for electric vehicle (EV) and hybrid electric vehicle (HEV) applications. In this paper, we propose the magnetic flux barrier design to improve the torque capability of the RPM-FS machine. The response surface optimization method was used to design and optimize the topology of flux barriers. The 2D finite element analysis shows that the proposed RPM-FS machine has a higher electromotive force than the conventional structure, with only a slight increase in cogging torque. Notably, an insertion of flux barriers could yield a reduction of magnetic flux leakage, an improvement of magnetic saturation capability, and an enhancement of working harmonics of the air-gap flux density. As a result, a significant improvement in torque capability, eddy current losses, and efficiency was obtained. Hence, the RPM-FS machine proposed in this work is capable of being used in EV and HEV applications.

Active torsional vibration suppression of integrated electric drive system based on optimal harmonic current instruction analytic calculation method

Torque fluctuation caused by flux harmonics in a permanent magnet synchronous motor (PMSM) leads to torsional vibrations in vehicle-integrated electric drive systems. To resolve this fluctuation, the coupling relationship between the torque fluctuation and harmonic current of the PMSM was analyzed by establishing an analytical model of the instantaneous torque of the PMSM. The analysis was performed considering the harmonic and saturation characteristics of the flux chain. An analytical calculation method for the reference harmonic-current instruction was proposed to suppress torque fluctuation. The proportional integral resonant (PIR) controller was designed to accurately control the actual current to follow the reference harmonic-current command. Thus, an active torsional vibration suppression method was developed. Simulation and experimental results showed that the proposed method can effectively reduce the amplitude of the 6th and 12th harmonic torque of the PMSM. The amplitude of each axis torque and gear-meshing force, corresponding to the harmonic frequency of the transmission system, is considerably reduced. The transmission stability is also significantly improved.

Performance Analysis and Optimization of a Novel Outer Rotor Field-Excited Flux-Switching Machine with Combined Semi-Closed and Open Slots Stator

Slotting effect in electric machines reduces flux per pole that effect magnetic flux density distribution in the air gap which induces harmonics in magnetic flux density causing flux pulsation, that in turn generates dominant torque pulsation in the form of cogging torque and torque ripples. To overcome the abovesaid demerits, a novel outer rotor field-excited flux-switching machine (OR-FSFSM) with a combined semi-closed and open slots stator is proposed in this study. The developed OR-FEFSM offers a high-power factor, due to the utilization of the semi-closed slot for armature coils. The open slot stator structure was chosen for the field excitation coil, which effectively suppresses leakage reluctance that causes flux pulsation. Thus, the influence of torque ripples is reduced, and the average torque is improved. In order to investigate the effectiveness of the proposed OR-FEFSM, a detailed study of stator slot and rotor pole combinations are performed. Based on simplified mathematical formulation, 12S/7P (stator slot/rotor poles), 12S/11P, 12S/13P, and 12S/17P are the most feasible combinations. Finite Element Analysis (FEA) based on comprehensive electromagnetic performance is performed on each combination, and found that 12S/13P offers the highest average torque of 4.62 Nm, whereas 3.72 Nm, 2.72Nm, and 1.68 Nm average torque is offered by 12S/17P, 12S/7P, and 12S/11P, respectively. Based on the initial analysis, 12S/13P was considered for further analysis and optimized using JMAG built-in Genetic Algorithm (GA). Moreover, thermal analysis was performed, and the proposed design was compared with the conventional design.

Mechanism of Torque Ripple Generation by Time and Space Harmonic Magnetic Fields in Permanent Magnet Synchronous Motors

The mechanism of torque ripple generation by time and space harmonic magnetic fields in permanent magnet synchronous motors is investigated to obtain advanced motor designs. The general expression between the torque ripples and harmonic air-gap flux densities in the motor is derived by using Maxwell stress tensor. Both the numerical and experimental verifications of this expression are carried out. By using this expression, the difference of the torque ripple generation between the surface and interior permanent magnet synchronous motors are discussed. Based on these investigations, the shape of the rotor surface of an interior permanent magnet motor is optimized. It is clarified that specific harmonic components of thetorque ripples in interior permanent magnet synchronous motors can be reduced to be nearly zero by optimizing the rotor surface shape.