Harmonic Electromotive Force Research Articles

Research on Performance of Interior Permanent Magnet Synchronous Motor with Fractional Slot Concentrated Winding for Electric Vehicles Applications

The fractional-slot, concentrated-winding, interior permanent magnet synchronous motor (FSCW IPMSM) has advantages, such as reducing motor copper consumption, improving flux-weakening capability, and motor fault tolerance, and has certain development potential in application fields such as electric vehicles. However, fractional-slot concentrated-winding motors often contain rich harmonic components due to their winding characteristics, leading to increased motor losses and back electromotive force harmonics, thereby affecting the efficiency and constant power speed regulation range of the motor. Based on this, this article first uses the winding function method to explore the inductance and saliency ratio of the interior permanent magnet synchronous motor with different slot pole combinations in the fractional-slot concentrated- winding of electric vehicles. Secondly, this article will establish a 2D finite element parameterized model to analyze and compare the performance of fractional-slot concentrated-winding motors with different slot pole combinations, including air gap magnetic density, back electromotive force distortion rate, overload multiple, and torque. The structural parameters of the motor were optimized with the objective of minimizing the torque ripple under the constraint of minimizing the average torque reduction. The motor slot width, permanent magnet angle, and permanent magnet pole arc angle were analyzed and optimized. The simulation results showed that 12 slots and 8 poles were the optimal design schemes, providing a theoretical basis for the selection of slot pole coordination in the fractional-slot concentrated-winding interior permanent magnet synchronous motor for electric vehicles.

Diagnostics of Interior PM Machine Rotor Faults Based on EMF Harmonics

This article presents a detailed study on the diagnosis of rotor faults in an Interior Permanent Magnet Machine based on a mathematical model. The authors provided a wide literature review, mentioning the fault diagnosis methods used for Permanent Magnet Machines. The research emphasizes the necessity of precise assumptions regarding winding construction to accurately analyze the additional harmonics appearing in rotor faults caused by electromotive force (EMF), i.e., rotor eccentricity and magnet damage. The article also discusses specific features appearing in the spectrum of air gap permeance functions and the impact of rotor eccentricity and magnet damage on PM flux density distribution and as a consequence on EMF stator windings. The novelty of the presented content is the analysis of induced EMFs for cases of the simultaneous occurrence of rotor eccentricity and PM damage. The findings of this study provide valuable insights for the diagnosis and understanding of internal asymmetries in Interior PM Machines.

Research on a Variable-Leakage-Flux Permanent Magnet Motor Control System Based on an Adaptive Tracking Estimator

Due to the characteristics of inductance parameter mismatch and back electromotive force harmonics caused by novel leakage flux branches and other non-ideal factors for the variable-leakage-flux permanent magnet (VLF-PM) motor, its control system suffers from a deteriorated performance of the rotor position estimation. To overcome the problems mentioned above, an adaptive tracking estimator of the rotor position is proposed in this paper for the VLF-PM motor control system. First, the proposed method simplifies the VLF-PM motor mathematical model and reduces the effect of inductance parameter variations according to the active flux concept. Then, robust and gradient descent algorithms are utilized to maintain the robustness of inductance parameter variations and eliminate the specific order harmonics owing to the novel leakage flux branches. Meanwhile, the accuracy and stability are enhanced. Furthermore, the position compensation based on the current adaptive tracking strategy is proposed to compensate the rotor position error caused by other non-ideal factors. Finally, the feasibility of the proposed estimated system is verified.

Analysis of Excitation Winding Induced EMF in Non-Overlapped Stator Wound Field Synchronous Machines

Different from the induced electromotive force (EMF) in armature winding, the induced EMF in excitation winding is detrimental to the performance of wound field synchronous machines by causing unstable excitation field and thus extra torque pulsation and losses. Moreover, it also imposes challenges to machine control, particularly for high-speed operation. This article investigates the induced EMF in the excitation winding of 3-phase non-overlapped stator wound field synchronous machines (SWFSMs). It has revealed that the amplitude of the excitation winding induced EMF is largely dependent on the slot-pole combination. Therefore, with suitable slot-pole combinations, the induced EMF issue will be significantly alleviated by eliminating low-order induced EMF harmonics. Although the excitation winding induced EMF can also be reduced by passive techniques, e.g., optimization and shaping of rotor pole arc, the average torque will be greatly degraded as well. Finally, the finite element predictions are validated by measurements on two prototyped non-overlapped SWFSMs.

Spin Elastodynamic Motive Force.

The spin-motive force (SMF) in a simple ferromagnetic monolayer caused by a surface acoustic wave is studied theoretically via spin-vorticity coupling (SVC). The SMF has two mechanisms. The first is the SVC-driven SMF, which produces the first harmonic electromotive force, and the second is the interplay between the SVC and the magnetoelastic coupling, which produces the dc and second harmonic electromotive forces. We show that these electric voltages induced by a Rayleigh-type surface acoustic wave can be detected in polycrystalline nickel. No sophisticated device structures, noncollinear magnetic structures, or strong spin-orbit materials are used in our approach. Consequently, it is intended to broaden the spectrum of SMF applications considerably.

Brushless Excitation Principle and Experimental Verification of Hybrid Excitation Synchronous Generator Based on Harmonic Magnetic Field

It is well known that the air-gap magnetic field of the permanent magnet synchronous generator (PMSG) is difficult to adjust. To overcome this challenge while maintaining the brushless feature of PMSGs, a hybrid excitation synchronous generator (HESG) based on inherent third harmonic field induction is proposed in this paper. The HESG adds a set of third harmonic windings with a pitch of 1/3 of the armature winding in the stator core and a set of harmonic windings with the same pitch as the third harmonic winding in the rotor core. Due to electromagnetic induction, the third harmonic field established by third harmonic windings in the stator induces the harmonic electromotive force (EMF) of six times the frequency in the rotor harmonic winding. This harmonic EMF is directly provided to the rotor excitation winding after rectifying by the diode rotating rectifier. The HESG has armature windings and third harmonic windings in the stator, and excitation windings, harmonic windings and permanent magnets in the rotor. In this article, the mechanism of stator third harmonic winding EMF, rotor harmonic EMF, and the brushless excitation are elaborated. The experimental results of adjustable armature winding voltages with controlling the stator third harmonic winding current have proven the feasibility of the proposed brushless excitation principle based on the third harmonic.

Identification of IPMSM Flux-Linkage Map for High-Accuracy Simulation of IPMSM Drives

This article proposes a precise identification scheme of an interior permanent-magnet synchronous motor (IPMSM) flux linkage through experimental tests considering motor nonlinearities, such as the magnetic saturation and spatial harmonics. In the proposed scheme, the flux linkage is identified based on the voltage equation of IPMSM. The fundamental and harmonic electromotive force in the rotor reference frame is obtained in real time by applying a discrete Fourier transform with the phase compensation of the time delay due to digital control and pulsewidth modulation. The effect of the inverter nonlinearity is compensated using an experimentally obtained lookup table. Based on the identified flux-linkage map, a flux-based IPMSM model that accurately simulates motor behavior can be constructed. The effectiveness of the proposed flux-linkage identification scheme is verified through the comparison of simulation and experimental results.

Efficiency Improvement of Permanent Magnet BLDC Motors for Electric Vehicles

A permanent magnet Brushless DC (BLDC) motor has been designed with different rotor configurations based on the arrangement of the permanent magnets. Rotor configurations strongly affect the torque and efficiency performance of permanent magnet electric motors. In this paper, different rotor configurations of the permanent magnet BLDC motor with parallel the Halbach array permanent magnet were compared and evaluated. Many applications of electric drives or air-crafts have recently preferred the surface-mounted permanent magnet design due to its ease of construction and maintenance. The finite element technique has been used for the analysis and comparison of different geometry parameters and rotor magnet configurations to improve efficiency and torque performance. A comprehensive design of a three-phase permanent magnet BLDC 35kW motor is presented and simulations were conducted to evaluate its design. The skewing rotor and Halbach magnet array are applied to the permanent surface-mounted magnet on the BLDC motor for eliminating torque ripples. In order to observe the skewing rotor effect, the rotor lamination layers were skewed with different angles and Halbach sinusoidal arrays. The determined skewing angle, the eliminated theoretically cogging torque, and the back electromotive force harmonics were also analyzed.

Back EMF Waveform Comparison and Analysis of Two Kinds of Electrical Machines

In this study, the back electromotive force (EMF) waveforms of a flux switching permanent magnet (FSPM) machine and variable flux memory permanent magnet (VFMPM) machine with same main dimension were researched. Firstly, the simulation result showed that the maximum amplitude of phase back EMF waveform of FSPM machine was 245% larger than that of the VFMPM machine, and this was verified by the experimental result (243%). Secondly, the phase back EMF harmonics of the FSPM machine and VFMPM machine were compared, including the enhance flux condition and weaken flux condition of VFMPM machine. At last, the mutual demagnetization effect, which led to the difference amplitudes of maximum back EMF waveform between FSPM machine and VFMPM machine was analyzed. The comparison and analysis of the back EMF waveform will provide some qualitative advice for the future application research of the FSPM machine and VFMPM machine, such as application selection, optimization control method and so on.

A Hybrid Filtering Stage-Based Rotor Position Estimation Method of PMSM with Adaptive Parameter.

The performance of sensorless control in a permanent magnet synchronous machine (PMSM) highly depends on the accuracy of rotor position estimation. Owing to its strong robustness, phase-locked loop (PLL) is widely used in rotor position estimation. However, due to the influence of harmonics existing in back electromotive force (EMF), estimation error occurs by using PLL. In this paper, a hybrid filtering stage-based PLL is proposed to improve the rotor position estimation. Adaptive notch filters and moving average filters are integrated together to eliminate harmonic EMF. To make the method effective under varying speed conditions, adaptive parameters design guidelines are provided, considering dynamic performance under a wide operating range. The proposed method can accurately detect rotor position even under harmonic EMF disturbances. It can also adjust the frequency adaptively based on the rotating speed of the rotor, which means the estimation performance is not deteriorated under rotating speed changing conditions. The simulation results verify the effectiveness of the proposed method.

Direct Harmonic Current Control Scheme for Dual Three-Phase PMSM Drive System

The performance of model predictive control mainly depends on the accuracy of model and parameters, such as the back electromotive force (EMF) harmonics in dual three-phase permanent magnet synchronous motors (PMSMs). However, the back EMF harmonics would vary with the operation conditions. Thus, the parameter mismatches in the harmonic subspace would be inevitable. In this article, a direct harmonic current control scheme is proposed to provide further harmonic current suppression under parameter mismatches in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">xy</i> subspace. First, deadbeat control concept is applied to calculate the reference voltage in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">αβ</i> subspace. This reference voltage vector is utilized to generate a group of control sets with different voltage vectors in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">xy</i> subspace. Then, a slide mode control scheme is provided to deal with the inaccurate parameters in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">xy</i> subspace. The reference voltage vector in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">xy</i> subspace is obtained with this slide mode control scheme without the remaining inductance parameters. Third, a two-step modulation method and cost function are discussed to further suppress the harmonic currents. The control sets generated by deadbeat control are optimized with the cost function. Moreover, a switching pattern with fixed switching frequency is proposed in this section. Finally, experimental results verify that proposed control scheme could further suppress the harmonic currents.

Compensation of Selective Current Harmonics for Switching-Table-Based Direct Torque Control of Dual Three-Phase PMSM Drives

Current harmonics are ubiquitous in dual three phase (DTP) permanent magnet synchronous machine (PMSM) drives. Due to back electromotive force (EMF) distortion, significant current harmonics are generated in the DTP-PMSM system. The influence of back EMF harmonics is investigated in this paper and a novel switching-table-based direct torque control method to compensate the selected current harmonics caused by the back EMF harmonics is proposed. It shows that by employing different optimal action time durations for voltage vectors in the z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> subspace and setting the synthetic voltage vectors to non-zero, the stator flux harmonics caused by the back EMF harmonics can be selectively compensated, as verified by experiments.

Analysis of armature winding open‐phase fault in multi‐phase annular brushless exciter at nuclear power plant

The multi-phase annular brushless exciter (MPABE) of nuclear power plants has suffered numerous armature winding open-phase faults (AWOPF) in the field operation. In order to achieve reliable protection of the MPABE, its AWOPF is systematically studied through theoretical analysis, simulation calculation and model machine experiments. First, proceeding from the armature current waveform in normal operation and the influence of the AWOPF on it, the armature reaction magnetomotive force (MMF) is analysed deeply. Then, the theoretical analysis about the harmonic electromotive force (EMF) induced by armature reaction MMF on the field winding is presented, obtaining the harmonic characteristics of field current: the even-order field harmonic currents increase obviously under the AWOPF. Finally, correlate experiments and simulations were performed on a customized experimental prototype. The experimental and simulation results are consistent and verify the conclusion of the theoretical analysis, which can serve as a theoretical basis for the monitoring and diagnosis method of the AWOPF in the MPABE.

Active Harmonic Suppression of Low-Reactance Multiphase Slotless Permanent Magnet Synchronous Machines

Harmonic suppression plays a key role in the current control of dual-three-phase (DTP) permanent magnet synchronous machines (PMSMs). Existing current control schemes are scarcely verified by designed DTP motor prototypes or consider the impact of inherent electromotive force (EMF) harmonics quantitatively. Also, few studies discuss the low-reactance case, which requires additional concerns for current prediction and modulation. Therefore, this article conceives and presents an improved deadbeat-based active current harmonic control scheme particularly for low-reactance PMSMs. From the aspect of motor design and finite-element analysis, the quantitative effect of EMF harmonics on control behaviors is analyzed. Based on the nonideal mathematical model (MMM) of the designed slotless PMSM with analyzed EMF harmonics, the proposed scheme is first introduced theoretically and verified by simulation. Subsequently, the slotless PMSM prototype fabrication and control experiments validate the proposed scheme and recognize the necessity of active harmonic suppression.

Research on a hybrid excitation PM synchronous generator with stator third harmonic winding excitation

This study presents a hybrid excitation permanent magnet synchronous generator (HEPMSG) with a stator third harmonic winding to solve the problems of adjusting the air-gap magnetic field of the permanent magnet synchronous machine (PMSM) and simplify the excitation system structure. The electromotive force (EMF) of the stator third harmonic winding, induced by the inherent third harmonic magnetic field in the air gap, provides the adjustable field current for the rotor field winding via the controllable rectification. The proposed machine structure is described, and the generation mechanism and the excitation principle of the stator third harmonic EMF are analysed. The conditions for maximum excitation current output are discussed, and the integrated design methods of the stator third harmonic winding and the rotor excitation winding are described. Based on the finite element method, the performances of the third harmonic excitation system are numerically compared for different stator third harmonic windings, and the open-circuit voltage regulation characteristics under different control angles are analysed. A 2.5 kW HEPMSG prototype with a stator third harmonic winding is manufactured and tested. The predicted and experimental results are in good agreement, which verifies the correctness of the excitation principle of the proposed HEPMSG.

Cost-Effective Single-Inverter-Controlled Brushless Technique for Wound Rotor Synchronous Machines

This paper proposes a cost-effective brushless technique for wound rotor synchronous machines (WRSMs). The proposed technique involves a traditional current-controlled voltage source inverter that utilizes a simple hysteresis-controller-based current control scheme and supplies three-phase currents to the armature winding of the machine. The supplied armature currents inherently contain fundamental-harmonic and third-harmonic current components. These unique armature current waveforms were previously realized by using dual-inverter-controlled schemes achieved with and without thyristor switches to develop brushless WRSM topologies. The fundamental-harmonic current component is applied to develop the main stator field, whereas the third-harmonic component is employed to realize the harmonic magnetomotive force, which induces a back electromotive force (EMF) in the harmonic winding located at the rotor periphery. The induced harmonic EMF is rectified to deliver a DC current to the rotor field winding through a full-bridge diode rectifier to achieve brushless operation. The proposed cost-effective brushless technique for WRSMs is validated using 2-D finite element analysis employing JMAG-Designer 19.1 to investigate the electromagnetic and electromechanical behaviors of the machine. Furthermore, the proposed technique is employed in machine topologies with different pole/slot combinations for the armature winding to achieve better performance.

Back EMF Harmonic Analysis of Permanent Magnet Magnetic Geared Machine

Permanent magnet magnetic geared machine (PM-MGM) is widely researched as a potential core component of electrical continuously variable transmission system. Due to the dual mechanical port structure, back electromotive force (EMF) characteristics of PM-MGMs are quite different from that of conventional permanent magnet (PM) machines. In this article, back EMF harmonic features of PM-MGMs are thoroughly analyzed. The back EMF harmonic amplitude and order are analytically deduced, it can be found that both of them are variable and related with normalized speed ratio. A simulation/experiment method is proposed to separate and calculate different flux linkage components. A novel distortion factor criterion for PM-MGMs is defined to evaluate the variable back EMF distortion value. Different from existing criteria, the proposed criterion is a function of normalized speed ratio, hence it is more comprehensive for PM-MGM back EMF comparison and machine design. The torque ripple caused by back EMF harmonics is also analyzed. A PM-MGM prototype has been manufactured, and back EMF features as well as validity of the proposed distortion factor are verified by experiment.

Effect Comparison of Zigzag Skew PM Pole and Straight Skew Slot for Vibration Mitigation of PM Brush DC Motors

The electromagnetic vibration of permanent magnet brush dc (PMBDC) motors has its distinct feature, where only slot-frequency related components exist. Skew slot technique is naturally recalled to mitigate the slot-frequency vibration. Unfortunately, the straight skew slot normally used is not as effective as the mitigation of tooth harmonic electromotive force (EMF) or cogging torque. First, in this paper, the principle of vibration mitigation by straight skew is discussed and compared with mitigation of tooth harmonic EMF and cogging torque. The reason for poor effect of straight skew slot is illustrated by a specifically-designed experiment and finite-element method (FEM) simulation. In order to solve this problem, the zigzag skew PM pole technique is proposed for PMBDC motors for the first time, which overcomes the disadvantage of straight skew slot. The pulsating radial force and bending moment, two main causes of electromagnetic vibration, are derived and analyzed analytically and by the three-dimensional FEM for zigzag skew PM poles. At last, the experiments on two PMBDC motors, one with straight skew slots and the other with zigzag skew PM poles, are conducted to verify the effectiveness of the zigzag pole technique.

Third Harmonic Current Injection in Fault-Tolerant Five-Phase Permanent-Magnet Motor Drive

This paper presents a third harmonic current injection method for a five-phase permanent-magnet (PM) motor with trapezoidal back electromotive force (EMF) under postfault field oriented control (FOC). The key of the proposed method is the third harmonic current online calculation and injection under postfault FOC. The postfault FOC lies in the fundamental decoupled model based on the concept of maintaining spatial circular rotation of fundamental PM flux linkage vector and magnetic motive force under open-circuit fault. Based on the mathematical model of torque pulsations caused by third harmonics of air-gap flux, the injected third harmonic current can be calculated by the radio of the amplitude of third harmonic EMF and fundamental EMF easily. The presented fault-tolerant control strategy can achieve the real time optimal current reference generation and third harmonic current injection under postfault FOC while reducing the torque pulsations. The effectiveness of the proposed method is verified by experimental results under various operation conditions.

Predictive control of permanent magnet synchronous motor with non‐sinusoidal flux distribution for torque ripple minimisation using the recursive least square identification method

To reduce the torque ripple of permanent magnet synchronous motor with non-sinusoidal flux distribution, a new method is presented in this study. This method is based on model predictive control (MPC). MPC is a model-based control and requires an accurate model of the motor. A sliding mode observer, accompanied with a recursive least square estimator, is utilised to determine the magnitudes of the harmonics of the back electromotive force (EMF) waveforms. The appropriate current harmonics, considering the back EMF harmonics, are injected to shape the motor current. The interaction of non-sinusoidal back EMF and the shaped current leads to torque ripple reduction. The experimental results verify the effectiveness of the proposed method.