Magnetic Flux Linkage Research Articles

Operation Method of Non-Salient Permanent Magnet Synchronous Machine for Extended Speed Range

This paper proposes an operation method for the extended speed range of a surface-mounted permanent magnet (SPM) synchronous machine. The proposed method is based on a novel winding changeover scheme. The SPM machine has low synchronous inductance and hence poor field weakening capability. To enhance its field weakening capability, the permanent magnet's flux linkage can be reduced by performing a winding changeover. The proposed operation method increases the base speed of the machine by 3.83 times. In contrast to available two-inverter schemes with four thyristor switches, the proposed scheme utilizes a single-inverter topology drive and six bidirectional switches for the winding changeover. The machine works in two modes: cumulative and differential. In the cumulative mode, winding has a high induced back electromotive force (EMF), whereas in the differential mode, it falls by 3.54 times. The base speed increases approximately by the same ratio. After the mode switch, field weakening control is applied to the machine to further increase the speed range to 3.83 per unit. The proposed operation method was simulated in a commercial two-dimensional finite element method software in both modes under no-load and load operating conditions. The transient analysis was performed during the winding changeover, and speed range operation analysis was also carried out. The experimental results are provided to verify the extension of the speed range operation of the proposed novel winding changeover scheme for an SPM machine.

Linear Method for Diagnosis of Inter-Turn Short Circuits in 3-Phase Induction Motors

When a turn-to-turn short fault occurs in an induction motor, it will be accompanied by vibration and heating, which will have adverse effects on the entire power system. Thus, turn-to-turn short fault diagnosis of the stator is required, and major accidents can be prevented if an inter-turn short circuit (ITSC), which is the early stage of a turn-to-turn short, can be detected. This study reinterprets Park’s vector approach using Direct-Quadrature(D-Q) transformation for the linear separation of ITSCs and proposes an ITSC diagnosis method by defining the magnetic flux linkage pulsation and current change in the event of a turn-to-turn short. It is difficult to diagnose because the turn-to-turn short current change in an ITSC is considerably different from the induction motor loss. Hence, it was found through analysis that when the current change is considered through an analysis of the relationship between inductance and the winding number, the ITSC current becomes slightly smaller than the steady-state current. This was verified using the D-Q synchronous reference frame over time. We proposed a linear separation of the ITSC diagnosis from the steady state by considering the minimum values of the pulsating current as feature points.

Dual-Slot Power-Pickup Structure for Contactless Strip Inductive Power Track System

In this paper, a dual-slot power pickup suitable for an inductive power track system was developed using contactless power transmission techniques. A new strip-type inductive power track with high magnetic flux density and magnetic field uniformity is proposed. A dual-slot type power-pickup structure with high magnetic flux linkage was designed using equivalent magnetic circuit model analysis to improve the power transmission capacity and transmitting efficiency. To verify the contactless transmission characteristics of the proposed strip-type inductive power track system, a 1.2 m long laboratory-scale inductive power track was constructed. The SPLSC topology was used as the compound resonant circuit of a full-bridge inverter. According to the experimental results, the maximum transmitting efficiency of overall system is 72.52% at an output power of 289.52 W.

PWM-Based Flux Linkage and Rotor Temperature Estimations for Permanent Magnet Synchronous Machines

Monitoring of rotor temperature in permanent magnet (PM) synchronous machines is of great significance as high temperatures can cause partial or even irreversible demagnetization of the PMs. Rotor temperature measurement unfortunately is particularly difficult in practice, since it is difficult to access temperature sensors on a rotating shaft. Nevertheless, rotor temperature can be predicted indirectly with the information of rotor magnet flux linkage, as PM remanence decreases with rotor temperature. In this article, a simple and relatively accurate method for the online estimation of PM flux linkage is presented, based on the measurement of current response to the standard space-vector pulsewidth modulation (PWM). This method uses the already-existing PWM voltage as the excitation signal in order to avoid the need for additional signal injection. Knowledge of machine parameters, such as inductances which may vary due to saturation, is not required. The proposed methodology is experimentally verified and applied to rotor temperature prediction.

Analysis and Suppression of Slotting and Cross-Coupling Effects on Current Control in PM Synchronous Motor Drives

This paper proposes a d–q cross-coupling current controller for permanent magnet synchronous motor (PMSM) drives. Slotting and cross-coupling effects in PMSMs cause the effective air-gap length to vary with the rotor angle and distort the distribution of the air-gap flux. Such distortions have a significant influence on the current control by changing the relationship between the stator currents and voltages. To investigate their effects, a d–q model is established in this paper, which is suitable for describing the voltage characteristics of the actual PMSMs. The model contains the angle-dependent parameters, the cross-coupling inductance between d–q axes, and the q -axis permanent magnet flux linkage, unlike the ideal d–q model. The transfer function matrix from the d–q currents to d–q voltages of PMSM is newly derived from the model. Based on that, the current controller with the feedback and feedforward terms of 2-by-2 matrix is proposed. It is designed so that the independent gains are in low-pass filter forms and the coupling control gains are zero with eliminating interference between d–q axes. The proposed controller contributes to providing the stable control performance by canceling the slotting and cross-coupling effects. The performance of the proposed current controller is verified by experimental results.

Finite Element Modeling and Analysis of High Power, Low-loss Flux-Pipe Resonant Coils for Static Bidirectional Wireless Power Transfer

This paper presents the optimal modeling and finite element analysis of strong-coupled, high-power and low-loss flux-pipe resonant coils for bidirectional wireless power transfer (WPT), applicable to electric vehicles (EVs) using series-series compensation topology. The initial design involves the modeling of strong-coupled flux-pipe coils with a fixed number of wire-turns. The ohmic and core loss reduction for the optimized coil model was implemented by creating two separate coils that are electrically parallel but magnetically coupled in order to achieve maximum flux linkage between the secondary and primary coils. Reduction in the magnitude of eddy current losses was realized by design modification of the ferrite core geometry and optimized selection of shielding material. The ferrite core geometry was modified to create a C-shape that enabled the boosting and linkage of useful magnetic flux. In addition, an alternative copper shielding methodology was selected with the advantage of having fewer eddy current power losses per unit mass when compared with aluminum of the same physical dimension. From the simulation results obtained, the proposed flux-pipe model offers higher coil-to-coil efficiency and a significant increase in power level when compared with equivalent circular, rectangular and traditional flux-pipe models over a range of load resistance. The proposed model design is capable of transferring over 11 kW of power across an airgap of 200 mm with a coil-to-coil efficiency of over 99% at a load resistance of 60 Ω.

Performance Analysis and Operating Limits of a Dual-Inverter Open-Winding IPMSM Drive

Operating capabilities of a dual-inverter open-winding interior permanent magnet synchronous motor (IPMSM) drive are investigated and compared with those of a conventional single-inverter drive in maximum torque per ampere (MTPA) and field-weakening (FW) regions. To predict the performance and operating limits of the drive systems with improved accuracy, the impact of saturation on inductances and permanent magnet (PM) flux linkage values are taken into account, and core, copper, friction and windage, and solid losses are considered in a wide speed range. Performance prediction is conducted using machine's electromagnetic parameters and losses that are obtained via finite element analysis, coupled with an optimization algorithm to find optimal operating points in MTPA and FW regions. The analytical findings are further validated against experimental results obtained from a 1-kW dual-inverter IPMSM motor drive.

Electromagnetic Performances and Main Parameter Sensitivity Effect on Unbalance Magnetic Flux in a New Single-Phase FEFSM with Segmental Rotor

Three-phase field excitation flux switching motor (FEFSM) with salient rotor structure has been introduced with their advantages of rotor easy temperature elimination and controllable FEC magnetic flux. Yet, the salient rotor structure is found to lead a longer magnetic flux path between stator and rotor parts, producing a weak flux linkage along with low torque performances. Hence, a new structure of single-phase FEFSM using segmental rotor with non-overlap windings is proposed with advantages of shorter magnetic flux path, light weight and robust rotor structure. Analysis on fundamental magnetic flux characteristics, armature and FEC magnetic flux linkages, cogging torque, back-Emf, various torque capabilities, refinement of unbalance magnetic flux, and torque-power versus speed characteristics are conducted using 2D FEA through JMAG Designer version 15. The results show that magnetic flux amplitude ratio has been improved by 41.2% while the highest torque and power achieved are 1.45 Nm and 343.8 W, respectively.

Method for flux linkage optimization of permanent magnet synchronous motor based on nonlinear dynamic analysis

This paper investigates the nonlinear dynamic behavior characteristics of PMSM and its application in the optimization of magnetic flux linkage. A new compact representation of the PMSM nonlinear dynamic differential equation is established to reduce the complexity of system parameters by using the affine transformation method. Accordingly, the numerical simulations under different parameters varying are given and the dynamic behavior of system is analyzed in detail to provide a reference for motor design. Then, according to the practical design and the above analysis results, a 30 kW PMSM 2D/3D model is designed by software ANSYS and the rated parameters and dimensions are obtained correspondingly. In addition, the nonlinear dynamic theory is used to analyze the system with variable $$\psi _f $$ parameters, and the flux linkage stable region of PMSM is obtained concurrently. Moreover, five situations of PMSM models with different magnetic flux linkages are simulated by using the finite element analysis method. The optimum value of flux linkage and the corresponding permanent magnet specifications and dimensions are obtained to illustrate the effectiveness and feasibility of our theory result.

Analysis, Modeling, and Current Trajectory Control of Magnetization State Manipulation in Variable-Flux Permanent Magnet Machines

Magnetization and demagnetization current control is a critical part of the variable-flux permanent magnet machine control, but the variable-flux properties and saturation effects deteriorate conventional current controller performances. Thus, this paper proposes an improved feed-forward current controller that compensates voltage variations during the magnetization and demagnetization manipulations, obtaining better control performances. The compensation voltages are analyzed by finite-element method, and a modified mathematical model is developed to present the relation among the voltages, the flux linkages, and the manipulation currents. This model considers induced voltage and variable electromotive force, which are caused by the change of the permanent magnet flux linkage during the manipulations. Based on the model, the induced voltage, the cross-coupling rotating voltage, and the resistance voltage are compensated in the proposed feed-forward controller. This controller is verified by experiments, showing fast response and accurate trajectory tracking advantages.

Optimal Design of Rotor Slot Geometry to Reduce Rotor Leakage Reactance and Increase Starting Performance for High-Speed Spindle Motors

This paper proposes optimal designs of three closed rotor slots geometries for reducing the rotor leakage reactance and increasing the starting performance of high-speed spindle motors. The optimal designs were developed using the response surface methodology and Finite Element Method (FEM). Three closed rotor slot geometries, namely closed, round, and oval were investigated through FEM calculation and validated by experimental measurement for improving starting performance parameters such as starting current, starting torque, magnetic flux linkage in starting condition, and efficiency. In this study, a starting performance analysis, including the alternative equivalent circuit method and flux linkage FEM analysis, was employed. The results show that among the three slot geometries, the optimal design of the circular closed rotor slot produces the lowest rotor leakage reactance and the highest magnetic flux linkage, starting torque, and efficiency. A comparison between the simulation and experimental results validated the accuracy of the proposed model with percentage error being approximately 8%.

Fault‐tolerant FOC for five‐phase SPMSM with non‐sinusoidal back EMF

A fault-tolerant field-oriented control (FOC) is proposed for five-phase surface-mounted permanent magnet synchronous motor (SPMSM) with non-sinusoidal back electromotive force under single-phase open-circuit fault. On the basis of the concept of preserving the circular rotation of fundamental magnetic motive force and PM flux linkage, the decoupled model of five-phase SPMSM under single-phase open-circuit fault is derived. To suppress the torque ripples caused by third-harmonic content of PM flux linkage, the closed-form solution of current references with zero-torque pulsation in the synchronous coordinate is presented. Then, the presented solution is used for obtaining optimum current references to achieve minimum stator winding losses and maximum available torque while satisfying the zero-torque-pulsation constraint. The optimal current references generation method is simple and is suitable for real-time implementation. The experimental results confirm that the proposed method can effectively suppress the torque ripples and produce lower stator winding losses as well as wider-torque operation range compared with traditional fault-tolerant FOC method.

Back EMF, Torque–Angle, and Core Loss Characterization of a Variable-Flux Permanent-Magnet Machine

An appropriate torque–angle selection can improve the torque-to-current ratio of a machine, converter size, and provide an optimal motor operation. A precise information of the back electromotive force (EMF) helps estimating the magnet flux linkage. An accurate determination of the core loss leads to a better machine design and efficiency estimation. This paper presents the back EMF, flux linkage, torque–angle, and core loss characterization of a variable-flux permanent-magnet machine. The magnetic properties of AlNiCo 9 magnet and the process of magnetization and demagnetization are also described. The no-load back EMF, torque–angle curves, and no-load core losses are measured and simulated for a 7.5-hp variable-flux machine for three different magnetization levels. Static torque–angle curves are obtained by varying the current advance angle and the rotor position. Simulations are performed using three different machine design softwares to validate the design, software accuracy, and machine models. The core losses are also obtained using an analytical method, which is first utilized to calculate losses in M19G29 laminations, and then implemented to estimate the core losses of the prototyped variable-flux machine. The experimental results are found to be in a good agreement with the simulation and the core losses compared well with the analytical data.

Study and experimental performance evaluation of flux intensifying PM motor with variable leakage magnetic flux

AbstractThis paper describes a flux intensifying permanent‐magnet (PM) motor with variable leakage magnetic flux. The unique feature of this proposed motor is the ability to passively adjust the magnetic flux linkage into the armature windings in proportion to the armature magnetomotive force and/or armature current phase. The magnetic circuit topology of the flux intensifying PM motor and the passive variable leakage magnetic flux are determined through FE analysis. Then, the driving performance is experimentally elucidated through comparison with that of a reverse salient pole type (flux weakening) PM motor without variable leakage magnetic flux.

Analytical Method for Magnetic Field and Electromagnetic Performances in Switched Reluctance Machines

This paper presents a new analytical method for the computation of magnetic field distributions and electromagnetic performances in switched reluctance machines (SRM). The proposed model is sufficiently general to be used with any number of stator slots and rotor poles with electrically excited. Due to the inherent nonlinear characteristics of SRM, the conventional analytic model has a limited accuracy which does not take into account the saturation. In order to calculate the accuracy and consider the local magnetic saturation on the stator and rotor teeth, the proposed method is based on the resolution of 2-D Laplace’s and Poisson’s equations in polar coordinates by the separation of variables technique. The solution region is divided into three types of regular subdomains, viz. air gap, stator slots and rotor slots. Magnetic field distributions, flux linkage, self-inductance, mutual inductance and static electromagnetic torque computed with the proposed analytical method are validated through finite-element method.

PWM‐based Flux linkage estimation for permanent magnet synchronous machines

Monitoring of rotor temperature in permanent magnet synchronous machines (PMSM) is of great importance as high temperature could cause partial or even irreversible demagnetisation of the permanent magnets (PMs). Rotor temperature measurement unfortunately is particularly difficult in practice, since it is difficult to access temperature sensors on a rotating shaft. Nevertheless, rotor temperature can be obtained indirectly with the information of rotor magnet flux linkage, as PM remanence decreases with rotor temperature. Here, a simple and relatively accurate method for online estimation of PM flux linkage is presented, based on the measurement of current response to the standard space-vector pulse width modulation (SV-PWM). This method uses the already-existing PWM voltage as the excitation signal in order to avoid any form of signal injection which produces undesirable disturbance to the system. Knowledge of machine parameters, such as inductances which may vary due to saturation, is not required. The proposed methodology has been verified in real-time simulation.

Influence Mechanism of Electromechanical Parameters on Transient Vibration of Electric Wheel System

<div class="section abstract"><div class="htmlview paragraph">Electric wheel systems of in-wheel motor driven vehicles consist of the motor controller, in-wheel motor and tire-suspension assembly. The coupling between the electromagnetic excitation and elastic structure gives rise to electromechanical dynamic issues. As for the structural layout of the electric wheel system, the driving motor is directly connected to the wheel without torsion dampers or transmission in the driveline, thus making the electric wheel structure a weak damping system. Moreover, the driving torque of electric wheel can change rapidly in various conditions of vehicle. As a result, the transient vibration problem becomes one of the key electromechanical dynamic issues in the electric wheel system. To investigate this problem, the electromechanical coupling model of the electric wheel system is established first. Then the transient responses of the electric wheel under abrupt changes of the driving torque are simulated. The results indicate that the tire mainly suffers from longitudinal shocks in the anti-phase rotational mode at 95 Hz and vibration in the in-phase rotational mode at 44Hz successively, while the motor vibrates in the in-phase rotational mode at 44Hz. As the electric wheel system is electromechanically coupled, the influence mechanism and rules of electromechanical parameters on the transient vibration are studied. The results show that the permanent magnet flux linkage increases damping ratio of the in-phase rotational mode in virtue of the electromagnetic stiffness and damping, thus further weakening transient vibration of motor. The anti-phase rotational mode is sensitive to tire’s stiffness. It is effective to optimize tire’s shock by adjusting tire’s stiffness. This paper reveals the electromechanical coupling mechanism of the electric wheel system, and provides reference for parameter design from the perspective of improvement in dynamic characteristics.</div></div>

Structural Design of Partitioned Stator Doubly Salient Permanent Magnet Generator for Power Output Improvement

Partitioned stator doubly salient permanent magnet generators (PS-DSPGs) have been extensively used for electrical generation mainly due to their high reliability, high electromotive force (EMF), and high-power output. Therefore, we aim to improve the output power of a PS-DSPG by designing the optimal configuration of generator pole structure. Electrical characteristics including the magnetic flux linkage distribution, phase EMF, cogging torque, voltage regulation, and power output profile were characterized by using the finite element method. After optimizing the generator pole structure including the angle of air gap arc width, it was found that the proposed PS-DSPG with 18/15 (stator/rotor) pole structure with optimized air gap arc width could produce higher EMF of about 23.24% than a conventional structure because this structure has the suitable number of pole structures. Also, an analysis of voltage regulation and power output profiles under the loaded condition were carried out, and it was indicated that the PS-DSPG based on the suitable 18/15-pole structure could provide the best machine performance where the output power is 11.63% higher than the conventional structure. Hence, the proposed PS-DSPG with 18/15-pole structure can appropriately be utilized for electrical generation, especially in low-speed operated generator applications.

Magnetization State Regulation Characteristic Study of Series Hybrid Permanent Magnet Axial Field Flux-Switching Memory Machine

Due to the short axis, high torque density, and wide permanent magnet (PM) flux linkage regulation range, the series hybrid PM axial field flux-switching memory machine (SHPM-AFFSMM) has been paid much attention. In order to extend its speed range, the way to generate an effective current pulse to regulate the magnetization state of the low coercive force PM is the key issue. The magnetization state regulation (MSR) method characterized with bidirectional and quantitative current pulse is presented to investigate the MSR characteristics of the SHPM-AFFSMM. Based on the proposed MSR method, the MSR characteristics of the researched machine, including the inductance characteristics, cogging torque, and permanent magnet flux density, are investigated by simulation and experiment.

Research on Fast Design of Key Variables of Bearingless Flux-Switching Motor Based on Variable Structure Magnetic Network

The bearingless flux-switching permanent magnet motor (BFSPMM) adopts the stator permanent magnet structure, which is beneficial to the heat dissipation of the permanent magnet and reduces the risk of demagnetization caused by the temperature rise of the permanent magnet. However, since BFSPMM adopts the double-salient structure, the design method of the traditional rotor permanent magnet type motor with sine wave back electromotive force cannot be directly applied. Thus, the design of the BFSPMM is complicated and time consuming. To this end, this paper proposes a method to quickly design the key parameters of the BFSPMM, such as optimum tooth width ratio, electromagnetic torque, winding coupled permanent magnet flux, suspension force, etc. First, in order to overcome the shortcoming of finite element time consuming, a new variable structure magnetic network model (VSMNM) of the BFSPMM is built considering the eccentricity of rotor. Second, the expressions of the optimal rotor-to-stator tooth width ratio and the coupling permanent magnet flux linkage in power winding are directly deduced based on the proposed VSMNM. Then, the electromagnetic torque is deduced based on the permanent magnet flux linkage, and the suspension force is deduced based on VSMNM. Finally, the fast design method proposed in this paper is verified to be effective by the finite-element analysis and the experimental results.