Permanent Magnet Demagnetization Research Articles

Optimization of Nd-Fe-B permanent magnet guideways with high-temperature stability

High-temperature superconducting (HTS) pinning Maglev systems are advantageous due to their ability to achieve large-scale passive-stabilized levitation. Elevated temperatures can lead to a reduction in the magnetic characteristics of the permanent magnet guideway (PMG), which may pose a risk to the safe functioning of HTS Maglev trains. In order to guarantee the secure and dependable functioning of HTS Maglev trains, it is necessary to augment the high-temperature stability of the PMG. This study involves simulating the high-temperature stability of present PMGs and developing a new PMG that exhibits greater performance. Magnetic field simulation is employed to compute the demagnetization of permanent magnets (PMs) in several typical PMGs, encompassing both reversible and irreversible scenarios, in order to examine the factors contributing to demagnetization and evaluate the thermal stability of the PMGs at elevated temperatures. The grade, size, and magnetization direction of the Halbach-type PMG are subsequently optimized and compared to the original Halbach-type PMG. Following this, ideas for further optimization are provided. The optimized Halbach-type PMG reduces the overall decay ratio of the highest magnetic flux density Bz by 5.77% compared to the existing Halbach-type PMG. Additionally, the irreversible decay ratio is decreased by 6.13% at 85 ℃. The levitation force decay ratio on the HTS bulks above the optimized Halbach-type PMG is decreased by 8.11% compared to the existing Halbach-type PMG. Additionally, the irreversible decay ratio is reduced by 9% at 85 ℃. This study provides valuable insights for enhancing the efficiency and performance of PMGs and HTS Maglev trains over extended periods of operation.

Optimization of Nd-Fe-B permanent magnet guideways with high-temperature stability

High-temperature superconducting (HTS) pinning Maglev systems are advantageous due to their ability to achieve large-scale passive-stabilized levitation. Elevated temperatures can lead to a reduction in the magnetic characteristics of the permanent magnet guideway (PMG), which may pose a risk to the safe functioning of HTS Maglev trains. In order to guarantee the secure and dependable functioning of HTS Maglev trains, it is necessary to augment the high-temperature stability of the PMG. This study involves simulating the high-temperature stability of present PMGs and developing a new PMG that exhibits greater performance. Magnetic field simulation is employed to compute the demagnetization of permanent magnets (PMs) in several typical PMGs, encompassing both reversible and irreversible scenarios, in order to examine the factors contributing to demagnetization and evaluate the thermal stability of the PMGs at elevated temperatures. The grade, size, and magnetization direction of the Halbach-type PMG are subsequently optimized and compared to the original Halbach-type PMG. Following this, ideas for further optimization are provided. The optimized Halbach-type PMG reduces the overall decay ratio of the highest magnetic flux density Bz by 5.77% compared to the existing Halbach-type PMG. Additionally, the irreversible decay ratio is decreased by 6.13% at 85 ℃. The levitation force decay ratio on the HTS bulks above the optimized Halbach-type PMG is decreased by 8.11% compared to the existing Halbach-type PMG. Additionally, the irreversible decay ratio is reduced by 9% at 85 ℃. This study provides valuable insights for enhancing the efficiency and performance of PMGs and HTS Maglev trains over extended periods of operation.

Loss And Temperature Rise Analysis of Permanent Magnet Motor Based on Magneto-thermal Coupling Field

Because of the situation of motor performance degradation caused by permanent magnet demagnetization and increased loss of built-in permanent magnet synchronous motor under high temperature working conditions, this paper optimizes the rotor magnetic circuit structure of the motor and uses amorphous alloys. The material stator core replaces the original ordinary silicon steel stator core to suppress the motor temperature increase and reduce the motor loss. Through simulation, comparative analysis and calculation, the result could show that losses and temperature increase are significantly reduced after optimization. Finally, temperature rise testing was conducted on the prototype, confirming the correctness of the improved model.

Electromagnetic–Thermal Characteristics Analysis of a Tubular Permanent Magnet Linear Generator for Free-Piston Engines

Temperature rise of the tubular permanent magnet linear generator (TPMLG) might lead to insulation failure and demagnetization of permanent magnets, affecting the safe and stable operation of other equipment and the entire system. Herein, a bidirectional electromagnetic–thermal coupling method for analyzing the electromagnetic loss and thermal characteristics of a TPMLG considering the effect of increased temperature on the permanent magnet was proposed. To study the electromagnetic–thermal characteristics of the TPMLG under stable power generation, a two-dimensional electromagnetic field model and a three-dimensional temperature field model were established and coupled. The temperature field of the TPMLG was numerically calculated using computational fluid dynamics over finite volume method under natural air cooling and forced air cooling conditions. Effects of loss and air flow velocity on the steady temperature field were investigated. Results indicated that copper loss increased by 24.5% considering the influence of temperature rise. The windings’ top central position in the TPMLG was the spot with the highest temperature of 127.8 °C and there was a potential demagnetization risk for the permanent magnets. Some reference for future research of clarifying thermal characteristics and cooling design was provided.

Permanent magnet synchronous motor demagnetization fault diagnosis based on leakage radial magnetic density

A method of demagnetization fault diagnosis of permanent magnet synchronous motors is proposed by measuring the radial magnetic density of the leakage field at the external space point of the motor. The method enables non-invasive diagnosis of motor permanent magnet demagnetization faults compared to other methods. In this paper, an analytical model of the radial magnetic density of the leakage field of a surface-mounted permanent magnet synchronous motor under no-load conditions is proposed, and its accuracy is verified by simulation. The influence mode of demagnetization fault on the radial magnetic density of the leakage field is analyzed, which provides a new idea for the diagnosis of motor demagnetization fault.

Online position error correction technique for sensorless control of multipole permanent magnet machines

In order to improve the reliability of electric machine drive systems, the position encoder is often replaced with an estimator, such as the extended Kalman filter. However, estimation errors can still occur, especially in machines with high pole number, commonly used in renewable energy systems. The high number of pole pairs amplifies the effect of estimation errors, leading to a substantial divergence between actual and controlled currents, potentially causing harm to the machine through the excessive heat generation or demagnetization of permanent magnets. To address this issue, an error compensation method has been proposed and tested in a control scheme for a tidal stream system based on a multipole dual-star permanent magnet synchronous generator. The method estimates the position error by determining the q-axis permanent magnet flux and correcting it through a PI regulator. Simulation results demonstrate the effectiveness of the proposed method, even with a non-null initial rotor position.

Comparative analysis of a mining truck motor with permanent magnets in a rotor and a synchronous homopolar motor without magnets in a drive

The relevance. Increasing need for using mining trucks with a diesel-electric (hybrid) drive for development of minerals. Improving operational and cost characteristics of the electric drive of mining trucks helps to reduce costs in the development of minerals. The main aim. To compare theoretically the performance of synchronous traction motors of various designs (a conventional design with permanent magnets inside a rotor and a homopolar design without permanent magnets with an excitation winding on a stator), optimized by the same method, in the drive of a mining truck. To optimize the motor design to reduce power loss and required inverter power, as well as to limit torque ripple and reduce the risk of permanent magnet demagnetization. Objects. Design of twelve-pole nine-phase synchronous AC motors with a rated power of 370 kW of various designs: a homopolar motor without permanent magnets with an excitation winding on the stator and a motor of a traditional design with permanent magnets in the rotor. Methods. Derivative-free optimization method; equivalent circuit method; mathematical modeling; two-dimensional finite element method. Results. Based on the analysis, the advantages and disadvantages of the considered motors were revealed. The advantage of the motor with permanent magnets in the rotor is reduction in active part length by 30 %. The advantage of the homopolar motor with an excitation winding on the stator are 4.6 times lower cost of active materials. In addition, the homopolar motor has a more reliable design, without the risk of overheating, demagnetization or deterioration of the properties of permanent magnets over time

Effect Analysis of Demagnetization of Permanent Magnet Synchronous Motor for Electric Drilling Tool on Air-gap Flux Density

Electric drilling tools have been developed in the field of drilling because of their high efficiency. As the core component of electric drilling tool, permanent magnet synchronous motor(PMSM) provides power for drilling tool. However, in the process of drilling, the permanent magnet of PMSM will appear demagnetization.The value of air-gap flux density affects the performance and efficiency of the motor directly. Demagnetization faults are divided into uniform demagnetization and local demagnetization.In order to study the influence of demagnetization of PMSM on the air-gap flux density, mechanism of permanent magnet is analyzed Firstly, and then establishing numerical model with analytical method. Finally, simulation motor demagnetization using finite element method(FEM) based on Maxwell. No-load and load operating state are analyzed under the two fault modes are considered in this paper, and compared with the healthy state of the motor. The analytical results show that when the demagnetization fault occurs in the motor permanent magnet, the air-gap flux density will decrease accordingly.The FEM method results show that with the increase of uniform demagnetization rate, the flux density of the air-gap almost decreases in proportion to the increase of demagnetization rate. The demagnetization of single pole permanent magnet has little effect on the magnetic density of the nearby permanent magnet, but it will lead to the imbalance of the whole electromagnetic field of the motor. The air-gap flux density can be used as a characteristic index to judge the fault of demagnetization.

Novel revolving heat pipe cooling structure of permanent magnet synchronous motor for electric vehicle

The high temperature rises and uneven axial temperature distribution of permanent magnet synchronous motors applied in electric vehicles can lead to demagnetization of permanent magnets and turn-to-turn short circuit failures in the windings. Thus, a cooling structure based on revolving and fixed annular heat pipes is proposed. That is the revolving heat pipes are installed in the rotor, which are further increasing the rotor's heat transfer efficiency under the centrifugal force of rotor rotation. The fixed annular heat pipes are installed in the stator to cool the windings, especially the end of the windings. The experiments are designed to derive the equivalent thermal conductivity of the proposed revolving and fixed annular heat pipes on this basis. The effectiveness of the proposed cooling structure is verified by computational fluid dynamics simulations which are conducted in three typical operating conditions of the motor used in electric vehicles. The results show that the temperature rise of the rotor, permanent magnet and winding are decreased by up to 70.39%, 69.4%, and 46.18% respectively by the proposed cooling structure. It indicated that the axial temperature rises distribution of heat generating parts can be effectively equalized, and the operating time under maximum torque condition can be effectively extended, that from 30 s to 100 s.

Optimized FCS-MPCC based on disturbance feedback rejection for IPMSMs under demagnetization fault in high-speed trains

This paper proposes an optimized finite control set model predictive current control (FCS-MPCC) strategy based on disturbance feedback rejection control (DFRC) method for interior permanent magnet synchronous motors (IPMSM) employed in high-speed trains. The strategy aims to mitigate the impact of parameter mismatch caused by permanent magnet demagnetization faults. Firstly, a discrete predicting model is established for IPMSMs, considering the mismatch in flux linkage, resistance, and inductance. The analysis is conducted to evaluate the impact of disturbances caused by demagnetization faults on the traditional FCS-MPCC. Secondly, second-order sliding mode disturbances observers (SMDOs) are utilized to detect real-time disturbances under demagnetization faults. The stability analysis of the second-order SMDOs is conducted using a Lyapunov function. Furthermore, disturbance controllers are developed to regulate the disturbances and generate compensating values for the FCS-MPCC. Lastly, experimental validation is performed on two IPMSMs to demonstrate the effectiveness of the proposed DFRC-based FCS-MPCC strategy against parameter mismatch issues caused by demagnetization faults.

Design and Analysis of Wide Speed Regulation of Variable Leakage Flux Reverse Salient-Pole Motor

In this article, a new variable leakage flux reverse salient-pole motor (VLF-RSPM) is raised to widen the speed range. The innovation is to realize both reverse salient-pole characteristics and variable leakage flux characteristics by using a method of adding magnetic bridges and magnetic barriers. Firstly, the evolution of the topological structure and working principle of the motor are introduced. Secondly, based on 2D Finite Element Analysis (FEA), the electromagnetic properties and noise of the motor are analyzed in detail, and the electromagnetic properties are contrasted with that of the conventional V-type synchronous motor (CVTSM). The results show that VLF-RSPM has the advantages of small torque ripple, strong magnetic weakening ability, low noise, high efficiency, and low risk of permanent magnet demagnetization under different conditions. In addition, it is verified that the proposed motor extends the speed range.

A Period Energy Method for Demagnetization Detection in Surface Permanent Magnet Motors with Search Coils

Irreversible demagnetization of permanent magnets (PMs) in PM synchronous motors (PMSMs) degrades the performance and efficiency of a machine and its drive system. There are numerous fault diagnosis methods for detecting demagnetization under steady-state conditions. However, only a few works could be found on fault diagnosis under dynamic conditions, whereas the dynamic operation of a motor is a very common scenario, e.g., electric vehicles. The voltage and current signal-based traditional fault detection method is not only affected by the structure of the motor, but it also becomes complicated to extract signals involving fault characteristics. Hence, this paper proposes a search coil-based online method for detecting demagnetization faults in PMSMs under dynamic conditions, which are not affected by the motor structure. To gather the flux of the stator tooth, flexible Printed circuit board (FPCB) search coils are positioned at the stator slot. The search coil is made up of two branches that are one pole apart and arranged in reverse sequence. In this installation option, the output signal in the fault state cannot be eliminated, and the output signal in the health state is zero. This paper defines only that characteristic value related to the position angle of the rotor. Further, the aim was to simultaneously eliminate the influence of elements like the search coil installation error and the inherent dispersion of the permanent magnet on the detection results. To characterize the fault degree, the measurement differential between the health state and the fault state is further integrated according to a predetermined angle range. Last but not least, speed-independent detection of individual permanent magnet demagnetization faults is possible using rotor position and stator tooth flux. A six-phase PMSM was used in experiments to show the efficiency of the suggested approach. The findings of the experiment demonstrate that the suggested strategy may precisely ascertain when a defect will occur.

Temperature Field Analysis of Oil-Cooled Heat Dissipation in High-Speed Permanent Magnet Synchronous Motor

With the development of high-speed permanent magnet synchronous motors (PMSM), the requirements for speed are getting higher and higher, and the power density increase is getting bigger and bigger. However, too high a loss density will cause motor heat dissipation difficulties, resulting in motor insulation aging and permanent synchronous magnet demagnetization failure, which seriously affects the safe operation of the motor. Therefore, it is necessary to analyze the fluid field and temperature field for oil-cooled high-speed PMSM. In this paper, a 40 kW back-wound oil-cooled high-speed PMSM is used as the research object. Firstly, a three-dimensional fluid-solid coupled heat transfer model of high-speed PMSM is established based on the parameters of the motor, and the fluid flow characteristics inside the motor are analyzed based on fluid dynamics and heat transfer theory, and then the overall and local temperature rise distributions of the motor are compared and analyzed to reveal the influence of the temperature rise of each component inside the high-speed permanent magnet synchronous motor after being cooled by the cooling structure. Secondly, based on the finite element model, the motor temperature rises and oil flow characteristics with oil flow rate are analyzed to come up with an optimized solution. Finally, the accuracy of the analysis method is verified by conducting temperature rise experiments on the prototype.

Detection of Trailing Edge PM Demagnetization in Surface PM Synchronous Motors

Irreversible demagnetization of permanent magnets (PM) in PM synchronous motors (PMSM) degrades the performance and efficiency of the machine and drive system. Demagnetizing MMF applied to PMs operating at high temperature is known as one of the leading root causes of irreversible PM demagnetization. This is most likely to cause of demagnetization on the trailing edge of the PMs in all poles, as witnessed by prior research and industrial case studies presented in this work. However, most of the work on detecting PM demagnetization focus on uniform or partial (local) PM demagnetization. In this paper, a comparative evaluation of existing test methods on the detectability of trailing edge PM demagnetization, is given. It is shown that it is difficult to detect this type of fault with back-EMF, stator current/voltage, vibration, or leakage flux-based analysis, since trailing edge demagnetization does not produce asymmetry between PMs. An experimental study on a 380 V, 8 pole, 1.8 kW surface PMSM with trailing edge PM demagnetization shows that airgap flux-based detection is the most reliable means of detecting this fault.

An Effective Nontransient Active Short-Circuit Method for PMSM in Electric Vehicles

This paper proposes an effective stepwise non-transient method for entering and exiting the Active Short Circuit (ASC) of Permanent Magnet Synchronous Motor (PMSM) to protect the safety of vehicle's drive system when fatal faults occur in the Electric Vehicles (EV) powertrain system with high motor speed. It's found that excessive transient current and overshoot voltage inevitably occur when ASC enters and exits directly, which may cause the demagnetization of permanent magnet and failure of Motor Controller Unit (MCU). The two-phase short-circuit is utilized as a transition step before entering and exiting three-phase ASC according to the rotor magnet position, and almost no transient current and overshoot voltage exist during the whole short-circuit period. Then there are no constraints of ASC for system design and the system material cost can be reduced. This approach is useful for function safety implement of MCU for EV application with fast attenuation rate of transient current, high robustness, and limited resources requirement. The method with effective suppression of transient current and overshoot voltage is verified by the experimental results from a 15kW PMSM test platform.

Demagnetization Fault Diagnosis of the Permanent Magnet Motor for Electric Vehicles Based on Temperature Characteristic Quantity

Permanent magnet motors are widely used in the driving system of electric vehicles because of their high power density and small size. However, the permanent magnet motor is prone to demagnetization due to the complex operating environment of electric vehicles and characteristics of permanent magnet motors. To ensure the normal operation of vehicles, the demagnetization fault diagnosis of permanent magnets should develop. In this study, the thermal behavior of a permanent magnet motor under local demagnetization fault is discussed. Results show that the demagnetization of permanent magnets has a significant effect on the temperature of the motor; thus, the temperature is added into input signals of the permanent magnet demagnetization fault diagnosis. The healthy state of the permanent magnet is predicted by the back propagation (BP) neural network to realize the demagnetization fault diagnosis. First, the demagnetization test platform is built to test the performance of the motor, and the current, torque, and temperature of the motor are measured according to different demagnetization degrees. Second, the demagnetization simulation model of the motor is established by the finite-element method, and the air gap magnetic field, loss, and temperature of the motor are analyzed. Lastly, the temperature, current, speed, and torque signals are selected as input signals of the neural network model, and the demagnetization rate of the rotor is taking as the output signal. The neural network prediction model is established and trained, and the good generalization ability is obtained.

Design of Spoke-Type Permanent Magnet Synchronous Generator for Low Capacity Wind Turbine Considering Magnetization and Cogging Torques

Permanent magnet synchronous generators (PMSGs) with high output density per unit volume are becoming widespread in wind-power generation systems. Among them, spoke-type PMSGs are more challenging to magnetize than other PMSGs, owing to their structural characteristics. Magnetization performance is critical because it is directly related to the demagnetization and mass productivity of permanent magnets, and load performance is reduced when non-magnetization occurs due to the low magnetization performance. Additionally, the starting performance is crucial in wind turbines and is influenced by the cogging torque of the PMSG. This is because starting a wind turbine with a large cogging torque is more challenging. Therefore, this study proposes a spoke-type PMSG rotor shape design for low capacity wind turbines that considers magnetization and cogging torques. We analyzed the principle of magnetization and the factors influencing magnetization performance, and designed a rotor shape with improved magnetization performance. Additionally, we applied an asymmetric rotor barrier structure to reduce the cogging torque and analyze the performance of the final model using finite element analysis. We analyzed the temperature saturation during the operation of the final model using a thermal network method and validated the irreversible demagnetization accordingly.

Magnetic stability of low corrective force PM in series hybrid magnet memory machine under inverter open-circuit fault

Variable flux memory machine (VFMM) can dynamically adjust its air-gap magnetic field by changing the magnetization states of the employed low corrective force (LCF) permanent magnets (PMs). Due to the demagnetization risk of LCF PMs under armature current, it is necessary to analyze their magnetic stability in various operation states. The magnetic stability of LCF PMs in series hybrid magnet VFMM (SHM-VFMM) under inverter open-circuit (IOC) fault is studied in this article. Firstly, the topology of the investigated SHM-VFMM is introduced, and the field-circuit coupled model of the machine under IOC fault is established. Then, the magnetic stabilities of LCF PMs during the normal and fault operations are analyzed and compared by using the finite element method. The effects of LCF PM demagnetization and fault current on torque are also studied. Afterward, the influence mechanism of the fault armature magnetomotive force (MMF) on LCF PM demagnetization is revealed by using the synthetic MMF graphic method. Finally, the main factor affecting the LCF PM demagnetization under IOC fault is highlighted and an effective method for recovering the magnetic stability of LCF PM is proposed.

Design of Multilayer Winding-Based Halbach Array PM Compulsator

Compulsator provides higher energy density and comparable power density for pulse power supply than capacitor-based sources. With the added feature of natural current, zero-crossing capabilities make compulsator the ideal choice for pulse power supply to electromagnetic launch applications. A multilayer Halbach array permanent magnet (PM) compulsator is designed to achieve the desired performance. The multilayer winding arrangement is considered to minimize the self-inductance and to maximize the short-circuit current capability of the compulsator. Thus, different winding configurations with series and parallel connections in the compulsator are presented in detail. The mathematical modeling of the designed compulsator is also presented in brief. The designed compulsator is simulated by considering temperature rise, PM demagnetization effect, and so on. The designed compulsator performance in a dead short circuit of all phases and with single-phase short-circuit condition is presented. The obtained results show that the designed compulsator achieves the target objective.

Analysis of Split-Tooth Stator PM Vernier Machines With Zero-Sequence Current Excitation

This article proposes a series of split-tooth stator permanent magnet (PM) Vernier machines with zero-sequence current excitation, which integrates enhanced torque density and flux adjustment capability. The key is to design the split tooth to exert desired dual magnetic field modulation effect so as to efficiently utilize the hybrid magnetic fields by the PM and zero-sequence current. Meanwhile, with the split-tooth design, the paralleled flux paths are achieved to offer improved flux regulation capability and reduced PM demagnetization risk. In this article, the machine topologies and operation principle are introduced. Hybrid excitation magnetic field is analyzed with the consideration of dual magnetic field modulation of split-tooth structure. Influences of split tooth and PM on torque and flux regulation capability are analyzed. Electromagnetic performances of the proposed machine are analyzed and compared. A prototype is manufactured and tested to validate the theoretical analysis.