Irreversible Demagnetization Of Permanent Magnet Research Articles

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.

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.

Fault-Tolerant Design Process of Spoke-Type IPM Motor Considering Irreversible Demagnetization of PM in Integrated Electric Brake System

In this article, a novel fault-tolerant design process of the spoke-type interior permanent magnet (IPM) motor is proposed to prevent the increase of cogging torque and torque ripple due to partial demagnetization fault and to minimize the motor size. First, unlike other research papers on the irreversible partial irreversible demagnetization of permanent magnet (PM), in this article, the effect of partial irreversible demagnetization faults on the cogging torque and torque ripple for the fault cases is investigated. Then, a novel fault-tolerant design process is proposed to solve the problem of partial demagnetization faults that increase the cogging torque and torque ripple. In the novel fault-tolerant design process, first, to solve the problem of increasing cogging torque and torque ripple due to the partial demagnetization fault, a process for implementing a uniform irreversible PM demagnetization is proposed. Second, to compensate for the motor torque constant decreased by degraded PM, which is caused by irreversible demagnetization of PM, a torque compensation coefficient is also proposed. The proposed fault-tolerant design process is applied to the motor design for the integrated electric brake (IEB) system that requires high torque density. In the optimal design process, Latin hypercube sampling (LHS), a kriging method, and a genetic algorithm are utilized. To verify the effectiveness of the proposed fault-tolerant design process, it is compared with the conventional optimized design results in which irreversible demagnetization of PM is not allowed at all to prevent the partial demagnetization faults. As a result of comparing the optimal design results, the proposed optimization model utilizing the fault-tolerant design process can significantly reduce the motor volume by 12.9%, compared to the conventional optimization model.

Demagnetization Fault Detection and Location in PMSM Based on Correlation Coefficient of Branch Current Signals

To address such challenges as an uncertain number of demagnetization poles of the permanent magnet synchronous motor (PMSM) and cases in which the fault cannot be located, this paper proposes a fault identification and location methodology based on the analysis of the motor stator current. First, the influence of the irreversible demagnetization of permanent magnets on the analytical model of the back electromotive force (Back-EMF) of the rotor in a single motor stator slot is analyzed. Moreover, considering the topology of the motor, the influence of the demagnetization fault on the stator phase current and branch current is analyzed. Since the stator phase currents cannot diagnose the partial demagnetization faults of PMSM with some topological structures, the stator branch current is selected as the signal for the identification and localization of the demagnetization fault. Secondly, the demagnetization fault diagnosis and mode recognition of the motor are carried out through the amplitude of the real-time branch current and the harmonic components of the PMSM. A sample database of demagnetization faults is established through calculation and normalization of the residual value of the stator branch current and the branch current of the healthy motor after demagnetization in one pole order. The fault threshold is obtained by analyzing the residual of the branch current of uniform demagnetization and the Pearson correlation coefficient of the fault sample database. Then, the correlation coefficient between the real-time branch current residual value of PMSM and the fault sample database is analyzed, and the number of demagnetization poles and the fault location are determined by the number and location of the calculated correlation coefficient exceeding the threshold. Finally, the feasibility and effectiveness of the proposed method are verified by the finite element analysis (FEA) results.

Ventilation structure design and heat transfer analysis of 3.3MW permanent magnet direct drive wind generators

For megawatt permanent magnet direct drive wind generator, with the increase of its power level, the insulation of the motor may be threatened by the increase of operating temperature, which may also lead to the irreversible demagnetization of permanent magnets. To solve this problem, a radial forced ventilation cooling structure was designed and established in this paper, based on a 3.3MW, 12rpm external rotor surface mount permanent magnet motor. The coupling relationship between electromagnetic field and temperature field is reasonably considered by iterative simulation method, and the temperature field and fluid flow are analyzed based on fluid–structure coupling method. The results show that the ventilation structure designed in this paper has a certain cooling effect and can meet the needs of its safe and stable operation. It has a certain reference significance for the cooling system design of megawatt permanent magnet direct drive wind generator.

ВИЗНАЧЕННЯ КООРДИНАТ ТОЧОК ПЕРЕМИКАНЬ ОПТИМАЛЬНИХ СТРАТЕГІЙ КЕРУВАННЯ ЯВНОПОЛЮСНИМИ СИНХРОННИМИ ДВИГУНАМИ З ПОСТІЙНИМИ МАГНІТАМИ

In this paper, a detailed analysis of the control algorithms for a permanent magnet synchronous motor in a wide range of speeds is carried out using the optimal strategies: "Maximum torque per ampere" (first zone), "Field weakening mode" (second zone) and "Maximum torque per volt" (third zone). A method for determining the boundaries of the first and second zones, as well as a method for determining the maximum static moment with which the motor can operate without the risk of irreversible demagnetization of permanent magnets, was proposed. It allows determining the maximum possible operating speed of the motor at a given load, the maximum motor load at a given speed, as well as the advisability of using the third control zone to achieve the maximum motor speed. References 19, figures 4.

Multi-Objective Optimization of Permanent Magnet Synchronous Motor for Electric Vehicle Considering Demagnetization

The irreversible demagnetization of permanent magnets causes the deterioration of the performance in permanent magnet synchronous motors (PMSMs), which are used for electric vehicles. NdFeB, which is the permanent magnet most commonly used in PMSMs for electric vehicles, is easily demagnetized at high temperatures. Because traction motors for electric vehicles reach high temperatures, and a high current can be instantaneously applied, permanent magnets of PMSM can be easily demagnetized. Therefore, it is important to study the demagnetization phenomenon of PMSMs for electric vehicles. However, since the demagnetization analysis procedure is complicated, previous studies have not been able to perform optimization considering demagnetization characteristics. In this study, we optimized the shape of a PMSM for electric vehicles by considering the demagnetization characteristics of permanent magnets using an automated design of experiments procedure. Using this procedure, a finite element analysis for each experimental point determined by a sampling method can be performed quickly and easily. The multi-objective function minimizes the demagnetization rate and maximizes the average torque, and the constraints are the efficiency and torque ripple. Various metamodels were generated for each of the multi-objective functions and constraints, and the metamodels with the best prediction performance were selected. By applying a multi-objective genetic algorithm, 1902 various optimal solutions were obtained. When the weight rate of the demagnetization rate to the torque was set to 0.1:0.9, the demagnetization rate and average torque were improved by 4.45% and 2.7%, respectively, compared to those of the initial model. The proposed multi-objective optimization method can guide the design of PMSMs for electric vehicles with high reliability and strong demagnetization characteristics.

Equivalent Magnetic Circuit Reluctance Optimization for Rotor Loss Reduction in Permanent Magnet Synchronous Motor for UPS-FESS

Due to poor heat dissipation of rotor, especially in flywheel energy storage system (FESS) for uninterruptible power supply (UPS), there is a higher risk of irreversible demagnetization by rotor temperature rising. Irreversible demagnetization of permanent magnets by rotor loss always is a critical problem of high-speed permanent magnet synchronous machine (PMSM). The stabilization and efficiency can be increased by reduction of rotor loss. By Finite Element Method simulations with experiment date, the rotor temperature rising of the prototype PMSM mainly comes from rotor loss induced by time harmonic. The distribution and components of prototype rotor loss are given. Rotor loss is analyzed by equivalent magnetic circuit with considering time harmonic magnetomotive force in this paper. According to analysis of rotor loss, this paper presents a method to reduce rotor loss without changing stator structure and winding current. This rotor structure optimization will not affect output performance of PMSM. The method has been proved to be available by the no-load experiment finally. It can greatly reduce the rotor loss in no-load operation when PMSM is driven in high-speed operation zone.

Comparison of Full-Area Simulation Method and Separated Simulation Method of Motor Temperature Field

Permanent magnet motor has become the main research direction of high power density motor, and the heat dissipation capability of the motor has become an important factor restricting the increase of motor power density. High-power density motor generates higher temperature when it works, and high temperature may cause motor insulation burnout, even irreversible demagnetization of permanent magnets. Therefore, thermal analysis and optimal design of cooling structure are very important for high power density motors. In this paper, a 3-D model of thermal simulation of permanent magnet motor is established, and the temperature field is calculated by two methods. 1. The fluid-solid coupling method is used to calculate the global temperature field of the motor and the cooling structure. 2. The fluid-solid coupling method is used to calculate the convective heat transfer coefficient of the cooling structure, then the heat transfer model is used to calculate the temperature field of the motor body. These two methods are introduced and compared in this paper, and the second method is considered to be well suited for optimal design of motor cooling structures.

A Novel Fault Tolerant Machine With Integral Slot Non-Overlapping Concentrated Winding

A novel fault tolerant machine with integral slot non-overlapping concentrated winding (ISNCW) is proposed in this paper. With the distribution of phase windings in axial, the proposed machine realized excellent isolation capability between different phases. The performance comparisons between the proposed machine and the traditional integer slot overlapping winding (ISOW) machine are made by the analytical method and finite element analysis (FEA). Compared to the ISOW machine, the proposed machine has better performance in low speed high torque applications, and much better fault tolerant capability and flux weakening capability. Especially, the proposed machine appears excellent performance in limiting the short circuit current and preventing the irreversible demagnetization of permanent magnet under short-circuit fault. The phase independent structure makes the maintenance and replacement of the fault module convenient and saves the maintenance cost further.

Rotor Structure on Reducing Demagnetization of Magnet and Torque Ripple in a PMa-synRM With Ferrite Permanent Magnet

A rotor structure of Permanent Magnet (PM)-assisted synchronous Reluctance Machine (PMa-synRM) with ferrite PM is presented in this paper, in which the irreversible demagnetization of PM and torque ripple are reduced. The bypass rib is proposed and added to the flux barrier of the rotor. The path for the demagnetizing field of armature windings is provided and the torque ripple can also be reduced by the bypass rib. Based on the 2-D finite-element analysis (FEA), the location and dimensions of the bypass rib are investigated and improved. A PMa-synRM with the proposed rotor structure is designed and compared with that using a conventional rotor. The field distributions for different currents are studied to explain the principle of the bypass rib. The results show that the PMa-synRM with the proposed rotor achieves higher antidemagnetization ability and lower torque ripple.

Principle and Design of a Novel Lorenz Force Type Bearingless Motor with Single-Axis Actively Regulated Capability

This paper proposes a novel Lorenz-force-type bearingless motor with single-axis actively positioned functionality. The novel motor consists of two slotless surface-mounted permanent magnet(SPM) motors, which have six skewed coils for each motor to constitute 3-phase windings and are in tandem along axial direction so as to achieve actively regulated axial motion. Additionally, two repulsive permanent magnet bearings (RPMBs) are used to passively stabilize radial- and tilting movements of the rotor. The slotless stator iron is employed for arrangement of the skewed coils in toroidal form. Compared with state-of-the-art single-axis actively controlled bearingless motors utilizing field weakening or strengthening effect of d-axis current to regulate axial movement, perhaps suffering irreversible demagnetization of permanent magnets especially at the time of start-up, the merit of this proposed motor is beneficial to prevent the demagnetization risk of permanent magnets. To verify the novel concept, firstly, theoretical analysis is carried out for modeling back electromagnetic force (back-EMF), axial force, drive torque. Followed by the analytical model, a detailed design process by integration of analytical method and finite element analysis (FEA) for the structural parameters are revealed. At last, 3-D FEA is performed to validate the correctness of analytical model, design process as well as to evaluate the performance of proposed motor.

Demagnetization Diagnosis of Permanent Magnet Synchronous Motor Using Frequency Analysis at Standstill Condition

Recently, electric vehicles have got significant attention because it is more eco-friendly and efficient than internal combustion engine vehicles. Instead of an internal combustion engine, the electric vehicle has a motor for propulsion. The permanent magnet synchronous motor which has permanent magnet instead of field winding in the rotor has especially higher efficiency and power density than other types of motor. When the irreversible demagnetization is occurred, drivers are exposed to high risk of accident by the fault operation of motor. Therefore, the irreversible demagnetization of permanent magnet should be detected to reduce the risk of accident. In this study, the demagnetization diagnosis method based on the result of locked rotor test is proposed. Based on short measurement time, the proposed diagnosis method aims to detect the demagnetization fault when an electric vehicle is at a complete standstill. The proposed method is verified through the finite element analysis.

Dynamic Irreversible Demagnetization Behavior of Line-start Permanent Magnet Synchronous Motors in the Starting Process

In the starting process of line-start permanent magnet synchronous motors, the relative lower flux density of the working point may cause irreversible demagnetization of permanent magnets. To research the dynamic irreversible demagnetization behavior, this article presents a sloped linear demagnetization model based on the time-stepping finite-element method. In this model, a new searching algorithm is used to quickly update the recoil line and the effective coercivity of each permanent magnet element so that the dynamic irreversible demagnetization effect can be considered effectively. Then the relationship between the demagnetization field and the rotor speed is studied, and the operation performances of the line-start permanent magnet synchronous motor after demagnetization in the starting process with different load conditions are compared. It is shown that the demagnetization field becomes larger with the rise of the rotor speed, and the demagnetization is more severe after a longer starting process with a larger load. Finally, the experimental validation on the characteristics of the dynamic irreversible demagnetization is performed by a line-start permanent magnet synchronous motor with a special rotor structure.

Detection of Demagnetization Fault in Interior Permanent Magnet Synchronous Motors for EV Based on UKF

In most applications, the permanent magnet flux linkage of interior permanent magnet synchronous motors is treated as a known constant value. However, high operation temperature, stator winding starting current impulsion, armature reaction and frequent field weakening control all may cause irreversible demagnetization of permanent magnet which has direct impacts on motor control performance. In order to implement demagnetization fault detection accurately, the nonlinear observation model is first set up allowing for the effects of magnetic saturation and cross saturation of IPMSM, and then the unscented Kalman filter (UKF) , based on dynamic data processing technology, is presented to implement flux linkage estimation and overcome the disadvantages of traditional extended Kalman filter (EKF). Finally, the simulation results are presented to verify the effectiveness of the proposed method, it is pointed that this method can estimate the permanent magnet flux linkage with the estimation error less than 3% in the full speed range of IPMSM, so it is fully competent for demagnetization fault detection, and consequently, can also prevent the deterioration of demagnetization and improve the reliability of drive system.

A Novel Starting Method of the Surface Permanent-Magnet BLDC Motors Without Position Sensor for Reciprocating Compressor

This paper describes a new position sensorless starting method, specialized for low-cost applications, of a brushless dc (BLDC) motor with a surface permanent-magnet (SPM) rotor to prevent demagnetization of permanent magnet and vibrations due to pulsating currents during the starting period. That the magnitude of peak current causes irreversible demagnetization of permanent magnet, has been measured through experimental tests. The proposed method limits the motor currents during the starting period to lower than the demagnetization currents by doing commutation depending on the level of the measured phase currents. Experimental results show that the proposed method implemented in an inverter for a BLDC motor-driven reciprocating compressor considerably reduces not only the pulsating currents but also the vibration of the compressor during starting.