It is very important to improve the parameters of the electric motor in order to improve its performance. One of the ways to improve the performance of electric motors is to use permanent magnets in the structure of induction motors. These types of motors are known as line start motors. The use of permanent magnets eliminates ohmic losses and increases efficiency. Due to the fact that permanent magnetism plays the most important role in these motors, the smallest change in the magnetic properties of the used magnet will cause malfunction of the machine. One of the important phenomena that changes the properties of the core magnet is the phenomenon of Demagnetization. Although this phenomenon has very destructive effects on engine performance, the design of electric motors is still done without considering this issue. In this article, a line start motor is designed. The numerical simulation results show that the performance and efficiency of the motor in the Demagnetization mode are significantly reduced. Also, the increased current in demagnetized motors causes a further decrease in the magnet's magnetic properties. This effect is progressively repeated many times until the property of the applied permanent magnet is lost. Finally, an analytical model was presented for examining and designing electric motors, considering the effects of Demagnetization. The results showed that the use of the analytical model of motor design considering the effects of Demagnetization can be a suitable alternative to the use of conventional methods in the design of electric motors.

Permanent magnet motors have been considered for a variety of applications due to their features such as high power density and high efficiency. One of the issues that should be investigated in the design of these motors is the Demagnetization problem. Usually, the Demagnetization analysis is carried out in a steady state, while Demagnetization effect in dynamic condition is more considerable due to pulse shaped of armature field. Based on this fact, in this paper, dynamic Demagnetization is investigated for an IPM V-shaped magnet. This study has been done for two types of magnet, each one in static & dynamic conditions and the results are compared. Moreover, the effect of flux weakening regime on Demagnetization is investigated.

In this paper, an analytical model is proposed for evaluating electromagnetic performances of permanent magnet vernier machines (PMVMs) under healthy and faulty conditions. The proposed model employs flexible magnetic equivalent circuit (MEC) method, which its accuracy can be selected by tunable parameters. The model is capable of considering the influence of saturation effect, skewed slots, slot leakage fluxes, and various winding arrangements for the machines with desired properties. First, the proposed model is used to predict the no-load performance of machine at healthy condition. Then, the machine loading behaviors under healthy and Demagnetization fault conditions are analyzed by the MEC model. Moreover, the results of the proposed model are compared and validated with those of 2-D finite element method (FEM) and 3-D FEM. Eventually, a specific pattern is extracted from the stator current spectrum to detect the Demagnetization fault.

Before sailing, submarines with ferromagnetic hulls are demagnetized to avoid damage and detection by sea mines and airborne systems. The increase in the residual magnetization of the submarine body after Demagnetization due to the rising and falling can reduce the effect of Demagnetization. This study aimed to investigate how internal hydrostatic pressure affects the magnetic signatures of a demagnetized submarine model. Magnetic sensors were placed at specific points under the body, and the changes in magnetic signatures were recorded when pressure was applied from 0 to 60 bar. The results show that by increasing the pressure up to 60 bar before Demagnetization, the magnetic field components originating from the sample's internal stresses showed a linear increase. After depressurization, there was an exponential decrease followed by a subsequent increase in permanent magnetization of about 6%. However, after Demagnetization, as the pressure increased up to 60 bar, the magnetic field generated by internal stresses in the sample increased by about 27%, but upon decreasing pressure, this magnetic field did not decrease but remained unchanged. This phenomenon negatively impacted the performance of the deperming process. Also, for further investigation, the increasing trend of magnetic signatures was evaluated at pressures of 30, 45, and 60 bar.

Permanent Magnets (PM), which are one of the most vulnerable and important components of permanent magnet machines, are at risk of Demagnetization for reasons such as overheating and corrosion. One of the most critical tasks of engineers in the industry is to prevent the machine's operation in the Demagnetization condition and replace the machine's defective PMs as much as possible. Demagnetization causes linkage flux reduction, electromagnetic force changes, and machine heating. This paper presents a new approach for demagnetized PM diagnosis in a permanent magnet linear synchronous machine using wavelet packet transform. Due to the high sensitivity to the flux changes, the electromotive force signal was selected as a detection signal. By examining this method in different Demagnetization cases, it is determined that this method has a proper performance. In this paper, the finite element software (Maxwell) and MATLAB were used to simulate the machine and analyze the data, respectively.

A double-sided axial flux Permanent Magnet (PM) generator which can be directly driven by small-scale low-speed turbines is highly suitable for use in renewable energy generation systems. Partial Demagnetization is a failure occurring under the high thermal operation of a Permanent Magnet machine. This paper focuses on partial Demagnetization fault diagnosis in a double-rotor double-sided axial flux PM generator using stator currents analysis under time-varying conditions. One of the most important problems in any fault diagnosis approach is the investigation of load and speed variation on the proposed indices. To overcome the aforementioned problems, this paper adopts a novelty detection algorithm based on the Hilbert–Huang transform for fault diagnosis. This approach relies on two steps: estimating the intrinsic mode functions (IMFs) by the empirical mode decomposition (EMD) and computing the instantaneous amplitude (IA) and Instantaneous Frequency (IF) of IMFs using the Hilbert transform. The more significant IMFs are determined using the Hilbert spectrum, which is applied for accurate fault diagnosis. The Partial Demagnetization severity can be evaluated based on the IMF’s energy value. The theoretical basis of the proposed method is presented. The effectiveness of the proposed method is verified by a series of simulation and experimental tests under different conditions.

Effects of post-sintering annealing treatment between 300 and 1000°C for up to 8 hrs time periods followed by either furnace cooling (FC) or air-cooling (AC) on the hard magnetic properties of some Nd-Fe-B based sintered magnets was investigated. It was shown that the intrinsic coercivity (Hci), second quadrant Demagnetization loop shape and thus the energy density (BH)maxvaried considerably as a result of the annealing treatment. However, no significant changes occurred in the remanence (J) values of the magnets. Annealing at 500°C for 1 hr followed by FC resulted in a considerable deterioration in the Demagnetization loop shapes and thus in (BH) max values in all the magnets. These changes were almost recoverable. By annealing at 500°C, followed by AC, no deterioration in the Demagnetization loop shape occurred for any of the magnets and thus there were some increases in (BH)max values of the magnets due to increase in their Hci values. The highest Hci in magnets A and C was obtained by a standard annealing treatment for 1 hr at 6000C, while in magnet B, the highest Hci occurred after an annealing treatment for 2 hrs at 500°C, both followed by AC. No deterioration in the Demagnetization loop shape was identified for any of the magnets either in FC or AC from 6000C. However, the coercivity enhancement in magnet A and in particular, in magnet B, was found to be much higher after AC than FC. In all the annealing treatments, the improvement in Hci and/or (BH)max values occurred in the first 1 or 2 hrs of annealing. Any further annealing beyond these times resulted in significant falls in the magnetic properties. Thus, long term annealing for up to 300 hrs at 400°C resulted in dramatic reductions in the hard magnetic properties, which could only be partially recovered. This behavior has been related to the oxidation of the magnets during long term annealing in a roughing pump vacuum. In this paper, the changes in Hci and (BH)max values during these annealing treatments are related to possible microstructural changes reported elsewhere.

An interior permanent magnet motor is a good option for traction application related to the induction motor and switched reluctance motor because of high mechanical rigidity and low Demagnetization risk. the design of this kind of motor is attractive for engineer despise the implementation cost of them in high constant speed power range (cpsr) is high. In this paper using combination of two ideas i.e. non-conventional air bridge and segmented permanent magnet a optimal design has been proposed. In this paper non-conventional air bridge is used for reducing the permanent magnet volume. The genetic algorithm has been applied to the goal function. Simulation results show the good performance of optimal design related the conventional design.

This paper presents the mechanical design and transient thermal analysis of a permanent magnet Brushless DC motor to be replaced with an induction motor and its gearbox for a propulsion application requiring 300 W and 220 RPM. This work presents a suitable method for direct motor drive design. The critical design criterion is based on magnet Demagnetization. The motor has magnets inset into the surface of the rotor to give a maximum field-weakening range. A prototype model is fabricated based on the presented method. Analytically based lumped circuit method for thermal analysis has been used to simulate the motor. Simulation results are compared with practical measurements. The comparison of the results shows that the presented method has a high efficiency in design and thermal analysis of BLDC motors.