Interior Permanent Magnet Motor Research Articles

Torque Estimation in High-Efficency IPM Synchronous Motor Drives

In modern electrical drives, the energy saving starts with the careful generation of the electromagnetic torque, which involves the electrical motor and its current control. A modern choice is represented by an anisotropic synchronous interior permanent magnet (IPM) motor combined with the maximum torque per ampere (MTPA) control technique. The MTPA locus brings along additional information that is worth deepening. In particular, this paper shows that a proper rearrangement of the torque expression in MTPA condition, merged with a simple least-square algorithm, returns an accurate online estimation of the electromagnetic torque. The effectiveness of the proposed method is proved by a worked out example, based on an IPM drive model fitted with finite-element analysis and experimental measurements, including motor saturation effects. The torque estimator extends its usability in the whole working region of the drive, even during transients outside the MTPA curve, and it comes almost for free. In this, the proposed method should be technically sound in many industrial applications.

Design Methodology for Variable Leakage Flux IPM for Automobile Traction Drives

This paper presents a novel methodology for the variable leakage flux interior permanent-magnet (VLF-IPM) motor taking advantage of the variable leakage flux property in the rotor core controlled by the $q$ -axis current, without any additional components. The fundamental phenomenon is explained with finite-element analysis results; then, the theoretical equations expressing the variable flux linkage controlled by the $q$ -axis current have been conducted. The proof-of-principle model was designed, and the fundamental properties, such as torque–speed envelope and efficiency map, were evaluated. It was shown that the proposed motor can reduce energy consumption on duty-cycle driving.

Air-Barrier Width Prediction of Interior Permanent Magnet Motor for Electric Vehicle Considering Fatigue Failure by Centrifugal Force

Recently, the interior permanent magnet (IPM) motors for electric vehicle (EV) traction motor are being extensively researched because of its high energy density and high efficiency. The traction motor for EV requires high power and high efficiency at the wide driving region. Therefore, it is essential to fully consider the characteristics of the motor from low speed to high-speed driving regions. Especially, when the motor is driven at high speed, a significant centrifugal force is applied to the rotor. Thus, the rotor must be stably structured and be fully endured at the critical speed. In this paper, aims to examine the characteristics of the IPM motor by adjusting the width of air-barrier according to the permanent magnet position which is critical in designing an IPM motor for EV traction motors and to conduct a centrifugal force analysis for grasping mechanical safety.

IPM 모터의 출력밀도 향상에 관한 연구

Recently, it has to design the motor to raise power density because of many necessary application, such as home appliances and hybrid electric vehicles. Power of motor is made up of the torque and speed. So, if the motor which is the same size and shape is designed to raise speed, power and power density are increase.BR However, it is not easy to control interior permanent magnet (IPM) motor at high speed due to voltage constraint. So, this paper proposed simple method to solve the high speed control problem in the motor design stage, when it assumes that motor drive system has to have current margin. Basic idea is changing number of turns and current while retaining the same magnetomotive force (MMF) in this paper.

Modeling, Analysis, and Testing of a Novel Spoke-Type Interior Permanent Magnet Motor With Improved Flux Weakening Capability

Spoke-type interior permanent magnet (IPM) machines are an attractive topology for high-performance electric motors, especially designed for vehicle traction applications. In this paper, a special design for a spoke-type IPM motor is presented to enhance motor flux-weakening capability in the operation over a wide speed range. The proposed design consists of a simple and robust mechanical device that includes radially displaceable rotor yokes, connected to the shaft by means of springs. At high speed, the centrifugal force prevails over the elastic one due to springs, causing the mobile yokes to displace radially and establish a partial magnetic short circuit between PMs. This increases PM leakage flux and consequently reduces the air-gap field. As a result, a mechanical flux weakening effect is achieved at high speed, which helps significantly to reduce the demagnetizing $\boldsymbol {d}$ -axis current to be injected by the inverter, along with the related copper losses and demagnetization issues. The proposed design is investigated in this paper using an analytical model whose parameters are computed by finite-element analysis. The effectiveness of the solution being set forth is successfully proven by some testing on a laboratory prototype. Experimental results are compared with analytical predictions showing a satisfactory accordance.

Rational Design Optimization Method for Reducing Cost and Improving Performance of Commonalized IPM Motors

In this paper, we propose an economically efficient optimal design method of different-size interior permanent magnet (IPM) motors to maximize their efficiency. Since the homothetic shape is used, the optimization design is, at once, performed. The use of the commonalized design can reduce the productive costs. Game theory is employed as an optimization method. The game theory can simultaneously increase the efficiency of all the IPM motors with the common and homothetic shape. So far, there are no previous reports considering both the economical efficiency and the motor performance simultaneously. Therefore, the proposed optimal design method of the commonalized different-size IPM motors using the game theory method achieves a high electrical efficiency in addition to the economical efficiency due to design optimization.

Investigation and Design of a High-Power Flux-Switching Permanent Magnet Machine for Hybrid Electric Vehicles

Flux-switching permanent magnet (FSPM) machines exhibit high torque density, high efficiency, and robust rotor structure. In this paper, a prototype of a high-power three-phase 12-stator-slot/10-rotor-pole FSPM motor used for hybrid electric vehicles (HEVs) is designed by finite-element analysis (FEA). First, the initial FEA model is improved by gradually taking into account lamination ${B}$ – ${H}$ curves due to different electrical frequencies, operation temperatures, 3-D end effect, and rotor eccentric. Thereafter, a modular manufacture method of the FSPM motor is discussed with the improved FEA model and validated by experimental measurements. Then, the measured overload capability of the FSPM motor is compared with that of an interior permanent magnet (IPM) motor used in Honda Civic, and the results indicate that the IPM motor exhibits significantly stronger overload capability, which is analyzed in depth from soft-iron materials, cooling conditions, and and so on. Finally, both the merits and demerits of FSPM motor employed for low-voltage and high-current HEV applications are highlighted.

Optimal Rotor Design of IPM Motor for Improving Torque Performance Considering Thermal Demagnetization of Magnet

This paper proposes a new design technique for improving torque performance of interior permanent magnet (IPM) motors with consideration of the thermal characteristic of magnet. To verify the driving performance of IPM motor at operating temperature, a magnetic-thermal coupled analysis was performed with a heat source, such as iron loss and copper loss, and the thermal characteristics of permanent magnet (PM) is considered to define the magnetic property. The optimization problem is formulated to minimize the harmonics of magnetic flux, which cause iron loss, as well as to maximize the output torque for satisfying the design target. To obtain an optimal rotor shape of the IPM motor, which is composed of both PM and ferromagnetic material, a multi-phase level set model is employed for representing the precise boundaries of the magnetic materials. A design example of a motor with Nd-Fe-B magnet, which has a tendency to be demagnetized at high temperature, is provided to verify the effectiveness of the proposed method.

Robust Optimization Considering Probabilistic Magnetic Degradation

This paper presents robust topology optimization of electromagnetic machines by considering the magnetic degradation caused by mechanical and thermal stresses in punching, shrinking fitting, and other manufacturing processes. The topology optimization is performed using two methods: one is the robust genetic algorithm in which random noises are added to the magnetic characteristic parameters and the other takes the deviations in the objective and constraint functions due to the degradation into account. These methods are applied to optimization of the flux barrier shapes in an interior permanent magnetic motor to find that one can successfully realize robust design.

Multimaterial Topology Optimization of Electric Machines Based on Normalized Gaussian Network

This paper presents a topology optimization method for multimaterial models based on the normalized Gaussian network. In this method, one can determine optimal shapes of machines that are composed of various materials, such as iron, magnetic, and non-magnetic material. The present method is applied to the optimization of the average torque for interior permanent magnet motor to determine the distributions of magnetic core and flux barrier as well as magnets. The optimization results show that average torque can be improved using as small amount of magnet as possible. In addition, the characteristic of the present method is discussed in detail.

Iron Loss Estimation Method for Rotating Machines Taking Account of Hysteretic Property

This paper investigates a novel estimation method for iron losses considering hysteretic property and skin effect simultaneously. In the proposed method, iron losses considering both hysteretic property and skin effect are estimated by utilizing a 1-D finite element method as a postprocessing of the usual 2-D analyses based on ordinary magnetization curve. To demonstrate the effectiveness of the proposed iron loss estimation method, we compare numerical results with measured ones. Furthermore, the proposed method is applied to iron loss analysis of an interior permanent magnet motor fed by pulsewidth modulation inverter.

Evaluation of Applying Retaining Shield Rotor for High-Speed Interior Permanent Magnet Motors

This paper proposes a novel rotor structure for high-speed interior permanent magnet motors to overcome huge centrifugal forces under high-speed operation. Instead of the conventional axial stacking of silicon-steel laminations, the retaining shield rotor is inter-stacked by high-strength stainless-steel plates to enhance the rotor strength against the huge centrifugal force. Both mechanical characteristics and electromagnetic behaviors of the retaining shield rotor are analyzed using finite-element method in this paper. Prototypes and experimental results are demonstrated to evaluate the performance. The analysis and test results show that the proposed retaining shield rotor could effectively enhance the rotor strength without a significant impact on the electromagnetic performance, while some design constraints should be compromised.

Modeling and V/F control of a Hysteresis Interior Permanent Magnet Motor

A hysteresis interior permanent-magnet (IPM) motor is a solid-rotor self-starting synchronous motor. Its rotor has a hysteresis ring made of composite material with high degree of hysteresis energy per unit volume. The Neodymium Boron Iron (Nd-B-Fe) magnets are buried inside the hysteresis ring. This paper presents the analytical modeling of a hysteresis IPM motor to investigate its starting and synchronization capability for different loading conditions. A V/F controller has been designed to operate the motor at variable speeds. Simulations have been carried out to obtain the run-up responses of a three-phase four-pole 208 V, 2.5 kW hysteresis IPM motor. Simulation results are presented and analyzed in this paper. Experimental investigations have been carried out for the same 2.5-kW motor. Both the simulation and experimental results are presented in this paper.

トポロジー最適化による埋込磁石同期モータの回転子形状最適化

This paper presents a new topology optimization method based on normalized Gaussian network (NGnet). In this method, the machine region is subdivided into small elements whose material states are determined from the output of NGnet so that the objective function is extremized under the given constraints. The present method is applied to shape optimization of the rotor in an interior permanent magnet motor. The rotor shape is optimized to minimize the torque ripple while keeping the average torque. It is shown that the optimization halves the torque ripple while the average torque remains unchanged. This result was validated through a comparison between the computed and measured torques.

Sensitivity Analysis of Torque Ripple Reduction of Synchronous Reluctance and Interior PM Motors

The main drawback of reluctance machines is a high torque ripple, due to the interaction between the stator magnetomotive force and the rotor structure. Adopting a rotor configuration characterized by several flux barriers per pole, there is a high influence of the rotor geometry on the machine performance in terms of both average torque and ripple. An optimization is often required to determine the optimal rotor geometry so as to achieve a high and smooth torque. Then, the geometry determined earlier should guarantee good performance for various operating points (i.e., changing the current amplitude and phase), as well as for small variations of the geometry. This paper investigates this aspect, showing the results of optimizations carried out on various machines. The impact of the geometry parameters is taken into account, and the sensitivity of the optimal solution to the geometry variation is pointed out. This paper highlights the difficulty to get a robust geometry as far as the torque ripple reduction is concerned. Finally, a few experimental results on a synchronous reluctance motor prototype will be presented, compared with finite-element analysis simulations for validation.

Design and Evaluation of Interior Permanent-Magnet Compressor Motors for Commercial Transcritical $\hbox{CO}_{2}$ (R-744) Heat Pump Water Heaters

This paper describes the design and experimental evaluation of two high-efficiency interior permanent-magnet (IPM) motors for use in a commercial transcritical $\hbox{CO}_{2}$ (R-744) heat pump water heater (HPWH). Two IPM topologies, a 36-slot 6-pole topology and a 9-slot 6-pole topology, were selected, optimized, and prototyped using a common flat-bar IPM rotor. The experimental analysis includes standard measurements of electrical machine parameters, and dynamometer tests. The initial measurements of the $\hbox{CO}_{2}$ compressor performance with a stock line-fed induction machine and the 36-slot 6-pole IPM configuration have been completed. This paper finds a small isentropic compressor efficiency improvement from using the 36-slot 6-pole IPM motor compared to the stock line-fed induction machine at rated operating conditions (essentially constant speed). This paper also expands the open literature on the impact of high-efficiency motor drives on $\hbox{CO}_{2}$ compressor operation and $\hbox{CO}_{2}$ HPWH systems.

Characteristics of Interior Permanent Magnet Synchronous Motor with Imperfect Magnets

This paper investigates the effect of demagnetization of the permanent magnets (PM) on the performance of interior permanent magnet motors. In order to remove the individual difference of the motors, several shapes of PMs are prepared, and the experiments are carried out with the same stator. This paper takes into account two types control strategy, V/f constant control and vector control. It is clarified that the stator current and the vibration acceleration are useful for the fault detection of demagnetized PMs under controlled by V/f constant. Under the vector control, the stator voltage and the vibration acceleration are useful for the detection of demagnetized PMs. Moreover, it is found that the fundamental component of stator voltage of the motor with magnets demagnetized in the axial direction is larger than that with magnets demagnetized in the radial direction.

Optimal Design of a Novel V-Type Interior Permanent Magnet Motor with Assisted Barriers for the Improvement of Torque Characteristics

This paper performs a study on the optimal design of V-type interior permanent magnet motors (VIPMMs), in which the rotor is equipped with assisted barriers for the improvement of average torque and torque ripple. The approach differs from the conventional interior permanent magnet motors, in which the reluctance torque due to saliency reaches a maximum value at a current phase angle located 45 electrical degrees with respect to the maximum value obtained from the magnetic torque produced by the rotor magnets. The adoption of assisted barriers is employed to improve the torque production by creating rotor asymmetry to allow the reluctance torque and the magnetic torque reach a maximum value near or at the same current phase angle. To evaluate the contribution, the frozen permeability method is utilized to segregate the torque into its reluctance and magnetic torque components. First, an iterative optimization is performed on a concept design of a 6/4 VIPMM for demonstrating the design principle based on finite element method. Then, the VIPMM is further optimized by algorithms, such as the kriging method and genetic algorithm for improving the torque characteristics and efficiency. As a result, the optimal VIPMM with assisted barriers shows the substantially improved performance compared with a conventional design.

Efficient forced vibration reanalysis method for rotating electric machines

Rotating electric machines are subject to forced vibration by magnetic force excitation with wide-band frequency spectrum that are dependent on the operating conditions. Therefore, when designing the electric machines, it is inevitable to compute the vibration response of the machines at various operating conditions efficiently and accurately. This paper presents an efficient frequency-domain vibration analysis method for the electric machines. The method enables the efficient re-analysis of the vibration response of electric machines at various operating conditions without the necessity to re-compute the harmonic response by finite element analyses. Theoretical background of the proposed method is provided, which is based on the modal reduction of the magnetic force excitation by a set of amplitude-modulated standing-waves. The method is applied to the forced response vibration of the interior permanent magnet motor at a fixed operating condition. The results computed by the proposed method agree very well with those computed by the conventional harmonic response analysis by the FEA. The proposed method is then applied to the spin-up test condition to demonstrate its applicability to various operating conditions. It is observed that the proposed method can successfully be applied to the spin-up test conditions, and the measured dominant frequency peaks in the frequency response can be well captured by the proposed approach.

Finite-Settling-Steps Direct Torque and Flux Control for Torque-Controlled Interior PM Motors at Voltage Limits

This paper proposes a voltage-limited finite-settling-step direct torque and flux control (FSS-DTFC) method with a constant switching frequency for torque-controlled interior permanent-magnet synchronous motors (IPMSMs). The proposed control law dynamically scales the voltage vectors on the hexagonal voltage boundary to ensure the maximum torque capabilities under the given operating conditions while simultaneously regulating the stator flux linkage magnitude under flux-weakening operation. Instead of relying on classical overmodulation methods at voltage limits, this paper developed two independent voltage truncation rules to facilitate the possible voltage vector choices. The analytical solution led to the dynamic voltage modification at each time step with respect to the available inverter voltage. The voltage-limited FSS-DTFC approach has potential advantages in achieving a fast transient torque trajectory and direct manipulation of the stator flux linkage while exploiting the maximum voltage excitation.