Interior Permanent Magnet Motor Research Articles

Level-Set-Based Optimal Stator Design of Interior Permanent-Magnet Motor for Torque Ripple Reduction Using Phase-Field Model

The interior permanent-magnet (IPM) motor is widely used in industrial applications due to its high power density. Despite this efficiency, the average torque increase achieved by the reluctance torque leads to high torque ripple, the major cause of motor noise and vibration. Therefore, many studies related to the size optimization have been performed to reduce this ripple effect. This paper suggests an optimal stator shape design for the IPM motor satisfying both improved torque performance and geometrical simplification for manufacturing. To control the geometrical complexity, the concepts of the phase-field model and the level-set method are employed. The optimization problem is formulated to minimize two values: the first is the torque ripple done by adjusting the torque values at any rotor position to constant target torque, and the second is the fictitious interface energy of the phase-field model as it narrows the interfacial region. The proposed method is applied to the structural stator design of a 12-pole 18-slot IPM motor developed as a power source for hybrid electric vehicles.

Topology Optimization of the Stator for Minimizing Cogging Torque of IPM Motors

This study presents a topology optimization method to reduce cogging torque, applied to the design of the stator core of an interior permanent magnet motor. The proposed method uses a reaction-diffusion equation and optimization is separately performed based on two objective functions: 1) minimization of the cogging torque itself, for a number of rotor positions; and 2) minimization of the magnetic energy variation. The optimization results show that configurations having dummy slots are desirable, but the number of dummy slots differs according to the objective function used.

Design Tradeoffs Between Constant Power Speed Range, Uncontrolled Generator Operation, and Rated Current of IPM Motor Drives

A closed-form approximate formulation is proposed to establish a relationship between the uncontrolled generator (UCG) operation of interior permanent-magnet (IPM) motors at high speed and the constant power speed range (CPSR) and drive current capabilities. High-saliency IPM motors of the PM-assisted synchronous reluctance type are mainly considered in the analysis, since they are proved to have the most favorable ratio between flux weakening capability and UCG voltage. The results of the analysis show the tight relationship between the uncontrolled overvoltage and the CPSR of the drive. Moreover, where the uncontrolled voltage is higher, the relationship between the CPSR and the motor current amplitude becomes stiffer: For small current variations, a large reduction of the speed range can occur. The analysis is validated experimentally on two motors of very different size (500 W and 1 MW).

Technique for partially strengthening electrical steel sheet of IPM motor using cavitation peening

Cavitation peening (CP), which utilises the impact caused by cavitation bubbles collapsing, can improve the fatigue strength of metallic materials as well as the yield stress and tensile strength. The rotor cores in interior permanent magnet motors use electrical steel sheet. In order to increase the permissible rotating speed of the motor and achieve high efficiency, the mechanical strength of the stress concentration area in the steel sheet where the magnet is pressed needs to be enhanced. In the present paper, to improve the yield stress and tensile strength, the steel sheet was peened by CP. The peening effect on these mechanical properties was evaluated by tensile and indentation tests. The experimental results from the tensile tests revealed that CP can increase the yield stress by 22% compared to that before CP. In addition, the yield stress and tensile strength increased along with the CP processing time.

Improvement of Convergence Characteristics for Steady-State Analysis of Motors With Simplified Singularity Decomposition-Explicit Error Correction Method*

In order to improve the convergence for steady-state analysis, the simplified singularity decomposition-explicit error correction (SD-EEC) method is developed. This paper proposes techniques to apply the simplified SD-EEC method to an interior permanent magnet (IPM) motor and to an induction motor. The usefulness of the techniques is verified through the applications to an interior permanent magnet (IPM) motor and an induction motor.

Reduction of Cogging Torque in IPM Motors by Using the Taguchi and Finite Element Method

This paper proposes a method for shape optimization for reduction of cogging torque in Interior Permanent Magnet (IPM) motor. In the process of optimization, use the Taguchi Experiment Design and The optimization is realized by analyses and simulations with Finite Element Analysis (FEA). The design optimization process is described and results are presented in this paper. Results from simulations, indicate reduction of cogging torque and torque ripple and doesn't considerable 1.16% decrease of the average of motor’s output torque.

Optimization of Rotor of Actual IPM Motor Using ON/OFF Method

For the design of an Interior Permanent Magnet (IPM) motor with small torque ripple and large driving torque, the optimal design method called the ON/OFF method is attractive, because a new magnetic circuit, which we could not imagined beforehand, may be obtained. In this paper, a non-parametric optimization technique to find a new magnetic circuit which minimizes a torque ripple and maximizes a driving torque of IPM motor is examined. The effectiveness of the ON/OFF method for the optimal design of a motor is examined by applying it to the design of the verification model of the IPM motor established by the technical committee of IEE of Japan. Factors affecting torque ripple and driving torque of the obtained optimal motor core are also discussed.

Improvement of Convergence Characteristics for Steady-State Analysis of Motors With Simplified Singularity Decomposition-Explicit Error Correction Method

In order to improve the convergence for steady-state analysis, the simplified singularity decomposition-explicit error correction (SD-EEC) method is developed. This paper proposes techniques to apply the simplified SD-EEC method to an interior permanent magnet (IPM) motor and to an induction motor. The usefulness of the techniques is verified through the applications to an interior permanent magnet (IPM) motor and an induction motor.

Optimization of Interior PM Motors With Machaon Rotor Flux Barriers

Interior permanent magnet (IPM) motors are normally designed with two or more flux barriers per pole. The form of such flux barriers has a direct impact on the torque developed by the IPM motor, with regards to both its average value and ripple. The Machaon structure includes flux barriers of different shape, aimed at reducing the torque ripple. Their shape depends on the number of poles, number of slots, winding arrangements, and PM volume used in the rotor. An optimization technique is adopted in order to determine the best shape of the flux barriers with the objective of achieving a smooth torque with a high average value.

Ultrafast Finite-Element Analysis of Brushless PM Machines Based on Space

A computationally efficient method is proposed for the steady-state performance simulation of brushless permanent-magnet (PM) motors. Only a minimum number of magnetostatic finite-element (FE) analysis (FEA) solutions are used in conjunction with space-time transformations, which are based on the periodicity specific to synchronous machines. For an example electronically controlled interior PM (IPM) motor with six teeth per pole and a distributed winding, a single nonlinear magnetostatic FE solution was employed to estimate the flux density time waveforms in the stator teeth and yoke. Other results include core losses, back electromotive force, and torque. The extension of the method to fractional-slot topologies with reduced number of teeth and concentrated (non-overlapping) coils is discussed with reference to a nine-slot six-pole IPM motor example. The computational time is reduced by one to two orders of magnitude as compared with more laborious time-stepping FEA. Successful validation was performed against experimental data and detailed FEA results.

Electromechanical system with IPM motor used in electric or hybrid vehicle

PurposeIn the last few years, the understanding of environmental problems has grown. Car producers – original equipment manufacturers – are aiming to reduce fuel consumption and pollution. In order to fulfil these aims, new technologies have been launched. Many hydraulics systems have been removed and replaced with electric ones, e.g. power steering, water and oil pump, etc. In this paper, an electromechanical subsystem used in an automotive application is analyzed. The subsystem is composed of interior permanent synchronous magnet motor and electronic control unit. The range of mechanical output power for studied system is up to 1 kW. The aim of this paper is to compare electromechanical systems working with different on‐board voltage levels in order to find the optimum balance between motors' and electronics' efficiency. This will help to decrease the total system's weight, the consequence of which will decrease fuel consumption and reduce CO2 emissions.Design/methodology/approachDuring the analysis, the reduced order modelling (ROM) techniques has been applied. First, with utilization of finite‐elemente‐methode the basic motor's parameter like: synchronous inductance and flux per pole as a function of the direct‐axis current and also the quadrature‐axis current are calculated. In the second step, these parameters are used in the system simulation. During this simulation, the maximum torque per ampere control strategy together with ROM techniques was used.FindingsAs a result, the performance of the system for different voltage levels has been obtained. Additionally, the important factors for an electromechanical system, such as maximum power density, sizing and cost of the total electromechanical system, have been compared.Practical implicationsThe performed comparison shows that the cost optimized system should work with the higher voltage, where the electric motor size is reduced ca. 25 per cent. This result is also valid for different electromechanical systems in an automotive area, e.g. automated manual transmission, engine cooling and electric compressor.Originality/valueIt is the first paper, where electric power steering system design for different on‐board voltage levels has been systematically analyzed and compared. Results from this paper can be also applied to different electromechanical systems mounted in hybrid or electric cars.

An Adaptive-Filter-Based Torque-Ripple Minimization of a Fuzzy-Logic Controller for Speed Control of IPM Motor Drives

This paper presents an adaptive-filter-based torque-ripple minimization (TRM) of a fuzzy-logic controller (FLC) for speed control of an interior permanent magnet (IPM) motor drive. A simple and effective first-order digital infinite impulse response filter is utilized to reduce the torque ripples introduced by the FLC. The gain of the filter is adapted online based on the magnitude of the torque ripple. The optimal position of the filter in the complete drive is also determined for effective TRM. The various sources of torque pulsations in a practical electric-machine drive are described. The main causes of the torque ripple in an FLC are also explained. A simulation model for closed vector control of an FLC-based IPM motor drive incorporating the proposed TRM technique is developed in Matlab/Simulink. The complete drive is also experimentally implemented using digital signal processor board DS1102 for a laboratory 1-hp IPM motor. The effectiveness of the proposed technique is investigated, both in simulation and experiment, at different operating conditions. It is found that the performance of the FLC-based IPM drive is improved significantly with the proposed TRM technique.

Design of rotor shape to reduce torque ripple in IPM motors

This paper presents a shape design sensitivity analysis of the effect of geometrical parameters on torque pulsations of an interior permanent magnet (IPM) synchronous motor. The analysis was conducted in two dimensions using the finite element method (FEM). Calculation results have been compared with experimental results.

Automatic Tracking of MTPA Trajectory in IPM Motor Drives Based on AC Current Injection

This paper deals with a novel approach for the real-time tracking of the maximum-torque-per-ampere (MTPA) trajectory of an interior permanent-magnet (IPM) motor drive. The proposed approach is based on the injection of proper test signals and allows the MTPA trajectory to be learned and updated in the drive during steady-state conditions. The analytical development of the estimation algorithm, which is supported by a complete validation by simulation, is given in this paper. Finally, experimental results are presented based on a prototype IPM drive system.

RNA Model of IPM Motor Using Variable Magnetomotive Forces and Variable Reluctances

Interior permanent magnet (IPM) motors have large amounts of torque and are much more efficient than other motors since they can utilize both magnetic torque and reluctance torque together. However, the current vector needs to be controlled to utilize both torques effectively. Hence, it is necessary to design and analyze motor drive circuits in addition to motor structures. We propose a method of calculating the characteristics of an IPM motor based on reluctance network analysis (RNA). The proposed RNA model of the IPM motor consists of multiple nonlinear reluctances and magnetomotive forces, which periodically change with the rotor position so that the rotary motion of the rotor can be simulated. The RNA model can easily be coupled with an electric circuit and mechanical system. Therefore, it is suitable for designing and analyzing the IPM motor-drive system. The validity of the proposed method is proved by comparing its results with those obtained from the finite element method (FEM).

Optimal design of an IPM motor using Taguchi and Rosenbrock's methods

Techniques for the design optimization for cogging torque minimization and average torque maximization of a high-speed 2-pole interior permanent magnet (IPM) synchronous motor are presented. It is shown by the finite element method (FEM) and measurement, that combined the Taguchi and Rosenbrock's methods is a very efficient and effective approach in robust design a high performance motor.

二層IPMモータの磁石配置最適化

The arrangement of permanent magnets in double-layer interior permanent-magnet motors is optimized for variable-speed applications. First, the arrangement of magnets is decided by automatic optimization. Next, the superiority of the optimized motor is discussed by considering d- and q-axis equivalent circuits that take into account the magnetic saturation of the rotor core. Finally, experimental verification is carried out with a prototype motor. It is confirmed that the maximum torque of the optimized motor under both low-speed and high-speed conditions is higher than that of conventional motors because of the relatively large q-axis inductance and small d-axis inductance. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 183(4): 54–63, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22348

Design Comparison of Fractional-Slot IPM Machine Types for an Electric Power Steering Application

This paper deals with the design comparison of interior permanent magnet (IPM) motors with fractional-slot winding configurations for an electric power steering (EPS) application. By making comparisons of these configurations based on cogging torque, torque ripple, average torque, and efficiency, an IPM rotor configuration has been chosen for use as a prototype motor. The Taguchi parameter method coupled with the finite element analysis (FEA) is employed to achieve the desired performance requirements within a reasonable geometry. To assess the rated current and thermal behavior of the motor, the lumped circuit models are conducted.

Reduction of Magnet Eddy-Current Loss in Interior Permanent-Magnet Motors With Concentrated Windings

In this paper, we develop stator and rotor shapes of interior permanent-magnet motors with concentrated windings in order to reduce the eddy-current loss of the magnets at high rotational speeds under field-weakening control. First, the main factors that cause the magnet eddy-current loss in the motor are investigated from the results of the 3-D finite-element method. The magnet eddy-current loss is separated into three components due to their origins, and the largest component is specified. With this result, an automatic shape optimization is carried out to determine the stator and rotor shapes, which reduce the magnet eddy-current loss without significant decreases in the torque. Finally, the proposed stator and rotor are manufactured in order to confirm the characteristics. The advantages over the conventional motor are clarified.

Core Losses and Torque Ripple in IPM Machines: Dedicated Modeling and Design Tradeoff

The proper combination of stator and rotor slot numbers is pursued in the design of interior permanent-magnet (IPM) motors with wide constant-power speed range. At high speed, in the flux-weakening region, the arising of stator and rotor iron losses due to magnetomotive-force (MMF) spatial harmonics limits the IPM motor performance. Torque ripple is another problem for this kind of machines, both at low and high speed. The numbers of stator slots and rotor equivalent slots have a major impact on both the loss and ripple aspects. A simplified model is proposed here in order to evaluate both problems with a general approach and point out the possible design tradeoff. With respect to previous models in the literature, both stator and rotor losses are included, and a more comprehensive approach is followed in the description of the rotor MMF harmonics. The model's effectiveness is tested through finite element analysis simulations and some experimental results. The proposed approach is useful for the selection of the IPM machine structure according to the specific requirements of the application.