Conventional Interior Permanent Magnet Research Articles

A Reverse-Salient Permanent Magnet Synchronous Motor and Its dq-Axis Current Distribution Laws

The reverse-salient permanent magnet synchronous motors (RSPMSMs) have attracted considerable attention in electric vehicles due to their wide constant-power speed range. However, the d-q-axis current distribution laws of the RSPMSM are absent, and the relationships between motor parameters and the constant-power speed range are still unclear. First, the flux-intensifying effects and d-q-axis current distribution laws of the RSPMSM are investigated. Second, the relationships between motor parameters and the constant-power speed range are summarized. Then, an RSPMSM with a wide constant-power speed range is proposed. The electromagnetic performance of the proposed RSPMSM is investigated by finite element method (FEM) simulations and is compared with a conventional interior permanent magnet synchronous motor (IPMSM). Finally, an RSPMSM prototype is manufactured and tested. The results show that the RSPMSM exhibits favorable characteristics such as a wide constant-power speed range, weak flux-weakening current, high permanent magnet operating point, strong short-circuit current suppression capability and high efficiency at a high speed. The constant-power speed range tested by the experiment reaches 5.5:1. Thus, the d-q-axis current distribution laws, the relationships between motor parameters and the constant-power speed range are of great significance to the design of the RSPMSM.

Improving the Flux-Weakening Capability of Interior Permanent Magnet Machines by Number of Turns Changing Methodology

In this paper, an interior permanent magnet (IPM) machine having two sets of windings with different number of turns is developed to improve the limited flux-weakening (FW) capability and efficiency, simultaneously. The flux-adjustable range appears to be somewhat limited because of the limited maximum inverter voltage and high magnetic saturation, which degrades the FW capability. To address its restricted FW capability, a unique winding-switching concept is introduced, in which auxiliary coils with lower turns alternately function as the secondary armature winding, resulting in flux-linkage reduction within the same phase. Winding topologies, design considerations, the FW principle, and FW computations have all been addressed. To validate the feasibility of the proposed FW enhancement strategy, a co-simulation procedure based on the 2D finite element method (FEM) and MatLab codes is used to determine the steady-state and FW performance characteristics of IPM machines with various winding topologies. All steady-state and FW performance characteristics of the conventional IPM machine and the proposed IPM machines have been compared quantitatively. Furthermore, to ensure the accuracy of the analytical and numerical calculations provided in this study, the predicted efficiency map of the original Toyota Prius 2010 IPM machine is validated using the efficiency measurements provided.

Comparison Study of Permanent Magnet Synchronous Machines With Consequent Pole and HUPM Rotor

The consequent permanent magnet (CPM) pole rotor and harmonic utilization permanent magnet (HUPM) rotor are promising candidates for electric machines with less rare earth materials. Therefore, this article focuses on the analysis and comparison of these rotor types in terms of air-gap flux density characteristics, magnet utilization, and torque density. In the first part, an analytical approach is used to investigate the magneto motive force (MMF) distribution of the rotor and air-gap flux density characteristics. In the second part, finite-element methods (FEMs) are used to compare both rotor topologies with a conventional interior permanent magnet (PM) and spoke PM rotor. The results show that CPM and HUPM rotors can reduce the volume of PMs compared with the conventional configurations. However, with the HUPM rotor, a higher torque density and magnet utilization ratio can be achieved at the same time.

A Novel Spoke-Type Asymmetric Rotor Interior Permanent Magnet Machine

This article proposes a novel spoke-type asymmetric interior permanent magnet (AIPM) rotor topology that employs an additional asymmetric flux barrier in each pole of interior permanent magnet (IPM) synchronous machines for torque density enhancement and torque pulsating suppression without introducing any extra cost. The proposed AIPM-I machine, an existing spoke-type AIPM-II machine with asymmetric rotor profile, and a conventional spoke-type IPM machine are designed and optimized with the same 12-slot/8-pole stator with nonoverlapping windings as well as the same rotor diameter and PM dimensions. The effect of asymmetric flux barrier dimensions on the proposed AIPM-I machine is investigated with particular emphasis on torque characteristics. The electromagnetic performance and rotor mechanical strength of final optimal designs of three machines are compared. It confirms that the proposed AIPM-I machine can achieve significant torque enhancement and torque ripple reduction across the wide current range while also showing significantly smaller cogging torque at open-circuit condition, compared with both existing AIPM-II and conventional IPM machines. Finally, a prototype of the proposed AIPM-I machine has been manufactured and measured for validation.

Comparison of Flux-Switching and Interior Permanent Magnet Synchronous Generators for Direct-Driven Wind Applications Based on Nelder–Mead Optimal Designing

The permanent magnet flux-switching machine (PMFSM) is one of the most promising machines with magnets inserted into the stator. To determine in which applications the use of PMFSM is promising, it is essential to compare the PMFSM with machines of other types. This study provides a theoretical comparison of the PMFSM with a conventional interior permanent magnet synchronous machine (IPMSM) in the gearless generator of a low-power wind turbine (332 rpm, 51.4 Nm). To provide a fair comparison, both machines are optimized using the Nelder–Mead algorithm. The minimized optimization objectives are the required power of frequency converter, cost of active materials, torque ripple and losses of a generator averaged over the working profile of the wind turbine. In order to reduce the computational time, the substituting profile method is applied. Based on the results of the calculations, the advantages and disadvantages of the considered machines were revealed: the IPMSM has significantly lower losses and higher efficiency than the PMFSM, and the PMFSM requires much less rare-earth magnets and copper and is, therefore, cheaper in mass production.

Modelling and analysis of a novel mechanical‐variable‐flux IPM machine with rotatable magnetic poles

In this study, a novel mechanical-variable-flux interior permanent magnet motor (MVF-IPMM) is presented, which employs rotatable magnetic poles and a mechanical flux-adjusting device placed on both sides of the rotor. The device can regulate the magnetic circuit by rotating magnetic poles and adjusting the angle of the magnetisation direction relative to the d-axis. Consequently, the flux-weakening capability is enhanced. The configuration and additional mechanical devices of the MVF-IPMM are introduced, respectively. Then, the operation principle and flux-adjusting mechanism are deeply investigated by using analytical models, whose parameters are computed by automatic dynamic analysis of mechanical system and finite-element analysis. Based on the simulation results, an electromechanical model is established to predict the performance of the motor. In addition, the electromagnetic characteristics of the mechanical-variable-flux- and conventional interior permanent magnet machines are compared. Finally, the effectiveness of the design is successfully proven by experimenting with a prototype.

Flux-Focusing Permanent Magnet Machines With Modular Consequent-Pole Rotor

In this paper, the modular consequent-pole (MCP) rotor is adopted in the fractional-slot interior permanent magnet (IPM) machine to utilize the strong flux-focusing effect and reduce the leakage flux. Hence, the torque density and utilization ratio of permanent magnet (PM) material can be improved. However, the unacceptable unbalanced magnetic force (UMF) may arise due to asymmetric airgap flux density produced by consequent-pole topology. Thus, a pole-shaping method based on three-sectional arcs is proposed to suppress it. Due to the relatively complex rotor structure, the multiobjective optimization combined finite-element method with genetic algorithm is performed in this paper. Furthermore, the electromagnetic performance of the IPM machine with MCP rotor (namely IPM-MCP machine), including the open-circuit airgap flux density, phase back EMF, torque, PM utilization ratio, efficiency, flux-weakening capability and UMF, are compared with the conventional surface-mounted PM (SPM), IPM, and consequent-pole IPM (IPM-CP) machines. It is demonstrated that the IPM-MCP machine obtains the largest output torque in these machines. Meanwhile, the IPM-MCP and IPM-CP machines respectively have >30% and >20% higher PM utilization ratio than the conventional SPM and IPM machines while they obtain similar torque ripple and efficiency. Moreover, the IPM-MCP machine can obtain much lower UMF than the IPM-CP machine due to the effective suppression of asymmetric airgap flux density. Finally, a 12-slot/10-pole IPM-MCP machine is fabricated to verify the analyses.

Comprehensive Sensitivity Analysis and Multiobjective Optimization Research of Permanent Magnet Flux-Intensifying Motors

In this paper, two permanent magnet flux-intensifying motors are designed and optimized to realize the characteristic of Ld > Lq and the flux-intensifying effect. Compared with the conventional interior permanent magnet motor with the characteristic of Ld , the advantages of a low irreversible demagnetization risk and a wide speed range can be obtained in the motors. To meet multiple design requirements effectively, a comprehensive sensitivity analysis method is first implemented to evaluate the influence of each design variable on the selected optimized objectives of output torque, reverse saliency ratio, and torque ripple. Second, a sequential nonlinear programming algorithm is used for realizing the multiobjective optimizations of strong-sensitive design variables. Then, the performances of the two optimal motors are analyzed and compared with the initial permanent magnet motor in detail. Finally, two prototype motors are manufactured and tested. Both the simulation and experimental results verify the validity of the new flux-intensifying motors and the optimization method.

A Novel Dual-Sided PM Variable Flux Memory Machine

Memory machine (MM) was regarded as a promising candidate for wide-speed-range applications [1]–[6]. Since the low coercive force (LCF) PM is employed in MM, the air-gap flux can be flexibly adjusted by changing the magnetization state (MS) of PM with a temporary current pulses. The speed range can be subsequently extended with high efficiency maintained. According to the magnetizing current pattern, MMs can be generally categorized into AC- [1]–[3] and DC-magnetized [4]–[6] types. The former MM normally employs vector-control algorithm to apply d-axis current pulse in stator windings to vary the magnetization level of LCF PMs, while the latter one adopts auxiliary DC magnetizing coils to facilitate the magnetization control. Besides, the rotor-PM topologies of MMs have structures similar to conventional interior PM machines, which shows comparable torque density with those conventional surface-mounted PM machines . Nonetheless, LCF magnets on the rotor generally suffer from to armature reaction demagnetization effect, and the integration of armature and magnetizing functions in the stator winding results in complicated online FW control. On the other hand, the stator-PM MMs have the advantages of easy online magnetization control, and a simple and robust salient rotor as well as easy thermal management can be obtained. Nevertheless, the fact that two kinds of PMs, i.e., NdFeB and LCF PMs, as well as two sets of windings are located on stator leads to excessively crowded stator space and low torque density. Therefore, this paper attempts to propose a novel dual-sided PM memory machine (DSPM-MM) by combing the distinct advantages of “high torque density” of rotor-PM MM and “simple online PM flux control” of stator-PM MM. In the proposed design, the consequent-pole NdFeB PMs are placed in the rotor, while LCF PMs are mounted between the adjacent stator teeth to enable flexible air-gap flux adjustment. The machine topology and operating principle are introduced and addressed, respectively. Then, the electromagnetic performance is analyzed, which confirms the feasibility of the proposed design.

Field-Weakening Capability of Interior Permanent-Magnet Machines With Salient Pole Shoe Rotors

Brushless permanent-magnet (BLPM) machines, with inherent advantages of high-power density and high efficiency, have been widely employed to achieve traction characteristics for traction applications. Generally, traction characteristics require high torque at low speed and wide field-weakening region keeping constant power. However, both conventional interior permanent-magnet (IPM) and surface-mounted permanent-magnet (SPM) machines suffer from high-speed issues in the field-weakening region. A different BLPM machine topology, the pole shoe topology, is proposed in this paper. Although the pole shoe machine is common in industrial variable speed drives employing constant torque regimes, it has not been previously considered for machines designed for a wide field-weakening region. For analysis and comparison, a conventional IPM machine, which is employed as the Nissan Leaf vehicle traction machine, is studied as a reference benchmark machine. Experimental results from this machine are used to validate the analysis presented in this paper. The design results show that the proposed pole shoe machine achieves better field-weakening performance, compared with the conventional IPM and SPM machine topologies.

Design and Performance Analysis of a Self-Start Radial Flux-Hysteresis Interior Permanent Magnet Motor

A self-start interior permanent magnet (IPM) motor can be a potential replacement of the conventional induction motor because of its high torque density, smaller size, higher efficiency, and power factor. Traditional self-start IPM motors are equipped with cage windings in the rotor for providing the starting as well as the damping torque. Cage-quipped IPM motors have limited starting and synchronization capabilities. This paper introduces a novel self-start radial flux (RF) hysteresis IPM motor. The rotor of the hysteresis IPM motor has a cylindrical hysteresis ring made of semi-hard magnetic material. High energy density Nd–B–Fe magnets are buried inside the rotor hysteresis ring. The ring is supported by a laminated steel sleeve, allowing the flux to travel radially inside the hysteresis ring. In this paper, the design and performance analysis of a 3-phase 4-pole 1-HP RF-hysteresis IPM motor is carried out using finite-element analysis. The performance of the designed RF-hysteresis IPM motor is compared with similar 1-HP circumferential flux type hysteresis and cage-equipped IPM motors. Based on analysis and simulation, the RF-hysteresis IPM motor demonstrates higher starting and synchronization capabilities than conventional self-start IPM motors.

High-Speed Solid Rotor Permanent Magnet Machines: Concept and Design

This paper proposes a novel solid rotor topology for an interior permanent magnet (IPM) machine, adopted in this case for an aircraft starter-generator design. The key challenge in the design is to satisfy two operating conditions that are a high torque at start and a high speed at cruise. Conventional IPM topologies that are highly capable of extended field weakening are found to be limited at high speed due to structural constraints associated with the rotor material. To adopt the IPM concept for high-speed operation, it is proposed to adopt a rotor constructed from semimagnetic stainless steel, which has a higher yield strength than laminated silicon steel. To maintain minimal stress levels and also minimize the resultant eddy current losses due to the lack of laminations, different approaches are considered and studied. Finally, to achieve a better tradeoff between the structural and electromagnetic constraints, a novel slitted approach is implemented on the rotor. The proposed rotor topology is verified using electromagnetic, static structural, and dynamic structural finite-element analyses. An experiment is performed to confirm the feasibility of the proposed rotor. It is shown that the proposed solid rotor concept for an IPM fulfils the design requirements while satisfying the structural, thermal, and magnetic limitations.

Electromagnetic Performance Analysis and Verification of a New Flux-Intensifying Permanent Magnet Brushless Motor With Two-Layer Segmented Permanent Magnets

Permanent magnet brushless (PMBL) motors have been widely applied in electric vehicles, since they inherently offer high efficiency, high power density, and free maintenance. However, because of the existing problem of uncontrollable flux, their constant-power speed range is relatively narrow. In order to gain a wide speed range, by employing the new concept of the flux-intensifying effect, a new flux-intensifying PMBL (FI-PMBL) motor is proposed in this paper. The proposed motor is innovatively designed, where the topology of two-layer segmented PMs and non-uniform air gap are adopted to make the corresponding $d$ -axis inductance $L_{d}$ become greater than the $q$ -axis inductance $L_{q}$ , which is far different from the conventional interior PM motor. By using the finite-element methods, the electromagnetic performances of the proposed motor are evaluated in detail. Simulation results show that the proposed motor possesses preferable flux-weakening capability and wide speed range. In addition, the experimental results of the FI-PMBL prototype are given to verify the performances of the motor.

토크 리플 저감을 위한 새로운 비대칭 하프-타입 영구자석 매입형 브러시리스 직류 모터 구조

This paper proposes a novel asymmetrical interior permanent magnet (IPM) brushless DC (BLDC) motor structure, which utilizes half-type permanent magnet (PM) configuration and has asymmetrical side gaps (slot next to the PMs) for reducing torque ripples. This structure uses 24% less volume of PMs than conventional IPM BLDC motor with a full set of magnets. The characteristics of the proposed motor are compared with three other half-type IPM BLDC motors through finite elements method (FEM) analysis, and the usefulness of the proposed motor was verified through experimental evaluation on prototypes of the conventional motor and proposed motor under various torque load conditions. This research obtained a high-performance IPM BLDC motor while decreasing manufacturing cost at the same time.

Optimal Rotor Shape Design of LSPM With Efficiency and Power Factor Improvement Using Response Surface Methodology

Recently Line Start Permanent Magnet Motor (LSPM) is a well-known motor due to its technical advantages in academic and industrial sector. The LSPM combines a permanent magnet rotor that allows higher motor efficiency during synchronous operation, and an induction motor squirrel cage rotor for starting the motor by connecting it directly to an A.C. Source. In this paper, we will deal with the efficiency and Power factor improvement of a 3.4kW, 2-pole, three-phase LSPM. The efficiency improvement can be effectively achieved by designing optimization of the rotor structure using response surface methodology (RSM) and finite element method. The optimized slot shape of PM was selected for the prototype machine, which improves the efficiency and power factor of LSPM. LSPM has a higher efficiency than (IM) and an advantage in constant speed operation regardless of the effect of load variation. It has permanent magnets (PMs) buried bellow the squirrel cage in rotor, thus operates in steady state as conventional interior permanent magnet synchronous motor (PMSM). Thus it combines the advantages of induction motor (robust construction and line-starting capability) and PMSM (high efficiency, power factor and torque density). The line start permanent magnet motor (LSPM) is noted as alternative routes comparing with the induction motor that it offers high efficiency and unity power factor [1].

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.

Design and analysis of high-power/high-torque density dual excitation switched-flux machine for traction drive in HEVs

This paper presents design viability studies and investigations of dual excitation switched-flux (DESF) motor as an applicant for traction drives in hybrid electric vehicles (HEVs). First of all, the main structure, the fundamental principle of operation and the design notion of the recommended DESF motor are discussed. Then, under certain limitations, specifications and performances of conventional interior permanent magnet synchronous (IPMS) motor, the preliminary performances of the recommended DESF motor are evaluated based on two-dimensional Finite Element Analysis (FEA). Since the initial performances fail to attain the target torque and power, design optimization based on deterministic approach of several DEFS motor parameters is applied in an attempt to attain the target performances. After a few cycles of design optimization, the improved DEFS motor has achieved the target power and torque of 123 kW and 333 Nm, respectively. In addition, due to definite advantage of robust rotor structure of DESF motor, rotor mechanical stress prediction at highest speed of 12,400 r/min is much lower than the mechanical stress in conventional IPMS motor. In conclusion, the final design DESF motor has the maximum torque of 11.97 Nm/kg and power density of 5.83 kW/kg, which is approximately 26% and 66% more than the torque and power density in existing IPMS motor.

Development of High Torque and High Power Density Hybrid Excitation Flux Switching Motor for Traction Drive in Hybrid Electric Vehicles

This paper presents design feasibility study and development of a new hybrid excitation flux switching motor (HEFSM) as a contender for traction drives in hybrid electric vehicles (HEVs). Initially, the motor general construction, the basic working principle and the design concept of the proposed HEFSM are outlined. Then, the initial drive performances of the proposed HEFSM are evaluated based on 2D-FEA, in which the design restrictions, specifications and target performances are similar with conventional interior permanent magnet synchronous motor (IPMSM) used in HEV. Since the initial results fail to achieve the target performances, deterministic design optimization approach is used to treat several design parameters. After several cycles of optimization, the proposed motor makes it possible to obtain the target torque and power of 333 Nm and 123 kW, respectively. In addition, due to definite advantage of robust rotor structure of HEFSM, rotor mechanical stress prediction at maximum speed of 12,400 r/min is much lower than the mechanical stress in conventional IPMSM. Finally, the maximum torque and power density of the final design HEFSM are approximately 11.41 Nm/kg and 5.55 kW/kg, respectively, which is 19.98% and 58.12% more than the torque and power density in existing IPMSM for Lexus RX400h.

Experimental Verification and Electromagnetic Analysis for Performance of Interior PM Motor According to Slot/Pole Number Combination

This paper reports on the experimental study on and analysis of the influence that the number of stator slots has on the performance of an interior PM (IPM) motor. First, for a conventional 6-pole IPM rotor, stators with 18, 27, and 36 slots that satisfy the same required and restricted conditions are designed. Next, the performances and parameters of each IPM motor, such as cogging torque, torque ripple, d- and q- axis inductance, and total harmonic distortion (THD) of back-EMF, are investigated using 2-D finite element analysis (FEA). Finally, test results for factors such as the d- and q-axis inductance, back-EMF, and cogging torque measurements are obtained to confirm the analysis results. From the results obtained in this work, it is concluded that the influence of the number of stator slots on IPM motor performance is quite significant.

Design and Finite-Element Analysis of Interior Permanent Magnet Synchronous Motor With Flux Barriers

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The paper presents a finite-element method-based design and analysis of interior permanent magnet synchronous motor with flux barriers (IPMSMFB). Various parameters of IPMSMFB rotor structure were taken into account at determination of a suitable rotor construction. On the basis of FEM analysis the rotor of IPMSMFB with three-flux barriers was built. Output torque capability and flux weakening performance of IPMSMFB were compared with performances of conventional interior permanent magnet synchronous motor (IPMSM), having the same rotor geometrical dimensions and the same stator construction. The predicted performance of conventional IPMSM and IPMSMFB was confirmed with the measurements over a wide-speed range of constant output power operation. </para>