High Reluctance Torque Research Articles

Study on Performance Improvement through Reducing Axial Force of Ferrite Double-Layer Spoke-Type Permanent Magnet Synchronous Motor with Core Skew

Recently, due to the price fluctuation and supply instability of rare earth mineral resources, there has been a lot of development of electric motors using non-rare-earth permanent magnets. As a result, motors using Dy-free permanent magnets and ferrite permanent magnets are being researched, and, in particular, ferrite permanent magnets often utilize spoke-type structures, which are magnetic flux concentrators, to compensate for their low coercivity and residual flux density. However, in general, spoke-type PMSMs do not use much reluctance torque, so double-layer spoke-type PMSMs have been studied for their more efficient design. Unlike general spoke-type PMSMs, double-layer spoke-type PMSMs can utilize high reluctance torque by increasing the difference between d-axis and q-axis reluctance. However, as the difference in magnetic resistance increases, vibration and noise are generated, which adversely affects the mechanical part and shortens the life of the motor. Although this problem seemed to be solved by applying core skew in the previous study, it was confirmed that the axial force caused by the axial leakage flux occurred in the maximum torque per ampere (MTPA) control section and the torque ripple was increased. Therefore, in this paper, a model that can apply symmetrical core skew and reduce axial force is proposed. First, the causes of the axial force generated in previous studies were analyzed. Based on the analysis of these causes, a new symmetrical core skew structure was proposed, and its justification was verified through FEA.

Performance Validation of PM Assisted SynRM and PMSM with Optimized Design for EV Application

This paper presents the comparison of Permanent Magnet-Assisted Synchronous Reluctance Motor (PMASynRM) and Permanent Magnet Synchronous Motor (PMSM) for the same design parameters and the evaluation of various performance parameters based on the Finite Element (FE) Method. FE Analysis is conducted after selecting the optimized design for PMASynRM and PMSM using an FE tool, with loading conditions to determine various performance parameters. This is achieved by maintaining the same motor dimensions and stator parameters while altering the rotor geometry for both motors. The final simulation results are discussed, and other performance parameters are recorded for comparison purposes. A PMASynRM is introduced, in which the problems of Synchronous Reluctance Motor (SynRM) can be eliminated with a permanent magnet in the rotor flux barrier. Due to higher flux barriers in PMASynRM, the reluctance torque is higher than in PMSM. If the magnet is placed very near to the air gap in PMSM, higher magnet torque is achieved, but due to the high reluctance torque in PMASynRM, the electromagnetic torque of PMASynRM is higher compared to PMSM. The research proves that the proposed design of PMASynRM is the best choice for Electric Vehicle (EV) applications. For PMASynRM, the shape of the flux barrier is not possible to change due to the design limitation of the FE software tool. Further analysis can be conducted by changing the shapes of the flux barriers to propose the most effective barriers. Basic theory and FE analysis of conventional PMSM and SynRM are reported in the literature. An optimal design is proposed through comparative analysis for EV applications to find out the best candidate for an EV motor.

Modeling and Simulation of Five-Phase Synchronous Reluctance Motor Fed By Five-Phase Inverter

Five-phase machine employment in electric drive system is expanding rapidly in many applications due to several advantages that they present when compared with their three-phase complements. Synchronous reluctance machines(SynRM) are considered as a proposed alternative to permanent magnet machine in the automotive industry because the volatilities in the permanent magnet price, and a proposed alternative for induction motor because they have no field excitation windings in the rotor, SyRM rely on high reluctance torque thus no needing for magnetic material in the structure of rotor. This paper presents dynamic simulation of five phase synchronous reluctance motor fed by five phase voltage source inverter based on mathematical modeling. Sinusoidal pulse width modulation (SPWM) technique is used to generate the pulses for inverter. The theory of reference frame has been used to transform five-phase SynRM voltage equations for simplicity and in order to eliminate the angular dependency of the inductances. The torque in terms of phase currents is then attained using the known magnetic co-energy method, then the results obtained are typical.

Investigation of influence the slot/pole combinations on the torque performance for synchronous reluctance machine with distributed and concentrated windings

This paper explores the electromagnetic performance comparison of three different types of synchronous reluctance machines. The investigated machines including, conventional full pitch distributed winding (24 slots/4 poles), an integer slot concentrated nonoverlapping winding (12 slots/4 poles), and fractional slot concentrated nonoverlapping winding (15 slots/8 poles). A finite element analysis JMAG Designer is used to validate the performance for all machines, and have been employed for the optimisation process to improve the torque density as well as to minimise torque ripple. Meanwhile, the current density, slot filling factor and specific dimensions, viz., stator outer diameter, stack length and air gap are designed to be constant. The result shows that for a DW-SynRM, a high value of average torque is achieved, and the torque ripple is lower. The result also demonstrates that the FSCW-SynRM can reach a low torque oscillation. Meanwhile, the ISCW-SynRM exhibit a high reluctance torque, but the torque ripple is a big challenge. On the whole, the distributed winding machine has the best performance compared to concentrated winding machines.

Design and analysis of a hybrid-excited wound field synchronous machine with high reluctance torque utilization

The paper proposes a hybrid-excited wound field synchronous machine (HE-WFSM), which can achieve high reluctance torque utilization. The key of the proposed HE-WFSM is that two permanent magnets (PMs) assist each rotor pole in forming an additional magnetic flux circle. It is opposite to the magnetic flux circle along the q-axis in the WFSM. The reduction of the q-axis flux can help to improve the saliency ratio and reluctance torque. Additionally, the asymmetrical flux linkage achieves a closest current phase angle between the maximum field torque and the maximum reluctance torque. To highlight the advantages of the proposed HE-WRSM, a general WFSM was adopted as the basic machine and analyzed under the same operating conditions. All performances of the basic machine and proposed HE-WFSM were predicted using finite element analysis (FEA) in Jmag-Designer. Finally, it was confirmed that the proposed HE-WRSM can achieve high reluctance torque utilization.

Improvement torque performances of interior permanent-magnet machines

Due to their excellent efficiency, power density and constant power speed region, interior permanent-magnet (IPM) machines are very suitable for electric vehicles (EVs). This paper proposed a new IPM rotor topology, which can offer high reluctance torque, wide constant power speed range and excellent overload capability. Besides, five rotor topologies with integral-slot distributed-windings IPM machines, including four existing IPM topologies and the proposed IPM topology, are designed optimally. Their characteristics, which include d-q axis inductances, saliency ratios, electromagnetic torques, corresponding torque ripples, back-electromotive forces (EMFs), overload capabilities and flux weakening performances are evaluated quantitatively. Finally, a three phase 48s8p hybrid rotor PM machine is built to verify the performances of the proposed IPM machine. This work provides some general concepts for machine developers who are willing to build IPM machines for high-performance EV applications.

Improvement of Reluctance Torque in Fault-Tolerant Permanent-Magnet Machines With Fractional-Slot Concentrated-Windings

Fault-tolerant permanent-magnet (FTPM) machines adopt fractional-slot concentrated-windings, thus reducing copper loss and improving fault tolerance. However, they usually suffer from insignificant reluctance torque. The novelty of this paper is to adopt some techniques to improve reluctance torque in FTPM machines, including rotor divisions between poles, two-layer interior magnets in oriented direction, and the specially designed flux barriers between two-layer magnets. The configuration of the newly designed FTPM machine is presented, and its inductance, electromagnetic torque, rotor losses, the flux-weakening capacity, and the speed range are analyzed by using the finite-element method. By using the new design, FTPM machines can offer high reluctance torque, low rotor losses, and good flux-weakening performance.

Improvement of Torque Capability of Permanent-Magnet Motor by Using Hybrid Rotor Configuration

This paper proposes a novel hybrid rotor permanent-magnet (HRPM) motor to improve torque capability, including average torque and torque ripple. The key of the proposed motor is that it can utilize high PM torque of surface-inserted PM (SPM) rotor module and high reluctance torque of interior PM (IPM) rotor module at the same time. Meanwhile, the shifting angle of SPMs and open angle of air barriers are introduced to improve the average torque and reduce the torque ripple, respectively. The two variables are employed to create circumferential asymmetry of the rotor for generating an angular difference of the electromagnetic torque between adjacent N-pole and S-pole, thus minimizing torque ripple. In order to evaluate the proposed motor, an IPM motor and a SPM motor with the same dimension and volume of PM are used as benchmarks. Through theoretical analysis and experimental test, it is verified that the proposed HRPM motor can offer higher torque density and lower torque ripple simultaneously.

EV and HEV Motor Development in TOSHIBA

Hybrid electric vehicles (HEVs) and electric vehicles (EVs) improve the efficiency of a drive and reduce CO2 emissions by regenerative braking and operating the engine under optimum conditions. To minimize the driving units, the motor size should be decreased and the maximum torque should be increased. Therefore, motors employing permanent magnets have been commonly used recently. For HEV and EV motors, Toshiba developed a motor that delivers a high reluctance torque, known as PRM, and has been applying it to various vehicles. This paper describes the current motor development status in TOSHIBA.

Iron Pole Shape Optimization of IPM Motors Using an Integrated Method

Abstract —An iron pole shape optimi zation method to reduce cogging torque in Interior Permanent Magnet (IPM) motors is developed by using the reduced basis technique coupled by finite element and design of experiments methods. Objective function is defined as the minimum cogging torque. The experimental design of Taguchi method is used to build the approximation model and to perform optimization. This method is demonstrated on the rotor pole sh ape optimization of a 4-poles/24-slots IPM motor. Index Terms—IPM motor, Cogging torque reduction, iron pole shape optimization, reduced basis technique, FEA, Design of Experiments (DOE) I. I NTRODUCTION Brushless permanent motors have been widely used in industrial applications because of their efficiency and power density. In particular, the spoke-type motor, which can concentrate flux from permanent magnets, has a high torque density per unit volume resulting from its high reluctance torque and structure for concentrating flux from permanent magnet. However, cogging torque and torque ripple can be increased due to a distortion of air gap flux density distribution in the IPM motors. This drawback is due to its asymmetric magnetic reluctance on the edge of the permanent magnet. There have been some developments for rotor pole shape optimization. Table I summarizes the literature by showing the type of optimization approach. Cogging torque reduction in IPM motors was performed using a rotor with flux barriers [1]–[3]. Eccentric pole design was proposed to compensate the armature reaction for reducing torque ripple [4]. To obtain better performance, the rotor pole shape was varied and divided into three parts. These consist of two end parts of eccentric surfaces and one uniform surface. Response surface methodology (RSM) was used during the design process [5]. The continuum shape design sensitivity formula and the finite element method are employed to calculate the sensitivity of flux linkage to the design variables, which determine the shape of iron pole piece [6]. They used B-Spline parameterization to optimize the design variables in order to provide the back-EMF waveform as close as possible to a sinusoidal form. The main challenge of current optimization methods, especially for complex one, is the number of design variables required for rotor pole shape optimization and the generality of the procedure. The first method has poor performance due to the loss in flux barriers. The second method is only suitable for motor rotation in one direction. Also, the later method is not a general approach to achieve the optimum rotor pole shape profile.

Design and Control of a Field Intensified Interior Permanent Magnet Synchronous Machine

Permanent magnet synchronous machines (PMSMs) have been used in various applications owing to the high power density of the magnets. Especially interior permanent magnet synchronous machines (IPMSMs) are attractive in high power density applications since IPMSMs can generate both magnet torque and reluctance torque, and the field weakening control can reduce the output voltage.However, a lot of field weakening current is required to generate a lot of reluctance torque, the carefully magnet design, the thick magnet is used, is needed not to demagnetize the magnet. Hence, the cost of the magnet increases and the operating temperature is limited.In this paper, a field intensified IPMSM (FIIPM) is proposed. The proposed FIIPM has a forward saliency and the positive current on the direct axis is added in order to the magnet to generate a reluctance torque. The technique of adding the positive current contributes the magnet not to demagnetize, and using a thick magnet to protect from the demagnetization is not necessary.This paper shows that IPMSMs are difficult to generate more reluctance torque than magnet torque by using a relationship between saliency and torque ratio. The FIIPM is introduced as a possible design option for high reluctance torque machine. The general characteristics of FIIPMs are analyzed using finite element analysis (FEA).

Performance evaluation of Synchronous reluctance motor and the other motors with the same distributed winding and stator configuration

This paper reports results from performance comparison on the high efficient reluctance torque motors. The compared motors were SynRM (Synchronous Reluctance Motor), SPMSM (Surface Permanent Magnet Synchronous Motor), IPMSM (Interior Permanent Magnet Synchronous Motor) and typically low-cost IM (Induction motor). The all tested motors has the same distributed winding stator and we evaluated the performance differences which is generated from the rotor configuration. It was found that the IPMSM was superior in terms of efficiency and SynRM was most lowest cost and its efficiency was higher than typical IM which has rotor copper losses.