Interior Permanent Magnet Machine Research Articles

Carrier Signal Injection-Based Sensorless Control for Permanent-Magnet Synchronous Machine Drives Considering Machine Parameter Asymmetry

This paper investigates the influence of asymmetric machine parameters on carrier signal injection-based sensorless control of permanent-magnet synchronous machines (PMSMs). With either rotating or pulsating signal injection, the second harmonic position errors arise due to the parameter asymmetry. Furthermore, it is found that for the two carriers, the second harmonic errors are different for resistance asymmetry but the same for inductance asymmetry. In order to suppress the position errors, the carrier signal selection guidelines are discussed for resistance asymmetry, while for inductance asymmetry, novel online compensation strategies with dual-frequency injection are also proposed. Finally, the theoretical analyses and proposed compensation methods are validated by experiments on an interior PM (IPM) machine with added phase resistance/inductance to simulate asymmetric conditions.

Design and Tests of a Four-Layer Fractional-Slot Interior Permanent-Magnet Motor

This paper deals with the design and testing of an interior permanent-magnet (IPM) machine that exhibits advanced features. It adopts fractional-slot (FS) nonoverlapped coil windings that reduces the end winding length, i.e., the Joule losses and machine cost. As a consequence, higher rated current can be supplied so that higher torque density and higher efficiency in a wide operating region can be reached. The rotor saliency increases the performance in flux-weakening operating region and the fault-tolerance capability. In order to decrease the torque ripple, it is important to minimize the interaction between the magnetomotive force (MMF) harmonics due to the stator currents and the rotor anisotropy. To do that, the winding has been optimized so as to minimize the MMF harmonics, taking advantage from the higher degree of freedom of the four-layer winding. However, the so-called slot-harmonics cannot be minimized by rearranging the winding coils. Hence, the rotor geometry has been designed so as to minimize the impact of such slot-harmonics. A 12-slot 10-pole IPM FS machine has been designed and manufactured. The experimental tests confirm the expectations.

Post-Demagnetization Performance Assessment for Interior Permanent Magnet AC Machines

This paper assesses the post-demagnetization performance of interior permanent magnet (IPM) ac machines by employing the more accurate recoil line approach based on a 2-D transient finite-element analysis (FEA). The method predicts continuous demagnetization of each magnet element undergoing partial demagnetization and evaluates the machine behavior after an event of short-circuit faults across its terminals. Along with the short-circuit faults, a failure in a drive controller or a position sensor, which may lead to a reverse voltage across the machine terminals that can eventually be more fatal and can cause significant reduction in the performance due to high levels of demagnetization, is analyzed as the worst case scenario. The FE predicted post-demagnetization performance is validated by experimental measurements in which a six-phase IPM machine designed for electric vehicle traction is allowed to lose its synchronization with the inverter when forced to operate on a torque–speed envelope, which is way beyond the drive voltage setting.

Analysis of an Interior Permanent-Magnet Machines with an Axial Overhang Structure based on Lumped Magnetic Circuit Model

This paper shows a new magnetic field analysis of an interior permanent magnet (IPM) machines with an axial overhang structure wherein the rotor axial length exceeds that of the stator. The rotor overhang used to increase torque density of the radial flux machine is difficult to analyze because of extra consideration of axial direction, and thus it is general for machine designer to take 3-D finite element analysis (FEA) capable of considering both radial and axial complicated geometry in the machine. However, it requires too much computing time for preliminary design especially for optimization process. Therefore, in this paper a 2-D analytic method using a lumped magnetic circuit model (LMCM) is proposed to overcome the problem. For the analysis of overhang effect, the magnetic circuit is separated and solved from overhang and non-overhang regions respectively. For the validation of proposed concept, 3-D finite element analysis (FEA) is performed. From the analysis results, it is shown that our new proposed method presents good performance in terms of calculating electromotive force (EMF) and torque within a short time. Therefore, the proposed model can be useful in design of IPM with an overhang structure.

Comparison between induction machine and interior permanent magnet machine for electric vehicle application

Purpose – The purpose of this paper is to make a quantitative comparison between induction machine (IM) and interior permanent magnet machine (IPM) for electric vehicle applications, in terms of electromagnetic performance and material cost. Design/methodology/approach – The analysis of IM is based on an analytical method, which has been validated by test. The analysis of IPM is based on finite element analysis. The popular Toyota Prius 2010 IPM is adopted directly, and the IM is designed with the same stator outer diameter and stack length as Prius 2010 IPM for a fair comparison. Findings – The torque capability of IM is lower than IPM for low electric loading and competitive to IPM for high electric loading. The maximum torque/power-speed characteristic of IM is competitive to IPM; while the rated torque/power-speed characteristic of IM is poorer than IPM. The power factor of IM is competitive and even better than IPM for high electric loading in low-speed region. The torque ripple of IM is comparable to IPM for high electric loading and much lower than IPM for low electric loading. The overall efficiency of IM is lower than IPM, and the maximum efficiency of copper squirrel cage IM is approximately 2-3 percent lower than IPM. The material cost of IM is about half of IPM when IM and IPM are designed with the same stator outer diameter and stack length. Originality/value – The electromagnetic performances and material costs of IM and IPM are quantitatively compared and discussed.

Design of synchronous reluctance and permanent magnet synchronous reluctance machines for electric vehicle application

Purpose – The purpose of this paper is to minimize the optimization parameter number of synchronous reluctance machine (SynRM) and permanent magnet (PM) assisted SynRM, and compare their relative merits with interior permanent magnet (IPM) machine for electric vehicle applications, in terms of electromagnetic performance and material cost. Design/methodology/approach – The analysis of electromagnetic performance is based on finite element analysis, by using software MAXWELL. The genetic algorithm is utilized for optimization. Findings – The rotor design of SynRM can be significantly simplified by imposing some reasonable conditions. The number of rotor design parameters can be reduced to three. The electromagnetic performance of SynRM is much poorer than that of IPM, although the material cost is much cheaper, approximately one-third of IPM. The ferrite-SynRM is competitive and even better than IPM especially for high electric loading, in terms of torque capability, torque-speed characteristic, power factor, threshold speed and efficiency. In addition, ferrite-assisted SynRM has great advantage over IPM in material cost, 55 percent cheaper. The performance of NdFeB-assisted SynRM is close to IPM in terms of torque capability, torque-speed characteristic, power factor, torque ripple and efficiency. The material cost of NdFeB-assisted SynRM is ∼25 percent lower than IPM. Originality/value – Some conditions, which can simplify the optimization of SynRM rotor, are discussed. The electromagnetic performances and material costs of SynRM, ferrite-assisted, NdFeB-assisted SynRMs and IPM are quantitatively compared and discussed.

Investigation of Integrated Charging and Discharging Incorporating Interior Permanent Magnet Machine With Damper Bars for Electric Vehicles

Integrated charging technology in electric vehicles is expected to reduce the overall cost as well as the weight of the vehicle, while leading to fast charging capability in the vehicle. Understanding the above, this paper puts an effort to exclusively investigate interior permanent magnet synchronous machine (IPMSM) drive incorporating damper bars in rotor for integrated charging application in electric vehicles. First, motivation for the employment of IPMSM with damper bars for integrated charging is provided and justified. Thereafter, a novel parameter determination method based on dq -axis theory to determine the parameters of a laboratory IPMSM with dampers is proposed and experimentally validated. The determined parameters are then employed to design, control, and compare the performance of an integrated charging system incorporating an IPMSM drive with and without damper bars. The developed system is then experimentally tested under both vehicle-to-grid and grid-to-vehicle modes, and results elicited from the investigations are discussed.

Effect of Multilayer Windings With Different Stator Winding Connections on Interior PM Machines for EV Applications

The interior permanent magnet (IPM) machine equipped with a fractional-slot concentrated winding (FSCW) has met an increasing interest in electric vehicle applications due to its higher power density and efficiency. Torque production is due to both PM and reluctance torques. However, one of the main challenges of FSCWs is their inability to produce a high-quality magnetomotive force (MMF) distribution, yielding undesirable rotor core and magnet eddy-current losses. Literature shows that the reduction of low-order space harmonics significantly reduces these loss components. Moreover, it has been previously shown that by employing a higher number of layers, although causing some reduction in the winding factor of the torque-producing MMF component, both machine saliency and reluctance torque components are improved. Recently, a dual three-phase winding connected in a star/delta connection has also shown promise to concurrently enhance machine torque of a surface-mounted PM machine while significantly reducing both rotor core and magnet losses. In this paper, a multilayer winding configuration and a dual three-phase winding connection are combined and applied to the well-known 12-slot/10-pole IPM machine with v-shaped magnets. The proposed winding layout is compared with a conventional double-layer winding, a dual three-phase double-layer winding, and a four-layer winding. The comparison is carried out using 2-D finite-element analysis. The comparison shows that the proposed winding layout, while providing similar output torque to a conventional double-layer three-phase winding, offers a significant reduction in core and magnet losses, correspondingly a higher efficiency, improves the machine saliency ratio, and maximizes the reluctance toque component.

A High-Fidelity Computationally Efficient Transient Model of Interior Permanent-Magnet Machine With Stator Turn Fault

An accurate transient model of interior permanent-magnet (IPM) machine with stator turn fault with due account of magnetic saturation is essential to develop robust and sensitive interturn fault detection algorithms and to evaluate drive controller performance and stability under fault conditions. This paper proposes a general method of modeling stator turn fault using flux linkage map of IPM machine under fault extracted from finite-element (FE) analysis. Simulation results from the proposed fault model are compared against FE and experimental results. The results show that the proposed model matches well with experimental data.

Impact of Rotor Design on Interior Permanent-Magnet Machines With Concentrated and Distributed Windings for Signal Injection-Based Sensorless Control and Power Conversion

This paper examines the relationship between rotor design, saliency-based signal injection sensorless control, and power conversion properties for four industrially relevant interior permanent-magnet machine configurations: a 36-slot 6-pole stator with v bar rotor, a 36-slot 6-pole stator with flat bar rotor, a 9-slot 6-pole stator with v bar rotor, and a 9-slot 6-pole stator with flat bar rotor. The influence of rotor geometric design variables over the range of current densities at the maximum torque per ampere angle was found using a design of experiments' methodology and standardized regression coefficients. Tradeoffs between sensorless control and power conversion properties are found using a Monte Carlo methodology. Power conversion and sensorless control properties were analyzed using hybrid static and time-stepping finite-element simulations.

Dynamic Loss Minimization of Finite Control Set-Model Predictive Torque Control for Electric Drive System

This paper proposes a dynamic optimization strategy of finite control set-model predictive torque control for permanent magnet synchronous machines, which takes into account the inverter losses and machine losses simultaneously. In order to reduce the switching losses (or to optimize the switching sequence) of the inverter, a recognized and feasible constrain which considers the accumulated ON/OFF times of the switches is implemented. The machine losses are taken into account by utilizing an optimal stator flux reference. An alternative loss model control method is proposed to calculate the optimal stator flux reference, which combines the conventional maximum torque/ampere method and the conventional loss model control method. Furthermore, a discrete-time machine model is introduced, which can reduce the predictive error at relative low switching frequency. The key results are illustrated by a combination of simulation and prototype interior permanent magnet machine drive measurements.

Variable Leakage Flux IPMSMs for Reduced Losses Over a Driving Cycle While Maintaining Suitable Attributes for High-Frequency Injection-Based Rotor Position Self-Sensing

Variable leakage flux (VLF) interior permanent-magnet synchronous machines (IPMSMs), which use intentional magnet leakage flux paths cross-coupled with the q-axis flux paths to reduce losses over driving cycles, have been introduced recently, but self-sensing has not been discussed for these machines. This paper focuses on the saliency angular offset attributes that are the primary metric for the well-established injection-based self-sensing methods. This paper begins by evaluating the effect of the intentionally designed cross-coupling in the VLF-IPMSM with rotor surface bridges on the saliency angular offset. This paper then proposes alternate rotor designs with side-loop structure that cause relatively linear and well-behaved cross-coupling that improves the load-dependent saliency angular offset characteristics. The effect of VLF properties on power conversion and driving cycle loss reduction capability is evaluated for the proposed designs. This paper also applies the concept of VLF design to conventional flux-weakening interior permanent-magnet machine rotor design and presents the loss reduction capability of such designs.

Enhanced Availability of Drivetrain Through Novel Multiphase Permanent-Magnet Machine Drive

This paper deals with a novel multiphase permanent-magnet (PM) machine drive to enhance drivetrain availability in electric traction applications. It describes the development of new winding configurations for six-phase PM brushless machines with 18 slots and eight poles, which eliminate and/or reduce undesirable space harmonics in the stator magnetomotive force. In addition to improved power/torque density and efficiency with a reduction in eddy current loss in rotor PMs and copper loss in end-windings, the developed winding configuration also enhances availability of drivetrain, in a variety of applications requiring a degree of fault tolerance, by employing it as two independent three-phase windings in a six-phase interior-PM machine, which is designed and optimized for a given set of specifications for an electric vehicle, under thermal, electrical, and volumetric constraints. This paper also describes the design and development of a six-phase inverter with independent control for both sets of three-phase windings. The designs of the motor and the inverter are validated by a series of preliminary tests on the prototype machine drive.

Optimal Designing of Permanent Magnet Cavity to Reduce Iron Loss of Interior Permanent Magnet Machine

The iron loss of the interior permanent magnet (PM) machine is larger when the machine runs at a higher speed. The great stator and rotor iron loss have a negative effect on the machine, so the PM cavity of the interior PM machine with a single-layer <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$U$ </tex-math></inline-formula> -shaped PM geometry is improved to reduce the iron loss of the machine in this paper. Meanwhile, the Taguchi method is utilized to optimize the improved PM cavity at the rated point, maximum torque point, and flux-weakening point, respectively. The effects of each optimization variable on the iron loss and electromagnetic torque of the machine are analyzed. Then, the optimization scheme of the improved PM cavity is achieved at each selected operating point, respectively. The final optimization scheme of the improved PM cavity will be concluded after the overall consideration of optimization schemes at the selected operating points. In addition, the electromagnetic torque ripple and cogging torque are also effectively reduced by adopting the improved PM cavity, which improves the running stability of the machine.

A High-Fidelity and Computationally Efficient Electrothermally Coupled Model for Interior Permanent-Magnet Machines in Electric Vehicle Traction Applications

Accurate temperature predictions for permanent-magnet machines are essential to prevent irreversible demagnetization and undesirable reduction in lifetime. This paper proposes a high-fidelity and computationally efficient electrothermally coupled model for interior permanent-magnet machines (IPMs) in electric vehicle (EV) traction applications. First, a high-fidelity IPM model accounting magnetic saturation, spatial harmonics, iron loss, and temperature effects is presented. The temperature effects on both the ${d}$ - and ${q}$ -axis flux-linkages and the torque in the proposed model are quantified. The IPM model with due account of temperature effect is integrated with a state-space lumped parameter thermal model to establish a high-fidelity and computationally efficient electrothermally coupled model for IPMs. Both the steady-state and driving cycle operations are simulated with the proposed model and the results are compared to those predicted by the machine model without considering temperature effect as well as by the machine model which only accounts for the temperature effect on the winding resistance. Considerable temperature differences between those predicted by the proposed model and those predicted by the latter two models are observed. Experimental validation of the proposed model is performed with a 10-kW IPM prototype machine operating in generating mode.

Analysis and Reduction of Magnet Loss by Deepening Magnets in Interior Permanent-Magnet Machines With a Pole/Slot Ratio of 2/3

Interior permanent-magnet (IPM) machines are desirable for electrical vehicles due to high power density and good flux-weakening capability. This paper focuses on the approaches to reduction of magnet eddy-current loss in IPM machines with a pole/slot ratio of 2/3, taking a 16-pole/24-slot machine as an example. By comparing permanent-magnet losses between a surface-mounted magnet machine and an IPM machine, the spatial filter effect on even-order stator magnetomotive force space harmonics is highlighted. Thereafter, the effect of magnet depth on magnet eddy-current loss is investigated. Moreover, the constraints on reduction effect of magnet’s depth, such as copper loss and torque ripple, are analyzed. A 16-pole/24-slot IPM machine prototype is manufactured after the tradeoff design. The experimental results validate the effect of magnet depth on reducing magnet losses.

Reduced Dysprosium Permanent Magnets and Their Applications in Electric Vehicle Traction Motors

Permanent magnet (PM) machines employing rare-earth magnets are receiving increasing interest in electrical vehicle (EV) traction applications. However, a significant drawback of PM machine-based EV tractions is the extremely high cost and volatile supply of rare-earth materials, especially for dysprosium (Dy), whose price is almost 6 times higher than neodymium. This paper describes a new Dy grain boundary-diffusion process for sintered Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sub> B magnets to maximize its effect on coercivity enhancement. The new process gains an 81% reduction in Dy consumption normally required by the conventional Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sub> B magnets for the equivalent performance and 17% higher remanence. The investigation into the application in an interior PM (IPM) machine for a small-sized EV traction shows that compared with the conventional Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sub> B magnets, despite the relatively low coercivity, the low-Dy-content magnets still withstand the thermal and demagnetization challenge over various driving operations. In addition, with the magnet’s high remanence and energy product, the machine gains significant torque and energy efficiency improvements. The analysis results are validated by a series of tests carried out on a prototype IPM machine with the new magnets.

3-D Effects of Rotor Step-Skews in Permanent Magnet-Assisted Synchronous Reluctance Machines

Permanent magnet assisted synchronous reluctance machines (PMA SynRM), stemming from the combination of synchronous reluctance and interior PM machine topologies, have recently gained increasing popularity as a viable candidate for electric vehicle traction applications due to concerns regarding the price volatility of rare-earth magnet materials. Their attractiveness can be attributed to their distinct torque production mechanism, which essentially relies on the reluctance torque component enabling the use of less expensive ferrites or bonded NdFeB magnet solutions. A drawback often associated with this machine topology is high torque ripple emanating from its intrinsically high salient nature [1]. Among several machine design techniques available to mitigate the high torque ripple, rotor step-skew is known to be one of the most effective and frequently incorporated solutions. When a step-skew is performed, it causes variation of magnetic flux density along the axial (skew) direction, and thus influences the machine's electromagnetic behavior [2]. Numerous methods are available in literature to account for the effects of skew using (either) 2D or 3D numerical finite element analysis (FEA), analytical, or semi-analytical approaches, the trade-off in each case being computational time versus accuracy. Due to the prohibitive computational time and numerical memory costs of 3D FEA, the prediction of a skewed machine's electromagnetic performance typically relies on 2D domain-based techniques, such as multi-slice 2D FEA [3] or more computationally efficient semi-analytical techniques [2] exhibiting comparable accuracy. A common limitation associated with these techniques is their inability to capture certain 3D phenomena, namely the end-effects and axial interaction between skewed steps, since they explicitly rely on the 2D domain [4]. The significance of such 3D effects is influenced by the axial length to airgap diameter ratio (viz. end-effect), the number of skewed steps, the skew angle and the structure of the machine topology under consideration. The quantification, and most importantly experimental verification, of the 3D effects associated with skewed PMA SynRMs has received limited attention in literature to date.

On-Load Voltage Distortion in Fractional-Slot Interior Permanent Magnet Machines

The mechanism and the influence of the on-load terminal phase voltage distortion by the armature reaction in interior permanent magnet (IPM) machines with fractional-slot concentrated windings (FSCWs) are investigated in this paper, by taking a 12-slot/8-pole machine as an example. The phenomenon is presented first, which shows that the peak voltage will be much higher than the fundamental value, especially under the flux-weakening operation. Then, the mechanism is investigated with the aid of the frozen permeability method. Due to the geometric feature of the FSCW IPM rotor, the armature reaction flux will asymmetrically enhance the local magnetic saturation in the tooth-tips and the rotor lamination region near the rotor ribs, which disrupt the smooth variation of phase flux linkage and lead to a voltage distortion. With the increasing of current advancing angle ( $\beta $ ), this effect will become more obvious and result in the higher distortion level. Furthermore, the influences of voltage distortion on the machine torque performance are investigated, which show that it will only contribute to the torque ripple in the constant torque region, but will largely reduce the flux-weakening operation region compared with the ideal one calculated by the fundamental voltages only. Finally, a prototype is manufactured and tested to validate the analyses.

Analysis of Iron Loss in Interior PM Machines With Distributed Windings Under Deep Field Weakening

This paper investigates the rotor cavity positioning and the combination of stator slot and rotor effective slot number on the eddy-current loss for interior permanent-magnet/reluctance machines operating under deep field-weakening conditions. A new closed-form expression for the stator and rotor eddy-current loss is developed. The optimal barrier-positioning for the minimum total loss and the effect on the eddy-current loss of varying the stator slot and rotor effective slot number are investigated for one-, two-, three-, and full-layered rotors.