Interior Permanent Magnet Machine Research Articles

Mechanical Stress in Rotors of Permanent Magnet Machines—Comparison of Different Determination Methods

In this work, different analytical methods for calculating the mechanical stresses in the rotors of permanent magnet machines are presented. The focus is on interior permanent magnet machines. First, an overview of eight different methods from the literature is given. Specific differences are pointed out, and a brief summary of the analytical approach for each method is provided. For reference purposes, a finite element model is created and simulated for each rotor geometry studied. A total of seven rotors rom representative automotive powertrains are considered in their specific speed range. The analytical methods are used to determine the maximum mechanical stress concentration factors for the seven rotor geometries, in which we are determined to find maximum mechanical stress as a final step of the analytical process. For each geometry and each respective operating speed range, the deviations from the finite element reference are determined. In addition, the error in the selected geometry variations is evaluated. A recommendation for the method with the lowest error considering all cases studied is given specifically for the stress in the airgap bridge and the central bridge.

Improved Small-Signal Injection-Based Online Multiparameter Identification Method for IPM Machines Considering Cross-Coupling Magnetic Saturation

A novel online multiparameter identification method is proposed for interior permanent magnet (IPM) machines considering cross-coupling magnetic saturation. The identification method is based on the combination of small-signal impedance model and fundamental frequency signal model under <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -axes. To analyze the nonlinearity of IPM machines, cross-coupling magnetic saturation effect is introduced into online multiparameter identification for the first time. Based on this model, a phase compensation strategy and orthogonal decomposition in phasor domain is proposed to decouple the complicated mathematical model into four linear equations. By injecting voltage small-signals into <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -axes, multiparameter of IPM machine including adjusted apparent inductance, incremental self-inductance, incremental mutual-inductance can be identified online in a wide operation region. During this process, no additional computing equipment is required. The proposed method is carried out on a tested IPM machine and verified by the finite-element analysis.

Integration of Measurement Vector Insertion With Discontinuous PWM to Improve Saliency-Based Sensorless Drive Position Estimation

Saliency-based position sensorless machine drive with the pulsewidth modulation (PWM) voltage switching frequency injection has advantages of high estimation bandwidth and low acoustic noise. However, multiple currents must be sampled every PWM cycle for spatial saliency calculation. Besides, the switching frequency voltage injection distorts the symmetric PWM voltage pattern. For these saliency-based drives, the PWM injection is the tradeoff between the transient estimation bandwidth and steady state estimation error. This article proposes a modified PWM voltage injection through the measurement vector insertion (MVI) for sensorless position estimation. By integrating the MVI with discontinuous PWM, the proposed injection maintains the symmetric PWM voltage for machine control. This MVI-based PWM (MVIPWM) improves the saliency-based drive among voltage harmonics, current harmonics, and position estimation error. The proposed MVIPWM injection is compared to other PWM injection methods on an interior permanent magnet machine. All advantages of MVIPWM on the saliency-based drive are verified by experimental results.

Inductance Characteristics of Flux-Switching Permanent Magnet Machine Based on General Air-Gap Filed Modulation Theory

Winding inductance is a crucial parameter of machines, which plays an essential role in flux-weakening capability, reluctance torque, power factor, etc. In this article, winding inductance characteristics of flux-switching permanent magnet (FSPM) machines are investigated from the perspective of air-gap modulation magnetic field. With the aid of the general air-gap field modulation theory, the air-gap magnetic field contributed by an arbitrary energized winding of FSPM machines is modeled and analyzed. Then, an analytical expression of winding inductance is derived based on winding function and single-phase magnetic field, through which the relationship between winding inductance and single-phase magnetic field harmonics is unveiled. It is found that the direct current (dc) and 2nd harmonic components of winding inductances in FSPM machines are caused by the dc and 2nd time-harmonic components of primitive harmonics, respectively, which are essentially different from that of traditional interior permanent magnet or reluctance machines. Finally, experiments on a prototype three-phase 12/10 FSPM machine are conducted to verify the theoretical analysis.

Efficiency modeling and comparison of surface and interior permanent magnet machines for electric vehicle

This paper presents the analysis and comparisons between the Surface Permanent Magnet (SPM) and Interior Permanent Magnet (IPM) Machines about their loss and efficiency characteristics. To calculate the airgap flux density and torque, an analytic model is created. The loss functions are derived using the key design parameters which have a great influence on the loss characteristic. As a result, the efficiency can be calculated. The relationship between the design parameters and efficiency characteristic is investigated adopting the proposed method. The efficiency of different driving cycles is also calculated and compared. Finally, some principles are obtained to help the initial design to fit the actual loading requirement. The analytic results are compared with those by Finite Elements Analysis (FEA), and a prototype is made and tested to validate the proposed method and analysis.

Design Considerations of Magnet Configurations in Interior Permanent Magnet Machines for High-Speed Traction Applications: A Comprehensive Study

This article presents a comprehensive comparison and the design considerations of three magnet configurations in interior permanent magnet (IPM) machines for high-speed traction applications. The study investigates single-V, double-V, and single-U magnet configurations. A multiphysic multiobjective optimization is used to enhance the three machines, which are designed with a constraint to fit in the same housing and have the same torque-speed curve. The optimized configurations are then compared with respect to multiple performance indices according to common design criteria for traction motors, including no-load characteristics, short circuit characteristics, demagnetization, torque, efficiency, loss distributions, continuous performance, and magnet volume. The study presents how multiphysics design requirements affect the selection of magnet configurations: a single-V rotor configuration can be selected to have the lowest magnet usage as well as high torque density; while the double-V design is suitable for noise-sensitive, high-efficiency applications but requires a rotor-cooling system; and the single-U design is a good candidate for managing tradeoffs among the other options while maintaining a high degree of freedom in the design.

ANFIS-Based Droop Control of an AC Microgrid System: Considering Intake of Water Treatment Plant

Provision of an efficient water supply system (WSS) is one of the top priorities of all municipals to ascertain adequate water supply to the city. Intake is the lifeline of the water supply system and largely effects the overall plant efficiency. The required power supply is generally fed from the main grid, and a diesel generator is commonly used as a power backup source. This results in high pumping cost as well as high operational cost. Moreover, due to operation of motor pumps and other auxiliary loads, frequent maintenance is required. Therefore, to avoid various challenges and to efficiently operate the intake system, microgrid concept has been introduced in this paper. Various distributed generations (DGs) such as solar photovoltaic (PV), interior permanent magnet machine (IPM) wind turbine generator and Battery energy storage system (BESS) are incorporated in the microgrid system. Additionally, a new approach based on adaptive neuro-fuzzy inference system (ANFIS) is proposed, where P-f and Q-V droop is considered while training the ANFIS data; after successful training, the microgrid voltage and frequency are controlled as per system requirement. Simulation of the microgrid system shows good results and comparison with the generalized droop control (GDC) method is done using MATLAB/Simulink software.

A Hybrid Calculation Method of Electromagnetic Vibration for Electrical Machines Considering High-Frequency Current Harmonics

This article proposes a hybrid evaluation method of electromagnetic force and vibration for electrical machines considering high-frequency current harmonics caused by the inverter. First, the permeance and armature magnetomotive force (MMF) is calculated based on the virtual MMF and the slot matrix. Then, the air-gap flux density and electromagnetic force construction process under arbitrary current is thoroughly studied. The vibration transfer function is obtained by utilizing the modal analysis and the modal test. Finally, the vibration can be calculated according to the modal superposition method. By applying this method to an interior permanent magnet machine, it can significantly reduce the computation efforts compared with the multiphysics procedure due to the extensive use of the finite-element method. In addition, the accuracy of this method is validated by conducting an experimental study.

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.

Efficiency Optimization of PWM-Induced Power Losses in Traction Drive Systems With IPM Machines Using Wide Bandgap-Based Inverters

This article investigates the total PWM-induced power losses in interior permanent magnet (IPM) machines excited by wide bandgap (WBG)-based voltage-source inverters with different pulsewidth modulation (PWM) schemes and a wide range of switching frequencies. The PWM current ripple characteristics are predicted and compared using an accurate analytical model. Three enhanced power loss estimation models are utilized to estimate the PWM-induced power losses in each of three major machine materials: the stator form-wound windings, the stator and rotor iron cores, and the permanent magnets in the rotor cavities. The variation trend of each loss component versus PWM frequency and modulation scheme is provided. Experiments have validated the model accuracy in two IPM machines designed for traction applications. Both measured and predicted results suggest that increasing the PWM frequency is beneficial for suppressing the PWM-induced power losses in IPM machines. In conjunction with the reduction in machine-related power losses, it has also been demonstrated that a higher PWM frequency in IPM drives with WBG-based inverter exhibits the appealing potential for improving the system-level efficiency in traction applications.

A General Pattern of Assisted Flux Barriers for Design Optimization of an Asymmetric V-Shape Interior Permanent Magnet Machine

In this work, a novel general pattern of assisted flux barriers in an asymmetric V-shape interior permanent magnet (AVIPM) machine is presented. The AVIPM machine has a symmetric permanent magnet (PM) structure and an asymmetric rotor core structure to realize the magnetic-field-shifting (MFS) effect. The general pattern can represent four possible types of assisted flux barriers at different positions on the rotor core and the final structure can be automatically determined by using optimization method. The advantage of the proposed optimization pattern is that the optimal design of assisted flux barriers in V-shape interior permanent magnet (VIPM) machines with high torque and low torque ripple can be generated within a short computing time. The proposed optimization method is applied to improve the structure of a conventional 8-pole 48-slot VIPM machine, which is commonly used for driving electric vehicles (EVs). A non-dominated sorting genetic algorithm II (NSGA-II) is used for the global optimization of both a VIPM machine and an AVIPM machine. The electromagnetic performance is computed using a finite element analysis (FEA). Moreover, a frozen permeability (FP) method is applied to perform an accurate separation of PM torque and reluctance torque. The results exhibit that the peak output torque of the AVIPM machine is increased by 8.7% compared to a conventional VIPM machine with the same PM volume due to the notable MFS effect. In the meantime, the AVIPM machine has a better overload capability due to the larger contribution of reluctance torque. Moreover, the proposed machine has high efficiency of over 97%.

Open-Circuit Electromagnetic Analysis of Interior Permanent Magnet Machines With Arbitrary Rotor Frame Using a 2-D Analytical Model

Two-dimensional (2-D) analytical modeling of interior permanent magnet (IPM) machines is quite challenging due to the nonuniform permeability of the rotor core. The choice of a non-cylindrical rotor frame (e.g., rotor frame with cosine shape) further increases the complexity of the model. This article presents a methodology for the 2-D modeling of IPM machines with cylindrical and non-cylindrical rotor frames. In this model, interior magnets are first mapped to the surface of the rotor body using the equivalent magnetic circuit model. In other words, the IPM machine is transformed into an equivalent surface-mounted permanent magnet (SPM) machine. The rotor shape is modeled by the proper adjustment of the permanent magnet (PM) magnetization pattern of the equivalent SPM machine. Next, the radial and tangential flux components of the equivalent (SPM) machine are computed by solving Maxwell’s relations and applying 2-D boundary conditions. The effect of the stator slotting on the distribution of magnetic flux is accounted using the theory of virtual current. The accuracy of the presented model is verified against the finite element (FE) and experimental measurements.

A Novel Analysis Method for Flatted Single-Layer Interior Permanent Magnet Machines Having Overhang Structure

This study describes a novel analysis method for interior permanent magnet (IPM) machines with an overhang, in which the rotor axial length exceeds that of the stator. Adopting an overhang structure facilitates the achievement of a high torque density per machine volume without increasing the stator size due to the additional magnetic flux of the rotor. However, the use of the three-dimensional (3-D) finite-element method (FEM) is inevitable, which requires substantial computation time and large computer memory to accommodate the overhang effect. Therefore, a new analysis method combined with a lumped magnetic equivalent circuit (MEC) is proposed to overcome the inefficient conventional approach. A new residual flux density can be derived by considering the magnetic flux paths in the overhang structure. Two-dimensional FEM combined with the residual accurately considers the IPM with overhang. The validity of the proposed concept is verified via 3-D FEM using several test models.

Comparative Study of Permanent Magnet, Conventional, and Advanced Induction Machines for Traction Applications

This paper investigates and compares the torque-generating capabilities and electromagnetic performance of advanced non-overlapping winding induction machines (AIM), conventional induction machines (CIM), and interior-permanent magnet (IPM) machines for electric vehicle (EV) applications. All investigated machines are designed based on the specifications of the Toyota Prius 2010 IPM machine. The steady-state and flux-weakening performance characteristics are calculated by employing the 2D finite element method and MatLab, and the obtained results are quantitatively compared. Furthermore, the torque-generating capabilities of three machines are investigated for different electric loadings, and the machine having the highest torque-generating capability is determined as AIM. Moreover, the major parameters affecting the torque-generating capability, such as magnetic saturation and magnet demagnetization, are examined in depth.

Computationally Efficient Analytical Model of Interior Permanent Magnet Machines Considering Stator Slotting Effects

Subdomain modeling is among the most reliable and accurate analytical tools for designing and analyzing permanent magnet machines. However, the application of the two-dimensional (2-D) subdomain model is mainly limited to permanent magnet machines with homogeneous rotor structures (with uniform permeability), such as surface-mounted or surface-inset permanent magnet machines. Solving Maxwell's equations and applying 2-D boundary conditions on structures with permanent magnets embedded in the rotor core, such as interior permanent magnet machines, are quite complex. Given the importance of enabling the tangential field component to capture accurate results, a 2-D hybrid analytical solution is proposed and applied to a multilayer interior permanent magnet machine. For this purpose, the radial components of the permanent magnet flux and the armature flux are first calculated using the magnetic circuit and the magnetic islands methods, respectively. Next, their respective tangential flux components are computed by solving Poisson's equation and applying a 1-D boundary condition along the tangential direction. Meanwhile, the stator slotting effect is included via the theory of virtual surface current. Finally, the steady-state performance metrics of the motor are calculated and verified via finite-element and experimental measurement.

On Torque Improvement by Current Harmonic Injection in Isotropic and Anisotropic Multiphase Machines

Multiphase machines give the possibility to increase the torque injecting and controlling current harmonics of different orders. This work investigates the current harmonic injection techniques for both isotropic and anisotropic machines. The proposed analysis shows that for anisotropic machines, both amplitudes and angles of the optimal current injection should not be predicted based on the back electromotive force only. An analytical model is used to assess the differences in terms of no load and load voltage spectra. Considering these differences, a current injection technique based on the harmonic content of the voltage waveforms is proposed. In addition, the analysis to determine the optimum amplitudes and angles to maximize the torque capability is carried out by means of finite-element analysis (FEA) and compared with the techniques based on the analytical model. The FEA is carried out for both surface permanent magnet and V-shaped interior permanent magnet (IPM) machines with dual-three-phase winding layouts and injecting the fifth harmonic of current. Finally, the proposed concept is validated via an experimental test on a dual-three-phase V-shaped IPM machine. The results show that current harmonic injection based on the voltage vectors is applicable for both isotropic and anisotropic machines with good accuracy.

Electrical machines surrogate‐based design optimization based on novel waveform targeting strategy with improvement of the computational efficiency

Electrical machine design optimization is an expensive procedure as it contains numerous variables and multiple objectives. Therefore, it might require hundreds of time-consuming finite element analyses (FEA). Surrogate models are one of the superior alternatives that can overcome the computational burden of FEA. However, in optimization problems with sensitive input-output relationships, surrogate models can lack accuracy or suffer from unreasonable initial FE-computational cost. To tackle this problem, this work presents a novel strategy called Waveform-Targeted Surrogate Modeling (WTSM) that improves the computational efficiency of surrogate-based design optimization of electrical machines by modifying the model construction process. In this paper, an Interior Permanent Magnet Machine (IPMSM) is studied to evaluate the proposed strategy's performance compared to the conventional Black Box Modeling (BBM) method. A two-step assessment procedure consisting of multiple scenarios has been developed to analyse the reliability of the WTSM concerning different training-validation datasets. Meanwhile, the Kriging model and Latin-Hypercube-Sampling (LHS) method are employed for surrogate model construction purposes. From the discussion and the results, it can be found that the proposed WTSM strategy can significantly increase the accuracy of the surrogate modelling procedure while the required computational cost can be reduced.

Analytical Minimization of Interior Permanent Magnet Machine Torque Pulsations by Design of Sculpted Rotor

A new and efficient analytical optimization methodology for the design of rotor features is developed and used in interior permanent magnet motors (IPM). The analytical methodology is based on an extended winding function theory to include the IPM rotor’s primary and secondary reluctance paths and the non-homogeneous airgap of the rotor sculpt features. The shape and placement of the rotor features, derived from the analytical-based optimization process, show the improvement in torque average and torque ripple of the IPM machine at a fraction of computational effort. The analytical optimization results are validated with finite element analysis via an exhaustive search.

Electromagnetic Analysis for Interior Permanent-Magnet Machine Using Hybrid Subdomain Model

This paper proposed a hybrid subdomain model (HSM) for calculating the magnetic field distribution of interior permanent-magnet (IPM) machine accounting for slotting effect, rotor saliency, and iron nonlinearity. In the constant permeability region, i.e., slots, slot-opening, and air-gap, three subdomains are introduced to represent their magnetic field. By applying the subdomains interface conditions and nonlinear boundary conditions, the analytical air-gap field solution can be obtained based on the governing Laplace and Poisson equation. For the iron region, the magnetic reluctance network (MRN) is proposed to account for rotor saliency iron and nonlinearity. The magnetic voltage source is introduced to represent the permanent-magnet (PM) while the air-gap flux source is used to replace the air-gap reluctance network, which is the key to guarantee the computational efficiency and high accuracy. The electromagnetic performances of both flat-shaped and V-shaped IPM machines are investigated to show the advantages of different IPM machine topologies analytically. The HSM predictions for both IPM machines are validated by finite-element (FE) analysis and experimental results.

Investigation of an Intensifying-flux Variable Flux-leakage Interior Permanent Magnet Machine for Wide Speed Range

In this paper, a novel intensifying-flux variable flux-leakage interior permanent magnet (IFVF-IPM) machine is proposed, in which flux barriers were designed deliberately between the adjacent poles to obtain intensifying-flux effect and variable flux-leakage property. The rotor topology and design principles of the proposed machine are also introduced. Then, a multi-objective optimization method is adopted based on the sensitivity analysis, and some design variables of IFVF-IPM machine with strong sensitivity are selected to optimization progress by using the non-dominated sorting genetic algorithm-II (NSGA-II). Moreover, the electromagnetic characteristics of conventional IPM machine, conventional IFVF-IPM machine (CIFVF-IPM) and the novel IFVF-IPM machine are compared based on the finite element analysis (FEA) method which includes flux linkage, inductances characteristic, torque-speed envelops and power characteristic, as well as evaluation of the risk of irreversible demagnetization. Finally, the experiment results show that the IFVF- IPM machine has a better performance in flux weakening capability for wide speed range and a lower risk of irreversible demagnetization, which indicates the validity and feasibility of the proposed machine.