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Most permanent magnet (PM) loss studies consider only eddy current loss and neglect hysteresis. In this article, the hysteresis behavior of two NdFeB PM grades with different magnetic properties is assessed when applied in a PMSM. Data from vibrating sample magnetometer measurements and hysteresis modeling are used as a base. In addition to the main magnetic phase, the samples contained magnetic phases with reduced coercivity. Such phases may contribute to hysteresis losses in a PM material. A new model is introduced to simulate the hysteresis of rare-earth magnets of any geometric shape in the second and first quadrants of the intrinsic BH -plane. The magnetic field strength distribution in the PM material of an electrical motor is analyzed by two-dimensional finite-element method. The results are used as the input data for an analytical hysteresis model. The results indicate that the hysteresis loss resulting from the structural imperfections and geometry of the magnet may introduce a considerable loss in NdFeB PMs applied in rotating electrical machines.

Four-quadrant (FQ) switches that have both bidirectional current and reverse-voltage blocking (RVB) capabilities are appealing candidates for use in current-source inverters (CSI) to significantly reduce the switch conduction losses. However, the FQ characteristics of these switches can create problems during switching events by causing transient overcurrent pulses that damage the inverter. Commutation methods for FQ switches in CSI topologies that address these challenges are presented in this article. Several key aspects of the performance and implementation of these commutation methods are explored for a high-power density 3 kW integrated motor drive incorporating both a current-source active rectifier and inverter stage that has been developed using these FQ switch methods. Experimental results demonstrate the benefits of implementing these commutation methods in CSIs that use FQ switches. The benefits include substantial efficiency improvement compared to the conventional CSI implemented with series power diodes as well as reduced mass and volume of passive components due to the high switching frequency (100 kHz).

The objective of this article is to propose the concept of and evaluate the potential performance of an integrated flux-switching permanent magnet (FSPM) motor–compressor that has rotor poles designed as airfoils to perform compression functions. The airfoil-shaped rotor functions as the rotor of both an electric motor and an axial-flow compressor. As a result, the integrated motor–compressor increases the compressor system compactness by eliminating the separation between the motor and compressor. In this article, the electromagnetic and thermodynamic designs are developed using sizing equations and mean line analysis. Four design configurations of the integrated motor–compressor are carried out and evaluated, including the continuous-skewed versus step-skewed structure and laminated steels versus soft magnetic composite (SMC) materials. The thermodynamic performance is calculated by mean line analysis and computational fluid dynamics (CFD). The electromagnetic performance and structural analysis are evaluated by finite element analysis (FEA). The comparisons of the integrated motor–compressor with conventional motor-driven compressors are conducted. Results from FEA and CFD verify the integrated motor–compressor.

This paper develops a real-time loss minimizing control technique on induction machines for dynamic load profiles. Steady-state loss minimization has been well addressed in the literature. However, when the steady-state optimal stator flux linkage is applied to highly dynamic load profiles, more losses are induced during transients due to the slow rotor flux dynamics. Several heuristic methods have been developed for real-time loss reduction, but they are not designed for minimum losses. Loss-minimizing flux trajectories have been generated by dynamic programming but require prior information of load profiles. In this paper, a real-time loss minimizing control technique is developed for applications without prior information of load profiles. It resembles the loss-minimizing stator flux trajectory generated by a modified dynamic programming method, which generates the best practical solution for unknown load profiles. The steady-state optimal solution for the stator flux linkage is derived based on the induction machine loss model. Both simulation and experimental results demonstrate the energy saving capability of the proposed method.

The objective of this article is to evaluate the self-cooling performance of a novel integrated flux-switching permanent magnet (FSPM) machine with an airfoil-shaped rotor. The rotor of the proposed integrated machine is functioning as both a rotor of the motor as well as an axial fan. It rotates to draw air from the ambient into the rotor and accelerate the flow through the rotor stage. The high-speed flow provides forced convection to the rotor, stator, windings, and magnets. Therefore, self-cooling is achieved. Accounting for manufacturing challenges of the airfoil blades, three-dimensional (3-D) printed blade caps are designed and assembled over the laminated rotor poles for the airfoil-shaped rotor. The electromagnetic performance of the continuous-skewed stator slot is compared with the step-skewed stator slot. Three housing configurations are proposed in terms of housing with radial inlets, housing with axial inlets, and no housing. The electromagnetic performance is verified by 3-D finite element analysis (FEA). The convective heat transfer coefficients of the three housing configurations are calculated by analytical methods and numerical simulations by 3-D computational fluid dynamics. The effect of encapsulations on the windings is also evaluated by FEA. A prototype machine is built and tested. Experimental results of measured temperature distributions on the stator and windings are included to validate the numerical simulation results.

This article proposes a high-frequency injection based dq -inductance estimation technique for synchronous machines. The d- and q -axis inductance is estimated using a single HFI between d and q axes, i.e., 45 $^\circ$ injection angle. The d - and q -axis incremental inductance variation over four quadrants dq -plane operating condition is evaluated. The proposed technique can operate in real-time without a controlled position or velocity from the load side. Neither previous knowledge of machine parameters nor computationally expensive regression processes are required. The proposed technique can be used to evaluate the sensitivity of inductive saliency based self-sensing to determine preferable self-sensing operating conditions for permanent magnet synchronous machines.

A technology revolution is unfolding around us as every major mode of transportation is in some stage of electrification, whether on land, sea, or in the air. All of these transportation modes depend on electric machines that play critical roles in both propulsion systems as well as in a wide variety of accessory equipment. Fuel economy and reduced emissions of greenhouse gases and other pollutants are major driving forces for electrified transportation. Despite the significant differences between these varied transportation modes, they all share strong motivations to make their electric machines and adjustable-speed drives smaller, lighter, and more efficient. An excellent example of this trend for the power electronic drives is provided by comparing the drive units in the Tesla S (2012) and Tesla 3 (2017). As shown in the side-by-side views provided in Figure 1, the drive unit shrank in size from an enclosure that matched the size of its main traction motor to a much smaller unit that, at first sight, appears to be a non-descript end-bell attached to one end of the motor. Rather than focusing here on how this impressive reduction in mass and volume was achieved (addressed later in this article), the key point here is that similar technology trends are under way in many of the other transportation modes as well, making electrified transportation increasingly appealing and competitive in the process.

This study investigates the thermal impact of using different winding topologies and different winding encapsulation materials on dual-stator 6/4 flux-switching permanent magnet (FSPM) machine with water jacket cooling. The thermal performance of four different design cases are compared using lumped-parameter thermal network models. The modelling of the heat transfer in the stator slot, machine air gap and water jacket channel are presented. It is shown that FSPM machines with circumferential winding and toroidal winding have different thermal limiting components and the winding encapsulation material has a different impact on the thermal performance of the two winding topologies. Prototype motors are built and tested to validate the thermal models.

This paper presents an analytical prediction and a multiconstrained nonlinear optimization of slotted permanent magnet linear synchronous motors (PMLSMs). Preferentially, an analytical model is developed for the fast and accurate design of slotted PMLSMs. In the process, two key techniques are used for the performance prediction: first, the Schwarz–Christoffel conformal mapping is used to take into account the slotting effects, and as a result, the normal and transverse components of the flux density produced by permanent magnets (PMs) and three-phase current can be calculated; and second, the two-dimensional end effects due to the finite length of moving parts are roughly reflected by the half-side leakage analysis, thereby predicting the second-order harmonic of the force/thrust pulsation. Subsequently, a systematic approach to the design optimization based on an iterative scheme is presented to search for solution set that belongs to the Pareto front. With no need for finite-element analysis or multivariable equation set, the proposed model can save much computational time to reach an optimal solution. The validity of analytical results is confirmed by finite element and experimental results.

This article investigates analytical methods for calculating mechanical stress on the rotor of Interior Permanent-Magnet Synchronous Machines (IPMSMs). First, two existing analytical methods for calculating the stress on rotor iron bridges were investigated using a flat-type IPMSM model. The calculations of centroid radii required by these methods were simplified by taking advantage of the symmetry. Then, an accurate function of the stress concentration factor (SCF) was developed to calculate the maximum mechanical stress (MMS) on the iron bridge from its reference stress. The trends of SCF and MMS changing with geometrical parameters were obtained during the statistical analysis of SCF. Using the proposed analytical method, MMS on the bilateral iron bridges of both flat- and V-type IPMSMs can be calculated accurately. Finite element analysis (FEA) shows that the proposed method has improved accuracy and generality in calculations of the MMS. The reliability of the FEA model and the proposed analytical method were further investigated in a plastic deformation experiment. Based on the experimental results, the limits of the stress models, selection of the failure criteria, and safety factor were discussed for high-speed IPMSM design.

Gallium nitride (GaN) high electron mobility transistor (HEMT) has a lateral device structure with wafer-level packaging, which is advantageous in minimizing parasitic parameters and overall device size. This type of packaging also has better thermal performance than conventional packaging due to low junction-to-bottom thermal resistances. It indicates copper layers in printed circuit boards can effectively serve as heat dissipation channels for the switching devices. When these copper traces and pours in the vicinity of the switching devices are carefully designed and shaped, they can also be utilized as an integrated output filter. In this article, a synchronous buck converter with a single-turn air-core integrated planar inductor is proposed to achieve both zero-voltage switching and high thermal performance of the GaN HEMTs. A new planar inductor design flowchart is introduced, and analytically estimated inductance and resistance are verified with simulation and experiment. Three different inductors are designed and fabricated to prove the improved thermal performance of the proposed converters.

This paper investigates the design and testing of a high-speed dual-stator 6/4 flux-switching permanent magnet (FSPM) machine. A dual-stator design is used to solve the issue of second harmonic presented in the flux linkage of conventional 6/4 FSPM machine. Different dual-stator designs are investigated and compared against each other in terms of the performance and manufacturability. Comparison between the proposed dual-stator 6/4 FPSM machine and a commonly seen 12/10 FSPM machine is done at 10 kW, 15000 rpm condition. Due to the 60% reduction of the fundamental frequency, a significant reduction in iron loss and magnet eddy current loss is observed, which leads to higher efficiency. A prototype dual-stator 6/4 FSPM motor is built and tested on a dynamometer set up to verify the analytical calculation and finite element analysis results. A comparison is made between measured data and simulation results, and good agreements are achieved.

Permanent magnet (PM) modular motor drives (MMDs) have been recognized as promising candidate machine drive propulsion units in electrified aircraft due to their high power density, high efficiency, and high fault tolerance. Heterarchical, distributed, and modular control schemes are preferred to enhance the system reliability by eliminating single points of failure (SPOFs) from controllers. To facilitate modular machine control design and analysis, a generalized module-level machine analysis and modeling framework has been developed. Module-level machine analysis reveals intra-module unbalanced inductances and inter-module unbalanced cross-coupled fluxes that differ from conventional machines due to asymmetric mutual slot leakage flux couplings among the modules. An asymmetric module-level machine model has been developed by using complex vectors and conjugate complex vectors. Due to the asymmetry, balanced three-phase module voltage excitation induces both positive and negative sequence module current responses when the modules are not evenly loaded. This feature deteriorates the inter-module independence of MMDs, especially under fault conditions where maximum inter-module independence is desired. A modular control with a negative sequence regulator is proposed to eliminate the undesired negative sequence component under uneven loading and fault conditions in order to achieve the desired high level of inter-module independence.

In this paper, radial and axial housing inlet and outlet designs are proposed to cool a novel high-speed integrated flux-switching motor-compressor. With special arrangements of inlets and outlets in the housing, thermal analysis shows that the end windings can be effectively cooled. The rotor poles of the proposed machine are designed in the shape of airfoils so that they function as the rotor of an axial-flow fan. As the machine rotates at high speed, air is drawn into the machine and accelerated in the rotor. In this process, the airflow also cools the machine through forced convection; as a result, the machine achieves self-cooling. In order to use this capability most effectively, it is necessary to optimize the air flow path within the machine in order to direct air to critical surfaces that must be cooled and also remain at a favorable point on the fan curve. This paper explores different housing inlet and outlet designs and their influence on the pressure drop and surface heat transfer coefficients. The electromagnetic performance is evaluated by 3-D finite element analysis (FEA), and 3-D computational fluid dynamics (CFD) simulations are used to evaluate the thermal-fluid performance including the convective heat transfer coefficient at different surfaces.

This paper evaluates the parameter sensitivity of deadbeat flux vector control for six-step operation of permanent magnet synchronous machines. The flux-based torque control law is speed-dependent, causing an increased parameter sensitivity at the lower-speed range of the field-weakening region. This paper uses a linear operating point model to analyze and compare different torque control laws for six-step operation. However, while insightful, these linear modeling techniques break down for torque components near the fundamental electrical frequency when the six-step operation’s nonlinearities start to dominate. The paper explains the different effects that can be seen in a six-step frequency response function. With this understanding, machines can be selected and build to have a more robust performance in six-step operation.

A current-source inverter (CSI) has a natural output voltage boost feature that can be advantageous for traction applications. Switching frequency is one of the easily-controlled variables that can be adjusted to improve the CSI efficiency at different operating points when the boost function is used. This paper investigates a CSI-based double-pulse test (DPT) measurement that mimics normal operation of the CSI. A loss model of the CSI is developed based on the CSI-type DPT experimental results. The impacts of the switching frequency and voltage boost ratio on the CSI efficiency and output voltage ripple are investigated. Based on the loss model, a genetic algorithm has been introduced that makes it possible to optimize the CSI's switching frequency and modulation index to maximize its efficiency under any desired operating condition.

Integration of power electronics and electric machines enables compact and lightweight motor drive design as it eliminates the needs for separate housings and long connecting cables. For a successful realization of the integrated motor drive (IMD) concept, two primary engineering challenges associated with power electronics design need to be addressed: high power density and high-temperature operation. This paper presents the design progression of a wide bandgap (WBG) device-based current-source inverter (CSI) aiming at high power density. Both benchtop (non-IMD) and IMD versions of 3 kW WBG-based CSIs have been developed, and their power density and thermal performance are evaluated. Design issues including trade-offs between power density and thermal performance of printed circuit boards (PCBs), switch configurations, cooling strategies, and several integration schemes are explored.

The objective of this research is to investigate a new modulation scheme for balanced voltage-source inverters to suppress the DC offset in phase currents when switch short-circuit faults occur. Because of its superior common-mode voltage cancellation capability, the balanced VSI is an excellent topology for mitigating electromagnetic interference (EMI), especially in power converters using wide-bandgap (WBG) power semiconductors. In addition, the balanced inverter topology offers valuable opportunities for fault-tolerant operation. When a switch fails as a short circuit, significant amounts of DC offset currents are induced in the phase currents if the baseline switching algorithm is not changed, risking damage to other healthy switches and inverter loads such as electric machines. A new modulation scheme is proposed for eliminating the DC offset currents while maintaining the balanced inverter’s power conversion capability. This new algorithm enhances the balanced inverter’s appeal by expanding its operating range to include fault-mode conditions with switch short-circuit faults.

Interior permanent magnet (IPM) machines are more commonly used in applications where constant power vs. speed operation is required. However, achieving IPM rotor design for a wide constant power speed ratio (CPSR) requires an iterative design process, thus driving design cycle time and cost higher. In this work, a design methodology is proposed to achieve wide CPSR using combinations of different types of pre-designed rotor cross-sections, i.e., hybrid rotor machines. The design constraints developed in this work are broadly applicable to any synchronous AC machine that allows for a relative offset between PM and reluctance torque components as an additional design degree of freedom.

Surface permanent magnet machines gain more and more attention over recent years due to their high power density and high efficiency. This paper compares the Vernier machine and surface permanent magnet synchronous machine in electromagnetic structure, operating principle, and steady-state performances. FEA results are used to verify the analytical equations for comparing Vernier machine and SPM machine performance, with the exact dimensions, in terms of back-EMF, cogging torque, torque generation capability, and torque ripple. Moreover, the machine's back-EMF and torque performances regarding magnet thickness show that the Vernier machine utilizes magnets better than the surface PM machine.