In this work, two strategies to mitigate common-mode currents caused by inverters connected between dc and ac systems are compared. The two strategies differ in terms of the presence or absence of a connection between the 'virtual ground point' and the earth ground. The comparison is made based on the mathematical analysis of the impedances involved in the system and through demonstrations on an experimental set-up.

This paper presents the model and design optimization of a propulsion system for an unmanned underwater vehicle (UUV) using a transverse flux motor (TFM) drive. The TFM's inherent ability to deliver high torque at low speeds makes it particularly well-suited for direct-drive propulsion, eliminating the need for gearing mechanisms. Unlike conventional motor architectures, the TFM leverages a three-dimensional flux path, enabling greater torque density in a compact form-an essential factor for space-constrained UUV applications. Both inner rotor and outer rotor TFM configurations are considered for this application, with design methodologies developed for each. A comparative analysis is conducted to evaluate key performance metrics of torque density and efficiency which are important for UUV propulsion.

Abstract Environmental concerns have pushed toward electrified technologies for off‐road vehicle actuations that can lower greenhouse gas emissions and reduce energy consumption. Replacing a central diesel engine with a dedicated electric machine (EM) as a prime mover for the hydraulic supply offers several opportunities for so‐called ePumps (aka electric‐driven pumps) to maximize energy efficiency and limit the usage of electric materials. This paper discusses the impact of different choices for the ePumps architecture (i.e., fixed vs. variable displacement pump; variable speed vs. fixed speed electrical machine), and on their main design parameters in terms of size and efficiency. Although the procedure followed in the study could be extended to different types of electric and hydraulic units, the paper particularly considers ePumps based on permanent magnet synchronous machines combined with axial piston machines. The importance of properly considering the ePump drive cycle and its cooling requirements is taken into account while addressing energy efficiency, mass, and overall compactness of the solution. The results show that an ePump based on a variable displacement pump, when compared to fixed displacement ePumps, reduces the electrical machine size both in volume and mass up to 40%, when the high‐pressure demand is not combined with high flow rate demand, thus decreasing the cost of the EM. In all drive cycles, the variable speed EM–fixed displacement pump architecture has a higher efficiency, ranging from 1% to 5%, compared to the case of fixed speed EM–variable displacement pump. Finally, the paper compares the advantages and shortcomings of each ePump architecture presented, based on representative drive cycles.

Electric Machines (EMs) have gained increasing importance in the mobile hydraulic industry as prime movers for hydraulic actuation systems. Therefore, their design and sizing are important aspects for any system layout architecture. The on-road vehicle industry has exploited EM versatility by proposing different sizes for various applications. However, off-road vehicles cannot borrow designs from on-road applications directly due to their unique challenges pertaining to drive cycle dynamics and limited space availability. Furthermore, considerations of the thermal limitations of EM and their cooling must also be studied to devise an effective methodology for designing prime movers suitable for mobile hydraulic applications. This paper proposes EM operational sizing strategies based on corner point operation, flux weakening and transient operation that can downsize EMs by carefully selecting sizing points from the operating domain. These strategies can leverage the operational capabilities of EMs and involve trade-offs in terms of EM compactness and efficiency. Therefore, based on a specific requirement, a given strategy can have certain benefits explored in this paper. The paper also examines two other downsizing methods based on switching the ePump architecture to variable displacement pump operation and improving the cooling performance. The paper considers a 5-ton mini excavator’s arm actuator as a reference application. The resulting EMs are compared in terms of size and efficiency to study the effectiveness of each operational sizing strategy. This paper uses a well-established genetic algorithm-based multi-objective algorithm to design a Permanent Magnet Synchronous Machine (PMSM) for each sizing strategy. The effect of cooling technology is considered in terms of limiting winding current density for the EMs, and the impact of cooling technology on the size and efficiency of the EM is also demonstrated. Finally, the effectiveness of the proposed operational sizing strategies in downsizing EMs is combined with, and compared to other methods like variable displacement operation and aggressive cooling to identify the best ways to obtain the most compact EMs for any hydraulic application.

This paper proposes a design methodology for power-dense and high-efficient electrohydraulic units (EHUs) that can be used to select design specifications for the electric machine (EM) for a given hydraulic machine (HM) architecture. The proposed method evaluates EHU performance considering both electric and hydraulic power losses. The compactness of the EHU is achieved by integrating an axial piston unit as HM inside a permanent magnet EM. The paper provides a sensitivity analysis for important EHU design specifications and discusses the best choices for reducing total mass and energy loss. The study finds that greater aspect ratios promote power-to-weight ratio, while high voltage promotes energy efficiency. The paper also discusses the choice of fixed versus variable displacement HMs, with the finding that a variable displacement unit helps address low efficiency limits of low-speed operation, particularly for low voltage electric machines. Additionally, variable displacement can also be used to reduce EM losses when meeting a flow-pressure demand. The proposed methodology has applications in fields such as off-road vehicles.

Homopolar AC Machines (HAMs) are of interest because of low rotor loss and the ability to operate at high speeds. These machines are frequently utilized in flywheel energy storage systems but are dominated by permanent magnet or induction machines in other contexts such as vehicle traction. The aim of this work is to explore a new type of homopolar machine. The Dual Rotor Homopolar AC Machine (DHAM) is proposed herein. The fundamental operating principles of the DHAM are explained, and its torque production and terminal characteristics are outlined. The permanent magnet version of the machine is shown to achieve an extended constant power speed range without impacting the PM field intensity, allowing the use of magnet materials with modest values of intrinsic coercive force. The machine includes a modular sectionalized stator, which is easy to wind and cool. The DHAM relies on sinusoidal airgap reluctances, and so the necessary rotor geometry is derived. A prototype machine is used to validate the operating principle.

In recent years, increasingly stringent emission regulations have spurred an electrification trend in off-highway vehicle technology. To address challenges such as the high cost of power electronics components, limited battery capacity, and the substantial modifications required for the vehicles, there is a pressing need to develop highspeed, cost-effective, compact, and efficient electro-hydraulic units capable of powering vehicle functions. In response to these demands, this paper introduces an innovative morphology for an electro-hydraulic unit and outlines the integration method for a crescent-type internal gear machine with a permanent magnet synchronous electric machine. The proposed morphology aims to minimize component count through a shaftless solution while incorporating a cooling system that utilizes the same working fluid as the hydraulic machine. The design approach utilizes a genetic algorithm optimization process to maximize overall energy efficiency and compactness. Insights gained from the optimization results shed light on the relationship between key design parameters and unit performance, enhancing the understanding of this electro-hydraulic unit. A prototype of the unit was manufactured and tested, demonstrating a volumetric efficiency ranging from 81 % to 97 % at a maximum rotational velocity of the pinion of 6000 rpm. These results validate both the morphology and the design approach, indicating the feasibility of designing compact electro-hydraulic units that leverage hydraulic machines with higher maximum rotational velocities than commercially available counterparts as a mean to enhance efficiency and compactness.

Geomagnetic disturbances (GMDs) give rise to geomagnetically induced currents (GICs) on the earth’s surface which find their way into power systems via grounded transformer neutrals. The quasi-dc nature of the GICs results in half-cycle saturation of the power grid transformers which in turn results in transformer failure, life reduction, and other adverse effects. Therefore, transformers need to be more resilient to dc excitation. This paper sets forth dc immunity metrics for transformers. Furthermore, this paper sets forth a novel transformer architecture and a design methodology which employs the dc immunity metrics to make it more resilient to dc excitation. This is demonstrated using a time-stepping 2D finite element analysis (FEA) simulation. It was found that a relatively small change in the core geometry significantly increases transformer resiliency with respect to dc excitation.

Electric Vehicles (EVs) are considered among one of the ‘clean’ energy technologies in the transportation sector because the vehicles themselves do not generate combustion emissions. However, the substantial environmental footprint associated with the materials needed to create these technologies (extraction, manufacturing, and solid waste at end of life) calls into question their ‘clean’ label. In addition, their increasing demand adds to the existing supply risk (SR) through the requirement of critical materials. To address this, the purpose of this study is to establish a design model for electric traction motors, which are used in EVs, that will address the SR issues early in the design stage. The design model incorporates a genetic algorithm with the following objectives: minimum motor mass, minimum energy consumption, and minimum SR-equivalent. The SR-equivalent objective prioritizes the minimization of materials with high SR. Using the case study of a surface-mounted permanent magnet synchronous motor, results show how each objective is related to each other and to the parameters chosen as variables. Further analysis shows the benefits of minimizing for SR-equivalent of required materials. Future work is needed to improve the design model in terms of other important metrics such as minimizing environmental impact and cost.

With the electrification trends affecting mobile hydraulics, there is a growing need for energy-efficient and compact hydraulic supply units driven by electric machines, also known as ePumps. This paper aims to compare various ePump designs that utilize different combinations of “best-in-class” commercially available hydraulic pumps and electric machines (EMs), to meet the requirements of a generic mobile hydraulic application. The paper intends to discuss the effect of the design architecture of the combination of a permanent magnet synchronous machine (PMSM), with several hydraulic pumps, including axial piston machines, bent axis piston machines, external gear machines, vane pumps, and radial piston pumps. A large combination of ePump architectures exists, and for engineers, it can be challenging to assess the pros and cons of each option for an electrified application. To address this challenge, in this paper, different commercially available pumps and an EM are chosen to evaluate key performance and design parameters such as drive cycle efficiencies, mass, and volume. Qualitative cost and power density considerations are also investigated. The effect of variable displacement ePump operation on the drive cycle is demonstrated for two ePump cases. By providing a benchmarking based on a generalized utilization cycle, this study serves as a guideline for selecting appropriate ePump architectures in electrified mobile hydraulic applications.

Common-mode inductors are generally designed so that their operation is in the magnetically linear region of the core material. Very few works consider magnetic hysteresis in the core in terms of the common-mode current waveform. This work validates one such magnetic model and enhances it by including the common-mode current due to the inductor's parasitic capacitance. This work establishes the considerable impact of hysteresis and parasitic capacitance on the ability of a common-mode inductor to reduce the common-mode current. (Statement A: Approved for Release. Distribution is unlimited #2022-0227)

With the recent electrification trends affecting mobile hydraulics, there is a rising demand for the development of energy-efficient and compact hydraulic supply units driven by electric machines. Such units capable of multi-quadrant operation are commonly known as electrohydraulic units (EHUs). Owing to inherent differences in the power densities of the two machines, efforts are required to make more compact electric machines in order to reduce the overall size of the resulting EHU. This paper discusses the optimal design of such an integrated EHU with a radial flux permanent magnet synchronous machine with flux weakening operation for a swashplate type axial piston machine. A flux weakening mode current control strategy extends the operating speeds of the electric machine to its maximum power by injecting a negative d-axis current. Such a flux weakening mode of operation can allow optimal sizing of the EHUs if the peak flow and pressure demands do not coincide. Based on a given work cycle and a reference hydraulic unit, a multi-objective genetic algorithm based design optimization is used to optimize the electric machine of the integrated EHU for the best efficiency and compactness. The EM design with flux weakening mode of operation are compared to the ones with max torque per amp mode of operation in terms of mass, torque density, and efficiency. Flux weakening based electric machine design allows sizing for maximum achievable power and helps not only to downsize the electric machine by 30% but also to save on the cost of the power electronics required.

Common-mode voltage and current in an electric machine are undesirable. Although the strategic placement of a common-mode inductor and dc input side capacitors may reduce the common-mode current produced by an electric drive system, the effectiveness of this mitigation is a function of machine parasitic capacitance. This engenders the need to insert another electrical component into the system to effectively mitigate the common-mode current. With this purpose, a common-mode shorting network for an inverter-based drive system is proposed in this work. This network, in conjunction with a common-mode inductor and dc input side capacitors, reduces the machine common-mode voltage and current. The proposed approach is experimentally demonstrated.

This paper presents an innovative design of an integrated electro-hydraulic (EH) flow generation unit able to operate in multiple quadrants. The proposed unit is composed of a hydraulic machine which can operate in either pumping or motoring mode, and an electric machine, which can operate as electric motor or generator. The adopted morphological integration of the two unit fulfills the goals of maximizing compactness, power to weight ratio, energy efficiency and quietness. The design results from a numerical optimization procedure that includes detailed simulation of both the electric machine and the hydraulic machine, using simulation tools previously developed by the authors, but combined for the first time in this work. After describing the optimization procedure, the paper focuses on the design integration aspects of the novel unit. A 9 kW prototype of the integrated unit was also fabricated and tested to verify its performance. Tests results show a measured overall energy efficiency up to 69%, demonstrating the potentials of the proposed concept, despite some limitations present in the first prototypes which could be addressed in future design refinements.

This chapter considers alternating current (AC) conductor losses and skin effect in the context of both strip conductors and then round conductors, and focuses on proximity effect. Skin effect is a phenomenon in which current density becomes concentrated at the outside of a conductor rather than being uniformly distributed. Skin effect is associated with AC currents and becomes increasingly pronounced as frequency increases. Proximity effect is a loss mechanism in which a time-varying field from nearby conductors induces eddy currents in a given conductor. The chapter aims to demonstrate why the two loss mechanisms may be treated separately. It also considers the calculation of the proximity-effect loss for an entire winding, and these losses for particular cases, including rotating machinery and a UI-core inductor. The chapter concludes by considering the ac conductor losses in rotating electric machinery and in a UI-core inductor.

Spatially tuning core permeability of an electromagnetic device enables superior performance. A permeability profile can be heuristically selected to improve the flux distribution in a device with a given geometry, but in order to fully leverage the capacity of spatial dependent permeability engineering, the geometry and the permeability should be optimized simultaneously. The work in this article herein presented sets forth a multiphysics design optimization paradigm that includes the permeability profile tuning in the context of both inductor and converter design. This approach enables the determination of Pareto optimal fronts consisting of a set of optimal solutions against competing objectives (e.g., mass and loss) under imposed constraints. To this end, computationally efficient analytical solutions of the heat transfer and electromagnetic formulations are derived for toroidal inductors, which are validated with finite-element analysis-based simulations. The software implemented in MATLAB 2018b is available online as an attachment to this article.

The operation of the buck converter can be in continuous mode or discontinuous mode. In a power electronic circuit, the semiconductors are one of the most significant sources of loss. For a given device, this loss has two components: the conduction loss associated with the forward voltage drop, which occurs as a part of conducting current, and the switching loss, which occurs when a device turns on or off. Switching losses are proportional to the voltage that the semiconductor must block in the off state and the value of current that was or will be conducted following the change in switching state. The chapter considers a passive air-cooled scenario in which the transistor and diode are each mounted on their own heat sink. It focuses on polypropylene film capacitors, which are very commonly used in power electronics applications. The chapter considers the electrothermal analysis of an operating point.

This chapter considers what is perhaps the most common method of numerical magnetic modeling—finite element analysis (FEA). It also considers the static conditions and the two-dimensional case, and Maxwell's equations that govern electromagnetics. The most straightforward approach is using a Gauss–Seidel iteration wherein the FEA is conducted with constant permeability. Based on the flux density in each element, the permeability of that element is adjusted, and the process is repeated until the solution converges in every element. The chapter focuses on using FEA as a means of design validation, one should mention that it is certainly possible to use FEA as the computational engine for design, especially for problems wherein the magnetic analysis is particularly difficult. The chapter provides a formulation and implementation in Cartesian coordinates.

Prediction of the common-mode self-capacitance of common-mode inductors is essential to their design in order to ensure effective operation over the frequency range of interest. This paper presents a model for the calculation of common-mode capacitance of a bus-bar-based common-mode inductor. An equivalent circuit of the inductor that accounts for high-frequency effects such as eddy currents in nanocrystalline cores is also set forth. The predicted and measured capacitances are compared for three such inductors.