This paper presents an improved rotor position estimation algorithm for ultra-high-speed surface mount permanent magnet synchronous machines (SPMSM). The proposed approach combines a synchronous frame back-EMF state filter and a motion observer structure to accurately estimate rotor position at speeds above 60 kRPM, where conventional position sensing techniques struggle. The state filter and motion observer are designed directly in the discrete domain considering necessary latch dynamics and computational delays. Simulation results for a 2-pole SPMSM show stable performance and close to zero phase lag position estimation at a fundamental frequency of 2.6 kHz. The implementation ensures stable control performance at sampling to fundamental frequency ratios as low as 4. A detailed experimental validation of the proposed algorithm on a high speed bearingless machine has been presented. Closed loop operation at 60 kRPM with a sampling frequency of 4 kHz, along with stable levitation of the bearingless machine was achieved. The proposed methodology is a significant advancement toward precise and reliable rotary motion state estimation for ultra-high-speed SPMSMs.

This work investigates bearingless motors configured to function as radial electrodynamic bearings (EDBs), focusing on the feasibility and effectiveness of different stator winding configurations and bearingless motors (BMs). A theoretical framework based on short-circuiting the suspension winding is developed to calculate shaft forces during eccentricity. This model integrates all possible radial flux bearingless motor configurations with p(s) = p +/- 1 or p(s) = 1 suspension pole-pairs in a unified manner that incorporates their electromechanical properties. The paper uses this model to analyze stability, investigate the systems' performance potential, and inform design decisions. It is shown that each configuration (BM type, winding type, pole-pair combination) offers distinct features and shortcomings when evaluated as an EDB that should be considered in the design process.

This paper proposes and develops a new analytic bearingless machine model that incorporates multiple airgap harmonic field interactions and has several advantages. The model can be used to address levitation performance requirements by developing force/torque regulation methods to precisely calculate commands to current regulators. This allows relaxing constraints during the design stage and has the potential to enable consideration of higher performance bearingless machines. Furthermore, analogous to torque enhancement in conventional electric machines, the proposed model can be used to identify options for suspension force enhancement in bearingless motors by controlling multiple magnetic field harmonics. This paper provides a detailed derivation of the model and shows how it can be used to improve force regulation accuracy and enhance force capacity. The paper finds that by controlling four airgap harmonic fields, instead of the typical two harmonics, force capacity can be increased by approximately 40%. Hardware measurements using a 10-phase bearingless induction machine validate the proposed model and force capacity increase.

Synchronous reluctance (SynR) machines are promising rare-earth material-free alternatives to permanent magnet machines. However, structural challenges limit their operating speed and power density. This paper proposes and investigates multi-material additive manufacturing (MMAM) as a key-enabler to realize power-dense and high-speed SynR machines. It does so by proposing designs that guide magnetic flux through solid rotors realized by selective placement of magnetic and non-magnetic materials. To explore this concept, first, material samples are additively manufactured and experimentally characterized to assess the structural and magnetic properties that can be expected for the proposed rotors. Second, the design space of each rotor type is explored using these measured properties within finite element analysis. The results reveal that MMAM can enable fabrication of SynR motors with power density levels that are at the leading edge of all conventional electric machine topologies. It is shown that tip speeds in excess of 300 m/s can be achieved, resulting in 3-4x improvement in power density over conventional SynR motors. A solid SynR rotor is printed in an experimental MMAM laser powder bed fusion system. The rotor is paired with an existing stator to create a functional SynR motor with a saliency ratio of 2.59 and torque rating of 4.15 Nm. This is the first publication of a SynR rotor prototype constructed via MMAM.

Levitation control of bearingless motors requires rotor displacement sensors. Recent research has explored selfsensing (sensorless) control which enables removing these sensors, but only for separated windings. Combined windings-where each coil can create torque and force-have been proven to be a critical component for realizing high performance bearingless motors for industrial applications. These applications are often cost-sensitive and require bearingless solutions with minimal overhead compared to traditional motors. Self-sensing control with combined windings removes barriers for wider adoption of bearingless technology-this paper forms the analytic basis for showing this is possible. The primary contribution is a unified modeling framework which encompasses several popular combined winding types found in the literature. For each winding type, winding functions are defined-each type with differing winding coil circuit arrangements and drive interfaces. The terminal inductance matrix and back-EMF is computed to include the effects of a non-centered rotor, and then transformed into decoupled torque and suspension force components. Through the presented transformations, all combined winding types support radial self-sensing, albeit with additional control complexity. Finite element simulations and hardware experiments validate the modeling approach. Future self-sensing research can build upon these models to design control algorithms and machines which work for any combined winding type.

Recent advancements in metal additive manufacturing (AM) show great potential to revolutionize the design and manufacturing of electromagnetic components used in the field of electrical engineering. Lattice structures directly printed by AM processes typically offer better structural performance with reduced weight, such as high stiffness, surface area, elongation, energy absorption, and porosity, than the solid counterpart. This paper aims to study the electromagnetic modeling of lattice structures used in additively manufactured magnetic cores or windings for electric machines. Three dimensional (3D) electromagnetic finite element (FE) analysis with high performance computing (HPC) shows the highest fidelity in predicting the electromagnetic performance of designs with lattice structures by preserving complex geometry details. FE-based homogenization methods have also been explored to potentially speed up concept design. A case study based on an additively manufactured axial-flux permanent magnet machine with a Hilbert pattern stator validates the discussed electromagnetic modeling approaches.

Torque-dense electric machines are beneficial across a wide range of applications. Unlike conventional three-phase stator windings that can only control a single spatial harmonic field in the airgap, multiphase, “multi-harmonic” windings can independently control multiple spatial harmonics, each corresponding to a different number of pole-pairs. These spatial harmonics can be used to create additional torque, thereby improving the torque-density and the response time by increasing the torque-to-rotor-inertia ratio. The existing literature on torque enhancement is limited to radial flux designs and considers it as a motor drive / control problem of injecting “time harmonic” currents, rather than machine design to control “spatial harmonics”. This paper investigates torque enhancement as a machine design problem in radial flux (RFPM) and axial flux PM (AFPM) machines to i) quantify the torque enhancement limits in terms of the machine design parameters, and ii) identify optimal harmonic current amplitudes to maximize torque density. The paper develops a 7-phase multi-harmonic AFPM and shows that it can achieve up to 33% improvement in torque capability and 65% improvement in torque-to-rotor-inertia ratio relative to an equivalent 3-phase design. Experimental results are provided to validate these findings, making this the first work to demonstrate torque enhancement in AFPM designs.

Science kits have been a staple of learning for some time, but in the era of COVID-19 at-home science kits took specific prominence in educational initiatives. In this paper, we delineate how kit-based education can be paired with virtual connection technology to enhance postsecondary and career exploration. The "Content, Connection and Careers" kit-based program has been developed to enable youth to explore electrical engineering principles while connecting virtually with university students to discuss engineering courses and careers. When assembled and wired up, the kit components become linear motors that use a magnetic force to pull a bolt into a pipe when youth press a button. This follows the same working principles as a doorbell or solenoid. These kits are supported by virtual learning sessions where youth connect with university students and faculty to fully understand the educational content, connect to peers and caring adults to share their learning, and explore careers that use electrical engineering skills. To investigate the effectiveness of the program, surveys were distributed to participants to understand whether the kits were simple enough for independent learning but robust enough to encourage additional self-exploration of more difficult topics with the aid of expert scientists and other adult role models. Additionally, youth were asked if the connections made with university faculty and students was beneficial in their thinking of postsecondary options and college engagement. Over 60 elementary and middle-school aged youth participated in the project. Over 80 percent of survey respondents self-reported improved knowledge of how an electromagnetic field works and how to build a simple electromagnet. Other results showed an increased understanding of engineering careers and courses required to study electric engineering in college. Before their experience in the project, very few of the young people had ever talked to university faculty or university students about their areas of research or their journey into the fields of science, technology, engineering, and math (STEM). This connection was described in the surveys as what the youth liked best about the project.

Multiphase electric machines offer benefits of fault tolerance and reduced power electronic switch ratings per phase. These machines are also capable of independently controlling multiple airgap fields with differing number of pole-pairs (spatial harmonics). This presents opportunity to improve torque density, magnetically levitate the rotor, and wirelessly transfer power to excite the rotor of wound-field synchronous machines. Although these performance improvement techniques have been studied separately in literature, there exists no general winding design approach that targets independent control of multiple airgap fields. This paper presents a generalized technique to design multiphase electric machine windings that can control the magnitude and angular location of multiple airgap magnetic fields, each with a different desired number of pole-pairs. Design examples are provided, and the control of different airgap harmonics is experimentally validated in two different prototype machines. The results show that the generalized approach presented in this paper is applicable across different motor topologies (radial and axial flux) and winding configurations (concentrated and distributed), demonstrating its utility for a wide range of application scenarios that benefit from the control of multiple airgap fields.

This paper presents an approach for rapidly and accurately scaling Bearingless Surface Permanent Magnet Machines (BSPMs) across a range of speeds and power, with aim to explore the performance potential and trade-offs across the design space of ultra-high-speed BPSMs. A computationally-efficient scaling algorithm with consideration of rotordynamic, structural, and current density limitations is proposed. The algorithm is applied to scale a 7.6kW, 160 kr/min reference BSPM to 10.4kW as a detailed case study, with FEA validation demonstrating the efficacy of the scaling approach. The validated algorithm is utilized to generate an example design space, and limiting constraints for achieving higher power and power density in BSPMs is identified. This study identifies that combined rotor structural and rotordynamic constraints limit the maximum achievable power at any given speed, while rotor structural and maximum slot current density constraints limit the maximum achievable speed when using the proposed scaling approach.

Electrification of off-highway vehicles offers the benefits of improved energy efficiency, enhanced control, and reduction in greenhouse gas emissions. However, progress towards electrification has been limited by the low torque density (30 $\rm{kNm/m}^{3}$ ) of conventional electric machines compared to mobile hydraulic machines (up to approximately 1000 $\rm{kNm/m}^{3}$ ). This paper reviews emerging variants of electric machines that offer a step improvement in torque density and potential pathway to enable electrified off-highway vehicles. First, sizing approaches for electric and hydraulic machines are developed, and torque-dense electric machines reviewed in literature are compared to commercial hydraulic machines to identify design trends in terms of speed, torque density, and power density. Next, key metrics are identified for the electric machine, based on which the following four emerging electric machine variants that promise to improve torque density are reviewed: i) multi-harmonic machines injection, ii) combined radial-axial flux machines, iii) magnetic gears, and iv) magnetically-geared machines. The findings from this review show that these new electric machines can achieve upwards of 300% improvement in electric machine torque density, with several designs exceeding 100 $\rm{kNm/m}^{3}$ , making them worthy candidates for further research to bridge the torque density gap with hydraulic machines.

Thermal power cycles using sCO2 as a working fluid place extreme demands on their turbomachinery components and their electric motors/generators. In this paper, new system topologies for sCO2 turbomachinery are proposed which take advantage of “bearingless” electric machine technology to improve performance. Bearingless motors/generators are a new type of electric machine which integrate the functionality of active magnetic bearings into the existing hardware of an electric motor/generator. The existing electromagnetic surfaces and materials are reused to enable controllable production of radial forces on the machine shaft. This is envisioned to improve hermetic direct-drive turbomachinery systems by either augmenting existing bearings (i.e., bearing assist) or replacing existing bearings (i.e., bearing removal). The state-of-the-art technologies for several bearing types (gas foil bearings, externally pressurized porous (EPP) gas bearings, and active magnetic bearings) and electric machines are reviewed to motivate the introduction of bearingless technology. Two system designs using bearingless machines are proposed and compared against existing commercial solutions in terms of maximum shaft weight, number of passthroughs into the hermetic environment, cost, and complexity. A case-study bearingless motor/generator is assessed via simulations and a hardware prototype to investigate practical considerations for using bearingless technology in sCO2 turbomachinery. The proposed bearingless solutions have potential to enable a new generation of sCO2 turbomachinery with improved reliability, reduced complexity, and lower cost. This paper shows that by transforming the motor/generator already present in turbomachinery into a bearingless motor/generator, the technical challenges involved with sCO2 can be overcome without adding significant cost.

Ring motors are electric machines that are typically characterized by having a hollow rotor / stator, a small difference between the inner and outer radii, and a large outer diameter relative to the axial length. The hollow portion of the ring motor allows integrating loads, such as an aerial or marine propeller, enabling power-dense systems. This paper reviews integrated ring motor designs from literature across different applications. Based on this review, first, design trends and performance parameters are identified and compared with conventional radial flux machines. Next, the bearing challenges posed by the unique form-factors of these machines are identified and approaches to realize bearings are presented. Finally, a research outlook is presented that identifies the benefits of applying multi-physics optimization, additive manufacturing, and bearingless machine technology to realize improved integrated ring motor designs.

Electrification of off-highway vehicles offers improved efficiency and reduction in greenhouse gas emissions. However, the extremely low power densities of electric machines relative to the hydraulics used in conventional off-highway vehicles makes electrification challenging. Although the recently proposed Hybrid Hydraulic Electric Architecture (HHEA) can overcome this limitation, it requires frequent switching between the pressure rails using switching valves resulting in losses. Fast switching minimizes the switching losses in these valves, which otherwise significantly reduce the overall efficiency of the system. The primary contribution of this paper is the design and optimization of a linear electromagnetic actuator for a fast-switching valve. This paper identifies the actuator requirements to enable fast switching and presents a design and optimization technique to realize actuators that meet the design objectives. In addition, a multi-physics approach is proposed to model the performance of the complete switching valve by considering the electromagnetic, fluidic, and mechanical physics. An optimal actuator design is obtained using the developed optimization framework, and the multi-physics model demonstrates that the selected design achieves a 30% reduction in throttling-related switching losses by switching 70% faster than comparable commercial valve designs.

Axial flux machines (AFM) are promising alternatives to radial flux machines for applications that benefit from high torque density and a large diameter to axial length ratio, such as in-wheel traction motors. However, the 3D flux paths in AFM present unique challenges to manufacturing laminated stator cores. This article positions metal additive manufacturing (AM) technology as a potential solution to manufacture unconventional electric machine components such as AFM stators by investigating novel lamination emulating geometric structures and material silicon composition as design handles. In this article, techniques to additively manufacture soft magnetic components for rotating electric machines are reviewed, and the Hilbert pattern is identified as a promising candidate to reduce eddy-current losses in these components. To further reduce the eddy current losses, this article investigates the use of 6.5% silicon steel, which has higher resistivity compared to conventional steel laminations. The results in this article show that the Hilbert structure is effective in reducing the eddy current losses by 50% compared to a solid structure with 3% silicon steel, and using 6.5% silicon steel further reduces the eddy current losses by 24%. Finally, a candidate AFM stator is designed with the Hilbert pattern and fabricated additively using 6.5% silicon steel. This machine is characterized and experimentally compared with an identical axial flux machine that uses a laminated stator. The results demonstrate the potential of metal AM technology to fabricate electric machine components with eddy current losses comparable to ultra-thin gauge laminations at frequencies up to 200 Hz and conventional 29 Ga laminations up to 480 Hz.

AC electrical machines have mostly been limited to 2D magnetic circuits due to the use of electrical-steel laminations, however, in recent years advances in non-traditional motor architectures such as axial flux show promise for increased torque and power densities. 3D magnetic circuits as required by axial flux motors are difficult to manufacture using laminations, and for other architectures impossible. Soft magnetic composites enable 3D flux pathways but at the expense of magnetic properties. In this study, an axial flux stator is fabricated from high-silicon electrical steel (Fe-6.5 wt%Si) using additive manufacturing with Hilbert cross-sectional geometry to limit eddy current losses and compared with electrical steel laminations of 0.127 mm and 0.35 mm. This shows comparable performance between the additively manufactured Hilbert stator and 0.35 mm laminations below 500 Hz. A torque loss of approximately 20% was observed due to 34% less magnetic material in the Hilbert stator than 0.127 mm laminations, but improved torque density for the stator by 13%. By designing for additive manufacturing, tooth area could be scaled up providing an electrical machine with 3D magnetic flux pathways with acceptable loss behaviour and good magnetic circuit properties, enabling further flexibility to electrical engineers in their pursuit of higher torque and power density.

To create bearingless motors with high-performance electromechanical power conversion, recent research has demonstrated the need for combined windings where each stator coil can contribute to both torque and force simultaneously. This paper examines popular combined winding designs found in literature—multiphase, parallel and bridge dual-purpose no-voltage (DPNV), and mid-point current injection (MCI)—and shows that they are all equivalent from the machine perspective: the same stator slot current results in the same airgap fields to create the same torque/force output. From this, it is concluded that all winding "types" are actually the same fundamental multiphase winding, but connected to the drive electronics in different configurations. The paper presents mapping between the different drive configurations by using proposed winding function equivalencies. Finally, inductance matrices and equivalent space vector models are presented, and nuances in the modeling and control are highlighted for each drive configuration. These findings are summarized in a manner that allows a drives engineer to quickly apply state-of-the-art motor drive current regulation techniques to a bearingless machine connected in any of these popular winding configurations.

Magnetically levitated motor systems create opportunities for new applications of electromechanical power conversion where high-speed and contact-free operation are required. These systems require position sensors and control algorithms for stable levitation which often require filters to reduce feedback noise. Noisy position feedback creates challenges for high-bandwidth estimation of velocity and disturbance force; however, these unmeasured states can be helpful for high-performance control algorithms. This common problem in drives for electric motors has been solved using the Luenberger-style motion state observer. This paper investigates the applicability of the observer to digitally-controlled magnetically levitated systems. First, the observer's embedded plant model is derived for discrete-time implementation. Then, it is shown that the most advantageous use-case of the observer is different for magnetically levitated systems versus rotary motor systems. Unlike motor systems, the zero-lag filtering property of observers is minimally useful, while the ability to estimate and reject disturbances yields significant performance improvements for applications that care about run-out. In a prototype bearingless motor, rotor run-out is reduced by 5x by using control techniques based on the proposed observer.

Advanced electric motor drives require high-performance control platforms to implement real-time control algorithms. Commercial rapid control prototyping platforms are often used to quickly evaluate various algorithms. Unfortunately, these platforms are expensive and closed-source which can make it difficult to implement ultra-custom research projects. This paper introduces an open-source electric motor drive control and sensing platform which has been developed and published freely online to promote a community of motor drive scholars. The platform includes hardware design files, firmware sources, and an extensive documentation website with tutorials and user guides. Motor control students, researchers, and designers can build and disseminate new knowledge using the open-source sandbox. It is flexible and high-performance to enable next generation research, while also being easy-to-use for learning electric drive controls. The controller is called the Advanced Motor Drive Controller (AMDC) which contains a powerful Xilinx Zynq-7000 dualcore real-time processor, programmable logic, and a plethora of inputs and outputs tailored specifically for the needs of advanced electric drives. Along with the AMDC, the Advanced Motor Drive Sensing (AMDS) system is developed and published online for modular voltage and current sensing. Experimental results are presented which show that the AMDC is capable of three-phase dq current regulation using 64-bit floating point math at control frequencies up to 400 kHz. The AMDC and AMDS platforms accelerate the development of motor drives, allowing researchers to reach a working solution faster while still maintaining complete control of the entire hardware and firmware stack.