Search

Active magnetic bearings (AMBs) provide reliable solution for high-speed rotors where oil-free and reliable operation are crucial. In high-power applications benefits of AMBs, compared to traditional rolling element bearings or fluid film bearings, are highly valued. Typical AMB rotors comprise 2 radial AMBs, which are designed with compressor or generator wheels integrated on the rotor. AMB dimensions and locations are carefully selected for each new application. The system design is being iterated such that the nodes of the lowest frequency rotor bending modes are sufficiently far away from the AMB and sensor nodes to ensure robust AMB control. The design is very challenging and cost sensitive. This work focuses on electromagnetic design, modelling, and control of fully levitated AMB-rotor with 3 radial AMBs. The additional bearing ensures that the same design can be re-used with different applications and regardless of the changes in locations of nodes of the first bending mode. The control plant is modelled based on flexible rotor dynamics; while bearing inductances and forces are modelled with 2D and 3D FEM electromagnetic simulations. The presented MIMO model-based control is coupled and centralized with 3 actuator-sensor pairs for radial suspension. The control design is verified in simulations using non-linear engineering models. Additionally, experimental identification results are included.

The paper addresses coupled loss and thermal analyses of a bearingless drive with an operating speed range of 17 00032 000 rpm. The drive is a part of a high-temperature heat pump system integrated in a high-speed compressor. This drive system comprises two bearingless motor units and an axial active magnetic bearing (AMB). The drive can be positioned horizontally or vertically. The positioning is directly related to the force necessary to raise and suspend the rotor. Furthermore, the amplitude of the suspension current has a significant effect on the motor winding and iron losses. The iron losses, eddy current losses in the magnets and losses in the bandage are investigated by 3D and 2D Finite Element Analysis (FEA). The influence of segmentation of the magnets on losses is analyzed. Friction losses of the coolant are calculated analytically, and all the losses obtained from the electromagnetic analysis are represented as distributed heat sources and coupled with the 3D thermal field analysis. The temperature fields are modelled under different motoring and suspension current conditions and evaluated for horizontal and vertical positions of the motor. As a precaution, demagnetization of the magnets is also considered.

Bearingless motor (BLM) technology offers a competitive solution to active magnetic bearings (AMBs) in high-speed applications. A bearingless drivetrain (BLDT) working as part of a kinetic compressor in a heat pump exceeding 0.5 MW and 25 000 rpm is open for questions: how should the geometry, materials, and parameters be chosen without exceeding the electromechanical and thermal limits; what rotor configuration would suit the heat pump; and how can the working fluid of the heat pump be used in the motor cooling? This paper presents the interdisciplinary design process of a BLDT as part of the compressor of a high-temperature heat pump (HTHP). The motor design process—the motor constituting the core driving the compressor of the heat pump, each interacting with the others, thus bringing about various design challenges—is summarized in a flowchart and subsequently elaborated on. Dimensioning rules for the bearingless structures are presented. Finite element analysis (FEA) is used to evaluate the surface and interior permanent magnet BLM structures under consideration. Different stack materials are considered and preliminary electromechanical optimization by a genetic algorithm is carried out. To ensure structural rigidity, FEA of electromagnetic, mechanical, thermal, and rotor dynamic performance is conducted. FEA of drive losses is carried out and cooling alternatives are considered, based on which temperature distributions and thermal stresses with the chosen cooling arrangements are calculated again with FEA. The power and performance of the structures are discussed. As a result of the analyses, a suitable hermetic motor design is chosen for the HTHP compressor drivetrain.

Typically, active magnetic bearings have been applied to high-speed rotors in medium to high power range to replace ball, roller, and oil-film bearings. They require less maintenance and provide number of unique benefits owing to contactless suspension and active control. Integrated compressor or turbines result in predictable rotor dynamics. This allows use of model-based controllers. The model-based centralized controllers outperform decoupled transfer function controllers, but they do require accurate plant models. For integrated wheels on a single rotor the control models comprise a rigid rotor and lowest frequency bending modes. The bending mode parameters related to node locations can be identified yielding controllers tuned to the applications. This work introduces drive train modelling and magnetic levitation control of 2 MW rotor and external load with flexible coupling. The model-based control is tested in the experimental setup and drive train frequency responses are compared to the modelled multi-rotor drive train dynamics.

Solid rotors are preferred choice of topology for high-speed applications due to their robustness against high centrifugal forces at high speeds, ease of manufacturability, and higher temperature range. However, for peripheral speeds lower than 200 m/s, laminated rotor structure is preferred because of lower eddy current losses resulting in higher efficiency. However, laminated rotors are complex to manufacture, sensitive to temperature and have vibration and mechanical integrity related issues. As a compromise between these two designs in terms of mechanical strength and efficiency, this study investigates a radial flux 2 MW, 15 krpm induction motor rotor core made of thick laminations. The baseline dimensions of the thick-lamination rotor design are calculated using analytical equations considering aspects such as mechanical stresses, rotordynamics, and bearing parameters. Lastly, the lamination to lamination contact behavior under unbalance load is analyzed for a simplified model and their effect on natural frequencies is studied.

The bearingless permanent magnet synchronous motor (BPMSM) is a compact motor structure that combines the motoring and bearing functions based on well-designed integrated windings for generating both torque and magnetic suspension force. In order to achieve a successful high-performance control design for the BPMSM, an adequate model of the rotor dynamics is essential. This paper proposes simplified multiple-input and multiple-output (MIMO) control approaches, namely the pole placement and the linear-quadratic regulator (LQR), that allow to carry out identification experiments in full levitation. Additionally, the stability of the MIMO levitation controller is verified with the rotation tests. Compared with other recently published works, the novelty of this paper is to experimentally demonstrate that a stable fully levitated five-degrees-of-freedom (5-DOF) operation of a bearingless machine can be achieved by the proposed approach, and thereby, options for commissioning of such a system are obtained.

This paper addresses the problem of measuring the electromagnetic flux in the air gap of the active magnetic bearing (AMB) without mechanical structure modifications. The designed and fabricated flux measurement and conditioning system based on the ultra-thin flexible Kapton-foil Hall sensors (developed by IFW Dresden Institute for Integrative Nanosciences) and signal amplifiers are presented. The flexible sensors are directly mounted on the curved surfaces of stator poles of the AMB and measure flux density in the AMB air gap. Then, the measurement itself and the conditioning system are verified in different measuring conditions of the heteropolar radial AMB with the air gap width of 0.4 mm. The measurement results were used in identifying crucial rotor flux-AMB system parameters. The proposed direct flux measurement system is successfully verified in the designed test rig in the presence of rotor position disturbances or coil current oscillation. The advantages and drawbacks of the presented measurement setup are discussed.

Design of High Speed (HS) electric machines is an iterative process that requires a multidisciplinary design team to accomplish the required performance. In this study, a design space method (DSM) is developed to streamline conceptual designing of a high-speed and high-power electric machine. The method uses analytical equations and a rotordynamic model to determine geometrical dimensions based on the application requirements. These dimensions create a feasible baseline design for the particular application. However, considering the dimensions as design variables and using the baseline design as a starting point, a multidimensional combination and interaction of the design variables and the correlated output for the particular topology of motor and performance range can be further studied for design exploration and optimization purposes. The study includes a test case where the baseline dimensions are determined and compared to an existing machine from literature, and then further explored to identify the sensitivity of different outputs with respect to different design variables. The method enables rapid design iterations, rotordynamics and rotor mass optimization. The baseline design can be also used as a starting point for the detailed design. Post-print / Final draft

High-speed solid-rotor induction machines (HSIMs) are popular within high-speed applications because of their high rotor structural integrity and their fairly well-established manufacturing process guaranteeing high quality series products. Designing a new high-speed electric machine requires a multidisciplinary team to accomplish the machine performance desired. In case of a high-speed machine design, the components and applied materials often reach their physical limits at the rated operating condition. Therefore, the design process is highly iterative and thus a systematic approach has a high potential to reduce the time of the design phase significantly. In this study, a systematic design process is proposed for a modular, multimegawatt (MMW) HSIM with three radial active magnetic bearings. The process includes a traditional multidisciplinary design flow with extra critical aspects of MMW high-speed machines: manufacturability, bearing system, housing and operating unit. In addition, the manufactured machine is reported. The proposed systematic design process is described, including several multidisciplinary critical design aspects of high-speed machinery. Post-print / Final draft

Presently, most heat demands globally are covered by burning fossil fuels, e.g., by using coal, which results in harmful emissions. For example, when burning oil, carbon dioxide emissions alone are estimated to be 3.2 times the mass of fuel (oil) burned. Other harmful emissions include those associated with increased health risks, e.g., sulfur dioxide and indirect climate gases. With new regulations following political initiatives such as a decarbonized Europe, the use of fossils is under pressure. Heat pumps provide clean heat production with efficient use of electricity. With the deployment of high-speed kinetic compressors, more applications with heat pumps become viable. The high-speed kinetic turbo compressors have a higher efficiency and better reliability than reciprocating oil-lubricated compressors. Oil-free compressor technology enables the use of the most efficient and ultra-low global warming potential working fluids, which in most cases are sensitive or unsuitable for bearing lubricants. In this work, the technology alternatives for high-speed oil-free compressors are analyzed. Based on the working conditions of 500 kW residential heat pump modules, a case study comparison between bearingless technology and a surface permanent magnet motor having a rotor with two active magnetic bearings is presented.

Active magnetic bearings (AMBs) offer frictionless suspension, vibration insulation, programmable stiffness, and damping, among other advantages, in levitated rotor applications. However, AMBs are inherently unstable and require accurate system models for the high-performance model-based multi-input multi-output control of rotor position. Control electronics with high calculation capacity and accurate sensors of AMBs provide an opportunity to implement various identification schemes. A variety of artificial excitation signal-based identification methods can thus be achieved with no additional hardware. In this paper, a selection of excitation signals, namely the pseudorandom binary sequence (PRBS), chirp signal, multisine, and stepped sine are presented, applied, and compared with the AMB system identification. From the identification experiments, the rotor-bearing system, the inner current control loop, and values of position and current stiffness are identified. Unlike recently published works considering excitation-based identification of AMB rotor systems, it is demonstrated that identification of the rotor system dynamics can be carried out using various well-established excitation signals. Application and feasibility of these excitation signals in AMB rotor systems are analyzed based on experimental results.

High-speed electrical machines have their advantages, such as higher power density than in traditional electrical machines, and disadvantages, such as very demanding and tailored design and manufacturing process. The manufacturing of the rotor for a high-speed electrical machine is extra complex. In a high-speed electrical machine, the rotor in normal operation experiences various types of loadings, such as centrifugal forces from the rotation, temperature gradients from the operational environment, losses generated in the electrical machine and loads from the process. A failure related to the mechanical integrity of a rotor leads to a halt and very probably to the complete malfunction of the machine. The aim of this study is to compare three different rotor constructions in a high-speed induction electrical machine operating at the megawatt power range. The first one is a full copper squirrel cage rotor that consists of 25 pieces (22 copper bars, two copper end rings and a steel shaft), the second is a slitted solid rotor with copper end rings that consists of three pieces and two materials, and the third is a slitted solid rotor made solely of structural steel consisting of one piece. Further, these rotors are compared in terms of their electromagnetic performance, applying the same stator structure. The manufacturing challenges are directly related to the number of individual parts needed for the construction of the full rotor. The base material for the rotor core of the studied high-speed induction machine is often structural steel that is magnetically soft, has moderate electrical resistivity, and can be combined with copper or aluminum cage winding which is non-magnetic and has high electrical conductivity. From the mechanical perspective, these materials are very different; e.g. high-strength copper (CuCrZr) has a 50 % higher thermal expansion coefficient, 13 % higher density, 600 % higher thermal conductivity, and approximately 50 % lower yield strength than common structural steel (S355). This complicates the rotor manufacturing, as the required tolerances for the assembly of the rotor components are very strict and depend on the final manufacturing method of the rotor. Post-print / Final draft

This paper presents the design of the optimization of multi-phase, 25000 rpm 180 – 280 kW SPM bearingless motors. The electromagnetic analysis investigates motor and suspension performance with high-quality silicon and iron-cobalt lamination materials. Structural rigidity of surface and buried permanent magnet motor structures made of said materials are compared. The main challenge in bearingless motor design is achieving high efficiency with possibility to control suspension forces. Motors of the same volume with different stator slot shapes, slot openings, tooth shapes, magnet thicknesses and angles are investigated. The main objectives of optimization are the minimization of torque ripple, force ripple, force error angle and efficiency. The design is optimized in FEM analysis. Power and performance limitations of selected geometries are investigated and discussed.

It is beneficial to use model-based control approaches for the position control of high-speed machines with a magnetically levitated rotor system, as the system inherently involves multiple inputs and outputs. There is always uncertainty in the model parameters, and thus, a robust control approach is a preferable choice. In this paper, an $H_{\infty}$ loop-shaping method for bearingless machine control synthesis is studied and compared with the widely used PID control approach. System identification experiments are conducted to validate the results and the controller performance in the prototype system.

High-speed electric machines require dedicated bearings. Active magnetic bearings (AMBs) provide economical solution for high-power rotors where oil-free operation and low operational costs are crucial. In high-power and high-speed applications benefits of contactless rotor suspension, e.g. compared to traditional rolling element bearings, as well as online monitoring and diagnostics are highly valued. AMBs offer low losses and balancing capabilities in integrated package. The design of the high-speed high-power induction machine rotor is very challenging and cost sensitive. Manufacturing limitations, thermal and cooling constraints, stress and rotor dynamic issues and total efficiency are interdependent. The space and power electronics are limited for bearings and control design, which have to provide robust rotor suspension. This work presents electromagnetic design, modelling, and control of fully levitated AMB-rotor for demanding application. The machine design offers very limited space but 3 radial bearing planes and separate axial AMB are used. The control plant is modelled based on flexible rotor dynamics; while bearing inductances and forces are modelled with 2D and 3D FEM electromagnetic simulations. The presented LQG model-based control is scalable from single axis axial suspension to coupled centralized 3 actuator-sensor pairs radial suspension. The control has to deal with considerable plant parameter variations because of saturation and high destabilizing position stiffness because of small airgaps. The control design is verified in simulations using non-linear engineering models.

Non-contact rotor position sensors are an essential part of control systems in magnetically suspended high-speed drives. In typical active magnetic bearing (AMB) levitated high-speed machine applications, the displacement of the rotor in the mechanical air gap is measured with commercially available eddy current-based displacement sensors. The aim of this paper is to propose a robust and compact three-dimensional position sensor that can measure the rotor displacement of an AMB system in both the radial and axial directions. The paper presents a sensor design utilizing only a single unified sensor stator and a single shared rotor mounted target piece surface to achieve the measurement of all three measurement axes. The sensor uses an inductive measuring principle to sense the air gap between the sensor stator and rotor piece, which makes it robust to surface variations of the sensing target. Combined with the sensor design, a state of the art fully digital signal processing chain utilizing synchronous in-phase and quadrature demodulation is presented. The feasibility of the proposed sensor design is verified in a closed-loop control application utilizing a 350-kW, 15,000-r/min high-speed industrial induction machine with magnetic bearing suspension. The inductive sensor provides an alternative solution to commercial eddy current displacement sensors. It meets the application requirements and has a robust construction utilizing conventional electrical steel lamination stacks and copper winding.

This paper presents the design and investigation of a photovoltaic‒flywheel system for household purposes. The main goal of this work is the electrical and mechanical integration of the electromechanical high speed kinetic energy storage as UPS (Uninterruptible Power Supply) with photovoltaic solar system. The paper contains calculation and division of photovoltaic panels system according to its integration with active magnetic bearing (AMB) flywheel and external electric grid. The photovoltaic solar installation costs as well as its size were considered. The composite shell AMB flywheel prototype configuration design (using CAD-software) and two different material variants are investigated and presented. In particularly, the structural composite shell stress calculations of two different materials vs rotational speed are performed using a direct coupling of SolidWorks and Matlab software. The analytical calculations of PV‒flywheel system are provided in order to choose optimal type of photovoltaic panels according to motor/generator flywheel and household energy system requirements. All elements of PV‒flywheel system as transducers, bridges, wiring diagrams, etc., are optimized using Simscape tools. Finally, short- and long-time simulations results of PV‒AMB‒flywheel system and initial experimental results are presented and discussed.

Many waste heat recovery and biomass applications offer opportunities for small-scale steam turbines to produce electricity and to improve systems’ energy efficiency. However, the currently used axial turbine-based technology is generally characterized by a relatively large physical size and poor design and off-design performances. To overcome these challenges, a new compact water-cooled high-speed radial outflow turbine concept is proposed. While the previous understanding of the chosen novel rotor water cooling approach indicates general system feasibility, improved turbine performance, and good potential, the scientific literature lacks relevant information. Since the design of high-speed machines is always case-dependent, every concept must be verified. Hence, to provide verification and new scientific information, this study combines analytical, numerical, and experimental analyses. The results predict turbine performance levels comparable with the previous radial outflow design, and its efficiency was found to exceed those of conventional turbines. During the experiments, the turbine also produced electricity from poor-quality steam, and its rotor dynamic behavior and magnetic bearing performance were close to the predicted results. These findings are considered a verification of the proposed concept. Furthermore, the rotor water cooling approach improved the stability of the system operation and although its physical behavior was not fully resolved, the study was able to verify its feasibility. In addition, at below 200 € /kW, the turbogenerator costs are competitive against competing technologies. Post-print / Final draft

Visual educational tools are important in contributing to skills in the electrical engineering profession. This paper introduces an active magnetic bearing (AMB) design tool used to teach important skills in modern high-speed technology to undergraduate students. The proposed tool is based on MATLAB, and it has a visual and easy-to-understand graphical interface. The paper describes how to use the tool and gives a design example of an axial AMB. The tools provide an opportunity to import the design directly to a finite element method (FEM) software in order to enable further analysis. The tool is also discussed from the perspectives of research and education. Post-print / Final draft

Rotor balancing is a procedure used to reduce the unbalance vibration of rotating machinery. Unbalance vibration creates forces to the bearings and causes harmful effects such as reducing their lifespan. Unbalance is caused simply because of the difference of the rotors axis of inertia and the rotating axis. In this paper, two balancing techniques are presented to reduce the unbalance vibration: one-plane balancing procedure used for two-plane balancing and a two-plane balancing procedure. Both balancing procedures take into account the cross effect between the planes. Rotor levitated with active magnetic bearings is balanced. Magnetic levitation is unstable so the xy-position of the rotor is measured on both rotor ends for the control purposes. The unbalance vibrations are analyzed from these position measurements so no additional hardware is required for the rotor balancing. Results are presented from a simulation model of an active magnetic bearing system. Comparison of the one-plane and two-plane balancing is provided. Post-print / Final draft

This paper presents the analysis of losses for one designed prototype bearingless surface permanent magnet motor (BLSPMM) with power of 80 kW and speed of 30000 rpm. A comparison of the analysis of 2 D and 3 D losses is presented. Detailed attention is paid to the eddy current losses of the surface magnets. The influence of the lamination and the segmentation of the magnets on the distribution of losses is discussed. The accuracy of the estimation of the losses for the thermal analysis is discussed. The improvement of efficiency with high-quality steel is considered. The losses are analyzed with Finite Element Method (FEM).

Bearingless motors combine torque generation and suspension force capabilities into one electromagnetic actuator. However, design optimization of bearingless motors is more complex than with traditional motor structures. The combined levitation and motoring performance cannot be quickly evaluated by using Computer Aided Design (CAD) tools applied in traditional motor designs. This work proposes a bearingless motor design chain. The initial dimensions of the test case motor are iteratively derived. The levitation performance is verified by using a lumped parameter model. The fine tuning of the rotor geometry is carried out by using the Finite Element Method (FEM). The objectives for the FEM optimization are a minimum torque ripple, minimum levitation force variations, and maximum torque and force capacities. Finally, experimental force angle measurements of a manufactured test case machine with a unique method are provided. Application of differential evolution is presented and discussed in both analytical and in FEM design steps.

The bearingless machine construction is optimal for high-speed machines as it reduces the axial length of the machine. It is crucial that the vibration levels of the rotor are under control during rotation. In the bearingless machine, the rotor is magnetically levitated with an integrated winding system alongside a standard motor winding. In this paper, a control approach is presented to regulate the rotor position in the radial and axial directions together with the speed control of the machine. The rotor vibration levels are verified by rotational tests.

Traditionally, active magnetic levitation systems in rotor applications comprise separate motor for torque production, two or more radial active magnetic bearings (AMBs) and one axial AMB. Such an arrangement produces long rotors. Resulting AMB-rotor systems are often supercritical making the levitation control challenging. The centralization of the torque and force producing actuators shortens the rotor and allows for better control of unbalance magnetic pull from the rotor eccentricity. However, traditional bearingless motors employ separate windings for torque and for force production using a single actuator. This in turn lengthens the motor flux paths, increases the stator diameters, and reduces efficiency. This work studies performance and limitations of three current injection methods applied for active levitation control where the same winding is used for torque and for levitation force production. The FEM time stepping simulation results are presented and quantitative comparison is given. The case study bearingless motor system is of considerable power and high speed ratings. The use of the single winding system with the current injection control is suitable for the high-power and high-speed bearingless motor applications.

This paper presents an online nonparametric frequency response estimation approach for the identification of rotor dynamics of a high-speed machine supported by an active magnetic bearing (AMB) system. The closed-loop identification estimation approaches (direct and indirect) are based on a sliding discrete Fourier transform (SDFT) method that is applied in conjunction with a known multisine excitation signal design. The feasibility of the proposed identification approach is verified with experimental results on an AMB system. According to the results, the SDFT-based identification approach is applicable to online identification of rotor system dynamics in a computationally efficient manner.

This paper presents design optimization of high-speed and high-power bearingless motor/generator. Because of absence of separate suspension windings, in addition to the motor windings, and tooth coil arrangement a compact and axially short actuator can be achieved. A surface PM and inset PM rotor geometries are compared. The twin bearingless solution with separate axial active magnetic bearing delivers 6 degrees of freedom self-bearing motor system suitable for pumps, compressors and blower applications with considerable loads and precise clearance control in every direction. Both torque and suspension radial forces are induced with superimposed bearing and motor currents. Optimal design in terms of motor and suspension performances is investigated using finite element method and time stepping simulations.

This paper presents a novel analytical method for electro-mechanical design of a high speed long-term flywheel energy storage system and thermal evaluation of possible operating modes of the system. Flywheel’s composite shell rotor along with the motor/generator unit are assumed to be placed into a sealed vacuum chamber, which presents a challenge of heat transfer, produced by rotor losses. Developed method takes into account thermal radiation properties of the rotor and is realised using Mathcad software, which allows for quick investigation of any flywheel configuration. The method involves calculations for preliminary rotor sizing and determining achievable operation modes, while keeping the rotor under a specified temperature limit. Results of using this method for studying dependencies of thermal performance on initial system parameters are presented and conclusions are drawn. Based on the conducted study, recommendations on system design considerations are given.

A robust control of an active magnetic suspension requires an accurate plant model and proper model uncertainties. Moreover, the selection of control design performance weighting functions is not straightforward. In this paper, the design of a centralized H ∞ controller of an active magnetic suspension is considered. Two design approaches are examined: an H ∞ loop-shaping control design procedure and a signal-based H ∞ control. The tuning of the design performance functions is carried out applying a genetic algorithm. The robust stability of the gain-scheduled H ∞ controller is verified in the presence of real parametric and non-parametric frequency-dependent uncertainties. Accurate models of the system and its uncertainties can be obtained using engineering models and frequency response functions of the test-rig. Finally, simulations and experimental results confirm the effectiveness of the signal-based H ∞ approach.

This paper discusses a closed-loop centralized control for a multi-input multi-output active magnetic bearing system. A genetic algorithm for design and a credible comparison of different controller structures are proposed. The evaluation of the design trade-offs of linear-quadratic and loop transfer recovery controllers are studied. The model-based controllers are compared with the classical PID controller and the cascaded PI/PD controller. The properties of the tested control configurations are examined using maximum singular values of the output sensitivity function of the closed-loop system and the tolerated disturbance at the input of the plant. Furthermore, indices such as measured peak output sensitivity, singular values of the uncertain control system, responses to the step reference position, step disturbance, and impulse force disturbance are examined. A good agreement between the simulation and the experimental results from the test-rig is shown.

In this work a design optimization of the high-speed buried-type interior permanent magnet bearingless motor with significant power for such machines is presented. The geometry, windings arrangement and magnets are adjusted from the non-levitated motor design to avoid the significant magnetic saturation and achieve the performance target without oversizing the machine. The analytical design is optimized in finite element method analysis. The effect of stator skew on machine performance is thoroughly investigated.

Bearingless motors combine the torque generation of electrical motors and the radial suspension force capabilities of traditional magnetic bearings. The magnetomotive force (MMF) distribution in the motor generates radial force interference. The interference force affects the angle between the actual and desired radial force. This angle is called the force error angle. For stable levitation of the rotor of the bearingless motor the force error angle must be minimized in the design phase of the machine. This paper presents an optimal rotor structure for minimization of the error angle in a high-speed interior permanent magnet bearingless motor with magnets embedded in the rotor surface.

This paper reports on a novel nonlinear controller for a single one-degree-of-freedom (1-DOF) Active Magnetic Bearing (AMB) system. The nonlinear feedback tools such as Lyapunov based techniques, control Lyapunov functions (CLFs), and feedback passivation control are developed. The control objective is to globally stabilize the mass position of an AMB with flux feedback. The flux-based control model for an AMB system is derived due to voltage switching strategy with voltage saturation. This strategy enables the flux control under a zero-bias operation. The proposed nonlinear CLF with a zero-bias can achieve a dynamic performance superior to that of a linear controller with the zero-bias or with the classical bias operations.

Active magnetic bearings (AMBs) are becoming very popular in high speed electrical machines applications in the last decade. As the interest in them grows the necessity to optimise all the aspects of their operation arises. This paper presents the analytical way of calculating losses of active magnetic bearings based on reluctance network method. The method provides fast estimation reducing development time and effort with accurate results. In the article the proposed method is compared with other popular losses estimation methods and verified with experimental results.

A commissioning and laboratory tests of an active magnetic bearing supported PM 3kW blower are presented. The motor operation is evaluated in no-load and load tests. An identification of AMB-rotor system, testing of H ∞ centralized control and mass-flow of the blower for recirculation of anode gas in a SOFC are discussed. The key results include comparison between analytical and measured values of an output sensitivity function of different MIMO controllers, measured efficiency and output motor power, and blower measurements.