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  • 1.
    Abrahamsson, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hedlund, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Prototype of Kinetic Energy Storage System for Electrified Utility Vehicles in Urban Traffic2012Conference paper (Refereed)
  • 2.
    Abrahamsson, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hedlund, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kamf, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    High-Speed Kinetic Energy Buffer: Optimization of Composite Shell and Magnetic Bearings2014In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 61, no 6, p. 3012-3021Article in journal (Refereed)
    Abstract [en]

    This paper presents the design and optimization of a high-speed (30 000 r/min) kinetic energy storage system. The purpose of the device is to function as an energy buffer storing up to 867 Wh, primarily for utility vehicles in urban traffic. The rotor comprises a solid composite shell of carbon and glass fibers in an epoxy matrix, constructed in one curing. The shell is optimized using a combined analytical and numerical approach. The radial stress in the shell is kept compressive by integrating the electric machine, thereby avoiding delamination. Radial centering is achieved through eight active electromagnetic actuators. The actuator geometry is optimized using a direct coupling between SolidWorks, Comsol, and Matlab for maximum force over resistive loss for a given current density. The optimization results in a system with 300% higher current stiffness than the reference geometry with constant flux area, at the expense of 33% higher power loss. The actuators are driven by semipassive H bridges and controlled by an FPGA. Current control at 20 kHz with a noise of less than 5 mA (95% CI) is achieved, allowing position control at 4 kHz to be implemented.

  • 3.
    Abrahamsson, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ögren, Jim
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hedlund, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A Fully Levitated Cone-Shaped Lorentz-Type Self-Bearing Machine With Skewed Windings2014In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 50, no 9, article id 8101809Article in journal (Refereed)
    Abstract [en]

    Brushless dc coreless electric machines with double-rotor and single-stator configuration have very low losses, since the return path of the magnetic flux rotates with the permanent magnets. The eddy-current loss in the stator is additionally very small due to the lack of iron, making it ideal for kinetic energy storage. This paper presents a design for self-bearing rotor suspension, achieved by placing the stator windings skewed on a conical surface. A mathematical analysis of the force from a skewed winding confined to the surface of a cone was found. The parametric analytical expressions of the magnitude and direction of force and torque were verified by finite-element method simulations for one specific geometry. A dynamic model using proportional-integral-differential control was implemented in MATLAB/Simulink, and the currents needed for the self-bearing effect were found by solving an underdetermined system of linear equations. External forces, calculated from acceleration measurements from a bus in urban traffic, were added to simulate the dynamic environment of an electrical vehicle.

  • 4.
    Hedlund, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Doktorand, Uppsala Universitet.
    Electrified Integrated Kinetic Energy Storage2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The electric car is a technically efficient driveline, although it is demanding in terms of the primary energy source. Most trips are below 50 km and the mean power required for maintaining speed is quite low, but the system has to be able to both provide long range and high maximum power for acceleration. By separating power and energy handling in a hybrid driveline, the primary energy source, e.g. a battery can be optimised for specific energy (decreasing costs and material usage). Kinetic energy storage in the form of flywheels can handle the short, high power bursts of acceleration and decceleration with high efficiency.

    This thesis focuses on the design and construction of flywheels in which an electric machine and a low-loss magnetic suspension are considered an integral part of the composite shell, in an effort to increase specific energy. A method of numerically optimising shrink-fitted composite shells was developed and implemented in software, based on a plane stress assumption, with a grid search optimiser. A composite shell was designed, analysed numerically and constructed, with an integrated permanent magnet synchronous machine. Passive axial lift bearings were optimised, analysed numerically for losses and lift force, and verified with experiments. Active radial electromagnets optimised for high stiffness per ohmic loss were built and analysed in terms of force and stiffness, both numerically and experimentally. Electronics and a high-speed measurement system were designed to drive the magnetic bearings and the electric machine. The control of these systems were implemented in an FPGA, and a notch-filter was designed to suppress eigenfrequencies to achieve levitation of the rotor. The spin-down losses of the flywheel in vacuum were found to be 1.7 W/Wh, evaluated at 1000 rpm.

    A novel switched reluctance machine concept was developed for hollow cylinder flywheels. This class of flywheels are shaft-less, in an effort to avoid the shaft-to-rim connection. A small-scale prototype was built and verified to correspond well to analytical and numerical models, by indirect measurement of the inductance through a system identification method.

  • 5.
    Hedlund, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Doktorand, Uppsala Universitet.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Pérez-Loya, Jesús José
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eddy Currents in a Passive Magnetic Axial Thrust Bearing for a Flywheel Energy Storage System2017In: International journal of applied electromagnetics and mechanics, ISSN 1383-5416, E-ISSN 1875-8800, Vol. 54, no 3, p. 389-404Article in journal (Refereed)
    Abstract [en]

    Two types of passive magnetic lift bearings were evaluated in terms of thrust force and eddy current losses. The first type of bearings were based on two sets of segmented Halbach arrays mounted in repulsive mode, and the second type was based on ring-magnets. The eddy-currents studied arose in the bearing due to manufacturing variations of magnetic remanence, and due to non-radial magnetization. Both a 3D time-dependent and a quasi-stationary Finite-Element Method (FEM) formulation were used, and the simulated results were compared with lift-force measurements from experiment. The losses were found (by FEM) to be in the order of 25 W at a rotational speed of 30000 rpm while lifting a 45 kg rotor with a stiffness of 359 N/mm.

  • 6.
    Hedlund, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Pérez-Loya, Jesús José
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Passive Axial Thrust Bearing for a Flywheel Energy Storage System2013Conference paper (Refereed)
  • 7.
    Hedlund, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Goncalves de Oliveira, Janaina
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Sliding Mode 4-Quadrant DCDC Converter for a Flywheel Application2013In: Control Engineering Practice, ISSN 0967-0661, E-ISSN 1873-6939, Vol. 21, no 4, p. 473-482Article in journal (Refereed)
    Abstract [en]

    A sliding mode control system for a 4-quadrant DCDC converter was designed and a low voltage prototype was constructed. The target application is a flywheel based all-electric driveline. Important qualities are current and voltage control, bidirectionality, and stability for a broad input voltage range, focusing on a smooth transition between operating quadrants. The control decisions were based entirely on the latest available measurements, implying that no memory needs reinitializing when changing quadrant. The boost control was based on a topology specific current source approximation. The control was found to be parameter invariant, regardless of high input/output dynamics variance.

  • 8.
    Hedlund, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Doktorand, Uppsala Universitet.
    Kamf, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Santiago, Juan de
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Reluctance Machine for a Hollow Cylinder Flywheel2017In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 10, no 3, article id 316Article in journal (Refereed)
    Abstract [en]

    A hollow cylinder flywheel rotor with a novel outer rotor switched reluctance machine (SRM) mounted on the interior rim is presented, with measurements, numerical analysis and analytical models. Practical experiences from the construction process are also discussed. The flywheel rotor does not have a shaft and spokes and is predicted to store 181 Wh/kg at ultimate tensile strength (UTS) according to simulations. The novel SRM is an axial flux machine, chosen due to its robustness and tolerance for high strain. The computed maximum tip speed of the motor at UTS is 1050 m/s . A small-scale proof-of-concept electric machine prototype has been constructed, and the machine inductance has been estimated from measurements of voltage and current and compared against results from analytical models and finite element analysis (FEA). The prototype measurements were used to simulate operation during maximal speed for a comparison towards other high-speed electric machines, in terms of tip speed and power. The mechanical design of the flywheel was performed with an analytical formulation assuming planar stress in concentric shells of orthotropic (unidirectionally circumferentially wound) carbon composites. The analytical approach was verified with 3D FEA in terms of stress and strain.

  • 9.
    Hedlund, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Lundin, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    de Santiago, Juan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Flywheel Energy Storage for Automotive Applications2015In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 8, no 10, p. 10636-10663Article, review/survey (Refereed)
    Abstract [en]

    A review of flywheel energy storage technology was made, with a special focus on the progress in automotive applications. We found that there are at least 26 university research groups and 27 companies contributing to flywheel technology development. Flywheels are seen to excel in high-power applications, placing them closer in functionality to supercapacitors than to batteries. Examples of flywheels optimized for vehicular applications were found with a specific power of 5.5 kW/kg and a specific energy of 3.5 Wh/kg. Another flywheel system had 3.15 kW/kg and 6.4 Wh/kg, which can be compared to a state-of-the-art supercapacitor vehicular system with 1.7 kW/kg and 2.3 Wh/kg, respectively. Flywheel energy storage is reaching maturity, with 500 flywheel power buffer systems being deployed for London buses (resulting in fuel savings of over 20%), 400 flywheels in operation for grid frequency regulation and many hundreds more installed for uninterruptible power supply (UPS) applications. The industry estimates the mass-production cost of a specific consumer-car flywheel system to be 2000 USD. For regular cars, this system has been shown to save 35% fuel in the U.S. Federal Test Procedure (FTP) drive cycle.

  • 10.
    Hedlund, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Stephan, Richard. M.
    Univ. Fed. Rio de Janeiro, Brazil.
    de Santiago, Juan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Goncalves de Oliveira, Janaína
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rodriguez, Elkin
    Univ. Fed. Rio de Janeiro, Brazil.
    Sotelo, Guilherme G.
    Univ Fed Fluminense, Brazil.
    Eigen frequency and damping in a passive magnetic bearing system2016Conference paper (Refereed)
    Abstract [en]

    A complete passive magnetic bearing system, consisting in a Permanent Magnet radial bearing and a Superconductive Magnetic Bearing has been simulated and constructed. The forces in both types of magnetic bearings are not linear. The non-linear behavior has been implemented in a FEM model and compared with linear models. A spin down test has been conducted to the built system and the Eigen frequencies have been recorded. The Eigen frequencies calculated with and without the non-linear behavior implemented in the model are very similar.

  • 11.
    Lundin, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Kamf, Tobias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Abrahamsson, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Santiago, Juan de
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hedlund, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    High Speed Flywheels for Vehicular Applications2014In: 14th International Symposium on Magnetic Bearings, Linz, Austria, 2014Conference paper (Refereed)
  • 12.
    Pérez-Loya, Jesus José
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rodriguez, E.
    Hedlund, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Stephan, R. M.
    Lundin, Urban
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Magnetic Modeling and Measurement of Forces Between Permanent Magnet Rings used as Passive Magnetic Bearings2013Conference paper (Refereed)
1 - 12 of 12
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