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<p>Research shows that flywheels have a significant potential for improving the performance of EV (Electric Vehicle) drivelines. Flywheels can be used as power buffers that even out the energy flow between the primary energy storage device and the EV traction motor. This improves the potential energy density and extends the lifetime of the primary energy storage device of the EV.</p><p>In this degree project a prototype of a flywheel-buffered driveline was constructed. The flywheel chosen was an electric motor/generator constructed at the Division of Electricity at Uppsala University. Lead acid batteries were used as the primary energy storage device in the driveline and the traction motor was a DC-motor.</p><p>Two DC/DC buck converters were designed for the driveline. The first limited the current from the batteries to the flywheel and the second controlled the power from the flywheel to the traction motor. Both converters were controlled by microcontrollers. The current limiter was controlled by a hysteresis controller and the DC-motor power was regulated manually, under the constraint of a maximum current PI-controller. The buck circuits were simulated in MATLAB Simulink prior to their construction.</p><p>The performance of the driveline was satisfactory, despite the poor efficiency of the DC-motor. The results showed that the efficiency of the flywheel and the power converters was relatively high and that the flywheel had excellent power-buffering properties.</p>

Research shows that flywheels have a significant potential for improving the performance of EV (Electric Vehicle) drivelines. Flywheels can be used as power buffers that even out the energy flow between the primary energy storage device and the EV traction motor. This improves the potential energy density and extends the lifetime of the primary energy storage device of the EV. In this degree project a prototype of a flywheel-buffered driveline was constructed. The flywheel chosen was an electric motor/generator constructed at the Division of Electricity at Uppsala University. Lead acid batteries were used as the primary energy storage device in the driveline and the traction motor was a DC-motor. Two DC/DC buck converters were designed for the driveline. The first limited the current from the batteries to the flywheel and the second controlled the power from the flywheel to the traction motor. Both converters were controlled by microcontrollers. The current limiter was controlled by a hysteresis controller and the DC-motor power was regulated manually, under the constraint of a maximum current PI-controller. The buck circuits were simulated in MATLAB Simulink prior to their construction. The performance of the driveline was satisfactory, despite the poor efficiency of the DC-motor. The results showed that the efficiency of the flywheel and the power converters was relatively high and that the flywheel had excellent power-buffering properties.

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As an energy storage device, the flywheel has significant advantages over conventional chemical batteries, including higher energy density, higher efficiency, longer life time, and less pollution to the environment. An effective flywheel system can be attributed to its good motor/generator (M/G) design. This thesis describes the research work on the design of a permanent magnet synchronous machine (PMSM) as an M/G suitable for integration in a flywheel energy storage system within a large hybrid electric vehicle (HEV). The operating requirements of the application include wide power and speed ranges combined with high total system efficiency. Along with presenting the design, essential issues related to PMSM design including cogging torque, iron losses and total harmonic distortion (THD) are investigated. An iterative approach combining lumped parameter analysis with 2D Finite Element Analysis (FEA) was used, and the final design is presented showing excellent performance. / Power Engineering and Power Electronics

One of the main challenges in order to make electric cars competitive with gas-powered cars is in the improvement of the electric power system. Although many of the energy sources currently used in electric vehicles have sufficientlyhigh specific energy, their applicability is limited due to low specific power. It would therefore be advantageous to create a driveline with the main energy storage separated from a smaller energy buffer, designed to have high power capabilities and to withstand frequent and deep discharge cycles. It has been found that rotating kinetic energy storage in flywheels is very well suited for this type of application. A composite shell, comprising an inner part made of glassfiber and an outer part made of carbonfiber, was analyzed analytically and numerically, designed, and constructed. The shell was fitted onto a metallic rotor using shrinkfitting. The cost of the shell, and the complexity of assembly, was reduced by winding the glass- and carbonfiber consecutively on a mandrel, and curing the complete assembly simultaneously. Thereby, the shell obtained an internal segmentation, without the need for fitting several concentric parts onto each other. The radial stress inside the composite shell was kept compressive thanks to a novel approach of using the permanent magnets of the integrated electric machine to provide radial mechanical load during rotation. Two thrust bearing units (one upper and one lower) comprising one segmented unit with the permanent magnets in a cylindrical Halbach configuration and one non-segmented unit in a up/down configuration were optimized, constructed and tested. Each thrust bearing unit generated 1040 N of repelling force, and a positive axial stiffness of 169 N/mm at the nominal airgap of 5 mm.  Two radial active magnetic bearings (one upper and one lower) were optimized, constructed and tested. By parameterizing the shape of the actuators, a numerical optimization of force over resistive loss from the bias currentcould be performed. The optimized shape of the electromagnets was produced by watercutting sheets of laminated steel. A maximum current stiffness of120 N/A at a bias current of 1.5 A was achieved.

The rapid release of energy in mechanisms is often limited by conversion of potential energy to kinetic energy. The use of a flywheel to store energy over time eliminates this constraint. Using this principle, a lightweight and compact energy transmission mechanism has been developed for robotic combat applications. The purpose of the proposed design is to throw an opposing robot ten or more feet into the air. This design incorporates a flywheel, a self-resetting dog clutch with built in shock absorbing rubber for impact mitigation, and an optimized four-bar linkage to deliver the energy. A mathematical model of the dynamic system has been developed to analyze and aid in the design process. Testing of subsystems was performed to validate the design. A final design is proposed with the recommendation that it be built and tested. A validated design is applicable to many real-world problems that require rapid kinetic energy release including reconnaissance robots required to hop high fences.

This master thesis was provided by ABB Cooperate Research in Västerås. This study has two major purposes: (1) to identify the characteristics of a flywheel energy storage system (FESS), (2) take the first steps in the development of a simulation model of a FESS. For the first part of this master thesis a literature reviews was conducted with focus on energy storage technologies in general and FESS in particular. The model was developed in the simulation environment PSCAD/EMTDC; with the main purpose to provide working model for future studies of the electrical dynamics of a flywheel energy storage system. The main conclusion of the literature review was that FESS is a promising energy storage solution; up to multiple megawatt scale. However, few large scale installations have so far been built and it is not a mature technology. Therefore further research and development is needed in multiple areas, including high strength composite materials, magnetic bearings and electrical machines. The model was implemented with the necessary control system and tested in a simulation case showing the operational characteristics.

Power systems on modern commercial transportation systems are moving to more electric based equipment, thus improving the reliability of the overall system. Electrical equipment on such systems will include some loads that require very high power for short periods of time, on the order of a few seconds, especially during acceleration and deceleration. The current approach to solving this problem is sizing the electrical grid for peak power, rather than the average. A method to efficiently store and discharge the pulsed power is necessary to eliminate the cost and weight of oversized generation equipment to support the pulsed power needs of these applications. Highspeed Flywheel Energy Storage Systems (FESS) are effectively capable of filling the niche of short duration, high cycle life applications where batteries and ultra capacitors are not usable. In order to have an efficient high-speed FESS, performing three important steps towards the design of the overall system are extremely vital. These steps are modeling, analysis and control of the FESS that are thoroughly investigated in this dissertation. This dissertation establishes a comprehensive analysis of a high-speed FESS in steady state and transient operations. To do so, an accurate model for the complete FESS is derived. State space averaging approach is used to develop DC and small-signal AC models of the system. These models effectively simplify analysis of the FESS and give a strong physical intuition to the complete system. In addition, they result in saving time and money by avoiding time consuming simulations performed by expensive packages, such as Simulink, PSIM, etc. In the next step, two important factors affecting operation of the Permanent Magnet Synchronous Machine (PMSM) implemented in the high-speed FESS are investigated in detail and outline a proper control strategy to achieve the required performance by the system. Next, a novel design algorithm developed by S.P. Bhattacharyya is used to design the control system. The algorithm has been implemented to a motor drive system, for the first time, in this work. Development of the complete set of the current- and speed-loop proportional-integral controller gains stabilizing the system is the result of this implementation. In the last part of the dissertation, based on the information and data achieved from the analysis and simulations, two parts of the FESS, inverter/rectifier and external inductor, are designed and the former one is manufactured. To verify the validity and feasibility of the proposed controller, several simulations and experimental results on a laboratory prototype are presented.

Utilizing flywheels to store and reuse energy from regenerative braking on locomotives is a new technology being developed in the Vibration Control and Electromechanics Lab at Texas A&M. This thesis focuses on the motion analysis of a locomotive mounted energy storage flywheel system for a variety of support motion inputs. Two input cases, sinusoidal floor input and ramp input, are analyzed in different sections. Simulation results and methods of ensuring the operating success of the flywheel system are provided at the end of each section. Section 1 introduces the problem and method being used to study the vibration under different circumstances. Section 2 analyzes the response of the flywheel system to sinusoidal floor input given by Ahmadian and Venezia 2000. Natural frequency and transmissibility of the system are utilized to explain the simulation results carried out in the frequency domain. It is found that the motion differences between flywheels(rotors) and magnetic bearings(stators) are guaranteed to be small. Section 3 emulates the locomotive traversing a bump with 1:150 slope. Simulation shows that catcher(backup) bearings are needed to limit the vibration of rotors through a bump. It is also found that gyroscopic effect causes problems in vibration isolation. Section 4 explores de-levitation method and installation of gimbals as possible remedies to this problem. Finally, a summary of simulation results from different input cases is made.