Juan de Santiago

Prototype of electric driveline with magnetically levitated double wound motor

This paper presents the ongoing work of constructing a complete driveline for an electric road vehicle, using a flywheel as auxiliary energy storage. The flywheel energy storage system (FESS) is connected in series between the main energy storage (batteries) and the wheel motor of the vehicle, allowing the batteries to deliver power to the system in an optimized way, while at the same time making efficient use of regenerative braking. A double wound permanent magnet electric machine is used to electrically separate the two sides. In order to minimize losses, the machine has a double rotor configuration and is suspended with magnetic bearings. A bench test set-up is being constructed to investigate the properties of this system in detail. This set-up will achieve a level of power and energy close to that of a full scale system. This will allow measurements of complete drive cycles to be performed, improving the understanding of the constituting components and optimization of the complete system.

Losses in axial-flux permanent-magnet coreless flywheel energy storage systems

This paper analyzes the losses of axial-flux permanent-magnet (AFPM) motor/generators integrated in flywheel energy storage applications with a coreless winding. This configuration has several advantages over traditional slotted ones for some applications since the losses in a toothless design are at a lower level than in an equivalent iron slotted devices. It has lower idle losses and potentially higher overall efficiency than conventional machines. 3-D finite element method (FEM) is used to calculate flux density in the air gap and to simulate the electromotive force (back EMF) and eddy current losses in the windings. A small-scale three-phase machine has been designed and constructed. Spin down tests have been performed in atmospheric pressure and at low pressure and eddy current, bearing and drag losses are presented.

Dual voltage driveline for vehicle applications

This paper presents a novel driveline where the load and the energy source are operated at different voltage levels and they are galvanically insulated. The element that couples both part of the driveline is a Two Voltage Level Machine (TVLM). The machine is formed of a self-excited rotor and a stator with two sets of electrically isolated windings for adjustable speed drive applications. Both sets of these three phase windings are independently operated at different voltages. The equivalent circuit of the TVLM is deduced and phasor diagrams are presented. A complete driveline is simulated and the performance of the complete system is discussed. The driveline is applicable in flywheel energy storage systems for vehicles and power conditioning in renewable energy production.

Calculation of Tooth Ripple Losses in Solid Poles

Abstract Tooth ripple losses in solid salient poles are calculated with analytical and semi-empirical methods. A numerical method based on the finite element method is presented in this article. The distribution of the eddy currents induced by the tooth ripple is obtained with this new method. The traditional analytic approach is based on some assumptions on the eddy current losses distribution that are finally verified with the Finite Element Method simulations presented. Analytic solutions of tooth ripple losses are only applicable to distributed windings with a homogeneous slot pitch while the method presented is applicable both to distributed and concentrated windings.

A Double Wound Flywheel System under Standard Drive Cycles: Simulations and Experiments

Flywheel systems are attractive for use in electric vehicles, being able to efficiently handle the large power needed for acceleration and regenerative braking. A double wound flywheel machine, divided in two different voltage levels by the windings, acting like a rotating transformer, is studied.The flywheel stator windings have two sides: a low voltage side connected to the battery and a high voltage side connected to the wheel motor. The load variations on the high voltage side have minimal affect on the low voltage side of the system, in which the speed control of the machine is performed.In this paper the functionality of the system is investigated by means of simulations and experiments. Different standard drive cycles are applied on the high voltage side to assess the effect of load variations in the system as a whole and particularly in the speed control. The response of the speed control system is investigated with computer simulations and experimental verification. The energy storage in the flywheel allows a steady power supply from the battery via the inverter, proving the functionality of the system.

Designing, simulations and experiments of a passive permanent magnet bearing

This paper presents simulations and experimental results for two types of Passive Permanent Magnet Bearings. The bearing system under investigation consists of two permanent magnet rings opposing to each other in two different config- urations. The influence of parameters, such as thickness and radius of permanent magnets, in the force is presented through FEM calculations. Two setups of passive magnetic bearings have been built. Static measurements of radial and axial forces are reported and results compared with simulations. Also, dynamic tests show the behavior of the bearing and the magnitudes of force in the foothold. The results are presented to show trends in the parameters, so the conclusions are applicable for other sizes and applications. As an example, the application as a top bearing for a 12 kW vertical axis wind turbine is considered.

Filter Influence on Rotor Losses in Coreless Axial Flux Permanent Magnet Machines

Electric vehicle technology is an interdisciplinary field in continuous development. It appears to be a margin for improvements. The Division for Electricity at Uppsala University is doing significant research in the field. The present thesis investigates electric machines for vehicular applications, both in the driveline and in the traction motor. Section 1 presents a driveline with two galvanically isolated voltage levels. A low power side is operated at the optimum voltage of the batteries, while a high power side is operated at a higher voltage leading to higher efficiencies in the traction motor. Both sides are coupled through a flywheel that stabilizes the power transients inherent to a drive cycle. A review of electric machine topologies for electric vehicles is presented in Section 2. The permanent magnet excited machine is the most suitable technology for an electric driveline. Section 3 is devoted to numerical models applied to electric machines. The equivalent circuit of a motor/generator with two sets of windings is first presented. This machine couples both sides of the driveline and drives the rotor of the flywheel. The electric parameters are calculated with custom FEM models. A discussion on slotless machines concludes with a simple model to analyze the magnetic field from one static 3D simulation. The tooth ripple losses in solid salient poles are also analyzed with a novel FEM approach. A complete description of the losses in electric machines gives a proper background for further discussion on efficiency. Section 4 presents the experimental work constructed to validate the theoretical models. The experiments include an axial flux, single wounded prototype, an axial flux, double wound prototype and a planed radial flux coreless prototype. Section 5 focuses on traction motors for electric vehicles. A simulated prototype illustrates a design and calculation process. The loss theory and the numerical methods presented in Section 3 are applied.

Development of an axial flux machine and control: Simulation and experimental set up

Simulation and experimental development of a driving system and control for an axial flux permanent magnet machine has been developed. The complete system, including the machine design and construction, has been accomplished due to the collaboration among different universities in Brazil and Sweden. Final experimental setup is aimed for testing a passive levitation system, which can be used as small flywheel energy storage. Simulations have been implemented using Simulink. The design and construction of different components of the driving system are presented, in a way so they can be reproduced. Control strategy has been implemented using Labview and Compact-Rio. Results show the functionality of the complete system at a nominal speed of 2800 rpm.

Harmonic Mitigation in a Coreless Double-Wound Flywheel Machine: Experimental Verification

This paper aims at analyzing harmonics and interharmonics present in a flywheel-based driveline developed at Uppsala University. The flywheel machine is a permanent magnet synchronous machine with two sets of windings in the stator, with a Wye–Wye connection as standard. Different sources of harmonic distortion have been evaluated. Flywheel machine simulations are performed in finite element method (FEM) (Comsol) and experimental verifications are presented. Several methods for harmonic mitigation have been evaluated. The driveline suffers almost exclusively from second-order harmonics but the THD (total harmonic distortion) seldom exceeds 5%. Very little interharmonics are present. A Delta–Wye connection of the flywheel eliminates most of the harmonics but at the expense of a high-phase current through the Delta connection. Grounding the neutral conductor in Wye connections increases the distortion.

A Power Buffer in an Electric Driveline: Two Batteries Are Better Than One

Fuel cells and high energy density batteries have limited overrated capacity and slow power response. Ultracapacitors and flywheels are proposed to overcome these limitations and to facilitate regenerative braking in hybrid and electric vehicles. The simulations presented in this paper show that a Secondary Energy Storage Unit (SESU) enhances the performance of the drivelines as previously suggested and provides additional improvements. A combined design of the primary energy source and the SESU reduces the total weight and volume and increases the battery lifetime. A full-electric driveline is simulated using a standard EPA FTP-75 drive cycle. Then the same vehicle is simulated with as SESU and the results are compared. The same is done for a hybrid driveline. Two drivelines are used as references and then enhanced with an SESU; four simulations are presented in total. Simulation results show that an energy storage device with very low energy and high power allows better battery selection and energy management.