Abstract

This thesis deals with the interaction of batteries and power electronic converters in automotive applications. Even if the additional heating caused by (unwanted) alternating currents is disregarded, there has been a concern that alternating currents can be harmful for batteries. For that reason, alternating currents can be filtered using capacitors and/or by sophisticated hardware. In this work, the concern whether alternating currents are harmful to batteries is studied particular focus on large, lithium-ion cells for use in automotive applications.First, the harmonic content in the battery current of two, commercial hybrid-electric busses were measured and analysed. The most prominent harmonic had a peak magnitude higher than 10% of the maximum direct current level (160 A) arising at frequencies below 150 Hz. The maximum amplitude detected of a harmonic caused by the voltage source converter’s switching action was around 10 A and occurred at a frequency of 2 kHz. An experimental setup with alternating current capability for evaluating large lithium-ion cells has been designed and built. Twelve lithium-ion cells were cycled at a rate if 1 C during approximately 2000 cycles (corresponding to approximately one year). The cells were cycled with an superimposed alternating current of 1 Hz, 100 Hz, or 1 kHz while the rest of the cells were cycled with direct current (only), injected with alternating current (only), or no current at all (calendar aging). No negative effects caused by the alternating current was identified in terms of capacity fade and power fade for the tested lithium-ion cells. A comparison between sinusoidal current-ripple charging and conventional constant-current constant-voltage charging was also carried out. Three lithium-ion cells were cycled (ten times) with different ac currents superimposed during charge. The results were analyzed statistically and no significant improvements in terms of charging time or charging efficiency were observed in any of the charging tests using an superimposed ac current. The injection of alternating currents into batteries for heating purposes has also been studied and a control method for battery heating using an ac current was proposed. The proposed controller is applicable regardless of the LIB’s subsequent impedance nature (capacitive, inductive or resistive). Further, a design process for the generation of magnified alternating currents in dc-dc converters was presented. By matching the switching frequency with the frequency where the LCL filter and the battery resonate, the current flowing in the semiconductors and the switching frequency could be reduced. In a small experimental setup using a single lithium-ion cell, using an LCL-resonant circuit and a full bridges witch arrangement, magnifications of up to 15.7 were reached. This allowed for a loss reduction in the semiconductors of up to 75%, when compared to an equivalent dc-dc converter enabled to produce anon-magnified ac current.  "p"QC 20190517

Abstract

With the increase in electric mobility, public and private charge facilities will be required to provide solutions adjusted to the actual needs and requirements. A new methodology for dimensioning charge stations for electric vehicles (EVs) is presented in this paper. Such proposal is based on the Markov chains, and uses as output rates, the capabilities of the charge station in providing energy from the sun through photovoltaic generation, stored energy in local batteries and also as a back-up the power grid. A numerical result is also presented for a better understanding of the process. Document type: Conference object

Abstract

Today's combustion engines have low efficiency and a large amount of useful energy converts to heat as waste in different type of vehicles. Improving the dynamics of the car body, injection system, the shape of the internal engine components and manipulating the fuel compositions have had influence on fuel economy, but still less than 50% of energy in the fuel is converted to useful mechanical power. Since the lost energy escapes through the exhaust system as heat, taking advantage of thermoelectricity, part of that energy can be converted to useful electrical energy, improving the overall efficiency. However, the output voltage from a thermoelectric generator is a function of hot and cold side temperature and since, the electrical system of the vehicle operates with constant voltage, the use of a power converter is necessary. In this paper, simulation and experimental results of such a high-efficiency converter(94-96%), designed for thermoelectric generators on heavy duty vehicles is presented and discussed. "p"QC 20150904