Power Electronic Architectures for Solar-Charged Electric Vehicles

Abstract

Anthropogenic climate change, resulting from drastic exploitation of fuel sources like gas and oil, has caused global warming as the most evident sign of releasing greenhouse emissions. One of the possible solutions is employing renewable energies. Renewable energy sources like photovoltaic (PV) cells and wind are emission free during operation. Electric vehicles (EVs) are the leading solution to the rising air pollution from the transportation sector; however, their deployment has been slow due to cost, range, and charging issues. One promising solution is to use the solar panel as an on-board source to partially charge the EV’s battery. However, there are some obstacles in developing on- board solar generation for EVs, mainly the PV-steel integration process, including concerns of cost, mass, efficiency, and durability, and the power electronic architecture cost, efficiency, and size/mass. This thesis focuses on designing optimal power electronic architectures for on-board solar generation. One main challenge is that the PV voltage is often low, and thus a high voltage gain is required to step up this voltage to that of the high- voltage EV traction battery. The first contribution of this thesis the proposal of a high step-up DC-DC converter with low input voltage ripple. This feature is important because having lower current ripple from solar cells helps to improve their reliability and performance. An experimental prototype validates the circuit theory. The second contribution is the proposal of a novel generalized methodology for switched-capacitor high step-up converters including coupled inductors and voltage multiplier cells, which are applicable in solar-charged EVs that do not require electrical isolation between the solar array and the high voltage battery. The generalized method can be used to design for the voltage gain required of any application with a minimum number of components. To illustrate the method, a novel high step-up converter is designed, built, and tested. The third contribution is the design of an integrated on-board solar charger including a flying capacitor active rectifier. The active rectifier is a reconfigurable topology which can act as the inverter for the motor drive when the EV is driving. This concept reduces the size and the number of components compared to a non- integrated approach. Next, the thesis considers how to best incorporate electrical isolation in the solar- charged EV power electronic architecture, if it is desired. Firstly, two power electronics interfaces for a solar-charged EV are simulated and investigated, one isolated and the other non-isolated, so that efficiency and component count can be compared. A model of a solar- charged Chevrolet Bolt is created to use as a simulation platform for comparing the isolated and non-isolated power electronics designs. Lastly, a novel isolated three-port converter is proposed for interfacing the solar arrays, low voltage battery, and high voltage battery. Electrical isolation is present between the high voltage battery and the other two ports. The performance of the converter is improved by employing differential power processing converters which will process only the power difference between the solar arrays. The proposed circuit has a low component count compared to a non-integrated approach. Overall, this thesis presents four novel power electronic topologies that can be used in solar- charged EVs. Though the focus in this thesis is the solar-charged EV application, the first two contributions can be applied to a variety of applications and represent general advances in the field of high step-up converters.