published_or_final_version / abstract / toc / Electrical and Electronic Engineering / Master / Master of Philosophy

Thesis (Master of Engineering in Electrical Engineering)--Cape Peninsula University of Technology, 2018. / The purpose of this paper was to design and develop an electrical power train for an Urban Concept electric vehicle geared to complete the Shell Eco-Marathon Africa in 2019. Various technologies which make up the electrical drive train of an electrical vehicle were also reviewed which include the battery pack, the battery management system, the motors, the motor management system and the human interface. Upon completion of this, the various topologies best suited for this project were selected, designed, constructed and developed. Two motors were re-designed and constructed for this vehicle and the motor drive was also constructed to control these motors. A Lithium-Ion battery pack was constructed and developed to drive the motors and an off-the-shelf battery management system was purchased and developed to suit the requirements for the Shell Eco- Marathon competition rules. A human interface was also developed in order for the driver to see various parameters of the electric vehicle defined by the Shell Eco-Marathon competition rules. After each component of the drive train was constructed, they underwent various testing procedures to determine the efficiency of each individual component and the overall efficiency for the complete drive train of this electric vehicle was ascertained. The Product Lifecycle Management Competency Centre group developed the chassis for this vehicle. For this reason, only the electric subsystems were evaluated and a simulation was completed of the complete drive train. After the complete drive train was constructed and all the individual subsystems evaluated and simulated, a vehicle with an overall efficiency of about sixty percent was expected and the completed drive train should be adequate enough to complete the entire Shell Eco-Marathon Africa circuit.

The purpose of the study is to analyze the energy use of battery electric vehicles (BEVs), to compare their energy usage with other different vehicle technologies, and ultimately to determine their suitability for recreational use. The possibility of applying such vehicles into South Africa’s game reserves is researched in terms of energy costs and evaluated. Calculations were made based on actual existing routes found in the Kruger National Park, and are presently used by tourists for sightseeing and to access the different camps within the park. Calculations were made on the forces acting on a vehicle driving through the different routes and terrains. These forces were then translated into fuel or energy consumption and subsequently into fuel and energy prices. The entire exercise was performed on alternative vehicle technologies in a hypothetical scenario. The calculations investigated the energy consumption and efficiency of a battery electric vehicle (BEV) and other vehicle technologies such as fuel cell electric vehicle (FCEV), hybrid electric vehicle (HEV), and lastly the internal combustion engine (ICEV) vehicle. It was found that the energy consumption of each vehicle technology revealed similar trends and ranking on most routes. However on certain routes, the energy usage difference amongst the different vehicle technologies became more pronounced. This can be attributed to the continuous demand of energy by the vehicle to maintain forward motion. It was found that in general, irrespective of the route profile, the route surface or its total distance, the highest energy efficiency is achieved by the battery electric vehicle (BEV), followed by the fuel cell electric vehicle (FCEV) and then by the combined hybrid electric vehicle (HEV) and lastly by the internal combustion engine (ICEV) vehicle. / Electrical Engineering / M. Tech. (Electrical Engineering)

The electric vehicles, as the most promising solution for achieving high fuel economy, have significantly better emission profile than conventional vehicles powered by fossil fuels. However, range anxiety and the limited accessible fast-charging infrastructures mainly restrain the drivers from adopting the electric vehicles that have much higher energy efficiency. Due to the internal and external factors, the cells in the battery pack degrade differently, leading to a usable capacity that is less than the available capacity if they are left unbalanced, which ultimately shortens the driving range. Therefore, an external circuitry, i.e. battery balancing circuit, that manages the unbalanced cells is installed to maximize the usable capacity, and thus, to prolong the driving range. However, the most commonly adopted balancing circuit is the dissipative balancing strategy in the large-scale electric vehicle productions, where the available capacity is underutilized. One of the most efficient redistributive balancing strategies that overcome the drawbacks of the dissipative one is converter-based strategy that monitors and regulates each paralleled-connected cell module. Nevertheless, installing the individual DC-DC converters on each module is not cost-friendly, and thus, reducing the cost of the converter-based balancing system becomes the priority for large adoptions of the redistributive balancing systems in electric vehicles. This thesis proposes a dual-cell link that integrates the functionalities of the auxiliary power module, battery gauging and battery balancing, leading to a low-cost solution comparable with the dissipative balancing. The topological improvements are made achieving 50% less number of the needed converters compared with the existing topologies. In addition, the integration and minimization are the design targets in terms of the main circuit components. The costly components, such as MOSFETs and magnetic components, are curtailed by 62.5%-75% and 50%-100%, respectively, with no sacrifices on the balancing speed. In order to achieve the magnetic integration, the detailed circuit model is developed using average- and small-signal modeling techniques. The design procedure for the half-full bridge converter with the cored transformer is firstly discussed, followed by a further minimized dual-half active bridge converter with a coreless transformer. Following the design procedure, two systems are characterized, built, tested and validated with the real batteries. Not only is the cost reduced, but also the balancing process is facilitated, which is realized by an additional balancing path. A DC current offset between the adjoining cells in one link can be introduced to the circuit by utilizing a normally undesired volt-amp imbalance in the transformer, which provides the extra cell-to-cell balancing path. An asymmetric duty cycle control is proposed to regulate the DC current offset so that the different balancing modes can be achieved. With the enabled cell-to-cell path, the balancing speed can be reduced by 50% compared with the conventional cell-to-stack only balancing methods with a state-of-charge difference of 20% between two adjoining cells. The auxiliary power module requires the proposed converters to work as efficiently as possible within its wide operating range. However, the efficiency of the half-bridge systems drops at light-load conditions due to the loss of the soft-switching capability and high conduction loss. In order to overcome this drawback, the variable frequency modulation is normally preferred. A conduction-loss based control criteria is proposed, inheriting the benefits of the conventional variable frequency modulation while maintaining the optimized conduction loss. It is validated on the converter prototype that the proposed control criteria can achieve 1-2% better efficiency with an extremely simple but robust control logic compared with the critical soft switching.