Design and evaluation of energy management systems for connected hybrid and electric vehicles

Abstract

Transportation is one of the most significant sources of emissions across various industries. With the effect of Paris Climate Agreement and the Green Deal, environmental concerns and technological progress push the development and market penetration of electric vehicles and hybrid electric vehicles. The number of electric and hybrid vehicles which can be considered as a stepping stone for electric vehicles are increasing day by day. On the other hand, transportation systems are becoming more efficient and safe by the improvement of the communication systems both on the vehicles and the infrastructure. There are significant improvements in connected and autonomous vehicles which has been started with the development of advanced driver assistance systems. The automotive industry, which plays a key role in the development of many accompanying technological ecosystems, is expected to be enhance more changes in the next 10 years than in the past 100 years. It is estimated that this transformation will dominance especially with the technologies progress in connected and autonomous vehicles. The main purpose of the study is to develop smart energy management strategies for connected, hybrid and electric vehicles and evaluate the benefits of developed smart energy management strategies. At the same time, the effects of the transition to electric vehicles in terms of energy consumption and environment is evaluated. For the optimization studies the Well-to-Wheels emission values are calculated and used in order to ensure apple-to-apple comparison. During the thesis study, three articles have been prepared and the preapared articles have been the substructure of the thesis. As of the date of submission of the thesis, one of the articles has been published and the requested revisions have been made for the other two articles and resubmitted. Prepared articles entitled as " Dynamic Programing Based Green Speed Advisory System Design for Mixed Platooning Vehicles", " Driving Cycle Based Energy Management Strategy Development for Range Extended Electric Vehicles " and " Comparative Study on Well-to-Wheels Emissions between Fully Electric and Conventional Automobiles in Istanbul". The article about the comparative study on Well-to-Wheels emissions has been published in the eighty-seventh issue of the "Transportation Research Part D" journal. Turkey's energy mix is analyzed and the emission factor of electricity production of Turkey is estimated in order to make appropriate comparisons during optimization studies. The Well-to-Wheels equivalent carbon dioxide emissions of the electricity is calculated. By considering energy sources, the Well-to-Wheels emission of Turkey is calculated as 520 g carbon dioxide equivalent per kWh. By using the carbon intensity of electricity, it is possible to compare the same variable for electric energy and fossil fuels for hybrid and electric vehicles. Vehicle models are created to use for model-based optimization studies. In order to develop an energy management system for serial hybrid vehicles, all critical subsystems are tested and a vehicle model which is validated by the test data is created. The model is developed by mathematical modelling of vehicle dynamics and testing the the electric motor, motor driver, battery cells and internal combustion engine. The developed models are validated by vehicle level testing on chassis dynamometer. A driving cycle based energy management strategy is developed for range extended electric vehicles to increase system efficiency and equivalent vehicle range. The results showed that; the optimized strategy can save CO2 emission by 6.21%, 1.77% and 0.58% for heavy, moderate and light traffic respectively. The usage of range extender in an efficient way by taking the traffic data into account extends the vehicle range, especially in heavy traffic conditions. For the hybrid vehicles which consumes both electric energy and fossil fuels, It will is important to compare the same value fort he objective function such as equivalent carbon dioxide emission. This study is a good example from this point of view. The developed energy management system will enable connected hybrid vehicles to be in more efficient way by using the route and traffic density information. In addition, vehicle emission maps are developed as a vehicle feature. The vehicles are tested on the chassis dynamometer and emission maps which are based on speed and wheel force are created. It is offered that vehicle emission maps can be used for optimization studies, especially in traffic with different types of vehicles. Considering that there are many ongoing studies on reducing tranportation based emissions, the use of the standardized emission maps are important for system level efficient use of connected vehicles. From this point of view, a multi-layer dynamic programing based optimizer is designed to minimize platooning Well-to-Wheels emissions of platooning vehicles where the platoon consists of an electric, a gasoline and a diesel vehicle. Vehicle emission maps and longitudinal dynamics are used for vehicle modelling. Tank-to-Wheels emission maps of internal combustion engine vehicles are produced by testing the vehicles on a chassis dynamometer. The optimization process has exploration and exploitation layers. The cost function is total Well-to-Wheels emission, design variable is speed trace, constraints are speed limits, traffic light states and vehicle accelerations limits. The test results show that the developed optimizer helps to achieve a 19.8% reduction in total Well-to-Wheels emissions for the defined use case. Thus, there is a significant emission saving potential in using speed advisory system for platooning vehicles through signalized intersections. On the other hand, driving cycles are used to examine the energy consumption and emission emissions of vehicles. In order to analyze the environmental effects of electric vehicles on a real driving cycle, a driving cycle has been developed for Istanbul by statistically analyzing the data collected on the determined routes. By using the developed driving cycle, the vehicle test are conducted. Acoording to the results electric vehicles emit 73.9 g carbon dioxide equivalent per kilometer on the same route, while gasoline vehicles emit 183.4 g equivalent carbon dioxide emissions. Therefore, the transition to electric vehicles should be strengthened by more widespread use of renewable energy in order to effectively reduce emissions associated with electric vehicles in general. At the same time, the results of this study can be a guide for policy makers. In summary, within the scope of the thesis electric carbon intensity of Turkey is calculated by considering Turkey's energy mix and Well-to-Wheels greenhouse gas emissions are analyzed both for conventional and electric vehicles are measured. A dynamic programing based optimizer is developed to decrease total Well-to-Wheels emissions of the mixed conventional and electric platooning vehicles through signalized intersections. Vehicle emission maps are generated both for electric and conventional vehicles for model-based optimization. A driving cycle based energy management strategy is developed for range extended electric vehicles to increase system efficiency and equivalent vehicle range. The vehicle model is developed by critical subsystem testing. An up to date driving cycle for Istanbul is developed (so called Istanbul Driving Cycle) by using collected traffic data across various sections of the city. An internal combustion engine vehicle and an electric vehicle are tested on a chassis dynamometer under the same conditions to determine specific energy consumption and specific emissions.