A major cause of CO2 emissions today is fossil fuel vehicles, and lowering these emissions is of key importance, resulting in increasing electrification and hybridisation nowadays. Turbochargers have been used for a long time to recycle exhaust gas heat losses to improve engine performance by compressing the intake air. This thesis investigates a turbocharger with an added electric machine, to see if further energy can be recovered from these gasses, as well as how to control this machine for improved transients during acceleration and reduced turbo lag. A complete Simulink model is created of the system, comprised of a variable geometry turbine, compressor, cylinder, electric motor and battery model. This plant model is then evaluated on test cycles, which results in consistently lowered brake-specific fuel consumption and quicker responses at the cost of electric charge. The results show that an electrically assisted turbocharger poses as a feasible option for further improvements in fuel economy and performance during transients for spark ignited engines.

The ever increasing demands on today's engine performance and emissions control is forcing the automotive industry to make use of innovative solutions. One of these is to apply the technology of VNT turbos on commercial petrol vehicles. When using a VNT turbo, the aspect ratio of the turbine can be altered while driving to suit the current operating window. In order to actually gain performance while using a VNT, the vanes have to be properly controlled using a suitable control strategy. In this project, direct collocation have been utilized through the usage of YOP which is an adaptation of CasADi in MATLAB to solve non-linear optimization problems. Comprehensive models of the turbocharger and the cylinders have been built and validated to properly represent a VEP4 LP engine from AUROBAY. The models are implemented in YOP to create and simulate different OCPs using the turbo speed as state and position of the vanes as control signal. With this model in YOP together with the air mass flow per second as reference, a good reference following together with decent values for relevant parameters can be accomplished. Other objective functions such as minimum time and maximal volumetric efficiency are also investigated in the project which yield likewise results. From the results it can be concluded that this type of model and control strategy can be used with success when studying optimal control of a VNT turbo.