Electric Machine Control Design for Hybrid Electric Vehicles
In order to achieve fuel efficiency and reduce emissions into the atmosphere, the automobile manufacturers have decided to escalate modern technologies such as Electric Vehicles (EVs) and Hybrid Electric Vehicle (HEVs). Vehicles with electrified powertrain exhibit degraded performance when operated in hot environments. When the operating and ambient temperatures rise, an electric drive suffers from torque derating, poor efficiency and loss of lifetime (aging) as its parameters change. Electric machine is the main component of an electrified powertrain. Among the available electric machines, induction machine has been used for the traction system of EVs and HEVs because of the advantages including reasonable cost, simpler control, enhanced power density and efficiency, consistent operation over wide speed range, elevated initial torque, technological development and universal availability. Induction machines are also very robust, have rugged construction and require little maintenance. Moreover, induction machines are inherently de-excited with respect to inverter fault hence highly recommended to be used in automobile industries for precautionary measures. This manuscripts presents the novel control schemes based on linear parameter varying theory for enhancing the performance of an induction machine based electrified powertrain. Linear parameter varying control theory is extensively used in time varying plants. Linear parameter varying observers and controllers based on linear parameter varying dynamics deliver robust platform for the estimation and control of electric drive system variables. In this dissertation, linear parameter varying based observer is designed for an electrified powertrain. The designed observer is used to estimate the thermally derated torque and flux of an electric powertrain. This estimation is extremely helpful in controller design for the performance improvement of electric drive system. Secondly, a robust control scheme is designed and developed in this thesis to address the torque derating problem. The designed observer-controller pair is used to manage the thermally derated torque of an electrified powertrain. The performance of the proposed linear parameter varying based observer-controller pair is evaluated for a light duty electric vehicle against Federal Urban Driving Schedule (FUDS) operating at various ambient temperatures, which is a common controller evaluation approach adapted by automotive community. Experiments are carried out on an induction machine electric drive, realized by the NI myRIO-1900, using FUDS driving cycle to investigate that the proposed technique is effective and delivers robust performance. Another contribution of this manuscript is the design and development of degradation control scheme for an electric powertrain. In the synthesis of this control scheme, meeting the road loads, ensuring efficient powertrain operation and minimizing the loss of lifetime (aging) of an electric machine are considered as three essential but conflicting targets. The effectiveness of the proposed control framework is tested for a direct drive electrified powertrain of a three-wheeled vehicle commonly found in urban transportation for Asian countries. The urban driving schedule based simulation results confirm that the lifetime of induction machine can be enhanced by appropriate controller design without compromising its performance.