Control of Micro-Hybrid Boosting
Nazari, Shima
2019
Abstract
Powertrain hybridization has been shown to greatly improve vehicle fuel economy, with significant additional component costs. A novel type of low voltage hybrid device, called a power split supercharger (PSS), has the potential to provide hybrid functionality at reduced system cost. The PSS is configured with a supercharger, a planetary gear set and a motor. The electric motor in the PSS system can be used in two discrete modes. It can drive the supercharger at variable speed and provide flexible boost pressure to the engine, or it can be employed to directly supply/receive torque to/from the crankshaft like a typical parallel hybrid powertrain. This work presents modeling, control design, optimization, and analysis of the PSS in fuel economy improvement of a light duty vehicle. The low-level controller for the air charge management of a twincharged engine with a PSS has to coordinated three actuators, throttle, wastegate, and the PSS in the nonlinear air path of the engine in a fraction of second to ensure fast engine torque control. A decentralized controller that uses the throttle to control intake manifold pressure and employs both the PSS and wastegate to control the boost pressure, in a master-slave configuration, is adopted. The controller was validated on a high fidelity GT-Power engine model and shown to effectively reduce the response time of the engine during critical transients to less than 0.5 second. During large torque requests, the supervisory energy management system in a vehicle equipped with a PSS must decide whether to use the electric motor to drive the supercharger or supply the motor torque directly to the crankshaft. An optimal control problem for energy management of the PSS was formulated and solved over the standard EPA drive cycles using dynamic programming (DP). The DP solution provides the best selection of operating mode as well as the potential fuel economy benefit of the system. The results show that the optimal controller often selects the parallel hybrid mode over the supercharging mode to minimize the fuel consumption of the vehicle. Moreover, the PSS provides 75% of full hybridization benefit and is as efficient as a two motor solution. An online energy management system that minimizes the equivalent fuel consumption of the engine and motor at each time instant was also developed and shown to have good agreement with the DP results. The simulation time trajectories were supplied to an engine dynamometer experimental setup, which demonstrated that the PSS and EGR combined improve the vehicle fuel economy by 35.5% over the FTP75 cycle compared to a baseline turbocharged engine. The fuel economy benefit of the PSS in combination with automation was also studied in this thesis. Automated vehicles can use a preview of the ahead traffic and plan their trajectory to minimize fuel consumption and maximize the benefit of a small hybrid system like the PSS. The fuel consumption minimization problem in a car following scenario for a vehicle equipped with a PSS was formulated and solved by sequential optimization of the velocity profile and energy management system. It was shown that with velocity smoothing a small hybrid system like the PSS can provide the fuel economy of a full hybrid powertrain at a lower cost.Subjects
Hybrid Electric Vehicles Optimal Energy Management Powertrain Electrification Supercharging Eco-driving
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