Optimal Control of a Mechanical Hybrid Powertrain

• Published in: IEEE transactions on vehicular technology Vol. 61; no. 2; pp. 485 - 497
• Main Authors: van Berkel, K., Hofman, T., Vroemen, B., Steinbuch, M.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.02.2012; Institute of Electrical and Electronics Engineers
• Subjects: Applied sciences; Continuously variable transmission (CVT); Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical machines; Electrical power engineering; Energy accumulation; Energy management; Engines; Exact sciences and technology; flywheel; Fuels; Ice; mechanical energy storage; Mechanical power transmission; Miscellaneous; Operation. Load control. Reliability; optimal control; Power networks and lines; Regulation and control; Torque; Various equipment and components; Vehicles; Design criterion; Flywheel; Mechanical component; Optimization method; Fuel consumption; Compact design; Gear; Optimization; Computation time; mechanical energy storage; Optimal strategy; Storage capacity; Optimal control; Power distribution; Mechanical characteristic; A priori estimation; Dynamic programming; Brake; Energy management; Cost lowering; Comparative study; Energy storage; Continuously variable transmission (CVT)
• ISSN: 0018-9545; 1939-9359
• DOI: 10.1109/TVT.2011.2178869

This paper presents the design of an optimal energy management strategy (EMS) for a low-cost mechanical hybrid powertrain. It uses mechanical components only-a flywheel, clutches, gears, and a continuously variable transmission-for its hybrid functionalities of brake energy recuperation, reduction of inefficient part-load operation of the engine, and engine shutoff during vehicle standstill. This powertrain has mechanical characteristics, such as a relatively small energy storage capacity in the form of the compact flywheel and multiple driving modes to operate the powertrain because of the use of clutches. The optimization problem is complex because it is two fold: 1) to find the optimal sequence of driving modes and 2) to find the optimal power distribution between the engine, the flywheel, and the vehicle. Dynamic programming is used to compute the globally optimal EMS for six representative driving cycles. The main design criterion is the minimization of the overall fuel consumption, subject to the system's kinematics, dynamics, and constraints. The results provide a benchmark of the fuel-saving potential of this powertrain design and give insight into the optimal utilization of the flywheel system. In addition, the complexity (and computation time) of the problem is reduced by a priori (static) optimization of the power distribution for each driving mode. Static optimization of a dynamic optimization problem yields a suboptimal solution; however, the results show that the consequences on the fuel saving are small with respect to the optimal one (the difference is <; 0.8%).