In this paper, the need to develop a control strategy and test apparatus for next generation hybrid vehicles was realized. The complexity of today’s and future hybrid vehicles necessitates the need for an equally advanced method of control that can extract the optimal fuel economy from the system as a whole.

A review of existing hybrid vehicle control strategies was performed. Overall, much research has been done on the optimization of series and parallel type vehicles, but virtually no information was found on the optimal use of advanced powersplit drivetrains. However, the control strategy concepts explored in the literature are useful, and can be extended to complex architectures like the General Motors Two-Mode design. The equivalent consumption minimization strategy (ECMS) method developed by Rizzoni et al at the Ohio State University has proven to be a well developed control strategy that has seen much progress over the last decade. Although it has been only demonstrated on parallel-type vehicles, it was chosen as the basis for the control strategy methodology.

An in-depth analysis on the Two-Mode transmission operation was performed. The fundamental equations for each of its range states were derived for future use in developing a plant model, and for use in control strategy development. The torque and speed capabilities of each of its modes and gears were analysed. A detailed plant model was created to form a virtual test bed for control strategy development purposes. The models use empirical data provided by manufactures, which ensures a reasonable level of accuracy in portraying component constraints and efficiencies. Building on the ECMS, a similar hybrid vehicle control strategy was developed for Two-Mode transmission based vehicles. It was modified to handle two degrees of freedom as required by the system. Its objective is to constantly minimize the total equivalent power use in the system which is defined as the sum of the chemical power in the fuel and the power used by the battery multiplied by an equivalency factor.

Overall, the control strategy provides a strong basis for the optimal control of nextgeneration hybrid vehicles incorporating powersplit transmissions. It is suggested that further research be explored in combining rule-based control methods with the developed optimization based method since rule-based methods can add the stability required for enhanced drivability.