HEV Modeling

Abstract

The objective of the energy management control is to minimize the vehicle fuel consumption, while maintaining the battery state of charge around a desired value. To this end, modeling for energy management may have two scopes: creating plant simulators to which an energy management strategy is applied for testing and development , or creating embedded models that are used to set up analytically and/or solve numerically the energy management problem. Plant models tend to be more accurate and computationally heavy than embedded control models. The main objective in both cases is to reproduce the energy flows within the powertrain and the vehicle, in order to obtain an accurate estimation of fuel consumption and battery state of charge, based on the control inputs and the road load. In some applications, other quantities may be of interest, such as thermal flows (temperature variation in engine, batteries, after-treatment, etc.), battery aging, pollutant emissions, etc. This chapter provides a concise overview of the modeling issues linked to the development and simulation of energy management strategies. The reader is referred to more specialized works for further details (e.g., [1]). Efficiency considerations are at the basis of the models described, which are suited for preliminary analysis and high-level energy management development. 2.2 Modeling for Energy Analysis Because of the losses in the powertrain, the net amount of energy produced at the wheels is smaller than the amount of energy introduced into the vehicle from external sources (e.g., fuel). Conversion losses take place when power is transformed into a different form (e.g., chemical into mechanical, mechanical into electrical, etc.). Similarly, when power flows through a connection device, friction losses and other inefficiencies reduce the amount of power at the device output. Energy losses in powertrain components are usually modeled using efficiency maps, i.e., tables that contain efficiency data as a function of the operating conditions (for example, the output torque and the rotational speed of the engine). Maps are built experimentally