Trajectory Optimization for the Engine–Generator Operation of a Series Hybrid Electric Vehicle

This paper presents a methodology of calculating the optimal torque and speed commands for the engine-generator system of a series hybrid electric vehicle (HEV). In series HEVs, the engine-generator subsystem provides electrical energy to the dc link. This paper proposes an optimal control strategy of the engine-generator subsystem to generate a desired amount of energy within a given period of time. The optimization algorithm, based on trajectory optimization, determines the torque and speed reference signals for the engine-generator subsystem that achieve maximum efficiency. A simplified version of the controller is also presented for online implementation. The proposed control strategy is compared with nonoptimized control techniques, and simulation results show the improvements in energy efficiency.

I. Introduction

The supervisory control of a series hybrid system has, among its tasks, to command the engine–generator subsystem to provide a requested amount of energy to the battery/motor system in a specified time. This task has to be performed in the most efficient way. Although the determination of the energy requested and the time that this energy has to be transferred are determined from a high-level system optimization, this task can be isolated and separately optimized.