Study On The Coordinated Control Issue In Parallel Hybrid Electric System

How to realize smooth power transfer under state-switch is one of the difficult control issues of Parallel Hybrid Electric System. However almost no research work related has been reported to present the details. Faced to such a challengeable problem this paper successfully accomplishes the whole research process, from definition analysis to algorithm development, from simulation to key technology studying and experimental verification, to solve the problem.It is the first time that the control issue of how to coordinate engine and motor under state-switch is defined as Coordinated Control Issue in this paper. Based on the analysis of dynamical characteristics of both engine and motor the reason and necessity of Coordinated Control Issue are further discussed.This paper also indicates that the algorithm to solve Coordinated Control Issue should be composed of two main parts: Torque Management Strategy and Coordinated Control Algorithm. Torque Management Strategy assigns torque as the major control variable and is responsible for the determination of not only state-switch conditions but also the target torque of both engine and motor according to the total torque command and the static engine efficient MAP. Coordinated Control Algorithm is constructed on the basis of Torque Management Strategy and its basic algorithm can be expressed as engine torque open-loop control with dynamical engine torque estimation and motor torque compensation.Coordinated Control Algorithms is preliminary verified by simulation testing with fixed state-switch conditions and consecutive state-switch conditions on offline and real-time simulation platforms.Two algorithms are put forward to solve the problem of on-board engine torque estimation, which is the key technology of Coordinated Control Algorithm. One is called the algorithm of engine torque estimation based on mean-value model and the other is called the algorithm of engine torque estimation based on instantaneous crankshaft speed. The advantages and disadvantages as well as application ranges of both algorithms are summarized according to the principles, algorithm modifications and experimental results. Consequently the algorithm of engine torque estimation based on instantaneous crankshaft speed is selected as the algorithm of on-board engine torque estimation when accuracy, generality and difficulty are compared. And self-designed MPC555 platform ensures the real time capability and high accuracy of engine torque estimation.It is finally manifested by the experimental results that Coordinated Control Algorithm can effectively reduce the fluctuation of total torque of engine and motor as well as the fluctuation of their speed and ensures smooth power transfer under state-switch.