With the rapid development of series-parallel hybrid electric vehicles (SPHEVs), mode transition from pure electrical drive to hybrid drive has attracted considerable attention. The presence of time delay due to response capacity of actuators and signal transmission of communication may cause decrease of speed tracking accuracy, even instable dynamics. Consequently, drivability of the SPHEV is unacceptable, and durability of the components is reduced. So far, plenty of control strategies have been proposed for mode transition, however, no previous research has been reported to deal with the time delay during mode transition.
In this paper, a dynamic model with time delay of hybrid electric system is established. Next, a mode transition time-delay controller is proposed based on a two degree of freedom internal model controller (2-DOF-IMC). Considering the control plant has three inputs (the engine output torque, clutch transmitted torque and traction motor output torque) and two outputs (the speeds of clutch driving part and driven part), the generalized inverse matrix is used to solve the non-square control problem for the inverse matrix calculation required by the IMC. Then, an anti-disturbance controller and a tracking controller are designed to ensure the control performance under different time delays. Finally, the results from MATLAB/Simulink software simulation and hardware-in-the-loop experiments both demonstrate that the proposed controller cannot only guarantee the stability of the system, but also improve speed tracking accuracy and vehicle performance.