An Efficient Two-Layer Optimal Torque Split Strategy for PHEV Considering Time-Delay Compensation

Improper torque division strategy in vehicles leads to unnecessary energy consumption as well as poor driving comfort and safety. Previous research ignores the time-delay phenomenon of vehicle power systems, hindering the further improvement of related performance. In this work, an efficient two-layer torque split strategy with the consideration of the time-delay phenomenon is proposed to improve tracking accuracy, reduce fuel consumption, and avoid battery electrical abuse. In the upper layer controller, an optimal energy management strategy (EMS) is developed to coordinate between the battery state and engine fuel consumption rate by solving a nonlinear optimization problem, generating the reference torque split scheme. The bottom layer controller is based on Time-delay Model Predict Control (TMPC), comprehensively considering the reference torque split scheme, future information, and vehicle power system information. This TMPC strategy reduces both the torque tracking error and velocity tracking error by exploiting the characteristics that hydraulic braking system (HBS), motor and engine have different response times. Event-trigger (ET) mechanism is introduced in the frame of TMPC for the trade-off between control performance and computation efficiency. Stability and feasibility are theoretically guaranteed by the invariant set method. Simulation results verify the effectiveness of the proposed strategy.