Safe operating envelope for electric semi-trailer: On safe driving conditions with electric trailer propulsion for heavy truck combinations using coordinated vehicle motion control

Abstract

With higher demands on electrification of the transport sector comes new challenges regarding the range of battery electric heavy vehicles. Installing batteries in the trailers of a heavy vehicle combination allows for an increase in range and also gives the opportunity of adding electric motors to the trailer. However using an electric trailer for propulsion may introduce stability issues which, if found, must be accounted for and controlled in order to not decrease the performance of the electric vehicle compared to the conventional tractor semi-trailer vehicles. This thesis presents an investigation on when and how an electric trailer can be used for propulsion and coordination of a heavy tractor semi-trailer vehicle combination. Definitions of what is regarded as safe motion of the vehicle is defined and a limiting operating envelope for the electric trailer is developed using data attained from simulations. Control systems which include control allocation are developed to coordinate the two vehicle units and to distribute forces among each of the available motion and steering actuators on the vehicle. The systems are verified and tested in a high fidelity simulation environment for two test cases, the first of which is to travel through an S-curve consisting of two opposing 90° turns and the second is the standardized "Sine with dwell" test (ISO 18375:2016). The proposed control systems perform well for the two presented test cases with some limitations regarding the scenario parameters. Additional predictive control systems are proposed as a possible improvement to the current systems. In the thesis, electric trailers are proven to, in concept, be a viable way of propelling, braking and controlling a two-unit vehicle combination using a safe operating envelope and control allocators.