Safe Distributed Control Allocation for Articulated Heavy Vehicles

Licentiate thesis, 2024

The electrification of trucks is now followed by the electrification of trailers. Additionally, the maximum allowed length of vehicle combinations has been increased in many countries to enhance efficiency. Electrification, increased variation, and complexity of multi-unit vehicle combinations have created the need for novel control allocation strategies. The traditional vehicle combinations are propelled only by the towing vehicle units: trucks or tractors. Braking forces are distributed proportionally to the axle loads, which is the safest approach. The modern combinations, on the other hand, may be propelled by multiple units. Regenerative braking may be performed by many electrified units, not necessarily in proportion to the axle loads. An optimal approach for the allocation of propulsion and brake forces into different vehicle units is power loss minimization. It may be more efficient to utilize only one of the vehicle units for propelling or regenerative braking from a power efficiency perspective. However, the most energy-efficient allocation may not be safe and can result in motion instability. For example, excessive regenerative braking with a tractor may lead to jackknifing. Hence, it is quite important to ensure the stability of the combination while allocating unit forces. This thesis introduces a safe operating envelope for vehicle combinations to ensure safe control allocation. Then the proposed safe operating envelope is tested using a real tractor-semitrailer combination, confirming its effectiveness in preventing yaw instabilities. In addition, some alternative methods in the force domain, and an alternative envelope in the tire slip domain are presented and evaluated with the real tests. The presented methods in this thesis showed promising performance in ensuring safety during the control allocation of unit forces at the combination level.