Hybrid control of container cranes

Hybrid cranes use ultracapacitors to store energy that is regenerated when lowering a container or during braking, and reuses this energy to assist the engine later on. A hybrid crane needs a system that optimizes the fuel cost by controlling in real time the two available power sources. Currently, the crane uses a rule-based heuristic strategy, which does not achieve optimal results and is difficult to tune. An alternative approach is Equivalent Consumption Minimization Strategy (ECMS), an optimization-based strategy of limited complexity that assigns a weight to the usage of the ultracapacitors that represents the equivalent ‘future fuel cost’. Two new strategies are presented that each have their own approach to this issue. The first uses feedback from the state of the ultracapacitors, the second uses predictions about the upcoming power demand. The new strategies are compared with the current system. The new strategies consistently outperform the current system, significantly improve the fuel savings, and increase the operational profits.