Abstract
In this paper, a power management strategy (PMS) has been developed for the control of energy storage in a system subjected to loads of random duration. The PMS minimises the costs associated with the energy consumption of specific systems powered by a primary energy source and equipped with energy storage, under the assumption that the statistical distribution of load durations is known. By including the variability of the load in the cost function, it was possible to define the optimality criteria for the power flow of the storage. Numerical calculations have been performed obtaining the control strategies associated with the global minimum in energy costs, for a wide range of initial conditions of the system. The results of the calculations have been tested on a MATLAB/Simulink model of a rubber tyre gantry (RTG) crane equipped with a flywheel energy storage system (FESS) and subjected to a test cycle, which corresponds to the real operation of a crane in the Port of Felixstowe. The results of the model show increased energy savings and reduced peak power demand with respect to existing control strategies, indicating considerable potential savings for port operators in terms of energy and maintenance costs.
Highlights
Energy storage is beneficial in situations where power production is intermittent or the load varies in intensity, as the objective of the storage is to mitigate variability in generation and demand by acting as a buffer
The optimal power management strategy (PMS) proposed in this paper was tested on a model of an rubber tyre gantry (RTG) crane equipped with a flywheel storage system
A power management strategy has been developed that minimises the energy costs associated with systems subjected to stochastic loads with a random duration
Summary
Energy storage is beneficial in situations where power production is intermittent or the load varies in intensity, as the objective of the storage is to mitigate variability in generation and demand by acting as a buffer. Flywheel energy storage systems (FESSs) in particular have been found suited for this task, as they show similar performance to supercapacitors, while being characterised by excellent ageing characteristics, which are independent of the charge rate or depth of discharge [1,18], allowing their lifetime to match that of the portal frame Their disadvantage is high standing losses, which are evident in more resilient designs (such as the use of normal ball bearings instead of magnetic bearings), as are the ones used on cranes; this does not affect the use for short power loads, and it only requires the storage to be charged shortly before use. An effective control strategy focused on storage in RTG cranes could have major benefits globally, as they are present in all major container ports and are a key element in the export and import processes Their activity is energy and power intense; it involves spending a large fraction of time idling before the lift cycle. The RTG model and the simulation results are presented and discussed in Section 4, with Section 5 presenting a summary of the work
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