engleski

HIERARCHICAL CONTROL OF A DIRECT CURRENT MICROGRID WITH ENERGY STORAGE SYSTEMS IN A DISTRIBUTED TOPOLOGY

A Microgrid (MG) is a standalone or grid-connected hybrid renewable system that uses distributed renewable and non-renewable energy sources and energy storage systems (ESSs) to supply power to local loads. The system is ordinarily based on power electronics, with interface converters allowing the sources to supply power to the system and the loads to draw power from the common bus in a controllable fashion. MG is normally designed such that renewable energy sources (RESs) supply the average load demand, while ESSs, non-renewable generation and the grid are used to ensure that the loads enjoy a continuous supply of power in the presence of variable RESs production. This thesis is focused on development of energy management systems (EMSs) for a standalone direct current (dc) MG which is supplied exclusively by RESs and ESSs. The special emphasis has been given to efficient management of batteries, the prevailing ESS technology. Designing the control of this kind of system without critical communication links between units is an attractive solution from both reliability and wiring hardware savings point of view. Therefore, the conventional droop control concept from the bulk ac power systems was utilized at the primary control level, because it requires only locally reachable measurements. However, the higher control level becomes a challenging task with an increase in the number of units with different characteristics and the topology complexity. It has to deal with RESs, which are controllable only within the limits imposed by natural phenomenon, while the battery recharging usually has to be done in a specific way. Moreover, the technical constraints such as stability margins and maintenance of acceptable voltage deviation within the system must also be respected while considering the aforementioned issues. An accurate battery model has been developed for use in the circuit design stage. Also, a battery management system (BMS) based on extended Kalman filter has been constructed and tested through simulations and experiments. Then, hardware in the loop model of the battery has been used in development stage of two coordination strategy methods for dc MG. First was assembled in a centralized way, while the other one utilized a distributed coordination concept based on power-line signalling (PLS).

Direct-current (dc); droop method; hierarchical control; energy management

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