Modeling, control and design of AC microgrids in islanded mode

Tesi per compendi de publicacions, amb diferents seccions retallades pels dret de l'editor The present doctoral thesis is focused on the analysis and design of control strategies for the secondary control layer of islanded AC microgrids without the use of communications. The work is submitted as a compendium of publications, composed by journals and international conference papers. The first contribution is a control strategy for the secondary control layer based on a switchable configuration, that does not require the use of communications. For stability analysis purposes, a closed-loop system modeling is presented, which is also used to determine design considerations for the control parameters. The second contribution is a complementary control strategy that improves the frequency regulation of the previous proposed control, using a dynamic droop gain in the primary layer. For this purpose, a time protocol that drives the variable parameters is proposed which guarantees an effectively reduction of the maximum frequency error without relying on complex techniques, maintaining the simplicity of the basis strategy and the non-use of communications. The third contribution is a multi-layer hierarchical control scheme that is composed by a droop-based primary layer, a time-driven secondary layer and an optimized power dispatch tertiary layer. The proposed control guarantees an excellent performance in terms of frequency restoration and power sharing. The fourth contribution is an improved secondary control layer strategy without communications, which presents superior operating performance compared with the previous proposals. The scheme is based on a event-driven operation of a parameter-varying filter which ensures perfect active power sharing and controllable accuracy for frequency restoration. A complete modeling that considers the topology of the MG and the electrical interaction between the DGs is derived for the stability analysis and to determine design guidelines for the key control parameters. For the purpose of analyzing and verifying the operational performance of the control schemes, an experimental MG was implemented, where selected tests were carried out. The obtained results are discussed and its relation with the doctoral thesis objectives analyzed. The thesis ends presenting conclusions and future research lines. La presente tesis doctoral se enfoca en el análisis y diseño de estrategias de control para la capa de control secundaria en micro