Análisis de la impedancia de salida en lazo cerrado de inversores funcionando en modo isla, utilizando esquemas droop

In this paper the island mode condition is analysed. The island mode refers to a microgrid that is not connected to the electrical grid and the inverters have to operate as a voltage source in parallel with others equipments of similar characteristics. This study focuses on how to interconnect the inverters without using any type of communication, by using droop schemes. First, an analisys is performed on how to obtain a certain value of output impedance by using an impedance loop. Then, we propose to use physical characteristics of the inverter and the type of controller to achieve results similar to those obtained by the impedance loop. In order to validate this analysis, simulations on parallel connection of several inverters supplying power to load are performed. Lastly some conclusions are presented.En este artículo se analiza la condición en modo isla, es decir cuando una microrred no se encuentra  conectada a la red eléctrica y por ende los inversores que hacen parte de la microrred deben operar como fuentes de tensión en paralelo, con otros equipos de similares características. La temática se centra en la forma de interconectar los inversores sin utilizar ningún tipo de comunicación, a través de esquemas droop. En primera instancia se analiza cómo obtener una impedancia de salida determinada a partir de un lazo de realimentación de impedancia; posteriormente, se plantea la forma de aprovechar las características físicas tanto del inversor, como del controlador, con el fin de alcanzar resultados similares a los que se logran utilizando la técnica de lazo de realimentación de impedancia. Para validar dicho análisis, se realizan simulaciones de inversores conectados en paralelo alimentando una carga y se dan conclusiones

Control of Distributed Uninterruptible Power Supply Systems

In the last years, the use of distributed uninterruptible power supply (UPS) systems has been growing into the market, becoming an alternative to large conventional UPS systems. In addition, with the increasing interest in renewable energy integration and distributed generation, distributed UPS systems can be a suitable solution for storage energy in micro grids. This paper depicts the most important control schemes for the parallel operation of UPS systems. Active load-sharing techniques and droop control approaches are described. The recent improvements and variants of these control techniques are presented