Assessing the reasons for islanding in rural networks with dispersed photovoltaic generation

摘要

The present work addresses the problem of islanding situations detected in a rural Medium Voltage network of Spain with Photovoltaic plants connected. With this purpose, the network has been modelled and simulated using the PowerFactory DIgSILENT software tool for simulation of power systems. Grid-connected dispersed generators have been also modelled as voltage sources inverters with power control schemes and embedded anti-islanding detection systems, based on the SFS (Sandia Frequency Shift) method. Different scenarios have been designed and simulated to study the main factors that influence the delay or even the absence of detection of islanding situations by the inverters' anti-islanding systems. The results obtained show that even with power mismatch between generation and load in the network, there are several factors that may negatively affect the functionality of these active anti-islanding systems making them inoperative. These factors are, among others, the following: 1. Variation of the protection delay trigger related to the interaction among the inverters. 2. Presence of dynamic loads, such as asynchronous motors and voltage-dependent devices as well as load characteristics. 3. The values of the gain factors (K) of SFS and PLL. 4. Configuration and parameterization of the P-Q power control loop of the inverters. These results are based on real islanding situations which have been registered on this MV distribution network located in the South - East of Spain. This paper is not intended to be a survey of SFS active method but to assess the influence and effect of various interacting factors in order to give some clues to determine under which conditions and scenarios the loss of main grid is not detected by antiislanding active methods embedded on DG plants. The research on the reasons for these islanding situations will lead to new recommendations in the configuration and implementation of the current anti-islanding systems. This work is being done in the context of the project PROINVER, in a consortium with seven technological companies and manufacturers and two research and technological centers and universities. The PROINVER project has as aim the development of new conversion and protection solutions for scenarios with an elevated implementation of dispersed and distributed generation, to guarantee signal quality and power supply. This project is financed by the MICINN (Ministerio de Ciencia e Innovacion-Gobierno de Espana) and the ERDF (European Regional Development Funds), and its objectives are aligned with the SET PLAN (European Strategic Energy Technology Plan) for low carbon strategy.