Power oscillation damping in standalone microgrids using integrated series compensator

This paper presents an integrated series converter scheme aimed to damp the power oscillations in microgrids (MGs) with decentralized control strategy and with dominated converter-based microsources (MSs). Power oscillation is an undesirable phenomenon in multi-source interconnected power systems which generally causes the degradation of power quality. In a microgrid, power oscillations can result in momentary overloading of the converters used to interface between the dc energy source and ac grid. These oscillations are more likely to happen when LCL filters are employed at the output stage of microsources [1]. A common method to mitigate these oscillations is the proper design of microsource controller. This approach, however, does not always lead to a robust controller. Furthermore, the controller structure and design becomes complicated and sometimes impractical as the controller is expected to perform other important control tasks like power sharing and voltage regulation. The proposed structure uses a small converter in series with the main parallel converter. As the series converter uses independent controller, the design of controller for the main converter can be relaxed. In this paper, the expression which shows the dependency of power variation to the frequency variation is obtained. Consequently, it is explained that how by introduction of a suitable series voltage, this dependency can be minimized and the oscillations can be damped. Small-signal modeling of the complete system is briefly presented and the proposed controller is discussed. Time domain simulations are used to validate the modeling and also to show the performance of the proposed structure.