Non-linear virtual impedance shaping strategy for predominantly resistive islanded power networks.

In the modern-day distribution network, converter-based distributed generators (DGs) are increasingly employed to supply power from renewables. One of the prominent issues in the use of decentralized control for this purpose is the inaccurate real power sharing amongst these DGs due to the voltage drops associated with the feeder/line impedances. The use of virtual voltage drop in the controller of these DGs is a popular approach to mitigate the impedance mismatch effects. This impedance shaping technique demonstrates improved power sharing, however, the selection of an appropriate value for it is a big challenge. This paper elaborates upon a droop-based VI shaping technique for converter-based DG through a non-linear variation for islanded networks which are predominantly resistive. Performance evaluation of this technique for a wide variety of loads including balanced (constant impedance), constant power, unbalanced, non-linear, and induction motor loads is done through detailed simulations. The proposed method is also tested for a mesh network. DG plug-and-play functionality performance and load variation on a modified 13-bus network is verified using the proposed control scheme. The range for control parameters for stability is verified through modeling and eigen value analysis. Experimental validation on a laboratory setup for the same has also been presented. • A non-linear relation between the output current and virtual impedance values is proposed to improve the proportional power-sharing of the DGs. • Improved proportional power-sharing is achieved by keeping the PCC voltage under acceptable limits and the non-linear parameter is also adjusted automatically. • The scheme idea is designed for low-voltage islanded systems and isolated systems where the DGs operate in inverse drop control. [ABSTRACT FROM AUTHOR]