Small-signal stability enhancement of communicationless parallel connected inverters

Abstract

In this paper, small-signal stability issues of parallel-connected voltage source inverters without control interconnections are addressed. The dynamic analysis performed showed that the system stability margin is reduced when the composition of the inverter connection impedance is neither purely inductive nor purely resistive, which are two common approximations found in the literature. Based on a multivariable approach, this paper proposes the application of decoupling to the control of parallel inverters in order to increase the stability range concerning the connection impedance composition R/X. It is shown that decoupling can significantly improve the system damping even without precise knowledge of actual R/X. Experimental results are presented and corroborate the presented ideas.

On power sharing and stability in autonomous inverter-based microgrids

“…Examples of such characteristics are low inertia, no inherent physical relation between network frequency and power balance, possibly large R/X ratio, etc. [11], [12]. Several modifications to droop control have been proposed [13], [14], where the stability problem is either ignored or simplified by dealing with a linear model.…”

Synchronization of Identical Oscillators Coupled Through a Symmetric Network With Dynamics: A Constructive Approach With Applications to Parallel Operation of Inverters

“…In the context of small power networks, such as the ones relevant to the problem of designing redundant systems based on parallel connected Uninterruptible Power Supplies (UPS) (see, e.g., [2,9,29], and references therein), one could have essentially purely resistive connecting admittances if the cable lengths are short enough [30], i.e. g 1 psq " g 2 psq " .…”

A robust decentralized controller design for inverter-based Microgrids with dynamic loads

“…In order to improve the power sharing performance in inverter-based Microgrids, several modifications of droop control were proposed, such as alternative droop control [3], [9], virtual output impedance [10]. However, the stability issue in Microgrids is either neglected or not analytically proved.…”