Transient droop control strategy for parallel operation of voltage source converters in an islanded mode microgrid

This paper investigates the small signal analysis of paralleled voltage source converters (VSCs) in an islanded multi bus microgrid. Studying small signal stability of a microgrid, it can be observed that dominant low-frequency modes of the system are highly sensitive to network configuration and the parameters of power sharing controller of VSCs. These low frequency modes are highly dependent to system parameters as well as operating points and as the demanded power increases, they drift to new locations that may eventually cause instability. To have a better transient characteristic in a microgrid, a novel transient control strategy based on the static droop characteristics is presented in this paper. To provide the active damping of the low-frequency power sharing modes at different loading conditions, the derivative terms of active and reactive powers have been added to droop functions. The transient droop gains are scheduled by small signal analysis of the power sharing mechanism in such a way that yield to desired transient and steady-state response. The proposed controller ensures a stable and robust performance of paralleled VSCs.