A Nonlinear Adaptive Backstepping Controller for Stabilizing the DC Bus Voltage of an Islanded Hybrid Microgrid

Abstract

A bidirectional interlinking converter (BIC) interconnects the ac and dc buses of a hybrid microgrid (HMG). Under certain operating conditions, the BIC may appear as constant power load to the dc bus causing low-frequency oscillations in it. This instability is observed during the power flow from dc to ac buses and is attributed to an interaction between the input and output impedances seen at the point of interface. In this article, an active damping scheme based on an adaptive backstepping controller (ABC) is proposed for the BIC of an islanded HMG to address the voltage instability in the dc bus. The proposed scheme can be easily integrated with a conventional backstepping controller and an attractive feature is its ability to disengage itself from the ac voltage controller of the BIC as soon as voltage oscillations in the dc bus die out. Thus, the active damper does not deteriorate the ac voltage quality at steady state. The proposed method uses fewer current sensors as compared with a recently reported active damping technique based on predictive control. Typical of a backstepping controller, large signal stability is ensured while deriving the control and adaptation laws. Experimental validation is included.