Online wideband identification of three-phase AC power grid impedances using an existing grid-tied power electronic inverter

Abstract

In smart grid applications, online wideband monitoring of AC power grid impedances is a key enabler of a set of capabilities, such as active filter tuning, adaptive control of inverters, and monitoring of local grid status, from which stability margins can be calculated. To evaluate the effectiveness of online wideband monitoring of AC power grid impedances in smart grid applications, this paper presents the implementation, in an embedded controller, of a recently proposed online Wideband System Identification (WSI) technique, validated via Hardware In the Loop (HIL) real-time simulation. The identification technique exploits an existing grid-tied inverter for the estimation of wide bandwidth AC grid impedances, on top of the original power conversion function. This is accomplished by super-imposing a small-signal Pseudo Random Binary Sequence (PRBS), a digital approximation of white noise which is wide bandwidth in nature, on the inverter switching commands so that all frequencies of interest can be excited at once. Then, after postprocessing, the wideband AC grid impedance can be extracted using appropriate cross correlation techniques. The present work focuses on the identification of balanced three-phase AC power grid impedances in the three-phase reference frame.