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

This paper presents an original implementation, in an embedded controller, of a recently proposed online wideband single-phase AC system impedance identification technique and its validation via a Hardware In the Loop (HIL) real-time simulation setup. The technique uses an existing grid-tied inverter for estimation of wide bandwidth single-phase AC grid impedance in addition to performing its original power conversion function. A small-signal Pseudo Random Binary Sequence (PRBS), a digital approximation of white noise, can be super-imposed on the inverter switching commands. This injected white noise signal is wide bandwidth in nature, and, using appropriate cross correlation techniques, the wideband AC grid impedance can be measured. In smart grid applications, online wideband monitoring of AC power grid impedances is a key enabler of a set of capabilities, such as health monitoring, active filter retuning, and adaptive control of inverters. To evaluate the effectiveness of the online wide bandwidth AC power impedance identification technique in all of these smart grid applications, the proposed HIL setup aims at the numerical evaluation of the identification technique performance as well as the evaluation of all practical implementation issues.