A Noninvasive Measurement Technique of Grid and Converter Wideband Impedance

Abstract

A novel technique has been proposed to simultaneously estimate the wideband Thevenin's impedance of the grid as well as the power electronic converter from measurements sampled at the point of common coupling. The proposed algorithm is non-invasive, thus it can estimate both the impedance of the utility grid as well as the grid-tied inverter from the voltage and current measurements at the point of common coupling. It works by utilizing the harmonic information obtained from the existing voltage and current waveforms. Therefore it can circumvent the requirement of any injecting device to estimate the wideband impedance. The algorithm works on an initial <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Predictor Generation</i> phase, which is an initialization phase based on the design parameters, and a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Realtime Estimation</i> phase which runs after the inverter is commissioned. The Realtime Estimation phase uses the Singular Value Decomposition technique to efficiently utilize the existing harmonic information for the prediction. The efficacy of the technique has been tested in EMTDC/PSCAD simulations of a grid-tied inverter system. Furthermore, a Power Hardware in Loop experimental set-up has been built to validate the simulation results and thus, prove the efficacy of the proposed algorithm. The results show a mean square error of 0.05 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Omega$</tex-math></inline-formula> and 0.5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\Omega$</tex-math></inline-formula> for the grid and inverter side respectively.