Improving the Summation Law for Harmonic Current Emissions of Parallel Operated PV Inverters by Considering Equivalent Grid Impedance

Abstract

For connection of a PV park to the electricity network, a pre-compliance study has to prove that the harmonic emissions at the point of common coupling (PCC) stays below the limits specified by the standards or local or national grid codes. An equation defined in IEC 61400-21 [1] is used to estimate the total harmonic current emission of the park at the PCC prior to installation. The equation uses the harmonic emission of a single inverter to predict the spectrum of the total current for a given number of identical inverters connected in parallel at the PCC. This paper considers the interaction of parallel operated inverters and the grid impedance. It proposes an approach based on the so called “equivalent grid impedance”, to improve the performance of summation law for evaluation of the current harmonics emissions at the PCC of PV parks. Improvement of this method would be helpful for power plant constructors.