A framework for the impedance selection in the “Voltage-Current Ratio Difference” method

Abstract

This paper presents a framework for the selection of the impedance in the “voltage-current ratio difference” method. This method, as an invasive method, determines the harmonic contributions without needing the exact value of utility and customer impedances. The variation of the “voltage-current ratios” (or “current–voltage ratios”) due to the connection of a known serial impedance (or parallel admittance) between the utility and customer is the main basis of this method. Since the value of the serial impedance (or parallel admittance) significantly affects the sensible implementation of the method, this paper aims to present a procedure to correctly select this impedance (or admittance). In this paper, a procedure for the selection of the serial impedance based on the requirements at the fundamental frequency and investigated harmonic orders is proposed. This procedure determines an initial case-specific range for the serial impedance depending on some characteristics of utility and customer (i.e. voltage magnitude, short-circuit ratio at the point of common coupling (PCC), and operation active as well as reactive power of customer). This initial range for the serial impedance can be restricted by requirements at the investigated harmonic orders. Nevertheless, the suitable range for serial impedance is relatively wide to be implemented in practical applications. This fact is demonstrated by a case study at medium-voltage level.