Online network impedance identification with wave-package and inter-harmonic signals

Abstract

In power system analysis the main supply at a point of common coupling (PCC) is often presented by its Thevenin or Norton equivalent. In most cases these models adequately define the electrical characteristics of a PCC and are commonly used for power flow evaluations, fault estimations, as well as stability and power quality assessments. To determine the equivalent impedance of a PCC through analytical calculation or simulation precisely may be challenging due to the complexity and time varying nature of power supply systems. Especially in medium-and low-voltage distribution networks with a high share of fluctuating consumers and generators a measurement may be required to exactly capture the equivalent impedance over time. This contribution presents a method, which can be used to identify varying equivalent parameters of an AC power system with high accuracy and time resolution. To identify the network impedance the system is excited with short sequences of current signals while measuring the corresponding voltage and current characteristics. The method is evaluated in a simulation model. Further on, impedance measurements on the low-voltage level are presented and discussed.

Spectral Grid Impedance Identification on the Low-, Medium- and High-Voltage Level – System Design, Realization and Measurement Results of Grid Impedance Measurement

“…The voltages and currents of the first interval where the switch is open (subscript 1) and the second interval where the load is pulsed by the switch (subscript 2) are transformed into the frequency domain with FFT-algorithms. In the frequency domain the complex spectra of the grid impedance G ( ) can be calculated as follows: Strategies to excite the grid with pulsed current sequences can be found in [16], [17] and [18]. With periodic pulse signals the grid impedance can be precisely measured at specific frequencies.…”

Coupled Harmonic Admittance Identification Based on Least Square Estimation

“…In case of absence of control parameters involved in analytical derivation of Norton, small-signal impedance modeling is an alternative way of modelling parameter estimation. In Reference [19], Authors excited the system with short sequences of current signals and identified its impedance by constructing the relationship between corresponding voltage and current characteristics. A study in Reference [20] is conducted using this method to analyze the terminal characteristics of a MMC (Modular Multilevel Converter) system.…”