Identification of Three-Phase Grid Impedance in the Presence of Parallel Converters

Abstract

Grid impedance is an important parameter which affects the control performance of grid-connected power converters. Several methods already exist for optimizing the converter control system based on knowledge of grid impedance value. Grid impedance may change rapidly due to fault or disconnection of a transmission line. Therefore, online grid identification methods have been recently proposed to have up-to-date information about the grid impedance value. This is usually done by perturbing the converter output current and measuring the response in output voltage. However, any parallel converters connected to the same interface point will cause errors, since the measured current differs from the current that is flowing through the grid interface point. This paper points out challenges and errors in grid impedance identification, caused by parallel converters and their internal control functions, such as grid-voltage support. Experimental grid-impedance measurements are shown from the power hardware-in-the-loop setup developed at DNV-GL Flexible Power Grid Lab.

Modern Power System Dynamics, Stability and Control

“…The influence of grid impedance which is an important parameter affecting the control performance of grid-connected power converters is addressed in [6] by Luhtala et al This paper points out challenges and errors in grid impedance identification, caused by parallel converters and their internal control functions, such as grid-voltage support. Experimental grid-impedance measurements are shown from the power hardware-in-the-loop setup developed at DNV-GL Flexible Power Grid Lab.…”

Online Parametric Estimation of Grid Impedance Under Unbalanced Grid Conditions

“…Therefore, a straightforward approach to characterize the grid impedance is to apply what is called harmonic linearization [1] at every desired frequency (ω). Here, the impedance identification is performed based on the positive-sequence measurements (v + (ω), i + (ω)), as expressed in Equation (16).…”

“…This cost effective approach requires no extra hardware, such as a network impedance analyzer. The grid impedance information can be used to enhance the operation of grid-connected inverters, e.g., online stability analysis [7,8], voltage control [9], adaptive current controller [10], low voltage ride through [11], anti-islanding detection of grid-connected inverters [12][13][14][15], and analysis of multi-parallel inverters system [16][17][18].…”

VSC plug‐and‐play operation using online grid parameter estimation for PI self‐tuning

“…For grid‐connected operations, the control tuning process requires the knowledge of the grid impedance in order to avoid stability issues, as well as to provide a satisfactory dynamic response [5], making previous studies necessary in order to characterise the system. In applications involving weak grids, there is a specific concern regarding the stability issues due to the interaction of the closed‐loop control performance with the grid itself, which becomes more relevant by considering the sampling, processing and pulse‐width modulation (PWM) delay effects [6–10], thus, emphasising on the need of a previous study regarding the grid's modelling.…”