Impedance-Based Stability Analysis in Grid Interconnection Impact Study Owing to the Increased Adoption of Converter-Interfaced Generators

Eduard Muljadi,Youngho Cho,Kyeon Hur,Yong Kang

doi:10.3390/en10091355

Abstract

This study investigates the emerging harmonic stability concerns to be addressed by grid planners in generation interconnection studies, owing to the increased adoption of renewable energy resources connected to the grid via power electronic converters. The wideband and high-frequency electromagnetic transient (EMT) characteristics of these converter-interfaced generators (CIGs) and their interaction with the grid impedance are not accurately captured in the typical dynamic studies conducted by grid planners. This paper thus identifies the desired components to be studied and subsequently develops a practical process for integrating a new CIG into a grid with the existing CIGs. The steps of this process are as follows: the impedance equation of a CIG using its control dynamics and an interface filter to the grid, for example, an LCL filter (inductor-capacitor-inductor type), is developed; an equivalent impedance model including the existing CIGs nearby and the grid observed from the point of common coupling are derived; the system stability for credible operating scenarios is assessed. Detailed EMT simulations validate the accuracy of the impedance models and stability assessment for various connection scenarios. By complementing the conventional EMT simulation studies, the proposed analytical approach enables grid planners to identify critical design parameters for seamlessly integrating a new CIG and ensuring the reliability of the grid.

Highlights

Power system planners conduct a series of studies to ensure the reliability of new capacity resources and to avoid their adverse impact on the grid [1,2]
Harmonics and resonance concerns of power electronics have been investigated widely in distribution systems, and they are crucial issues to be addressed for the integration of converter interfaced generators (CIGs) [3,4,5,6,7]
Motivated by the emerging change in grid characteristics and possible complications encountered without advancing the grid interconnection process, this paper identifies the new studies required to incorporate the characteristics of a new CIG

Summary

Introduction

Power system planners conduct a series of studies to ensure the reliability of new capacity resources and to avoid their adverse impact on the grid [1,2]. If the converter is connected to a weak alternating current (AC) system, certain operating conditions or parameter settings can result in system instability [9,10] These studies have focused rather on the interaction among the converters and the grid impedance. When the converter and grid impedance characteristics are unknown, it is possible to measure the converter and grid impedance online for the stability assessment and adaptive control [25,26] These studies have not fully incorporated the harmonic stability concerns observable in grid operations. PSCAD/EMTDC simulations validate the accuracy of the impedance models and stability assessment for the selected connection scenarios

Modeling of Converter-Interfaced Generator Impedance

Impedance Equation with Converter Dynamics

Validation of Impedance Equation

Equivalent Impedance Modeling

System Configuration

Connection Point Variation

Control Parameter Variation

Distance Variation

Converter Disconnection Contingency

Conclusions