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Fast Critical Clearing Time Calculation for Power Systems with Synchronous and Asynchronous Generation

Xuezao Wang, Yijun Xu, Wei Gu, Kai Liu, Shuai Lu, Mert Korkali, Lamine Mili

TL;DR

The paper tackles transient stability assessment in power systems with high levels of converter-interfaced generation (CIGs) by introducing a trajectory-sensitivity-based method to quickly estimate the critical clearing time (CCT). It derives post-fault trajectory sensitivities for systems with both synchronous generators and grid-following converters, and defines a norm-based stability index to drive a linear-interpolation scheme for CCT estimation. Key contributions include analytic CCT expressions for mixed SG/CIG networks, a practical SN-based interpolation approach, and demonstrated computational efficiency gains over traditional time-domain simulations. The approach enables faster, near real-time stability analysis in modern grids and informs the integration of high-CIG scenarios, with future work on grid-forming converters and uncertainty modeling.

Abstract

The increasing penetration of renewables is replacing traditional synchronous generation in modern power systems with low-inertia asynchronous converter-interfaced generators (CIGs). This penetration threatens the dynamic stability of the modern power system. To assess the latter, we resort to the critical clearing time (CCT) as a stability index, which is typically computed through a large number of time-domain simulations. This is especially true for CIG-embedded power systems, where the complexity of the model is further increased. To alleviate the computing burden, we developed a trajectory sensitivity-based method for assessing the CCT in power systems with synchronous and asynchronous generators. This allows us to obtain the CCT cost-effectively. The simulation results reveal the excellent performance of the proposed method.

Fast Critical Clearing Time Calculation for Power Systems with Synchronous and Asynchronous Generation

TL;DR

The paper tackles transient stability assessment in power systems with high levels of converter-interfaced generation (CIGs) by introducing a trajectory-sensitivity-based method to quickly estimate the critical clearing time (CCT). It derives post-fault trajectory sensitivities for systems with both synchronous generators and grid-following converters, and defines a norm-based stability index to drive a linear-interpolation scheme for CCT estimation. Key contributions include analytic CCT expressions for mixed SG/CIG networks, a practical SN-based interpolation approach, and demonstrated computational efficiency gains over traditional time-domain simulations. The approach enables faster, near real-time stability analysis in modern grids and informs the integration of high-CIG scenarios, with future work on grid-forming converters and uncertainty modeling.

Abstract

The increasing penetration of renewables is replacing traditional synchronous generation in modern power systems with low-inertia asynchronous converter-interfaced generators (CIGs). This penetration threatens the dynamic stability of the modern power system. To assess the latter, we resort to the critical clearing time (CCT) as a stability index, which is typically computed through a large number of time-domain simulations. This is especially true for CIG-embedded power systems, where the complexity of the model is further increased. To alleviate the computing burden, we developed a trajectory sensitivity-based method for assessing the CCT in power systems with synchronous and asynchronous generators. This allows us to obtain the CCT cost-effectively. The simulation results reveal the excellent performance of the proposed method.

Paper Structure

This paper contains 18 sections, 24 equations, 3 figures, 3 tables, 1 algorithm.

Table of Contents

  1. Introduction
  2. Preliminaries
  3. The Dynamic Model for Modern Power Systems
  4. Synchronous Generators
  5. Asynchronous Generators
  6. CCT as the Evaluation Metric for System Stability
  7. The Proposed Method for Calculating CCT for Synchronous and Asynchronous Generation
  8. The CIG-embedded Power System Trajectory Sensitivity to Fault Clearing Time
  9. CCT Calculation Considering Synchronous and Asynchronous Generation
  10. Case Studies
  11. Calculation of CCT Using The Proposed Method
  12. Test System Setup
  13. Demonstration of the Proposed Method
  14. Validation of the Proposed Method
  15. Computing Efficiency
  16. ...and 3 more sections

Figures (3)

  • Figure 1: CCT calculation of CIG-embedded power system using the proposed method for (a) synchronous generators and (b) asynchronous generators.
  • Figure 2: Simulation of state variables of CIG-embedded power system on the different values of $T_{cl}$ with its (a) and (b) for synchronous generators and (c)-(f) for asynchronous generators.
  • Figure 3: Simulation of state variables of traditional IEEE $39$-bus system on the different values of $T_{cl}$ with its (a) for $\omega$ and (b) for $\delta$.