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Dominant Transient Stability of the Co-located PLL-Based Grid-Following Renewable Plant and Synchronous Condenser Systems

Bingfang Li, Songhao Yang, Qinglan Wang, Xu Zhang, Huan Xie, Chuan Qin, Zhiguo Hao

Abstract

Deploying synchronous condensers (SynCons) near grid-following renewable energy sources (GFLRs) is an effective and increasingly adopted strategy for grid support. However, the potential transient instability risks in such configurations remain an open research question. This study investigates the mechanism of dominant synchronization instability source transition upon SynCon integration and proposes a straightforward approach to enhance system stability by leveraging their interactive characteristics. Firstly, a dual-timescale decoupling model is established, partitioning the system into a fast subsystem representing phase-locked loop (PLL) dynamics and a slow subsystem characterizing SynCon rotor dynamics. The study then examines the influence of SynCons on the transient stability of nearby PLLs and their own inherent stability. The study shows that SynCon's voltage-source characteristics and its time-scale separation from PLL dynamics can significantly enhance the PLL's stability boundary and mitigate non-coherent coupling effects among multiple GFLRs. However, the dominant instability source shifts from the fast-time-scale PLL to the slow-time-scale SynCon after SynCon integration. Crucially, this paper demonstrates that the damping effect of PLL control can also be transferred from the fast to the slow time scale, allowing well-tuned PLL damping to suppress SynCon rotor acceleration. Consequently, by utilizing SynCon's inherent support capability and a simple PLL damping loop, the transient stability of the co-located system can be significantly enhanced. These conclusions are validated using a converter controller-based Hardware-in-the-Loop (CHIL) platform.

Dominant Transient Stability of the Co-located PLL-Based Grid-Following Renewable Plant and Synchronous Condenser Systems

Abstract

Deploying synchronous condensers (SynCons) near grid-following renewable energy sources (GFLRs) is an effective and increasingly adopted strategy for grid support. However, the potential transient instability risks in such configurations remain an open research question. This study investigates the mechanism of dominant synchronization instability source transition upon SynCon integration and proposes a straightforward approach to enhance system stability by leveraging their interactive characteristics. Firstly, a dual-timescale decoupling model is established, partitioning the system into a fast subsystem representing phase-locked loop (PLL) dynamics and a slow subsystem characterizing SynCon rotor dynamics. The study then examines the influence of SynCons on the transient stability of nearby PLLs and their own inherent stability. The study shows that SynCon's voltage-source characteristics and its time-scale separation from PLL dynamics can significantly enhance the PLL's stability boundary and mitigate non-coherent coupling effects among multiple GFLRs. However, the dominant instability source shifts from the fast-time-scale PLL to the slow-time-scale SynCon after SynCon integration. Crucially, this paper demonstrates that the damping effect of PLL control can also be transferred from the fast to the slow time scale, allowing well-tuned PLL damping to suppress SynCon rotor acceleration. Consequently, by utilizing SynCon's inherent support capability and a simple PLL damping loop, the transient stability of the co-located system can be significantly enhanced. These conclusions are validated using a converter controller-based Hardware-in-the-Loop (CHIL) platform.

Paper Structure

This paper contains 23 sections, 51 equations, 18 figures, 5 tables.

Table of Contents

  1. Introduction
  2. System Modeling
  3. System Overview
  4. Dynamic Model of SynCon
  5. Dynamic Model of PLLs
  6. Singular Perturbation Model of the co-located System
  7. Mechanism of Instability Source Transfer Induced by SynCon Integration
  8. SynCon's Role in Enhancing Fast Time-Scale Coherent PLLs Stability
  9. SynCon's Role in Mitigating Multi-Converter Non-Coherent Disturbances
  10. Emergence of Slow Time-Scale SynCon Angle Instability
  11. The Instability Source Transfer: From Fast to Slow Time Scales
  12. Dual-Timescale Stability Enhancement Based on Classical PLL Damping Control
  13. The Damping Control effect Transfer: From Fast to Slow Time Scales
  14. Dual Time Scale Stabilization Control Scheme
  15. Discussion
  16. ...and 8 more sections

Figures (18)

  • Figure 1: Topology of the co-located GFLR and SynCon System.
  • Figure 2: Relationships of different frames in vector space.
  • Figure 3: Control structure and time scale division of the GFLR-SynCon system.
  • Figure 4: Uncertainty boundary zone and conservative stability boundary of the perturbed system.
  • Figure 5: Comparison of equivalent dynamic systems of PLL and SynCon.
  • ...and 13 more figures