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

TL;DR

This paper analyzes the transient stability of grid-following renewable plants with synchronous condensers, revealing how SynCon integration shifts the dominant instability source and proposing a damping strategy to improve overall stability.

Contribution

It introduces a dual-timescale model to understand stability shifts and demonstrates a simple damping method to enhance transient stability in co-located systems.

Findings

SynCon integration shifts dominant instability from PLL to SynCon.

Proper PLL damping can suppress SynCon rotor acceleration.

The proposed approach improves stability validated by CHIL platform.

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.