A Novel Decoupled LVRT Control Strategy for Transient Voltage Stability Enhancement of IBRs Using Voltage-Angle Coupling Analysis

TL;DR

This paper introduces a new decoupled LVRT control strategy for inverter-based resources that improves transient voltage stability by addressing voltage angle coupling issues caused by PLL errors.

Contribution

It proposes a power angle decoupled LVRT control method that mitigates voltage stability problems caused by voltage angle coupling in IBRs.

Findings

Decoupled LVRT effectively suppresses overvoltage and low voltage issues.

The proposed control improves transient voltage stability under large disturbances.

Analysis confirms the method's robustness through case studies.

Abstract

With the fast-increasing penetration of inverter-based resources (IBRs), the voltage support capability of the grid following (GFL) IBRs under low voltage ride through (LVRT) control significantly influences the transient voltage stability of the power system. The existing LVRT adjusts the q-axis current to regulate reactive power injection. However, under a large disturbance, the phase-locked loop (PLL) error invalidates the proportional relationship between the q-axis current and reactive power, consequently causing deviation in the actual reactive power injection of the IBR. Besides, the variation of IBR current, determined by the PLL phase and LVRT, also directly influences the transient voltage. To address this issue, the specific influence of PLL error on active and reactive power injection is first analyzed under LVRT control. In addition, by combining the LVRT and PLL dynamics, the mechanisms of three voltage problems caused by voltage angle coupling are revealed. overvoltage, low voltage, and DC-side overvoltage. The specific scenarios in which these voltage stability problems occur are also obtained by the voltage-vector-triangle graphic. Furthermore, a power angle decoupled LVRT control is proposed to eliminate the influence of voltage angle coupling. Finally, the mechanism analysis and effectiveness of the decoupled LVRT are verified in the case study.