Analysis of Resonance Between a VSC-HVDC Converter and the AC Grid

TLDR

The study aims to analyze the 1270 Hz resonance between a VSC‑HVDC converter and the 525 kV AC grid and to identify control or impedance‑adapter solutions that prevent it. An impedance‑based stability model was developed and simulated, evaluating the ratio of grid to equivalent impedance and mapping the negative‑real‑part frequency range, with equipment grouped into subsectors to simplify analysis. The analysis revealed a 1270 Hz resonance after line disconnections and showed that avoiding the negative‑real‑part region in each subsector is a sufficient, though not necessary, condition for system stability.

Abstract

A 1270 Hz resonance occurred between ±350 kV/ 1000 MW Luxi back-to-back voltage source converter based high-voltage dc transmission (VSC-HVDC) converter and the 525 kV ac grid after disconnection of several ac transmission lines. To understand the resonance and find a solution, the impedance-based stability analysis model considering different equipment is first established. Then, the resonance is analyzed and repeated in the simulation based on the established model. The system stability can be judged by the ratio of grid impedance to the equivalent impedance of all parallel-connected equipment with the converter. To evaluate the occurrence and risk of resonance, the frequency range where the impedance has a negative-real-part has been searched and studied. In order to narrow the negative-real-part region to avoid potential resonance, solutions such as control strategy improvement and passive or active impedance adapter may be applicable and are discussed. For a complex system containing various equipment, the equipment can be divided into several subsectors to avoid modeling all possible combinations of equipment, which can be exhausting. And analysis has shown sufficient but not necessary condition to stabilize the system is to avoid the negative-real-part region in each sector.