Design-Oriented Transient Stability Analysis of Grid-Connected Converters with Power Synchronization Control

TL;DR

This paper analyzes the transient stability of grid-connected converters with power synchronization control, revealing conditions for synchronization, critical clearing angles, and re-synchronization capabilities, supported by simulations and experiments.

Contribution

It provides a phase portrait-based analysis of PSC-VSC transient stability, identifying critical clearing angles and re-synchronization features, which are novel insights for system protection design.

Findings

PSC-VSC maintains synchronization if equilibrium points exist after disturbance.

Critical clearing angle equals the power angle at the unstable equilibrium point.

PSC-VSC can re-synchronize after one cycle of oscillation even beyond the CCA.

Abstract

The power synchronization control (PSC) has been increasingly used with voltage-source converters (VSCs) connected to the weak ac grid. This paper presents an in-depth analysis on the transient stability of the PSC-VSC by means of the phase portrait. It is revealed that the PSC-VSC will maintain synchronization with the grid as long as there are equilibrium points after the transient disturbance. In contrast, during grid faults without any equilibrium points, the critical clearing angle (CCA) for the PSC-VSC is identified, which is found equal to the power angle at the unstable equilibrium point of the post-fault operation. This fixed CCA facilitates the design of power system protection. Moreover, it is also found that the PSC-VSC can still re-synchronize with the grid after around one cycle of oscillation, even if the fault-clearing angle is beyond the CCA. This feature reduces the risk of system collapse caused by the delayed fault clearance. These findings are corroborated by simulations and experimental tests.