PROJECT TITLE :

Large Signal Large Signal Synchronizing Instability of PLL - Based VSC Connected to Weak AC Grid

ABSTRACT:

Voltage source converter (VSC) dominated power systems have a similar large signal synchronisation instability as traditional power systems, which is becoming more often documented and studied. Large signal instability of phase-locked loop (PLL) synchronised VSCs linked to weak ac grids is examined in this article. The dynamics of the PLL are examined first, and an additional feedback loop is found to be introduced, which has a negative effect on the PLL's performance. The rotor motion model of a synchronous generator (SG) is then used to construct an analysis model. The large-signal stability study is carried out using the equal-area method based on the proposed model. Two key causes of high signal instability have been identified. Equilibrium does not exist in the SG grid-connected system for two reasons: mechanical power input curve and electromagnetic restoring force curve don't meet at an intersection. Insufficient decelerating area causes the system to be unable to transition from the initial point to the current equilibrium point, which is the subject of the second type of transition. As well as uncovering the physical mechanism, the proposed analysis provides direction for future improvements.