Subsynchronous oscillation of PV plants integrated to weak AC networks

摘要

The grid-connected photovoltaic (PV) power is booming, and large-scale PV power is mostly integrated to grid through long transmission lines; however, PV systems may face the threat of subsynchronous oscillation (SSO) when AC system strength is weak. This study establishes the sequence impedance model of grid-connected PV system; mechanism and characteristic of SSO in PV plants integrated to weak AC networks are delved into through impedance-based analysis method. The results show that, under certain conditions, the impedance of PV system is capacitive in the subsynchronous frequency domain, when the networks are weak and the PV capacity is high, the resonance may occur between the capacitive PV system and inductive AC grid. In addition, a smaller proportional gain of current loop may increase the risk of SSO; however, a larger proportional gain and integral gain of phase-locked loop can ease the SSO. Finally, time domain simulation based on PSCAD/EMTDC is conducted to validate the results of the impedance-based analysis. The research here can provide guidance to the project of scaled PV plants integrated to weak AC networks in some sense.