Analysis and Enhancement of Synchronization Stability in Grid-forming PV Systems Using Torque Component Quantification

With the rapid deployment of distributed PVs, the stability issues become a serious concern for power systems. As a solution, the grid-forming control (GFM) featuring active regulation of voltage and frequency emerges. Among various GFM schemes, the DC-link voltage synchronous control has attracted tremendous attention as it can stabilize the DC-link voltage of PV systems and utilize the stored energy of their DC-link capacitors to mimic the inertia support. However, a PV system using the DC-link voltage synchronous control (PV-DVSC) can cause low-frequency oscillations (LFOs) under certain operating conditions. To mitigate such risks, this paper investigates the mechanism of LFO and associated suppression method, utilizing the torque component quantification. Firstly, a torque analysis model of the PV-DVSC is established to elucidate the contribution of different control loops on LFO from a torque vector perspective. Additionally, the impacts of key parameters on LFO are quantitatively assessed via the damping and synchronizing torques. Leveraging these torques, a torque-oriented phase compensator (TOPC) is designed, targeting a positive torque to effectively suppress the unstable LFO even under extreme conditions such as desynchronization. Finally, the validity of above analysis and proposed TOPC strategy are verified through simulation control-hardware-in-the-loop test results.