Impact of Active Frequency Support Control of Photovoltaic on PLL-Based Photovoltaic of Wind-Photovoltaic-Thermal Coupling System
Cai Yan, Wei Yao, Jinyu Wen
Abstract
The coupling systems formed by wind power, photovoltaics, and thermal generators possess broad application prospects. To build grid-friendly renewable energy stations, active frequency support control (AFSC) is adopted. There are potential risks on subsynchronous oscillation (SSO) dominated by the phase-locked loop (PLL) based photovoltaic considering AFSC of photovoltaic. The impact of AFSC on PLL dominant SSO mode (PLL-SSOM) of the photovoltaic is still not clear. To address that, this paper firstly observes the SSO characteristics of the wind-photovoltaic-thermal coupling system (WPTCS) with AFSC. Considering the second-order rotor motion equation of the thermal generator and ignoring the dynamics of DFIG, a simplified model of WPTCS with AFSC is established. Compared with the detailed model, the correctness of the simplification is verified. Based on that, the transfer function of additional AFSC is derived. The study reveals that the root cause of the impact of AFSC on PLL-SSOM is that AFSC will make the synchronous torque and damping torque corresponding to the PLL-SSOM transform each other. Finally, the frequency-domain and time-domain simulation results verify the correctness of the model simplification and theoretical analysis.