Analysis and Suppression of Sub-Synchronous Oscillation of Photovoltaic Power Generation Based on Damping Torque Method

Aiming at the problem that the mechanism of sub-synchronous oscillation in photovoltaic power generation connected to weak AC system is unknown in low frequency band, a small signal model of photovoltaic power generation connected to weak AC system is established, its oscillation modes are analyzed, the participation of each state variable in each oscillation mode is calculated, and the promotion of damping torque method is put forward. Damping torque modeling is used to reveal the oscillation mechanism, identify the leading link, analyze the influence of working conditions, controller bandwidth and grid stiffness on system stability, and finally design additional ones according to the conclusion of mechanism analysis. The results show that the increase of input power, the decrease of DC voltage loop bandwidth and PLL loop bandwidth, and the decrease of grid stiffness will lead to the decrease of system damping and stability. Finally, the electromagnetic simulation model of photovoltaic power generation connected to weak AC system is built in PSCAD/EMTDC platform to verify the effectiveness of the damping torque modeling analysis results and the effectiveness of SSDC.