Abstract: The power output of bundled photovoltaic (PV) and thermal generators which connect power grid through series compensation AC system is a reasonable and operable scheme. Based on the modified IEEE SSR first benchmark model which integrated with grid-connected PV, complex torque coefficient method and time-domain simulation method are used to analyze the effects of PV on subsynchronous oscillation characteristics of pwer system. According to the transmission delay of speed deviation signal of the generator and phase compensation principle, active and reactive type additional damping controller and mixed additional damping controller are designed based on multi-channel structure. It is demonstrated that the additional damping controller does not affect the stability operation of gird-connection PV. The idea of configuring additional damping controller in PV inverter can be used as a backup plan to suppress SSO of thermal power unit. The influence of gird-connection PV capacities and types of additional damping controller on suppressing SSO are also analyzed, frequency-domain and time-domain simulation results show that the larger grid-connected PV capacity, the better suppression effects on SSO. Compared to single additional damping control, the hybrid additional damping controller has a better suppression effects on SSO.