For the subsynchronous resonance(SSR) in a series-compensated system with a multi-mass synchronous generator, this paper introduces a suppression method by adding a subsynchronous damping controller(SSDC) to the photovoltaic(PV) power generation. Firstly, by using eigenvalue analysis method, it can be demonstrated that the effective input signal of SSDC is the remote signal and the effective output signal of SSDC is the reference value of the d-axis inner ring or outer loop of PV, so as to solve the delay problem of input signal communication, the input signal is improved by the weighted combination of local signals, which makes the electrical damping of SSR mode improved. Time-domain simulation results are presented to validate the theoretical analysis and show the effectiveness of the improved approach.