The principle and influence analysis of suppressing ultra-low frequency oscillation by using additional GPSS control

The distribution of power energy in China has promoted the development of long-distance and large-capacity ultra-high voltage direct current transmission projects. The asynchronous interconnection of power grids has become the mainstream trend, which makes the sending-end system dominated by hydropower have serious frequency stability problems. Therefore, this paper first analyzes the damping properties of the speed control system of hydropower units, and reveals that the negative damping caused by the phase lag of the speed control system is the root cause of the ultra-low frequency oscillation. Secondly, a method of using the lead-lag link of GPSS to compensate the phase lag of the speed control system to improve the damping is proposed, which can effectively suppress the ultra-low frequency oscillation under the requirement of frequency modulation performance. Then the root locus method is used to analyze the control parameters, and it is concluded that the appropriate GPSS control parameters can effectively improve the stability of the system. Finally, a single-machine single-load model is built by PSCAD/EMTDC electromagnetic simulation platform to verify the effectiveness of the GPSS to suppress ultra-low frequency oscillation.