1.College of Electrical Engineering, Sichuan University, Chengdu 610065, China;2.High-tech Branch of Sichuan Shuneng Electric Power Co., Ltd., Chengdu 610041, China;3.State Grid Sichuan Electric Power Research Institute, Chengdu 610041, China

Small signal modeling is the basis for the quantitative analysis of stability characteristics and multi-controller parameter optimization of variable-speed pumped storage units with full-size converter (FSC-VSPSU). Since the response time scale of frequency converter systems is at millisecond level and that of hydraulic turbine system is at second level, the stability characteristics of the pumped storage unit in fast-power mode and generation state are largely restricted by the hydraulic turbine. Aiming at the problem that the conventional hydraulic turbine model cannot accurately reflect the operation characteristics of the pumped storage units, an improved small signal model for the hydraulic turbine considering the initial operation condition is proposed. It can reflect the influence of the initial operating load and water head of the hydraulic turbine on the stability characteristics, and the model parameters are easy to obtain. Combined with the generator, excitation system, governor system and converter models, the small signal model and electromagnetic transient simulation model of FSC-VSPSU in generation state are constructed. The small signal stability characteristics of the pumped storage unit are studied by eigenvalue analysis method. It is found that the unit has the risk of ultra-low frequency oscillation, and the key factors are extracted. Furthermore, the parameter setting principle of the governor system is given.