Multi-scale oscillation characteristics and stability analysis of pumped-storage unit under primary frequency regulation condition with low water head grid-connected

Abstract

This paper aims to study the multi-scale oscillation characteristics and stability of pumped storage unit(PSU) under primary frequency regulation(PFR) condition with low water head grid-connected. Firstly, a novel nonlinear mathematical model of pumped storage unit governing system(PSUGS) considering the nonlinear characteristics of diversion tunnel is established, and the nonlinear state equations under power control mode is deduced. On this basis, the bifurcation characteristics and dynamic response process of PSUGS system with coupled first-order, third-order and fifth-order synchronous generator are studied respectively, and the effects of different order synchronous generator on the nonlinear PSUGS system are compared. In addition, the transient characteristics of the nonlinear PSUGS system considering the fifth order synchronous generator under different water heads are studied. Finally, the sensitivity of the regulation system parameters of PSU under PFR with low water head is analyzed, and the effects of hydraulic, mechanical and electrical factors on the multi-scale oscillation characteristics and stability of the nonlinear PSUGS system are revealed. The results show that the stability of PSU considering the first-order synchronous generator is less than that considering the third-order and fifth-order synchronous generator. The stability of PSU considering the third-order synchronous generator is close to that considering the fifth-order synchronous generator. In the operation of PSU, the lower the water head, the smaller the stability of the system. Under PFR condition, the nonlinear PSUGS system meets the supercritical Hopf bifurcation. During PFR oscillation of the unit, the high-frequency wavelet is excited by the generator excitation system and is sensitive to the q-axis parameters of the generator. The low-frequency wavelet is mainly excited by the power grid and mapped with the water hammer effect in the dynamic process. The research results of this paper provide a theoretical basis for the stability analysis and optimal regulation of PSU under PFR condition with low water head.