Nonlinear simulation of speed variation of variable-speed unit under large disturbance by Simulink

Abstract

The variable-speed pumped storage plant (VSPSP) has become an innovative technology and new orientation in recent years. Investigation of dynamic processes in operating and control of VSPSP is of great importance for safety, stability and efficiency. In this paper, a nonlinear integrated model for dynamic processes of VSPSP with doubly fed induction machines (DFIMs) is built based on Simulink. From the comparison between simulation results and on-site measurement data of a fixed-speed pumped storage plant (FSPSP), the model under load rejection is validated. Meanwhile, maximum rotational speed during transient processes is a key indicator for the safety of pumped storage units. Hence, the transient process and performance of VSPSP under load rejection are simulated and analyzed by using the model, and the speed variation of the variable-speed unit is specifically investigated. The speed rising value and relative speed rising value will decrease when the initial value increases because of the momentum conversion mechanism and the torque characteristic of pump-turbine. The result demonstrates that, if the initial speed increases in the operating range of variable-speed unit under load rejection, the maximum speed will not rise significantly, and there is a certain safety margin from the maximum allowable speed.