Dynamic modeling and favorable speed command of variable-speed pumped-storage unit during power regulation

Abstract

Variable-speed pumped-storage unit (VSPSU) has advantages in flexibility, efficiency, and reliability. It has become a state-of-the-art technology in pumped-storage industry. However, there is little research about the transient process of VSPSU working at a favorable speed command during power regulation. To study the issue, a refined model considering hydraulic–mechanical and electrical subsystems is built in this work. All submodels are created by the authors as individual modules on Simulink platform, and these modules can be easily combined to model different VSPSUs. For the VSPSU that uses a doubly fed induction machine and adopts the fast power control strategy, there are several speed constraints. To satisfy the speed constraints during transient process, the speed command is adjusted to avoid exceeding the allowable speed variation range and eliminate the oscillation caused by the S-shaped region, while being guided by the optimal speed to achieve higher efficiency. The faster the speed command changes, the more rapid the power regulation could be. But fast-changing speed command also leads to larger pressure fluctuations in penstocks. Hence, different schemes of the speed command are compared, and suitable schemes are proposed by comprehensively considering the balance between rapidity and safety. The dynamic model and analysis of favorable speed command can provide support and advice for engineering practice.