Mass-Block-Dragging-Based Starting Method for Synchronous Generator/Motor of Gravity Energy Storage System

A gravity energy storage system (GESS) typically adopts the synchronous generator-motor (SGM) that is directly connected to the grid, in order to provide inertia and reactive power support to power systems with high penetration of renewable energy. However, due to the lack of line-starting capability, it is a critical challenge for a GESS to meet the frequent start-stop requirements in practice. To solve this problem, an SGM starting method based on mass block (MB) dragging is proposed in this study, for a chain-rail-based slope GESS (SGESS) as example. Through the analysis of the loss components of GESS, an optimal mass determination method for the starting MB is derived. The MB-dragging-based starting of 1-kW and 500-kW chain-rail-based SGESSs are then simulated and analyzed, and the dynamic grid-connection characteristics of the SGM started by different starting MBs are compared. Finally, the MB-dragging-based starting of the 1-kW chain-rail-based SGESS prototype is tested for validation, and an experiment bench of SGM-grid connection is established to emulate the starting and grid-connection processes and evaluate their impacts on the grid. The experiment results demonstrate that the proposed method suppresses the inrush current successfully and enables smooth starting of SGM.