Power Regulation Characteristics for Fixed-Speed and Variable-Speed Units Sharing Common Pipelines under Small Fluctuations

The variable speed pumped storage units (VSPSUs) with full-size converter (FSC) have the advantages of a wide regulation range and excellent control performance, and the VSPSU with FSC is conducive to maintaining power system stability due to the fast power regulation. However, the scheme of two units sharing common pipelines is widely used in current pumped storage plants. Due to hydraulic coupling interactions of a shared pipeline, there is a hydraulic disturbance between different units. When the plants need to be regulated according to grid demand, the distribution of the power regulation between the fixed-speed and variable-speed pumped storage units (FS-VSPSUs) in the system of two units sharing common pipelines and the hydraulic disturbance law urgently need to be investigated. Therefore, a numerical simulation model of the FS-VSPSUs sharing common pipelines, incorporating VSPSU with FSC, is established based on Matlab/Simulink using the improved transfer function method (TFM); Fixed-speed and variable-speed units (FS-VSUs) are simulated to study the dynamic response characteristics of the units under power fluctuations, and the active power response rapidity of the FSU and VSU are analyzed separately; Stability indicators are selected to assess the stability of different units during power regulation. The results show that: the active power response rapidity of VSU is faster and better, with two indicators of the rapidity advantage that can reach 94% on average compared to the FSU. However, in terms of stability, the power regulation of FSU is far superior to the stability of the VSU, with five indicators of the stability showing an advantage ranging from 28% to 86%, with an average of 69%. This paper provides theoretical support for the power regulation characteristics of the FS-VSPSUs sharing common pipelines.