Stator Flux-Regulatory Excitation Control in Converter-Fed Synchronous
Machines for Pumped-Storage Variable-Speed Hydropower
Abstract
Pumped-storage hydropower is seen as a promising solution for efficient,
large-scale energy storage. One competitive technical solution is the
variable-speed hydropower plant (VSHP) configured with a converter-fed
synchronous machine (CFSM). These machines are operated with one extra
degree of freedom that is not usually optimized, where the CFSM’s
rotor-side DC excitation interacts with the stator-side AC excitation.
Depending on machine loading, the CFSM will be utilized in conditions
far from its original design. In order to deal with this issue, this
paper presents a stator flux control (SFC) method for regulating VSHPs
in a more efficient way by adjusting the field current to prevent the
machine from operating with over-magnetization independent of loading
condition, as well as better utilizing the stator-fed converter current,
maximizing the utilization of the CFSM. The derived first-principle
analytical equations for the proposed SFC have been validated and
analyzed in the Matlab/Simulink environment for a large 45 MVA, 375 rpm
CFSM, with the measured saturation curve as input. Finally, dynamic
transitions between different levels of pumping power reveal the SFC’s
ability to help to maintain a unity stator flux in the machine, enabling
optimal operation independent of loading level.