Power Flow Modeling to Variable-Speed Pumped Storage (VSPS) Including Inner Constraints of Doubly-Fed Induction Machine (DFIM)

Solution to the inner constraints of variable-speed pumped storage (VSPS) with the doubly-fed induction machine (DFIM) is related to stator voltage, thus dependent on the system power flow, which has not been studied yet. This paper proposes a power flow model for grid-connected DFIM-VSPS considering inner constraints. Firstly, analytical expression of the mechanical power and rotor speed of the reversible pump-turbine under the maximum power-point tracking (MPPT) mode is derived. Then power and torque constraints are included to propose power flow model of the DFIM-VSPS, which is solved together with power system constraints simultaneously. Afterwards, the initial values of the magnitude and phase angle of the rotor voltage of DFIM are set by the optimal rotor speed to improve the flat-voltage start and avoid iteration divergence. Finally, simulation results of New England test system are provided to validate the feasibility and accuracy of the proposed method.