Fast Convergence to the steady-state Operating Point of a VFT Park Using the Limit Cycle Method and a Reduced Order Model

In this paper, a new and efficient VFT park model suitable for stability and dynamic analyses of asynchronous links is presented. This model allows the simulation of multi-unit VFTs operated in parallel in order to increase the power transfer between two electric power systems. The backbone of the VFT model relies on a reduced order model of a wound-rotor induction machine. The computation of the steady-state operating point is achieved with the limit cycle method based on a Newton method and the Poincare map. This approach is particularly useful for the fast determination of the steady-state operating point of the variable frequency transformer because of the inherently large inertia of its rotary machine, which may cause a prolonged transient response after a system disturbance. The computation of the steady-state operating point with the limit cycle method paves the way to carry-out efficient stabitity studies. The steady-state operating point of a VFT park consisting of five 100 MW VFT units is computed for its energization, step power transfer and fault scenarios.