Transient Stability Assessment in Hybrid AC/DC Systems via Port Energy

This paper proposes a novel transient stability assessment (TSA) method for hybrid AC/DC systems with VSC-HVDC via port energy. The port energy of VSC-HVDC is described as the function of port state variables and control variables. The representation of port energy greatly enhances the accuracy of the transient stability study and can be extended to arbitrarily power electronics devices. At the same time, this approach can avoid formulating energy function with the complex internal controls of VSC-HVDC. Furthermore, iterative potential energy boundary surface (IPEBS) is employed to TSA. The maximum potential energy is searched on the instability of rotor angle’s swing curves as the critical energy through the dot product criterion. Then, the influence of the VSC-HVDC for transient stability is studied, including the VSC-HVDC transmission capacity of active and reactive power. The accuracy of the proposed energy function calculation is discussed via the different fault location. The feasibility and validity of the proposed method are demonstrated via the modified IEEE 39-bus hybrid AC/DC system.