An emergency power modulation strategy for multi-infeed HVDC systems

Based on differential geometric theory, a novel nonlinear emergency modulation strategy for multi-infeed HVDC systems to enhance the transient stability of AC system in the presence of large disturbances is presented in this paper. Taking the HVDC systems as a variable admittance connected at the inverter or rectifier AC bus, the analytical description of the relationship of the variable admittance and active power flows of each generator can be derived. The traditional generator dynamic equations can thus be expressed with the variable admittance of HVDC systems as an additional state variable and changed to an affine form, which is suitable for the global linearization method being used to determine its control variable. An important feature of the proposed method is that, the modulated DC power is an adaptive and nonlinear function of the AC system states, and it can be realized by local feedback and less transmitted data from the adjacent generators. The design procedure is tested on a dual-infeed hybrid AC/DC system.