AC/DC Hybrid Power System Transient Simulation And Stability Analysis And Parameter Optimization

With the countrywide interconnection and power transmission from West to East, more and more HVDC systems have been established during the several years. The fundamental framework of Chinese national power grid has been developed into a large-scale multi-area ultra-high-voltage AC/DC hybrid power system, as a result the characteristics of the system stability become more and more complicated. It is necessary and desirable to enhance the mathematical tools for researching the stability and analyzing the control method of the power system. On the Basis of the HVDC model and the relationship between the AC and DC systems, new digital computation techonolgy therefore is studied as follows:The current load flow method used for AC/DC hybrid power system is improved with the currents of convector transformer. Thus the restrict equations of the DC system is derived, which is used to form a novel bi-directional iteration approach. Meanwhile, a network division method, named two-level tree model, is developed to partition the AC/DC systems into one root-node and several leaf-nodes with AC/DC tie-lines buses. The method is easy to implement, and its convergence precision and speed is preserved well.A novel continuation power flow method for static voltage stability analysis of large-scale AC/DC hybrid power system is designed. With the restrict equations of the DC system, the predictor and the corrector of the continuous power flow method are improved as well as the switch strategy of the HVDC system is proposed while the AC voltage fluctuation. The effectiveness and efficiency of this method is proved on the South China AC/DC power grid system.The electromechanical transient simulation arithmetic of the AC system is further extended to apply to AC/DC system which could consider the complex control model of HVDC, such as HVDC regulator, VDCOL, modulation controller, bipolar block logic and auto-restart function. Promising effect is suggested by the case studies on Central-China East-China test power system.A scheme using time domain simulation to optimize HVDC regulator parameters is carried out with a new objective function to enhance the stability of both the AC system and the DC system. Trajectory sensitivity method is utilized to compute the gradient vector of the dynamic performance index of the power system with respect to the HVDC regulator parameters to be tuned. Furthermore, the search direction for updating the HVDC regulator parameters is given, and new HVDC regulator parameter configuration could be found for better angle stability. The result is tested on the 4-machine 2-area test power system.