An Improved Approach for AC-DC Power Flow Calculation With Multi-Infeed DC Systems

An improved approach based on sequential method for the AC-DC power flow calculation is proposed in this paper. This approach solves the convergence problem caused by voltage violations at AC buses during the power flow calculation for the DC subsystems. The convergence property can be significantly improved by adjusting the converter transformer tap position flexibly. In order to adjust the tap position of the converter transformer flexibly, three mainly modifications are proposed. Firstly, the equations for whole DC systems are decoupled into individual DC systems so as to easily figure out which DC system's tap position needs adjustment. Secondly, the tap ratio of a converter transformer is selected as an alternative state variable to replace the cosine of the control angle when necessary. Thirdly, the Newton-Raphson method is utilized to solve DC subsystems instead of the method using the linear equations. Furthermore, a theoretical analysis of the advantages of the proposed approach is also presented. Numerical simulations and practical applications show that the proposed approach meet the requirement of different system operating conditions and has advantages in terms of convergence and speed. The proposed approach has been successfully integrated into the Energy Management System (EMS) for China Southern Power Grid.

[1]  G. Durga Prasad,et al.  A heuristic method for the real-time load flow solution of integrated multiterminal AC-DC power systems , 1993 .

[2]  J Arrillaga,et al.  Computer Modelling of Electrical Power Systems: Arrillaga/Computer Modelling of Electrical Power Systems , 2001 .

[3]  P. Kundur,et al.  Power system stability and control , 1994 .

[4]  L. L. Grigsby,et al.  A new approach to AC/DC power flow , 1991 .

[5]  B. J. Harker,et al.  Computer Modelling of Electrical Power Systems , 1983 .

[6]  Hongbin Sun,et al.  A new generation of EMS implemented in Chinese electric power control centers , 2008, 2008 IEEE Power and Energy Society General Meeting - Conversion and Delivery of Electrical Energy in the 21st Century.

[7]  Juan Yu,et al.  An Unfixed Piecewise-Optimal Reactive Power-Flow Model and its Algorithm for AC-DC Systems , 2008, IEEE Transactions on Power Systems.

[8]  Q. F. Ding,et al.  A new approach to AC/MTDC power flow , 1997 .

[9]  K. R. Padiyar,et al.  POWER FLOW ANALYSIS IN MTDC-AC SYSTEMS—A NEW APPROACH , 1994 .

[10]  Wilsun Xu,et al.  A Harmonically Coupled Admittance Matrix Model for AC/DC Converters , 2007, IEEE Transactions on Power Systems.

[11]  C. P. Arnold,et al.  A simple improvement to sequential AC/DC power flow algorithms , 1990 .

[12]  Robert Fischl,et al.  Multiple power flow solutions of small integrated AC/DC power systems , 2000, 2000 IEEE International Symposium on Circuits and Systems. Emerging Technologies for the 21st Century. Proceedings (IEEE Cat No.00CH36353).

[13]  Claudio A. Canizares,et al.  Point of collapse and continuation methods for large AC/DC systems , 1993 .