Practical model for large-scale AC-DC system power flow calculation

Abstract

This paper proposes a robust, non-divergent model for large-scale AC-DC power flow calculation. By introducing relaxation parameters into power flow equations, the conventional power flow model was turned into a non-linear programming model to minimize the sum of squares of the relaxation parameters with operation constrains and DC station control modes. The interior point method (IPM) was used to solve the model. The dimension of the correction equations was reduced into the same size as that of conventional Newton-Raphson method. Cholesky factorization with approximation minimum degree (AMD) algorithm was utilized to solve the correction equations to improve the implementation efficiency. The proposed model and algorithm have the following features: 1) no special start process is needed; 2) it has strong robustness for power grids with plenty of small or negative impedance branches; 3) it has robust convergent property in the feasible region, around the boundary of the feasible region and beyond the feasible region. Power flow calculation on test system with 6891 buses and 8 high voltage direct current (HVDC) transmission lines validated the efficiency of the proposed algorithm. © 2011 Chinese Society for Electrical Engineering.