Representation of line optimisation control in unified power-flow controller model for power-flow analysis

Drawing on constrained optimisation based on Newton's method, a systematic and general method for determining optimal reference inputs to unified power-flow controllers (UPFCs) in steady-state operation is developed. The method is directly applicable to UPFCs operation with a high-level line optimisation control. Through the selection of weighting coefficients used in the objective function which is formed from the weighted difference between the specified reference inputs and their optimal values, the method represents the priority assigned for any UPFC control function in constraint or limit resolution. Another key advance reported is that of combining the sparse Newton's method with the continuation technique for solving the nonlinear constrained optimisation. The composite algorithm extends substantially the region of convergence achieved with the conventional Newton's method. The method uses a general and flexible UPFC model based on nodal voltages developed. Any UPFC control functions together with operating limits can be included in the model. The steady-state formulation developed together with its software implementation is tested with a practical long-distance transmission interconnection where a UPFC is required.