Nonlinear parameter estimation experiments for static load modelling in electric power systems

In the paper, we consider the problem of estimating the parameters of static power system load models intended for use in load flow studies that incorporate the variation of active and reactive power with busbar voltages. A number of load model forms are considered, where the parameter estimation task involves the iterative solution of nonlinear equations. The use of the Newton method to obtain the parameters proved to be unsatisfactory in many instances. Alternative iterative techniques such as the BFGS and modified BFGS methods are explored, and computational experience using actual field data is reported in the paper. The work reported in the paper suggests that the modified BFGS method offers more reliable performance than the other three methods under many conditions, including severe data noise. It is also shown that the optimal parameter set may not be unique in certain cases, and that the initial guess of the unknown parameters is instrumental in the computational performance of the methods. Further evaluation of the results reveals that complicated models need not necessarily be used to obtain satisfactory results.