Load Model Parameter Estimation by Transmission-Distribution Co-Simulation

In this paper, a novel approach for parameter estimation of static load models based on co-simulation of transmission and distribution dynamic simulators is presented. The advantage of a co-simulation based approach is that the aggregated response of the underlying three-phase unbalanced distribution system can be simulated. In this approach, the combined transmission and distribution dynamics is simulated with information exchanged at the distribution substation buses at each time step. The aggregated response (voltages, active and reactive powers) at the distribution substation bus is then fitted through a constrained linear least squares optimization to obtain the parameters of an equivalent load model. The validity of the proposed load modeling approach is demonstrated to estimate the parameters of a ZIP load model, with results being invariant to, perturbations with different magnitude and location, for multiple operating points, and under single and multiple instances of distribution feeder interfaced to transmission simulator. Furthermore, comparative studies between co-simulation approach and transmission only simulation with equivalenced loads modeled using parameters obtained through proposed approach is provided to illustrate the capability of the presented method in capturing load characteristics of distribution grid.