Improved Ward Equivalent Modeling Method for Interconnected Power Grids Based on Sensitivity Matrix

To simplify the interconnected power system, the current power flow calculation depends too much on computer performance and storage capacity. In this paper, equivalent modeling is carried out for IEEE39 node system with reactive power generator set. Firstly, the conventional Ward equivalent model (C-Ward) and the extended Ward equivalent model (E-Ward) are introduced in detail, and the nonlinear error sources of the two equivalent models are analyzed in the power flow calculation. The analysis results show the C-Ward equivalent model is obtained when the external network node voltage and the injected power at the boundary nodes are constant values, which will cause corresponding errors due to changes in the internal network conditions. Based on this, an improved Ward equivalent model (M-Ward) considering three kinds of sensitivity matrix is proposed. Based on the actual situation, two scenarios are set up considering the power system generator processing fluctuations and the short-circuit fault of the power grid. The accuracy of the model is evaluated by the relative error and the safety error coefficient. Finally, M-Ward method is the most accurate conclusion.