Real-Time Voltage Stability Assessment for Load Areas Based on the Holomorphic Embedding Method

—This paper proposes a method of real-time voltage stability assessment for load areas, in which the proximity to voltage collapse point at each bus can be accurately evaluated. Based on the non-iterative holomorphic embedding method (HEM), the voltage of each bus for different loading levels in the load area is quickly screened out by only performing one-time power flow calculation. A power series derived by the HEM with a physical germ solution makes sure that the P-V curve is in conformity with that from conventional continuous power flow. Therefore, the voltage stability margin can be evaluated by plugging a value into the embedded complex variable of the power series. An adaptive two-stage Pade approximants method is also proposed based on the power series to improve its convergence. Thus, on one hand, it enables more accurate prediction of the voltage collapse point; on the other hand, reduces the computational burden on large power systems. The proposed method is illustrated in detail on a 4-bus test system and then demonstrated on a load area of Northeast Power Coordinating Council 48-geneartor, 140-bus power system.