The Analytical Investigation Of Thevenin Equivalent And Load Security Domain

Due to the complexity of voltage stability, using Thevenin equivalent model andparameter in application of voltage stability analysis become one of the hot researchin related fields. Using Thevenin equivalent simplified model of power system canquickly analyze load voltage stability.On the analysis of power flow equations based on non-destructive system,derivation of the relationship curve between power and voltage, get maximum powerof load. Because of Thevenin equivalent parameters change, the relationship curvebetween voltage and power also changed accordingly. Simulation results show thatThevenin equivalent parameters have a greater impact on voltage stability analysis.The key of obtaining Thevenin equivalent is the equivalent parameter ofThevenin equivalent. Due to the load side a run of points can be measured less state, itneeds to be run using point and its neighborhood directly and speedily work outThevenin equivalent parameters for obtaining equivalent parameters measurement.Based on local information is the difficult. Compared with the general methods，Inaddition to the use of the load power and bus voltage amplitude, but also taking intoaccount the change of voltage phase; In the strike of the initial values, use theequivalent electric potential phasor as the phase reference axis, and it is in line withthe logic of the Thevenin equivalent; In the correction of the parameters, take fullaccount of the relationship between load changes and the change of the load busvoltage phasor or equivalent parameters, which makes the modified Theveninequivalent system could reflect the actual characteristics of the voltage-load on theload side and to achieve the equivalent. Numerical examples show the reasonablenessand accuracy of the equivalent system.With Thevenin equivalence parameters can calculate load security domain basedon the voltage level constraint, if the load power is within the range of stable interval,the load node voltage will above the constraint level. Thevenin equivalent potential isrelated to constraint voltage and Thevenin equivalent electric potential is related torunning voltage. For obtaining accurate load margin Thevenin equivalent parametershas significant impact. As running status change Thevenin equivalent parameters willchange. So Thevenin equivalent parameters need amendments, with correctionThevenin equivalent system can reflect the actual characteristics of the load sidevoltage-load, achieved the equivalent purpose. Adoped 36 nodes system shows that tracking thevenin equivalent parameters can be correct load security domains, makesloading. Correct of load security domain has basically the same power-voltagecharacteristics of PSASP program analysis results, proved the reasonableness andaccuracy of equivalent systems.