| Voltage stability becomes a prominent problem with the constant expansion ofthe power system and the increment of customers’ demand. Voltage stabilitybecomes one of hotspots due to voltage collapse accidents occurred in manycountries. The research of static voltage stability has got widespread used as mostvoltage instability is monotone in the power system.The thesis described the effect of on-load tap changers on voltage stability andthe mechanism of voltage instability. Additionally, this thesis introduced the discreteand the continuous model of OLTC, analyzed positive and negative regulatingeffects on voltage stability, and studied the factors that lead to positive and negativeregulating effects.This paper studied the calculation expressions of Thevenin equivalentparameters considering the OLTC dynamic characteristics based on existingliterature. The expressions of Thevenin dynamic equivalent impedance and loadstatic equivalent impedance were derived. The method applied synchronousdetection of node voltage increment and load current injection, which can trackThevenin dynamic equivalent impedance in real time and accuracy. The condition ofmaximum power of nonlinear system was proved. The condition is that the Thevenindynamic equivalent impedance mode should be equal to the load equivalentimpedance mode. The expressions of dynamic equivalent impedance were derivedbased on the pi model of OLTC, and studied the correction method of Jacobianmatrix when ratio changed. Impedance modulus margin was used to analyze theeffect of OLTC dynamic on voltage stability. The state of system, weak nodes andnegative regulating effect were distinguished analysis of Impedance modulus marginunder the regulation of the ratio. Finally the correctness of the proposed method wasdemonstrated through the simulation of IEEE14-bus and IEEE30-bus systems.Impedance modulus margin index can effectively distinguish weak nodes and stateof the system considering the OLTC dynamic characteristics. |
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