Voltage Stability Assessment Of HVAC/DC Systems Based On Eigenvalue Method

The high voltage direct current(HVDC) electricity transmission don't have the angle stability problem, and can adjust power quickly, so HVDC transmission is widely used in the world's power system, specially when the power is huge and the transmission distance is long. Under this circumstance, there is reciprocity between the HVAC and HVDC system.To make sure the stability of the HVAC/DC system, it is very important to analyze the HVAC/DC system by using systematic methods. A mode analysis method based on eigenvalue decomposition is used to analyze the voltage stability. In this method, the smallest eigenvalue is used to evaluate voltage stability of power system, important system information is included in their correlative eigenvector.This article deeply analyzes the mode information's application on the voltage stability, first improve the Newton method, combine the AC power flow equations, the DC converter equations, the DC net equations, calculate the HVAC/DC system power flow result, then get the Jacbian's smallest eigenvalue and the correlative left and right eigenvectors, then the buses' participation factors are calculated by them. According to the participation factors, the voltage stability's weak buses are found. It is effective to improve the system's voltage stability by taking measurement on these buses. This article also discusses the influence of system's voltage stability with respect to some other system parameters, including the converter controlling modes and the power basic value ratio. When the converter controlling mode is changed from constant power to constant current, the voltage stability of power systems is improved. Finally, two IEEE normal test systems are used to simulate, the effection of using the eigenvalue method to evaluate the voltage stability of HVAC/DC systems is proved.