Extinction Angle Modulation in UHVDC Systems for Improving Voltage Stability of Weak AC Power System

摘要

In the case of ultra high voltage direct current (UHVDC) transmission system feeding into AC system with low short circuit ratio, voltage stability problem of the AC system is prominent. It's easy that AC system disturbances cause low order harmonic resonance, large temporary overvoltage and multiple commutation failures. To solve the problem, an extinction angle modulation control is proposed. By changing the reference value of extinction angle, the reactive power flow of the converter station will be changed and part of the reactive power from fixed capacitors will provide a real contribution to the strength of AC system. The effect of the proposed method is validated and compared with commutation failure prediction control that is used in practical HVDC projects. The results show that the extinction angle modulation can help to make the AC system stronger, optimize system response under ac disturbance and reduce the risk of commutation failure, which has better effect than commutation failure prediction control.