Calculating the coupling reactance voltage of HVDC power transmission system based on new-type converter transformer

In a traditional 12-pulse HVDC power transmission system, because of the coupling reactance voltage in AC bus, the commutation of one bridge will lead to a certain distortion of AC voltage in the other bridge, while the existence of voltage distortion can make the two bridges fail in commutation simultaneously or successively. The HVDC power transmission system based on new-type converter transformer has a new electrical tie-line structure and its change of current transformation relation can influence the coupling reactance voltage in AC bus. This paper analyzes this relation in theory and builds a mathematical model to calculate the new coupling reactance voltage. Simulation results show that the theory is right and the model is ideal. It is expected that this study can be of help in solving similar problems existing in commutation failures.