Enhancement of Commutation Reliability of an HVDC Inverter by Means of an Inductive Filtering Method

A new filter-commutated inverter (FCI) is proposed in this paper to enhance the commutation reliability of the HVDC systems applied in the high-voltage fields. The topology of the FCI is established based on an inductive filtering method, which mainly consists of a new converter transformer, fully tuned (FT) branches, inverter bridges, and a related control system. Unlike the traditional line-commutated inverter (LCI), the equivalent commutating impedance of the FCI includes not only the transformer leakage impedance but also the total impedance of the FT branches. The mathematical model is established to express such equivalent commutating impedance. Based on this, the commutation performance of the FCI is investigated in detail by comparing with LCI. Besides, the commutation reliability is evaluated under different operating conditions (e.g., normal operation, balanced, and unbalanced faults). Both the simulation and the experimental results validate the theoretical analysis, and indicate that the FCI with the use of the inductive filtering method can greatly increase the commutation margin of the HVDC systems, enhance the commutation reliability of the inverter, and prevent the occurrence of commutation failures.