A decentralized protection scheme for converters utilizing a DC-link inductor

This paper proposes a fully passive protection scheme for DC link inductors whose geometry is characterized by a substantial distance between the rectifier and inverter stations. Inductors of this type can be found intrinsically in very long high-power cables-as in HVDC transmission for example-as well as in DC-links for high-power current source inverters. In such applications the inductor must be duly protected against overvoltages as well as against overcurrents potentially occurring as consequence of an open-circuit or a short-circuit fault respectively. The distance between the inductor terminals prevents the use of well-known localized protections like, for example, simple freewheeling diodes. A key role in the protection scheme proposed by the authors is played by the largely available transient suppressor diodes (often commercially identified as "Tranzorbs") and the solution is kept very simple and reliable by employing only rugged diodes and thyristors. The protection relies only on the energy stored in the inductor without the need of any external supervision circuit or any information exchange between the distant inductor terminals. Experimental results are presented and a generalization of the scheme to a broader application is also introduced