Modified Z-Source DC Circuit Breaker With Enhanced Performance During Commissioning and Reclosing

Solid-state dc circuit breaker (SSCB) plays a very important role in the dc system protection against fast rising overload and short-circuit faults. Among various SSCB topologies, z-source dc circuit breakers (ZSCBs) have a great ability to interrupt the fault at a much faster rate, without even using a fault sensing circuit. However, ZSCBs suffer from various issues such as: 1) high starting current in the main thyristor (SCR), 2) unwanted power flow in the load during commissioning and reclosing of ZSCBs, and 3) negative current flow through the load at starting/reclosing of the ZSCB. These problems arise due to the fact that the z-source series capacitor stays charged even after the fault is interrupted or cleared. Unwanted power flow, negative current circulation in the load needs special attention especially in unidirectional loads and also in electromechanical systems. Hence, this article proposes a modified ZSCB to address the aforementioned problems. The proposed topology employs power semiconductor devices such as IGBTs to discharge the capacitor before the next interruption cycle. Initially, a detailed analysis, with simulation and experimental validation showing the issues with the existing ZSCB is presented. Later, a detailed analysis of the proposed modified ZSCB is presented, followed by an extensive simulation and experimental validation on a laboratory scale 120-V/3.5-A (400 W) prototype.