Efficient integration of buck converter into an active rectifier for DC-fault current limitation in DC networks

Abstract

Voltage Source Converters (VSCs) operating as active rectifiers inherently lack current-limiting capabilities for faults occurring on the DC side due to the presence of freewheeling diodes in IGBT or MOSFET structures. This limitation leads to uncontrolled fault currents, flowing from the AC to the DC network, that can jeopardize the safety of power electronic components. Additionally, the challenge is compounded in DC networks, where DC circuit breakers must interrupt high fault currents, fed by the AC side, without the benefit of current zero crossings. To address these issues, this paper presents a novel topology that integrates a classical buck DC/DC converter into a VSC to regulate the currents of faults occurring in DC network, thereby improving the protection of the converter and aiding DC circuit breakers in interrupting the fault. The advantage of the proposed topology lies in that under normal operating conditions, the buck converter is totally bypassed, thus improving the efficiency of the topology. When a fault is detected within the DC microgrid, the buck converter is connected in series with the VSC to control the current flowing from the AC to DC network. Simulation results using MATLAB/Simulink validate the effectiveness of the proposed topology in completely controlling the current at the DC side of converter, thus demonstrating significant improvements in fault management, system reliability, and converter protection.