Analysis and Control of a Hybrid DC Circuit Breaker to Protect Multiterminal VSC-HVDC Grid and Stabilize DC Voltage Oscillations

The integration of DC circuit breakers (DC CBs) and DC reactors (DCRs) is essential for protecting multiterminal voltage source converter high voltage direct current (MT-VSC-HVDC) systems and limiting both the magnitude and rate of rise of fault current. However, the inclusion of large DCRs increases the electrical distance among VSCs and might destabilize DC voltage dynamics. This research studies this challenge and identifies the stability limits for the incorporation of large DCR values. Furthermore, a novel DC current damping control (DC CDC) strategy is proposed and implemented on hybrid DC CBs. The hybrid DC CB incorporates a supercapacitor full-bridge submodule in its main branch to operate as a virtual (frequency-shaped) resistor and dampen system oscillations. Time-domain simulations validate the effectiveness of the DC CBs in protecting the MT-VSC-HVDC system and mitigating DC voltage oscillations.