Availability evaluation of Multi-Terminal DC networks with DC circuit breakers

DC / DC converters as DC circuit-breakers in HVDC networks operation

“…The time between when the short-circuit occurs and when it is detected is crucial in this task, and actually is in the order of ms [16], [8] and [9], which represents some cycles in the DC/DC converter switching frequency (between 1-20 kHz [5]). Obviously, if we increase the switching frequency we can obtain better behaviors from the point of view of breaker.…”

“…However, if we use the DC/DC converter as DC circuit breaker, we obtain the curve shown in figure 7b. We can observe in it that once the short-circuit happens, there is a time τ 1 while the short-circuit is not detected and the current increases, this τ 1 is in the order of 5 ms [16], [8] and [9]. Once the short-circuit is detected, we observe a time, τ 2 , which we can define as the time elapsed since the fault is detected and the current through the inductance is zero, instant in which the switches are opened.…”

“…Another interesting fact is that DC/DC converters could be also employed as DC circuit-breakers. This property is very important in the further development and establishment of MT-HVDC networks, because until now there is no device which can assure safety of an electric circuit from damage caused by overload or short circuit, as it exits in AC systems [8], [9] . For this reason, and because the proposed DC-DC converter includes an AC stage, there are instants in which the current passes through zero.…”

Analysis of VSC-based HVDC system under DC faults

“…In terms of DC faults, most of the work focuses on fault detection and isolation, either; through the use of DC Circuit Breakers [10] or via utilization of existing AC Circuit Breakers and fast acting switches [11,12]. Analysis of the effects of a line-toline fault, and a brief analysis of line-to-earth faults on VSC systems was carried out in [13] - [15].…”

“…Simulation results using Matlab/Simulink toolbox SymPowerSystem will be provided to verify all mathematical analysis. Unlike line-to-line faults, which experience total discharging of the DC link capacitor [10,13], line-to-earth faults result in a partially connected system, with the DC voltage unable to fall to zero due to the recharging of the DC link-capacitors and cable capacitance. Oscillation of the DC Voltage, and hence, the system fault current is dependent on the formation of current loops created by shared earths within the system.…”