Recently, studies on connecting distributed generation (DG) to power distribution systems through DC links have been actively conducted. When a fault in feeder of this power distribution system occurs, a voltage dip can happen in the grid. In order to prevent voltage dips, there are several solutions such as the application of a superconducting fault current limiter (SFCL). If a SFCL with a larger impedance is applied, the voltage dip of the grid is effectively prevented. However, this action can bring about the malfunction or the delayed operation of the over-current relay (OCR) due to the decreased fault current, which causes another problem of protection coordination between the protective relays. On the other hand, if the impedance of the SFCL is too low, excessive reactive power is supplied by the fault ride-through (FRT) regulation and the active power is reduced. This causes an active power imbalance on the DC link and increases the DC link’s voltage. As previous solutions to prevent the rise of DC links’ voltage, the deloading method and the application of a chopper resistor have been suggested. In this paper, a technique called active power tracking control (APTC), was proposed to suppress the rise of DC links’ voltage. Case studies considering the impedance of SFCL in the constructed power distribution system were carried out, and the rise of DC links’ voltage could be effectively suppressed without any significant delay in the operation of the OCR. This study is expected to solve both the voltage dip of the grid and the rise of DC links’ voltage when distributed generation is connected to a grid.

Due to the increase in DC load and DC Power generation, the need for DC power system is emerging. Accordingly, FRT (fault ride through) and LVRT (low voltage ride through), which are related regulations for renewable energy sources, have been enacted, and operation algorithms of each converter are required for this. However, the operation of the converter according to LVRT regulations causes DC voltage fluctuations. In the current study, DC voltage fluctuation is suppressed through converter control of DC-linked battery. The controller was designed from the relational equation between DC voltage and instantaneous power of battery. The pattern of DC voltage fluctuations to the output of the PV (photovoltaic), which is a DC power generation source, was confirmed, and voltage fluctuation suppression was verified by applying the designed converter cooperation algorithm and controller.

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In this paper, direct current (DC) fault current limiting and interrupting operation of hybrid DC circuit breaker (DCCB) using double quench, which consists of DCCB, a series resonance circuit, power electronic switch, surge arrestor, two separated current limiting reactor/resistor, and two superconducting elements, were suggested. The suggested hybrid DCCB can perform the interrupting operation after twice or once DC fault current limiting operation according to DC fault current amplitude. To verify the effective operation of the suggested hybrid DCCB, the modeling for the components of DCCB, the surge arrestor, and the SCE was carried out and its DC operational characteristics were analyzed. Through the analysis of the modeling results for the suggested hybrid DCCB, the advantages of hybrid DCCB were discussed.

DC faults cause severe disruption in not only the DC system but also the AC system because the fault current is very large and rapidly increases. The DC circuit breaker used to separate the DC faults from the power system is still being researched, but it is very expensive due to the use of multiple power semiconductors to interrupt a large fault current in a short time. However, if the quench characteristic of a superconductor is used, the amplitude of fault current can be reduced. Therefore, it is possible to effectively interrupt a large fault current even if a relatively cheap mechanically passive DC circuit breaker is used. In the current study, a superconducting hybrid DC circuit breaker is proposed, and the limiting characteristics of each element are analyzed. By using two superconducting elements, the quench occurs sequentially twice according to the magnitude of the fault current, and the current-limiting reactor and resistance are used. If a current-limiting reactor is used in the DC system, the fault current rises slowly at the beginning of the fault, and the use of resistance can reduce the magnitude of the fault current. The inductance of the current-limiting reactor and resistance parameter settings of the hybrid DC circuit breaker was analyzed by the step-changing case method, and the interrupting characteristic of the DC circuit breaker was improved.