Search Results (4)

The development of high-performance DC circuit breakers (DCCBs) and rapid fault detection schemes is a crucial and challenging part of advancing Modular Multilevel Converter (MMC) HVDC grids. This paper introduces a new current-limiting DCCB that uses the differential discharge times of shunt capacitors to generate artificial current zero-crossings, thus facilitating arc quenching. This mechanism significantly reduces the effect of fault currents on the MMC. The shunt capacitors and arresters in the proposed breaker also offer voltage support during faults, effectively stopping transient traveling waves from spreading to nearby non-fault lines. This feature creates an effective line protection boundary in multi-terminal HVDC systems. Additionally, a fast fault detection scheme with primary and backup protection is proposed. A four-terminal MMC-HVDC (±500 kV) simulation model is built in PSCAD/EMTDC to validate the scheme. The results demonstrate the excellent fault detection performance of the proposed method. The voltage and current behavior during the interruption process of the new DCCB is also analyzed and compared with that of a hybrid DCCB. Full article

A reliable and cost-effective mechanical direct current circuit breaker (DCCB) is a promising solution for DC interruption. However, the typical mechanical DCCB has difficulty in interrupting a rated current, because the high oscillating current superimposed on the rated current generates a steep current slope at current zero-crossing (CZC) points, which makes it difficult for the vacuum interrupter to extinguish the arc. The objective of this paper is to present a novel DCCB topology with a gradually increasing counter-current. It utilizes a full-controlled converter, a semi-controlled full bridge, and an LC oscillation branch to generate a gradually increasing counter-current, which is superimposed on any fault current and generates a smooth current slope at CZC points. The proposed DCCB topology is modeled with PSCAD, and the current slope and the initial transient interruption voltage (ITIV) at CZC are analyzed and compared with the typical mechanical DCCB. The results indicate that the current slope at CZC decreases by 57–84% in full-range current interruptions, and the ITIV can be reduced by the same extent. Additionally, the performance of the proposed DCCB is evaluated in a four-terminal HVDC system. A cost and performance comparison is conducted among the main topologies. The obtained results show that the proposed DCCB is a reliable solution for the multi-terminal HVDC system. Full article

The work in this paper is applied to the Zhangbei Power grid. In the flexible direct current (DC) power system, the fault current rises extremely fast when a DC fault occurs. The requirements for the peak of breaking current and fault energy absorption of DC circuit breakers (DCCBs) increase linearly, which significantly increases the cost of the equipment. Therefore, in order to reduce the design difficulty of DCCBs, this paper proposes a strategy to control energy after the fault occurs. Firstly, the energy dimension is added on the basis of the traditional vector control of MMC, which constitutes a three-dimensional energy direct control. Subsequently, the architectures of energy fluctuation control and feedforward control are proposed. The influencing mechanisms for the peak fault current, peak fault voltage and energy dissipation are analyzed. Finally, the simulation of energy fluctuation control and feedforward control is constructed on PSCAD/EMTDC. The simulation results show that the energy fluctuation control is obviously better than the conventional three-dimensional energy control, and the feedforward energy control is further improved on this basis. Compared with the conventional vector control, the peak energy is reduced by 45.43% and the peak current is reduced by 25.39%, which helps to simplify the equipment design and reduce the equipment cost. Full article

While traditional AC mechanical circuit breakers can protect AC circuits, many other DC power distribution technologies, such as DC microgrids (MGs), yield superior disruption performance, e.g., faster and more reliable switching speeds. However, novel DC circuit breaker (DCCB) designs are challenging due to the need to quickly break high currents within milliseconds, caused by the high fault current rise in DC grids compared to AC grids. In DC grids, the circuit breaker must not provide any current crossing and must absorb surges, since the arc is not naturally extinguished by the system. Additionally, the DC breaker must mitigate the magnetic energy stored in the system inductance and withstand residual overvoltages after current interruption. These challenges require a fundamentally different topology for DCCBs, which are typically made using solid-state semiconductor technology, metal oxide varistors (MOVs), and ultra-fast switches. This study aims to provide a comprehensive review of the development, design, and performance of DCCBs and an analysis of internal topology, the energy absorption path, and subcircuits in solid-state (SS)-based DCCBs. The research explores various novel designs that introduce different structures for an energy dissipation solution. The classification of these designs is based on the fundamental principles of surge mitigation and a detailed analysis of the techniques employed in DCCBs. In addition, our framework offers an advantageous reference point for the future evolution of SS circuit breakers in numerous developing power delivery systems. Full article