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Continuous expansion in the scale of high-voltage flexible direct current (DC) transmission systems has resulted in higher requirements for clearing fault currents. The hybrid DC circuit breaker, as the most promising DC circuit breaker, can effectively isolate and remove the faults that occur in DC power grids. At present, hybrid DC circuit breakers can be divided into two types: two port and multiport. Two-port DC circuit breakers are used in a single line and have the advantages of simple and flexible control. Multiport DC circuit breakers are used at the DC bus and control the fault isolation operation of multiple lines connected to the bus. When compared to two-port DC circuit breakers, multiport DC circuit breakers significantly reduce the number of configurations, reduce costs, and occupy less space. First, this article classifies hybrid DC circuit breakers into two-port and multiport categories, and refines and organizes the two major categories. Then, it analyzes the functionality, reliability, control complexity, and economy of each scheme based on the topology structures proposed in the current literature. Finally, prospects for future research on hybrid DC circuit breakers are presented. [ABSTRACT FROM AUTHOR]

The multi-terminal modular multi-level converter-based high voltage direct current (MMC-HVDC) grid with short circuit protection equipment (SCPE) is so complex that it is difficult to estimate its fault current and analyze the performance of SCPE by conventional time-domain numerical calculation method, it meets three big obstacles. This paper has made significant progress in overcoming these obstacles. 1). By applying the modern electrical circuit theory, a systematic formulation of the differential equation set for fault current calculation is developed to avoid a lot of complex and cumbersome matrix manual calculations. 2). A novel Y-Delta transformation in the s-domain is proposed to develop an eliminating virtual node approach for a complex MMC-HVDC grid, including the ring, radial, and hybrid topologies. 3). It is difficult to solve the equivalent circuit of MMC-HVDC grid with SCPE since SCPE is a timevariable-nonlinear circuit. A canonical voltage source model of SCPE is established to transform the time-variable-nonlinear circuit into a piecewise linear circuit. Based on the three significant progresses, a DC fault current fast-computing method of MMC-HVDC grid with SCPE is put forward to deal with all kinds of MMC-HVDC grids with several kinds of SCPEs. Then, the performance of several kinds of SCPE is analyzed and compared by this method. Consequently, the proposed DC fault current fast-computing method is a new powerful tool to estimate the fault current of MMC-HVDC grid and analyze the performance of SCPE. [ABSTRACT FROM AUTHOR]

In recent years, with the rapid development of high-voltage flexible direct current (DC) transmission systems, more and more multi-port high-voltage DC systems have been successfully put into operation. Therefore, the number of connecting ports on the DC bus is gradually increasing, which necessitates higher requirements for clearing fault current. To better protect the DC power grid, this paper integrates a DC fault current limiter with a multi-port DC circuit breaker. This article proposes a modular cascaded multi-port hybrid DC circuit breaker topology. It also elaborates on the topology structure, working principle, and control program under three different fault conditions. It completes the theoretical derivation and analysis of the circuit breaker fault isolation process, as well as the parameter design of the core components. Finally, a model is established in PSCAD/EMTDC for simulation verification. The application performance of the circuit breaker in four-terminal DC systems is studied and analyzed, and the current-limiting effect of the multi-port DC circuit breaker proposed in this article is demonstrated. In addition, the disconnection performance and energy consumption of the arrester have been improved to a certain extent, which has good feasibility and economy. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

As the penetration of distributed energy resources (DER) has increased, research on direct current (DC) power transmission and distribution has been actively performed. The DC system has the advantage of high-power transmission efficiency. However, it has a very large and rapid increase in fault current in the DC system directly after a fault occurs. As one of the countermeasures, studies on the application of the superconducting fault current limiter (SFCL) into the DC system have been conducted to protect major facilities from DC fault current, which is expected to alleviate the power burden on the DC circuit breaker through its quench operation. Among the studied DC SFCLs, the trigger-type DC SFCL using a transformer, which can achieve the peak DC fault current-limiting operation, has been suggested. However, the DC fault current-limiting operation, in the case of the DC SFCL with a current-limiting reactor (CLR), was analyzed to not be effectively executed in the steady state since the transient state directly follows the fault occurrence. In this paper, the DC fault current-limiting operation of a twice-quench trigger type SFCL using a transformer considering magnetizing current and its CLR was analyzed. Through DC fault current-limiting experiments according to the inductance of its current-limiting reactor (CLR), the effective current-limiting design of twice-quench trigger type SFCL using a transformer was described. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

As the utilization of DC systems increases worldwide, the importance of DC cutoff technology is increasing. We proposed a hybrid DC cutoff technology combining an SFCL (superconducting fault-current-limiter) and a mechanical DC circuit breaker. This model can perform a fault-current-limiting operation through the quenching of the SFCL and a breaking operation through an artificial cutoff zero point of a mechanical DC circuit breaker. In particular, the SFCL is responsible for the growth of the initial fault current according to the DC characteristics. As the DC system's supply and demand increase, the DC system's capacity also increases. Therefore, the fault-current-limiting capability of the SFCL should be increased according to the increasing DC system breaking capacity. The fault-current-limiting capability can be increased by increasing the superconducting wires used in the SFCL. Current commercially available SFCLs use bifilar-helical-type and bifilar-spiral-type winding methods. These have the disadvantage of increased volume with increased capacity. To compensate for these disadvantages, we proposed a bifilar-meander-type winding method. In this paper, a new bifilar-meander-type winding method was introduced. In addition, the structural and electromagnetic parts of the existing winding method and the bifilar-meander-type winding method were compared and analyzed for differences. The program used for this analysis is the electromagnetic analysis Maxwell program. As a result, it was confirmed that the bifilar-meander-type winding method is superior to the conventional bifilar-helical and bifilar-spiral types. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents the DC fault transient study of a meshed DC grid with high-temperature superconducting (HTS) HVDC cables to integrate offshore wind power. A four-terminal meshed DC grid model with a ±100 kV DC voltage rating is developed. DC circuit breakers (DCCBs) are implemented in the DC grid to deal with DC cable faults. To conduct the fault transient study, the fault scenarios with different fault locations and protection delays are studied. The sensitivity study versus different DC fault locations reveals that the faults on the faulted cable will not cause the quenching of healthy cables. The sensitivity study considering different DC fault protection delays demonstrates that the HTS cables have a current-limiting effect and the long delay of DC fault protection does not result in large fault current and the quenching of healthy cables. Extensive simulations in PSCAD/EMTDC validate the founding. [ABSTRACT FROM AUTHOR]

This paper proposes a thyristor-based hybrid DC circuit breaker (HDCCB), which is composed of a fast mechanical circuit breaker and an LC resonant circuit with thyristor switches. The proposed HDCCB provides a zero-crossing point for fault current by injecting a resonant current in the reverse direction of the fault current. The proposed HDCCB has a low conduction loss in normal operation using a mechanical circuit breaker, and it offers the advantages of low cost, high reliability, and large capacity using thyristor switches instead of IGBT switches. It also has the design flexibility to adjust the magnitude of the injection current depending on the fault current level. A bidirectional HDCCB is also proposed by adding several components to the developed unidirectional HDCCB, which can offer compact system size and low system cost. Design considerations of the proposed structure are discussed. The validity of the proposed HDCCB is verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

Piezoelectrically actuated fast mechanical switches provide a low-loss conduction path in hybrid circuit breakers for protecting medium-voltage direct-current systems. As the desired actuation speed approaches the driving limit of a piezoelectric actuator, excessive vibration starts to dominate its underdamped travel curves, resulting in insulation failures and delayed switching in the fast mechanical switch. To improve the underdamped travel curves into critically damped travel curves, several switching motion control schemes with active damping filters are proposed in this paper. The switching motion controllers are based on an electromechanical model of a fast mechanical switch with experimentally identified parameters. According to hardware implementation tests, the proposed closed-loop control schemes optimized the switch travel curves with a 56% reduction in the undershoot and a 75% reduction in the settling time. Equipped with the critically damped travel curves, the piezoelectrically actuated fast mechanical switch is better suited for sequential submodule operations to reduce the interruption time, the peak current and the fault energy to be absorbed in hybrid circuit breakers. [ABSTRACT FROM AUTHOR]

High-voltage direct current (HVDC) circuit breaker development and deployment strongly depend on the testing process, which ensures that the HVDC circuit breakers will satisfy design requirements. This article presents an HVDC circuit breaker test bench circuit configuration that can provide controllable large output currents to simulate different fault conditions for the current breaking test and high output voltage for the dielectric withstand test. The current breaking test circuit is based on multiple cascaded power converters connected in parallel to provide the necessary output current capability. Each cascaded power converter is composed of multiple cells that are operated by a phase-shifted pulsewidth-modulated signal for greater controllability and higher quality of the output waveform. The dielectric withstand test circuit is a simple high-voltage source with a low power rating that can also be used to charge the test bench and the internal circuitry of the circuit breaker that is to be tested. The proposed test bench ensures that fault conditions can be replicated accurately and offers greater flexibility by being able to test mechanical, semiconductor-based, or hybrid HVDC circuit breakers with different current and voltage ratings on the same hardware without any changes. The idea and the operating principle of the proposed test bench are verified experimentally on a downscaled system that consists of three cascaded power converters connected in parallel with three cells per cascaded power converter and with a total equivalent switching frequency of 92.5 kHz. [ABSTRACT FROM AUTHOR]

The modern DC grid is predominantly inductive due to several factors, including line inductance, and the use of current-limiting inductors to control fault current rising rates. These network inductances store a significant amount of energy during regular operation, which is either dissipated or freewheeled to ensure safe current breaking. This research article proposed a highly efficient bidirectional DC circuit breaker topology that not only provides safe current breaking but also effectively recovers the post-current breaking energy from the network's inductance instead of dissipation. An extensive simulation investigation is performed in PSIM software to test the breaker capability for a 400V/400A DC system and the laboratory-scale 48V/1A experimental setup has been developed and employed for further validation purposes. • Modern DC grids have large system inductance which stores significant energy during normal operation. • Developed a bidirectional DCCB topology with regenerative current breaking capability. • Provide efficient current breaking in highly inductive DC network. • Enhancing efficiency and safety of the DC grids by harnessing the energy stored in inductive components. [ABSTRACT FROM AUTHOR]

The high di/dt before zero-crossings easily leads to delayed or failed operations for the active current injection mechanical DC circuit breaker, especially for small direct current interruptions. The pre-charging process also makes this type of circuit breaker hard to realize repeat operations economically in the high voltage DC system. This paper proposes a novel DC circuit breaker and its design method that deeply coordinating a superconducting fault current limiter with the active current injection DC circuit breaker. This method significantly reduces di/dt before current zero-crossings and enables repeat operations economically. Besides limiting fault currents, the superconducting fault current limiter also charges the resonance capacitor flexibly in the circuit breaker, realizing the injected reverse current keep a constant proportion to the arbitrary fault current. Validations of the flexible capacitor charge and repeat operations are made by simulation and low voltage experiments. The charging times are within 2.5 ms and the reverse current keeps 1.2 to 1.7 times over the fault current under arbitrary conditions. Di/dt at current zero is reduced by 80% under 30% of rated interruption capacity. Flexible capacitor charge experiments are consistent with the simulation design. The superconducting tapes can recover within 300 ms to support repeat operations. [ABSTRACT FROM AUTHOR]

A new series-type hybrid circuit breaker (S-HCB) concept for dc fault protection is reported that is fundamentally different from other prior-art hybrid circuit breakers (HCB) or solid-state circuit breakers (SSCB) in the literature. The S-HCB conducts its load current through metal wires instead of power semiconductor switches and curtails its fault current to near zero throughout the entire opening process of a series mechanical switch. It offers the low on-resistance of the conventional mechanical contacts for normal operation and µs-scale fault response even faster than the fast-acting SSCBs. A proof-of-concept S-HCB prototype experimentally demonstrates the interruption of a fault current of 30 A within 10 μs at a dc voltage of 600 V. The operating principle, simulation, and experimental results are discussed in this letter. [ABSTRACT FROM AUTHOR]

DC circuit breakers (DCCBs) are used to clear short-circuit faults in several milliseconds. However, short-circuit fault current can reach extreme values. Fault current limiters (FCLs) can present high inductance values during the short-circuit fault period. Thus, they have received considerable attention for reducing the high current breaking requirements of DCCBs. Three types of magnetic flux-coupling solid-state FCLs are designed in this paper, which include mutual inductors and several power electronic switches. In addition, the FCL impedance can be controlled by power electronic switches. By comparing the current limit capacities and structural complexities among the three types of FCLs, a more applicable limiter referred to as a flux-coupling DC current limiter (FCDCCL) can be installed on VSC DC grids. Finally, a simulation model is built in PSCAD/EMTDC based on a ± 10 kV/400 A DC system. The simulation results verify that a significant change in the limiting current can be achieved by the proposed FCDCCL, which can be extended to actual VSC DC grids. [ABSTRACT FROM AUTHOR]

This letter presents a new low-voltage direct-current fault current bypass-based solid-state circuit breaker (SSCB) using silicon-carbide mosfets. The proposed SSCB provides the possibility to select the clamping voltage of metal–oxide varistors (MOVs) close to the nominal voltage of the dc system. This reduces voltage overshoots across the main switch and snubber components and extends the maximum allowable dc bus voltage on the SSCB. The MOVs are removed from the power line, and their leakage currents are completely eliminated. The clamping voltage of the MOV and its surge energy rating is considered to optimize the MOV. The dv/dt across the main switchis controlled by an auxiliary capacitor, where a design procedure is presented to optimize its value. Also, the stored inductive energy of the line inductor in dc systems is bypassed using an auxiliary branch and prevented from flowing through the faulty section to enhance the safety. LTspice simulations are presented to show the significance of the proposed SSCB. The experiments of 375 V/170 A/2.4 μs and 600 V/163 A/2.4 μs verify the effectiveness of the proposed design in practice. [ABSTRACT FROM AUTHOR]

Recently, with the development of renewable energy such as solar power and wind power, the dc grid has garnered attention and the dc circuit breakers essential to the dc grid have been actively studied. The dc solid-state circuit breaker (dc SSCB) can quickly break the fault current within 1 ms compared with a mechanical circuit breaker, which does the same in several tens of milliseconds. The previous thyristor dc SSCB cannot naturally charge the commutation capacitor for fault current breaking, and thus its control of operation is complicated. Thus, this article proposes a new thyristor dc SSCB, which can naturally charge the commutation capacitor without complicated switching operation. It can not only perform the fast breaking of fault current, but also the operating duties of reclosing and rebreaking. The operating characteristics of the proposed dc SSCB are verified by the experimental results. [ABSTRACT FROM AUTHOR]

DC fault protection is the bottleneck that restricts the development of modular multilevel converter based high voltage direct current (MMC-HVDC) system. Superconducting fault current limiters (SFCL) is an ideal protection device that can significantly limit short circuit current and enhance the fault tolerance ability of MMC-HVDC system. At present, several topologies of SFCLs have been proposed, but there is no systematical study of their current-limiting characteristics in MMC-HVDC. This paper studies the development process of DC short-circuit faults in MMC-HVDC system, and analyzes its demand for fault current limiting. Then, resistive type, saturated iron core type and hybrid type SFCL are modeled and their limiting effect of critical fault current under DC pole-to-pole fault is tested. By comparison, the current-limiting characteristics of three types of SFCL are concluded. Results show that resistive SFCL has best performance in steady state, while saturated iron core SFCL has best performance in transient state. The current-limiting characteristic of hybrid type SFCL is between the other two types. [ABSTRACT FROM AUTHOR]

Currently, we are developing an AC/DC conversion technology with the development of power semiconductors. Accordingly, DC is attracting attention because it is advantageous in the current transmission system. However, it has a problem that the cut-off technology required for DC system operation has not been secured yet. We are researching and developing a DC cut-off technology in several ways. We proposed a model that combines a superconducting fault current limiter and a DC circuit breaker. This is a configuration which a superconducting fault current limiter and a mechanical DC circuit breaker are connected in series. The superconducting fault current limiter limits the initial fault current and the mechanical DC circuit breaker cuts off the fault current. The mechanical DC circuit breaker consists of a high-speed DC switch, a LC divergent oscillation circuit and a surge arrester. This creates an artificial zero-point by affecting the blocking of the DC fault current according to the LC diverging oscillation circuit. In this paper, we analyzed the effect of the LC divergent oscillation circuit on the superconducting DC circuit breaker according to Reactor (L) and Capacitor (C). As a result, we analyzed the operating characteristics of the superconducting DC circuit breaker according to the application of the LC divergent oscillation circuit using the PSCAD/EMTDC program. Also, we confirmed the characteristics of the initial fault current limit rate of the superconducting fault current limiter and the possibility of controlling how the LC divergent oscillation circuit affects the DC arc generated at the opening of the mechanical DC contacts. [ABSTRACT FROM AUTHOR]

Medium voltage direct current (MVDC) power systems are in their early phase of development, but the lack of efficient and reliable DC circuit breakers is currently one of the most significant bottlenecks for widespread adoption of MVDC applications. Compared to protection devices in high voltage direct current (HVDC) systems, MVDC circuit breakers are expected to interrupt fault currents with higher rates of rise in more power-dense and more controllable structures. A hybrid approach with a piezoelectrically actuated fast mechanical switch in parallel to a solid-state circuit breaker is expected to meet the above requirements. A prototype of a 15 kV-class piezoelectrically actuated fast mechanical switch is presented in this paper. The prototype demonstrates an actuator opening time of 1 ms, a breakdown voltage of over 20 kV, and a continuous current rating of 500 A. After integrating the fast mechanical switch into a hybrid circuit breaker testbed, the fast mechanical switch was able to open within 1.5 ms and the fault was cleared within 5 ms. Therefore, piezoelectrically actuated fast mechanical switches can enable fast, reliable and controllable protection for various MVDC systems like electric ships, electric aircraft and microgrids that integrate distributed energy resources. [ABSTRACT FROM AUTHOR]

The DC short-circuit fault occurring on the overhead line endangers the modular multilevel converter based high voltage direct current (MMC-HVDC) grids. An optimized protection coordination (OPC) strategy with a global fault current limiting control is proposed to limit the DC fault current in this article, which can suppress the rising rate of the global fault current, and at the same time, the fault area can be identified quickly and the relevant DC circuit breakers can be pre-operated. To realize the OPC strategy, a rapid fault identification method based on the current change rate and Pearson correlation coefficient is designed. The proposed rapid protection strategy can decrease the peak value of DC fault current by reducing the rising rate of current and shortening the protection time. Simulation and experimental results verify the effectiveness of the proposed strategy under both balanced and unbalanced grid-side voltage conditions. The adoption of the proposed control is beneficial for MMCs to safely ride through DC short-circuit fault in a continuous operation manner. [ABSTRACT FROM AUTHOR]

Modular multilevel converter (MMC) based medium voltage DC (MVDC) distribution system has become a promising option in the future smart grid architecture due to many distinguishing features. However, MMC-MVDC distribution system is prone to face the short-term outage problem during bipolar DC faults, so how to implement DC fault ride-through (FRT) capability for MMC-MVDC is still a challenge. This paper intends to change the redundant half-bridge submodules (HBSMs) of the HB-MMC into the redundant full-bridge submodules (FBSMs), thus, a practical DC FRT method is proposed by using the combination of the hybrid MMC and the hybrid DC circuit breakers (CBs) for the MMC-MVDC system. Then, the DC fault current characteristics of the MMC with the proposed FRT method are discussed. Lastly, data analysis and simulations of a three-terminal MMC-MVDC system have been performed in PSCAD/EMTDC to validate the effectiveness of the proposed DC FRT method. The proposed DC FRT method is not only easy to implement, but also reduces the requirements and the investment of the DC CB. [ABSTRACT FROM AUTHOR]

Currently, power semiconductors (IGBT, Thyristor, etc.) are used for the stability and high reliability of DC system operation. However, we have proposed a current limiting DC circuit breaker with superconducting winding to improve the stability of the DC system. This is superior in terms of fast cut-off speed and economy of power semiconductors, and is suitable for changes to the Point to Loads DC system that will be expanded in the future. A superconducting DC circuit breaker is a model in which a superconducting current limiter and a DC circuit breaker are combined. The superconducting fault current limiter uses a superconducting wire made of GdBCO material to limit the initial fault current to lower the current level of the fault current, and the DC circuit breaker blocks the reduced fault current from the superconducting fault current limiter by configuring a mechanical cutoff switch, passive elements L, C and SPD. In this paper, this superconducting DC circuit breaker model was designed and tested by giving two variables, and the operating characteristics were analyzed. The first is the superconducting wire connection method, and the second is the power supply voltage. In addition, the initial fault current, the time when the zero point of the fault current is generated, and the time when the shutdown is completed were compared and analyzed. As a result, it was confirmed that the helical type showed a higher current limiting rate than the spiral type, and the result of reaching a fast current zero point was confirmed. [ABSTRACT FROM AUTHOR]

DC circuit breaker plays an important role in the reliability of HVdc system, but the large number of expensive press-pack insulated-gate bipolar transistors (IGBTs) is used at present, which is a serious impediment to HVdc development. Thus, the low-price integrated gate commutated thyristor (IGCT) becomes a promising alternative device. This letter presents a low-cost HVdc circuit breaker with high current breaking capability based on IGCTs. The topology and principle of the proposed HVdc circuit breaker are introduced at first. Then, the parameter design is analyzed. A scaled-down test successfully demonstrates the high current breaking capability of 15 kA. In the end, the cost comparison shows that this scheme can achieve 61.8% cost reduction of the commutation branch. [ABSTRACT FROM AUTHOR]

To ensure the reliability and flexibility of direct current (dc) system, direct current circuit breakers (DCCBs) are in urgent demand. Compared with solid-state and hybrid DCCBs, mechanical DCCBs have features of low operating losses and investment, showing bright application prospects. Until now, without concern about transient operating voltages (TOV) in the whole dc system, the reclosing of DCCB is still an open problem, and it is the emphasis of this article. First, overview of TOV in typical pseudobipolar dc system is introduced. Then, focused on hardware, electrical characteristic of a novel mechanical DCCB is analyzed, and verification tests are carried out in our laboratory. By taking interaction between the dc system, DCCB, and lines into consideration, distribution patterns of TOV under different faults and its mechanism are revealed. Based on TOV, novel reclosing strategy is proposed for mechanical DCCBs, and case studies are conducted in PSCAD/EMTDC for verification. Remarkable advantages of novel reclosing strategy are: fault type could be identified without operating any component of DCCB after fault current interruption; no risk of reclosing a permanent fault point; an explicit time could be reserved for the dielectric recovery of temporary fault point. [ABSTRACT FROM AUTHOR]

Power flow controllers and circuit breakers are important devices in a DC grid, and combining them and expanding their ports can save many components. This paper proposes an integrated multiport DC power flow controller with a DC circuit breaker that can achieve power flow control and fault removal on multiple DC lines during steady and fault states, respectively. First, the device's topology based on modular multilevel converters is proposed, and the principles of power flow control and self-power balance based on bridge arm voltage are introduced. Second, it is improved by adding a fault removal capability. The equivalent circuit and fault currents in different time sequences are analyzed, and the component parameter selection method is designed. Third, in the PSCAD/EMTDC, the power flow control and fault removal capabilities are verified using three conditions: flow control, line fault, and bus fault. Finally, the number of components and steady-state losses are analyzed. Overall, the proposed device has power flow control and fault removal functions as well as a certain limiting effect on the fault current, which greatly reduces the system construction cost. [ABSTRACT FROM AUTHOR]

Faults on the dc line threaten the stability and reliability of the modular-multilevel-converter-based HVDC (MMC-HVDC) systems. Fault current limiting is one of the crucial steps to handle the dc line fault. In this paper, a mutual-inductance-type fault current limiter (MFCL) using coupled reactors and few power electronic switches is proposed. Compared with the conventional dc reactors, it can automatically limit the fault current during the current rising stage with an increased equivalent inductance and accelerate the decline of the current by reducing the inductance of the discharge circuit. Consequently, the fault current stress and the total capacity of required arresters are decreased. Compared with the existing power electronic-type fault current limiters, the proposed MFCL provides an inexpensive and potential solution to the suppression of dc fault current using simple fault current limiting topology with fewer power electronic switches. The simulation case study and hardware experiments are carried out to verify the performance and practicality of the proposed MFCL. [ABSTRACT FROM AUTHOR]

SCR-based solid-state dc circuit breaker (SCR-DCCB) topologies have been widely studied for replacing the traditional expensive insulated-gate bipolar transistor (IGBT) based DCCB. Yet, the existing SCR-DCCB cannot be actively turned-off since SCR is a half-controlled device. In this letter, an active Z-source DCCB (AZ-DCCB) is proposed by the combination of IGBT and SCR. The proposed AZ-DCCB has advantages of simple and compact topology, economical design, low conduction losses, and active and bidirectional current breaking capacity. The operation process of the proposed AZ-DCCB is discussed in detail, and the designing principle of circuit parameters is also presented. Experimental results verified the effectiveness of the proposed AZ-DCCB. [ABSTRACT FROM AUTHOR]

This paper proposes a coupled inductor-based hybrid dc circuit breaker topology with zero current switching for fast fault interruption in dc systems. A series resonant circuit comprising of the secondary winding of a two-winding coupled inductor and a charged capacitor (commutation capacitor) is switched on during fault to inject a counter-current pulse, and, consequently, force a zero crossing of fault current. Proposed solution facilitates arcless breaking for a mechanical circuit breaker due to zero current turn-off. The proposed circuit breaker exhibits fast fault response ($\sim$ 30  $\mu$ s), and the response time is programmable based on the design of the coupled inductor and commutation capacitor. Furthermore, presented solution mitigates the requirement of energy-absorbing elements for demagnetizing the dc network following fault interruption, in contrast to conventional dc breakers. The paper also presents two modified circuit-breaker topologies to achieve unipolar voltage profile on the capacitor, which will enable the use of electrolytic capacitors for commutation so that the capacitor stack size is reduced in high-voltage applications. Detailed analysis and design equations are presented to explain the operation of the proposed topologies. Functionality of the proposed circuit breakers is verified through simulation, and experimental results are based on two laboratory prototypes. [ABSTRACT FROM AUTHOR]

Medium voltage direct current (MVdc) distribution system has numerous advantages over medium voltage alternative current distribution system. However, two shortcomings of the existing hybrid direct current circuit breaker (DCCB) with load current switch, including high construction cost and high operating losses, have constrained the application of existing hybrid DCCBs in MVdc distribution system. To overcome these two shortcomings, a novel multi-port hybrid DCCB with negative voltage source (NVS) has been proposed in this paper. First, the general topology and working principle of the multi-port hybrid DCCB with NVS are presented. Then, focused on the current commutation method and economic performance, comparisons between different hybrid DCCBs have been carried out. The analysis shows that by using multi-port hybrid DCCB with NVS, the construction cost could be reduced dramatically and the operating losses could be reduced to be comparable with alternative current circuit breaker, which are negligible. In the end, to fill the blank of experimental research, based on the topology of multi-port hybrid DCCB with NVS, a prototype with rating voltage of 2 kV has been established, and the test result have verified the multi-port hybrid DCCB with NVS. [ABSTRACT FROM AUTHOR]

Conventional air dc circuit breakers face the problems of complex arc motion control and arc back-commutation. In order to simplify the arc motion control, solve the arc back-commutation, and shorten the breaking time, this paper proposes an arc squeeze method, which stretches the arc in the insulating slit to make the arc voltage rise. The arc voltage acts as counter voltage to the system voltage and causes the current to cross zero, and then, current interruption is completed. For the experimental study, a test device was designed and made. The effects of different structural parameters (penetration depth of insulating plate, slit cross section circumference, and area) and external parameters (operating speed of insulating plate and peak circuit current) on the arc voltage increase during the breaking process were studied and analyzed. The interruption time of fault current with maximum value within 12–22 kA is quite short (about 5 ms). [ABSTRACT FROM AUTHOR]

It is known that most of the renewable energy resources are the DC type. However, DC microgrids do not have zero crossing in current and voltage. This results in serious concerns about the circuit breaking and fault current limiting in the power system. Conventional thyristor‐based DC fault current limiters (FCLs) may provide possible solutions for this problem. Unfortunately, a permanent interruption would arise on the system in case of a temporary fault. For this reason, this proposal aims to develop an integration system of the circuit breaker and FCL using a feedback‐controlled zero‐voltage switching method. In this proposed model, a load current is detected and an appropriate switch signal is thus generated by the controller based on the feedback‐control strategy. Once the load current is beyond the predefined value, the switch will be opened to reduce the current immediately for a period of time set by the timer in advance. Then, the switch will be closed again to raise the current continuously until the overload threshold is reached. The switching transition duration is located at the resonant zero voltage, so that no switching power is required. Both simulation and practical performance results confirm that an expected constant load current can be well controlled over an expected range. [ABSTRACT FROM AUTHOR]

The main weakness of the half-bridge modular multilevel converter-based high-voltage direct current (MMC-HVDC) system lies in its immature solution to extremely high current under direct current (DC) line fault. The development of the direct current circuit breaker (DCCB) remains constrained in terms of interruption capacity and operation speed. Therefore, it is essential to limit fault current in the MMC-HVDC system. An enhanced fault current-limiting circuit (EFCLC) is proposed on the basis of fault current study to restrict fault current under DC pole-to-pole fault. Specifically, the EFCLC consists of fault current-limiting inductance L F C L and energy dissipation resistance R F C L in parallel with surge arrestor. L F C L reduces the fault current rising speed, together with arm inductance and smoothing reactor. However, in contrast to arm inductance and smoothing reactor, L F C L will be bypassed via parallel-connected thyristors after blocking converter to prevent the effect on fault interruption speed. R F C L shares the stress on energy absorption device (metal oxide arrester) to facilitate fault interruption. The DCCB requirement in interruption capacity and breaking speed can be satisfied effortlessly through the EFCLC. The working principle and parameter determination of the EFCLC are presented in detail, and its effectiveness is verified by simulation in RT-LAB and MATLAB software platforms. [ABSTRACT FROM AUTHOR]

With the development of HVdc transmission technology, the isolation of dc faults is becoming increasingly important. As the most effective solution, hybrid HVdc circuit breaker (CB) is not mature enough, which has restricted its engineering application. Accordingly, this paper proposes an auxiliary dc CB scheme suitable for HVdc grid. In this scheme, the traditional half-bridge modular multilevel converter (MMC) is partially innovated to have the ability of auxiliary breaking operation. With the effect of the MMC auxiliary breaking (MAB) operation at both ends of the fault line, the dc fault current can be easily interrupted and isolated by low-cost CB unit installed in the dc transmission line. The equivalent circuit under MAB process is analyzed, and the fault isolation sequences are designed. Furthermore, the economic comparative analysis among three schemes is performed. Finally, a four-terminal bipolar HVdc grid test model is built in PSCAD/EMTDC; in addition, an MMC prototype with proposed scheme is also developed. The simulation and experimental results validate the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

With the rapid development of multiterminal direct current (MTDC) grids, high-voltage direct current circuit breakers (HV-DCCB) capable of interrupting currents within 5 ms are in urgent demand. The mechanical DCCB has always been one of the main proposals for HV-DCCBs. The current commutation is the prerequisite for mechanical DCCBs to interrupt currents successfully. Focused on the current commutation difficulty, a novel mechanical DCCB has been investigated in this paper. A simulation model of the novel mechanical DCCB in MTDC system for fault current interruption was established in PSCAD. By analyzing the simulation results, the detailed transient varying patterns of current, voltage, and energy in the novel mechanical DCCB during its interruption process are revealed. To verify the feasibility of the novel mechanical DCCB, a prototype was developed in the lab, and current interruption tests were carried out on the prototype. Experimental results have shown that a current of 5.3 kA can be interrupted by the prototype within 3 ms. In the end, failures that occurred in initial experiments are discussed and relative protection measures have been proposed. By adopting these measures, failures are successfully avoided and the normal operation of the novel mechanical DCCB are ensured. [ABSTRACT FROM AUTHOR]

The direct-current (dc) fault-clearance capability of the modular multilevel converter (MMC) is a key issue for overhead line applications of voltage source converter-based high-voltage dc (VSC-HVDC) transmission systems. An MMC integrated with a dc circuit breaker (IDCB-MMC) is proposed to provide a cost-effective DC fault clearance and isolation solution. A mechanical switch (MS) and a load commutation switch are connected in series as the main branch of the dc circuit breaker. DC fault currents can be forced to transfer to converter- and line-side energy absorbing branches when submodule bypass protection and dc circuit breaker interrupting operations are coordinated. Therefore, the bulky and costly solid-state branch that uses numerous semiconductor devices and surge arresters can be eliminated. The dc fault clearance and isolation capability of the IDCB-MMC were verified through the simulation results for one pole of a 1000 MW/±320 kV VSC-HVDC system. Compared with an MMC that uses half-bridge SMs, the IDCB-MMC only requires few additional capacitors and switching devices and a simple MS, thereby resulting in several advantages, such as low cost, footprint requirements, and additional conduction losses. [ABSTRACT FROM AUTHOR]

Active current injection circuit breakers (ACICBs), which utilize the mechanical switch and a parallel-connected precharged capacitor, have broad application prospects in future multiterminal dc grids. However, with the increase of system voltage, the precharged capacitor leads to the great cost and size being spent on the charging circuit and auxiliary commutating appliances. To address this shortcoming, an innovative dc circuit breaker (DCCB) based on a magnetic induction current commutation module (MICCM) is proposed. The influence of the main component parameters on the commutation performance is investigated by calculation, in which the self-, mutual, and stray inductances are involved. Besides, the validity of calculation is experimentally proved. Then, by applying the MICCM to the ACICB, the breaking characteristics of the ACICB are analyzed in detail. Finally, a 10-kV DCCB prototype is developed, verifying the feasibility of current commutation concept and the validity of simulated interruption results. Our studies show that a 10-kA bidirectional fault current can be interrupted successfully with a commutation duration less than 250 μs. [ABSTRACT FROM PUBLISHER]

Transformer-type superconducting fault current limiter (TSFCL) interruption system is a current breaking technology proposed by applying a transformer, superconductor, andmechanical dc circuit breaker. When the fault occurs, the fault current is limited due to the operation of the counter electromotive force by the transformer and the quenching of the superconductor. The fault current is then interrupted by the mechanical dc circuit breaker. In this paper, the transition and the interrupting behavior was analyzed according to the applied voltage to secure the stability and reliability of a TSFCL interruption system using the PSCAD EMTDC program. As a result, it was able to improve the current breaking time and the breaking capacity. Also, the burden imposed on a mechanical dc circuit breaker was reduced fivefold. [ABSTRACT FROM AUTHOR]

Interruption of DC fault current in a DC system is more complex as compared to the AC one due to the high rate of rise of fault current and absence of natural zero crossing. Fast and hard switching action in DC current interruption causes excessive voltage across the circuit breaker. This paper investigates a new type of solid-state DC circuit breaker namely current releasing DC circuit breaker. The mechanism of current interruption in the current releasing DC circuit breaker is analyzed through an aggregated model. The design procedure is defined and simulation results are presented. In addition, a sensitivity analysis is carried out. Finally, the experimental results from a lab-scale prototype as a proof of concept are demonstrated. This study confirms that the current interruption time of the current releasing DC circuit breaker is remarkably less than the typical solid-state DC circuit breakers and it requires less number of semiconductors in its main breaking branch. Although the current releasing DC circuit breaker does not have any surge arrester in its structure, its switching surge voltage is significantly limited. [ABSTRACT FROM AUTHOR]

This paper proposes a novel fault ride-through protection scheme for multiterminal dc (MTDC) networks connecting large-scale offshore wind parks. The proposed scheme introduces an MTDC network with a hybrid fault current limiter (FCL), which consists of a high-temperature superconducting FCL (HTS-FCL) and series braking resistor (SBR) integrated with low-loss mechanical dc circuit breaker (DCCB). The aim of HTS-FCL is to provide fast quenching, limit the dc fault current within the interrupting capacity of the DCCB, and reduce the dc fault current to certain levels such that converters can sustain prolonged periods of operation without blocking. Also, SBR allows automatic reclosing of DCCBs following a temporary fault, thereby enhancing the network security and reliability. Mechanical DCCBs with the proposed hybrid limiter are installed at the terminating points of each dc cable. The proposed protection scheme is based on differential current approaches with fault clearing time of few milliseconds, which gives enhanced network selectivity and reliability. A four-terminal meshed MTDC network with the proposed hybrid FCL is modeled in PSCAD/EMTDC. The obtained simulation results confirm successful dc fault isolation and network recovery for different dc fault scenarios. [ABSTRACT FROM PUBLISHER]

There is an urgent need for the fault current limiter to guarantee the stability of the dc system. For this reason, the improved inductive superconducting fault current limiter (SFCL) is designed and its working principle is addressed. By analyzing the transient characteristics of the dc fault in modular multilevel converter based dc system, the current-limiting effects of the proposed SFCL are studied in detail. According to the current-limiting requirements and the coordination among the converter, the fault current limiter and the dc circuit breaker, the desired impedance of the SFCL is discussed in this paper. Finally, the effectiveness and correctness of the analyses have been verified by the simulation results based on the PSCAD/EMTDC simulation [ABSTRACT FROM PUBLISHER]

The complexity of DC side short circuit fault current interruption has been identified as a major drawback of realization of multi-terminal HVDC grids. Although application of superconducting fault current limiters (SFCLs) in protection of HVDC systems based on slow protective schemes has been studied in the literature, its application in meshed HVDC systems based on modern and fast protective schemes has not been investigated, yet. This paper scrutinizes the SFCL application in the meshed HVDC grids protected by the fast DC protective schemes and fast hybrid DC circuit breakers. The purpose of SFCL application is to reduce the current interruption requirement of the HVDC circuit breaker and size of its elements. This research analyzes the requirements of suitable SFCL considering the fault operation behaviors of local protective relays and the hybrid DC circuit breakers. The results show that the appropriated SFCL can reduce fault current peak, size of current limiting inductor and also fault identification time. The application of SFCL not only reduces the size of surge arrester in the hybrid DC circuit breaker, but also can significantly decrease the current stress on the hybrid DC circuit breaker. [ABSTRACT FROM AUTHOR]

A resistive switching superconducting fault current limiter (SFCL) for DC networks with a nominal voltage of 3.5 kV and a nominal current of 2 kA was developed, produced, and tested. The SFCL has two main units-an assembly of superconducting modules and a high-speed vacuum circuit breaker. The assembly of superconducting modules consists of nine (3 × 3) parallel-series connected modules. Each module contains four parallel-connected 2G high-temperature superconducting (HTS) tapes. The results of SFCL tests in the short-circuit emulation mode with a maximum current rise rate of 1300 A/ms are presented. The SFCL is capable of limiting the current at a level of 7 kA and break it 8 ms after the current-limiting mode begins. The average temperature of HTS tapes during the current-limiting mode increases to 210 K. After the current is interrupted, the superconductivity recovery time does not exceed 1 s. [ABSTRACT FROM AUTHOR]

• Comparison of current limitation between the high inductance and low inductance superconducting fault current limiter (SFCL) • Comparison of interruption of the DC solid-state circuit breaker (SSCB) with the high inductance and low inductance SFCL. • DC network protection using SFCL to limit the fault current and DC SSCB to interrupt the fault current for electric aircraft. • Coordination between SFCL and SSCB using overcurrent detection. • Effective current limitation by SFCL leading to lower current interruption capability requirement for DC SSCB. The onboard direct current (DC) system in electric aircraft could face a severe fault current, which is tens of times the nominal current in a short-circuit fault. It is critical to limit the fault current and clear the fault within a few milliseconds to prevent any damage to the DC system. A protection method using a resistive superconducting fault current limiter (SFCL) with a solid-state DC circuit breaker (SSCB) to manage the DC short-circuit fault is proposed and experimentally verified. A bifilar SFCL coil prototype with two types of connection to achieve low and high inductance is designed and tested, which reduces the fault current considerably from 2000 A to below 1000 A. The performance when integrating the low and high inductance SFCL with a solid-state DC circuit breaker are investigated. It is found that when integrating the SFCL with the SSCB, a high voltage is induced across the high inductance SFCL during current interruption tests. In terms of reliability and durability, the low inductance SFCL is preferred to integrate with the SSCB. The experimental results show that the low inductance SFCL can be an effective solution to protect the DC system from severe fault currents and then SSCB can rapidly and reliably interrupt the fault current at 1000 A. © 2017 Elsevier Inc. All rights reserved. [ABSTRACT FROM AUTHOR]

The unavailability of high-capacity HVdc circuit breakers (CBs) is one of the key stoppers for building HVdc multiterminal networks. As the dc does not have a natural current zero, its interruption is very different. The objective of this paper is to propose a new type of dc CB (DCCB), including a current-limiting part and an interrupting part, which can interrupt a high short-circuit current. Experimental results show that the current-limiting part containing superconductor tapes and parallel resistance can limit the fault current from 20 to 1 or 2 kA very quickly within 1 ms. The interrupting part using the self-oscillation method can break this limited current. Therefore, this type of DCCB has the ability of interrupting a high short-circuit current. [ABSTRACT FROM PUBLISHER]

This paper proposes a dc circuit breaker for voltage source converter (VSC) based high-voltage dc transmission (HVDC) systems. Technical challenges for applying dc circuit breakers are to increase blocking voltage and to suppress surge voltage at the current clearing. The proposed dc circuit breaker is a solid-state breaker which consists of a number of semiconductor devices in series. It maintains equal voltage balancing among the devices to apply it to high-voltage applications. Moreover, the surge voltage across the circuit breaker is reduced by employing a freewheeling diode. Considering a system rated at 300 MW in power and 250 kV in dc voltage, the conduction loss of the proposed circuit breaker is estimated to be 0.045% of the rated power. The value is smaller than the power loss of the VSCs. A downscaled HVDC system rated at 10 kW in power and 360 V in dc voltage was built and tested. A series of experimental results demonstrates the dc fault clearing and rapid restoration of power transmission. [ABSTRACT FROM AUTHOR]