High voltage direct current (HVDC) systems are now well integrated into AC systems in many jurisdictions. The integration of renewable energy sources (RESs) is a major focus and the role of HVDC systems is expanding. However, the protection of HVDC systems against DC faults is a challenging issue that can have negative impacts on the reliable and safe operation of power systems. Practical solutions to protect HVDC grids against DC faults without a widespread power outage include: 1) using DC circuit breakers (CBs) to isolate the faulty DC-link, 2) using a proper converter topology to interrupt the DC fault current, and/or 3) using high-power DC transformers and DC hubs at strategic points within DC grids. The application of HVDC CBs is identified as the best approach that satisfies both DC grids and connected AC grids’ requirements. This article reports a comprehensive review of HVDC CBs technologies, including recent significant attempts in the development of modern HVDC CBs. The functional analysis of each technology is presented. Additionally, different technologies based on information obtained from literature are compared. Finally, recommendations for the improvement of CBs are presented.

/pdf/hvdc-circuit-breakers-a-comprehensive-review-41s3apcrt9.pdf

HVDC Circuit Breakers: A Comprehensive Review

Low Voltage Direct Current (LVDC) distribution systems potentially enable more efficient power distribution and wider uptake of distributed renewables and energy storage. They do however present significant fault protection and safety challenges. To address these, the use of advanced protection techniques or significant system redesign is required. This paper reviews these protection key challenges, and presents experimental results of a prototype advanced protection scheme designed to help enable LVDC distribution networks for utility applications. The developed scheme is DC current direction-based and uses multiple intelligent electronic devices (IEDs) relays in combination with controllable solid-state circuit breakers to detect and locate DC faults. This scheme provides selective protection tripping within sub-millisecond timescales. A scaled laboratory demonstrator that emulates an LVDC distribution network is used as a test platform. It allows the characterisation of the transient behaviour for various fault conditions and locations. The developed protection algorithm is implemented in LabVIEW, and its performance against such fault conditions is tested within this environment.

/pdf/validation-of-fast-and-selective-protection-scheme-for-an-26p6jc24m3.pdf

Validation of fast and selective protection scheme for an LVDC distribution network

This letter presents a new low-voltage direct-current fault current bypass-based solid-state circuit breaker (SSCB) using silicon-carbide <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet s. 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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">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.

Fault Current Bypass-Based LVDC Solid-State Circuit Breakers

A novel solid state circuit breaker (SSCB), which uses the cathode-short MOS-controlled thyristor (CS-MCT) as the main switch to achieve high power efficiency, is proposed for direct current (dc) microgrid protection. The proposed SSCB features the commutating circuit with a one-shot triggering characteristic and a compact size, which makes the SSCB realize a simple tripping process and easy integration. Furthermore, the SSCB charges the commutating capacitor and offers the interruption capability before the main switch is turned on . This avoids the possible failure of the breaker under the fault that occurs at the initial stage of the turn- on of the main switch, thus providing highly reliable and robust interruption capability for the SSCB. Circuit analysis and design guidelines are discussed in detail through the mathematical modeling. Moreover, the practical value and the feasibility of the SSCB are validated by 600-V/15-kW prototype experiments and further verified in dc microgrids through simulations.

Design and Experimental Verification of an Efficient SSCB Based on CS-MCT

This paper introduces a DC transmission grid with fault tolerant inductor-capacitor-inductor (LCL) voltage source converters (VSCs) and using slow protection system based on mechanical DC circuit breakers (CBs). LCL VSC inherently regulates DC fault current to levels that converter can sustain for prolonged periods which avoids IGBT tripping and brings significant advantage in security and reliability aspects. Simple mechanical DC CBs are used at DC bus bars and connecting points of each DC cable, in the same manner as it is normal practice used with AC transmission protection. The protection logic is based on differential methods which gives excellent selectivity and reliability. The fault clearing time is in the order of 30–60ms which allows for reliable protection decision making. The simulation results obtained from a four-terminal DC grid modeled on PSCAD platform confirm successful DC fault isolation and grid recovery for a range of severe DC fault scenarios.

/pdf/dc-transmission-grid-with-low-speed-protection-using-ixrhqrkwcu.pdf

DC transmission grid with low speed protection using mechanical DC circuit breakers

DC distribution networks are able to effectively improve the energy efficiency and easy integration of distributed generations. However, the reliable dc circuit breaker is an essential requisite for the wide application of dc power. This paper proposes a self-powered solid-state circuit breaker (SSCB) with a digitally controlled current–time profile for both ultrafast short-circuit protection and overcurrent protection. The fault detection unit detects short-circuit or overcurrent conditions by sensing the sampling resistance voltage and delivers these voltage signals to a low-cost microprocessor to realize the protection operation of the SSCB. A pulsewidth modulation (PWM) current limiting protection method with time interval $T_{d}$ is proposed to avoid nuisance tripping caused by inrush current during power electronic load startup. The time interval is properly selected based on the transient thermal properties of silicon carbide (SiC) junction gate field-effect transistors (JFETs). In order to verify the dynamic response of the SSCB, a SiC JFET-based circuit breaker prototype is designed and fabricated for result confirmation.

A SiC JFET-Based Solid State Circuit Breaker With Digitally Controlled Current-Time Profiles

The increasing load density of direct current (DC) distribution system leads to an increase in system capacity and short-circuit fault current. However, due to the limited capacity of a single semiconductor device, solid state circuit breaker (SSCB) with one semiconductor device is difficult to apply to high current applications. This paper proposes a 400V/300A intelligent SSCB with 8 parallel normally-on SiC JFETs as the main static switch, a Microprocessor Unit (MCU) as the intelligent controller and a fast-starting isolated DC/DC converter as the protection driver. This article focuses on Current sharing and balancing among the parallel SiC JFETs. The short circuit experiment was performed using the designed SSCB prototype. The experimental results show that the proposed SSCB can realize short-circuit protection in several microseconds and overload protection in several hundred microseconds. In addition, good dynamic and static current sharing effect is achieved in this paper.

A 400V/300A Ultra-Fast Intelligent DC Solid State Circuit Breaker Using Parallel Connected SiC JFETs

This paper presents a self-powered solid state circuit breaker (SSCB) for medium voltage DC distribution systems with three cascaded normally-on SiC JFETs as the solid state switch and a microprocessor as the gate driver. The SSCB can draw power directly from the DC bus without any external auxiliary DC power source. The designed gate driver circuit achieves a dynamic and static balancing of the voltage distribution between the cascaded SiC JFETs during fault isolation. In addition, in order to verify the function of the proposed SSCB, a 2 kV SSCB prototype is built. The experimental results suggest that the proposed SSCB can realize comprehensive protection for different fault situations to prevent the mal-operation of SSCB possibly caused by capacitive load start-up.

A 2 kV Intelligent DC Solid State Circuit Breaker Using Series Connected SiC JFETs

Energy storage system plays an important role to operate the DC microgrid stably and improve power quality. When it is connected to the DC system through the bidirectional DC/DC converter, the energy storage system is of great significance to study fault characteristics of the energy storage converter for the rational design of relay protection. This paper investigates system response characteristics of energy storage systems in different fault stages under constant voltage control and droop control when short-circuit faults occur in DC microgrid, and compares effects of the two control methods on short-circuit fault characteristics. The results show that different control modes have a certain restraining effect on the fault behavior of DC microgrid, but the inrush current is too large at instantaneous failure. Therefore, the latching control should be carried out in time; meanwhile, a reliable and effective protection device should be added. In addition, the research shows that the capacitance and line parameters at the dc grid side also have influences on fault response characteristics of the energy storage converter. Finally, the simulation model of DC microgrid connected to the energy storage system is built on PSCAD / EMTDC to verify correctness of the theoretical analysis results.

Short-Circuit Fault Analysis of Energy Storage System Converter with Different Control in DC Microgrid

The embodiment of the invention discloses a low-voltage DC intelligent switch control system. The low-voltage DC intelligent switch control system comprises a main switch, a sampling circuit, a control circuit and a DC/DC forward-flyback circuit, wherein the sampling circuit is used for acquiring voltage drop between a drain and a source of the main switch, the voltage drop is a sampling signal, the control circuit is used for judging a main switch fault according to the sampling signal and then giving out an open instruction, and the DC/DC forward-flyback circuit is used for receiving an action instruction and controlling the main switch to switch off according to the open instruction. According to the low-voltage DC intelligent switch control system disclosed by the embodiment of the invention, the sampling circuit is used for acquiring the voltage drop between the drain and the source of the main switch, the voltage drop is the sampling signal, the control circuit is used for judging the main switch fault according to the sampling signal and then giving out the open instruction, the DC/DC forward-flyback circuit is used for receiving the action instruction and controlling the main switch to switch off according to the open instruction, so that the main switch can be controlled to be switched off within short time, and the fault isolation speed is improved.

Low-voltage DC intelligent switch control system

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