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

State-of-the-art silicon carbide (SiC) power devices provide superior performance over silicon devices with much higher switching frequencies/speed and lower losses. High switching speed is preferred for achieving low switching loss, yet high dv/dt and di/dt can result in high EMI emission during switching transients. These switching dynamics can be controlled by the device gate driving strategy. The multi-level active gate driver (AGD) approach is able to tradeoff the switching losses with the dv/dt and di/dt for each switching transient. A novel three-level (3-L) AGD for SiC power mosfet trajectory control is introduced. Its turn-off profile has a shorter turn-off delay compared to any existing methodology. Accordingly, a comprehensive datasheet-driven trajectory model for the online model-based optimization of the 3-L turn-off is introduced. The main factors that impact the 3-L turn-off performance are analyzed with this model. The experimental results of double pulse tests validate the approach. Additionally, the benefits of the proposed 3-L AGD method over two-stage turn-off and conventional gate drivers on the market are illustrated through experiments.

Adaptive Multi-Level Active Gate Drivers for SiC Power Devices

Protection techniques for DC microgrid- A 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 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.

Coupled Inductor-Based Zero Current Switching Hybrid DC Circuit Breaker Topologies

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

Distributed power generation integration can effectively improve the reliability and economy of dc distribution network operation. However, it is difficult to evaluate the fault behaviors caused by the diversification of distributed generation, which might render preexisting protection schemes invalid and even cause damage to power electronic equipment. When different distributed generators access a voltage source converter (VSC)-based dc system, an in-depth study of fault characteristics is of great significance to design relay protection. This paper investigated the short-circuit fault characteristics of VSC-based dc distribution networks containing distributed generation systems. The fault responses of different fault stages for three kinds of distributed generators (photovoltaic power system, supercapacitor energy storage system, and wind power generation system) were investigated to provide an intuitive comparison of fault behaviors. The effects of these distributed generators on the magnitude and peak time of fault current were analyzed. It was found that the dc cable parameters and these distributed power generators’ dc-link capacitors have great impacts on the fault behaviors of dc distribution networks. Detailed analyses based on MATLAB calculations are presented, and simulation results based on power systems computer aided design/electromagnetic transients including dc verified the effectiveness of the proposed transient fault models.

Comparative Study of Short-Circuit Fault Characteristics for VSC-Based DC Distribution Networks With Different Distributed Generators

Solid-state circuit breakers (SSCBs) inherently have excellent protection performance, thus they are popular for DC distribution protection. However, the safety and reliability of the SSCBs are limited by the rapid response ability of their own gate drivers. In this study, a self-powered SSCB with a normally-on silicon carbide (SiC) junction gate field-effect transistor (JFET) is proposed as the solid-state switch, whose gate drivers are optimised as well. First, both an optimised fault detection circuit and a designed forward–flyback DC/DC converter of the SSCB gate driver have been presented to achieve fast protection during the course of fault isolation. Then, the detailed analyses of the gate driver circuit parameters effect on protection speed are further investigated based on circuit theory and MATLAB calculation. In order to compare and analyse the dynamic responses of the SSCB with and without optimisation, the actual interruption tests of the fabricated SiC JFET circuit breaker prototype and the employed prototype 400 V DC distribution system have been carried out. The results show that the implementation approach is able to improve protection speed for the SSCBs within the order of a few microseconds.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-pel.2017.0283

Design optimisation of self-powered gate driver for ultra-fast DC solid-state circuit breakers using SiC JFETs

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

The utility model discloses a parallel type intelligent direct current protection switch, and belongs to the technical field of direct current protection switches. The circuit comprises a main switchmodule, a sampling module, a single-chip microcomputer control module, an optocoupler isolation module and a driving module. Eight wide bandgap semiconductor devices SiC JFETs connected in parallel are uniformly arranged in a main switch module connected to a direct-current circuit, a sampling module is connected to the two ends of the main switch module in parallel for signal sampling, and meanwhile the sampling module is connected with an optocoupler isolation module and a single-chip microcomputer control module in a matched mode; the output end of the single-chip microcomputer control module is connected with the driving module, four driving circuits of the same structure are evenly arranged in the driving module, each driving circuit is connected with every two adjacent SiC JFETs in the main switch module, the SiCJFETs are driven to be connected and disconnected, and parallel current sharing is achieved. According to the utility model, the problem of current sharing during parallel connection in the prior art is solved, and the purposes of reducing conduction loss and protecting different levels of current are achieved.

Parallel type intelligent direct current protection switch

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