Development of DC Circuit Breakers for Medium-Voltage Electrified Transportation

Medium-voltage DC (MVDC) distribution is an enabling technology for the electrification of transportation such as aircraft and shipboard. One main obstacle for DC distribution is the lack of adequate circuit fault protection. The challenges are due to the rapidly rising fault currents and absence of zero crossings in DC systems compared to AC counterparts. Existing DC breaker solutions lack comprehensive consideration of energy efficiency, power density, fault interruption speed, reliability, and implementation cost. In this thesis, two circuit topologies of improved DC circuit breakers are developed: the resonant current source based hybrid DC breaker (RCS-HDCB) and the high temperature superconductor fault current limiter based solid state DC breaker (HTS-FCL-SSDCB). The RCS-HDCB utilizes a controllable resonant current source based upon wide bandgap (WBG) switches that enable low loss and fast fault interruption due to the fast switching speed. The voltage applied by the controllable resonant current source is much lower than the rated voltage of the DC breaker, allowing the utilization of significantly lower voltage rated WBG switches. The conduction path\u27s sole component is a fast-actuating ultra-low resistance vacuum interrupter for high efficiency during normal operation. As the second DC breaker concept, the HTS-FCL-SSDCB is subdivided into a fault current limiter (FCL) and solid state DC breaker (SSDCB). The FCL is based upon a high temperature superconductor cable which has natural fault current limiting capabilities while having negligible insertion losses for normal load currents. The SSDCB utilizes WBG switches to decrease conduction losses compared to Silicon-based breakers. The FCL reduces fault current such that the number of semiconductive switches in the SSDCB is minimized. Both breakers feature a metal-oxide varistor device in parallel to clamp overvoltages and dissipate energy after fault interruption. Modeling, simulation, and analysis in electrical and thermal domains are conducted to verify the functionality of the DC circuit breakers. The simulation results confirm the feasibility of these two DC breakers in their proposed applications of 2.4 kV electric aircraft and 20 kV shipboard MVDC distribution systems

Semiconductor devices in solid-state/hybrid circuit breakers: current status and future trends

Circuit breakers (CBs) are the main protection devices for both alternating current (AC) and direct current (DC) power systems, ranging from tens of watts up to megawatts. This paper reviews the current status for solid-state circuit breakers (SSCBs) as well as hybrid circuit breakers (HCBs) with semiconductor power devices. A few novel SSCB and HCB concepts are described in this paper, including advantage and limitation discussions of wide-band-gap (WBG) devices in basic SSCB/HCB configuration by simulation and 360 V/150 A experimental verifications. Novel SSCB/HCB configurations combining ultra-fast switching and high efficiency at normal operation are proposed. Different types of power devices are installed in these circuit breakers to achieve adequate performance. Challenges and future trends of semiconductor power devices in SSCB/HCB with different voltage/power levels and special performance requirements are clarified

Fault Discrimination Using SiC JFET Based Self-Powered Solid State Circuit Breakers in a Residential DC Community Microgrid

This thesis validates the use of ultra-fast normally-on SiC JFET based self-powered solid state circuit breakers (SSCBs) as the main protective device for a 340Vdc residential DC community microgrid. These SSCBs will be incorporated into a radial distribution system so that line to line short circuit faults and other types of faults can be isolated anywhere within the microgrid. Because of the nature and characteristics of short circuit fault inception in DC microgrids, the time-current trip characteristics of protective devices must be several orders of magnitude of faster than conventional circuit breakers. The proposed SSCB detects short circuit faults by sensing its drain-source voltage rise, and draws power from the fault condition to turn and hold off the SiC JFET. The new two-terminal SSCB can be directly placed in a circuit branch without requiring any external power supply or additional wiring. To achieve the coordination between upstream and downstream SSCBs in the DC community microgrid, a little change has been made to the proposed SSCB. A resistor in the schematic of SSCB has been changed to a potentiometer to have a different response time to short circuit fault. In order to figure out the value of that potentiometer to get the best coordination, a transfer function is derived. LTspice VI and PLECS are used to verify the analytical work in the design. In the simulation layout, the DC community microgrid has been simplified to a radial system and 5 SSCBs are connected in series. Short circuit fault is applied at different locations in the DC system to test the effectiveness of the coordination scheme

Development of a current limiting solid-state circuit breaker based on wide-band gap power semiconductor devices for 400V DC microgrid protection

Popularity of DC distribution systems is increasing for many residential and industrial applications such as data centres, commercial and residential buildings, telecommunication systems, and transport power networks etc. Compared to AC systems, they have demonstrated higher power efficiency, less complexity, and more readiness of integrating with various local power sources and DC electronic loads. However, one of the major technical issues hindering this trend is the lack of effective DC fault protection devices/circuits. Although conventional electromechanical circuit breakers work well in AC systems, they are not suitable for DC systems due to their long response time (ranging from tens of milliseconds to hundreds of milliseconds). Such a long response time is far beyond the withstand time (typically tens of microseconds) of most power electronic devices in short-circuit operating conditions. In contrast, Solid-State Circuit Breakers (SSCBs) are able to offer ultrafast switching speed thanks to the modern power semiconductor devices which can turn off in microseconds or even in tens of nanoseconds. Furthermore, the ever-increasing fault current level in DC systems poses a significant mechanical and thermal stress on the whole DC system. Therefore, the desire for the protection devices with the feature of fast switching speed along with the current-limiting capability has prompted intensive research in this area over the last decade in both academia and industry. However, the relatively high conduction losses and limited short-circuit capability are two of the major drawbacks of SSCBs. With the growing maturity and increasingly commercial availability of Wide-Bandgap (WBG) semiconductor devices, a SSCB based-on WBG devices is a promising solution to alleviate the issues since WBG semiconductors have demonstrated superior material properties over the conventional silicon material such as lower specific on-resistance, higher junction temperatures and higher breakdown voltage. This research aims to design and develop a WBG-based solid-state circuit breaker for a 400V DC microgrid application. To accomplish this task, this work starts with a comprehensive review of DC microgrid technology followed by an extensive review of the state-of-the-art DC circuit breakers. Then, to develop a circuit topology for the proposed SSCB, a practical current limiter is analysed, simulated, and evaluated. Based on this topology, the proposed SSCB is configured with a high-voltage normally-on Silicon Carbide Junction Field Effect Transistors (SiC-JFETs) cascading a low-voltage normally-off power MOSFET. This solution offers several advantages. For example, it does not require any additional sensing and tripping circuitry for short-circuit protection and therefore has a fast response speed. Meanwhile, the use of power SiC JFETs tends to reduce the conduction losses and enhance the short-circuit robustness of SSCBs. In addition, it offers the feature of current limiting which could ease the thermal and mechanical stresses on the whole DC system. The operating process of the proposed SSCB is analysed and the analytical results are compared with the simulated results; In the end, a prototype SSCB has been built and evaluated for short-circuit protection in a 400V DC system. In addition, to effectively suppress the overvoltage at the turn-off of SSCBs, a novel hybrid snubber circuit has been proposed by taking into account the advantages offered by both conventional Resistor-Capacitor-Diode (RCD) snubbers and Metal-Oxide Varistors (MOVs). Finally, other functions of the proposed SSCBs including overload protection, over temperature protection and protection coordination have been investigated and some operating issues such as false tripping and SSCB reset have been addressed

Novel current-limiting strategy for solid-state circuit breakers (SSCB) without additional impedance

Current-limiting strategies for solid-state circuit breaker (SSCB) without adding impedance is introduced in this paper. With the current limitation of novel phase-shifting method, the advantages are simple hardware structure, relatively low cost, no heat generation, low weight and small size. Current-limiting capability is exploited with qualities of good control accuracy and robustness. The principle and theoretical analysis of phase-shifting current-limiting method are detailed introduced together with simulation/experimental verifications

Power Semiconductors for An Energy-Wise Society

This IEC White Paper establishes the critical role that power semiconductors play in transitioning to an energy wise society. It takes an in-depth look at expected trends and opportunities, as well as the challenges surrounding the power semiconductors industry. Among the significant challenges mentioned is the need for change in industry practices when transitioning from linear to circular economies and the shortage of skilled personnel required for power semiconductor development. The white paper also stresses the need for strategic actions at the policy-making level to address these concerns and calls for stronger government commitment, policies and funding to advance power semiconductor technologies and integration. It further highlights the pivotal role of standards in removing technical risks, increasing product quality and enabling faster market acceptance. Besides noting benefits of existing standards in accelerating market growth, the paper also identifies the current standardization gaps. The white paper emphasizes the importance of ensuring a robust supply chain for power semiconductors to prevent supply-chain disruptions like those seen during the COVID-19 pandemic, which can have widespread economic impacts.The white paper highlights the importance of inspiring young professionals to take an interest in power semiconductors and power electronics, highlighting the potential to make a positive impact on the world through these technologies.The white paper concludes with recommendations for policymakers, regulators, industry and other IEC stakeholders for collaborative structures and accelerating the development and adoption of standards

Design and Implementation of High-Efficiency, Lightweight, System-Friendly Solid-State Circuit Breaker

Direct current (DC) distribution system has shown potential over the alternative current (AC) distribution system in some application scenarios, e.g., electrified transportation, renewable energy, data center, etc. Because of the fast response speed, DC solid-state circuit breaker (SSCB) becomes a promising technology for the future power electronics intensive DC energy system with fault-tolerant capability. First, a thorough literature survey is performed to review the DC-SSCB technology. The key components for DC-SSCB, including power semiconductors, topologies, energy absorption units, and fault detection circuits, are studied. It is observed that the prior studies mainly focus on the basic interruption capability of the DC-SSCB. There are not so many studies on SSCB’s size optimization or system-friendly functions. Second, an insulated gate bipolar transistor (IGBT) based lightweight SSCB is proposed. With the reduced gate voltage, the proposed SSCB can limit the peak fault current without the bulky and heavy fault current limiting the inductor, which exists in the conventional SSCB circuit. Thus, the specific power density of the SSCB is substantially improved compared with the conventional design. Meanwhile, to understand the impact of different design parameters on the performance of SSCB, an analytical model is built to establish the relationship between SSCB dynamic performance and operating conditions considering the key components and circuit parasitics. Simulation and test results demonstrate the accuracy of the proposed model. To limit the fault current with the proposed SSCB without a current limiting inductor, power semiconductors need to operate in the active region temporarily. During this interval, a severe voltage oscillation has been observed experimentally, leading to the DC-SSCB overstress and eventually the failure. A detailed MATLAB/Simulink model is built to understand the mechanism causing the voltage oscillation. Three suppression methods using enhanced gate drive circuitry are proposed and compared. Test results based on a 2kV/1kA SSCB prototype demonstrate the effectiveness of the proposed oscillation mitigation method and the accuracy of the derived model. Meanwhile, when the system fault impedance is close to zero (e.g., high di/dt), the influence of the parasitic inductance contributed by interconnection (e.g., bus bar, module package, etc.) cannot be neglected. To study the influence of the bus bar connections on SSCB with high di/dt, a Q3D extractor is adopted to extract the parasitic parameters of the SSCB and understand the influence of different bus bar connections. A vertical bus bar is proposed to suppress the side effect and verified by the Q3D extractor and experimental results. Finally, a system-friendly SSCB is demonstrated. The proposed gate drive enables the SSCB to operate in the current limitation mode for the overcurrent limitation. The current limitation level and limitation time can be tuned by the gate drive. Then, this dissertation provides an all-in-one solution with integrated circuitries as the fault detector, actuator for the semiconductor’s operating status regulation, and coordinated control. This allows the developed SSCB to limit system fault current not exceeding short-circuit current rating (SCCR) and also take different responses under different fault cases. The feasibility and the effectiveness of the proposed system-friendly SSCB are validated with experimental results based on a 200V/10A SSCB demonstrator

Short-Circuit Protection for Low-Voltage DC Distribution Systems Based on Solid-State Circuit Breakers

Proper short-circuit protection in dc distribution systems has provided an austere challenge to researchers as the development of commercially-viable equipment providing fast operation, coordination and reliability still continues. The objective of this thesis is to analyze issues associated with short-circuit protection of low-voltage dc (LVDC) distribution systems and propose a short-circuit protection methodology based on solid-state circuit breakers (SSCBs) that provides fault-current limiting (FCL). Simulation results for a simplified notional 1-kVdc distribution system, performed in MATLAB/SIMULINKTM, would be presented to illustrate that SSCB solutions based on reverse-blocking integrated gate-commutated thyristors (RB-IGCT) are feasible for low-voltage dc distribution systems but requires connecting several devices in parallel to open fast-rising fault currents. To validate the implementation of the FCL function, the coordination between upstream and downstream SSCBs during a fault at different operating conditions of the system is presented. In addition, several fault-detection techniques would be compared by means of the let-through energies, and the impact of FCL on the thermal handling requirements of the RB-IGCT would also be discussed

Novel current-limiting strategy for solid-state circuit breakers (SSCB) without additional impedance

Current-limiting strategies for solid-state circuit breaker (SSCB) without adding impedance is introduced in this paper. With the current limitation of novel phase-shifting method, the advantages are simple hardware structure, relatively low cost, no heat generation, low weight and small size. Current-limiting capability is exploited with qualities of good control accuracy and robustness. The principle and theoretical analysis of phase-shifting current-limiting method are detailed introduced together with simulation/experimental verifications