DC fault isolation study of bidirectional dual active bridge DC/DC converter for DC transmission grid application

Fast isolation and detection of DC faults is currently a limiting factor in high power DC transmission grid development. Recent research has shown that the role of DC/DC converters is becoming increasingly important in solving various DC grid challenges such as voltage stepping, galvanic isolation and power regulation. This paper focuses on an additional important feature of bidirectional dual active bridge (DAB) DC-DC converters which make it attractive for future DC grids; it's inherent fault isolation capability which does not need control intervention to limit fault current in case of the most severe DC faults. Detailed analytical, simulation and experimental study are performed by subjecting the converter to DC short circuit faults at its DC voltage terminals. The results obtained have shown significant advantage of DAB where fault current is less than rated current during the fault duration. Thus no control action is necessary from the non-faulted bridge to limit fault current and no external DC circuit breakers are required. This advantage makes DAB converter feasible for DC grid integration

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

Multi-kilowatt modularized spacecraft power processing system development

A review of existing information pertaining to spacecraft power processing systems and equipment was accomplished with a view towards applicability to the modularization of multi-kilowatt power processors. Power requirements for future spacecraft were determined from the NASA mission model-shuttle systems payload data study which provided the limits for modular power equipment capabilities. Three power processing systems were compared to evaluation criteria to select the system best suited for modularity. The shunt regulated direct energy transfer system was selected by this analysis for a conceptual design effort which produced equipment specifications, schematics, envelope drawings, and power module configurations

Turboelectric distributed propulsion protection system design trades

The NASA N3-X blended-wing body with turboelectric distributed propulsion concept is being studied to achieve N+3 goals such as reduced noise, emissions, and improved energy efficiency. The electrical distribution system is cryogenic in order to maximize its efficiency and increase the power density of all associated components, while the motors, generators, and transmission lines are superconducting. The protection of a superconducting DC network poses unique electrical and thermal challenges due to the low impedance of the superconductor and operation in the superconducting or quenched states. For a given TeDP electrical system architecture with fixed power ratings, conventional and solid-state circuit breakers combined with superconducting fault-current limiters are examined with both voltage and current source control to limit and interrupt the fault current. To estimate the protection system weight and losses, scalable models of cryogenic bidirectional current-source converters, cryogenic bidirectional IGBT solid-state circuit breakers, and resistive-type superconducting fault current limiters are developed to assess how the weight and losses of these components vary as a function of nominal voltage and current and fault current ratings. The scalable models are used to assess the protection system weight for several trade-offs. System studies include the trade-off in fault-current limiting capability of SFCL on CB mass, alongside the fault-current limiting capability of the converter and its impact on CB fault-current interruption ratings and weight

Architecture, Voltage and Components for a Turboelectric Distributed Propulsion Electric Grid

The development of a wholly superconducting turboelectric distributed propulsion system presents hide unique opportunities for the aerospace industry. However, this transition from normally conducting systems to superconducting systems significantly increases the equipment complexity necessary to manage the electrical power systems. Due to the low technology readiness level (TRL) nature of all components and systems, current Turboelectric Distributed Propulsion (TeDP) technology developments are driven by an ambiguous set of system-level electrical integration standards for an airborne microgrid system (Figure 1). While multiple decades' worth of advancements are still required for concept realization, current system-level studies are necessary to focus the technology development, target specific technological shortcomings, and enable accurate prediction of concept feasibility and viability. An understanding of the performance sensitivity to operating voltages and an early definition of advantageous voltage regulation standards for unconventional airborne microgrids will allow for more accurate targeting of technology development. Propulsive power-rated microgrid systems necessitate the introduction of new aircraft distribution system voltage standards. All protection, distribution, control, power conversion, generation, and cryocooling equipment are affected by voltage regulation standards. Information on the desired operating voltage and voltage regulation is required to determine nominal and maximum currents for sizing distribution and fault isolation equipment, developing machine topologies and machine controls, and the physical attributes of all component shielding and insulation. Voltage impacts many components and system performance

Solid State Protective Device Topological Trade-offs for Mvdc Systems

Presently accepted approaches to protection are “Unit-Based” which means the power converter(s) feeding the bus coordinate with no-load electromechanical switches to isolate faulted portions of the bus. However, “Breaker-Based” approaches, which rely upon solid state circuit breakers for fault mitigation can result in higher reliability of power and potentially higher survivability. The inherent speed of operation of solid state protective devices will also play a role in fault isolation, hence reducing stress level on all system components. A comparison study is performed of protective device topologies that are suitable for shipboard distribution systems rated between 4kVdc and 20kVdc from the perspectives of size and number of passive components required to manage the commutation energy during sudden fault events and packaging scalability to higher current and voltage systems. The implementation assumes a multi-chip Silicon Carbide 10kV, 240A MOSFET/JBS diode module. A static fault simulator device is proposed to characterize DC faults

Application of multiple resistive superconducting fault-current limiters for fast fault detection in highly interconnected distribution systems

Superconducting fault-current limiters (SFCLs) offer several benefits for electrical distribution systems, especially with increasing distributed generation and the requirements for better network reliability and efficiency. This paper examines the use of multiple SFCLs in a protection scheme to locate faulted circuits, using an approach which is radically different from typical proposed applications of fault current limitation, and also which does not require communications. The technique, referred to as “current division discrimination” (CDD), is based upon the intrinsic inverse current-time characteristics of resistive SFCLs, which ensures that only the SFCLs closest to a fault operate. CDD is especially suited to meshed networks and particularly when the network topology may change over time. Meshed networks are expensive and complex to protect using conventional methods. Simulation results with multiple SFCLs, using a thermal-electric superconductor model, confirm that CDD operates as expected. Nevertheless, CDD has limitations, which are examined in this paper. The SFCLs must be appropriately rated for the maximum system fault level, although some variation in actual fault level can be tolerated. For correct coordination between SFCLs, each bus must have at least three circuits that can supply fault current, and the SFCLs should have identical current-time characteristics

A compound current limiter and circuit breaker

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. The protection of sensitive loads against voltage drop is a concern for the power system. A fast fault current limiter and circuit breaker can be a solution for rapid voltage recovery of sensitive loads. This paper proposes a compound type of current limiter and circuit breaker (CLCB) which can limit fault current and fast break to adjust voltage sags at the protected buses. In addition, it can act as a circuit breaker to open the faulty line. The proposed CLCB is based on a series L-C resonance, which contains a resonant transformer and a series capacitor bank. Moreover, the CLCB includes two anti-parallel power electronic switches (a diode and an IGBT) connected in series with bus couplers. In order to perform an analysis of CLCB performance, the proposed structure was simulated using MATLAB. In addition, an experimental prototype was built, tested, and the experimental results were reported. Comparisons show that experimental results were in fair agreement with the simulation results and confirm CLCB’s ability to act as a fault current limiter and a circuit breaker

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

Architecture, Voltage, and Components for a Turboelectric Distributed Propulsion Electric Grid

The development of a wholly superconducting turboelectric distributed propulsion system presents unique opportunities for the aerospace industry. However, this transition from normally conducting systems to superconducting systems significantly increases the equipment complexity necessary to manage the electrical power systems. Due to the low technology readiness level (TRL) nature of all components and systems, current Turboelectric Distributed Propulsion (TeDP) technology developments are driven by an ambiguous set of system-level electrical integration standards for an airborne microgrid system (Figure 1). While multiple decades' worth of advancements are still required for concept realization, current system-level studies are necessary to focus the technology development, target specific technological shortcomings, and enable accurate prediction of concept feasibility and viability. An understanding of the performance sensitivity to operating voltages and an early definition of advantageous voltage regulation standards for unconventional airborne microgrids will allow for more accurate targeting of technology development. Propulsive power-rated microgrid systems necessitate the introduction of new aircraft distribution system voltage standards. All protection, distribution, control, power conversion, generation, and cryocooling equipment are affected by voltage regulation standards. Information on the desired operating voltage and voltage regulation is required to determine nominal and maximum currents for sizing distribution and fault isolation equipment, developing machine topologies and machine controls, and the physical attributes of all component shielding and insulation. Voltage impacts many components and system performance