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Large-scale electric aircraft is a disruptive technology to address the environmental impact of air travel. Fault current limitation is crucial to realise the safety and reliability of the electric aircraft, in particular for large-scale electric aircraft using DC distribution network. This paper investigates the behavior of the resistive SFCL under different cryogenic cooling systems including liquid nitrogen and helium gas circulation cooling systems for the electric aircraft DC distribution network. Electromagnetic and thermoelectric models were used to predict the characteristics of resistive SFCL. The simulation results demonstrate that it is promising to design resistive SFCL using liquid nitrogen cooling as well as helium gas circulation cooling systems, which offer flexibility for SFCL cryogenic cooling system for electric aircraft applications.

A general shipboard power system contains multiple electrical machine sets to provide electrical power with different ratings for both the propulsion system and the ship service. In order to achieve the most compact design and maximize the weight reduction, a study of using a single dual wound generator to replace the electrical machine sets is presented in this paper. It consists of dual two-layer windings of different pole numbers which use the same slots and share one prime mover, producing two independent power supplies. This paper verifies a dual wound machine designed for no electromagnetic coupling by algebraically analyzing the spatial harmonic magnetic field distribution. Further verification of the absence of electromagnetic coupling due to both the airgap and slot leakage fluxes is provided by 2D finite element modeling. The dual wound generator prototype using the principle is designed, built and experimentally tested. The experimental results match well with the simulation results, validating the independence of the two power outputs and showing that the winding end-turns also do not couple. The results are significant for applications where multiple independent power supplies are needed, or where an auxiliary power supply is needed which could be drawn from an existing traction motor.

The annual growth rate of aircraft passengers is estimated to be 6.5%, and the CO2 emissions from current large-scale aviation transportation technology will continue to rise dramatically. Both NASA and ACARE have set goals to enhance efficiency and reduce the fuel burn, pollution, and noise levels of commercial aircraft. However, such radical improvements require radical solutions. With the current traditional aircraft designs based on gas turbines or piston engines, these goals are infeasible. Small-scale aircraft have successfully proven emission reductions using energy storage systems, such as Alice aircraft. This paper involves an investigation of the possibility of using superconducting magnetic energy storage (SMES)/battery hybrid energy storage systems (HESSs) instead of generators as backup power sources to improve system efficiency and reduce emissions. Two different power system architectures of electric aircraft (EA) were compared in terms of reliability and stability in a one-generator failure scenario. As weight is crucial in EA designs, the weights of the two systems were compared, including the generators and energy storage systems. The two EA systems were built in Simulink/MATLAB to compare their reliability and stability. With the currently available technologies, based on the energy density of 250 Wh/kg for lithium-ion batteries and a power density of 8.8 kW/kg for generators, the use of the generators as backup sources proved more efficient than the use of HESS. The break-even point was observed at 750 Wh/kg for battery energy density. Any value more than the 750 Wh/kg energy density makes HESS lighter and more efficient than generators.

The HTSConductor on Round Core (CORC) Cables have been widely recognized as the proper candidate for superconducting applications such as the high-field magnets and power transmission cables. This article presents the modeling of HTS CORC cables using the FEM H -formulation model merged into the package COMSOL Multi-physics. The 2D and 3D H -formulation models of HTS CORC cables were compared and analyzed. There were two important parameters in our CORC design: (1) the gap angle between the HTS tapes in a single layer, and, (2) the degree of twist for HTS tapes (normally identified as the pitch). The 2D CORC model has much faster solving speed over the 3D model and sometimes is able to model the AC loss in a reasonable range, while, the 3D CORC model has the advantages over 2D CORC model with respect to more information in each sector with the different conditions of two parameters above, and more realistic loss calculation.

Flux diverters (FDs) are used in High Temperature Superconducting (HTS) transformers for AC loss reduction and flux optimization. In this paper, a 2D axial symmetric superconducting winding model is proposed and two designs of flux diverters are applied to the windings. A homogenization approach is used to analyze the windings with large turn numbers. The key parameters including the number, width, height and the spatial positions of the FDs are adjusted for AC loss and magnetic flux analysis. The means of obtaining optimum designs of the FDs is provided and can be used to develop new winding designs with FDs, which contributes to better electromagnetic performance and higher efficiency of HTS transformers.

Impulse breakdown voltage is one of the most important factors for the designation of the R-SFCLs. However, no research about the polarity effect on standard lightning impulse in LN2/insulation barrier composite systems has been reported. The objective of this paper is to study the polarity effect on the standard lightning impulse in the LN2/insulation barrier composite systems. The 50% impulse breakdown voltage was measured with a pair of the needle to plane electrodes with the 0.05 mm thick PTFE film. The gap length of the two electrodes was 10 mm. The distance between the needle electrode and the insulation barrier was varied. The time delays during the breakdown progress were recorded by the oscilloscope. The breakdown path was determined by the arc traces on the PTFE films. The results showed that the 50% impulse breakdown voltage of the LN2/insulation barrier composite increased with the insulation barrier get closer to the needle electrode. The results of the time delays reflect that in negative polarity, all the breakdowns occurred in the tail of the waveform. In positive polarity, most of the breakdowns occurred in the head of the waveform. With the barrier get closer to the insulation barrier, the longer time delay T delay was in both polarities. And the probability of wave tail breakdown increased in positive polarities. The arc traces on the PTFE showed that all the breakdowns were occurred through the PTFE film.

Resistive type fault current limiters (SFCLs) have attracted lots of attention from research interests and engineering applications, due to their self-triggering, fast and effective fault current limitation ability. Fast recovery of SFCL after quench is highly attractive, yet still remains challenge when recover with load compared to recovering without load. We investigated the dependence of recovery time of a helical SFCL coil on the ratio of prospective current over critical current I pros/ I c. A multilayer simulation model was built in MATLAB/Simulink to investigate the electro-thermal behavior of SFCL coil during a fault and recovery period, and the model was validated by experimental results. Quench simulations were carried out under different I pros/ I c, ranging from 15 to 119 and in different recovery conditions including recovery with load condition and recovery without load condition, while keeping the fault duration of 100 ms. We observed that the SFCL coil reached 85 K and 195 K at the time when the fault was cleared, in the quench tests with I pros/ I c = 15 and 119, respectively. SFCL coil recovered without load in 0.5 s to 10 s, depending on the ratio of I pros/ I c.

Utilizing renewable energy sources (RESs) to their full potential provides an opportunity for lowering carbon emissions and reaching a state of carbon neutrality. DC transmission lines have considerable potential for the integration of RESs. However, faults in DC transmission lines are challenging due to the lack of zero-crossing, large fault current magnitudes and a short rise time. This research proposes using a superconducting fault current limiter (SFCL) for effective current limitation in PV-based DC systems. To properly design an SFCL, the present work investigates the effect of copper stabilizer thickness on SFCL performance by using an accurate multilayer thermoelectric model. In the MATLAB/Simulink platform, the SFCL has been modeled and tested using different copper stabilizer thicknesses to demonstrate the effectiveness of the SFCL model in limiting the fault current and the impact of the copper stabilizer thickness on the SFCL’s performance. In total, four different thicknesses of the copper stabilizer were considered, ranging from 10 μm to 80 μm. The current limitation and voltage profile for each thickness were evaluated and compared with that without an SFCL. The developed resistance and temperature profiles were obtained for various thicknesses to clarify the mechanisms behind the stabilizer-thickness impact. An SFCL with an 80 µm copper stabilizer can reduce the fault current to 5.48 kA, representing 71.16% of the prospective current. In contrast, the fault current was reduced to 27.4% of the prospective current (2.11 kA) when using a 10 µm copper stabilizer.

Previous studies on magnetization AC loss of high temperature superconducting (HTS) coated conductors (CCs) taken into account the ideally sinusoidal external magnetic field, or non-sinusoidal by considering only the harmonics in phase with the fundamental component. However, realistically magnetic field often contains harmonics with different phase angles and amplitudes. In this paper, magnetization AC loss in HTS CC was studied, considering the phase angle $\varphi $ of each harmonic; assuming superconductor is subjected to external magnetic field which is distorted by the $3^{\mathrm {rd}}$ and the $5^{\mathrm {th}}$ harmonics. Phase angle of each harmonic was considered in the range of 0 to $\pi $ and amplitude of fundamental magnetic field, was assumed as 10, 20, 50, and 100 mT. Different distortion level of magnetic field was considered too. It is concluded that phase angle of field harmonic has a significant effect on magnetization loss of HTS CCs.

HVDC circuit breakers are of increasing importance, as multi-terminal high voltage DC (HVDC) transmission becomes a commercial reality. Multiple HVDC breaker technologies have been developed, and are starting to appear as proof-of-concept installations on real networks. Information about them is however distributed widely in the literature. This article describes the underlying challenges, the leading candidate solutions, and discusses the requirements and construction of the component sub-assemblies. Its goal is to provide a comprehensive overview of the field.

With the popularization of electric vehicles, vehicle-to-grid (V2G) has become an indispensable technology to improve grid economy and reliability. However, battery aging should be mitigated while providing V2G services so as to protect customer benefits and mobilize their positivity. Conventional battery anti-aging V2G scheduling methods mainly offline operates and can hardly be deployed online in hardware equipment. This paper proposes a novel online battery anti-aging V2G scheduling method based on a novel two-stage parameter calibration framework. In the first stage, the V2G scheduling is modeled as an optimization problem, where the objective is to reduce grid peak-valley difference and mitigate battery aging. The online deployment of the developed optimization-based V2G scheduling is realized by a rule-based V2G coordinator in the second stage, and a novel parameter calibration method is developed to adjust controller hyper-parameters. With the parameter calibration process, the global optimality and real-time performance of V2G strategies can be simultaneously realized. The effectiveness of the proposed methodologies is verified on a practical UK distribution network. Simulation results indicate that it can effectively mitigate battery aging in providing V2G services while guaranteeing algorithm real-time performance.

An asymmetric dependence of the critical current on the direction of an applied magnetic field in HTS coated conductors has a non-trivial influence on the AC loss of coil windings. We report the modelled influence of real conductor critical current asymmetry on the AC loss characteristics of a 1 MVA HTS transformer design previously demonstrated by the Robinson Research Institute as well as a stand-alone coil having the same geometrical and electrical parameters as the low voltage (high current) winding of the transformer. We compare two commercial HTS conductors with distinctive differences in their critical current asymmetry and show a maximum variation of 15% and 29% in the calculated AC loss of the transformer and the stand-alone coil winding, respectively, when the conductor orientation is varied in the top and bottom halves of the windings. AC loss simulation giving consideration to asymmetric conductor critical current before winding the transformer could lead to substantial AC loss reduction even using the same amount of conductor and the same transformer design.

Wind energy is seen as one of the main pillars of renewable energy. However, the intermittent nature of these sources still poses as a major challenge. Moreover, sensitivity to grid faults and response to load changes are also main concerns.Superconducting devices have been introduced to solve grid faults and energy storage problems associated with renewable energy sources. Nevertheless, the cost of superconducting materials was still a major drawback for their application in power grids.In this paper, a novel power electronics circuit is used to connect the superconducting magnetic energy storage (SMES) to a DC system based on a doubly fed induction generator wind turbine. The proposed system merges energy storage function and the fault current limiting function into one device which is referred to as SMES-FCL in this paper.The role played by the SMES-FCL is studied under various scenarios that may affect the whole system. The study of the system is carried in MATLAB/SIMULINK where the system is simulated in standalone and grid-connected modes. In the end, the proposed SMES-FCL control circuit is tested in a small-scale DC system experimentally.

DC system protection is more challenging than that for AC system due to the rapid rate of rise of the fault current and absence of natural current zero-crossing in DC systems. Superconducting fault current limiter (SFCL) in DC systems is a promising technology to reduce the fault current level and the rate of rise of the fault current, and also SFCLs have no resistance during normal operation. In this paper, the behaviors of an SFCL coil are investigated under both low impedance and high impedance fault conditions in DC systems. In the low impedance fault condition system, the SFCL coil performs effective limitation of the fault current level under different prospective fault current levels. The application of SFCLs with limited inductance in the DC system can be a potential solution to effectively suppress the fault current under low impedance short-circuit faults. The SFCL coil under the high impedance fault condition can only limit the prospective fault current when it is much higher than the critical current of the coil.

High-density power conversion and energy storage solutions were and are being explored for use in Electric Aircraft (EA). A superconducting magnetic energy storage (SMES) system is a promising candidate due to its fast response and ability to satisfy large pulse loads as is expected from EA. For the SMES, Dual Active Bridge (DAB) converters can offer high-density power conversion and provide galvanic isolation. This paper proposes a design methodology for a bidirectional DC/DC converter using DAB converter and a MOSFET-based chopper to interface SMES. This paper includes analysis, performance prediction, and needs for implementation in EA. The DAB/SMES system has been successfully designed, analyzed, and is being optimized for application in EA.

The distributed propulsion aircraft with HTS electrical system is a novel concept for future airliners, which can reduce by more than 70% fuel burn and NO x emissions. The circuit breakers ensure the security of this novel aircraft by isolating electrical faults timely. Solid-state circuit breakers (SSCBs) are preferred due to their fast response and high performance in the cryogenic circumstance. However, the high conduction loss of SSCBs impedes their further application. A mechanical switch using liquid nitrogen (LN 2 ) as an arc extinguishing medium shows excellent DC current interruption performance. The LN 2 switch is characterized with extremely low contact resistance, and the proper use may reduce the conduction loss of power switches significantly. Nevertheless, the effect of metal type arc chutes on the arcing process in the LN 2 is still not clear. Thus the objective of this paper is to understand the effect of metal type arc chutes on the current interruption performance of LN 2 . Silicon iron arc chutes are employed. Neodymium (NdFeB) magnets are used to stretch the arc into the arc chutes. The maximum interrupting current is 1 kV/ 2 kA when only magnets are applied. Further applying the arc chutes leads to a significant drop in the arc voltage and interruption performance. Since the high relative permeability of silicon iron weakens the magnetic field acting on the arc, metal type arc chutes are not recommended. 1 kV / 10 kA fault current is successfully cleared by the combination of resistance type superconducting fault current limiter (R-SFCL) and LN 2 switch with magnets, during which the R-SFCL responds to the fault within 420 μs, compensating the long clear time of the LN 2 switch.

It is of great industrial interest and academic importance to investigate current harmonics impacts on AC losses of superconductors, especially in large-scale power devices. However, only effect of amplitude of in-phase current harmonics on AC loss has been studied in the works of literature. We numerically characterized nonsinusoidal AC loss of superconducting tape carrying harmonic currents with orders below 20th versus phase angles. A drastic AC loss variation was found when phase angle was considered for harmonic components. We observed that different harmonic orders show different AC loss profile versus phase angle.

Large scale resistive superconducting fault current limiters (SFCLs) have attracted great interest in electric power systems and aviation applications due to their compactness, lightweight, automatic fault current limiting, and fast recovery characteristics. Noninductive coil wound with stacked conductors in parallel connection is commonly used to achieve high current rating for SFCL. It is of great significance and engineering value to minimize ac losses in the noninductive coil by optimizing the configuration of the stacked conductors in order to reduce the thermal load for the cooling system. In this article, multiple possible configurations of noninductive stacks where each turn is composed of one, two, and three conductors, respectively, were proposed. Numerical models were developed to investigate the effect of noninductive stack configuration on ac loss. Eight-turn noninductive solenoidal coils wound with the noninductive stacks mentioned in the above were also simulated. It is concluded that the configuration of the noninductive stack significantly affects the perpendicular magnetic field distribution in the end edges of the stack. Single-layer configurations have limited magnetic field cancellation effect. The stack configuration with low ac loss and simple structure was suggested.

A nearly all-superconducting power system is considered as a promising path to realize Turboelectric distributed propulsion (TeDP) Aircraft. The options of power switches are rather limited and only cryogenic power electronics are into the scope so far. A mechanical switch using LN2 as an arc extinguishing medium (LN2 switch) can be a promising alternative that has lower conduction loss. However, basic research on current interruption in LN2 is still lacking, especially the effect of magnetic fields. The objective of this paper is to understand the effect of the magnetic field on DC current interruption by LN2. Interruptions under different magnetic fields are tested. A two-stage arcing process is observed under the magnetic field. Stage 1 is similar to that in the air while stage 2 is distinguished as interactions between vaporized LN2 and arc. 600 V DC/ 1 kA is interrupted by LN2 under 62.5 mT successfully. The interruption current is 8 times higher than that of without magnetic field applied. The magnetic field strengthens arc cooling by enhancing arc motion in LN2. Adding no burden to refrigeration, an LN2 switch can be a promising application in HTS electrical system.

High temperature superconductor (HTS) techniques can be used to design high efficiency power or traction transformers with considerable AC loss and volume reduction compared with conventional transformers. Further, HTS transformers are environmental friendly, with no risk of fire hazard or pollution. In this paper, superconductor windings of a transformer are modeled and flux diverters (FDs) are applied to the ends of windings for magnetic field and AC loss analysis. A homogenization approach is used to save computation cost of the model. The distribution of AC loss is quantized for analysis. Observations suggest that the flux diverters optimize flux distribution and are conducive to AC loss reduction.

A new switchgear named Liquid Nitrogen Insulated metal-enclosed Switchgear (LNIS) is proposed, which uses LN2 as an insulation medium to substitute SF 6 in Gas Insulated metal-enclosed Switchgears (GIS). Power loss of the LNIS is only about 1/8 of the same level GIS, making the novel switchgear a fascinating technology for future power systems. To make the switchgear more compact and efficient, LN2 is also used as an arc extinguishing medium of disconnecting switches. Thus, closed-loop current that can up to thousands of amps should be interrupted by LN2. However, AC current interruption ability of LN2 is still unknown. The objective of this paper is to obtain the AC current interruption properties of LN2. Experiments are conducted with currents ranging from 700 A to 4 kA. AC current of 2950 A (Peak value) is interrupted by LN2 successfully. The maximum arc energy during the interruption is about 437 J, far less than the Joul heat generated by the rated current flow. Arc energy during interruption doesn't burn extra burden on the cooling system. Thus, AC current interruption ability of LN 2 could meet requirements for LNIS.

Superconducting fault current limiters (SFCLs) are foreseen to be critical and promising candidates in power system applications, due to their automatic fault current limiting performance, low loss, size compactness and light weight. A helical bifilar coil which is composed of one inner winding and one outer winding was developed, and these two windings were wound on the same coil bobbin with opposite directions and connected in parallel. Experiments were carried out to characterize the fault current limitation behavior of the helical bifilar coil in flux flow mode, when the prospective fault current falls in over-critical current regime yet still within 2 times of the coil's critical current. The current limiting performance of the helical bifilar coil in flux flow mode was demonstrated and discussed.

A combination of resistive type superconducting fault current limiters (R-SFCLs) and mechanical-type DC circuit breaker is a reliable way to protect the medium voltage and high voltage DC systems. Using the insulation barrier plays an important role in enhancing the insulation strength of R-SFCL. It promotes the development of R-SFCLs to a higher voltage level. However, the bubbles effect on the DC flashover characteristics of the insulation barrier is unknown. The objective of this paper is to obtain the DC flashover characteristics of insulation film with and without bubbles in liquid nitrogen (LN2). In the experiments, a triangle-plane electrode was put horizontal and immersed in LN2. A 14 W heater was placed right below the gap of two electrodes. Negative flashover characteristics of PTFE and Kapton were studied with different gap distances. The results show that the negative flashover voltage of PTFE film increases with the increase of gap distance both in conditions with and without bubbles. The shorter the gap distance between the triangle and plane electrodes is, the stronger the influence of bubbles on the negative flashover voltage is. The flashover voltage of PTFE is 1.15 times of Kapton both in the conditions with and without bubbles. The results could be used to design the insulation structure of high voltage R-SFCLs.

Hybrid electric propulsion could be the solution to the ambitious environmental targets of the aerospace industry. Fully-superconducting machines have the potential to deliver the step-change in specific torque, power, and efficiency capabilities required for large civil transport aircraft applications. However, fully-superconducting machines are still in their infancy. This article investigates the electromagnetic design of two different stator design concepts for an ac fully-superconducting machine for an aerospace distributed fan motor application. A benchmark aerospace specification of 1 MW was chosen and the design of a conventional permanent-magnet machine was used to assess the performance of the two equivalent fully-superconducting ac motor designs. Following the guidelines from an experimental study of the losses in a small ac stator prototype with MgB 2 coils, a fully-superconducting air-cored stator design and a new yokeless stator design are proposed. Both ac superconducting machine designs use superconducting bulk magnets mounted on a rotor core and an MgB 2 superconducting stator winding. This article discusses the key design issues of the two stator layouts in relation to the current aerospace targets for efficiency and power density.

Application of high-temperature superconducting devices become promising in power networks, and transportation, including ship, train, and electric aircraft propulsion systems, with the advantages of light weight, compact size, and high efficiency, compared to conventional devices. In reality, electric networks-either in grid or transportation propulsion system-are polluted with harmonics due to the widespread use of power electronic devices and nonlinear loads. It is essential to explore the dependency of harmonic ac losses of different coil configurations carrying nonsinusoidal current. We modeled and compared harmonic ac loss behaviors in three coil configurations, single pancake coil (SPC), double pancake coil (DPC), and solenoid coil (SNC), where SPC and SNC are wound by identical wire length and DPC has twice conductor number compared to SPC. The research work has been carried out by means of H-formulation finite element method in a 2-D axisymmetric modeling environment of COMSOL Multiphysics. We explored and reported ac losses in these three coil structures carrying nonsinusoidal current with the third and the fifth harmonic orders, respectively, under different total harmonic distortion (THD) and fundamental current levels. It has been concluded that ac loss in these coils first decreases with the increase of the third harmonic content, when THD of the third harmonic 0.2. AC loss in coils monotonically increases with the increase of the fifth harmonic, drastically. We found that ac loss in SPC carrying the third harmonic and the fifth harmonic at different THD are more than 3.8 times of that in DPC; ac loss in SPC carrying either third or fifth harmonics at different THD are around 4.5 times of that in SNC.

Driven by the requirements of reducing air pollutant gas emissions and fuel consumption, the concepts of more electric ship and electric aircraft are attracting increasing attention. Medium voltage DC (MVDC) distribution architectures have been proposed as potential candidates to transmit and distribute energy from generators to motors in these applications. However, the low impedance in MVDC systems results in extremely fast propagation speed of fault currents. Therefore, it is necessary to interrupt the DC fault in a very short period. This paper investigates a solid-state circuit breaker with an ultrafast interruption speed as a main breaker for a hybrid DC circuit breaker. A simulation model of the hybrid circuit breaker is established using PLECS software to evaluate the performance of the main breaker. A 1 kV solid-state main breaker prototype based on series and parallel connected insulated gate bipolar transistors (IGBTs) is built. Series and parallel connection of IGBTs are implemented to increase the voltage and current level. The maximum voltage across the solid-state circuit breaker is limited to 1.8 kV during current interruption. The solid-state main breaker prototype is experimentally tested under dynamic current conditions. The solid-state main breaker prototype successfully interrupts current of 400 A within 300 microseconds and presents good voltage balancing as well as current sharing performance. The experimental results show good agreement with the simulation results.

Integrated full electric propulsion systems eliminate the direct mechanical coupling between the prime mover and the propeller, enabling easier connection of multiple prime movers and allowing more equitable and fuel-efficient engine loading. These features are important in both cruise ship and naval warship design. Propulsion and ship service systems require different electrical ratings. The general solution is to use multiple electrical machine sets. To approach the most compact design and maximise the weight reduction, a dual wound machine is considered in this paper. It has dual two-layer windings which share the same slots and uses one prime mover, to produce two independent power supplies. This paper designs a dual wound machine with no electromagnetic coupling due to the airgap fields, by algebraically analyzing the harmonic distribution. Further verification of the nil electro-magnetic coupling due to both the airgap and slot leakage fluxes is provided by 2D finite element modeling. Both loaded and unloaded conditions are considered.

It is crucial to achieve a high safety and reliability standard in future electric propulsion aircraft (EPA). Due to low short-circuit impedance and high rate of fault current rise in EPA systems, the superconducting fault current limiter (SFCL) plays a promising role, with advantages of lightweight, high efficiency, and compact size compared with conventional FCL. A novel helical bifilar coil is proposed, which is composed of two windings wound in opposite directions on the same bobbin; these are connected in series to achieve equal current sharing and a noninductive circuit. The 12-mm-wide stainless steel-reinforced superconducting tape from AMSC was used for the windings. To characterize the proposed helical bifilar coil connected in series (BCS), AC loss tests under three frequencies and quench tests under prospective fault current up to 2223 A were carried out. They were compared with the results measured from a conventional helical bifilar coil connected in parallel (BCP) that had an identical specification to the BCS. It was concluded that the AC losses measured in the BCP are dependent on the current and frequency. The fault current was suppressed effectively by the BCS at the first half peak from 2223 to 495 A, corresponding to 22.3% of the prospective fault current. The quench performance of BCP was also tested and discussed.

The mitigation of peak-valley difference and transient power fluctuation are both of great significance to the economy and stability of the power grid. This paper proposes a novel vehicle-to-grid behavior management method that can provide peak-shaving and fast power balancing service to the grid simultaneously. Firstly, a multi-time scale vehicle-to-grid behavior management framework is designed to enable large-scale optimization and real-time control at the same time in vehicle-to-grid scheduling. Then, the grid peak-shaving requirement is modeled as an optimization problem in a centralized V2G state coordinator, where the charging behavior of all grid-connected electric vehicles can be synergistically scheduled. The optimization variable is designed as a group of vehicle-to-grid state control signals that can respond to grid peak-shaving requirements. Further, a V2G power controller is designed to manage the vehicle charging power in real time based on the sampled grid frequency state and discrete state control signals. In the developed scheduling method, the charging power of grid-connected electric vehicles is scheduled by the cooperation between the V2G state coordinator and the power controller. The effectiveness of the proposed methodologies is verified on a microgrid system, and results indicate that the V2G scheduling can achieve multi-time scale grid power balancing. This work can bring dual benefits, enabling system operators to use cheap solutions to manage energy networks and allowing vehicle owners to gain profits from providing V2G services to the grid.

Medium voltage direct current (MVDC) systems have been proposed for a variety of applications including offshore wind farm collector system and transport electrification. An efficient and reliable hybrid DC circuit breaker is critical for MVDC system protection. The operating speed of the hybrid DC circuit breaker heavily relies on the speed of the mechanical circuit breaker. Two types of actuators: moving magnet actuator and moving coil actuator using electromagnetic interaction are compared in this paper for the operation of a medium voltage vacuum interrupter. The Finite Element software package COMSOL is used to simulate the static and dynamic performance of each actuator topology. The paper focuses on comparing the advantages and disadvantages of these two actuator topologies particularly for vacuum interrupter application. The moving coil actuator is found to have better dynamic performance and is more suitable for medium voltage vacuum interrupter application.

AC losses in superconductors are essential for the design of cooling system for large scale power applications. Magnesium diboride (MgB 2 ) superconducting wires have been investigated and manufactured over the last decade due to cheap raw materials and flexibility for coil design. In addition, multifilamentary MgB 2 wires have been manufactured to reduce ac losses. In this paper, self-field ac losses of multifilamentary MgB 2 wires with magnetic barrier are investigated using both experimental and numerical methods. A short straight wire sample and a coil sample are tested under various temperatures and frequencies between 16-and 128-Hz. The test results show that the transportation loss is independent of the operating temperature. On basis of both theoretical and numerical study, it is found that hysteresis loss in superconductor accounts only for a small fraction of the transportation losses, ferromagnetic hysteresis loss in the magnetic barrier dominates when the transport current is low, whereas eddy current loss dominates when the transport current is close to the critical current.