Resistive Superconducting Fault Current Limiter AC Loss Measurements and Analysis

Resistive superconducting fault current limiters (SFCLs) offer the advantages of low weight and compact structure. Multistrand magnesium diboride (MgB2) wire can be used in the SFCL coil design to increase the transport current capacity. A monofilament 0.36-mm MgB2 wire with a stainless-steel sheath was used to build three SFCL coils with 3 strands, 16 (9+7) strands, and 50 (28+22) strands of the MgB2 wire. The quench current level and ac losses in the MgB2 wire are critical design parameters for a resistive SFCL. The experimental results showed that the measured quench current densities reduced as the strand number increased and the ac losses increased as the strand number increased. An axisymmetric 2-D finite-element (FE) model therefore was built to analyze the current distribution and the ac losses in the coil. The multistranded coil FE model showed that proximity effect can modify the current distribution in the strands. This not only reduces the current carrying ability but also increases the ac losses nonlinearly. The FE model confirmed the issues highlighted by the experimental testing. Finally, a winding method for the multistrand coil has been proposed to reduce the impact of these effects.</p

Resistive superconducting fault current limiter coil design using multistrand MgB2 wire

Resistive superconducting fault current limiters (SFCLs) offer the advantages of low weight and compact structure. Magnesium diboride (MgB2) in simple round wire form has been previously tested and shown to be suitable as a low-cost resistive SFCL. The primary objective of this work was to design a resistive SFCL for an 11-kV substation using multiple MgB2 wire strands. This paper will look into the options for the coil design. Two types of low-inductance solenoidal coils, namely, the series-connected coil and the parallel-connected coil, were theoretically examined and compared. This paper also reports the experimental results of two multistrand MgB 2 prototype coils used as a resistive SFCL. This paper demonstrates the potential of SFCL coils using multistrand MgB2 wire for distribution network levels.</p

Simulation of a power electronic conversion system with short-term energy storage for actively controlled wave energy converters

A simulation study is conducted to assess the feasibility of a Wave Energy Converter Power Electronic Converter architecture to achieve a four quadrant torque demand resulting from an active control strategy. The system consists of four induction generators controlled by three phase inverters, a DC bus with short term energy storage provided by supercapacitors and batteries, and an active rectifier to control the DC bus voltage and provide AC power to the grid. The components are realistically modelled and it is shown that the torque and speed requirements of the active control strategy can be achieved and that the electrical energy storage can provide required reactive power on a wave-by-wave time scale and longer term energy supply during a lull in wave excitation. The WaveSub WEC is used as a target device in order to make a meaningful study with realistic inputs. However the architecture of the PEC system is applicable to any device with a bi-directional rotary PTO requiring four-quadrant active control at the generators. Furthermore the PEC architecture and simulation model are readily expandable to arrays of wave energy converters.</p

Simulation of a power electronic conversion system with short-term energy storage for actively controlled wave energy converters

A simulation study is conducted to assess the feasibility of a Wave Energy Converter Power Electronic Converter architecture to achieve a four quadrant torque demand resulting from an active control strategy. The system consists of four induction generators controlled by three phase inverters, a DC bus with short term energy storage provided by supercapacitors and batteries, and an active rectifier to control the DC bus voltage and provide AC power to the grid. The components are realistically modelled and it is shown that the torque and speed requirements of the active control strategy can be achieved and that the electrical energy storage can provide required reactive power on a wave-by-wave time scale and longer term energy supply during a lull in wave excitation. The WaveSub WEC is used as a target device in order to make a meaningful study with realistic inputs. However the architecture of the PEC system is applicable to any device with a bi-directional rotary PTO requiring four-quadrant active control at the generators. Furthermore the PEC architecture and simulation model are readily expandable to arrays of wave energy converters.</p

Vehicle-to-grid management for multi-time scale grid power balancing

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.</p

Experimental Tests of DC SFCL under Low Impedance and High Impedance Fault Conditions

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

Influence of Structure Parameters of Flux Diverters on Performance of Superconducting Energy Storage Coil

This article studies the influence of flux diverters (FDs) on energy storage magnets using high-temperature superconducting (HTS) coils. Based on the simulation calculation of the H equation finite-element model, FDs are placed at both ends of HTS coils, and the position and structure are optimized. The impact of the diverter structural parameters on the energy storage of the HTS energy storage magnet is explored, and an optimized diverter structure is designed. The rectangle is the most basic structure of FDs, so this article first optimizes the structure of the rectangular FDs and then performs various slotting treatments on the optimized FDs. By comparison, it is concluded that the concave FDs have the best energy storage effect. Then, based on the optimization of the concave FDs, a Γ-shaped structure is obtained, further improving the magnet's energy storage effect. The conclusion of the influence factors can be applied to the optimization design of diverter structures and provide a new perspective for improving energy storage.</p

Resistive Superconducting Fault Current Limiter AC Loss Measurements and Analysis

Resistive superconducting fault current limiters (SFCLs) offer the advantages of low weight and compact structure. Multistrand magnesium diboride (MgB2) wire can be used in the SFCL coil design to increase the transport current capacity. A monofilament 0.36-mm MgB2 wire with a stainless-steel sheath was used to build three SFCL coils with 3 strands, 16 (9+7) strands, and 50 (28+22) strands of the MgB2 wire. The quench current level and ac losses in the MgB2 wire are critical design parameters for a resistive SFCL. The experimental results showed that the measured quench current densities reduced as the strand number increased and the ac losses increased as the strand number increased. An axisymmetric 2-D finite-element (FE) model therefore was built to analyze the current distribution and the ac losses in the coil. The multistranded coil FE model showed that proximity effect can modify the current distribution in the strands. This not only reduces the current carrying ability but also increases the ac losses nonlinearly. The FE model confirmed the issues highlighted by the experimental testing. Finally, a winding method for the multistrand coil has been proposed to reduce the impact of these effects.</p

Hybrid Power System Topology and Energy Management Scheme Design for Hydrogen-Powered Aircraft

The electrification of the aviation industry is a major challenge to realizing net-zero in the global energy sector. Fuel cell (FC) hybrid electric aircraft (FCHEV) demonstrate remarkable competitiveness in terms of cruise range and total economy. However, the process of simply hybridizing different power supplies together does not lead to an improvement in the aircraft economy, since a carefully designed power system topology and energy management scheme are also necessary to realize the full benefit of FCHEV. This paper provides a new approach towards the configuration of the optimal power system and proposes a novel energy management scheme for FCHEA. Firstly, four different topologies of aircraft power systems are designed to facilitate flexible power flow control and energy management. Then, an equivalent model of aircraft hydrogen consumption is formulated by analyzing the FC efficiency, FC aging, and BESS aging. Using the newly established model, the performance of aircraft can be quantitatively evaluated in detail to guide FCHEA design. The optimal aircraft energy management is realized by establishing a mathematical optimization model with the reduction of hydrogen consumption and aging costs as objectives. An experimental aircraft, NASA X-57 Maxwell, is used to provide a detailed performance evaluation of different power system topologies and validate the effectiveness of the energy management scheme. The new approach represents a guide for future power system design and energy management of electric aircraft.</p