Superconducting Magnetic Energy Storage Coil Research Articles

Demonstration and thermal equilibrium analysis of a 10 kJ capacity energy storage coil made of MgB2 with liquid hydrogen indirect cooling

We have demonstrated an advanced superconducting power conditioning system, in which a superconducting magnetic energy storage (SMES) device, a generator based on a fuel cell (FC), and an electrolyzer are used to compensate for electricity fluctuations over a wide frequency range, combined with a liquid hydrogen storage system to both cool the SMES and provide pure hydrogen gas to the FC and other gas-dependent systems. To manufacture the coils for the SMES, we used MgB2, whose critical temperature is below the boiling temperature of hydrogen. We developed a 10 kJ SMES coil system indirectly cooled by liquid hydrogen using thermosyphon passive heat exchange to isolate the flammable hydrogen from the electrical components. We performed a successful demonstration of this system for both DC and AC currents ramped at different rates. In the present study, we use computer simulations involving heat balance equations to evaluate the stability of the system. The results obtained are expected to lead to the design of future large-capacity energy storage systems, such as the MJ class, which offer comparable performance to conventional NbTi SMES devices.

Uses of Superconducting Magnetic Energy Storage Systems in Microgrids under Unbalanced Inductive Loads and Partial Shading Conditions

Superconducting magnetic energy storage (SMES) systems are characterized by their high-power density; they are integrated into high-energy density storage systems, such as batteries, to produce hybrid energy storage systems (HESSs), resulting in the increased performance of renewable energy sources (RESs). Incorporating RESs and HESS into a DC bus to obtain a DC microgrid concept is considered a more attractive option for solving system reliability and stability issues. In this paper, we focus on employing SMES systems based on their characteristics of a fast response and high efficiency, which contribute to increased battery lifespan, and reducing the mismatch between the energy supplied by the renewable energy source and the load demand by compensating for the effects of partial shading on the PV system on the DC bus side and the imbalance in loads on the other side of the AC bus. The incremental conductance algorithm (INC) is used for maximum power point tracking (MPPT) in the PV system. Fuzzy logic control (FLC) is proposed for the generation of control signals for the DC–DC chopper used to charge/discharge the SMES coil. Simulations using MATLAB/Simulink were then carried out to assess the proposed models of the (standalone and grid) connection systems.

AC Loss Measurement of Double Pancakes Wound With MgB2 Rutherford Type Superconductor

Double pancakes (DPs) for a Superconducting Magnetic Energy Storage (SMES) coil have been developed using MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Rutherford type superconductors. The DPs with 400 mm ID and about 600 mm OD were wound with Rutherford type conductors cabled by twisting multi-filamentary MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> strands. For use in an indirect cooling system, the DPs and thin pure copper sheets as thermal conductors were alternately stacked, and the SMES coil was assembled. In the experiment, while continuous triangular current waveforms up to 600 A and DC current were supplied to two configurations of the SEMS coil, the AC loss at 4.2 K was measured by calorimetric method. By comparing the losses under each excitation and configuration, the AC loss in the SMES coil and an eddy current loss in the copper sheets were obtained, separately. The resultant AC loss in the SMES coil was in agreement with the theoretical values.

Operation Scenario of Mobile SMES for On-Site Eigenvalue Measurement of Electric Power System

Eigenvalues are essential values for discussing the stable operation of the power system. However, the eigenvalues vary in real-time, and their distribution is complex in the power system. The authors conduct a design study on a 1 MJ-class mobile superconducting magnetic energy storage (SMES), enabling the eigenvalue measurement while changing locations. To achieve the weight saving and heat load reduction of the SMES coil, the authors applied the force-balanced coil (FBC) configuration to minimize the required mass of structures. Cryocoolers cool the SMES coil composed of MgB <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> Rutherford cables with a temperature range of 10 K to 20 K. The layout of the compressors requires at least 1 m away from the SMES coil due to the leakage magnetic field. The heat load calculation results show that the mobile SMES keeps over 90% of the energy cycle efficiency during the on-site eigenvalue measurement. Moreover, from the calculation results on the thermal time constant and the re-cooling time of the SMES coil, the eigenvalue measurement can immediately be restarted with the reduced power of SMES in urban areas. The eigenvalue measurement intervals in the suburbs will be every two days.

Evaluation of Operating Characteristics of Coils Wound With No-Insulation REBCO Bundle Conductor for SMES

Superconducting magnetic energy storage (SMES) has the advantages of high efficiency, longevity, and excellent instantaneous response with high power. However, it has the disadvantage of having a very low energy storage density in comparison to other power storage devices. The no-insulation coil (NI coil) is expected to be a winding method capable of achieving both high current density and high thermal stability. It is predicted that if this NI coil technology can be used for SMES, it will be possible to improve energy storage density by achieving higher current density. Because the SMES is a power device, it is generally preferred for coils to be designed with high current and low inductance. Therefore, in this study, we considered adopting the winding method in which a bundle conductor using of multiple no-insulation REBCO tapes is wound without electrical insulation (hereinafter referred to as “bundle NI coil”) for SMES coils. However, because the REBCO tapes in the bundle conductors are not electrically insulated from one another and the bundles also have no electrical insulation between one another, the time variation of the current distribution in the bundle NI coil becomes extremely complicated. Therefore, we developed a computer program that analyzes and evaluates the current distribution in a bundle NI coil, and for application to SMES, we numerically investigated the behavior during charge and discharge of a coil wound with a no-insulation bundle REBCO conductor. Furthermore, a small bundle NI coil was constructed and tested to confirm the validity of the developed computer program, and the time variation of the current distribution in the bundle conductor was based on the analysis results. In addition, the effect of the NI bundle coil on the storage efficiency when used to SMES was investigated experimentally and numerically.

Adaptive Neuro Sliding Mode Control of Superconducting Magnetic Energy Storage System

ABSTRACT In this paper, an adaptive RBF neural network-based sliding mode controller is developed for superconducting magnetic energy storage (SMES) installed in a wind–diesel power system. Due to sudden load and wind power variations in a wind–diesel power system, power imbalances may force the system frequency to deviate from its nominal value and drive the system to operate in an unstable mode. Therefore, in a wind–diesel power system using a converter interface, a fast-acting and high power density SMES device is interconnected to carry the required power exchange whenever power imbalances occur. Based on switching manifold design, a sliding mode controller is developed to control the charging and discharging operations of SMES coil as per the power requirements, and the same is achieved by controlling the converter. A neural network using a radial basis function (RBF) is developed to estimate the unknown function of the system. Lyapunov stability analysis is conducted to guarantee the asymptotic stability of the system. MATLAB simulations are carried out and are presented to show the improved performance with the system exposed to disturbances in load and wind power.

Mitigation of pulsed power load effect on power system using FLC-SMES

Integration of the pulsed power load (PPL) into the power system leads to high fluctuations in the frequency and voltage at the point of common coupling (PCC). This paper presents an effective solution to overcome these issues related to the PPL using the superconducting magnetic energy storage (SMES) system that has the features of high power capability and fast response. The fuzzy logic control technique (FLC) is employed to control the interfaced DC–DC chopper of the SMES to regulate the active power of the PCC and the state-of-charge (SOC) of the SMES coil. Two scenarios have been addressed with/without integrating the SMES conversion system. The on-time of the studied PPL is 0.1s with a total power of 5.7 MW, which is considered a high power demand in a short period. The simulation results based on MATLAB/Simulink show the high performance of the proposed system based on the FLC-SMES to minimize the voltage and frequency fluctuations during the operation of PPL.

Integration of PV system with SMES based on model predictive control for utility grid reliability improvement

This paper describes the integration of a photovoltaic (PV) renewable energy source with a superconducting magnetic energy storage (SMES) system. The integrated system can improve the voltage stability of the utility grid and achieve power leveling. The control schemes employ model predictive control (MPC), which has gained significant attention in recent years because of its advantages such as fast response and simple implementation. The PV system provides maximum power at various irradiation levels using the incremental conductance technique (INC). The interfaced grid side converter of the SMES can control the grid voltage by regulating its injected reactive power to the grid, while the charge and discharge operation of the SMES coil can be managed by the system operator to inject/absorb active power to/from the grid to achieve the power leveling strategy. Simulation results based on MATLAB/Simulink® software prove the fast response of the system control objectives in tracking the setpoints at different loading scenarios and PV irradiance levels, while the SMES injects/absorbs active and reactive power to/from the grid during various events to improve the voltage response and achieve power leveling strategy.

A novel concept of SMES-based interline DC dynamic voltage restorer

The fast-response feature from a superconducting magnetic energy storage (SMES) device is favored for suppressing instantaneous voltage and power fluctuations, but the SMES coil is much more expensive than conventional battery energy storage device. In order to improve the energy utilization rate and reduce the energy storage cost under multiple-line power distribution conditions, this paper investigates a new interline DC dynamic voltage restorer (IDC-DVR) scheme with one SMES coil shared among multiple compensating circuits. In this new concept, an improved current-voltage (I/V) chopper assembly, which has a series of input/output power ports, is introduced to connect the single SMES coil with multiple power lines, and thus to satisfy with independent energy exchange requirement of any line to be compensated. Specifically, if two or more power lines have simultaneous compensating demands, the SMES coil can be selectively controlled to compensate the preferable line according to the priority order of the line. The feasibility of the proposed scheme is technically verified to maintain the transient voltage stability in multiple-line voltage swell and sag cases caused by either output voltage fluctuations from external power sources or power demand fluctuations from local sensitive loads. The simulation results lay some technical bases to develop a cost-effective SMES-based IDC-DVR for the use in various DC distribution networks.

Application of SMES Technology in Improving the Performance of a DFIG-WECS Connected to a Weak Grid

Wind Turbine Generator (WTG) has become one of the most popular renewable-based power generation that is broadly connected to electricity grids worldwide. Till the year 2019, the total WTGs installed worldwide reached about 650.8GW. The WTG is interfaced to the electricity grid through power electronic converters with a proper control algorithm to facilitate a smooth power delivery as well as maintaining the system voltage and frequency stability during wind intermittency. However, power grids are usually subjected to load expansion which affects the stiffness of the grid and hence its stability. A weak electricity grid exhibits voltage instability that may affect the performance of WTGs and in some cases may lead to serious damages to the wind turbines and the entire system. In this paper, superconducting magnetic energy storage (SMES) technology based on fuzzy logic controller is implemented to effectively resolve this issue and improve the overall performance of WTGs. Hysteresis current and fuzzy logic-based control system is proposed to control the energy exchange between the SMES coil and the investigated system. Results show the effectiveness of the SMES to improve the overall system performance and along with the fault ride-through capability of the doubly-fed induction generator (DFIG).

Theoretical and experimental investigation of R&W and W&R SMES coils wound with large-scale MgB2 Rutherford cables operated around liquid hydrogen temperature

We have developed the system called Advanced Superconducting Power Conditioning System (ASPCS) composed of a Superconducting Magnetic Energy Storage (SMES), a fuel cell and a water electrolyzer for effective use of renewable energy such as wind and solar power generation. We have been investigating about the SMES coil using the large-scale Rutherford-type conductors made of commercially-available MgB2 wires. Due to strain sensitivity even before heat treatment for MgB2 production, the design for large-scale Rutherford cables both in the wind and react (W&R) method, and the react and wind (R&W) method applied to coil fabrication has to be done cautiously to prevent the degradation of the IC by the optimizing design parameters such as the twist pitch and the cable compaction. Especially for the R&W method using heat-treated wires, other factors like handling during the coil production process which affect the conductor and coil IC should be also considered. To evaluate the applied strains during the manufacturing process, we conducted theoretical investigation on the strains applied to individual filaments caused by wire-bending. We developed a test coil designed for the R&W method based on analyzing those factors. Furthermore, we measured the coil IC-B-T characteristics and compared to those of other test coils made by the W&R method.

Minimum power loss based design of SMES as influenced by coil material

• Optimizing the dimensions of the SMES coil to achieve minimum coil loss • The Genetic Algorithm (GA) is utilized to minimize the coil loss as a multi-objective function • Optimal AC loss, refrigeration loss and total loss of SMES coil • Different coil materials are considered to select the best material with minimum coil loss. • The effect of the twist pitch and circumferential stress on the total losses in the SMES coil is studied. Superconducting magnetic energy storage (SMES) system is one of the commonly used techniques by the end-users to mitigate the voltage sag at their premises from the distribution system. The SMES is a superconductor coil wound on a nonmagnetic core. The paper is aimed at optimizing the dimensions of the coil to achieve minimum coil loss. The Genetic Algorithm (GA) is utilized to minimize the coil loss as a multi-objective function with indices including AC loss and refrigeration loss. The results show that the optimal total loss of SMES coil at capacity energy of 4 MJ is 85.04 W against 114.5 W in a previous work. The corresponding optimal dimensions of the coil which include the inner diameter, outer diameter and coil length are 0.19, 0.2 and 2.17 m, respectively. Different low-temperature superconductivity coil materials at operating temperature of 4.2 o K are considered to select the best material with minimum coil loss. The results conclude that Nb–Ti material achieves minimum coil loss when compared with MgB 2 and YBCO. The effect of the twist pitch and circumferential stress on the total losses in the SMES coil is studied.

Mobile Superconducting Magnetic Energy Storage for On-Site Estimations of Electric Power System Stability

Renewable energy and electric power liberalization have become important watchwords for present electric power systems. However, the stability of electric power systems is also a serious concern. Superconducting magnetic energy storage (SMES) systems are a promising candidate for the on-line evaluation of power system stability. From the viewpoint of the mobility of SMES systems, the authors carried out a design study on a 1 MJ-class mobile SMES system using MgB 2 Rutherford cables. The results showed that 1) the 1 MJ-class mobile SMES components can be installed in a 40 feet dry container; 2) because of the effect of the force-balanced coil design, the SMES coil can be excited up to 2.0 T or 3.0 T without reinforcements for the MgB 2 Rutherford cables; and 3) the 1 MJ-class mobile SMES coil can be cooled using 3 or 4 sets of conventional cryocoolers, including the cooling system for a 80 K thermal shield at a cooling temperature of 20 K or 10K. Therefore, the engineering feasibility of the 1 MJ-class mobile SMES system using MgB 2 Rutherford cables is confirmed.

Development of MgB&lt;sub&gt;2&lt;/sub&gt; Rutherford Cable for Large-scale SMES Coils Cooled by Liquid Hydrogen

To realize the practical application of Superconducting Magnetic Energy Storage (SMES) systems cooled by liquid hydrogen, MgB2 is promising as a material for SMES coils in terms of reducing cost in the future and enabling high critical temperature above the temperature of liquid hydrogen. Major technological development issues to realize the application of SMES coils are fabrication of the Rutherford superconducting cable with a kA-class current capacity and fabricating the coils using both Wind and React (W&R) and React and Wind (R&W) methods. Since there is little data regarding the allowable bending strain of the MgB2 strand before heat treatment, an experiment was conducted and it was determined to be approximately 4 % before the fabrication of the cable. The Rutherford cable was designed and developed based on analysis of the space curve theory because the complex bending strain is exposed to the MgB2 filaments during the cable and coil fabrication processes. However, the critical currents measured using cables developed according to the design were degraded approximately 30%. This degradation can be explained as being due to local deformation of the strands caused by compression at the cross-over point between the strands of the conductor. The broken sections of the Nb barrier, which were observed by reviewing SEM images of the strand cross-section, can cause degradation of the critical current. Two double pancake coils, which were primarily wound using the Rutherford cables and manufactured applying both the R&W and W&R methods for the purpose of comparing fabrication processes, were connected in series to excite the coils. As a result, an operating current of 600 A was successfully achieved.

Study on Conceptual Designs of Superconducting Coil for Energy Storage in SMES

Superconducting Magnetic Energy Storage (SMES) is an exceedingly promising energy storage device for its cycle efficiency and fast response. Though the ubiquitous utilization of SMES device is restricted because of the immense cost of cryogenic refrigeration system to sustain the superconducting state but with the continuous evolution of high Tc superconductors, SMES is turning into a major contender to the existing energy storage devices in the future. Among its several parts, the superconducting coil is considered to be the most crucial segment of this technology and the inductance generated in the coil determines the quantity of stored energy. In this paper, the possible geometrical configurations of SMES coil have been demonstrated. High Tc superconducting tapes are usually employed to form these configurations worldwide. BSCCO (Bismuth strontium calcium copper oxide)-2223 tape superconductor has been considered for studying the conceptual designs of superconducting coil of SMES. Before estimating the results, the value of critical current at different magnetic field densities and temperatures have been addressed through the study of superconducting tape characterization. Numerical results and the relationship among the several parameters for both the solenoid and toroid configurations in different specifications have been presented. Based on the results, the size ratio in solenoid and the mean toroid diameter in toroid arrangement is found to play the vigorous roles in the generation of inductance and hence the energy storage. The results also match the propensity of other studies. Suggestions for maximum energy gain from a specific solenoid configuration have been provided. Future research scopes with alternative superconducting tapes and limitations of this study have been briefly conferred.

Enhancement of DFIG LVRT Capability During Extreme Short-Wind Gust Events Using SMES Technology

Wind energy is one of the premier renewable energy sources that have gained popularity during the last decade. Among the currently available wind energy conversion systems (WECS), doubly fed induction generator-based technology has been widely employed due to its superior advantageous. The key features of the DFIG-based WECS include its ability to capture more wind energy and support the grid with large reactive power during short disturbance events. On the other hand, DFIG is very sensitive to grid faults which affect its fault ride through (FRT) capability. Furthermore, extreme wind gust even for short durations may lead to the violation of the low voltage ride through (LVRT) threshold limits set by worldwide transmission line operators. This situation cannot be mitigated by the turbine blades pitch controller since the response of the pitch mechanical control is much slower than the rapid dynamic change in the wind speed during short duration of wind gust events. While DFIG FRT capability has been discussed in several papers in the literature, not much attention was given to the mitigation of the effects of extreme wind gust of short duration on the DFIG performance. In this paper, the effect of various levels of wind gust on the performance of a DFIG-based wind energy conversion grid-connected system is investigated and mitigated using a new controller for superconducting magnetic energy storage (SMES) unit. A combination of hysteresis current and fuzzy logic controllers is employed to control the voltage source converter and the DC-DC chopper interfacing the SMES coil with the investigated system. Simulation results reveal the effectiveness of the proposed SMES controller that can be easily implemented within existing as well as new WECS installations.

Stability Analysis of MgB2 Coils for SMES Application Consisting of Large-Scale Rutherford Cables

MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> wires have been provided by several manufacturers, showing enough critical current (Ic) for practical applications in relatively low-field. Because the MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> has critical temperature above boiling temperature of hydrogen, dc power distribution system with low carbon emission using MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> superconducting magnetic energy storage (SMES), named advanced superconducting power conditioning system has been proposed. For the system, the MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> coil production technology obtaining 30 kJ stored energy the investigation about the SMES coil consists of 600 A, 1.7-T Rutherford-type conductors made of commercially-available MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> wires. Due to strain sensitivity before/after heat treatment for MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> production, the proper designs of the large-scale twisted conductors both in wind and react, react and wind methods are needed, choosing optimized twist pitches and cable compaction factors. To demonstrate the SMES coil performance, we have been carried out the test campaign of conductors and small prototype coils in various temperature and background field conditions. These results are used for a computer simulation for estimating full size double pancake coil performance of the system, based on the non-steady state heat conduction analysis. The calculated result seems to be a good tool for predicting coil performance for the large capacity energy storage operation.

Design and Demonstration of a Double-pancake Coil for SMES using MgB2 Multi-strand cable

MgB2 round wires are now commercially available with applicable critical current density in magnetic fields up to 5 T. One of the promising applications using MgB2 is a superconducting magnetic energy storage (SMES) coil. In our project, multi-strand cables with 600 A nominal current are designed for double-pancake (DP) coils with 400 mm inner diameter. The coil production processes in our project are wind-and-react (W&R) and react-and-wind (R&W) methods, in which a Rutherford-type cable consisting of eight (W&R) or ten wires (R&W) with specific twist pitch is reacted and then used to wind the DP coils, to investigate the suitable manufacturing process for MgB2 coils. The final goal is to fabricate five-stacked DP coils, made up of four DP coils by the R&W method and one DP by the W&R method with a total number of 512 turns, forming a 30 kJ SMES coil and to demonstrate compensation of voltage fluctuation on the BUS line of 48 V DC in a micro grid consisting of renewable energy source and liquid hydrogen supply system in our project. The first DP coils made by the two manufacturing processes are constructed and tested with regard to their properties such as critical current density in liquid helium to keep uniform temperature distribution throughout the coils.

Feasibility Study of MgB2Cable for Pancake Coil of Energy Storage Device

Superconducting magnetic energy storage (SMES) devices of several tens of kJ class are generally suitable for voltage compensation for microgrids, which produce and distribute electric power to restricted areas. MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> material has been developed with superconducting properties by decreasing the production cost. Since hydrogen energy would be widely utilized to realize society with low carbon emission and stored in liquid state for reducing its volume, the power distribution system consisting of MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> SMES for compensation of voltage fluctuations cooled by the liquid hydrogen would be effective by synergy effect. However, the MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> introduction to large-scale devices is still not enough and under investigation. Our group carried out the investigations to develop MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> cable and pancake coil for the SMES device with specific capacity. The bending strain-sensitive characteristic of MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> material forces us to design the twisted conductors and pancake coils with various parameters properly within its tolerable bending strains of both before/after heat treatment. The conductor design for small pancake coils and large SMES coils is shown in this research, as well as the demonstration results of a small test coil fabricated as a prototype of SMES coil.

Effect of cryogenic temperature on electrical parameters of copper coil used in SMES

With the inclusion of renewable energy sources, the variability of the power supply has increased. To reduce this variability, energy storage equipments such as superconducting magnetic energy storage (SMES) are required. The energy is stored in SMES coil, making its design very crucial. This paper presents the effect of cryogenic temperature on the resistance and inductance of air core solenoid. The experiment is performed on the copper wire wound over teflon and copper formers. The published mathematical model for the calculation of the coil inductances is taken and results are compared with measurements performed with an LCR meter. The difference between the measured and calculated inductance value for both coils is found to be less than 10% at 300 K. The cryogenic temperature is maintained by first using a liquid nitrogen bath and later by cryocooler.