Currently, Lithium-ion batteries (LiB) are widely applied in energy storage devices in smart grids and electric vehicles. The state of charge (SOC) is an indication of the available battery capacity, and is one of the most important factors that should be monitored to optimize LiB’s performance and improve its lifetime. However, because the SOC relies on many nonlinear factors, it is difficult to estimate accurately. This paper presented the design of an effective SOC estimation method for a LiB pack Battery Management System (BMS) based on Kalman Filter (KF) and Artificial Neural Network (ANN). First, considering the configuration and specifications of the BMS and LiB pack, an ANN was constructed for the SOC estimation, and then the ANN was trained and tested using the Google TensorFlow open-source library. An SOC estimation model based on the extended KF (EKF) and a Thevenin battery model was developed. Then, we proposed a combined mode EKF-ANN that integrates the estimation of the EKF into the ANN. Both methods were evaluated through experiments conducted on a real LiB pack. As a result, the ANN and KF methods showed maximum errors of 2.6% and 2.8%, but the EKF-ANN method showed better performance with less than 1% error.

Predicting the output power of wind generators is essential to improve grid flexibility, which is vulnerable to power supply variability and uncertainty. Digital twins can help predict the output of a wind turbine using a variety of environmental data generated by real-world systems. This paper dealt with the development of a physics-based output prediction model (P-bOPM) for a 10 MW floating offshore wind turbine (FOWT) for a digital twin. The wind power generator dealt with in this paper was modeled considering the NREL 5 MW standard wind turbine with a semi-submersible structure. A P-bOPM of a 10 MW FOWT for a digital twin was designed and simulated using ANSYS Twin Builder. By connecting the P-bOPM developed for the digital twin implementation with an external sensor through TCP/IP communication, it was possible to calculate the output of the wind turbine using real-time field data. As a result of evaluating the P-bOPM for various marine environments, it showed good accuracy. The digital twin equipped with the P-bOPM, which accurately reflects the variability of the offshore wind farm and can predict the output in real time, will be a great help in improving the flexibility of the power system in the future.

This paper discusses the design and electromagnetic analysis of an induction-type coilgun system with a pulse power module. The voltage, current, force, velocity, acceleration, and efficiency of the coilgun system were analyzed using the finite-element method (FEM). A simplified FEM model was developed for ensuring both accuracy and rapid calculation times. Based on the results of the electromagnetic analysis, the geometry of the coilgun system was defined with the Taguchi method. The coil-type armature was applied for increasing the mutual inductance and projectile force. The electromagnetic analysis results were also compared with the analytical analysis results. The designed coilgun system was found to exhibit high energy efficiency and safety of the system. The design specifications and analysis results concerning the coilgun can, hence, be effectively utilized to develop a large-scale multistage induction-type coilgun system.

NI (no-insulation) superconducting coils using rare-earth barium-copper-oxide (REBCO) wires have been widely applied in various superconducting magnets due to superior electric, mechanical and thermal performance. Yet, NI coils present the intrinsic drawbacks of charging delays and heat losses by leakage current. MI (metal insulation) windings have also been proposed to increase the turn-to-turn contact resistance and improve the coil's mechanical strength. Both NI and MI REBCO conduction-cooled coils require additional thermal paths to a cryocooler, leading to the use of epoxies between interfaces. However, the use of epoxy requires precaution to prevent delamination problems or the loss of the NI characteristic when the epoxy penetrates through the winding turns. In this study, we propose a new winding technique, soldered metal insulation (SMI), to decrease the contact resistance of MI coils while providing enhanced thermal characteristics. To verify the effectiveness of SMI, both a small MI coil and a small SMI coil are fabricated, and their electrical performances are compared. For the SMI coil, In-Bi solder is tinned on a STS (stainless steel) tape that is co-wound with the REBCO wire; the SMI coil is then heated to make soldered contacts between the winding turns. The resulting time constant and contact resistance are investigated by performing sudden discharging experiments.

As the demand for eco-friendly energy increases, hydrogen energy and liquid hydrogen storage technologies are being developed as an alternative. Hydrogen has a lower liquefaction point and higher thermal conductivity than nitrogen or neon used in general cryogenic systems. Therefore, the application of hydrogen to cryogenic systems can increase efficiency and stability. This paper describes the design and analysis of a cryogenic cooling system for an electric propulsion system using liquid hydrogen as a refrigerant and energy source. The proposed aviation propulsion system (APS) consists of a hydrogen fuel cell, a battery, a power distribution system, and a motor. For a lab-scale 5 kW superconducting motor using a 2G high-temperature superconducting (HTS) wire, the HTS motor and cooling system were analyzed for electromagnetic and thermal characteristics using a finite element method-based analysis program. The liquid hydrogen-based cooling system consists of a pre-cooling system, a hydrogen liquefaction system, and an HTS coil cooling system. Based on the thermal load analysis results of the HTS coil, the target temperature for hydrogen gas pre-cooling, the number of buffer layers, and the cryo-cooler capacity were selected to minimize the thermal load of the hydrogen liquefaction system. As a result, the hydrogen was stably liquefied, and the temperature of the HTS coil corresponding to the thermal load of the designed lab-scale HTS motor was maintained at 30 K.

Bypassing transient current through copper (Cu) stabilizer layers reduces heat generation and temperature rise of high-temperature superconducting (HTS) conductors, which could protect HTS cables from burning out during transient conditions. The Cu layer connected in parallel with HTS tape layers impacts current distribution among layers and variations of phase resistance in either steady-state or transient conditions. Modeling the multilayer HTS power cable is important for transient studies. However, existing models of HTS power cables have only proposed HTS cables without the use of a Cu-former layer. To overcome this problem, the authors proposed a multilayer HTS power cable model that used a Cu-former layer in each phase for transient study. It was observed that resistance of the HTS conductor increased significantly in the transient state due to a quenching phenomenon, which made the transient current mainly flow into the Cu-former layers. Since resistance of the Cu-former layer has a significant impact on the transient current, detailed modeling of the Cu-former layer is described in this study. The feasibility of the developed HTS cable model is evaluated in the PSCAD/EMTDC program.