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This paper proposes a new circuit topology for SMES (superconducting magnetic energy storage), which is based on a pulse link concept of two converters. A two quadrant dc chopper and a dc/ac converter connected via high frequency dc pulse link voltage. This concept has two advantages. All semi-conductor switches operate under soft-switching condition, which results in low loss generation and possibility to increase switching frequency. The other advantage is eliminating smoothing capacitor between two conversion stages. By these advantages, the proposed converter has possibility to achieve high efficiency and power density with rich controllability. This paper describes operation principles of the proposed converter. First experimental verification of this concept was conducted with small scale setup. [ABSTRACT FROM PUBLISHER]

Magnets of the synchrotron which extracts the accelerated beams are excited by a pulse operation power supply, and then the load fluctuation should be a severe problem. An energy storage system, such as superconducting magnetic energy storage (SMES), fly-wheel generator so far, will be required for compensating the pulse electric power, and reducing the disturbances of the connected power line. The system is expected to protect the instantaneous voltage drop and the load fluctuation. Present status of R & D and the features for the energy storage systems are discussed. The application of the energy storage systems to synchrotrons for the medical use is described. The compensation of the typical pulse electric power of the synchrotron for the cancer therapy is studied, and the operation cost saving and the cost performance of the SMES system are discussed. [ABSTRACT FROM AUTHOR]

RASMES (Research Association of Superconducting Magnetic Energy Storage) in Japan developed a road map of SMES for fluctuating electric power compensation of renewable energy systems. Based on the progress of large superconducting coils, the technical status is already established to develop the several MWh class SMES for frequency control, load fluctuation compensation, and generation fluctuation compensation. With integrated operations of several dispersed SMES systems, it is expected that the 100 MWh class SMES for load fluctuation leveling (peak cut) can be introduced in the period of 2020-30, and the first 1 GWh class SMES for daily load leveling can be installed in the period of 2030-40. From the results of Japanese national projects, experimental device developments and SMES design studies, if the output power of SMES is 100 MW, the target cost of SMES can be evaluated with 2000 USD/kW of the unit cost per output power (the unit cost per kW). [ABSTRACT FROM AUTHOR]

The objective of this work is to discuss the concept of back-to-back interconnection systems with energy storage, especially with a Superconducting Magnetic Energy Storage (SMES) incorporated into a back-to-back DC link. In this case, each converter of the back-to-back system is used as a power conditioning system for the SMES coils. Since the AC–DC converter can be designed independently of the frequency of the power system, a two-way switch is connected to the AC side of each converter. This two-way switch can select the interconnected power systems. By using the two-way switches, this system can provide the stored energy in the SMES system to each interconnected power system through two AC–DC converters. For instance, lower-cost power of each power network can be stored through two converters during the off-peak hours and made available for dispatch to each power network during periods of demand peak. Then this system increases the reliability of electric power networks and enables the economical operations depending on the power demand. This paper describes the unique operations of the back-to-back interconnection with SMES and discuses the optimal SMES configuration for a 300-MW-class back-to-back interconnection. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(2): 37–43, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20482 [ABSTRACT FROM AUTHOR]

Power supply for the large-scale accelerator magnets draws a large amount of power from the utility network. For an example, the new proton accelerator complex for high intensity beam (Japan Particle Accelerator Research Complex, J-PARC) is under construction at the Tokai campus of Japan Atomic Energy Agency (JAEA) as a joint project between KEK and JAEA. The J-PARC SO GeV proton synchrotron (50 GeV-PS) magnets power supplies are constructed with IGBT and IEGT, then the power factor is almost 100%. However, the swing of an active power becomes almost 170 MW, although the average power is about 50 MW. Such large pulse power will give un-allowed disturbances to an ac power line. A SMES system will be required for compensating such as pulse electric power and reducing the disturbances. Case study on circuit configuration of the power supply with SMES and present status of the R & D for the SMES system will be discussed. [ABSTRACT FROM AUTHOR]

A superconducting force-balanced coil (FBC), which is geometrically one tenth the size of a 100 MJ class SMES coil, has been developed. The FBC is a helically wound hybrid coil of toroidal field coils and a solenoid. This coil configuration can minimize the required mass of the structure for induced electromagnetic forces. The model FBC with an outer diameter of 0.53 m will have 270 kJ magnetic energy at the critical magnetic field of 7.1 T using NbTi strands. The critical coil current and self inductance are 552 A and 1.8 H, respectively. The diameter of the NbTi strand is 1.17 mm. The hand-made winding of the model FBC was carried out without reinforcing materials such as stainless steel wires. The first experiment was conducted with liquid helium cooling. The quench properties of the model FBC were mainly investigated. The first quench current is 293 A, which is 53% of the critical coil current. Training phenomena were observed in the model FBC without any sudden decreases in the quench current. After 33 successive excitations the quench current improved to 419 A, and it was successfully excited up to 5.4 T without reinforcing materials for the NbTi strand. This fact demonstrates a primary capability of the FBC as a SMES coil. [ABSTRACT FROM AUTHOR]

A one tenth sized model coil based on the force-balanced coil (FBC) design for 100-MJ class SMES has been designed. This coil is a hand-made coil using NbTi superconductors, and the winding of the model FBC is now in progress. The FBC is a helically wound hybrid coil of toroidal field coils and a solenoid. This coil can minimize the mechanical stress and the required mass of the structure for induced electromagnetic forces. The model FBC with an outer diameter of 0.53 m will have the stored energy of 270 kJ at the maximum magnetic field of 7.0 T. The winding form is made of aluminum alloy and slots are cut on its surface with the shape of the helical winding. From the results of the cooling test with liquid nitrogen, the significant deformations of the winding form have not been observed. The winding of the model coil is carried out without reinforcing materials for the NbTi strand. The in-plane curvature of helical coils causes the winding errors. Then after a slight winding tension is applied to the NbTi strand, each winding is adjusted to be fixed in its place. The experiments will be conducted with liquid helium cooling. The DC power supply for the model FBC can simulate various SMES operations. As a first step, the ramp-rate dependence of the superconducting properties of the model coil will be investigated in order to evaluate the mechanical stress in the helical windings without the reinforcing materials for the NbTi strand. [ABSTRACT FROM AUTHOR]

Superconducting magnetic energy storage (SMES) systems can be used to improve power supply quality and reliability. In addition, large amounts of power can be drawn from a small stored energy supply. Nevertheless, the strong electromagnetic force caused by high magnetic fields and coil current is a serious problem for SMES. To cope with this problem, we propose a new coil design, the tilted toroidal coil (TTC). The TTC, obtained from the toroidal field coil (TFC) system by varying two pitching angles, allows the balancing of the electromagnetic force in the major radius direction, maintaining the same manufacturing simplicity of the TFC system. After determining balanced configurations through computer simulation, we built an experimental device to confirm the feasibility of the balancing effect. [ABSTRACT FROM AUTHOR]

Examines the relation between stress and the magnetic field of superconducting toroidal field coil used for high field tokamak. Virial theorem of electromagnetic structure; Minimization of stress working in the coil; Toroidal shell model with circular cross section.

Describes the concept of force-balanced coil (FBC) which is a helical-winding toroidal coil for superconducting magnetic energy storage systems. Capability of the coil to reduce the centering force of toroidal field coil (TFC); FBC cost parameters; Coil dimensions; Ampere-meters of superconductors; Surface area of the coil in comparison with the TFC and the solenoid.

Higher magnetic field is of great advantage to superconducting magnetic energy storage because it promises a compact device. However, it does not affect the serious problem of huge electromagnetic forces caused by high magnetic fields and large coil current. Electromagnetic stresses, reaching as much as several hundred bars, thus become a major factor in determining whether a large-size strong magnetic field system can be established. In order to solve this problem, we have proposed the force-balanced coil (FBC) concept that reduces the huge centering electromagnetic forces by balancing them with the hoop forces caused by the toroidal current. Then we designed and fabricated a small-size superconducting FBC system to demonstrate the FBC concept. It was successfully excited up to near rated current. It is shown that the FBC system has the potential for simplifying the supporting structures and making the facility compact. © 1999 Scripta Technica, Electr Eng Jpn, 128(3): 82–91, 1999 [ABSTRACT FROM AUTHOR]