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The research and development status of the superconducting magnetic energy storage (SMES) and the application of the SMES to the accelerator magnet power supply are discussed. The progress of power semiconductor has shown the availability of SMES for stabilizing the power system and maintaining power quality along with controlling the frequency fluctuation.

The article discusses a dc loop type distribution system using high temperature superconducting (HTS) cable. Findings reveal that the system is effective in reducing transmission losses in the cable and in easy installation of superconducting devices.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.solener.2005.04.007 Byline: Sung-Jun Park (a), Feel-Soon Kang (b), Su Eog Cho (c), Chae-Joo Moon (d), Hae-Kon Nam (a), Toshifumi Ise (e) Keywords: Dc-to-dc converter; Parallel driving; Peak current control mode; Photovoltaic system Abstract: This paper proposes a modified converter for use in photovoltaic system. In the modified converter, the voltage ratio of output to input is equal to that of the general boost converter. The difference between the two converters is the configuration of output terminal. Therefore, the working voltage of an output capacitor and the value of its capacitance can be lower than those of the general boost converter. This paper also presents an efficient parallel driving scheme to increase output power and to reduce the output voltage ripple. The parallel driving method using the modified converter and current mode control gives a good solution for alleviating the current sharing unbalance problem. It reduces the output voltage ripple by increasing the equivalent switching frequency of the modified converter. The performance of the proposed converter system is verified through computer-aided simulations and experimental results. Author Affiliation: (a) Department of Electrical Engineering, Chonnam National University, 300 Yongbong-dong, Puk-gu, Gwangju 500-757, Republic of Korea (b) Department of Control and Instrumentation Engineering, Hanbat National University, San 16-1, Duckmyong, Yuseong, Daejeon 305-719, Republic of Korea (c) Department of Electrical Engineering, Pusan National University, Changjurn, Gumjung, Busan 609-735, Republic of Korea (d) Department of Electrical Engineering, Mokpo National University, 61 Dorim-ri, Cheonggye-myeon, Muan-gun, Jeonnam 534-729, Republic of Korea (e) Department of Electrical Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita 565-0871, Japan Article History: Received 26 April 2004; Revised 31 March 2005; Accepted 11 April 2005 Article Note: (miscellaneous) Communicated by: Associate Editor Arturo Morales-Acevedo

This paper presents a new multilevel pulswidth-modulation (PWM) inverter scheme for the use of stand-alone photovoltaic systems. It consists of a PWM inverter, an assembly of LEVEL inverters, generating staircase output voltages, and cascaded transformers. To produce high-quality output voltage waves, it synthesizes a large number of output voltage levels using cascaded transformers, which have a series-connected secondary. By a suitable selection of the secondary turn-ratio of the transformer, the amplitude of an output voltage appears at the rate of an integer to an input dc source. Operational principles and analysis are illustrated in depth. The validity of the proposed system is verified through computer-aided simulations and experimental results using prototypes generating output voltages of an 11 level and a 29 level, respectively, and their results are compared with conventional counterparts. Index Terms--Harmonic distortion, multilevel systems, photovoltaic power systems, pulsewidth-modulated (PWM) inverters, transformers.

From the viewpoint of high quality output voltage generation in a residential photovoltaic system, a multilevel inverter employing cascaded transformers can become a good substitute for the conventional pulse width modulated inverters and other multilevel counterparts. However, to obtain more sinusoidal output voltage waves, it should increase the number of switching devices and transformers resulting in a cost increase. To alleviate this problem, an efficient switching pattern is proposed and applied to a multilevel inverter equipped with two cascaded transformers, which have a series-connected secondary. Operational principle and analysis are illustrated focusing on a change of the switching pattern. High-performance of the proposed multilevel scheme embedded in a photovoltaic power conditioning system is verified by computer-aided simulations and experimental results. Keywords: Cascaded transformer; Multilevel inverter; Photovoltaic system; Pulse-width-modulated inverter

The current control system is designed for power supplies to the Large-Helical Device (LHD) superconducting coils. The experimental results are presented and discussed in case of coil excitation using these control systems.

Magnetically coupled superconducting coils in large helical devices were examined in terms of current control, based on an H-infinity control scheme.

A rectifier type superconducting fault current limiter is investigated in the context of inductance and current rating of coil.

The power conditioning system for superconducting magnetic energy storage in the International Thermonuclear Experimental Reactor is investigated.

Superconducting magnetic energy storage is used with a solid-state phase shifter in controlling load fluctuation, system frequency and harmonic voltage in an electric power system. The combined system has been named SuperSMES and is predicted to be a highly-effective controller independent of its location. Simulation results indicate that SuperSMES with the proposed controller located far from the generator can stabilize the power swing as effectively as the SMES located at the generator terminal.

The use of the SuperSMES in controlling harmonics and negative sequence components in line current and voltage has been described. A SuperSMES is made up of inverters connected in series to a power system and another inverted in parallel and a superconducting magnet for energy storage. It can be used as a source of sinusoidal and balanced voltage to loads which are sensitive to voltage distortion and unbalancing. It also prevents current harmonics and unbalance in three-phase lines of the distribution system.

A design method of volt/turn for minimizing life cost of a superconducting transformer is proposed. In addition a three phase 40kVA transformer was designed. The optimal volt/turn was 1.1 V in the example case and it is around 1/10 of the conventional transformer. Results indicate that the optimized volt/turn will be around 1 volts which is considerably lower than the volt/turn ratio of a conventional transformer of 10 to 20 volts.