Advances in both superconducting technologies and the necessary power electronics interface have made SMES a viable technology for high power utility and defense applications. The power industry's demands for more flexible, reliable and fast active power compensation devices make the ideal opportunity for SMES applications. However, in order to make this technology attractive to the deregulated utility market, it is necessary for industry to provide cost-effective systems. The information presented herein is taken from results to date of a DARPA technology Reinvestment Program SMES Commercialization Demonstration. This program is currently in the design and risk reduction phase. Completion is expected in 2001. This system will provide +/- 100 MW peak and +/- 50 MW oscillatory power with 100 MJ of stored energy. The base line for the coil design assumes a cable-in-conduit conductor (CICC), with rated voltage of 24 kV, and operating at nominal temperature of 4.5 K. This paper reviews the possible utility industry applications and discusses a number of technical issues and trade-offs resulting from the design optimization process for SMES utility applications. The conductor design options, system configuration, current/voltage levels and insulation issues for a low temperature superconducting coil are discussed. The power electronics interfaces (system configuration, circuit topology and devices and switching technologies) are also discussed. Finally, consideration is given to the impact of the new business environment, potential markets and overall cost.

SMES for power utility applications: a review of technical and cost considerations

This paper presents the modeling and simulation results of a superconducting magnetic energy storage (SMES) system for power transmission applications. This is the largest SMES coil ever built for power utility applications and has the following unique design characteristics: 50 MW (96 MW peak), 100 MJ, 24 kV dc interface. As a consequence of the high-power and high-voltage interface, special care needs to be taken with overvoltages that can stress the insulation of the SMES coil, especially in its cryogenic operating environment. The transient overvoltages impressed on the SMES coil are the focus of this investigation. Suppression methods were also studied to minimize transients. The simulation is based on detailed coil and multiphase gate turn-off (GTO)-based chopper models. The study was performed to assist in the design of the SMES coil insulation, transient protection, and the power electronics specification and interface requirements.

Transient modeling and simulation of a SMES coil and the power electronics interface

This article presents the modeling and control of the integration of a StatCom (static-synchronous compensator) with SMES (superconducting magnetic energy storage system) and its dynamic response to system oscillations caused by a three-phase fault. It has been shown that the StatCom-SMES combination can be very effective in damping power system oscillations. Adding energy storage enhances the performance of a StatCom and possibly reduces the MVA ratings requirements of the StatCom operating alone. This is important for a cost/benefit analysis of installing flexible AC transmission system controllers on utility systems. It should be noted that, in this study, the StatCom provides a real power flow path for SMES, but the SMES controller is independent of the StatCom controller. While the StatCom is ordered to absorb or inject reactive power, the SMES is ordered to absorb/inject real power. It was also observed that the location where the combined compensator is connected is important for improvement of overall system dynamic performance. Although the use of a reactive power controller seems more effective in a load area, this simulation study shows that a StatCom with real power capability can damp the power system oscillations more effectively, thereby stabilizing the system faster-if the StatCom-SMES controller is located near a generation area rather than a load area.

StatCom-SMES

This paper discusses the integration of a static synchronous compensator (STATCOM) with an energy storage system in damping power oscillations. The performance of the STATCOM, a self-commutated solid-state voltage inverter, call be improved with the addition of energy storage. In this study, a 100 MJ SMES coil is connected to the voltage source inverter front-end of a STATCOM via a DC-DC chopper. The dynamics of real and reactive power responses of the integrated system to system oscillations are studied using an electromagnetic transient program PSCAD/sup TM//EMTDC/sup TM/ and the findings are presented. The results show that, depending on the location of the STATCOM-SMES combination, simultaneous modulation of real and reactive power can significantly improve the performance of the combined compensator. The paper also discusses some of the control aspects in the integrated system.

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Dynamic performance of a static synchronous compensator with energy storage

Multi-level two-quadrant boost choppers are proposed for superconducting magnetic energy storage (SMES) and other applications with inductive energy storage such as magnetic resonance imaging (MRI) and switched reluctance motor drives. The advantages of multi-level power conversion includes lower current ripple, lower switching loss and better voltage sharing, as illustrated with a 3-level power converter as an example. Its operation principle and PWM strategies are investigated, and a small signal model is developed for control design. Simulation results are used to verify the analysis.

Multi-level 2-quadrant boost choppers for superconducting magnetic energy storage

Transmission and distribution power systems are presently experiencing tremendous changes in both load requirements and system operation. End-users demand increased reliability and power quality. System operations change to optimize the distribution and number of generation sources to take advantage of load diversity and fuel availability. Superconducting Magnetic Energy Storage (SMES) and modern power electronics systems emerge as technologies enabling power utility systems to adapt to these changes. These systems deliver services unique and previously unavailable and the authors suggest the term Superconducting Power Systems to describe them. Babcock and Wilcox (B and W) is working with Anchorage Municipal Light and Power (ML and P) to design, manufacture and install a 50 MW, 1,800 MJ system in Anchorage, Alaska. The system will be commissioned in early 1998.

X. Huang

Papers

Superconducting power delivery systems for transmission and distribution applications