Design of a High Temperature Superconducting Coil for Energy Storage Applications

Abstract

Besides applications in magnetic resonance imaging (MRI) and particle accelerators, superconductors have been proposed in power systems for use in fault current limiters, cables and energy storage. Since its introduction in 1969, superconducting magnetic energy storage (SMES) has become one of the most power-dense storage systems, with over 1 kW/kg, placing them in the category of high power technologies, along with supercapacitors and flywheels. The discovery of high temperature superconductors (HTS) in 1986, with transition temperatures of over 90 K, brought a series of advantages over low temperature superconducting magnets (operating below 4.2 K), which include a higher operating temperature, of up to 77 K, improved thermal stability and higher critical current in magnetic fields. This has enabled the use of SMES in projects requiring large power pulses and quick response time, such as grid scale balancing services. However, due to large costs of superconducting tape, exceeding $100/m, only small scale magnets, with storage capacity below 1 MJ have been built.

This project’s aim is to study the design of a HTS coil for use in energy storage systems. A methodology is proposed for a parametric design of a superconducting magnet using second generation high temperature tape, made with Yttrium Barium Copper Oxide(YBCO). The process takes into account the target energy stored, the output power and the voltage of the magnet, the latter of which has a direct impact on peak transport current required, and hence, the choice of tape and operating temperature. The search algorithm is scripted in R, with a function that takes the deliverable energy, power and voltage as input parameters and returns the near-optimum configuration of a coil that uses the minimum length of tape, achieved through discrete optimisation.

The resulting configuration is used in a MATLAB/Simulink simplified model of a DC microgrid. The operation of the coil is assessed during two scenarios, simulating a demand and surplus of power, respectively. The bidirectional power flow between the coil and the circuit is enabled by a two quadrant DC-DC chopper, controlled using PWM generated by a closed loop PI controller. The effect of increasing the controller gains by an order of magnitude is observed in the quicker response of the coil and a lower variation of DC link capacitor voltage.

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Identifiers

ORCID for Andreas, Walter Zimmermann: orcid.org/0000-0002-6383-2053

ORCID for Suleiman Sharkh: orcid.org/0000-0001-7335-8503

ORCID for Yifeng Yang: orcid.org/0000-0002-3874-6735

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