Superconducting Power Filter for DC Electrical Grids
Résumé
With the rapid advance of power electronics technologies, DC electrical grids are expanding at every scale and various high temperature superconducting devices are being developed to operate in such grids. Up to now applications of superconductivity with a clear impact in the electrical sector have been HTS power cables and fault current limiters. Various prototypes have been built and tested around the world either in the industry or research institutions. These technologies have demonstrated the potential to address increasing power transmission demand and protection against faults in electrical grids. In the present work, a new application of HTS technology for DC grids is introduced. The device referred to as “superconducting power filter” aims at increasing the stability of DC grids by adding a current-dependent resistance to a classical RLC filter. The device is closely related to a resistive fault current limiter (r-ScFCL), but here the superconductor is expected to be operated around its critical current thereby remaining in the superconducting state during load fluctuations, with the option of providing timely over-current protection if required. In comparison with other stabilization techniques, a superconducting power filter achieves a fully passive stabilization without limiting significantly the energy transferred to the load in nominal operation. To clarify its operation, a simple circuit constituted of an ideal constant DC voltage source and a controlled power load connected through a RLC filter in series with a superconducting power filter is considered. Using an electrical-thermal model of the device, the stability of the DC grid is assessed depending on the design parameters of the device. The corresponding experimental setup has been assembled to back up the numerical results. We built a superconducting power filter with a non-inductive coil wound with BSCCO and cooled down at 77 K in liquid nitrogen. The hereafter reported results confirmed that a superconducting power filter can indeed provide a stabilizing functionality in DC grids.