Incorporation of a SMES coil into a superconducting LVdc transmission system

The performance of a superconducting low voltage direct current (LVdc) transmission system can be significantly enhanced through the addition of a superconducting magnetic energy storage (SMES) coil. The power conversion equipment necessary for connecting a SMES coil to a dc system is much simpler and easier to control than the interface needed to connect a SMES coil to an ac system. There is also added flexibility if the LVdc system is mesh connected. The LVdc system already has the power conditioning necessary for connection to the ac load and supply systems. The SMES coil can be connected to the LVdc mesh either through a dedicated dc-dc converter or it can be added directly into the mesh and controlled using the converters already present on the mesh. The rectifier voltage regulation schemes control the charging and discharging of the coil. If one of the rectifiers is supplied by a unit-connected generator, a simpler rectifier scheme can be used, and the generator field excitation control can be used to control the SMES coil. The SMES coil could then be used both to level generator loading and provide added reliability in case of disturbances on the ac supply system.