1. Field of the Invention
This invention relates to a superconducting energy stabilizer having multiple load connections employing DC-DC conversion. In particular, the invention relates to an energy stabilizer which utilizes energy stored in a superconducting inductive energy storage device to stabilize the delivery of energy to a DC or AC load or to retrieve and store regenerated energy supplied by the load. Additionally, the invention can supply stored energy to a utility or to an industrial electrical DC or AC distribution system to maintain the level of energy supplied to the consumers.
2. Background of the Prior Art
Prior art superconducting energy storage systems have been directed to the storage of energy derived from an alternating current power system and to the return of the stored energy to the alternating current (AC) power system. Typically, energy is stored during periods of low energy demand when surplus energy exists and is returned to the power system when energy demand is high.
One such system appears in Peterson et al., U.S. Pat. No. 4,122,512. Peterson et. al. uses a reversible alternating to direct current converter to convert the alternating current obtained from the AC power system into direct current for storage in a superconducting magnet and for converting the stored direct current into alternating current for return to the AC power system. This type of system, while providing for the efficient storage and return of energy to the AC power system, cannot perform the simultaneous storage and release of energy.
Another superconducting energy storage system described in Higashino, U.S. Pat. No. 4,695,932, discloses an energy storage circuit which converts three-phase alternating current to direct current for storage in a superconducting energy storage coil. A DC capacitor and chopper circuit are used to control the amount of direct current in the superconducting energy storage coil. According to Higashino, this configuration allows the current capacity of the converter to be scaled down in accordance with service power established by the current rating of the coil, and also allows a reduction of operation losses.
Known superconducting energy storage systems provide for the efficient storage and return of energy but cannot perform the simultaneous storage and release of energy. In addition, Higashino has a practical problem of charging the superconductive energy storage coil with a capacitor whose voltage must correspond to the voltage of the AC power system. For a 480 Volt AC system this would be around 650 volts DC. This voltage is too high to charge the superconducting energy storage coil near its maximum rated current, unless the coil is significantly oversized to accommodate the higher voltage value. Normally, a voltage of ten to twenty volts would be more appropriate for charging the coil. Even if Higashino's system used a step down transformer at the AC line in order to drop the capacitor bank voltage, the capacitor bank would need to provide a higher current which results in higher losses and costs due to a bigger magnet current and size.
In addition, these systems do not provide a means to boost the current delivered by the superconducting energy storage coil. If a utility or industrial electrical distribution system needs higher current than the magnet current, the known system using a chopper and a capacitor can not provide such a function.
Visser et al., U.S. Pat. No. 4,962,354, issued to Superconductivity, Inc. on Oct. 9, 1990 describes a superconducting voltage stabilizer. The superconducting voltage stabilizer comprises an AC/DC converter, a voltage regulator, an energy storage cell and a superconducting energy storage coil. Alternating current is converted to direct current and is stored in a superconducting energy storage coil. The stored direct current is released to an energy storage cell which in turn delivers the energy to a load. Energy is released in a controlled fashion according to the energy requirements of the load to thereby stabilize the load's operation. This patent, U.S. Pat. No. 4,962,354, is incorporated herein by reference.