Electrical transmission or interconnection systems – Plural supply circuits or sources
Reexamination Certificate
1999-03-30
2002-05-28
Ballato, Josie (Department: 2836)
Electrical transmission or interconnection systems
Plural supply circuits or sources
C307S052000, C307S150000
Reexamination Certificate
active
06396167
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of power distribution systems managing electrical power distributed between connected power sources and energy storage element over a regulated bus. More particularly, the present invention relates to distributed power sources and stores in a power distribution system.
BACKGROUND OF THE INVENTION
Microsatellites and Nanosatellites in low earth orbits require the collection of sufficient power for onboard instruments and are low weight and low volume satellites. Because the overall surface area of a microsatellite or nanosatellite is small, body-mounted solar cells are incapable of providing enough power. Deployment of traditional, rigid, solar arrays necessitates larger satellite volumes and weights, and also requires extra apparatus needed for pointing toward the sun to collect solar energy. Nanosats are small orbital satellite becoming increasingly used for space communications because of the decreased deployment costs and lightweight. Nanosats inherently have a limited amount of available power because of a limited amount of space for mounting solar cells. Additionally, because of the small size of the nanosatellite, there is a weight penalty when deploying rigid solar panels with tracking and pointing mechanisms. Satellites have long used means for stowing and deploying a large area of solar cells with minimum weight and volume. This has been accomplished by utilizing solar cells on deployable flat panels that require pointing and that can be sized for various desired power levels. Deployable flat panels disadvantageously require pointing and tracking means as well as rigid deployable flat panels.
In traditional space power systems, individual DC power source devices such as solar cells, and DC energy storage devices such as batteries, have been connected in a series to develop sufficient voltage levels to be useful for supplying power to loads on the satellites. Series connections have been used in both regulated and unregulated buses within a centralized power management and distribution system. Traditionally, individual solar cells have been connected in a series to develop sufficient voltage and are then delivered to the power distribution system. A regulated bus is one where a precise voltage level is maintained and supplied to the loads. To maintain energy balance, the voltage regulator must throttle the amount of current supplied to the bus as required by the loads at each instant of time. Typically, the regulation of the amount of current that a series connection of power sources supply to the bus has been accomplished by the use of shunt dissipators. These dissipators sense the bus voltage and determine whether the voltage status level is low, indicating that the amount of current being supplied is low, or the voltage status level is high, indicating that the amount of current being supplied is high. Regulated adjustments are then made in the amount of current being supplied to maintain a constant voltage on the regulated bus.
Many power sources and energy storage devices operate efficiently and can be managed better for longer life if controlled at the individual device level. A solar panel comprises a plurality of parallel connected strings each of which comprises a plurality of series connected solar cells. For solar cells connected in a series, the weakest cell in the series provides the least amount of current. The weakest series connected solar cell will limit the power output of all of the other solar cells in that series. Hence, the weakest solar cell in the series will limit overall efficiency of that string. In addition, if the current mismatch between the weakest cell and all the other solar cells becomes too great, then the weakest cell will be driven into reverse bias, which could cause damage to the cell and eventual failure of the entire string. To avoid this failure, bypass diodes have been used to shunt current around the affected cell effectively disconnecting it from the string.
Similarly, energy storage devices must be current-matched so they will all charge and discharge at the same rate. The charge cycle is more critical in that overcharging at a high rate can cause damage to the individual storage devices. Each series of storage devices may include a network of bypass electronics as standard procedures on spacecraft to control the charging of individual energy storage devices. Energy storage devices are also typically connected in series. In the event of a failure of one of the storage devices, the entire string of series connected storage devices will fail. Bypass diodes are used to remove from a string one or more of the storage devices, then the string will not produce the desired voltage level, thereby creating a mismatch between operational and failed strings. The voltage level mismatch results in unequal load sharing between the parallel strings of storage devices. A string with a bypassed failed storage device will provide a lesser voltage level than the fully operational strings of storage devices, and the string with the failed storage device will contribute less to the supply of power delivered by the remaining operational strings, thereby reducing overall storage capacity of the storage devices. Further still, satellite power distribution systems typically operate using a single regulator for a string of connected devices and a failure of any one of the devices can cause a catastrophic system failure without the addition of redundant regulators with the attendant addition in complexity and weight. These and other disadvantages will be solved or reduced using the present invention.
SUMMARY OF THE INVENTION
An object of the invention is to collect, store and or distribute power within a power distribution system.
Another object of the invention is to efficiently collect solar power using solar cells deployed on a satellite.
Yet another object of the invention is to conform solar cells to a curved surface with each cell receiving differing amounts of solar illumination providing respective differing amounts of unequal power efficiently managed by a power management system.
Still another object of the invention is to provide a power management system having a plurality of DC power sources and DC energy stores connected to a common regulated bus through respective regulators.
A further object of the invention is to provide a power management system having a plurality of indivisible DC power sources and or indivisible DC energy stores connected to a common regulated bus through respective regulators for operationally isolating the sources and stores from each other.
Yet a further object of the invention is to provide a power management system having a plurality of indivisible DC power sources and or indivisible DC energy stores connected to a common regulated bus through respective regulators for operationally isolating the sources and stores from each other enabling graceful degradation of power distribution in the event that any one or more of the sources or stores fail.
The present invention is directed towards a power distribution system particularly useful for satellites, including microsatellites and nanosatellites. In one form, a deployable power sphere having a curved surface is preferably used to support attached solar cells that may be, for example, disposed in a grid along longitudes and latitudes corresponding and conforming to the shape of a sphere and are used to collect solar energy for a satellite. The solar cells could also be deployed in other grids, such as a hexagonal grid, or in a random arrangement, but conforming to the curved exterior of the power sphere. The power sphere itself need not be a perfect sphere, and may assume any volumetric shape, so long as the solar cells conformed to the exterior curved surface. The solar energy illuminates the conforming solar cells with uneven radiation intensity, and the power distribution system serves to collect this uneven intensity radiation with a high degree of efficiency. The power sphere offers a soluti
Carian Peter J.
Prater Alonzo
Simburger Edward J.
Ballato Josie
Deberadinis Robert L.
Reid Derrick Michael
The Aerospace Corporation
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