Electrical transmission or interconnection systems – Plural load circuit systems – Control of current or power
Reexamination Certificate
1999-02-26
2001-01-30
Ballato, Josie (Department: 2836)
Electrical transmission or interconnection systems
Plural load circuit systems
Control of current or power
C323S263000, C323S909000
Reexamination Certificate
active
06181027
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to machines that require high DC currents to be distributed over significant distances to multiple high current loads. More particularly, the present invention relates to an economical DC current distribution method and apparatus for use with electronic devices having fairly constant and well defined DC current requirements and that do not exhibit large dynamic variation or that are substantially buffered by capacitors at each load.
2. Description of Related Art
The use of an AC to DC converter or DC to DC converter at each load is a known way to provide for distributing DC power to each load without the negative effects of resistive voltage drop and ground shift as is experienced in a simple metal conductor distribution system. Each converter acts as a power supply for its' load. This approach is expensive in that numerous complex power control circuits are required in the system. It becomes even more expensive when redundancy is required to be built into the distribution system since a redundant supply or converter is needed for each load. Also when the power distribution system becomes large, distributed converters must be placed at intervals of several meters along a cable of ten meters or more. Such placement often presents a problem of instability and noise in the paralleling circuits and sensing circuits.
U.S. Pat. No. 5,319,536 issued to Malik, is an example of paralleling in which three converters,
11
,
13
and
15
are connected in parallel to load
23
.
U.S. Pat. No. 5,500,791 issued to Kheraluwala et al. teaches solving these problems by providing a dual active bridge converter generating 100,000 Hertz AC power square wave output which can be converted to DC by a converter at each load. The converters of Kheraluwala need not have such massive magnetic paths as would be required by a 60 Hertz system but there is still the need for a transformer, rectifier and possibly a voltage regulator at each load.
U.S. Pat. No. 5,254,877 issued to Tice et al. is another example of additional active power supply units being added along a distribution line. In Tice et al. a control panel provides power and communicates with smoke detectors and intrusion detectors. The line conductors
14
a
and
14
b
of Tice et al. serve as both signaling lines and power distribution lines and as is usual, the detectors farthest from the control panel would receive attenuated power levels. Tice et al. overcome this attenuation by providing distributed power supplies with synchronizing circuits, the added power supplies sense and respond to power pulses from the main control panel to inject supplemental amounts of power into the line during the power distribution time intervals. These added power supplies are relatively costly and they themselves require an external source of power such as from a AC power receptacle.
U.S. Pat. No. 5,777,276 issued to Zhu describes distribution of power on a computer motherboard using an auxiliary conductor system to reduce voltage loss due to high currents through resistive areas in the contact regions between connector posts and conductive layers buried in the motherboard. In the motherboard of Zhu, the conductors themselves are considered to have negligible resistive losses which of course is not the case in machines having larger distribution distances. The teachings of Zhu do not account for voltage loss in the original conductor or the auxiliary conductor and therefore his teachings do not concern voltage variations as a function of distance.
U.S. Pat. No. 4,788,449 issued to Katz describes a matrix of loads being supplied by a column of power supplies and redundantly by a row of power supplies. Although this teaching may solve a problem of the prior art with a short circuit in one load causing failure of power to all others in the same row, this teaching does not solve the problem of DC power attenuation at the farthest most load such as load
15
for example
The present invention overcomes these inadequacies, problems and disadvantages of the prior art by means of the apparatus and method of the invention which is summarized below.
SUMMARY OF THE INVENTION
An advantage of the present invention is that the size of the DC power distribution cables can be a smaller gauge without excessively sacrificing voltage regulation at each distributed load. Another way of stating this advantage is that by dividing a power distribution conductor into a power distribution conductor and a similarly sized sense conductor, significantly better voltage regulation may be obtained at each load to which power is being distributed. The improved regulation at each load is accomplished without requiring an increase in the combined conductivity of the power and sense conductors over that needed in a single power distribution conductor.
Another advantage of the instant invention is that multiple redundant power supplies, each with remote sensing, may be provided at a base module, redundantly supplying power to multiple modules without the problem of instability that often accompanies such redundant systems.
A further advantage of this invention is that a module may be removed from the system or a module may be added to the system without excessively changing the regulation of voltage provided to other modules.
Another advantage of the invention is provided by permitting implementation of current controlling resistors to be in the form of cable wire. Such implementation serves multiple purposes. It simplifies connections while balancing currents to loads and at the same time provides parallel paths in a power cable, which has the effect of lowering overall resistance power losses. It also has the benefit of distributing the heat over a wider area so that extra cooling or heat sinks are not needed.
These and other advantages of the invention, which will become apparent to the reader, are obtained by a novel arrangement of current carrying conductors which tailor and balance current delivered to each load. Tailoring of current to a load is accomplished by a current controlling resistance at each load. Balance of voltages between loads is accomplished by allowing a sense conductor to carry excess currents from one load to another. Current substantially equal to that drawn by each load is injected from current supply conductors to the sense conductors at or near each load. Current controlling resistances are embodied in lengths of wire in certain embodiments.
REFERENCES:
patent: 3098192 (1963-07-01), Levy, Jr. et al.
patent: 3532936 (1970-10-01), Kuster
patent: 4551668 (1985-11-01), Kammiller
patent: 4585987 (1986-04-01), Prue, Jr. et al.
patent: 4635057 (1987-01-01), Schaefer
patent: 4788449 (1988-11-01), Katz
patent: 5254877 (1993-10-01), Tice et al.
patent: 5319536 (1994-06-01), Malik
patent: 5448155 (1995-09-01), Jutras
patent: 5500791 (1996-03-01), Kheraluwala et al.
patent: 5672997 (1997-09-01), Shield
patent: 5777276 (1998-07-01), Zhu
patent: 5977757 (1999-11-01), Felps
Ballato Josie
Hesse Karl O.
International Business Machine Corp.
Roberto Rios
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