Electrical transmission or interconnection systems – Plural load circuit systems – Selectively connected or controlled load circuits
Reexamination Certificate
2000-07-28
2002-11-19
Fleming, Fritz (Department: 2836)
Electrical transmission or interconnection systems
Plural load circuit systems
Selectively connected or controlled load circuits
C307S083000
Reexamination Certificate
active
06483205
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a circuit and device for simultaneous control of multiple transformers and in which each transformer's power output can be individually controlled, and which is particularly useful for any transformer control but especially for welding transformers where high power control requirements normally militate toward costly independent controls.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 5 862,041 and U.S. Pat. No. 5,852,555, both to the inventor of the present invention, describe dual inverter power supplies in which a series of switches are controlled by a pair of oscillators to control a pair of separately operable input:coils of a transformer. The general technique involved control of the two oscillators by a phase controller in order to vary the timing of the two oscillators to control a transformer output. This invention had as its goal the very close control of a transformer by utilizing eight switches, two oscillators and a phasing control to achieve exact control over a transformer.
One of the problems in general with respect to welding transformers is that once a good high voltage direct current power supply is available, limiting a particular welding appliance to use a single output transformer and especially its own control, can be cost prohibitive. In order that welding power distribution systems could be utilized more effectively, it would be advantageous for as much of the equipment downstream of the high voltage direct current supply to work in an interrelated way to provide several welding stations depending upon a single high voltage direct current supply. Put another way, for a single high voltage direct current supply, it would be advantageous to be able to provide control to a plurality of downstream transformers with due consideration to control parameters including even power distribution, control to prevent undue power consumption by one or more users, feedback control to enable power regulation in a manner as closely approximate to individual control as possible, and a form of control which can attempt to minimize power waste. If this control can be accomplished along with the elimination of physical elements of the equipment, such as individual controllers and the like, welding power supply units can be manufactured much more inexpensively to increase the opportunities for and cost barriers to providing more inexpensive welding processes and products.
The problems with earlier designs relating to transformers include switching loss, combined with the saturation loss and the current density. inefficiency. Earlier controls based upon duty cycle alone, or phasing alone have been unable to address the above problem of providing a distributed control. Most of the controls involving phasing can rapidly adapt to a new current or power output set point, but concentrated rather than distributed control is the main theme of the operating solution.
What is therefore needed is a circuit and device which enables high current at high frequency to be distributed and controlled with an interrelated control of such distribution so as to eliminate individual controllers and their accompanying cost. The needed method should include, for the utilization of a single equipment set for conversion of the standard AC to high voltage DC power source, for multiple controlled elements of equipment, such as welding transformers. Even more importantly, the needed circuit and device should provide itself with the capability for monitoring, and feedback to provide precise voltage, or current, or power to the fusing or welding electrodes.
SUMMARY OF THE INVENTION
An improved circuit and device uses a set of eight switches, four of which are connected to the positive terminal, and four of which are connected to the negative terminal of a high voltage direct current power supply. The eight switches are attached in a distributed and overlapping manner to the inputs of up to six welding transformers. Pulse width modulation is utilized to distributively control power to the six welding transformers. Each welding transformers two port input is dependent upon four of the switches at any given time to determine its duty cycle and power output. Each of the six welding transformers two port input is dependent upon a different four of the eight switches.
By reducing the pulse width of one switch, two of the transformers are affected. Of the two transformers affected, the total output of each transformer depends upon four total switches, three switches of which are associated not only with the transformer being affected, but also of three other transformers.
A controller which controls each wave form controls the pulse width of each switches square wave, affecting the length of the pulse width control wave form pulling in the outer edges toward the center to shorten the length of duration during which each switch is in its “on” position. Affecting the pulse width of one switch affects two transformers, but the other transformer can also be affected by three other switches.
The controller is programmed to provide precise control by computing the pulse width duration of each of the switches in order to provide the needed power and pulse duration to each of the switches in order to deliver the power protocol demanded. Power demanded may be by feed forward control, or interactive feedback may be provided. In terms of the mathematical relationship of controlling six transformers with eight switches, only two transformers can be absolutely independently controlled at the same time. However, by utilizing a heuristic protocol controller in which the power to the six transformers can be controlled within given limits, all six of the transformers can be controlled so long as their power consumption is not grossly different, one from another.
REFERENCES:
patent: 3710147 (1973-01-01), Lee
patent: 5852555 (1998-12-01), Martin
patent: 5862041 (1999-01-01), Martin
patent: 5991167 (1999-11-01), Van Lerberghe
patent: 6064580 (2000-05-01), Watanabe et al.
patent: 6268587 (2001-07-01), Kooken et al.
Fleming Fritz
Harrington Curtis L.
Polk Sharon
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