Electric heating – Metal heating – By arc
Reexamination Certificate
2000-08-18
2002-10-29
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
By arc
Reexamination Certificate
active
06472633
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a welding apparatus and method. More specifically, it relates to an apparatus and method for paralleling the outputs of a plurality of welding power supplies.
BACKGROUND OF THE INVENTION
Different welding applications typically require different amounts of welding current. Most welding applications can be performed satisfactorily with welding currents of 1000 amps or less. Some welding applications, however, require welding currents in excess of 1000 amps. Certain submerged arc welding and electric slag welding applications, for example, require welding currents as high as 2000 to 3000 amps.
Welding power supply manufacturers generally manufacture power supplies having different welding current output capacities for use in connection with the various welding applications. These manufacturers provide many different off-the-shelf welding power supplies to handle welding applications requiring 1000 amps or less. This is because the vast majority of welding applications require current falling within this range and there is a demand for machines of this size.
On the other hand, the number of welding applications that require currents in excess of 1000 amps is much smaller. The availability of off-the-shelf power supplies for these applications is much more limited. Manufacturers are less willing to manufacture machines for which overall demand is low. An alternative to the limited selection of off-the-shelf power supplies capable of supplying in excess of 1000 amps is therefore desirable.
Finding an off-the-shelf power supply capable of welding at very high currents (e.g. 2000 amps and above) is even more difficult, if not impossible. Often times, the only solution is to have a machine custom built for the particular application at hand. This of course can be very expensive. It is also desirable, therefore, to have an alternative solution for welding applications requiring currents of 2000 amps and above.
As previously mentioned, different welding jobs require different amounts of welding current. A single company may be involved with a large number of these different welding applications. If the company generally only performs welding applications requiring low welding currents, it may only own lower current capacity machines.
Occasionally, the company may have the need to perform a welding application requiring a welding current that exceeds the capacity of its existing machines. The cost of purchasing a new power supply to handle the current demands of the higher current application may not be warranted. In this situation, it is desirable to leverage the lower current capacity machines owned by the company to provide the current for the higher current application.
One way that this is done is to connect the outputs of the lower current capacity machines in parallel with each other. Each of the connected machines provides a portion of the needed current for the application. This is one way to get higher current from several lower current capacity machines.
Prior art welding systems of this type use paralleled machines all operating in the same mode, either in the constant voltage mode or the constant current mode. Constant current (CC) mode, as used herein, means that the welding current output of the power supply is regulated or controlled to be substantially equal to a set value. Constant voltage (CV) mode, as used herein, means that the welding voltage output of the power supply is regulated or controlled to be substantially equal to a set value.
The output voltage of each constant current machine in a constant current system is typically unregulated and floats. This allows the welding load voltage to vary without adversely affecting the performance of the individual paralleled power supplies.
The output voltage of each individual constant voltage machine in a constant voltage system, however, is regulated. This can cause problems because the output voltages of the paralleled machines are connected in parallel across the welding load. Each machine, therefore, attempts to regulate the load voltage and maintain it at its own set level. If the set levels for each machine are different, even slightly different, the machines will fight with each other to regulate the load voltage. During this struggle, one machine typically ends up providing most or all of the load current and the other machine effectively shuts down.
One such prior art constant voltage welding system uses a remote command signal. The command signal is an adjustable zero to 10 volt DC signal. This prior art command signal is independent of, and not related to, the welding output of any of the paralleled power supplies. The same command signal is supplied to each of the power supplies. The output voltage of each machine is responsive to the command signal and in theory, each machine regulates its welding voltage to the same set value.
The problem with this prior art method is that each machine has its own internal component tolerances and gain function. The set voltage for each machine differs slightly as a result. One machine may be set to a welding voltage output of 30 volts by the command signal and another power supply may be set to 29.5 volts by the same command signal. The power supply set to 29.5 volts will attempt to reduce the welding load voltage while the power supply set to 30 volts will attempt to increase it. This inevitably results in the first machine shutting down and the second machine taking the entire load.
A constant voltage welding system using paralleled machines wherein the machines do not struggle with each other to regulate the load voltage is therefore desirable.
SUMMARY OF THE PRESENT INVENTION
According to a first aspect of the invention, an apparatus for paralleling a plurality of welding power supply outputs includes an input stage, an output stage and a balancing circuit. The input stage is configured to receive a reference signal indicative of a welding output of a first power supply. The output stage is configured to deliver a command signal usable by a second power supply having a welding output responsive to the command signal. The balancing circuit is connected to receive the reference signal from the input stage and to provide the command signal to the output stage as a function of the reference signal.
The reference signal is indicative of the welding current of the first power supply in one alternative and the welding output of the second power supply is a welding current responsive to the command signal in another alternative.
In one alternative, the apparatus is configured to provide a contactor control signal to the second power supply in response to the first welding power supply switching on. The apparatus is configured to provide a contactor control signal to the second power supply in response to the flow of welding current from the first power supply in another alternative embodiment.
According to a second aspect of the invention, an apparatus for paralleling the outputs of a plurality of welding power supplies includes a balancing circuit configured to electrically communicate with a first power supply and a second power supply. The balancing circuit receives a reference signal indicative of a welding output of the first power supply and delivers a command signal usable by the second power supply having a welding output responsive to the command signal. The command signal is a function of the reference signal.
The welding output of the first power supply is a welding current and the reference signal is indicative of the welding current of the first power supply in one alternative. The welding output of the second power supply is a welding current responsive to the command signal in yet another alternative.
According to a third aspect of the invention, an apparatus for paralleling the outputs of a plurality of welding power supplies includes a balancing circuit configured to provide a command signal. The command signal is usable by a second power supply having a welding output responsive to the command
Croll Mark W.
Illinois Tool Works Inc.
Pilarski John H.
Shaw Clifford C.
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