Electric heating – Metal heating – By arc
Reexamination Certificate
1999-11-03
2001-01-23
Walberg, Teresa (Department: 3742)
Electric heating
Metal heating
By arc
C363S089000
Reexamination Certificate
active
06177645
ABSTRACT:
The present invention relates to the art of electric arc welding and plasma arc cutting and more particularly to a single phase power supply module used individually or in combination to provide an electric arc welder and/or in combination to construct a plasma arc cutter.
INCORPORATION BY REFERENCE
In accordance with the invention, a universal single phase module including a novel combination of circuits is combined in novel architectures to create a number of electric arc welders and/or plasma arc cutters having defined capacities. A novel combination of a specific power factor correcting circuit and a particular high speed DC to DC converter converts a single phase power source into a DC output voltage capable of use in electric arc welding and/or plasma arc cutting. A number of power factor correcting circuits are used with DC to DC converters or other types of power supplies for low quality low power applications. Such circuits and converters are well documented. For instance, an article by Peter N. Wood entitled
Fluorescent Ballast Design Using Passive P. F. C. and Crest Factor Control
by International Rectifier discloses passive and active power factor correcting circuits for use with lighting ballast. The active circuit is a boost converter and the primary passive circuit is a 50% valley fill circuit. These power factor correcting circuits are used in lighting systems using pulsating voltage which is not used in the invention; however, this article is incorporated by reference herein as background information. It does show common power factor correcting circuits, even though these circuits are not the type used in the present invention. In power supplies, especially low energy, pulsating supplies, power factor correction is usually accomplished by a boost converter at the output of the full wave rectifier. Such converter can be rapidly switched to cause the input current to track the line voltage at the input of the rectifier; however, boost converters require that output voltage of the converter be greater than the peak voltage of the input AC voltage. The present invention is a module which has a relatively low output voltage that must be combined to provide high voltage for plasma arc cutting; consequently, boost converters are not applicable to the invention. Patents showing boost converts as power factor correcting are Wilkinson U.S. Pat. No. 4,677,366; Sood 5,235,504; and, Choi 5,612,609, which patents are incorporated as background information.
The present invention relates to a universal module that is used for electric arc welding and/or plasma arc cutting, which module is powered by a single phase AC voltage and has an output with sufficient range to produce the necessary current and voltage for high energy applications. The only module construction to accomplish this objective is disclosed in a copending application by assignee, which application is not prior art, but is incorporated herein as Ser. No. 390,494, filed Mar. 16, 1998.
Items incorporated by reference herein are background information and do not teach the present invention, although the copending application incorporated by reference herein does teach a module using controlled high speed switching of a full bridge inverter to correct the power factor of the input power supply. The technologies incorporated by reference herein need not be repeated in a description of the present invention.
BACKGROUND OF INVENTION
With the increase in the industrial use of electric arc welders, there is a demand for welders having output voltages between a minimum of 0-20 volts DC and a maximum of 50-100 volts DC. The welders require output currents between 100 amps and 1000 amperes. Welders rated at certain voltages and currents were separately designed. Smaller welders were constructed differently than larger welders. Most electric arc welders utilize a power supply using the topography of a DC to DC converter. Such converters are controlled by a pulse width modulation operated at a high speed pulse rate, such as 10—20 kHz. Such inverters are specially designed for either high power output or low power output. A number of inverter designs were required for a manufacturer to offer a total line of welders, especially for industrial use. Since welder manufacturers had to offer a large number of different welders having different sizes and ratings, research and development, the engineering and inventory requirements are costly and require a tremendous number of technical employees. This costly situation has been acerbated by the advent of plasma arc cutters, which units must be offered by manufacturers of electric arc welders. Although plasma arc cutters require power supplies quite similar to electric arc welders, the operating points for plasma cutters involves substantially higher output voltages with drastically lower output currents. By adding plasma arc cutters to the product line with electric arc welders, still additional design activity, inventory and service cost has been experienced. Thus, a manufacturer of electric arc welders and plasma arc cutters have several different power supplies, each of which is dedicated to a size and mode of operation for a welder or a cutter. In summary, inventory, support personnel, design personnel, inventory and service demands on a manufacturer offering a full line of electric arc welders and plasma arc cutters is substantial. Thus, only large, well capitalized manufacturers can enter into and maintain a viable competitive position in the rapidly developing field of electric arc welders and plasma arc cutters. Even such manufacturers experience decreased profits due to the high cost of maintaining a full line of products.
THE PRESENT INVENTION
The costs and extreme capital requirements needed to offer a full line of electric arc welders and plasma arc cutters are overcome by the present invention, which invention relates to a particular designed single phase module and to construction of a large number of welders and cutters from the novel single phase module. An attempt to produce a universal module is disclosed in copending application Ser. No. 39,494 filed Mar. 16, 1998. This prior application suggests a universal module using a power factor correcting inverter stage, controlled by a standard chip, which inverter stage is combined with an output inverter. The input inverter stage utilized switching of four switches in a full wave bridge to produce power factor correction of the input source. Three phase implementation of the module uses the switching control chip for a three phase input to the module. Such arrangement is complex and does not allow the module designed for a three phase power source to be used with single phase power source.
Power factor correcting circuits are well known for use in lighting systems. These circuits can be passive, such as a valley fill circuit, or active, such as a boost converter circuit. Valley fill circuits have not been widely used in different electrical systems. Indeed, the basic power factor correcting circuit for lighting systems has been the boost converter circuit. This power factor correcting circuit is not applicable for a universal module to be used in electric arc welding and/or plasma arc cutting, since the output of the circuit must be greater than the peak input of the power source. Since a power supply must be capable of operating with an input the power source varies between 200 VAC and 600 VAC, a boost power factor correcting circuit is not applicable for use in the present invention. The output voltage circuit would need to be over 800 volts DC. Although a valley fill power factor correcting circuit may be applicable, it could only be used for extremely small welders and/or for plasma arc cutters. Use of a valley fill circuit could not be used for a wide range of welders and cutters, which is the basic objective of the present invention. Thus, the use of complicated power factor correcting circuits now available as integrated circuit chips and boost converter power factor correcting circuits are not applicable for
Church Larry L.
Matthews William T.
Lincoln Global Inc.
Van Quang
Vickers Daniels & Young
Walberg Teresa
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