Method and system for controlling the output of an engine driven welder

• US 5,670,070 A
• Filed: 08/31/1995
• Issued: 09/23/1997
• Est. Priority Date: 08/31/1995
• Status: Expired due to Term

• Current Assignee: Lincoln Global Incorporated (Lincoln Electric Holdings Incorporated)
• Original Assignee: Lincoln Electric Company (Lincoln Electric Holdings Incorporated)
• Inventors: Schraff, Scott Joseph, Osowski, Denis Michael, Clark, Keith Leon
• Primary Examiner(s): Shaw, Clifford C.
• Application Number:
  US08/522,454
• Time in Patent Office: 754 Days
• Field of Search: 219/137 PS, 219/130.33, 219/133, 219/134
• US Class Current: 219/130.33
• CPC Class Codes: B23K 9/0953 using computing means

Abstract

A method and system of controlling the output current/voltage characteristic curve of an engine driven alternator welder with a maximum open circuit output voltage, including a rotary engine, a three phase alternator, a rectifier bridge having a number of electronic switching devices for directing current to the output at an operating point determined by the firing angle of the switching devices, a sensor for sensing output current, a sensor for sensing output voltage, and a microprocessor output control device for controlling the firing angles of said switching devices in response to the sensed current and sensed voltage. The method and system comprise a device for creating a desired fixed slope operating current/voltage characteristic curve; an arrangement for sensing the present operating current/voltage point of the welder; and, a control for changing the firing angles of the switching devices to shift the current operating point to a new operating point on the desired, fixed slope current/voltage curve of the welder. Preferably, the switching devices include an SCR for each phase of the alternator.

Claims

1. A method of controlling the output current/voltage characteristic curve of an engine driven welder with a maximum open circuit output voltage, including a rotary engine, a three phase alternator, rectifier bridge having a number of electronic switching means for directing current to said output determined by the firing angle of said switching means during an appropriate half cycle, means for sensing output current, means for sensing output voltage, and a microprocessor output control device for controlling said firing angles of said switching means in response to the sensed current and sensed voltage, said method comprises the steps of:

(a) manually selecting one of several modes of operation, each of which has a preselected output characteristic curve with a fixed slope;

(b) causing said selection of said mode to create a first and second slope parameter with said parameters for a given mode being indicative of a known, fixed slope for said current/voltage characteristic output curve, said fixed slope defined by said first and second parameters corresponding to said selected mode;

(c) periodically generating a voltage value indicative of the real time sensed output voltage;

(d) combining said voltage value with said first slope parameter to give a voltage slope coordinate;

(e) periodically generating a current value indicative of the real time sensed output current;

(f) combining said current value with said second slope parameter to give a current slope coordinate;

(g) adding said voltage slope coordinate and said current slope coordinate to create a regulation term indicative of the present operating point of the welder;

(h) creating a desired set point for said regulation term, said set point being on a desired, target parallel characteristic curve having said fixed slope and manually adjusted to a line having an open circuit voltage less than said maximum open circuit voltage of said welder;

(i) creating an error signal by subtracting said set point and said regulation term; and

,

(j) changing the firing angle of said switching means in response to the magnitude of said error signal to force said regulation term toward said set point.

2. The method as defined in claim 1 including the additional step of:

(k) increasing the magnitude of said error signal in accordance with the difference between the current regulation term and a prior regulation term.

3. The method defined in claim 2 wherein said changing step includes the steps of:

(k) sensing the previous firing angles; and

,

(l) incrementing the firing angles in accordance with the magnitude of said error signal.

4. The method of claim 2 wherein said switching means are SCRs.

5. The method as defined in claim 1 wherein said manual adjustment is by a switching device having many adjusted positions for said parallel, target characteristic curve.

6. The method defined in claim 1 wherein said changing step includes the steps of:

(k) sensing the previous firing angles; and

,

(l) incrementing the firing angles in accordance with the magnitude of said error signal.

7. The method of claim 6 wherein said switching means are SCRs.

8. The method of claim 1 wherein said switching means are SCRs.

9. A system for controlling the output current/voltage characteristic curve of an engine driven welder with a maximum open circuit output voltage, said welder including a rotary engine, a three phase alternator, rectifier bridge having a number of electronic switching means for directing current to said output determined by the firing angle of said switching means during an appropriate half cycle, means for sensing output current, means for sensing output voltage, and a microprocessor output control device for controlling said firing angles of said switching means in response to the sensed current and sensed voltage, said system comprises:

means for manually selecting one of several modes of operation, each of which has a preselected output characteristic curve with a fixed slope;

means for causing said selection of said mode to create a first and second slope parameter with said parameters for a given mode being indicative of a known, fixed slope for said current/voltage characteristic output curve, said fixed slope defined by said first and second parameters corresponding to said selected mode;

means for periodically generating a voltage value indicative of the real time sensed output voltage;

means for combining said voltage value with said first slope parameter to give a voltage slope coordinate;

means for periodically generating current value indicative of the real time sensed output current;

means for combining said current value with said second slope parameter to give a current slope coordinate;

means for adding said voltage slope coordinate and said current slope coordinate to create a regulation term indicative of the present operating point of the welder;

means for creating a desired set point for said regulation term, said set point being on a parallel, desired, target characteristic curve having said fixed slope and manually adjusted to a line having an open circuit voltage less than said maximum open circuit voltage of said welder;

means for creating an error signal by subtracting said set point and said regulation term; and

, means for changing the firing angle of said switching means in response to the magnitude of said error signal to force said regulation term toward said set point.

10. The system as defined in claim 9 wherein said angle changing means includes means for sensing the previous firing angles;

and, means for incrementing the firing angle in accordance with the magnitude of said error signal.

11. The system as defined in claim 9 wherein said switching means are SCRs.

12. A method of controlling the output current/voltage characteristic curve of an engine driven welder with a maximum open circuit output voltage, including a rotary engine, a three phase alternator, rectifier bridge having a number of electronic switching means for directing current to said output determined by the firing angle of said switching means during an appropriate half cycle, means for sensing output current, means for sensing output voltage, and a microprocessor output control device for controlling said firing angles of said switching means in response to the sensed current and sensed voltage, said method comprises the steps of:

(a) creating a desired fixed slope operating current/voltage characteristic curve;

(b) sensing the present operating current/voltage point of said engine driven welder;

(c) creating a desired set point on said curve;

(d) comparing said present operating point and said desired set point to provide an error signal; and

,

(e) changing said firing angles of said switching means in response to said error signal to shift said present operating point to said desired set point on said created current/voltage curve.

13. A system of controlling the output current/voltage characteristic curve of an engine driven welder with a maximum open circuit output voltage, including a rotary engine, a three phase alternator, rectifier bridge having a number of electronic switching means for directing current to said output determined by the firing angle of said switching means during an appropriate half cycle, means for sensing output current, means for sensing output voltage, and a microprocessor output control device for controlling said firing angles of said switching means in response to the sensed current and sensed voltage, said system comprises:

means for creating a desired fixed slope operating current/voltage characteristic curve;

means for sensing the present operating current/voltage point of said engine driven welder;

means for creating a desired set point on said curve;

means for comparing said desired set point and said present operating point and providing an error signal; and

, means for changing said firing angles of said switching means in response to said error signal to shift said operating point to said desired set point on said created current/voltage curve.

14. A system as defined in claim 13 wherein said switch means are SCRs.