US 5,670,070 AGranted

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

AssigneeThe Lincoln Electric Company

InventorsKeith Leon Clark, Denis Michael Osowski, Scott Joseph Schraff

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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.

Claims14

Dependent claims

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.

8 more elements

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.

7 more elements

Dependencies are inferred from the claim text.