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EP-4529500-B1 - WELDING POWER SOURCE, WELDING SYSTEM WITH SUCH WELDING POWER SOURCE, DC-AC SELECTOR STAGE AND METHOD OF CONTROLLING A WELDING POWER SOURCE

EP4529500B1EP 4529500 B1EP4529500 B1EP 4529500B1EP-4529500-B1

Inventors

  • N, Thilak Raj
  • NATARAJAN, Govindaraj
  • Shanmugam, Paramasivam
  • PULENDIRAN, Sathish

Dates

Publication Date
20260506
Application Date
20230523

Claims (15)

  1. A welding power source (102) comprising: a primary rectifier (200) to converter alternating-current (AC) input power to direct-current (DC) power; an inverter (204) to convert the DC power to an AC signal; a transformer (206) to transform the AC signal to a transformed AC signal having different voltage and current characteristics than the AC signal; a secondary rectifier (210) to rectify the transformed AC signal to generate DC weld power; the welding power source (102) being characterised by : a DC-AC selector stage (400) to receive the DC weld power and configurable in a DC power mode and in an AC power mode, the DC-AC selector stage (400) comprising a first switch element (Q1) including a first switch and a first relay (RL1) arranged in parallel and a second switch element (Q2) including a second switch and a second relay (RL2) arranged in parallel; and a weld controller (208) to control the first and second switches and the first and second relays (RL1, RL2) to select the DC power mode in which the DC weld power passes through the DC-AC selector stage (400) to first and second output power terminals (130a, 130b) of the welding power source (102) and to select the AC power mode in which the DC weld power is converted to AC weld power by the DC-AC selector stage (400) and supplied to the first and second output power terminals (130a, 130b).
  2. The welding power source (102) of claim 1, wherein: during the DC power mode, the weld controller (208) is operable to keep the first and second relays (RL1, RL2) closed to bypass the first and second switches; and during the AC power mode, the weld controller (208) is operable to keep the first and second relays (RL1, RL2) open.
  3. The weld power source of claim 1, wherein: during the DC power mode, the weld controller (208) is operable to keep the first and second switches on; and during the AC power mode, the controller is operable to switch the first and second switches on and off to convert the DC weld power to the AC weld power.
  4. The welding power source (102) of claim 1, wherein: the transformer (206) has on its secondary side first and second end taps and a center tap; the secondary rectifier (210) receives transformer output signals from the first and second end taps and supplies the DC weld power to the DC-AC selector stage (400) on a first voltage line; and the DC-AC selector stage (400) is connected to the center tap of the transformer (206) via a second voltage line.
  5. The welding power source (102) of claim 4, wherein: the first relay (RL1) and the first switch are between the first voltage line and the first output power terminal (130a); and the second relay (RL2) and the second switch are between the second voltage line and the second output power terminal (130b).
  6. The welding power source (102) of claim 4, wherein: the DC-AC selector stage (400) further comprises a third switch element (Q3) including a third switch and a fourth switch element (Q4) comprising a fourth switch; the third switch is between the first voltage line and the second output power terminal (130b); and the fourth switch is between the second voltage line and the first output power terminal (130a).
  7. The welding power source (102) of claim 6, wherein: during the DC power mode, the weld controller (208) is operable to keep the first and second relays (RL1, RL2) closed and the third and fourth switches in an off state; and during the AC power mode, the controller is operable to keep the first and second relays (RL1, RL2) open and to switch the first, second, third, and fourth switches on and off to convert the DC weld power to AC weld power.
  8. The welding power source (102) of claim 1, wherein the DC-AC selector stage (400) further comprises a third switch element (Q3) including a third switch and a fourth switch element (Q4) comprising a fourth switch, the first, second, third, and fourth switch elements (Q1, Q2, Q3, Q4) being arranged as an H-bridge, wherein the weld controller (208) is operable to control the DC-AC selector stage (400) as a full-bridge inverter during the AC power mode.
  9. The welding power source (102) of claim 1, wherein the first switch is a sole switch of the first switch element (Q1), and the second switch is a sole switch of the second switch element (Q2).
  10. The welding power source (102) of claim 1, wherein the secondary rectifier (210) is a full-bridge rectifier comprising four diodes.
  11. A welding system (100) comprising: the welding power source (102) of claim 1; a cable assembly (108); and a TIG welding torch (110) to receive weld power from the welding power source (102) via the cable assembly (108), wherein: the welding system (100) is operable in a DC TIG welding mode in which the welding power source (102) supplies the DC weld power to the TIG welding torch (110), and the welding system (100) is operable in an AC TIG welding mode in which the welding power source (102) supplies the AC weld power to the TIG welding torch (110).
  12. A DC-AC selector stage (400) for a welding power source (102), comprising: a first switch element (Q1) comprising a first relay (RL1) and a first switch arranged in parallel between an output of a secondary rectifier (210) downstream of a transformer (206) and a first output power terminal (130a) of the welding power source (102); a second switch element (Q2) comprising a second relay (RL2) and a second switch arranged in parallel between a center tap of the transformer (206) and a second output power terminal (130b) of the welding power source (102); a third switch element (Q3) comprising a third switch between the output of the secondary rectifier (210) and the second output power terminal (130b); and a fourth switch element (Q4) comprising a fourth switch between the center tap of the transformer (206) and the first output power terminal (130a), wherein: the DC-AC selector stage (400) is configured to be operable in an AC power mode in which the first and second relays (RL1, RL2) are in an open state and the first, second, third, and fourth switches are operated as an H-bridge inverter to convert DC power to AC weld power; and the DC-AC selector stage (400) is configured to be operable in a DC power mode in which the first and second relays (RL1, RL2) are in a closed state and the third and fourth switches are in an off state to pass DC weld power to the first and second weld output terminals (130a, 130b) of the welding power source (102).
  13. The DC-AC selector stage (400) of claim 12, wherein the first, second, third, and fourth switch elements (Q1, Q2, Q3, Q4) are operable as a full-bridge inverter in the AC power mode.
  14. A method of controlling a welding power source (102), comprising: selecting an AC power mode by controlling first, second, third, and fourth switches arranged in an H-bridge configuration to convert DC weld power to AC weld power; the method being characterised by : selecting a DC power mode by closing first and second relays (RL1, RL2) that respectively bypass the first and second switches and by keeping the third and fourth switches in an off state.
  15. The method of claim 14, further comprising: supplying the AC weld power to a TIG welding torch (110) during the AC power mode; and supplying the DC weld power to the TIG welding torch (110) during the DC power mode.

Description

The present invention relates to a welding power source capable of delivering both DC and AC weld power for welding operations, in particular a welding power source having circuitry for bypassing components of an AC power stage during DC welding operation, and more particularly to a welding power source, a welding system with such power source, a DC-AC selector stage for a welding power source, and a method of controlling a welding power source, see claims 1, 11, 12 and 14 (US 2005/006367 A1 describing the preamble of claims 1, and 14). BACKGROUND Welding power sources typically generate output weld power for a welding or cutting process by converting input alternating-current (AC) power from AC mains or a generator to direct-current (DC) power, and then converting the DC power to output power suitable for the welding or cutting process via a weld process regulator. The output power required for many welding operations is DC power. AC weld power can also be used in certain types of welding operations such as, for example, in tungsten inert gas (TIG) welding, where the electric welding arc is formed between a non-consumable tungsten electrode and the workpiece. While DC power may be preferable in some TIG welding operations, such as when welding certain types of steel, AC TIG weld power is more typically used to weld aluminum. Further, manual ignition of the welding arc, e.g., via a "scratch start," is difficult to achieve in TIG welding. More advance welding power sources often include circuitry to generate high-frequency (HF) AC power that can be used to initiate the welding arc in TIG welding without touching the electrode to the workpiece, thereby significantly simplifying arc ignition. However, inclusion of circuitry to generate AC power for TIG operations can potentially introduce power losses that impact the power efficiency of the welding power source during DC welding operations. INVENTION According to a first aspect of the present invention, a welding power source is defined in claim 1. According to a second aspect of the present invention, a welding system with such welding power source is defined in claim 11. According to a third aspect of the present invention, a DC-AC selector stage for a welding power source is defined in claim 12. According to a fourth aspect of the present invention, a method of controlling a welding power source is defined in claim 14. Further preferred embodiments of these four aspects of the present invention are defined in their dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an illustration of an example welding system in which the techniques and circuitry described herein may be implemented.FIG. 2 is a high-level block diagram of a welding power source capable of delivering both DC and AC weld power for welding operations.FIG. 3 is a circuit diagram of an inverter-based DC-AC selector stage in a welding power source operable in a DC weld power mode and in an AC weld power mode.FIG. 4 is a circuit diagram of an example implementation of an inverter-based DC-AC selector stage in a welding power source, including DC bypass circuitry and operable in a DC weld power mode and in an AC weld power mode.FIG. 5 is a flow diagram showing operations for selecting an AC power mode and a DC power mode by controlling components of the DC-AC selector stage. DETAILED DESCRIPTION Overview A welding power source comprises a DC-AC selector stage configurable to supply either DC weld power or AC weld power to output power terminals of the welding power source. The DC-AC selector stage comprises a first switch element including a first switch and a first relay arranged in parallel, and a second switch element including a second switch and a second relay arranged in parallel. A weld controller controls the first and second switches and the first and second relays to select a DC power mode in which the DC weld power passes through the DC-AC selector stage to the output power terminals and to select an AC power mode in which DC weld power is converted to AC weld power and supplied to the output power terminals. Example Implementations An example welding system 100 suitable for implementing the techniques and circuitry described herein is shown in the high-level functional block diagram of FIG. 1. Welding system 100 includes: a welding power source 102; a wire electrode feeder 106 coupled to the welding power source 102; a cable assembly 108 coupled to the wire electrode feeder 106; a torch 110 coupled to the cable assembly 108 and having a metal contact tip 111 that extends from an end of the torch 110; and a gas supply 112 (e.g., a gas container) coupled to the cable assembly 108 to supply shielding gas. A workpiece 114 is coupled to the welding power source 102 through at least a return path/cable 115. In this example, because welding system 100 includes a wire electrode feeder 106 and a gas supply 112, the system is capable of performing Gas Metal Arc Welding (GMAW), such as M