Method and apparatus for providing welding-type power using dual forward converters

Abstract

A method and apparatus for providing welding-type power, the method comprising receiving input power and pulse width modulating a first forward converter and a second forward converter such that the two forward converters operate as a pulse width modulated dual forward converter to provide a welding-type output. A phase relationship between the first forward converter and the second forward converter is selected from at least two available phase relationships using a controller. The controller includes a pwm module and the pwm module includes a phase relationship module. The at least two available phase relationships are at least two of variable phase shift, fixed phase interleaving, and in-phase lock. The selected phase relationship is maintained over a predetermined output range.

Description

TECHNICAL FIELD

[0001] The present disclosure relates generally to the field of welding-type power supplies. More specifically, the present invention relates to welding-type power supplies having two forward converters. BACKGROUND

[0002] The present disclosure is an improvement to the welding-type power supplies shown in U.S. Patent 8,952,293, U.S. Patent 8,455,794, and U.S. Patent Publication US 2018-0304393, each of which is incorporated herein by reference and will be used as the basis for background and description of PSDFs (Phase Shifted Double Forward Converters) in welding applications. The improvement can also be applied to PSDFs used in battery chargers as described in U.S. Patent 8,179,100, which is also incorporated herein by reference. As used herein, welding-type power supply refers to a power supply that can provide welding-type power. As used herein, welding-type power refers to power suitable for welding, plasma cutting, induction heating, and / or hot wire welding / preheating (including laser welding and cladding).

[0003] Welding-type power supplies generally convert AC power to an output suitable for welding-type operations. The output power is provided at appropriate voltage and / or current levels, and can be controlled and regulated according to process requirements. Many industrial welding and cutting processes have dynamic load voltage and current requirements that cannot be met by the output of a static power supply. For example, arc starting, electrode characteristics, length of the effective arc, operator technique, etc. can all have an impact on instantaneous voltage requirements. Typically, these dynamic requirements above average load conditions are of short duration (from about 1 millisecond to a few seconds) and only occupy a small fraction of the overall welding or cutting time. Therefore, the power supply should be able to provide both average load requirements and dynamic load requirements.

[0004] Currently, in some welding-type power supplies, single forward or double forward converter circuits are used to meet these dual requirements. Average load requirements generally dictate the thermal aspects of the power supply circuit design, and thus the size and ratings of components such as transformers, heat sinks, power devices, cooling fans, etc. However, to accommodate the short dynamic loads of welding and cutting power supplies, components are often selected that can handle the short but extreme requirements. This can result in oversized components for the circuit, or lack of efficiency when the power supply is operated under average conditions.

[0005] Welding-type power supplies based on PSDF can better cope with both static and dynamic load demands without some of the inefficiencies of other designs. For example, welding-type power supplies based on PSDF can vary the output voltage at the welding or cutting torch by manipulating the duty cycles of two forward converter circuits. Prior art PSDF welding-type power supplies found in US Patent 8,952,293 and US Patent 8,455,794 increase the synchronized duty cycles of a pair of forward converter circuits in response to an increased output voltage demand. They then vary the phase shift between the duty cycles in response to further increases in the output voltage demand. They also adjust the time needed to reset the transformer core via leading (start of pulse) or trailing (end of pulse) edge compensation.

[0006] By processing in this way, the phase shift can be improved, reducing control losses. Prior art patent US 8,952,293 describes a "lead" and "lag" converter circuit (forward converter). Lead refers to operating in a phase-shifted mode where one converter starts its PWM (pulse width modulation) cycle before the other (i.e. leads). Lag refers to the other converter starting its PWM cycle after the first (i.e. lags). The '293 patent describes how the leading converter shifts phase to in-phase and out-of-phase as the lagging converter remains fixed in its PWM timing. The '293 patent describes taking some action as the phase shift increases to allow the forward converter transformer to have sufficient time to fully reset.

[0007] These actions can include skipping a complete pulse, reducing the duty cycle of the pulse by delaying the new phase-shift leading edge, or starting the new pulse before the core has fully reset and then reducing the pulse width by adjusting the trailing edge to allow the core more time to reset at the end of the pulse. Skipping or reducing the pulse width of the leading converter causes a transient disturbance in the control. This means that the control loop does not get the total duty cycle (phase shift plus leading duty cycle and lagging duty cycle) that it is trying to command in response to the dynamic needs of the welding arc. This can result in unwanted welding arc disturbances such as arc interruptions or undershoots or overshoots in current, thereby requiring weld process control.

[0008] Starting the new pulse before the core has fully reset can also result in a conduction instant while the core de-excitation current is still flowing. In addition, if the control loop further increases the phase shift, this can result in an additional consecutive cycle with the core not fully reset and can result in transformer saturation.

[0009] Some prior art PSDF-based welding-type power supplies operate in-phase most of the time (the pulses from each converter start and end at the same time) to provide the static or average demand of the welding process. Under transient dynamic conditions, the voltage required by the welding arc is higher than what the in-phase operation of the converter circuits can satisfy, so the prior art PSDF-based welding-type power supplies will move out of phase (so that the pulses from one converter start at a different time than the pulses from the other converter). Once the dynamic conditions are gone, they will again operate in-phase. During the time when the two converters are operating in-phase, they share the load current. Thus, each converter is operating at half current. This provides more efficient operation by reducing losses in the semiconductor switches and transformers.

[0010] However, during the time when the converters are operating in the phase-shifted mode, the losses can be significantly higher because each converter is now carrying the full current alone. Thus, it is desirable that the two converters not operate in the phase-shifted mode for extended periods of time and / or at increased current levels. The '293 patent describes means to limit the time and / or reduce the current level during phase-shifted operation.

[0011] The '293 patent teaches a control that can drive the operation of the converters into the phase-shifted mode during high current conditions even though the actual arc voltage can not be higher than normal. This can occur, for example, when pulsed GMAW (GMAW-P) welding and the welding process requires the current to be driven from a relatively low background current level (e.g., 40-100 amps) to a relatively high peak current (e.g., 400-600 amps) in a short duration (e.g., 0.5 to 1.0 milliseconds). To overcome the effects of the circuit impedance and inductance (including the inductance of the welding cable), the PSDF shifts out of phase to provide sufficient drive voltage to ramp up the current level at the required di / dt rate. This situation is caused by the generation of the welding process waveform and not directly by the dynamic changes in the arc voltage (which can occur during SMAW welding).

[0012] The relationship between the duty cycle and the actual output voltage is not ideal and is typically described with an output droop. When the two converter circuits shift from in-phase to out-of-phase operation, particularly at higher output currents, the output voltage will momentarily decrease instead of increasing as the control expects. This momentary decrease in voltage appears as a non-linearity or discontinuity in the control loop. This non-linearity can cause arc disturbances when the control is forced to "catch-up" and further increase the phase shift to obtain the desired output voltage. This non-linearity can also cause the PSDF to be "caught" in the phase-shifted mode and not transition back to in-phase operation naturally.

[0013] Some prior art PSDF-based welding-type power supplies typically limit the maximum switching duty cycle to between 0.4 and 0.5 in order to provide sufficient time for transformer core reset. This limitation must take into account various non-ideal parameters and conditions, such as gate drive delay and voltage rise time on the switch at switch-off. Some prior art operate both converters of a PSDF in-phase under most operating conditions, and only phase-shift to out-of-phase under transient dynamic load conditions. They found that it is desirable to utilize a maximum switching duty cycle (Dmax) as close to 0.5 as practical to provide the widest operating window for in-phase operation. However, the effects of gate drive delay and voltage rise time can vary depending on the switching current, which is related to the output load current. Prior art PSDF-based welding-type power supplies typically select a single DMax for all load currents, and the Dmax actually used is not as high as possible for some load currents.

[0014] When a PSDF-based welding-type power supply is operated at low voltage and / or low current, the PWM pulse width is reduced to such low values that it is difficult to consistently generate switching cycles. Control in some prior art PSDF-based welding-type power supplies typically causes the converters to skip a certain number of switching cycles, then skip one or more cycles with very small pulse widths. This control can result in increased current ripple, overshoot or undershoot, or inconsistent behavior when operated at low current and low voltage. Generally, PWM switching behavior becomes more consistent at higher current levels and / or higher voltage levels.

[0015] U.S. Patent Publication US 2018-0304393 teaches improved phase shifting, full or partial compensation of duty cycle based on output load current, modification of Dmax based on output load current, and improved low voltage / low current operation. Phase shifting is improved by fixing the PWM timing of one converter and adjusting the leading and trailing edges of the other converter to reduce control losses and achieve the total duty cycle required for control. Full or partial compensation of duty cycle based on output load current is taught to help linearize the control. The maximum duty cycle (Dmax) is modified based on output load current in order to provide a wider operating window for in-phase operation. Operation at low voltage and / or low current is improved by disabling one converter in the low output case to reduce pulse skipping. Once the minimum PWM duty cycle ON time has been reached, the PWM OFF time is increased in a controlled manner to further increase the operating window in which consistent pulse widths can be commanded.

[0016] In general, the prior art operates in PSDF mode (phase-shifted double forward mode). Both converters respond to a control signal such that an increase in the control signal will first increase the in-phase duty cycle of both forward converters. Further increases in the control signal beyond a certain limit will cause both converters to operate in a partially or fully phase-shifted manner until an upper limit is reached representing full phase shift and maximum duty cycle (Dmax) for each converter.

[0017] While the prior art discussed herein is an improvement over earlier welding power supplies, further reduction of output current ripple, especially in some modes of operation, and increased duty cycle resolution, especially in some modes of operation, can improve arc performance and reduce arc interruptions. SUMMARY

[0018] According to a first aspect of the disclosure, a method of providing welding-type power includes receiving input power and pulse width modulating a first forward converter and a second forward converter such that both forward converters operate as a pulse width modulated double forward converter to provide a welding-type output. A phase relationship between the first forward converter and the second forward converter is selected from at least two available phase relationships. The at least two available phase relationships are at least two of variable phase shift, fixed phase interleaving, and in-phase lock. The selected phase relationship is maintained over a predetermined output range.

[0019] According to a second aspect of the disclosure, a welding-type power supply includes a double forward converter and a controller. The double forward converter has a first converter and a second converter. The controller includes a PWM module that sets a PWM timing signal, and the PWM module includes a phase relationship module having a plurality of timing outputs connected to the double forward converter.

[0020] In an alternative, selecting the phase relationship is performed in response to at least one of: feedback response to the welding-type output, user input, and process selection.

[0021] In another alternative, selecting the phase relationship is performed in response to user input indicative of at least one of: a desired output current, a desired peak output current, and a desired output voltage.

[0022] In one embodiment, selecting the phase relationship is performed in response to at least one of: a user-selected SMAW process, a user-selected GTAW process, and a user-selected GMAW process.

[0023] In various embodiments, selecting the phase relationship is performed in response to feedback response to at least one of: a welding-type output current, a welding-type output voltage, a welding-type peak current, and a welding-type output power.

[0024] In one alternative, maintaining the selected phase relationship over a substantial output range includes maintaining the selected phase relationship over at least half of a rated output.

[0025] In another alternative, maintaining the selected phase relationship over a substantial output range includes maintaining the selected phase relationship over a range of duty cycles.

[0026] In one embodiment, the forward converters are stacked forward converters and their outputs are combined.

[0027] In various embodiments, the phase relationship module has an input and is responsive to the input, the input being connected to receive at least one of: feedback response to a welding-type output, user input, and a process selection.

[0028] In one alternative, the input of the phase relationship module is connected to receive user input indicative of at least one of: a desired output current, a desired peak output current, and a desired output voltage.

[0029] In another alternative, the input of the phase relationship module is connected to receive at least one of: a user-selected SMAW process, a user-selected GTAW process, and a user-selected GMAW process.

[0030] In one embodiment, the input of the phase relationship module is connected to receive feedback response to at least one of: a welding-type output current, a welding-type output voltage, a welding-type peak current, and a welding-type output power.

[0031] In various embodiments, the phase relationship module is responsive to a welding-type output current greater than half of a rated output.

[0032] Other principles and advantages will become apparent to the skilled person on reading the following drawings, detailed description, and appended claims. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is an exemplary welding-type power supply unit;

[0034] Figure 2 Two forward converter circuits are shown;

[0035] Figure 3is a circuit diagram illustrating one embodiment of a power circuit having two forward converter circuits;

[0036] Figure 4 is a circuit diagram illustrating a second embodiment of a power circuit having two forward converter circuits;

[0037] Figures 5a to 5e shows relative phase of two converters in PSDF mode of operation;

[0038] Figures 6a to 6d shows relative phase of two converters in alternative PSDF mode of operation;

[0039] Figures 7a to 7c shows relative phase of two converters in LIP mode of operation;

[0040] Figures 8a to 8c shows relative phase of two converters in FPS mode of operation;

[0041] Figure 9 shows output ripple current components of two converters in LIP or PSDF mode of operation;

[0042] Figure 10 shows output ripple current components of two converters in FPS mode of operation;

[0043] Figure 11 shows a control circuit or error module;

[0044] Figure 12 shows a portion of a controller, namely, a PWM module; and

[0045] Figure 13 shows a sub-module that is part of a phase relationship module.

[0046] Before one or more embodiments are described in detail, it is to be understood that the application is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The application is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and not limitation. DETAILED DESCRIPTION

[0047] While the present disclosure will be illustrated with reference to specific topologies and specific control schemes for generating welding-type output, it should first be understood that welding-type power supplies and methods of generating welding-type power can also be implemented with other circuitry and other control schemes.

[0048] The present invention can be best understood with reference to the prior art. The power circuitry used herein can be the power circuitry found in prior art patent US 8,952,293 and prior art US patent publication US 2018-0304393. The prior art describes how this circuitry operates in a PSDF mode of operation. In general, the present invention provides a pulse width modulated dual forward converter with three modes of operation, also referred to as three phase relationships. The present invention provides a PSDF mode of operation (or variable phase shift mode) as well as two additional modes: in-phase lock mode (LIP) and fixed phase stagger mode (FPS). As used herein, variable phase shift refers to causing a phase shift of the output of one converter relative to the output of another converter in response to at least one of a duty cycle, a current command, a user set point, and an output. As used herein, in-phase lock refers to a fixed relative phase that is in-phase. As used herein, fixed phase stagger refers to a fixed relative phase that is out-of-phase.

[0049] US 8,952,293 and prior art US patent publication US 2018-0304393 teach a PSDF mode of operation. Two forward converter circuits 24 and 26 Figure 2 ) provide a welding power output whereby these two converters operate in-phase during most of the time while producing a load current and load voltage within the “normal” range. During transient events, when the load voltage exceeds the volt-amp load line capability of these two in-phase converters, one converter will be shifted out-of-phase relative to the second converter so that the combined output of these two converters produces a higher load voltage to meet the demand of the transient event. Once the transient event is no longer present, these two converters will again operate in-phase to meet the “normal” load demand.

[0050] This control system responds to the static and dynamic demands of the welding arc or output load on the welding power supply. In response to the control signal, the PWM pulse width of these two in-phase converters will increase as the load current or load voltage increases, thereby requiring the power supply to increase its output. Once these two in-phase converters reach a maximum pulse width (Dmax), further increases in the control signal will cause one of the converters to begin to shift out-of-phase with the second converter so that the combined output of these two converters further increases. Further increases in the control signal will cause further increases in the phase shift relationship until a maximum phase shift is reached (i.e., full out-of-phase, for example) at which point no further phase shift will occur.

[0051] At this point, the maximum output of the two phase-shifted converters has been reached. In response to a decrease in the control signal, for example when the transient event has ended and normal load conditions have returned, the phase shift between the two converters will decrease. Further decrease in the control signal will cause the phase shift relationship to decrease further until the two converters are again operating in phase at maximum duty cycle. Further decrease in the control signal beyond this point will cause the PWM pulse width of the two in-phase converters to decrease.

[0052] For too long a time or for too large an output load current as indicated by the feedback signal, the control system can limit the operation of the two converters in a fully or partially phase-shifted manner. The control system can force the two converters to phase shift back to in-phase or limit the operation of the two converters so that they can only operate in phase as a means of thermal protection of the two converters and to prevent excessive thermal stress due to operation in the phase-shifted mode for long periods of time. The relative phase between the leading converter and the lagging converter is controlled so that the control is satisfied and sufficient time is always guaranteed for the two converters to reset their respective transformers. Load line compensation can be used to improve the transition between the in-phase and phase-shifted modes of operation.

[0053] In the case where the in-phase duty cycles of the leading and lagging converters have reached a certain minimum value, a low current mode is entered and further decrease in the control signal will cause each converter (leading and lagging) to take turns skipping a certain period of operation so that only one converter is on and providing the load in each PWM switching period. At this point, the two converters continue to operate in their respective in-phase relationship but only one of the converters is turned on alternately in a given period.

[0054] Preferably, the two converters operate in phase at a certain duty cycle in response to the control signal. An increase in the control signal beyond a certain limit (i.e., once both in-phase duty cycles have reached a maximum value DMAX) will cause the two converters to phase shift to be completely out of phase but within approximately their in-phase duty cycle 1 / 2. Further increase in the control signal will cause the duty cycle of the two completely phase-shifted converters to increase until the maximum duty cycle (DMAX) of the two converters is reached again. The PSDF mode provides a range of duty cycles and phase shifts in response to the control signal. The control range given by these modes in response to the control signal is approximately 0 to 2*DMAX or approximately 0 to 0.9 (or 0 to 1.0).

[0055] The present invention provides a second mode of operation: the lock-in-phase (LIP) mode. This mode provides a control system that locks the operation of the forward converters to be in phase. The relative phase is fixed at zero or in phase. For the LIP mode, the PWM pulse widths of both converters are responsive to a control signal. The control system can provide a duty cycle response for the LIP mode such that the entire range of the control signal will provide a control range of 0 to DMAX (e.g., 0 to 0.45 or 0 to 0.50). This can provide a finer control resolution compared to the PSDF mode where the entire range of the control signal must provide approximately twice the range of the effective duty cycle range (i.e., 0 to 2 x DMAX, or 0 to 0.9, or 0 to 1.0). The load line or output voltage characteristic provided by the LIP mode can meet the "normal" load voltage requirements, but can not have enough voltage or load line to provide the dynamic or transient load voltage required for certain welding processes (such as SMAW). The LIP mode can be advantageous for certain welding processes. For example, GTAW where there are no high dynamic load voltage demands.

[0056] The present invention provides a third mode of operation, the fixed phase stagger mode: the FPS mode provides a control system that locks the forward converters 24 and 26 to operate in a fully phase-shifted mode. The relative phase is fixed at approximately 0.5 or 50% of the PWM period (i.e., fully phase shifted). The relative phase can be fixed at a value other than 50% (e.g., 40% to 60%) such that the two converters still operate out of phase and each carries the full load current during its respective operating duty cycle. Alternatives provide other fixed phases.

[0057] The control system can provide a duty cycle response for the FPS mode such that the entire range of the control signal will provide a control range of 0 to DMAX (e.g., 0 to 0.45 or 0 to 0.50). This can provide a finer control resolution compared to the PSDF mode where the entire range of the control signal must provide approximately twice the range of the effective duty cycle range (i.e., 0 to 2 x DMAX, or 0 to 0.9, or 0 to 1.0).

[0058] The FPS mode can reduce the output ripple current. The effective ripple frequency of the combined output of the two forward converters will be 2 times that of the in-phase or partial phase-shifted mode of operation (i.e., the LIP mode or the PSDF mode). This increase in the ripple frequency can result in a corresponding decrease in the peak-to-peak magnitude of the ripple current, thereby increasing the minimum output current. The FPS mode can provide a full dynamic voltage range similar to the PSDF mode, which can be advantageous for certain welding processes.

[0059] Similar to the phase-shift mode of the PSDF mode, in the FPS mode each transformer carries the full load current. Thus, it can be desirable to limit the FPS mode to an output current level (i.e., for example, a preset current) such that the average output current is less than the full-rated value of the machine. For example, the FSP mode can be limited to a current range of 1 / 2 of the full-rated value of the machine (i.e., limit the FSP mode to 150 amperes or less on a 300-ampere machine). The FPS mode can be advantageous, for example, for low-current SMAW, where the increase in minimum current and the ability to provide high dynamic voltage can meet the need to prevent arc interruption and improve welding performance. 1

[0060] The preferred embodiments of a PSDF-based welding-type power supply and control thereof can be implemented by the circuitry shown in the '293 patent and U.S. Patent Publication US 2018-0304393, and the control is the same as described herein, except as otherwise stated.

[0061] Figure 1 is an exemplary welding-type power supply unit 10 that powers, controls, and provides supplies for a welding or cutting operation in accordance with aspects of the present disclosure. The user-facing side of the power supply unit 10 contains a control panel 12 through which a user can control the supply of materials (such as power, gas flow, wire feed, etc.) to a welding or cutting torch 14 and / or select a process. A workpiece lead clamp 16 is typically connected to the workpiece to close the electrical circuit between the cutting torch 14, the workpiece, and the supply unit 10 and ensure proper current flow. It should be noted that in some embodiments, such as for stick welding operations, the welding torch 14 can be an electrode. The portability of the unit 10 is dependent on a set of wheels 18 that enable a user to move the power supply unit 10 to the location of the weld. The welding-type power supply unit 10 receives input power from a typical source such as utility power, engine power, battery power, fuel cell units, etc. The welding-type power supply unit 10 provides welding-type output (welding-type power) across the workpiece clamp and the cutting torch.

[0062] The internal components of the power supply unit 10 convert the input power (from a wall outlet or other AC or DC voltage source (such as a generator, battery, or other power source)) into an output that is consistent with the voltage, current, and / or power requirements of the welding arc or cutting arc maintained between the workpiece and the welding torch 14. Figure 2 An exemplary block diagram of components that can be included in a welding or plasma cutting power supply unit 10 is shown. In particular, Figure 2 ​A welding-type power circuit is shown that includes a main power supply 20 that receives input power and outputs direct current (DC) to a power circuit 22 that includes a first converter circuit 24 and a second converter circuit 26. The main power supply 20 can be transformer-based, include a rectifier, or include one or more converters such as a buck converter, a boost converter, a cuk converter, an inverter, etc.

[0063] The converter circuits 24, 26 are used to combine their respective outputs at a single node that feeds a filter inductor 28 that supplies an output voltage 30 (i.e., V_output) for a welding or cutting operation. As used herein, a welding-type power circuit refers to a power circuit system that receives input power and provides welding-type power. A welding arc or cutting arc 32 is supplied with a welding or cutting current 33 and is connected to a ground 34. In one embodiment, a separate inductor (one for each converter circuit) can be used in place of the filter inductor 28. In other embodiments, the inductor 28 can have multiple windings for combining the outputs of the two converter circuits 24, 26. A user interface or control panel 12 provides signals to the controller 25.

[0064] The controller 25 provides control signals to the converter circuit 24 on line 201 to control the turn-on and turn-off of the switches therein. When lines are used herein to refer to a single line shown on a drawing, it refers to one or more cables that carry multiple signals (such as multiple power signals, and / or multiple feedback signals, and / or multiple control signals). The controller 25 receives feedback from the converter circuit 24 on line 202, preferably voltage and / or current. The controller 25 also provides control signals to the converter circuit 26 on line 205 to control the turn-on and turn-off of the switches therein. The controller 25 receives feedback from the converter circuit 24 on line 206, preferably voltage and / or current. In some embodiments, the controller 25 also provides control signals to the main power supply 20 on line 209 and receives feedback on line 210. The controller 25 receives user input signals from the user interface 12 on line 212. The controller 25 receives feedback signals from the output on lines 214, 215, and 216. As used herein, a controller refers to digital and analog circuitry, discrete or integrated circuitry, microprocessors, DSPs, FPGAs, etc., and software, hardware, and firmware located on one or more circuit boards that control all or a portion of a welding-type system or a device such as a power supply, power source, engine, or generator. The preferred embodiment provides that the controller 25 includes hardware and logic circuitry.

[0065] In one embodiment, power supply 20 may be a DC source, such as a battery. In other embodiments, power supply 20 may be a circuit that rectifies incoming alternating current (AC) to convert it to DC. Figure 2 In the exemplary block diagram shown, each converter circuit 24, 26 is connected to a single main power supply 20. In other embodiments, circuits 24, 26 may be powered by a separate power supply. In a further embodiment, circuits 24, 26 may be connected in parallel or in series with capacitors 36, 56 of the converter circuits 24, 26 to the main power supply 20. In embodiments where circuits 24, 26 are connected in series with a single main power supply 20, each converter circuit receives half of the total voltage from the main power supply 20, which allows the use of lower voltage components within the converter circuits 24, 26.

[0066] Figure 3 This is a circuit diagram illustrating one embodiment of the power circuit 22, including the two forward converter circuits 24 and 26, according to various aspects of this embodiment. The controller 25 can be as follows: Figure 2 The connections are made as shown. As previously described, the main power supply 20 provides DC power to the first converter circuit 24 and the second converter circuit 26. In the first inverter circuit 24, a voltage is first supplied across the capacitor 36. Then, a pair of power semiconductor switches 38, 40 chop the DC voltage and supply it to the transformer 42 on one side of the primary winding 44. The transformer 42 converts the chopped primary voltage into a secondary voltage suitable for cutting or welding an electric arc and supplies this secondary voltage to the secondary winding 46 of the transformer 42. The secondary voltage is then rectified by rectifier diodes 48, 50 and supplied to the filter inductor 28. A set of diodes 52, 54 provides a freewheeling path that allows the magnetizing current stored in the transformer 42 to flow when the pair of semiconductor switches 38, 40 are turned off, thus resetting the magnetic flux or energy stored in the transformer core.

[0067] Similarly, in the second converter circuit 26, a voltage is first supplied across capacitor 56. Then, a pair of power semiconductor switches 58, 60 chop the DC voltage and supply it to transformer 62 on one side of the primary winding 64. Transformer 62 converts the chopped primary voltage into a secondary voltage and supplies it to the secondary winding 66 of transformer 62. The secondary voltage is then rectified by rectifier diodes 68, 70 and supplied to filter inductor 28. A set of diodes 72, 74 provides a freewheeling path that allows the magnetizing current stored in transformer 62 to flow when the pair of semiconductor switches 58, 60 are turned off, thus resetting the magnetic flux or energy stored in the transformer core.

[0068] The combined rectified secondary voltage is supplied to the output 30 of the welding or cutting power supply, and a welding or cutting current or welding-type output current 33 is output from the circuit 24, 26. As used herein, welding-type output current refers to current suitable for welding, plasma cutting, induction heating, and / or hot wire welding / preheating, including laser welding and laser cladding. In other embodiments, the forward converter circuit 24, 26 can include additional components or circuits, such as a snubber circuit, voltage clamp, resonant "lossless" snubber circuit or clamp, gate drive circuit, pre-charge circuit, pre-regulator circuit, and the like. Further, as previously mentioned, the forward converter circuits 24, 26 can be arranged in parallel or in series according to the present embodiments, meaning that the capacitors 36, 56 can be connected in series or in parallel. Additionally, in further embodiments, the output of the first converter circuit 24 and the output of the second converter circuit 26 can be connected in series. In this embodiment, a single ground is configured to support both circuits 24, 26, and the output of the diodes 48, 50 of the first converter circuit 24 are coupled with the output of the diodes 68, 70 of the second converter circuit 26 before entering the inductor 28. A more detailed description of the operation of this circuit can be found in the '293 patent.

[0069] Figure 4 Another embodiment of the converters 24 and 26 is shown, in which the controller 25 provides a switching signal / timing signal to the switches. The converters operate from the same DC bus 402 and provide a combined welding-type output. The output current 401 flows in the output inductor 403. In this alternative, the converters 24 and 26 operate in a stacked manner, meaning that they are connected in a series arrangement, such that each converter operates from VBUS / 2. 1 / 2.

[0070] Figures 5a to 5e A PSDF mode of operation is shown. The relative phase and PWM duty cycle of the two converters respond to the control signal. PWM1 is the timing signal (on / off signal) of one of the converters 24 and 26, and PWM2 is the timing signal (on / off signal) of the other converter. It does not matter which is the leading converter and which is the lagging converter. It can be seen that, before the duty cycle reaches 0.45 (Dmax), they remain in phase, while after Dmax (0.45), the phase changes by a maximum of 0.5.

[0071] Figures 6a to 6d An alternative PSDF mode of the above operation is shown. The converters 24 and 26 operate in phase before reaching the maximum duty cycle (Dmax), and as the control signal increases, the two converters jump phase to be completely out of phase, but each converter is at a duty cycle of 0.5. 1The further increase in control signal will further increase the out of phase duty cycle until each converter again operates at maximum duty cycle with a full phase shift. PWM1 is the timing signal (on / off signal) for one of the converters 24 and 26 and PWM2 is the timing signal (on / off signal) for the other converter. It does not matter which is the leading converter and which is the lagging converter. It can be seen that the phase shift is at a maximum of 0.5.

[0072] Figures 7a to 7c The LIP mode of operation is shown. The converters 24 and 26 are locked in phase and the in phase duty cycle of both converters is responsive to the control signal. PWM1 is the timing signal (on / off signal) for one of the converters 24 and 26 and PWM2 is the timing signal (on / off signal) for the other converter. It does not matter which converter is referred to as the leading converter and which is referred to as the lagging converter. They are locked in phase for all duty cycles.

[0073] Figures 8a to 8c The FPS mode of operation is shown in which both converters are locked fully out of phase at all phase duty cycles. The duty cycles of both converters are responsive to the control signal. This embodiment provides a relative phase of 50%. Alternatives provide other relative phases including relative phases from 40% to 50% and from 25% to 50%. PWM1 is the timing signal (on / off signal) for one of the converters 24 and 26 and PWM2 is the timing signal (on / off signal) for the other converter. It does not matter which is the leading converter and which is the lagging converter.

[0074] Figure 9 and Figure 10 The effect of the FPS mode ( Figure 10 ) on the output ripple current component of I_output compared to the LIP mode or PSDF mode ( Figure 9 ) when operating in phase is shown. The FPS mode can have a reduced peak to peak size of the ripple and have an increased frequency of the ripple component. The reduced peak to peak size can be advantageous for certain welding processes such as low current SMAW as the minimum current level reached at the ripple trough is increased. This can reduce arc interruption and make the welding arc more stable and consistent.

[0075] Figure 11 A control circuit or error module that can be used to generate the control signal that can be used as an input to set the operating PWM duty cycle and phase shift in accordance with the three different modes of operation (LIP, FPS and PSDF) is shown. Figure 11The error module is a control module that provides an error or control signal. As used herein, a control module can be digital or analog and includes hardware or software that performs a specified control function. As used herein, a module refers to software and / or hardware that cooperate to perform one or more tasks and can include digital commands, control circuitry, power circuitry, network hardware, etc. The illustrated control module is a typical closed loop circuit with a current feedback input (IFB) that is proportional to or representative of the actual output current (I_output) of the welding power supply. Inverter 1101 inverts IFB and provides it to differential operational amplifier 1102. The IREF input provides a commanded or desired operating output current. IREF can be generated by a welding process module such that IREF provides the necessary characteristics for the welding arc. IREF can be constant or can vary based on time, voltage feedback, or other conditions. (e.g., hot start, arc start, dig, droop, etc.) The differential signal (VDIFF) is generated by operational amplifier 1102 and provided to operational amplifier 1103, which provides an output control signal (also referred to as an error signal) that is typically scaled, for example, from 0 to 10 volts. This control circuit can be implemented in hardware, software, or a combination thereof. Alternative control circuits can be used, including those implemented in software. Generating a pulse width from the error signal is well within the prior art and typically uses a linear relationship where the maximum pulse width corresponds to the maximum error signal.

[0076] Figure 12 A portion of the controller is shown, namely, the PWM module 1200, and includes an error module 1201 and a phase relationship module 1202. The error module 1201 can be Figure 11 The phase relationship module 1202 can be implemented as described below and converts the control signal to a range of PWM duty cycle values for PWM1 and PWM2 with either a fixed phase relationship or a variable phase relationship between PWM1 and PWM2. The outputs of PWM1 and PWM2 are timing outputs provided to inverters 24 and 26. In alternative embodiments, this is implemented using other controllers. As used herein, a Pwm module is a module that sets the pulse width of an inverter, including setting the start time and end time of a pulse.

[0077] The preferred embodiment provides that the conversion of the control error signal to a PWM duty cycle by the PWM module 1202 can produce a 0 to 45% duty cycle range with a fixed phase of 0 when the controller is operating in LIP mode. The preferred embodiment provides that the conversion of the control error signal to a PWM duty cycle by the PWM module 1202 can produce a 0 to 45% duty cycle range with a fixed phase of 50% when the controller is operating in FPS mode. The preferred embodiment provides that the conversion can produce a 0 to 90% effective duty cycle range when the combined effects of the PWM duty cycle and the relative phase shift are considered when the controller is operating in PSDF mode. Thus, for a given range of control signals (e.g., 0 to 10V), a finer PWM duty cycle control resolution can be achieved for LIP and FPS modes as compared to PSDF mode. For example, in LIP or FPS mode, the PWM duty cycle range / control signal range = 45% / 10V = 4.5% per volt of control signal. Whereas in PSDF mode, the PWM duty cycle range / control signal range = 90% / 10V = 9% per volt of control signal.

[0078] The preferred embodiment of the present application provides that one of the three modes (LIP, PSDF, FPS) is selected in response to a user selected process. Alternatives provide that the mode is selected in response to a programmed process, in response to a sensing, or automatically. Other alternatives provide that the mode is selected in response to other conditions other than a process (e.g., material type, welding process type, output required, etc.).

[0079] Each mode of operation can be referred to as a phase relationship. The phase relationship of PSDF is variable, the phase relationship of LIP is in-phase lock, and the phase relationship of FPS is fixed phase interleaved. Figure 13 A sub-module 1301 is shown that is part of the phase relationship module 1202. The phase relationship module 1202 (and sub-module 1301) selects a phase relationship and maintains the selected phase relationship over a predetermined output range. As used herein, maintaining a phase relationship over a predetermined output range means that the phase relationship selected from variable phase shift, fixed phase interleaved, and in-phase lock does not change as the output is varied in size over the predetermined range. As used herein, a phase relationship module is a control module that selects a relative phase relationship of at least two inverter circuits from at least two available phase relationships in response to an input thereto, wherein the at least two available phase relationships are at least two of variable phase shift, fixed phase interleaved, and in-phase lock, and wherein the selected phase relationship is maintained over a predetermined output range.

[0080] Module 1301 selects one mode of operation (or phase relationship) from three modes of phase or phase relationship (LIP, FPS, or PSDF). Module 1202 generates two PWM signals with pulse width (PWM values) and phase shift relationship based on the selected mode of operation. Sub-module 1301 receives the error / control signal from module 1201 and provides the desired pwm control signal. Module 1301 includes a logic module 1303 that receives as inputs the control / error signal, the welding process signal, the feedback signal, the user input, and the bus, intermediate, or input signals. Alternatives use more or fewer and / or different inputs.

[0081] Logic module 1303 determines the desired mode type based on the inputs. For example, as noted above, it can be advantageous to select one PWM mode of operation for a particular welding process (such as LIP for GTAW), another PWM mode for another welding process (such as FPS for SMAW), and a third mode of operation for another welding process (such as PSDF for GMAW or pulsed GMAW). Based on the inputs, the appropriate mode of operation and the appropriate pwm signals are generated. Once the mode is selected, the particular desired output can be readily provided, and such operation can be according to the prior art. However, the prior art fails to show selection of the appropriate mode, particularly as taught herein, nor does it show phase relationship module 1202 and sub-module 1301.

[0082] The PWM mode can be pre-selected based on a pre-selected welding process, which means that the PWM mode can be set in a static condition when the output of the welding power supply is not enabled. Additional inputs can be combined to pre-select the PWM mode in a static condition, or to dynamically select the PWM mode when the welding output is provided. For example, the FPS mode can be selected for SMAW when the user preset current is below a certain level; the PSDF mode can be selected for SMAW when the current is above a certain level; and the LIP mode can be selected for SMAW when the preset current is above another, higher level. The preferred embodiment provides that the selected phase relationship is maintained over a predetermined range of output.

[0083] In one embodiment, the module 1202 comprises three parallel sub-modules 1301, each for LIP, PSDF, and FPS. Each module can be identical but have some different inputs for that process, and each module has an output consistent with one of the modes described above and shown in FIGS. 5-8. This embodiment provides that each module 1303 performs an "and" operation on the various inputs and enables the output of the module 1305 when all inputs are logic 1. One module 1301 can be for the LIP mode, so if a GTAW process is selected, that control is enabled. If another process other than GTAW is selected, that control is disabled and another sub-module 1301 will be enabled for the desired mode. The PWM mode can be preselected based on the preselected welding process, or preselected in a static condition, or dynamically selected while providing the welding output.

[0084] Either the preferred single sub-module 1301 or the alternative multiple parallel sub-modules 1301 can have a welding process input that includes waveform generation information for selecting the PWM mode of operation. For example, the FPS mode can be selected during the low current or background current level of the pulse or other waveform, while the LIP or PSDF mode is selected for the high current or other portion of the welding waveform. As part of the PWM mode selection logic, the input that enables the output (such as the welding torch trigger switch) can be used as an input to the control module. This logic input can be used to allow the PWM mode of operation to be changed only in a static condition when the output is not enabled, or can be used to allow the PWM mode to be changed dynamically when the output is enabled. Other embodiments provide that the phase relationship is maintained over at least half of the rated output of the welding-type power supply. One embodiment provides that the FPS phase relationship is used for the lower 50% of the output range, and then the LIP or PSDF phase relationship is used for the upper 50% of the range. Another embodiment provides that the phase relationship is maintained over a certain duty cycle range (e.g., from 25% to 50%).

[0085] DC bus voltage, AC line voltage, rectified line voltage, or a scaled signal representative of the magnitude of one of these voltages can be used as an additional input to the control module. For example, a multi-voltage input welding power supply rated for two inputs (e.g., 115 VAC and 230 VAC) can select the FPS mode for the lower line voltage and the LIP or PSDF mode for the higher line voltage. The lower line voltage (115 VAC) can generate a reduced DC bus voltage and subsequently a reduced welding output load line compared to the higher line voltage, and generate a fixed PWM operating mode. The FPS mode can be used to compensate for the lower line voltage and provide a higher welding output load line for it, while the LIP mode or PSDF mode can be used for the higher line voltage so that similar output load lines are generated for both line voltages.

[0086] The lower line voltage (115 VAC) can also enable a reduction in output current rating compared to the higher line voltage, for the reason that each of the two forward converters carries the full load current in the FPS mode compared to sharing the load current in the in-phase operating mode (LIP, in-phase PSDF).

[0087] The additional inputs can include, for example, IFB and VFB indicative of the actual output current and voltage. One or both of the IFB and VFB can be used as an input to select the PWM operating mode. For example, the LIP mode can be selected for an OCV (open circuit voltage) condition of the welding power supply as a means to reduce the average OCV. This condition can override another selected PWM mode, such as the FPS mode that can be selected based on the welding process (e.g., SMAW) and a preset current level. A time delay can be required to be satisfied before the OCV condition overrides the pre-selected PWM mode.

[0088] Many modifications can be made to the present disclosure without departing from the intended scope thereof. Therefore, it is to be understood that what is described herein is a method and apparatus for a welding-type power supply and a method of providing welding-type power that fully satisfies the objectives and advantages sought. Although a particular embodiment of the present disclosure has been described, it is apparent that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

Claims

1. A method of providing welding-type power, the method comprising: receiving input power; pulse width modulating a first forward converter and a second forward converter based on a control signal such that the first forward converter and the second forward converter operate as a pulse width modulated dual forward converter to provide a welding-type output; selecting a phase relationship from at least two available phase relationships between the first forward converter and the second forward converter, wherein the at least two available phase relationships are at least two of a variable phase shift, a fixed phase stagger, and an in-phase lock; adjusting the control signal based on the selected phase relationship to provide an effective duty cycle range of the first forward converter and the second forward converter, wherein the effective duty cycle range for the variable phase shift phase relationship is greater than the effective duty cycle range for the fixed phase stagger phase relationship and the in-phase lock phase relationship; and maintaining the selected phase relationship over a predetermined output range.

2. The method of claim 1, wherein, selecting the selected phase relationship is performed in response to at least one of a feedback response to the welding-type output, a user input, and a process selection.

3. The method of claim 2, wherein, selecting the selected phase relationship is performed in response to a user input indicative of at least one of a desired output current, a desired peak output current, and a desired output voltage.

4. The method of claim 2, wherein, selecting the selected phase relationship is performed in response to at least one of a user selected SMAW process, a user selected GTAW process, and a user selected GMAW process.

5. The method of claim 2, wherein, selecting the selected phase relationship is performed in response to a feedback response to at least one of a welding-type output current, a welding-type output voltage, a welding-type peak current, and a welding-type output power.

6. The method of claim 1, wherein, maintaining the selected phase relationship over a substantial output range includes maintaining the selected phase relationship over at least half of a rated output.

7. The method of claim 1, wherein, maintaining the selected phase relationship over the predetermined output range includes maintaining the selected phase relationship over a predetermined duty cycle range.

8. The method of claim 1, wherein, pulse width modulating the first forward converter and the second forward converter includes pulse width modulating a first forward converter and a second forward converter in a stacked arrangement and combining a first forward converter output with a second forward converter output together.

9. A welding-type power supply comprising: a dual forward converter having a first forward converter and a second forward converter; and a controller, wherein the controller includes a pwm module configured to set a pwm timing signal based on a control signal representative of a desired welding-type output, and wherein the pwm module includes a phase relationship module having a plurality of timing outputs connected to the dual forward converter. wherein the phase relationship module is configured to select a phase relationship from at least two available phase relationships between the first forward converter and the second forward converter, wherein the at least two available phase relationships are at least two phase relationships of variable phase shift, fixed phase interleaving, and in-phase lock, and to maintain the selected phase relationship within a predetermined output range; and the pwm module is configured to adjust the control signals to provide an effective duty cycle range of the first forward converter and the second forward converter based on the selected phase relationship, wherein the effective duty cycle range for the variable phase shift phase relationship is greater than the effective duty cycle range for the fixed phase interleaving phase relationship and the in-phase lock phase relationship.

10. The welding power supply of claim 9, wherein, The phase relationship module has an input and is responsive thereto, wherein the input is connected to receive at least one of a feedback response to the welding-type output, a user input, and a process selection.

11. The welding power supply of claim 10, wherein, The input is connected to receive a user input indicative of at least one of a desired output current, a desired peak output current, and a desired output voltage.

12. The welding power supply of claim 10, wherein, The input is connected to receive at least one of a user-selected SMAW process, a user-selected GTAW process, and a user-selected GMAW process.

13. The welding power supply of claim 10, wherein, The input is connected to receive a feedback response to at least one of a welding-type output current, a welding-type output voltage, a welding-type peak current, and a welding-type output power.

14. The welding power supply of claim 13, wherein, The phase relationship module is responsive to a welding-type output current greater than one-half of a rated output.

15. The welding power supply of claim 9, wherein, The first forward converter and the second forward converter are stacked.

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