Welding power supply

Abstract

To provide a welding power supply device which can be adjusted to desired welding conditions.SOLUTION: In the welding power supply device, the power storage unit stores power when any one of the three switching elements is in a conductive state, and outputs a current from at least one switching element to a welding electrode in contact with an object to be welded when any one of the three switching elements is in a non-conductive state. A first signal generator generates, based on a reference clock, three pulses in which a phase of a switching control cycle in each phase is shifted by 120 degrees, and generates three first signals for pulse modulation corresponding to each phase from the generated three pulses. A second signal generation unit generates three second signals for adjusting a conduction time, which is a period of a conduction state of each switching element, based on the three first signals. The drive unit outputs a third signal for applying a predetermined voltage to each switching element to each switching element based on the three second signals, and brings each switching element into a conductive state or a non-conductive state.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This invention relates to a welding power supply device. [Background technology]

[0002] Resistance welding is one method of welding metals. Resistance welding is a welding method in which the material to be welded is sandwiched between electrodes and an electric current is passed through it, generating heat due to the electrical resistance of the metal, which then melts it. For example, there are resistance welding machines equipped with multiple inverter-type welding power supply units to increase welding capacity and output (see Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 09-085458 [Overview of the project] [Problems that the invention aims to solve]

[0004] Good welding quality depends on the characteristics of the materials being welded. For example, when laminating metal foils using resistance welding, the welding quality is unstable due to variations in the surface properties and condition of the metal foils being welded. Therefore, good welding quality is achieved by adjusting the welding conditions (e.g., energizing time, etc.) according to the characteristics of the materials being welded. For this reason, it is desirable that the welding power supply unit can appropriately adjust the welding conditions.

[0005] The technology of this disclosure aims to provide a welding power supply device that can be adjusted to desired welding conditions. [Means for solving the problem]

[0006] The technology of this disclosure employs the following technical means to solve the above problems. One embodiment of the technology of this disclosure is a welding power supply device used for resistance welding. The welding power supply device comprises a switching element, a power storage unit, a first signal generation unit, a second signal generation unit, and a drive unit. The switching element consists of three switching elements corresponding to the first to third phases, respectively. The power storage unit stores energy when any one of the three switching elements becomes conductive, and outputs current from at least one switching element to the welding electrode in contact with the workpiece when it becomes non-conductive. The first signal generation unit generates three pulses corresponding to each phase based on a reference clock, and generates three first signals for pulse modulation corresponding to each phase from the three generated pulses. There are three second signal generation units, each corresponding to the first to third phases. The second signal generation units also generate three second signals based on the three first signals to adjust the conduction time, which is the period of conduction of each switching element. The drive unit is provided in three parts, one for each of the first to third phases. The drive unit also outputs a third signal to each switching element based on three second signals, applying a predetermined voltage to each switching element, thereby causing each switching element to be either conductive or non-conductive.

[0007] The first signal generation unit is configured to generate three pulses in which the phase of the switching control period in each phase is shifted by 120 degrees. [Effects of the Invention]

[0008] According to one aspect of the technology of this disclosure, the energizing time can be adjusted to obtain the desired welding quality. In other words, the technology of this disclosure can provide a welding power supply that can be adjusted to desired welding conditions. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram of the welding machine according to the first embodiment. [Figure 2] This figure shows an example of the circuit configuration of a welding power supply device according to the first embodiment. [Figure 3] It is a diagram showing a configuration example of a three-phase carrier waveform generation circuit according to the first embodiment. [Figure 4] It is a diagram showing a circuit configuration example of a ring counter according to the first embodiment. [Figure 5] It is a diagram showing a timing chart of three-phase pulses according to the first embodiment. [Figure 6] It is a diagram showing a configuration example of a sawtooth wave generation circuit according to the first embodiment. [Figure 7] It is a diagram showing a timing chart of three-phase sawtooth waves according to the first embodiment. [Figure 8] It is a diagram showing a pulse waveform of a three-phase interleaved method according to the first embodiment. [Figure 9] It is a diagram showing an output waveform of a welding power supply device of a three-phase interleaved method according to the first embodiment. [Figure 10] It is a diagram showing an output waveform of a welding power supply device of a single-phase inverter method. [Figure 11] It is a diagram showing a flowchart of a welding quality determination process in a welding power supply device according to a modified example. [Figure 12] (A) is a diagram showing an example of an output waveform when the welding quality according to the modified example is qualified. (B) is a diagram showing an example of an output waveform when the welding quality according to the modified example is unqualified.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments according to the technology of the present disclosure will be described with reference to the drawings. The same or equivalent components, members, and processes shown in each drawing are denoted by the same reference numerals, and redundant explanations will be omitted as appropriate.

[0011] <First Embodiment> (Resistance Welder) FIG. 1 is a schematic configuration diagram of a welding machine 100 according to the present embodiment, and an example of a resistance welding machine is shown. The welding machine 100 according to the present embodiment mainly includes a welding power supply device 10 and a welding head 90. The welding power supply device 10 is a device that controls the current (welding current) and voltage (welding voltage) required for welding. Further, the welding power supply device 10 is electrically connected to the welding head 90 by predetermined conductive wires Wa, Wb. The welding head 90 is a device mainly including a drive unit (not shown), a pressing unit (not shown), and two electrodes 91a, 91b. Further, the welding head 90 is driven as follows by the current and voltage supplied from the welding power supply device 10. The welding head 90 brings the electrodes 91a, 91b into contact with a workpiece M installed between the two electrodes (welding electrodes) 91a, 91b, presses the workpiece M with a certain force, and causes a welding current to flow through the workpiece M. The workpiece M is two or more metal materials (welding materials) in a non-joined state. Therefore, a part of the metal material of the workpiece M melts and solidifies due to resistance heating (Joule heat). As a result, two or more metal materials are joined.

[0012] With the above configuration, the welding machine 100 according to the present embodiment can perform laminated welding of metal foils. In the laminated welding of metal foils, the welding quality is not stable due to variations in the properties and states of the surfaces of the metal foils. As an example of the laminated welding of metal foils having such characteristics, the laminated welding of aluminum foils can be mentioned. The laminated welding of aluminum foils is performed, for example, in the manufacturing process of conductive polymer aluminum electrolytic capacitors and the like.

[0013] (Welding quality during resistance welding) The inventors of the present application have intensively studied the conditions for obtaining stable welding quality in the manufacturing process of conductive polymer aluminum electrolytic capacitors and the like. As a result, the inventors of the present application have specified that in order to obtain stable welding quality, a welding current in the range of 500 [A] to 1000 [A] requires a conduction time of 30 [msec] or more (ensuring an appropriate conduction time).

[0014] (Difficulty in ensuring an appropriate conduction time) Linear-controlled welding power supplies have a current control characteristic in which the welding current rises in a straight line. In such welding power supplies, the energizing time is 30 msec or less (for example, a maximum of 25 msec). Therefore, linear-controlled welding power supplies cannot ensure an appropriate energizing time to obtain stable welding quality in laminated welding of aluminum foil. As a result, linear-controlled welding power supplies have insufficient welding power capacity.

[0015] In a linearly controlled welding power supply, the control circuit controls the voltage applied to the gate (G) of the power MOSFET (Power Metal-Oxide-Semiconductor Field-Effect Transistor) so that the output value matches a preset target value. When the applied voltage to the gate (G) is low, the resistance between the drain (D) and source (S) of the power MOSFET increases. When the applied voltage to the gate (G) is high, the resistance between the drain (D) and source (S) of the power MOSFET decreases. In this way, a linearly controlled welding power supply makes the output value track the target value by changing the resistance between the drain (D) and source (S) of the power MOSFET, similar to a variable resistor. When such linear control is performed, conduction losses (conduction loss = ((storage voltage) - (output voltage)) × (output current)) occur due to the resistance between the drain (D) and source (S) of the power MOSFET. Due to these conduction losses, the power MOSFET may overheat or a voltage drop in the storage voltage may occur. Therefore, linearly controlled welding power supplies cannot output welding current for extended periods. To extend the energizing time, one might consider increasing the number of parallel connections between energy storage devices (capacitors) and power MOSFETs. However, such a configuration increases the number of components in the welding power supply. Consequently, the size, weight, and manufacturing cost of the welding power supply increase. Therefore, the proposed configuration is not applicable to mass-produced products.

[0016] (Difficulty in adjusting the welding current) One factor that affects welding quality is the heat generated during resistance welding. The heat generated during resistance welding is calculated as (contact resistance) × (output current). 2 It can be expressed as × (energizing time). In other words, the amount of heat generated in resistance welding changes in proportion to the values ​​of each parameter (welding condition) of the welding current and energizing time. Therefore, it is necessary to fine-tune the values ​​of each parameter in order to suppress the heat generated in resistance welding. Note that since the amount of heat generated in resistance welding is proportional to the square of the welding current, it is difficult to achieve good welding quality by adjusting the welding current. Therefore, it is preferable to achieve welding quality by suppressing the heat generated in resistance welding by adjusting the energizing time, which is one of the welding conditions.

[0017] As mentioned above, linear-controlled welding power supplies cannot ensure long energizing times, making it difficult to achieve good welding quality by adjusting the energizing time. Other welding power supplies include, for example, single-phase inverter type welding power supplies. These power supplies rectify the input alternating current (AC) into direct current (DC), and then convert it to high-frequency AC, configured to energize at a constant value. Therefore, these power supplies have an inverter circuit, which has multiple switches and converts DC current to AC current by switching control according to a predetermined frequency. In such welding power supplies, the switching frequency is approximately 10 kHz. Consequently, the energizing time in single-phase inverter type welding power supplies is adjusted in units of 100 μsec. Thus, in the case of single-phase inverter type welding power supplies, the adjustment unit for energizing time is not suitable for fine-tuning, making it difficult to achieve good welding quality.

[0018] (Three-phase interleaved welding power supply) In view of the above, the welding power supply device 10 according to this embodiment is equipped with a three-phase switching node as a method for adjusting welding conditions, and employs an interleaved method for switching control. Furthermore, the welding power supply device 10 operates three switching nodes with a fundamental frequency of 10 kHz and is configured to use PWM (Pulse Width Modulation) control to shift the phase of the switching period of each switching node by 120 degrees.

[0019] As a result, the welding power supply unit 10 according to this embodiment operates at a total frequency of 30 kHz, even though the fundamental frequency of each switching node is 10 kHz. Therefore, the welding power supply unit 10 according to this embodiment can ensure an appropriate energizing time, which could not be achieved with a linearly controlled welding power supply unit. Furthermore, the welding power supply unit 10 can also fine-tune the energizing time, which could not be achieved with a single-phase inverter type welding power supply unit. In other words, the welding power supply unit 10 can be adjusted to the desired welding conditions and achieve good welding quality.

[0020] (Circuit configuration) Figure 2 shows an example of the circuit configuration of a welding power supply unit 10 (a three-phase interleaved welding power supply unit) according to this embodiment. As shown in Figure 2, the welding power supply unit 10 mainly includes a switching power supply 11, bulk capacitors 12, MOSFETs 13a to 13c, power inductors 15a to 15c, a welding command circuit 16, feedback circuits 171 to 173, and an error amplifier 18. Furthermore, the welding power supply unit 10 includes a three-phase carrier waveform generation circuit 20, PWM circuits 30a to 30c, gate drive circuits 31a to 31c, and active clamps 32a to 32c. In addition, the welding power supply unit 10 includes a control circuit (CPU: Central Processing Unit) 70, an ADC (AD converter) 60, and the like.

[0021] The switching power supply 11 is an inverter circuit that converts a single-phase alternating current voltage (AC: voltage in the range of 200[V] to 240[V]) to a direct current voltage (DC: 20[V]). The switching power supply 11 is also connected to the bulk capacitor 12. The switching power supply 11 outputs the converted DC voltage to the bulk capacitor 12. Therefore, the switching power supply 11 corresponds to a power supply circuit.

[0022] The bulk capacitor 12 is a high-capacity high-CV capacitor, for example, with a capacity of approximately 1,200,000 [μF] (= 150,000 [μF] x 8 units). The bulk capacitor 12 is installed for the purpose of stabilizing the power line. The charge stored in the bulk capacitor 12 is discharged when the welding output is activated.

[0023] MOSFETs 13a to 13c are field-effect transistors, and when a voltage is applied between the gate (G) and source (S), the connection between the drain (D) and source (S) becomes ON (conductive). MOSFETs 13a to 13c also correspond to switching nodes. Figure 2 shows an example of using N-channel (N-Ch) type MOSFETs 13a to 13c as switching nodes. N-channel type MOSFETs 13a to 13c turn ON when a positive voltage is applied to the gate (G) relative to the source (S).

[0024] In this embodiment, an example using a MOSFET as the switching element is shown, but it is not limited to this. A semiconductor switch such as an IGBT (Insulated Gate Bipolar Transistor) may also be used as the switching element.

[0025] In this embodiment, three MOSFETs 13a to 13c are provided, assuming three-phase PWM control. Specifically, it includes MOSFET 13a corresponding to the first phase (phase A), MOSFET 13b corresponding to the second phase (phase B), and MOSFET 13c corresponding to the third phase (phase C). In the following description, the MOSFET 13a of the first phase will be referred to as "MOSFET 13a of phase A," the MOSFET 13b of the second phase as "MOSFET 13b of phase B," and the MOSFET 13c of the third phase as "MOSFET 13c." Furthermore, when referring to each of the MOSFETs 13a to 13c of the first to third phases collectively, it will be referred to as "MOSFET 13n."

[0026] In MOSFET 13n, the gate terminal (G terminal) is connected to the output terminals of the gate drive circuits 31a to 31c. The drain terminal (D terminal) is connected to the output terminal of the bulk capacitor 12. The source terminal (S terminal) is connected to the input terminals of the power inductors 15a to 15c.

[0027] MOSFET13n is switched on or off based on the input signal at its gate terminal. Specifically, the A-phase MOSFET13a is switched ON / OFF (conducting / non-conducting state is controlled) according to the A-phase PWM signal input to its gate terminal from the first-phase (A-phase) gate drive circuit 31a. The B-phase MOSFET13b is switched ON / OFF according to the second-phase (B-phase) PWM signal input to its gate terminal from the second-phase (B-phase) gate drive circuit 31b. The C-phase MOSFET13c is switched ON / OFF according to the third-phase (C-phase) PWM signal input to its gate terminal from the third-phase (C-phase) gate drive circuit 31c. The gate drive circuits 31a to 31c for the first to third phases will be described later.

[0028] Diodes 14a to 14c are provided in the path between the source terminal of MOSFET 13n and the input terminals of power inductors 15a to 15c. Specifically, it includes diode 14a corresponding to the first phase (phase A), diode 14b corresponding to the second phase (phase B), and diode 14c corresponding to the third phase (phase C). In the following explanation, diode 14a for the first phase will be referred to as "diode 14a for phase A," diode 14b for the second phase as "diode 14b for phase B," and diode 14c for the third phase as "diode 14c." Furthermore, when referring to the diodes 14a to 14c for the first to third phases collectively, they will be referred to as "diode 14n."

[0029] Diode 14n is a rectifier that restricts the flow of electricity to one direction. Diode 14n also conducts when MOSFET 13n is OFF (non-conductive state), supplying welding current to the workpiece M. Specifically, the A-phase diode 14a conducts when the A-phase MOSFET 13a is OFF, supplying welding current to the workpiece M. The B-phase diode 14b conducts when the B-phase MOSFET 13b is OFF, supplying welding current to the workpiece M. The C-phase diode 14c conducts when the C-phase MOSFET 13c is OFF, supplying welding current to the workpiece M.

[0030] Note that diode 14n may be replaced with a MOSFET. For example, a synchronous rectifier converter can be constructed by inputting signals complementary to the gate signals of each MOSFET 13a to 13c from phase A to phase C to the gate terminals of the replaced MOSFETs.

[0031] The power inductors 15a to 15c are located in the path between the source terminal of the MOSFET 13n and the connection terminal of the conductive wire Wa that supplies current to the workpiece M. Specifically, the system includes a power inductor 15a corresponding to the first phase (phase A), a power inductor 15b corresponding to the second phase (phase B), and a power inductor 15c corresponding to the third phase (phase C). In the following explanation, the power inductor 15a of the first phase will be referred to as "power inductor 15a of phase A," the power inductor 15b of the second phase as "power inductor 15b of phase B," and the power inductor 15c of the third phase as "power inductor 15c of phase C." Furthermore, when referring to the power inductors 15a to 15c of the first to third phases collectively, they will be referred to as "power inductor 15n."

[0032] The input terminal of the A-phase power inductor 15a is connected to the source terminal of the A-phase MOSFET 13a. The input terminal of the B-phase power inductor 15b is connected to the source terminal of the B-phase MOSFET 13b. The input terminal of the C-phase power inductor 15c is connected to the source terminal of the C-phase MOSFET 13c. The output terminals of each power inductor 15a to 15c from A to C are aggregated and connected to the connection terminal of the conductive wire Wa that carries current to the workpiece M.

[0033] The power inductor 15n is an energy storage device that smooths the pulse waveform by charging the input current and discharging it at a predetermined timing. Specifically, the A-phase power inductor 15a smooths the A-phase waveform by charging the current that flows when the A-phase MOSFET 13a is ON (conducting) and discharging the current when it is OFF. The B-phase power inductor 15b smooths the B-phase waveform by charging the current that flows when the B-phase MOSFET 13b is ON and discharging the current when it is OFF. The C-phase power inductor 15c smooths the C-phase waveform by charging the current that flows when the C-phase MOSFET 13c is ON and discharging the current when it is OFF.

[0034] In this embodiment, the power inductor 15n exhibits an inductance reduction rate of approximately 25% at an oscillation frequency of 10 kHz and a peak current of 500 A. In other words, this embodiment uses a power inductor with good DC superimposition characteristics such that the inductance value does not drop sharply even when a large current flows.

[0035] The welding command circuit 16 is located in the path between the input terminal of the error amplifier 18 and the output terminal of the control circuit 70.

[0036] The input terminal of the welding command circuit 16 is connected to the output terminal of the control circuit 70. The output terminal of the welding command circuit 16 is connected to the input terminal of the error amplifier 18.

[0037] The welding command circuit 16 generates a reference voltage corresponding to the current value, voltage value, and energizing time according to the welding command. The welding command is input from the control circuit 70. Therefore, the welding command circuit 16 is set based on the input signal from the control circuit 70 and generates a reference voltage according to the set welding command.

[0038] Feedback circuits 171 to 173 are circuits that perform target control by returning the output signal as an input signal. In this embodiment, three feedback circuits 171 to 173 are provided, corresponding to constant current control, constant voltage control, and constant power control. Specifically, it includes a current feedback circuit 171 corresponding to constant current control, a voltage feedback circuit 172 corresponding to constant voltage control, and a power feedback circuit 173 corresponding to constant power control. When referring collectively to the feedback circuits 171 to 173 for constant current control, constant voltage control, and constant power control, they are referred to as "feedback circuit 17n".

[0039] The feedback circuit 17n performs target control of current, voltage, or power by inputting the output current, output voltage, or output power to the error amplifier 18. The current feedback circuit 171 is provided in the path between the input terminal of the error amplifier 18 and the connection terminal of the CT (Current Transformer) 40. The CT 40 is provided in the path between the power inductor 15n and the connection terminal of the conductive wire Wa that carries current to the workpiece M. The CT 40 is a current transformer that converts a large current into a small current (low current).

[0040] The input terminal of the current feedback circuit 171 is connected to the connection terminal of the CT40. The output terminal of the current feedback circuit 171 is connected to the input terminal of the error amplifier 18. The CT40 converts the output current from the power inductor 15n and outputs the converted current to the current feedback circuit 171. The current feedback circuit 171 inputs the current converted by the CT40 to the error amplifier 18.

[0041] The voltage feedback circuit 172 is located in the path between the input terminal of the error amplifier 18 and the connection terminal of the RC filter 50. The RC filter 50 is located between the connection terminals of the conductive wires Wa and Wb that carry current to the workpiece M. When the load terminal is open (high impedance), no current flows, causing the output voltage to oscillate between 0[V] and the charging voltage. If this is fed back into voltage feedback, the oscillation will not stop, and the control system will oscillate. The RC filter 50 prevents this, smooths the output when the load terminal is open, suppresses noise, and stabilizes the control system.

[0042] The input terminal of the voltage feedback circuit 172 is connected to the connection terminal of the RC filter 50. The output terminal of the voltage feedback circuit 172 is connected to the input terminal of the error amplifier 18. The RC filter 50 suppresses noise that appears in the output voltage during welding (e.g., ripple dependent on the switching frequency) and outputs the suppressed voltage to the voltage feedback circuit 172. The voltage feedback circuit 172 inputs the voltage suppressed by the RC filter 50 to the error amplifier 18.

[0043] The power feedback circuit 173 is located in the path between the input terminal of the error amplifier 18 and the output terminals of the current feedback circuit 171 and the voltage feedback circuit 172.

[0044] The input terminals of the power feedback circuit 173 are connected to the output terminals of the current feedback circuit 171 and the voltage feedback circuit 172. The output terminals of the power feedback circuit 173 are connected to the input terminals of the error amplifier 18.

[0045] The power feedback circuit 173 inputs the output power, based on the output current of the current feedback circuit 171 and the output voltage of the voltage feedback circuit 172, to the error amplifier 18.

[0046] Each of the feedback circuits 171-173 is configured with a feedback signal switching circuit 17s located after it.

[0047] The switching circuit 17s is a switching circuit that switches between three control methods: constant current control, constant voltage control, and constant power control, according to the control method switching signal. The control method switching signal is input from the control circuit 70. Therefore, the switching circuit 17s sets the control method based on the input signal from the control circuit 70 and switches the control method according to the set control method.

[0048] The switching circuit 17s, when the set control method is constant current control, connects the output terminal of the current feedback circuit 171 to the input terminal of the error amplifier 18, switching the circuit connection so that the output current feedback signal is input to the error amplifier 18. Furthermore, when the set control method is constant voltage control, the switching circuit 17s connects the output terminal of the voltage feedback circuit 172 to the input terminal of the error amplifier 18, switching the circuit connection so that the output voltage feedback signal is input to the error amplifier 18. Finally, when the set control method is constant power control, the switching circuit 17s connects the output terminal of the power feedback circuit 173 to the input terminal of the error amplifier 18, switching the circuit connection so that the output power feedback signal is input to the error amplifier 18.

[0049] The error amplifier 18 is located in the path between the feedback circuit 17n and the PWM circuits 30a to 30c.

[0050] The input terminal of the error amplifier 18 is connected to the output terminal of the welding command circuit 16, and via the switching circuit 17s, to the output terminal of the feedback circuit 17n. The output terminal of the error amplifier 18 is connected to the input terminals of the first phase (phase A) to the third phase (phase C) PWM circuits 30a to 30c. The first to third phase PWM circuits 30a to 30c will be described later.

[0051] The error amplifier 18 is an error amplifier that compares the reference voltage (target value) generated according to the welding command with the feedback signal and amplifies the resulting error. Specifically, when the control method is constant current control, the error amplifier 18 receives the feedback signal from the current feedback circuit 171 and outputs the amplified error to each of the PWM circuits 30a to 30c. When the control method is constant voltage control, the error amplifier 18 receives the feedback signal from the voltage feedback circuit 172 and outputs the amplified error to each of the PWM circuits 30a to 30c. Furthermore, when the control method is constant power control, the error amplifier 18 receives the feedback signal from the power feedback circuit 173 and outputs the amplified error to each of the PWM circuits 30a to 30c.

[0052] The three-phase carrier waveform generation circuit 20 is located in the path between the control circuit 70 and the PWM circuits 30a to 30c.

[0053] The input terminals of the three-phase carrier waveform generation circuit 20 are connected to the output terminals of the control circuit 70. The output terminals of the three-phase carrier waveform generation circuit 20 are connected to the input terminals of the first phase (phase A) to the third phase (phase C) PWM circuits 30a to 30c.

[0054] The three-phase carrier waveform generation circuit 20 is a first signal generation circuit that generates the carrier clocks A to C (first signals, carriers A to C) for each of the first phase (phase A) to the third phase (phase C). Specifically, the three-phase carrier waveform generation circuit 20 receives a control signal (ON / OFF control signal) from the control circuit 70 that controls the output of the reference clock.

[0055] The three-phase carrier waveform generation circuit 20 generates three 10 kHz pulses based on a 60 kHz reference clock, with the phase of the switching control period (switching frequency) shifted by 120 degrees for each phase. The three-phase carrier waveform generation circuit 20 also generates three sawtooth waves for PWM modulation from each of the generated pulses, corresponding to each phase. Each sawtooth wave corresponds to the carrier clocks A to C for each phase.

[0056] The three-phase carrier waveform generation circuit 20 outputs the generated first-phase (A-phase) carrier clock A to the first-phase (A-phase) PWM circuit 30a. The three-phase carrier waveform generation circuit 20 also outputs the generated second-phase (B-phase) carrier clock B to the second-phase (B-phase) PWM circuit 30b. Furthermore, the three-phase carrier waveform generation circuit 20 outputs the generated third-phase (C-phase) carrier clock C to the third-phase (C-phase) PWM circuit 30c. The three-phase carrier waveform generation circuit 20 will be described later using Figure 3.

[0057] The PWM circuits 30a to 30c are located in the path between the gate drive circuits 31a to 31c and the error amplifier 18 and the three-phase carrier waveform generation circuit 20. In this embodiment, assuming three-phase PWM control, three PWM circuits 30a to 30c are provided. Specifically, there is a PWM circuit 30a corresponding to the first phase (phase A), a PWM circuit 30b corresponding to the second phase (phase B), and a PWM circuit 30c corresponding to the third phase (phase C).

[0058] In the following explanation, the first-phase PWM circuit 30a will be referred to as "Phase A PWM circuit 30a," the second-phase PWM circuit 30b as "Phase B PWM circuit 30b," and the third-phase PWM circuit 30c as "Phase C PWM circuit 30c." Furthermore, when referring to all three phase PWM circuits 30a to 30c together, they will be called "PWM circuit 30n."

[0059] The input terminal of the A-phase PWM circuit 30a is connected to the output terminal of the error amplifier 18 and the output terminal of the three-phase carrier waveform generation circuit 20 that outputs carrier clock A. The output terminal of the A-phase PWM circuit 30a is connected to the input terminal of the first-phase (A-phase) gate drive circuit 31a. The input terminal of the B-phase PWM circuit 30b is connected to the output terminal of the error amplifier 18 and the output terminal of the three-phase carrier waveform generation circuit 20 that outputs carrier clock B. The output terminal of the B-phase PWM circuit 30b is connected to the input terminal of the second-phase (B-phase) gate drive circuit 31b. The input terminal of the C-phase PWM circuit 30c is connected to the output terminal of the error amplifier 18 and the output terminal of the three-phase carrier waveform generation circuit 20 that outputs carrier clock C. The output terminal of the C-phase PWM circuit 30c is connected to the input terminal of the third-phase (C-phase) gate drive circuit 31c.

[0060] The PWM circuit 30n is a circuit that adjusts the time (conductive state time: duty cycle) for which MOSFET 13n is ON, and is a second signal generation circuit that outputs an adjustment PWM signal (second signal). PWM control is a control that changes the ratio (duty cycle) of the high level (ON) and low level (OFF) of the pulse signal. Furthermore, PWM control repeatedly switches between ON and OFF, generating a pulse waveform (pulse signal, i.e., PWM signal) with a constant period of ON and OFF from a constant voltage, and changing the ON time width. Therefore, the PWM circuit 30n outputs a PWM signal to each gate drive circuit 31a to 31c to change the ON time width of MOSFET 13n. Specifically, the A-phase PWM circuit 30a receives the amplified error from the error amplifier 18 and the carrier clock A from the three-phase carrier waveform generation circuit 20, and outputs an A-phase PWM signal to the first-phase (A-phase) gate drive circuit 31a to change the time width during which the A-phase MOSFET 13a is ON. The B-phase PWM circuit 30b receives the amplified error from the error amplifier 18 and the carrier clock B from the three-phase carrier waveform generation circuit 20, and outputs a B-phase PWM signal to the second-phase (B-phase) gate drive circuit 31b to change the time width during which the B-phase MOSFET 13b is ON. The C-phase PWM circuit 30c receives the amplified error from the error amplifier 18 and the carrier clock C from the three-phase carrier waveform generation circuit 20, and outputs a C-phase PWM signal to the third-phase (C-phase) gate drive circuit 31c to change the time width during which the C-phase MOSFET 13c is ON.

[0061] In this configuration, the B-phase PWM signal is output based on the B-phase carrier clock B, whose switching period phase is shifted by 120 degrees relative to the A-phase carrier clock A. The C-phase PWM signal is output based on the C-phase carrier clock C, whose switching period phase is shifted by 120 degrees relative to the B-phase carrier clock B. The A-phase PWM signal is output based on the A-phase carrier clock A, whose switching period phase is shifted by 120 degrees relative to the C-phase carrier clock C.

[0062] As a result, the PWM signals from phase A to phase C are output at timings shifted by 120 degrees in phase. In this embodiment, the carrier clocks from phase A to phase C have a basic control frequency of 10 kHz. The phase of the output period of each carrier clock is shifted by 120 degrees in each phase. Therefore, the welding power supply unit 10 according to this embodiment operates at a control frequency of 30 kHz.

[0063] The gate drive circuits 31a to 31c are located in the path between the MOSFET 13n and the PWM circuit 30n. In this embodiment, assuming three-phase PWM control, three gate drive circuits 31a to 31c are provided. Specifically, there is a gate drive circuit 31a corresponding to the first phase (phase A), a gate drive circuit 31b corresponding to the second phase (phase B), and a gate drive circuit 31c corresponding to the third phase (phase C).

[0064] In the following explanation, the first phase gate drive circuit 31a will be referred to as "phase A gate drive circuit 31a," the second phase gate drive circuit 31b as "phase B gate drive circuit 31b," and the third phase gate drive circuit 31c as "phase C gate drive circuit 31c." Furthermore, when referring to the gate drive circuits 31a to 31c of the first to third phases collectively, they will be referred to as "gate drive circuit 31n."

[0065] The input terminal of the A-phase gate drive circuit 31a is connected to the output terminal of the A-phase PWM circuit 30a. The output terminal of the A-phase gate drive circuit 31a is connected to the gate terminal of the A-phase MOSFET 13a. The input terminal of the B-phase gate drive circuit 31b is connected to the output terminal of the B-phase PWM circuit 30b. The output terminal of the B-phase gate drive circuit 31b is connected to the gate terminal of the B-phase MOSFET 13b. The input terminal of the C-phase gate drive circuit 31c is connected to the output terminal of the C-phase PWM circuit 30c. The output terminal of the C-phase gate drive circuit 31c is connected to the gate terminal of the C-phase MOSFET 13c.

[0066] Each gate drive circuit 31a to 31c from phase A to phase C is supplied with a drive power supply V PA ~VPC A power supply is provided. The drive reference potentials COMA to COMC are input to each gate drive circuit 31a to 31c of phases A to C from a connection terminal installed downstream of each MOSFET 13a to 13c of phases A to C (a connection terminal installed between the source terminal of MOSFET 13n and the connection terminal of diode 14n).

[0067] The gate drive circuit 31n is a drive circuit (third signal generation circuit) that controls the ON / OFF state of MOSFET 13n by outputting a gate signal (third signal) for applying a voltage between the gate (G) and source (S) of MOSFET 13n. Specifically, the A-phase gate drive circuit 31a outputs a gate signal (A-phase gate signal A) for applying a positive voltage to the gate (G) of the source (S) of A-phase MOSFET 13a, based on the PWM signal (A-phase PWM signal) from the A-phase PWM circuit 30a. As a result, while a voltage is applied to the gate (G) of A-phase MOSFET 13a, the connection between the drain (D) and source (S) remains ON. The B-phase gate drive circuit 31b outputs a gate signal (B-phase gate signal B) for applying a positive voltage to the gate (G) of the source (S) of B-phase MOSFET 13b, based on the PWM signal (B-phase PWM signal) from the B-phase PWM circuit 30b. As a result, the B-phase MOSFET 13b is ON between its drain (D) and source (S) while a voltage is applied to its gate (G). The C-phase gate drive circuit 31c outputs a gate signal (C-phase gate signal C) to apply a positive voltage to the gate (G) of the source (S) of the C-phase MOSFET 13c, based on the PWM signal (C-phase PWM signal) from the C-phase PWM circuit 30c. As a result, the C-phase MOSFET 13c is ON between its drain (D) and source (S) while a voltage is applied to its gate (G).

[0068] In this configuration, after the A-phase MOSFET 13a is turned ON, the B-phase MOSFET 13b is turned ON. Next, after the B-phase MOSFET 13b is turned ON, the C-phase MOSFET 13c is turned ON. Then, after the C-phase MOSFET 13c is turned ON, the A-phase MOSFET 13a is turned ON again.

[0069] As a result, in the welding power supply device 10 according to this embodiment, the ON / OFF timing of each MOSFET 13a to 13c from phase A to phase C is shifted by a predetermined period of time due to the phase of the switching frequency being shifted by 120 degrees in each phase.

[0070] In the welding power supply device 10, the above-mentioned PWM control is used to control the supply of welding current. When any of the MOSFETs 13n among the MOSFETs 13a to 13c of phases A to C are ON, the power inductor 15n is charged, and when any of the MOSFETs 13n are OFF, the welding current is supplied from the power inductor 15n to the workpiece M.

[0071] As a result, the welding power supply unit 10 can extend the energizing time, which is one of the welding conditions, to an appropriate time. Furthermore, even though the welding power supply unit 10 is single-phase with a control frequency of 10 kHz, it operates at a control frequency of 30 kHz through three-phase PWM control. As a result, the energizing time in the welding power supply unit 10 can be finely adjusted compared to single-phase.

[0072] (Noise reduction measures #1) The path between the source terminal of MOSFET13n and the input terminal of power inductor 15n is called the phase node. The gate (G) of MOSFET13n is driven with respect to the phase node. In a switching power supply (hereinafter referred to as a "switching power supply"), a bootstrap circuit is generally used for the gate drive circuit of the high-side (upper leg) switching element (the gate drive circuit of the high-side MOSFET). The bootstrap circuit consists of a diode and a bootstrap capacitor.

[0073] However, when a bootstrap circuit is applied to the welding power supply device 10 according to this embodiment, the power supply for multiple bootstrap circuits corresponding to each of the MOSFETs 13a to 13c from phase A to phase C becomes common. In such a configuration, surge noise generated in one phase may affect another phase.

[0074] Therefore, in the welding power supply device 10 according to this embodiment, a gate drive circuit 31n with specific parts isolated is applied as a measure against surge noise. Specifically, the welding power supply device 10 employs gate drive circuits 31a to 31c for each MOSFET 13a to 13c from phase A to phase C, with each specific part ((a): first output part, and (b) to (d): first to third input parts) isolated, as described below. Here, isolation means electrically and physically separating signals between individual components in the circuit. (a): Output signals (PWM signals) from each PWM circuit 30a to 30c from phase A to phase C; (b): Input signals (gate signals) to each MOSFET 13a~13c from phase A to phase C; (c): Power supply (V) for driving each gate drive circuit 31a to 31c from phase A to phase C PA ,V PB ,V PC ); (d): Driving reference potentials (COMA, COMB, COMC) for each gate drive circuit 31a to 31c from phase A to phase C.

[0075] (Noise reduction measures #2) At the phase node, surge noise is generated due to the influence of the power inductor when the MOSFET is turned OFF. Therefore, in switching power supplies, one method to suppress surge noise is to add an RC snubber circuit to the phase node. An RC snubber circuit consists of a resistor and a capacitor.

[0076] However, if an RC snubber circuit is added to the welding power supply device 10 according to this embodiment (i.e., an RC snubber circuit is added to each phase node from phase A to phase C), the capacitances from phase A to phase C are coupled via the RC snubber circuit. Therefore, surge noise generated in a specific phase may be transmitted to another phase via the RC snubber circuit, potentially causing malfunctions.

[0077] Furthermore, the output reactor stores energy proportional to the square of the output current. When each of the MOSFETs 13a to 13c in phases A through C is OFF, the stored energy appears as a surge voltage between the drain (D) and source (S) of MOSFET 13n. If the surge voltage exceeds the withstand voltage rating between the drain (D) and source (S), MOSFET 13n will fail.

[0078] In switching power supplies with low output current (e.g., 100[A] or less), surges can be suppressed by power supply wiring and printed circuit board wiring. Furthermore, as mentioned above, this can be mitigated by adding an RC snubber circuit between the drain (D) and source (S) of the MOSFET13n. However, in the case of welding power supplies, the output current is large. Therefore, the surge voltage also becomes large. As a result, a surge voltage several times greater than the power supply voltage occurs, causing the MOSFET13n to fail.

[0079] Furthermore, when adding an RC snubber circuit as a surge noise countermeasure, the capacitance of the resistor and capacitor cannot be determined unless the output inductance of the welding power supply is known. The output inductance of the welding power supply includes not only the output reactor but also the parasitic components of the conductive wires (strand wires) leading to the welding electrodes. The thickness and length of the conductive wires vary depending on the welding equipment on which the welding power supply is installed. Therefore, the output inductance cannot be uniquely determined. Thus, adding an RC snubber circuit is not an effective measure against surge noise in welding power supplies (the constants of the RC snubber circuit must be changed according to the conductive wires leading to the welding electrodes).

[0080] Therefore, in the welding power supply device 10 according to this embodiment, instead of adding an RC snubber circuit to the phase node as a measure against surge noise, the phase nodes are isolated from each other. Specifically, the welding power supply device 10 adopts the measure of adding the following active clamp circuit.

[0081] Active clamps 32a to 32c are composed of a diode and a Zener diode. A Zener diode is a constant voltage diode that can provide a constant voltage even when the current changes.

[0082] The active clamps 32a to 32c are located between the drain (D) and gate (G) of the MOSFET 13n. Specifically, they include an active clamp 32a corresponding to the first phase (phase A), an active clamp 32b corresponding to the second phase (phase B), and an active clamp 32c corresponding to the third phase (phase C).

[0083] In the following explanation, the active clamp 32a of the first phase will be referred to as "active clamp 32a of phase A," the active clamp 32b of the second phase as "active clamp 32b of phase B," and the active clamp 32c of the third phase as "active clamp 32c of phase C." Furthermore, when referring to all the active clamps 32a to 32c of the first to third phases together, they will be referred to as "active clamp 32n."

[0084] The active clamp 32n operates to ensure that the drain voltage of MOSFET 13n does not exceed the Zener voltage. The Zener voltage is set to a value greater than the charging voltage of bulk capacitor 12 and less than the rated voltage between the drain (D) and source (S) of MOSFET 13n.

[0085] Thus, in the welding power supply unit 10 according to this embodiment, surge noise countermeasures are implemented without adding an RC snubber circuit to the phase node. Therefore, the welding power supply unit 10 does not experience malfunctions caused by surge noise generated in one phase being transmitted to another phase via an RC snubber circuit. Furthermore, the welding power supply unit 10 can implement surge noise countermeasures that do not depend on the output inductance.

[0086] (Configuration of a three-phase carrier waveform generation circuit) Figure 3 shows an example of the configuration of the three-phase carrier waveform generation circuit 20 according to this embodiment. As shown in Figure 3, the three-phase carrier waveform generation circuit 20 mainly includes an oscillator 21, a ring counter 22, and sawtooth wave generation circuits 23a to 23c, etc.

[0087] The input terminal of oscillator 21 is connected to the output terminal of control circuit 70. The output terminal of oscillator 21 is connected to the input terminal of ring counter 22. The output terminal of ring counter 22 is connected to the input terminals of sawtooth wave generation circuits 23a to 23c. The output terminals of sawtooth wave generation circuits 23a to 23c are connected to the input terminal of PWM circuit 30n.

[0088] The oscillator 21 outputs a 60 kHz reference clock. The oscillator 21 is driven according to the ON / OFF control signals from the control device 70. The oscillator 21 outputs the reference clock in accordance with the ON signal and stops outputting the reference clock in accordance with the OFF signal.

[0089] The ring counter 22 generates three 10 kHz pulses based on a 60 kHz reference clock output from the oscillator 21, with each phase shifted by 120 degrees in the switching control period. Specifically, the ring counter 22 generates a 10 kHz pulse for phase B, which is 120 degrees in phase with respect to phase A. The ring counter 22 also generates a 10 kHz pulse for phase C, which is 120 degrees in phase with respect to phase B. The ring counter 22 also generates a 10 kHz pulse for phase A, which is 120 degrees in phase with respect to phase C.

[0090] Figure 4 shows an example of the circuit configuration of the ring counter 22 according to this embodiment. As shown in Figure 4, the ring counter 22 mainly includes a D-FF (D flip-flop circuit) 221, an OR circuit 222, and an inverter circuit 223, etc.

[0091] The D-FF221 is a logic circuit capable of storing 1 bit of information and constitutes a sequential circuit that determines the current output based on past inputs. The D-FF221 also has two input terminals, a D terminal and a CK terminal, and one output terminal, a Q terminal. The information to be stored (0 or 1) is input as a D signal from the D terminal. The driving clock signal (Low or High) is input from the CK terminal. The stored information is output as a Q signal from the Q terminal. The CK terminal of the D-FF221 is connected to the output terminal of the oscillator 21. Therefore, the driving clock signal corresponds to a 60 kHz reference clock.

[0092] The ring counter 22 according to this embodiment includes five stages of D-FF2211~2215 to generate three 10 kHz pulses, each with a 120-degree phase shift in the switching control period for each phase, based on a 60 kHz reference clock.

[0093] The five D-FF2211~2215 units are connected by sequentially linking their Q and D terminals. Specifically, the Q terminal of D-FF2211 is connected to the D terminal of D-FF2212. The Q terminal of D-FF2212 is connected to the D terminal of D-FF2213. The Q terminal of D-FF2213 is connected to the D terminal of D-FF2214. The Q terminal of D-FF2214 is connected to the D terminal of D-FF2215.

[0094] The D-FF221 stores the D signal when the reference clock rises. On the other hand, when the reference clock is in any of the three states of High, falling, and Low, regardless of the signal value of the D signal, the D-FF221 outputs the immediately previous stored value as the Q signal. Thus, in the configuration of this embodiment, the N-stage D-FF221 n (for example, D-FF2211) outputs the immediately previous stored value from the Q terminal to the D terminal of the (N + 1)-stage D-FF221 n+1 (for example, D-FF2212) when the reference clock is in any of the three states of High, falling, and Low. In other words, the five-stage D-FF2211 to 2215 according to this embodiment transfer the immediately previous stored value from the previous-stage D-FF221 n to the next-stage D-FF221 n+1 in order when the reference clock is in any of the three states of High, falling, and Low.

[0095] The Q signal of the first-stage D-FF2211 is input as an A-phase pulse to the A-phase sawtooth wave generation circuit 23a. The Q signal of the third-stage D-FF2213 is input as a B-phase pulse to the B-phase sawtooth wave generation circuit 23b. The Q signal of the fifth-stage D-FF2215 is input as a C-phase pulse to the C-phase sawtooth wave generation circuit 23c.

[0096] The OR circuit 222 is a logic circuit that outputs a signal value of "1" (Low signal) when any of the plurality of input signals has a signal value of "1" (High signal). The input terminals of the OR circuit 222 are connected to the Q terminals of the five-stage D-FF2211 to 2215. The output terminal of the OR circuit 222 is connected to the input terminal of the inverter circuit 223.

[0097] The Q signals of the five-stage D-FF2211 to 2215 are all input to the OR circuit 222. Therefore, the OR circuit 222 outputs a signal value of "0" as the output signal when all five input signals (Q signals) have a signal value of "0 (zero)". The OR circuit 222 outputs a signal value of "1" as the output signal when any of the five input signals has a signal value of "1".

[0098] The inverter circuit 223 is a logic circuit that inverts the input signal. The inverter circuit 223 also has one input terminal and one output terminal. When the input signal from the input terminal has a signal value of "0" (Low signal), the inverter circuit 223 outputs a signal value of "1" (High signal) from its output terminal. The inverter circuit 223 is located in the path between the OR circuit 222 and the first-stage D-FF 2211. Therefore, when the input signal from the OR circuit 222 has a signal value of "0", the first-stage D-FF 2211 receives a signal value of "1" from its D terminal.

[0099] Figure 5 is a timing chart of the three-phase pulses PLa to PLc according to this embodiment. Figure 5 shows the B-phase pulse PLb, which is 10 kHz and shifted in phase by 120 degrees relative to the A-phase. It shows the C-phase pulse PLc, which is 10 kHz and shifted in phase by 120 degrees relative to the B-phase. It shows the A-phase pulse PLa, which is 10 kHz and shifted in phase by 120 degrees relative to the C-phase.

[0100] The ring counter 22 according to this embodiment generates three-phase pulses PLa to PLc as shown in Figure 5, with the above configuration.

[0101] When the first reference clock CL rises, the D-FF2211 stores the D signal. Subsequently, the D-FF2211 outputs the stored value "1" as the Q signal while the reference clock CL is in one of three states: High, Falling, or Low. As a result, the D-FF2211 outputs an A-phase pulse (High signal) until the reference clock CL rises again. Therefore, the period from the first rise of the reference clock CL to the rise of the second reference clock CL corresponds to the period during which the A-phase pulse is a High signal, i.e., the A-phase H pulse width.

[0102] When the second reference clock CL rises, D-FF2211 stores the signal value "0" from the inverter circuit 223 as the D signal. Subsequently, D-FF2211 outputs the stored value "0 (zero)" as the Q signal while the reference clock CL is in one of three states: High, Falling, or Low. As a result, D-FF2211 outputs an A-phase pulse (Low signal) until the reference clock CL rises again. When the second reference clock CL rises, D-FF2212 stores the previously input signal value "1" from D-FF2211 as the D signal. Subsequently, D-FF2212 outputs the stored value "1" as the Q signal while the reference clock CL is in one of three states: High, Falling, or Low.

[0103] When the reference clock CL rises for the third time, D-FF2211 stores the signal value "0" from inverter circuit 223 as the D signal. Subsequently, D-FF2211 outputs the stored value "0" as the Q signal while the reference clock CL is in one of three states: High, Falling, or Low. As a result, D-FF2211 outputs an A-phase pulse (Low signal) until the reference clock CL rises again. When the reference clock CL rises for the third time, D-FF2212 stores the previously input signal value "0" from D-FF2211 as the D signal. Subsequently, D-FF2212 outputs the stored value "0" as the Q signal while the reference clock CL is in one of three states: High, Falling, or Low. As a result, a Q signal with a signal value of "0" is input to the D terminal of D-FF2213 from D-FF2212. Furthermore, when the reference clock CL rises for the third time, the D-FF2213 stores the previously input signal value "1" from the D-FF2212 as the D signal. Subsequently, the D-FF2213 outputs the stored value "1" as the Q signal while the reference clock CL is in one of three states: High, Falling, or Low. As a result, the D-FF2213 outputs a B-phase pulse (High signal) until the reference clock CL rises again.

[0104] Therefore, the period from the rise of the third reference clock CL to the rise of the fourth reference clock CL corresponds to the period during which the B-phase pulse is a High signal, i.e., the H pulse width of the B-phase.

[0105] Thus, the ring counter 22 according to this embodiment includes five stages of D-FF2211~2215. Furthermore, the ring counter 22 sets a signal value of "1" (High signal) in accordance with the rising edge of the 60[kHz] reference clock CL to the Nth stage D-FF221 n D-FF221 from the N+1th stage n+1 The signal is transmitted to the following devices. Furthermore, the ring counter 22 outputs the Q signal of the first stage D-FF2211 as an A-phase pulse, the Q signal of the third stage D-FF2213 as a B-phase pulse, and the Q signal of the fifth stage D-FF2215 as a C-phase pulse.

[0106] As a result, the output period of the High signal in the pulse becomes 10 kHz, and the phase of the output period shifts by 120 degrees in each of the three phases. Consequently, the welding power supply device 10 according to this embodiment operates at 30 kHz as a whole.

[0107] Returning to the explanation of Figure 3, the sawtooth wave generation circuits 23a to 23c generate three sawtooth waves for PWM modulation corresponding to each phase from the A-phase to C-phase pulses PLa to PLc generated by the ring counter 22.

[0108] Therefore, in this embodiment, the circuit located downstream of the ring counter 22 is equipped with three sawtooth wave generation circuits 23a to 23c. Specifically, it includes a sawtooth wave generation circuit 23a corresponding to the first phase (phase A), a sawtooth wave generation circuit 23b corresponding to the second phase (phase B), and a sawtooth wave generation circuit 23c corresponding to the third phase (phase C).

[0109] In the following explanation, the first-phase sawtooth wave generation circuit 23a will be referred to as "phase A sawtooth wave generation circuit 23a," the second-phase sawtooth wave generation circuit 23b as "phase B sawtooth wave generation circuit 23b," and the third-phase sawtooth wave generation circuit 23c as "phase C sawtooth wave generation circuit 23c." Furthermore, when referring collectively to each of the first to third-phase sawtooth wave generation circuits 23a to 23c, they will be referred to as "sawtooth wave generation circuit 23n."

[0110] The A-phase sawtooth wave generation circuit 23a outputs the A-phase sawtooth wave for A-phase PWM modulation as the A-phase carrier clock A to the A-phase PWM circuit 30a. The B-phase sawtooth wave generation circuit 23b outputs the B-phase sawtooth wave for B-phase PWM modulation as the B-phase carrier clock B to the B-phase PWM circuit 30b. The C-phase sawtooth wave generation circuit 23c outputs the C-phase sawtooth wave for C-phase PWM modulation as the C-phase carrier clock C to the C-phase PWM circuit 30c.

[0111] Figure 6 shows an example of the configuration of the sawtooth wave generation circuit 23n according to this embodiment. As shown in Figure 6, the sawtooth wave generation circuit 23n mainly includes a transistor (Tr) 231, a capacitor (Capacitor) 232, a constant current source (Current Source) 233, and a buffer (Buffer) 234.

[0112] Transistor 231 is a switching element that turns ON (conducts) when a voltage above a predetermined value is applied to its base terminal, allowing current to flow between its collector and emitter. Capacitor 232 is a charger that stores charge when a DC voltage is applied. Constant current source 233 is a power supply that can supply a constant current regardless of the load size. Buffer 234 has the function of lowering the output impedance of the sawtooth wave generation circuit 23n. Buffer 234 also has the function of preventing leakage from the constant current source 233 to the PWM circuit 30n.

[0113] The base terminal of transistor 231 is connected to the output terminal of ring counter 22. The collector terminal of transistor 231 is connected to the first terminals of capacitor 232 and constant current source 233. The emitter terminal of transistor 231 is connected to the second terminals of capacitor 232 and constant current source 233.

[0114] The sawtooth wave generation circuit 23n stores energy in the capacitor 232 by controlling the ON / OFF state of the transistor 231 and supplying current from the constant current source 233, and outputs a sawtooth wave via the buffer 234 when the capacitor 232 discharges.

[0115] Figure 7 shows the timing chart of the three-phase sawtooth waves SAWa to SAWc according to this embodiment. In the following explanation, when referring to each sawtooth wave SAWa to SAWc from phase A to phase C, it will be called "sawtooth wave SAWn". Also, when referring to each pulse PLa to PLc from phase A to phase C, it will be called "pulse PLn".

[0116] When the sawtooth wave generation circuit 23n receives a pulse PLn from the ring counter 22, it initializes the voltage of the sawtooth wave SAWn (resets the voltage value to "0 (zero)"). Subsequently, when the transistor 231 is in a non-conducting state (OFF), the sawtooth wave generation circuit 23n receives a constant current from the constant current source 233 to the capacitor 232, and charge is stored.

[0117] As a result, the sawtooth wave generation circuit 23n changes (increases) the voltage at a constant rate until it reaches the peak voltage Vsaw of the sawtooth wave SAWn. At this time, the sawtooth wave generation circuit 23n adjusts the voltage value of the peak voltage Vsaw of the sawtooth wave so that it is greater than the feedback signal, so that the duty cycle of the PWM signal does not become 100%.

[0118] The duty cycle of a PWM signal can be expressed as (H pulse width / pulse period), and the pulse period can be expressed as (H pulse width + L pulse width). The H pulse width is the period during which the pulse is a High signal, and the L pulse width is the period during which the pulse is a Low signal. Therefore, a PWM signal duty cycle of 100% means that the pulse period is the same as the H pulse width, which means that the device is constantly energized.

[0119] The sawtooth wave generation circuit 23n adjusts the voltage value of the sawtooth wave peak voltage Vsaw by changing the current value output from the constant current source 233. The current value can be changed by setting the resistance value of the cermet trimmer (trimmer resistor / semi-fixed resistor) of the constant current source 233.

[0120] As described above, the welding power supply unit 10 according to this embodiment employs a three-phase interleaved method and operates as follows. Based on a 60 kHz reference clock, the welding power supply unit 10 generates three 10 kHz pulses PLa to PLc, each with a 120-degree phase shift in the switching control period for each phase. The welding power supply unit 10 also generates three carrier clocks A to C for PWM modulation corresponding to each phase from each pulse PLa to PLc. The welding power supply unit 10 outputs PWM signals for each phase according to each carrier clock A to C, whose switching period phase is shifted by 120 degrees. The welding power supply unit 10 also controls the ON / OFF state of the switching elements for each phase based on the PWM signals for each phase.

[0121] In this configuration, the three-phase interleaved welding power supply device 10 according to this embodiment shifts the phase of the switching frequency by 120 degrees in each phase, causing the ON / OFF timing of each switching element in the three phases to be shifted by a predetermined amount of time.

[0122] The three-phase interleaved welding power supply unit 10 uses the above-mentioned PWM control to control the supply of welding current. When any of the three-phase switching elements are ON, the power inductor 15n is charged, and when any of the MOSFETs 13n are OFF, the welding current is supplied from the power inductor 15n to the workpiece M. As a result, the welding power supply unit 10 can extend the energizing time, which is one of the welding conditions, to an appropriate time. In other words, the three-phase interleaved welding power supply unit 10 can achieve a longer energizing time that could not be output by a linearly controlled welding power supply unit.

[0123] Furthermore, even though the welding power supply unit 10 is single-phase with a control frequency of 10 kHz, it operates at a control frequency of 30 kHz through three-phase PWM control. As a result, the energizing time of the welding power supply unit 10 can be finely adjusted compared to single-phase power.

[0124] The control frequency (30 kHz) of the three-phase interleaved welding power supply unit 10 according to this embodiment is higher than the control frequency (10 kHz) of the single-phase inverter type welding power supply unit. Therefore, the energizing time can be finely adjusted in the three-phase interleaved welding power supply unit 10. In other words, the three-phase interleaved welding power supply unit 10 allows for fine adjustment of the energizing time, which was not possible with the single-phase interleaved welding power supply unit.

[0125] Furthermore, the three-phase interleaved welding power supply unit 10 allows for fine adjustment of welding conditions, improving responsiveness in lamination welding of aluminum foil, where contact resistance changes rapidly. Here, "responsiveness" refers to the responsiveness of the control function of the welding power supply unit 10. When the control frequency is 10 [kHz], the control period is 100 [μsec]. In contrast, the three-phase interleaved welding power supply unit 10 according to this embodiment is configured to operate at a control frequency of 30 [kHz]. As a result, the control period becomes 33 [μsec], which is shorter than the control period when the control frequency is 10 [kHz]. For example, when the joining of the workpieces M progresses and the contact resistance decreases, the current increases. Therefore, it is necessary to perform control to suppress the increase in current. In this case, the three-phase interleaved welding power supply unit 10 can perform control with a period shorter than 100 [μsec]. Therefore, the three-phase interleaved welding power supply unit 10 has improved responsiveness to fluctuations in the workpiece M (load).

[0126] Thus, in the three-phase interleaved welding power supply device 10 according to this embodiment, the energizing time can be extended and fine-tuned, so an appropriate energizing time can be secured and stable welding quality can be obtained.

[0127] (Verification of the three-phase interleaved system) Figure 8 shows the pulse waveforms of the three-phase interleaved system according to this embodiment. As an operation verification of the three-phase interleaved system according to this embodiment, the output of the pulse waveforms generated in each phase was verified. Figure 8 shows the verification results. CH1 shows the output waveform when the reference clock CL is 60 [kHz]. CH2 shows the output waveform of the A-phase pulse PLa generated based on the 60 [kHz] reference clock CL. CH3 shows the output waveform of the B-phase pulse PLb generated based on the 60 [kHz] reference clock CL. CH4 shows the output waveform of the C-phase pulse PLc generated based on the 60 [kHz] reference clock CL.

[0128] As shown in Figure 8, the pulses PLa to PLc of each phase are single-phase and have a control frequency of 10 kHz. Furthermore, the phase of the switching control period of the pulse PLb of phase B is shifted by 120 degrees relative to that of phase A. The phase of the switching control period of the pulse PLc of phase C is shifted by 120 degrees relative to that of phase B. The phase of the switching control period of the pulse PLa of phase A is shifted by 120 degrees relative to that of phase C. In the three-phase interleaved system according to this embodiment, as described above, the phase of the switching control period is shifted by 120 degrees for each phase pulse, so it operates at a combined control frequency of 30 kHz for all three phases.

[0129] Figure 9 shows the output waveforms of the three-phase interleaved welding power supply device 10 according to this embodiment. As an operational verification of the three-phase interleaved system according to this embodiment, each output was verified when constant current control was performed with an energizing time of 100 [msec]. Figure 9 shows the verification results. CH1 shows the waveform of the welding command. CH2 shows the waveform of the output current. CH3 shows the waveform of the charging voltage. CH4 shows the waveform of the output voltage.

[0130] Figure 10 shows the output waveforms of a single-phase inverter type welding power supply unit. Specifically, Figure 10 shows the outputs when constant current control is applied with an energizing time of 30 [msec]. CH1 shows the output voltage waveform. CH2 shows the output current waveform. As shown in Figure 10, in the single-phase inverter type, when the set value of the energizing time is small, the ripple component of the output waveform is large and the fluctuation range is also large. Here, the ripple component refers to the pulsating component of current and voltage.

[0131] In contrast, as shown in Figure 9, in the three-phase interleaved method according to this embodiment, the phase of the switching frequency is shifted by 120 degrees in each phase, which suppresses the generation of ripple components that appear in the output voltage during welding, depending on the switching frequency (achieving low noise).

[0132] When the ripple component is large, the current supplied to the workpiece M fluctuates in strength. Therefore, if the generation of the ripple component can be suppressed, a stable welding current can be supplied to the workpiece M. As a result, if a stable welding current can be supplied to the workpiece M, the workpiece M can be heated more efficiently, and the welding quality can be improved.

[0133] Thus, the three-phase interleaved welding power supply device 10 according to this embodiment allows for adjustment to desired welding conditions, resulting in good welding quality.

[0134] (Modified example: Weld quality judgment function) In resistance welding, the welding result, i.e., the quality of the weld, is determined by welding conditions such as welding output (current, voltage, power, etc.), energizing time, and applied pressure. The waveform of the welding output is an important criterion for judging the quality of the weld.

[0135] Therefore, in this modified example, a method (weld quality determination function) is disclosed that monitors the waveform of the welding output and determines the quality of the welding based on the monitoring results.

[0136] In this modified method, the acceptable range of variation in welding output is defined as the tolerance range (mask) for welding quality. Then, it is determined whether or not the variation in the output waveform is within the tolerance range. If the variation in the output waveform is within the tolerance range, the welding quality is considered "good (acceptable)".

[0137] The difference between the first embodiment and this modified example is whether or not it has a welding quality determination function. Therefore, the welding power supply device according to this modified example is the same as the welding power supply device 10 according to the first embodiment. Accordingly, in the following description, the welding power supply device according to this modified example will be referred to as "welding power supply device 10" as in the first embodiment.

[0138] This modified example shows how a control circuit 70 in the welding power supply unit 10 executes a predetermined program to realize a welding quality determination function. The control circuit 70 is one or more processors. The control circuit 70 also realizes a predetermined function by, for example, reading a program previously stored in non-volatile memory (ROM: Read Only Memory) into volatile memory (RAM: Random Access Memory) and executing instruction codes defined as the program.

[0139] Figure 11 is a flowchart showing the welding quality determination process in a modified welding power supply device 10. In this modified welding power supply device 10, the control circuit 70 executes the processing procedure shown in Figure 11 to realize the welding quality determination function.

[0140] The control circuit 70 obtains the welding output value (current value) (step S11). The control circuit 70 also obtains the welding current value from, for example, the ADC 60.

[0141] The control circuit 70 determines whether the acquired value is within an acceptable range (step S12). The control circuit 70 also determines whether the welding current value is within an acceptable range of current value fluctuations as a welding quality. The acceptable range of current value fluctuations as a welding quality is pre-set in the control device 70. The range can be set in the control circuit 70 by, for example, setting two critical values, an upper limit and a lower limit of the fluctuation range, as a set of data, and storing multiple such data in units of welding time. As a result, the control device 70 compares the welding current value with the upper and lower limits of the fluctuation range corresponding to the elapsed welding time, and determines whether the welding current value is within an acceptable range from the comparison result.

[0142] If the control circuit 70 determines that the acquired value is within the acceptable range (step S12: YES), it determines that the welded product is a good product and assigns the welding quality of the welded product a "pass" rating (step S13).

[0143] Figure 12(A) shows an example of the output waveform when the welding quality of this modified example is acceptable. Figure 12(B) shows an example of the output waveform when the welding quality of this modified example is unacceptable. Figures 12(A) and 12(B) show the allowable range MSK of the welding output. The allowable range MSK is a range that has two critical values ​​at the same time. Also, as shown in Figure 12(A), the critical values ​​(upper and lower limits of the fluctuation range) of the allowable range MSK differ between welding elapsed time A and welding elapsed time B. Therefore, multiple data points for the allowable range MSK are stored per welding time unit.

[0144] As shown in the OK region of Figure 12(A), the control circuit 70 determines that the welding current value is within the acceptable range if it is below the upper limit and above the lower limit of the fluctuation range corresponding to the elapsed welding time. On the other hand, if the control circuit 70 determines that the acquired value is outside the acceptable range (step S12: NO), it determines that the welded product is defective and assigns a "failure" rating to the welding quality of the welded product (step S14).

[0145] As shown in the NG region of Figure 12(B), the control circuit 70 determines that the welding current value is outside the acceptable range if it is greater than the upper limit of the fluctuation range corresponding to the elapsed welding time. Alternatively, it determines that the welding current value is outside the acceptable range if it is less than the lower limit of the fluctuation range corresponding to the elapsed welding time. Subsequently, the control circuit 70 displays on a display device (not shown) connected to the welding power supply device 10 whether the welding quality of the welded work is "acceptable" or "unacceptable".

[0146] As described above, the welding power supply device 10 according to this modified example has a welding quality determination function. This allows the welding power supply device 10 to monitor the waveform of the welding output during welding and, based on the monitoring results, to indicate whether the welding is good or bad.

[0147] Furthermore, the present disclosure proposes a welding power supply device 10 employing a three-phase interleaved system. As described above, the welding quality determination function proposed in this modified example monitors whether or not there is little noise included in the welding output. As explained in the first embodiment, the three-phase interleaved system can achieve low noise because the OFF times of each MOSFET 13a to 13c in the three-phase output can be complemented by each other. Therefore, the three-phase interleaved system has a high probability of yielding good results in welding quality determination. Thus, the three-phase interleaved welding power supply device 10 of the present disclosure can provide stable welding quality in the manufacturing process and is expected to improve product yield.

[0148] The present invention is not limited to the embodiments and modifications described above, and various modifications are possible without departing from the spirit of the invention. Furthermore, each configuration shown in the embodiments and modifications can be combined arbitrarily. In other words, although the present invention is described in accordance with the embodiments, it is understood that it is not limited to those embodiments or structures. The technology of this disclosure also includes various modifications and variations within the equivalent range. In addition, various combinations and forms, as well as other combinations and forms that include only one, more, or fewer of those elements, also fall within the scope and conceptual range of the technology of this disclosure. [Explanation of symbols]

[0149] 10: Welding power supply equipment; 12: Bulk capacitors; 13a~13c,13n: MOSFET; 171~173,17n: Feedback circuit; 18: Error amplifier; 20: Three-phase carrier waveform generation circuit; 30a~30c,30n:PWM circuit; 31a~31c,31n: Gate drive circuit; 32a~32c,32n: Active clamp; 50: RC filter; 91a, 91b: Welding electrodes; PLa~PLc,PLn: Pulse

Claims

1. A welding power supply device used for resistance welding, Three switching elements corresponding to the first to third phases, A power storage unit that stores energy when any one of the three switching elements becomes conductive, and outputs current from at least one switching element to a welding electrode in contact with the workpiece when it becomes non-conductive, A first signal generation unit generates three pulses corresponding to each phase based on a reference clock, and generates three first signals for pulse modulation corresponding to each phase from the three generated pulses. A second signal generation unit generates three second signals that adjust the conduction time, which is the period of conduction of each switching element, based on the three first signals, Based on the three aforementioned second signals, three drive units output a third signal to each of the switching elements to apply a predetermined voltage to each of the switching elements, thereby causing each of the switching elements to be in a conductive state or a non-conductive state. Equipped with, The first signal generation unit is, The system is configured to generate three pulses in which the phase of the switching control period in each of the aforementioned phases is shifted by 120 degrees. The aforementioned drive unit is The first input portion from the second signal generation unit, The output portion to the switching device, The second input section of the power supply for driving, It has a third input portion for the driving reference potential, The gate of the switching element is configured to be driven using a bootstrap circuit. The multiple bootstrap circuits corresponding to each of the switching elements are configured to be connected to a common power supply. The aforementioned drive unit is A welding power supply device configured to isolate each of the first input section, the second input section, the third input section, and the output section from each phase.

2. The switching element is a field-effect transistor, An active clamp is provided between the drain and gate of the aforementioned field-effect transistor. The aforementioned active clamp is It is composed of a diode and a Zener diode. The welding power supply device according to claim 1, wherein the drain voltage of the field-effect transistor is operated to be less than the Zener voltage.

3. A feedback unit that feeds back output signals corresponding to constant current control, constant voltage control, and constant power control as input signals, A switching unit that switches the input signal to be used as a feedback signal according to each of the above control methods, The system further includes an error amplification unit that compares a target value generated according to a welding command with the feedback signal and amplifies the resulting error. The welding power supply device according to claim 1, wherein the error amplification unit inputs the amplified error to the second signal generation unit and performs one of the following: target control of current, target control of voltage, or target control of power.

4. The system further includes a filter section to suppress noise appearing in the output voltage during resistance welding, When the control method is the constant voltage control, The aforementioned feedback unit is The welding power supply device according to claim 3, wherein the output voltage after noise suppression from the filter unit is fed back as the input signal.

5. A welding power supply device used for lamination welding of metal foils, Three field-effect transistors corresponding to the first to third phases, A power inductor that stores energy when any one of the three field-effect transistors becomes conductive, and outputs current from at least one switching element to a welding electrode in contact with the workpiece when it becomes non-conductive, A three-phase carrier waveform generation circuit generates three pulses corresponding to each phase based on a reference clock, and generates three carrier clocks for pulse modulation corresponding to each phase from the three generated pulses. Three PWM circuits that generate three PWM signals to adjust the conduction time, which is the duration of the conduction state of each field-effect transistor, based on the three carrier clocks, Based on the three PWM signals, three gate drive circuits output gate signals to each field-effect transistor to apply a predetermined voltage to each field-effect transistor, thereby causing each field-effect transistor to be in a conductive or non-conductive state. Equipped with, The three output terminals of the three-phase carrier waveform generation circuit are connected to the input terminals of each of the PWM circuits. The output terminals of each of the aforementioned PWM circuits are connected to the input terminals of each of the aforementioned gate drive circuits. The output terminals of each of the gate drive circuits are connected to the gate terminals of each of the field-effect transistors. The source terminal of each of the aforementioned field-effect transistors is connected to the input terminal of the power inductor. The three-phase carrier waveform generation circuit is The pulse corresponding to the second phase is generated such that the phase of the switching control period of the second phase field-effect transistor is shifted by 120 degrees relative to the phase of the switching control period of the first phase. The pulse corresponding to the third phase is generated such that the phase of the switching control period of the third phase field-effect transistor is shifted by 120 degrees relative to the phase of the switching control period of the second phase. The phase of the switching control period of the first phase field-effect transistor is shifted by 120 degrees relative to the phase of the switching control period of the third phase, thereby generating the pulse corresponding to the first phase. It is configured in such a way, The gate drive circuit is, The first input terminal from the PWM circuit, The output terminal to the field-effect transistor, The second input terminal of the power supply for driving the device, It has a third input terminal for the driving reference potential, The gate of the field-effect transistor is configured to be driven using a bootstrap circuit. The multiple bootstrap circuits corresponding to each of the field-effect transistors are configured to be connected to a common power supply. The gate drive circuit is, A welding power supply device configured such that each terminal of the first input terminal, the second input terminal, the third input terminal, and the output terminal is isolated for each phase.

Images