JP2021058898A - Welding power source device - Google Patents

Abstract

To prevent a failure due to a secondary breakdown of a switching element even if a deviatively magnetized state of a transformer continues.SOLUTION: A welding power source device has an inverter unit for converting DC electric power into high-frequency electric power, a transformer for converting the high-frequency electric power generated by the inverter unit into a prescribed voltage, an electric current detector for detecting an electric current Ip flowing through a primary coil of the transformer, and an excess electric current detector for producing an excess electric current signal OCP when an electric current value Id detected by the electric current detector exceeds a reference value Vs. When the excess electric current detector produces the excess electric current signal OCP, the inverter unit stops operation once and then starts again. When the excess electric current signal OCP is generated a prescribed number of times in a prescribed time, the inverter unit stops operation.SELECTED DRAWING: Figure 2

Description

The present invention relates to a welding power supply device.

In the inverter type welding power supply device, many inventions have already been made to prevent damage caused by an excessive current flowing through the switching element due to the demagnetization of the transformer. Patent Document 1 proposes a method of stopping for a certain period of time when the current flowing through the switching element becomes abnormal, and then starting from the opposite polarity when the abnormality is detected when restarting. Further, in Patent Document 2, the exciting current of the transformer is calculated from the primary current flowing through the transformer and the output current of the welding power supply according to the turns ratio of the transformer, and when the calculated exciting current exceeds the reference value, the half cycle is calculated. A method of stopping the driving of the switching element for a period has also been proposed.

Japanese Unexamined Patent Publication No. 62-10786 Japanese Patent No. 2973564

In an inverter type welded power supply device, if the transformer is continuously demagnetized and an excessive current repeatedly flows through the switching element in a short time, there is a problem that the switching element is damaged due to secondary yielding.

Patent Document 1 proposes a method for overcurrent protection by demagnetization of a transformer to operate and to restart as soon as possible when paused. Further, in Patent Document 2, when the transformer is demagnetized, the driving of the switching element is only stopped for a period of half a cycle. Therefore, in Patent Documents 1 and 2, when the demagnetized state of the transformer continues, it is not possible to prevent the overcurrent from repeatedly flowing through the switching element in a short time, and it is not possible to prevent the failure due to the secondary yield of the switching element.

An object of the present invention is to prevent a failure due to secondary yielding of a switching element even if the demagnetized state of the transformer continues.

In order to solve the above-mentioned problems, the invention of claim 1 is
Inverter section that converts DC power to high frequency power,
A transformer that converts the high-frequency power generated by the inverter unit into a predetermined voltage, and
A current detector that detects the current flowing through the primary winding of the transformer, and
An overcurrent detector that generates an overcurrent signal when the current value detected by the current detector exceeds the reference value, and
A welding output unit that rectifies high-frequency power converted to the predetermined voltage by the secondary winding of the transformer into DC power, and
Is equipped with
When the overcurrent detector emits the overcurrent signal, the inverter unit temporarily stops the operation and then restarts the inverter unit, and stops the operation when the overcurrent signal is generated a predetermined number of times within a predetermined time. ,
It is a welding power supply device characterized by this.

The invention of claim 2 is
When the inverter unit is restarted after temporarily stopping the operation, the on-time of the switching element of the inverter unit is gradually increased.
The welding power supply device according to claim 1.

According to the present invention, even if the demagnetized state of the transformer continues, it is possible to prevent a failure due to the secondary yield of the switching element.

It is a connection diagram of the welding power-source device which concerns on embodiment of this invention, and is a block diagram of each function. It is a timing chart at the time of restarting after the inverter part is temporarily stopped by the overcurrent signal which concerns on embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Embodiment]
FIG. 1 is a connection diagram of a welding power supply device according to an embodiment of the present invention and a block diagram of each function. Hereinafter, each block will be described with reference to the figure. The DC power supply 1 outputs a DC voltage and a DC current to the inverter unit 2, and includes, for example, a rectifier circuit for rectifying an AC power supply having a commercial frequency and a smoothing capacitor for smoothing.

The inverter unit 2 converts the DC voltage and DC current input from the DC power supply 1 into high-frequency DC voltage and DC current, and outputs the DC voltage and DC current to the transformer 3. The inverter unit 2 is a full-bridge type inverter and includes four switching elements 21 to 24. In this embodiment, IGBTs (insulated gate bipolar transistors) are used as the switching elements 21 to 24. The switching elements 21 to 24 are not limited to IGBTs, and may be MOSFETs (Metal Oxide Semiconductor Field Effect Transistor) or the like.

The transformer 3 applies a high-frequency voltage input from the inverter unit 2 to the primary winding, transforms it into a voltage corresponding to the turns ratio of the primary winding and the secondary winding, and outputs the voltage to the welding output unit 4. ..

The welding output unit 4 includes diodes 51 and 52 and a DC reactor 6, converts high-frequency voltage input from the secondary winding of the transformer 3 into DC, smoothes the current, and creates an arc load as the welding current Iw. Output to 7.

The current detector CT detects the primary winding current Ip of the transformer 3 and outputs the primary current value Id to the overcurrent detection unit 8.

When the absolute value of the primary current value Id exceeds the overcurrent detection reference value Vs, the overcurrent detection unit 8 generates an overcurrent signal OCP that switches from Low to High, and outputs the overcurrent signal OCP to the control unit 25 of the inverter unit 2. As shown in FIG. 2, the waveform of the primary current value Id has both positive and negative polarities. Therefore, when the primary current Id falls beyond the lower limit value −Vs and rises above the upper limit value Vs, the overcurrent is overcurrent. The detection unit 8 switches the overcurrent signal OCP from Low to High, and when the primary current Id returns from the lower limit value −Vs to the upper limit value Vs, the overcurrent detection unit 8 changes the overcurrent signal OCP from High to Low. Switch.

The inverter unit 2 is composed of blocks of switching elements 21 to 24, a control unit 25, and a drive unit 26.

The control unit 25 of the inverter unit 2 outputs a signal PWM for driving the switching elements 21 to 24 to the drive unit 26, and performs the following processing based on the overcurrent signal OCP of the overcurrent detection unit 8 to perform a stop signal. St is output to the drive unit 26.
1) At the moment when the overcurrent signal OCP of the overcurrent detection unit 8 is switched from Low to High, the control unit 25 outputs a stop signal St (High) to the drive unit 26, and the drive unit 26 is the inverter unit 2 by the stop signal St. The drive of the switching elements 21 to 24 of the above is temporarily stopped, and the inverter unit 2 is temporarily stopped.
2) After a predetermined time has elapsed since the inverter unit 2 temporarily stopped the operation, the control unit 25 switches the stop signal St output to the drive unit 26 from High to Low. When the stop signal St becomes Low, the drive unit 26 restarts the drive of the switching elements 21 to 24 of the inverter unit 2, but at the time of restart, the time width (maximum duty ratio) that the switching elements 21 to 24 can be turned on is set. The control unit 25 controls the AC conversion frequency (inverter frequency) to be gradually expanded every half cycle, and restarts by a so-called soft start.
3) When the overcurrent signal OCP, which is the output of the overcurrent detection unit 8, is switched from Low to High within a predetermined time more than a predetermined number of times, the control unit 25 switches the stop signal St from Low to High, and the drive unit 26 changes the stop signal St from Low to High. The drive of the switching elements 21 to 24 of the inverter unit 2 is stopped, and the operation of the inverter unit 2 is stopped. Since the state in which the stop signal St in this case is High is held until the operator turns off the power switch (not shown) of the welding power supply device, the inverter unit 2 keeps the state in which the operation is stopped.

The drive unit 26 of the inverter unit 2 drives the switching elements 21 to 24 based on the drive signal PWM of the control unit 25. However, only when the stop signal St from the control unit 25 is Low, the switching elements 21 to 24 of the inverter unit 2 are driven, and when the stop signal St is High, the driving of the switching elements 21 to 24 is stopped.

As described above, the inverter unit 2 turns on / off the DC voltage and DC current input from the DC power supply 1 from the switching elements 21 to 24, converts them into high-frequency DC voltage and DC current, and outputs the DC voltage and DC current to the transformer 3. .. Further, when the current flowing through the switching element exceeds the reference value by the overcurrent signal OCP of the overcurrent detection unit 8, the overcurrent protection operation for suspending the drive of the switching elements 21 to 24 is performed, but the overcurrent protection operation is performed within a predetermined time. When this overcurrent protection operation is performed more than the number of times, the inverter unit 2 stops the operation.

FIG. 2 is a timing chart illustrating an operation when the transformer 3 according to the embodiment of the present invention is demagnetized and the overcurrent detection unit 8 generates an overcurrent signal OCP. Hereinafter, the operation when the inverter unit 2 is temporarily stopped by the overcurrent signal OCP and then restarted will be described with reference to the figure.

FIG. 3A is a primary winding current Ip flowing from the inverter unit 2 to the transformer 3. The AC conversion frequency (inverter frequency) of the inverter unit 2 in the embodiment of the present invention is 50 kHz, and a high frequency AC current of 50 kHz flows through the primary winding of the transformer 3 as shown in FIG. .. FIG. 3B is a primary current value Id which is an output of the current detector CT, and has a waveform corresponding to the primary winding current Ip of the transformer 3. Before time t0, the transformer 3 is not demagnetized, and as shown in FIG. 6A, the primary winding current Ip of the transformer 3 has a well-balanced waveform in both positive and negative directions.

Time t0: At time t0, the transformer 3 gradually begins to be demagnetized due to factors such as variations in the switching speeds of the switching elements 21 to 24. Then, the exciting inductance of the transformer 3 becomes small, and as shown in FIG. 3A, the primary winding current Ip of the current transformer 3 loses its balance between positive and negative, and either the positive or negative current becomes large. Although the figure (a) shows a case where the current on the positive side becomes large, the current on the negative side may become large.

At time t1: time t1, when the demagnetization of the transformer 3 becomes large and the primary current value Id exceeds the overcurrent detection reference value Vs of the overcurrent detection unit 8, as shown in FIG. As shown in FIG. 3C, the overcurrent detection unit 8 switches the overcurrent signal OCP from Low to High. Then, as shown in FIG. 3D, the control unit 25 of the inverter unit 2 immediately switches the stop signal St from Low to High. Since the stop signal St is switched to High, the drive unit 26 suspends the drive of the switching elements 21 to 24 of the inverter unit 2 until the point of t2. Since the inverter unit 2 was temporarily stopped, the primary winding current Ip and the primary current value Id of the transformer 3 became zero as shown in FIGS. (A) and (b), and as shown in FIG. The overcurrent signal OCP switches from High to Low.

Time t1 to t2: During the period from the time t1 when the inverter unit 2 is temporarily stopped by the overcurrent signal OCP to the time t2 when it is restarted, the control unit 25 keeps the stop signal St at High as shown in FIG. Since the drive unit 26 stops driving the switching elements 21 to 24 of the inverter unit 2, the inverter unit 2 is temporarily stopped. The pause period from time t1 to t2 is set to a short period of 100 μS in the embodiment of the present invention, and it is intended to degauss the current transformer used in the current detector CT. When a non-magnetized current detector CT such as a current shunt is used, the period can be set shorter than 100 μS.

Time t2: At time t2, as shown in FIG. 3D, the stop signal Ts switches from High to Low. Since the stop signal St is switched to Low, the drive unit 26 restarts the driving of the switching elements 21 to 24 of the inverter unit 2, and the inverter unit 2 restarts. However, the control unit 25 of the inverter unit 2 does not restart the time width in which the switching elements 21 to 24 can be turned on at the maximum duty, but as described below, the control unit 25 increases the maximum duty from 10% to 100% in 10% increments. The AC conversion frequency (inverter frequency) is gradually increased every half cycle.

Times t2 to t3: The time width during which the switching elements 21 to 24 can be turned on at the time 2 when the inverter unit 2 starts restarting is 10% of the maximum duty, and is 10 every half cycle of the AC conversion frequency (inverter frequency). Increase by%. In the embodiment of the present invention, the maximum duty is set to 8 μS, which increases from 0.8 μS of 10% in steps of 0.8 μS in increments of 10 μS at time t2, and becomes 100% at time t3 when 100 μS has elapsed. It becomes 8 μS of. Therefore, as shown in FIG. 3A, the primary winding current Ip of the transformer 3 becomes a current waveform in which the width and the amplitude gradually increase from time t2 to t3.

As described above, when the overcurrent detection unit 8 generates the overcurrent signal OCP (when switching from Low to High), the control unit 25 of the inverter unit 2 switches the stop signal St from Low to High for 100 μS. After pausing, the stop signal St is switched from High to Low, restarted by soft start in a period of 100 μS, and overcurrent protection operation is performed. However, in a short period of about 100 μS, the transformer 3 is not demagnetized, and the demagnetized state of the transformer 3 remains. Therefore, if the state in which this overcurrent flows is repeated too frequently, a high temperature portion called a heat spot is generated due to the repeated flow of the overcurrent in the semiconductor chips of the switching elements 21 to 24, resulting in secondary breakdown. Will be caused, and the switching elements 21 to 24 will be damaged.

As a countermeasure, in the embodiment of the present invention, when the overcurrent protection operation is repeated eight times in 3 mS, the control unit 25 of the inverter unit 2 switches the stop signal St to High and changes the High state. Hold. Therefore, since the stop signal St is kept in the high state, the drive unit 26 stops the operation of the switching elements 21 to 24 of the inverter unit 2. The reason why the number of times is set to 8 times in 3 mS is that the period during which the maximum collector current of the IGBTs used in the switching elements 21 to 24 can flow continuously and repeatedly is limited to several mS. Therefore, the maximum on-time Ton = 8 μS of the switching elements 21 to 24, the pause time T = 100 μS during overcurrent protection, the repeated detection time of the overcurrent protection operation Ts = 3 mS, and the number of repeated detections of the overcurrent protection operation Ns = 8. In the case of times, the time during which a current close to the maximum collector current flows from the switching element 21 to 24 can be obtained by the following equation.
(Ton / T) x Ts x Ns = (8/100) x 3 mS x 8 = 1.92 mS
By suppressing the time during which a current close to the maximum collector current is flowing within a few mS, the secondary yield of the IGBT is prevented. The control unit 25 of the inverter unit 2 holds the stop signal St in High until the operator turns off the power switch of the welding power supply device. Therefore, the inverter until the power switch of the welding power supply device is turned off. Part 2 keeps the stopped state. By this measure, the operation of the inverter unit 2 can be stopped before the secondary yield of the switching elements 21 to 24 is reached, and the damage due to the secondary yield of the switching elements 21 to 24 can be prevented.

As described above, the transformer 3 after the overcurrent protection is temporarily stopped has not been sufficiently degaussed and is in a demagnetized state. Therefore, the maximum duty width during which the switching elements 21 to 24 can be turned on is maximum. When restarted at, the overcurrent signal OCP at time t1 in the figure (c) immediately returns to the time point at which it switches from Low to High. Therefore, by gradually expanding to the maximum duty in the period from time t2 to t3, the temporary stop due to the overcurrent due to the demagnetization of the transformer 3 does not occur frequently again, and by restarting by this soft start. , The frequency of pauses due to overcurrent protection can be reduced, the overcurrent detection unit 8 can prevent the overcurrent signal OCP from being generated 8 times or more in 3 mS, and the secondary yield of the switching elements 21 to 24 can be reduced. This has the effect of reducing the frequency with which the inverter unit 2 falls into a stopped state in order to prevent the above.

1 DC power supply 2 Inverter 3 Transformer 4 Welding output 6 DC reactor 7 Arc load 8 Overcurrent detector 21 to 24 Switching element 25 Control 26 Drive 51, 52 Diode CT Current detector Ip Primary winding current Id Primary Current value Iw Welding current St Stop signal Vs Overcurrent detection reference value PWM Switching element drive signal

Claims (2)

Inverter section that converts DC power to high frequency power,
A transformer that converts the high-frequency power generated by the inverter unit into a predetermined voltage, and
A current detector that detects the current flowing through the primary winding of the transformer, and
An overcurrent detector that generates an overcurrent signal when the current value detected by the current detector exceeds the reference value, and
A welding output unit that rectifies high-frequency power converted to the predetermined voltage by the secondary winding of the transformer into DC power, and
Is equipped with
When the overcurrent detector emits the overcurrent signal, the inverter unit temporarily stops the operation and then restarts the inverter unit, and stops the operation when the overcurrent signal is generated a predetermined number of times within a predetermined time. ,
A welding power supply that is characterized by this. When the inverter unit is restarted after temporarily stopping the operation, the on-time of the switching element of the inverter unit is gradually increased.
The welding power supply device according to claim 1.

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