Control circuit and power converter equipped with said control circuit

Abstract

The present invention provides a power converter and control circuit that can prevent false firing without adding any circuitry. [Solution] A control circuit 5 that controls a power conversion circuit (inverter circuit 2) having switching elements TR1 and TR2 connected in series performs a charging operation by turning switching element TR2 on and off a predetermined number of times N1 while keeping switching element TR1 off, before the start of the power conversion operation by switching elements TR1 and TR2. The charging operation charges the reverse bias capacitor Cs of the drive circuit 62 that drives the switching element TR2. Therefore, the power conversion device A1 can prevent the switching element TR2 from misfiring due to insufficient charging of the reverse bias capacitor.

Description

Technical Field

[0001] The present invention relates to a control circuit for controlling a power conversion circuit and a power conversion device including the control circuit.

Background Art

[0002] There is a drive circuit for driving a switching element that includes a reverse bias capacitor. The reverse bias capacitor is charged when the switching element is on and applies a reverse bias voltage to the switching element when it is off. For example, when the high-side switching element turns on, a voltage dV / dt with a large rate of change is applied to the low-side switching element. At this time, a pulse current corresponding to the capacitance of the parasitic capacitor flows through the low-side switching element, and when the voltage between the gate and emitter rises and exceeds the threshold voltage, misfiring occurs. If the reverse bias capacitor is sufficiently charged, the voltage between the gate and emitter does not exceed the threshold voltage, so misfiring can be prevented. However, immediately after the start of the power conversion operation, the reverse bias capacitor is not yet sufficiently charged, so the reverse bias voltage may be insufficient and misfiring may occur. Various methods for preventing such misfiring have been proposed.

[0003] For example, a method is known in which a capacitor is added in parallel between the gate and emitter to increase the gate charge amount of the switching element, thereby suppressing the rate of change (dV / dt) of the gate voltage. However, in this method, the rise speed during turn-on and the fall speed during turn-off decrease, so the switching loss increases. In addition, it is necessary to add a capacitor.

[0004] Patent Document 1 discloses a gate drive circuit that can prevent false firing by another method. In this gate drive circuit, a short-circuit transistor is connected between the gate and emitter of the IGBT, and the short-circuit transistor is turned off only when the voltage of the reverse bias capacitor is above a predetermined value. In this gate drive circuit, false firing can be prevented because the gate and emitter are short-circuited by the short-circuit transistor when the voltage of the reverse bias capacitor is low. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 7-15949 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, the invention described in Patent Document 1 requires the addition of a circuit for detecting the voltage of the reverse bias capacitor and comparing it to a predetermined value, as well as a short-circuit transistor. Consequently, the circuit configuration of the gate drive circuit becomes more complex. Furthermore, the added circuits increase the size of the gate drive circuit and increase manufacturing costs.

[0007] The present invention was conceived under the circumstances described above, and its objective is to provide a power conversion device and control circuit that can prevent false firing without adding any circuits. [Means for solving the problem]

[0008] To solve the above problems, the present invention employs the following technical means.

[0009] A control circuit provided by a first aspect of the present invention is a control circuit for controlling a power conversion circuit having a first switching element and a second switching element connected in series, wherein, before the start of the power conversion operation by the first switching element and the second switching element, a charging operation is performed in which the second switching element is turned on and off a first predetermined number of times while the first switching element remains off.

[0010] In a preferred embodiment of the present invention, during the charging operation, the first switching element is turned on and off a second predetermined number of times while the second switching element remains off.

[0011] In a preferred embodiment of the present invention, the first switching element is located on the high side, and the second switching element is located on the low side.

[0012] In a preferred embodiment of the present invention, the power conversion circuit further comprises a third switching element and a fourth switching element connected in series, wherein the third switching element is located on the high side and the fourth switching element is located on the low side, and during the charging operation, the third switching element is kept off while the fourth switching element is turned on and off a predetermined number of times.

[0013] A power conversion device provided by a second aspect of the present invention comprises a control circuit provided by a first aspect of the present invention, the power conversion circuit, a first drive circuit that outputs a first drive signal to the first switching element, and a second drive circuit that outputs a second drive signal to the second switching element, wherein the second drive circuit includes a reverse bias capacitor that outputs a reverse bias voltage when the second switching element is off, and the control circuit charges the reverse bias capacitor by the charging operation. [Effects of the Invention]

[0014] According to the present invention, the control circuit performs a charging operation by turning the second switching element on and off a predetermined number of times while keeping the first switching element off before the start of the power conversion operation. This charging operation charges the reverse bias capacitor of the second drive circuit. Therefore, the power conversion device according to the present invention can prevent the second switching element from misfiring due to insufficient charging of the reverse bias capacitor. Furthermore, the power conversion device according to the present invention only requires a change in the control circuit and does not require the addition of a new circuit to the drive circuit.

[0015] Other features and advantages of the present invention will become more apparent from the detailed description below with reference to the accompanying drawings. [Brief explanation of the drawing]

[0016] [Figure 1] This figure shows the overall configuration of a welding power supply device equipped with a power converter according to the first embodiment. [Figure 2] This is a timing chart showing the signals of the power converter according to the first embodiment. [Figure 3] This is a timing chart showing the signals of a first modified example of the power converter according to the first embodiment. [Figure 4] This is a timing chart showing the signals of a second modified example of the power converter according to the first embodiment. [Figure 5] This figure shows the overall configuration of the power conversion device according to the second embodiment. [Figure 6] This figure shows the overall configuration of a welding power supply device equipped with a power conversion device according to the third embodiment. [Modes for carrying out the invention]

[0017] Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings, using a welding power supply device equipped with the power conversion device according to the present invention as an example.

[0018] [First Embodiment] FIG. 1 is a diagram for explaining a power conversion device A1 according to the first embodiment, and is a diagram showing the overall configuration of a welding power supply device including the power conversion device A1.

[0019] The welding power supply device generates an arc between the tip of the electrode of the welding torch B and the workpiece W, and supplies power to the arc. The welding power supply device includes a DC power supply 1, a power conversion device A1, a transformer 3, a rectifier circuit 4, and a current sensor 7. The power conversion device A1 includes an inverter circuit 2, a control circuit 5, and drive circuits 61 to 64.

[0020] The DC power supply 1 outputs a DC voltage, and includes, for example, a rectifier circuit that rectifies an AC voltage input from the power system and a smoothing capacitor. Note that the configuration of the DC power supply 1 is not limited, and any device that outputs a DC voltage to the inverter circuit 2 may be used.

[0021] The inverter circuit 2 converts the DC voltage input from the DC power supply 1 into a high-frequency voltage and outputs it to the transformer 3. The inverter circuit 2 is a single-phase full-bridge type inverter and includes four switching elements TR1 to TR4. In this embodiment, MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) are used as the switching elements TR1 to TR4. Note that the switching elements TR1 to TR4 are not limited to MOSFETs, and may be IGBTs (Insulated Gate Bipolar Transistors), bipolar transistors, or the like.

[0022] Switching elements TR1 and TR2 are connected in series, with the source terminal of TR1 connected to the drain terminal of TR2. The drain terminal of TR1 is connected to the positive side of DC power supply 1, and the source terminal of TR2 is connected to the negative side of DC power supply 1, forming a bridge structure. Switching elements TR3 and TR4 are connected in series, with the source terminal of TR3 connected to the drain terminal of TR4. The drain terminal of TR3 is connected to the positive side of DC power supply 1, and the source terminal of TR4 is connected to the negative side of DC power supply 1, forming a bridge structure. Each of the switching elements TR1 to TR4 has a freewheeling diode connected in antiparallel.

[0023] The gate terminal of switching element TR1 receives a drive signal output from drive circuit 61. The gate terminal of switching element TR2 receives a drive signal output from drive circuit 62. The gate terminal of switching element TR3 receives a drive signal output from drive circuit 63. The gate terminal of switching element TR4 receives a drive signal output from drive circuit 64. Each switching element TR1 to TR4 can be switched on and off based on the drive signal. This converts the DC voltage into a high-frequency voltage. The high-frequency voltage is output from the output line connected to the connection point between switching element TR1 and switching element TR2, and from the output line connected to the connection point between switching element TR3 and switching element TR4. Switching elements TR1 and TR3 are located on the positive side of the DC power supply 1, and are therefore high-side switching elements. Switching elements TR2 and TR4 are located on the negative side of the DC power supply 1, and are therefore low-side switching elements.

[0024] Transformer 3 transforms the high-frequency voltage output by inverter circuit 2 and outputs it to rectifier circuit 4. Transformer 3 comprises a primary winding 31 and a secondary winding 32. One input terminal of primary winding 31 is connected to the connection point between switching elements TR1 and TR2. The other input terminal is connected to the connection point between switching elements TR3 and TR4. One output terminal of secondary winding 32 is connected to one input terminal of rectifier circuit 4, and the other output terminal is connected to the other input terminal of rectifier circuit 4. The secondary winding 32 is provided with a center tap in addition to the two output terminals. The primary winding 31 and secondary winding 32 are each wound around a core (not shown) and are magnetically coupled to each other. The configuration of transformer 3 is not limited.

[0025] The rectifier circuit 4 is a full-wave rectifier circuit using the center tap of the transformer 3, rectifying the high-frequency current output by the transformer 3 and outputting it as a DC current. The rectifier circuit 4 comprises two rectifier diodes 41 and 42 and a DC reactor 43. The anode terminals of the rectifier diodes 41 and 42 are connected to the respective output terminals of the secondary winding 32 of the transformer 3, and their cathode terminals are connected to each other. The DC reactor 43 is connected in series between the connection point on the cathode side of the rectifier diodes 41 and 42 and the output terminal a of the welding power supply, stabilizing the output current. The center tap of the transformer 3 is connected to the output terminal b of the welding power supply. The DC current output by the rectifier circuit 4 flows to the welding torch B as the welding current. Note that the configuration of the rectifier circuit 4 is not limited.

[0026] The current sensor 7 is located on the connection line between the center tap of the transformer 3 and output terminal b. It detects the output current of the welding power supply and outputs it to the control circuit 5 as a current detection signal. The placement of the current sensor 7 is not limited.

[0027] The control circuit 5 controls the inverter circuit 2 and is implemented, for example, by a microcomputer. When the control circuit 5 receives an ON operation signal from the torch switch 59, it generates control signals S1 to S4 to control the inverter circuit 2 and outputs them to the drive circuits 61 to 64, respectively. A detailed explanation of the control circuit 5 will be given later.

[0028] Each of the drive circuits 61 to 64 generates a drive signal based on the control signals S1 to S4 input from the control circuit 5. Drive circuit 61 outputs the drive signal generated based on control signal S1 to the switching element TR1. Drive circuit 62 outputs the drive signal generated based on control signal S2 to the switching element TR2. Drive circuit 63 outputs the drive signal generated based on control signal S3 to the switching element TR3. Drive circuit 64 outputs the drive signal generated based on control signal S4 to the switching element TR4. The drive signal is a signal obtained by amplifying the control signals to a high voltage.

[0029] The drive circuit 61 is powered by a power supply 69. The power supply 69 includes, for example, a pulse transformer and a rectifier / smoothing circuit, which rectifies and smooths the pulse current input via the pulse transformer and supplies it to the drive circuit 61. The configuration of the power supply 69 is not limited. The drive circuit 61 includes a push-pull circuit Sw, a resistor Rp, capacitors Cp and Cs, and a diode Ds.

[0030] The push-pull circuit Sw is a circuit in which an NPN transistor and a PNP transistor are connected in series. In the push-pull circuit Sw, the control signal S1 is input to the base terminal of each transistor, and a drive signal, which is an amplified version of the control signal S1, is output from the connection point between the NPN transistor and the PNP transistor. Note that the drive circuit 61 may include other amplification circuits instead of the push-pull circuit Sw.

[0031] Capacitor Cp has one end connected to the output terminal of the push-pull circuit Sw and the other end connected to the gate terminal of the switching element TR1. Capacitor Cp functions as a speed-up capacitor. Resistor Rp is connected in parallel with capacitor Cp. Resistor Rp functions as a limiting resistor to allow a small current to flow when the switching element TR1 is turned on.

[0032] Capacitor Cs has one end connected to the reference potential terminal of the push-pull circuit Sw and the other end connected to the source terminal of the switching element TR1. Capacitor Cs is charged when the switching element TR1 is ON and functions as a reverse bias capacitor, applying a reverse bias voltage between the gate and source when the switching element TR1 is OFF. Diode Ds is connected in parallel with capacitor Cp. The cathode terminal of diode Ds is connected to the source terminal of the switching element TR1 and the anode terminal is connected to the reference potential terminal of the push-pull circuit Sw. Diode Ds is a Zener diode and limits the charging voltage of capacitor Cs. The configuration of drive circuits 62 to 64 is the same as that of drive circuit 61.

[0033] When the control circuit 5 receives an ON operation signal from the torch switch 59, it outputs control signals S1 to S4 to control each of the switching elements TR1 to TR4 in the inverter circuit 2. The drive circuits 61 to 64 each generate a drive signal based on the input control signals S1 to S4 and input it to the gate electrodes of each of the switching elements TR1 to TR4. In this embodiment, the control circuit 5 outputs a signal for charging operation (a charging signal, described later) before the signal for power conversion operation (a current control signal, described later) as control signals S1 to S4. In addition, in this embodiment, the control circuit 5 performs output current control and feedback controls the output current of the welding power supply based on the current signal input from the current sensor 7. The control method by the control circuit 5 is not limited. The control circuit 5 has a set value setting unit 51, a current control unit 52, a charging signal generation unit 53, and a control signal output unit 54 as its functional configuration.

[0034] The setting value setting unit 51 is a functional configuration for setting setting values. The operator sets the setting values ​​for each parameter of the welding conditions by operating an operating means (not shown). The setting value setting unit 51 changes the setting values ​​of the parameters in response to the operation signals input from the operating means. The setting value of the parameter being set is displayed on a display device (not shown). The operator changes the setting value to the desired value by operating the operating means while looking at the setting value displayed on the display device. The welding condition parameters include welding current and welding voltage. The setting value setting unit 51 outputs the set welding current setting value as a current command value to the current control unit 52.

[0035] The current control unit 52 is a functional configuration for controlling the output current of the welding power supply unit. The current control unit 52 feedback-controls the output current of the welding power supply unit based on the current detection signal input from the current sensor 7. Specifically, the current control unit 52 generates current control signals Sa1 to Sa4 based on the difference between the current value corresponding to the current detection signal and the current command value input from the set value setting unit 51, and outputs the current control signals Sa1 to Sa4 to the control signal output unit 54. The current control signals Sa1 to Sa4 are signals for controlling the switching elements TR1 to TR4, respectively. The inverter circuit 2 performs power conversion operations according to the current control signals Sa1 to Sa4.

[0036] The charging signal generation unit 53 is a functional configuration for generating charging signals Sb1 to Sb4. Charging signals Sb1 to Sb4 are signals that cause the inverter circuit 2 to perform a charging operation to charge the capacitors Cs of the drive circuits 62 and 64. The charging operation involves keeping the high-side switching elements TR1 and TR3 off while switching the low-side switching elements TR2 and TR4 on and off a predetermined number of times N1. Charging signals Sb1 to Sb4 are signals for controlling the switching elements TR1 to TR4, respectively. Charging signals Sb1 and Sb3 are low-level signals. Charging signals Sb2 and Sb4 are signals that switch between low-level and high-level signals a predetermined number of times N1. The predetermined number of times N1 is, for example, 3 times in this embodiment, but is not limited to this. The predetermined number of times N1 is the number of times the voltage of the capacitor Cs can be charged to a predetermined voltage V0, and is preset based on experiments or simulations. The charging signal generation unit 53 outputs the generated charging signals Sb1 to Sb4 to the control signal output unit 54.

[0037] The control signal output unit 54 is configured to output control signals S1 to S4. When an ON operation signal is input from the torch switch 59, the control signal output unit 54 outputs the charging signals Sb1 to Sb4 generated by the charging signal generation unit 53 as control signals S1 to S4. After all charging signals Sb1 to Sb4 have reached a low level, the current control unit 52 outputs the current control signals Sa1 to Sa4. The inverter circuit 2 switches each switching element TR1 to TR4 on and off according to the control signals S1 to S4. As a result, the inverter circuit 2 performs a charging operation according to the charging signals Sb1 to Sb4 before starting the power conversion operation according to the current control signals Sa1 to Sa4.

[0038] Figure 2 is a timing chart showing the signals of power converter A1. Figure (a) shows the time variation of control signal S1. Figure (b) shows the time variation of control signal S2. Figure (c) shows the time variation of control signal S3. Figure (d) shows the time variation of control signal S4. Figure (e) shows the time variation of the voltage V2 across capacitor Cs of drive circuit 62. Although not shown, the time variation of the voltage V4 across capacitor Cs of drive circuit 64 is similar to that shown in Figure (e).

[0039] At time t0, the torch switch 59 is pressed, and an ON operation signal is input. As a result, the control circuit 5 outputs control signals S1 to S4. The control signal output unit 54 first outputs the charging signals Sb1 to Sb4 generated by the charging signal generation unit 53 as control signals S1 to S4. In this embodiment, charging signals Sb1 to Sb4 are output from time t0 to time t7, and the inverter circuit 2 performs a charging operation. The period during which charging signals Sb1 to Sb4 are output is called the charging operation period. As shown in Figures 2(a) and (c), during the charging operation period, control signals S1 and S3 (charging signals Sb1 and Sb3) are low-level signals. On the other hand, as shown in Figures 2(b) and (d), during the charging operation period, control signals S2 and S4 (charging signals Sb4 and Sb4) are signals that are switched between low level and high level a predetermined number of times N1 (3 times).

[0040] From time t1 to time t2, control signals S2 and S4 are at a high level. During this period, in inverter circuit 2, switching elements TR1 and TR3 are off, and switching elements TR2 and TR4 are on. As a result, the capacitor Cs of drive circuit 62 (64) is charged, and as shown in Figure 2(e), the voltage V2 (V4) rises. Subsequently, from time t2 to time t3, control signals S2 and S4 are at a low level. During this period, in inverter circuit 2, all switching elements TR1 to TR4 are off. As a result, charging of the capacitor Cs of drive circuit 62 (64) stops, and as shown in Figure 2(e), the voltage V2 (V4) does not change.

[0041] Similarly, during the period from time t3 to time t4, and from time t5 to time t6, the capacitor Cs of the drive circuit 62(64) is charged, and the voltage V2(V4) rises. At time t6, the voltage V2(V4) is approximately the predetermined voltage V0, and each capacitor Cs is sufficiently charged.

[0042] Subsequently, from time t7, the control signal output unit 54 outputs the current control signals Sa1 to Sa4 generated by the current control unit 52 as control signals S1 to S4. The inverter circuit 2 performs power conversion operations according to the current control signals Sa1 to Sa4. The period during which the current control signals Sa1 to Sa4 are output is defined as the power conversion operation period. As shown in Figures 2(a) to (d), during the power conversion operation period, control signals S1 and S4 (current control signals Sa1 and Sa4) are simultaneously at a high level, and during this period, control signals S2 and S3 (current control signals Sa2 and Sa3) are at a low level. Conversely, control signals S2 and S3 (current control signals Sa2 and Sa3) are simultaneously at a high level, and during this period, control signals S1 and S4 (current control signals Sa1 and Sa4) are at a low level. Although not shown in Figure 2, after control signals S1 and S4 switch from high level to low level, a dead time is provided during which all control signals S1 through S4 are at a low level before control signals S2 and S3 switch to high level.

[0043] At time t7, when the power conversion operation starts, even if the control signal S1 becomes high and the switching element TR1 turns on, the voltage V2 is around the predetermined voltage V0 and the capacitor Cs of the drive circuit 62 is sufficiently charged, so false firing of the switching element TR2 can be prevented. Also, at time t8, even if the control signal S3 becomes high and the switching element TR3 turns on, the voltage V4 is around the predetermined voltage V0 and the capacitor Cs of the drive circuit 64 is sufficiently charged, so false firing of the switching element TR4 can be prevented.

[0044] Next, the effects of the power converter A1 and the control circuit 5 will be explained.

[0045] According to this embodiment, before the start of the power conversion operation, the control circuit 5 performs a charging operation by turning the low-side switching elements TR2 and TR4 on and off a predetermined number of times N1 while keeping the high-side switching elements TR1 and TR3 off. This charging operation charges the capacitors Cs of the drive circuits 62 and 64. Therefore, the power converter A1 can prevent false firing of the switching elements TR2 and TR4 due to insufficient charging of the capacitors Cs of the drive circuits 62 and 64. Furthermore, the power converter A1 only requires a change in the control by the control circuit 5 compared to a conventional power converter, and does not require the addition of new circuits to the drive circuits 61 to 64.

[0046] In the first embodiment described above, the charging operation was described as an operation in which only the capacitors Cs of the drive circuits 62 and 64 are charged, but it is not limited to this. For example, the charging operation may be an operation in which all the capacitors Cs of the drive circuits 61 to 64 are charged. Generally, false firing due to insufficient charging of capacitors Cs often occurs in low-side switching elements. Therefore, in the above embodiment, in order to prevent false firing of low-side switching elements, which are prone to false firing, and to shorten the time required for the charging operation, the charging operation is set to charge only the capacitors Cs of the drive circuits 62 and 64 of the low-side switching elements TR2 and TR4. However, in order to prevent false firing due to insufficient charging of capacitors Cs from occurring in high-side switching elements as well, a charging operation that charges all the capacitors Cs of the drive circuits 61 to 64 is preferable.

[0047] The following describes a first modified example in which the charging signal generation unit 53 generates charging signals Sb1 to Sb4 for a charging operation that charges all capacitors Cs in the drive circuits 61 to 64.

[0048] The charging operation according to the first modified example involves keeping the high-side switching elements TR1 and TR3 off, switching the low-side switching elements TR2 and TR4 on and off a predetermined number of times N1, and then, keeping the low-side switching elements TR2 and TR4 off, switching the high-side switching elements TR1 and TR3 on and off a predetermined number of times N2. The charging signal generation unit 53 according to the first modified example sets the charging signals Sb1 and Sb3 to a low level while switching the charging signals Sb2 and Sb4 between a low level and a high level a predetermined number of times N1, and then sets the charging signals Sb2 and Sb4 to a low level while switching the charging signals Sb1 and Sb3 between a low level and a high level a predetermined number of times N2. In this modified example, the predetermined number of times N2 is, for example, 3, the same as the predetermined number of times N1, but is not limited to this. The predetermined number of times N2 may be different from the predetermined number of times N1. The predetermined number of cycles N2 is the number of times the voltage of the capacitor Cs in the drive circuits 61 and 63 can be charged to a predetermined voltage V0, and is set in advance based on experiments or simulations.

[0049] Figure 3 is a timing chart showing each signal of the first modified example. Figures 3(a) to (d), like Figures 2(a) to (d), show the time variation of control signals S1 to S4, respectively. Figure 3(e) shows the time variation of the voltage V1 across capacitor Cs of drive circuit 61. Although not shown, the time variation of the voltage V3 across capacitor Cs of drive circuit 63 is the same as in Figure 3(e). Figure 3(f) shows the time variation of the voltage V2 across capacitor Cs of drive circuit 62. Although not shown, the time variation of the voltage V4 across capacitor Cs of drive circuit 64 is the same as in Figure 3(f).

[0050] In the first modified example, the charging operation period is from time t0 to time t13. As shown in Figures 3(a) to (d), in the first modified example, the time variation of control signals S1 to S4 from time t0 to time t7 is the same as in Figure 2. Also, as shown in Figure 3(f), the time variation of voltage V2 from time t0 to time t7 is the same as in Figure 2. During this period, the control signals S1 and S3 (charging signals Sb1 and Sb3) are at a low level, and the switching elements TR1 and TR3 are off, so as shown in Figure 3(e), the voltage V1 (V3) does not change.

[0051] From time t7 to time t13, as shown in Figures 3(b) and (d), the control signals S2 and S4 (charging signals Sb4 and Sb4) are low-level signals. On the other hand, as shown in Figures 3(a) and (c), the control signals S1 and S3 (charging signals Sb1 and Sb3) are signals that switch between low and high levels a predetermined number of times N2 (3 times).

[0052] From time t7 to time t8, control signals S1 and S3 are at a high level. During this period, in inverter circuit 2, switching elements TR2 and TR4 are off, and switching elements TR1 and TR3 are on. As a result, the capacitor Cs in drive circuit 61 (63) is charged, and the voltage V1 (V3) rises. Subsequently, from time t8 to time t9, control signals S1 and S3 are at a low level. During this period, in inverter circuit 2, all switching elements TR1 to TR4 are off. As a result, charging of the capacitor Cs in drive circuit 61 (63) stops, and the voltage V1 (V3) does not change.

[0053] Similarly, during the period from time t9 to time t10, and from time t11 to time t12, the capacitors Cs of the drive circuit 61 (63) are charged, and the voltage V1 (V3) rises. At time t12, the voltage V1 (V3) is approximately the predetermined voltage V0, and each capacitor Cs is sufficiently charged.

[0054] Subsequently, from time t13, the control signal output unit 54 outputs the current control signals Sa1 to Sa4 generated by the current control unit 52 as control signals S1 to S4. At time t13, when the power conversion operation starts, even if the control signal S1 (S4) goes high and the switching element TR1 (TR4) turns on, the voltage V2 (V3) is around the predetermined voltage V0 and the capacitor Cs of the drive circuit 62 (63) is sufficiently charged, so false firing of the switching element TR2 (TR3) can be prevented. Also, at time t14, even if the control signal S2 (S3) goes high and the switching element TR2 (TR3) turns on, the voltage V1 (V4) is around the predetermined voltage V0 and the capacitor Cs of the drive circuit 61 (64) is sufficiently charged, so false firing of the switching element TR1 (TR4) can be prevented.

[0055] In this modified example, the case where the low-side capacitor Cs is charged first, followed by the high-side capacitor Cs, is described, but this is not the only case. The high-side capacitor Cs may be charged first, followed by the low-side capacitor Cs. Furthermore, the charging operation may differ from the above, and may only charge the capacitors Cs of the drive circuits 61 and 63.

[0056] In the first embodiment described above, the charging operation was described as an operation in which the capacitors Cs of the drive circuits 62 and 64 are charged simultaneously, but it is not limited to this. For example, the charging operation may be an operation in which the capacitor Cs of the drive circuit 62 is charged first, and then the capacitor Cs of the drive circuit 64 is charged.

[0057] The following describes a second modified example in which the charging signal generation unit 53 generates charging signals Sb1 to Sb4 for a charging operation in which the capacitor Cs of the drive circuit 62 is charged first, and then the capacitor Cs of the drive circuit 64 is charged.

[0058] The charging operation according to the second modified example involves first turning the low-side switching element TR2 on and off a predetermined number of times N1 while keeping the high-side switching elements TR1 and TR3 off, and then turning the low-side switching element TR4 on and off a predetermined number of times N1. While switching element TR2 is being turned on and off, switching element TR4 is off. Also, while switching element TR4 is being turned on and off, switching element TR2 is off. The charging signal generation unit 53 according to the second modified example sets the charging signals Sb1 and Sb3 to low-level signals. Furthermore, while the charging signal generation unit 53 switches the charging signal Sb2 between low and high levels a predetermined number of times N1, it sets the charging signal Sb4 to a low level, and then while switching the charging signal Sb4 between low and high levels a predetermined number of times N1, it sets the charging signal Sb2 to a low level.

[0059] Figure 4 is a timing chart showing each signal in the second modified example. Figures 4(a) to (d) show the time variation of control signals S1 to S4, similar to Figures 2(a) to (d). Figure 4(e) shows the time variation of the voltage V2 across capacitor Cs in the drive circuit 62, similar to Figure 2(e). Figure 4(f) shows the time variation of the voltage V4 across capacitor Cs in the drive circuit 64.

[0060] In the second modified example, the charging operation period is from time t0 to time t13. As shown in Figures 4(a) to (d), from time t0 to time t7, the control signals S1, S3, S4 (charging signals Sb1, Sb3, Sb4) are low-level signals. On the other hand, the control signal S2 (charging signal Sb2) is a signal that switches between low level and high level a predetermined number of times N1 (3 times). As shown in Figure 4(e), the time change of voltage V2 from time t0 to time t7 is the same as in Figure 2. On the other hand, as shown in Figure 4(f), the voltage V4 does not change during this period.

[0061] As shown in Figures 4(a) to (d), from time t7 to time t13, control signals S1, S2, S3 (charging signals Sb1, Sb2, Sb3) are low-level signals. On the other hand, control signal S4 (charging signal Sb4) is a signal that switches between low level and high level a predetermined number of times N1 (3 times). As shown in Figure 4(f), the time change of voltage V4 from time t7 to time t13 is the same as from time t1 to time t7 in Figure 4(e). On the other hand, as shown in Figure 4(e), voltage V2 does not change during this period.

[0062] Subsequently, from time t13, the control signal output unit 54 outputs the current control signals Sa1 to Sa4 generated by the current control unit 52 as control signals S1 to S4. At time t13, when the power conversion operation starts, even if the control signal S1 becomes high and the switching element TR1 turns on, the voltage V2 is at approximately the predetermined voltage V0 and the capacitor Cs of the drive circuit 62 is sufficiently charged, so false firing of the switching element TR2 can be prevented. Also, at time t14, even if the control signal S3 becomes high and the switching element TR3 turns on, the voltage V4 is at approximately the predetermined voltage V0 and the capacitor Cs of the drive circuit 64 is sufficiently charged, so false firing of the switching element TR4 can be prevented.

[0063] In this modified example, the case where the capacitor Cs of drive circuit 62 is charged first, followed by the charging of the capacitor Cs of drive circuit 64, is described, but this is not the only case. The capacitor Cs of drive circuit 64 may be charged first, followed by the charging of the capacitor Cs of drive circuit 62. Furthermore, the charging operation may differ from the above, and the capacitors Cs of drive circuits 61 to 64 may be charged one by one in sequence.

[0064] In the first embodiment, a welding power supply unit equipped with a power converter A1 was described as an example, but the invention is not limited to this. The power converter A1 may be used in devices other than a welding power supply unit.

[0065] [Second Embodiment] Figure 5 is a diagram illustrating a power converter A2 according to a second embodiment of the present invention, and shows the overall configuration of the power converter A2. In Figure 5, elements that are the same or similar as those in the above embodiment are denoted by the same reference numerals as in the above embodiment, and redundant explanations are omitted. The power converter A2 according to this embodiment differs from the power converter A1 according to the first embodiment in that the inverter circuit 2 is a three-phase full-bridge type inverter.

[0066] The inverter circuit 2 according to this embodiment is a three-phase full-bridge type inverter. The inverter circuit 2 is equipped with six switching elements TR1 to TR6. Switching elements TR5 and TR6 are connected in series, with the source terminal of switching element TR5 connected to the drain terminal of switching element TR6. The drain terminal of switching element TR5 is connected to the positive side of the DC power supply 1, and the source terminal of switching element TR6 is connected to the negative side of the DC power supply 1, forming a bridge structure.

[0067] In this embodiment, the control circuit 5 outputs control signals S1 to S6 to control each switching element TR1 to TR6 of the inverter circuit 2 when an ON operation signal is input from the start switch 58. In this embodiment, the charging signal generation unit 53 generates charging signals Sb1 to Sb6 to cause the inverter circuit 2 to perform a charging operation to charge the capacitors Cs of the drive circuits 62, 64, and 66. The charging operation in this embodiment is an operation in which the low-side switching elements TR2, TR4, and TR6 are turned on and off a predetermined number of times N1 while the high-side switching elements TR1, TR3, and TR5 are turned off. Charging signals Sb1, Sb3, and Sb5 are low-level signals. Charging signals Sb2, Sb4, and Sb6 are signals that have been switched between low level and high level a predetermined number of times N1.

[0068] The current control unit 52 generates current control signals Sa1 to Sa6 for power conversion operation and outputs these current control signals Sa1 to Sa6 to the control signal output unit 54. When the start switch 58 inputs an ON operation signal, the control signal output unit 54 outputs the charging signals Sb1 to Sb6 generated by the charging signal generation unit 53 as control signals S1 to S6, and after all charging signals Sb1 to Sb6 have become low levels, it outputs the current control signals Sa1 to Sa6 generated by the current control unit 52.

[0069] The power converter A2 according to this embodiment further includes drive circuits 65 and 66. Drive circuit 65 generates a drive signal based on a control signal S5 input from control circuit 5 and outputs the generated drive signal to switching element TR5. Drive circuit 66 generates a drive signal based on a control signal S6 input from control circuit 5 and outputs the generated drive signal to switching element TR6. The configuration of drive circuits 65 and 66 is the same as that of drive circuits 61 to 64.

[0070] According to this embodiment, before the start of the power conversion operation, the control circuit 5 performs a charging operation by turning the low-side switching elements TR2, TR4, TR6 on and off a predetermined number of times N1 while keeping the high-side switching elements TR1, TR3, TR5 off. This charging operation charges the capacitors Cs of the drive circuits 62, 64, and 66. Therefore, the power converter A2 can prevent false firing of the switching elements TR2, TR4, and TR6 due to insufficient charging of the capacitors Cs of the drive circuits 62, 64, and 66. Furthermore, the power converter A2 only requires a change in the control by the control circuit 5 compared to the conventional power converter, and does not require the addition of new circuits to the drive circuits 61 to 66. In addition, the power converter A2 has the same configuration as the power converter A1 and achieves the same effects as the power converter A1.

[0071] [Third Embodiment] Figure 6 is a diagram illustrating a power converter A3 according to a third embodiment of the present invention, and shows the overall configuration of a welding power supply device equipped with the power converter A3. In Figure 6, elements that are the same or similar as those in the above embodiments are denoted by the same reference numerals as in the above embodiments, and redundant explanations are omitted. The power converter A3 according to this embodiment differs from the power converter A1 according to the first embodiment in that the inverter circuit 2 is a single-phase half-bridge type inverter.

[0072] The inverter circuit 2 according to this embodiment is a single-phase half-bridge type inverter. The inverter circuit 2 is equipped with two switching elements TR1 and TR2, but does not have switching elements TR3 and TR4. Furthermore, the power converter A3 according to this embodiment does not have drive circuits 63 and 64.

[0073] In this embodiment, the control circuit 5 outputs control signals S1 and S2 to control the respective switching elements TR1 and TR2 of the inverter circuit 2 when an ON operation signal is input from the torch switch 59. In this embodiment, the charging signal generation unit 53 generates charging signals Sb1 and Sb2 to cause the inverter circuit 2 to perform a charging operation to charge the capacitor Cs of the drive circuit 62. The charging operation in this embodiment is an operation in which the low-side switching element TR2 is turned on and off a predetermined number of times N1 while the high-side switching element TR1 is kept off. The charging signal Sb1 is a low-level signal. The charging signal Sb2 is a signal that has been switched between a low level and a high level a predetermined number of times N1.

[0074] The current control unit 52 generates current control signals Sa1 and Sa2 for power conversion operation and outputs these current control signals Sa1 and Sa2 to the control signal output unit 54. When the torch switch 59 inputs an ON operation signal, the control signal output unit 54 outputs the charging signals Sb1 and Sb2 generated by the charging signal generation unit 53 as control signals S1 and S2. After all charging signals Sb1 and Sb2 have reached a low level, the control signal output unit 54 outputs the current control signals Sa1 and Sa2 generated by the current control unit 52.

[0075] According to this embodiment, before the start of the power conversion operation, the control circuit 5 performs a charging operation by turning the low-side switching element TR2 on and off a predetermined number of times N1 while keeping the high-side switching element TR1 off. This charging operation charges the capacitor Cs of the drive circuit 62. Therefore, the power converter A3 can prevent false firing of the switching element TR2 due to insufficient charging of the capacitor Cs of the drive circuit 62. Furthermore, the power converter A3 only requires a change in the control by the control circuit 5 compared to a conventional power converter, and does not require the addition of new circuits to the drive circuits 61 and 62. In addition, the power converter A3 has the same configuration as the power converter A1 and achieves the same effects as the power converter A1.

[0076] As can be seen from the first to third embodiments, the configuration of the inverter circuit 2 according to the present invention is not limited. Furthermore, although the first to third embodiments described a case in which the control circuit 5 outputs control signals to the drive circuits 61 to 66 that drive the switching elements TR1 to TR6 constituting the inverter circuit 2, the invention is not limited to this. The control circuit 5 according to the present invention can be applied when it outputs control signals to each of the drive circuits of two switching elements connected in series.

[0077] The control circuit and power conversion device according to the present invention are not limited to the embodiments described above. The specific configuration of each part of the control circuit and power conversion device according to the present invention can be modified in various ways. [Explanation of Symbols]

[0078] A1-A3: Power converter, 2: Inverter circuit, TR1-TR6: Switching element, 61-66: Drive circuit, Cs: Capacitor, 5: Control circuit

Claims

1. A control circuit for controlling a power conversion circuit having a first switching element and a second switching element connected in series, Before the power conversion operation by the first switching element and the second switching element begins, a charging operation is performed in which the second switching element is turned on and off a predetermined number of times while the first switching element remains off. Control circuit.

2. In the aforementioned charging operation, the first switching element is turned on and off a second predetermined number of times while the second switching element remains off. The control circuit according to claim 1.

3. The first switching element is located on the high side, and the second switching element is located on the low side. The control circuit according to claim 1.

4. The power conversion circuit further comprises a third switching element and a fourth switching element connected in series, The third switching element is located on the high side, and the fourth switching element is located on the low side. In the charging operation, the third switching element is also kept off, and the fourth switching element is turned on and off a predetermined number of times. The control circuit according to claim 3.

5. A control circuit according to any one of claims 1 to 4, The aforementioned power conversion circuit, A first drive circuit that outputs a first drive signal to the first switching element, A second drive circuit that outputs a second drive signal to the second switching element, Equipped with, The second drive circuit includes a reverse bias capacitor that outputs a reverse bias voltage when the second switching element is off. The control circuit charges the reverse bias capacitor by the charging operation. Power converter.

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