JP2012095442A - Welding power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a welding power supply device with less sputter, which uses a DC reactor DCL of a closed loop configuration.SOLUTION: The welding power supply device includes: a DC power supply circuit; an inverter circuit for turning a DC voltage to a high frequency AC voltage; a main transformer for attaining a voltage suitable for welding; a secondary rectifier circuit for rectifying the output of the main transformer; the DC reactor of a closed loop for smoothing the rectified output; an output current detection circuit for detecting an output current; a PID control circuit for inputting the output current and executing PID control; and a main control circuit for controlling the inverter circuit on the basis of PID control signals. The welding power supply device is provided with an inductance coefficient circuit for generating an inductance coefficient corresponding to the inductance value of the DC reactor and calculating the inductance coefficient on the basis of the output current, and the proportional gain, integration gain and differential gain of the PID control are changed based on the inductance coefficient in the PID control circuit to quicken the responsiveness of the PID control.

Description

  The present invention relates to PID control for controlling output of an inverter circuit in a welding power source apparatus.

  In conventional arc welding, the output in a small current region becomes unstable and arc breakage easily occurs. In order to prevent this problem, a DC reactor having a ring core (closed loop) configuration is used, and an arc value is suppressed by increasing an inductance value in a small current region.

FIG. 7 is an electrical connection diagram of a conventional welding power source apparatus. The operation of the prior art will be described with reference to FIG.
The DC power supply circuit shown in the figure is formed by a primary rectifier circuit DR1 that rectifies the output of the three-phase AC commercial power supply AC and converts it into a DC voltage, and a smoothing capacitor C1 that smoothes the voltage converted to the DC voltage. .

  The bridge-connected inverter circuit shown in FIG. 7 is formed by the first switching element TR1 to the fourth switching element TR4, and repeats conduction and interruption to convert a DC voltage into a high-frequency AC voltage.

  The transformer INT converts the high-frequency AC voltage into a voltage suitable for arc machining. The secondary rectifier circuit DR2 rectifies the output of the transformer INT and converts it into a DC voltage suitable for arc machining, and a DC reactor (having a closed loop configuration) DCL smoothes the rectified DC voltage and supplies it to the load.

  The output current detection circuit ID detects the output current and outputs it as an output current detection signal Id. The output current setting circuit IR sets a predetermined output current setting signal Ir.

  The conventional PID (proportional / integral / differential) control circuit shown in FIG. 8 obtains the difference between the value of the output current detection signal Id and the value of the output current setting signal Ir and outputs it as a differential signal Dd. , A first multiplier MD1 that multiplies the differential signal Dd by a predetermined proportional gain Kp and outputs it as a first multiplication signal Md1, and an integrator IC that integrates the differential signal Dd and outputs it as an integration signal Ic. And a second multiplier MD2 that multiplies the integrated signal Ic by a predetermined integral gain Ki and outputs the result as a second multiplied signal Md2, and a differentiator IC that differentiates the differential signal Dd and outputs it as a differentiated signal Ic. A third multiplier MD3 that multiplies the differential signal Ic by a predetermined differential gain Ki and outputs the result as a third multiplication signal Md3, a first multiplication signal Md1, a second multiplication signal Md2, and a third multiplication signal Md3. Add multiplication signal Md3 It is formed by an adder AD output as Pid control signal Te.

  The main control circuit SC performs pulse width modulation control that modulates the pulse width at a constant pulse frequency, performs pulse width modulation control according to the Pid control signal, and outputs the first output control signal Sc1 and the first output control signal Sc1 that are shifted from each other by a half cycle. 2 output control signal Sc2.

  The inverter drive circuit SR outputs a first switching element drive signal Tr1 to a fourth switching element drive signal Tr4 that drive the inverter circuit according to the first output control signal Sc1 and the second output control signal Sc2.

  FIG. 9 is a characteristic diagram of the output current value and the inductance value of the DC reactor DCL having a closed loop configuration. In the same figure, in the small current region (for example, 25 A), the inductance value increased to 50 μH, and using this characteristic, the inductance value in the small current region was increased to suppress arc interruption. However, when the proportional gain Kp, integral gain Ki, and differential gain Kd of the PID control circuit are set to predetermined values that, for example, the output current conforms to 100 A, the inductance value greatly changes in the small current region, and the respective gains are adapted. Sex will collapse.

  In the control method of the arc welder of Patent Document 1, PID control is described.

JP 2004-268095 A

In the conventional welding power source device, in order to suppress the arc break in the small current region, a DC reactor having a ring core (closed loop) configuration having the characteristics shown in FIG. 9 is used, and the inductance value in the small current region is increased. The arc break was suppressed. That is, in a DC reactor having a closed loop characteristic, as shown in FIG. 9, when the output current is in a small current region, for example, 50 A or less, the inductance value increases rapidly. Was suppressed.
However, in the PID control circuit, the proportional gain, integral gain, and differential gain are set so that the inductance value of the DC reactor is stable and the output current conforms to the value of 100 A. Therefore, the inductance of the DC reactor in a small current region When the value increases rapidly, the compatibility of the proportional gain, integral gain, and differential gain is lost, and the response of PID control is delayed. In this state, when the output current is reduced immediately after the transition from the arc state to the short circuit state to suppress the occurrence of sputtering, the output current oscillates due to the delay in the response of PID control, leading to an increase in the amount of sputtering.

  Therefore, an object of the present invention is to provide a welding power source apparatus that has a small amount of spatter and that is difficult to break an arc in a small current region.

  In order to solve the problems described above, the invention of claim 1 is directed to welding a DC power supply circuit that converts commercial AC power into DC voltage, an inverter circuit that converts the DC voltage into high frequency AC voltage, and the high frequency AC voltage. A main transformer for converting to an AC voltage suitable for the output, a secondary rectifier circuit for rectifying the output of the main transformer, a closed-loop DC reactor for smoothing the rectified output, and detecting the smoothed output current An output current detection circuit that controls the inverter circuit based on the PID control signal, a PID control circuit that performs PID control of the output current detection value and a predetermined output current set value and outputs the PID control signal as a PID control signal And a control circuit, generating an inductance coefficient corresponding to the inductance value of the DC reactor, and generating the output current detection value And a inductance coefficient circuit for calculating the inductance coefficient, and the PID control circuit changes a proportional gain, an integral gain and a differential gain of the PID control signal based on the inductance coefficient. Device.

  According to a second aspect of the present invention, the inductance coefficient circuit includes a predetermined first output current reference value and a predetermined second output current reference value that is larger than the first output current reference value. When the output current detection value is less than or equal to the first output current reference value, the first inductance coefficient is obtained; when the output current detection value is greater than or equal to the second output current reference value, the second inductance coefficient is obtained; 2. The welding power source device according to claim 1, wherein when the output current detection value increases from the first output current reference value toward the second output current reference value, the inductance coefficient continuously decreases. It is.

  The invention according to claim 3 is characterized in that the PID control circuit increases the proportional gain, integral gain, and differential gain when an inductance coefficient corresponding to the inductance value increases. It is.

  According to the present invention, in a welding power source apparatus that feeds back output power by PID control using a closed loop DC reactor, a change in the inductance value of the DC reactor is sequentially detected via an inductance coefficient, and the change in the inductance value is detected. By changing the proportional gain, integral gain, and derivative gain of PID control according to the PID control, the response of PID control in the small current region where the inductance value of the DC reactor increases becomes faster, and immediately after the transition from the arc state to the short circuit state When the current is reduced to suppress the occurrence of sputtering, the PID control response becomes faster and the oscillation of the output current can be prevented. By preventing this oscillation, the occurrence of spatter is reduced, leading to improved welding quality.

FIG. 3 is an electrical connection diagram of the welding power source apparatus according to the first embodiment. It is a detailed view of a PID control circuit and an inductance coefficient circuit. It is a correlation diagram of an output current value and an inductance coefficient. FIG. 6 is a waveform diagram for explaining the operation of the first embodiment. FIG. 5 is an electrical connection diagram of a welding power source device according to a second embodiment. 6 is a detailed diagram of a PID control circuit according to a second embodiment. FIG. It is an electrical connection figure of the welding power supply device of a prior art. It is a detailed view of a PID control circuit of the prior art. FIG. 6 is a characteristic diagram of an output current value and an inductance value of a closed loop DC reactor.

  FIG. 1 is an electrical connection diagram of the welding power source apparatus according to the first embodiment. In the figure, components having the same reference numerals as those in the electrical connection diagram of the conventional welding power source apparatus shown in FIG. 7 perform the same operations, and thus the description thereof will be omitted.

  The inductance coefficient circuit LO shown in FIG. 2 converts an inductance value that changes according to the value of the output current detection signal Id into an inductance coefficient L corresponding to the inductance value, and outputs it. When the value of the output current detection signal Id is smaller than a predetermined first output current reference value Ir1 (for example, 10 A), the inductance value 100 μH is converted into an inductance coefficient L = 10 by the inductance coefficient circuit LO shown in FIG. When the value of the output current detection signal Id is in the range of 10A to 40A, the inductance coefficient L is calculated from the inductance coefficient conversion formula of (−0.3Id + 13), and the inductance coefficient L decreases from 10 to 1. At this time, the inductance value corresponding to the inductance coefficient L = 10 to 1 continuously decreases from 100 μH to 10 μH. Next, the value of the output current detection signal Id is larger than the second output current reference value Ir2 (for example, 40 A), and the inductance value is converted from 10 μH to the inductance coefficient L = 1 and output.

  FIG. 3 is a correlation diagram between the output current detection value and the inductance coefficient when the inductance value of the DC reactor is converted into the inductance coefficient by the inductance coefficient circuit LO, and the value of the output current detection signal Id ranges from 10A to 40A. In this case, the inductance coefficient decreases from 10 to 1 in inverse proportion to the increase in the output current detection signal Id, and the inductance value at this time decreases from 100 μH to 10 μH.

  FIG. 2 is a detailed diagram of the PID control circuit. For example, when power is turned on, an initial proportional gain corresponding to an output current detection value of 100 A is set to Kpo, an integral gain is set to Kio, and a differential gain is set to Kdo. When the output current detection value changes in the range of 10A to 40A, the inductance coefficient L calculated from the inductance coefficient conversion formula of (−0.3Id + 13) is input to the formula of Kp = Kpo × (0.4L + 0.6). Then, an optimal proportional gain Kp is calculated, and the first multiplier MD1 multiplies the differential signal Dd by the calculated proportional gain Kp and outputs the result as the first multiplied signal Md1. Subsequently, the differential signal Dd is integrated by the integrator IC and output as the integrated signal Ic, and the optimum value calculated by the second multiplier MD2 from the integrated signal Ic and the equation Ki = Kio × (0.1L + 0.9). Is multiplied by the integral gain Ki and output as a second multiplied signal Md2. Further, the differential signal Dd is differentiated by the differentiator DC and output as the differential signal Dc, and the optimum signal calculated by the third multiplier MD3 from the differential signal Dc and the equation Kd = Kdo × (0.2L + 0.8). The product is multiplied by the differential gain Kd and output as a third multiplication signal Md3. The adder AD adds the first multiplication signal Md1, the second multiplication signal Md2, and the third multiplication signal Md3, and outputs the result as a Pid control signal.

  4A and 4B are waveform diagrams for explaining the operation of the first embodiment. FIG. 4A shows an output current waveform, and FIG. 4B shows an enlarged view of the output current waveform at the time of a short circuit.

Next, the operation of the first embodiment will be described with reference to FIGS.
When the transition from the short-circuit state to the arc state at time t = t1 shown in FIG. 4A and the value of the output current detection signal Id reaches 150 A, the inductance coefficient circuit LO shown in FIG. When larger than Ir2 (40A), the inductance value 10 μH is converted into an inductance coefficient L = 1 and output.

  The PID control circuit inputs an inductance coefficient L = 1, calculates from the equation of Kp = Kpo × (0.4L + 0.6), and sets the proportional gain Kp. At the same time, the integral gain Ki is set by calculating from the equation Ki = Kio × (0.1L + 0.9). Further, the differential gain Kd is set by calculating from the equation Kd = Kdo × (0.2L + 0.8). At this time, it becomes the same value as the proportional gain Kpo, the integral gain Kio, and the differential gain Kdo set before the time t = t1, for example, when the output current detection value is 100A.

  At time t = t1 to t2 shown in FIG. 4A, the value of the output current detection signal Id becomes 50A to 150A during arc generation, and the inductance coefficient circuit LO continues the inductance coefficient L = 1, and the PID control circuit Is multiplied by the differential signal Dd and the calculated proportional gain Kp by the first multiplier MD1 and output as the first multiplication signal Md1, and the integration signal Ic and the integration gain KI calculated by the second multiplier MD2 are output. Are multiplied and output as a second multiplication signal Md1, and the third multiplier MD3 multiplies the differential signal Dc by the calculated differential gain Kd and outputs the result as a third multiplication signal Md3. The adder AD adds the first multiplication signal Md1, the second multiplication signal Md2, and the third multiplication signal Md3, and outputs the result as a Pid control signal.

  The main control circuit SC performs pulse width modulation control according to the Pid control signal, and outputs a first output control signal Sc1 and a second output control signal Sc2 that are shifted from each other by a half cycle. At this time, the inductance value of the DC reactor DCL in the closed loop configuration is 10 μH from FIG.

  When the transition from the arc state to the short-circuit state at time t = t2, the output current is reduced to 25 A for a predetermined time, for example, 1 ms from the occurrence of the short-circuit in order to suppress the occurrence of spatter that occurs at the time of the short-circuit. Let At this time, in the prior art, the inductance coefficient of the DC reactor DCL is 1, and even if the inductance value shown in FIG. 9 is increased from 10 μH to 55 μH, the inductance coefficient does not change, and the increase in the inductance value delays the response of the PID control. As shown in FIG. 4B, the output current oscillates due to a delay in the response of the PID control, and spatter is generated and the amount of spatter increases.

  Therefore, in the present invention, when the value of the output current detection signal Id decreases to 25 A immediately after the transition from the arc state to the short-circuit state at time t = t2 shown in FIG. 4B, the inductance coefficient circuit LO becomes (− Inductance coefficient L = 1 is changed to 5.5 from the inductance coefficient conversion equation of 0.3Id + 13). At this time, the inductance value increases to 55 μH.

  The PID control circuit inputs the inductance coefficient L = 5, 5 and obtains the proportional gain corresponding to the output current detection value 25A from the equation of Kp = Kpo × (0.4L + 0.6). The proportional gain Kp at this time is Kp = 2.8 Kpo. At the same time, the integral gain corresponding to the output current detection value 25A is obtained from the equation Ki = Kio × (0.1L + 0.9). The integral gain ki at this time is Ki = 1.45Kio. Further, the differential gain corresponding to the output current detection value 25A is obtained from the equation of Kd = Kdo × (0.2L + 0.8). The differential gain Kd at this time is Kd = 1.9 Kdo.

  At time t = t2 to t3 shown in FIG. 4A, the PID control circuit increases the proportional gain, the integral gain, and the differential gain according to the increase of the inductance coefficient L = 5.5. The response of PID control becomes faster, and even if the inductance value of the DC reactor DCL increases to 55 μH when the output current value shown in FIG. 9 is 25 A, the output current shown in FIG. The amount of spatter that occurs when shifting from a short circuit to a short circuit is reduced.

  As described above, by changing the proportional gain, integral gain, and differential gain of PID control based on the inductance coefficient corresponding to the inductance value of DC reactor DCL, the responsiveness of feedback of PID control becomes faster, and the short-circuit state from the arc state When suppressing the occurrence of sputtering by reducing the current immediately after shifting to, the oscillation of the output current can be prevented by increasing the responsiveness of PID control, leading to a reduction in the occurrence of sputtering.

Explanation about the second embodiment.
In the first embodiment described above, the inductance coefficient circuit LO converts the inductance coefficient L corresponding to the inductance value based on the output current value, and inputs the converted inductance coefficient L to the PID control circuit. The proportional gain, integral gain, and derivative gain are changed based on this to control the responsiveness of PID control. However, the output current detection value is directly input to the current corresponding PID control circuit shown in FIG. In addition, the response speed of the PID control may be controlled by changing the differential gain.

This operation will be described with reference to FIGS.
At time t = t1 shown in FIG. 4A, when the state changes from the short-circuit state to the arc state and the value of the output current detection signal Id becomes 150 A, for example, the current corresponding PID control circuit shown in FIG. With the value 150A as an input, the proportional gain is calculated from the equation (Kpo × 1) shown in FIG. The proportional gain Kp at this time is Kp = Kpo. At the same time, the integral gain is calculated from the equation (Kio × 1). The integral gain Ki at this time is Ki = Kio. Further, the differential gain is calculated from the equation (Kdo × 1). At this time, the differential gain Kd is Kd = Kdo.

  At time t = t1 to t2 shown in FIG. 4A, when the value of the output current detection signal Id is 50A to 150A during arc generation, the current corresponding PID control circuit calculates the proportional gain Kp calculated at time t = t1. The integral gain Kd and the differential gain Ki are added and output as a Pid control signal.

  At time t = t2 shown in FIG. 4B, when the value of the output current detection signal Id decreases to 25A from the arc state to the short circuit state, the current corresponding PID control circuit inputs the output current detection value 25A. Thus, the proportional gain Kp at this time is Kp = 2.8 Kpo, calculated from the equation of Kp = Kpo × (−0.12Id + 5.8) shown in FIG. At the same time, it is calculated from the equation Ki = Kio × (−0.03Id + 2.2), and the integral gain Ki at this time is Ki = 1.45Kio. Further, it is calculated from an equation of Kd = Kdo × (−0.06Id + 3.4), and the differential gain Kd at this time is Kd = 1.9 Kdo.

  As described above, the changes in the proportional gain Kp, the integral gain Kd, and the differential gain Ki according to the change in the output current value are the same as those in the first embodiment.

AD Adder C1 Smoothing Capacitor DC Differentiator Dc Differentiated Signal DD Differential Differentiator Dd Differential Signal DCL DC Reactor (Closed Loop Configuration)
DR1 primary rectifier circuit DR2 secondary rectifier circuit ID output current detection circuit Id output current detection signal INT main transformer IC integrator Ic integration signal IR output current setting circuit Ir output current setting signal (output current setting value)
LO Inductance factor circuit L Inductance factor M Work piece MD1 First multiplier Md1 First multiplication signal MD2 Second multiplier Md2 Second multiplication signal MD3 Third multiplier Md3 Third multiplication signal PID PID control Circuit (proportional / integral / derivative control circuit)
Pid Pid control signal PIDI Current corresponding PID control circuit (proportional / integral / differential control circuit)
SC main control circuit Sc1 first output control signal Sc2 second output control signal SR inverter drive circuit TH torch TR1 first switching element TR2 second switching element TR3 third switching element TR4 fourth switching element Tr1 first 1 switching element drive signal Tr2 2nd switching element drive signal Tr3 3rd switching element drive signal Tr4 4th switching element drive signal

Claims (3)

  DC power supply circuit that converts commercial AC power into DC voltage, inverter circuit that converts the DC voltage into high-frequency AC voltage, main transformer that converts the high-frequency AC voltage into AC voltage suitable for welding, and the main transformer A secondary rectifier circuit for rectifying the output of the voltage generator, a closed-loop DC reactor for smoothing the rectified output, an output current detection circuit for detecting the smoothed output current, and the output current detection value In a welding power supply apparatus comprising: a PID control circuit that performs PID control of an output current set value and outputs the output current as a PID control signal; and a main control circuit that controls the inverter circuit based on the PID control signal. An inductor that generates an inductance coefficient corresponding to an inductance value and calculates the inductance coefficient based on the detected output current value The scan coefficient circuit is provided, the PID control circuit changes the proportional gain, integral gain and derivative gain of the PID control signal based on the inductance coefficient, it welding power supply apparatus according to claim.   The inductance coefficient circuit has a predetermined first output current reference value and a predetermined second output current reference value larger than the first output current reference value, and the output current detection value is the first output current reference value. The first inductance coefficient is selected when the output current reference value is less than or equal to 1, the second inductance coefficient is selected when the output current detection value is greater than or equal to the second output current reference value, and the output current detection value is 2. The welding power source device according to claim 1, wherein the inductance coefficient continuously decreases when the first output current reference value increases toward the second output current reference value.   The welding power supply apparatus according to claim 1, wherein the PID control circuit increases the proportional gain, integral gain, and differential gain when an inductance coefficient corresponding to the inductance value increases.

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