A device for realizing induction heating and DC demagnetization of a workpiece on the same coil

Abstract

The present invention provides a device for realizing induction heating and DC demagnetization of a workpiece on the same coil, characterized in that it includes a medium frequency induction heater output channel and a DC demagnetization current output channel, the medium frequency induction heater output channel and the DC demagnetization current output channel are connected to the same induction coil, and the medium frequency induction heater output channel and the DC demagnetization current output channel are electrically isolated from each other. The present invention only requires one device and a coil wound on a pipeline, and can output medium frequency induction heating current and DC demagnetization current on this coil at the same time, thereby realizing simultaneous heating and demagnetization. This not only simplifies on-site installation and operation, making operation simple, but more importantly, it ensures welding quality, and the equipment is highly reliable and not easily damaged.

Description

Technical Field

[0001] The invention relates to a device which can output medium frequency induction heating current and direct current demagnetization current on one coil at the same time, and can be applied to on-site pipeline construction and maintenance. Background Art

[0002] For oil and gas pipelines that are in the on-site construction stage or have already been built, geomagnetism, high-speed fluid, lightning, machining and other reasons may cause the pipeline to be magnetized, resulting in welding magnetic blow. The welding position, welding strength and non-destructive testing cannot meet the technical standards. Therefore, the pipe mouth needs to be demagnetized during welding. In addition, since the magnetism of long-distance pipelines exists in the entire pipeline (not just at the pipe mouth), continuous demagnetization is required during welding, that is, demagnetization is performed while welding.

[0003] When welding the pipe mouth, in addition to demagnetization, preheating treatment is also required (welding is completed at a certain basic temperature). This preheating treatment generally uses induction heating. Therefore, when welding the pipe mouth, induction heating and demagnetization are often required at the same time.

[0004] In order to achieve induction heating and demagnetization of the pipe mouth, the existing technical means require the use of two devices, an induction heater and a demagnetizer, at the same time, and a welding machine is also required to achieve welding of the pipe mouth. To this end, it is necessary to wind a medium-frequency induction coil and a medium-frequency induction coil on the pipeline. These two coils are respectively passed through the medium-frequency induction current of the induction heater and the DC demagnetization current of the demagnetizer, and the two cannot run at the same time. This leads to a complex on-site installation structure and cumbersome operating procedures. The more serious problem is that due to repeated cycles in the three processes of heating, demagnetization and welding, the welding process cannot be carried out continuously, resulting in unstable temperature of the pipe mouth during welding, affecting the welding quality. Moreover, due to the strong electromagnetic induction of the medium-frequency induction coil to the demagnetization coil, equipment with this structure is also easily damaged. Summary of the invention

[0005] The technical problem to be solved by the present invention is that: an induction heating machine and a demagnetizing machine need to be used simultaneously to realize induction heating and demagnetization of a pipe mouth.

[0006] In order to solve the above technical problems, the technical solution of the present invention is to provide a device for realizing induction heating and DC demagnetization of a workpiece on the same coil, characterized in that it includes an intermediate frequency induction heater output channel and a DC demagnetization current output channel, the intermediate frequency induction heater output channel and the DC demagnetization current output channel are connected to the same induction coil, and the intermediate frequency induction heater output channel and the DC demagnetization current output channel are electrically isolated from each other, wherein:

[0007] The inverter frequency f1 of the medium frequency induction heater output channel is between 5000Hz and 20000Hz; the maximum output medium frequency current of the medium frequency induction heater output channel The design range of is 200~1000A, and the design range of output medium frequency voltage U1 is 300~1000V;

[0008] The chopping frequency f2 of the DC demagnetization current output channel is between 8000Hz and 30000Hz; the maximum output current of the DC demagnetization current output channel is The design range is 200~800A, and the design range of output DC voltage U2 is 10~60V;

[0009] A resonant capacitor group is arranged in the output channel of the medium frequency induction heater, and the medium frequency AC voltage of the output channel of the medium frequency induction heater is loaded on the induction coil via the resonant capacitor group, and the DC voltage component generated after the DC demagnetization current output from the DC demagnetization current output channel is applied to the induction coil is isolated by the resonant capacitor group;

[0010] An LC filter circuit 1 composed of a reactor 1 and a filter capacitor group and an LC filter circuit 2 composed of a reactor 2 and a filter capacitor group are arranged in the DC demagnetization current output channel. The DC demagnetization current outputted by the DC demagnetization current output channel is loaded on the induction coil via the LC filter circuit 1 and the LC filter circuit 2. The LC filter circuit 1 is used to filter out the chopped AC component in the DC demagnetization current and suppress the pulsation caused by the DC chopping. The LC filter circuit 2 is used to eliminate the interference of the medium frequency induction heater output channel on the DC demagnetization current output channel.

[0011] Preferably, the induction heating power of the output channel of the medium frequency induction heater is independently adjustable from 0.1 kW to 80 kW.

[0012] Preferably, the DC demagnetization current of the DC demagnetization current output channel is independently adjustable from 0A to 400A.

[0013] Preferably, a three-phase rectifier bridge 1 is arranged in the output channel of the medium frequency induction heater, and the three-phase AC power supply is rectified by the three-phase rectifier bridge 1 to output a DC voltage, and the DC voltage first passes through the filter capacitor and then is input into the charging buffer circuit, and the DC voltage output by the charging buffer circuit is input into the inverter filter capacitor group via the filter inductor L; the DC voltage output by the inverter filter capacitor group is input into the IGBT inverter bridge via the non-inductive capacitor, and the IGBT inverter bridge completes the current conversion under the control of the main controller board, and converts the DC voltage into a medium frequency AC voltage, and the medium frequency AC voltage is loaded on the induction coil via the resonant output circuit and the resonant capacitor group.

[0014] Preferably, the two output ends of the resonant output circuit are respectively connected to one of the resonant capacitor groups and then connected to the induction coil, and the main controller board samples the voltage across any one resonant capacitor group through a voltage transformer.

[0015] Preferably, the two output ends of the resonant output circuit are connected to a resonant capacitor group and then connected to the induction coil, the main controller board samples the voltage across the resonant capacitor group through a voltage transformer, and a DC blocking capacitor is connected in series to the voltage transformer.

[0016] Preferably, the reactor 1 is a reactor with an inductance value of L1, and the capacitance value of the filter capacitor group is C, then: and

[0017] Preferably, the second reactor is a reactor with an inductance value of L2, and the capacitance value of the filter capacitor group is C, then:

[0018] Preferably, a three-phase dry-type transformer is arranged in the DC demagnetization current output channel, the three-phase AC power flows through the primary winding of the three-phase dry-type transformer, and the three-phase inductive power output by the secondary winding of the three-phase dry-type transformer is rectified by the three-phase rectifier bridge 2 and then outputs a DC voltage; the DC voltage output by the three-phase rectifier bridge 2 flows through the pre-filter capacitor group, the chopper voltage regulator, the inductor 1, the filter capacitor group and the inductor 2 in sequence and then is loaded on the induction coil.

[0019] The present invention only requires one device and a coil wound on the pipeline, and can output medium frequency induction heating current and DC demagnetization current on the coil at the same time, thus achieving simultaneous heating and demagnetization. This not only simplifies the installation and operation on site, making the operation simple, but more importantly, ensures the welding quality, and the equipment is highly reliable and not easy to be damaged. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the circuit of this embodiment. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0022] The present invention first designs a circuit that can output intermediate frequency current and direct current on one coil at the same time, and can isolate the higher intermediate frequency induced voltage, and designs an intermediate frequency induced current inverter and a direct current chopper voltage regulator on the power supply, and both are independently adjustable through the PWM pulse width regulation method, and finally outputs the intermediate frequency induction heating current and the direct current demagnetization current on the same coil at the same time. In the present invention, the output of the intermediate frequency induction heating inverter and the output of the direct current demagnetization current are isolated from the input power supply.

[0023] like Figure 1 As shown, the present embodiment discloses a device for realizing induction heating and DC demagnetization of a workpiece on the same coil, including a medium frequency induction heater output channel and a DC demagnetization current output channel, wherein the medium frequency induction heater output channel and the DC demagnetization current output channel are connected to the same induction coil COIL, and the medium frequency induction heater output channel and the DC demagnetization current output channel are electrically isolated from each other.

[0024] The inverter frequency f1 of the medium frequency induction heater output channel is between 5000Hz and 20000Hz, which can achieve independent output well. The maximum output medium frequency current of the medium frequency induction heater output channel The design range of the output medium frequency voltage U1 is 200~1000A(AC), and the design range of the output medium frequency voltage U1 is 300~1000V(AC). In this embodiment, the inverter frequency f1 of the output channel of the medium frequency induction heater is 8000Hz, and the maximum output medium frequency current is The invention is further described by taking 400A (AC) and the output medium frequency voltage U1 of about 600V (AC) as an example. The induction heating power of the output channel of the medium frequency induction heater is independently adjustable from 0.1kW to 80kW.

[0025] The chopping frequency f2 of the DC degaussing current output channel is between 8000Hz and 30000Hz, which can achieve a good balance between high efficiency and low cost, and avoid the inverter frequency of the medium frequency induction heater. The design range of the output voltage U2 is 200~800A(DC), and the design range of the output DC voltage U2 is 10~60V(DC). In this embodiment, the chopping frequency f2 of the DC demagnetization current output channel is 16000Hz, and the maximum output current is The present invention is further described by taking the output DC voltage U2 as 400A (DC) and 20V (DC) as an example. The DC demagnetization current of the DC demagnetization current output channel is independently adjustable from 0A to 400A (can be turned off).

[0026] After adopting the above circuit structure, the medium frequency induction heating current and the DC degaussing current will affect each other: the induction coil COIL has both medium frequency voltage and DC voltage components. The medium frequency induction heating current will generate a relatively high medium frequency voltage on the induction coil COIL, with an amplitude of hundreds of volts. This voltage (medium frequency voltage component) must be suppressed so as not to affect the operation of the DC degaussing circuit. On the other hand, the DC degaussing current also needs to flow through the same coil (including the extension cable), which will generate a DC voltage component of tens of volts on the coil. This DC component must also be isolated and cannot enter the medium frequency transformer coil, and cannot enter the medium frequency voltage feedback signal channel.

[0027] To solve the above problems, the specific circuit of the present invention is as follows Figure 1 As shown, the three-phase 380VAC power supply is supplied to the medium frequency induction heater output channel and the DC demagnetization current output channel via the main circuit breaker K1. The DSP main controller board MB samples the three-phase voltages VA, VB, and VC output by the main circuit breaker K1.

[0028] In the output channel of the medium frequency induction heater, the three-phase 380VAC power supply is rectified by the three-phase rectifier bridge BD1 and then outputs a DC voltage. The DC voltage first passes through the filter capacitor C4 and then enters the charging buffer circuit. In this embodiment, the charging buffer circuit is composed of a buffer contactor KP2, a buffer resistor RB1 and a self-recovery fuse FL. The self-recovery fuse FL is connected in series with the buffer resistor RB1 and then in parallel with the buffer contactor KP2. In this embodiment, the DC current output by the filter capacitor C4 is sampled by the shunt SF1, and a DC ammeter ID1 is set to display the DC current output by the filter capacitor C4. The DC voltage output by the charging buffer circuit is input to the inverter filter capacitor group GCA2 after passing through the filter inductor L. In this embodiment, a DC voltage meter VD1 is set to display the DC voltage output by the filter inductor L. The DC voltage output by the inverter filter capacitor group GCA2 is sequentially input into the IGBT inverter bridge through the non-inductive capacitor C2 and the non-inductive capacitor C3. The IGBT inverter bridge completes the conversion under the control of the DSP main controller board MB and converts the DC voltage into a medium frequency AC voltage. The DSP main control board MB detects the medium-frequency AC current output by the IGBT inverter bridge through the current sensor CT2. The output end of the IGBT inverter bridge is connected to the output terminal TEM1, and the output terminal TEM1 is connected to the input terminal TEM2. The input terminal TEM2 is connected to the output terminal TEM3 via the resonant output circuit and the resonant capacitor group C5, and the output terminal TEM3 is connected to the induction coil COIL. The medium-frequency AC voltage output by the IGBT inverter bridge is loaded on the induction coil COIL via the resonant output circuit and the resonant capacitor group C5. The resonant output circuit includes a medium-frequency isolation transformer T, and the primary winding of the medium-frequency isolation transformer T is connected to the input capacitor group C1. The resonant capacitor group C5 is connected to the secondary winding of the medium-frequency isolation transformer T. Elimination and design of interference of DC demagnetization current on the output channel of the medium-frequency induction heater: When the DC demagnetization current is applied to the induction coil COIL (including the extension cable), a DC voltage component of several tens of volts will be generated. In the present invention, the DC voltage component is isolated by the resonant capacitor group C5 and does not enter the secondary winding of the medium-frequency isolation transformer T. It can be as follows Figure 1 As shown, the resonant capacitor group C5 is designed to be two groups connected in series, and the two groups of resonant capacitor groups C5 are respectively connected to the two output ends of the secondary winding of the medium frequency isolation transformer T. The DSP main controller board MB samples the voltage across any one group of resonant capacitor groups C5 through the voltage transformer PT, and there is no DC component on the voltage transformer PT. Another feasible way is to have only one group of resonant capacitor groups C5, and the secondary winding of the medium frequency isolation transformer T is connected to the output terminal TEM3 via the resonant capacitor group C5. The DSP main controller board MB also samples the voltage across the resonant capacitor group C5 through the voltage transformer PT, and at this time, a small DC blocking capacitor is connected in series to the voltage transformer PT.

[0029] The three-phase 380VAC power supply output from the main circuit breaker K1 is input into the DC demagnetization current output channel via the circuit breaker K2. In the DC demagnetization current output channel, the three-phase 380VAC power supply flows through the primary winding of the three-phase dry-type transformer, and the three-phase inductive power supply output from the secondary winding of the three-phase dry-type transformer is rectified by the three-phase rectifier bridge BD2 and then outputs a DC voltage. In this embodiment, the inverter control board samples the output of the three-phase dry-type transformer through a current transformer. The DC voltage output by the three-phase rectifier bridge BD2 flows through the filter capacitor group GCA3, the chopper regulator VSTI, the reactor L1, the filter capacitor group GCA1 and the reactor L2 in sequence, and then is loaded on the induction coil COIL through the output terminal TEM3.

[0030] Filter calculation and design of DC chopper output circuit: In the above circuit, the filtering of DC chopper output circuit is completed by reactor L1 (0.1mH) and filter capacitor group GCA1 (4×600uF):

[0031] The output circuit L1=0.1mH(100uH), the filter capacitor GCA1 capacitance C=2400uF, so the LC time constant is: Calculated in microseconds:

[0032] The chopping frequency f2 is calculated as 16kHz, so the half period is

[0033] Since 2040uS>>31.25uS, the output filter can effectively filter out the chopped AC component and achieve a smooth DC output.

[0034] On the other hand: For the chopping frequency f2 = 16kHz, the inductive reactance of the reactor L1 is: 2πf2L1 = 2 × 3.14 × 0.0001 × 16000 = 10Ω, and the overshoot current is calculated by dividing half of the output DC voltage U2 by the inductive reactance, which is: This is for a maximum output current of 400A. It is very small compared to DC, so the pulsation caused by DC chopping can be effectively suppressed.

[0035] Calculation and design of the elimination of the interference of the medium frequency induction heater on the DC degaussing circuit: The elimination of the interference of the medium frequency induction heater output channel on the DC degaussing current output channel is completed by the reactor L2 (1mH) and the filter capacitor group GCA1 (4×600uF):

[0036] Since the demagnetization DC output voltage is relatively low, for the intermediate frequency voltage of several hundred volts, the intermediate frequency current on the induction coil COIL is basically determined by the intermediate frequency voltage and the inductive reactance of the reactor L2.

[0037] The inductive reactance of the reactor L2 under the inverter frequency f1=8000Hz of the medium frequency induction heater output channel is 2πf1L2=2×3.14×0.001×8000=50.24Ω. The output medium frequency voltage U1 of the medium frequency induction heater output channel is calculated as 600V, so the amplitude of the medium frequency current component flowing into the DC demagnetization current output channel is U1 / 2πf1L2=600 / 50.24=11.94A (this is the medium frequency current component of 8000Hz).

[0038] What may affect the normal operation of the DC demagnetization current output channel is the voltage rather than the current. Therefore, it is also necessary to calculate the capacitive reactance of the filter capacitor group GCA1 at the inverter frequency f1 = 8000Hz to calculate the level of the interference voltage. Then the capacitive reactance of the filter capacitor group GCA1 (4×600=2400uF) at the inverter frequency f1=8000Hz is: 1 / 2πf1C=1000000 / (2×3.14×8000×2400)=0.0083Ω. Therefore, due to the output of the intermediate frequency induced current / voltage, the intermediate frequency voltage component generated at both ends of the filter capacitor group GCA1 is It is only 0.5% of the output DC voltage U2=20V. Due to the existence of the reactor L2 (1mH), it will not affect the normal operation of the DC degaussing circuit at all.

[0039] In this embodiment, a microprocessor DSP is used to complete digital control and various enhanced functions to meet customer requirements for operation and process.

Claims

1. A device for realizing induction heating and DC demagnetization of a workpiece on the same coil, characterized in that: It includes a medium frequency induction heater output channel and a DC demagnetization current output channel, which are connected to the same induction coil, and the medium frequency induction heater output channel and the DC demagnetization current output channel are electrically isolated from each other, wherein: The inverter frequency f1 of the medium frequency induction heater output channel is between 5000Hz and 20000Hz; the maximum output medium frequency current of the medium frequency induction heater output channel The design range of is 200~1000A, and the design range of output medium frequency voltage U1 is 300~1000V; The chopping frequency f2 of the DC demagnetization current output channel is between 8000Hz and 30000Hz; the maximum output current of the DC demagnetization current output channel is The design range is 200~800A, and the design range of output DC voltage U2 is 10~60V; A resonant capacitor group is arranged in the output channel of the medium frequency induction heater, and the medium frequency AC voltage of the output channel of the medium frequency induction heater is loaded on the induction coil via the resonant capacitor group, and the DC voltage component generated after the DC demagnetization current output from the DC demagnetization current output channel is applied to the induction coil is isolated by the resonant capacitor group; An LC filter circuit 1 composed of a reactor 1 and a filter capacitor group and an LC filter circuit 2 composed of a reactor 2 and a filter capacitor group are arranged in the DC demagnetization current output channel. The DC demagnetization current outputted by the DC demagnetization current output channel is loaded on the induction coil via the LC filter circuit 1 and the LC filter circuit 2. The LC filter circuit 1 filters out the chopped AC component in the DC demagnetization current and suppresses the pulsation caused by the DC chopping. The LC filter circuit 2 eliminates the interference of the intermediate frequency induction heater output channel on the DC demagnetization current output channel. A three-phase rectifier bridge 1 is arranged in the output channel of the intermediate frequency induction heater. The three-phase AC power supply outputs a DC voltage after being rectified by the three-phase rectifier bridge 1. The DC voltage first passes through the filter capacitor and then is input into the charging buffer circuit. The DC voltage output by the charging buffer circuit is input into the inverter filter capacitor group through the filter inductor L; the DC voltage output by the inverter filter capacitor group is input into the IGBT inverter bridge through the non-inductive capacitor. The IGBT inverter bridge completes the current conversion under the control of the main controller board, and converts the DC voltage into an intermediate frequency AC voltage. The intermediate frequency AC voltage is loaded on the induction coil through the resonant output circuit and the resonant capacitor group; A three-phase dry-type transformer is arranged in the DC demagnetization current output channel, a three-phase AC power source flows through the primary winding of the three-phase dry-type transformer, and a three-phase inductive power source output by the secondary winding of the three-phase dry-type transformer is rectified by a three-phase rectifier bridge 2 and then outputs a DC voltage; the DC voltage output by the three-phase rectifier bridge 2 flows sequentially through a pre-filter capacitor group, a chopper voltage regulator, the reactor 1, the filter capacitor group and the reactor 2 and then is loaded on the induction coil.

2. The device for realizing induction heating and DC demagnetization of a workpiece on the same coil as claimed in claim 1, characterized in that: The induction heating power of the output channel of the medium frequency induction heater is independently adjustable from 0.1 kW to 80 kW.

3. The device for realizing induction heating and DC demagnetization of a workpiece on the same coil as claimed in claim 1, characterized in that: The DC demagnetization current of the DC demagnetization current output channel is independently adjustable from 0A to 400A.

4. The device for realizing induction heating and DC demagnetization of a workpiece on the same coil as claimed in claim 1, characterized in that: The two output ends of the resonant output circuit are respectively connected to one of the resonant capacitor groups and then connected to the induction coil. The main controller board samples the voltage at both ends of any group of resonant capacitor groups through a voltage transformer.

5. The device for realizing induction heating and DC demagnetization of a workpiece on the same coil as claimed in claim 1, characterized in that: The two output ends of the resonant output circuit are connected to a resonant capacitor group and then connected to the induction coil. The main controller board samples the voltage at both ends of the resonant capacitor group through a voltage transformer, and a DC blocking capacitor is connected in series to the voltage transformer.

6. The device for realizing induction heating and DC demagnetization of a workpiece on the same coil as claimed in claim 1, characterized in that: The reactor 1 is selected as a reactor with an inductance value of L1, and the capacitance value of the filter capacitor group is C, then: and 7. The device for realizing induction heating and DC demagnetization of a workpiece on the same coil as claimed in claim 1, characterized in that: The second reactor is a reactor with an inductance value of L2, and the capacitance value of the filter capacitor group is C, which satisfies:

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