CN1303750C - Soft-switch hidden-arc welding contrarariant power supply with double closed-loop control - Google Patents

Abstract

The present invention relates to a soft-switch hidden-arc welding inversion power supply with double-closed loop control, wherein a current voltage detecting sector is connected with a phase shift type pulse width modulation sector after connected with a slope compensation sector in parallel. The current voltage detecting sector is also connected with a controller by an error amplifier. The controller is also connected with a drive sector. The output end of the drive sector is connected with an inversion bridge. The sectors form the peak current control circuit of an inner ring. The average current control of an outer ring adopts fuzzy intelligent control. A magnetic switch is connected between the secondary pole of a high frequency power transformer and a secondary high frequency rectification filtration sector. The present invention enhances system dynamic performance by the double-closed loop control. The power transformer adopts an open structure to enhance the heat efficiency of the power supply. The magnetic switch acts with excitation inductance and leakage inductance to realize a soft switch in a total range.

Description

Soft-switching submerged arc welding inverter power supply with double closed-loop control

(1) Technical field

The invention relates to the technical field of mechatronics, in particular to the technical field of high-frequency soft-switching inverter technology and double-closed-loop intelligent control, and specifically refers to a soft-switching submerged arc welding inverter power supply with double-closed-loop control.

(2) Background technology

At present, in the field of submerged arc welding, due to the large current and high power required by the process, the traditional submerged arc welding power supply is mainly based on silicon rectifier and thyristor rectifier. The rectifier power supply is relatively reliable and technically mature, but The equipment is bulky, heavy, high in energy consumption, low in efficiency, and due to its structural reasons, its dynamic characteristics are not ideal enough. The more advanced hard-switching inverter has small size, high efficiency, high technical content and high added value, but the working environment of the device is relatively harsh, the switching loss is large, and high-order harmonics will cause grid pollution, so a buffer circuit is required. The improvement of the inverter frequency is also limited. Specifically, the high-power inverter arc welding power supply mainly has the following problems:

(1) Reliability issues Due to the harsh operating environment of the welding machine, the requirements for its reliability are very high. At present, due to high frequency parasitic oscillation, frequent and complex load changes, electromagnetic interference, magnetic bias and other reasons, especially in the case of high power, the power supply of ordinary inverter welding machines has insufficient reliability.

(2) Harmonic interference At present, the inverter welding machines on the market basically work in the hard switching mode, and the harmonics generated during the switching process will feed back to the power grid, causing pollution to the power grid; at the same time, it will also cause serious electromagnetic interference.

(3) Control performance of the welding machine The control cycle of the inverter welding machine is short, and the dynamic response of the whole machine is fast. However, this advantage has not been paid enough attention and reflected in the existing products, and the arc control is still limited to the traditional control mode and design ideas, and the performance advantages of the inverter have not been fully utilized.

(4) Power factor problem Inverter welding machines that work with hard switches have distortions in their working waveforms and high-order harmonics, which reduce the power factor.

(5) The high-frequency power transformer has large transmission power and serious temperature rise, which is limited by the production level of magnetic materials and the production cost of welding machines. The window of magnetic materials and the effective magnetic conduction area cannot be too large, which increases the structural design, thermal design and electrical design of the transformer. technical difficulty.

Using soft switching technology is a good way to solve these problems, but compared with hard switching technology, soft switching inverter technology has a higher technical starting point. The development of soft switching inverters requires a deeper understanding of the soft switching mechanism. To understand and research, we must fully understand the parasitic parameters of devices, and master the law and mechanism of soft-switching resonant commutation. Moreover, the soft-switching inverter welding machine currently under research basically adopts the ordinary full-bridge phase-shift soft-switching topology. Although the implementation method is relatively simple, there are narrow soft-switching ranges and large commutation losses. During the reverse recovery process of the diode, The voltage overshoot and ringing phenomenon caused by vibration seriously affect the safe, stable and reliable operation of the inverter.

Equipment using high-frequency inverter technology is basically in the laboratory stage. Even the domestic high-frequency inverter submerged arc welding power supply that has passed the national appraisal also belongs to the hard switching working mode. After searching, the soft-switching submerged arc inverter has no technical achievements at present, let alone put it on the market. Especially the use of fuzzy intelligent control for the power supply is still blank. The design idea of the welding system is still based on the traditional arc control method. The adjustment performance of the control system is not well combined with the control performance of the inverter arc welding power supply. The main reason is that the response speed and adjustment accuracy of the wire feeding system are difficult to guarantee. , although the use of fuzzy control technology has achieved certain results, fuzzy control basically stays in manual adjustment and design of fuzzy control rules, and the selection of membership functions is relatively subjective. Since the optimization of fuzzy control rules involves a huge search space, traditional The optimization method of this method has a considerable amount of calculation, and there are many restrictions on the performance evaluation function, so it is difficult to obtain the optimal control rule.

(3) Contents of the invention

The purpose of the present invention is to solve the deficiencies in the above-mentioned prior art, and provide a soft-switching submerged arc welding inverter power supply with double closed-loop control. The power supply solves the main problems of the traditional submerged arc welding power supply through the research, development and application of the new soft switching technology, on the basis of fully utilizing and digging intelligent control means, and provides a development platform and interface for the intelligent welding control system.

A soft-switching submerged arc welding inverter power supply with double closed-loop control according to the present invention includes an electromagnetic compatibility link, a rectification and filtering link, a phase-shift full-bridge inverter link, a high-frequency power transformer, and a secondary high-frequency rectification and filtering link , the average current and voltage detection link, the phase-shift pulse width modulation link, the drive link, the network voltage detection link and the voltage current and overheating protection link, which is characterized in that, after the inner loop current detection link is connected with the slope compensation link, the same as described The phase-shift pulse width modulation link is connected, and the average current voltage detection link is also connected with a controller through an error amplifier. After the controller is connected with the slope compensation link, it is connected with the phase shift pulse width modulation link. The phase-shift pulse width modulation link is also connected with the drive link, the output of the drive link is connected with the phase-shift full-bridge inverter link, the above-mentioned inner loop current detection link, slope compensation link, phase-shift pulse width modulation link, The driving link and the phase-shifting full-bridge inverter link constitute an inner loop peak current control circuit; a magnetic switch is connected in series between the secondary of the high-frequency power transformer and the secondary high-frequency rectifying and filtering link.

In order to better realize the present invention, the radiator and the secondary pole of the high-frequency power transformer in the phase-shifting full-bridge inverter link are connected with temperature sensors; the primary DC bus side of the rectification and filtering link adopts LC filtering; the The high-frequency power transformer adopts an open structure with gaps between the windings.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

1. The present invention realizes full-range soft switching, greatly reduces the switching loss and electrical stress of the power tube, improves the working conditions, reduces electromagnetic interference, and improves the efficiency of the whole machine.

2. On the basis of the power main circuit, the present invention adds an inner loop power supply control circuit, through double closed loop control, improves the dynamic performance of the system and overcomes the magnetic bias phenomenon.

3. The power transformer of the present invention adopts an open structure, which saves the resonant inductance and improves the thermal efficiency of the power supply.

4. The present invention improves power supply reliability and process adaptability through various effective protection measures.

(4) Description of drawings

Fig. 1 is a system overall block diagram of the present invention;

Fig. 2 is a schematic diagram of the main circuit of the present invention;

Fig. 3 is the circuit schematic diagram of error amplification, phase shifting and driving links of the present invention;

Fig. 4 is the schematic circuit diagram of the single-chip microcomputer fuzzy control system of the present invention;

Fig. 5 is a schematic diagram of the external characteristic switching circuit of the present invention;

Fig. 6 is a schematic diagram of an overheating detection and protection circuit of the present invention;

Fig. 7 is a block diagram of the overall system flow of the present invention.

(5) Specific implementation methods

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

As shown in Figure 1, the three-phase power frequency alternating current is processed by electromagnetic compatibility, rectified and filtered to become smooth direct current, which is used as the bus voltage (AC- DC); the control system makes the switching tube turn on and off at zero voltage according to the control rules, so as to obtain 25KHz high-frequency high-voltage power (DC-AC), and then through high-frequency transformer transformation, magnetic switch and secondary high After frequency rectification and filtering, tens of volts of direct current (AC-DC) suitable for the submerged arc welding process is obtained, and the welding task is completed together with the wire feeding traveling mechanism. The control and driving circuit controls the normal operation of the power supply and the wire feeding mechanism through the regulator according to the detected welding voltage, current and inner loop current.

As shown in Figure 2, the power frequency grid is connected to the rectifier block B1, connected to the filter links L1, C2, C3, C4, C5, R1, R2, and then connected to the inverter bridge VT1~VT4 (that is, SKM300GB124D), C6~C8, the output is connected to The primary stage of the high-frequency power transformer T1, the secondary poles of the transformer are connected in series with the magnetic switches LS1 and LS2, and then output direct current through the high-frequency full-wave rectification circuit D1~D8, the freewheeling diode D9~D12, the filter link L2, C12, C13, and C14, and the above link Constitute the power main circuit. After the inner loop current detection link HALL1 is connected with the slope compensation link, it is connected with the PWM generation link UC3879, the average current and voltage detection link HALL2 is connected with the error amplifier, PI controller U1 or fuzzy controller 80C552 through the J1 interface, and the output is the same as the PWM generation link The 3 pins of UC3879 are connected, the output terminals 7, 8, 12, 13 of UC3879 are respectively connected with the 14, 15 pins of the 4 driving links EXB841, and the output of the driving links are respectively connected with the G, The E poles are connected, and the above links form a power control circuit. The temperature sensor RRZ is directly installed on the radiator and the secondary pole of the transformer, the output is connected to the secondary transformation circuit U27, U28, U25, D15, and the output is connected to the switching switch 4051. The over-current detection HALL2 is connected to 4051 to realize over-current protection; the voltage detection signal is also connected to 4051 to realize pulse width limitation; the auxiliary power supply is respectively connected to active components such as op amp, UC3879, EXB841. The three-phase power frequency alternating current is rectified by the three-phase rectifier bridge _B1 after electromagnetic compatibility treatment, and then filtered by _L1 , _C2 , and _C3 to become smooth direct current, and the full-bridge inverter is composed of four IGBT power transistors VT ₁ ~ VT ₄ device, C ₆ ~ C ₈ are resonant capacitors, assisting the realization of soft switching. The inverted high-frequency (25KHz) square wave signal is stepped down by the transformer T ₁ and passed through the magnetic switch (L _S1 , L _S2 ), and the high-frequency rectification is connected in parallel by fast diodes (D ₁ ~ D ₄ , D ₅ ~ D ₈ ) The formed full-wave rectification circuit is completed, and then output after being smoothed by the output inductor L ₂ .

As shown in Figure 3, _J1 is the average current feedback signal of the outer ring, and _J2 is the given voltage signal. After the two are compared, the output signal of the regulator (analog circuit or single-chip microcomputer, which can be jumped) is used as the phase-shifting chip UC3879 The input signal of J ₃ is the peak current feedback signal of the inner loop, which is superimposed with the compensation signal and enters the 19 pin of UC3879, and is compared with the error signal inside UC3879, so that UC3879 outputs the corresponding phase-shifted four-way PWM waveform. The four pairs of complementary phase-shifting signals enter the integrated drive chip EXB841 respectively, and output the drive signals of the inverter bridge switch tubes VT ₁ -VT ₄ .

As shown in Figure 4, the single-chip PCB80C552 system is the core of the fuzzy control of the outer loop current. The deviation between the outer loop sampling current and the given signal is fuzzy, fuzzy inference and defuzzification inside the single-chip computer. The output signal is used as the 3-pin of UC3879 The input signal is compared with the injected current to determine the magnitude of the phase shift of the drive signal, thereby controlling the output of the power supply. At the same time, the system also serves as the control core of the entire welding system.

As shown in Figure 5, the output voltage Uf of the submerged arc welding inverter is detected, judged and analyzed in real time, and the trailing current is controlled by limiting the minimum effective output pulse width. An overcurrent protection circuit is added to the circuit. When the detected current signal If exceeds a given value, the switching circuit will switch to a relatively low output value, so that the effective output pulse width is zero, and the inverter bridge is turned off. Using this external drag control method, there are two additional benefits: First, because the peak control of the inner loop is particularly sensitive to signal changes, the minimum pulse width limit can avoid the peak control of the inner loop under the condition of narrow pulse width. Second, when welding with low current, if the arc length is relatively short, the welding machine can automatically increase the current to promote the droplet transfer, and it is not easy to extinguish the arc.

As shown in Figure 6, thermal protection is mainly to prevent damage and inverter failure caused by overheating of devices in some special cases. The invention utilizes PTC type RRZ thermistors and installs them on the transformer secondary coil and heat sink respectively. When the temperature rises, the protection circuit works and cuts off the driving signal, and the inverter bridge stops working. When the temperature drops, the drive signal is turned on, and the inverter bridge starts to work. Two measures have been taken for closing protection. One is to use LC filter on the primary DC bus side and connect a large filter inductance in series. On the one hand, it limits the current growth rate, on the other hand, it improves the primary current waveform and reduces high-order harmonics. Improve the power factor; another measure is to use a delay to ensure that the main circuit is turned on first, and then the control circuit is turned on. It can also prevent false triggering and damage to power devices at the moment of startup.

As shown in Figure 7, its core is the single-chip PCB80C552 system. After initialization, scan the given signal of the keyboard and display it. After comparing with the feedback current of the outer loop, the output enters UC3879 through a fuzzy algorithm to control the phase-shifting PWM signal. At the same time, it protects the power supply according to the feedback current and voltage signal, and controls the wire feeding mechanism to be effective. work.

The high-frequency power transformer adopts an open structure with gaps between the windings. In the high-power soft-switching arc welding inverter, the functions of the high-frequency transformer include: (1) electrical isolation; (2) step-down; (3) magnetic coupling to transmit energy; (4) participating in the soft switching process of the power switch tube . The first three functions are the same as traditional arc welding inverters. However, this last feature is a new addition specific to soft-switching arc welding inverters. The leakage inductance of the power transformer has nothing to do with the state variables such as the excitation current and the winding conduction current, but only depends on the structural parameters of the winding. If the inner diameter r ₀ , thickness h ₁ of the primary winding, the thickness h ₂ of the secondary winding and the insulation distance δ between the two windings become larger, the leakage inductance of the transformer will increase. Therefore, the windings of traditional high-frequency power transformers often have to be designed as a closed structure in which each turn of the coil is coupled as closely as possible. In the new soft-switching arc welding inverter, the leakage inductance of the transformer is used to cooperate with the excitation inductance to realize zero-voltage soft switching, and the leakage inductance of the high-frequency transformer has been transformed into an active factor. Therefore, the present invention proposes and adopts an open transformer applicable to a high-power soft-switching arc welding inverter. The winding of this transformer is very similar to the structure of the radiator, and its effective heat dissipation area is more than 10 times larger than that of the traditional closed transformer, which greatly reduces the thermal resistance of the transformer.

Embodiments of the present invention have the following characteristics:

1. The main power circuit of the present invention adopts a novel full-bridge phase-shifting zero-voltage soft switching topology (as shown in FIG. 2 ) with a magnetic switch. This circuit topology is based on the traditional basic phase-shift full-bridge zero-voltage inverter, and two saturated inductors (magnetic switches) are connected in series at the secondary pole of the transformer. When the passing volt-seconds are low (small current), In the high-impedance off state, after the volt-second exceeds a certain value, the inductor is saturated and the low-impedance conduction. In this way, during the common conduction time of the secondary rectifier diodes, that is, in the freewheeling and non-working state of the transformer, the secondary of the transformer can be disconnected from the rectifier circuit, so that the transformer can be kept in an inductive state. By setting the excitation inductance and excitation current reasonably, Obtain appropriate excitation energy, broaden the soft switching range of the lagging bridge arm switching tube, thereby reducing the loss of circulating current and duty cycle, and greatly improving the efficiency of the power supply; the topology of the phase-shifting full-bridge inverter circuit with magnetic switches , can realize full-range zero-voltage soft switching.

2. The present invention adopts a double-closed-loop constant current (with external drag) control system (as shown in FIG. 3 ) which combines outer-loop average value fuzzy intelligent control-inner-loop peak current control. Submerged arc welding is generally high-current thick-wire welding, and the arc is flat. In order to obtain good arc elasticity and weld shape, to ensure stable heat input during welding, to obtain good welding quality, and to avoid short circuits, The pulse width is too narrow to affect stable operation. The present invention adopts the external characteristic of constant current with external drag. The constant current external characteristics of traditional welding machines are obtained by using the average current control mode. In this mode, the current sampling signal is the average value of multiple inverter cycles, so it is difficult to accurately, appropriately, and transiently respond to the working status of the power device, and cannot realize real-time and effective monitoring and protection of the power device, and the control effect is effective. Larger hysteresis. The present invention organically combines the current average value control and the current peak value control modes, uses the Hall current sensor to respectively detect the primary inductance current (peak current) of the transformer and the average output current of the power supply, and compares the average current signal with the given signal to form a system In the outer loop average current control mode, the error signal is sent to the PWM comparator together with the superposition of the peak current and slope compensation signal after being calculated by the regulator (80C552 single-chip microcomputer, which shares the platform with the wire feeding system, as shown in Figure 4), and then obtained When the PWM pulse is turned off, the working state of the switching tube is controlled by the driving circuit, thereby forming the inner loop of the peak current. The addition of the inner loop peak current mode has significantly improved the transient closed-loop response of the system, and accelerated the transient response to changes in input voltage and output load, and has a simple and automatic magnetic flux balance function (to solve transformer bias) and Instantaneous peak current limiting function, inherent pulse-by-pulse current limiting function and automatic current sharing parallel function improve the dynamic characteristics of the system and the reliability of the whole machine. The deviation between the average current sampled by the outer loop and the given signal and its rate of change are used as the input of the fuzzy intelligent control to enter the single-chip microcomputer (the adjustment and compensation link, that is, the fuzzy controller). Fuzzy reasoning, and then defuzzify the reasoning results, and turn them into analog quantities, which are used as the control given signal of the inner loop. The introduction of the fuzzy control of the average value of the outer ring ensures the constant current section of the external characteristics of the submerged arc welding inverter; the realization of fuzzy-peak control improves the process adaptability of the submerged arc welding inverter.

In order to solve the shortcomings of low short-circuit current and insufficient arc thrust of the constant current external characteristic power supply, and to ensure that the IGBT works in a suitable pulse width range during a short circuit, the present invention adopts the constant current external drag characteristic (as shown in Figure 5). The output voltage (Uf) of the submerged arc welding inverter is detected, judged and analyzed in real time, and the trailing current is controlled by limiting the minimum effective output pulse width. Overcurrent protection is added to the circuit. When the detected current signal (If) exceeds a given value, the switching circuit will switch to a relatively low output value, so that the output pulse width is zero, and the inverter bridge is turned off. In addition, the introduction of external dragging can avoid the unstable phenomenon caused by the peak control of the inner ring under the condition of narrow pulse; when welding with low current, if the arc length is short, the welding machine can automatically increase the current to promote the droplet transfer , not easy to extinguish the arc.

3. The present invention realizes real-time monitoring and protection (overheating, overcurrent, overvoltage and undervoltage, closing protection and soft start, as shown in Figure 6) to the power switch device, same as the new soft switch main circuit and the above-mentioned control method With the cooperation, the reliability of the inverter submerged arc welding power supply and the system is further improved. Thermal protection is mainly to prevent damage and inverter failure caused by overheating of devices in some special cases. The present invention adopts overheating detection and protection circuit, utilizes PTC type RRZ thermistor, installs them respectively on the transformer primary coil and heat sink, when the temperature rises, the protection circuit works and cuts off the drive signal, and the inverter bridge stops working; when the temperature drops After that, the drive signal is turned on, and the inverter bridge starts to work. Two measures have been taken for closing protection. One is to use LC filter on the primary DC bus side and connect a large filter inductance in series. On the one hand, it limits the current growth rate, on the other hand, it improves the primary current waveform and reduces high-order harmonics. Improve the power factor; another measure is to use a delay to ensure that the main circuit is turned on first, and the control circuit is turned on later. It can also prevent power devices from being damaged due to false triggering at the moment of start-up. The single-chip 80C552 system is the control core of the overall system, and it is also a common platform for the fuzzy control of the average value of the outer ring and the fuzzy control of wire feeding.

4. The present invention adopts a new open structure high-frequency power transformer, uses its own excitation inductance and leakage inductance to realize soft switching and significantly improves heat dissipation.

As described above, the present invention can be preferably realized.

Claims (4)

1. soft switch submerged-arc welding inverter with two closed-loop controls, comprise the electromagnetic compatibility link, the rectifying and wave-filtering link, phase-shift type full-bridge inverting link, high-frequency power transformer, secondary filtering high-frequency rectifier link, average current voltage detecting link, phase-shift type pulse-width modulation link, drive link, net is pressed and is detected link and electric current and voltage and overtemperature protection link, it is characterized in that, after interior circular current detects link and the slope-compensation link is connected, be connected with described phase-shift type pulse-width modulation link, described average current voltage detecting link also is connected with controller by error amplifier, controller is with after the slope-compensation link is connected, be connected with described phase-shift type pulse-width modulation link, described phase-shift type pulse-width modulation link also is connected with the driving link, the output that drives link is connected with phase-shift type full-bridge inverting link, and above-mentioned interior circular current detects link, the slope-compensation link, phase-shift type pulse-width modulation link, drive link and phase-shift type full-bridge inverting link and constitute interior ring peak current control circuit; Be serially connected with magnetic switch between the secondary and secondary filtering high-frequency rectifier link of described high-frequency power transformer.

2. a kind of soft switch submerged-arc welding inverter with two closed-loop controls according to claim 1 is characterized in that radiator in the described phase-shift type full-bridge inverting link and the secondary temperature sensor that is connected with of high-frequency power transformer.

3. a kind of soft switch submerged-arc welding inverter with two closed-loop controls according to claim 1 is characterized in that, the elementary dc bus side of described rectifying and wave-filtering link adopts LC filtering.

4. a kind of soft switch submerged-arc welding inverter with two closed-loop controls according to claim 1 is characterized in that, described high-frequency power transformer adopts Open architecture, leaves the slit between the winding.

Images