Welding power source power factor correction system

Abstract

The application discloses a welding power source power factor correction system and belongs to the technical field of welding power sources. The welding power source is obtained by rectifying and inverting grid voltage; the correction system comprises a voltage acquisition module, a current given module and a controller. The voltage acquisition module is used for obtaining a voltage sampling signal corresponding to a pulsating direct-current voltage obtained by rectifying grid input; the current given module is used for outputting a current given signal with a pulsating component corresponding to the pulsating direct-current voltage according to the voltage sampling signal; and the controller is used for superimposing the current given signal with the pulsating component and a current feedback signal of a welding power source output loop to generate a duty cycle for controlling inverter operation, so that the welding power source output current is synchronized with the input pulsating direct-current voltage. The welding power source power factor is effectively improved.

Description

Technical Field

[0001] This invention relates to a power factor correction system for welding power supplies, belonging to the field of welding power supply technology. Background Technology

[0002] Welding power supplies are high-power electrical equipment, and their power factor affects the quality of the power grid. Especially in large factories or construction sites, where hundreds of welding machines work together, a low power factor will seriously increase the burden on the power grid.

[0003] Traditional methods to improve the power factor of welding power supplies include increasing the input inductance or using a PFC circuit. However, input inductors are bulky and expensive, while PFC circuits are complex and have low reliability. Therefore, their application in practice is greatly limited. Summary of the Invention

[0004] To address the problems of increased system size and low circuit reliability in existing methods for improving the power factor of welding power supplies, this invention provides a welding power supply power factor correction system.

[0005] The present invention provides a welding power factor correction system, wherein the welding power source is obtained by rectification and inversion from the power grid input;

[0006] The correction system includes:

[0007] The voltage acquisition module is used to obtain the voltage sampling signal corresponding to the pulsating DC voltage obtained after rectification of the grid input;

[0008] The current setting module is used to output a current setting signal with a pulsating component corresponding to the pulsating DC voltage based on the voltage sampling signal.

[0009] The controller is used to superimpose the current command signal with pulsating components and the current feedback signal of the welding power supply output circuit to generate the duty cycle of the control inverter, so that the output current of the welding power supply fluctuates synchronously with the input pulsating DC voltage.

[0010] According to the welding power factor correction system of the present invention, the duty cycle changes from small to large as the pulsating DC voltage changes from trough to peak.

[0011] According to the welding power factor correction system of the present invention, the correspondence between the current command signal with pulsating component and the pulsating DC voltage is as follows:

[0012] ,

[0013] In the formula for A current input signal that constantly contains pulsating components. The base welding current setpoint, The superposition coefficient is the coefficient for stacking. It is a pulsating DC voltage.

[0014] According to the welding power factor correction system of the present invention, the calculation is performed. Duty cycle :

[0015] ,

[0016] In the formula Based on the steady-state duty cycle, The gain of the output current closed-loop proportional regulator. for The current feedback signal at any time.

[0017] According to the welding power factor correction system of the present invention, the circuit structure of the voltage acquisition module includes a Zener diode D1, a current-limiting resistor R1, a resistor R2, a resistor R3, a resistor R4, an optocoupler U1, an NPN transistor Q1, and a load capacitor C1.

[0018] One end of the Zener diode D1 is connected to the positive output terminal of the pulsating DC voltage, and the other end of the Zener diode D1 is connected to one end of the current limiting resistor R1. The other end of the current limiting resistor R1 is connected to the negative output terminal of the pulsating DC voltage through the light-emitting diode of the optocoupler U1.

[0019] The collector of the phototransistor inside the optocoupler U1 is connected to the power supply VCC, and the emitter of the phototransistor is connected to the base of the NPN transistor Q1. The collector of the NPN transistor Q1 is connected to the power supply VCC, the base of the NPN transistor Q1 is connected to the power supply ground via resistor R2, and the emitter of the NPN transistor Q1 is connected to the power supply ground via resistor R3. The emitter of the NPN transistor Q1 is connected to the negative terminal of the load capacitor C1, the positive terminal of the load capacitor C1 is connected to one end of resistor R4, and the other end of resistor R4 is connected to the power supply VCC.

[0020] The positive terminal of the load capacitor C1 outputs a voltage sampling signal.

[0021] According to the welding power factor correction system of the present invention, the current setting module includes a potentiometer.

[0022] One end of the potentiometer is connected to the positive terminal of the load capacitor C1, and the other end of the potentiometer is connected to the power supply ground.

[0023] The potentiometer provides a DC voltage level corresponding to the base welding current setpoint by adjusting the sliding terminal. After the voltage sampling signal is superimposed on the positive terminal of the load capacitor C1, the superimposed voltage signal is obtained; after transformation, a current setpoint signal with pulsating components is obtained.

[0024] According to the welding power factor correction system of the present invention, the output current of the welding power supply output circuit is made to fluctuate synchronously with the pulsating DC voltage, thereby making the phase of the grid voltage waveform consistent with the phase of the grid input current waveform.

[0025] According to the welding power factor correction system of the present invention, the welding power source includes:

[0026] The rectifier module is used to convert three-phase AC grid voltage into pulsating DC voltage;

[0027] The filtering module is used to filter pulsating DC voltage to obtain a low-fluctuation DC voltage.

[0028] The inverter module is used to convert low-fluctuation-amplitude pulsating DC voltage into high-frequency, high-voltage AC voltage according to pulse width modulation instructions;

[0029] A transformer is used to convert high-frequency alternating current into high-frequency, low-voltage alternating current for welding purposes.

[0030] The secondary rectifier module is used to convert high-frequency, low-voltage AC power into DC power with superimposed high-frequency ripple;

[0031] The reactor is connected to the positive output terminal of the secondary rectifier module to filter out high-frequency ripple in the DC power and obtain DC power with low-frequency power frequency pulsation.

[0032] The negative output terminal of the secondary rectifier module is connected to a current transformer to collect the current feedback signal output by the welding power supply.

[0033] The welding load is connected between the output terminal of the reactor and the output terminal of the current transformer.

[0034] The beneficial effects of this invention are as follows: This invention detects the voltage waveform after three-phase rectification of the AC input of the welding power supply, and superimposes the voltage fluctuation signal onto the given terminal of the welding power supply. This causes the output current of the welding power supply to change from a constant current output to a pulsating DC output. The amplitude and phase of the DC output pulsation correspond to the amplitude and phase of the input voltage pulsation. Consequently, the transformer primary current, mapped from the output current, also fluctuates accordingly, with its frequency and amplitude corresponding to the input voltage waveform. The higher the overlap between the input voltage and current waveforms of the welding power supply, the higher the power factor of the power supply. This invention utilizes the characteristic that the welding arc does not have high requirements for the welding current ripple coefficient. By synchronizing the input voltage waveform and the output current pulsation waveform, it effectively improves the power factor of the welding power supply and reduces the impact on the power grid.

[0035] This invention improves the power factor by controlling the output current waveform, eliminating the need for an independent PFC conversion branch and simplifying the circuit structure. It also improves system reliability while ensuring welding performance. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the welding power factor correction system of the present invention.

[0037] Figure 2 This is the circuit schematic of the voltage acquisition module and the current setting module. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Specific Implementation Method 1: Combination Figure 1 and Figure 2 As shown, the present invention provides a welding power supply power factor correction system, wherein the welding power supply is obtained by rectification and inversion from the power grid input;

[0040] The correction system includes:

[0041] The voltage acquisition module is used to obtain the voltage sampling signal corresponding to the pulsating DC voltage obtained after rectification of the grid input;

[0042] The current setting module is used to output a current setting signal with a pulsating component corresponding to the pulsating DC voltage based on the voltage sampling signal.

[0043] The controller is used to superimpose the current command signal with pulsating components and the current feedback signal of the welding power supply output circuit to generate the duty cycle of the control inverter, so that the output current of the welding power supply fluctuates synchronously with the input pulsating DC voltage.

[0044] This implementation improves the grid-side input current waveform, reduces current harmonics, and enhances the power factor by making the welding output current fluctuate with the bus pulsating voltage, thus making the grid input current waveform follow the grid voltage waveform.

[0045] In this embodiment, after receiving a given signal superimposed with input voltage information, the controller adjusts the pulse width of the PWM output waveform accordingly, outputting a larger pulse width at the peak of the input voltage and a smaller pulse width at the trough of the input voltage. Consequently, the output current fluctuates with the input voltage fluctuations instead of being a constant current output. The output current is mapped to the primary current, and the input current fluctuates with the input voltage fluctuations, thereby increasing the overlap between the input voltage waveform and the input current waveform and effectively improving the power factor of the power supply.

[0046] In this embodiment, the duty cycle changes from small to large as the pulsating DC voltage goes from trough to peak.

[0047] The output current ripple amplitude is adjusted proportionally to the ripple coefficient of the rectified voltage. As the rippled DC voltage rises from the trough to the peak, the ripple component of the voltage sampling signal increases synchronously, and the amplitude of the current command signal with ripple component output by the current command module increases accordingly. The inverter duty cycle output by the controller also increases from small to large. The increase in duty cycle improves the inverter output capability, and the output current of the welding power supply increases synchronously with the rippled DC voltage. Conversely, as the voltage falls from the peak to the trough, the duty cycle decreases from large to small, and the output current decreases synchronously. Ultimately, the output current follows the fluctuation of the bus ripple voltage, corrects the harmonics of the grid current, and improves the power factor.

[0048] Furthermore, the correspondence between the current command signal with pulsating components and the pulsating DC voltage is as follows:

[0049] ,

[0050] In the formula for A current input signal that constantly contains pulsating components. The base welding current setpoint, The superposition coefficient is the coefficient for stacking. It is a pulsating DC voltage.

[0051] The voltage acquisition module acquires the voltage signal after three-phase AC rectification, processes it through the corresponding circuit, and applies it to the basic welding current setpoint, so that the setpoint signal is superimposed with the rectified input voltage information.

[0052] Due to the mapping effect of current, the output current and They are approximately equal.

[0053] The current input signal is superimposed with a pulsating component proportional to the pulsating DC voltage on the basic welding current, so that the current input fluctuates synchronously with the bus voltage. By adjusting the superposition coefficient, the amplitude of the pulsating component can be changed, thereby suppressing grid harmonics and improving the overall power factor while ensuring the basic welding current.

[0054] Basic welding current setpoint The welding process is preset according to the thickness of the workpiece to be welded.

[0055] The controller receives information superimposed with the input voltage. The pulse width of the PWM output drive waveform is adjusted accordingly.

[0056] calculate Duty cycle :

[0057] ,

[0058] In the formula Based on the steady-state duty cycle, The gain of the output current closed-loop proportional regulator. for The current feedback signal at any time.

[0059] The duty cycle is calculated based on the basic steady-state duty cycle, and the duty cycle is corrected in real time according to the difference between the current given signal and the current feedback signal. When the pulsating DC voltage increases, the current given increases, and the duty cycle increases accordingly, driving the actual output current to follow the change of the pulsating current given, so as to realize that the output current follows the synchronous fluctuation of the bus pulsating voltage, while ensuring the accuracy of the welding current closed-loop control.

[0060] The controller is based on the given value of the basic welding current. Determine the basic steady-state duty cycle corresponding to the width. It controls the turn-on and turn-off times of electronic switching devices in the inverter.

[0061] As an example, combined Figure 2 As shown, the circuit structure of the voltage acquisition module includes a Zener diode D1, a current-limiting resistor R1, a resistor R2, a resistor R3, a resistor R4, an optocoupler U1, an NPN transistor Q1, and a load capacitor C1.

[0062] One end of the Zener diode D1 is connected to the positive output terminal of the pulsating DC voltage, and the other end of the Zener diode D1 is connected to one end of the current limiting resistor R1. The other end of the current limiting resistor R1 is connected to the negative output terminal of the pulsating DC voltage through the light-emitting diode of the optocoupler U1.

[0063] The collector of the phototransistor inside the optocoupler U1 is connected to the power supply VCC, and the emitter of the phototransistor is connected to the base of the NPN transistor Q1. The collector of the NPN transistor Q1 is connected to the power supply VCC, the base of the NPN transistor Q1 is connected to the power supply ground via resistor R2, and the emitter of the NPN transistor Q1 is connected to the power supply ground via resistor R3. The emitter of the NPN transistor Q1 is connected to the negative terminal of the load capacitor C1, the positive terminal of the load capacitor C1 is connected to one end of resistor R4, and the other end of resistor R4 is connected to the power supply VCC.

[0064] The positive terminal of the load capacitor C1 outputs a voltage sampling signal.

[0065] The load capacitor C1 can adjust the phase of the pulsating component to achieve pulsating phase matching.

[0066] Zener diode D1 is used to reduce the voltage drop of the voltage signal; optocoupler U1 is an isolation optocoupler. Figure 2 As shown, the voltage signals from pins 1 and 2 are transmitted to pins 3 and 4 via photoelectric conversion. The NPN transistor Q1, resistors R2, R3, and R4 form a voltage follower, transmitting the optocoupler output voltage signal to the load capacitor. The load capacitor C1 can adjust the phase of the voltage signal; by adjusting the capacitance of C1, the phase superimposed on the given signal can be corrected.

[0067] The voltage acquisition module employs an optocoupler-isolated sampling, emitter-follower buffer, and RC-isolated direct-coupled circuit structure to achieve electrical isolation between the high-voltage bus and the low-voltage control circuit, thereby improving circuit safety and anti-interference capabilities. Simultaneously, it directly extracts the pulsating component of the pulsating DC voltage through analog circuitry, facilitating the output current to synchronously follow the bus voltage pulsation.

[0068] The current setting module includes a potentiometer.

[0069] One end of the potentiometer is connected to the positive terminal of the load capacitor C1, and the other end of the potentiometer is connected to the power supply ground.

[0070] The potentiometer provides a DC voltage level corresponding to the base welding current setpoint by adjusting the sliding terminal. After the voltage sampling signal is superimposed on the positive terminal of the load capacitor C1, the superimposed voltage signal is obtained; after transformation, a current setpoint signal with pulsating components is obtained.

[0071] In this embodiment, by making the output current of the welding power supply output circuit fluctuate synchronously with the pulsating DC voltage, the phase of the grid voltage waveform is made consistent with the phase of the grid input current waveform.

[0072] In this embodiment, the input voltage and input current have the same phase and approximately equal amplitude:

[0073] ,

[0074] In the formula For three-phase AC input current, The system's equivalent proportionality coefficient is derived from... , The efficiency is determined by the transformer turns ratio and the overall efficiency.

[0075] Combination Figure 1 As shown, the main circuit of the welding power supply includes:

[0076] The rectifier module is used to convert three-phase AC grid voltage into pulsating DC voltage;

[0077] The filtering module is used to filter the pulsating DC voltage, reduce the fluctuation amplitude of the pulsating DC, and obtain a low-fluctuation DC voltage.

[0078] The inverter module is used to convert low-fluctuation-amplitude pulsating DC voltage into high-frequency, high-voltage AC voltage according to pulse width modulation instructions;

[0079] A transformer is used to convert high-frequency alternating current into high-frequency, low-voltage alternating current suitable for welding.

[0080] The secondary rectifier module is used to convert high-frequency, low-voltage AC power into DC power with superimposed high-frequency ripple;

[0081] The reactor is connected to the positive output terminal of the secondary rectifier module to filter out high-frequency ripple in the DC power and obtain DC power with low-frequency power frequency pulsation.

[0082] The negative output terminal of the secondary rectifier module is connected to a current transformer to collect the current feedback signal output by the welding power supply.

[0083] The welding load is connected between the output terminal of the reactor and the output terminal of the current transformer.

[0084] Figure 1 and Figure 2 In the diagram, A represents the positive output terminal of the pulsating DC voltage, i.e., the positive output terminal of the rectifier module, and B represents the negative output terminal of the pulsating DC voltage, i.e., the negative output terminal of the rectifier module.

[0085] The pulsating DC voltage obtained after rectification by the rectifier module for:

[0086] ,

[0087] In the formula The power frequency input voltage for phase a is... This is the power frequency input voltage for phase b. This is the power frequency input voltage for phase c.

[0088] Experimental results show that this invention can improve the power factor from 0.93 to 0.96-0.98 for a 400A welding power supply with a 60uF filter capacitor.

[0089] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A welding power supply power factor correction system, characterized in that, The welding power source is obtained from the grid input after rectification and inversion; The correction system includes: The voltage acquisition module is used to obtain the voltage sampling signal corresponding to the pulsating DC voltage obtained after rectification of the grid input; The current setting module is used to output a current setting signal with a pulsating component corresponding to the pulsating DC voltage based on the voltage sampling signal. The controller is used to superimpose the current command signal with pulsating components and the current feedback signal of the welding power supply output circuit to generate the duty cycle of the control inverter, so that the output current of the welding power supply fluctuates synchronously with the input pulsating DC voltage.

2. The welding power supply power factor correction system according to claim 1, characterized in that, The duty cycle changes from small to large as the pulsating DC voltage goes from trough to peak.

3. The welding power factor correction system according to claim 1, characterized in that, The correspondence between the current input signal with pulsating components and the pulsating DC voltage is as follows: ， In the formula for A current input signal that constantly contains pulsating components. The base welding current setpoint, The superposition coefficient is the coefficient for stacking. It is a pulsating DC voltage.

4. The welding power supply power factor correction system according to claim 3, characterized in that, calculate Duty cycle : ， In the formula Based on the steady-state duty cycle, The gain of the output current closed-loop proportional regulator. for Constant current feedback signal.

5. The welding power supply power factor correction system according to claim 3, characterized in that, The circuit structure of the voltage acquisition module includes a Zener diode D1, a current-limiting resistor R1, a resistor R2, a resistor R3, a resistor R4, an optocoupler U1, an NPN transistor Q1, and a load capacitor C1. One end of the Zener diode D1 is connected to the positive output terminal of the pulsating DC voltage, and the other end of the Zener diode D1 is connected to one end of the current limiting resistor R1. The other end of the current limiting resistor R1 is connected to the negative output terminal of the pulsating DC voltage through the light-emitting diode of the optocoupler U1. The collector of the phototransistor inside the optocoupler U1 is connected to the power supply VCC, and the emitter of the phototransistor is connected to the base of the NPN transistor Q1. The collector of the NPN transistor Q1 is connected to the power supply VCC, the base of the NPN transistor Q1 is connected to the power supply ground via resistor R2, and the emitter of the NPN transistor Q1 is connected to the power supply ground via resistor R3. The emitter of the NPN transistor Q1 is connected to the negative terminal of the load capacitor C1, the positive terminal of the load capacitor C1 is connected to one end of resistor R4, and the other end of resistor R4 is connected to the power supply VCC. The positive terminal of the load capacitor C1 outputs a voltage sampling signal.

6. The welding power factor correction system according to claim 5, characterized in that, The current setting module includes a potentiometer. One end of the potentiometer is connected to the positive terminal of the load capacitor C1, and the other end of the potentiometer is connected to the power supply ground. The potentiometer provides a DC voltage level corresponding to the given value of the basic welding current by adjusting the sliding terminal. After the voltage sampling signal is superimposed on the positive terminal of the load capacitor C1, the superimposed voltage signal is obtained. The current command signal with pulsating components is obtained after transformation.

7. The welding power factor correction system according to claim 1, characterized in that, By making the output current of the welding power supply output circuit fluctuate synchronously with the pulsating DC voltage, the phase of the grid voltage waveform is made consistent with the phase of the grid input current waveform.

8. The welding power supply power factor correction system according to claim 1, characterized in that, The welding power source includes: The rectifier module is used to convert three-phase AC grid voltage into pulsating DC voltage; The filtering module is used to filter pulsating DC voltage to obtain a low-fluctuation DC voltage. The inverter module is used to convert low-fluctuation-amplitude pulsating DC voltage into high-frequency, high-voltage AC voltage according to pulse width modulation instructions; A transformer is used to convert high-frequency alternating current into high-frequency, low-voltage alternating current for welding purposes. The secondary rectifier module is used to convert high-frequency, low-voltage AC power into DC power with superimposed high-frequency ripple; The reactor is connected to the positive output terminal of the secondary rectifier module to filter out high-frequency ripple in the DC power and obtain DC power with low-frequency power frequency pulsation. The negative output terminal of the secondary rectifier module is connected to a current transformer to collect the current feedback signal output by the welding power supply. The welding load is connected between the output terminal of the reactor and the output terminal of the current transformer.

Images