Precision low-stress photovoltaic ultrasonic welding control method and system

Abstract

The application discloses a kind of precise low-stress photovoltaic ultrasonic welding control method and system, the method includes: based on finite element model and the pressure distribution that ultrasonic vibration welding head is applied to ribbon, the welding quality and damage risk between ribbon and battery piece are evaluated, and the pressure distribution that evaluation result meets standard is selected as preferred pressure distribution;During welding, the actual temperature of welding head and the actual molten pool shape of welding point are observed, and the actual temperature and the pressure applied to welding head are adjusted accordingly;After welding, if multiple indicators detected all reach standard, then it is determined that welding is qualified.The above technical scheme is used, the pressure distribution applied to ribbon and battery piece is evaluated in advance by finite element model, and the appropriate pressure distribution is selected, to ensure the welding quality while reducing the damage risk;Based on the observation and adjustment of temperature and molten pool shape during welding, the welding quality is improved.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic module manufacturing technology, and in particular to a precision low-stress photovoltaic ultrasonic welding control method and system. Background Technology

[0002] The photovoltaic industry is developing towards higher efficiency and higher reliability. Gridless photovoltaic modules have become the next generation of mainstream technology due to their advantages such as increased illumination area, reduced silver paste consumption, and improved conversion efficiency.

[0003] Gridless photovoltaic modules use high-density solder strips (≤0.3mm spacing) to connect to the cells in a shingled manner. Traditional photovoltaic welding uses servo motors and ball screws for driving, which results in large backlash and strong inertial oscillations, leading to a high rate of microcracks in the cells (manifested as exposed grid lines, solder strip misalignment, and excessive stress).

[0004] To address the issues of backlash and inertial oscillation and improve welding precision, an ultrasonic-assisted welding approach was initially adopted. However, the ultrasonic welding approach also encountered problems in its application, including high stress between the welding strip and the battery cell, which easily led to incomplete welds and failed to meet the actual welding quality requirements. Summary of the Invention

[0005] Purpose of the invention: This invention provides a precision low-stress photovoltaic ultrasonic welding control method and system, aiming to solve the technical problems of high stress between the solder strip and the cell during the ultrasonic welding process of photovoltaic modules, which easily leads to incomplete welding.

[0006] Technical Solution: This invention provides a precision low-stress photovoltaic ultrasonic welding control method, comprising: after the solar cell is transported to the work station, determining the grid line position of the solar cell and aligning the welding strip with the grid line of the solar cell; evaluating the welding quality and damage risk between the welding strip and the solar cell based on a finite element model and the pressure distribution applied to the welding strip by the ultrasonic vibration welding head, and selecting a pressure distribution that meets the evaluation criteria as the preferred pressure distribution; the finite element model is established based on the contact stress distribution between the welding strip and the solar cell; the pressure distribution applied to the welding strip by the welding head is such that the pressure in the middle area is higher than the pressure in the edge area; the ultrasonic vibration welding head executes the preferred pressure distribution to weld the welding strip and the solar cell; during the welding process, observing the actual temperature of the welding head and the actual molten pool morphology of the welding point, adjusting the actual temperature accordingly based on whether the actual temperature exceeds the standard temperature range, and adjusting the pressure applied by the welding head accordingly based on whether the actual molten pool width is greater than the standard molten pool width; after welding is completed, detecting the actual molten pool width, welding strip offset, exposed grid line width, and cold weld condition, and if all meet the standards, the welding is considered qualified.

[0007] Specifically, it also includes: the ultrasonic vibration welding head is also provided with a flexible film, through which the vibration is transmitted to the contact interface between the welding strip and the battery cell.

[0008] Specifically, the amplitude of the ultrasonic vibration welding head is set to 11 μm to 13 μm.

[0009] Specifically, the establishment of the finite element model includes: the battery cell is set as a composite structure of silicon substrate and surface electrode, the solder ribbon is set as an elasto-plastic body, the flexible film of the ultrasonic vibration welding head is set as a linear elastic material, the ultrasonic vibration welding head is set as an elastic body, the solder ribbon and the battery cell grid lines are set as frictional contact, and the flexible film and the solder ribbon are set as binding contact.

[0010] Specifically, the interfacial plastic strain value at the contact interface between the welding strip and the battery cell is calculated. If the interfacial plastic strain value is greater than the standard plastic strain value, the welding quality is considered qualified. The maximum stress on the battery cell is calculated. If the maximum stress is less than the standard stress, the damage risk is considered qualified.

[0011] Specifically, the standard plastic strain value is 0.05, and the standard stress is 100 MPa.

[0012] Specifically, the preferred pressure distribution has a maximum pressure of 35mN to 45mN in the middle region and a maximum pressure of 22mN to 28mN in the edge region.

[0013] Specifically, the standard temperature range is 245℃ to 255℃; the standard weld pool width is 70μm; if the actual weld pool width is smaller than the standard weld pool width, the pressure applied by the welding head is increased.

[0014] Specifically, if the actual weld pool width is between 82μm and 90μm, the solder strip offset is less than or equal to 2μm, the exposed width of the grid line is less than 10μm, and the resistance of the contact area between the solder strip and the cell is greater than or equal to 25mΩ, then the welding is considered qualified.

[0015] This invention also provides a precision low-stress photovoltaic ultrasonic welding control system, comprising: a linear ultrasonic motor drive module, a calculation unit, an ultrasonic vibration-assisted welding module, an observation unit, and a detection unit, wherein: the linear ultrasonic motor drive module is used to determine the grid line position of the solar cell after it is transported to the workstation, and align the welding strip with the grid line of the solar cell; the calculation unit is used to evaluate the welding quality and damage risk between the welding strip and the solar cell based on a finite element model and the pressure distribution applied to the welding strip by the ultrasonic vibration welding head, and select the pressure distribution that meets the evaluation criteria as the preferred pressure distribution; the finite element model is established based on the contact stress distribution between the welding strip and the solar cell; the pressure distribution applied to the welding strip by the welding head is such that the pressure in the middle region is higher than the pressure in the edge region; the ultrasonic vibration... The auxiliary welding module includes: an ultrasonic vibration welding head, a flexible pressure unit, and a temperature sensor. The pressure sensor is mounted on the flexible pressure unit. The ultrasonic vibration welding head transmits vibration to the welding strip through the flexible pressure unit, enabling the ultrasonic vibration welding head to perform optimized pressure distribution for welding between the welding strip and the battery cell. The observation unit is used to observe the actual temperature of the welding head and the actual molten pool morphology of the welding point during the welding process. Based on whether the actual temperature exceeds the standard temperature range, the actual temperature is adjusted accordingly. Based on whether the actual molten pool width is greater than the standard molten pool width, the pressure applied by the welding head is adjusted accordingly. The detection unit is used to detect the actual molten pool width, welding strip offset, exposed grid line width, and cold solder joints after welding. If all meet the standards, the welding is considered qualified.

[0016] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: ultrasonic welding is used to improve the positioning accuracy between the welding strip and the grid line; the welding pressure distribution between the welding strip and the battery cell is evaluated in advance by using a finite element model, and a suitable pressure distribution is selected to ensure welding quality while reducing the risk of damage; the welding quality is improved based on the observation and adjustment of temperature and molten pool morphology during the welding process. Attached Figure Description

[0017] Figure 1 A schematic flowchart of the precision low-stress photovoltaic ultrasonic welding control method provided by the present invention;

[0018] Figure 2 This is a schematic diagram of the structure of the linear ultrasonic motor drive module provided by the present invention;

[0019] Figure 3 A cross-sectional view of the ultrasonic vibration welding module provided by the present invention;

[0020] Figure 4 A schematic diagram of the sensor arrangement for the multi-parameter sensing module provided by the present invention;

[0021] 1, 2 - Piezoelectric ceramic sheet; 3 - Elastomer; 4 - Movers; 5 - Ultrasonic vibration module; 6 - Welding head; 7 - Flexible pressure unit; 8 - Temperature sensor. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0023] See Figure 1 This is a flowchart illustrating the precision low-stress photovoltaic ultrasonic welding control method provided by the present invention.

[0024] In this embodiment of the invention, after the battery cell is transported to the work station, the grid line position of the battery cell is determined, and the solder ribbon is aligned with the grid line of the battery cell.

[0025] In practice, a line scan camera (5μm / pixel resolution) can be used to acquire images of the grid lines of the battery cell, and the center position of the grid lines (error ±1μm) can be calculated using an edge detection algorithm.

[0026] In specific implementation, μm mentioned in this invention refers to micrometer.

[0027] See Figure 2 This is a schematic diagram of the linear ultrasonic motor drive module provided by the present invention.

[0028] In practical implementation, a V-shaped linear ultrasonic motor can be selected, such as... Figure 2 As shown, the structure includes piezoelectric ceramic sheets (1 and 2), an elastomer (3), and a mover (4). The stator is a composite structure of piezoelectric ceramic sheet and elastomer, and the mover (4) is made of silicon nitride (Si3N4), with a positioning accuracy of ≤±100nm. A linear ultrasonic motor drives a ribbon reel (the ribbon is typically 15μm thick and 0.3mm wide) to precisely move along the XY direction based on visual feedback data (displacement accuracy ±100nm), aligning the front end of the ribbon to the center of the first grid line of the first solar cell (deviation ≤1μm).

[0029] In this embodiment of the invention, based on the finite element model and the pressure distribution applied to the welding strip by the ultrasonic vibration welding head, the welding quality and damage risk between the welding strip and the battery cell are evaluated, and the pressure distribution that meets the evaluation results is selected as the preferred pressure distribution.

[0030] In this embodiment of the invention, the finite element model is established based on the contact stress distribution between the solder strip and the battery cell.

[0031] In practical implementation, considering material properties, contact mechanics, ultrasonic vibration loads, and multiphysics coupling effects, a finite element model of the contact stress distribution between the solar cell and the solder ribbon is established. The solar cell can be configured as a composite structure of a silicon substrate and surface electrodes, the solder ribbon as an elasto-plastic body, the flexible film as a linear elastic material, and the ultrasonic welding head as an elastic body. The contact between the solder ribbon and the solar cell's main grid can be configured as frictional contact, while the contact between the flexible film and the solder ribbon can be configured as binding contact. For the model's mesh generation, the contact area between the solar cell and the solder ribbon, considered a critical region, can be finely meshed, while non-critical regions can be sparsely meshed. The flexible film uses at least three layers of elements to capture bending stress. The solar cell and solder ribbon can use 8-node hexahedral reduced integration elements (C3D8R), and the flexible film can use 4-node shell elements (S4R) (these are the unit types in the finite element software Abaqus). A static pressure of 80 N was applied to the welding strip using an ultrasonic vibration welding head and kept constant. The control time step was set to 20 increments per cycle to simulate the contact stress distribution between the welding strip and the battery cell, and the equivalent plastic strain (PEEQ) value to evaluate whether the welding strip yielded.

[0032] In practical implementation, an elastoplastic body is a solid material that possesses both elastic and plastic deformation characteristics. Its mechanical behavior is divided into two stages: elastic and plastic. Under the action of external force, an elastoplastic body simultaneously produces recoverable elastic deformation and irreversible plastic deformation. When the external force is removed, some deformation can be recovered (elastic deformation), while some is permanently retained (plastic deformation). This matches the characteristics of welding strips.

[0033] In practical applications, linear elastic materials refer to materials where stress and strain exhibit a linear relationship within the elastic range, allowing them to completely recover their original shape after unloading, with deformation proportional to the external force. This aligns with the characteristics of flexible films.

[0034] In this embodiment of the invention, the pressure distribution applied by the welding head to the welding strip is such that the pressure in the middle region is higher than the pressure in the edge region.

[0035] In this embodiment of the invention, the interfacial plastic strain value at the contact interface between the solder strip and the battery cell is calculated. If the interfacial plastic strain value is greater than the standard plastic strain value, the welding quality is deemed to be qualified. The maximum stress on the battery cell is calculated. If the maximum stress is less than the standard stress, the damage risk is deemed to be qualified.

[0036] In this embodiment of the invention, the standard plastic strain value is 0.05 and the standard stress is 100 MPa.

[0037] In practice, after a long period of testing and experimentation, it was determined that setting the plastic strain value and the standard stress to 0.05 and 100 MPa respectively is more appropriate. This can balance the welding strength and the probability of microcracks at the same time, which can ensure the quality of welding and avoid damage to the battery cells caused by excessive stress.

[0038] In practical implementation, different pressure distribution combinations were traversed during the simulation based on the finite element model. In these combinations, the pressure in the middle region was set to 30mN to 50mN, and the pressure in the edge region to 20mN to 30mN. The welding quality and damage risk were evaluated. When the interface plastic strain PEEQ > 0.05, it indicated an effective bond between the weld strip and the cell grid lines; a maximum principal stress of <100MPa for the cell was considered a safe value. The simulation results are as follows:

[0039] (1) Middle area: 30mN, edge area: 30mN, welding strength: 1.2N / mm, probability of microcrack: 5%;

[0040] (2) Middle area: 40mN, edge area: 25mN, welding strength: 1.8N / mm, probability of microcrack <1%;

[0041] (3) Middle area: 50mN, edge area: 20mN, welding strength: 2.0N / mm, probability of microcrack: 15%.

[0042] The simulation results show that the maximum pressure in the middle region is 35mN to 45mN, and the maximum pressure in the edge region is 22mN to 28mN. The preferred pressure setting for the middle region is 40mN, and the pressure setting for the edge region is 25mN, which can balance the welding strength and the probability of microcracks.

[0043] In practice, the pressure values ​​in the central and edge regions are determined based on finite element simulation models combined with experimental verification, rather than entirely predetermined empirical solutions. Because of the flexible film in the central region, insufficient contact stress due to film deformation or ultrasonic vibration attenuation can lead to insufficient welding energy and the risk of incomplete welds. In the edge regions, excessive stress can cause microcracks in the solar cells. Through simulation and pressure distribution adjustment, a central pressure of 40 mN is set to ensure effective welding, while an edge pressure of 25 mN is used to avoid cell damage. Typical solar cell warpage scenarios include convex and concave warpage. To match this warpage, the welding pressure distribution is adjusted: 40 mN in the central region and 25 mN in the edge region. This also actively adapts to the bending deformation (warpage) of the solar cell itself, achieving uniform contact between the solder strip and the main grid, ensuring welding quality and reliability.

[0044] In practice, the range of the middle region can be centered on the center line of the interface between the solder ribbon and the cell grid line, and occupy 1 / 6 to 2 / 3 of the interface area. The range of the edge region is the surrounding area excluding the middle region.

[0045] In this embodiment of the invention, the ultrasonic vibration welding head performs a preferred pressure distribution to weld the welding strip and the battery cell.

[0046] In practical implementation, for example, if the preferred pressure distribution is 40mN in the middle region and 25mN in the edge region, a buffer zone can be set in the boundary region between the middle and edge regions. The pressure in the buffer zone can be gradually reduced from the pressure in the middle region to the pressure in the edge region. The specific pressure gradient reduction method can be calculated through fitting or other methods. The area of ​​the buffer zone can be set to occupy 1 / 6 to 1 / 3 of the contact interface area, with half in the middle region and the other half in the edge region.

[0047] In this embodiment of the invention, the ultrasonic vibration welding head is further provided with a flexible film, through which the vibration is transmitted to the contact interface between the welding strip and the battery cell.

[0048] In specific implementations, the thickness of the flexible film is 40µm to 60µm, preferably 50µm. The flexible film is typically made of high-performance polymer composite materials, which are materials composed of high-performance polymers as the matrix (continuous phase) and reinforced with carbon fibers, aramid fibers, glass fibers, SiC particles, etc. (reinforcing phases).

[0049] See Figure 3 This is a cross-sectional view of the ultrasonic vibration welding module provided by the present invention.

[0050] In specific implementation, the ultrasonic vibration welding module includes an ultrasonic vibration module 5, a welding head 6, a flexible pressure unit 7, and a temperature sensor 8. Multiple pressure sensors are set on the flexible pressure unit. When welding begins, the welding head presses down, and the flexible pressure unit contacts the battery cell at a speed of 0.1 mm / s. The pressure sensors provide real-time feedback on the pressure at each point (initial pressure 20 mN).

[0051] In practical implementation, the voltage distribution of the ultrasonic vibration module can be calculated based on the preferred pressure distribution scheme. The electrical energy is then converted into the corresponding mechanical energy to obtain the corresponding pressure distribution.

[0052] In practical implementation, the flexible film directly contacts the solder ribbon, and the inclusion of the flexible film is one of the key improvements of this invention. A longitudinal vibration transducer (frequency 30kHz, amplitude 10μm) excites ultrasonic vibration, which is transmitted to the interface between the solder ribbon and the solar cell through the flexible film. The flexible film itself is soft and deformable; during vibration transmission, its elasticity and compliance transform harmful sliding friction into beneficial rolling / elastic friction, optimizing pressure distribution and thus improving the interaction of the welding interface at the microscale. This achieves low-friction welding, effectively reducing the frictional resistance between the solder ribbon and the solar cell. The coefficient of friction can be reduced from 0.3 to 0.1. Therefore, while applying the same pressure to the solder ribbon, the stress applied to the solar cell can be effectively reduced, ensuring welding effectiveness while minimizing damage to the solar cell.

[0053] In this embodiment of the invention, during the welding process, the actual temperature of the welding head and the actual molten pool shape of the welding point are observed. Based on whether the actual temperature exceeds the standard temperature range, the actual temperature is adjusted accordingly. Based on whether the actual (maximum) molten pool width is greater than the standard molten pool width, the pressure applied to the welding head is adjusted accordingly.

[0054] In this embodiment of the invention, the standard temperature range is 245°C to 255°C; the standard weld pool width is 70 μm; if the actual weld pool width is smaller than the standard weld pool width, the pressure applied by the welding head is increased.

[0055] In practice, the temperature of the welding area is monitored, and the temperature is stabilized at 245℃ to 255℃, preferably 250±2℃, by adjusting the power of the heating module of the welding head.

[0056] In practice, pressure and temperature are maintained for a standard time period (which can be set according to the actual application scenario, usually 5 seconds). During this period, the molten pool morphology is continuously monitored. If the maximum molten width of a certain area is only 65μm (below the threshold of 70μm), the control system immediately triggers the flexible pressure unit of the corresponding point or area to increase the pressure by 5mN to compensate for the shrinkage of the molten pool, thereby increasing the molten width.

[0057] In this embodiment of the invention, after welding is completed, the actual weld pool width, weld strip offset, exposed grid line width, and cold weld condition are detected. If all of these meet the standards, the welding is deemed qualified.

[0058] In this embodiment of the invention, after welding is completed, the line scan camera scans the weld strip again. If the actual molten pool width is between 82μm and 90μm (minimum width greater than or equal to 82μm, maximum width less than or equal to 90μm), the weld strip (maximum) offset is less than or equal to 2μm, the exposed part (maximum) width of the grid line is less than 10μm (reflecting the degree of microcracks), and the resistance of the contact part between the weld strip and the cell is greater than or equal to 25mΩ (reflecting the welding quality, effective bonding, and no cold welds), then the welding is considered qualified.

[0059] In this embodiment of the invention, the amplitude of the ultrasonic vibration welding head is set to 11 μm to 13 μm.

[0060] In practice, based on long-term testing and feedback from welding results, setting the amplitude of the ultrasonic vibration welding head to 11μm to 13μm can effectively improve the uniformity of the weld width, that is, improve the welding quality. Preferably, the amplitude is set to 12μm.

[0061] In practical implementation, tests have shown that using the method provided by this invention, the yield of photovoltaic modules reaches 99.3%, and the photoelectric conversion efficiency is 26.4% (an improvement of 1.6 percentage points), meeting the manufacturing requirements of high-performance gridless photovoltaic modules.

[0062] See Figure 4 This is a schematic diagram of the sensor arrangement of the multi-parameter sensing module provided by the present invention.

[0063] This invention also provides a precision low-stress photovoltaic ultrasonic welding control system, comprising: a linear ultrasonic motor drive module, a calculation unit, an ultrasonic vibration-assisted welding module, an observation unit, and a detection unit, wherein: the linear ultrasonic motor drive module is used to determine the grid line position of the solar cell after it is transported to the workstation, and align the welding strip with the grid line of the solar cell; the calculation unit is used to evaluate the welding quality and damage risk between the welding strip and the solar cell based on a finite element model and the pressure distribution applied to the welding strip by the ultrasonic vibration welding head, and select the pressure distribution that meets the evaluation criteria as the preferred pressure distribution; the finite element model is established based on the contact stress distribution between the welding strip and the solar cell; the pressure distribution applied to the welding strip by the welding head is such that the pressure in the middle region is higher than the pressure in the edge region; the ultrasonic vibration-assisted welding module... The welding assistance module includes: an ultrasonic vibration welding head, a flexible pressure unit, and a temperature sensor. The pressure sensor is mounted on the flexible pressure unit. The ultrasonic vibration welding head transmits vibration to the welding strip through the flexible pressure unit, enabling the ultrasonic vibration welding head to perform optimized pressure distribution for welding between the welding strip and the battery cell. The observation unit is used to observe the actual temperature of the welding head and the actual molten pool morphology of the welding point during the welding process. Based on whether the actual temperature exceeds the standard temperature range, the actual temperature is adjusted accordingly. Based on whether the actual molten pool width is greater than the standard molten pool width, the pressure applied by the welding head is adjusted accordingly. The detection unit is used to detect the actual molten pool width, welding strip offset, exposed grid line width, and cold solder joint condition after welding. If all meet the standards, the welding is considered qualified.

[0064] In specific implementations, the precision low-stress photovoltaic ultrasonic welding control system provided by this invention, wherein the units or modules used to perform functions, steps or methods can refer to the precision low-stress photovoltaic ultrasonic welding control method provided by this invention.

Claims

1. A photovoltaic ultrasonic welding control method, characterized by, The method comprises the following steps: After the battery piece is transported to the work station, the grid line position of the battery piece is determined, and the welding strip is aligned with the grid line of the battery piece; Based on the finite element model and the pressure distribution applied by the ultrasonic vibration welding head on the welding strip, the welding quality and damage risk between the welding strip and the battery piece are evaluated, the interface plastic strain value of the contact interface between the welding strip and the battery piece is calculated, and if the interface plastic strain value is greater than the standard plastic strain value, the welding quality is determined to be qualified; The maximum stress on the battery piece is calculated, and if the maximum stress is less than the standard stress, the damage risk is determined to be qualified; the pressure distribution that meets the standard in the evaluation result is selected as the optimal pressure distribution; the finite element model is established based on the contact stress distribution between the welding strip and the battery piece; the ultrasonic vibration welding head is also provided with a flexible film; the pressure distribution applied by the welding head on the welding strip is that the pressure in the middle region is higher than that in the edge region; The ultrasonic vibration welding head executes the optimal pressure distribution to perform welding between the welding strip and the battery piece; During the welding process, the actual temperature of the welding head and the actual molten pool shape of the welding point are observed, the actual temperature is adjusted accordingly based on whether the actual temperature exceeds the standard temperature range, and the pressure applied by the welding head is adjusted accordingly based on whether the actual molten pool width is greater than the standard molten pool width; After the welding is completed, the actual molten pool width, the welding strip offset, the grid line bare part width, and the virtual welding condition are detected, and if all meet the standard, the welding is determined to be qualified.

2. The photovoltaic ultrasonic welding control method of claim 1, wherein, Further comprising: The thickness of the flexible film is 40-60 μm.

3. The photovoltaic ultrasonic welding control method of claim 2, wherein, The amplitude of the ultrasonic vibration welding head is set to 11-13 μm.

4. The photovoltaic ultrasonic welding control method of claim 2, wherein, The establishment of the finite element model comprises: the battery piece is set as a composite structure of a silicon substrate and a surface electrode, the welding strip is set as an elastoplastic body, the flexible film of the ultrasonic vibration welding head is set as a linear elastic material, the ultrasonic vibration welding head is set as an elastic body, and the welding strip and the battery piece grid line are set as frictional contact, and the flexible film and the welding strip are set as bundled contact.

5. The photovoltaic ultrasonic welding control method of claim 2, wherein, The standard plastic strain value is 0.05, and the standard stress is 100 MPa.

6. The photovoltaic ultrasonic welding control method of claim 2, wherein, The optimal pressure distribution has a maximum pressure of 35-45 mN in the middle region and a maximum pressure of 22-28 mN in the edge region.

7. The photovoltaic ultrasonic welding control method of claim 1, wherein, The standard temperature range is 245-255 °C; the standard molten pool width is 70 μm; and if the actual molten pool width is less than the standard molten pool width, the pressure applied by the welding head is increased.

8. The photovoltaic ultrasonic welding control method of claim 1, wherein, The detection of the actual molten pool width, the welding strip offset, the grid line bare part width, and the virtual welding condition, if all meet the standard, determines that the welding is qualified, which comprises: If the actual molten pool width is between 82-90 μm, the welding strip offset is less than or equal to 2 μm, the grid line bare part width is less than 10 μm, and the resistance of the contact part between the welding strip and the battery piece is greater than or equal to 25 mΩ, the welding is determined to be qualified.

9. A photovoltaic ultrasonic welding control system characterized by, Comprising: A linear ultrasonic motor driving module, a calculation unit, an ultrasonic vibration assisted welding module, an observation unit, and a detection unit, wherein: The linear ultrasonic motor driving module is used to determine the grid line position of the battery piece after the battery piece is transported to the work station, and align the welding strip with the grid line of the battery piece. The computing unit is configured to evaluate the welding quality and damage risk between the welding strip and the battery piece based on the finite element model and the pressure distribution applied by the ultrasonic vibration welding head on the welding strip, calculate the interface plastic strain value of the contact interface between the welding strip and the battery piece, and determine that the welding quality is qualified if the interface plastic strain value is greater than the standard plastic strain value; calculate the maximum stress on the battery piece, and determine that the damage risk is qualified if the maximum stress is less than the standard stress; and select the pressure distribution meeting the standard as the optimal pressure distribution; the finite element model is established based on the contact stress distribution between the welding strip and the battery piece; the ultrasonic vibration welding head is further provided with a flexible film; and the pressure distribution applied by the welding head on the welding strip is that the pressure in the middle region is higher than that in the edge region. The ultrasonic vibration assisted welding module comprises an ultrasonic vibration welding head, a flexible pressure unit and a temperature sensor, the pressure sensor is arranged on the flexible pressure unit, the ultrasonic vibration welding head transmits vibration to the welding strip through the flexible pressure unit, and is used for the ultrasonic vibration welding head to execute the optimal pressure distribution and perform welding between the welding strip and the battery piece. The observation unit is configured to observe the actual temperature of the welding head and the actual molten pool shape of the welding point during the welding process, adjust the actual temperature correspondingly based on whether the actual temperature exceeds the standard temperature range, and adjust the pressure applied by the welding head correspondingly based on whether the actual molten pool width is greater than the standard molten pool width. The detection unit is configured to detect the actual molten pool width, the welding strip offset, the width of the exposed part of the grid line and the virtual welding condition after the welding is completed, and determine that the welding is qualified if all of them meet the standard.

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