Gradient current control method and system for horizontal electroplating equipment

Abstract

The present application belongs to the field of photovoltaic solar cell manufacturing and electroplating technology, and particularly relates to a gradient current control method and system for horizontal electroplating equipment, which comprises the following steps: in step S1, a sensor sends a trigger signal when the front of a cell piece enters a starting position in an anode box region; in step S2, a PLC controller controls a rectifier to output a preset initial current value; in step S3, taking the trigger signal as a time starting point, the rectifier is controlled to keep the current constant and increase the current step length cycle by cycle according to a pre-established current-time step mapping relationship, until the cell piece completely enters and reaches a target working current; in step S4, the target working current is kept constant; and in step S5, when the tail of the cell piece starts to exit, the step decrease is symmetrically performed, and the current is decreased cycle by cycle to a preset final value. The present application makes the total current change synchronously with the instantaneous electroplating area through the step current, keeps the local current density constant, and eliminates overplating at the head and tail.

Description

Technical Field

[0001] This invention relates to the fields of photovoltaic solar cell manufacturing and electroplating technology, specifically to a gradient current control method and system for horizontal electroplating equipment. Background Technology

[0002] In the metallization process of photovoltaic cells (such as heterojunction (HJT) and TOPCon cells), copper electroplating technology is gradually replacing traditional silver paste screen printing due to its advantages such as low cost and high conductivity. Horizontal electroplating equipment is widely used because of its high degree of automation and good compatibility.

[0003] One common type of horizontal electroplating equipment employs an "external conductivity" design. Its structure is as follows: the cathode contact rollers are positioned outside the electrolyte surface of the electroplating tank, not in contact with the solution; the anode is immersed in the electrolyte within the anode box. An anode box is placed between a pair of cathode rollers. The solar cells to be plated are transported horizontally, their edges sliding in contact with the cathode rollers to form a cathode circuit. The advantage of this design is that it avoids problems such as corrosion, solution contamination, and uneven current distribution caused by prolonged immersion of the cathode rollers in the electrolyte.

[0004] However, this equipment structure has an inherent problem: the dynamic change in the effective plating area. When the leading edge of the solar cell enters the anode box area from the cathode roller, only a small portion of the area is exposed to the electric field. If the total current applied at this time is the target current, the local current density will far exceed the process window, leading to severe over-plating at the leading edge. Typical manifestations include: coarse plating grains, surface nodules, scorching, and even burning through the underlying functional layer. Similarly, as the tail of the solar cell leaves the anode area, the effective area gradually decreases. If the current does not decrease accordingly, over-plating at the tail will also occur, severely affecting the plating uniformity and cell yield.

[0005] In existing technologies, some electroplating power supplies have a soft-start function, and their current rise curve is a preset fixed-time function, which is unrelated to the real-time position and area of ​​the solar cell, and cannot solve the problem of local current density mismatch caused by dynamic changes in area. Another existing solution uses a vision system to detect the plating area in real time and control the current in a closed loop, but the system is expensive and has a large response delay, making it difficult to adapt to high-speed production lines. Another solution divides the anode box into multiple independent sections along the transmission direction and supplies power to each section separately. Although this can partially alleviate the problem, the structure is complex, the hardware cost is high, and there are still current steps between sections.

[0006] Therefore, there is an urgent need for a low-cost, high-reliability current control method to solve the problem of overplating at the beginning and end of the plating tank caused by dynamic changes in the plating area in external conductive horizontal electroplating equipment. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and to provide a stepped current control method and system for horizontal electroplating equipment. This method uses stepped current to make the total current change synchronously with the instantaneous electroplating area, maintains a constant local current density, effectively solves the problem of overplating at the head and tail of the battery cell, improves the uniformity of the coating and the product yield, and has the advantages of low cost and easy promotion.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a gradient current control method for a horizontal electroplating apparatus. The horizontal electroplating apparatus includes an electroplating tank, an anode box immersed in an electrolyte, a pair of cathode contact rollers disposed outside the electrolyte and located on both sides of the anode box, and a conveying mechanism for horizontally transporting solar cells. During transport, the surface of the solar cells slides into contact with the cathode rollers to form a cathode conductive circuit. The control method includes: Step S1: When the leading edge of the solar cell begins to enter the starting position of the anode box area, a trigger signal is sent by the sensor; Step S2: After receiving the trigger signal, the PLC controller controls the rectifier to output a preset initial current value; Step S3: Taking the trigger signal as the starting point of time, the PLC controller controls the rectifier to maintain a constant output current in each step cycle according to the current-time step mapping relationship established in advance based on the constant transmission speed of the battery cell, the width of the battery cell and the size of the anode box. After each step cycle, the output current is increased by a preset current step size so that when the battery cell is fully entered into the anode box area, the output current reaches the target operating current. Step S4: After the solar cell is fully inside the anode box area, maintain a constant target operating current output; Step S5: When the leading edge of the solar cell begins to exit the anode box area, the PLC controller controls the rectifier to perform a step-down descent symmetrical to step S3. The current remains constant within each step cycle, and after each step cycle, the output current is reduced by a preset current step size until the solar cell completely leaves the anode box area, at which point the current drops to a preset final value. By triggering an initial micro-current when the solar cell enters, using a step-up descent that follows linear area growth, maintaining a constant current after complete entry, and performing a symmetrical step-down descent when the cell exits, the total electroplating current is kept synchronized with the instantaneous plating area of ​​the solar cell. This keeps the local current density constant within the process window, completely solving the inherent over-plating problem at the head and tail of external conductive horizontal electroplating equipment. Furthermore, this method is based on time-feedforward control, eliminating the need for a complex feedback system, making it simple, low-cost, and robust.

[0009] In some embodiments, the method for establishing the current-time step mapping relationship is as follows: based on the cell width W, transmission speed v, and target current density J, a slope function I(t) = J × W × v × t that represents the linear change of ideal current with time is determined, and this linear slope is discretized into a step wave with a step period as the time interval and a current step size as the increment; the current step size ΔI is based on... The calculation is performed, where I_max is the target operating current, T is the total time required for the solar cell to enter the anode box region from the start, and Δt is the step period. A linear ramp function is determined based on the solar cell width, transmission speed, and target current density, and discretized into a step wave. A formula for calculating the current step size is also provided. This scheme transforms continuous linear area changes into step-like instructions easily executed by the rectifier, solving the problem that ordinary industrial rectifiers cannot output a perfect linear ramp. While reducing hardware performance requirements, it ensures control accuracy with a near-constant current density.

[0010] In some embodiments, the step period is 0.1 to 0.5 seconds, the current step size is 2 mA to 20 mA, and the initial current value is 1 mA to 10 mA. This parameter range balances the smoothness of the step approximation with the rectifier's responsiveness, avoiding excessive current density fluctuations caused by an excessively long step period, while also preventing the step period from exceeding the device's response limit due to an excessively short step period. This allows the control method to adapt to the process requirements of different battery cell specifications and transmission speeds.

[0011] In some embodiments, the initial current value is 5mA, the step period is 0.2 seconds, and the current step size is 5mA. This parameter combination is a specific value optimized for conventional cell size and transmission speed. It can minimize local current density fluctuations while ensuring stable output of the rectifier in each step period, providing directly usable control parameters for mass production and exhibiting excellent practicality.

[0012] In some embodiments, in step S5, the trigger signal for the stepped descent is provided by another sensor located on the anode box outlet side, or calculated by the PLC controller based on the cell transfer speed and cell length. Both methods can accurately capture the moment when the tail begins to exit, ensuring that the stepped descent is strictly synchronized with the reduction of the remaining plating area. The calculation method eliminates the need for additional sensors, further reducing system costs; the sensor method offers higher detection accuracy and anti-interference capabilities, and can be flexibly selected.

[0013] In some embodiments, in step S2, the initial current output serves to confirm circuit continuity and as the starting point for the step-up process, avoiding abrupt changes from zero current to the first step. This ensures that the solar cell obtains a safe micro-current as soon as it forms a conductive circuit. On the one hand, this verifies the reliability of the cathode contact, preventing open circuits or arcing due to poor contact; on the other hand, it eliminates current overshoot caused by the zero-current jump, protecting the fragile initial plating layer at the solar cell tip and laying the foundation for subsequent uniform electroplating.

[0014] In some embodiments, for battery cells with chamfered or non-rectangular heads, the current-time step mapping relationship is a non-linear mapping, and the current step size corresponding to each step period is adjusted according to a preset area change function, so that the local current density remains constant. For battery cells with chamfered or non-rectangular heads, the current-time step mapping relationship is defined as a non-linear mapping, and the current step size corresponding to each step period is adjusted according to a preset area change function. This solution extends the applicability of the present invention from standard rectangular battery cells to irregularly shaped battery cells. Through non-uniform step compensation, even if the area growth is non-linear, the local current density can still remain constant, thus achieving the same effect of eliminating over-plating at the head and tail and improving the uniformity of the entire cell.

[0015] The present invention also provides a gradient current control system for a horizontal electroplating apparatus, for implementing the gradient current control method of the horizontal electroplating apparatus, characterized in that it includes: A conveying mechanism for horizontally transporting battery cells at a constant speed; An electroplating tank is provided with an anode box, in which an anode is placed and immersed in an electrolyte. A pair of cathode contact rollers are positioned outside the electrolyte surface and on both sides of the anode box along the transmission direction, for sliding contact with the surface of the battery cell to form a cathode conductive circuit; A rectifier is used to output controllable direct current. The first sensor, located at the inlet side of the anode box, is used to detect the arrival of the leading edge of the solar cell; A PLC controller, connected to the first sensor and the rectifier, is configured to execute the gradient current control method for the horizontal electroplating equipment. This gradient current control system for the horizontal electroplating equipment allows for the implementation of the gradient current control method simply by adding sensors and updating the PLC control program to existing horizontal electroplating equipment. The modification cost is extremely low, making it easy to promote and use in industry.

[0016] In some embodiments, a second sensor is also included, disposed on the outlet side of the anode box, for triggering the stepped descent step. Adding the second sensor makes the detection of the tail exit moment more direct and accurate, avoiding calculation errors caused by cell length tolerances or transmission speed fluctuations, further improving the accuracy and reliability of the tail stepped descent control, and ensuring the consistency of the tail coating quality.

[0017] In some embodiments, the PLC controller sends a current setpoint to the rectifier via an analog output module or a digital communication protocol; the transmission mechanism is a constant-speed transmission mechanism to ensure a constant transmission speed of the solar cells. Sending current commands through a standardized interface ensures the accuracy and real-time nature of the setpoint transmission; the constant-speed transmission mechanism ensures a constant transmission speed of the solar cells, thereby enabling the precise execution of the time-based current-time ladder mapping relationship, ensuring the accuracy and stability of feedforward control at the system level.

[0018] The beneficial effects of this invention are: First, by employing a stepped current control method, the output current changes synchronously with the instantaneous electroplating area as the solar cell enters and exits the anode box region, maintaining the local current density within the process window. Only an initial micro-current is applied to the head of the solar cell, with the current gradually increasing as the immersion area increases. This avoids problems such as scorching and nodulation caused by excessive current due to an insufficient area at the head. When the solar cell exits from the tail, the current is symmetrically reduced in a stepped manner, preventing over-plating due to the gradually decreasing area and increasing current density at the tail. Actual tests show that under constant current control, the length of scorching defects at the solar cell head can reach 5-10 mm, while using the method of this invention, the length of defects at both the head and tail is shortened to less than 1 mm, or even completely eliminated.

[0019] Secondly, electroplating begins at the tip of the solar cell under extremely low current density conditions, resulting in small and dense initial crystal nuclei that provide an ideal growth substrate for subsequent electroplating. Throughout the electroplating process, the local current density remains constant, ensuring uniform coating thickness from tip to tip, consistent grain growth conditions, and a highly uniform microstructure. This not only improves the appearance quality but also guarantees the electrical and mechanical properties of the coating.

[0020] Third, under traditional constant current control methods, the over-plating area at the head is prone to developing a loose and rough plating structure, which is susceptible to peeling and corrosion during subsequent processes or use, leading to leakage or performance degradation. This invention eliminates over-plating defects at the source, avoiding reliability risks caused by plating quality issues, significantly improving key electrical performance parameters such as fill factor and open-circuit voltage of the solar cells, and effectively ensuring product yield.

[0021] Fourth, no major hardware modifications are required to existing horizontal electroplating equipment. Only the addition of low-cost photoelectric sensors to the existing equipment is needed, or existing sensors can be used directly by modifying the PLC program. No changes to the equipment's hardware structure are required. The stepped control method has low requirements for the dynamic response speed of the rectifier; ordinary industrial rectifiers can meet the needs, resulting in extremely low overall modification costs.

[0022] Fifth, a time-based feedforward control strategy is adopted. The current step is set based on deterministic parameters such as the cell transfer speed and anode box width, and is not affected by fluctuations in external factors such as plating solution temperature, concentration, and flow state. Even with slight fluctuations in the transfer speed, because the current step is directly bound to time, it can still maintain a good current-area matching effect, ensuring the stability and consistency of electroplating quality. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0024] Figure 1 This is a schematic flowchart of the stepped current control method according to an embodiment of the present invention; Figure 2 This is a side view of the external conductive method of the horizontal electroplating equipment according to an embodiment of the present invention; Figure 3 This is a top view schematic diagram of the external conductive method of the horizontal electroplating equipment according to an embodiment of the present invention; Figure 4 This is a comparison chart of current setting curves under different control modes in embodiments of the present invention, wherein... Figure 4 (a) shows the curve for a conventional constant current setting. Figure 4 (b) is the theoretical linear current curve. Figure 4 (c) is the stepped gradient current curve of the present invention; Figure 5 This is a schematic diagram comparing the grid line morphology of the battery cell before and after applying the method of the present invention, wherein... Figure 5 Image (a) shows the head grid morphology under normal settings. Figure 5 (b) shows the morphology of the gate line after applying the method of the present invention; Figure 6 This is a schematic diagram of the gradient current control system according to an embodiment of the present invention. Detailed Implementation

[0025] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings, are intended to cover non-exclusive inclusion.

[0027] The directional and positional terms used in this invention, such as up, down, front, back, left, right, inside, outside, top, bottom, side, etc., are merely for reference to the accompanying drawings. Therefore, the directional and positional terms used are for illustrating and understanding this invention, and not for limiting the scope of protection of this invention.

[0028] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments: like Figure 2 and Figure 3 As shown, the external conductive horizontal electroplating equipment applicable to the embodiments of the present invention includes an electroplating tank 1, an anode box 2, a pair of cathode contact rollers 4a and 4b, and a conveying mechanism 5 composed of multiple conveying rollers.

[0029] An anode is disposed inside the anode box 2, and the anode box 2 is filled with electrolyte 3. The side of the anode box 2 facing the battery cell 6 has an open structure so that the electric field can act on the surface of the battery cell 6, and this open area is the effective electroplating area.

[0030] A pair of cathode contact rollers 4a and 4b are both disposed above the surface of the electrolyte 3, i.e., outside the electrolyte 3, and are located on both sides of the anode box 2 along the transport direction of the solar cell 6. Cathode contact roller 4a is located on the inlet side of the anode box 2, and cathode contact roller 4b is located on the outlet side of the anode box 2. Driven by the conveying mechanism 5, the solar cell 6 is transported horizontally in the direction indicated by the arrow. The edge of the plated surface of the solar cell 6 slides in contact with the cathode contact rollers 4a and 4b, respectively, thereby forming a cathode conductive circuit.

[0031] During the electroplating process, the head of the solar cell 6 enters the projection area of ​​the anode box 2 first, followed by the main body, and finally the tail exits. The width of the anode box 2 along the transport direction of the solar cell 6 is L.

[0032] like Figure 1As shown, the present invention provides a gradient current control method for a horizontal electroplating equipment, specifically including steps S1 to S5. In this embodiment, each step is controlled by a PLC controller as the core, coordinating the sensors and rectifier to complete the process.

[0033] Step S1: A first sensor, which is a photoelectric sensor, is installed on the inlet side of the anode box 2. When the battery cell 6 is conveyed forward under the drive of the conveying mechanism 5, and its leading edge begins to enter the starting position of the anode box 2 area, the first sensor detects the arrival of the battery cell 6 and immediately sends a trigger signal to the PLC controller. This trigger signal marks the formal start of the electroplating process and serves as the time reference point for subsequent steps S2 and S3.

[0034] Step S2: After receiving the trigger signal described in step S1, the PLC controller immediately controls the rectifier to output a preset initial current value. In this embodiment, the initial current value is set to 5 mA.

[0035] The purpose of this initial current value is to confirm that the cathode conductive circuit has been reliably turned on, and at the same time to provide a non-zero starting point for the step-up in step S3. If the current jumps directly from zero to the first step current value, current overshoot or instantaneous high current density may occur. Setting the initial current value effectively avoids this abrupt change, making the transition smoother.

[0036] Step S3: Taking the trigger signal mentioned in step S1 as the starting point of time, the PLC controller controls the rectifier to perform step-up according to the constant transmission speed of the battery cell 6, the width of the battery cell 6 and the size of the anode box 2, and the pre-established current-time step mapping relationship.

[0037] The method for establishing the current-time ladder mapping relationship is as follows: Let the width of the solar cell 6 be W, the transmission speed of the conveying mechanism 5 be v, and the target current density be J. Since the instantaneous plated area S(t) of the solar cell 6 entering the anode box 2 is linearly related to time t, S(t) = W × v × t, in order to keep the current density J constant, the ideal total current should be a linear ramp function I(t) = J × W × v × t that is proportional to time.

[0038] The aforementioned continuous linear slope is discretized into a stepped wave with a step period Δt as the time interval and a current step size ΔI as the increment. The current step size ΔI is determined according to the formula... The calculation is as follows: I_max is the target operating current, and T is the total time required for cell 6 to move from the initial entry point to complete entry into the anode box 2 region. L is the width of anode box 2 along the transmission direction.

[0039] In this embodiment, the width W of the battery cell 6 is 156 mm, the transmission speed v of the conveying mechanism 5 is 100 mm / s, the width L of the anode box 2 along the transmission direction is 200 mm, and the calculated complete entry time T is 2 seconds. The target current density J is taken as 2 amperes per square decimeter, and the calculated target operating current I_max is approximately 25 mA. The step period Δt is set to 0.2 seconds, the number of steps is 10, and the current step size ΔI is 5 mA.

[0040] Based on the above mapping relationship, the PLC controller executes the following stepped current sequence: The output current remains at 5 mA during the period from 0 to 0.2 seconds; The output current remains at 10 mA during the period from 0.2 to 0.4 seconds; The output current remains at 15 mA during the period from 0.4 to 0.6 seconds; And so on, the output current remains at 25 mA during the period from 1.8 to 2.0 seconds.

[0041] Within each step cycle Δt, the PLC controller sends the current setpoint to the rectifier via the analog output module or digital communication protocol, and the rectifier outputs a constant DC current. After one step cycle, the PLC controller increases the current setpoint by one current step ΔI, and this cycle continues until the battery cell 6 is completely inside the anode box 2 area, at which point the output current exactly reaches the target operating current I_max.

[0042] Step S4: After the solar cell 6 has fully entered the anode box 2 region, the output current has reached the target operating current I_max. At this time, the PLC controller controls the rectifier to maintain a constant I_max output, and the main body of the solar cell 6 undergoes normal electroplating under a stable target current density. This constant current stage continues until the leading edge of the tail of the solar cell 6 begins to exit the anode box 2 region.

[0043] Step S5: When the leading edge of the tail of the solar cell 6 begins to exit the anode box 2 area, the step descent step is triggered. There are two ways to obtain this trigger signal: First, a second sensor located on the outlet side of the anode box 2 detects the arrival of the leading edge of the tail of the solar cell 6 and sends a trigger signal to the PLC controller; second, the PLC controller calculates the time point at which the leading edge of the tail reaches the outlet side of the anode box 2 based on the transmission speed v of the solar cell 6 and the total length of the solar cell 6, and uses this as the trigger moment.

[0044] After receiving the trigger signal, the PLC controller controls the rectifier to perform a stepped descent symmetrical to step S3. In this embodiment, the step period Δt remains 0.2 seconds, and the current step size ΔI remains 5 mA. The stepped current sequence executed by the PLC controller is as follows: During the first 0.2 seconds after triggering, the output current remains at 20 mA; During the second 0.2 seconds, the output current remains at 15 mA; During the third 0.2-second period, the output current remains at 10 mA; During the fourth 0.2-second period, the output current remains at 5 mA; After this, the battery cell 6 completely leaves the anode box 2 area, and the current drops to 0 mA or the preset standby value.

[0045] As the remaining plating area at the tail of the battery cell 6 decreases linearly over time, the output current decreases synchronously in a stepwise manner, and the tail current density is always maintained within the preset process window, thereby effectively avoiding over-plating at the tail.

[0046] Control effect comparison To clearly illustrate the technical effects of the present invention, Figure 4 A comparison of current setting curves under three different control modes is presented. Figure 4 In the middle (a), the conventional constant current control mode is used. When the battery cell comes into contact with the anode, the rectifier outputs the full current I_max. At this time, the immersion area is extremely small, resulting in an extremely high instantaneous current density at the head, which causes charring. Figure 4 In Figure (b), the theoretical linear current curve shows that the current rises and falls linearly with time, and the current density remains constant. However, this requires extremely high dynamic response performance from the rectifier, which is costly to achieve. Figure 4 (c) is the stepped gradient current curve of the present invention. By approximating the linear slope with a stepped wave, the requirements for the dynamic response capability of the rectifier are significantly reduced while ensuring that the current density is basically constant. Ordinary industrial rectifiers can handle this task.

[0047] Figure 5 Furthermore, a microscopic comparison of the grid line morphology at the head of the battery cell before and after using the method of the present invention is provided. Figure 5 In the middle (a), the grid line morphology under conventional constant current control is shown. It can be seen that the coating surface is rough and there are obvious scorching and nodule defects. Figure 5 (b) shows the grid morphology after using the method of the present invention. The coating surface is flat and dense, with fine and uniform grains, which is completely consistent with the coating quality in the middle of the battery cell.

[0048] Variant implementation When the head of the solar cell 6 has a chamfer or a non-rectangular shape, the instantaneous plated area of ​​the solar cell 6 entering the anode box 2 changes with time, which is no longer a strictly linear relationship, but a certain nonlinear function.

[0049] In this case, the area change function of the plated area of ​​the solar cell 6 as a function of displacement is determined in advance by measurement or calculation. Accordingly, the current-time step mapping relationship based on steps S3 and S5 is adjusted to a nonlinear mapping. The current step size corresponding to each step period is no longer kept constant, but is adjusted periodically according to the area change function. For example, in the chamfered head region, the area growth is slower, and the corresponding current step size is set to a smaller value; in the uniform cross-section region, the area growth returns to linear, and the current step size returns to a constant value. Through this nonlinear step compensation, the local current density remains constant throughout the entire length of the solar cell 6, which can also achieve the technical effect of eliminating over-plating at the head and tail and improving the uniformity of the entire cell.

[0050] like Figure 6 As shown, the present invention also provides a gradient current control system for a horizontal electroplating device.

[0051] The system includes a conveying mechanism 5, which is a constant-speed conveying mechanism used to horizontally transport the battery cells 6 at a constant speed v, ensuring the accurate execution of the current-time step mapping relationship.

[0052] The system includes an electroplating tank 1, an anode box 2 is provided in the electroplating tank 1, and an anode is provided in the anode box 2 and immersed in an electrolyte 3.

[0053] The system includes a pair of cathode contact rollers 4a and 4b, which are positioned outside the electrolyte 3 and located at the inlet and outlet sides of the anode box 2 along the transport direction, respectively. The cathode contact rollers 4a and 4b are used for sliding contact with the surface of the solar cell 6 to form a cathode conductive circuit.

[0054] The system includes a rectifier for outputting a controllable DC current. The rectifier receives a current setpoint command from the PLC controller and adjusts the output current accordingly.

[0055] The system includes a first sensor, which is located at the inlet side of the anode box 2 to detect the arrival of the leading edge of the battery cell 6 and send a trigger signal to the PLC controller to start step S1.

[0056] The system includes a PLC controller, which is connected to both the first sensor and the rectifier. The PLC controller is configured to execute the gradient current control method, specifically including the control logic in steps S1 to S5. The PLC controller sends the current setpoint to the rectifier via an analog output module or a digital communication protocol.

[0057] Furthermore, the system also includes a second sensor located on the outlet side of the anode box 2. This second sensor detects the arrival of the leading edge of the tail of the solar cell 6 and sends a trigger signal to the PLC controller to initiate the stepped descent process in step S5. When the second sensor is not present, the PLC controller calculates the trigger time based on the transmission speed v of the conveyor mechanism 5 and the total length of the solar cell 6.

[0058] Industrial applicability The method and system of this invention can be widely applied to the copper electroplating metallization process of photovoltaic solar cells (especially heterojunction (HJT) and TOPCon cells), and are also applicable to other substrate processing processes requiring horizontal electroplating. This invention requires no major hardware modifications to existing equipment; it can be implemented solely through software upgrades, and has promising prospects for industrial application.

[0059] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this invention; the scope of protection of this invention is defined by the claims in the claims, and all equivalent changes and modifications made in accordance with this invention are within the scope of protection of this patent.

Claims

1. A gradient current control method for a horizontal electroplating apparatus, the horizontal electroplating apparatus comprising an electroplating tank, an anode box immersed in an electrolyte, a pair of cathode contact rollers disposed outside the electrolyte and located on both sides of the anode box, and a conveying mechanism for horizontally conveying solar cells. During transport, the surface of the solar cell slides into contact with the cathode roller to form a cathode conductive circuit; its characteristic is: The control method includes: Step S1: When the leading edge of the solar cell begins to enter the starting position of the anode box area, a trigger signal is sent by the sensor; Step S2: After receiving the trigger signal, the PLC controller controls the rectifier to output a preset initial current value; Step S3: Taking the trigger signal as the starting point of time, the PLC controller controls the rectifier to maintain a constant output current in each step cycle according to the current-time step mapping relationship established in advance based on the constant transmission speed of the battery cell, the width of the battery cell and the size of the anode box. After each step cycle, the output current is increased by a preset current step size so that when the battery cell is fully entered into the anode box area, the output current reaches the target operating current. Step S4: After the solar cell is fully inside the anode box area, maintain a constant target operating current output; Step S5: When the leading edge of the cell begins to exit the anode box area, the PLC controller controls the rectifier to perform a step-down symmetrical to step S3. The current is kept constant in each step cycle. After each step cycle, the output current is reduced by a preset current step size until the cell completely leaves the anode box area, at which point the current drops to a preset final value.

2. The gradient current control method for horizontal electroplating equipment according to claim 1, characterized in that: The method for establishing the current-time step mapping relationship is as follows: Based on the cell width W, transmission speed v, and target current density J, determine the slope function I(t) = J × W × v × t, which represents the linear change of ideal current with time. Discretize this linear slope into a step wave with a step period as the time interval and a current step size as the increment; the current step size ΔI is based on... The calculation is performed, where I_max is the target operating current, T is the total time required for the cell to move from the beginning of its entry into the anode box region to its complete entry into the anode box region, and Δt is the step period.

3. The gradient current control method for horizontal electroplating equipment according to claim 2, characterized in that: The step period is 0.1 seconds to 0.5 seconds, the current step size is 2mA to 20mA, and the initial current value is 1mA to 10mA.

4. The gradient current control method for horizontal electroplating equipment according to claim 3, characterized in that: The initial current value is 5mA, the step period is 0.2 seconds, and the current step size is 5mA.

5. The gradient current control method for horizontal electroplating equipment according to claim 1, characterized in that: In step S5, the trigger signal for the stepped descent is provided by another sensor located on the outlet side of the anode box, or calculated by the PLC controller based on the cell transmission speed and cell length.

6. The gradient current control method for horizontal electroplating equipment according to claim 1, characterized in that: In step S2, the initial current output serves to confirm the circuit is conducting and as the starting point for the step-up, avoiding a sudden change from zero current to the first step.

7. The gradient current control method for horizontal electroplating equipment according to claim 1, characterized in that: For battery cells with chamfered or non-rectangular heads, the current-time step mapping relationship is a non-linear mapping. The current step size corresponding to each step period is adjusted according to a preset area change function to keep the local current density constant.

8. A gradient current control system for a horizontal electroplating apparatus, used to implement the gradient current control method for the horizontal electroplating apparatus as described in any one of claims 1 to 7, characterized in that: include: A conveying mechanism for horizontally transporting battery cells at a constant speed; An electroplating tank is provided with an anode box, in which an anode is placed and immersed in an electrolyte. A pair of cathode contact rollers are positioned outside the electrolyte surface and on both sides of the anode box along the transmission direction, for sliding contact with the surface of the battery cell to form a cathode conductive circuit; A rectifier is used to output controllable direct current. The first sensor, located at the inlet side of the anode box, is used to detect the arrival of the leading edge of the solar cell; A PLC controller, connected to the first sensor and the rectifier, is configured to execute the gradient current control method of the horizontal electroplating equipment.

9. The gradient current control system for the horizontal electroplating equipment according to claim 8, characterized in that: It also includes a second sensor located on the outlet side of the anode box for triggering the stepped descent step.

10. The gradient current control system for the horizontal electroplating equipment according to claim 8, characterized in that: The PLC controller sends the current setting value to the rectifier through an analog output module or a digital communication protocol; the transmission mechanism is a constant speed transmission mechanism to ensure a constant transmission speed of the battery cells.

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