Photovoltaic string voltage boosting control method, circuit and device

Abstract

The application relates to a photovoltaic string voltage boosting control method, a circuit and equipment. The method can be applied to a photovoltaic string control circuit. The photovoltaic string control circuit comprises at least two photovoltaic strings. Each photovoltaic string comprises at least two adjacent target photovoltaic panels. A series-parallel switching circuit is arranged between different target photovoltaic panels. The method comprises the following steps: acquiring a current working condition and a current open-circuit voltage of the photovoltaic string control circuit; judging whether the current open-circuit voltage meets a voltage abnormality judgment condition corresponding to the current working condition; if the current open-circuit voltage meets the voltage abnormality judgment condition, gradually increasing the number of target photovoltaic panels in series according to a preset control logic, and re-acquiring the open-circuit voltage and judging after each series number is increased, until the open-circuit voltage does not meet the voltage abnormality judgment condition, or the number of target photovoltaic panels participating in series reaches a maximum series number. The application can solve the problem that a photovoltaic system cannot normally operate due to insufficient open-circuit voltage.

Description

Technical Field

[0001] This application relates to the field of photovoltaic power generation system control technology in the new energy industry, specifically a photovoltaic string boost control method, equipment, and storage medium. Background Technology

[0002] The selection of the open-circuit voltage threshold for photovoltaic (PV) string converters is influenced by the grid voltage; under higher grid voltages, the required open-circuit voltage for PV systems is higher. If more PV panels are added to increase the margin, the overall power output of the PV string grid will rise to a higher level, potentially exceeding the unit's power limit. Without adding more PV panels, their open-circuit voltage will decrease over time, leading to a reduced actual lifespan for PV panels in areas with high grid voltages.

[0003] In related technologies, the common methods for boosting the voltage of photovoltaic strings are to use a DC / DC converter to chop and boost the voltage of the photovoltaic strings, or to add photovoltaic panels to increase the cascade voltage. However, the introduction of a DC / DC converter increases the system cost. Summary of the Invention

[0004] This application provides a photovoltaic string boost control method, circuit, and device to achieve low-cost and safe photovoltaic string boost.

[0005] In a first aspect, this application provides a photovoltaic string boost control method. The method is applied to a photovoltaic string, wherein the photovoltaic string includes at least two photovoltaic strings, each photovoltaic string includes at least two photovoltaic panels, and at least some of the target photovoltaic panels are provided with a series-parallel switching circuit. The series-parallel switching circuit includes a main switch circuit and an RC pre-charge buffer branch connected in parallel. The main switch circuit is provided with a first relay, and the RC pre-charge buffer branch is provided with a resistor, a capacitor and a second relay connected in series. The target photovoltaic panels belong to different photovoltaic strings. The method includes: acquiring the current operating condition and the current open-circuit voltage of the photovoltaic string control circuit; determining whether the current open-circuit voltage meets the voltage anomaly judgment condition corresponding to the current operating condition; if the current open-circuit voltage meets the voltage anomaly judgment condition, according to preset control logic, controlling the first and second relays in the corresponding series-parallel switching circuit to operate sequentially, increasing the number of target photovoltaic panels connected in series step by step, and re-acquiring and judging the open-circuit voltage after each increase in the number of series stages, until the open-circuit voltage no longer meets the voltage anomaly judgment condition, or the number of target photovoltaic panels participating in the series connection reaches the maximum number of series stages.

[0006] In one implementation, the voltage anomaly determination condition includes at least one of the following: the open-circuit voltage is unstable; the open-circuit voltage does not reach the voltage threshold corresponding to the current operating condition.

[0007] In one implementation, the target photovoltaic panel includes at least a first photovoltaic panel, a second photovoltaic panel, a third photovoltaic panel, and a fourth photovoltaic panel, wherein the first photovoltaic panel and the third photovoltaic panel are arranged adjacent to each other at the end of the first photovoltaic string, and the second photovoltaic panel and the fourth photovoltaic panel are arranged adjacent to each other at the end of the second photovoltaic string.

[0008] In one optional implementation, the second end of the first photovoltaic panel is connected to the first end of the second photovoltaic panel via a first switching unit; the second end of the second photovoltaic panel is connected to the first end of the fifth photovoltaic panel via a second switching unit; the second end of the third photovoltaic panel is connected to the first end of the fourth photovoltaic panel via a third switching unit; the second end of the fourth photovoltaic panel is connected to the first end of the sixth photovoltaic panel via a fourth switching unit; the second end of the first photovoltaic panel is connected to the first end of the third photovoltaic panel via a fifth switching unit; the first end of the second photovoltaic panel is connected to the first end of the fourth photovoltaic panel via a sixth switching unit; the second end of the second photovoltaic panel is connected to the second end of the fourth photovoltaic panel via a seventh switching unit; and the first end of the fifth photovoltaic panel is connected to the first end of the sixth photovoltaic panel via an eighth switching unit.

[0009] In one optional implementation, switching the connection topology state according to preset control logic includes controlling the corresponding on / off units to connect the second photovoltaic panel, the first photovoltaic panel, and the third photovoltaic panel in series.

[0010] In one optional implementation, the preset control logic further includes controlling the corresponding on / off units to connect the second photovoltaic panel, the first photovoltaic panel, the fourth photovoltaic panel, and the third photovoltaic panel in series.

[0011] In one implementation, controlling the first and second relays in the corresponding series-parallel switching circuit to operate sequentially includes: first turning on the second relay in the corresponding series-parallel switching circuit; turning on the first relay in the corresponding series-parallel switching circuit after the voltage stabilizes; and turning off the second relay in the corresponding series-parallel switching circuit after the voltage stabilizes again.

[0012] Secondly, this application provides a photovoltaic string control circuit, wherein the photovoltaic string includes at least two photovoltaic strings, each photovoltaic string includes at least two adjacent target photovoltaic panels, and a series-parallel switching circuit is provided between different target photovoltaic panels. The series-parallel switching circuit includes a main switch circuit and an RC pre-charge buffer branch connected in parallel. A first relay is provided in the main switch circuit, and a resistor, a capacitor and a second relay are connected in series in the RC pre-charge buffer branch. The photovoltaic string control circuit is controlled by the method described in the first aspect.

[0013] In one implementation, the photovoltaic string control circuit includes at least a first photovoltaic string and a second photovoltaic string, and the target photovoltaic panel includes at least a first photovoltaic panel, a second photovoltaic panel, a third photovoltaic panel, and a fourth photovoltaic panel. The first photovoltaic panel and the third photovoltaic panel are arranged adjacent to each other at the tail of the first photovoltaic string, and the second photovoltaic panel and the fourth photovoltaic panel are arranged adjacent to each other at the tail of the second photovoltaic string.

[0014] In one implementation, the second end of the first photovoltaic panel is connected to the first end of the second photovoltaic panel via a first switching unit; the second end of the second photovoltaic panel is connected to the first end of the fifth photovoltaic panel via a second switching unit; the second end of the third photovoltaic panel is connected to the first end of the fourth photovoltaic panel via a third switching unit; the second end of the fourth photovoltaic panel is connected to the first end of the sixth photovoltaic panel via a fourth switching unit; the second end of the first photovoltaic panel is connected to the first end of the third photovoltaic panel via a fifth switching unit; the first end of the second photovoltaic panel is connected to the first end of the fourth photovoltaic panel via a sixth switching unit; the second end of the second photovoltaic panel is connected to the second end of the fourth photovoltaic panel via a seventh switching unit; and the first end of the fifth photovoltaic panel is connected to the first end of the sixth photovoltaic panel via an eighth switching unit.

[0015] In one optional implementation, the switching unit includes a main switch circuit and an RC pre-charge buffer branch connected in parallel. The main switch circuit is provided with a first relay, and the RC pre-charge buffer branch is provided with a resistor, a capacitor and a second relay connected in series.

[0016] In one optional implementation, the photovoltaic string includes at least two photovoltaic strings, each photovoltaic string includes at least two adjacent target photovoltaic panels, and a series-parallel switching circuit is provided between different target photovoltaic panels.

[0017] Thirdly, a photovoltaic device is also provided, including a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other through the communication bus; the memory is used to store computer programs; and the processor, when executing the program stored in the memory, implements the photovoltaic string boost control method described in any of the second aspects above.

[0018] Fourthly, a storage medium is also provided, wherein the storage medium stores instructions that, when executed on a computer, cause the computer to perform any of the photovoltaic string boost control methods described in the second aspect above.

[0019] Fifthly, a computer program product containing instructions is also provided, which, when run on a computer, causes the computer to execute the photovoltaic string boost control method described in any of the second aspects above.

[0020] The technical solutions provided in this application have the following advantages compared with the prior art: The method provided in this application can be applied to a control circuit that includes multiple photovoltaic strings and a series-parallel switching circuit is configured between the target photovoltaic panels within the strings. By acquiring the open-circuit voltage of the photovoltaic strings in the current topology state and comparing it with the voltage anomaly judgment condition, if the voltage anomaly judgment condition is met, the series-parallel state of the target photovoltaic panels is switched according to a preset logic, and then the detection and verification are repeated until the voltage meets the threshold requirement. This method does not require additional voltage boosting hardware, and the open-circuit voltage can be gradually increased through topology reconstruction, which can effectively solve the problems of system failure to start and shortened photovoltaic panel life caused by insufficient open-circuit voltage. Attached Figure Description

[0021] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] One or more embodiments are illustrated by way of example with reference numerals in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0024] Figure 1 This is a schematic diagram of a photovoltaic string circuit provided in an embodiment of this application.

[0025] Figure 2 A schematic flowchart illustrating a photovoltaic string boost control method provided in an embodiment of this application; Figure 3 A schematic flowchart illustrating another photovoltaic string boost control method provided in this application; Figure 4 This is a schematic diagram of the structure of an on / off unit provided in an embodiment of this application; Figure 5 A schematic diagram of a photovoltaic string circuit topology provided in an embodiment of this application; Figure 6This is a schematic diagram of the structure of a photovoltaic device provided in an embodiment of this application. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] The following disclosure provides numerous different embodiments or examples for implementing various structures of this application. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the scope of this application. Furthermore, reference numerals and / or letters may be repeated in different examples. Such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed.

[0028] It should be noted that the photovoltaic string boost control method provided in this application embodiment can be applied to a photovoltaic string control circuit. The photovoltaic string control circuit includes at least two photovoltaic strings, each photovoltaic string includes at least two adjacent target photovoltaic panels, and a series-parallel switching circuit is provided between different target photovoltaic panels.

[0029] As an example, please see Figure 1 , Figure 1 This is a schematic diagram of a photovoltaic string circuit provided in an embodiment of this application. Figure 1As shown, the circuit can include four target photovoltaic panels: a first photovoltaic panel, a second photovoltaic panel, a third photovoltaic panel, and a fourth photovoltaic panel. The first photovoltaic panel, a first switching unit, a third photovoltaic panel, a second switching unit, and a fifth photovoltaic panel are cascaded sequentially to form an upper series branch. The second photovoltaic panel, a third switching unit, a fourth photovoltaic panel, a fourth switching unit, and a sixth photovoltaic panel are cascaded sequentially to form a lower series branch. The second end of the first photovoltaic panel is connected to the first end of the second photovoltaic panel through the first switching unit; the second end of the second photovoltaic panel is connected to the first end of the fifth photovoltaic panel through the second switching unit; the second end of the third photovoltaic panel is connected to the first end of the fourth photovoltaic panel through the third switching unit; the second end of the fourth photovoltaic panel is connected to the first end of the sixth photovoltaic panel through the fourth switching unit; the second end of the first photovoltaic panel is connected to the first end of the third photovoltaic panel through the fifth switching unit; the first end of the second photovoltaic panel is connected to the first end of the fourth photovoltaic panel through the sixth switching unit; and the second end of the second photovoltaic panel is connected to the second end of the fourth photovoltaic panel through a seventh switching unit. The first end of the photovoltaic panel is connected to the first end of the sixth photovoltaic panel through the eighth switching unit. By controlling the on / off state of each switching unit, the series and parallel connection relationship between the first, second, third, and fourth photovoltaic panels can be adjusted, thereby dynamically changing the output voltage, current, and power characteristics of the photovoltaic array to adapt to different lighting conditions and optimize power generation efficiency. The positive and negative output terminals of the photovoltaic array are connected to the positive and negative DC input terminals of the converter, respectively, to send the photovoltaic DC power into the converter to complete the power conversion. The inverting input terminal of the operational amplifier is connected to the two output terminals of the photovoltaic array through two voltage divider resistors. A negative feedback network consisting of a resistor and a capacitor in parallel is set between the inverting input and the output terminal to realize voltage scaling and high-frequency noise suppression. The non-inverting input terminal is configured with an RC filter network and a reference level branch to provide stable bias and common-mode filtering for the circuit. The circuit finally outputs the AD_PV analog sampling signal, converting the high voltage on the photovoltaic side into a low voltage signal suitable for the analog-to-digital converter, which is used for subsequent array topology control and converter MPPT (Maximum Power Transmission Point). Power Point Tracking (MPTS) provides voltage feedback for tracking and system monitoring.

[0030] It should be noted that the number of target photovoltaic panels in this application can be multiple. Figure 1 This application uses only four target photovoltaic panels as an example. However, the number of other photovoltaic panels besides the target panels can also be multiple. Figure 1 Let's take two examples.

[0031] Please see Figure 2 , Figure 2 This is a schematic flowchart illustrating a photovoltaic string boost control method provided in an embodiment of this application. Figure 2 As shown, the method may include, but is not limited to, the following steps: S1. Obtain the current operating condition and current open-circuit voltage of the photovoltaic string control circuit.

[0032] In the embodiments of this application, the operating conditions of the photovoltaic string control circuit may include startup standby (i.e., before starting normal operation) or load operation (i.e., normal grid-connected power supply).

[0033] In some embodiments, the open-circuit voltage can be the DC-side voltage of the photovoltaic string.

[0034] In some embodiments, if the current operating condition is under load, the current open-circuit voltage can be the optimization voltage of the photovoltaic string boost control circuit.

[0035] For example, with Figure 1 Taking the photovoltaic string circuit shown as an example, under the current photovoltaic string topology determined by the on / off states of the first to eighth on / off units, the downstream converter is first controlled to be in an unloaded state where it stops working, so that the total output terminal of the photovoltaic array is open-circuited. Then, through the differential voltage sampling circuit composed of an operational amplifier, voltage divider resistors and RC network, the voltages at the positive and negative ends of the total output terminal of the photovoltaic array are collected. The high-voltage side voltage is scaled by the differential operational amplifier at a fixed ratio and the high-frequency ripple interference is filtered out by the RC network. It is then converted into an AD_PV analog signal with amplitude adapted to the range of the analog-to-digital converter and sent to the control unit. After proportional conversion, the control unit obtains the actual open-circuit voltage value of the photovoltaic string under the current series-parallel configuration.

[0036] S2. Determine whether the current open-circuit voltage meets the voltage anomaly judgment conditions corresponding to the current operating condition.

[0037] In the embodiments of this application, the voltage anomaly determination conditions include at least one of the following: the open circuit voltage is unstable; the open circuit voltage does not reach the voltage threshold corresponding to the current operating condition.

[0038] As an example, taking the current operating condition as startup standby as an example, it is determined whether the current open circuit voltage reaches the voltage threshold corresponding to the startup standby operating condition.

[0039] As another example, taking the current operating condition as load operation as an example, it is determined whether the current open circuit voltage is stable and whether the current open circuit voltage reaches the voltage threshold corresponding to the load operation condition.

[0040] In some embodiments, multiple sets of open-circuit voltage sampling values ​​can be continuously collected within a preset time window. If the voltage fluctuation amplitude of multiple sets of sampling values ​​exceeds a preset deviation threshold, the open-circuit voltage is determined to be unstable.

[0041] For example, judging under load operating conditions. Figure 1Taking the example of whether the open-circuit voltage of the photovoltaic string circuit shown reaches the voltage threshold corresponding to the current operating condition, the current open-circuit voltage obtained by S1 is compared with the voltage threshold corresponding to the load operating condition. If the current open-circuit voltage has reached or exceeded the voltage threshold corresponding to the load operating condition, it means that the voltage level output by the series-parallel structure between the first, second, third, and fourth photovoltaic panels can support the subsequent stable power generation operation of the converter, and there is no need to adjust the circuit topology. The current control process ends directly. If the current open-circuit voltage is lower than the set voltage threshold, it means that the output voltage of the existing topology cannot meet the minimum operating voltage requirement of the converter. It is necessary to adjust the series-parallel relationship between the first, second, third, and fourth photovoltaic panels, and then execute step S3.

[0042] For example, taking the determination of whether the current open-circuit voltage is stable under load operation as an example, multiple sets of AD_PV analog signals are continuously collected within the set determination window. The corresponding open-circuit voltage values ​​are obtained through analog-to-digital conversion and proportional conversion. Then, the fluctuation amplitude of multiple sets of sampled values ​​is calculated and compared with the preset stability deviation threshold. If the fluctuation difference of multiple sets of voltages is within the allowable deviation range, it is determined that the open-circuit voltage of the photovoltaic string under the current topology has reached a steady state. If the voltage fluctuation exceeds the stability deviation range, it is determined that the open-circuit voltage is still in a switching transient or operating condition fluctuation state.

[0043] In some embodiments, the voltage threshold can be set to a threshold range. For example, the minimum value of this threshold range can be determined by the peak value of the grid voltage and a preset adjustment coefficient. The adjustment coefficients corresponding to different operating conditions can be the same or different.

[0044] S3. If the current open-circuit voltage meets the voltage anomaly judgment condition, according to the preset control logic, control the first and second relays in the corresponding series-parallel switching circuit to operate sequentially, gradually increasing the number of target photovoltaic panels in series, and re-collecting and judging the open-circuit voltage after each increase in the number of series stages, until the open-circuit voltage no longer meets the voltage anomaly judgment condition, or the number of target photovoltaic panels participating in the series reaches the maximum number of series stages.

[0045] For example, with Figure 1 Taking the photovoltaic string circuit shown as an example, when the current open-circuit voltage meets the voltage anomaly determination condition, the series-parallel connection relationship between the first to sixth photovoltaic panels is reconstructed by changing the on / off state combination of the first to eighth on / off units. For example, the originally parallel photovoltaic strings are switched to a series structure, increasing the number of target photovoltaic panels in series, thereby increasing the total open-circuit voltage. Then, a new open-circuit voltage is collected again and the determination is made again. The above process is repeated until the open-circuit voltage meets the voltage anomaly determination condition.

[0046] In some embodiments, the series-parallel connection relationship between target photovoltaic panels can be switched according to a preset series-parallel switching procedure based on the stability of the open-circuit voltage. For example, please refer to [link to example]. Figure 3 , Figure 3 This is a flowchart illustrating another photovoltaic string boost control method provided in this application.

[0047] S31. Determine whether the current open-circuit voltage is stable. If yes, execute S34; otherwise, execute S32.

[0048] For example, within a set judgment window, multiple sets of AD_PV analog signals are continuously acquired, and the corresponding open-circuit voltage values ​​are obtained through analog-to-digital conversion and proportional conversion. Then, the fluctuation amplitude of multiple sets of sampled values ​​is calculated and compared with a preset stability deviation threshold. If the fluctuation difference of multiple sets of voltages is within the allowable deviation range, it is determined that the open-circuit voltage of the photovoltaic string under the current topology has reached a steady state, and then the process jumps to step S34. If the voltage fluctuation exceeds the stability deviation range, it is determined that the open-circuit voltage is still in a switching transient or operating condition fluctuation state, and then the process jumps to step S32 to perform a topology switching operation.

[0049] S32. According to the preset control logic, the number of target photovoltaic panels connected in series is increased step by step.

[0050] For example, according to the pre-set series cascade increasing switching sequence, corresponding control signals are sent to the first to eighth switching units. By changing the switching combination state of each switching unit, the series and parallel connection relationship between the first photovoltaic panel, the second photovoltaic panel, the third photovoltaic panel, and the fourth photovoltaic panel is adjusted, so that the number of target photovoltaic panels in series increases, thereby increasing the output voltage.

[0051] In some embodiments, according to preset control logic, the number of target photovoltaic panels connected in series is increased step by step, including controlling the corresponding on / off units to connect the second photovoltaic panel, the first photovoltaic panel, and the third photovoltaic panel in series in sequence.

[0052] For example, the fifth switching unit is turned on while the third switching unit is turned off, and the first switching unit is kept on while the other switching units remain off. At this time, the second photovoltaic panel is disconnected from the original lower series branch, and its output terminal is cascaded with the corresponding terminal of the first photovoltaic panel through the fifth switching unit. The first photovoltaic panel and the third photovoltaic panel are kept in positive series through the first switching unit, and finally a path is formed in which the second photovoltaic panel, the first photovoltaic panel, and the third photovoltaic panel are connected in series end to end, thereby increasing the number of series stages and raising the output voltage.

[0053] Optionally, according to preset control logic, the number of target photovoltaic panels connected in series is increased step by step, and the method further includes: controlling the corresponding on / off units to connect the second photovoltaic panel, the first photovoltaic panel, the fourth photovoltaic panel, and the third photovoltaic panel in series in sequence.

[0054] For example, if the second, first, and third photovoltaic panels are connected in series, and step S32 needs to be executed again, the fifth switching unit remains closed to maintain the cascaded relationship between the second and first photovoltaic panels. At the same time, the first switching unit is disconnected to cut off the direct series path between the right end of the first photovoltaic panel and the left end of the third photovoltaic panel. Then, the sixth switching unit is closed to connect the right output node of the first photovoltaic panel to the left input node of the fourth photovoltaic panel, connecting the fourth photovoltaic panel to the rear of the first photovoltaic panel in the series link. Next, the seventh switching unit is closed to connect the right output node of the fourth photovoltaic panel to the left input node of the third photovoltaic panel, reconnecting the third photovoltaic panel to the rear of the fourth photovoltaic panel in the series link. Throughout the process, the second, third, fourth, and eighth switching units remain open to ensure that the fifth and sixth photovoltaic panels are not connected to the main power circuit. Ultimately, the current flows sequentially through the second photovoltaic panel, the fifth switching unit, the first photovoltaic panel, the sixth switching unit, the fourth photovoltaic panel, the seventh switching unit, and the third photovoltaic panel, forming a four-unit series path with the second, first, fourth, and third photovoltaic panels cascaded in the forward direction, further increasing the total output open-circuit voltage of the string.

[0055] In this embodiment, the photovoltaic string connection topology can be adjusted by a series-parallel step-by-step switching method to achieve graded and controllable boosting of open-circuit voltage and bus voltage. The number of boost stages can be matched according to the actual voltage conditions and the voltage requirements of different operating conditions. At the same time, the switching operation is concentrated at the low-voltage node at the end of the string, which can reduce the voltage withstand selection criteria of switching devices and buffer circuits and control hardware costs.

[0056] S33. Obtain the current open-circuit voltage and return to execute S31.

[0057] For example, after executing step S32, the differential voltage sampling circuit collects the voltage signal at the total output terminal of the photovoltaic string again, and obtains the open-circuit voltage value corresponding to the current new topology through proportional conversion and analog-to-digital conversion. Then, it returns to execute step S31 again to determine the stability of the newly collected open-circuit voltage, and continues to iterate until the open-circuit voltage enters a stable state.

[0058] S34. Determine whether the current open-circuit voltage has reached the corresponding preset voltage threshold. If yes, end the current control process; otherwise, execute S32.

[0059] For example, after step S31 determines that the current open-circuit voltage is in a stable state, the steady-state open-circuit voltage value is compared with a preset voltage threshold that adapts to the minimum operating voltage requirement of the converter. If the steady-state open-circuit voltage has reached or exceeded the preset voltage threshold, it means that the output voltage of the current series-parallel topology of the photovoltaic array has met the system operating conditions, and the control process ends. If the steady-state open-circuit voltage still has not reached the preset voltage threshold, it means that the number of target photovoltaic panels in series is insufficient and the total output voltage is too low. Then, the process returns to step S32 and continues to perform the next level topology switching according to the preset switching sequence to further increase the number of target photovoltaic panels in series to improve the string open-circuit voltage.

[0060] In some embodiments, if the current operating condition is a startup standby condition, the photovoltaic string boost control method provided in this application embodiment may include the following steps: A1: When the photovoltaic string starts up, obtain the first open-circuit voltage and determine whether the first open-circuit voltage reaches the preset first voltage threshold.

[0061] It should be noted that when the photovoltaic strings are started up, the initial connection state of the circuit is that each photovoltaic string is normally connected. Figure 1 Taking the photovoltaic string shown as an example, when the photovoltaic string is started, it enters the preset initial connection state by default: the first on / off unit, the second on / off unit, the third on / off unit, and the fourth on / off unit are all closed, and the fifth to eighth on / off units are all open. Under this configuration, each photovoltaic string maintains a normal interconnection structure of independent series connection.

[0062] For example, when the photovoltaic string starts up, the voltage between the positive and negative terminals of the total output terminal of the photovoltaic array under the current initial connection topology is collected, and the first open circuit voltage is obtained through proportional conversion and analog-to-digital conversion, and then compared with the preset first voltage threshold.

[0063] In some embodiments, the first voltage threshold may be the minimum voltage value required for the normal startup of the converter.

[0064] A2: If the first open-circuit voltage is less than the first voltage threshold, then the series-parallel connection status between the target photovoltaic panels is switched according to the preset control logic.

[0065] For example, if the measured first open-circuit voltage is less than the first voltage threshold, it means that the output voltage of the current photovoltaic panel series-parallel configuration is insufficient to drive the inverter to start operation. According to the preset topology control logic, the corresponding drive signal is output to the first to eighth switching units. By changing the switching state combination of each switching unit, the series-parallel connection relationship between the target photovoltaic panels is adjusted to increase the number of target photovoltaic panels in series in turn, thereby raising the total open-circuit voltage of the string until the output voltage reaches the threshold condition required for startup.

[0066] By implementing the embodiments of this application, the open-circuit voltage of the photovoltaic string under the current topology can be obtained and compared with the corresponding voltage threshold. If the voltage does not meet the standard, the series and parallel states of the target photovoltaic panel are switched according to the preset logic, and the detection and verification are repeated until the voltage meets the threshold requirement. This method does not require additional voltage boosting hardware. The open-circuit voltage can be gradually increased by topology reconstruction, which can effectively solve the problems of system failure to start and shortened photovoltaic panel life caused by insufficient open-circuit voltage.

[0067] In some embodiments, photovoltaic panels can be added at the end of each photovoltaic string to increase voltage margin, alleviate the start-up threshold pressure under high grid voltage, and offset the open-circuit voltage drop caused by long-term operation degradation of the components. However, it is necessary to calculate the total power of the string to avoid the output power of the entire string exceeding the rated power limit of the unit.

[0068] In some embodiments, each switching unit for adjusting the series-parallel relationship between target photovoltaic panels may include a main switching circuit and an RC pre-charge buffer branch connected in parallel. The main switching circuit includes a first relay, and the RC pre-charge buffer branch includes a resistor, a capacitor, and a second relay connected in series. As an example, please refer to... Figure 4 , Figure 4 This is a schematic diagram of the structure of an on / off unit provided in an embodiment of this application.

[0069] In one implementation, the first and second relays in the corresponding series-parallel switching circuit are controlled to operate sequentially, including: first turning on the second relay in the corresponding series-parallel switching circuit, turning on the first relay in the corresponding series-parallel switching circuit after the voltage stabilizes, and turning off the second relay in the corresponding series-parallel switching circuit after the voltage stabilizes again.

[0070] In the embodiments of this application, if the voltage fluctuation amplitude relative to the current reference value does not exceed a preset fluctuation threshold within a preset time period, the voltage can be determined to be in a stable state.

[0071] For example, when performing each level of series switching, the second relay of the RC absorption circuit of the corresponding branch is first turned on to precharge the buffer capacitor to suppress the switching impact. After the open circuit voltage fluctuation stabilizes within the set range, the relay used to maintain the parallel connection state of the corresponding photovoltaic panel is turned off, and then the first relay of the corresponding main switch circuit is turned on. After the topology switching is completed, the second relay of the RC branch is turned off to avoid steady-state losses.

[0072] In this embodiment, an RC snubber circuit can be used to effectively mitigate transient voltage surges caused by topology switching, ensuring a smooth voltage transition throughout the process and reducing power fluctuations caused by topology changes.

[0073] The method for controlling boosting of photovoltaic strings provided in the present application is further described below with reference to specific examples. As an example, please refer to Figure 5 , Figure 5 which is a schematic diagram of a photovoltaic string circuit topology provided in an embodiment of the present application. As shown in Figure 5 , a shift register may be used to control the contactors in the circuit. When controlling the photovoltaic string circuit as shown in Figure 5 , the contactors K1 to K16 are initially configured in an off state. After the converter is started, K2, K10, K6 and K14 are controlled to pull in. At this time, the photovoltaic panels are connected in a conventional series connection manner, and are equally divided into two parallel paths to enter the converter. At this time, the AD_PV value at the open-circuit voltage is read, that is, the photovoltaic open-circuit voltage value. It is determined whether the open-circuit voltage is within a suitable range (for example, peak grid voltage × 1.2 + 30 < AD_PV value < 1000V).

[0074] If the open-circuit voltage is within the suitable range, the control is performed according to the following process: The converter normally performs the MPP function. At this time, the monitored AD_PV value is the optimization-seeking voltage after the photovoltaic starts to work. The unit detects the AD_PV value in real time, and determines whether the optimization-seeking voltage monitored by the read AD_PV is within a suitable threshold range (for example, peak grid voltage × 11.2 < AD_PV < 780V). If the optimization-seeking voltage is within the suitable threshold range, the inverter operates normally. If the optimization-seeking voltage is lower than the suitable range, K1, K4 and K8 are controlled to pull in, and then K2 is disconnected. It is determined whether the AD_PV value is stable. If not stable, the photovoltaic optimization-seeking continues to run. If stable, it means that the capacitors in the circuits where K1, K4 and K8 are located have completed charging, which ensures that the voltage of the entire photovoltaic string does not drop during the networking process, and suppresses the node voltage sudden change during switching changes in the switching process. Then, K1 is disconnected. At this time, the string connection manner changes, and the photovoltaic power point will change accordingly. It is necessary to determine again whether the AD_PV value is stable. If not stable, the photovoltaic optimization-seeking continues to run. If stable, K3 and K7 are pulled in to complete the change of the string connection manner, so as to realize boosting.

[0075] After the string boosting change is completed, the MPP function is run until the AD_PV voltage is stable and the power is stable, and then it is detected whether the voltage after string boosting is not less than 1.2 times the peak grid voltage. If yes, the converter operates normally.

[0076] If it is detected that the voltage after string boosting is still lower than 1.2 times the peak grid voltage, the second transformation of the photovoltaic panel string connection manner is started.

[0077] Control K8, K12, K16, and K13 to engage and determine if the AD_PV value is stable. If it is not stable, continue the photovoltaic optimization process. If it is stable, it means that the capacitors in the circuit containing K12 and K16 have finished charging, preventing the voltage of the entire photovoltaic string from dropping.

[0078] Controls K7 and K14 are disconnected. At this time, the capacitors in the circuit containing K8 and K13 are charged, suppressing voltage surges. The AD_PV value is then checked for stability. If it is not stable, the photovoltaic optimization process continues. If it is stable, K11 and K15 are engaged, and the AD_PV value is checked again. If it is not stable, the photovoltaic optimization process continues. If it is stable, the grid-connected voltage boost is completed.

[0079] Disconnect K8, K13, and K16 to suppress voltage spikes after string boosting. Then check if the voltage after string boosting is not lower than 1.2 times the peak grid voltage. If it is, operate the converter normally. If it is lower than 1.2 times the peak grid voltage, wait for the photovoltaic power to drop below 200W before cutting off the photovoltaic system.

[0080] By executing the following control process, the power point remains unchanged while the voltage increases by 50V after each string boost conversion. This effectively prevents the photovoltaic system from being cut off due to a low optimization voltage, resulting in a voltage below the peak voltage and wasted power.

[0081] If the open-circuit voltage is not within the appropriate range, the converter cannot operate the MPP function normally. In this case, the value monitored by AD_PV is the open-circuit voltage before the photovoltaic system starts normal operation. The control process is as follows: Control K1, K4, and K8 to engage, then disconnect K2. Determine if the AD_PV value is stable. If it is not stable, continue waiting. If it is stable, it means that the capacitors in the circuit containing K1, K4, and K8 have completed charging, ensuring that the open-circuit voltage of the entire photovoltaic string does not drop during the grid connection process, and smoothing out sudden changes in node voltage during switching.

[0082] Then, control K1 to disconnect and determine whether the AD_PV value is stable. If it is not stable, continue to wait for the K4 and K8 capacitor circuits to finish charging. If it is stable, then engage K3 and K7 to complete the boost conversion in string mode.

[0083] After completing the string boost change, check if the boosted voltage is not lower than the peak grid voltage × 1.2 + 30. If so, the inverter operates normally and executes the MPP function. During the MPP function, if the output voltage drops below 1.2 times the peak grid voltage, disconnect K1. At this point, the string mode changes, and the photovoltaic power point adjusts. It's necessary to determine if the AD_PV value is stable (fluctuating ±5V). If not, continue photovoltaic optimization. If stable, engage K3 and K7 to complete the string boost change. After completing the string boost change, run the MPP function until the AD_PV voltage and power are stable. Then check if the boosted voltage is not lower than 1.2 times the peak grid voltage. If so, the inverter operates normally. If the boosted voltage is still lower than 1.2 times the peak grid voltage, begin the second string mode change for the photovoltaic panels and start the second grid boost. Control K8, K12, K16, and K13 to engage and determine if the AD_PV value is stable. If it is not stable, continue the photovoltaic optimization process. If it is stable, it means that the capacitors in the circuit containing K12 and K16 have finished charging, preventing the voltage of the entire photovoltaic string from dropping.

[0084] Disconnect K7 and K14. At this time, the capacitors in the circuits containing K8 and K13 charge, suppressing voltage surges. Determine if the AD_PV value is stable. If not, continue photovoltaic optimization. If stable, engage K11 and K15, and determine if the AD_PV value is stable again. If not, continue photovoltaic optimization. If stable, complete the grid boost. Disconnect K8, K13, and K16 to suppress voltage surges after string boosting. Then check if the boosted string voltage is not lower than 1.2 times the peak grid voltage. If so, operate the converter normally. If lower than 1.2 times the peak grid voltage, wait until the photovoltaic power drops below 200W before disconnecting the photovoltaic system.

[0085] If the voltage after the photovoltaic string is boosted is still lower than the peak value of the grid voltage × 1.2 + 30, then the second change of the photovoltaic string configuration begins. Controls K8, K12, K16, and K13 are engaged to determine if the AD_PV value is stable. If it is not stable, continue waiting. If it is stable, it means the capacitors in the circuit containing K12 and K16 have finished charging, preventing a drop in the voltage of the entire photovoltaic string.

[0086] Controls K7 and K14 are disconnected. At this time, the capacitors in the circuit containing K8 and K13 are charged, suppressing voltage surges. Check if the AD_PV value is stable. If not, continue waiting; if stable, then engage K11 and K15. After engaging, check if the AD_PV value is stable. If not, continue waiting; if stable, the network boost is complete.

[0087] Disconnect K8, K13, and K16 to suppress voltage spikes after the string boost change. Then check if the boosted string voltage is not lower than the peak value of the grid voltage × 1.2 + 30. If it is, the converter will run normally. If it is lower than the peak value of the grid voltage × 1.2 + 30, the fault message indicates that the photovoltaic string performance is insufficient and the photovoltaic panels need to be replaced or photovoltaic panels need to be added at the nodes close to the converter.

[0088] Corresponding to the above method embodiments, this application also provides a photovoltaic device, such as... Figure 6 As shown, it includes a processor 601, a communication interface 602, a memory 603, and a communication bus 604, wherein the processor 601, the communication interface 602, and the memory 603 communicate with each other through the communication bus 604. Memory 603 is used to store computer programs; When processor 601 executes a program stored in memory 603, it performs the following steps: S1. Obtain the current operating condition and current open-circuit voltage of the photovoltaic string control circuit; S2. Determine whether the current open-circuit voltage meets the voltage anomaly judgment condition corresponding to the current operating condition; S3. If the current open-circuit voltage meets the voltage anomaly judgment condition, according to the preset control logic, the number of target photovoltaic panels in series is increased step by step, and the open-circuit voltage is re-acquired and judged after each increase in the number of series stages, until the open-circuit voltage no longer meets the voltage anomaly judgment condition, or the number of target photovoltaic panels participating in the series reaches the maximum number of series stages.

[0089] The communication bus mentioned in the aforementioned photovoltaic equipment can be a Peripheral Component Interconnect (PCI) bus or an Extended Industry Standard Architecture (EISA) bus, etc. This communication bus can be divided into address bus, data bus, control bus, etc. For ease of illustration, only one thick line is used to represent it in the diagram, but this does not indicate that there is only one bus or one type of bus.

[0090] The communication interface is used for communication between the aforementioned photovoltaic equipment and other devices.

[0091] The memory may include random access memory (RAM) or non-volatile memory, such as at least one disk storage device. Optionally, the memory may also be at least one storage device located remotely from the aforementioned processor.

[0092] The processors mentioned above can be general-purpose processors, including central processing units (CPUs), network processors (NPs), etc.; they can also be digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0093] In another embodiment provided in this application, a storage medium is also provided, which stores instructions that, when run on a computer, cause the computer to execute the control method of any of the charging circuits described in the above embodiments.

[0094] In another embodiment provided in this application, a computer program product containing instructions is also provided, which, when run on a computer, causes the computer to execute the control method of the charging circuit described in any of the above embodiments.

[0095] In the above embodiments, implementation can be achieved entirely or partially through software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented entirely or partially in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this application are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a storage medium or transmitted from one storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium (e.g., solid state disk (SSD)).

[0096] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0097] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0098] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application are included within the scope of protection of this application.

Claims

1. A photovoltaic string boost control method, characterized in that, The method is applied to a photovoltaic string control circuit, which includes at least two photovoltaic strings, each of which includes at least two adjacent target photovoltaic panels. A series-parallel switching circuit is provided between different target photovoltaic panels. The series-parallel switching circuit includes a main switch circuit and an RC pre-charge buffer branch connected in parallel. A first relay is provided in the main switch circuit, and a resistor, a capacitor, and a second relay are connected in series in the RC pre-charge buffer branch. The method includes: Obtain the current operating condition and current open-circuit voltage of the photovoltaic string control circuit; Determine whether the current open-circuit voltage meets the voltage anomaly determination criteria corresponding to the current operating condition; If the current open-circuit voltage meets the voltage anomaly determination condition, according to the preset control logic, the first and second relays in the corresponding series-parallel switching circuit are controlled to operate sequentially, increasing the number of target photovoltaic panels connected in series step by step. After each increase in the number of series stages, the open-circuit voltage is re-acquired and judged until the open-circuit voltage no longer meets the voltage anomaly determination condition, or the number of target photovoltaic panels participating in the series reaches the maximum number of series stages.

2. The method according to claim 1, characterized in that, The voltage anomaly determination criteria include at least one of the following: Open-circuit voltage is unstable; The open-circuit voltage has not reached the voltage threshold corresponding to the current operating condition.

3. The method according to claim 1, characterized in that, The photovoltaic string control circuit includes at least a first photovoltaic string and a second photovoltaic string, and the target photovoltaic panel includes at least a first photovoltaic panel, a second photovoltaic panel, a third photovoltaic panel and a fourth photovoltaic panel. The first photovoltaic panel and the third photovoltaic panel are arranged adjacent to each other at the tail of the first photovoltaic string, and the second photovoltaic panel and the fourth photovoltaic panel are arranged adjacent to each other at the tail of the second photovoltaic string.

4. The method according to claim 3, characterized in that, The second end of the first photovoltaic panel is connected to the first end of the second photovoltaic panel via a first switching unit; the second end of the second photovoltaic panel is connected to the first end of the fifth photovoltaic panel via a second switching unit; the second end of the third photovoltaic panel is connected to the first end of the fourth photovoltaic panel via a third switching unit; the second end of the fourth photovoltaic panel is connected to the first end of the sixth photovoltaic panel via a fourth switching unit; the second end of the first photovoltaic panel is connected to the first end of the third photovoltaic panel via a fifth switching unit; the first end of the second photovoltaic panel is connected to the first end of the fourth photovoltaic panel via a sixth switching unit; the second end of the second photovoltaic panel is connected to the second end of the fourth photovoltaic panel via a seventh switching unit; and the first end of the fifth photovoltaic panel is connected to the first end of the sixth photovoltaic panel via an eighth switching unit.

5. The method according to claim 4, characterized in that, The step of progressively increasing the number of the target photovoltaic panels connected in series according to a preset control logic includes: Control the corresponding on / off units to connect the second photovoltaic panel, the first photovoltaic panel, and the third photovoltaic panel in series.

6. The method according to claim 5, characterized in that, The step of progressively increasing the number of the target photovoltaic panels connected in series according to a preset control logic further includes: Control the corresponding on / off units to connect the second photovoltaic panel, the first photovoltaic panel, the fourth photovoltaic panel, and the third photovoltaic panel in series.

7. The method according to claim 1, characterized in that, The control of the first and second relays in the corresponding series-parallel switching circuit to operate sequentially includes: First, connect the second relay in the corresponding series-parallel switching circuit. After the voltage stabilizes, connect the first relay in the corresponding series-parallel switching circuit. After the voltage stabilizes again, disconnect the second relay in the corresponding series-parallel switching circuit.

8. A photovoltaic string control circuit, characterized in that, The photovoltaic string control circuit includes at least two photovoltaic strings, each photovoltaic string including at least two adjacent target photovoltaic panels, and a series-parallel switching circuit is provided between different target photovoltaic panels. The series-parallel switching circuit includes a main switch circuit and an RC pre-charge buffer branch connected in parallel. A first relay is provided in the main switch circuit, and a resistor, a capacitor and a second relay are connected in series in the RC pre-charge buffer branch. The photovoltaic string control circuit is controlled by the method described in any one of claims 1-7.

9. A photovoltaic device, characterized in that, It includes a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other through the communication bus; Memory, used to store computer programs; A processor, when executing a program stored in memory, implements the method of any one of claims 1-7.

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