A method for detecting insulation impedance of a photovoltaic string, a controller and a medium

Abstract

The application discloses a kind of insulation impedance detection methods of photovoltaic group string, controller and medium, it is related to photovoltaic field, by controlling the connection between photovoltaic channel and main circuit to establish the current relationship of whole loop of photovoltaic system, by the current relationship of whole loop, the impedance of all photovoltaic channel corresponding photovoltaic group string is determined, and then by controlling the disconnection between photovoltaic channel and main circuit to construct the independent loop of single photovoltaic channel, current relationship can be established at common ground point for this independent loop at this time, to establish the insulation impedance of the photovoltaic group string corresponding to the photovoltaic channel of the independent loop according to the current relationship of the independent loop and the impedance determined independently calculated;Finally realize the independent calculation and detection of the insulation impedance of the photovoltaic group string corresponding to single photovoltaic channel, realize MPPT level insulation impedance detection, when detecting that insulation impedance exists problem, specific photovoltaic group string position can also be quickly positioned, reduce artificial investigation cost.

Description

Technical Field

[0001] This invention relates to the field of photovoltaics, and in particular to a method, controller, and dielectric for detecting the insulation impedance of a photovoltaic string. Background Technology

[0002] With the continuous development of photovoltaic (PV) systems, PV strings, as their basic circuit topology, have been widely used. In PV systems, the energized parts of the PV string must maintain a sufficiently high insulation resistance with respect to the ground; a decrease or failure in insulation resistance can lead to safety risks. Existing insulation resistance detection methods primarily measure the overall insulation resistance between the positive and negative terminals of the entire PV array. This approach can only identify whether there is an anomaly in the overall insulation resistance of the PV array, but it cannot accurately pinpoint which specific MPPT (Maximum Power Point Tracking) branch within the PV array has an abnormal insulation resistance. Therefore, there is a technical problem of insufficient fault location accuracy. Thus, how to achieve more precise insulation resistance detection has become an urgent technical problem to be solved. Summary of the Invention

[0003] The purpose of this invention is to provide a method, controller, and medium for detecting the insulation impedance of photovoltaic strings, aiming to solve the technical problem of how to detect the insulation impedance of photovoltaic strings at the MPPT level in a photovoltaic system.

[0004] To address the aforementioned technical problems, this invention provides a method for detecting the insulation impedance of a photovoltaic string, applied to the controller of a photovoltaic system, wherein the photovoltaic system includes a main circuit and several photovoltaic channels; the method for detecting the insulation impedance of the photovoltaic string includes: Control the connection of the plurality of photovoltaic channels to the DC side of the main circuit; The impedance of all photovoltaic strings corresponding to the several photovoltaic channels is determined based on the current relationship at the common grounding point in the photovoltaic system. For any photovoltaic channel in the photovoltaic system, an independent loop for that photovoltaic channel is constructed by disconnecting the connection between that photovoltaic channel and the main circuit; Based on the current relationship of the common grounding point of the photovoltaic system for the independent circuit and the impedance, the insulation impedance of the photovoltaic string corresponding to any photovoltaic channel is determined.

[0005] Optionally, the photovoltaic channel includes a photovoltaic string and a DC / DC circuit. The photovoltaic string is connected to two DC ports on the first DC side of the DC / DC circuit via a DC switch. The main circuit includes a main switch and a DC / AC circuit. The main switch is connected in parallel between two DC ports on the DC side of the DC / AC circuit and in parallel between two DC ports on the second DC side of the DC / DC circuit. Controlling the connection of the plurality of photovoltaic channels to the DC side of the main circuit includes: Control the closing of several DC switches corresponding to the several photovoltaic channels; The impedance sum of all photovoltaic strings corresponding to the several photovoltaic channels is determined based on the current relationship at the common grounding point in the photovoltaic system, including: The main switch is disconnected, and a first current relationship is established at the common grounding point of the photovoltaic system. Control the main switch to close, and establish a second current relationship at the common grounding point of the photovoltaic system; The sum of impedances of all photovoltaic strings corresponding to the plurality of photovoltaic channels is obtained by subtracting the second current relationship from the first current relationship.

[0006] Optionally, each of the photovoltaic channels is connected to the main circuit using an independent DC switch; Constructing an independent loop for any photovoltaic channel by disconnecting it from the main circuit includes: Disconnect the DC switch corresponding to any of the photovoltaic channels; Control the closing of DC switches corresponding to other photovoltaic channels; the other photovoltaic channels are photovoltaic channels other than any of the photovoltaic channels mentioned above.

[0007] Optionally, based on the current relationship of the common grounding point of the photovoltaic system with respect to the independent loop and the impedance, the insulation impedance of the photovoltaic string corresponding to any photovoltaic channel is determined, including: A third current relationship is established at the common grounding point of the photovoltaic system for the independent loop of any photovoltaic channel. The fourth current relationship is established at the common grounding point of the photovoltaic system, forming a loop composed of other photovoltaic channels; Based on the third current relationship, the fourth current relationship, and the impedance, determine the insulation impedance of the photovoltaic string corresponding to any photovoltaic channel.

[0008] Optionally, among the plurality of photovoltaic channels, M photovoltaic channels share the same DC switch and are connected to the main circuit; the photovoltaic system also includes M-1 sub-switches that are connected one-to-one with M-1 photovoltaic channels among the M photovoltaic channels, the first end of the sub-switch being connected to any DC port on the first DC side of the DC / DC circuit in the corresponding photovoltaic channel, and the second end being connected to the common grounding point; Constructing an independent loop for any photovoltaic channel by disconnecting it from the main circuit includes: Disconnect the DC switch corresponding to any of the photovoltaic channels; If any of the photovoltaic channels has a corresponding connected sub-switch, the sub-switch corresponding to any of the photovoltaic channels is controlled to be disconnected to construct an independent loop for any of the photovoltaic channels.

[0009] Optionally, if any of the photovoltaic channels is one of the M-1 photovoltaic channels; based on the current relationship of the common grounding point of the photovoltaic system for the independent circuit and the impedance, the insulation impedance of the photovoltaic string corresponding to any of the photovoltaic channels is determined, including: When the sub-switch corresponding to any photovoltaic channel is closed and the corresponding DC switch is open, the fifth current relationship of the independent loop of any photovoltaic channel is established at the common grounding point of the photovoltaic system; When the sub-switch corresponding to any photovoltaic channel is disconnected and the corresponding DC switch is disconnected, the sixth current relationship of the independent loop of any photovoltaic channel is established at the common grounding point of the photovoltaic system. The insulation impedance of the photovoltaic string corresponding to any photovoltaic channel is determined based on the fifth and sixth current relationships.

[0010] Optionally, if any of the photovoltaic channels is one of the M photovoltaic channels other than the M-1 photovoltaic channel; based on the current relationship of the common grounding point of the photovoltaic system for the independent circuit and the impedance, the insulation impedance of the photovoltaic string corresponding to any of the photovoltaic channels is determined, including: When the DC switch corresponding to any of the photovoltaic channels is disconnected, a seventh current relationship is established at the common grounding point of the photovoltaic system; the seventh current relationship is the current relationship of all photovoltaic channels except the M photovoltaic channels that form a loop; Based on the seventh current relationship and the impedance, determine the component sum of the photovoltaic strings corresponding to the M-path photovoltaic channels; The insulation impedance of the photovoltaic string corresponding to each photovoltaic channel in the M-1 photovoltaic channels is obtained by subtracting the sum of the components.

[0011] Optionally, the photovoltaic system further includes resistive elements that are connected to each of the sub-switches in a one-to-one manner. The first end of the resistive element is connected to the second end of the corresponding sub-switch, and the second end is connected to the common grounding point.

[0012] To address the aforementioned technical problems, the present invention also provides a controller for a photovoltaic system, comprising: Memory, used to store computer programs; A processor for implementing the steps of the photovoltaic string insulation impedance detection method as described above.

[0013] To address the aforementioned technical problems, the present invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the aforementioned photovoltaic string insulation impedance detection method.

[0014] This invention provides a method for detecting the insulation impedance of photovoltaic (PV) strings. It establishes the current relationship of the entire PV system loop by controlling the connection between the PV channel and the main circuit. The impedance of the PV strings corresponding to all PV channels is determined based on this current relationship. Then, by controlling the disconnection between the PV channel and the main circuit, an independent loop for each PV channel is constructed. At this point, the current relationship can be established separately for this independent loop at the common grounding point. Based on the current relationship of this independent loop and the determined impedance, the insulation impedance of the PV strings corresponding to this PV channel is calculated independently. Ultimately, this achieves independent calculation and detection of the insulation impedance of the PV strings corresponding to a single PV channel, enabling MPPT-level PV string insulation impedance detection. When an insulation impedance problem is detected, the specific PV string location can be quickly pinpointed, reducing manual troubleshooting costs.

[0015] The present invention also provides a controller for a photovoltaic system and a computer-readable storage medium, which have the same beneficial effects as the above-mentioned method for detecting the insulation impedance of photovoltaic strings. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the prior art and embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A schematic flowchart of a photovoltaic string insulation impedance detection method provided by the present invention; Figure 2A schematic diagram of the structure of a photovoltaic system provided by the present invention; Figure 3 A flowchart illustrating a method for detecting the insulation impedance of a photovoltaic string when each photovoltaic channel uses an independent DC switch, provided by the present invention. Figure 4 This is a schematic diagram of the structure of the first photovoltaic system with a shared DC switch provided by the present invention; Figure 5 A flowchart illustrating the first method for detecting the insulation impedance of photovoltaic strings in a photovoltaic system with a shared DC switch provided by the present invention. Figure 6 This is a schematic diagram of the structure of a second type of photovoltaic system with a shared DC switch provided by the present invention; Figure 7 A flowchart illustrating the second method for detecting the insulation impedance of photovoltaic strings in a photovoltaic system with a shared DC switch provided by the present invention; Figure 8 This is a schematic diagram of the structure of a photovoltaic system controller provided by the present invention. Detailed Implementation

[0018] The core of this invention is to provide a method, controller, and medium for detecting the insulation impedance of photovoltaic strings. This method enables independent calculation and detection of the insulation impedance of a single photovoltaic channel corresponding to a photovoltaic string, thereby achieving MPPT-level insulation impedance detection of photovoltaic strings. When an insulation impedance problem is detected, the specific photovoltaic string location can be quickly identified, reducing manual troubleshooting costs.

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] See Figure 1 As shown, Figure 1 This invention provides a flowchart illustrating a method for detecting the insulation impedance of a photovoltaic string. To address the aforementioned technical problems, this invention provides a method for detecting the insulation impedance of a photovoltaic string, applied to the controller of a photovoltaic system. The photovoltaic system includes a main circuit and several photovoltaic channels. The method for detecting the insulation impedance of a photovoltaic string includes: S11: Controls the connection of several photovoltaic channels to the DC side of the main circuit; S12: Determine the sum of impedances of all photovoltaic strings corresponding to several photovoltaic channels based on the current relationship at the common grounding point in the photovoltaic system; It's easy to understand that the insulation impedance of a photovoltaic (PV) string refers to the resistance between the DC positive and DC negative terminals of the PV string and the ground (grounding point). To effectively detect the insulation impedance of PV strings in a PV system, the entire detection method and the detection device implementing this method use a common grounding point in the PV system as a reference potential. The insulation impedance of the PV string is calculated by measuring the voltage to ground at a specific node. To ensure consistency in the voltage measurement to ground, several PV channels and the entire PV system share the same common grounding point. This common grounding point provides a stable, zero-voltage reference point for the insulation impedance detection.

[0021] It should be noted that a photovoltaic (PV) channel is an independent DC current path. It starts from a group of PV strings, passes through DC cables and DC / DC converters (DC-to-DC converters), and finally reaches the DC bus, connecting to the DC side of the PV inverter. In practical applications, this is typically implemented using an MPPT loop. During normal operation, the outputs of several PV channels are connected to the DC bus in the PV system, and then to the DC side of the PV inverter in the main circuit, thus achieving current collection from all PV strings. At this point, the various PV channels and the main circuit constitute a complete loop in the PV system. The current relationship within this loop (specifically based on KCL) represents the sum of the insulation resistances of all PV strings in the PV system.

[0022] S13: For any photovoltaic channel in the photovoltaic system, an independent loop for any photovoltaic channel is constructed by disconnecting the connection between any photovoltaic channel and the main circuit; S14: Based on the current relationship and impedance of the common grounding point of the photovoltaic system for independent circuits, determine the insulation impedance of the photovoltaic string corresponding to any photovoltaic channel.

[0023] Understandably, to effectively detect the insulation impedance of photovoltaic strings in a photovoltaic system, after detecting the sum of the insulation impedances of all photovoltaic strings in the system, this application further constructs an independent loop for each photovoltaic channel to achieve more accurate detection of the insulation impedance of a set of photovoltaic strings corresponding to each photovoltaic channel. This independent loop of the photovoltaic channel possesses an independently valid Kirchhoff's Current Law (KCL). Therefore, the insulation impedance of the photovoltaic string corresponding to this independent loop can be independently expressed using the KCL of this independent loop, and further combined with the calculated result of the impedance sum to solve for the insulation impedance of the photovoltaic string corresponding to this photovoltaic channel separately. Ultimately, this achieves the detection of the insulation impedance of the photovoltaic string corresponding to a single photovoltaic channel in the photovoltaic system. Steps S13 and S14 are executed for any photovoltaic channel in the photovoltaic system, ultimately obtaining the insulation impedance of the photovoltaic string corresponding to each photovoltaic channel, thus achieving the detection of the insulation impedance at the photovoltaic channel level. If the insulation impedance test result of any photovoltaic channel exceeds the insulation impedance limit, an alarm will be triggered. This alarm can directly and accurately locate a specific photovoltaic channel, achieving precise insulation impedance alarm for each photovoltaic channel.

[0024] It should be noted that an independent loop for any photovoltaic channel refers to a system that has no electrical connection to any other photovoltaic channel in the photovoltaic system (all other photovoltaic channels besides that specific channel) or the main circuit. This application does not impose any particular limitations on the specific implementation of the photovoltaic system or its individual photovoltaic channels. The number of photovoltaic channels can be flexibly set according to actual application requirements. DC / DC circuits can be installed in the photovoltaic channels to process the DC power output from the photovoltaic strings before outputting it to the DC bus. The common grounding point is merely a reference point for measuring voltage to ground and does not imply a direct connection between a node in the photovoltaic system and the common grounding point.

[0025] This invention provides a method for detecting the insulation impedance of photovoltaic (PV) strings. By first determining the impedance sum and then constructing an independent loop for each PV channel, the insulation impedance of the PV string corresponding to a single PV channel can be solved. This method enables insulation impedance detection at the PV channel (MPPT) level in PV systems, effectively improving the accuracy of insulation impedance detection in PV systems. When an abnormality in the insulation impedance is detected in a PV system, it can accurately locate which PV channel in which the insulation abnormality occurs, enabling rapid and accurate location of the specific string with the fault, reducing manual troubleshooting costs.

[0026] See Figure 2 As shown, Figure 2This invention provides a schematic diagram of a photovoltaic system. As an optional embodiment, the photovoltaic channel includes a photovoltaic string and a DC / DC circuit. The photovoltaic string is connected to two DC ports on the first DC side of the DC / DC circuit via a DC switch. The main circuit includes a main switch and a DC / AC circuit. The main switch is connected in parallel between two DC ports on the DC side of the DC / AC circuit and also in parallel between two DC ports on the second DC side of the DC / DC circuit. Controlling the connection of several photovoltaic channels to the DC side of the main circuit, including: Control the closing of several DC switches corresponding to several photovoltaic channels; Based on the current relationship at the common grounding point in the photovoltaic system, the impedance sum of all photovoltaic strings corresponding to several photovoltaic channels is determined, including: The main switch is disconnected, and the first current relationship is established at the common grounding point in the photovoltaic system. Control the main switch to close, and establish a second current relationship at the common grounding point in the photovoltaic system; The difference between the second current relationship and the first current relationship is used to obtain the sum of the impedances of all photovoltaic strings corresponding to several photovoltaic channels.

[0027] Understandably, to facilitate the management of each photovoltaic (PV) channel, a DC switch is typically connected in series in each PV channel. The controller can control whether the PV channel is connected to the DC bus by controlling the opening and closing of the DC switch. Therefore, by controlling the closing of the DC switches corresponding to all PV channels, all PV channels can be connected to the DC side of the main circuit, that is, connected to the DC bus of the PV system. At this time, all PV channels and the main circuit together form a complete loop of the PV system. At the same time, a main switch is connected in parallel across the two ends of the DC side of the PV inverter. The closed or open state of the main switch will form two loops respectively. Based on the current relationship constructed based on these two loops, the impedance of all PV strings corresponding to all PV channels can be calculated.

[0028] As a specific embodiment, such as Figure 2As shown, assuming there are a total of n photovoltaic channels in the photovoltaic system (MPPT1, MPPT2, ..., MPPTn as shown in the figure), each photovoltaic channel includes two strings (string 1 and string 2 corresponding to MPPT1, string 3 and string 4 corresponding to MPPT2, ..., string 2n-1 and string 2n corresponding to MPPTn), a DC switch DC SW, and a DC / DC circuit. The photovoltaic strings are connected in parallel between the two DC ports on the first DC side of the DC / DC circuit. The DC output of each photovoltaic channel is output to the DC bus BUS of the photovoltaic system through the DC / DC circuit when the DC switch DC SW is turned on. The positive DC output terminal of each photovoltaic channel (one DC port on the second DC side of the DC / DC circuit) is connected to the positive terminal BUS+ of the DC bus, and the negative DC output terminal (the other DC port on the second DC side of the DC / DC circuit) is connected to the negative terminal BUS- of the DC bus. Finally, the output terminals of each photovoltaic channel are connected in parallel to each other, and the parallel circuit is connected in series with the DC / AC circuit through the DC side of the DC / AC circuit. The AC side of the DC / AC circuit is connected to the power grid. The voltage at the positive terminal of the DC output of the first photovoltaic channel is PV1+, and the voltage at the negative terminal of the DC output of the first photovoltaic channel is PV1-. The voltage at the positive terminal of the DC output of the nth photovoltaic channel is PVn+, and the voltage at the negative terminal of the DC output of the nth photovoltaic channel is PVn-. To facilitate subsequent impedance detection, a voltage sensor BSTCT is installed at the positive terminal of the DC output of each photovoltaic channel to detect the voltage to ground at the positive terminal of the DC output of the photovoltaic channel. To facilitate the subsequent construction of different states to determine the insulation impedance, a main switch S is connected in parallel on the DC side of the inverter circuit.

[0029] It should be noted that, for ease of explanation, Figure 2 The insulation impedance of each photovoltaic channel and the DC bus is represented by resistors in the circuit. For example, in the first photovoltaic channel, the insulation impedance of the positive terminal of the photovoltaic string to ground is represented by the equivalent resistance R1, and the insulation impedance of the negative terminal of the photovoltaic string to ground is represented by the equivalent resistance R2; in the second photovoltaic channel, the insulation impedance of the positive terminal of the photovoltaic string to ground is represented by the equivalent resistance R3, and the insulation impedance of the negative terminal of the photovoltaic string to ground is represented by the equivalent resistance R4; in the nth photovoltaic channel, the insulation impedance of the positive terminal of the photovoltaic string to ground is represented by the equivalent resistance R2n-1, and the insulation impedance of the negative terminal of the photovoltaic string to ground is represented by the equivalent resistance R2n; the insulation impedance of the positive terminal of the DC bus to ground is represented by the equivalent resistance Rs, and the insulation impedance of the negative terminal to ground is represented by the equivalent resistance Rq. These equivalent resistances are the insulation impedance of a certain node relative to the common grounding point PE, and are not actual resistive elements installed in the circuit.

[0030] The following is based on Figure 2The photovoltaic system shown details the specific process for determining the impedance. First, it's necessary to close the DC switches corresponding to all photovoltaic channels to connect all photovoltaic channels to the DC side of the main circuit. Then, KCLs are constructed for the two states of the main switch; with the main switch S open, the current relationship is written at the common ground point PE based on the KCL, yielding the first current relationship: (1) in, This refers to the voltage between the positive DC output terminal of the first photovoltaic channel and the common ground point PE. R1 is the equivalent resistance (i.e., the positive insulation resistance of the photovoltaic string corresponding to the first photovoltaic channel); since all photovoltaic channels are connected to the DC bus at this time, the voltage at the negative terminal of the DC output of each photovoltaic channel is the same and equal to the negative terminal voltage of the DC bus; therefore, It is the voltage between the negative terminal of the DC bus and the common grounding point PE when the main switch S is open, and it is also the voltage between the negative terminal of the DC output of each photovoltaic channel and the common grounding point PE. This refers to the voltage between the positive DC output terminal of the second photovoltaic channel and the common ground point PE. R3 is the equivalent resistance value (i.e., the positive insulation resistance of the photovoltaic string corresponding to the second photovoltaic channel). Let be the voltage between the positive DC output terminal of the nth photovoltaic channel and the common ground point PE. R2n-1 is the equivalent resistance value (i.e., the positive insulation resistance of the photovoltaic string corresponding to the nth photovoltaic channel). R2 is the equivalent resistance value (i.e., the negative insulation impedance of the photovoltaic string corresponding to the first photovoltaic channel). R4 is the equivalent resistance value (i.e., the negative insulation impedance of the photovoltaic string corresponding to the second photovoltaic channel). R2n is the equivalent resistance value (i.e., the negative insulation impedance of the photovoltaic string corresponding to the nth photovoltaic channel). Rq is the equivalent resistance value (i.e., the negative insulation resistance of the DC bus).

[0031] Rearranging terms in equation (1), we get: (2) On the other hand, with the main switch S closed, the current relationship at the common ground point PE is written based on KCL, resulting in the second current relationship: (3) in, It is the voltage between the negative terminal of the DC bus and the common grounding point PE when the main switch S is closed, and it is also the voltage between the negative terminal of the DC output of each photovoltaic channel and the common grounding point PE. Rs is the equivalent resistance (i.e., the positive insulation resistance of the DC bus). The positive DC output terminal of each photovoltaic channel is connected to the positive terminal of the DC bus via a DC / DC circuit. Simultaneously, a unidirectional diode is incorporated in the output circuit of the DC / DC circuit at the positive DC output terminal, directing the current flow from the photovoltaic channel to the DC bus. Therefore, although the positive DC output terminal of each photovoltaic channel is connected to the positive terminal of the DC bus, the voltage at the positive DC output terminals of each photovoltaic channel will not be completely identical. Furthermore, the voltage at the positive terminal of the DC bus depends on the photovoltaic channel with the highest output voltage. This is the positive voltage of the DC bus.

[0032] Rearranging terms in equation (3), we get: (4) Then subtracting equation (2) from equation (4) yields: (5) Thus, the impedance of all photovoltaic strings corresponding to all photovoltaic channels is obtained, i.e., the left side of equation (5). The insulation impedance corresponding to the DC bus can be directly measured with a megohmmeter during the power outage maintenance of the photovoltaic system, or through the inverter circuit.

[0033] It should be noted that the voltage parameters in the above current relationships are all detected by voltage sensors or other means after the control DC switch and / or main switch have completed their respective actions. This embodiment uses a photovoltaic channel including photovoltaic strings and a DC / DC circuit, and a main circuit including a DC / AC circuit (Direct Current to Alternating Current, DC to AC inverter), i.e., a photovoltaic inverter, as an example for illustration. In practical applications, other photovoltaic systems with different architectures can also be applied in reference to this embodiment, and are not limited to the implementation method in this embodiment. This application does not make any special limitations on the specific implementation in other application scenarios.

[0034] Specifically, by using the current relationship between the main switch and the two states when all photovoltaic channels are connected to the DC bus, the sum of the insulation impedances of all photovoltaic strings in the photovoltaic system corresponding to all photovoltaic channels can be effectively determined, so as to further determine the insulation impedance of the photovoltaic string corresponding to a single photovoltaic channel.

[0035] See Figure 3 As shown, Figure 3This invention provides a flowchart illustrating a method for detecting the insulation impedance of a photovoltaic string when each photovoltaic channel uses an independent DC switch. As an optional embodiment, several photovoltaic channels are connected to the main circuit using independent DC switches. Constructing an independent loop for any photovoltaic channel by disconnecting it from the main circuit includes: Disconnect the DC switch corresponding to any photovoltaic channel; Control the closing of DC switches corresponding to other photovoltaic channels; other photovoltaic channels are photovoltaic channels other than any other photovoltaic channel.

[0036] As an optional embodiment, based on the current relationship and impedance of the common grounding point of the photovoltaic system for independent loops and determining the insulation impedance of the photovoltaic string corresponding to any photovoltaic channel, the method includes: The third current relationship is established at the common grounding point of a photovoltaic system to create an independent loop for any photovoltaic channel; The fourth current relationship is established at the common grounding point of the photovoltaic system to form a loop consisting of other photovoltaic channels; Based on the third current relationship, the fourth current relationship, and impedance, determine the insulation impedance of the photovoltaic string corresponding to any photovoltaic channel.

[0037] It is easy to understand that, in practical applications, there are various ways to implement DC switches for cost considerations. This embodiment takes the example of each photovoltaic channel using an independent DC switch to further illustrate insulation impedance detection. The circuit topology when each photovoltaic channel uses an independent DC switch is as follows: Figure 2 As shown, the first photovoltaic channel uses DC switch DC SW1, the second photovoltaic channel uses DC switch DC SW2, and the nth photovoltaic channel uses DC switch DC SWn. Each DC switch includes at least two contacts, connected in series between the positive terminal of the photovoltaic string and one DC port on the first DC side of the DC / DC circuit, and between the negative terminal of the photovoltaic string and the other DC port on the first DC side of the DC / DC circuit. In this case, an independent loop for any photovoltaic channel can be effectively constructed simply by controlling the opening of the DC switch corresponding to any photovoltaic channel.

[0038] As a specific embodiment, based on Figure 2 The flowchart of the insulation impedance detection method for photovoltaic strings implemented in the photovoltaic system topology shown is as follows: Figure 3 As shown, the steps of the above embodiment are first performed to determine the sum of the impedances of all photovoltaic strings corresponding to all photovoltaic channels. Then, taking the determination of the insulation impedance of the photovoltaic string corresponding to the first photovoltaic channel as an example, the subsequent steps are further explained.

[0039] After determining the impedance, first disconnect the DC switch DC SW1 corresponding to the first photovoltaic channel, and keep the DC switches DC SW2 to DC SWn corresponding to the other photovoltaic channels closed. At this time, the first photovoltaic channel is in a separate loop, and the other photovoltaic channels and the main circuit are in a single loop. In this state, write the current relationship of the separate loop at the common ground point PE based on KCL to obtain the third current relationship: (6) in, This is the voltage between the negative terminal of the DC output of the first photovoltaic channel and the common ground point PE when DC SW1 is disconnected.

[0040] Rearranging equation (6) yields: (7) At the same time, based on KCL, the current relationship of the loop formed by other photovoltaic channels and the main circuit is written at the common grounding point PE, resulting in the fourth current relationship: (8) in, This is the voltage between the negative terminal of the DC bus and the common ground point PE, currently (DC SW1 is off), and also the voltage between the negative terminal of the DC output of other photovoltaic channels and the common ground point PE. Rearranging equation (8) yields: (9) Then, combining the previously obtained impedance and corresponding relationship, we can solve equations (2), (7), and (9) simultaneously. Specifically, by adding equation (7) and equation (9), the left side of the equation becomes equal to the left side of equation (2), ultimately yielding: (10) Simultaneously due to impedance and for: (11) In formula (11) ; ; By combining equations (10) and (11), we can obtain: ; This determines the insulation impedance of the photovoltaic string corresponding to the first photovoltaic channel. The insulation impedance of the photovoltaic strings corresponding to other photovoltaic channels is calculated and determined in a similar manner, which will not be elaborated here. In practical applications, the insulation impedance of the photovoltaic strings corresponding to each photovoltaic channel can be calculated sequentially by disconnecting the DC switches corresponding to each photovoltaic channel.

[0041] Specifically, for cases where each photovoltaic channel is connected to the DC bus via an independent DC switch, it is only necessary to add voltage detection between the negative terminal of the DC output of that photovoltaic channel and the common grounding point PE to combine impedance and calculation to obtain the corresponding insulation impedance value of that channel.

[0042] As an optional embodiment, M photovoltaic channels among the several photovoltaic channels share the same DC switch connected to the main circuit; the photovoltaic system also includes M-1 sub-switches that are connected one-to-one with M-1 photovoltaic channels among the M photovoltaic channels. The first end of the sub-switch is connected to any DC port on the first DC side of the DC / DC circuit in the corresponding photovoltaic channel, and the second end is connected to the common ground point; M is a positive integer. Constructing an independent loop for any photovoltaic channel by disconnecting it from the main circuit includes: Disconnect the DC switch corresponding to any photovoltaic channel; If any photovoltaic channel has a corresponding connected sub-switch, control the corresponding sub-switch of any photovoltaic channel to disconnect in order to construct an independent loop for any photovoltaic channel.

[0043] As an optional embodiment, if any photovoltaic channel is one of the M-1 photovoltaic channels; based on the current relationship and impedance of the common grounding point of the photovoltaic system for independent loops, and determining the insulation impedance of the photovoltaic string corresponding to any photovoltaic channel, including: When the sub-switch corresponding to any photovoltaic channel is closed and the corresponding DC switch is open, the fifth current relationship is established at the common grounding point of the photovoltaic system for the independent loop of any photovoltaic channel. When the sub-switch corresponding to any photovoltaic channel is disconnected and the corresponding DC switch is disconnected, the sixth current relationship of the independent loop of any photovoltaic channel is established at the common grounding point of the photovoltaic system. The insulation impedance of the photovoltaic string corresponding to any photovoltaic channel is determined based on the fifth and sixth current relations.

[0044] As an optional embodiment, if any photovoltaic channel is one of the M photovoltaic channels other than the M-1 photovoltaic channel; based on the current relationship and impedance of the common grounding point of the photovoltaic system for independent loops, and determining the insulation impedance of the photovoltaic string corresponding to any photovoltaic channel, including: When the DC switch corresponding to any photovoltaic channel is disconnected, a seventh current relationship is established at the common grounding point of the photovoltaic system; the seventh current relationship is the current relationship of all photovoltaic channels except M photovoltaic channels forming a loop; The components of the photovoltaic string corresponding to the M-path photovoltaic channel are determined based on the seventh current relationship and impedance. Subtracting the insulation impedance of the photovoltaic string corresponding to each photovoltaic channel in the M-1 photovoltaic channel from the component sum, we can obtain the insulation impedance of the photovoltaic string corresponding to any photovoltaic channel.

[0045] Understandably, for cost considerations, some photovoltaic channels may share a single DC switch. In this case, to construct an independent circuit for a single photovoltaic channel, a sub-switch needs to be added to a group of photovoltaic channels sharing a single DC switch. The sub-switch is connected in parallel between the negative DC output terminal of a certain photovoltaic channel and the grounding point. When the voltage to ground of the negative DC output terminal of a certain photovoltaic channel is detected, the voltage detection circuit between the negative DC output terminal of a certain photovoltaic channel and the grounding point can be controllably cut off or connected, thereby constructing a separate current relationship for that photovoltaic channel and realizing the construction of an independent circuit for that photovoltaic channel.

[0046] To enable independent detection of the insulation impedance of each photovoltaic channel, for a photovoltaic channel with M shared DC switches, at least M-1 sub-switches need to be set up so that the M-1 photovoltaic channels corresponding to the M-1 sub-switches can form independent loops and independently detect the insulation impedance. The insulation impedance of the remaining photovoltaic channel can also be obtained by combining components and calculation.

[0047] As a specific example, it is assumed that two of the n photovoltaic channels share the same DC switch. See [link to relevant documentation]. Figure 4 As shown, Figure 4 This is a schematic diagram of the first type of photovoltaic system with a shared DC switch provided by the present invention; taking the first and second photovoltaic channels sharing a DC switch DC SW1 as an example, a sub-switch S1 and a corresponding series-connected resistor element Rm are added to the second photovoltaic channel. The insulation impedance detection process of the entire photovoltaic system is described below. Figure 5 As shown, Figure 5 This is a flowchart illustrating the first method for detecting the insulation impedance of photovoltaic strings in a photovoltaic system with a shared DC switch, provided by the present invention.

[0048] First, the steps described in the previous embodiment are performed to determine the impedance of all photovoltaic strings corresponding to all photovoltaic channels. Then, the insulation impedance testing process for the two shared DC SW1 photovoltaic channels is explained in detail. The insulation impedance testing process for other photovoltaic channels is similar. Figure 3 The implementation method shown is the same, and will not be described again in this application.

[0049] After determining the impedance sum, first disconnect the two shared DC switches DC SW1. Then, with the main switch open and closed respectively, write the current relationship at the common ground point PE based on KCL. This process is similar to writing the first and second current relationships. That is, perform another impedance sum test on the loop formed by the other photovoltaic channels and the main circuit besides these two. At this time, obtain the first impedance component sum of the photovoltaic strings corresponding to the other photovoltaic channels (other photovoltaic channels besides these two). Then, subtract the first impedance component sum from the impedance sum to obtain the component sum of the photovoltaic strings corresponding to these two (M) photovoltaic channels. Specifically, by performing another impedance sum test on the loop formed by the other photovoltaic channels and the main circuit besides these two, we can obtain: (12) in, This is the voltage between the negative terminal of the DC bus and the common ground point PE when DC SW1 is open and the main switch S is open. It is also the voltage between the negative terminal of the DC output of other photovoltaic channels (other photovoltaic channels besides these two) and the common ground point PE. This is the voltage between the negative terminal of the DC bus and the common ground point PE when DC SW1 is open and the main switch S is closed. It is also the voltage between the negative terminal of the DC output of other photovoltaic channels (other photovoltaic channels besides these two) and the common ground point PE.

[0050] Then, by combining equations (12) and (5), we can obtain the sum of the components of the photovoltaic strings corresponding to these two (M) photovoltaic channels: (13) After obtaining the component sums of the photovoltaic strings corresponding to the two (M) photovoltaic channels, the independent loop of the second photovoltaic channel is further constructed through a sub-switch. Sub-switch S1 is then disconnected; at this point, both sub-switch S1 and DC switch DC SW1 are open. Based on KCL, the current relationship of the independent loop of the second photovoltaic channel is written at the common ground point PE, resulting in the fifth current relationship: (14) in, Let S1 be the voltage between the negative DC output terminal of the second photovoltaic channel and the common ground point PE in the current state (sub-switch S1 is open and DC switch DC SW1 is open). Then close sub-switch S1. At this time, sub-switch S1 is closed and DC switch DC SW1 is open. Based on KCL, write the current relationship of the independent loop of the second photovoltaic channel at the common ground point PE, and obtain the sixth current relationship: (15) in, This is the voltage between the negative DC output terminal of the second photovoltaic channel and the common ground point PE in the current state (sub-switch S1 is closed and DC switch DC SW1 is open).

[0051] By combining equations (14) and (15), we can obtain: (16) Thus, the insulation impedance of the photovoltaic string corresponding to the second photovoltaic channel is determined. Then, by subtracting the insulation impedance of the photovoltaic string corresponding to the second photovoltaic channel from the sum of the components of the photovoltaic strings corresponding to these two (M) photovoltaic channels, that is, subtracting equation (16) from equation (13), the insulation impedance of the photovoltaic string corresponding to the first photovoltaic channel can be obtained: .

[0052] Specifically, the single-channel insulation impedance detection process for M photovoltaic channels sharing a single DC switch can refer to the steps described above, and will not be repeated here. For M photovoltaic channels sharing a common DC switch, in addition to adding a voltage sampling signal between the negative terminal of the DC output of each photovoltaic channel and the common grounding point, at least M-1 sub-switches need to be added. The insulation impedance detection of a single photovoltaic channel is determined by combining the closed or open states of the main switch and the sub-switches.

[0053] The following example, using the insulation impedance detection process of three photovoltaic channels sharing a single DC switch, will further illustrate this; see [link to relevant documentation]. Figure 6 As shown, Figure 6 This is a schematic diagram of the second type of photovoltaic system with a shared DC switch provided by the present invention. Taking the first, second, and third photovoltaic channels sharing a DC switch DC SW1 as an example, a sub-switch S1 and a corresponding series-connected resistor Rm are added to the second photovoltaic channel, and a sub-switch S2 and a corresponding series-connected resistor Rm are added to the second photovoltaic channel. The insulation impedance detection process for the entire photovoltaic system is described below. Figure 7 As shown, Figure 7 This is a flowchart illustrating the second method for detecting the insulation impedance of photovoltaic strings in a photovoltaic system with a shared DC switch, provided by the present invention.

[0054] First, the steps described in the previous embodiment are performed to determine the impedance of all photovoltaic strings corresponding to all photovoltaic channels. Then, the insulation impedance testing process for the three common DC SW1 photovoltaic channels is explained in detail. The insulation impedance testing process for other photovoltaic channels besides these three is similar. Figure 3 The implementation method shown is the same, and will not be described again in this application.

[0055] After determining the impedance sum, first disconnect the DC switch DC SW1 shared by these three paths. Then, with the main switch open and closed respectively, write the current relationship at the common ground point PE based on KCL. This process is similar to the process of writing the first and second current relationships. That is, perform another impedance sum test on the loop formed by the photovoltaic channels other than these three paths and the main circuit. At this time, obtain the second impedance component sum of the photovoltaic strings corresponding to the other photovoltaic channels (other than these three paths). Then subtract the second impedance component sum from the impedance sum to obtain the component sum of the photovoltaic strings corresponding to these three (M) photovoltaic channels. Specifically, by performing another impedance sum test on the loop formed by the photovoltaic channels other than these three paths and the main circuit, we can obtain: (17) in, This is the voltage between the negative terminal of the DC bus and the common ground point PE when DC SW1 is open and the main switch S is open. It is also the voltage between the negative terminal of the DC output of other photovoltaic channels (other photovoltaic channels besides these three) and the common ground point PE. This is the voltage between the negative terminal of the DC bus and the common ground point PE when DC SW1 is open and the main switch S is closed. It is also the voltage between the negative terminal of the DC output of other photovoltaic channels (other photovoltaic channels besides these three) and the common ground point PE.

[0056] Then, by combining equations (17) and (5), we can obtain the sum of the components of the photovoltaic strings corresponding to these three (M) photovoltaic channels: (18) After obtaining the component sums of the photovoltaic strings corresponding to these three (M) photovoltaic channels, the independent loop of the second photovoltaic channel is further constructed using sub-switch S1, and the independent loop of the third photovoltaic channel is constructed using sub-switch S2. Sub-switch S1 is then disconnected; at this point, both sub-switch S1 and DC switch DC SW1 are open. Based on KCL, the current relationship of the independent loop of the second photovoltaic channel is written at the common ground point PE, resulting in the fifth current relationship of the second photovoltaic channel: (19) in, Let S1 be the voltage between the negative DC output terminal of the second photovoltaic channel and the common ground point PE in the current state (sub-switch S1 is open and DC switch DC SW1 is open). Then close sub-switch S1. At this time, sub-switch S1 is closed and DC switch DC SW1 is open. Based on KCL, write the current relationship of the independent loop of the second photovoltaic channel at the common ground point PE, and obtain the sixth current relationship of the second photovoltaic channel: (20) in, This is the voltage between the negative DC output terminal of the second photovoltaic channel and the common ground point PE in the current state (sub-switch S1 is closed and DC switch DC SW1 is open).

[0057] By combining equations (19) and (20), we can obtain: ;(twenty one) This determines the insulation impedance of the photovoltaic string corresponding to the second photovoltaic channel. Further, sub-switch S2 is disconnected. At this point, sub-switch S2 is open and DC switch DC SW1 is also open. Based on KCL, the current relationship of the independent loop of the third photovoltaic channel is written at the common ground point PE, resulting in the fifth current relationship of the third photovoltaic channel: ;(twenty two) in, Let S2 be the voltage between the negative DC output terminal of the third photovoltaic channel and the common ground point PE in the current state (sub-switch S2 is open and DC switch DC SW1 is open). Then close sub-switch S2. At this time, sub-switch S2 is closed and DC switch DC SW1 is open. Based on KCL, write the current relationship of the independent loop of the third photovoltaic channel at the common ground point PE, and obtain the sixth current relationship of the third photovoltaic channel: ;(twenty three) in, This is the voltage between the negative DC output terminal of the third photovoltaic channel and the common ground point PE in the current state (sub-switch S2 is closed and DC switch DC SW1 is open).

[0058] By combining equations (22) and (23), we can obtain: ;(twenty four) Thus, the insulation impedance of the photovoltaic string corresponding to the third photovoltaic channel is determined. Then, by subtracting the insulation impedance of the photovoltaic string corresponding to the second photovoltaic channel and the third photovoltaic channel from the sum of the components of the photovoltaic strings corresponding to these three (M) photovoltaic channels, that is, subtracting equations (21) and (24) from equation (18), the insulation impedance of the photovoltaic string corresponding to the first photovoltaic channel can be obtained: .

[0059] As an optional embodiment, the photovoltaic system also includes a resistor element connected to a sub-switch in a one-to-one correspondence, with the first end of the resistor element connected to the second end of the corresponding sub-switch and the second end connected to a common grounding point.

[0060] Understandably, to ensure safety, a resistor element connected in series with the sub-switch can be set to ensure the safety and reliability of the sub-switch operation. After the sub-switch and the resistor element are connected in series, they are connected in parallel to the two ends of the negative insulation impedance of the photovoltaic string corresponding to a certain photovoltaic channel. The resistor element is a physical component that is actually set in the circuit. Its resistance value can be determined according to the approximate resistance value of the negative insulation impedance of the photovoltaic string it is connected to. Generally, it needs to be less than the resistance value of the negative insulation impedance of the corresponding photovoltaic string.

[0061] It should be further noted that the number of sub-switches can be adjusted according to actual application requirements. A preferred embodiment is the use of M-1 sub-switches as described in the above embodiment. Alternatively, M sub-switches corresponding one-to-one with the M photovoltaic channels can be set to achieve independent detection for each channel. This application does not impose any particular limitations here. Regarding the specific types and implementation methods of the sub-switches and resistive elements, this application does not impose any particular limitations here. The sub-switches can be implemented using physical switches or through logic control, as long as they can achieve the disconnection or connection of the voltage detection circuit between the negative DC output terminal and the grounding point of the corresponding photovoltaic channel.

[0062] See Figure 8 As shown, Figure 8 This invention provides a schematic diagram of the structure of a photovoltaic system controller. To solve the above-mentioned technical problems, this invention also provides a photovoltaic system controller, comprising: Memory 21 is used to store computer program 212; Processor 22 is used to implement the steps of the photovoltaic string insulation impedance detection method as described above.

[0063] The processor 22 may include one or more processing cores, such as a quad-core processor or an octa-core processor. The processor 22 may be implemented using at least one hardware form selected from DSP (Digital Signal Processor), FPGA (Field-Programmable Gate Array), and PLA (Programmable Logic Array). The processor may also include a main processor and a coprocessor. The main processor, also known as the central processing unit, is used to process data in the wake-up state; the coprocessor is a low-power processor used to process data in the standby state. In some embodiments, the processor 22 may integrate a GPU (graphics processing unit), which is responsible for rendering and drawing the content to be displayed on the screen. In some embodiments, the processor 22 may also include an AI (Artificial Intelligence) processor, which is used to handle computational operations related to machine learning.

[0064] The memory 21 may include one or more computer-readable storage media, which may be non-transitory. The memory 21 may also include high-speed random access memory and non-volatile memory, such as one or more disk storage devices or flash memory devices. In this embodiment, the memory 21 is used to store at least the following computer program 212, which, after being loaded and executed by the processor 22, can implement the relevant steps of the photovoltaic string insulation impedance detection method disclosed in any of the foregoing embodiments. In addition, the resources stored in the memory 21 may also include an operating system 211 and data, and the storage method may be temporary or permanent storage. The operating system 211 may include Windows, Unix, Linux, etc. The data may include, but is not limited to, the data in the photovoltaic string insulation impedance detection method.

[0065] In some embodiments, the controller of the photovoltaic system may further include a display screen, an input / output interface 25, a communication interface 24, a power supply 23, and a communication bus 26. Those skilled in the art will understand that... Figure 8 The diagram does not constitute a limitation on the controller of the photovoltaic system and may include more or fewer components than shown.

[0066] For an introduction to the controller for a photovoltaic system provided by this invention, please refer to the embodiment of the above-mentioned method for detecting the insulation impedance of photovoltaic strings. This invention will not be described again here.

[0067] To address the aforementioned technical problems, the present invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the aforementioned photovoltaic string insulation impedance detection method.

[0068] It is understood that if the methods in the above embodiments are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and executes all or part of the steps of the methods described in the various embodiments of this application. Specifically, the computer-readable storage medium may include, but is not limited to, any type of disk, including floppy disks, optical disks, and portable hard drives, or any type of media or device suitable for storing instructions or data, etc., and this application does not make any special limitations here.

[0069] For an introduction to the computer-readable storage medium provided by this invention, please refer to the above-described embodiment of the method for detecting the insulation impedance of photovoltaic strings; the present invention will not be described in detail here.

[0070] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatuses disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the method section. It should also be noted that in this specification, 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.

[0071] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for detecting the insulation impedance of a photovoltaic string, characterized in that, A controller for a photovoltaic system, the photovoltaic system including a main circuit and several photovoltaic channels; the insulation impedance detection method for the photovoltaic string includes: Control the connection of the plurality of photovoltaic channels to the DC side of the main circuit; The impedance of all photovoltaic strings corresponding to the several photovoltaic channels is determined based on the current relationship at the common grounding point in the photovoltaic system. For any photovoltaic channel in the photovoltaic system, an independent loop for that photovoltaic channel is constructed by disconnecting the connection between that photovoltaic channel and the main circuit; Based on the current relationship of the common grounding point of the photovoltaic system for the independent circuit and the impedance, the insulation impedance of the photovoltaic string corresponding to any photovoltaic channel is determined.

2. The method for detecting the insulation impedance of a photovoltaic string according to claim 1, characterized in that, The photovoltaic channel includes a photovoltaic string and a DC / DC circuit. The photovoltaic string is connected to two DC ports on the first DC side of the DC / DC circuit via a DC switch. The main circuit includes a main switch and a DC / AC circuit. The main switch is connected in parallel between two DC ports on the DC side of the DC / AC circuit and also in parallel between two DC ports on the second DC side of the DC / DC circuit. Controlling the connection of the plurality of photovoltaic channels to the DC side of the main circuit includes: Control the closing of several DC switches corresponding to the several photovoltaic channels; The impedance sum of all photovoltaic strings corresponding to the several photovoltaic channels is determined based on the current relationship at the common grounding point in the photovoltaic system, including: The main switch is disconnected, and a first current relationship is established at the common grounding point of the photovoltaic system. Control the main switch to close, and establish a second current relationship at the common grounding point of the photovoltaic system; The sum of impedances of all photovoltaic strings corresponding to the plurality of photovoltaic channels is obtained by subtracting the second current relationship from the first current relationship.

3. The method for detecting the insulation impedance of a photovoltaic string according to any one of claims 1 to 2, characterized in that, Each of the photovoltaic channels is connected to the main circuit via an independent DC switch. Constructing an independent loop for any photovoltaic channel by disconnecting it from the main circuit includes: Disconnect the DC switch corresponding to any of the photovoltaic channels; Control the closing of DC switches corresponding to other photovoltaic channels; the other photovoltaic channels are photovoltaic channels other than any of the photovoltaic channels mentioned above.

4. The method for detecting the insulation impedance of a photovoltaic string according to claim 3, characterized in that, Based on the current relationship of the common grounding point of the photovoltaic system with respect to the independent circuit and the impedance, the insulation impedance of the photovoltaic string corresponding to any photovoltaic channel is determined, including: A third current relationship is established at the common grounding point of the photovoltaic system for the independent loop of any photovoltaic channel. The fourth current relationship is established at the common grounding point of the photovoltaic system, forming a loop composed of other photovoltaic channels; Based on the third current relationship, the fourth current relationship, and the impedance, determine the insulation impedance of the photovoltaic string corresponding to any photovoltaic channel.

5. The method for detecting the insulation impedance of a photovoltaic string according to any one of claims 1 to 2, characterized in that, Among the several photovoltaic channels, M photovoltaic channels share the same DC switch and are connected to the main circuit; the photovoltaic system also includes M-1 sub-switches that are connected one-to-one with M-1 photovoltaic channels among the M photovoltaic channels. The first end of each sub-switch is connected to any DC port on the first DC side of the DC / DC circuit in the corresponding photovoltaic channel, and the second end is connected to the common grounding point. Constructing an independent loop for any photovoltaic channel by disconnecting it from the main circuit includes: Disconnect the DC switch corresponding to any of the photovoltaic channels; If any of the photovoltaic channels has a corresponding connected sub-switch, the sub-switch corresponding to any of the photovoltaic channels is controlled to be disconnected to construct an independent loop for any of the photovoltaic channels.

6. The method for detecting the insulation impedance of a photovoltaic string according to claim 5, characterized in that, If any of the photovoltaic channels is one of the M-1 photovoltaic channels; based on the current relationship of the common grounding point of the photovoltaic system for the independent circuit and the impedance, determine the insulation impedance of the photovoltaic string corresponding to any of the photovoltaic channels, including: When the sub-switch corresponding to any photovoltaic channel is closed and the corresponding DC switch is open, the fifth current relationship of the independent loop of any photovoltaic channel is established at the common grounding point of the photovoltaic system; When the sub-switch corresponding to any photovoltaic channel is disconnected and the corresponding DC switch is disconnected, the sixth current relationship of the independent loop of any photovoltaic channel is established at the common grounding point of the photovoltaic system. The insulation impedance of the photovoltaic string corresponding to any photovoltaic channel is determined based on the fifth and sixth current relationships.

7. The method for detecting the insulation impedance of a photovoltaic string according to claim 6, characterized in that, If any of the photovoltaic channels is one of the M photovoltaic channels other than the M-1 photovoltaic channel; based on the current relationship of the common grounding point of the photovoltaic system for the independent circuit and the impedance, determine the insulation impedance of the photovoltaic string corresponding to any of the photovoltaic channels, including: When the DC switch corresponding to any of the photovoltaic channels is disconnected, a seventh current relationship is established at the common grounding point of the photovoltaic system; the seventh current relationship is the current relationship of all photovoltaic channels except the M photovoltaic channels that form a loop; Based on the seventh current relationship and the impedance, determine the component sum of the photovoltaic strings corresponding to the M-path photovoltaic channels; The insulation impedance of the photovoltaic string corresponding to each photovoltaic channel in the M-1 photovoltaic channels is obtained by subtracting the sum of the components.

8. The method for detecting the insulation impedance of a photovoltaic string according to claim 5, characterized in that, The photovoltaic system also includes resistive elements that are connected to each of the sub-switches in a one-to-one manner. The first end of the resistive element is connected to the second end of the corresponding sub-switch, and the second end is connected to the common grounding point.

9. A controller for a photovoltaic system, characterized in that, include: Memory, used to store computer programs; A processor for implementing the steps of the method for detecting the insulation impedance of a photovoltaic string as described in any one of claims 1 to 8.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the steps of the method for detecting the insulation impedance of a photovoltaic string as described in any one of claims 1 to 8.

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