A photovoltaic system and an optimizer positioning method thereof

Abstract

The application provides a photovoltaic system and an optimizer positioning method thereof. The optimizer positioning method first sets output voltage limit value and / or output current limit value for optimizers in each photovoltaic string by an inverter, and controls each optimizer to start; then, for parallel no-voltage-difference photovoltaic strings connected to a Boost circuit, the inverter controls at least one of the optimizers to change output voltage at least once, actively creates a voltage difference between the parallel no-voltage-difference photovoltaic strings, and further constructs long strings and short strings connected in parallel to form a circulating current; since the circulating current causes the electrical states of the optimizers in the long strings and the short strings to be different, the electrical states of the optimizers can be used to distinguish the photovoltaic strings to which the optimizers belong, and thus the optimizer distinction between different photovoltaic strings connected to the Boost circuit is automatically realized, that is, the string-level positioning of the optimizers is realized.

Description

Technical Field

[0001] This application relates to the field of photovoltaic power generation technology, and in particular to a photovoltaic system and its optimizer positioning method. Background Technology

[0002] The optimizer in a photovoltaic (PV) system, also known as a PV power optimizer, is specifically a DC-input, DC-output MLPE (Module Level Power Electronics). By connecting in series with the PV modules and employing predictive current and voltage technology, it ensures that the PV modules are always in optimal operating condition. This addresses the impact of shading, inconsistent orientation, or differences in module electrical specifications on power generation in PV power plants, achieving maximum power output from the PV modules and increasing system power generation.

[0003] In a solar photovoltaic power generation system with optimizers, the inverter and optimizer communicate via a PLC (Power Line Communication). The inverter contains a PLC master node controller, and the optimizer is a PLC slave node. After the optimizer and inverter are installed in the system, the inverter master node needs to know the topology location information of each optimizer connected to the inverter system to facilitate command control and status positioning during later operation. If the inverter lacks the topology location information of the optimizers, crosstalk may cause it to search for optimizers from other systems, affecting the inverter master node's judgment and error control.

[0004] Currently, the topology location information for each optimizer still needs to be manually entered in sequence. However, if this entry process only achieves the correspondence between each optimizer and each Boost circuit of the inverter, when the number of photovoltaic strings connected to the Boost circuit is greater than 1, if the inverter master node does not know which optimizers are in the same string, it will affect its judgment of long strings, incorrectly issue limiting values, and cause the sum of the output voltages of the entire string of optimizers to exceed the voltage that the inverter can withstand, resulting in overvoltage damage to the inverter. Summary of the Invention

[0005] In view of this, this application provides a photovoltaic system and its optimizer location method to automatically distinguish optimizers between different photovoltaic strings connected to the Boost circuit.

[0006] To achieve the above objectives, this application provides the following technical solution:

[0007] The first aspect of this application provides an optimizer positioning method for parallel photovoltaic strings in a photovoltaic system, the photovoltaic system including: an inverter and corresponding photovoltaic strings connected to each Boost circuit in the DC bus front stage; the optimizer positioning method includes:

[0008] The inverter sets output voltage and / or output current limits for the optimizers in each photovoltaic string.

[0009] The inverter controls the startup of each of the optimizers;

[0010] For the parallel photovoltaic strings with no voltage drop connected to the Boost circuit, the inverter controls one of the optimizers to change the output voltage at least once, and distinguishes the photovoltaic strings to which each optimizer belongs by the electrical state of each optimizer.

[0011] Optionally, the output voltage can be changed, including: active bypass; or,

[0012] If the inverter has set the output voltage limit value for each of the optimizers, then after the inverter controls each of the optimizers to start, the method further includes: the inverter controlling the output voltage of each of the optimizers to reach the output voltage limit value; and changing the output voltage, including: increasing or decreasing the output voltage limit value.

[0013] Optionally, the inverter controls one of the optimizers to change its output voltage at least once, and distinguishes the photovoltaic string to which each optimizer belongs based on its electrical state, including:

[0014] The inverter controls any one of the optimizers in the undetermined photovoltaic string to change its output voltage;

[0015] After each time the inverter controls the corresponding optimizer to change its output voltage, it detects the electrical state of each optimizer and, based on the electrical state, determines each optimizer that is in the same photovoltaic string as the optimizer that changed its output voltage, and determines that other optimizers belong to other photovoltaic strings, until the inverter can distinguish the photovoltaic strings to which each of the corresponding optimizers belongs.

[0016] Optionally, the electrical state includes at least one of output voltage, output current, and operating state;

[0017] If the direction of changing the output voltage is to decrease, then the optimizers located in the same photovoltaic string as the optimizer that changes the output voltage include:

[0018] The optimizer that satisfies at least one of the following conditions: output voltage is greater than a preset voltage value, output current is less than a preset negative current value, and the operating state is reverse input state;

[0019] If the direction of changing the output voltage is to increase, then the optimizers located in the same photovoltaic string as the optimizer that changes the output voltage include:

[0020] The optimizer is defined as one that satisfies at least one of the following conditions: output voltage is less than the preset voltage value, output current is greater than the preset positive current value, and the operating state is a positive output state.

[0021] Optionally, if the inverter has set the output voltage limit value for each of the optimizers, then the output voltage is used as the output voltage limit value instead of the condition that the output voltage is greater than the preset voltage value; and the output voltage is less than the output voltage limit value instead of the condition that the output voltage is less than the preset voltage value.

[0022] If the inverter has set the output current limit value for each of the optimizers, then the condition that the output current is less than the preset negative current value is replaced by the output current limit value that is negative; and the condition that the output current is greater than the preset positive current value is replaced by the output current limit value that is positive.

[0023] Optionally, for the parallel zero-dropout photovoltaic string connected to the Boost circuit, before the inverter controls one of the optimizers to change its output voltage at least once, the following steps are also included:

[0024] The inverter determines whether the electrical states of each optimizer in the parallel photovoltaic string connected to the Boost circuit are consistent.

[0025] If all the electrical states are consistent, then the corresponding parallel photovoltaic string is determined to be the parallel photovoltaic string with no voltage difference.

[0026] If the electrical states are not consistent, the inverter first determines that the optimizer whose output current is greater than a preset positive current value or less than a preset negative current value belongs to the same photovoltaic string; then, if the number of photovoltaic strings in the corresponding parallel photovoltaic strings is greater than 2, it determines that the other photovoltaic strings are the parallel no-voltage photovoltaic strings.

[0027] Optionally, if the inverter has already set the output current limit value for each of the optimizers, then:

[0028] The output current limit value, which is positive, is used instead of the condition that the output current is greater than the preset positive current value.

[0029] The condition that the output current is less than the preset negative current value is replaced by the output current limit value where the output current is negative.

[0030] Optionally, before the inverter determines whether the electrical states of each optimizer in the parallel photovoltaic string connected to the Boost circuit are consistent, the method further includes:

[0031] The inverter determines whether the optimizer connected to each Boost circuit has been distinguished;

[0032] If the optimizers connected to each Boost circuit have been identified, then the inverter is executed to determine whether the electrical states of each optimizer in the parallel photovoltaic string connected to the Boost circuit are consistent.

[0033] If the optimizers connected to each Boost circuit are not distinguished, the inverter controls the input terminals of the corresponding Boost circuits to maintain a short-circuit state for a preset duration according to preset rules, and determines the optimizers connected to each Boost circuit based on the output electrical parameters of all the optimizers under each short-circuit state; then the inverter performs the step of determining whether the electrical states of each optimizer in the parallel photovoltaic string connected to the Boost circuit are consistent.

[0034] Optionally, the output electrical parameters include: output voltage, and / or, output current;

[0035] The inverter determines the optimizer connected to each Boost circuit based on the output electrical parameters of all optimizers under each short-circuit state, including:

[0036] In each short-circuit state, for each optimizer whose output voltage is zero and / or whose output current is greater than a preset current value or is the output current limit value, the inverter determines that it is connected to the Boost circuit in the input short-circuit state; for each optimizer whose output voltage is not zero and / or whose output current is zero, the inverter determines that it is not connected to the Boost circuit in the input short-circuit state.

[0037] Optionally, the inverter controls the corresponding Boost circuit input terminals to maintain a short-circuit state for a preset duration according to preset rules, including:

[0038] The inverter controls each Boost circuit input to maintain a short-circuit state for a preset duration; or...

[0039] The inverter groups all Boost circuits sequentially, and each time controls some of the Boost circuit input terminals in the current group to remain in a short-circuit state for a preset time. The current group is then grouped again according to the different states of the Boost circuit input terminals until the current group contains only one Boost circuit.

[0040] A second aspect of this application also provides a photovoltaic system, comprising: an inverter and at least one photovoltaic string;

[0041] One or at least two optimizers with their outputs connected in series are provided between the two ends of the photovoltaic string, and the input of the optimizer is connected to at least one photovoltaic module.

[0042] The inverter is equipped with at least one Boost circuit in the front stage of the DC bus, and the input terminal of each Boost circuit is used to connect at least one corresponding photovoltaic string.

[0043] The controller in the inverter, acting as the master node, communicates with each of the optimizers and is used to execute the optimizer positioning method for parallel photovoltaic strings in the photovoltaic system as described in any of the first aspects above.

[0044] Optionally, each Boost circuit is independent of the inverter; or,

[0045] Each Boost circuit is integrated into the inverter, and the output of each Boost circuit is connected to the DC side of the inverter circuit in the inverter through the DC bus.

[0046] Optionally, the input terminal of the Boost circuit is connected to one connection port on the DC side of the inverter, or at least two connection ports connected in parallel.

[0047] The connection port connects to one of the photovoltaic strings, or the connection port connects to at least two of the photovoltaic strings in parallel via a bus terminal.

[0048] The optimizer positioning method for parallel photovoltaic strings in the photovoltaic system provided in this application firstly sets output voltage and / or output current limits for the optimizers in each photovoltaic string by the inverter and controls each optimizer to start up; then, for the parallel photovoltaic strings with no voltage difference connected to the Boost circuit, the inverter will control one of the optimizers to change its output voltage at least once, actively creating an inter-string voltage difference for the parallel photovoltaic strings with no voltage difference, thereby constructing parallel long strings and short strings to form a circulating current; since the circulating current will cause the electrical states of the optimizers in the long strings and short strings to be different, the photovoltaic strings to which each optimizer belongs can be distinguished by the electrical state of each optimizer, thereby automatically realizing the differentiation of optimizers between different photovoltaic strings connected to the Boost circuit, that is, realizing string-level positioning of optimizers. Attached Figure Description

[0049] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0050] Figures 1 to 3 These are three flowcharts illustrating the optimizer positioning method for parallel photovoltaic strings in a photovoltaic system provided in the embodiments of this application.

[0051] Figure 4 This is a schematic diagram of the structure of a photovoltaic system provided in an embodiment of this application;

[0052] Figure 5 This is a schematic diagram of the structure of a photovoltaic string provided in an embodiment of this application;

[0053] Figure 6 This is a schematic diagram of the specific structure of the photovoltaic system provided in the embodiments of this application. Detailed Implementation

[0054] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] In this application, 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 limitation, 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 that element.

[0056] This application provides a method for optimizing a photovoltaic system to automatically distinguish between optimizers for different photovoltaic strings connected to a Boost circuit.

[0057] The photovoltaic system includes: an inverter, and corresponding photovoltaic strings connected to each Boost circuit in the DC bus stage of the inverter; and at least one Boost circuit is connected to at least two photovoltaic strings in parallel. See also Figure 1 The optimizer location method for parallel photovoltaic strings in this photovoltaic system includes:

[0058] S101, The inverter sets the output voltage limit value and / or output current limit value for the optimizer in each photovoltaic string.

[0059] In practical applications, the output voltage limit value Ulmt = 10V and the output current limit value Ilmt = 2A can be set, but they are not limited to these. The values ​​of both can be set according to actual needs, and they are all within the protection scope of this application.

[0060] S102, Inverter controls the startup of each optimizer.

[0061] The inverter controls the startup process of each optimizer, specifically: the inverter sends an activation command to each optimizer, causing each optimizer to enter operating mode and increase the output voltage through soft start. If an output voltage limit value Ulmt has been set in step S101, the increase in the output voltage of each optimizer will eventually reach the output voltage limit value Ulmt. If the output voltage limit value Ulmt has not been set in step S101, the increase in the output voltage of each optimizer can eventually reach the rated output voltage.

[0062] In practical applications, when the input terminal of a Boost circuit is connected to at least two parallel photovoltaic strings with the same voltage, these photovoltaic strings can be called parallel zero-voltage photovoltaic strings. For the parallel zero-voltage photovoltaic strings connected to the Boost circuit, step S103 needs to be executed. When at least two Boost circuits are connected to parallel zero-voltage photovoltaic strings, step S103 needs to be executed for each of the connected parallel zero-voltage photovoltaic strings.

[0063] S103, the inverter controls one of the optimizers to change the output voltage at least once, and distinguishes the photovoltaic string to which each optimizer belongs by the electrical state of each optimizer.

[0064] In practical applications, controlling the optimizer to change the output voltage can be achieved by directly controlling the corresponding optimizer to actively bypass. In this case, the output voltage of the corresponding optimizer is zero, and the voltage of its photovoltaic string will decrease.

[0065] Alternatively, when the output voltage limit value Ulmt is set in step S101, and step S102 makes the output voltage of each optimizer reach the output voltage limit value Ulmt: the control optimizer in step S103 to change the output voltage can also be achieved by increasing the output voltage limit value Ulmt of the corresponding optimizer, at which time the output voltage of the corresponding optimizer will also increase; or, the control optimizer in step S103 to change the output voltage can also be achieved by decreasing the output voltage limit value Ulmt of the corresponding optimizer, at which time the output voltage of the corresponding optimizer will also decrease, for example, to between zero and the output voltage limit value Ulmt in S101.

[0066] For a Boost circuit with at least two photovoltaic strings connected in parallel with the same voltage, if the inverter controls any one of the optimizers to actively bypass or reduce the output voltage limit Ulmt, the voltage of that photovoltaic string will decrease, which is equivalent to making that photovoltaic string shorter, so it can be called a short string; while the other photovoltaic strings maintain their original voltage, which is equivalent to maintaining their original length, and can be called long strings relative to the short string. Conversely, if the inverter controls any one of the optimizers to increase the output voltage limit Ulmt, it will make that string a long string, while the other photovoltaic strings will become short strings.

[0067] Regardless of the method used to change the output voltage of any optimizer, long and short strings will appear in the corresponding parallel photovoltaic strings with no voltage difference. At this time, a circulating current will be formed between the parallel long and short strings, with the long string injecting current into the short string. If the output current limit value Ilmt is not set in step S101, the injected current value will be determined according to the voltage difference between the long and short strings. If the output current limit value Ilmt has been set in step S101, the injected current value will not exceed the output current limit value Ilmt. Taking two photovoltaic strings with the same voltage connected in parallel as an example, the output current of each optimizer in the long string is the output current limit value Ilmt, while the output current of each optimizer in the short string is -Ilmt, that is, a negative output current limit value. At the same time, each optimizer in the long string is in a positive output state, while each optimizer in the short string is in a negative input state. Furthermore, since the long and short series are connected in parallel, when the output voltage limit value Ulmt is not set in step S101, the output voltage of each optimizer in the short series is its rated output voltage, while the voltage shared by the output terminals of each optimizer in the long series will be lower than its rated output voltage but greater than 0V; when the output voltage limit value Ulmt is set in step S101, the output voltage of each optimizer in the short series is the output voltage limit value Ulmt, while the voltage shared by the output terminals of each optimizer in the long series will be lower than the output voltage limit value Ulmt but will still be greater than 0V.

[0068] Based on at least one of the output voltage, output current, and operating state of each optimizer, as the electrical state of the corresponding optimizer, at least each optimizer in the photovoltaic string whose voltage has been changed in the current state can be identified. Taking the simultaneous setting of the output voltage limit value Ulmt and the output current limit value Ilmt in step S101 as an example: If the corresponding photovoltaic string is changed to a short string, the specific behavior of each optimizer is: output voltage of Ulmt, output current of -Ilmt, and operating state of reverse input. These optimizers belong to the same photovoltaic string as the optimizer whose output voltage is currently reduced. If the corresponding photovoltaic string is changed to a long string, the specific behavior of each optimizer is: output voltage less than Ulmt, output current of Ilmt, and operating state of forward output. These optimizers belong to the same photovoltaic string as the optimizer whose output voltage is currently increased. If only two photovoltaic strings are connected in parallel, it can be determined that the remaining optimizers belong to another photovoltaic string. If there are more photovoltaic strings connected in parallel, the above-mentioned control of changing the output voltage can be performed multiple times to identify multiple photovoltaic strings whose voltages have been changed, until all optimizers are identified to their respective photovoltaic strings, thus achieving optimizer location for all parallel photovoltaic strings with no voltage difference.

[0069] The optimizer positioning method for parallel photovoltaic strings provided in this embodiment allows the inverter to actively create inter-string voltage differences for the corresponding photovoltaic strings each time it controls one of the optimizers to change its output voltage, thereby constructing parallel long strings and short strings to form a circulating current. Since the circulating current causes the electrical states of the optimizers within the long and short strings to differ, the electrical states of each optimizer can be used to distinguish the photovoltaic strings to which they belong. This automatically achieves the differentiation of optimizers between different photovoltaic strings connected to the Boost circuit, that is, it achieves string-level positioning of the optimizers, which is beneficial for the inverter to control the differences of each photovoltaic string.

[0070] Based on the previous embodiment, in the optimizer location method of the parallel photovoltaic string in the photovoltaic system, in step S103, the inverter controls one of the optimizers to change its output voltage at least once, and distinguishes the photovoltaic string to which each optimizer belongs based on its electrical state. Specifically, the inverter controls any one of the optimizers in the undetermined photovoltaic string to change its output voltage; and after each time the inverter controls the corresponding optimizer to change its output voltage, it detects the electrical state of each optimizer, and determines each optimizer in the same photovoltaic string as the optimizer that changed its output voltage, and determines that other optimizers belong to other photovoltaic strings, until the inverter achieves the distinction of the photovoltaic strings to which each optimizer belongs.

[0071] As described in the previous embodiment, the electrical state includes at least one of output voltage, output current, and operating state; at this time:

[0072] If the direction of changing the output voltage in step S103 is to decrease, then each optimizer in the same photovoltaic string as the optimizer that changes the output voltage will be an optimizer that satisfies at least one of the following conditions: the output voltage is greater than a preset voltage value, the output current is less than a preset negative current value, and the operating state is reverse input state.

[0073] If the direction of changing the output voltage in step S103 is to increase, then each optimizer in the same photovoltaic string as the optimizer that changes the output voltage is specifically an optimizer that meets at least one of the following conditions: the output voltage is less than a preset voltage value, the output current is greater than a preset positive current value, and the working state is a positive output state.

[0074] The preset values ​​used for comparison and judgment mentioned above can all be determined according to the actual situation, as long as they can characterize the occurrence of circulating current in the parallel photovoltaic strings. It should be noted that if the output voltage limit value Ulmt is set in step S101, the conditions regarding the output voltage being greater than the preset voltage value under the two output voltage change directions can be replaced with: the output voltage is the output voltage limit value Ulmt; and the condition regarding the output voltage being less than the preset voltage value can be replaced with: the output voltage is less than the output voltage limit value Ulmt. If the output current limit value Ilmt is set in step S101, the conditions regarding the output current being less than the preset negative current value under the two output voltage change directions can be replaced with: the output current is the negative output current limit value Ilmt; and the condition regarding the output current being greater than the preset positive current value can be replaced with: the output current is the positive output current limit value Ilmt.

[0075] Taking step S101, where both the output voltage limit value Ulmt and the output current limit value Ilmt are set, and the direction of the output voltage is changed to decrease, as an example: For at least two parallel photovoltaic strings with the same voltage connected to the Boost circuit, after the inverter controls any one of the optimizers to decrease the output voltage, a circulating current will be formed between the parallel long and short strings. At this time, the output current of each optimizer in the short string is -Ilmt (i.e., a negative output current limit value); when two photovoltaic strings are connected in parallel, there is only one long string, and the output current of each optimizer in the long string is the output current limit value Ilmt; when three photovoltaic strings are connected in parallel, there will be two long strings, and the output current of each optimizer in the long string is Ilmt / 2; and so on, when n photovoltaic strings are connected in parallel, there will be n-1 long strings, and the output current of each optimizer in the long string is Ilmt / (n-1). Regardless of the number of photovoltaic modules connected in series or parallel, the optimizers in the long string will all be in a forward output state, while the optimizers in the short string will all be in a reverse input state. Furthermore, the output voltage of each optimizer in the short string will be the output voltage limit value Ulmt, while the output voltage of each optimizer in the long string will be between 0 and Ulmt.

[0076] After the first control of any optimizer to reduce its output voltage, based on the electrical state of each optimizer, it is possible to identify the optimizers belonging to the short string in the current state, and determine that these optimizers belong to the same photovoltaic string as the optimizer whose output voltage is being reduced. At this point, if only two photovoltaic strings are connected in parallel, the optimizers with an output voltage between 0 and Ulmt, an output current of Ilmt, and a positive output state belong to the aforementioned long string, i.e., the other photovoltaic string. The principle of changing the direction of the output voltage to increase can be deduced by analogy and will not be elaborated further.

[0077] It should be noted that if there are n photovoltaic strings connected in parallel, where n is an integer greater than 2, after controlling any optimizer to change its output voltage for the first time, the remaining optimizers (for example, if the output voltage is changed to decrease for the first time, the output voltage is between 0 and Ulmt, the output current is Ilmt / (n-1), and the operating state is positive output) can be identified as belonging to another n-1 photovoltaic strings, but their specific photovoltaic string to which they belong cannot yet be determined. Although these photovoltaic strings currently have the same length, after controlling any of their optimizers to change its output voltage again, new short strings and long strings can be constructed again. By going through the above electrical state identification process again, the optimizers in the photovoltaic strings whose voltage has been changed can be distinguished again. Repeating the above process until all the optimizers in all photovoltaic strings are located, the optimizer location for all parallel photovoltaic strings with no voltage difference can be achieved.

[0078] Based on the above embodiments, it should be noted that after system installation, there may be a situation where photovoltaic strings of unequal length are connected in parallel in the initial state. In this case, after each optimizer is started, the electrical state of each optimizer can be judged. If the electrical states of the optimizers in the parallel photovoltaic strings are inconsistent, a short string or a long string with a different length than the other photovoltaic strings can be directly identified. If two photovoltaic strings are connected in parallel, there is no need to perform the above-mentioned control process of changing the output voltage. If more photovoltaic strings are connected in parallel, one photovoltaic string with a special length can be identified first, thereby reducing one subsequent control process of changing the output voltage.

[0079] That is, based on the above embodiments, the optimizer positioning method for parallel photovoltaic strings in the photovoltaic system provided in this embodiment, such as... Figure 2 As shown, for the parallel photovoltaic string connected to the Boost circuit, before executing step S103, it also includes:

[0080] S201, The inverter determines whether the electrical states of each optimizer are consistent.

[0081] If all electrical states are consistent, the corresponding parallel photovoltaic string is determined to be a parallel photovoltaic string with no voltage difference, and step S103 can be executed directly. If the electrical states are not consistent, step S202 is executed first, and if the number of photovoltaic strings in the corresponding parallel photovoltaic string is greater than 2, the other photovoltaic strings are determined to be parallel photovoltaic strings with no voltage difference, and step S103 is executed.

[0082] S202. The inverter determines that the optimizer whose output current is greater than the preset positive current value or less than the preset negative current value belongs to the same photovoltaic string.

[0083] If the output current limit value Ilmt has been set in step S101, then in step S202, the condition that the output current is greater than the preset positive current value can be replaced by the output current limit value that the output current is positive; and the condition that the output current is less than the preset negative current value can be replaced by the output current limit value that the output current is negative.

[0084] Let's take step S101, where both the output voltage limit value Ulmt and the output current limit value Ilmt are set, as an example for further explanation:

[0085] Suppose that the input of a Boost circuit is connected in parallel with three photovoltaic strings, two of which are of the same length and longer than the other photovoltaic string. That is, the input is connected in parallel with two long strings and one short string. After each optimizer starts, the two long strings inject current into the short string. The electrical state of the optimizer in the short string is: output voltage Ulmt, output current -Ilmt, and operating state is reverse input. The electrical state of the optimizer in the two long strings is: output voltage between 0 and Ulmt, output current Ilmt / 2, ​​and operating state is forward output. Thus, each optimizer in the short string can be identified, and then step S103 is executed on the two long strings.

[0086] Suppose that the input of a Boost circuit is connected in parallel with three photovoltaic strings, two of which are of the same length and shorter than the other photovoltaic string. That is, the input is connected in parallel with two short strings and one long string. After each optimizer starts, the long string injects current into the two short strings. The electrical state of the optimizer in the long string is: the output voltage is between 0 and Ulmt, the output current is Ilmt, and the operating state is positive output. The electrical state of the optimizer in the two short strings is: the output voltage is Ulmt, the output current is -Ilmt / 2, ​​and the operating state is reverse input. Thus, each optimizer in the long string can be identified, and then step S103 is executed for the two short strings.

[0087] The same logic applies to the case of multiple photovoltaic modules connected in series and parallel, which will not be elaborated here.

[0088] In this embodiment, steps S201 and S202 can directly determine each optimizer in a photovoltaic string of a specific length, making the string-level positioning process of the optimizer simpler.

[0089] In practical applications, if the correspondence between each optimizer and each Boost circuit of the inverter has been established through manual input after system installation, then string-level positioning of all optimizers can be achieved through any of the above embodiments. However, if the above manual input process is not performed after system installation, or if the manual input process is considered to be inefficient and prone to errors, then the inverter can first distinguish the photovoltaic strings connected to each Boost circuit. That is, the optimizer positioning method for parallel photovoltaic strings in this photovoltaic system can, based on the above embodiments, also be as follows: Figure 3 (in order to be in) Figure 2 As shown in the example (based on step S102), after step S102, it also includes:

[0090] S301, The inverter determines whether the optimizer connected to each Boost circuit has been distinguished.

[0091] If the optimizers connected to each Boost circuit have been identified, then for the parallel photovoltaic strings connected to the Boost circuit, step S201 is executed.

[0092] If the optimizer connected to each Boost circuit is not distinguished, then step S302 is executed first, and then step S201 is executed for the parallel photovoltaic strings connected to the Boost circuit.

[0093] S302. The inverter controls the input terminals of the corresponding Boost circuits to maintain a short-circuit state for a preset duration according to preset rules, and determines the optimizer connected to each Boost circuit based on the output electrical parameters of all optimizers under each short-circuit state.

[0094] In step S302, the inverter controls the input terminals of the corresponding Boost circuits to maintain a short-circuit state for a preset duration according to preset rules. Specifically, the inverter can control the input terminals of each Boost circuit to maintain a short-circuit state for a preset duration one by one; or, the inverter can group all Boost circuits sequentially, control some Boost circuit input terminals in the current group to maintain a short-circuit state for a preset duration each time, and regroup the current group according to the different states of the Boost circuit input terminals until the current group contains only one Boost circuit.

[0095] In practical applications, the output electrical parameters may include: output voltage and / or output current. In step S302, the inverter determines the optimizer connected to each Boost circuit based on the output electrical parameters of all optimizers under each short-circuit state. Specifically, this may include: under each short-circuit state, for optimizers whose output voltage is zero and / or whose output current is greater than a preset current value or is at the output current limit value, the inverter determines that they are connected to the Boost circuit in the input short-circuit state; for optimizers whose output voltage is not zero and / or whose output current is zero, the inverter determines that they are not connected to the Boost circuit in the input short-circuit state.

[0096] If the output current limit value Ilmt is not set in step S101, the output current of each optimizer in the photovoltaic string connected to the Boost circuit in the short-circuit state will reach the short-circuit current, which can be identified by exceeding a preset current value; however, if the output current limit value Ilmt has been set in step S101, the output current of each optimizer in the photovoltaic string connected to the Boost circuit in the short-circuit state can only reach the output current limit value Ilmt.

[0097] Consider a scenario where an inverter needs to automatically determine the Boost circuits and string-level positioning of each optimizer. After power-on, it first sends a search command to each optimizer, causing each optimizer to send its own serial number to the inverter. Then, in step S101, it sets the output voltage limit value Ulmt and the output current limit value Ilmt for the optimizers. Then, in step S102, it controls each optimizer to start and raise its output voltage to the output voltage limit value Ulmt. After that, it executes steps S301 and S302 to determine the Boost circuits connected to each optimizer. At this time, for the parallel photovoltaic strings connected to the Boost circuits, it first identifies a photovoltaic string of a special length through steps S201 and S202. If necessary, it can execute step S103 for the parallel photovoltaic strings with no voltage difference connected to the corresponding Boost circuits. Then, based on the differences in the electrical states of each optimizer in these photovoltaic strings, it classifies these optimizers according to the photovoltaic strings they belong to, and locates all optimizers belonging to the same photovoltaic string. The above process enables automatic string-level networking and location of all optimizers, avoiding the need for manual input of information for each optimizer, improving networking efficiency and reducing the probability of errors.

[0098] Another embodiment of this application also provides a photovoltaic system, such as Figure 4 As shown, it includes: an inverter 200 and at least one photovoltaic string 100; wherein:

[0099] The inverter 200 has at least one Boost circuit 201 at the front end of the DC bus, and the input terminal of each Boost circuit 201 is used to connect at least one corresponding photovoltaic string 100.

[0100] It is worth noting that, such as Figure 4 As shown, each Boost circuit 201 can be integrated into the inverter 200, and the output terminal of each Boost circuit 201 is connected to the DC side of the inverter circuit 202 in the inverter 200 via a DC bus. In practical applications, each Boost circuit 201 can also be independent of the inverter 200 (not shown), depending on the specific application environment, and all are within the protection scope of this application.

[0101] Depending on the model, the inverter 200 is connected to the corresponding applicable single-phase or three-phase power grid.

[0102] like Figure 5 As shown, an optimizer 102 with one or at least two output terminals connected in series is provided between the two ends of the photovoltaic string 100, and the input terminal of the optimizer 102 is connected to at least one photovoltaic module 101.

[0103] The controller in inverter 200, acting as the master node, communicates with each optimizer 102 and is used to execute the optimizer positioning method for parallel photovoltaic strings in the photovoltaic system described in any of the above embodiments. The specific execution process and principle of this optimizer positioning method can be found in the above embodiments and will not be repeated here.

[0104] like Figure 4 and Figure 6 As shown, when the main circuit of inverter 200 includes inverter circuit 202 and at least one boost circuit 201, inverter 200 can contain m boost circuits (e.g., m boost circuits). Figure 6 The Boost 1, ... Boost x, ... Boost m shown are positive integers greater than or equal to 1.

[0105] In practical applications, the input terminals of each Boost circuit 201 can be connected to only one connection port on the DC side of the inverter 200, or they can be connected to at least two parallel connection ports on the DC side of the inverter 200. The settings of the input terminals of each Boost circuit 201 can be the same or different, depending on the specific application environment, and all are within the protection scope of this application. The connection ports connected to the input terminals of each Boost circuit 201 can be connected to one photovoltaic string 100, or at least two photovoltaic strings 100 can be connected in parallel through a bus terminal; depending on the specific application environment, all are within the protection scope of this application.

[0106] Specifically, each Boost circuit 201 has one input terminal, which can also be called an MPPT port. Each MPPT port can be divided into two parallel connection ports inside the inverter 200, which can be called PV ports. Of course, each MPPT port can also directly become a PV port. Each PV port can connect to one photovoltaic string 100, or connect two parallel photovoltaic strings 100 through a bus terminal. A system can connect no less than two photovoltaic strings 100.

[0107] See Figure 5 and Figure 6Assume each photovoltaic string 100 includes n photovoltaic modules (PV modules 1 to n as shown in the figure), where n is a positive integer greater than or equal to 2. When the inverter 200 is a single-camera system, n is less than or equal to 25; when the inverter 200 is a three-camera system, n is less than or equal to 50. Since the system is entirely equipped with optimizers 102, each photovoltaic module must include one photovoltaic unit and one optimizer 102. The photovoltaic unit includes at least one photovoltaic module 101, which is connected to the input of the optimizer 102. The outputs of all optimizers 102 in the photovoltaic string 100 are connected in series; that is, the positive output of optimizer 102 is connected to the negative output of the previous optimizer 102, the negative output of optimizer 102 is connected to the positive output of the next optimizer 102, and finally connected to a PV port of the inverter 200.

[0108] It should be noted that the number of photovoltaic modules in different photovoltaic strings 100 connected to the same system is allowed to be different, the series and parallel connection methods of photovoltaic strings 100 connected to different MPPT ports are allowed to be different, and the power of photovoltaic units is allowed to be different.

[0109] In practical applications, in this inverter 200, each Boost circuit's MPPT port may or may not be connected to a photovoltaic string 100, or it may be connected to one to three photovoltaic strings 100. However, at least one Boost circuit's MPPT port may be connected to at least two photovoltaic strings 100. For example, in a three-phase residential inverter, each MPPT port may be connected to two photovoltaic strings 100. In practical applications, the parallel photovoltaic strings connected to each MPPT port may be two photovoltaic strings 100 in parallel, or more than two photovoltaic strings 100 in parallel, depending on the specific application environment, and all of these are within the scope of protection of this application.

[0110] Figure 6 The diagram shows a parallel photovoltaic string structure in a photovoltaic system where all optimizers 102 are installed. It consists of two photovoltaic strings (PV string 1 and PV string 2 as shown in the diagram) 100 connected in parallel. PV string 1 contains n1 photovoltaic modules, and PV string 2 contains n2 photovoltaic modules. n1 and n2 can be the same or different. If n1 and n2 are the same, the pair of parallel photovoltaic strings can be called identical parallel strings. If n1 and n2 are different, the pair of parallel photovoltaic strings can be called different parallel strings.

[0111] The main steps of this optimizer localization method are explained below:

[0112] (1) The execution of this optimizer location method has certain prerequisites.

[0113] The inverter controller, as the master node, can automatically form a network through step S302 described in the above embodiment, or can distinguish all optimizer information of parallel photovoltaic strings connected to the same MPPT port through manually entered information, but it cannot distinguish the specific photovoltaic string to which each optimizer is located.

[0114] (2) In this optimizer positioning method, the output electrical parameters of each optimizer are first set.

[0115] Referring to step S101 in the above embodiment, the inverter master node sends a setting command to each optimizer, including the output voltage limit value Ulmt and the output current limit value Ilmt. These can be set according to actual needs, for example, Ulmt = 10V and Ilmt = 2A, but are not limited to these. During this process, each optimizer is in a safe mode with an output of 1V.

[0116] (3) Then the startup control of each optimizer in the optimizer location method can be executed.

[0117] Referring to step S102 in the above embodiment, the inverter master node broadcasts an activation command. Upon receiving the activation command, the optimizer switches from safe mode to operating mode, begins a soft start, and gradually increases the output voltage until it reaches the output voltage limit value Ulmt. Then, the inverter master node collects the voltage and current status of all optimizers.

[0118] (4) Then execute the determination of the electrical status of each optimizer in the optimizer positioning method.

[0119] Refer to steps S201 and S202 in the above embodiments; in step S201, the inverter master node can determine the voltage and current state after the optimizer starts: if all optimizers have an output voltage of Ulmt and an output current of 0A, it indicates that no circulating current has been formed, and the parallel photovoltaic strings can be determined to be identical parallel strings (i.e., the aforementioned parallel photovoltaic strings without voltage difference); if the output voltage of some optimizers is between Ulmt and 0V and the output current is Ilmt, while the output voltage of other optimizers is Ulmt and the output current is -Ilmt, it indicates that the lengths of the parallel photovoltaic strings are not the same, i.e. Figure 6 The different number of optimizers in the parallel photovoltaic strings shown indicates that the parallel photovoltaic strings are differential parallel strings.

[0120] by Figure 6Taking the structure shown as an example, if it is determined to be a differential parallel string, then all optimizers with output voltage between Ulmt and 0V and output current of Ilmt can be positioned as the same photovoltaic string; while all optimizers with output voltage of Ulmt and output current of -Ilmt can be positioned as another photovoltaic string; once the positioning is complete, the process can end. However, if it is determined to be the same parallel string, then step (5) needs to be performed.

[0121] (5) For any optimizer in the parallel photovoltaic string whose photovoltaic string to which it belongs is not determined, that is, for any optimizer in the above-mentioned parallel photovoltaic string without voltage difference, change the output voltage control.

[0122] Referring to step S103 in the above embodiment, taking active bypass control as an example, the inverter master node can arbitrarily select one of the optimizers and send an active bypass command to it. After receiving the active bypass command, the optimizer will switch from the operating mode to the active bypass mode, its output is bypassed, and there is no output voltage, thus... Figure 6 In the structure shown, the two photovoltaic strings that were originally connected in parallel become dissimilar, leading to circulating current. At this point, the inverter master node will collect the voltage and current states of all optimizers.

[0123] Then, the inverter master node will determine the optimizer's voltage and current status after startup: all optimizers with output voltage between Ulmt and 0V and output current of Ilmt can be identified as belonging to the same photovoltaic string; while all optimizers with output voltage of Ulmt and output current of -Ilmt, as well as optimizers that are actively bypassed, can be identified as belonging to another photovoltaic string. At this point, the identification is complete, and the process can end.

[0124] Through the above process, given the information of all optimizers connected to the MPPT ports of each Boost circuit, the system can automatically distinguish the photovoltaic string to which the optimizer belongs for parallel photovoltaic strings, thus achieving string-level positioning of the optimizer.

[0125] Similar or identical parts between the various embodiments in this specification can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for system or system embodiments, since they are basically similar to method embodiments, the description is relatively simple, and relevant parts can be referred to the description of the method embodiments. The systems and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment solution according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0126] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0127] The features described above regarding the disclosed embodiments can be substituted for or combined with each other to enable those skilled in the art to implement 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 can 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 optimizing the location of parallel photovoltaic strings in a photovoltaic system, characterized in that, The photovoltaic system includes: an inverter and corresponding photovoltaic strings connected to each Boost circuit in the DC bus front stage; the photovoltaic strings include optimizers connected to photovoltaic modules; the optimizer positioning method includes: The inverter sets output voltage and / or output current limits for the optimizers in each photovoltaic string. The inverter controls the startup of each of the optimizers; For the parallel photovoltaic strings with no voltage drop connected to the Boost circuit, the inverter controls one of the optimizers to change the output voltage at least once, and distinguishes the photovoltaic strings to which each optimizer belongs by the electrical state of each optimizer.

2. The optimizer positioning method for parallel photovoltaic strings in a photovoltaic system according to claim 1, characterized in that, Changing the output voltage includes: active bypass; or, If the inverter has set the output voltage limit value for each of the optimizers, then after the inverter controls each of the optimizers to start, the method further includes: the inverter controlling the output voltage of each of the optimizers to reach the output voltage limit value; and changing the output voltage, including: increasing or decreasing the output voltage limit value.

3. The optimizer positioning method for parallel photovoltaic strings in a photovoltaic system according to claim 1, characterized in that, The inverter controls one of the optimizers to change its output voltage at least once, and distinguishes the photovoltaic string to which each optimizer belongs based on its electrical state, including: The inverter controls any one of the optimizers in the undetermined photovoltaic string to change its output voltage; After each time the inverter controls the corresponding optimizer to change its output voltage, it detects the electrical state of each optimizer and, based on the electrical state, determines each optimizer that is in the same photovoltaic string as the optimizer that changed its output voltage, and determines that other optimizers belong to other photovoltaic strings, until the inverter can distinguish the photovoltaic strings to which each of the corresponding optimizers belongs.

4. The optimizer positioning method for parallel photovoltaic strings in a photovoltaic system according to claim 3, characterized in that, The electrical state includes at least one of the following: output voltage, output current, and operating state; If the direction of changing the output voltage is to decrease, then the optimizers located in the same photovoltaic string as the optimizer that changes the output voltage include: The optimizer that satisfies at least one of the following conditions: output voltage is greater than a preset voltage value, output current is less than a preset negative current value, and the operating state is reverse input state; If the direction of changing the output voltage is to increase, then the optimizers located in the same photovoltaic string as the optimizer that changes the output voltage include: The optimizer is defined as one that satisfies at least one of the following conditions: output voltage is less than the preset voltage value, output current is greater than the preset positive current value, and the operating state is a positive output state.

5. The optimizer positioning method for parallel photovoltaic strings in a photovoltaic system according to claim 4, characterized in that, If the inverter has set the output voltage limit value for each of the optimizers, then the output voltage is used as the output voltage limit value instead of the condition that the output voltage is greater than the preset voltage value; The condition that the output voltage is less than the preset voltage value is replaced by the condition that the output voltage is less than the preset voltage value; If the inverter has set the output current limit value for each of the optimizers, then the output current limit value with a negative output current is used instead of the condition that the output current is less than the preset negative current value. The output current limit value, where the output current is positive, is used instead of the condition that the output current is greater than the preset positive current value.

6. The optimizer positioning method for parallel photovoltaic strings in a photovoltaic system according to any one of claims 1 to 5, characterized in that, For the parallel zero-dropout photovoltaic string connected to the Boost circuit, before the inverter controls one of the optimizers to change its output voltage at least once, the following steps are also included: The inverter determines whether the electrical states of each optimizer in the parallel photovoltaic string connected to the Boost circuit are consistent. If all the electrical states are consistent, then the corresponding parallel photovoltaic string is determined to be the parallel photovoltaic string with no voltage difference. If the electrical states are not consistent, the inverter first determines that the optimizer whose output current is greater than a preset positive current value or less than a preset negative current value belongs to the same photovoltaic string; then, if the number of photovoltaic strings in the corresponding parallel photovoltaic strings is greater than 2, it determines that the other photovoltaic strings are the parallel no-voltage photovoltaic strings.

7. The optimizer positioning method for parallel photovoltaic strings in a photovoltaic system according to claim 6, characterized in that, If the inverter has set the output current limit value for each of the optimizers, then: The output current limit value, which is positive, is used instead of the condition that the output current is greater than the preset positive current value. The condition that the output current is less than the preset negative current value is replaced by the output current limit value where the output current is negative.

8. The optimizer positioning method for parallel photovoltaic strings in a photovoltaic system according to claim 6, characterized in that, Before the inverter determines whether the electrical states of each optimizer in the parallel photovoltaic string connected to the Boost circuit are consistent, the method further includes: The inverter determines whether the optimizer connected to each Boost circuit has been distinguished; If the optimizers connected to each Boost circuit have been identified, then the inverter is executed to determine whether the electrical states of each optimizer in the parallel photovoltaic string connected to the Boost circuit are consistent. If the optimizers connected to each Boost circuit are not distinguished, the inverter controls the input terminals of the corresponding Boost circuits to maintain a short-circuit state for a preset duration according to preset rules, and determines the optimizers connected to each Boost circuit based on the output electrical parameters of all the optimizers under each short-circuit state; then the inverter performs the step of determining whether the electrical states of each optimizer in the parallel photovoltaic string connected to the Boost circuit are consistent.

9. The optimizer positioning method for parallel photovoltaic strings in a photovoltaic system according to claim 8, characterized in that, The output electrical parameters include: output voltage, and / or, output current; The inverter determines the optimizer connected to each Boost circuit based on the output electrical parameters of all optimizers under each short-circuit state, including: In each short-circuit state, for each optimizer whose output voltage is zero and / or whose output current is greater than a preset current value or is the output current limit value, the inverter determines that it is connected to the Boost circuit in the input short-circuit state; for each optimizer whose output voltage is not zero and / or whose output current is zero, the inverter determines that it is not connected to the Boost circuit in the input short-circuit state.

10. The optimizer positioning method for parallel photovoltaic strings in a photovoltaic system according to claim 8, characterized in that, The inverter controls the corresponding Boost circuit input terminals to maintain a short-circuit state for a preset duration according to preset rules, including: The inverter controls each Boost circuit input to maintain a short-circuit state for a preset duration; or... The inverter groups all Boost circuits sequentially, and each time controls some of the Boost circuit input terminals in the current group to remain in a short-circuit state for a preset time. The current group is then grouped again according to the different states of the Boost circuit input terminals until the current group contains only one Boost circuit.

11. A photovoltaic system, characterized in that, include: Inverter and at least one photovoltaic string; One or at least two optimizers with their outputs connected in series are provided between the two ends of the photovoltaic string, and the input of the optimizer is connected to at least one photovoltaic module. The inverter is equipped with at least one Boost circuit in the front stage of the DC bus, and the input terminal of each Boost circuit is used to connect at least one corresponding photovoltaic string. The controller in the inverter, acting as a master node, communicates with each of the optimizers and is used to execute the optimizer positioning method for parallel photovoltaic strings in a photovoltaic system as described in any one of claims 1 to 10.

12. The photovoltaic system according to claim 11, characterized in that, Each Boost circuit is independent of the inverter; or, Each Boost circuit is integrated into the inverter, and the output of each Boost circuit is connected to the DC side of the inverter circuit in the inverter through the DC bus.

13. The photovoltaic system according to claim 11 or 12, characterized in that, Each Boost circuit is integrated into the inverter. Inside the inverter, the input terminal of the Boost circuit is connected to one connection port on the DC side of the inverter, or at least two connection ports connected in parallel. The connection port connects to one of the photovoltaic strings, or the connection port connects to at least two of the photovoltaic strings in parallel via a bus terminal.

Images