Power system, inverter and method thereof, power converter and method thereof

Abstract

The invention provides a power system, an inverter and a method thereof, and a power converter and a method thereof, and relates to the field of photovoltaic technology, the inverter sends a voltage control instruction to at least one power converter in a first direct current string in response to string voltage mismatch of at least one direct current string; the first direct-current string is a direct-current string with the maximum string output voltage and / or the minimum string output voltage in the direct-current strings; the voltage control instruction comprises a voltage down-regulation instruction for the power converter in the direct current string with the maximum string output voltage, and / or a voltage up-regulation instruction for the power converter in the direct current string with the minimum string output voltage; the power converter responds to the received voltage control instruction and adjusts the output voltage of the direct current output end. Therefore, in combination with the adjustment of the power converter, the power generation loss is avoided, the combination of more photovoltaic strings with large differences and the complex station building environment are supported, and the stability of the system is improved.

Description

Technical Field

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

[0002] A photovoltaic (PV) inverter includes a DC-DC converter circuit for DC-DC boosting and an inverter circuit for DC-AC conversion. The input of the DC-DC converter circuit is connected to the PV strings. When the initial component configuration of the power plant is inconsistent, such as different PV string lengths, or when there are significant mismatches in the environment, such as shading, some PV strings may have low output voltages, resulting in a large deviation between the voltage of some PV strings and the DC bus voltage. Since the thermal stress of the DC-DC converter circuit is strongly related to the power and the voltage difference across the circuit, a large voltage difference will cause significant thermal stress in the components of the DC-DC converter circuit branches due to a larger boost ratio. Normally, for equipment safety, the DC-DC converter circuit will actively reduce the input power to avoid triggering derating, but this can easily lead to system power generation losses. Summary of the Invention

[0003] In view of this, this application provides a power system, an inverter and a method thereof, and a power converter and a method thereof, aimed at reducing power generation losses.

[0004] In a first aspect, this application provides a power system, including: an inverter and at least a DC string,

[0005] The inverter includes at least a DC-DC converter circuit and an inverter circuit. The input terminal of the DC-DC converter circuit is connected to at least one DC string. The output terminals of each DC-DC converter circuit are connected in parallel to the input terminal of the inverter circuit. The DC string includes a power converter. The power converter includes a DC input terminal and a DC output terminal. The DC input terminal is used to connect to a DC power supply. The DC output terminals of each power converter in the DC string are connected in series to the input terminal of the DC-DC converter circuit.

[0006] The inverter is configured to send a voltage control command to at least one power converter in a first DC string in response to a string voltage mismatch occurring in at least one of the DC strings; wherein the first DC string is the DC string with the largest and / or smallest string output voltage among all the DC strings; the voltage control command includes: a voltage reduction command for the power converter in the DC string with the largest string output voltage, and / or a voltage increase command for the power converter in the DC string with the smallest string output voltage;

[0007] The power converter is used to adjust the output voltage of the DC output terminal in response to the received voltage control command.

[0008] Optionally, before sending the voltage control command to at least one of the power converters in the first DC string, the inverter is further configured to:

[0009] Determine the adjustment range of a specified electrical parameter of at least one of the power converters in the first DC string;

[0010] Based on the adjustment range, a voltage control command is generated.

[0011] Optionally, before generating the voltage control command based on the adjustment amplitude, the inverter is further configured to:

[0012] Determine the current allowable adjustment range of at least one of the power converters in the first DC string;

[0013] If the adjustment amplitude does not exceed the adjustment range, then the voltage control command is generated based on the adjustment amplitude.

[0014] Optionally, if the adjustment amplitude exceeds the adjustment range, the inverter is further configured to:

[0015] Pause the transmission of the voltage control command, or generate a first command based on the current allowable adjustment range of the power converter and send the first command to the power converter.

[0016] Optionally, if the adjustment amplitude exceeds the adjustment range, the inverter is further configured to: if the first DC string only includes the DC string with the largest output voltage among all the DC strings, take the DC string with the smallest output voltage among all the DC strings as the new first DC string, and perform the adjustment amplitude of the specified electrical parameter of the power converter of the first DC string and subsequent steps.

[0017] If the first DC string only includes the DC string with the smallest output voltage among all the DC strings, the DC string with the largest output voltage among all the DC strings is taken as the new first DC string, and the adjustment range of the specified electrical parameters of at least one of the power converters of the first DC string and subsequent steps are performed.

[0018] If the first DC string only includes the DC string with the largest and smallest output voltage among all the DC strings, then the transmission of the voltage control command is suspended, or a first command is generated based on the current allowable adjustment range of the power converter and sent to the power converter.

[0019] Optionally, the inverter, specifically used for determining the adjustment range of a specified electrical parameter of at least one of the power converters of the first DC string, is configured to...

[0020] Determine the voltage difference between the output voltage and the bus voltage of the DC string that has a voltage mismatch; calculate the voltage difference and subtract a preset voltage difference threshold to obtain the total voltage adjustment range;

[0021] Based on the total voltage adjustment range, determine the voltage adjustment range or current adjustment range of each power converter in the first DC string.

[0022] Optionally, the inverter, which determines the adjustment range of a specified electrical parameter of at least one of the power converters of the first DC string, is specifically used for:

[0023] Based on the output voltage of each DC string connected to the inverter, determine the total adjustment range of the voltage for increasing the voltage of the DC string with the smallest output voltage, or determine the total adjustment range of the voltage for decreasing the voltage of the DC string with the largest output voltage.

[0024] Based on the total voltage adjustment range, determine the voltage adjustment range or current adjustment range of each power converter in the first DC string.

[0025] Optionally, the inverter is further configured to, after executing the sending of the voltage control command to the power converter, if a string voltage mismatch still exists, return to execute the determination of the adjustment range of the specified electrical parameters of at least one of the power converters of the first DC string and subsequent steps.

[0026] Optionally, based on the total adjustment magnitude of the voltage, the voltage adjustment magnitude of each power converter in the first DC string is determined, and the inverter is specifically used for...

[0027] When the first DC string is the DC string with the largest or smallest output voltage among all the DC strings, the total adjustment amplitude is evenly distributed to the target amplitude of the voltage obtained by each power converter in the first DC string, and the target amplitude or the amplitude obtained by multiplying the target amplitude by a preset ratio is determined as the adjustment amplitude of the voltage of the power converter in the first DC string.

[0028] When the first DC string has the largest and smallest output voltage among all the DC strings, the total adjustment amplitude is allocated to each first DC string to obtain the adjustment sub-amplitude of the voltage allocated to each first DC string; the adjustment sub-amplitude is evenly distributed to each power converter in the corresponding first DC string to obtain the target voltage amplitude; the target amplitude or the amplitude obtained by multiplying the target amplitude by a preset voltage ratio is determined as the adjustment amplitude of the power converter voltage in the first DC string; for the DC string with the largest output voltage, the target voltage amplitude is negative, and for the DC string with the smallest output voltage, the target voltage amplitude is positive.

[0029] Optionally, the inverter is also used for,

[0030] With the power converter power remaining constant, the target amplitude of the power converter current is determined based on the target amplitude of the power converter voltage. The target amplitude of the current or the amplitude obtained by multiplying the target amplitude of the current by a preset current ratio is used as the adjustment amplitude of the power converter current in the first DC string. For the DC string with the largest output voltage, the target amplitude of the current is positive, and for the DC string with the smallest output voltage, the target amplitude of the current is negative.

[0031] Optionally, the inverter, specifically used for determining the adjustment range of a specified electrical parameter of at least one of the power converters of the first DC string, is configured to...

[0032] For DC strings with the largest output voltage, a negative voltage preset value is used as the adjustment range of the power converter voltage, or a positive current preset value is used as the adjustment range of the power converter current.

[0033] For the DC string with the smallest output voltage, a positive voltage preset value is taken as the adjustment range of the power converter voltage, or a negative current preset value is taken as the adjustment range of the power converter current; the voltage preset value and the current preset value are both values ​​used to achieve repeated adjustment of the power converter.

[0034] Optionally, generating the voltage control command based on the adjustment amplitude includes:

[0035] For the DC string with the largest output voltage among the DC strings, a voltage reduction command is generated to indicate the step-down of the power converter based on the voltage adjustment range, or a voltage reduction command is generated to indicate the step-up of the power converter based on the current adjustment range.

[0036] For the DC string with the smallest output voltage among all the DC strings, a voltage increase command is generated based on the voltage adjustment range to indicate the power converter to boost the voltage, or a voltage increase command is generated based on the current adjustment range to indicate the power converter to reduce the current.

[0037] Optionally, the power converter is specifically configured to, in response to a received voltage control command, adjust the output voltage based on the adjustment range of the specified electrical parameter if the adjustment range of the specified electrical parameter does not exceed the current allowable adjustment range of the power converter.

[0038] If the adjustment range of the specified electrical parameter exceeds the current allowable adjustment range of the electrical parameter of the power converter, the output voltage will be adjusted to the maximum adjustable voltage value according to the adjustment direction indicated by the voltage control command.

[0039] Optionally, the step of sending a voltage control command to at least one power converter in the first DC string in response to a string voltage mismatch in at least one of the DC strings includes:

[0040] In response to the absolute value of the voltage difference between the input voltage of the DC-DC converter circuit corresponding to at least one of the DC strings and the DC bus voltage exceeding a voltage difference threshold, a voltage control command is sent to at least one of the power converters in the first DC string.

[0041] And / or,

[0042] In response to the temperature of the corresponding DC-DC converter circuit in at least one of the DC strings exceeding a preset temperature threshold, a voltage control command is sent to at least one of the power converters in the first DC string.

[0043] Optionally, the first instruction is an electrical parameter adjustment range set based on the endpoint value of the adjustment range currently allowed by the power converter.

[0044] The aforementioned power system can, when a voltage mismatch occurs in the DC-DC converter circuit, causing an excessive voltage difference between the input voltage and the bus voltage of the corresponding DC-DC converter circuit, lower the output voltage of the power converter in the string with the largest output voltage and / or raise the output voltage of the power converter in the string with the smallest output voltage. This avoids the excessive voltage difference directly reducing the output power of the DC-DC converter circuit and causing power generation losses, and also avoids the impact on the lifespan of devices caused by the large thermal stress resulting from the excessive voltage difference.

[0045] Secondly, this application also provides an inverter control method in a power system, wherein the inverter includes at least a DC-DC converter circuit and an inverter circuit, the input terminal of the DC-DC converter circuit is connected to at least one DC string, the output terminals of each DC-DC converter circuit are connected in parallel to the input terminal of the inverter circuit, the DC string includes a power converter, the power converter includes a DC input terminal and a DC output terminal, the DC input terminal is used to connect to a DC power supply, and the DC output terminals of each power converter in the DC string are connected in series to the input terminal of the DC-DC converter circuit;

[0046] The inverter is configured to send a voltage control command to at least one of the power converters in the first DC string in response to a string voltage mismatch in at least one of the DC strings, so that the power converter adjusts the output voltage of the DC output terminal in response to the received voltage control command.

[0047] Wherein, the first DC string is: the DC string with the largest and / or smallest output voltage among all the DC strings; the voltage control command includes: a voltage reduction command for the power converter in the DC string with the largest output voltage, and / or a voltage increase command for the power converter in the DC string with the smallest output voltage.

[0048] The inverter control method mentioned above in a power system, when a voltage mismatch occurs in the DC string, causing an excessive voltage difference between the input voltage and the bus voltage of the corresponding DC-DC converter circuit, controls the power converter of the string with the largest output voltage in the inverter control system to lower the output voltage, and / or controls the power converter of the string with the smallest output voltage to raise the output voltage, thereby reducing the voltage difference between the bus voltage at the input terminal of the corresponding DC-DC converter circuit, reducing power generation losses, and avoiding large thermal stress on the devices due to excessive voltage difference.

[0049] Thirdly, this application also provides a power converter control method in a power system, the power system comprising: an inverter and at least one DC string; the inverter comprising at least one DC conversion circuit and an inverter circuit, the input terminal of the DC conversion circuit being connected to at least one of the DC strings, the output terminals of each DC conversion circuit being connected in parallel to the input terminal of the inverter circuit, the DC string comprising a power converter, the power converter comprising a DC input terminal and a DC output terminal, the DC input terminal being used to connect to a DC power supply, and the DC output terminals of each power converter in the DC string being connected in series to the input terminal of the DC conversion circuit;

[0050] The power converter is configured to adjust the output voltage of its DC output terminal in response to a voltage control command received from the inverter. When the output voltage of the first DC string containing the power converter is at its maximum, the voltage control command is a voltage reduction command sent by the inverter to the power converter in response to a voltage mismatch in at least one of the DC strings. When the output voltage of the first DC string containing the power converter is at its minimum, the voltage control command is a voltage increase command sent by the inverter to the power converter in response to a voltage mismatch in at least one of the DC strings.

[0051] The aforementioned power converter control method in a power system can receive voltage control commands sent by the inverter and adjust the output voltage of the DC string to which it belongs, thereby reducing the output voltage of the first DC string with the largest output voltage and / or increasing the output voltage of the first DC string with the smallest output voltage, reducing the voltage difference between the bus voltages at the input terminals of the corresponding DC converter circuit, reducing power generation losses, and avoiding large thermal stress on the devices due to excessive voltage difference.

[0052] Fourthly, this application also provides an inverter, comprising: at least one DC-DC converter circuit and an inverter circuit, wherein the input terminal of the DC-DC converter circuit is connected to at least one DC string, and the output terminals of each DC-DC converter circuit are connected in parallel to the input terminal of the inverter circuit, wherein the DC string includes a power converter;

[0053] The inverter is configured to send a voltage control command to at least one power converter in a first DC string in response to a string voltage mismatch occurring in at least one of the DC strings; the first DC string is the DC string with the largest and / or smallest string output voltage among the DC strings; the voltage control command includes: a voltage reduction command for the power converter in the DC string with the largest string output voltage, and / or a voltage increase command for the power converter in the DC string with the smallest string output voltage.

[0054] The aforementioned inverter can send a voltage control command to the power converter of the first DC string when a string voltage mismatch occurs, causing the output voltage of the DC string with the largest output voltage to decrease and the output voltage of the DC string with the smallest output voltage to increase. This reduces the voltage difference between the input terminal of the DC-DC converter circuit and the bus voltage, enabling the power system to support combinations of more diverse strings and complex substation environments, thereby improving the safety and stability of system operation.

[0055] Fifthly, this application also provides a power converter, which includes a DC input terminal and a DC output terminal. The DC input terminal is used to connect to a DC power supply, and the DC output terminal of each power converter is connected in series to the input terminal of the DC conversion circuit of an inverter.

[0056] The power converter is configured to adjust the output voltage of its DC output terminal in response to a voltage control command received from the inverter. When the output voltage of the first DC string containing the power converter is at its maximum, the voltage control command is a voltage reduction command sent by the inverter to the power converter in response to a voltage mismatch in at least one of the DC strings. When the output voltage of the first DC string containing the power converter is at its minimum, the voltage control command is a voltage increase command sent by the inverter to the power converter in response to a voltage mismatch in at least one of the DC strings.

[0057] The aforementioned power converter is installed in the DC string of a power system to regulate the appropriate voltage output from the DC string to the DC conversion circuit of the inverter, avoiding excessively high or low voltage output to the connected DC conversion circuit. This enables the power system to support combinations of more diverse strings and complex substation environments, thereby improving system stability.

[0058] At least one embodiment provided in this application can reduce power generation losses. Attached Figure Description

[0059] To more clearly illustrate the technical solutions in this embodiment or the prior art, the drawings used in the description of the embodiment or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0060] Figure 1 A schematic diagram of a circuit structure for a power converter in a DC string in a power system is provided in an embodiment of this application.

[0061] Figure 2 A schematic diagram of a circuit structure for setting a power converter in a portion of a DC string in a power system, provided in an embodiment of this application;

[0062] Figure 3 A schematic diagram of a circuit structure for setting up a power converter for a portion of the DC power supply in a portion of a DC string in a power system, provided in an embodiment of this application;

[0063] Figure 4A schematic diagram illustrating the process of an inverter sending a voltage control command to a power converter, provided in an embodiment of this application;

[0064] Figure 5 A schematic diagram of the structure of a power system provided in this application embodiment;

[0065] Figure 6 This is a schematic diagram of a power system control process provided in an embodiment of this application. Detailed Implementation

[0066] When the initial component configuration of a photovoltaic power station is inconsistent, such as with strings of different lengths, or when there are significant environmental mismatches such as shading, some photovoltaic strings may have low output voltages. This can lead to a large deviation between the voltage of some photovoltaic strings and the DC bus voltage, resulting in string voltage mismatch. Since the thermal stress in the DC-DC converter circuit of the inverter is strongly related to the power and the voltage difference across the circuit, a larger voltage difference and a higher boost ratio will cause greater thermal stress to the DC-DC converter circuit components.

[0067] For equipment safety, DC-DC converter circuits typically reduce input power. However, reducing input power will trigger the inverter to operate at its derated value, reducing the inverter's output power and resulting in less electricity being delivered to the grid, thus causing a loss in system power generation.

[0068] To reduce power generation losses caused by string voltage mismatch, at least one embodiment provided in this application allows for the reduction of the output voltage of the power converter in the string with the largest output voltage when a DC string voltage mismatch occurs. This is achieved by controlling the power converter in the string with the smallest output voltage to increase its output voltage, thereby reducing the voltage difference between the input voltage of the DC-DC converter circuit connected to the string with the smallest output voltage and the DC bus, reducing its boost ratio, and thus reducing power generation losses.

[0069] Furthermore, at least one embodiment provided in this application can also improve the flexibility of system adjustment, support more combinations of photovoltaic strings with significant differences and complex site construction environments, and improve system stability.

[0070] To provide a more detailed understanding of the features and technical content of the embodiments of this application, the implementation of the embodiments of this application will be described in detail below with reference to the accompanying drawings. The accompanying drawings are for illustrative purposes only and are not intended to limit the embodiments of this application. In the following technical description, for ease of explanation, several details are used to provide a full understanding of the disclosed embodiments. However, one or more embodiments may still be implemented without these details. In other cases, well-known structures and devices may be simplified in their depiction to simplify the drawings.

[0071] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this application described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0072] Unless otherwise stated, the term "multiple" means two or more.

[0073] In this embodiment, the character " / " indicates that the objects before and after it are in an "or" relationship. For example, A / B means: A or B.

[0074] The term "and / or" describes an association between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or A and B.

[0075] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0076] See Figure 1 The diagram shows a circuit structure of a DC string with a power converter in a power system. The power system includes: an inverter and at least one DC string. The inverter includes at least one DC conversion circuit and an inverter circuit. The input terminal of the DC conversion circuit is connected to the at least one DC string. The output terminals of each DC conversion circuit are connected in parallel to the input terminal of the inverter circuit. The DC string includes a power converter, which includes a DC input terminal and a DC output terminal. The DC input terminal is used to connect to a DC power supply. The DC output terminals of each power converter in the DC string are connected in series to the input terminal of the DC conversion circuit.

[0077] The output of an inverter can supply power to the grid or a load.

[0078] For example, the power converter described above can be a module-level power electronics (MLPE) device, which is a power electronic device used in a photovoltaic system to perform fine-grained control of one or more photovoltaic modules; the DC power supply described above can be a photovoltaic cell, etc., providing a DC source for the power system. Communication can be established between the inverter and the power converter, for example, using PLC, RS485, or wireless communication methods; the DC converter described above can be a Boost converter.

[0079] The aforementioned DC string circuit includes a power converter, and there are various implementations in terms of circuit connection structure, as shown in the following examples:

[0080] In one possible implementation, each DC string of the power system is equipped with at least one power converter, for example, such as Figure 1 In the power system shown, each DC power source (photovoltaic panel) in each DC string is equipped with a corresponding power converter. Specifically, Figure 1 The DC string A in the middle is equipped with n DC sources PV a1 PV a2 ……PV an and n power converters OP a1 OP a2 ...OP an Furthermore, the DC source and the power converter are configured in a one-to-one correspondence, for example, PV a1 The corresponding OP is set. a1 PV a2 The corresponding OP is set. a2 , ...PV an The corresponding OP is set. an Similarly, Figure 1 Each DC source in the DC string B also has a corresponding power converter. Alternatively, see... Figure 2 The diagram shows a circuit structure in a power system where power converters are installed for each DC source in a DC string.

[0081] In another possible implementation, power converters are installed on a portion of the DC strings in the power system. These selected DC strings are those where the voltage difference between the output voltage (which can be referenced from historical records or determined based on worker experience) and the DC bus voltage exceeds a voltage difference threshold. Examples include DC strings that are too long or too short (too many or too few DC power supplies connected in series), and strings whose output voltage is easily affected by environmental factors. See also [example description]. Figure 3The diagram shows a circuit structure for a partial DC string power converter in a power system, with the following settings: Figure 3 If the number of DC sources in DC string C is too large and the DC string is too long, it will pull up the output voltage to the DC bus, resulting in an excessive voltage difference between the output voltage of DC string C and the DC bus voltage, exceeding the voltage difference threshold. Therefore, the appropriate option is... Figure 3 In a power system, DC sources in DC string D are equipped with power converters to regulate and reduce the output voltage of DC string D. DC sources in DC string C can be equipped with power converters, or they can be left unequipped to reduce costs. Furthermore, power converters can be installed for each DC source in DC string D, or only a portion of the DC power sources can be equipped with power converters.

[0082] An inverter is configured to send a voltage control command to at least one power converter in a first DC string in response to a string voltage mismatch occurring in at least one DC string; the first DC string is defined as the DC string with the largest and / or smallest string output voltage among all DC strings; the voltage control command includes a voltage reduction command for the power converter in the DC string with the largest string output voltage, and / or a voltage increase command for the power converter in the DC string with the smallest string output voltage; the power converter is configured to adjust the output voltage at its DC output terminal in response to the received voltage control command.

[0083] Understandably, the first DC string mentioned above is a DC string equipped with a power converter.

[0084] In summary, this application aims to reduce the voltage difference between the input voltage of the DC-DC converter circuit and the bus voltage in a power system, thereby avoiding the problem of string voltage mismatch. In one approach, a voltage control command (voltage reduction command) is sent to at least one power converter in the first DC string with the highest output voltage to reduce its output voltage. Specifically, the bus voltage meets the voltage required for grid connection, and the DC-DC converter circuit connected to the DC string with the highest output voltage operates in bypass mode (the DC-DC converter circuit does not boost the output voltage of the DC string). The bus voltage is equal to the output voltage of the DC string with the highest output voltage. Therefore, sending a voltage control command (voltage reduction command) to the first DC string with the highest output voltage to reduce its output voltage can reduce the bus voltage, thereby reducing the voltage difference between the voltage output to the corresponding DC-DC converter circuit of the DC string with the lowest output voltage in the power system and the bus voltage. In another approach, a voltage control command (voltage increase command) is sent to at least one power converter in the first DC string with the lowest output voltage to increase the output voltage of the DC string with the lowest output voltage in the power system, thereby reducing the voltage difference between the voltage output by the DC string with the lowest output voltage to the corresponding DC-DC converter circuit and the bus voltage.

[0085] Based on the above embodiments, the inverter sends a voltage control command to at least one power converter in the first DC string. Specific possible implementations include: the inverter sending a voltage control command to any one power converter in each DC string included in the first DC string; or sending a voltage control command to some power converters in each DC string included in the first DC string; or sending a voltage control command to all power converters in each DC string included in the first DC string.

[0086] Based on the above embodiments, the above response to at least one power converter in the first DC string experiencing string voltage mismatch can be implemented in various ways, as follows:

[0087] In one possible implementation, a voltage control command is sent to at least one power converter in the first DC string in response to the absolute value of the voltage difference between the input voltage of the DC-DC converter circuit corresponding to at least one DC string and the DC bus voltage exceeding a preset voltage difference threshold. For example, the inverter can acquire the DC bus voltage and the input voltage of the DC-DC converter circuit corresponding to each DC string; if the absolute value of the voltage difference between the input voltage of the DC-DC converter circuit corresponding to any DC string and the DC bus voltage (e.g., 350V) exceeds the voltage difference threshold (e.g., 300V), a voltage control command is sent to at least one power converter in the first DC string.

[0088] In another possible implementation, in response to the temperature of the DC-DC converter circuit corresponding to at least one DC string exceeding a preset temperature threshold, a voltage control command is sent to at least one power converter in the first DC string. For example, the inverter acquires the temperature of the DC-DC converter circuit corresponding to each DC string; if the temperature of the DC-DC converter circuit corresponding to any DC string exceeds the temperature threshold, then there is a string voltage mismatch in the DC string.

[0089] Of course, based on the two possible implementation methods mentioned above, a voltage control command can also be sent to at least one power converter in the first DC string if the absolute value of the voltage difference between the input voltage of the DC converter circuit corresponding to at least one DC string and the DC bus voltage (e.g., 350V) exceeds a preset voltage difference threshold (e.g., 300V) and it is determined that the temperature of the DC converter circuit corresponding to at least one DC string exceeds a preset temperature threshold.

[0090] The input terminal of the aforementioned DC-DC converter circuit is connected to a DC string to boost the voltage at the input terminal of the DC-DC converter circuit according to the given value of the DC bus voltage. However, due to inconsistent initial component configurations in the power plant, such as varying lengths of photovoltaic strings in the system, or environmental factors such as shading of photovoltaic panels, the output voltage of a certain DC string may deviate significantly from the DC bus voltage. In order to boost the voltage to the given value of the DC bus voltage, the DC-DC converter circuit will use a large boost ratio, increasing the thermal stress on the related components of the DC-DC converter circuit (Boost converter). For equipment safety, the DC-DC converter circuit will actively reduce the input power, but this will trigger derating, resulting in power generation losses in the system.

[0091] Therefore, configuring power converters in DC strings allows for flexible adjustment of the voltage or current output from the DC string to the corresponding DC-DC converter circuit without reducing the photovoltaic module power. This reduces the voltage difference between the input voltage and the DC bus voltage of the DC-DC converter circuit, ensuring safe operation and preventing derating. Therefore, in addition to conventional methods of adjusting the DC-DC converter circuit for voltage boosting, the power converters in each DC string can be adjusted accordingly. This reduces the problem of string voltage mismatch caused by excessively high or low output voltages in one or more DC strings (e.g., different output voltages due to varying string lengths), and minimizes the voltage difference between the input voltage and the DC bus voltage. This improves system adjustment flexibility, supports combinations of photovoltaic strings with significant differences and complex site construction environments, and enhances system stability.

[0092] When adjusting the power converter as described above, a corresponding adjustment range is required to generate a voltage control command. Therefore, before sending a voltage control command to at least one of the power converters in the first DC string, the inverter is further configured to: determine the adjustment range of a specified electrical parameter of at least one of the power converters in the first DC string; and generate a voltage control command based on the adjustment range.

[0093] Optionally, the adjustment range can be directly generated into a voltage control command and sent to the power converter for processing. Specifically, the power converter, in response to the received voltage control command, adjusts the output voltage based on the adjustment range of the specified electrical parameter if the adjustment range of the specified electrical parameter does not exceed the current allowable adjustment range of the power converter; if the adjustment range of the specified electrical parameter exceeds the current allowable adjustment range of the electrical parameter, the output voltage is adjusted to the maximum adjustable voltage value according to the adjustment direction indicated by the voltage control command. This ensures adjustment within the current allowable adjustment range of the power converter, avoiding inappropriate commands that could cause the power converter to deviate from its maximum power operating point or operate in an unstable range, leading to secondary problems such as power generation losses.

[0094] Optionally, before generating voltage control commands based on the aforementioned adjustment range, the inverter and power converter can communicate bidirectionally to determine the current allowable adjustment range of the power converter, and whether the adjustment range falls within this range, before further generating voltage control commands for adjustment. The specific implementation method is as follows:

[0095] Before generating a voltage control command based on the adjustment range, the inverter determines the currently allowed adjustment range of at least one of the power converters in the first DC string; if the adjustment range does not exceed the adjustment range, then the generation of the voltage control command based on the adjustment range is executed. However, if the adjustment range exceeds the adjustment range, the inverter can take several possible measures to adjust, such as:

[0096] One possible measure is to pause sending the voltage control command if the adjustment amplitude exceeds the adjustment range, or to generate a first command based on the current allowable adjustment range of the power converter and send the first command to the power converter.

[0097] Another possible measure is as follows: If the adjustment range exceeds the adjustment range, and the first DC string only includes the DC string with the largest output voltage among all the DC strings, the DC string with the smallest output voltage among all the DC strings is taken as the new first DC string, and the adjustment range of the specified electrical parameters of at least one of the power converters of the first DC string and subsequent steps are executed; if the first DC string only includes the DC string with the smallest output voltage among all the DC strings, the DC string with the largest output voltage among all the DC strings is taken as the new first DC string, and the adjustment range of the specified electrical parameters of at least one of the power converters of the first DC string and subsequent steps are executed; if the first DC string only includes the DC strings with the largest and smallest output voltage among all the DC strings, the transmission of the voltage control command is suspended, or a first command is generated based on the current allowable adjustment range of the power converter and sent to the power converter.

[0098] For example, the first instruction described above is an electrical parameter adjustment range set based on the endpoint value of the adjustment range currently allowed by the power converter.

[0099] Based on the above embodiments, there are several possible implementation methods for determining the above adjustment range, which are described below:

[0100] In the first implementation, considering the boosting situation of the DC-DC converter circuit, specifically, the voltage difference between the output voltage and the bus voltage of the DC string that has a string voltage mismatch is determined; the voltage difference is calculated and a preset voltage difference threshold is subtracted to obtain the total voltage adjustment amplitude; based on the total voltage adjustment amplitude, the voltage adjustment amplitude or current adjustment amplitude of each power converter in the first DC string is determined.

[0101] In the second implementation, the boost effect of the DC-DC converter circuit is not considered. The power converters in the first DC string are directly adjusted. Any deviations from their current allowable adjustment range are then adjusted by the DC-DC converter circuit. Specifically, based on the output voltages of each DC string connected to the inverter, the total adjustment range for increasing the voltage of the DC string with the lowest output voltage, or the total adjustment range for decreasing the voltage of the DC string with the highest output voltage, is determined. Based on this total voltage adjustment range, the voltage or current adjustment range for each power converter in the first DC string is determined.

[0102] It should be noted that the output voltages of the multiple DC strings connected to the inverter may differ. Based on the above, if the output voltage of the DC string with the lowest output voltage is too low, the boost ratio of its connected DC-DC converter circuit will be too high, potentially triggering derating. Therefore, this application aims to increase the output voltage of the DC string with the lowest output voltage or decrease the output voltage of the DC string with the highest output voltage. Furthermore, when determining the adjustment range of the output voltage, the output voltage of the DC string with the lowest output voltage can be boosted based on the output voltages of the other DC strings connected to the inverter. For example, the output voltage can be boosted based on the output voltage of the second lowest or highest DC string among the other DC strings connected to the inverter, and the difference between the output voltage of the second lowest or highest DC string and the output voltage of the lowest DC string can be used as the total voltage adjustment range for that DC string. Similarly, when determining the adjustment range of the output voltage, the output voltage of the DC string with the highest output voltage can be depressed based on the output voltages of the other DC strings connected to the inverter. For example, the output voltage can be boosted based on the output voltage of the second highest DC string among the other DC strings connected to the inverter.

[0103] Furthermore, based on the total adjustment magnitude of the voltage, the adjustment magnitude of the voltage of each power converter in the first DC string can be determined, specifically as follows:

[0104] When the first DC string is the DC string with the largest or smallest output voltage among all the DC strings, the total adjustment amplitude is evenly distributed to the target amplitude of the voltage obtained by each power converter in the first DC string, and the target amplitude or the amplitude obtained by multiplying the target amplitude by a preset ratio is determined as the adjustment amplitude of the voltage of the power converter in the first DC string.

[0105] When the first DC string is the DC string with the largest and smallest output voltage among all the DC strings, the total adjustment amplitude is allocated to each first DC string to obtain the adjustment sub-amplitude of the voltage allocated to each first DC string; the adjustment sub-amplitude is evenly distributed to each power converter in the corresponding first DC string to obtain the target voltage amplitude; the target amplitude or the amplitude obtained by multiplying the target amplitude by a preset voltage ratio is determined as the adjustment amplitude of the power converter voltage in the first DC string.

[0106] For the DC string with the largest output voltage, the target amplitude of the voltage is negative; for the DC string with the smallest output voltage, the target amplitude of the voltage is positive.

[0107] Of course, the adjustment range of the current can be further determined. Specifically, when the power of the power converter remains unchanged, the target range of the power converter current is determined according to the target range of the power converter voltage. The target range of the current or the target range of the current multiplied by a preset current ratio is used as the adjustment range of the power converter current in the first DC string. For the DC string with the largest output voltage, the target range of the current is positive, and for the DC string with the smallest output voltage, the target range of the current is negative.

[0108] The above can be done in one go, with the adjustment range set based on the target range, or in multiple adjustments, where an adjustment ratio can be set for multiple adjustments, such as adjusting by 20% each time, with the target range multiplied by 20% as the adjustment range.

[0109] In addition, a small preset value (e.g., 0.1V or 0.1A, which can be set as needed) can be preset in the inverter to set the adjustment range for multiple adjustments. Specifically, for the DC string with the largest string output voltage, a negative voltage preset value is taken as the adjustment range of the power converter voltage, or a positive current preset value is taken as the adjustment range of the power converter current; for the DC string with the smallest string output voltage, a positive voltage preset value is taken as the adjustment range of the power converter voltage, or a negative current preset value is taken as the adjustment range of the power converter current; the voltage preset value and the current preset value are both values ​​used to achieve repeated adjustments of the power converter.

[0110] In summary, there are several possible implementation methods in determining the specific adjustment range, which will be introduced in detail below:

[0111] In the first implementation method, the inverter sends a voltage control command to the power converter, specifying the adjustment range of electrical parameters (e.g., voltage, current) allowed by the power converter. The power converter then adjusts its output electrical parameters in response to the received voltage control command. Therefore, see [link to relevant documentation]. Figure 4 The diagram shows a flow chart of an inverter sending voltage control commands to a power converter. The specific steps for the inverter to send voltage control commands to the power converter are as follows:

[0112] Step S401: In response to the occurrence of string voltage mismatch in at least one DC string, determine the current allowable adjustment range of at least one power converter in the first DC string.

[0113] The power converter and inverter have bidirectional communication. The inverter can obtain feedback information packets from the power converter in real time and obtain the current allowable adjustment range of the power converter from the information packets. For example, the current allowable adjustment range of the power converter is [-2V, 2V]. When the inverter uses a voltage adjustment range of -0.1V, it is determined that -0.1V is within the current allowable adjustment range of the power converter [-2V, 2V]. This avoids the situation where the adjustment range of the command issued by the inverter exceeds the current allowable adjustment range of the power converter.

[0114] Step S402: If the adjustment range of the power converter electrical parameters used to indicate the power converter electrical parameters does not exceed the adjustment range, then a voltage control command is generated based on the adjustment range and sent to the power converter.

[0115] There are several ways to determine the adjustment range of the electrical parameters of the power converter in an inverter, as shown in the following examples:

[0116] In the first approach, the voltage difference that needs to be adjusted between the DC bus voltage and the input voltage of the DC-DC converter circuit is calculated. Based on the difference exceeding a preset voltage difference threshold and the number of power converters in the DC string whose output voltage needs adjustment, the adjustment range of the power converter's electrical parameters is determined. Subsequently, if the adjustment range does not exceed the current allowable adjustment range of the power converter, a voltage control command is generated based on the adjustment range and issued to the power converter in one go to achieve a large-scale and rapid adjustment.

[0117] In the second method, a fixed step size is preset for multiple adjustments. This fixed step size indicates the step size of the power converter's adjustment of electrical parameters each time.

[0118] In the third method, a relative value of the electrical parameter is set for multiple adjustments. That is, an adjustment ratio of an electrical parameter can be set for multiple adjustments, such as adjusting by 20% each time.

[0119] The first method described above allows for one-time adjustment, which is convenient and efficient. However, the second and third methods, after the inverter sends a command to the power converter to be controlled, can promptly grasp the operating status of the power converter based on the two-way communication between the inverter and the power converter. They can also collect the output voltage of the corresponding DC string of the power converter to determine the adjustment situation. This avoids the problem of system instability caused by excessive adjustment range when adjusting all at once.

[0120] Step S403: If the adjustment range of the power converter electrical parameters exceeds the adjustment range, then pause sending the voltage control command, or generate a first command based on the current allowable adjustment range of the power converter and send the first command to the power converter.

[0121] If the adjustment range of the power converter's electrical parameters exceeds the allowable adjustment range of the power converter, adjusting according to this adjustment range will cause the power converter to deviate from the maximum power operating point or operate in an unstable operating range, resulting in secondary problems such as power generation loss. In this case, it is necessary to suspend the generation and transmission of voltage control commands based on this adjustment range.

[0122] Furthermore, based on the current allowable adjustment range of the power converter and the required adjustment direction (boost or buck), a new adjustment amplitude can be determined and a first instruction can be generated and sent to the corresponding power converter. Optionally, the first instruction can be an electrical parameter adjustment amplitude set based on the endpoint value of the current allowable adjustment range of the power converter. For example, if the adjustment amplitude of the power converter's electrical parameter is set to 2.5V, which exceeds the current allowable adjustment range of the power converter [-2V, 2V], then based on the adjustment amplitude of 2.5V, it is known that the power converter needs to perform a boost adjustment. Combining the current allowable adjustment range of the power converter [-2V, 2V], a new adjustment amplitude of 2V is determined, and a first instruction is generated, sent to the corresponding power converter, and the subsequent boost adjustment ends. Subsequently, buck adjustment can be performed in conjunction with the DC string with the largest output voltage in the power system to reduce the bus voltage, thereby reducing the voltage difference between the DC string output voltage and the bus voltage.

[0123] Through steps S401-S403, when the inverter sends voltage control commands, it will adjust the voltage based on the current allowable adjustment range of the power converter to avoid exceeding the actual operating range and capability range of the power converter.

[0124] In the second implementation method, the inverter sends a voltage control command to the power converter. The power converter responds to the received voltage control command and adjusts itself according to its current allowed electrical parameters (e.g., voltage, current) adjustment range. The specific steps of the power converter adjustment can be as follows:

[0125] Step S501: In response to the received voltage control command, if the electrical parameter adjustment value indicated by the voltage control command does not exceed the current allowable electrical parameter adjustment range of the power converter, then the output voltage is adjusted based on the electrical parameter adjustment value indicated by the voltage control command.

[0126] Step S502: If the electrical parameter adjustment value indicated by the voltage control command exceeds the current allowable electrical parameter adjustment range of the power converter, then adjust the output voltage to the maximum adjustable voltage value according to the adjustment direction indicated by the voltage control command.

[0127] It should be noted that when the electrical parameter adjustment value is the current adjustment value, if the current adjustment value is positive, the adjustment direction is to increase the current; if the current adjustment value is negative, the adjustment direction is to decrease the current. Furthermore, adjusting the output voltage to the maximum adjustable voltage value according to the adjustment direction indicated by the voltage control command means adjusting to the endpoint value of the corresponding adjustment direction within the current allowable electrical parameter adjustment range of the power converter. For example, if the allowable adjustment range of the power converter is set to [-2A, 2A], if the electrical parameter adjustment value is 3A (positive), then according to the positive endpoint value of 2A within the allowable adjustment range, the power converter increases the current by 2A; if the electrical parameter adjustment value is -3A (negative), then according to the negative endpoint value of -2A within the allowable adjustment range, the power converter decreases the current by 2A. Similarly, when the electrical parameter adjustment value is the voltage adjustment value, if the voltage adjustment value is positive, the adjustment direction is to increase the voltage; if the current adjustment value is negative, the adjustment direction is to decrease the voltage. For example, if the power converter is set to have an allowable adjustment range of [-2V, 2V], and the electrical parameter adjustment value is 3V (positive value), then the power converter will boost the voltage to 2V based on the positive endpoint value of 2V in the allowable adjustment range; if the electrical parameter adjustment value is -3V (negative value), then the power converter will step down the voltage to 2V based on the negative endpoint value of -2V in the allowable adjustment range.

[0128] Furthermore, in the second implementation described above, the voltage control command determination process in the inverter sending voltage control commands to the power converter can be as follows: The inverter calculates that the voltage difference between the output voltage of the DC string with the lowest output voltage and the bus voltage (e.g., 350V) exceeds the voltage difference threshold (e.g., 300V) by 50V. When the DC string with the lowest output voltage is used as the first DC string for boost control, the average voltage boost required by one power converter can be determined based on the number of power converters in the first DC string. Assuming there are 20 power converters, each power converter needs to boost by 2.5V. The adjustment range ΔV = 2.5V is determined for instructing the power converter to adjust the voltage, and this voltage adjustment range ΔV = 2.5V is used to generate a voltage control command, which is then sent to at least one power converter in the first DC string. Alternatively, current reduction control can be performed on the first DC string. The target current value corresponding to a 50V boost is determined for the first DC string while maintaining constant power, and a voltage control command is generated based on this target current value and sent to one power converter in the first DC string.

[0129] Based on the above embodiments, the first DC string is the DC string with the highest and / or lowest output voltage among all DC strings. Therefore, the first DC string can be the DC string with the highest output voltage in the power system, or the DC string with the lowest output voltage in the power system, or even both the highest and lowest voltage DC strings in the power system. Thus, the voltage control command sent by the inverter to the power converter can have multiple indication methods, specifically as follows:

[0130] In the first possible implementation, the voltage control command sent to the power converter in the DC string with the lowest output voltage is a voltage increase command. This is because the voltage output from the DC string with the lowest output voltage to the corresponding DC bus in the power system is too low, resulting in an excessive voltage difference between the output voltage of this DC string and the DC bus voltage. This causes the DC string to deviate from its maximum power point when regulated solely by the corresponding DC-DC converter circuit, leading to voltage mismatch. Therefore, a power converter is configured for this DC string, and the output voltage of the DC string is increased by controlling the power converter within the DC string, thereby reducing the voltage difference. Consequently, the voltage control command set for the power converter in the DC string with the lowest output voltage is a voltage increase command.

[0131] Specifically, for the DC string with the smallest output voltage among all the DC strings, a voltage increase command is generated based on the voltage adjustment range to indicate the power converter to boost the voltage, or a voltage increase command is generated based on the current adjustment range to indicate the power converter to reduce the current.

[0132] When the voltage increase command instructs the power converter to reduce the current boost amplitude, the first method in step S401 above can be used. For example, assuming the system's allowable voltage difference threshold is 300V, when the calculated voltage difference exceeds 300V, such as 350V, the excess difference is calculated to be 50V. (See [reference needed]). Figure 5 The diagram shows a power system structure where the power converters in the DC string can be connected one-to-one with a DC source (e.g., ...). Figure 5 In DC string 1, DC source PV101 is connected to power converter OP101, DC source PV102 is connected to power converter OP102, ... DC source PV120 is connected to power converter OP120; and see also Figure 5 In DC string 2, DC source PV201 is connected to power converter OP201, DC source PV202 is connected to power converter OP202, ... DC source PV210 is connected to power converter OP210.

[0133] by Figure 5Taking the shortest DC string 2 with the lowest output voltage as an example, and using DC string 2 as the first DC string, the number of power converters in DC string 2 is set to 10 (see...). Figure 5 The medium-power converters OP201-OP210 can determine the average voltage increase required by a power converter (5V), and determine the adjustment range ΔV = 5V for the power converter. When ΔV = 5V is within the allowable adjustment range of the power converters in the first DC string, a voltage control command of ΔV = 5V is generated and sent to one or more power converters in the first DC string. (Since the outputs of the power converters in this DC string are connected in series and the current is consistent, other power converters in this DC string that have not received the command will automatically adjust their output voltage according to the adjusted current value.) Alternatively, the second method described above can be used, for example, by presetting a fixed step size voltage adjustment range ΔV = 1V for multiple adjustments. When the inverter starts regulation and determines that ΔV = 1V does not exceed the current allowable regulation range of the power converters in the DC string to be controlled, and determines that the actual voltage regulation range required by each power converter in DC string 1 is 5V, a voltage control command is generated based on ΔV = 1V and sent to at least one power converter in the first DC string. After one regulation, it is clear that the regulation requirement is not met (at this time, the voltage difference between the output voltage and the bus voltage of the DC string with voltage mismatch after steady state still exceeds the voltage difference threshold). The inverter can continue to adjust based on ΔV = 1V. The output voltage of the first DC string is readjusted step by step (each adjustment must ensure that ΔV does not exceed the current allowable voltage adjustment range of the power converter in the first DC string) until the adjustment requirements are met (e.g., the voltage difference between the output voltage of the DC string with voltage mismatch and the bus voltage no longer exceeds the voltage difference threshold after steady state). Alternatively, the third method described above can be used. For example, after determining that each power converter in DC string 1 needs a 5V boost, the adjustment range of the power converter's electrical parameters is further determined as ΔV = 5V × 20% = 1V. Then, if ΔV = 1V does not exceed the current allowable adjustment range of the power converter to be controlled, a voltage control command is generated based on ΔV = 1V and sent to the power converter to be controlled. After one adjustment, the adjustment requirements are clearly not met. Subsequently, the inverter can continue to recalculate and determine the magnitude of the electrical parameters that each power converter needs to improve. Then, it multiplies the magnitude of the electrical parameters by 20% to determine the new adjustment magnitude ΔV of the electrical parameters of the power converter. If the new ΔV meets the current allowable adjustment range of the power converter, it generates the corresponding voltage control command based on the new ΔV and sends it to the power converter until the adjustment requirements are met, and performs boost regulation.

[0134] When the voltage increase command instructs the power converter to reduce the current reduction amplitude, the first method in step S401 above can also be used. For example, the voltage difference (e.g., 350V) between the output voltage of the DC string with the smallest output voltage and the bus voltage exceeds the voltage difference threshold (e.g., 300V) by 50V. The DC string 2 with the smallest output voltage is then used as the first DC string for current reduction. If the output power of the DC string 2 remains unchanged, the target current value that needs to be adjusted if the DC string 2 is boosted by 50V is determined. This target current value is used as the current adjustment amplitude. If the current adjustment amplitude does not exceed the current allowable adjustment range of the power converter in the first DC string, the current adjustment amplitude is used to generate a voltage control command and sent to one of the power converters in the first DC string for current reduction. Alternatively, the second method can be used. For example, a fixed step size for current reduction amplitude is preset. The current adjustment ΔI is performed multiple times, and each adjustment must ensure that ΔI does not exceed the current adjustment range currently allowed by the power converter in the first DC string with the lowest output voltage. Alternatively, a third method can be used. For example, the voltage difference between the output voltage of the DC string 2 with the lowest output voltage and the bus voltage (e.g., 350V) is set to exceed the voltage difference threshold (e.g., 300V) by 50V. The DC string 2 with the lowest output voltage is used as the first DC string for current reduction. With the output power of the DC string 2 remaining unchanged, the target current value corresponding to the 50V boost of the DC string 2 is determined. The target current value is multiplied by the current adjustment ratio to determine the current adjustment range. If the current adjustment range does not exceed the current allowable adjustment range of the power converter in the DC string 2, the current adjustment range is used to generate a voltage control command and sent to one of the power converters in the DC string 2 for current reduction. Subsequently, the difference between the output voltage of the DC string with the smallest output voltage and the bus voltage exceeds the voltage difference threshold (e.g., 300V), and the new target current value that needs to be adjusted for this difference under the condition of constant power. Based on the current adjustment ratio and the new target current value, a new current adjustment range is determined, and within the current allowable adjustment range of the corresponding power converter, a voltage control command is generated based on the new current adjustment range and sent to one of the power converters in the first DC string for adjustment until the adjustment requirements are met, and current reduction adjustment is performed.

[0135] Of course, the voltage increase command can also be a combination of indicating the voltage increase magnitude of the power converter and indicating the current decrease magnitude of the power converter, for example, for... Figure 5 The DC string 2 with the lowest output voltage first uses boost regulation on a portion of the above difference (e.g., 20V) and current reduction regulation on the other portion (30V).

[0136] Specifically, a voltage control command (voltage increase command) is sent to at least one power converter in the DC string with the lowest output voltage. Upon receiving the command, the power converter determines a reference value based on its current output electrical parameters and the adjustment range (voltage increase or current decrease) indicated by the command. The power converter then outputs based on this reference value. (See [link to relevant documentation]). Figure 1 Since the power converters connected in series on the same DC string are connected in series, when the current of one power converter connected in the same DC string decreases, the current of the other power converters connected in series with that power converter will also increase accordingly, thereby automatically adjusting and reducing the output voltage of the DC string.

[0137] In the second possible implementation, for the DC string with the largest output voltage among the various DC strings, a voltage reduction command is generated based on the voltage adjustment magnitude to instruct the power converter to step down, or a voltage reduction command is generated based on the current adjustment magnitude to instruct the power converter to step up. Since the voltage output to the DC bus from the DC string with the largest output voltage in the power system is too high, the DC-DC converter circuit enters bypass mode and does not perform voltage boosting. Therefore, the output voltage of the DC string with the largest output voltage is equal to the bus voltage. Consequently, a voltage reduction command can be sent to the DC string with the largest output voltage to reduce the bus voltage, thereby reducing the voltage difference between the output voltage of the DC string with the smallest output voltage in the power system and the DC bus voltage, thus minimizing the problem of string voltage mismatch and deviation from the maximum power operating point.

[0138] Specifically, the aforementioned voltage reduction command can instruct the power converter to reduce the voltage drop by a certain amount. Specifically, it can employ the first method in step S402 above. For example, see [link to example]. Figure 5 The diagram shows the structure of a power system, wherein, a... Figure 5 DC string 1 is the longest and has the highest output voltage, while DC string 2 is the shortest and has the lowest output voltage. Therefore, we first calculate the voltage difference between the output voltage of DC string 2 (which has the lowest output voltage) and the bus voltage (e.g., 350V). Then, we calculate the difference between this voltage difference and a voltage difference threshold (e.g., 300V) (50V). This difference is then distributed to each power converter in DC string 1 to obtain the voltage drop of each power converter. Figure 1 The medium DC string 1 contains 20 power converters (see...) Figure 5For medium-power converters OP101-OP120, each power converter has a step-down voltage of 2.5V. If this step-down voltage is within the allowable adjustment range of the power converter, a voltage reduction command is generated based on this step-down voltage. Alternatively, the second method described above can be used. For example, a fixed step-down voltage is preset (e.g., 1V) for multiple step-down adjustments. Each adjustment requires determining if the fixed step-down voltage is within the current allowable adjustment range of the power converter, and then generating a voltage reduction command based on this fixed step-down voltage. Alternatively, the third method described above can be used. For example, a preset fixed ratio value (e.g., 20%) is set for multiple adjustments. Each adjustment process can be as follows: the total step-down voltage required for the DC string 1 with the highest output voltage (e.g., 50V) is multiplied by this ratio value to obtain the current step-down voltage (i.e., 50 multiplied by 20% equals 10V). This step-down voltage is then distributed to each power converter in DC string 1 to obtain the step-down voltage of each power converter (e.g., 1V). Figure 1 The DC string 1 contains 20 power converters, and each power converter has a step-down voltage of 0.5V. As long as the current step-down voltage of each power converter does not exceed the current allowable adjustment range of the power converters in the DC string, a corresponding voltage reduction command is generated to perform step-down regulation of the output voltage of the DC string with the largest output voltage.

[0139] The aforementioned voltage reduction command can also be used to instruct the power converter to increase the current boosting range. Specifically, the first method in step S402 can be adopted. For example, firstly, the voltage difference between the output voltage of the DC string 2 with the lowest output voltage and the bus voltage is calculated, and then the difference between this voltage difference and the voltage difference threshold (e.g., 50V) is calculated. With the DC string output power remaining unchanged, the DC string 1 with the highest output voltage is determined as the target current value to be adjusted corresponding to the 50V boost of the first DC string. This target current value is used as the current adjustment range. If the current adjustment range does not exceed the current allowable adjustment range of the power converter in the first DC string, the current adjustment range is used to generate a voltage control command and sent to one of the power converters in the first DC string for current boosting. Alternatively, the second method can be adopted, for example... One approach is to perform multiple current boost adjustments using a preset fixed step current value. Each adjustment requires determining whether the current boost amplitude of the fixed step is within the allowable adjustment range of the power converter, and then generating a voltage reduction command based on the current boost amplitude of the fixed step. Alternatively, a third approach can be used. For example, a preset fixed current ratio value is set for multiple adjustments. Specifically, the DC string 1 with the highest output voltage is determined as the total current boost amplitude corresponding to the total voltage drop required for the first DC string while keeping the power constant. This total current boost amplitude is multiplied by the ratio value to obtain the current boost amplitude. If the current current boost amplitude does not exceed the current allowable adjustment range of the power converter in the DC string 1, the current boost amplitude generates a corresponding voltage reduction command and sends it to one of the power converters in the DC string 1 to perform current boost adjustment on the DC string with the highest output voltage. Of course, the voltage reduction command can also instruct the power converter to reduce the voltage by a certain amount and to increase the current by a certain amount. For example, for the DC string 1 with the highest output voltage, a portion of the difference (e.g., 20V) can be reduced by a certain amount, and the other portion (30V) can be increased by a certain amount.

[0140] The DC string with the highest output voltage is controlled by a voltage reduction command, which lowers the output voltage and increases the output current (power remains constant), causing the DC bus voltage to decrease accordingly. Specifically, a voltage control command (voltage reduction command) is sent to at least one power converter in the DC string with the highest output voltage. Upon receiving the command, the power converter determines a reference value based on its current output electrical parameters and the adjustment range (voltage drop or current increase) indicated by the command. The power converter then outputs based on this reference value, resulting in an increase in its current while maintaining constant power. See [link to relevant documentation]. Figure 5Since the power converters connected in series on the same DC string are connected in series, when the current of one power converter connected in the same DC string increases, the current of the other power converters connected in series with that power converter will also increase accordingly, thereby automatically adjusting and reducing the output voltage of the DC string.

[0141] Based on the above embodiments, see Figure 6 The diagram illustrates a power system control flow. In one specific implementation, the inverter's control process for DC string voltage mismatch issues in the system is as follows:

[0142] S601, Obtain the DC bus voltage and the input voltage of the DC-DC converter circuit.

[0143] The output terminal of the DC string is connected to the input terminal of the corresponding DC-DC converter circuit.

[0144] S602. If the absolute value of the voltage difference between the input voltage of a DC-DC converter circuit and the DC bus voltage exceeds the voltage difference threshold (DC string voltage mismatch exists), then it is determined that at least one DC string has experienced string voltage mismatch.

[0145] If the absolute value of the voltage difference between the input voltage of the DC-DC converter circuit and the DC bus voltage in the system does not exceed the voltage difference threshold (there is a voltage mismatch in the DC strings), then there are no DC strings with voltage mismatch in the power system, no adjustment is required, and the subsequent steps end.

[0146] S603. Determine the current allowable adjustment range of the power converter of the first DC string.

[0147] The first DC string is the DC string with the highest and / or lowest output voltage among all DC strings. The first DC string is equipped with a power converter. The voltage control command for the DC string with the highest output voltage can indicate the voltage reduction or current increase, while the voltage control command for the DC string with the lowest output voltage can indicate the voltage increase or current decrease.

[0148] S604. Determine whether the adjustment range of the power converter electrical parameters used to indicate the power converter exceeds the current allowable adjustment range of the power converter of the first DC string.

[0149] This example uses a multi-adjustment method. The method for generating the adjustment range can be found in the second method of step S402 above, which gives a fixed adjustment range step size, or in the third method, which sets a ratio value.

[0150] S605. If the adjustment range used to indicate the electrical parameters of the power converter does not exceed the adjustment range, a voltage control command is generated based on the adjustment range and sent to the power converter, and the above steps S601 and subsequent steps are re-executed.

[0151] S606. If the adjustment range of the power converter electrical parameters exceeds the adjustment range, then suspend sending voltage control commands, or generate a first command based on the current allowable adjustment range of the power converter and send the first command to the power converter.

[0152] According to steps S601-S606 above, the power converter of this application can adjust within the allowable adjustment range based on its current operating parameters, avoiding passive adjustment exceeding expectations, such as exceeding the adjustment capability boundary of the power converter itself. Specifically, closed-loop adjustment achieves the purpose of adjustment under the premise that the final output voltage or current value of the power converter does not exceed the adjustment limit of the power converter. If the power converter adjustment reaches the limit value, and there is still a situation in the system where the voltage difference between the input voltage of the DC conversion circuit and the DC bus voltage exceeds the voltage difference threshold, the above-mentioned method of the inverter sending a voltage reduction command to the power converter in the DC string with the largest string output voltage and sending a voltage increase command to the power converter in the DC string with the smallest string output voltage can be adopted. For example, in step S602, if at least one DC string is detected to have string voltage mismatch, the inverter, in executing steps S603-S605, first selects the first DC string with the smallest output voltage in the system for processing, and sends a voltage increase command to at least one power converter in the first DC string with the smallest output voltage. When the power converter can adjust the output electrical parameters to the limit of the currently allowed adjustment range (i.e., after step S606 above, continuing to execute steps S601-S602), and it is determined that there is still a situation where the voltage difference between the input voltage of the DC-DC converter circuit and the DC bus voltage exceeds the voltage difference threshold, the inverter executes steps S603-S605 to send a voltage reduction command to at least one power converter in the string with the largest output voltage among the DC strings in the system. This reduces the bus voltage, thereby further narrowing the voltage difference between the input voltage of the DC-DC converter circuit and the DC bus voltage in the DC string connection where string voltage mismatch occurs, and avoiding derating caused by the DC-DC converter circuit due to an excessively high boost ratio. Of course, after step S606 above, continuing to execute steps S601-S602 to determine that there is still a situation where the voltage difference between the input voltage of the DC-DC converter circuit and the DC bus voltage exceeds the voltage difference threshold can also send a warning to the user.

[0153] Based on the above embodiments, optionally, in response to the occurrence of string voltage mismatch in at least one DC string, in addition to sending a voltage control command to at least one power converter in the first DC string, a warning can be further issued to the user to indicate the DC string with string voltage mismatch problem. The warning can also correspond to the voltage difference and temperature information determined above.

[0154] Optionally, the aforementioned first DC string may include the DC string with the highest and / or lowest output voltage among all DC strings. Further, the first DC string may also include the DC strings connected to the DC-DC converters with the N lowest input voltages in the power system, and / or the DC strings connected to the DC-DC converters with the N highest input voltages in the power system. The method for determining the DC-DC converters with the N lowest input voltages in the power system can be: sorting the input voltages of the DC-DC converters in the power system to determine the N lowest input voltage DC-DC converters in the power system (N is a positive integer); or, determining a target low voltage value based on the inverter bus voltage, and using the DC-DC converters with input voltages less than or equal to the target low voltage value as the DC-DC converters with the lowest input voltages in the power system. Similarly, the method for determining the N highest input voltage DC-DC converters in the power system is based on the same principle as the method for determining the N lowest input voltage DC-DC converters in the power system, and can also be determined by sorting or setting a corresponding target high voltage value, which will not be elaborated here.

[0155] The above are some implementation methods of a power system provided by the embodiments of this application. Based on this, this application also provides a corresponding inverter control method in a power system.

[0156] An inverter control method in a power system, wherein the inverter includes at least a DC-DC converter circuit and an inverter circuit, the input terminal of the DC-DC converter circuit is connected to at least one DC string, the output terminals of each DC-DC converter circuit are connected in parallel to the input terminal of the inverter circuit, the DC string includes a power converter, the power converter includes a DC input terminal and a DC output terminal, the DC input terminal is used to connect to a DC power supply, and the DC output terminals of each power converter in the DC string are connected in series to the input terminal of the DC-DC converter circuit;

[0157] The inverter is configured to send a voltage control command to at least one of the power converters in the first DC string in response to a string voltage mismatch in at least one of the DC strings, so that the power converter adjusts the output voltage of the DC output terminal in response to the received voltage control command.

[0158] Wherein, the first DC string is: the DC string with the largest and / or smallest output voltage among all the DC strings; the voltage control command includes: a voltage reduction command for the power converter in the DC string with the largest output voltage, and / or a voltage increase command for the power converter in the DC string with the smallest output voltage.

[0159] Based on the above-mentioned inverter control method in a power system, when the inverter determines that there is a DC string with a voltage mismatch in the system, it will send a voltage control command to the first DC string in the system, and by issuing a command to lower the output voltage of the DC string with the largest output voltage in the system, and / or issuing a command to raise the output voltage of the DC string with the smallest output voltage in the system. In this way, the problem of triggering derating and generating power loss caused by excessive voltage difference between the output voltage of the DC string with voltage mismatch and the DC bus voltage is reduced, as well as the problem of large thermal stress on the DC conversion circuit is reduced.

[0160] In one possible implementation, before sending the voltage control command to at least one of the power converters in the first DC string, the method further includes:

[0161] Determine the adjustment range of a specified electrical parameter of at least one of the power converters in the first DC string;

[0162] Based on the adjustment range, a voltage control command is generated.

[0163] Optionally, before generating the voltage control command based on the adjustment amplitude, the method further includes:

[0164] Determine the current allowable adjustment range of at least one of the power converters in the first DC string;

[0165] If the adjustment amplitude does not exceed the adjustment range, then the voltage control command is generated based on the adjustment amplitude.

[0166] Optionally, if the adjustment amplitude exceeds the adjustment range, the transmission of the voltage control command is paused, or a first command is generated based on the current allowable adjustment range of the power converter and sent to the power converter.

[0167] Optionally, if the adjustment amplitude exceeds the adjustment range, and the first DC string only includes the DC string with the largest output voltage among all the DC strings, the DC string with the smallest output voltage among all the DC strings is taken as the new first DC string, and the adjustment amplitude of the specified electrical parameters of at least one of the power converters of the first DC string and subsequent steps are executed.

[0168] If the first DC string only includes the DC string with the smallest output voltage among all the DC strings, the DC string with the largest output voltage among all the DC strings is taken as the new first DC string, and the adjustment range of the specified electrical parameters of at least one of the power converters of the first DC string and subsequent steps are performed.

[0169] If the first DC string only includes the DC string with the largest and smallest output voltage among all the DC strings, then the transmission of the voltage control command is suspended, or a first command is generated based on the current allowable adjustment range of the power converter and sent to the power converter.

[0170] Optionally, determining the adjustment range of a specified electrical parameter of at least one of the power converters in the first DC string includes,

[0171] Determine the voltage difference between the output voltage and the bus voltage of the DC string that has a voltage mismatch; calculate the voltage difference and subtract a preset voltage difference threshold to obtain the total voltage adjustment range;

[0172] Based on the total voltage adjustment range, determine the voltage adjustment range or current adjustment range of each power converter in the first DC string.

[0173] Optionally, determining the adjustment range of a specified electrical parameter of at least one of the power converters in the first DC string includes:

[0174] Based on the output voltage of each DC string connected to the inverter, determine the total adjustment range of the voltage for increasing the voltage of the DC string with the smallest output voltage, or determine the total adjustment range of the voltage for decreasing the voltage of the DC string with the largest output voltage.

[0175] Based on the total voltage adjustment range, determine the voltage adjustment range or current adjustment range of each power converter in the first DC string.

[0176] Optionally, after executing the step of sending the voltage control command to the power converter, the method further includes: if a string voltage mismatch still exists, returning to execute the step of determining the adjustment range of a specified electrical parameter of at least one of the power converters of the first DC string and subsequent steps.

[0177] Optionally, determining the voltage regulation magnitude of each power converter in the first DC string based on the total regulation magnitude of the voltage includes:

[0178] When the first DC string is the DC string with the largest or smallest output voltage among all the DC strings, the total adjustment amplitude is evenly distributed to the target amplitude of the voltage obtained by each power converter in the first DC string, and the target amplitude or the amplitude obtained by multiplying the target amplitude by a preset ratio is determined as the adjustment amplitude of the voltage of the power converter in the first DC string.

[0179] When the first DC string has the largest and smallest output voltage among all the DC strings, the total adjustment amplitude is allocated to each first DC string to obtain the adjustment sub-amplitude of the voltage allocated to each first DC string; the adjustment sub-amplitude is evenly distributed to each power converter in the corresponding first DC string to obtain the target voltage amplitude; the target amplitude or the amplitude obtained by multiplying the target amplitude by a preset voltage ratio is determined as the adjustment amplitude of the power converter voltage in the first DC string; for the DC string with the largest output voltage, the target voltage amplitude is negative, and for the DC string with the smallest output voltage, the target voltage amplitude is positive.

[0180] Optionally, the method further includes:

[0181] With the power converter power remaining constant, the target amplitude of the power converter current is determined based on the target amplitude of the power converter voltage. The target amplitude of the current or the amplitude obtained by multiplying the target amplitude of the current by a preset current ratio is used as the adjustment amplitude of the power converter current in the first DC string. For the DC string with the largest output voltage, the target amplitude of the current is positive, and for the DC string with the smallest output voltage, the target amplitude of the current is negative.

[0182] Optionally, determining the adjustment range of a specified electrical parameter of at least one of the power converters in the first DC string includes:

[0183] For DC strings with the largest output voltage, a negative voltage preset value is used as the adjustment range of the power converter voltage, or a positive current preset value is used as the adjustment range of the power converter current.

[0184] For the DC string with the smallest output voltage, a positive voltage preset value is taken as the adjustment range of the power converter voltage, or a negative current preset value is taken as the adjustment range of the power converter current; the voltage preset value and the current preset value are both values ​​used to achieve repeated adjustment of the power converter.

[0185] Optionally, generating the voltage control command based on the adjustment amplitude includes:

[0186] For the DC string with the largest output voltage among the DC strings, a voltage reduction command is generated to indicate the step-down of the power converter based on the voltage adjustment range, or a voltage reduction command is generated to indicate the step-up of the power converter based on the current adjustment range.

[0187] For the DC string with the smallest output voltage among all the DC strings, a voltage increase command is generated based on the voltage adjustment range to indicate the power converter to boost the voltage, or a voltage increase command is generated based on the current adjustment range to indicate the power converter to reduce the current.

[0188] Furthermore, this application also provides a power converter control method in a power system, the power system comprising: an inverter and at least one DC string; the inverter comprising at least one DC conversion circuit and an inverter circuit, the input terminal of the DC conversion circuit being connected to at least one of the DC strings, the output terminals of each DC conversion circuit being connected in parallel to the input terminal of the inverter circuit, the DC string comprising a power converter, the power converter comprising a DC input terminal and a DC output terminal, the DC input terminal being used to connect to a DC power supply, and the DC output terminals of each power converter in the DC string being connected in series to the input terminal of the DC conversion circuit;

[0189] The power converter is configured to adjust the output voltage of its DC output terminal in response to a voltage control command received from the inverter. When the output voltage of the first DC string containing the power converter is at its maximum, the voltage control command is a voltage reduction command sent by the inverter to the power converter in response to a voltage mismatch in at least one of the DC strings. When the output voltage of the first DC string containing the power converter is at its minimum, the voltage control command is a voltage increase command sent by the inverter to the power converter in response to a voltage mismatch in at least one of the DC strings.

[0190] Based on the above-described power converter control method in a power system, the power converter receives voltage control commands from the inverter and adjusts the output voltage of the series-connected DC strings. This reduces the problems of generation losses caused by excessive voltage difference between the output voltage of the DC strings and the DC bus voltage due to voltage mismatch, as well as the problem of excessive thermal stress on the DC conversion circuit.

[0191] In one possible implementation, adjusting the output voltage at the DC output terminal in response to a voltage control command received from the inverter includes:

[0192] In response to the received voltage control command, if the adjustment range of the specified electrical parameter does not exceed the current allowable adjustment range of the power converter, the output voltage is adjusted based on the adjustment range of the specified electrical parameter; if the adjustment range of the specified electrical parameter exceeds the current allowable adjustment range of the electrical parameter of the power converter, the output voltage is adjusted to the maximum adjustable voltage value according to the adjustment direction indicated by the voltage control command.

[0193] This application embodiment also provides an inverter, including: at least one DC-DC converter circuit and an inverter circuit, wherein the input terminal of the DC-DC converter circuit is connected to at least one DC string, and the output terminals of each DC-DC converter circuit are connected in parallel to the input terminal of the inverter circuit, and the DC string includes a power converter; the inverter is used to send a voltage control command to at least one power converter in a first DC string in response to a string voltage mismatch in at least one DC string; the first DC string is: the DC string with the largest and / or the smallest output voltage among all DC strings; the voltage control command includes: a voltage down adjustment command for the power converter in the DC string with the largest output voltage, and / or a voltage up adjustment command for the power converter in the DC string with the smallest output voltage.

[0194] This application also provides a power converter, which includes a DC input terminal and a DC output terminal. The DC input terminal is used to connect to a DC power supply, and the DC output terminals of each power converter in the DC string are connected in series to the input terminal of the DC conversion circuit of the inverter.

[0195] The power converter is used to adjust the output voltage of the DC output terminal in response to the voltage control command sent by the received inverter. When the string output voltage of the first DC string where the power converter is located is at its maximum, the voltage control command is a voltage reduction command sent by the inverter to the power converter in response to the string voltage mismatch of at least one DC string. When the string output voltage of the first DC string where the power converter is located is at its minimum, the voltage control command is a voltage increase command sent by the inverter to the power converter in response to the string voltage mismatch of at least one DC string.

[0196] This application also provides corresponding devices and computer storage media for implementing the solutions provided in this application.

[0197] The device includes a memory and a processor. The memory is used to store instructions or code, and the processor is used to execute the instructions or code to enable the device to perform an inverter control method or a power converter control method in a power system according to any embodiment of this application.

[0198] The computer storage medium stores code. When the code is run, the device running the code implements an inverter control method or a power converter control method in a power system according to any embodiment of this application.

[0199] In the embodiments of this application, the terms "first" and "second" (if they exist) are used only as name identifiers and do not represent the order of first and second.

[0200] As can be seen from the above description of the embodiments, those skilled in the art can clearly understand that all or part of the steps in the methods of the above embodiments can be implemented by means of software plus a general-purpose hardware platform. Based on this understanding, the technical solution of this application can be embodied in the form of a software product. This computer software product can be stored in a storage medium, such as a read-only memory (ROM) / RAM, magnetic disk, optical disk, etc., including several instructions to cause a computer device (which may be a personal computer, a server, or a network communication device such as a router) to execute the methods described in various embodiments or some parts of the embodiments of this application.

[0201] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on its differences from other embodiments. In particular, the apparatus embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0202] The above description is merely an exemplary implementation of this application and is not intended to limit the scope of protection of this application.

Claims

1. An electric power system, characterized by The application relates to an inverter and at least one DC string. The inverter comprises at least one DC conversion circuit and an inversion circuit, the input end of the DC conversion circuit is connected to the at least one DC string, the output end of each DC conversion circuit is connected in parallel to the input end of the inversion circuit, the DC string comprises a power converter, the power converter comprises a DC input end and a DC output end, the DC input end is used for connecting a DC power supply, and the DC output end of each power converter in the DC string is connected in series to the input end of the DC conversion circuit. The inverter is used for sending a voltage control instruction to at least one power converter in a first DC string in response to the occurrence of a string voltage mismatch in the at least one DC string, the first DC string is a DC string with the maximum output voltage and / or the minimum output voltage in each DC string, the voltage control instruction comprises a voltage down-regulation instruction for the power converter in the DC string with the maximum output voltage and / or a voltage up-regulation instruction for the power converter in the DC string with the minimum output voltage. The power converter is used for adjusting the output voltage of the DC output end in response to the received voltage control instruction. Before the voltage control instruction is sent to at least one power converter in the first DC string, the inverter is further used for:

2. The power system of claim 1, wherein, determining the adjustment range of the specified electrical parameter of at least one power converter in the first DC string; generating the voltage control instruction based on the adjustment range. Before the voltage control instruction is generated based on the adjustment range, the inverter is further used for:

3. The power system of claim 2, wherein, determining the current adjustment range of at least one power converter in the first DC string; if the adjustment range does not exceed the adjustment range, the voltage control instruction is generated based on the adjustment range. If the adjustment range exceeds the adjustment range, the inverter is further used for:

4. The power system of claim 3, wherein, suspending the sending of the voltage control instruction, or generating a first instruction based on the current adjustment range of the power converter and sending the first instruction to the power converter. If the adjustment range exceeds the adjustment range, the inverter is further used for: if the first DC string only comprises the DC string with the maximum output voltage in each DC string, taking the DC string with the minimum output voltage in each DC string as a new first DC string, and performing the determination of the adjustment range of the specified electrical parameter of at least one power converter in the first DC string and the subsequent steps.

5. The power system of claim 3, wherein, If the first DC string only comprises the DC string with the minimum output voltage in each DC string, taking the DC string with the maximum output voltage in each DC string as a new first DC string, and performing the determination of the adjustment range of the specified electrical parameter of at least one power converter in the first DC string and the subsequent steps. ​ In a case where the first DC string includes only the DC string with the maximum output voltage and the DC string with the minimum output voltage among the DC strings, the voltage control instruction is suspended, or a first instruction is generated based on a current adjustment range allowed by the power converter and sent to the power converter.

6. The power system of claim 2, wherein, The inverter is specifically configured to: determine a voltage difference between an output voltage of a DC string with a string voltage mismatch and a bus voltage; calculate the voltage difference minus a preset voltage difference threshold to obtain a total voltage adjustment range; determine a voltage adjustment range or a current adjustment range of each power converter in the first DC string based on the total voltage adjustment range.

7. The power system of claim 2, wherein, The inverter is specifically configured to: determine a total voltage adjustment range for voltage up-regulation of the DC string with the minimum output voltage or for voltage down-regulation of the DC string with the maximum output voltage among the DC strings connected to the inverter based on the output voltages of the DC strings; determine a voltage adjustment range or a current adjustment range of each power converter in the first DC string based on the total voltage adjustment range.

8. The power system of any of claims 2-7, wherein, The inverter is further configured to, after the voltage control instruction is sent to the power converter, if the string voltage mismatch still exists, return to the step of determining the adjustment range of the specified electrical parameter of the at least one power converter in the first DC string and subsequent steps.

9. The power system of claim 6 or 7, characterized in that, The inverter is specifically configured to: in a case where the first DC string is the DC string with the maximum output voltage or the minimum output voltage among the DC strings, divide the total adjustment range equally to each power converter in the first DC string to obtain a target voltage adjustment range, and determine the target voltage adjustment range or a range obtained by multiplying the target voltage adjustment range by a preset proportion as the voltage adjustment range of the power converter in the first DC string; in a case where the first DC string is the DC string with the maximum output voltage and the DC string with the minimum output voltage among the DC strings, divide the total adjustment range to each first DC string to obtain an adjustment sub-range of the voltage allocated to each first DC string, divide the adjustment sub-range equally to each power converter in the corresponding first DC string to obtain a target voltage adjustment range, and determine the target voltage adjustment range or a range obtained by multiplying the target voltage adjustment range by a preset voltage proportion as the voltage adjustment range of the power converter in the first DC string, wherein the target voltage adjustment range of the DC string with the maximum output voltage is negative, and the target voltage adjustment range of the DC string with the minimum output voltage is positive.

10. The power system of claim 9, wherein, The inverter is further configured to, In the case that the power converter power is constant, the target amplitude of the power converter current is determined according to the target amplitude of the power converter voltage, the target amplitude of the current or the amplitude of the current multiplied by a preset current ratio is determined as the adjustment amplitude of the power converter current in the first DC group string, for the DC group string with the maximum group string output voltage, the target amplitude of the current takes a positive value, and for the DC group string with the minimum group string output voltage, the target amplitude of the current takes a negative value.

11. The power system of claim 3, wherein, The determination of the adjustment amplitude of the specified electrical parameter of at least one of the power converters in the first DC group string, the inverter, in particular, For the DC group string with the maximum group string output voltage, a negative voltage preset value is taken as the adjustment amplitude of the power converter voltage, or a positive current preset value is taken as the adjustment amplitude of the power converter current; For the DC group string with the minimum group string output voltage, a positive voltage preset value is taken as the adjustment amplitude of the power converter voltage, or a negative current preset value is taken as the adjustment amplitude of the power converter current; the voltage preset value and the current preset value are both values for realizing repeated adjustment of the power converter.

12. The power system of claim 3, wherein, The generation of the voltage control instruction based on the adjustment amplitude includes: For the DC group string with the maximum output voltage in each of the DC group strings, a voltage down instruction indicating voltage reduction of the power converter is generated based on the adjustment amplitude of the voltage, or a voltage down instruction indicating current increase of the power converter is generated based on the adjustment amplitude of the current; For the DC group string with the minimum output voltage in each of the DC group strings, a voltage up instruction indicating voltage increase of the power converter is generated based on the adjustment amplitude of the voltage, or a voltage up instruction indicating current decrease of the power converter is generated based on the adjustment amplitude of the current.

13. The power system according to claim 1, wherein The power converter is specifically configured to, in response to the received voltage control instruction, if the adjustment amplitude of the specified electrical parameter does not exceed the current allowed adjustment range of the power converter, adjust the output voltage based on the adjustment amplitude of the specified electrical parameter; If the adjustment amplitude of the specified electrical parameter exceeds the current allowed electrical parameter adjustment range of the power converter, the output voltage is adjusted to the maximum adjustable voltage value in the adjustment direction indicated by the voltage control instruction.

14. The power system according to claim 1, wherein The sending of the voltage control instruction to at least one of the power converters in the first DC group string in response to the occurrence of group string voltage mismatch in at least one of the DC group strings includes: In response to the absolute value of the voltage difference between the input voltage of the DC conversion circuit corresponding to at least one of the DC group strings and the DC bus voltage exceeding a voltage difference threshold value, the voltage control instruction is sent to at least one of the power converters in the first DC group string; And / or, In response to the temperature of the DC conversion circuit corresponding to at least one of the DC group strings exceeding a preset temperature threshold value, the voltage control instruction is sent to at least one of the power converters in the first DC group string.

15. The power system of claim 5 or 7, wherein, The first instruction is an electrical parameter adjustment range set based on the endpoint value of the current allowable adjustment range of the power converter.

16. A method of inverter control in a power system, characterized by, The inverter includes at least a DC-DC converter circuit and an inverter circuit. The input terminal of the DC-DC converter circuit is connected to at least one DC string. The output terminals of each DC-DC converter circuit are connected in parallel to the input terminal of the inverter circuit. The DC string includes a power converter. The power converter includes a DC input terminal and a DC output terminal. The DC input terminal is used to connect to a DC power supply. The DC output terminals of each power converter in the DC string are connected in series to the input terminal of the DC-DC converter circuit. The inverter is configured to send a voltage control command to at least one of the power converters in the first DC string in response to a string voltage mismatch in at least one of the DC strings, so that the power converter adjusts the output voltage of the DC output terminal in response to the received voltage control command. Wherein, the first DC string is: the DC string with the largest and / or smallest output voltage among all the DC strings; the voltage control command includes: a voltage reduction command for the power converter in the DC string with the largest output voltage, and / or a voltage increase command for the power converter in the DC string with the smallest output voltage.

17. A method of controlling a power converter in a power system, characterized by, The power system includes: an inverter and at least one DC string; the inverter includes at least one DC conversion circuit and an inverter circuit, the input terminal of the DC conversion circuit is connected to at least one of the DC strings, the output terminals of each DC conversion circuit are connected in parallel to the input terminal of the inverter circuit, the DC string includes a power converter, the power converter includes a DC input terminal and a DC output terminal, the DC input terminal is used to connect to a DC power supply, and the DC output terminals of each power converter in the DC string are connected in series to the input terminal of the DC conversion circuit; The power converter is configured to adjust the output voltage of its DC output terminal in response to a voltage control command received from the inverter. When the output voltage of the first DC string containing the power converter is at its maximum, the voltage control command is a voltage reduction command sent by the inverter to the power converter in response to a voltage mismatch in at least one of the DC strings. When the output voltage of the first DC string containing the power converter is at its minimum, the voltage control command is a voltage increase command sent by the inverter to the power converter in response to a voltage mismatch in at least one of the DC strings.

18. An inverter, characterized by include: At least one DC converter circuit and an inverter circuit are provided, wherein the input terminal of the DC converter circuit is connected to at least one DC string, and the output terminals of each DC converter circuit are connected in parallel to the input terminal of the inverter circuit, and the DC string includes a power converter. The inverter is configured to send a voltage control command to at least one power converter in a first DC string in response to a string voltage mismatch occurring in at least one of the DC strings; the first DC string is the DC string with the largest and / or smallest string output voltage among the DC strings; the voltage control command includes: a voltage reduction command for the power converter in the DC string with the largest string output voltage, and / or a voltage increase command for the power converter in the DC string with the smallest string output voltage.

19. A power converter, comprising: The power converter includes a DC input terminal and a DC output terminal. The DC input terminal is used to connect to a DC power supply, and the DC output terminal of each power converter is connected in series to the input terminal of the DC conversion circuit of the inverter. The power converter is configured to adjust the output voltage of its DC output terminal in response to a voltage control command received from the inverter. When the output voltage of the first DC string containing the power converter is at its maximum, the voltage control command is a voltage reduction command sent by the inverter to the power converter in response to a voltage mismatch in at least one of the DC strings. When the output voltage of the first DC string containing the power converter is at its minimum, the voltage control command is a voltage increase command sent by the inverter to the power converter in response to a voltage mismatch in at least one of the DC strings.

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