A power conversion system and a control method and controller thereof

Abstract

The application provides a power conversion system, a control method and a controller thereof, and belongs to the technical field of power conversion systems. The system comprises at least two first power conversion devices and one second power conversion device. The second power conversion device determines at least one slow start execution device in each first power conversion device, controls the slow start execution device to perform a slow start operation, and controls the main switch of the remaining first power conversion device to be closed with zero voltage difference. Since the number of slow start execution devices is less than the total number of first power conversion devices, and the slow start execution devices are different in each system starting period, the frequency of the first power conversion device being closed with voltage difference in the whole life cycle of the system is significantly reduced, the service life is effectively prolonged, the concentrated life loss of the power conversion system can be distributed to the main switches of all first power conversion devices in the time dimension, and the overall service life is significantly prolonged from the system level.

Description

Technical Field

[0001] This application relates to the field of power conversion system technology, specifically to a power conversion system and its control method and controller. Background Technology

[0002] In the field of power conversion technology, there are often situations where power conversion devices are cascaded to transmit electrical energy. For example, a power conversion system includes a first power conversion device and a second power conversion device. The first power conversion device is connected to the second power conversion device through a switch, and the two devices can be connected when the switch is closed.

[0003] However, in existing applications, the two ends of the switch still need to withstand a significant voltage difference at the moment of closing. This switch closing operation with voltage difference will generate electrical stress impact on the switch contacts, causing contact erosion and seriously affecting the service life of the switch and the power conversion equipment to which the switch belongs. Summary of the Invention

[0004] In view of this, this application aims to provide a power conversion system and its control method, controller and power conversion equipment to solve the problem in the related art that the switch closing with differential pressure seriously affects the service life of the switch and its associated power conversion equipment.

[0005] In a first aspect, this application provides a power conversion system, comprising: at least two first power conversion devices and one second power conversion device, wherein... The output side of each of the first power conversion devices is connected to the input side of the second power conversion device through a corresponding main switch, and each main switch is connected in parallel with a soft-start circuit; The second power conversion device is configured to perform a system startup operation during the current system startup cycle, the system startup operation including: At least one soft start execution device is determined in each of the first power conversion devices, the number of soft start execution devices is less than the total number of the first power conversion devices, and the soft start execution device of the current system startup cycle is different from the soft start execution device of the previous system startup cycle. The main switches and soft-start circuits of each of the aforementioned soft-start execution devices are controlled to perform soft-start operations in order to establish a target operating voltage on the input side of the second power conversion device; The control unit adjusts the output voltage of the other first power conversion devices besides the soft start execution device according to the target operating voltage, and closes its main switch when its output voltage reaches the target operating voltage.

[0006] In one optional implementation, the second power conversion device is specifically configured as follows: Obtain the cumulative number of times each of the first power conversion devices performs the soft-start operation; Based on the cumulative number of executions corresponding to each of the first power conversion devices, at least one soft-start execution device is determined among the first power conversion devices.

[0007] In one optional implementation, the second power conversion device is specifically configured as follows: The power conversion device with the fewest cumulative execution counts will be selected as the soft-start execution device.

[0008] In one alternative implementation, the first power conversion device with the fewest cumulative execution times includes multiple devices; The second power conversion device is specifically configured as follows: Choose any one of the first power conversion devices with the fewest cumulative execution counts as the soft start execution device; Alternatively, according to a preset polling rule, a soft-start execution device can be selected from among the multiple first power conversion devices with the fewest cumulative execution times.

[0009] In one alternative implementation, each of the first power conversion devices corresponds to a unique device code; The second power conversion device is specifically configured as follows: Among the multiple first power conversion devices with the fewest cumulative execution times, the first power conversion device with the smallest device code is determined as the soft start execution device.

[0010] In one optional implementation, the second power conversion device is specifically configured as follows: Verify whether each of the first power conversion devices has been marked as having performed a soft start operation; If at least one of the first power conversion devices is marked as not having performed a soft start operation, a soft start execution device is determined from the first power conversion devices marked as not having performed a soft start operation, and the soft start execution device is marked as having performed a soft start operation; If each of the first power conversion devices is marked as having performed a soft start operation, then each of the first power conversion devices is marked as not having performed a soft start operation, and the soft start execution device is determined from among the first power conversion devices marked as not having performed a soft start operation.

[0011] In one optional implementation, the second power conversion device is specifically configured as follows: According to the preset soft start sequence, the first power conversion device among the first power conversion devices that have not performed a soft start operation is designated as the soft start execution device.

[0012] In one optional implementation, the second power conversion device is specifically configured to send a soft-start command to the soft-start execution device; The soft-start execution device is specifically configured as follows: In response to the soft-start command, the target operating voltage is output, and its own soft-start circuit is closed to increase the voltage on the input side of the second power conversion device; When the voltage deviation between the input side of the second power conversion device and the target operating voltage is within a preset deviation range, the device controls its main switch to close and its soft-start circuit to disconnect.

[0013] In one optional implementation, the first power conversion device includes a DC / DC conversion circuit, and the second power conversion device includes a DC / AC conversion circuit.

[0014] In one optional implementation, one side of the DC / DC conversion circuit is connected to the input side of the first power conversion device, and the other side of the DC / DC conversion circuit is connected to the DC side of the DC / AC conversion circuit through a corresponding main switch. The soft-start circuit is connected in parallel across the two ends of the main switch. The AC side of the DC / AC conversion circuit is connected to the output side of the second power conversion device.

[0015] Secondly, this application provides a control method for a power conversion system, applied to a second power conversion device in the power conversion system, the method comprising: Execute a system startup operation during the current system startup cycle. The system startup operation includes: At least one soft-start execution device is determined in each of the first power conversion devices of the power conversion system; The number of the soft start execution devices is less than the total number of the first power conversion devices, and the soft start execution devices in the current system startup cycle are different from the soft start execution devices in the previous system startup cycle. The power conversion system includes at least two first power conversion devices and one second power conversion device. The output side of each first power conversion device is connected to the input side of the second power conversion device through a corresponding main switch, and each main switch is connected in parallel with a soft start circuit. The main switches and soft-start circuits of each of the aforementioned soft-start execution devices are controlled to perform soft-start operations in order to establish a target operating voltage on the input side of the second power conversion device; The control unit adjusts the output voltage of the other first power conversion devices besides the soft start execution device according to the target operating voltage, and closes its main switch when its output voltage reaches the target operating voltage.

[0016] In one optional implementation, at least one soft-start execution device is determined in each of the first power conversion devices of the power conversion system, including: Obtain the cumulative number of times each first power conversion device in the power conversion system performs a soft-start operation; Based on the cumulative number of executions corresponding to each of the first power conversion devices, at least one soft-start execution device is determined among the first power conversion devices.

[0017] In one optional implementation, determining at least one soft-start execution device among the first power conversion devices based on the cumulative execution count corresponding to each of the first power conversion devices includes: Choose any one of the first power conversion devices with the fewest cumulative execution counts as the soft start execution device; Alternatively, according to a preset polling rule, a soft-start execution device can be selected from among the multiple first power conversion devices with the fewest cumulative execution times.

[0018] In one optional implementation, at least one soft-start execution device is determined in each of the first power conversion devices of the power conversion system, including: Verify whether each of the first power conversion devices has been marked as having performed a soft start operation; If at least one of the first power conversion devices is marked as not having performed a soft start operation, a soft start execution device is determined from the first power conversion devices marked as not having performed a soft start operation, and the soft start execution device is marked as having performed a soft start operation; If each of the first power conversion devices is marked as having performed a soft start operation, then each of the first power conversion devices is marked as not having performed a soft start operation, and the soft start execution device is determined from among the first power conversion devices marked as not having performed a soft start operation.

[0019] In one alternative implementation, determining the soft-start execution device among the first power conversion devices that have not performed soft-start operation includes: According to the preset soft start sequence, the first power conversion device among the first power conversion devices that have not performed a soft start operation is designated as the soft start execution device.

[0020] Thirdly, this application provides a controller including a memory, a processor, and a computer program stored in the memory and executed by the processor, wherein the processor executes the computer program to implement the steps of the power conversion system control method provided in any embodiment of the second aspect of this application.

[0021] Based on the above, the power conversion system provided in this application includes at least two first power conversion devices and one second power conversion device. The second power conversion device determines at least one soft-start execution device among the first power conversion devices and controls each soft-start execution device to perform a soft-start operation to establish a target operating voltage on the input side of the second power conversion device. Then, it controls the remaining first power conversion devices other than the soft-start execution device to close their main switches when their output voltage reaches the target operating voltage, achieving zero-differential closing. Since the number of soft-start execution devices is less than the total number of first power conversion devices, and the soft-start execution device in the current system startup cycle is different from the soft-start execution device in the previous system startup cycle, the frequency of differential closing is significantly reduced for any first power conversion device throughout the entire life cycle of the power conversion system. This extends the interval time of contact erosion caused by differential closing, thereby effectively extending the service life of each first power conversion device. Compared with the related technology that simultaneously controls each first power conversion device to perform a soft-start operation, this solution can distribute the concentrated life loss over time to the main switches of all first power conversion devices, thereby significantly extending the overall service life at the system level. Attached Figure Description

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

[0023] Figure 1 This is a schematic diagram of a power conversion system provided in an embodiment of this application.

[0024] Figure 2 This is a flowchart of a power conversion system control method provided in an embodiment of this application.

[0025] Figure 3 This is a structural block diagram of a controller provided in an embodiment of this application. Detailed Implementation

[0026] 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 skilled in the art without creative effort are within the scope of protection of this application.

[0027] As mentioned earlier, in the field of power conversion technology, there are often situations where power conversion devices are cascaded to transmit electrical energy. For example, a power conversion system includes a first power conversion device and a second power conversion device. The first power conversion device is connected to the second power conversion device through a switch. Closing the switch enables the first power conversion device to be connected to the second power conversion device, and correspondingly, opening the switch enables the first power conversion device to be disconnected from the second power conversion device.

[0028] However, in existing applications, the two ends of the switch still need to withstand a significant voltage difference at the moment of closing. This switch closing operation with voltage difference will generate electrical stress impact on the switch contacts, causing contact erosion and seriously affecting the service life of the switch and the power conversion equipment to which the switch belongs.

[0029] To address the aforementioned issues, this application provides a power conversion system comprising multiple first power conversion devices and one second power conversion device. By controlling each first power conversion device to execute a rotating, selective soft-start control mechanism, the soft-start operation with differential voltage closing during the power conversion system startup process is rotated, allocated, and scheduled. This effectively avoids the problem of synchronous concentrated loss of lifespan across all main switches while ensuring the original soft-start safety. The lifespan loss is distributed across time and devices, thus solving the problem of synchronous loss of main switch lifespan during each startup of multiple parallel power conversion devices, which limits the overall system lifespan. This achieves the goal of extending the operating lifespan of individual first power conversion devices and the overall system.

[0030] Based on the above core concept, embodiments of this application provide a power conversion system, including at least two first power conversion devices and one second power conversion device, combined with... Figure 1 As shown, taking n first power conversion devices as an example, namely first power conversion device A1, first power conversion device A2... first power conversion device An and second power conversion device B.

[0031] Each first power conversion device is equipped with a main switch and a soft-start circuit. The output side of each first power conversion device is connected to the input side of the second power conversion device through the corresponding main switch. Furthermore, each main switch is connected in parallel with a soft-start circuit, which includes a soft-start switch and a soft-start resistor connected in series. The second power conversion device is also communicatively connected to each first power conversion device and can send control commands to each first power conversion device to control the operation of each first power conversion device.

[0032] Combination Figure 1As shown, each of the first and second power conversion devices includes a power conversion circuit for realizing electrical power conversion. Taking the first power conversion device A1 as an example, the positive output terminal of the power conversion circuit a1 serves as the positive output terminal DC1+ of the first power conversion device A1, and is connected to a common DC bus positive terminal Bus+ via the main switch K12. The soft-start circuit, which is formed by the soft-start switch K11 and the soft-start resistor R11 connected in series, is connected in parallel with the main switch K12. The negative output terminal of the power conversion circuit a1 serves as the negative output terminal DC1- of the first power conversion device A1, and is connected to the common DC bus negative terminal Bus-. The connection methods of other first power conversion devices with the main switch, soft-start circuit, and DC bus can refer to the above content. Figure 1 As shown, details will not be elaborated here. The DC bus is connected to the input side of the second power conversion device B; of course, this DC bus can also be considered as the input side of the second power conversion device B. In practical applications, the output side of the second power conversion device B can be connected to downstream loads, such as the AC power grid, which will not be detailed here.

[0033] It should be noted that in practical applications, there are multiple optional integration methods among the main switch, soft-start circuit, first power conversion device, and second power conversion device. In one optional embodiment, the main switch and soft-start circuit can be integrated with the first power conversion device to improve the convenience of the first power conversion device controlling the operation of its corresponding main switch and soft-start circuit. In another optional embodiment, both the main switch and soft-start circuit are integrated with the second power conversion device. In yet another optional embodiment, the main switch and soft-start circuit can be independently integrated into the same device, independent of both the first and second power conversion devices, i.e., providing a device focused on configuring the main switch and soft-start circuit. Of course, other integration methods are also possible, which will not be detailed here, and are also within the scope of protection of this application as long as they do not exceed the core concept of this application.

[0034] As an optional implementation, the power conversion circuit in the first power conversion device may include a DC / DC conversion circuit, and the power conversion circuit in the second power conversion circuit may be a DC / AC conversion circuit. In practical applications, one side of the DC / DC conversion circuit is connected to the input side of the first power conversion device, and the other side of the DC / DC conversion circuit is connected to the DC side of the DC / AC conversion circuit through a corresponding main switch. The soft-start circuit is connected in parallel across the two ends of the main switch, and the AC side of the DC / AC conversion circuit is connected to the output side of the second power conversion device and further connected to the aforementioned downstream load.

[0035] Combination Figure 1As shown, in one optional implementation, the second power conversion device further includes a controller b2. This controller b2 is communicatively connected to each of the first power conversion devices (not shown in the figure), and is configured to execute the system startup control logic described in this application, including selecting a soft-start execution device and sending control commands. In another optional implementation, a controller (not shown in the figure) can also be integrated into the first power conversion device. This controller is communicatively connected to the other first and second power conversion devices, and executes the system startup logic described in this application through the controller integrated into the first power conversion device. Alternatively, an independent system controller (not shown in the figure) can be provided outside of each of the first and second power conversion devices. This system controller can communicate with each of the first and second power conversion devices to execute the system startup control logic provided in this application. The specific system startup process will be discussed later and will not be detailed here.

[0036] In this application embodiment, each startup process of the power conversion system is defined as a system startup cycle. Based on this, the currently executing startup process corresponds to the current system startup cycle, and the previous startup process corresponds to the previous system startup cycle.

[0037] Based on the above, the second power conversion device B is configured to perform a system startup operation in the current system cycle, which may specifically include the following steps.

[0038] First, at least one soft-start execution device is determined among each of the first power conversion devices. The rule for determining the soft-start execution device is that the number of determined soft-start execution devices is less than the total number of first power conversion devices, that is, only a portion of the first power conversion devices are used as soft-start execution devices, and the soft-start execution device in the current system startup cycle is different from the soft-start execution device in the previous system startup cycle. As will be seen in the following content, the soft-start execution device defined in this embodiment refers to the first power conversion device that, in any system startup cycle, is selected by the second power conversion device and needs to first establish the target operating voltage on the input side of the second power conversion device through its own soft-start circuit.

[0039] In one optional implementation, the second power conversion device B first obtains the cumulative number of times each of the first power conversion devices has performed a soft-start operation, and determines at least one soft-start execution device among the first power conversion devices based on the cumulative number of executions corresponding to each first power conversion device. For example, the controller b2 can maintain a counter list in memory, corresponding to each of the first power conversion devices. Whenever a first power conversion device is successfully selected and completes the soft-start task, its corresponding counter is incremented by one. When a new round of selection is performed, the controller b2 reads the counter values ​​of all first power conversion devices, i.e., the cumulative number of executions. Obtaining the cumulative number of executions of each first power conversion device can provide a quantifiable and traceable data basis for achieving long-term, balanced lifetime loss amortization, making the selection strategy of the soft-start execution device more objective and evidence-based. In practical applications, the basic execution flow of the soft-start operation described in this embodiment is as follows: close the soft-start switch, so that the current output by the power conversion circuit in the first power conversion device charges the downstream DC bus through the soft-start resistor until the working voltage on the input side of the second power conversion device B meets the requirements, then close the main switch in the soft-start circuit and open the soft-start switch. The specific execution process will be detailed in the following process.

[0040] Understandably, in order to make the number of times each first power conversion device performs a soft start operation more evenly, in the current system startup cycle, the first power conversion device with the fewest cumulative execution times can be selected as the soft start execution device. This setting can ensure that during long-term operation, the number of soft start operations undertaken by all first power conversion devices in the power conversion system tends to be consistent, maximizing the uniformity of lifetime loss distribution.

[0041] Combination Figure 1 In the power conversion system shown, during the current system startup cycle, the first power conversion device A1 has a cumulative startup count of 5 times, and the first power conversion devices A2 and A3 have a cumulative startup count of 4 times. According to the aforementioned rules, the first power conversion devices A2 and A3 can be used as soft start execution devices.

[0042] It is understandable that the reason why all front-stage power conversion devices in a power conversion system experience concentrated and synchronous lifespan loss is that each front-stage power conversion device performs a soft-start operation simultaneously, and the main switches in each front-stage power conversion device simultaneously perform differential voltage closing operations. In practical applications, any front-stage power conversion device can establish the required operating voltage on the input side of the downstream power conversion device through a soft-start operation. Based on this, as a preferred implementation, when there are multiple first power conversion devices with the fewest cumulative execution times, one of them can be selected as the soft-start execution device. That is, in each system startup cycle, only one first power conversion device is selected as the soft-start execution device, thereby minimizing the number of first power conversion devices that simultaneously perform soft-start operations (i.e., perform differential voltage closing). While meeting the system startup requirements, this minimizes the frequency of soft-start operations performed by the first power conversion devices, thereby reducing lifespan loss and extending service life.

[0043] In one alternative implementation, any one of the first power conversion devices with the fewest cumulative execution times can be used as the soft start execution device. Following the previous example, any one of the first power conversion devices A2 and A3 can be used as the soft start execution device.

[0044] In another optional implementation, a soft-start execution device can be determined from among the multiple first power conversion devices with the fewest cumulative execution counts according to a preset polling rule. In practical applications, to achieve unified control of all devices in the power conversion system while meeting necessary communication requirements, each first power conversion device in the power conversion system corresponds to a unique device code. Based on this, the first power conversion device with the smallest device code among the multiple first power conversion devices with the fewest cumulative execution counts can be determined as the soft-start execution device. Continuing the previous example, the device code corresponding to first power conversion device A2 is A2, and the device code corresponding to first power conversion device A3 is A3. If both are first power devices with the fewest cumulative execution counts, then first power conversion device A2 can be selected as the soft-start execution device. Compared to randomly selecting the soft-start execution device, using the inherent device code as a deterministic selection criterion simplifies the decision-making logic while ensuring selection fairness, making the system behavior more predictable and stable.

[0045] Determining the easing-start device based on the cumulative number of easing-start operations can intuitively reflect the historical operating status of each first power conversion device, and by favoring the selection of devices with fewer easing-start operations, it leads to a balanced state. Those skilled in the art will understand that alternative strategies to achieve the same purpose include recording other parameters directly or indirectly related to lifespan loss, which will not be listed here, but are also within the scope of protection of this application as long as they do not exceed the core idea of ​​this application.

[0046] This application embodiment also provides another method for determining the soft-start execution device. Specifically, during any system startup cycle, the second power conversion device adds an identifier to each first power conversion device. The identifiers are divided into two categories: one indicating that a soft-start operation has been performed, signifying that the corresponding first power conversion device has already performed a soft-start operation; and the other indicating that a soft-start operation has not been performed, signifying that the corresponding first power conversion device has not yet performed a soft-start operation. In practical applications, the above two identifiers can be implemented in various forms. For example, the controller b2 can allocate a bit in the memory for each first power conversion device, using different values ​​to represent the identifier. For instance, when the bit corresponding to a certain first power conversion device is written with a 1, it indicates that the first power conversion device has performed a soft-start operation; conversely, when the bit is written with a 0, it indicates that the first power conversion device has not performed a soft-start operation. Of course, other methods can also be used to represent the above identifiers, which will not be listed here.

[0047] Based on the above, during the current system startup cycle, the second power conversion device can first verify whether each of the first power conversion devices has been marked as having performed a soft start operation. If at least one of the first power conversion devices is marked as not having performed a soft start operation, the soft start execution device is determined from among the first power conversion devices marked as not having performed a soft start operation, and that soft start execution device is marked as having performed a soft start operation. Conversely, if all the first power conversion devices are marked as having performed a soft start operation, all the first power conversion devices are marked as not having performed a soft start operation, and the soft start execution device is determined from among the first power conversion devices marked as not having performed a soft start operation.

[0048] Combination Figure 1In the power conversion system shown, power conversion devices A1, A2, and A3 are initially marked as not having performed a soft start operation. During the first system startup, following a preset soft start sequence (e.g., A1→A2→A3), the first device, A1, is selected as the soft start execution device and marked as having performed a soft start operation. Correspondingly, during the second system startup, power conversion devices A2 and A3 are marked as not having performed a soft start operation. Therefore, among these, A2 is selected as the soft start execution device and marked as having performed a soft start operation. During the third system startup, the only device marked as not having performed a soft start operation, A3, is selected as the soft start execution device and marked as having performed a soft start operation. At this point, all power conversion devices are marked as having performed a soft start operation. During the fourth system startup, the second power conversion device B verifies that all first power conversion devices are marked as having performed a soft start operation. Therefore, all first power conversion devices are first reset to not having performed a soft start operation. Then, according to the aforementioned rules, the first first power conversion device (i.e., first power conversion device A1) among the first power conversion devices marked as not having performed a soft start operation is selected as the soft start execution device.

[0049] It should be noted that the aforementioned preset start-up sequence can be determined based on the device code of each first power conversion device, or it can be determined by other information, such as the communication address and installation order of the first power conversion device, which will not be listed here.

[0050] The selection mechanism based on marked status and preset soft-start order provided in this embodiment performs absolutely fair rotation based on the number of devices. The logic is simple and there is no need to record the number of historical times. It is particularly suitable for scenarios where the number of devices is fixed and they are not frequently replaced, ensuring absolute balance in the soft-start operation of each first power conversion device during long-term operation of the power conversion system.

[0051] After determining the soft-start execution device, the second power conversion device controls the main switch and soft-start circuit of each soft-start execution device to perform soft-start operation in order to establish the target operating voltage on the input side of the second power conversion device.

[0052] It should be noted that the target operating voltage mentioned in this embodiment refers to the steady-state voltage value that is expected to be established and maintained on the DC bus (i.e., the input side of the second power conversion device) after the power conversion system has started up, such as the DC bus voltage setting value required for the operation of a photovoltaic inverter. In practical applications, the target voltage value can be a fixed value or a value that is dynamically adjusted according to the operating conditions. The specific process of the soft-start execution device establishing the target operating voltage will be described in detail in subsequent embodiments and will not be described here.

[0053] As an optional implementation, controller b2 in the second power conversion device B broadcasts a soft-start command to each soft-start execution device. Each soft-start execution device responds to the soft-start command, i.e., performs a soft-start operation; specifically, the soft-start execution device outputs the target operating voltage, combined with... Figure 1 As shown, taking the first power conversion device A1 as an example, the power conversion circuit a1 outputs the target operating voltage and simultaneously controls its own soft-start circuit to close, that is, controls the soft-start switch K11 to close. The power conversion circuit a1 charges the second power conversion device B through the soft-start circuit to increase the voltage on the input side of the second power conversion device B. At the same time, the soft-start execution device also monitors the voltage on the input side of the second power conversion device B during the soft-start process, that is, monitors the voltage on the side of the main switch K12 near the second power conversion device B. When the voltage deviation between the input side of the second power conversion device B and the target operating voltage is within the preset deviation range, it determines that the closing requirement of the main switch K12 is met, that is, it controls its own main switch K12 to close. After the main switch K12 closes, it controls its own soft-start circuit to open, that is, it controls the soft-start switch K11 to open. At this time, the input side voltage of the second power conversion device B rises to the target operating voltage, thus completing the soft-start operation. It is understandable that when the main switch K12 is closed, the soft-start circuit has not yet been disconnected, and the voltage across the soft-start resistor R11 is applied to the main switch K12, which causes the main switch K12 to close with differential voltage, resulting in the burning of the contacts of the main switch K12.

[0054] In practical applications, the input side of the first power conversion device is connected to a DC power supply. This DC power supply can be a photovoltaic module, an energy storage battery, or both. This application does not limit the specific selection of the DC power supply. The input voltage of the first power conversion device is the output voltage of the DC power supply. Depending on the input voltage, the soft-start execution device outputs the target operating voltage in two scenarios: First, if the input voltage of the soft-start execution device is greater than or equal to a preset voltage threshold, the input voltage is directly used as the target operating voltage output. Second, if the input voltage of the soft-start execution device is less than the preset voltage threshold, the soft-start execution device performs a boost operation, raising the input voltage to the preset target operating voltage and outputting the target operating voltage. It is understood that the preset voltage threshold needs to be set in conjunction with the operating voltage required for the normal startup of the subsequent second power conversion device. This application does not limit the specific value of the preset voltage threshold.

[0055] When the input voltage of the second power conversion device reaches the target operating voltage, the remaining first power conversion devices (excluding the soft-start actuator) are further controlled to adjust their output voltage according to the target operating voltage, and close their main switches when their output voltage reaches the target operating voltage. The purpose of this step is to control the other first power conversion devices not selected as soft-start actuators to connect to the system in a way that minimizes losses to the main switch. These devices do not need to undergo the soft-start resistor charging process again, but directly adjust their own output target operating voltage to ensure that the voltage applied to both sides of the main switch is consistent, thereby achieving zero-differential closing.

[0056] As an optional implementation, after confirming that the input voltage of the second power conversion device B has reached the target bus voltage, controller b2 can send a grid connection command to all other first power conversion devices. This command may include the current target operating voltage. Upon receiving the grid connection command, each first power conversion device adjusts the output target operating voltage of its own power conversion circuit and finally closes its own main switch.

[0057] For example, in combination Figure 1As shown, after the first power conversion device A1 completes its soft-start operation and closes the main switch K12, the input voltage of the second power conversion device B is the target operating voltage V_target. Controller b2 then sends a grid connection command to both the first power conversion devices A2 and A3, indicating that the target operating voltage is V_target and requesting them to prepare for closing. Upon receiving the grid connection command, the first power conversion device A2 adjusts its output voltage until it equals V_target. Since the voltage on the side of the main switch closest to the second power conversion device B is also V_target, the voltage difference across the main switch K22 is close to zero, and the first power conversion device A2 directly controls the main switch K22 to close. The first power conversion device A3 performs the same process to close K32, which will not be repeated here.

[0058] In summary, the power conversion system provided in this application includes at least two first power conversion devices and one second power conversion device. The second power conversion device determines at least one soft-start execution device among the first power conversion devices and controls each soft-start execution device to perform a soft-start operation to establish a target operating voltage on the input side of the second power conversion device. Then, it controls the remaining first power conversion devices (excluding the soft-start execution devices) to close their main switches when their output voltage reaches the target operating voltage, achieving zero-differential closing. Since the number of soft-start execution devices is less than the total number of first power conversion devices, and the current system startup cycle is slow... The starting device differs from the soft-start device in the previous system startup cycle. For any first power conversion device, the frequency of differential voltage closing is significantly reduced throughout the entire life cycle of the power conversion system. This extends the interval between contact burnouts caused by differential voltage closing, thereby effectively extending the service life of each first power conversion device. Compared to related technologies that simultaneously control each first power conversion device to perform soft-start operation, this solution can distribute the concentrated lifespan loss over time across the main switches of all first power conversion devices, thus significantly extending the overall service life at the system level.

[0059] The working process of the power conversion system provided in this application embodiment is described below in conjunction with specific application scenarios: The power conversion system is a photovoltaic power supply system. The first power conversion equipment specifically includes combiner boxes in the photovoltaic power generation system, assuming there are 20 units. The combiner boxes are used to combine and monitor the outputs of multiple photovoltaic strings, and contain DC / DC boost modules. Each combiner box has a soft-start circuit at its output terminal, i.e., a main switch and a soft-start circuit. The DC / DC boost modules are connected to the subsequent second power conversion circuit through the soft-start circuit. The second power conversion equipment specifically includes inverters, which can be large centralized or string inverters. Their input DC bus is connected to the outputs of multiple combiner boxes.

[0060] Based on the above system configuration, the inverter internally maintains a record of the soft-start operations performed by each combiner box. On the first day of startup, the inverter selects the combiner box with the fewest cumulative execution counts in the historical record, say box 5, and sends it a soft-start command. Combiner box 5 performs the soft-start operation independently, establishing the target operating voltage on the inverter input side and then closing its main switch. Subsequently, the inverter commands the remaining combiner boxes to adjust their output voltage to the target operating voltage and then close their respective main switches under zero-differential voltage conditions. The entire startup process is completed smoothly, with only box 5 experiencing a significant differential voltage closing loss. On the second day of startup, the controller checks the records and finds that box 5's count has increased by one, and box 4's cumulative execution count has changed from the fewest to not the fewest. Therefore, the inverter selects a new device with the fewest cumulative execution counts, such as box 12, to perform the soft-start. This process continues in the same manner.

[0061] Understandably, the original related technologies focused on the peak lifespan loss of all main switches during each startup. However, the power conversion system provided in this application can distribute this loss across 20 startups. Statistically, the frequency of differential voltage closing for each main switch is reduced to 1 / 20 of the original frequency. This fully utilizes the total lifespan potential of the entire system's main switch set, significantly extending the overall system lifespan and avoiding system maintenance due to premature failure of individual main switches.

[0062] This application also provides a control method for a power conversion system, applicable to any of the power conversion systems provided in the foregoing embodiments. Specifically, it can be applied to a second power conversion device in the power conversion system, or to a first power conversion device in the power conversion system. Of course, it can also be applied to other controllers independent of the first and second power conversion devices. Taking the second power conversion device performing a system startup operation during the current system startup cycle of the power conversion system as an example, the system startup operation may include... Figure 2 The following steps are shown.

[0063] S100. Determine at least one soft start execution device among the first power conversion devices of the power conversion system.

[0064] The rule for determining the soft start execution device is as follows: the number of determined soft start execution devices is less than the total number of first power conversion devices, that is, only a portion of the first power conversion devices are used as soft start execution devices, and the soft start execution devices of the current system startup cycle are different from those of the previous system startup cycle.

[0065] In one optional implementation, the second power conversion device first obtains the cumulative number of times each first power conversion device performs a soft start operation, and determines at least one soft start execution device among each first power conversion device based on the cumulative number of executions corresponding to each first power conversion device.

[0066] Understandably, in order to make the number of times each first power conversion device performs a soft start operation more evenly, in the current system startup cycle, the first power conversion device with the fewest cumulative execution times can be selected as the soft start execution device. This setting can ensure that during long-term operation, the number of soft start operations undertaken by all first power conversion devices in the power conversion system tends to be consistent, maximizing the uniformity of lifetime loss distribution.

[0067] It is understandable that the reason why all front-stage power conversion devices in a power conversion system experience concentrated and synchronous lifespan loss is that each front-stage power conversion device performs a soft-start operation simultaneously, and the main switches in each front-stage power conversion device simultaneously perform differential voltage closing operations. In practical applications, any front-stage power conversion device can establish the required operating voltage on the input side of the downstream power conversion device through a soft-start operation. Based on this, as a preferred implementation, when there are multiple first power conversion devices with the fewest cumulative execution times, one of them can be selected as the soft-start execution device. That is, in each system startup cycle, only one first power conversion device is selected as the soft-start execution device, thereby minimizing the number of first power conversion devices that simultaneously perform soft-start operations (i.e., perform differential voltage closing). While meeting the system startup requirements, this minimizes the frequency of soft-start operations performed by the first power conversion devices, thereby reducing lifespan loss and extending service life.

[0068] In one optional implementation, any one of the first power conversion devices with the fewest cumulative execution counts can be selected as the soft-start execution device. In another optional implementation, a soft-start execution device can be determined from the multiple first power conversion devices with the fewest cumulative execution counts according to a preset polling rule. In practical applications, to achieve unified control of all devices in the power conversion system while meeting necessary communication requirements, each first power conversion device in the power conversion system corresponds to a unique device code. Based on this, the first power conversion device with the smallest device code among the multiple first power conversion devices with the fewest cumulative execution counts can be selected as the soft-start execution device.

[0069] This application embodiment also provides another method for determining the soft start execution device. Specifically, in any system startup cycle, the second power conversion device adds an identifier to each first power conversion device. The identifier is divided into two categories: one is that a soft start operation has been performed, indicating that the corresponding first power conversion device has performed a soft start operation, and the other is that a soft start operation has not been performed, indicating that the corresponding first power conversion device has not yet performed a soft start operation.

[0070] Based on the above, during the current system startup cycle, the second power conversion device can first verify whether each of the first power conversion devices has been marked as having performed a soft start operation. If at least one of the first power conversion devices is marked as not having performed a soft start operation, the soft start execution device is determined from among the first power conversion devices marked as not having performed a soft start operation, and that soft start execution device is marked as having performed a soft start operation. Conversely, if all the first power conversion devices are marked as having performed a soft start operation, all the first power conversion devices are marked as not having performed a soft start operation, and the soft start execution device is determined from among the first power conversion devices marked as not having performed a soft start operation.

[0071] The selection mechanism based on marked status and preset soft-start order provided in this embodiment performs absolutely fair rotation based on the number of devices. The logic is simple and there is no need to record the number of historical times. It is particularly suitable for scenarios where the number of devices is fixed and they are not frequently replaced, ensuring absolute balance in the soft-start operation of each first power conversion device during long-term operation of the power conversion system.

[0072] S110 controls the main switches of each soft-start execution device and the soft-start circuit to perform soft-start operation in order to establish the target operating voltage on the input side of the second power conversion device.

[0073] It should be noted that the target operating voltage mentioned in this embodiment refers to the steady-state voltage value that is expected to be established and maintained on the DC bus (i.e., the input side of the second power conversion device) after the power conversion system has started up, such as the DC bus voltage setting value required for the operation of a photovoltaic inverter. In practical applications, the target voltage value can be a fixed value or a value that is dynamically adjusted according to the operating conditions. The specific process of the soft-start execution device establishing the target operating voltage will be described in detail in subsequent embodiments and will not be described here.

[0074] As an optional implementation, the controller in the second power conversion device broadcasts a soft-start command to each soft-start execution device. Each soft-start execution device responds to the soft-start command, i.e., performs a soft-start operation; specifically, the soft-start execution device outputs the target operating voltage, combined with... Figure 1As shown, taking the first power conversion device A1 as an example, the power conversion circuit a1 outputs the target operating voltage and simultaneously controls its own soft-start circuit to close, that is, controls the soft-start switch K11 to close. The power conversion circuit a1 charges the second power conversion device B through the soft-start circuit to increase the voltage on the input side of the second power conversion device B. At the same time, the soft-start execution device also monitors the voltage on the input side of the second power conversion device B during the soft-start process, that is, monitors the voltage on the side of the main switch K12 near the second power conversion device B. When the voltage deviation between the input side of the second power conversion device B and the target operating voltage is within the preset deviation range, it determines that the closing requirement of the main switch K12 is met, that is, it controls its own main switch K12 to close. After the main switch K12 closes, it controls its own soft-start circuit to open, that is, it controls the soft-start switch K11 to open. At this time, the input side voltage of the second power conversion device B rises to the target operating voltage, thus completing the soft-start operation.

[0075] S120, the other first power conversion devices besides the control soft start execution device adjust their own output voltage according to the target working voltage, and close their own main switch when their own output voltage reaches the target working voltage.

[0076] The purpose of this step is to control other first power conversion devices that were not selected as soft-start actuators to connect to the system in a way that reduces losses to the main switch. These devices no longer need to go through the soft-start resistor charging process, but directly adjust their own output target operating voltage to ensure that the voltage applied on both sides of the main switch is consistent, thereby achieving zero-differential closing.

[0077] As an optional implementation, after confirming that the input voltage of the second power conversion device has reached the target bus voltage, a grid connection command can be sent to all other first power conversion devices. This command may include the current target operating voltage. Upon receiving the grid connection command, each first power conversion device adjusts the output target operating voltage of its own power conversion circuit and finally closes its own main switch.

[0078] In summary, the power conversion system control method provided in this application determines at least one soft-start execution device in each first power conversion device, controls each soft-start execution device to perform a soft-start operation to establish a target operating voltage on the input side of the second power conversion device, and then controls the remaining first power conversion devices other than the soft-start execution devices to close their main switches when their output voltage reaches the target operating voltage, thereby achieving zero-differential closing. Since the number of soft-start execution devices is less than the total number of first power conversion devices, and the soft-start execution device in the current system startup cycle is different from the soft-start execution device in the previous system startup cycle, for any first power conversion device, the frequency of differential closing is significantly reduced throughout the entire life cycle of the power conversion system, extending the interval time of contact erosion caused by differential closing, thereby effectively extending the service life of each first power conversion device. For the power conversion system, compared with the related technology of simultaneously controlling each first power conversion device to perform a soft-start operation, this solution can distribute the concentrated life loss over time to the main switches of all first power conversion devices, thereby significantly extending the overall service life at the system level.

[0079] Below, for reference Figure 3 The controller provided in this embodiment of the invention may include at least one processor 100, at least one communication interface 200, at least one memory 300, and at least one communication bus 400. In this embodiment of the invention, the number of processor 100, communication interface 200, memory 300, and communication bus 400 is at least one, and the processor 100, communication interface 200, and memory 300 communicate with each other through communication bus 400; obviously, Figure 3 The communication connections shown for the processor 100, communication interface 200, memory 300, and communication bus 400 are optional. Optionally, the communication interface 200 can be an interface of a communication module, such as the interface of a GSM module; the processor 100 may be a central processing unit (CPU), an application-specific integrated circuit (ASIC), or one or more integrated circuits configured to implement embodiments of the present invention.

[0080] The memory 300 may include high-speed RAM memory, and may also include non-volatile memory, such as at least one disk storage device.

[0081] Specifically, the processor 100 is used to execute the application program in the memory to implement the steps of the power conversion system control method described above.

[0082] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0083] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0084] Those skilled in the art will understand that the contents disclosed herein can be varied and modified in many ways. For example, the various devices or components described above can be implemented in hardware, or in software, firmware, or a combination of some or all of the three.

[0085] Furthermore, while this disclosure makes various references to certain elements of systems according to embodiments of this disclosure, any number of different elements may be used and operated on clients and / or servers. Elements are merely illustrative, and different aspects of the system and method may use different elements.

[0086] This disclosure uses flowcharts to illustrate the steps of a method according to embodiments of this disclosure. It should be understood that the preceding or following steps are not necessarily performed in exact order. Instead, the steps can be processed in reverse order or simultaneously. Furthermore, other operations can be added to these processes.

[0087] Those skilled in the art will understand that all or part of the steps in the above methods can be implemented by a computer program instructing related hardware, and the program can be stored in a computer-readable storage medium, such as a read-only memory. Optionally, all or part of the steps in the above embodiments can also be implemented using one or more integrated circuits. Accordingly, each module / unit in the above embodiments can be implemented in hardware or as a software functional module. This disclosure is not limited to any particular combination of hardware and software.

[0088] Unless otherwise defined, all terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. It should also be understood that terms such as those defined in a common dictionary should be interpreted as having a meaning consistent with their meaning in the context of the relevant art, and not as having an idealized or highly formalized meaning, unless expressly defined herein.

[0089] The foregoing description is intended to illustrate the present disclosure and should not be construed as limiting it. While several exemplary embodiments of the present disclosure have been described, those skilled in the art will readily understand that many modifications may be made to the exemplary embodiments without departing from the novel teachings and advantages of the present disclosure. Therefore, all such modifications are intended to be included within the scope of the present disclosure as defined by the claims. It should be understood that the foregoing description is intended to illustrate the present disclosure and should not be construed as limiting it to the specific embodiments disclosed, and modifications to the disclosed embodiments and other embodiments are intended to be included within the scope of the appended claims. The present disclosure is defined by the claims and their equivalents.

Claims

1. A power conversion system, characterized in that, include: At least two first power conversion devices and one second power conversion device, wherein, The output side of each of the first power conversion devices is connected to the input side of the second power conversion device through a corresponding main switch, and each main switch is connected in parallel with a soft-start circuit; The second power conversion device is configured to perform a system startup operation during the current system startup cycle, the system startup operation including: At least one soft start execution device is determined in each of the first power conversion devices, the number of soft start execution devices is less than the total number of the first power conversion devices, and the soft start execution device of the current system startup cycle is different from the soft start execution device of the previous system startup cycle. The main switches and soft-start circuits of each of the aforementioned soft-start execution devices are controlled to perform soft-start operations in order to establish a target operating voltage on the input side of the second power conversion device; The control unit adjusts the output voltage of the other first power conversion devices besides the soft start execution device according to the target operating voltage, and closes its main switch when its output voltage reaches the target operating voltage.

2. The power conversion system according to claim 1, characterized in that, The second power conversion device is specifically configured as follows: Obtain the cumulative number of times each of the first power conversion devices performs the soft-start operation; Based on the cumulative number of executions corresponding to each of the first power conversion devices, at least one soft-start execution device is determined among the first power conversion devices.

3. The power conversion system according to claim 2, characterized in that, The second power conversion device is specifically configured as follows: The power conversion device with the fewest cumulative execution counts will be designated as the soft-start execution device.

4. The power conversion system according to claim 3, characterized in that, The first power conversion device with the fewest cumulative execution times includes multiple devices; The second power conversion device is specifically configured as follows: Choose any one of the first power conversion devices with the fewest cumulative execution counts as the soft start execution device; Alternatively, according to a preset polling rule, a soft-start execution device can be selected from among the multiple first power conversion devices with the fewest cumulative execution times.

5. The power conversion system according to claim 4, characterized in that, Each of the first power conversion devices corresponds to a unique device code; The second power conversion device is specifically configured as follows: Among the multiple first power conversion devices with the fewest cumulative execution times, the first power conversion device with the smallest device code is determined as the soft start execution device.

6. The power conversion system according to claim 1, characterized in that, The second power conversion device is specifically configured as follows: Verify whether each of the first power conversion devices has been marked as having performed a soft start operation; If at least one of the first power conversion devices is marked as not having performed a soft start operation, a soft start execution device is determined from the first power conversion devices marked as not having performed a soft start operation, and the soft start execution device is marked as having performed a soft start operation; If each of the first power conversion devices is marked as having performed a soft start operation, then each of the first power conversion devices is marked as not having performed a soft start operation, and the soft start execution device is determined from among the first power conversion devices marked as not having performed a soft start operation.

7. The power conversion system according to claim 6, characterized in that, The second power conversion device is specifically configured as follows: According to the preset soft start sequence, the first power conversion device among the first power conversion devices that have not performed a soft start operation is designated as the soft start execution device.

8. The power conversion system according to claim 1, characterized in that, The second power conversion device is specifically configured to send a soft start command to the soft start execution device; The soft-start execution device is specifically configured as follows: In response to the soft-start command, the target operating voltage is output, and its own soft-start circuit is closed to increase the voltage on the input side of the second power conversion device; When the voltage deviation between the input side of the second power conversion device and the target operating voltage is within a preset deviation range, the device controls its main switch to close and its soft-start circuit to disconnect.

9. The power conversion system according to any one of claims 1 to 8, characterized in that, The first power conversion device includes a DC / DC conversion circuit, and the second power conversion device includes a DC / AC conversion circuit.

10. The power conversion system according to claim 9, characterized in that, One side of the DC / DC conversion circuit is connected to the input side of the first power conversion device, and the other side of the DC / DC conversion circuit is connected to the DC side of the DC / AC conversion circuit through a corresponding main switch. The soft-start circuit is connected in parallel across the two ends of the main switch. The AC side of the DC / AC conversion circuit is connected to the output side of the second power conversion device.

11. A control method for a power conversion system, characterized in that, The method includes: Execute a system startup operation during the current system startup cycle. The system startup operation includes: At least one soft-start execution device is determined in each of the first power conversion devices of the power conversion system; The number of the soft start execution devices is less than the total number of the first power conversion devices, and the soft start execution devices in the current system startup cycle are different from the soft start execution devices in the previous system startup cycle. The power conversion system includes at least two first power conversion devices and one second power conversion device. The output side of each first power conversion device is connected to the input side of the second power conversion device through a corresponding main switch, and each main switch is connected in parallel with a soft start circuit. The main switches and soft-start circuits of each of the aforementioned soft-start execution devices are controlled to perform soft-start operations in order to establish a target operating voltage on the input side of the second power conversion device; The control unit adjusts the output voltage of the other first power conversion devices besides the soft start execution device according to the target operating voltage, and closes its main switch when its output voltage reaches the target operating voltage.

12. The method according to claim 11, characterized in that, At least one soft-start execution device is determined among the first power conversion devices of the power conversion system, including: Obtain the cumulative number of times each first power conversion device in the power conversion system performs a soft-start operation; Based on the cumulative number of executions corresponding to each of the first power conversion devices, at least one soft-start execution device is determined among the first power conversion devices.

13. The method according to claim 11, characterized in that, The step of determining at least one slow-start execution device among the first power conversion devices based on the cumulative execution count corresponding to each of the first power conversion devices includes: Choose any one of the first power conversion devices with the fewest cumulative execution counts as the soft start execution device; Alternatively, according to a preset polling rule, a soft-start execution device can be selected from among the multiple first power conversion devices with the fewest cumulative execution times.

14. The method according to claim 11, characterized in that, At least one soft-start execution device is determined among the first power conversion devices of the power conversion system, including: Verify whether each of the first power conversion devices has been marked as having performed a soft start operation; If at least one of the first power conversion devices is marked as not having performed a soft start operation, a soft start execution device is determined from the first power conversion devices marked as not having performed a soft start operation, and the soft start execution device is marked as having performed a soft start operation; If each of the first power conversion devices is marked as having performed a soft start operation, then each of the first power conversion devices is marked as not having performed a soft start operation, and the soft start execution device is determined from among the first power conversion devices marked as not having performed a soft start operation.

15. The method according to claim 14, characterized in that, The step of determining the soft-start execution device in the first power conversion device that is marked as not performing soft-start operation includes: According to the preset soft start sequence, the first power conversion device among the first power conversion devices that have not performed a soft start operation is designated as the soft start execution device.

16. A controller comprising a memory, a processor, and a computer program stored in the memory and executed by the processor, characterized in that, When the processor executes the computer program, it implements the steps of the control method for the power conversion system as described in any one of claims 11 to 15.

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