A power device, photovoltaic system and control method

Abstract

This application discloses a power device, a photovoltaic system, and a control method. The power device includes: N DC / DC circuits; N is an integer greater than or equal to 2; the first input terminal of each DC / DC circuit is connected to the first terminal of the corresponding multi-channel photovoltaic string; the second input terminals of the N DC / DC circuits converge to a common terminal, which is connected to the second terminals of all photovoltaic strings; the output terminals of the N DC / DC circuits are connected to a DC bus; at the input terminals of the DC / DC circuits, an uncontrollable fuse and an excitation fuse are provided in the loop formed between the first and second terminals of any photovoltaic string. This scheme can achieve reliable protection of the photovoltaic string, saves on trip switches, and facilitates maintenance.

Description

Technical Field

[0001] This application relates to the field of photovoltaic fault protection technology, specifically to a power device, a photovoltaic system, and a control method. Background Technology

[0002] For power devices connected to multiple photovoltaic (PV) strings, the relevant technology uses a trip switch to combine the current from multiple PV strings into a single stream before connecting it to a DC / DC circuit. In the event of a short circuit or reverse connection of the PV strings, the trip switch corresponding to the faulty PV string is disconnected to achieve fault isolation.

[0003] However, since the trip switch is an active disconnecting device, the bus needs to draw power from one photovoltaic string before the trip switch is closed. This solution cannot confirm the fault status and connection status of the photovoltaic string, and the photovoltaic string supplying power to the trip switch may be faulty, causing the trip switch to fail to draw power and thus fail to disconnect. Moreover, once the trip switch is damaged, the entire inverter needs to be maintained, which is complicated. Summary of the Invention

[0004] In view of this, this application provides a power device, a photovoltaic system, and a control method that can achieve reliable protection of photovoltaic strings, save on trip switches, and facilitate maintenance.

[0005] This application provides a power device, comprising: N DC / DC circuits; where N is an integer greater than or equal to 2; The first input terminal of each DC / DC circuit is connected to the first terminal of the corresponding multi-channel photovoltaic string. The second input terminals of N DC / DC circuits are combined into a common terminal, which is connected to the second terminal of all photovoltaic strings. The output terminals of N DC / DC circuits are connected to the DC bus; At the input of the DC / DC circuit, an uncontrollable fuse and an excitation fuse are provided in the loop formed between the first and second poles of any photovoltaic string.

[0006] One possible implementation also includes: a controller and branch current sensors installed in each photovoltaic string; the DC / DC circuit is a boost circuit; The controller is used to determine that the i-th photovoltaic string is reverse-connected based on the fact that the current measured by the current sensor of the i-th branch is greater than a first current threshold, there is a reverse current in the i-th photovoltaic string, and the voltage of the i-th photovoltaic string is greater than a first voltage threshold. The controller then controls the switch in the DC / DC circuit corresponding to the i-th photovoltaic string to close, so that the uncontrollable fuse in the loop of the i-th photovoltaic string will automatically disconnect.

[0007] One possible implementation also includes: a main circuit current sensor disposed at the first input pole of each DC / DC circuit; The controller is also used to control the switch in the DC / DC circuit corresponding to the i-th photovoltaic string to open based on the current measured by the main current sensor being greater than the second current threshold and the input voltage of the DC / DC circuit that is not reverse-connected being lower than the second voltage threshold, so that the uncontrollable fuse in the loop of the i-th photovoltaic string will automatically disconnect.

[0008] In one possible implementation, the controller is further configured to repeatedly control the switch in the DC / DC circuit corresponding to the i-th photovoltaic string to open and close during the switching process in the DC / DC circuit corresponding to the i-th photovoltaic string, when the current measured by the current sensor of the i-th branch is less than a third current threshold, or when the input voltage of the DC / DC circuit that is not reverse-connected is greater than a third voltage threshold, until the current measured by the current sensor of the i-th branch is zero when the switch is open, so that the uncontrollable fuse in the loop of the i-th photovoltaic string breaks by itself.

[0009] One possible implementation also includes: a controller and branch current sensors installed in each photovoltaic string; the DC / DC circuit is a boost circuit; The controller is used to determine that a short circuit fault has occurred in the i-th photovoltaic string when the current measured by the current sensor of the i-th branch is greater than the fourth current threshold, there is a reverse current in the i-th photovoltaic string, and the voltage of the i-th photovoltaic string is less than the fourth voltage threshold. The controller then controls the switch in the DC / DC circuit corresponding to the i-th photovoltaic string to close, so that the uncontrollable fuse in the loop of the i-th photovoltaic string will automatically disconnect.

[0010] One possible implementation also includes: a main circuit current sensor disposed at the first input pole of each DC / DC circuit; The controller is also used to control the switch in the DC / DC circuit corresponding to the i-th photovoltaic string to close when the current measured by the main current sensor is greater than the fifth current threshold, so that the uncontrollable fuse in the loop of the i-th photovoltaic string will automatically disconnect.

[0011] In one possible implementation, the controller is also used to repeatedly control the switch in the DC / DC circuit corresponding to the i-th photovoltaic string to open and close repeatedly during the switching process in the DC / DC circuit corresponding to the i-th photovoltaic string, when the current measured by the current sensor of the i-th branch is less than the sixth current threshold, until the current measured by the current sensor of the i-th branch is zero when the switch is opened, so that the uncontrollable fuse in the loop of the i-th photovoltaic string breaks by itself.

[0012] One possible implementation also includes: a controller; the controller is used to control the excitation fuse to open when the DC bus is short-circuited.

[0013] One possible implementation also includes: a DC switch and a DC / AC circuit; N DC / DC circuits converging on a DC bus; A DC switch is connected between the junction of N DC / DC circuits and the input terminal of a DC / AC circuit.

[0014] This application also provides a photovoltaic system, including the power devices described above.

[0015] This application also provides a control method for a power device, the power device including: N DC / DC circuits and a branch current sensor disposed in each photovoltaic string; the DC / DC circuit is a boost circuit; The methods include: Based on the current measured by the current sensor of the i-th branch, it is determined that the i-th photovoltaic string has a reverse connection or short circuit fault. Control the closing of the switch in the DC / DC circuit corresponding to the i-th photovoltaic string; The first input terminal of each DC / DC circuit is connected to the first terminal of the corresponding multi-channel photovoltaic string. The second input terminals of the N DC / DC circuits converge to form a common terminal, which is connected to the second terminals of all photovoltaic strings. The output terminals of the N DC / DC circuits are connected to the DC bus. At the input terminals of the DC / DC circuits, an uncontrollable fuse and an excitation fuse are provided in the loop formed between the first terminal and the second terminal of any photovoltaic string.

[0016] One possible implementation involves determining whether the i-th photovoltaic string has a reverse connection or short circuit fault based on the current measured by the current sensor of the i-th branch, specifically including: If the current measured by the current sensor of the i-th branch is greater than the first current threshold, and there is a reverse current in the i-th photovoltaic string, and the voltage of the i-th photovoltaic string is greater than the first voltage threshold, then the i-th photovoltaic string is determined to be reverse connected; if the current measured by the current sensor of the i-th branch is greater than the fourth current threshold, and there is a reverse current in the i-th photovoltaic string, and the voltage of the i-th photovoltaic string is less than the fourth voltage threshold, then the i-th photovoltaic string is determined to be short-circuited.

[0017] In one possible implementation, the power device further includes: a main circuit current sensor disposed at the first input pole of each DC / DC circuit; The method also includes: If it is determined that the i-th photovoltaic string is reverse-connected, based on the fact that the current measured by the main circuit current sensor is greater than the second current threshold and the input voltage of the DC / DC circuit that is not reverse-connected is lower than the second voltage threshold, the switch in the DC / DC circuit corresponding to the i-th photovoltaic string is controlled to open, so that the uncontrollable fuse in the loop of the i-th photovoltaic string will automatically disconnect. If a short circuit is detected in the i-th photovoltaic string, and the current measured by the main current sensor is greater than the fifth current threshold, the switch in the DC / DC circuit corresponding to the i-th photovoltaic string is closed, causing the uncontrollable fuse in the i-th photovoltaic string loop to trip automatically.

[0018] One possible implementation method also includes: If it is determined that the i-th photovoltaic string is reverse-connected, during the opening process of the switch in the DC / DC circuit corresponding to the i-th photovoltaic string, the current measured by the current sensor of the i-th branch is less than the third current threshold, or the input voltage of the DC / DC circuit that is not reverse-connected is greater than the third voltage threshold. Repeatedly control the opening and closing of the switch in the DC / DC circuit corresponding to the i-th photovoltaic string until the current measured by the current sensor of the i-th branch is zero when the switch is opened, so that the uncontrollable fuse in the loop of the i-th photovoltaic string breaks by itself. When a short circuit is detected in the i-th photovoltaic string, during the opening and closing of the switch in the DC / DC circuit corresponding to the i-th photovoltaic string, the current measured by the current sensor of the i-th branch is less than the sixth current threshold. The switch in the DC / DC circuit corresponding to the i-th photovoltaic string is repeatedly opened and closed until the current measured by the current sensor of the i-th branch is zero when the switch is opened, causing the uncontrollable fuse in the loop of the i-th photovoltaic string to break automatically.

[0019] One possible implementation method also includes: controlling the excitation fuse to open when the DC bus is short-circuited.

[0020] The power device provided in this application features an uncontrollable fuse and an excitation fuse in the loop formed between the first and second poles of any photovoltaic string. This allows for isolation in the event of a fault in any photovoltaic string or any DC / DC circuit, achieving reliable protection for the photovoltaic strings through a combination of passive and active protection. Compared to protection solutions using trip switches, the power device provided in this application eliminates the need for an additional power supply circuit to the DC bus and avoids the need for custom-designed components when the number of photovoltaic strings changes. Both the uncontrollable fuse and the excitation fuse can be maintained independently, making operation and maintenance flexible and convenient. Attached Figure Description

[0021] Figure 1 A schematic diagram of a first type of power device provided in an embodiment of this application; Figure 2 This is a schematic diagram of a second type of power device provided in an embodiment of this application; Figure 3 A schematic diagram of a third type of power device provided in the embodiments of this application; Figure 4 A schematic diagram of a fourth type of power device provided in the embodiments of this application; Figure 5 A schematic diagram of the fifth type of power device provided in the embodiments of this application; Figure 6 A schematic diagram of a sixth type of power device provided in the embodiments of this application; Figure 7A schematic diagram of the seventh type of power device provided in the embodiments of this application; Figure 8 This is a flowchart of a control method for a power device provided in an embodiment of this application. Detailed Implementation

[0022] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the embodiments of this application will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0023] See Figure 1 This figure is a schematic diagram of the first type of power device provided in the embodiments of this application.

[0024] Figure 1 The power device provided in the illustrated embodiment includes N DC / DC circuits, where N is an integer greater than or equal to 2; these are the first DC / DC circuit 101 to the Nth DC / DC circuit 10N.

[0025] This application does not specifically limit the number of photovoltaic strings connected to each DC / DC circuit; the number of photovoltaic strings connected to each DC / DC circuit may be equal or unequal. This application's embodiments use an example of each DC / DC circuit connecting M photovoltaic strings, where M is an integer greater than or equal to 1.

[0026] In this configuration, the first input terminal of each DC / DC circuit is connected to the first terminal of the corresponding multi-channel photovoltaic (PV) string. The second input terminals of the N DC / DC circuits converge to a common terminal, which is then connected to the second terminals of all PV strings. Specifically, the first input terminal of the first DC / DC circuit 101 is connected to the first PV string PV1 up to the Mth PV string PV1M. Similarly, the first input terminal of the Nth DC / DC circuit 10N is connected to the Nth... M-M+1 photovoltaic string PVN M-M+1, until the Nth M photovoltaic string PVN M.

[0027] The second input terminal of the first DC / DC circuit 101 to the second input terminal of the Nth DC / DC circuit 10N converge to form a common terminal, which is the second terminal of all photovoltaic strings. That is, the common terminal connects the first photovoltaic string PV1 to the Mth photovoltaic string PV1M, and also connects to the Nth photovoltaic string. M-M+1 photovoltaic string PV N M-M+1, until the Nth M photovoltaic string PVN The second pole of M.

[0028] This application does not specifically limit the polarity of the first and second poles; the input terminals of each DC / DC circuit can share a common positive or negative pole. This application's embodiment uses the example of the first pole being positive, the second pole being negative, and the input terminals of each DC / DC circuit sharing a common negative pole for illustration.

[0029] The outputs of N DC / DC circuits are connected to the DC bus, meaning the positive outputs of the N DC / DC circuits are connected to the positive DC bus BUS+, and the positive outputs of the N DC / DC circuits are connected to the negative DC bus BUS-. At the input of the DC / DC circuits, an uncontrollable fuse and an excitation fuse are installed in the loop formed between the first and second terminals of any photovoltaic string.

[0030] This application does not specifically limit the location or number of uncontrollable fuses and excitation fuses, as long as both an uncontrollable fuse and an excitation fuse are provided in the loop formed between the first and second poles of any photovoltaic string. For example, each photovoltaic string can have one uncontrollable fuse and one excitation fuse, some photovoltaic strings can share one excitation fuse, or all photovoltaic strings can share one excitation fuse. For safety reasons, when the number of photovoltaic strings connected to the DC / DC circuit is greater than 3, each photovoltaic string needs to have its own uncontrollable fuse.

[0031] This application does not limit the parameters of the uncontrollable fuse or the energizing fuse. For example, the rated current of the uncontrollable fuse can be 25A to 35A, and the rated current of the energizing fuse can be 400A to 550A.

[0032] Figure 1 In the illustrated embodiment, each photovoltaic string corresponds to an uncontrollable fuse FA, and all photovoltaic strings share a single excitation fuse FB. When a fault occurs in a photovoltaic string, such as a short circuit or reverse connection, the uncontrollable fuse FA corresponding to that photovoltaic string is disconnected, thus isolating the faulty photovoltaic string from the power device. Similarly, if a fault occurs in a DC / DC circuit, causing a short circuit on the DC bus BUS, the fault can be isolated by disconnecting the excitation fuse FB, achieving isolation between each photovoltaic string and the power device. Therefore, the power device provided in this application can achieve fault isolation by passively disconnecting the uncontrollable fuse FA on the faulty photovoltaic string loop in the event of a fault in any photovoltaic string; and can achieve fault isolation by actively disconnecting the excitation fuse FB in the event of a fault in any DC / DC circuit.

[0033] The power device provided in this application embodiment has an uncontrollable fuse and an excitation fuse in the loop formed between the first and second poles of any photovoltaic string. This allows for isolation in the event of a fault in any photovoltaic string or any DC / DC circuit, achieving reliable protection for the photovoltaic string through a combination of passive and active protection. Compared to technical solutions using trip switches for protection, the power device provided in this application does not require an additional power supply circuit for the DC bus, and does not require custom-designed components when the number of photovoltaic strings changes. Both the uncontrollable fuse and the excitation fuse can be maintained independently, making operation and maintenance flexible and convenient.

[0034] One possible implementation of the power device provided in this application embodiment further includes: a controller and a branch current sensor disposed in each photovoltaic string; this application embodiment uses a DC / DC circuit as a boost circuit as an example for description.

[0035] See Figure 2 This figure is a schematic diagram of a second type of power device provided in an embodiment of this application.

[0036] The controller 200 is configured to determine that the i-th photovoltaic string is reverse-connected based on the following: the current measured by the current sensor of the i-th branch is greater than a first current threshold; the i-th photovoltaic string has reverse current; and the voltage of the i-th photovoltaic string is greater than a first voltage threshold. The controller then controls the switch in the DC / DC circuit corresponding to the i-th photovoltaic string to close. Here, i is greater than or equal to 1 and less than or equal to N. M is an integer.

[0037] For ease of understanding, the embodiments in this application are all described using i=1 as an example. The first branch current sensor CT1 is located on the branch where the first photovoltaic string PV1 is connected to the first DC / DC circuit 101. When the current flowing through the first photovoltaic string PV1 is a reverse current greater than a first current threshold, and the voltage of the first photovoltaic string PV1 is greater than a first voltage threshold, it means that the first photovoltaic string PV1 forms a loop with other photovoltaic strings connected to the first DC / DC circuit 101, that is, the first photovoltaic string PV1 is reverse-connected.

[0038] When the fault current flowing through the fuse is large, the arc energy generated by the fuse melting is high and difficult to extinguish quickly, which may prevent reliable disconnection of the fault circuit. Therefore, in order to transfer the large fault current flowing through the first photovoltaic string PV1, the controller 200 controls the switch T1 in the first DC / DC circuit 101 corresponding to the first photovoltaic string PV1 to close, so that the photovoltaic string in normal working condition on the first DC / DC circuit 101 forms a circuit with the switch T1 in the first DC / DC circuit 101, thereby bypassing the first photovoltaic string PV1 that has been reverse-connected. At this time, the current path in the first DC / DC circuit 101 is as follows: Figure 2 As indicated by the middle arrow.

[0039] This application does not specifically limit the type of switch in the DC / DC circuit. The switch in the DC / DC circuit can be a fully controllable switching transistor, that is, it can control the switching transistor to be turned on and off. For example, the switching transistor can include an insulated gate bipolar transistor (IGBT), a power metal-oxide-semiconductor field-effect transistor (Power MOSFET), or a gate turn-off thyristor (GTO), etc.

[0040] The power device provided in this application determines that the photovoltaic string is reverse-connected when the current in the branch where the photovoltaic string is located is greater than a first current threshold, the i-th photovoltaic string has a reverse current, and the voltage of the photovoltaic string is greater than a first voltage threshold. By controlling the closing of the switch in the DC / DC circuit corresponding to the photovoltaic string, the fault large current is transferred, which provides a prerequisite for the reliable disconnection of the fuse corresponding to the photovoltaic string.

[0041] In one possible implementation, the power device provided in this application embodiment further includes a main circuit current sensor disposed at the first input pole of each DC / DC circuit.

[0042] See Figure 3 This figure is a schematic diagram of a third type of power device provided in an embodiment of this application.

[0043] Figure 3 In the embodiment shown, the controller 200 is further configured to control the switch in the DC / DC circuit corresponding to the i-th photovoltaic string to open when the current measured by the main circuit current sensor CTA is greater than the second current threshold and the input voltage of the non-reverse DC / DC circuit is lower than the second voltage threshold, so that the uncontrollable fuse in the loop of the i-th photovoltaic string will automatically disconnect; the relationship between the second current threshold and the first current threshold is not limited, for example, the second current threshold is less than the first current threshold.

[0044] In this application embodiment, a DC / DC circuit that is not reverse-connected refers to a DC / DC circuit in which all photovoltaic strings connected are not reverse-connected.

[0045] Because the arc energy generated during the fuse melting process is insufficient when the current flowing through the fuse is low, and the recovery voltage at the break point is large when the voltage across the fuse is high, the arc is difficult to extinguish and prone to reignition in both cases, which may cause the fuse to fail to break. Therefore, when the current measured by the main circuit current sensor CTA is greater than the second current threshold, and the input voltage of the non-reverse DC / DC circuit is lower than the second voltage threshold, it means that the uncontrollable fuse FA in the first photovoltaic string PV1 loop has the conditions to reliably break. At this time, the controller 200 controls the switch T1 in the first DC / DC circuit 101 to open, which enables the uncontrollable fuse FA in the first photovoltaic string PV1 loop to reliably break.

[0046] The power device provided in this application determines that the uncontrollable fuse in the loop containing the reverse-connected photovoltaic string can reliably trip when the input current of the DC / DC circuit corresponding to the reverse-connected photovoltaic string is greater than a second current threshold and the input voltage of the non-reverse-connected DC / DC circuit is lower than a second voltage threshold. In this case, controlling the switch in the DC / DC circuit corresponding to the photovoltaic string to disconnect ensures reliable tripping of the uncontrollable fuse, resulting in high safety.

[0047] In one possible implementation, the controller is further configured to repeatedly control the switch in the DC / DC circuit corresponding to the i-th photovoltaic string to open and close during the switching process in the DC / DC circuit corresponding to the i-th photovoltaic string, when the current measured by the current sensor of the i-th branch is less than a third current threshold, or the input voltage of the non-reverse-connected DC / DC circuit is greater than a third voltage threshold, until the current measured by the current sensor of the i-th branch is zero when the switch is open; causing the uncontrollable fuse in the loop of the i-th photovoltaic string to trip automatically. The relationship between the third current threshold and the first current threshold is not limited; for example, the third current threshold may be less than the first current threshold.

[0048] See also Figure 3 During the switching-off process of the first DC / DC circuit 101, if the current measured by the first branch current sensor CT1 is less than the third current threshold, or the input voltage of the non-reverse DC / DC circuit is greater than the third voltage threshold, it indicates that the uncontrollable fuse FA in the loop of the first photovoltaic string PV1 has not successfully tripped. Therefore, in order to transfer the large fault current and ensure the reliable isolation of the first photovoltaic string PV1, the controller 200 repeatedly controls the switch T1 in the first DC / DC circuit 101 to open and close. When the switch T1 is open, the current measured by the first branch current sensor CT1 is zero, indicating that the uncontrollable fuse FA in the loop of the first photovoltaic string PV1 has successfully tripped, and the first photovoltaic string PV1 has been isolated.

[0049] The power device provided in this application determines that the uncontrollable fuse in the loop containing the reverse-connected photovoltaic string has failed to reliably trip when the branch current of the reverse-connected photovoltaic string exceeds a third current threshold, or the input voltage of the non-reverse-connected DC / DC circuit exceeds a third voltage threshold. In this case, repeatedly opening and closing the switch in the DC / DC circuit corresponding to the photovoltaic string can transfer the large fault current, ensuring reliable tripping of the uncontrollable fuse corresponding to the photovoltaic string, thus providing high safety.

[0050] The above embodiments use a reverse connection fault in a photovoltaic string as an example to illustrate the working principle of the power device provided in this application. In the event of a short circuit fault in the photovoltaic string, the power device provided in this application can also reliably disconnect the faulty photovoltaic string, as detailed below with reference to the embodiments.

[0051] In one possible implementation, the controller is configured to determine that a short-circuit fault has occurred in the i-th photovoltaic string based on the fact that the current measured by the current sensor of the i-th branch is greater than a fourth current threshold, there is a reverse current in the i-th photovoltaic string, and the voltage of the i-th photovoltaic string is less than a fourth voltage threshold, and then control the switch in the DC / DC circuit corresponding to the i-th photovoltaic string to close.

[0052] See also Figure 2 The power device provided in the embodiment. When the current flowing through the first photovoltaic string PV1 is a reverse current greater than the fourth current threshold, and the voltage of the first photovoltaic string PV1 is less than the fourth voltage threshold, it means that the first photovoltaic string PV1 forms a loop with other photovoltaic strings connected to the first DC / DC circuit 101, and the voltage drop across the first photovoltaic string PV1 is small, that is, the first photovoltaic string PV1 has a short circuit fault.

[0053] When the fault current flowing through the fuse is large, the arc energy generated by the fuse melting is high and difficult to extinguish quickly, which may prevent reliable disconnection of the fault circuit. Therefore, in order to transfer the large fault current flowing through the first photovoltaic string PV1, the controller 200 controls the switch T1 in the first DC / DC circuit 101 corresponding to the first photovoltaic string PV1 to close, so that the photovoltaic string in normal working condition on the first DC / DC circuit 101 forms a circuit with the switch T1 in the first DC / DC circuit 101, thereby bypassing the first photovoltaic string PV1 that has been reverse-connected. At this time, the current path in the first DC / DC circuit 101 is as follows: Figure 2 As indicated by the middle arrow.

[0054] The power device provided in this application determines that a short circuit has occurred in a photovoltaic string when the current in the branch where the photovoltaic string is located is greater than the fourth current threshold, there is a reverse current in the i-th photovoltaic string, and the voltage of the photovoltaic string is less than the fourth voltage threshold. By controlling the closing of the switch in the DC / DC circuit corresponding to the photovoltaic string, the fault current is transferred, which provides a prerequisite for the reliable disconnection of the fuse corresponding to the photovoltaic string.

[0055] In one possible implementation, the controller is further configured to control the switch in the DC / DC circuit corresponding to the i-th photovoltaic string to close automatically based on the current measured by the main circuit current sensor being greater than the fifth current threshold, thereby causing the uncontrollable fuse in the i-th photovoltaic string loop to trip automatically; the relationship between the fourth current threshold and the fifth current threshold is not limited, for example, the fifth current threshold is less than the fourth current threshold.

[0056] See also Figure 3 The power device provided in this embodiment may fail to break the fuse because the arc energy generated during the fuse blowing process is insufficient when the current flowing through the fuse is low. This arc is difficult to extinguish and prone to reignition. Therefore, when the current measured by the main circuit current sensor CTA is greater than the second current threshold, it indicates that the uncontrollable fuse FA in the first photovoltaic string PV1 loop has the conditions to reliably break. At this time, the controller 200 controls the switch T1 in the first DC / DC circuit 101 to open, enabling the uncontrollable fuse FA in the first photovoltaic string PV1 loop to reliably break.

[0057] The power device provided in this application, when the input current of the DC / DC circuit corresponding to the reverse-connected photovoltaic string exceeds a fifth current threshold, determines that the uncontrollable fuse in the loop containing the short-circuited photovoltaic string can reliably disconnect. At this time, controlling the switch in the DC / DC circuit corresponding to the photovoltaic string to open ensures reliable disconnection of the uncontrollable fuse, resulting in high safety.

[0058] In one possible implementation, the controller is further configured to repeatedly control the switch in the DC / DC circuit corresponding to the i-th photovoltaic string to open and close repeatedly during the switching process in the DC / DC circuit corresponding to the i-th photovoltaic string, when the current measured by the current sensor of the i-th branch is less than the sixth current threshold, until the current measured by the current sensor of the i-th branch is zero when the switch is open, causing the uncontrollable fuse in the loop of the i-th photovoltaic string to break automatically; the relationship between the fourth current threshold and the sixth current threshold is not limited, for example, the sixth current threshold is less than the fourth current threshold.

[0059] See also Figure 3During the switching off process of the first DC / DC circuit 101, if the current measured by the first branch current sensor CT1 is less than the sixth current threshold, it indicates that the uncontrollable fuse in the loop of the first photovoltaic string PV1 has not successfully tripped. Therefore, in order to transfer the large fault current and ensure the reliable isolation of the first photovoltaic string PV1, the controller 200 repeatedly controls the switch T1 in the first DC / DC circuit 101 to open and close. When the switch T1 is open, the current measured by the first branch current sensor CT1 is zero, which indicates that the uncontrollable fuse FA in the loop of the first photovoltaic string PV1 has successfully tripped, and the first photovoltaic string PV1 has been isolated.

[0060] The power device provided in this application, when the branch current of the photovoltaic string experiencing reverse connection exceeds the sixth current threshold, determines that the uncontrollable fuse on the switching circuit of the photovoltaic string experiencing reverse connection has failed to reliably trip. At this time, controlling the switch in the DC / DC circuit corresponding to the photovoltaic string to repeatedly open and close can transfer the large fault current, ensuring that the uncontrollable fuse corresponding to the photovoltaic string reliably trips, thus providing high safety.

[0061] The power device provided in this application embodiment can also reliably disconnect uncontrollable fuses when multiple photovoltaic modules experience reverse connection or short circuit faults simultaneously. Each photovoltaic module can be controlled according to the control logic provided in the above embodiment.

[0062] For example, see continue. Figure 3 In the embodiment shown, the first photovoltaic string PV1 is reverse-connected, and the Nth... M photovoltaic string PVN In the event of a short circuit fault in M, the controller 200 determines that the first photovoltaic string PV1 is reverse-connected based on the following: the current measured by the first branch current sensor CT1 is greater than a first current threshold, there is a reverse current in the first photovoltaic string, and the voltage of the first photovoltaic string PV1 is greater than a first voltage threshold. The controller then controls the switch T1 in the first DC / DC circuit 101 to close. M-branch current sensor CTN The current measured by M is the fourth current threshold and the Nth current. The M photovoltaic string has reverse current, and the Nth string... The voltage of photovoltaic string M is less than the fourth voltage threshold, thus determining the Nth voltage threshold. When a short circuit fault occurs in the M photovoltaic string, the switch TN in the NDC / DC circuit 10N closes.

[0063] The above embodiments describe the reliable disconnection method of the uncontrollable fuse in the power device provided by the embodiments of this application when the photovoltaic module fails. In the case of internal faults in the power device, such as when a DC / DC circuit fault causes a short circuit in the DC bus, the power device provided by the embodiments of this application can also achieve reliable disconnection by activating the fuse, which will be explained in detail below.

[0064] One possible implementation of the power device provided in this application embodiment further includes: a controller.

[0065] See Figure 4 This figure is a schematic diagram of the fourth type of power device provided in the embodiments of this application.

[0066] Figure 4 In the illustrated embodiment, the controller 200 controls the excitation fuse FB to open when the DC bus BUS is short-circuited. This application does not specifically limit the method by which the controller 200 identifies a short circuit in the DC bus BUS. A short circuit in the DC bus BUS can be determined by detecting that the voltage of the DC bus BUS is lower than a seventh voltage threshold and the current in each DC / DC circuit exceeds a seventh current threshold. By controlling the excitation fuse FB to open, the controller 200 can disconnect all photovoltaic modules from the DC bus BUS, achieving fault isolation.

[0067] The power device provided in this application embodiment can also disconnect the photovoltaic module from the power device by controlling the excitation fuse to disconnect in the event of an internal fault in the power device, thereby achieving effective fault isolation in an active control manner and ensuring high reliability.

[0068] One possible implementation of the power device provided in this application embodiment further includes: a DC switch and a DC / AC circuit.

[0069] See Figure 5 This figure is a schematic diagram of the fifth type of power device provided in the embodiments of this application.

[0070] Figure 5 In the power device shown, N DC / DC circuits converge at the DC bus BUS. A DC switch 300 is connected between the convergence point of the N DC / DC circuits and the input terminal of the DC / AC circuit 400. The DC switch 300 is used to achieve fault isolation between the DC / DC circuits and the DC / AC circuit 400.

[0071] The above embodiments are all illustrated using the example of all photovoltaic strings sharing a single excitation fuse. In some possible implementations, the excitation fuses in the power devices provided in this application can be selected in other quantities or connection methods, which will be described below with reference to the accompanying drawings.

[0072] See Figure 6 This figure is a schematic diagram of the sixth type of power device provided in the embodiments of this application.

[0073] and Figure 1 The difference is that, Figure 6 In the embodiment shown, each photovoltaic string corresponds to an excitation fuse FB, i.e., N M-channel photovoltaic strings correspond to N There are M excitation fuses FB, each of which is connected to the negative terminal of the corresponding photovoltaic string.

[0074] See Figure 7 This figure is a schematic diagram of the seventh type of power device provided in the embodiments of this application.

[0075] and Figure 1 The difference is that, Figure 7 In the illustrated embodiment, each M N / 2 photovoltaic strings together correspond to one excitation fuse FB, that is, N M-channel photovoltaic strings correspond to 2 excitation fuses FB.

[0076] for Figure 6 and Figure 7 The power device shown has a controller 200 for controlling all excitation fuses FB to open when the DC bus BUS is short-circuited.

[0077] Based on the power devices provided in the above embodiments, this application also provides a photovoltaic system.

[0078] The photovoltaic system provided in this application includes any of the power devices provided in the above embodiments. Since the loop formed between the first and second poles of any photovoltaic string in the power device is equipped with an uncontrollable fuse and an excitation fuse, isolation can be achieved in the event of a fault in any photovoltaic string or any DC / DC circuit. Reliable protection of the photovoltaic string is achieved through a combination of passive and active protection. Therefore, compared with the technical solution of using a trip switch for protection, the photovoltaic system provided in this application does not require an additional power supply circuit for the DC bus, and does not require custom-made components when the number of photovoltaic strings changes. Furthermore, the excitation fuse can be shared by multiple photovoltaic strings, saving hardware costs. Both the uncontrollable fuse and the excitation fuse can be maintained independently, making operation and maintenance flexible and convenient. The photovoltaic system provided in this application can include a distributed inverter system or a string inverter system.

[0079] Based on the power devices provided in the above embodiments, this application also provides a control method for the power devices. The control method for the power devices provided in this application is applied to any of the power devices provided in the above embodiments. The power device includes: N DC / DC circuits and branch current sensors disposed in each photovoltaic string; the DC / DC circuits are boost circuits; the first input terminal of each DC / DC circuit is connected to the first terminal of the corresponding multi-channel photovoltaic string, and the second input terminals of the N DC / DC circuits converge to form a common terminal, which is connected to the second terminals of all photovoltaic strings; the output terminals of the N DC / DC circuits are connected to a DC bus; at the input terminals of the DC / DC circuits, an uncontrollable fuse and an excitation fuse are provided in the loop formed between the first terminal and the second terminal of any photovoltaic string.

[0080] See Figure 8 The figure is a flowchart of a power device control method provided in an embodiment of this application.

[0081] The method includes: S10: Determine whether the i-th photovoltaic string has a reverse connection or short circuit fault based on the current measured by the current sensor of the i-th branch.

[0082] For example, the controller of the power device can determine that the first photovoltaic string has a reverse connection or short circuit fault based on the current measured by the first branch current sensor being greater than the threshold and the presence of reverse current in the first photovoltaic string.

[0083] S20: Control the closing of the switch in the DC / DC circuit corresponding to the i-th photovoltaic string.

[0084] For example, if the controller of the power device determines that a reverse connection or short circuit fault has occurred in the first photovoltaic string, it can control the switch in the DC / DC circuit corresponding to the first photovoltaic string to close, so as to transfer the fault large current.

[0085] The power device control method provided in this application can determine whether a reverse connection or short circuit fault has occurred in the photovoltaic string corresponding to the branch current sensor based on the current measured by the branch current sensor. By controlling the closing of the switch in the DC / DC circuit corresponding to the photovoltaic string, the large fault current is transferred, which provides a prerequisite for the reliable tripping of the fuse corresponding to the photovoltaic string.

[0086] One possible implementation involves determining whether a reverse connection or short circuit fault has occurred in the i-th photovoltaic string based on the current measured by the current sensor of the i-th branch, specifically including: If the current measured by the current sensor of the i-th branch is greater than the first current threshold, and there is a reverse current in the i-th photovoltaic string, and the voltage of the i-th photovoltaic string is greater than the first voltage threshold, then the i-th photovoltaic string is determined to be reverse connected; if the current measured by the current sensor of the i-th branch is greater than the fourth current threshold, and there is a reverse current in the i-th photovoltaic string, and the voltage of the i-th photovoltaic string is less than the fourth voltage threshold, then the i-th photovoltaic string is determined to be short-circuited.

[0087] In one possible implementation, the power device further includes: a main circuit current sensor disposed at the first input pole of each DC / DC circuit; and a control method further including: If it is determined that the i-th photovoltaic string is reverse-connected, the current measured by the main circuit current sensor is greater than the second current threshold and the input voltage of the DC / DC circuit that is not reverse-connected is lower than the second voltage threshold. Then, the switch in the DC / DC circuit corresponding to the i-th photovoltaic string is turned off, so that the uncontrollable fuse in the loop of the i-th photovoltaic string breaks by itself.

[0088] If a short circuit is detected in the i-th photovoltaic string, and the current measured by the main current sensor is greater than the fifth current threshold, the switch in the DC / DC circuit corresponding to the i-th photovoltaic string will be closed, causing the uncontrollable fuse in the i-th photovoltaic string loop to trip automatically.

[0089] The power device control method provided in this application can determine whether the uncontrollable fuse in the loop containing a photovoltaic string experiencing a reverse connection or short circuit fault can reliably trip by using the current measured by the main circuit current sensor or the input voltage of a non-reverse-connected DC / DC circuit. If the uncontrollable fuse reliably trips, the switch in the corresponding DC / DC circuit of the photovoltaic string is opened, ensuring reliable tripping of the uncontrollable fuse and providing high safety.

[0090] One possible implementation of the control method further includes: If the i-th photovoltaic string is reverse-connected, during the opening and closing of the switch in the DC / DC circuit corresponding to the i-th photovoltaic string, the current measured by the current sensor of the i-th branch is less than the third current threshold, or the input voltage of the DC / DC circuit that is not reverse-connected is greater than the third voltage threshold. The switch in the DC / DC circuit corresponding to the i-th photovoltaic string is repeatedly opened and closed until the current measured by the current sensor of the i-th branch is zero when the switch is opened, causing the uncontrollable fuse in the loop of the i-th photovoltaic string to break automatically.

[0091] When a short circuit is detected in the i-th photovoltaic string, during the opening and closing of the switch in the DC / DC circuit corresponding to the i-th photovoltaic string, the current measured by the current sensor of the i-th branch is less than the sixth current threshold. The switch in the DC / DC circuit corresponding to the i-th photovoltaic string is repeatedly opened and closed until the current measured by the current sensor of the i-th branch is zero when the switch is opened, causing the uncontrollable fuse in the i-th photovoltaic string loop to break automatically.

[0092] The power device control method provided in this application can determine whether the uncontrollable fuse in the loop containing the photovoltaic string experiencing a reverse connection or short circuit fault has reliably tripped by measuring the current from the main circuit current sensor or the input voltage of the DC / DC circuit that is not reverse-connected. When the uncontrollable fuse has not reliably tripped, the method controls the switch in the DC / DC circuit corresponding to the photovoltaic string to repeatedly open and close, thereby transferring the large fault current and ensuring that the uncontrollable fuse corresponding to the photovoltaic string reliably trips, resulting in high safety.

[0093] One possible implementation of the control method further includes: When the DC bus is short-circuited, the control excitation fuse is disconnected.

[0094] The power device control method provided in this application embodiment can also disconnect the photovoltaic module from the power device by controlling the excitation fuse to disconnect in the event of an internal fault in the power device, thereby achieving effective fault isolation in an active control manner with high reliability.

[0095] The controller provided in this application embodiment may include software to implement the control methods described above. Alternatively, the controller provided in this application embodiment may include hardware to implement the control methods described above. Or, the controller provided in this application embodiment may include both software and hardware, using a combination of software and hardware to execute the control methods described above.

[0096] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0097] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A power device, characterized by, include: N DC / DC circuits; N is an integer greater than or equal to 2; The first input terminal of each DC / DC circuit is connected to the first terminal of the corresponding multi-channel photovoltaic string, and the second input terminals of N DC / DC circuits are combined into a common terminal, which is connected to the second terminals of all the photovoltaic strings. The output terminals of N DC / DC circuits are connected to a DC bus; At the input terminal of the DC / DC circuit, an uncontrollable fuse and an excitation fuse are provided in the loop formed between the first pole and the second pole of any photovoltaic string.

2. The power device of claim 1, wherein, Also includes: The controller and the branch current sensor installed in each of the photovoltaic strings; The DC / DC circuit is a boost circuit; The controller is configured to determine that the i-th photovoltaic string is reverse-connected based on the fact that the current measured by the current sensor of the i-th branch is greater than a first current threshold, the i-th photovoltaic string has a reverse current, and the voltage of the i-th photovoltaic string is greater than a first voltage threshold. The controller then controls the switch in the DC / DC circuit corresponding to the i-th photovoltaic string to close, so that the uncontrollable fuse in the loop of the i-th photovoltaic string will automatically disconnect.

3. The power device of claim 2, wherein, Also includes: A main circuit current sensor is installed at the first input pole of each DC / DC circuit; The controller is further configured to, based on the fact that the current measured by the main circuit current sensor is greater than the second current threshold and the input voltage of the DC / DC circuit that is not reverse-connected is lower than the second voltage threshold, control the switch in the DC / DC circuit corresponding to the i-th photovoltaic string to open, so that the uncontrollable fuse in the loop of the i-th photovoltaic string will automatically disconnect.

4. The power device of claim 3, wherein, The controller is further configured to repeatedly control the switch in the DC / DC circuit corresponding to the i-th photovoltaic string to open and close during the switching process in the DC / DC circuit corresponding to the i-th photovoltaic string, until the current measured by the current sensor of the i-th branch is less than a third current threshold, or the input voltage of the DC / DC circuit that is not reverse-connected is greater than a third voltage threshold, until the current measured by the current sensor of the i-th branch is zero when the switch is open, so that the uncontrollable fuse in the loop of the i-th photovoltaic string breaks by itself.

5. The power device of claim 1, wherein, Also includes: The controller and the branch current sensor installed in each of the photovoltaic strings; The DC / DC circuit is a boost circuit; The controller is configured to determine that a short circuit fault has occurred in the i-th photovoltaic string when the current measured by the current sensor of the i-th branch is greater than a fourth current threshold, there is a reverse current in the i-th photovoltaic string, and the voltage of the i-th photovoltaic string is less than a fourth voltage threshold. The controller then controls the switch in the DC / DC circuit corresponding to the i-th photovoltaic string to close, so that the uncontrollable fuse in the loop of the i-th photovoltaic string will automatically disconnect.

6. The power device of claim 5, wherein, Also includes: A main circuit current sensor is installed at the first input pole of each DC / DC circuit; The controller is further configured to control the switch in the DC / DC circuit corresponding to the i-th photovoltaic string to close when the current measured by the main current sensor is greater than the fifth current threshold, so that the uncontrollable fuse in the loop of the i-th photovoltaic string will automatically disconnect.

7. The power device of claim 6, wherein, The controller is further configured to repeatedly control the switch in the DC / DC circuit corresponding to the i-th photovoltaic string to open and close during the process of the switch being turned off in the DC / DC circuit corresponding to the i-th photovoltaic string, when the current measured by the i-th branch current sensor is less than the sixth current threshold, until the current measured by the i-th branch current sensor is zero when the switch is turned off, so that the uncontrollable fuse in the loop of the i-th photovoltaic string breaks by itself.

8. The power device of claim 1, wherein, Also includes: Controller; The controller is used to control the excitation fuse to open when the DC bus is short-circuited.

9. The power device according to any of claims 1-8, characterized by Also includes: DC switches and DC / AC circuits; N of the aforementioned DC / DC circuits converge on the DC bus; The DC switch is connected between the N bus points of the DC / DC circuits and the input terminal of the DC / AC circuit.

10. A photovoltaic system characterized by, Includes the power device as described in any one of claims 1-9.

11. A control method for a power device, characterized in that, The power device includes: N DC / DC circuits and branch current sensors installed in each photovoltaic string; the DC / DC circuits are boost circuits; The method includes: Based on the current measured by the current sensor of the i-th branch, it is determined that the i-th photovoltaic string has a reverse connection or short circuit fault; Control the closing of the switch in the DC / DC circuit corresponding to the i-th photovoltaic string; The first input terminal of each DC / DC circuit is connected to the first terminal of the corresponding multiple photovoltaic strings. The second input terminals of the N DC / DC circuits converge to a common terminal, which is connected to the second terminals of all the photovoltaic strings. The output terminals of the N DC / DC circuits are connected to a DC bus. An uncontrollable fuse and an excitation fuse are provided in the loop formed between the first terminal and the second terminal of any photovoltaic string at the input terminal of the DC / DC circuit.

12. The method of claim 11, wherein, The step of determining whether the i-th photovoltaic string has a reverse connection or short circuit fault based on the current measured by the current sensor of the i-th branch specifically includes: If the current measured by the current sensor of the i-th branch is greater than the first current threshold, and there is a reverse current in the i-th photovoltaic string, and the voltage of the i-th photovoltaic string is greater than the first voltage threshold, then the i-th photovoltaic string is determined to be reverse-connected; if the current measured by the current sensor of the i-th branch is greater than the fourth current threshold, and there is a reverse current in the i-th photovoltaic string, and the voltage of the i-th photovoltaic string is less than the fourth voltage threshold, then the i-th photovoltaic string is determined to be short-circuited.

13. The method of claim 12, wherein, The power device further includes: a main circuit current sensor disposed at the first input pole of each DC / DC circuit; The method further includes: If it is determined that the i-th photovoltaic string is reverse-connected, based on the fact that the current measured by the main circuit current sensor is greater than the second current threshold and the input voltage of the DC / DC circuit that is not reverse-connected is lower than the second voltage threshold, the switch in the DC / DC circuit corresponding to the i-th photovoltaic string is controlled to open, so that the uncontrollable fuse in the loop of the i-th photovoltaic string breaks by itself. If a short circuit is detected in the i-th photovoltaic string, and the current measured by the main current sensor is greater than the fifth current threshold, the switch in the DC / DC circuit corresponding to the i-th photovoltaic string is controlled to close, causing the uncontrollable fuse in the loop of the i-th photovoltaic string to disconnect automatically.

14. The method of claim 13, wherein, The method further includes: If it is determined that the i-th photovoltaic string is reverse-connected, during the process of the switch in the DC / DC circuit corresponding to the i-th photovoltaic string being opened, the current measured by the current sensor of the i-th branch is less than the third current threshold, or the input voltage of the DC / DC circuit that is not reverse-connected is greater than the third voltage threshold. The switch in the DC / DC circuit corresponding to the i-th photovoltaic string is repeatedly opened and closed until the current measured by the current sensor of the i-th branch is zero when the switch is opened, so that the uncontrollable fuse in the loop of the i-th photovoltaic string breaks by itself. When a short circuit is determined to occur in the i-th photovoltaic string, during the opening and closing of the switch in the DC / DC circuit corresponding to the i-th photovoltaic string, if the current measured by the current sensor of the i-th branch is less than the sixth current threshold, the switch in the DC / DC circuit corresponding to the i-th photovoltaic string is repeatedly opened and closed until the current measured by the current sensor of the i-th branch is zero when the switch is opened, causing the uncontrollable fuse in the loop of the i-th photovoltaic string to break automatically.

15. The control method according to claim 11, characterized by, The method further includes: When the DC bus is short-circuited, the excitation fuse is controlled to open.

Images