A protection device, protection method, and photovoltaic power generation system.

Abstract

This application discloses a protection device, protection method, and photovoltaic power generation system for a photovoltaic power generation system, relating to the field of photovoltaic power generation technology. The protection device includes: an interface, a protection switch, a DC bus, and a controller. The device connects at least two photovoltaic units through the interface. These at least two photovoltaic units are coupled to the DC bus within the device to form at least two branches, each branch connecting at least one photovoltaic unit. The protection switch is used to disconnect all or part of the photovoltaic units from the DC bus, allowing up to three photovoltaic units to be directly connected in parallel. The controller is used to control the protection switch to open when a fault in the photovoltaic power generation system is determined based on parameter detection values ​​of the branches or the DC bus. Using this device, photovoltaic units and lines can be effectively protected when a fault occurs in the photovoltaic power generation system, with low power loss.

Description

Technical Field

[0001] This application relates to the field of photovoltaic power generation technology, and in particular to a protection device, short-circuit protection method and photovoltaic power generation system for a photovoltaic power generation system. Background Technology

[0002] Photovoltaic (PV) power generation is a technology that converts light energy into electrical energy using the photovoltaic effect at semiconductor interfaces. A typical PV system includes photovoltaic (PV) units, an inverter, and AC power distribution equipment. To achieve higher output voltage or current, PV units are usually formed by connecting multiple PV modules in series and parallel. To improve the power generation efficiency of the PV system, the PV units are connected to devices with independent MPPT (Maximum Power Point Tracking) functionality.

[0003] Currently, to improve the DC ratio (the ratio of photovoltaic unit power to inverter input power) of photovoltaic power generation systems, each MPPT device is typically connected to at least two photovoltaic units. Taking a short circuit in one photovoltaic unit or its connected circuit as an example, the short-circuit current is the sum of the output currents of the other connected photovoltaic units. When there is only one connected photovoltaic unit, the short-circuit current is small and can be withstood by the photovoltaic unit and the circuit. However, when there are two or more connected photovoltaic units, the short-circuit current is larger. To protect the photovoltaic unit and the circuit, a fuse can be connected in series at the positive and / or negative output terminals of the photovoltaic unit, causing the fuse to blow and protecting the photovoltaic unit and the circuit.

[0004] However, since the fusing current of fuses is generally high, while the output current of each photovoltaic unit is low, the sum of the short-circuit currents of multiple photovoltaic units is difficult to reach the fusing current of the fuse. As a result, the fuse cannot effectively protect the photovoltaic units and lines. Furthermore, the large internal resistance of the fuse will also lead to a large power loss in the photovoltaic power generation system. Summary of the Invention

[0005] This application provides a protection device, protection method, and photovoltaic power generation system that can effectively protect photovoltaic units and lines when the photovoltaic power generation system fails, and has low power loss.

[0006] In a first aspect, embodiments of this application provide a protection device for a photovoltaic power generation system, applied to a photovoltaic power generation system. The device includes: an interface, a protection switch, a DC bus, and a controller. The device connects to at least two photovoltaic units via the interface. These at least two photovoltaic units are connected in parallel with the DC bus within the device to form at least two branches, each branch connecting at least one photovoltaic unit. The protection switch is used to disconnect all or part of the photovoltaic units from the DC bus, allowing up to three photovoltaic units to be directly connected in parallel. When the controller determines that a fault has occurred in the photovoltaic power generation system based on parameter detection values ​​of the branches or the DC bus, it controls the protection switch to open.

[0007] Because the protective switch of this device allows up to three photovoltaic units to be directly connected in parallel when it is open, when one photovoltaic unit can withstand the current output from two photovoltaic units, if a photovoltaic unit fails, at most two normal photovoltaic units will output current to it. This current is within the withstand range of the failed photovoltaic unit, thus protecting the photovoltaic modules and wiring from damage. Furthermore, since only a protective switch is added to the circuit, its resistance is lower than that of a fuse, reducing the loss rate of the photovoltaic system. In addition, because fuses are no longer used, the Y-shaped wiring harness, which previously had built-in fuses, no longer needs to be located at the bottom of the inverter or DC combiner box of the photovoltaic power generation system; it can be configured on the photovoltaic unit side, thereby reducing cable costs.

[0008] In conjunction with the first aspect, in one possible implementation, the parameter detection value is the reverse current value, and the controller is specifically used to determine that there is a fault in the photovoltaic power generation system when the reverse current value of a branch is greater than the first current value.

[0009] When a branch has a large reverse current, it indicates that the DC current output from other branches is flowing back into this branch, which means that a short circuit fault has occurred in this branch.

[0010] In conjunction with the first aspect, in a first possible implementation, the device connects at least three photovoltaic units through the interface, wherein at most two of the photovoltaic units are directly connected in parallel to the DC bus, and each of the remaining photovoltaic units is connected in series with at least one of the protection switches and then connected in parallel to the DC bus.

[0011] In some embodiments, a photovoltaic unit or line can only withstand the output current of one photovoltaic unit. When at most two photovoltaic units are directly connected in parallel to the DC bus, if a photovoltaic unit has a short circuit fault, at most one normal photovoltaic unit will output a short circuit current to it, and the remaining photovoltaic units can be directly disconnected. At this time, the short circuit current is within the tolerance range of the faulty photovoltaic unit, thereby protecting the photovoltaic module and line from damage.

[0012] In conjunction with the first aspect, in a second possible implementation, the device connects at least three photovoltaic units through the interface, wherein at most three of the photovoltaic units are directly connected in parallel to the DC bus, and each of the remaining photovoltaic units is connected in series with at least one of the protection switches and then connected in parallel to the DC bus.

[0013] In some embodiments, a photovoltaic unit or line can withstand the output current of two photovoltaic units. Therefore, when up to three photovoltaic units are directly connected in parallel to the DC bus, if a photovoltaic unit experiences a short circuit fault, at most two normal photovoltaic units will output short circuit current to it, and the remaining photovoltaic units can be directly disconnected. At this time, the short circuit current is within the tolerance range of the faulty photovoltaic unit, thereby protecting the photovoltaic module and line from damage.

[0014] In conjunction with the first aspect, in a third possible implementation, the device connects three photovoltaic units via the interface. Two photovoltaic units are directly connected in parallel to the DC bus, and the third photovoltaic unit is connected in series with at least one of the protective switches and then in parallel to the DC bus. The controller can control the protective switches to disconnect in the event of a short-circuit fault, thereby protecting the photovoltaic units and lines in the photovoltaic system.

[0015] In conjunction with the first aspect, in a fourth possible implementation, the device connects three photovoltaic units via the interface. Two photovoltaic units are connected in series with at least one of the protective switches and then connected in parallel to the DC bus. The third photovoltaic unit is directly connected in parallel to the DC bus. The controller can open the protective switch in the event of a short-circuit fault, reducing the current flowing into the photovoltaic unit experiencing the short-circuit fault to zero, thereby protecting the photovoltaic units and lines in the photovoltaic system.

[0016] In conjunction with the first aspect, in a fifth possible implementation, the device connects four photovoltaic units via the interface. Two photovoltaic units are first connected in parallel and then in series with at least one of the protective switches, and then connected in parallel to the DC bus. The other two photovoltaic units are directly connected in parallel to the DC bus. The controller can control the protective switches to open in the event of a short-circuit fault, thereby protecting the photovoltaic units and lines in the photovoltaic system.

[0017] In conjunction with the first aspect, in the sixth possible implementation, the device connects four photovoltaic units through the interface. Two photovoltaic units are directly connected in parallel, and the remaining two photovoltaic units are connected in series with at least one of the protective switches, then in parallel with the two photovoltaic units, and finally connected in parallel to the DC bus. The controller can control the protective switches to open in the event of a short-circuit fault, thereby protecting the photovoltaic units and lines in the photovoltaic system.

[0018] In conjunction with the first aspect, in the seventh possible implementation, the device connects four photovoltaic units through the interface. One photovoltaic unit is connected in series with at least one of the protective switches and then connected in parallel to the DC bus. The other three photovoltaic units are directly connected in parallel to the DC bus. In this case, the photovoltaic unit or line can withstand the output current of two photovoltaic units, and the controller can control the protective switch to open in the event of a short-circuit fault, thereby protecting the photovoltaic units and lines in the photovoltaic system.

[0019] In conjunction with the first aspect, in the eighth possible implementation, the device connects four photovoltaic units via the interface. Three of the photovoltaic units are first connected in parallel, then in series with at least one of the protective switches, and finally connected in parallel to the DC bus. The other photovoltaic unit is directly connected in parallel to the DC bus. In this configuration, the photovoltaic unit or line can withstand the output current of two photovoltaic units. The controller can disconnect the protective switch in the event of a short-circuit fault, thereby protecting the photovoltaic units and lines in the photovoltaic system.

[0020] In conjunction with the first aspect, in the ninth possible implementation, when the photovoltaic unit is connected in series with a protection switch, the protection switch is connected in series with the positive or negative output terminal of the photovoltaic unit. By controlling the protection switch to open, the circuit of the corresponding photovoltaic unit can be disconnected.

[0021] In conjunction with the first aspect, in the tenth possible implementation, when the photovoltaic unit is connected in series with the two protection switches, the two protection switches are respectively connected in series with the positive output terminal and the negative output terminal of the photovoltaic unit. By redundantly setting the protection switches, the fault tolerance of the system is improved, and the connection between the short-circuited photovoltaic unit and the system can be completely cut off, facilitating maintenance and repair.

[0022] In conjunction with the first aspect, in the eleventh possible implementation, when multiple photovoltaic units are first connected in parallel and then connected in series with a protection switch, the positive output terminals of the multiple photovoltaic units are connected in parallel and then connected in series with a protection switch, or the negative output terminals of the multiple photovoltaic units are connected in parallel and then connected in series with another protection switch. By controlling the protection switch to open, the circuit of the corresponding photovoltaic unit can be controlled to be disconnected.

[0023] In conjunction with the first aspect, in the twelfth possible implementation, when multiple photovoltaic units are first connected in parallel and then connected in series with two protection switches, the positive output terminals of the multiple photovoltaic units are connected in parallel and then connected in series with one protection switch, and the negative output terminals of the multiple photovoltaic units are connected in parallel and then connected in series with another protection switch. By redundantly setting the protection switches, the fault tolerance of the system is improved.

[0024] In conjunction with the first aspect, in the thirteenth possible implementation, the controller is used to control the protection switch to open when the reverse current of a branch is greater than the first current value, specifically including: the controller is used to determine that the reverse current of a branch is greater than the first current value when the absolute value of the current of a branch is greater than the absolute value of the current of the DC bus, and then control the protection switch to open.

[0025] This is because when there is no short-circuit fault, the output current of all photovoltaic units flows into the DC bus, and the absolute value of the current in the DC bus is greater than the absolute value of the current in any branch. When a photovoltaic unit experiences a short-circuit fault, the output current of the other normal photovoltaic units will flow to the short-circuited photovoltaic unit. At this time, the absolute value of the current in the DC bus is less than the absolute value of the current in any branch.

[0026] In conjunction with the first aspect, in the fourteenth possible implementation, the device further includes: a first current sensor and a second current sensor; the first current sensor is used to acquire the absolute value of the current of the DC bus and send it to the controller; the second current sensor is used to acquire the absolute value of the current of a preset branch and send it to the controller.

[0027] The controller determines whether there is a short circuit fault in a photovoltaic unit or line by comparing the absolute value of the current in the branch with the absolute value of the current in the DC bus.

[0028] In conjunction with the first aspect, in the fifteenth possible implementation, the device further includes: a power circuit;

[0029] The power circuit is a DC-DC converter or a DC-AC converter.

[0030] In conjunction with the first aspect, in a sixteenth possible implementation, the device further includes: a first voltage sensor and a DC switch; the DC bus is connected to the input terminal of the power circuit via the DC switch; the first voltage sensor is used to acquire the absolute value of the voltage of the DC bus and send it to the controller.

[0031] In conjunction with the first aspect, in the seventeenth possible implementation, the controller is used to control the protection switch to open when the reverse current of the existing branch is greater than the first current value, specifically including: when the current direction of the existing branch is opposite to the preset current direction, the controller determines that the reverse current of the existing branch is greater than the first current value, and controls the protection switch to open.

[0032] This is because when a photovoltaic unit experiences a short circuit fault, the current from all other normal photovoltaic units flows into the branch containing the faulty photovoltaic unit, causing the current detection direction of the branch containing the faulty photovoltaic unit to be opposite to the preset direction when it is normal. Conversely, when the branch containing the photovoltaic unit is normal, but there is a short circuit fault in other branches, the branch containing the photovoltaic unit outputs current to the branch with the short circuit fault, and the current detection direction in other branches is opposite to the preset current direction.

[0033] In conjunction with the first aspect, in the eighteenth possible implementation, the device further includes: a third current sensor and a fourth current sensor; the third current sensor is used to acquire the current detection direction of the first detection point and send it to the controller, the first detection point being located in any branch; the fourth current sensor is used to acquire the current detection direction of the second detection point and send it to the controller, all other branches except the branch where the first detection point is located converge at the second detection point.

[0034] In conjunction with the first aspect, in the nineteenth possible implementation, the controller is specifically used to: control the protection switch to open when the current detection direction of the first detection point is opposite to the preset current direction of the first detection point, or when the current detection direction of the second detection point is opposite to the preset current direction of the second detection point.

[0035] In conjunction with the first aspect, in the twentieth possible implementation, the protection device further includes: a power circuit; the power circuit is a DC-DC converter circuit or a DC-AC converter circuit.

[0036] In conjunction with the first aspect, in a twenty-first possible implementation, the device further includes: a fifth current sensor, a second voltage sensor, and a DC switch; the DC bus is connected to the input terminal of the power circuit via the DC switch; the fifth current sensor is used to acquire the absolute value of the current of the DC bus and send it to the controller; the second voltage sensor is used to acquire the absolute value of the voltage of the DC bus and send it to the controller.

[0037] In conjunction with the first aspect, in the twenty-second possible implementation, when a short circuit occurs inside the protection device, a short circuit occurs on the DC bus, or a short circuit occurs on the DC bus of the subsequent circuit, the voltage of the DC bus will decrease and the current will increase. Therefore, the controller is also used to: control the DC switch to open when the absolute value of the current of the DC bus is greater than the second current value and the absolute value of the voltage of the DC bus is less than the first voltage value, thereby protecting the circuit.

[0038] In conjunction with the first aspect, in the twenty-third possible implementation, when the photovoltaic unit and the protection unit are connected in series or in parallel and then connected to the device through the interface, the protection switch is also used to prevent the protection unit from triggering a protection action when disconnected.

[0039] That is, when upgrading a photovoltaic power generation system that currently uses a protection unit, it is not necessary to remove the protection unit so that it can be directly connected to the circuit breaker protection device.

[0040] In conjunction with the first aspect, in the twenty-fourth possible implementation, the protection unit includes at least one of the following: a fuse, an optimizer, and a shutdown box.

[0041] In conjunction with the first aspect, in the twenty-fifth possible implementation, when the device includes at least two protective switches, the at least two protective switches are controlled by the same controller or by multiple controllers.

[0042] In conjunction with the first aspect, in one possible implementation, the controller is specifically used to determine that a fault has occurred in the photovoltaic power generation system when the detected parameter value of a branch exceeds a first preset parameter value range, or when the detected parameter value of the DC bus exceeds a second preset parameter value range. The detected parameter value can be at least one of voltage, current, power, or temperature values.

[0043] When the measured parameter values ​​are abnormal, such as a decrease in branch voltage, an increase in current, an increase in power, or an increase in temperature, it can be determined that a short circuit fault has occurred in that branch.

[0044] In conjunction with the first aspect, in one possible implementation, the controller is specifically used to determine that a fault has occurred in the photovoltaic power generation system when the leakage current detection value of the DC bus is greater than a third current value, or when the leakage current detection value of a branch is greater than a fourth current value. When an abnormal leakage current detection value occurs, it indicates that a leakage current fault has occurred in the photovoltaic power generation system. Using the solution of this application, a leakage current fault can be defined, the branch where the leakage current fault occurs can be determined, or the leakage current fault can be located on the DC bus.

[0045] In conjunction with the first aspect, in one possible implementation, the controller is specifically used to determine that a fault has occurred in the photovoltaic power generation system when it is determined, based on the current detection values ​​of all branches, that an arc fault has occurred in a branch, or based on the current detection value of the DC bus, that an arc fault has occurred on the DC bus. Specifically, the controller can determine whether an arc fault exists based on the degree of deviation between the current detection value and a preset standard value.

[0046] In conjunction with the first aspect, in one possible implementation, the controller is also used to control the protection switch to open or close according to the control instructions sent by the host computer, thereby realizing the active control of the protection switch.

[0047] In conjunction with the first aspect, in one possible implementation, at most three photovoltaic units are directly connected in parallel to one interface, or at most three photovoltaic units are connected in parallel within the device through their respective interfaces.

[0048] In conjunction with the first aspect, in one possible implementation, the protective switch is a rotary DC disconnector or a DC circuit breaker.

[0049] In conjunction with the first aspect, in one possible implementation, the controller is also used to control the closing of the protection switch when it is determined that the fault has been cleared or after a preset time has elapsed.

[0050] In conjunction with the first aspect, in one possible implementation, the protection device further includes a DC / DC converter. The DC bus is connected to the input terminal of the DC / DC converter, and the output terminal of the DC / DC converter is the output terminal of the protection device for the photovoltaic power generation system. The DC / DC converter is used to convert the DC power obtained from the DC bus into DC power before outputting it. In this case, the protection device for the photovoltaic power generation system is a step-up DC combiner box.

[0051] In conjunction with the first aspect, in one possible implementation, the protection device further includes a DC / AC converter, with the DC bus connected to the input terminal of the DC / AC converter, and the output terminal of the DC / AC converter serving as the output terminal of the protection device for the photovoltaic power generation system. The DC / AC converter is used to convert the DC power obtained from the DC bus into AC power for output. In this case, the protection device for the photovoltaic power generation system is an inverter.

[0052] Secondly, this application also provides a protection method for a photovoltaic power generation system, applied to a control and protection device. The device connects at least two photovoltaic units via an interface. These at least two photovoltaic units are coupled to a DC bus within the device to form at least two branches, each branch connecting at least one photovoltaic unit. A protection switch is used to disconnect all or part of the photovoltaic units from the DC bus, allowing up to three photovoltaic units to be directly connected in parallel. The method includes:

[0053] When a fault is detected in the photovoltaic power generation system based on the parameter detection values ​​of the branch or DC bus, the control protection switch is disconnected.

[0054] In conjunction with the second aspect, in one possible implementation, the parameter detection value is the reverse current value. A fault in the photovoltaic power generation system is determined based on the parameter detection value of the branch or DC bus, specifically including:

[0055] When the reverse current value of a branch exceeds the first current value, it is determined that there is a fault in the photovoltaic power generation system.

[0056] Using this method, when the protective switch is open, up to three photovoltaic units are directly connected in parallel. Therefore, when one photovoltaic unit can withstand the current output by two photovoltaic units, when a photovoltaic unit fails, at most two normal photovoltaic units will output current to it. At this time, the current is within the withstand range of the failed photovoltaic unit, thus protecting the photovoltaic modules and lines from damage.

[0057] In conjunction with the second aspect, in one possible implementation, the parameter detection value is the reverse current value. A fault in the photovoltaic power generation system is determined based on the parameter detection value of the branch or DC bus, specifically including:

[0058] When the reverse current value of a branch exceeds the first current value, it is determined that there is a fault in the photovoltaic power generation system.

[0059] In conjunction with the second aspect, in a first possible implementation, the device further includes a power circuit, the DC bus is connected to the input terminal of the power circuit via a DC switch, and the method further includes: controlling the DC switch to open when the absolute value of the current of the DC bus is greater than a second current value and the absolute value of the voltage of the DC bus is less than a first voltage value.

[0060] Using this method, the short-circuit current can be cut off in time when a positive or negative short circuit occurs inside the protection device or when a short circuit occurs on the downstream bus, thereby protecting the device and the downstream circuit.

[0061] In conjunction with the second aspect, in the second possible implementation, the power circuit is a DC-DC converter circuit or a DC-AC converter circuit.

[0062] In conjunction with the second aspect, in one possible implementation, the parameter detection value is at least one of voltage, current, power, or temperature values. A fault in the photovoltaic power generation system is determined based on the parameter detection values ​​of the branch or DC bus, specifically including:

[0063] When the parameter detection value of the branch exceeds the first preset parameter value range, or when the parameter detection value of the DC bus exceeds the second preset parameter value range, it is determined that the photovoltaic power generation system has failed.

[0064] In conjunction with the second aspect, one possible implementation involves determining a photovoltaic power generation system fault based on parameter detection values ​​of a branch or DC bus, specifically including:

[0065] When the leakage current detection value of the DC bus is greater than the third current value, or when the leakage current detection value of a branch is greater than the fourth current value, it is determined that the photovoltaic power generation system has failed.

[0066] In conjunction with the second aspect, one possible implementation involves determining a photovoltaic power generation system fault based on parameter detection values ​​of a branch or DC bus, specifically including:

[0067] When an arc fault is detected in a branch based on the current detection values ​​of all branches, or when an arc fault is detected in the DC bus based on the current detection values ​​of the DC bus, a fault is determined to have occurred in the photovoltaic power generation system. Thirdly, this application also provides a photovoltaic power generation system comprising at least two photovoltaic units and the protection device described in any of the above implementations. Each photovoltaic unit includes at least one photovoltaic module. When a photovoltaic unit includes multiple photovoltaic modules, the photovoltaic modules can be connected in series or in a hybrid configuration.

[0068] The controller of the protection device for this photovoltaic power generation system can control the protection switch to open when a fault is detected in the photovoltaic power generation system based on the parameter detection values ​​of the branch or DC bus, so that up to three photovoltaic units can be directly connected in parallel. This protects the photovoltaic units and lines in the photovoltaic system, and because only a protection switch is added to the circuit, its resistance is smaller than that of a fuse, thus reducing the loss rate of the photovoltaic system.

[0069] In conjunction with the third aspect, in the first possible implementation, the system further includes: a protection unit, wherein the photovoltaic unit and the protection unit are connected in series or in parallel and then connected to the protection device through the interface.

[0070] Therefore, when upgrading a photovoltaic power generation system that currently uses a protection unit, it is not necessary to remove the protection unit so that it can be directly connected to the circuit breaker protection device.

[0071] In conjunction with the third aspect, in the second possible implementation, the protection unit can be a combination of one or more of a fuse, an optimizer, and a shutdown box.

[0072] When the protection device includes a power circuit, the power circuit can be a DC-DC converter circuit. When the power circuit is a DC-DC converter circuit, the DC-DC converter circuit can specifically be a boost circuit, a buck circuit, or a buck-boost circuit. In this case, the protection device can also be a DC combiner box of a photovoltaic power generation system.

[0073] Power circuits can also be DC-AC conversion circuits, i.e., inverters (or inverter circuits), used to convert DC power into AC power for output.

[0074] When the protection device does not include a power circuit, the protection device can be connected as an independent device to the DC combiner box or the input terminal of the inverter of the photovoltaic power generation system.

[0075] As can be seen from the above technical solutions, the solution provided in this application has at least the following advantages:

[0076] The protection device for photovoltaic power generation systems provided in this application embodiment can be applied to photovoltaic power generation systems. When the protection switch of this device is disconnected, it allows up to three photovoltaic units to be directly connected in parallel. For example, when two photovoltaic units are directly connected in parallel to the DC bus inside the device, if one of the photovoltaic units experiences a short-circuit fault, only one normal photovoltaic unit will output a short-circuit current to it. At this time, the short-circuit current is within the tolerance range of the faulty photovoltaic unit, thereby protecting the photovoltaic modules and lines from damage. The specific connection method between the photovoltaic units and the protection switch can be configured according to actual needs. The controller of this protection device can determine when a fault occurs in the photovoltaic power generation system based on the parameter detection value of the branch or DC bus, and control the protection switch to disconnect, allowing up to three photovoltaic units to be directly connected in parallel, thereby protecting the photovoltaic units and lines in the photovoltaic system. Furthermore, since only a protection switch is added to the circuit, its resistance is smaller than that of a fuse, reducing the loss rate of the photovoltaic system. In addition, since fuses are no longer used, the Y-shaped cable harness, which was originally used for the built-in fuse, no longer needs to be set at the bottom of the inverter or DC combiner box of the photovoltaic power generation system, but can be configured on the photovoltaic unit side, thereby reducing cable costs. Attached Figure Description

[0077] Figure 1 Schematic diagram of a protection device used in the prior art Figure 1 ;

[0078] Figure 2 Schematic diagram of a protection device used in the prior art Figure 2 ;

[0079] Figure 3 Schematic diagram of a protection device used in the prior art Figure 3 ;

[0080] Figure 4 A schematic diagram of a branch provided in an embodiment of this application;

[0081] Figure 5 A schematic diagram of another branch provided in an embodiment of this application;

[0082] Figure 6A A schematic diagram of a protection device provided in an embodiment of this application;

[0083] Figure 6B A schematic diagram of another protection device provided in the embodiments of this application;

[0084] Figure 6C A schematic diagram of yet another protection device provided in the embodiments of this application;

[0085] Figure 7 A schematic diagram of another protection device provided in the embodiments of this application;

[0086] Figure 8 A schematic diagram of yet another protection device provided in the embodiments of this application;

[0087] Figure 9 A schematic diagram of another protection device provided in the embodiments of this application;

[0088] Figure 10 A schematic diagram of another protection device provided in the embodiments of this application;

[0089] Figure 11 A schematic diagram of yet another protection device provided in the embodiments of this application;

[0090] Figure 12 A schematic diagram of another protection device provided in the embodiments of this application;

[0091] Figure 13 A schematic diagram of another protection device provided in the embodiments of this application;

[0092] Figure 14 A schematic diagram of yet another protection device provided in the embodiments of this application;

[0093] Figure 15 A schematic diagram of another protection device provided in the embodiments of this application;

[0094] Figure 16 A schematic diagram of another protection device provided in the embodiments of this application;

[0095] Figure 17 A schematic diagram of yet another protection device provided in the embodiments of this application;

[0096] Figure 18 A schematic diagram of another protection device provided in the embodiments of this application;

[0097] Figure 19 A schematic diagram of another protection device provided in the embodiments of this application;

[0098] Figure 20A A schematic diagram of yet another protection device provided in the embodiments of this application;

[0099] Figure 20B A schematic diagram of another protection device provided in the embodiments of this application;

[0100] Figure 20C A schematic diagram of another protection device provided in the embodiments of this application;

[0101] Figure 21A schematic diagram of another protection device provided in the embodiments of this application;

[0102] Figure 22 A flowchart illustrating a short-circuit protection method provided in this application embodiment;

[0103] Figure 23 A flowchart illustrating another short-circuit protection method provided in this application embodiment;

[0104] Figure 24 This is a schematic diagram of a photovoltaic power generation system provided in an embodiment of this application. Detailed Implementation

[0105] To improve the DC ratio of a photovoltaic power generation system, each MPPT device is typically connected to at least two or more photovoltaic units. To protect the photovoltaic units and lines in the event of a short circuit, a fuse (or circuit breaker) is connected in series at the positive and / or negative output terminals of the photovoltaic unit. The following explanation uses an example of each MPPT device connected to three branches. The principle is similar when each MPPT device is connected to more branches, and will not be elaborated further here.

[0106] See also Figures 1 to 3 .in, Figure 1 A schematic diagram showing that both the positive and negative output terminals of a photovoltaic unit are connected in series with fuses; Figure 2 A schematic diagram showing a fuse connected in series with the positive output terminal of a photovoltaic unit; Figure 3 This is a schematic diagram of a fuse connected in series with the negative output terminal of a photovoltaic unit.

[0107] Each branch includes a photovoltaic module 101. The three branches are connected in parallel before the switch 102 and then connected to the MPPT device 103 through the DC switch 102. Figure 1 fuse1-fuse6 Figure 2 Fuse1-Fuse3 and Figure 3 Fuse1-Fuse3 in the circuit are fuses that melt when the current in the circuit is too high to protect the photovoltaic modules and the circuit.

[0108] However, due to the relatively small actual output current of the photovoltaic unit, the fuse is difficult to blow. Taking a fuse with a rated current of 15A as an example, according to the standard specifications for fuses, the allowable current when the fuse does not blow can reach 1.13 × 15 = 16.95A. The current required to blow within one hour is 1.35 × 15 = 20.25A. However, the short-circuit current is insufficient to meet the current required for the fuse to blow, so the fuse may not blow, resulting in ineffective protection of the photovoltaic unit and the line. In addition, the internal resistance of each fuse can reach 9 milliohms, resulting in significant power loss and heat generation. In some embodiments, due to the need to protect the cable, the Y-shaped harness with the built-in fuse needs to be placed at the bottom of the device, which further increases the cable cost.

[0109] To address the aforementioned technical problems, this application provides a protection device, a short-circuit protection method, and a photovoltaic power generation system, which can effectively protect the photovoltaic unit and the line when a short circuit occurs in the photovoltaic unit or the line, and has low power loss. The following is a detailed description in conjunction with the accompanying drawings.

[0110] In the following description, terms such as "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature specified with "first," "second," etc., may explicitly or implicitly include one or more of that feature.

[0111] In this application, unless otherwise expressly specified and limited, the term "connection" shall be interpreted broadly. For example, "connection" may be a fixed connection, a detachable connection, or an integral part; it may be a direct connection or an indirect connection through an intermediate medium.

[0112] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of this application will be clearly described below with reference to the accompanying drawings.

[0113] Device Example 1:

[0114] In the following embodiments, a single photovoltaic unit may include a photovoltaic module, or it may be formed by connecting multiple photovoltaic modules in series and parallel. For example, multiple photovoltaic modules may be connected in series to form a photovoltaic string, and multiple photovoltaic strings may be connected in parallel to form a photovoltaic unit. This application does not specifically limit the number of photovoltaic modules included in a photovoltaic unit; those skilled in the art can set it according to actual needs. Furthermore, this application does not specifically limit the electrical parameters of a single photovoltaic module. The output voltages of multiple photovoltaic units connected to the same device may be the same or different; this application does not specifically limit this.

[0115] The protection device provided in this application embodiment is applied to a photovoltaic power generation system. It can connect at least two photovoltaic units through an interface. After the photovoltaic units are connected through the interface, they can be directly connected in parallel to the DC bus inside the device, or connected in series with the protection switch and then connected in parallel to the DC bus, so as to collect the output current of the photovoltaic units to the DC bus, thereby forming at least two branches inside the device. Each branch is connected to at least one photovoltaic unit. The form of the branches is described in detail below.

[0116] See Figure 4 This figure is a schematic diagram of a branch provided in an embodiment of this application.

[0117] The branch includes a photovoltaic unit 101a1. The positive output terminal of the photovoltaic unit 101a1 is the positive output terminal of the branch, and the negative output terminal of the photovoltaic unit 101a1 is the negative output terminal of the branch. This distinction will not be made in the following description of the embodiments.

[0118] See Figure 5 This figure is a schematic diagram of another branch provided in an embodiment of this application.

[0119] This branch road can include multiple Figure 4 The branch shown therefore includes at least two photovoltaic units, for example, 101a1, 101a2, ... 101ai in sequence. In some embodiments, when the branch includes multiple photovoltaic units, the branch may also include a protective switch (not shown) to protect the photovoltaic units and the line.

[0120] It is understood that the branch in the embodiments of this application is a concept in the field of electrical engineering, referring to the path through which the branch current flows in a parallel circuit, continuing in... Figure 5 For example, the line where photovoltaic unit 101a1 is located can be called a branch, and the line formed by photovoltaic unit 101a1 and photovoltaic unit 101a1 connected in parallel can also be called a branch.

[0121] The positive output terminals of each photovoltaic unit are combined to form the positive output terminal of the branch, and the negative output terminals of each photovoltaic unit are combined to form the negative output terminal of the branch.

[0122] In the following embodiments, "branch" specifically refers to all Figure 4 The branch shown and Figure 5 The term "branch" refers to all branches except the main branch (DC bus).

[0123] The working principle of this protection device will be explained in detail below with reference to the attached diagram.

[0124] See Figure 6A The figure is a schematic diagram of a protection device provided in an embodiment of this application.

[0125] The protection device 200 includes an interface and protection switches S1-S1. M-1 DC bus and controller (not shown in the figure).

[0126] The device 200 can connect to at least two photovoltaic units via an interface. This application does not specify the number of photovoltaic units that can be connected. The at least two photovoltaic units are coupled to a DC bus inside the device to form at least two branches, and each branch is connected to at least one photovoltaic unit.

[0127] When this protection device is applied to a photovoltaic power generation system, the DC bus specifically includes a positive DC bus and a negative DC bus.

[0128] Among them, protective switches S1-S M-1 It is used to disconnect all or part of the photovoltaic units from the DC bus, so that up to three photovoltaic units can be directly connected in parallel. In other words, it is used to connect up to three photovoltaic units directly in parallel to the DC bus inside the device when disconnected.

[0129] For example, when a single photovoltaic unit experiences a short-circuit fault, if the faulty photovoltaic unit can withstand the output current of one other normal photovoltaic unit, then the protection switch S1-S M-1 When disconnected, at most two photovoltaic units are directly connected in parallel inside the device, and the values ​​of i and j in the figure are 2.

[0130] For example, when a single photovoltaic unit experiences a short-circuit fault, if the faulty photovoltaic unit can withstand the output current of two other normal photovoltaic units, then the protection switch S1-S M-1 When disconnected, up to 3 photovoltaic units are directly connected in parallel inside the device, and the values ​​of i and j in the figure are 3.

[0131] The specific values ​​of i and j are determined by the actual current withstand value of the photovoltaic unit, and are not specifically limited in this embodiment. It should be noted that... Figure 6A The diagram shown is for ease of illustration and explanation only. The i photovoltaic units in the diagram are actually connected in parallel inside the protection device.

[0132] For ease of explanation, the following description uses the example of i and j being 2. In other embodiments, the principle is similar when i and j are 3, which will not be repeated here.

[0133] The controller is used to disconnect the protection switch when a fault is determined to have occurred in the photovoltaic power generation system based on the parameter detection values ​​of the branch or DC bus. The following explanation uses a short-circuit fault as an example. Specifically, when the parameter detection value is a reverse current value, the controller is used to determine that a fault exists in the photovoltaic power generation system if the reverse current value of a branch exceeds a first current value.

[0134] The following explains the principle by which the controller implements its protection function.

[0135] When there is no short-circuit fault, the current from all branches flows into the DC bus. Therefore, the absolute value of the current on the DC bus is greater than the absolute value of the current in any branch, and the current flows from the positive terminal of the photovoltaic unit to the positive DC bus. However, when a short-circuit fault occurs in any branch, the output current from all other normal branches flows to the branch with the short-circuit fault. This causes the voltage of the DC bus to drop, and the current direction of some branches changes to flow towards the branch with the short-circuit fault, meaning that the reverse current of some branches is greater than a first current value. The first current value can be determined according to the actual situation, and this application does not impose a specific limitation. Preferably, in order to detect the short-circuit fault as early as possible and trigger the protection action of the protection switch, the first current value can be a small value, such as 0. That is, when a branch has a reverse current, the controller controls the protection switch to open.

[0136] At this point, the controller determines that a short circuit fault has occurred in a photovoltaic unit or line, and the control protection switch is disconnected to protect the photovoltaic unit and line.

[0137] In some embodiments, the protection device 200 further includes a power circuit 201 for power conversion, which may be a DC / DC converter or a DC / AC converter.

[0138] When the power circuit 201 is a DC-DC converter circuit, the DC-DC converter circuit can specifically be a boost circuit, a buck circuit, or a buck-boost circuit. In this case, the protection device can be used as a DC combiner box for a photovoltaic power generation system. This application does not make any specific limitations on this.

[0139] When the power circuit 201 is a DC-AC circuit, it is used to convert DC power into AC power for output. In this case, the protection device can be used as an inverter for a photovoltaic power generation system.

[0140] In other embodiments, the protection device may also be installed as a separate device at the input end of the DC combiner box or inverter of the photovoltaic power generation system.

[0141] In summary, the protection device provided in this application embodiment can connect to multiple photovoltaic units via an interface. When the protection switch of the device is disconnected, up to three photovoltaic units are directly connected in parallel within the device to protect the photovoltaic modules and lines from damage. The specific connection method between the photovoltaic units and the protection switch can be configured according to actual needs. The controller of the device can control the protection switch to open when the reverse current of a branch exceeds a first current value, thereby protecting the photovoltaic units and lines in the photovoltaic system. Furthermore, since only a protection switch is added to the circuit, its resistance is smaller than that of a fuse, thus reducing the loss rate of the photovoltaic system. In addition, since fuses are no longer used, the Y-shaped cable harness, which was originally used for built-in fuses, no longer needs to be located at the bottom of the inverter or DC combiner box of the photovoltaic power generation system, but can be configured on the photovoltaic unit side, thereby reducing cable costs.

[0142] The above explanation uses the example of allowing a faulty photovoltaic module to withstand reverse current from other photovoltaic modules. In practical applications, to better comply with safety regulations, the protective switch is used to disconnect all photovoltaic units from the DC bus. See details... Figure 6B As shown.

[0143] See Figure 6B This figure is a schematic diagram of another protection device provided in an embodiment of this application.

[0144] Figure 6B and Figure 6A The difference is that it also includes protection switches S01 and S02, which disconnects all photovoltaic units from the DC bus when all protection switches are off, that is, disconnects all interfaces from the DC bus.

[0145] Furthermore, the above descriptions all use the example of up to three photovoltaic units directly connected in parallel to one interface. In other embodiments, up to three photovoltaic units are connected in parallel within the device through corresponding interfaces. For specific implementation details, please refer to [link to relevant documentation]. Figure 6C As shown.

[0146] In some embodiments, the controller determines that the reverse current of a branch is greater than the first current value when the absolute value of the current in the branch is greater than the absolute value of the current in the DC bus, or when the reverse current of a branch is greater than the first current value, and controls the protection switch to open. The working principle of the controller is explained below with reference to the specific implementation method.

[0147] Device Example 2:

[0148] The following explanation will take the connection of the protection device to two photovoltaic units as an example.

[0149] See Figure 7This figure is a schematic diagram of another protection device provided in an embodiment of this application.

[0150] The protection device 200 is connected to two photovoltaic units 101a1 and 101a2 via an interface.

[0151] After the two photovoltaic units are connected in parallel within the protection device 200, they are connected to the power circuit 201 via a DC switch 102. The DC switch 102 is used to protect the circuit, and in some embodiments, it can be omitted and short-circuited.

[0152] At least one photovoltaic unit is also connected in series with a protection switch S1.

[0153] The following explains the principle by which the controller uses the absolute value of the detected current to achieve the protection function.

[0154] When there is no short-circuit fault, the current from the two photovoltaic units flows into the DC bus, and the absolute value of the current on the DC bus (the absolute value of the current detected at detection point A or detection point B) is greater than the absolute value of the current in any branch (the absolute value of the current detected at detection point C or detection point D).

[0155] When a photovoltaic unit experiences a short circuit fault, the output current of another normal photovoltaic unit will flow to the short-circuited photovoltaic unit. At this time, the absolute value of the current on the DC bus is less than the absolute value of the current in any branch.

[0156] When the absolute value of the current in a branch is greater than the absolute value of the current in the DC bus, the controller will open the protection switch S1.

[0157] Specifically, when a short circuit fault occurs in the branch where photovoltaic unit 101a1 is located, the protection switch S1 is opened, causing photovoltaic unit 101a2 to stop outputting current, thereby protecting the photovoltaic unit and the line; when a short circuit fault occurs in the branch where photovoltaic unit 101a2 is located, the protection switch S1 is opened, causing the short-circuited branch to be disconnected, and photovoltaic unit 101a1 can continue to output current to device 200, maintaining normal operation.

[0158] In some embodiments, the magnitude and direction of the current can be detected by a current sensor, and the current sensor sends the detection result to the controller of the device 200.

[0159] The above implementation can be achieved by detecting the absolute value of the current at point A or B using a first current sensor, and by detecting the absolute value of the current at point C or D using a second current sensor.

[0160] In some embodiments, the protection switch S1 can be connected in series with the positive output terminal of the photovoltaic unit 102a2, or in series with the negative output terminal of the photovoltaic unit 102a2. Alternatively, a photovoltaic unit can be connected in series with both the positive and negative output terminals of the photovoltaic unit 102a2 to achieve redundant control. This application embodiment does not specifically limit this.

[0161] The following explains the principle by which the controller uses the detection of current direction to achieve protection functions.

[0162] When there is no short-circuit fault, the current direction at detection point C and detection point D can be set to a preset direction, such as the positive direction.

[0163] When a short circuit fault occurs in the branch where photovoltaic unit 101a1 is located, the output current of photovoltaic unit 101a2 flows into the branch where photovoltaic unit 101a1 is located, causing the current direction at detection point C to be opposite to the preset current direction, i.e., negative. At this time, the controller controls the protection switch S1 to open, causing photovoltaic unit 101a2 to stop outputting current, thereby protecting the photovoltaic unit and the line. Conversely, when a short circuit fault occurs in the branch where photovoltaic unit 101a2 is located, the output current of photovoltaic unit 101a1 flows into the branch where photovoltaic unit 101a2 is located, causing the current direction at detection point D to be opposite to the preset current direction. At this time, the controller controls the protection switch S1 to open, breaking the short circuit in the branch, while photovoltaic unit 101a1 can continue to output current to the protection device 200 normally.

[0164] This method can be achieved by detecting the current direction at point C using a third current sensor and the current direction at point D using a fourth current sensor.

[0165] In the above embodiments, detection points C and D can also be located on the negative output side of the corresponding photovoltaic unit, or one can be located on the positive output side of the photovoltaic unit and the other on the negative output side of the photovoltaic unit. In this case, the working principle of the controller is similar, and will not be described again here.

[0166] In summary, when the protection device connects two photovoltaic units via an interface, its controller can open the protection switch to ensure that the current in any branch is less than a first current value when the absolute value of the branch current is greater than the absolute value of the DC bus current, or when the direction of the branch current is opposite to the preset current direction. This protects the photovoltaic units and the circuit. Furthermore, since only a protection switch is added to the circuit, its resistance is much smaller than that of a fuse (in some embodiments, the internal resistance of the applied protection switch is only about 0.3 milliohms, which is less than that of a fuse), thus reducing loss rate. In addition, the Y terminal can be configured on the photovoltaic unit side, thereby reducing cable costs.

[0167] The above embodiments are illustrated using the protection device connected to two photovoltaic units as an example. However, in order to improve the DC ratio of the photovoltaic power generation system, the protection device is usually connected to 3, 4, or even more photovoltaic units. The working principle of each device connected to 3 photovoltaic units will be explained below.

[0168] Device Example 3:

[0169] See Figure 8 This figure is a schematic diagram of another protection device provided in an embodiment of this application.

[0170] The positive output terminals of the three photovoltaic units are connected in parallel inside the protection device and then connected to the power circuit 201 through the DC switch 102. The DC switch 102 is used for the protection circuit, but in practical applications, it can also be omitted and short-circuited.

[0171] Photovoltaic unit 101a1 is connected in series with protection switch S1 and then in parallel to the DC bus. Photovoltaic unit 101a3 is connected in series with protection switch S2 and then in parallel to the DC bus.

[0172] The following explains the principle by which the controller uses the absolute value of the detected current to achieve the protection function.

[0173] When there is no short-circuit fault, the output current of the three photovoltaic units flows into the DC bus. Therefore, the absolute value of the current in the DC bus (the absolute value of the current detected at detection point A or detection point B) is greater than the absolute value of the current in any branch (the absolute value of the current detected at detection points C, D and E).

[0174] When a photovoltaic unit experiences a short-circuit fault, the output current of other normal photovoltaic units will flow to the photovoltaic unit with the short-circuit fault. This causes the absolute value of the current on the DC bus to be less than the absolute value of the current in any branch.

[0175] When the absolute value of the current on the DC bus is less than the absolute value of the current in any branch, the controller of the protection device controls the protection switches S1 and S2 to open so that the current flowing into the short-circuit branch is zero, thereby protecting the photovoltaic unit and the line.

[0176] This implementation method can be achieved by using a first current sensor to detect the absolute value of the current in the DC bus (i.e., detection point A or B) and a second current sensor to detect the absolute value of the current in any branch (i.e., detection point C, D or E).

[0177] The following explains the principle by which the controller uses the detection of current direction to achieve protection functions.

[0178] When there is no short-circuit fault, the current direction at points C, D, and E can be set to a preset current direction, such as the positive direction.

[0179] When a photovoltaic unit experiences a short circuit fault, the output current of other normal photovoltaic units will flow to the photovoltaic unit with the short circuit fault, causing the current direction in the photovoltaic unit with the short circuit fault to be opposite to the preset direction. At this time, the controller controls the protection switches S1 and S2 to open so that the current flowing into the short circuit branch is zero, thereby protecting the photovoltaic unit and the line.

[0180] This method can be achieved by using three current sensors to detect the current direction of the three first-type photovoltaic unit branches respectively.

[0181] In another possible implementation, to reduce the number of current sensors used, the presence of a short-circuit fault can be determined by detecting the current direction at points G and F. When a short-circuit fault exists in the branch containing photovoltaic units 101a1 and 101a3, the current detection direction at point H will be opposite to the preset current direction. Similarly, when a short-circuit fault exists in the branch containing photovoltaic unit 101a2, the current detection direction at point G will be opposite to the preset current direction. The controller can then disconnect the protection switch to protect the photovoltaic units and the circuit when the current detection direction at points H and G is opposite to the preset current direction.

[0182] This method can detect the current direction at point G using a third current sensor and the current direction at point H using a fourth current sensor, which reduces the number of current sensors used compared to the previous method.

[0183] In some embodiments, the protection switch S1 or protection switch S2 can also be deactivated and short-circuited. In this case, after the controller controls the protection switch to open, the current flowing into the branch of the short-circuit fault can be less than the first current value.

[0184] In summary, when this protection device is connected to three photovoltaic units via an interface, the controller can open the protection switch to ensure that the current in any branch is less than a first current value when the absolute value of the current in a photovoltaic unit is greater than the absolute value of the DC bus current, or when the current direction in a branch is opposite to a preset current direction. This protects the photovoltaic units and the circuit. Furthermore, since only a protection switch is added to the circuit, its resistance is smaller than that of a fuse, thus reducing loss rate. Additionally, the Y-terminal can be configured on the photovoltaic unit side, thereby reducing cable costs.

[0185] Device Example 4:

[0186] See Figure 9 This figure is a schematic diagram of another protection device provided in an embodiment of this application.

[0187] Photovoltaic units 101a1 and 101a2 are directly connected in parallel inside the protection device and then connected to the DC bus. Photovoltaic unit 101a3 is connected in series with the protection switch S1 and then connected in parallel to the DC bus of the device.

[0188] The DC switch 102 is used to protect the circuit, and in some embodiments, it can be omitted and short-circuited. For example, the protection switch S1 is connected in series with the negative terminal of the photovoltaic unit 101a3. In some embodiments, the protection switch S1 can also be connected in series with the positive terminal of the photovoltaic unit 101a3.

[0189] The following explains the principle by which the controller uses the absolute value of the detected current to achieve the protection function.

[0190] When there is no short-circuit fault, the current of each branch flows into the DC bus. Therefore, the absolute value of the current in the DC bus (the absolute value of the current detected at detection point A or detection point B) is greater than the absolute value of the current in any branch (the absolute value of the current detected at detection points C, D, E and F).

[0191] When a short-circuit fault occurs in a branch, the output current of the normal branch will flow to the branch with the short-circuit fault. This causes the absolute value of the current in the DC bus to be less than the absolute value of the current in any branch.

[0192] Therefore, when the absolute value of the current in a branch is greater than the absolute value of the current in the DC bus, the controller of the protection device will open the protection switch S1. Specifically, when a short-circuit fault occurs in the branch where photovoltaic unit 101a3 is located, the opening of protection switch S1 ensures that the current flowing into the faulty branch is zero, allowing photovoltaic units 101a1 and 101a2 to continue outputting current normally. When a short-circuit fault occurs in the branches where photovoltaic units 101a1 and 101a2 are located, the opening of protection switch S1 stops the branch where photovoltaic unit 101a3 is located from outputting current to the faulty branch, thereby protecting the photovoltaic unit and the line.

[0193] This implementation method can be achieved by using a first current sensor to detect the absolute value of the current in the DC bus (detection point A or detection point B), and a second current sensor to detect the absolute value of the current in any branch (detection point C, D, E or F). In other words, two current sensors are required.

[0194] The following explains the principle by which the controller uses the detection of current direction to achieve protection functions.

[0195] When there is no short-circuit fault, the current direction at detection points E and F can be set to a preset direction, such as the positive direction.

[0196] When a short circuit fault occurs in the branch where photovoltaic unit 101a3 is located, the current direction at detection point E will be opposite to the preset current direction; when a short circuit fault occurs in the branches where photovoltaic units 101a1 and 101a2 are located, the current direction at detection point F will be opposite to the preset current direction.

[0197] Therefore, this implementation method can be achieved by using two current sensors to detect the current direction at points E and F respectively. When there is a detection result in the current direction that is opposite to the preset current direction, the controller controls the protection switch S1 to open to protect the photovoltaic unit and the line.

[0198] See Figure 10 This figure is a schematic diagram of another protection device provided in an embodiment of this application.

[0199] Figure 10 The protection device shown is Figure 9 The difference lies in that the protection switch S1 is connected in series at the negative output terminals of photovoltaic units 101a1 and 101a2 (or it can be connected in series at the positive output terminals of photovoltaic units 101a1 and 101a2). The working principle of the controller is similar to that described above, and will not be repeated here in the embodiments of this application.

[0200] The detection points C, D, and E described in the above embodiments can also be located on the negative output side of the corresponding photovoltaic unit.

[0201] In summary, when this protection device is connected to three photovoltaic units via an interface, its controller can disconnect the protection switch to protect the photovoltaic units and the circuit when the absolute value of the current in any branch exceeds the absolute value of the current on the DC bus, or when the current direction in any branch is opposite to the preset current direction. Furthermore, since only a protection switch is added to the circuit, its resistance is lower than that of a fuse, thus reducing loss rate. Additionally, the Y-terminal can be configured on the photovoltaic unit side, thereby reducing cable costs.

[0202] The above embodiments are illustrated using the example of each device having 3 photovoltaic units at its input terminal. The working principle when each device is connected to 4 photovoltaic units is explained below.

[0203] Device Example 5: See Figure 11 This figure is a schematic diagram of another protection device provided in an embodiment of this application.

[0204] The positive output terminals of the four photovoltaic units are connected to the protection switch S1 on the positive DC bus inside the protection device, and the negative output terminals of each first-class photovoltaic unit branch are connected to the negative DC bus after being connected in series with a protection switch inside the protection device.

[0205] The following explains the principle by which the controller uses the absolute value of the detected current to achieve the protection function.

[0206] When there is no short-circuit fault, the current from the four photovoltaic units flows into the DC bus. Therefore, the absolute value of the current in the DC bus (the absolute value of the current detected at detection point A or B) is greater than the absolute value of the current in any branch (the absolute value of the current detected at detection points C, D, E, and F).

[0207] When a photovoltaic unit experiences a short-circuit fault, the output current of other normal photovoltaic units will flow to the photovoltaic unit with the short-circuit fault. At this time, the absolute value of the current on the DC bus is less than the absolute value of the current in any branch. The controller controls the protection switch to open so that the current in the short-circuit branch is 0.

[0208] This implementation method can be achieved by using a first current sensor to detect the absolute value of the current at points A and B on the DC bus, and a second current sensor to detect the absolute value of the current in any branch of the first type of photovoltaic unit (any point among detection points C, D, E, or F).

[0209] The following explains the principle by which the controller uses the detection of current direction to achieve protection functions.

[0210] When there is no short-circuit fault, the current direction at points C, D, E, and F can be set to a preset direction, such as the positive direction.

[0211] When a photovoltaic unit experiences a short circuit fault, the output current of other normal photovoltaic units will flow to the short-circuited photovoltaic unit, causing the current direction in the branch where the short-circuited photovoltaic unit is located to be opposite to the preset direction. At this time, the controller controls the protection switch to open so that the current flowing into the faulty branch is zero, thereby protecting the photovoltaic unit and the line.

[0212] This method can be achieved by using four current sensors to detect the current direction of the four first-type photovoltaic unit branches respectively.

[0213] In another possible implementation, in order to reduce the number of current sensors used, the presence of a short circuit fault can also be determined by detecting the current direction at points G and F.

[0214] When there is no short-circuit fault, the current direction at points G and H can be set to a preset direction, such as the positive direction.

[0215] When a short circuit fault occurs in the branch where photovoltaic units 101a1, 101a3 and 101a4 are located, the current detection direction at point H will be opposite to the preset current direction. When a short circuit fault occurs in the branch where photovoltaic unit 101a2 is located, the current detection direction at point G will be opposite to the preset direction.

[0216] This method can be achieved by using two current sensors to detect the current direction at points G and H respectively.

[0217] In some embodiments, the protection switches S1, S2 and S3 can also be deactivated and short-circuited. In this case, the controller controls the protection switches to open so that the current flowing into the short-circuit branch is less than the first current value to protect the photovoltaic unit and the line.

[0218] See Figure 12 This figure is a schematic diagram of another protection device provided in an embodiment of this application.

[0219] Figure 12 As another possible implementation, with Figure 11 The difference shown is that the positive output terminals of photovoltaic unit 101a1 and photovoltaic unit 101a2 are connected to protection switch S1 and then connected to the positive DC bus through protection switch S1; the positive output terminals of photovoltaic unit 101a3 and photovoltaic unit 101a4 are connected to protection switch S6 and then connected to the positive DC bus through protection switch S6.

[0220] At this time, the controller can adopt Figure 11 The corresponding working principle will not be described in detail in the embodiments of this application.

[0221] See Figure 13 This figure is a schematic diagram of another protection device provided in an embodiment of this application.

[0222] Figure 13 As another possible implementation, with Figure 11 The difference between the two methods is that: a protection switch is connected in series at the positive output terminal of each photovoltaic unit and then converges to the positive DC bus; a protection switch is connected in series at the negative output terminal of each photovoltaic unit and then converges to the negative DC bus. This redundant protection switch configuration further enhances safety, ensuring that the branch containing the photovoltaic unit can be disconnected.

[0223] At this time, the controller can adopt Figure 11 The corresponding working principle will not be described in detail in the embodiments of this application.

[0224] It is understood that the detection points C, D, E and F described in the above embodiments can also be located on the negative output side of the corresponding photovoltaic unit.

[0225] In summary, when this protection device is connected to four photovoltaic units via an interface, its controller can open the protection switch to ensure that the current in any branch is less than a first current value when the absolute value of the branch current exceeds the absolute value of the DC bus current, or when the current direction of a photovoltaic unit is opposite to the preset current direction. This protects the photovoltaic units and the circuit. Furthermore, since only a protection switch is added to the circuit, its resistance is smaller than that of a fuse, thus reducing loss rate. Additionally, the Y-terminal can be configured on the photovoltaic unit side, thereby reducing cable costs.

[0226] Device Example 6:

[0227] See Figure 14 This figure is a schematic diagram of another protection device provided in an embodiment of this application.

[0228] Photovoltaic units 101a1 and 101a2 are connected in parallel to the DC bus of the device, and the branches containing photovoltaic units 101a3 and 101a4 are connected in series with a protection switch and then connected to the DC bus of the device.

[0229] Specifically, the positive output terminals of the two Class I photovoltaic unit branches are connected to the positive DC bus after being combined, and the negative output terminals of the two Class I photovoltaic unit branches are connected to the negative DC bus after being connected in series with a protection switch.

[0230] The positive output terminals of photovoltaic units 101a1 and 101a2 are connected to the positive DC bus through protection switch S1, and the negative output terminals of photovoltaic units 101a1 and 101a2 are connected to the negative DC bus through protection switch S2.

[0231] In some embodiments, the protective switches S1 and S2 can also be deactivated and short-circuited.

[0232] The following explains the principle by which the controller uses the absolute value of the detected current to achieve the protection function.

[0233] When there is no short-circuit fault, the current of each branch flows into the DC bus. Therefore, the absolute value of the current in the DC bus (the absolute value of the current detected at detection point A or B) is greater than the absolute value of the current in any branch (the absolute value of the current detected at detection points C, D, E, F, G, and H).

[0234] When a short circuit fault occurs in a branch, the output current of the normal branch will flow to the short-circuited branch, which causes the absolute value of the DC bus current to be less than the absolute value of the current in any branch.

[0235] Therefore, when the absolute value of the current in a branch is greater than the absolute value of the current in the DC bus, the controller of the device will open the protection switches S1-S4, so that the current flowing into the faulty branch is zero, thereby protecting the photovoltaic unit and the line.

[0236] This implementation method can be achieved by using a first current sensor to detect the absolute value of the current at point A or B on the DC bus, and a second current sensor to detect the absolute value of the current at any one of C, D, E, F, G, or H.

[0237] The following explains the principle by which the controller uses the detection of current direction to achieve protection functions.

[0238] When there is no short-circuit fault, the current direction at detection point G and detection point H can be set to a preset direction, such as the positive direction.

[0239] When a short circuit fault occurs in the branch where photovoltaic units 101a3 and 101a4 are located, the current direction at point H will be opposite to the preset direction; when a short circuit fault occurs in the branch where photovoltaic units 101a1 and 101a2 are located, the current direction at point G will be opposite to the preset direction. Therefore, the controller can determine that a short circuit fault exists when the current detection direction at either point H or point G is opposite to the preset current direction and control the protection switches S1-S4 to open, so that the current flowing into the faulty branch is zero, thereby protecting the photovoltaic units and the line.

[0240] This method can be achieved by using two current sensors to detect the current direction at points G and H respectively.

[0241] In some embodiments, switches S1, S3, and S4 can also be deactivated and short-circuited. In this case, the controller controls the protection switch to open so that the current flowing into the short-circuit branch is less than the first current value, thereby protecting the photovoltaic unit and the line.

[0242] See Figure 15 This figure is a schematic diagram of another protection device provided in an embodiment of this application.

[0243] Figure 15 The implementation method shown is the same as Figure 14 The difference is that the positive output terminals of photovoltaic units 101a3 and 101a4 are connected to the positive DC bus through protection switch S3, the negative output terminal of photovoltaic unit 101a3 is connected to the negative DC bus through protection switch S4, and the negative output terminal of photovoltaic unit 101a4 is connected to the negative DC bus through protection switch S5.

[0244] At this time, the controller can adopt Figure 14 The corresponding working principle protects the photovoltaic unit and the circuit, which will not be described in detail in the embodiments of this application.

[0245] See Figure 16 This figure is a schematic diagram of another protection device provided in an embodiment of this application.

[0246] Figure 16 The implementation method shown is the same as Figure 14 The difference is as follows: 101a1 and 101a2 are connected in parallel. The positive output terminals of photovoltaic units 101a1 and 101a2 are connected to the positive DC bus via protection switch S1, and the negative output terminals are connected to the negative DC bus via protection switch S4. The positive output terminal of photovoltaic unit 101a3 is connected to the positive DC bus, and the negative output terminal is connected to the negative DC bus via protection switch S2. The positive output terminal of photovoltaic unit 101a4 is connected to the positive DC bus via protection switch S3, and the negative output terminal is connected to the negative DC bus via protection switch S4.

[0247] At this time, the controller can adopt Figure 14 The corresponding working principle protects the photovoltaic unit and the circuit, which will not be described in detail in the embodiments of this application.

[0248] The detection points C, D, E and F described in the above embodiments can also be located on the negative output side of the corresponding photovoltaic unit.

[0249] In summary, when this protection device is connected to four photovoltaic units via an interface, its controller can open the protection switch to reduce the current in any branch to a first current value when the absolute value of the current in any branch is greater than the absolute value of the current in the DC bus, or when the current direction in any branch is opposite to a preset current direction. This protects the photovoltaic units and the circuit. Furthermore, since only a protection switch is added to the circuit, its resistance is smaller than that of a fuse, thus reducing loss rate. Additionally, the Y-terminal can be configured on the photovoltaic unit side, thereby reducing cable costs.

[0250] Device Example 7:

[0251] See Figure 17 This figure is a schematic diagram of another protection device provided in an embodiment of this application.

[0252] Photovoltaic units 101a1 and 101a2 are directly connected in parallel inside the device. The positive output terminals of photovoltaic units 101a1 and 101a2 are connected to the positive DC bus through protection switch S1, and the negative output terminals are connected to the negative DC bus through protection switch S2. Photovoltaic units 101a3 and 101a4 are also directly connected in parallel inside the device. The positive output terminals of photovoltaic units 101a3 and 101a4 are connected to the positive DC bus through protection switch S3, and the negative output terminals are connected to the negative DC bus through protection switch S4.

[0253] The following explains the principle by which the controller uses the absolute value of the detected current to achieve the protection function.

[0254] When there is no short-circuit fault, the current of each branch flows into the DC bus. Therefore, the absolute value of the current in the DC bus (the absolute value of the current detected at detection point A or B) is greater than the absolute value of the current in any branch (the absolute value of the current detected at detection points C, D, E, F, G, and H).

[0255] When a short-circuit fault occurs in a branch, the output current of the normal branch will flow to the branch with the short-circuit fault. This causes the absolute value of the current in the DC bus to be less than the absolute value of the current in any branch.

[0256] This implementation can be achieved by using one current sensor to detect the absolute value of the current at point A or B on the DC bus, and another current sensor to detect the absolute value of the current at any one of C, D, E, F, G, or H.

[0257] The following explains the principle by which the controller uses the detection of current direction to achieve protection functions.

[0258] When there is no short-circuit fault, the current direction at points G and H can be set to a preset direction, such as the positive direction.

[0259] When a short circuit fault occurs in the branch where photovoltaic units 101a1 and 101a2 are located, the current direction at point G will be opposite to the preset current direction; when a short circuit fault occurs in the branch where photovoltaic units 101a3 and 101a4 are located, the current direction at point H will be opposite to the preset current direction. Therefore, the controller can determine that a short circuit fault exists when the current detection direction at either point G or H is opposite to the preset current direction and control the protection switches S1-S4 to open, so that the current flowing into the faulty branch is zero, thereby protecting the photovoltaic units and the line.

[0260] In some embodiments, at least one of the protective switches S1 and S2 can be deactivated and short-circuited, or at least one of the protective switches S3 and S4 can be deactivated and short-circuited, or any one of the protective switches S1 and S2 and any one of the protective switches S3 and S4 can be deactivated and short-circuited, thereby reducing the number of protective switches connected in series and lowering costs. In this case, after the controller controls the remaining protective switches to open, the current flowing into the branch with the short-circuit fault is reduced to less than a first current value, thereby protecting the photovoltaic unit and the line.

[0261] In summary, this protection device connects to four photovoltaic units via an interface. Its controller can disconnect the protection switch when the absolute value of the current in a branch exceeds the absolute value of the current on the DC bus, or when the current direction in a branch is opposite to a preset current direction. This ensures that the current in any branch is less than a first current value, thus protecting the photovoltaic units and the circuit. Furthermore, since only a protection switch is added to the circuit, its resistance is lower than that of a fuse, thereby reducing loss rate. Additionally, the Y-terminal can be configured on the photovoltaic unit side, further reducing cable costs.

[0262] The above embodiments illustrate the working principle of the controller when the protection device is connected to 3 and 4 photovoltaic units. In some real-time examples, each device can also be connected to more photovoltaic units. The working principle of the controller when the number of photovoltaic units connected to each device is greater than 4 is described in detail below.

[0263] Device Example 8:

[0264] Taking the protection device connected in parallel to M first-type photovoltaic unit branches via an interface as an example. Here, M is an integer greater than or equal to 3, at most j photovoltaic units are directly connected to the DC bus inside the device, and each of the remaining photovoltaic units is connected in parallel to the DC bus after being connected in series with at least one protection switch.

[0265] When a photovoltaic unit is connected in series with a protection switch, the protection switch is connected in series at either the positive or negative output terminal of the photovoltaic unit; when a photovoltaic unit is connected in series with two protection switches, the protection switches are connected in series at both the positive and negative output terminals of the photovoltaic unit to achieve redundant protection.

[0266] When a single photovoltaic unit experiences a short circuit fault, the value of j is 0, 1, or 2 if the faulty photovoltaic unit can withstand the output current of one other normal photovoltaic unit; and the value of j is 0, 1, 2, or 3 if the faulty photovoltaic unit can withstand the output current of two other normal photovoltaic units.

[0267] The following explanation uses a value of j = 2 as an example.

[0268] See Figure 18 This figure is a schematic diagram of another protection device provided in an embodiment of this application.

[0269] Two photovoltaic units are directly connected in parallel to the DC bus, and the remaining (M-2) photovoltaic units are connected in parallel to the DC bus after being connected in series with a protection switch.

[0270] The following explains the principle by which the controller uses the absolute value of the detected current to achieve the protection function.

[0271] When there is no short-circuit fault, the current of all photovoltaic units flows into the DC bus, and the absolute value of the current in the DC bus (the absolute value of the current detected at detection point A or detection point B) is greater than the absolute value of the current in any branch.

[0272] When a photovoltaic unit experiences a short circuit fault, the output current of other normal photovoltaic units will flow to the branch where the short-circuited photovoltaic unit is located. At this time, the absolute value of the current on the DC bus is less than the absolute value of the current in any branch where the photovoltaic unit is located.

[0273] When the absolute value of the current in a branch is greater than the absolute value of the current on the DC bus, the controller of device 200 controls the protection switches S1-S... M-2 Disconnect to ensure that the current in any branch is less than a first preset current, thereby protecting the photovoltaic unit and the circuit.

[0274] The above implementation can be achieved by detecting the absolute value of the current at point A or point B using a first current sensor, and by detecting the absolute value of the current in any branch using a second current sensor.

[0275] The following explains the principle by which the controller uses the detection of current direction to achieve protection functions.

[0276] When there is no short-circuit fault, the current direction at detection point G and detection point H can be set to a preset direction, such as the positive direction.

[0277] Point G can be located at the positive or negative output terminal of any branch. The positive output terminals of all branches except the branch where point G is located converge at point H, or the negative output terminals of all branches except the branch where point G is located converge at point H.

[0278] When a short-circuit fault occurs in the branch containing point G, current from all other branches flows into the branch containing point G, causing the current detection direction at point G to be opposite to the preset direction. When the branch containing point G is normal, but a short-circuit fault occurs in other branches, the branch containing point G outputs current to the branch with the short-circuit fault, and the current detection direction at point H is opposite to the preset current direction. Therefore, when the current detection direction at point G or point H is opposite to the preset direction, the controller determines that a short-circuit fault has occurred and controls the protection switches S1-S... M-2 All circuits are disconnected to ensure that the current in any branch is less than the first current value, thereby protecting the photovoltaic unit and the circuit.

[0279] This method can be achieved by detecting the current direction at point G using a third current sensor and the current direction at point H using a fourth current sensor.

[0280] In some embodiments, protective switches S1-S M-2It can also be connected to the negative output terminal of the corresponding photovoltaic unit, or a protection switch can be connected in series at both the positive and negative output terminals of the photovoltaic unit. Redundant protection switches can improve fault tolerance.

[0281] In some embodiments, at least one protective switch may be connected in series in all branches of the first type of photovoltaic unit. In this case, the controller controls the protective switch to open, so that the current in any branch is zero.

[0282] In summary, when this protection device is connected to at least three photovoltaic unit branches via an interface, its controller can open the protection switch to reduce the current in any branch to a first current value when the absolute value of the current in any branch is greater than the absolute value of the current in the DC bus, or when the direction of the current in a branch is opposite to the preset current direction. This protects the photovoltaic units and the circuit. Furthermore, since only a protection switch is added to the circuit, its resistance is smaller than that of a fuse, thus reducing loss rate. Additionally, the Y terminal can be configured on the photovoltaic unit side, thereby reducing cable costs.

[0283] Device Example 9:

[0284] See Figure 19 This figure is a schematic diagram of another protection device provided in an embodiment of this application.

[0285] Each i photovoltaic unit is directly connected in parallel inside the device and then connected to the DC bus of the device through at least one protection switch in series. N is an integer greater than or equal to 2.

[0286] When a single photovoltaic unit experiences a short circuit fault, the value of i is 2 if the faulty photovoltaic unit can withstand the output current of one other normal photovoltaic unit; and the value of i is 2 or 3 if the faulty photovoltaic unit can withstand the output current of two other normal photovoltaic units.

[0287] The following explains the principle by which the controller uses the absolute value of the detected current to achieve the protection function.

[0288] When there is no short-circuit fault, the current of all branches flows into the DC bus, and the absolute value of the current in the DC bus (the absolute value of the current detected at detection point A or detection point B) is greater than the absolute value of the current in any branch.

[0289] When a photovoltaic unit experiences a short circuit fault, the output current of other normal photovoltaic units will flow to the branch where the short-circuited photovoltaic unit is located. At this time, the absolute value of the current on the DC bus is less than the absolute value of the current in any branch.

[0290] When the absolute value of the current in a branch is greater than the absolute value of the current on the DC bus, the controller of the protection device controls the protection switches S1-S. NDisconnect to ensure that the current in any branch is less than a first preset current, thereby protecting the photovoltaic unit and the circuit.

[0291] The above implementation can be achieved by detecting the absolute value of the current at point A or point B using a first current sensor, and by detecting the absolute value of the current in any branch using a second current sensor.

[0292] The following explains the principle by which the controller uses the detection of current direction to achieve protection functions.

[0293] When there is no short-circuit fault, the current direction at detection point G and detection point H can be set to a preset direction, such as the positive direction.

[0294] Point G can be located at the positive or negative output terminal of any branch. The positive output terminals of all branches except the branch where point G is located converge at point H, or the negative output terminals of all branches except the branch where point G is located converge at point H.

[0295] When a short-circuit fault occurs in the branch containing point G, current from all other branches flows into the branch containing point G, causing the current detection direction at point G to be opposite to the preset direction. When the branch containing point G is normal, but a short-circuit fault occurs in other branches, the branch containing point G outputs current to the branch with the short-circuit fault, and the current detection direction at point H is opposite to the preset current direction. Therefore, when the current detection direction at point G or point H is opposite to the preset direction, the controller determines that a short-circuit fault has occurred and controls the protection switches S1-S... N All circuits are disconnected, thereby protecting the photovoltaic units and the wiring.

[0296] This method can be achieved by detecting the current direction at point G using a third current sensor and the current direction at point H using a fourth current sensor.

[0297] In some embodiments, protective switches S1-S N It can also be connected to the negative output terminal of the corresponding branch, or a protection switch can be connected in series at both the positive and negative output terminals of the corresponding branch. By redundantly setting the protection switch, the fault tolerance can be improved.

[0298] In summary, when this protection device is connected to at least two photovoltaic units via an interface, its controller can open the protection switch to reduce the current in any branch to a first current value when the absolute value of the current in any branch is greater than the absolute value of the current in the DC bus, or when the direction of the current in a branch is opposite to the preset current direction. This protects the photovoltaic units and the circuit. Furthermore, since only a protection switch is added to the circuit, its resistance is smaller than that of a fuse, thus reducing loss rate. Additionally, the Y terminal can be configured on the photovoltaic unit side, thereby reducing cable costs.

[0299] Device Example 10:

[0300] See Figure 20A This figure is a schematic diagram of another protection device provided in an embodiment of this application.

[0301] At most j photovoltaic units are directly connected to the DC bus inside the device. (Mj) photovoltaic units are connected to the DC bus in series with at least one switch inside the device. At most i photovoltaic units are directly connected in parallel inside the device and then connected in series with at least one protective switch before being connected to the DC bus of the device. N is an integer greater than or equal to 2.

[0302] When a single photovoltaic unit experiences a short circuit fault, if the faulty photovoltaic unit can withstand the output current of one other normal photovoltaic unit, the value of i is 2, and the value of j can be 0, 1, or 2; if the faulty photovoltaic unit can withstand the output current of two other normal photovoltaic units, the value of i is 2 or 3, and the value of j can be 0, 1, 2, or 3.

[0303] At this point, in order to ensure that the current in any branch is less than the maximum current that the photovoltaic unit and the line can withstand when a short circuit fault occurs, so that the short circuit current in any branch will not damage the photovoltaic unit and the line, the number of protection switches required is (M+N-2).

[0304] The following explains the principle by which the controller uses the absolute value of the detected current to achieve the protection function.

[0305] When there is no short-circuit fault, the current from all branches flows into the DC bus. Therefore, the absolute value of the DC bus current (the absolute value of the detected current at point A or point B) is greater than the absolute value of the current in any branch. However, when a short-circuit fault occurs in any branch, the output current from all other normal branches flows to the branch with the short-circuit fault. This results in no current flowing through the DC bus, meaning the absolute value of the DC bus current is less than the absolute value of the current in any branch.

[0306] To reduce the number of current sensors used, the above implementation can be achieved using two current sensors: one current sensor detects the absolute value of the current at point A or B on the DC bus, and the other current sensor detects the absolute value of the current in any branch.

[0307] When the absolute value of the DC bus current is less than the absolute value of the branch current, the controller activates the protective switches S1-S. M+N-2 All branches are disconnected so that the current in any branch is less than the first current value.

[0308] The following explains the principle by which the controller uses the detection of current direction to achieve protection functions.

[0309] When there is no short circuit fault, the current direction at detection point G or H can be set to a preset direction, such as the positive direction.

[0310] When a short-circuit fault occurs in the branch containing point G, current from all other branches flows into the branch containing point G, causing the current detection direction at point G to be opposite to the preset direction. When the branch containing point G is normal, but a short-circuit fault occurs in other branches, the branch containing point G outputs current to the branch with the short-circuit fault, and the current detection direction at point H is opposite to the preset current direction. Therefore, when the current detection direction at point G or point H is opposite to the preset direction, the controller determines that a short-circuit fault has occurred and controls the protection switches S1-S... M+N-2 All circuits are disconnected to ensure that the current in any branch is less than the first current value, thereby protecting the photovoltaic unit and the circuit.

[0311] Point G can be located in any branch. The positive outputs of all branches except the branch where point G is located converge at point H, or the negative outputs of all branches except the branch where point G is located converge at point H.

[0312] In some embodiments, protective switches S1-S M-2 It can also be connected to the negative output terminal of the corresponding photovoltaic unit, or a protection switch can be connected in series at both the positive and negative output terminals of the photovoltaic unit. Redundant protection switches can improve fault tolerance.

[0313] In some embodiments, at least one protection switch may be connected in series in each of the M photovoltaic unit branches shown in the figure. In this case, the controller controls the protection switch to open, so that the current in any branch is zero.

[0314] In some embodiments, the protection switch S M-1 -S M+N-2 It can also be connected to the negative output terminal of the corresponding branch, or a protection switch can be connected in series at both the positive and negative output terminals of the second type of photovoltaic unit branch. By redundantly setting the protection switch, the fault tolerance can be improved.

[0315] In summary, when this protection device is connected to multiple photovoltaic (PV) units via an interface, the connection of these PV units can be implemented in various combinations. The controller of this protection device can disconnect the protection switch when the absolute value of the current in any branch is greater than the absolute value of the current on the DC bus, or when the current direction in any branch is opposite to a preset current direction. This ensures that the current in any branch is less than a first current value, thereby protecting the PV units and the circuit. Furthermore, since only a protection switch is added to the circuit, its resistance is smaller than that of a fuse, thus reducing loss rate. In addition, the Y terminal can be configured on the PV unit side, thereby reducing cable costs.

[0316] Furthermore, you can also see Figure 20BThis figure is a schematic diagram of another protection device provided in an embodiment of this application.

[0317] The device supports the connection of photovoltaic units and protection units in series or parallel. The diagram illustrates this by showing i photovoltaic units connected in parallel with intervals through protection units. In some embodiments, the protection unit can also be connected in series with the photovoltaic units; for example, the protection unit can be located at point G in the diagram.

[0318] The protection unit Q can be one or more of the following: fuse, optimizer, and shut-off box. It can also be other circuit devices that can protect the circuit when a short circuit fault occurs. This application does not specifically limit this.

[0319] The value of k in the figure can be determined according to the actual situation, and this application embodiment does not impose specific limitations on it.

[0320] At this time, the protection switch is also used to prevent the protection unit from triggering protection action when it is disconnected. That is, when the photovoltaic power generation system currently using the protection unit is being upgraded, it is not necessary to remove the protection unit so that it can be directly connected to the circuit breaker protection device.

[0321] It should be noted that when a single photovoltaic unit experiences a short circuit fault, if the faulty photovoltaic unit can withstand the output current of one other normal photovoltaic unit, the value of i is 2 in order to avoid triggering the protection action of the protection unit; if the faulty photovoltaic unit can withstand the output current of two other normal photovoltaic units, the value of i is 2 or 3 in order to avoid triggering the protection action of the protection unit.

[0322] The above embodiments illustrate the working principle of the controller of the protection device when a short circuit fault occurs in the photovoltaic unit or the line where the photovoltaic unit is located. The following describes the working principle of the controller when a positive and negative short circuit, a DC bus short circuit, or a short circuit occurs in the DC bus of the subsequent circuit occurs inside the protection device.

[0323] In other embodiments, see also [link to relevant documentation]. Figure 20C The device also includes a power converter 2001, through which some or all of the photovoltaic units are coupled to the DC bus. The power converter 2001 is a DC / DC converter, such as a BOOST circuit, used to boost DC power.

[0324] Device Example 11:

[0325] See Figure 21 This figure is a schematic diagram of another protection device provided in an embodiment of this application.

[0326] Figure 21 The implementation method shown is the same as Figure 20AThe difference is that it also includes a DC switch 102 installed on the positive and negative DC buses.

[0327] When a short circuit occurs inside the protection device, such as a positive or negative short circuit, a short circuit on the DC bus, or a short circuit occurs on the DC bus of the downstream circuit (i.e., a short circuit occurs between the positive and negative DC buses at points A and B), the voltage of the DC bus will decrease and the current will increase. Therefore, points A or B can be used as detection points. When the absolute value of the voltage at the detection point is lower than the first voltage value and the absolute value of the current is greater than the second current value, the controller controls the DC switch 102 to open to cut off the short circuit current.

[0328] When the controller uses the absolute value of the detected current to achieve the protection function, there is already a current sensor in the DC branch that can measure the absolute value of the current at point A or point B. At this time, only a voltage sensor needs to be added to measure the absolute value of the voltage at point A or point B.

[0329] When the controller uses current direction detection to achieve protection function, it is necessary to add a current sensor (i.e., the fifth current sensor) to measure the absolute value of the current at point A or point B, and then add a voltage sensor to measure the absolute value of the voltage at point A or point B.

[0330] The second current value and the first voltage value can be determined according to the actual situation, and the embodiments of this application do not impose specific limitations on them.

[0331] This embodiment uses Figure 20A The device shown is used as an example for explanation. It can be understood that the same solution provided in this embodiment can be used for the devices provided in embodiments one to ten. This embodiment will not be described in detail here.

[0332] In summary, the protection device provided in this application can not only protect the photovoltaic unit and the line when a short circuit fault occurs in the photovoltaic unit or the line where the photovoltaic unit is located, but also promptly cut off the short circuit current when a short circuit occurs inside the protection device, a short circuit occurs on the DC bus, or a short circuit occurs on the DC bus of the downstream circuit, thereby protecting the circuit.

[0333] Device Example Twelve:

[0334] The above explanation uses the reverse current value to detect short-circuit faults as an example. The following explains the principle of using other parameter detection values ​​to achieve fault detection.

[0335] See also Figure 6A Specifically, the controller is used to determine that a fault has occurred in the photovoltaic power generation system when the parameter detection value of a branch exceeds a first preset parameter value range, or when the parameter detection value of the DC bus exceeds a second preset parameter value range. The parameter detection value can be at least one of voltage, current, power, or temperature values.

[0336] When parameter detection values ​​are abnormal, such as a decrease in branch voltage, an increase in current, an increase in power, or an increase in temperature, it can be determined that a short circuit fault has occurred in that branch. This application embodiment does not specifically limit the first and second preset parameter value ranges; these ranges can be pre-calibrated and stored in the controller for later retrieval.

[0337] In some embodiments, the controller determines that a fault has occurred in the photovoltaic power generation system when the leakage current detection value of the DC bus is greater than the third current value, or when the leakage current detection value of a branch is greater than the fourth current value.

[0338] When an abnormal leakage current detection value is detected, it indicates that a leakage current fault has occurred in the photovoltaic power generation system. Using the solution of this application, the leakage current fault can be identified, determining the branch where the leakage current fault occurs, or locating the leakage current fault at the DC bus. In some embodiments, the controller is specifically used to determine that a fault has occurred in the photovoltaic power generation system when it is determined, based on the current detection values ​​of all branches, that an arc fault has occurred in a branch, or based on the current detection value of the DC bus, that an arc fault has occurred on the DC bus. Specifically, the controller can determine whether an arc fault exists based on the degree of deviation between the current detection value and a preset standard value.

[0339] The controller is also used to control the protection switch to open or close according to the control instructions sent by the host computer, thereby realizing active control of the protection switch.

[0340] The protective switch in the embodiments of this application and the above embodiments can be a rotary DC disconnect switch or a DC circuit breaker. The controller is also used to control the protective switch to close after determining that the fault has been cleared or after a preset time has elapsed.

[0341] In summary, the protection device for photovoltaic power generation systems provided in this application embodiment can effectively protect photovoltaic units and lines when the photovoltaic power generation system fails, thereby improving the safety of the photovoltaic power generation system.

[0342] Method Implementation Examples

[0343] This application also provides a protection method for a photovoltaic power generation system, used to control the protection device provided in the above embodiments. This method can be executed by the controller of the protection device.

[0344] This method determines when a fault occurs in the photovoltaic power generation system based on the parameter detection values ​​of the branch or DC bus, and then controls the protection switch to disconnect.

[0345] Specifically, the parameter detection value is the reverse current value. A fault in the photovoltaic power generation system is determined based on the parameter detection values ​​of the branch or DC bus, including:

[0346] When the reverse current value of a branch exceeds the first current value, it is determined that there is a fault in the photovoltaic power generation system.

[0347] The details are explained below.

[0348] See Figure 22 The figure is a flowchart of a short-circuit protection method provided in an embodiment of this application.

[0349] The method includes the following steps:

[0350] S2201: Obtain current detection results.

[0351] S2202: When the reverse current in a branch is greater than the first current value, the control protection switch is opened, and the branch includes at least one of the photovoltaic units.

[0352] The principle behind the protection function is explained below.

[0353] When there is no short-circuit fault, the current from all branches flows into the DC bus. Therefore, the absolute value of the current on the DC bus is greater than the absolute value of the current in any branch, and the current flows from the positive terminal of the photovoltaic unit to the positive DC bus. However, when a short-circuit fault occurs in any branch, the output current from all other normal branches flows to the branch with the short-circuit fault. This causes the voltage of the DC bus to drop, and the current in some branches flows towards the branch with the short-circuit fault, meaning that the reverse current in some branches is greater than a first current value. The first current value can be determined according to the actual situation, and this application does not impose a specific limitation. Preferably, in order to detect the short-circuit fault as early as possible and trigger the protection action of the protection switch, the first current value can be a small value, such as 0. That is, when a reverse current occurs in a branch, the protection switch is opened to protect the photovoltaic unit and the line.

[0354] Specifically, protection functions can be achieved by detecting the absolute value of the current or by detecting the direction of the current, as explained below.

[0355] The following explains the principle of using the absolute value of the detected current to achieve the protection function.

[0356] When there is no short-circuit fault, the current from all branches flows into the DC bus, so the absolute value of the DC bus current is greater than the absolute value of the current in any branch. However, when a short-circuit fault occurs in any branch, the output current from all other normal branches flows to the branch with the short-circuit fault. This results in no current flowing through the DC bus, meaning the absolute value of the DC bus current is less than the absolute value of the current in any branch.

[0357] Therefore, when the absolute value of the DC bus current is less than the absolute value of the branch current, the control protection switch is opened so that the current in any branch is less than the first current value.

[0358] The following explains the principle of using current direction detection to achieve protection function.

[0359] Select a first detection point G on any branch. The positive outputs of all branches except the branch where point G is located are converged at the second detection point H, or the negative outputs of all branches except the branch where point G is located are converged at the second detection point H.

[0360] When there is no short-circuit fault, the current direction at detection points G and H can be set to a preset direction, such as the positive direction.

[0361] When a short-circuit fault occurs in the branch containing point G, current from all other branches flows into the branch containing point G, causing the current detection direction at point G to be opposite to the preset direction. When the branch containing point G is normal, but other branches have short-circuit faults, the branch containing point G outputs current to the branch with the short-circuit fault, and the current detection direction at point H is opposite to the preset current direction. Therefore, when the current detection direction at point G or point H is opposite to the preset direction, a short-circuit fault is determined, and the control protection switch is opened to ensure that the current in any branch is less than the first current value, thereby protecting the photovoltaic unit and the line.

[0362] In summary, when the method provided in this application is applied to a protection device, the protection switch is controlled to open when the reverse current of a branch is greater than the first current value. Specifically, when the absolute value of the branch current is greater than the absolute value of the DC bus current, or when the direction of the branch current is opposite to the preset current direction, the protection switch is controlled to open so that the current of any branch is less than the first current value, thereby protecting the photovoltaic unit and the line.

[0363] See also Figure 21 In some embodiments, the device further includes a power circuit, and the DC bus is connected to the input terminal of the power circuit through a DC switch. In this case, the present application also provides another control method for the device, which is used to protect the circuit when a positive or negative short circuit occurs inside the device or when a short circuit occurs on the downstream bus. The details are described below.

[0364] See Figure 23 The figure is a flowchart of another short-circuit protection method provided in an embodiment of this application.

[0365] The method includes the following steps:

[0366] S2301: Get the absolute value of the current current and the absolute value of the voltage of the current DC bus.

[0367] S2302: When the absolute value of the DC bus current is greater than the second current value and the absolute value of the DC bus voltage is less than the first voltage value, the DC switch is controlled to open.

[0368] When a short circuit occurs inside the protection device, either positive or negative, or a short circuit occurs in the DC bus of the downstream circuit, i.e., a short circuit occurs between the positive and negative DC buses at points A and B, the voltage of the DC bus will decrease and the current will increase. Therefore, points A or B can be used as detection points. When the absolute value of the voltage at the detection point is lower than the first voltage value and the absolute value of the current is greater than the second current value, the controller controls the DC switch to open to cut off the short circuit current.

[0369] The second current value and the first voltage value can be determined according to the actual situation, and the embodiments of this application do not impose specific limitations on them.

[0370] In summary, this method can promptly cut off the short-circuit current when a positive or negative short circuit occurs inside the protection device or when a short circuit occurs on the downstream bus, thereby protecting the device and the downstream circuit.

[0371] The following describes a method for fault diagnosis using other parameter detection values.

[0372] When the parameter detection value is at least one of voltage, current, power, or temperature, a fault is determined in the photovoltaic power generation system based on the parameter detection value of the branch or DC bus, specifically including:

[0373] When the parameter detection value of the branch exceeds the first preset parameter value range, or when the parameter detection value of the DC bus exceeds the second preset parameter value range, it is determined that the photovoltaic power generation system has failed.

[0374] When troubleshooting leakage current faults, the photovoltaic power generation system fault is determined based on the parameter detection values ​​of the branch or DC bus, specifically including:

[0375] When the leakage current detection value of the DC bus is greater than the third current value, or when the leakage current detection value of a branch is greater than the fourth current value, it is determined that the photovoltaic power generation system has failed.

[0376] When diagnosing arc faults, the photovoltaic power generation system is determined to have a fault based on the parameter detection values ​​of the branch or DC bus, specifically including:

[0377] When an arc fault is detected in a branch based on the current detection values ​​of all branches, or when an arc fault is detected in the DC bus based on the current detection values ​​of the DC bus, a fault is determined to have occurred in the photovoltaic power generation system.

[0378] In summary, the protection method for photovoltaic power generation systems provided in this application can effectively protect photovoltaic units and lines when the photovoltaic power generation system fails, thereby improving the safety of the photovoltaic power generation system.

[0379] Example of a photovoltaic power generation system:

[0380] Based on the protection device for photovoltaic power generation systems provided in the above embodiments, this application also provides a photovoltaic power generation system, which will be described in detail below with reference to the accompanying drawings.

[0381] See Figure 24 The figure is a schematic diagram of a photovoltaic power generation system provided in an embodiment of this application.

[0382] The photovoltaic power generation system 2400 includes at least two photovoltaic units and protection devices.

[0383] The photovoltaic unit is formed by connecting at least one photovoltaic module in series and parallel.

[0384] The protection device can be connected to at least two photovoltaic units via an interface. The at least two photovoltaic units are connected in parallel with the DC bus inside the device to form at least two branches, and each branch is connected to at least one of the photovoltaic units.

[0385] The protection switch of the protection device is used to allow up to three photovoltaic units to be directly connected in parallel to the DC bus inside the device when disconnected.

[0386] The protection device also includes a controller. For a description of the controller, please refer to the above embodiments. This embodiment will not be repeated here.

[0387] Furthermore, the protection device may also include a power circuit 201 for power conversion.

[0388] In some embodiments, the power circuit 201 can be a DC-DC converter circuit. When the power circuit 201 is a DC-DC converter circuit, the DC-DC converter circuit can specifically be a boost circuit, a buck circuit, or a buck-boost circuit. This application does not make any specific limitation in this regard.

[0389] In some embodiments, the power circuit 201 can be a DC-AC conversion circuit, i.e., an inverter (or inverter circuit), used to convert DC power into AC power for output.

[0390] This embodiment uses Figure 20A The device shown is used as an example for illustration. It can be understood that the same solution provided in this embodiment can be used for the devices provided in embodiments one to eleven. This embodiment will not be described in detail here.

[0391] In summary, the photovoltaic power generation system provided by this application allows the controller to open the protection switch when the protection device of the photovoltaic power generation system is connected to multiple photovoltaic units via an interface, provided that the reverse current of a branch exceeds a first current value. Specifically, the controller opens the protection switch when the absolute value of the current in any branch exceeds the absolute value of the current in the DC bus, or when the current direction of any branch is opposite to a preset current direction, so that the current in any branch is less than the first current value, thereby protecting the photovoltaic units and lines in the photovoltaic system. Furthermore, since only a protection switch is added to the circuit, its resistance is smaller than that of a fuse, thus reducing the loss rate of the photovoltaic system. In addition, since fuses are no longer used, the Y-shaped wire harness, which was originally used for built-in fuses, no longer needs to be located at the bottom of the inverter or DC combiner box of the photovoltaic power generation system, but can be configured on the photovoltaic unit side, thereby reducing the cable cost of the photovoltaic power generation system.

[0392] The controller described in this application embodiment can be an application-specific integrated circuit (ASIC), a programmable logic device (PLD), or a combination thereof. The PLD can be a complex programmable logic device (CPLD), a field-programmable gate array (FPGA), a generic array logic (GAL), or any combination thereof; this application embodiment does not impose specific limitations.

[0393] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0394] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A photovoltaic inverter, characterized in that, It includes multiple DC-DC converter circuits, one DC-AC converter circuit, a rotary DC disconnect switch, a DC bus, multiple interfaces, and a controller; Each of the DC-DC converter circuits is used to connect multiple photovoltaic units via the DC bus and at least one of the interfaces; The rotary DC disconnect switch includes multiple protection switches, which are connected between the DC bus of each DC-DC converter and the multiple interfaces to control the switching on and off of each DC-DC converter circuit and the multiple photovoltaic units. Each DC-DC converter circuit is connected to the multiple photovoltaic units through the multiple protection switches to form multiple branches. Each branch is connected to at least one photovoltaic unit, and at least one branch includes two or three photovoltaic units. The two or three photovoltaic units are connected in parallel inside the photovoltaic inverter through corresponding interfaces. The output of each DC-DC converter circuit is connected in parallel with the input of the DC-AC converter circuit. The controller is configured to, based on the parameter detection values ​​of the branch or DC bus, determine when the photovoltaic inverter malfunctions, and control all the multiple protection switches connected to the DC-DC conversion circuit where the fault occurs to disconnect the multiple photovoltaic units in the branch from the DC bus. Furthermore, at least one protection switch is connected within the at least one branch to reduce the number of photovoltaic units connected in parallel in the at least one branch when the photovoltaic inverter malfunctions, ensuring that two of the multiple photovoltaic units are connected in parallel to each other.

2. The photovoltaic inverter according to claim 1, characterized in that, The parameter detection value includes the reverse current value of the branch. The controller is used to determine that the photovoltaic inverter has failed when the reverse current value of the branch is greater than a first current value.

3. The photovoltaic inverter according to claim 1, characterized in that, The controller is configured to determine that the photovoltaic inverter has malfunctioned when the parameter detection value of the branch exceeds a first preset parameter value range, or when the parameter detection value of the DC bus exceeds a second preset parameter value range, and control all the multiple protection switches of the rotary DC disconnect switch to disconnect the multiple photovoltaic units from the DC bus.

4. The photovoltaic inverter according to claim 1, characterized in that, The parameter detection value includes the absolute value of the current of the DC bus. The controller is used to determine that the photovoltaic inverter has failed when the absolute value of the current of the DC bus is greater than a second current value and the absolute value of the voltage of the DC bus is less than a first voltage value, and to control all the multiple protection switches of the rotary DC disconnect switch to disconnect the multiple photovoltaic units from the DC bus.

5. The photovoltaic inverter according to any one of claims 1 to 4, characterized in that, The controller is also used to control the protection switch to disconnect the faulty branch from the DC bus when an arc or overcurrent fault occurs in a branch.

6. The photovoltaic inverter according to any one of claims 1 to 4, characterized in that, The parameter detection values ​​include the current detection value of the branch or the current detection value of the DC bus. The controller is specifically used to control the protection switch to disconnect the faulty branch from the DC bus or to control all protection switches to disconnect when it is determined that there is an arc fault in the branch based on the current detection value of the branch or an arc fault in the DC bus based on the current detection value of the DC bus.

7. The photovoltaic inverter according to any one of claims 1 to 4, characterized in that, The parameter detection values ​​include the leakage current detection value of the DC bus or the leakage current detection value of the branch. The controller is specifically used to control the protection switch to disconnect the faulty branch from the DC bus or to control all protection switches to disconnect when the leakage current detection value of the DC bus is greater than a third current value or the leakage current detection value of the branch is greater than a fourth current value.

8. The photovoltaic inverter according to any one of claims 1 to 4, characterized in that, Also includes: First current sensor and second current sensor; The first current sensor is used to acquire the detection result of the current or voltage of the DC bus and send the detection result to the controller so that the controller can control the protective switch of the rotary DC disconnect switch to turn off based on the detection result. The second current sensor is used to acquire the detection result of the current or voltage of the at least one branch and send the detection result to the controller so that the controller can control the protective switch of the rotary DC disconnect switch to turn off based on the detection result.

9. The photovoltaic inverter according to any one of claims 1 to 4, characterized in that, The parameter detection values ​​include the absolute value of the current and the current direction or voltage value, so that the controller can determine whether the photovoltaic inverter has malfunctioned, including reverse current, overcurrent or overvoltage.

10. The photovoltaic inverter according to claim 1, characterized in that, The controller is configured to consider the photovoltaic inverter as faulty when the reverse current value of the branch is greater than the first current value, and control the rotary DC disconnect switch of the faulty branch to disconnect all the photovoltaic units from the DC bus, so that all the photovoltaic units connected to the faulty branch are disconnected from the DC-DC conversion circuit of the faulty branch.

11. A protection method for a photovoltaic inverter, characterized in that, The parameter detection values ​​of the branch or DC bus are obtained. The DC bus is used to connect the input of multiple DC-DC converter circuits. Each DC-DC converter circuit is connected to multiple photovoltaic units through a rotary DC disconnect switch to form at least two branches. Each branch is connected to at least one photovoltaic unit, and at least one branch includes two or three photovoltaic units. The two or three photovoltaic units are connected in parallel inside the photovoltaic inverter through corresponding interfaces. The output of each DC-DC converter circuit is connected in parallel with the input of the DC-AC converter circuit. When a fault is detected in the photovoltaic inverter based on the parameter detection value of the branch or DC bus, multiple protection switches in the rotary DC disconnect switch connected to the DC-DC conversion circuit where the fault occurs are controlled to disconnect all the multiple photovoltaic units from the DC bus. At least one protection switch is connected in at least one branch to reduce the number of photovoltaic units connected in parallel in the at least one branch when the photovoltaic inverter fails, so that there are two photovoltaic units connected in parallel with each other among the multiple photovoltaic units.

12. The protection method according to claim 11, characterized in that, When the parameter detection value of the branch exceeds the first preset parameter value range, or when the parameter detection value of the DC bus exceeds the second preset parameter value range, the photovoltaic inverter is considered to have failed. The rotary DC disconnect switch of the faulty branch is controlled to disconnect the DC-DC conversion circuit of the branch from the multiple photovoltaic units, or the multiple protection switches of the rotary DC disconnect switch are controlled to disconnect all the multiple photovoltaic units from the DC bus. The parameter detection values ​​include voltage, current, power or temperature values.

Images