Protection device and method for photovoltaic power generation system, and photovoltaic power generation system

Abstract

To provide a protection device and a protection method for a photovoltaic power generation system in relation to the field of photovoltaic power generation technology.SOLUTION: A protection device includes an interface, a protection switch, a direct current bus, and a controller. The device is connected to at least two photovoltaic units by using the interface, the at least two photovoltaic units are connected to the direct current bus inside the device to form at least two branches, and each branch is connected to at least one photovoltaic unit. The protection switch is configured to disconnect all or some of the photovoltaic units from the direct current bus, to enable a maximum of three photovoltaic units to be directly connected in parallel. According to the device, a photovoltaic unit and a line can be effectively protected with reduced power loss when the photovoltaic power generation system is faulty.SELECTED DRAWING: Figure 6A

Description

[Technical field]

[0001] This application claims priority to PCT International Patent Application No. PCT / CN2020 / 084500, filed with the State Intellectual Property Office of the People's Republic of China on April 13, 2020, and entitled "SHORT CIRCUIT PROTECTION APPARATUS, SHORT CIRCUIT PROTECTION METHOD, AND PHOTOVOLTAIC POWER GENERATION SYSTEM," which is incorporated herein by reference in its entirety.

[0002] The present application relates to the field of photovoltaic technology, and in particular to a protection device for a photovoltaic system, a short circuit protection method, and a photovoltaic system. [Background technology]

[0003] Photovoltaic power generation is a technology that utilizes the photovoltaic effect of semiconductor interfaces to convert light energy into electrical energy. A photovoltaic power generation system may usually include a photovoltaic section, an inverter, an AC power distributor, etc. In order to obtain a relatively large output voltage or output current, the photovoltaic section is usually formed by connecting multiple photovoltaic components in a certain series and / or parallel connection manner. To improve the power generation efficiency of the photovoltaic power generation system, the photovoltaic section is connected to a component with an independent MPPT (Maximum Power Point Tracking) function.

[0004] Currently, in order to improve the DC ratio (the ratio of the power of the photovoltaic unit to the input power of the inverter) of the photovoltaic power generation system, each MPPT component is usually connected to at least two photovoltaic units. In an example where a photovoltaic unit or a line on which a photovoltaic unit is located is short-circuited, the short-circuit current is the sum of the output currents of the other photovoltaic units connected. When there is only one other photovoltaic unit connected, the short-circuit current is relatively small and the photovoltaic unit and the line can withstand this short-circuit current. However, when there are two or more photovoltaic units connected, the short-circuit current is relatively large. In order to protect the photovoltaic unit and the line, one or more fuses may be connected in series to the positive output end and / or the negative output end of the photovoltaic unit, so that the fuse blows to protect the photovoltaic unit and the line.

[0005] However, since the fuse current of the fuse is usually relatively large and the output current of each photovoltaic unit is relatively small, the sum of the short-circuit currents of the photovoltaic units is unlikely to reach the fuse current of the fuse. Therefore, the fuse cannot effectively protect the photovoltaic units and the line. In addition, the resistance of the fuse is relatively large, which may cause a relatively large power loss in the photovoltaic system.

[0006] In order to improve the DC ratio of the photovoltaic power generation system, each MPPT component is usually connected to at least two or more photovoltaic sections. In addition, the positive output end and / or the negative output end of the photovoltaic section are connected in series with one or more fuses to protect the photovoltaic section and the line when the photovoltaic section or the line is short-circuited. In the following, an example in which each MPPT component is connected to three branches will be described. The principle is similar when each MPPT component is connected to more branches, and the details will not be described again in this description.

[0007] Please refer to Figures 1 to 3. Figure 1 is a schematic diagram in which both the positive output end and the negative output end of the photovoltaic unit are connected in series to a fuse. Figure 2 is a schematic diagram in which the positive output end of the photovoltaic unit is connected in series to a fuse. Figure 3 is a schematic diagram in which the negative output end of the photovoltaic unit is connected in series to a fuse.

[0008] Each branch includes one photovoltaic component 101. The three branches are connected in parallel before a switch 102 and then connected to an MPPT component 103 using a DC switch 102. fuse1-fuse6 in Fig. 1, fuse1-fuse3 in Fig. 2, and fuse1-fuse3 in Fig. 3 are fuses that blow when the current in the line is too large to protect the photovoltaic component and the line. However, since the actual output current of the photovoltaic unit is relatively small, it is unlikely that the fuse will blow. Take a fuse with a rated current of 15A as an example. According to the provisions of the fuse standard, the maximum allowable current when the fuse does not blow is 1.13×15=16.95A, and the current required for the fuse to blow in one hour is 1.35×15=20.25A. However, it is unlikely that the short circuit current will reach the current required for the fuse to blow. Therefore, the fuse may not blow, and the photovoltaic unit and the line cannot be effectively protected. In addition, the resistance of each fuse may be up to 9 milliohms. Therefore, there is a problem that the power loss and heat generation are relatively large. In some embodiments, since the cable needs to be protected, a Y harness with built-in fuse needs to be placed under the device, which further increases the cable cost. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] China Patent Application Publication No. 101939660 Summary of the Invention

[0010] The present application provides a protection device and method for a photovoltaic system, and a photovoltaic system, which effectively protect the photovoltaic unit and the line while reducing power loss when a fault occurs in the photovoltaic system. [Means for solving the problem]

[0011] According to a first aspect, an embodiment of the present application provides a protection device for a photovoltaic system. The device is applied to the photovoltaic system, and includes an interface, a protection switch, a DC bus, and a controller. The device is connected to at least two photovoltaic units using the interface, and the at least two photovoltaic units are connected in parallel to the DC bus in the device to form at least two branches, and each branch is connected to at least one photovoltaic unit. The protection switch is configured to disconnect all or part of the photovoltaic units from the DC bus so as to allow up to three photovoltaic units to be directly connected in parallel. When it is determined that there is a fault in the photovoltaic system based on the parameter detection value of the branch or the parameter detection value of the DC bus, the controller controls the protection switch to an open state.

[0012] When the protection switch of the device is in an open state, up to three photovoltaic units are directly connected in parallel. Therefore, if one photovoltaic unit can withstand the output current of two photovoltaic units, up to two normal photovoltaic units will output current to the photovoltaic unit when the photovoltaic unit is faulty. In this case, the current is within the allowable range of the faulty photovoltaic unit, which protects the photovoltaic components and lines from damage. In addition, only a protection switch is added to the circuit, and the resistance of the protection switch is less than the resistance of the fuse, so the loss rate and loss of the photovoltaic system are reduced. In addition, since fuses are no longer used, the Y harness, which is originally used for built-in fuses, can be placed on the photovoltaic unit side instead of under the inverter or DC combiner box of the photovoltaic system, which further reduces the cable cost.

[0013] Regarding the first aspect, in a possible implementation, the parameter detection value is a reverse current value, and the controller is particularly configured to determine that there is a fault in the photovoltaic system when the reverse current value of the branch exceeds a first current value.

[0014] When the reverse current of a branch is relatively large, this indicates that the direct current output by another branch flows back into the branch, and therefore it can be determined that a short circuit fault exists in the branch.

[0015] Regarding the first aspect, in a first possible implementation example, the device is connected to at least three photovoltaic units using an interface, with up to two photovoltaic units directly connected in parallel to a DC bus, and each remaining photovoltaic unit being connected in series with at least one protection switch and then connected in parallel to the DC bus.

[0016] In some embodiments, a photovoltaic section or line can only withstand the output current of one photovoltaic section. In the case where up to two photovoltaic sections are directly connected in parallel to a DC bus, when a photovoltaic section is faulted by a short circuit, up to one normal photovoltaic section will output a short circuit current to this photovoltaic section, and the other photovoltaic sections may be directly disconnected. In this case, the short circuit current falls within the allowable range of the faulty photovoltaic section, thereby protecting the photovoltaic components and lines from damage.

[0017] Regarding the first aspect, in a second possible implementation example, the device is connected to at least three photovoltaic units using an interface, with up to three photovoltaic units being directly connected in parallel to a DC bus, and each remaining photovoltaic unit being connected in series with at least one protection switch and then connected in parallel to the DC bus.

[0018] In some embodiments, a photovoltaic section or line can withstand the output current of two photovoltaic sections. Therefore, in the case where up to three photovoltaic sections are directly connected in parallel to a DC bus, when a photovoltaic section is faulted by a short circuit, up to two normal photovoltaic sections can output the short circuit current to the photovoltaic section and directly disconnect the other photovoltaic sections. In this case, the short circuit current falls within the allowable range of the faulty photovoltaic section, thereby protecting the photovoltaic components and lines from damage.

[0019] Regarding the first aspect, in a third possible implementation, the device is connected to three photovoltaic units using an interface, two photovoltaic units are directly connected in parallel to a DC bus, and the remaining one photovoltaic unit is connected in series with at least one protection switch and then connected in parallel to the DC bus. When a short circuit fault occurs, the controller can control the protection switch to an open state, thereby protecting the photovoltaic units and the lines of the photovoltaic system.

[0020] Regarding the first aspect, in a fourth possible implementation example, the device is connected to three photovoltaic units using an interface, two photovoltaic units and at least one protection switch are individually connected in series and then connected in parallel to a DC bus, and another photovoltaic unit is directly connected in parallel to the DC bus. When a short circuit fault occurs, the controller can control the protection switch to an open state, so that the current flowing through the photovoltaic unit with the short circuit fault becomes zero, thereby protecting the photovoltaic units and lines of the photovoltaic system.

[0021] Regarding the first aspect, in a fifth possible implementation example, the device is connected to four photovoltaic units using an interface, first two photovoltaic units are connected in parallel, then the two photovoltaic units connected in parallel and at least one protection switch are connected in series and then connected in parallel to a DC bus, and the other two photovoltaic units are directly connected in parallel to a DC bus. When a short circuit fault occurs, the controller can control the protection switch to an open state, thereby protecting the photovoltaic units and the line of the photovoltaic system.

[0022] Regarding the first aspect, in a sixth possible implementation example, the device is connected to four photovoltaic units using an interface, two photovoltaic units are directly connected in parallel, and the other two photovoltaic units and at least one protective switch are individually connected in series, and then the other two photovoltaic units and at least one protective switch individually connected in series are connected in parallel before the two photovoltaic units are connected in parallel to the DC bus. When a short-circuit fault occurs, the controller can control the protective switch to an open state, thereby protecting the photovoltaic units and the lines of the photovoltaic system.

[0023] Regarding the first aspect, in a seventh possible implementation example, the device is connected to four photovoltaic units using an interface, one photovoltaic unit and at least one protection switch are connected in series and then connected in parallel to a DC bus, and the other three photovoltaic units are directly connected in parallel to a DC bus. In this case, the photovoltaic unit or line can withstand the output current of two photovoltaic units, and when a short circuit fault occurs, the controller can control the protection switch to an open state, thereby protecting the photovoltaic unit and the line of the photovoltaic system.

[0024] Regarding the first aspect, in an eighth possible implementation example, the device is connected to four photovoltaic units using an interface, first three photovoltaic units are connected in parallel, then the three photovoltaic units connected in parallel and at least one protection switch are connected in series and then connected in parallel to a DC bus, and another photovoltaic unit is directly connected in parallel to a DC bus. In this case, the photovoltaic units or lines can withstand the output current of two photovoltaic units, and when a short circuit fault occurs, the controller can control the protection switch to be in an open state, thereby protecting the photovoltaic units and lines of the photovoltaic system.

[0025] Regarding the first aspect, in a ninth possible implementation example, when the photovoltaic unit is connected in series to one protection switch, the protection switch is connected in series to the positive output end or the negative output end of the photovoltaic unit. By controlling the protection switch to be in an open state, the line on which the corresponding photovoltaic unit is located can be controlled to be disconnected.

[0026] Regarding the first aspect, in a tenth possible implementation example, when the photovoltaic unit is connected in series to two protection switches, the two protection switches are connected in series to the positive output end and the negative output end of the photovoltaic unit, respectively. By increasing redundancy and arranging the protection switches, the fault tolerance performance of the system is improved, and the connection between the photovoltaic unit and the system with a short circuit can be completely cut off to facilitate maintenance.

[0027] Regarding the first aspect, in an eleventh possible implementation example, when multiple photovoltaic units are first connected in parallel and then connected in series to one protective switch, the positive output ends of multiple photovoltaic units are connected in parallel and then connected in series to one protective switch, or the negative output ends of multiple photovoltaic units are connected in parallel and then connected in series to another protective switch. By controlling the protective switch to be in an open state, the line on which the corresponding photovoltaic unit is located can be controlled to be disconnected.

[0028] Regarding the first aspect, in a twelfth possible implementation example, when a plurality of photovoltaic units are first connected in parallel and then connected in series to two protection switches, the positive output ends of the plurality of photovoltaic units are connected in parallel and then connected in series to one protection switch, and the negative output ends of the plurality of photovoltaic units are connected in parallel and then connected in series to the other protection switch. By increasing redundancy and arranging the protection switches, the fault tolerance performance of the system is improved.

[0029] Regarding the first aspect, in a thirteenth possible implementation example, the controller being configured to control the protection switch to an open state when the reverse current of the branch exceeds a first current value particularly includes determining that the reverse current of the branch exceeds the first current value and controlling the protection switch to an open state when the absolute value of the current of the branch exceeds the absolute value of the current of the DC bus.

[0030] The reason for this is as follows: when there is no fault due to a short circuit, the output currents of all the photovoltaic units join together and flow into the DC bus, so the absolute value of the current in the DC bus exceeds the absolute value of the current in any branch. When a fault due to a short circuit occurs in a photovoltaic unit, the output current of the other normal photovoltaic units flows into the photovoltaic unit with the short circuit. In this case, the absolute value of the current in the DC bus becomes smaller than the absolute value of the current in any branch.

[0031] Regarding the first aspect, in a fourteenth possible implementation example, the apparatus further includes a first current sensor and a second current sensor, where the first current sensor is configured to acquire an absolute value of the current of the DC bus and send the absolute value to the controller, and the second current sensor is configured to acquire a predetermined absolute value of the current of the branch and send the absolute value to the controller.

[0032] The absolute value of the branch current is compared with the absolute value of the DC bus current to determine whether a short circuit fault exists in the photovoltaic section or line.

[0033] Regarding the first aspect, in a fifteenth possible implementation, the apparatus further includes a power circuit; The power circuit is a DC-DC converter circuit or a DC-AC converter circuit.

[0034] Regarding the first aspect, in a sixteenth possible implementation example, the apparatus further includes a first voltage sensor and a DC switch, where the DC bus is connected to the input end of the power circuit using the DC switch, and the first voltage sensor is configured to obtain an absolute value of the voltage of the DC bus and send the absolute value to the controller.

[0035] Regarding the first aspect, in a seventeenth possible implementation example, the controller being configured to control the protection switch to an open state when the reverse current of the branch exceeds a first current value particularly includes determining that the reverse current of the branch exceeds the first current value and controlling the protection switch to an open state when the current direction of the branch is opposite to a default current direction.

[0036] The reason for this is as follows: when a fault due to a short circuit occurs in a photovoltaic unit, a current flows in the branch in which the faulty photovoltaic unit is located from the branch in which the other normal photovoltaic unit is located, and in this case, the current detection direction of the branch in which the faulty photovoltaic unit is located is opposite to the default direction when the photovoltaic unit is normal. When a branch in which a photovoltaic unit is located is normal and a fault due to a short circuit occurs in another branch, the branch in which the photovoltaic unit is located outputs a current to the branch in which the fault due to the short circuit exists, and in this case, the current detection direction of the other branch is opposite to the default current direction.

[0037] Regarding the first aspect, in an eighteenth possible implementation example, the device further includes a third current sensor and a fourth current sensor, wherein the third current sensor is configured to obtain a current detection direction of the first detection point and send the current detection direction to the controller, where the first detection point is located in one of the branches, and the fourth current sensor is configured to obtain a current detection direction of the second detection point and send the current detection direction to the controller, where all branches other than the branch where the first detection point is located are gathered at the second detection point.

[0038] Regarding the first aspect, in a 19th possible implementation example, the controller is particularly configured to control the protection switch to an open state when the current detection direction of the first detection point is opposite to a default current direction of the first detection point or when the current detection direction of the second detection point is opposite to a default current direction of the second detection point.

[0039] Regarding the first aspect, in a twentieth possible implementation example, the protection device further includes a power circuit, and the power circuit is a direct current-direct current (DC-DC) conversion circuit or a direct current-alternating current (DC-AC) conversion circuit.

[0040] Regarding the first aspect, in a twenty-first possible implementation example, the apparatus further includes a fifth current sensor, a second voltage sensor, and a DC switch, wherein the DC bus is connected to the input end of the power circuit using the DC switch, the fifth current sensor is configured to acquire an absolute value of the current of the DC bus and send the absolute value to the controller, and the second voltage sensor is configured to acquire an absolute value of the voltage of the DC bus and send the absolute value to the controller.

[0041] Regarding the first aspect, in a twenty-second possible implementation example, when the positive pole and the negative pole are shorted, or when the DC bus is shorted in the protection device, or when the DC bus of the adjacent circuit is shorted, the DC bus voltage decreases and the DC bus current increases. Thus, the controller is further configured to control the DC switch to an open state when the absolute value of the DC bus current exceeds the second current value and the absolute value of the DC bus voltage is less than the first voltage value, thereby protecting the circuit.

[0042] Regarding the first aspect, in a 23rd possible implementation example, when the photovoltaic unit and the protection unit are connected in series or parallel and then connected to the device using the interface, the protection switch is further configured to prevent the protection unit from initiating a protection operation when in an open state.

[0043] In other words, the protector is directly connected to the open circuit protection device so that the protector does not have to be removed and disposed of when the photovoltaic system currently using the protector is restored.

[0044] Regarding the first aspect, in a 24th possible implementation example, the protection unit includes at least one of a fuse, an optimizer, and a disconnect box.

[0045] Regarding the first aspect, in a twenty-fifth possible implementation example, when the device includes at least two protection switches, the at least two protection switches are controlled by the same controller or multiple controllers.

[0046] Regarding the first aspect, in a possible implementation, the controller is particularly configured to determine that the photovoltaic system has a fault when a detected parameter value of the branch exceeds a first predefined parameter value range or when a detected parameter value of the DC bus exceeds a second predefined parameter value range, The detected parameter value may be at least one of a voltage value, a current value, a power value or a temperature value.

[0047] When the parameter detection values ​​are abnormal, for example, when the voltage of a branch decreases, the current of a branch increases, the power of a branch increases, and the temperature of a branch increases, it can be determined that a fault due to a short circuit exists in the branch.

[0048] Regarding the first aspect, in a possible implementation example, the controller is particularly configured to determine that there is a fault in the photovoltaic system when the leakage current detection value of the DC bus exceeds a third current value or when the leakage current detection value of the branch exceeds a fourth current value. When the leakage current detection value is abnormal, this indicates that there is a leakage current fault in the photovoltaic system. According to the solution of the present application, it is possible to identify the location of the leakage current fault to determine the branch in which the leakage current fault exists, or to identify the location of the leakage current fault in the DC bus.

[0049] Regarding the first aspect, in a possible implementation example, the controller is particularly configured to determine that there is a fault in the photovoltaic system when it determines that there is an arc fault in the branch based on the current detection values ​​of all the branches, or when it determines that there is an arc fault in the DC bus based on the current detection value of the DC bus. In particular, the controller may determine whether there is an arc fault based on the degree of offset of the current detection value with respect to a predetermined reference value.

[0050] Regarding the first aspect, in a possible implementation, the controller is further configured to control the protection switch to an open or closed state according to a control instruction sent by the host computer to perform active control of the protection switch.

[0051] Regarding the first aspect, in possible implementations, up to three photovoltaic units are directly connected in parallel and then connected to one interface, or up to three photovoltaic units are connected in parallel within the device using corresponding interfaces.

[0052] Regarding the first aspect, in a possible implementation the protection switch is a rotary DC switch disconnector or a DC circuit breaker.

[0053] Regarding the first aspect, in a possible implementation, the controller is further configured to control the protection switch to a closed state after a predetermined time has elapsed if it is determined that the fault has been removed.

[0054] Regarding the first aspect, in a possible implementation, the protection device further includes a DC / DC converter, an input end of the DC / DC converter is connected to a DC bus, an output end of the DC / DC converter is an output end of the protection device of the photovoltaic power generation system, and the DC / DC converter is configured to convert the DC obtained from the DC bus into an output DC. In this case, the protection device of the photovoltaic power generation system is a step-up DC combiner box.

[0055] Regarding the first aspect, in a possible implementation, the protection device further includes a DC / AC converter, an input end of the DC / AC converter is connected to a DC bus, an output end of the DC / AC converter is an output end of the protection device of the photovoltaic power generation system, and the DC / AC converter is configured to convert the DC obtained from the DC bus into AC for output. In this case, the protection device of the photovoltaic power generation system is an inverter.

[0056] According to a second aspect, the present application further provides a method for protecting a photovoltaic system. The method is applied to a control and protection device. The protection device is connected to at least two photovoltaic units using an interface, and the at least two photovoltaic units are connected to a DC bus in the device to form at least two branches, each branch being connected to at least one photovoltaic unit, and the protection switch is configured to disconnect all or some of the photovoltaic units from the DC bus such that up to three photovoltaic units are directly connected in parallel. The method includes: controlling the protective switch to an open state when it is determined that there is a fault in the photovoltaic system based on the parameter detection values ​​of the branch or the parameter detection values ​​of the DC bus; Includes.

[0057] Regarding the second aspect, in a possible implementation example, the parameter detection value is a reverse current value, and the step of determining that there is a fault in the photovoltaic power generation system based on the parameter detection value of the branch or the parameter detection value of the DC bus includes: determining that the photovoltaic system has a fault when the reverse current value of the branch exceeds a first current value; In particular:

[0058] According to this method, when the protection switch is in an open state, up to three photovoltaic units are directly connected in parallel. Therefore, if one photovoltaic unit can withstand the output current of two photovoltaic units, up to two normal photovoltaic units will output current to the photovoltaic unit when the photovoltaic unit is faulty. In this case, the current falls within the allowable range of the faulty photovoltaic unit, thereby protecting the photovoltaic components and lines from damage.

[0059] Regarding the second aspect, in a possible implementation example, the parameter detection value is a reverse current value, and the step of determining that there is a fault in the photovoltaic power generation system based on the parameter detection value of the branch or the parameter detection value of the DC bus includes: determining that the photovoltaic system has a fault when the reverse current value of the branch exceeds a first current value; In particular:

[0060] Regarding the second aspect, in a first possible implementation example, the apparatus further includes a power circuit, an input end of which is connected to a DC bus using a DC switch, and the method further includes a step of controlling the DC switch to an open state when the absolute value of the current of the DC bus exceeds a second current value and the absolute value of the voltage of the DC bus is less than the first voltage value.

[0061] According to this method, when the positive and negative poles are short-circuited within the protective device or when the adjacent circuit busbar is short-circuited, the short-circuit current can be interrupted in a timely manner, thereby protecting the device and the adjacent circuits.

[0062] Regarding the second aspect, in a second possible implementation, the power circuit is a direct current to direct current (DC-DC) conversion circuit or a direct current to alternating current (DC-AC) conversion circuit.

[0063] Regarding the second aspect, in a possible implementation example, the parameter detection value is at least one of a voltage value, a current value, a power value, or a temperature value, and the step of determining that there is a fault in the photovoltaic power generation system based on the parameter detection value of the branch or the parameter detection value of the DC bus includes: determining that the photovoltaic system has a fault when the parameter detection value of the branch exceeds a first predetermined parameter value range or when the parameter detection value of the DC bus exceeds a second predetermined parameter value range; In particular:

[0064] Regarding the second aspect, in a possible implementation example, the step of determining that there is a fault in the photovoltaic power generation system based on the parameter detection values ​​of the branch or the parameter detection values ​​of the DC bus comprises: determining that a fault exists in the photovoltaic system when the leakage current detection value of the DC bus exceeds a third current value or when the leakage current detection value of the branch exceeds a fourth current value; In particular:

[0065] Regarding the second aspect, in a possible implementation example, the step of determining that there is a fault in the photovoltaic power generation system based on the parameter detection values ​​of the branch or the parameter detection values ​​of the DC bus comprises: determining that a fault exists in the photovoltaic system when it is determined based on the current detection values ​​of all the branches that a fault exists due to an arc in the branch, or when it is determined based on the current detection value of the DC bus that a fault exists due to an arc in the DC bus; In particular:

[0066] According to a third aspect, the present application further provides a photovoltaic system including at least two photovoltaic sections and a protection device according to any one of the above implementations. Each photovoltaic section includes at least one photovoltaic component. When the photovoltaic section includes multiple photovoltaic components, the photovoltaic components may be connected in series or in parallel.

[0067] When it is determined that the photovoltaic system has a fault based on the parameter detection value of the branch or the parameter detection value of the DC bus, the controller of the protection device of the photovoltaic system can control the protection switch to be in an open state, so that up to three photovoltaic units are directly connected in parallel, thereby protecting the photovoltaic units and the line of the photovoltaic system. In addition, only the protection switch is added to the circuit, and the resistance of the protection switch is less than the resistance of the fuse, so that the loss rate and loss of the photovoltaic system are further reduced.

[0068] Regarding the third aspect, in a first possible implementation example, the system further includes a protection unit, and the photovoltaic unit and the protection unit are connected in series or in parallel and then connected to the protection device using the interface.

[0069] Thus, the protector does not need to be removed and disposed of when the photovoltaic system currently using the protector is restored, and the protector is directly connected to the open circuit protection device.

[0070] Regarding the third aspect, in a second possible implementation, the protection unit may be one or a combination of a fuse, an optimizer, and a disconnect box.

[0071] When the protection device includes a power circuit, the power circuit may be a direct current-direct current (DC-DC) conversion circuit. When the power circuit is a DC-DC conversion circuit, the DC-DC conversion circuit may be a boost circuit, a buck circuit, or a buck-boost circuit, among others. In this case, the protection device may be a DC combiner box of a photovoltaic system.

[0072] Alternatively, the power circuit may be a direct current to alternating current (DC-AC) conversion circuit, ie, an inverter (also referred to as an inverter circuit), configured to convert direct current to alternating current for output.

[0073] If the protection device does not include a power circuit, the protection device may be connected as an independent device to the input end of a DC combiner box or inverter of a photovoltaic system.

[0074] From the above technical solutions, it can be seen that the solutions provided in this application have at least the following effects:

[0075] The protection device of the photovoltaic system provided in the embodiment of the present application may be applied to the photovoltaic system. When the protection switch of the device is in an open state, up to three photovoltaic units are directly connected in parallel. For example, when two photovoltaic units are directly connected in parallel to a DC bus in the device, when one photovoltaic unit is faulted by a short circuit, only one normal photovoltaic unit outputs a short circuit current to the photovoltaic unit. In this case, the short circuit current falls within the allowable range of the faulty photovoltaic unit, thereby protecting the photovoltaic components and the line from damage. The specific connection manner between the photovoltaic units and the protection switch may be set based on actual requirements. When the controller of the protection device can determine that the photovoltaic system has a fault based on the parameter detection value of the branch or the parameter detection value of the DC bus, the controller controls the protection switch to be in an open state, so that up to three photovoltaic units are directly connected in parallel, thereby protecting the photovoltaic units and the line of the photovoltaic system. In addition, only a protection switch is added to the circuit, and the resistance of the protection switch is less than the resistance of the fuse, so the loss rate and loss of the photovoltaic system are reduced. In addition, since the fuse is no longer used, the Y harness, which is originally used for the built-in fuse, can be placed on the photovoltaic side instead of under the inverter or DC combiner box of the photovoltaic system, which further reduces the cable cost. [Brief description of the drawings]

[0076] [Figure 1] 1 is a schematic diagram of a protection device used in the prior art. [Diagram 2] 2 is a schematic diagram of a protection device used in the prior art. [Diagram 3] FIG. 3 is a schematic diagram of a protection device used in the prior art. [Figure 4] FIG. 2 is a schematic diagram of a branch according to an embodiment of the present application; [Diagram 5] FIG. 2 is a schematic diagram of another branch according to an embodiment of the present application. [Figure 6A] 1 is a schematic diagram of a protection device according to an embodiment of the present application; [Figure 6B] FIG. 2 is a schematic diagram of another protection device according to an embodiment of the present application. [Figure 6C] FIG. 2 is a schematic diagram of yet another protection device according to an embodiment of the present application. [Figure 7] FIG. 2 is a schematic diagram of another protection device according to an embodiment of the present application. [Figure 8] FIG. 2 is a schematic diagram of yet another protection device according to an embodiment of the present application. [Figure 9] 1 is a schematic diagram of yet another protection device according to an embodiment of the present application; [Figure 10] FIG. 2 is a schematic diagram of another protection device according to an embodiment of the present application. [Figure 11] FIG. 2 is a schematic diagram of yet another protection device according to an embodiment of the present application. [Figure 12] 1 is a schematic diagram of yet another protection device according to an embodiment of the present application; [Figure 13] FIG. 2 is a schematic diagram of another protection device according to an embodiment of the present application. [Figure 14] FIG. 2 is a schematic diagram of yet another protection device according to an embodiment of the present application. [Figure 15] 1 is a schematic diagram of yet another protection device according to an embodiment of the present application; [Figure 16] FIG. 2 is a schematic diagram of another protection device according to an embodiment of the present application. [Figure 17] FIG. 2 is a schematic diagram of yet another protection device according to an embodiment of the present application. [Figure 18] 1 is a schematic diagram of yet another protection device according to an embodiment of the present application; [Figure 19] FIG. 2 is a schematic diagram of another protection device according to an embodiment of the present application. [Figure 20A] FIG. 2 is a schematic diagram of yet another protection device according to an embodiment of the present application. [Figure 20B] 1 is a schematic diagram of yet another protection device according to an embodiment of the present application; [Figure 20C] 1 is a schematic diagram of yet another protection device according to an embodiment of the present application; [Figure 21] FIG. 2 is a schematic diagram of another protection device according to an embodiment of the present application. [Figure 22] 2 is a flowchart of a short circuit protection method according to an embodiment of the present application. [Diagram 23] 4 is a flowchart of another short circuit protection method according to an embodiment of the present application. [Figure 24] 1 is a schematic diagram of a photovoltaic power generation system according to an embodiment of the present application. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0077] In order to improve the DC ratio of the photovoltaic power generation system, each MPPT component is usually connected to at least two or more photovoltaic sections. In addition, the positive output end and / or the negative output end of the photovoltaic section are connected in series with one or more fuses to protect the photovoltaic section and the line when the photovoltaic section or the line is short-circuited. In the following, an example in which each MPPT component is connected to three branches will be described. The principle is similar when each MPPT component is connected to more branches, and the details will not be described again in this description. 。

[0078] In order to solve the above technical problems, the present application provides a protection device, a short circuit protection method, and a photovoltaic power generation system that effectively protect a photovoltaic unit and a line while reducing power loss when the photovoltaic unit or the line is short-circuited. Hereinafter, a detailed description will be given with reference to the accompanying drawings.

[0079] The terms "first," "second," etc., used hereinafter, are intended to be descriptive only and are not to be construed as indicating or suggesting the relative importance of the indicated technical features or as implicitly indicating the quantity of the indicated technical features. Thus, a feature qualified by "first," "second," etc. may explicitly or implicitly include one or more such features.

[0080] In this application, unless otherwise expressly limited, the term "connect" should be interpreted broadly. For example, a "connect" may be a fixed connection, a removable connection, an integral connection, a direct connection, or an indirect connection through an intermediate medium.

[0081] In order to facilitate understanding of the technical solutions of the present invention for those skilled in the art, the technical solutions of the embodiments of the present application are described clearly and comprehensively hereinafter with reference to the accompanying drawings in the embodiments of the present application.

[0082] Device embodiment 1 The photovoltaic unit of the following embodiments may include one photovoltaic component, or may be formed by connecting multiple photovoltaic components in series and / or in parallel. For example, multiple photovoltaic units are first connected in series to form a photovoltaic string, and then multiple photovoltaic strings are connected in parallel to form a photovoltaic unit. The specific number of photovoltaic components included in the photovoltaic unit in this embodiment of the present application is not limited to a specific one, and may be set by those skilled in the art based on actual requirements. In addition, the electrical parameters of the photovoltaic component unit in this embodiment of the present application are not limited to a specific one. The output voltages of multiple photovoltaic units connected to the same device may be the same or different, which is not limited to a specific one in this embodiment of the present application.

[0083] The protection device provided in this embodiment of the present application is applied to a photovoltaic system, and the protection device can be connected to at least two photovoltaic units using an interface. After the photovoltaic units are connected to the protection device using an interface, the photovoltaic units can be directly connected in parallel to a DC bus in the device, or the photovoltaic units and the protection switch can be connected in series and then connected in parallel to a DC bus, so that the output currents of the photovoltaic units are merged and flow into the DC bus, and at least two branches are formed in the device. Each branch is connected to at least one photovoltaic unit. Hereinafter, the state of the branches will be described in detail first.

[0084] FIG. 4 is a schematic diagram of a branch according to an embodiment of the present application.

[0085] A branch includes one photovoltaic unit 101a1, the positive output end of the photovoltaic unit 101a1 is the positive output end of the branch, and the negative output end of the photovoltaic unit 101a1 is the negative output end of the branch, which will not be described in the following embodiments.

[0086] FIG. 5 is a schematic diagram of another branch according to an embodiment of the present application.

[0087] 4, and thus includes, for example, at least two photovoltaic units (101a1, 101a2, ..., 101ai, in that order). In some embodiments, when a branch includes multiple photovoltaic units, the branch may further include a protection switch (not shown) that provides protection between the photovoltaic units and the line.

[0088] The branch in this embodiment of the present application is a concept in an electric field, and can be understood to refer to a route through which a shunt current of a parallel circuit flows. Continuing to explain the example of FIG. 5, the line on which the photovoltaic unit 101a1 is located may be regarded as one branch, and the line formed after the photovoltaic unit 101a1 and the photovoltaic unit 101a1 are connected in parallel may also be regarded as one branch.

[0089] The positive output ends of all the photovoltaic sections are brought together to form the positive output end of a branch, and the negative output ends of all the photovoltaic sections are brought together to form the negative output end of a branch.

[0090] In the following embodiments, the term "branch" is a general term for all branches particularly shown in Figs. 4 and 5, that is, a general term for all branches excluding the trunk (DC bus).

[0091] The working principle of the protection device will now be described in detail with reference to the accompanying drawings.

[0092] FIG. 6 is a schematic diagram of a protection device according to an embodiment of the present application.

[0093] The protection device 200 is an interface, a protection switch S 1 ~S M-1 , a DC bus and a controller (not shown).

[0094] The device 200 may be connected to at least two photovoltaic units using an interface. The number of photovoltaic units connected is not limited to a specific number in this application. At least two photovoltaic units are connected to a DC bus in the device to form at least two branches, and each branch is connected to at least one photovoltaic unit.

[0095] When the protection device is applied to a photovoltaic system, the DC busbars particularly include a positive DC busbar and a negative DC busbar.

[0096] Protection switch S 1 ~S M-1 is configured to disconnect all or part of the photovoltaic units from the DC bus so that up to three photovoltaic units are directly connected in parallel, in other words, the protection switch S 1 ~S M-1 is configured, when in an open state, to allow up to three photovoltaic sections to be directly connected in parallel to a DC bus within the device.

[0097] For example, if a fault occurs in one photovoltaic section due to a short circuit, and the faulty photovoltaic section can withstand the output current of another normal photovoltaic section, the protection switch S 1 ~S M-1 When is in the open state, up to two photovoltaic sections are directly connected in parallel in the device. In this example, the values ​​of i and j in the diagram are 2.

[0098] As another example, if a fault occurs in one photovoltaic section due to a short circuit, and the faulty photovoltaic section can withstand the output current of the other two normal photovoltaic sections, the protection switch S 1 ~S M-1 When is in the open state, up to three photovoltaic sections are directly connected in parallel in the device. In this example, the values ​​of i and j in the diagram are 3.

[0099] In particular, i and j are determined by the actual current tolerance of the photovoltaic unit, which is not limited to a specific one in the present embodiment of the present application. It should be noted that Fig. 6 is only for the purpose of facilitating illustration and explanation, and in reality, the i photovoltaic units in the figure are connected in parallel in the protection device.

[0100] For ease of explanation, the following describes an example where the value of i and j is 2. In some other embodiments, the principle is similar when the value of i and j is 3, and the details are not described again in this application.

[0101] The controller is configured to control the protection switch to an open state when it is determined that the photovoltaic power generation system has a fault based on the parameter detection value of the branch or the parameter detection value of the DC bus. A fault caused by a short circuit will be described below as an example. In particular, when the parameter detection value is a reverse current value, the controller is particularly configured to determine that the photovoltaic power generation system has a fault when the reverse current value of the branch exceeds a first current value.

[0102] The principle of implementing the protection function by the controller will be described below.

[0103] When there is no short circuit fault, the currents of all the branches join together and flow into the DC bus. Therefore, the absolute value of the current of the DC bus exceeds the absolute value of the current of any branch. The current direction is from the anode of the photovoltaic unit to the positive DC bus. When a short circuit fault exists in any branch, the output currents of all other normal branches flow into the branch where the short circuit fault exists. In this case, the voltage of the DC bus decreases, and the current direction of the branch swings toward the branch where the short circuit fault exists, in other words, the reverse current of the branch exceeds the first current value. The first current value may be determined based on an actual case. This is not limited to a specific one in this embodiment of the present application. Preferably, the first current value may be a relatively small value, for example 0, in order to find a short circuit fault as early as possible and start the protective operation of the protective switch. In other words, when a reverse current occurs in the branch, the controller controls the protective switch to be in an open state.

[0104] In this case, the controller determines that a fault due to a short circuit exists in the photovoltaic section or line, and controls the protection switch to an open state to protect the photovoltaic section and line.

[0105] In some embodiments, the protection device 200 further includes a power circuit 201, which is configured to convert power, and which may be a direct current / direct current (DC / DC) conversion circuit or a direct current / alternating current (DC / AC) conversion circuit.

[0106] When the power circuit 201 is a DC / DC conversion circuit, the DC / DC conversion circuit may be a boost circuit, a buck circuit, or a buck-boost circuit. In this case, the protection device may be a DC combiner box of a photovoltaic power generation system. This application is not limited to this.

[0107] When the power circuit 201 is a DC / AC circuit, the DC / AC circuit is configured to convert DC to AC for output. In this case, the protection device may be used as an inverter for a photovoltaic system.

[0108] In some other embodiments, the protection device may be an independent device located at the input end of the DC combiner box or inverter of the photovoltaic system.

[0109] In summary, the protection device provided in this embodiment of the present application can be connected to multiple photovoltaic units using an interface. When the protection switch of the device is in an open state, up to three photovoltaic units are directly connected in parallel in the device to protect the photovoltaic components and lines from damage. The specific connection manner between the photovoltaic units and the protection switch can be set based on actual requirements. When the reverse current of the branch exceeds a first current value, the controller of the device can control the protection switch to be in an open state to protect the photovoltaic units and lines of the photovoltaic system. In addition, only a protection switch is added to the circuit, and the resistance of the protection switch is less than the resistance of the fuse, so that the loss rate and loss of the photovoltaic system are further reduced. In addition, since the fuse is no longer used, the Y harness, which is originally used for the built-in fuse, can be placed on the photovoltaic unit side instead of being placed under the inverter or DC combiner box of the photovoltaic system, which further reduces the cable cost.

[0110] The above description takes an example in which a faulty photovoltaic component is made to withstand the reverse current from another photovoltaic component. In practical application, to better meet the safety specification requirements, the protection switch is configured to disconnect all photovoltaic parts from the DC bus. Please refer to Figure 6B for details.

[0111] FIG. 6B is a schematic diagram of another protection device according to an embodiment of the present application.

[0112] FIG. 6B differs from FIG. 6A in that it further includes protection switches S01 and S02, which disconnect all photovoltaic units from the DC busbar when all protection switches are in an open state, in other words, the connection lines between all interfaces and the DC busbar are disconnected.

[0113] In addition, the above description uses an example in which up to three photovoltaic units are directly connected in parallel and then connected to one interface. In some other embodiments, up to three photovoltaic units are connected in parallel in the device using corresponding interfaces. For a specific implementation, see FIG. 6C.

[0114] In some embodiments, when the absolute value of the current in the branch exceeds the absolute value of the current in the DC bus, or when the reverse current in the branch exceeds a first current value, the controller specifically determines that the reverse current in the branch exceeds the first current value, and controls the protection switch to an open state. The working principle of the controller is described below with reference to a specific implementation example.

[0115] Device embodiment 2 An example in which a protection device is connected to two photovoltaic units will be described below.

[0116] FIG. 7 is a schematic diagram of another protection device according to an embodiment of the present application.

[0117] The protection device 200 is connected to the two photovoltaic units 101a1 and 101a2 using an interface.

[0118] The two photovoltaic units are connected in parallel in a protection device 200 and then connected to a power circuit 201 using a DC switch 102. The DC switch 102 is configured to protect the circuit. In some embodiments, instead of placing a DC switch 102, a direct connection may be made.

[0119] Furthermore, at least one photovoltaic unit is connected in series with the protection switch S1.

[0120] The principle of implementing a protection function by a controller using the absolute value of the detected current will be described below.

[0121] When there is no fault due to a short circuit, the currents of the two photovoltaic sections join together and flow into the DC bus, and the absolute value of the current in the DC bus (the absolute value of the detected current at detection point A or detection point B) exceeds the absolute value of the current in either branch (the absolute value of the detected current at detection point C or detection point D).

[0122] If a fault occurs in one photovoltaic section due to a short circuit, the output current of the other normal photovoltaic sections will flow through the photovoltaic section with the short circuit. In this case, the absolute value of the current in the DC bus will be smaller than the absolute value of the current in any of the branches.

[0123] When the absolute value of the branch current exceeds the absolute value of the DC bus current, the controller controls the protection switch S1 to the open state.

[0124] In particular, when a fault due to a short circuit exists in the branch in which the photovoltaic unit 101a1 is located, the protection switch S1 is in an open state, which protects the photovoltaic unit and the line by stopping the photovoltaic unit 101a2 from outputting current. When a fault due to a short circuit exists in the branch in which the photovoltaic unit 101a2 is located, the protection switch S1 is in an open state, which disconnects the branch with the short circuit, allowing the photovoltaic unit 101a1 to continue outputting current to the device 200 and maintain a normal operating state.

[0125] In some embodiments, the magnitude and direction of the current may be detected using a current sensor, which communicates the detection results to a controller of the device 200 .

[0126] In the above implementation, the absolute value of the current at point A or point B can be detected using a first current sensor, and the absolute value of the current at point C or point D can be detected using a second current sensor.

[0127] In some embodiments, the protection switch S1 may be connected in series to the positive output end of the photovoltaic unit 102a2, or may be connected in series to the negative output end of the photovoltaic unit 102a2, or one photovoltaic unit may be connected to each of the positive output end and the negative output end of the photovoltaic unit 102a2 to implement redundant control. This is not limited to a specific embodiment of the present application.

[0128] The principle of how the controller implements a protection function using the direction of the detected current will be described below.

[0129] When there is no short circuit fault, the current direction at detection point C and detection point D may be set to a default direction, for example, to the positive direction.

[0130] When a fault occurs due to a short circuit in the branch where the photovoltaic unit 101a1 is located, the output current of the photovoltaic unit 101a2 flows in the branch where the photovoltaic unit 101a1 is located, and therefore the current direction at the detection point C becomes opposite to the default current direction, which is a negative direction. In this case, the controller controls the protection switch S1 to be in an open state, which stops the photovoltaic unit 101a2 from outputting current, thereby protecting the photovoltaic unit and the line. When a fault occurs due to a short circuit in the branch where the photovoltaic unit 101a2 is located, the output current of the photovoltaic unit 101a1 flows in the branch where the photovoltaic unit 101a2 is located, and therefore the current direction at the detection point D becomes opposite to the default current direction. In this case, the controller controls the protection switch S1 to be in an open state, which disconnects the branch with the short circuit, and allows the photovoltaic unit 101a1 to continue to output current to the protection device 200 normally.

[0131] In this manner, the current direction at point C can be detected using the third current sensor, and the current direction at point D can be detected using the fourth current sensor.

[0132] The detection points C and D in the above embodiment may be located at the negative output end of the corresponding photovoltaic unit, or one may be located at the positive output end of the photovoltaic unit and the other at the negative output end of the photovoltaic unit. In this case, the working principle of the controller is the same, and the details will not be described again in this description.

[0133] In summary, when the protection device is connected to two photovoltaic units using an interface, when the absolute value of the current in the branch exceeds the absolute value of the current in the DC bus, or when the current direction in the branch is opposite to the default current direction, the controller of the protection device controls the protection switch to open, so that the current in both branches is less than the first current value, thereby protecting the photovoltaic unit and the line. In addition, only the protection switch is added to the circuit, and the resistance of the protection switch is less than the resistance of the fuse (in some embodiments, the resistance of the applied protection switch is only about 0.3 milliohms, which is less than the resistance of the fuse), so that the loss rate and loss are further reduced. In addition, the Y terminal can also be placed on the photovoltaic unit side, so that the cable cost is reduced.

[0134] In the above embodiment, an example in which a protection device is connected to two photovoltaic units is described. However, currently, in order to improve the DC ratio of a photovoltaic power generation system, it is common to connect a protection device to three, four, or five or more photovoltaic units. Hereinafter, the operation principle in the case where each device is connected to three photovoltaic units will be described first.

[0135] Device embodiment 3 FIG. 8 is a schematic diagram of yet another protection device according to an embodiment of the present application.

[0136] The positive output ends of the three photovoltaic power units are connected in parallel in a protection device and then connected to a power circuit 201 using a DC switch 102. The DC switch 102 is configured to protect the circuit. In practical application, a direct connection may be made instead of disposing the DC switch 102.

[0137] The photovoltaic unit 101a1 and the protective switch S1 are connected in series and then connected to a DC bus, and the photovoltaic unit 101a3 and the protective switch S2 are connected in series and then connected in parallel to the DC bus.

[0138] The principle of implementing a protection function by a controller using the absolute value of the detected current will be described below.

[0139] When there is no short circuit fault, the output currents of the three photovoltaic units join together and flow into the DC bus, so that the absolute value of the DC bus current (the absolute value of the detected current at detection point A or detection point B) exceeds the absolute value of the current in any branch (the absolute value of the detected current at detection point C, detection point D, and detection point E).

[0140] When a fault occurs in a photovoltaic section due to a short circuit, the output current of the other normal photovoltaic sections flows through the photovoltaic section with the fault due to the short circuit. In this case, the absolute value of the current in the DC bus becomes smaller than the absolute value of the current in any branch.

[0141] When the absolute value of the DC bus current is smaller than the absolute value of the current in either branch, the controller of the protection device controls the protection switches S1 and S2 to be in the open state, so that the current flowing in the branch with the short circuit becomes zero, thereby protecting the photovoltaic unit and the line.

[0142] In this implementation, the absolute value of the DC bus current (i.e., detection point A or B) can be detected using a first current sensor, and the absolute value of the current in any branch (i.e., detection point C, D or E) can be detected using a second current sensor.

[0143] The principle of how the controller implements a protection function using the direction of the detected current will be described below.

[0144] When there is no short circuit fault, the current direction at points C, D and E may be set to a default current direction, for example, to the positive direction.

[0145] When a short circuit occurs in the photovoltaic section, the output current of the other normal photovoltaic sections flows through the photovoltaic section with the short circuit fault, and the current direction of the photovoltaic section with the short circuit fault becomes opposite to the default direction. In this case, the controller controls the protection switches S1 and S2 to be in the open state, so that the current flowing through the branch with the short circuit becomes zero, thereby protecting the photovoltaic section and the line.

[0146] In this manner, the current directions of the three first type photovoltaic section branches can be detected individually using the three current sensors.

[0147] In another possible implementation example, in order to reduce the number of current sensors used, whether or not a fault due to a short circuit exists may be determined by detecting the current direction at points G and F, instead of the above. When a fault due to a short circuit occurs in the branch in which the photovoltaic units 101a1 and 101a3 are located, the current detection direction at point H becomes opposite to the default current direction. When a fault due to a short circuit occurs in the branch in which the photovoltaic unit 101a2 is located, the current detection direction at point G becomes opposite to the default current direction. When the current detection direction at point H or point G is opposite to the default current direction, the controller may control the protection switch to an open state to protect the photovoltaic units and the line.

[0148] In this manner, the current direction at point G can be detected using a third current sensor, and the current direction at point H can be detected using a fourth current sensor. Compared to the implementations above, this allows a reduction in the number of current sensors used.

[0149] In some embodiments, instead of arranging the protection switch S1 or the protection switch S2, a direct connection may be made, in which case, after the controller controls the protection switch to an open state, the current flowing through the branch where the short circuit fault exists becomes less than the first current value.

[0150] In summary, when the protection device is connected to three photovoltaic units using an interface, the controller can control the protection switch to open when the absolute value of the current in the photovoltaic unit exceeds the absolute value of the current in the DC bus, or when the current direction of the branch is opposite to the default current direction, so that the current in any branch is less than the first current value, thereby protecting the photovoltaic unit and the line. In addition, only the protection switch is added to the circuit, and the resistance of the protection switch is less than the resistance of the fuse, so that the loss rate and loss are further reduced. In addition, the Y terminal can also be placed on the photovoltaic unit side, so that the cable cost is reduced.

[0151] Device embodiment 4 FIG. 9 is a schematic diagram of yet another protection device according to an embodiment of the present application.

[0152] The photovoltaic units 101a1 and 101a2 are directly connected in parallel within the protection device and then connected to a DC bus, and the photovoltaic unit 101a3 and the protection switch S1 are connected in series and then connected in parallel to the DC bus of the device.

[0153] The DC switch 102 is configured to protect the circuit. In some embodiments, a direct connection may be made instead of disposing the DC switch 102. An example will be described in which the protection switch S1 is connected in series to the negative electrode of the photovoltaic unit 101a3. In some embodiments, the protection switch S1 may be connected in series to the anode of the photovoltaic unit 101a3 instead.

[0154] The principle of implementing a protection function by a controller using the absolute value of the detected current will be described below.

[0155] When there are no short-circuit faults, the currents of all branches join together and flow into the DC bus, and therefore the absolute value of the DC bus current (the absolute value of the detected current at detection point A or detection point B) exceeds the absolute value of the current in any of the branches (the absolute value of the detected current at detection points C, D, E, and F).

[0156] When a short circuit occurs in a branch, the output current of the normal branch flows through the branch with the short circuit, and the absolute value of the DC bus current becomes smaller than the absolute value of the current in any branch.

[0157] Therefore, the controller of the protection device controls the protection switch S1 to be in an open state when the absolute value of the current in the branch exceeds the absolute value of the current in the DC bus. In particular, when a fault due to a short circuit exists in the branch in which the photovoltaic unit 101a3 is located, the protection switch S1 is in an open state, so that the current flowing through the branch in which the fault exists becomes zero, and furthermore, the photovoltaic units 101a1 and 101a2 can output current normally. When a fault due to a short circuit exists in the branch in which the photovoltaic units 101a1 and 101a2 are located, the protection switch S1 is in an open state, so that the branch in which the photovoltaic unit 101a3 is located stops outputting current to the branch in which the fault exists, and thus the photovoltaic units and the line are protected.

[0158] In this embodiment, the absolute value of the DC bus current (detection point A or detection point B) can be detected using a first current sensor, and the absolute value of the current of any branch (any one of detection points C, D, E, and F) can be detected using a second current sensor; in other words, two current sensors are required.

[0159] The principle of how the controller implements a protection function using the direction of the detected current will be described below.

[0160] When there is no short circuit fault, the current direction at detection points E and F may be set to a default direction, for example, to the positive direction.

[0161] When a fault due to a short circuit occurs in the branch in which the photovoltaic unit 101a3 is located, the current direction at the detection point E becomes opposite to the default current direction. When a fault due to a short circuit occurs in the branch in which the photovoltaic units 101a1 and 101a2 are located, the current direction at the detection point F becomes opposite to the default current direction.

[0162] Therefore, this implementation can be implemented by using two current sensors to detect the current direction at points E and F separately. When the detected current direction is found to be opposite to the predetermined current direction, the controller controls the protection switch S1 to an open state to protect the photovoltaic unit and the line.

[0163] FIG. 10 is a schematic diagram of another protection device according to an embodiment of the present application.

[0164] The protection device in Fig. 10 differs from the protection device in Fig. 9 in that the protection switch S1 is connected in series to the negative output ends of the photovoltaic units 101a1 and 101a2 (or may be connected in series to the positive output ends of the photovoltaic units 101a1 and 101a2). In this case, the working principle of the controller is similar to the above description, and the details will not be described again in this embodiment of the present application.

[0165] Alternatively, the detection points C, D and E in the above embodiment may be located on the negative output end side of the corresponding photovoltaic unit.

[0166] In summary, when the protection device is connected to three photovoltaic units using an interface, 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 in any branch is opposite to the default current direction, the controller of the protection device can control the protection switch to open to protect the photovoltaic unit and the line. In addition, only the protection switch is added to the circuit, and the resistance of the protection switch is less than the resistance of the fuse, so the loss rate and loss are further reduced. In addition, the Y terminal can also be placed on the photovoltaic unit side, so the cable cost is reduced.

[0167] In the above embodiment, an example is described in which the input end of each device includes three photovoltaic units. Hereinafter, the working principle in the case where each device is connected to four corresponding photovoltaic units will be described.

[0168] Device embodiment 5 FIG. 11 is a schematic diagram of yet another protection device according to an embodiment of the present application.

[0169] The positive output ends of the four photovoltaic units are gathered together at a protection switch S1 on the positive DC bus in the protection device, and the negative output ends of each first-type photovoltaic unit branch and one protection switch are connected in series in the protection device and then gathered together at the negative DC bus.

[0170] The principle of implementing a protection function by a controller using the absolute value of the detected current will be described below.

[0171] When there is no short circuit fault, the currents of the four photovoltaic sections join together and flow into the DC bus, so that the absolute value of the DC bus current (the absolute value of the detected current at detection point A or B) exceeds the absolute value of the current in any branch (the absolute value of the detected current at detection points C, D, E and F).

[0172] When a fault occurs in a photovoltaic section due to a short circuit, the output current of the other normal photovoltaic sections flows through the photovoltaic section with the fault due to the short circuit. In this case, the absolute value of the current in the DC bus becomes smaller than the absolute value of the current in any branch, and the controller controls the protection switch so that it is in an open state, so that the current flowing through the branch with the short circuit becomes zero.

[0173] In this embodiment, the absolute value of the current of the DC bus, i.e., points A and B, can be detected using a first current sensor, and the absolute value of the current of any of the first type photovoltaic section branches (any one of detection points C, D, E and F) can be detected using a second current sensor.

[0174] The principle of how the controller implements a protection function using the direction of the detected current will be described below.

[0175] When there is no short circuit fault, the current direction at points C, D, E and F may be set to a default direction, for example, positive direction.

[0176] When a fault occurs in a photovoltaic section due to a short circuit, the output current of the other normal photovoltaic sections flows through the photovoltaic section with the short circuit, and thus the current direction of the branch in which the photovoltaic section with the short circuit is located becomes opposite to the default direction. In this case, the controller controls the protection switch to be in an open state, so that the current flowing through the faulty branch becomes zero, thereby protecting the photovoltaic section and the line.

[0177] In this implementation, the current directions of the four first type photovoltaic section branches can be detected individually using four current sensors.

[0178] In another possible implementation, in order to reduce the number of current sensors used, whether or not a short circuit fault exists may be determined by detecting the current direction at points G and F, instead of the above.

[0179] When there is no short circuit fault, the current direction at points G and H may be set to a default direction, for example, to the positive direction.

[0180] When a fault due to a short circuit occurs in the branch containing the photovoltaic units 101a1, 101a3, and 101a4, the current detection direction at point H becomes opposite to the default current direction. When a fault due to a short circuit occurs in the branch containing the photovoltaic unit 101a2, the current detection direction at point G becomes opposite to the default direction.

[0181] In this manner, the current directions at points G and H can be detected separately using two current sensors.

[0182] In some embodiments, instead of arranging the protection switches S1, S2 and S3, a direct connection may be made, in which case the controller controls the protection switches to an open state, so that the current flowing through the shorted branch is less than a first current value, thereby protecting the photovoltaic unit and the line.

[0183] FIG. 12 is a schematic diagram of yet another protection device according to an embodiment of the present application.

[0184] FIG. 12 shows another possible implementation, which differs from that shown in FIG. 11 in that the positive output end of photovoltaic unit 101a1 and the positive output end of photovoltaic unit 101a2 are brought together at protection switch S1 and connected to the positive DC bus using protection switch S1, and the positive output end of photovoltaic unit 101a3 and the positive output end of photovoltaic unit 101a4 are brought together at protection switch S6 and connected to the positive DC bus using protection switch S6.

[0185] In this case, the controller may use the working principle corresponding to Fig. 11. Details will not be described again in this embodiment of the present application.

[0186] FIG. 13 is a schematic diagram of another protection device according to an embodiment of the present application.

[0187] Figure 13 shows another possible implementation, which differs from the one shown in Figure 11 in that the positive output end of each photovoltaic unit is connected in series with one protective switch and then grouped together at the positive DC bus, and the negative output end of each photovoltaic unit is connected in series with one protective switch and then grouped together at the negative DC bus. Safety can be further improved by arranging the protective switches with increased redundancy, and the branch with the photovoltaic unit can be surely disconnected.

[0188] In this case, the controller may use the working principle corresponding to Fig. 11. Details will not be described again in this embodiment of the present application.

[0189] It is noted that alternatively, the detection points C, D, E and F of the above embodiments may be at the negative output end of the corresponding photovoltaic section.

[0190] In summary, when the protection device is connected to four photovoltaic units using an interface, the controller of the protection device can control the protection switch to open when the absolute value of the current in the branch exceeds the absolute value of the current in the DC bus, or when the current direction of the photovoltaic unit is opposite to the default current direction, so that the current in any branch is less than the first current value, thereby protecting the photovoltaic unit and the line. In addition, only the protection switch is added to the circuit, and the resistance of the protection switch is less than the resistance of the fuse, so that the loss rate and loss are further reduced. In addition, the Y terminal can also be placed on the photovoltaic unit side, so that the cable cost is reduced.

[0191] Device embodiment 6 FIG. 14 is a schematic diagram of yet another protection device according to an embodiment of the present application.

[0192] The photovoltaic units 101a1 and 101a2 are connected in parallel and then connected to the DC bus of the device, and the photovoltaic units 101a3 and 101a4 are each connected in series to a certain branch and one protection switch and then connected to the DC bus of the device.

[0193] In particular, the positive output ends of the two first-type photovoltaic unit branches are brought together and then connected to a positive DC bus, and the negative output ends of each of the two first-type photovoltaic unit branches and one protection switch are connected in series, then brought together and connected to the negative DC bus.

[0194] The positive output ends of the photovoltaic units 101a1 and 101a2 are connected to a positive DC bus bar using a protection switch S1, and the negative output ends of the photovoltaic units 101a1 and 101a2 are connected to a negative DC bus bar using a protection switch S2.

[0195] In some embodiments, a direct connection may be made instead of placing protection switches S1 and S2.

[0196] The principle of implementing a protection function by a controller using the absolute value of the detected current will be described below.

[0197] When there are no short-circuit faults, the currents of all branches join together and flow into the DC bus, and therefore the absolute value of the DC bus current (the absolute value of the detected current at detection point A or B) exceeds the absolute value of the current in any of the branches (the absolute value of the detected current at detection points C, D, E, F, G and H).

[0198] If a short circuit occurs in a branch, the output current of the normal branch flows through the branch with the short circuit. In this case, the absolute value of the DC bus current is smaller than the absolute value of the current in any branch.

[0199] Therefore, when the absolute value of the branch current exceeds the absolute value of the DC bus current, the device controller controls the protection switches S1 to S4 to the open state, thereby reducing the current flowing through the faulty branch to zero, thereby protecting the photovoltaic unit and the line.

[0200] In this embodiment, the absolute value of the current of the DC bus, i.e., point A or point B, can be detected using a first current sensor, and the absolute value of the current of any one of C, D, E, F, G and H can be detected using a second current sensor.

[0201] The principle of how the controller implements a protection function using the direction of the detected current will be described below.

[0202] When there is no short circuit fault, the current direction of the detection points G and H may be set to a default direction, for example, the positive direction.

[0203] When a fault due to a short circuit occurs in the branch in which the photovoltaic units 101a3 and 101a4 are located, the current direction at point H becomes opposite to the predetermined direction. When a fault due to a short circuit occurs in the branch in which the photovoltaic units 101a1 and 101a2 are located, the current direction at point G becomes opposite to the predetermined direction. Therefore, when the current detection direction at either point H or point G is opposite to the predetermined current direction, the controller determines that a fault due to a short circuit exists and can control the protection switches S1 to S4 to be in an open state, so that the current flowing through the branch in which the fault occurs becomes zero, thereby protecting the photovoltaic units and the line.

[0204] In this embodiment, the current directions at points G and H can be detected separately using two current sensors.

[0205] In some embodiments, instead of arranging the protection switches S1, S3 and S4, a direct connection may be made, in which case the controller controls the protection switches to an open state, so that the current flowing through the shorted branch is less than a first current value, thereby protecting the photovoltaic unit and the line.

[0206] FIG. 15 is a schematic diagram of yet another protection device according to an embodiment of the present application.

[0207] The implementation shown in FIG. 15 differs from the implementation in FIG. 14 in that the positive output ends of photovoltaic units 101a3 and 101a4 are brought together and then connected to the positive DC bus using protective switch S3, the negative output end of photovoltaic unit 101a3 is connected to the negative DC bus using protective switch S4, and the negative output end of photovoltaic unit 101a4 is connected to the negative DC bus using protective switch S5.

[0208] In this example, the controller may use the working principle corresponding to Fig. 14 to protect the photovoltaic section and the line. Details will not be described again in this embodiment of the present application.

[0209] FIG. 16 is a schematic diagram of another protection device according to an embodiment of the present application.

[0210] The implementation shown in Fig. 16 differs from the implementation in Fig. 14 in that the photovoltaic units 101a1 and 101a2 are connected in parallel, the positive output ends of the photovoltaic units 101a1 and 101a2 are brought together and then connected to a positive DC bus using a protection switch S1, the negative output ends of the photovoltaic units 101a1 and 101a2 are connected to a negative DC bus using a protection switch S4, and the positive output end of the photovoltaic unit 101a3 is connected to a positive DC bus using a protection switch S2, the positive output end of the photovoltaic unit 101a4 is connected to a positive DC bus using a protection switch S3, and the negative output end of the photovoltaic unit 101a4 is connected to a negative DC bus using a protection switch S4.

[0211] In this example, the controller may use the working principle corresponding to Fig. 14 to protect the photovoltaic section and the line. Details will not be described again in this embodiment of the present application.

[0212] Alternatively, the detection points C, D, E and F in the above embodiment may be located on the negative output end side of the corresponding photovoltaic section.

[0213] In summary, when the protection device is connected to the four photovoltaic units using the interface, 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 in any branch is opposite to the default current direction, the controller of the protection device can control the protection switch to open, so that the current in any branch is less than the first current value, thereby protecting the photovoltaic units and the line. In addition, only the protection switch is added to the circuit, and the resistance of the protection switch is less than the resistance of the fuse, so that the loss rate and loss are further reduced. In addition, the Y terminal can also be placed on the photovoltaic unit side, so that the cable cost is reduced.

[0214] Device embodiment 7 FIG. 17 is a schematic diagram of yet another protection device according to an embodiment of the present application.

[0215] Photovoltaic units 101a1 and 101a2 are directly connected in parallel within the device. The positive output ends of the photovoltaic units 101a1 and 101a2 are connected to a positive DC bus bar using a protection switch S1, and the negative output ends are connected to a negative DC bus bar using a protection switch S2. Photovoltaic units 101a3 and 101a4 are directly connected in parallel within the device. The positive output ends of the photovoltaic units 101a3 and 101a4 are connected to a positive DC bus bar using a protection switch S3, and the negative output ends are connected to a negative DC bus bar using a protection switch S4.

[0216] The principle of implementing a protection function by a controller using the absolute value of the detected current will be described below.

[0217] When there are no short-circuit faults, the currents of all branches join together and flow into the DC bus, and therefore the absolute value of the DC bus current (the absolute value of the detected current at detection point A or B) exceeds the absolute value of the current in any of the branches (the absolute value of the detected current at detection points C, D, E, F, G and H).

[0218] When a short circuit occurs in a branch, the output current of the normal branch flows through the branch with the short circuit, and the absolute value of the DC bus current becomes smaller than the absolute value of the current in any branch.

[0219] In this embodiment, the absolute value of the current of the DC bus, i.e., point A or point B, can be detected using a current sensor, and the absolute value of the current of any one of C, D, E, F, G and H can be detected using another current sensor.

[0220] The principle of how the controller implements a protection function using the direction of the detected current will be described below.

[0221] When there is no short circuit fault, the current direction at points G and H may be set to a default direction, for example, to the positive direction.

[0222] When a fault due to a short circuit occurs in the branch in which the photovoltaic units 101a1 and 101a2 are located, the current direction at point G becomes opposite to the default current direction. When a fault due to a short circuit occurs in the branch in which the photovoltaic units 101a3 and 101a4 are located, the current direction at point H becomes opposite to the default current direction. Therefore, when the current detection direction at either point G or point H is opposite to the default current direction, the controller determines that a fault due to a short circuit exists and can control the protection switches S1 to S4 to be in an open state, thereby reducing the current flowing through the branch in which the fault occurs to zero, thereby protecting the photovoltaic units and the line.

[0223] In some embodiments, in order to reduce the number of protective switches connected in series and thereby reduce costs, a direct connection may be made instead of arranging at least one of the protective switches S1 and S2, a direct connection may be made instead of arranging at least one of the protective switches S3 and S4, or a direct connection may be made instead of arranging either one of the protective switches S1 and S2 and either one of the protective switches S3 and S4. In this case, the controller controls the remaining protective switches to be in an open state, so that the current flowing through the branch where the short-circuit fault exists can be made less than the first current value, thereby protecting the photovoltaic unit and the line.

[0224] In summary, when the protection device is connected to four photovoltaic units using an interface, the controller of the protection device can control the protection switch to open when the absolute value of the current in the branch exceeds the absolute value of the current in the DC bus or the current direction of the branch is opposite to the default current direction, so that the current in any branch is less than the first current value, thereby protecting the photovoltaic units and the line. In addition, only the protection switch is added to the circuit, and the resistance of the protection switch is less than the resistance of the fuse, so that the loss rate and loss are further reduced. In addition, the Y terminal can also be placed on the photovoltaic unit side, so that the cable cost is reduced.

[0225] In the above embodiment, the operation principle of the controller is described when the protection device is connected to three photovoltaic units and when it is connected to four photovoltaic units. In some embodiments, each device may be connected to a larger number of photovoltaic units. Hereinafter, the operation principle of the controller when each device is connected to five or more photovoltaic units will be described in detail.

[0226] Device embodiment 8 For example, the protection device is connected in parallel to M first-type photovoltaic unit branches using an interface, where M is an integer equal to or greater than 3, and a maximum of j photovoltaic units are directly connected to a DC bus within the device, and each of the remaining photovoltaic units is individually connected in series with at least one protection switch and then connected in parallel to the DC bus.

[0227] When the photovoltaic unit is connected in series to one protection switch, the protection switch is connected in series to the positive output end or the negative output end of the photovoltaic unit. When the photovoltaic unit is connected in series to two protection switches, the protection switches are connected in series to the positive output end and the negative output end of the photovoltaic unit to provide redundant protection.

[0228] In the event of a fault due to a short circuit in one photovoltaic unit, if the faulty photovoltaic unit can withstand the output current of one other normal photovoltaic unit, the value of j is 0, 1, or 2, and if the faulty photovoltaic unit can withstand the output current of two other normal photovoltaic units, the value of j is 0, 1, 2, or 3.

[0229] Below, an example where j is 2 will be explained.

[0230] FIG. 18 is a schematic diagram of yet another protection device according to an embodiment of the present application.

[0231] Two photovoltaic units are directly connected in parallel to a DC bus, and each of the other (M-2) photovoltaic units is connected in series with one protection switch and then connected in parallel to the DC bus.

[0232] The principle of implementing a protection function by a controller using the absolute value of the detected current will be described below.

[0233] When there are no short circuit faults, the currents of all the photovoltaic sections join together and flow into the DC bus, and the absolute value of the DC bus current (the absolute value of the detected current at detection point A or detection point B) exceeds the absolute value of the current in any branch.

[0234] When a fault occurs in a photovoltaic section due to a short circuit, the output current of other normal photovoltaic sections flows in the branch in which the short-circuited photovoltaic section is located. In this case, the absolute value of the current in the DC bus becomes smaller than the absolute value of the current in the branch in which the photovoltaic section is located for each photovoltaic section.

[0235] When the absolute value of the branch current exceeds the absolute value of the DC bus current, the protective switch S is switched to the open state. 1 ~S M-2 The controller of the device 200 controls the current in either branch to be less than the first predetermined current, thereby protecting the photovoltaic section and the line.

[0236] In the above implementation, the absolute value of the current at point A or point B can be detected using a first current sensor, and the absolute value of the current in either branch can be detected using a second current sensor.

[0237] The principle of how the controller implements a protection function using the direction of the detected current will be described below.

[0238] When there is no short circuit fault, the current direction of the detection points G and H may be set to a default direction, for example, the positive direction.

[0239] Point G may be at the positive output end or the negative output end of any branch, and the positive output ends of all branches other than the branch with point G are gathered at point H, or the negative output ends of all branches other than the branch with point G are gathered at point H.

[0240] If a fault due to a short circuit occurs in the branch where point G is located, the currents of all other branches flow into the branch where point G is located, and in this case, the current detection direction of point G becomes opposite to the default direction. If the branch where point G is located is normal and a fault due to a short circuit occurs in another branch, the branch where point G is located outputs a current to the branch where the fault due to the short circuit exists, and in this case, the current detection direction of point H becomes opposite to the default current direction. Therefore, when the current detection direction of point G or point H is opposite to the default direction, the controller determines that a fault due to a short circuit exists, and sets the protection switch S to the open state. 1 ~S M-2 By controlling all of the above by the controller, the current in any branch is less than the first current value, thereby protecting the photovoltaic section and the line.

[0241] In this manner, the current direction at point G can be detected using the third current sensor, and the current direction at point H can be detected using the fourth current sensor.

[0242] In some embodiments, the protection switch S 1 ~S M-2 may be connected to the negative output end of the corresponding photovoltaic unit, and one protection switch is connected in series with each of the positive and negative output ends of the photovoltaic unit. By arranging the protection switches with increased redundancy, fault tolerance can be improved.

[0243] In some embodiments, at least one protection switch may be connected in series with each of all the first type photovoltaic section branches, and in this case, the controller controls the protection switch to an open state, so that the current in each branch becomes zero.

[0244] In summary, when the protection device is connected to at least three photovoltaic unit branches using an interface, the controller of the protection device can control the protection switch to open 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 the branch is opposite to the default current direction, so that the current in any branch is less than the first current value, thereby protecting the photovoltaic unit and the line. In addition, only the protection switch is added to the circuit, and the resistance of the protection switch is less than the resistance of the fuse, so that the loss rate and loss are further reduced. In addition, the Y terminal can also be placed on the photovoltaic unit side, so that the cable cost is reduced.

[0245] Apparatus embodiment 9 FIG. 19 is a schematic diagram of another protection device according to an embodiment of the present application.

[0246] Each of the i photovoltaic sections is connected in series in the device and connected in series to at least one protective switch, and then connected to the DC busbar of the device, where N is an integer equal to or greater than 2.

[0247] In the event that a fault occurs in one photovoltaic section due to a short circuit, if the faulty photovoltaic section can withstand the output current of one other normal photovoltaic section, the value of i is 2, and if the faulty photovoltaic section can withstand the output current of two other normal photovoltaic sections, the value of i is 2 or 3.

[0248] The principle of implementing a protection function by a controller using the absolute value of the detected current will be described below.

[0249] When there are no short-circuit faults, the currents of all branches join together and flow into the DC bus, and the absolute value of the DC bus current (the absolute value of the detected current at detection point A or detection point B) exceeds the absolute value of the current in any of the branches.

[0250] When a fault occurs in a photovoltaic section due to a short circuit, the output current of the other normal photovoltaic sections flows in the branch in which the short-circuited photovoltaic section is located. In this case, the absolute value of the current in the DC bus becomes smaller than the absolute value of the current in any branch.

[0251] When the absolute value of the branch current exceeds the absolute value of the DC bus current, the protective switch S is switched to the open state. 1 ~S N The controller of the protection device controls the current in either branch to be less than a first predetermined current, thereby protecting the photovoltaic section and the line.

[0252] In the above implementation, the absolute value of the current at point A or point B can be detected using a first current sensor, and the absolute value of the current in either branch can be detected using a second current sensor.

[0253] The principle of how the controller implements a protection function using the direction of the detected current will be described below.

[0254] When there is no short circuit fault, the current direction of the detection points G and H may be set to a default direction, for example, the positive direction.

[0255] Point G may be at the positive output end or the negative output end of any branch, and the positive output ends of all branches other than the branch with point G are gathered at point H, or the negative output ends of all branches other than the branch with point G are gathered at point H.

[0256] If a fault due to a short circuit occurs in the branch where point G is located, the currents of all other branches flow into the branch where point G is located, and in this case, the current detection direction of point G becomes opposite to the default direction. If the branch where point G is located is normal and a fault due to a short circuit occurs in another branch, the branch where point G is located outputs a current to the branch where the fault due to the short circuit exists, and in this case, the current detection direction of point H becomes opposite to the default current direction. Therefore, when the current detection direction of point G or point H is opposite to the default direction, the controller determines that a fault due to a short circuit exists, and sets the protection switch S to the open state. 1 ~S N All of this is controlled by a controller, thereby protecting the photovoltaic section and the lines.

[0257] In this manner, the current direction at point G can be detected using the third current sensor, and the current direction at point H can be detected using the fourth current sensor.

[0258] In some embodiments, the protection switch S 1 ~S N may be connected to the negative output end of the corresponding branch, and one protection switch is connected in series with each of the positive and negative output ends of the corresponding branch. By arranging the protection switches with increased redundancy, fault tolerance can be improved.

[0259] In summary, when the protection device is connected to at least two photovoltaic units using an interface, the controller of the protection device can control the protection switch to open 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 the branch is opposite to the default current direction, so that the current in any branch is less than the first current value, thereby protecting the photovoltaic unit and the line. In addition, only the protection switch is added to the circuit, and the resistance of the protection switch is less than the resistance of the fuse, so that the loss rate and loss are further reduced. In addition, the Y terminal can also be placed on the photovoltaic unit side, so that the cable cost is reduced.

[0260] Apparatus embodiment 10 FIG. 20A is a schematic diagram of yet another protection device according to an embodiment of the present application.

[0261] A maximum of j photovoltaic units are directly connected to a DC bus in the device, (Mj) photovoltaic units and at least one switch are connected in series in the device before being connected to the DC bus, and a maximum of i photovoltaic units are directly connected in parallel in the device and connected in series to at least one protective switch before being connected to the DC bus of the device, where N is an integer equal to or greater than 2.

[0262] In the case where a fault occurs in one photovoltaic section due to a short circuit, when the faulty photovoltaic section can withstand the output current of one other normal photovoltaic section, the value of i may be 2 and the value of j may be 0, 1 or 2, and when the faulty photovoltaic section can withstand the output current of two other normal photovoltaic sections, the value of i is 2 or 3 and the value of j is 0, 1, 2 or 3.

[0263] In this case, to allow the current in any branch to be less than the maximum current value that the photovoltaic units and lines can withstand when a short circuit fault is present, (M+N-2) protection switches are required to prevent the photovoltaic units and lines from being damaged by the short circuit current in any branch.

[0264] The principle of implementing a protection function by a controller using the absolute value of the detected current will be described below.

[0265] When there is no short circuit fault, the currents of all branches join together and flow into the DC bus, so the absolute value of the DC bus current (the absolute value of the current detected at point A or point B) exceeds the absolute value of the current in any branch. When there is a short circuit fault in any branch, the output currents of all other normal branches flow into the branch where the short circuit fault exists. In this case, no current flows into the DC bus, in other words, the absolute value of the current in the DC bus is smaller than the absolute value of the current in any branch.

[0266] To reduce the number of current sensors used, the above implementation can be implemented using two current sensors: one current sensor detects the absolute value of the DC bus current, i.e. point A or point B, and the other current sensor detects the absolute value of the current in either branch.

[0267] When the absolute value of the current in the DC bus is less than the absolute value of the current in the branch, the protective switch S is set to the open state. 1 ~S M+N-2 The controller controls all of the above so that the current in each branch is less than the first current value.

[0268] The principle of how the controller implements a protection function using the direction of the detected current will be described below.

[0269] When there is no short circuit fault, the current direction at detection point G or H may be set to a default direction, for example, to the positive direction.

[0270] If a fault due to a short circuit occurs in the branch where point G is located, the currents of all other branches flow into the branch where point G is located, and in this case, the current detection direction of point G becomes opposite to the default direction. If the branch where point G is located is normal and a fault due to a short circuit occurs in another branch, the branch where point G is located outputs a current to the branch where the fault due to the short circuit exists, and in this case, the current detection direction of point H becomes opposite to the default current direction. Therefore, when the current detection direction of point G or point H is opposite to the default direction, the controller determines that a fault due to a short circuit exists, and sets the protection switch S to the open state. 1 ~S M+N-2 By controlling all of the above by the controller, the current in any branch is less than the first current value, thereby protecting the photovoltaic section and the line.

[0271] Point G may be present on any branch, and the positive output ends of all branches except the branch with point G are brought together at point H, or the negative output ends of all branches except the branch with point G are brought together at point H.

[0272] In some embodiments, the protection switch S 1 ~S M-2 may be connected to the negative output end of the corresponding photovoltaic unit, and one protection switch is connected in series with each of the positive and negative output ends of the photovoltaic unit. By arranging the protection switches with increased redundancy, fault tolerance can be improved.

[0273] Alternatively, in some embodiments, at least one protection switch may be connected in series with each of the M photovoltaic branch shown in the figure, where the controller controls the protection switch to an open state, thereby causing the current in each branch to be zero.

[0274] In some embodiments, the protection switch S M-1 ~S M+N-2may be connected to the negative output end of the corresponding branch, and one protection switch is connected in series with each of the positive and negative output ends of the second type photovoltaic section branch. By arranging the protection switches with increased redundancy, the fault tolerance can be improved.

[0275] In summary, when the protection device is connected to multiple photovoltaic units using an interface, and the connection to multiple photovoltaic units may be implemented using a combination of multiple ways, when the absolute value of the current of any branch exceeds the absolute value of the current of the DC bus, or when the current direction of any branch is opposite to the default current direction, the controller of the protection device can control the protection switch to be in an open state, so that the current of any branch becomes less than the first current value, thereby protecting the photovoltaic units and the line. In addition, only the protection switch is added to the circuit, and the resistance of the protection switch is less than the resistance of the fuse, so that the loss rate and loss are further reduced. In addition, the Y terminal can also be placed on the photovoltaic unit side, so that the cable cost is reduced.

[0276] Further, reference is made to Fig. 20B, which is a schematic diagram of yet another protection device according to an embodiment of the present application.

[0277] The photovoltaic section and the protection section can be connected in series or in parallel before being connected to the device. In this figure, an example is described in which any two of the i photovoltaic sections are connected in parallel using the protection section. In some embodiments, the protection section may be connected in series to the photovoltaic section, unlike this. For example, the protection section may be located at the position of point G in the figure.

[0278] The protection unit Q may be one or a combination of a fuse, an optimizer, and a disconnection box, or may be another component that can protect the circuit when a short circuit fault occurs in the circuit, which is not limited in this embodiment of the present application.

[0279] The value of k in the figure may be determined based on practical cases, and this embodiment of the present application is not limited to a specific one.

[0280] In this example, the protection switch is further configured to prevent the protector from initiating a protection action when in an open state, i.e., the protector is directly connected to the open circuit protection device so that the protector does not have to be removed and disposed of when the photovoltaic system currently using the protector is restored.

[0281] It should be noted that in the case where a fault occurs due to a short circuit in one photovoltaic unit, if the faulty photovoltaic unit can withstand the output current of one other normal photovoltaic unit and prevent the protection unit from initiating a protection operation, the value of i is 2, and if the faulty photovoltaic unit can withstand the output currents of the other two normal photovoltaic units and prevent the protection unit from initiating a protection operation, the value of i is 2 or 3.

[0282] The above embodiment describes the working principle of the controller of the protection device when a fault occurs due to a short circuit in the photovoltaic unit or the line in which the photovoltaic unit is located. Hereinafter, the working principle of the controller will be described when the positive and negative poles are short-circuited, or the DC busbar is short-circuited in the protection device, or the DC busbar of the adjacent circuit is short-circuited.

[0283] For some other embodiments, see Fig. 20C. In this example, the device further includes a power converter 2001. Some or all of the photovoltaic section is connected to a DC bus using the power converter 2001. The power converter 2001 is a DC / DC converter configured to perform boost conversion on DC, such as a BOOST circuit.

[0284] Device embodiment 11 FIG. 21 is a schematic diagram of another protection device according to an embodiment of the present application.

[0285] The implementation shown in FIG. 21 differs from that of FIG. 20 in that it further includes DC switches 102 located on the positive DC bus and the negative DC bus.

[0286] When the positive and negative poles are short-circuited, or when the DC busbar is short-circuited in the protection device, or when the DC busbar of the adjacent circuit is short-circuited, in other words, when there is a short circuit between the positive DC busbar and the negative DC busbar with points A and B, the voltage of the DC busbar decreases and the current of the DC busbar increases. Therefore, points A or B may be used as the detection point. When the absolute value of the voltage of the detection point is less than a first voltage value and the absolute value of the current of the detection point is greater than a second current value, the controller controls the DC switch 102 to be in an open state to cut off the short-circuit current.

[0287] When the controller performs a protection function using the absolute value of the detected current, a current sensor capable of measuring the absolute value of the current at point A or point B already exists in the DC branch, and in this case, it is only necessary to add a voltage sensor to measure the absolute value of the voltage at point A or point B.

[0288] If the controller uses the direction of the detected current to perform a protection function, a current sensor (i.e., a fifth current sensor) needs to be added to measure the absolute value of the current at point A or point B, and a voltage sensor needs to be added to measure the absolute value of the voltage at point A or point B.

[0289] The second current value and the first voltage value may be determined based on practical cases, and the present embodiment of the present application is not limited to these.

[0290] In this embodiment, the device shown in Fig. 20A is taken as an example for explanation. It can be understood that the solution provided in this embodiment may also be used in the devices provided in the device embodiments 1 to 10, and the details will not be described again in this embodiment.

[0291] In summary, the protection device provided in this embodiment of the present application not only protects the photovoltaic unit and the line when a fault due to a short circuit occurs in the photovoltaic unit or the line on which the photovoltaic unit is located, but also can timely cut off the short-circuit current when the anode and negative electrode are short-circuited, or when the DC busbar is short-circuited within the protection device, or when the DC busbar of an adjacent circuit is short-circuited, thereby protecting the circuit.

[0292] Apparatus embodiment 12 In the above, an example is described in which a fault due to a short circuit is detected using a reverse current value. Hereinafter, the principle of performing fault detection using another parameter detection value will be described.

[0293] Further, see Fig. 6. The controller is particularly configured to determine that the photovoltaic system has a fault when the detected parameter value of the branch exceeds a first predefined parameter value range or when the detected parameter value of the DC bus exceeds a second predefined parameter value range. The detected parameter value may be at least one of a voltage value, a current value, a power value or a temperature value.

[0294] When the parameter detection value is abnormal, for example, when the voltage of the branch decreases, the current of the branch increases, the power of the branch increases, and the temperature of the branch increases, it can be determined that a short circuit fault exists in the branch. In this embodiment of the present application, the first predefined parameter value range and the second predefined parameter value range are not limited to a specific one. The range may be pre-calibrated and stored in the controller, and will be taken into account when the range is to be used.

[0295] In some embodiments, the controller determines that there is a fault in the photovoltaic system when the leakage current detection value of the DC bus exceeds a third current value or when the leakage current detection value of the branch exceeds a fourth current value.

[0296] When the leakage current detection value is abnormal, this indicates that a leakage current fault exists in the photovoltaic power generation system. According to the solution of the present application, it is possible to identify the location of the leakage current fault to determine the branch in which the leakage current fault exists, or to identify the location of the leakage current fault in the DC bus. In some embodiments, the controller is particularly configured to determine that the photovoltaic power generation system has a fault when it is determined that an arc fault exists in the branch based on the current detection values ​​of all the branches, or when it is determined that an arc fault exists in the DC bus based on the current detection value of the DC bus. In particular, the controller may determine whether an arc fault exists based on the degree of offset of the current detection value with respect to a predetermined reference value.

[0297] The controller is further configured to control the protection switch to an open or closed state according to control instructions sent by the host computer to implement active control of the protection switch.

[0298] The protection switch in this embodiment and the above embodiments of the present application may be a rotary DC switch disconnector or a DC circuit breaker. The controller is further configured to control the protection switch to a closed state after a predetermined time has elapsed when it is determined that the fault has been removed.

[0299] In summary, with the protection device for the photovoltaic system provided in this embodiment of the present application, the photovoltaic section and the line can be effectively protected when there is a fault in the photovoltaic system, thereby improving the safety of the photovoltaic system.

[0300] Method embodiments An embodiment of the present application further provides a protection method for a photovoltaic system, which is used to control the protection device provided in the above embodiment, and the method may be executed by a controller of the protection device.

[0301] In this method, when it is determined that there is a fault in the photovoltaic power generation system based on the detected parameter values ​​of the branch or the detected parameter value of the DC bus, the protective switch is controlled to be in an open state.

[0302] In particular, the parameter detection value is a reverse current value, and the step of determining that there is a fault in the photovoltaic power generation system based on the parameter detection value of the branch or the parameter detection value of the DC bus includes: determining that the photovoltaic system has a fault when the reverse current value of the branch exceeds a first current value; In particular:

[0303] Details are explained below.

[0304] FIG. 22 is a flow chart of a short circuit protection method according to an embodiment of the present application.

[0305] The method includes the following steps.

[0306] S2201: The current detection result is acquired.

[0307] S2202: Control a protection switch to an open state when a reverse current of a branch exceeds a first current value, the branch including at least one photovoltaic unit.

[0308] The principle of implementing the protection function will now be described.

[0309] When there is no short circuit fault, the currents of all the branches join together and flow into the DC bus. Therefore, the absolute value of the current of the DC bus exceeds the absolute value of the current of any branch. The current direction flows from the anode of the photovoltaic unit to the positive DC bus. When a short circuit fault exists in any branch, the output currents of all other normal branches flow into the branch where the short circuit fault exists. In this case, the voltage of the DC bus decreases, and the current direction of the branch swings toward the branch where the short circuit fault exists, in other words, the reverse current of the branch exceeds the first current value. The first current value may be determined based on an actual case. This is not limited to a specific one in this embodiment of the present application. Preferably, the first current value may be a relatively small value, for example 0, in order to find a short circuit fault as early as possible and start the protective operation of the protective switch. In other words, when a reverse current occurs in the branch, the protective switch is controlled to be in an open state to protect the photovoltaic unit and the line.

[0310] In particular, the protection function may be implemented using the absolute value of the detected current or the direction of the detected current.

[0311] The principle of implementing a protection function using the absolute value of the detected current will be described below.

[0312] When there is no short circuit fault, the currents of all branches join together and flow into the DC bus, so the absolute value of the DC bus current exceeds the absolute value of any branch current. When there is a short circuit fault in any branch, the output currents of all other normal branches flow into the branch with the short circuit fault. In this case, no current flows into the DC bus, in other words, the absolute value of the DC bus current is smaller than the absolute value of any branch current.

[0313] Thus, when the absolute value of the current in the DC bus is smaller than the absolute value of the current in the branches, the protection switch is controlled to an open state, so that the current in both branches is less than the first current value.

[0314] The principle of implementing a protection function using the direction of the detected current will be described below.

[0315] A first detection point G is selected from any branch, and the positive output ends of all branches other than the branch with point G are gathered at a second detection point H, or the negative output ends of all branches other than the branch with point G are gathered at the second detection point H.

[0316] When there is no short circuit fault, the current direction at the detection points G and H may be set to a default direction, for example, to the positive direction.

[0317] When a fault due to a short circuit occurs in the branch where point G is located, the currents of all other branches flow into the branch where point G is located, and in this case, the current detection direction of point G is opposite to the default direction. When the branch where point G is located is normal and a fault due to a short circuit occurs in another branch, the branch where point G is located outputs a current to the branch where the fault due to the short circuit exists, and in this case, the current detection direction of point H is opposite to the default current direction. Therefore, when the current detection direction of point G or point H is opposite to the default direction, it is determined that a fault due to a short circuit exists, and the protection switch is controlled to be in an open state, so that the currents of all branches become less than the first current value, thereby protecting the photovoltaic unit and the line.

[0318] In summary, according to the method provided in this embodiment of the present application, when the method is applied to a protection device, the protection switch is controlled to be in an open state when the reverse current of the branch exceeds a first current value, particularly when the absolute value of the current of the branch exceeds the absolute value of the current of the DC bus, or the current direction of the branch is opposite to the default current direction, the protection switch is controlled to be in an open state, so that the current of any branch is less than the first current value, thereby protecting the photovoltaic unit and the line.

[0319] Further, refer to (FIG. 21). In some embodiments, the device further includes a power circuit, and the input end of the power circuit is connected to a DC bus bar by using a DC switch. In this case, the embodiment of the present application further provides another device control method, which is used to protect the circuit when the positive and negative poles are shorted in the device or when the adjacent circuit bus bar is shorted. A detailed description is given below.

[0320] FIG. 23 is a flow chart of another short circuit protection method according to an embodiment of the present application.

[0321] The method includes the following steps.

[0322] S2301: The absolute value of the current of the target DC bus and the absolute value of the voltage of the DC bus are obtained.

[0323] S2302: Control the DC switch to be in an open state when the absolute value of the current of the DC bus exceeds a second current value and the absolute value of the voltage of the DC bus is less than a first voltage value.

[0324] When the positive and negative poles are short-circuited in the protection device, or when the DC busbars of adjacent circuits are short-circuited, in other words, when there is a short circuit between the positive DC busbar and the negative DC busbar with points A and B, the voltage of the DC busbar decreases and the current of the DC busbar increases. Therefore, points A or B may be used as detection points. When the absolute value of the voltage of the detection point is less than a first voltage value and the absolute value of the current of the detection point is greater than a second current value, the controller controls the DC switch to be in an open state to interrupt the short-circuit current.

[0325] The second current value and the first voltage value may be determined based on practical cases, and the present embodiment of the present application is not limited to these.

[0326] In summary, according to this method, when the anode and the cathode are short-circuited within the protective device or when the adjacent circuit busbar is short-circuited, the short-circuit current can be interrupted in a timely manner, thereby protecting the device and the adjacent circuits.

[0327] The following describes a method for determining a fault using alternative parameter detection values.

[0328] When the parameter detection value is at least one of a voltage value, a current value, a power value, and a temperature value, determining that the photovoltaic power generation system has a fault based on the parameter detection value of the branch or the parameter detection value of the DC bus, determining that the photovoltaic system has a fault when the parameter detection value of the branch exceeds a first predetermined parameter value range or when the parameter detection value of the DC bus exceeds a second predetermined parameter value range; In particular:

[0329] When determining whether a fault occurs due to leakage current, the step of determining whether a fault exists in the photovoltaic power generation system based on the parameter detection value of the branch or the parameter detection value of the DC bus includes: determining that a fault exists in the photovoltaic system when the leakage current detection value of the DC bus exceeds a third current value or when the leakage current detection value of the branch exceeds a fourth current value; In particular:

[0330] When determining whether a fault is caused by an arc, determining that a fault exists in the photovoltaic power generation system based on a parameter detection value of the branch or a parameter detection value of the DC bus, determining that a fault exists in the photovoltaic system when it is determined that a fault exists in the branch based on the current detection values ​​of all the branches, or when it is determined that a fault exists in the DC bus based on the current detection value of the DC bus; In particular:

[0331] In summary, according to the method for protecting a photovoltaic system provided in this embodiment of the present application, the photovoltaic unit and the line can be effectively protected when there is a fault in the photovoltaic system, thereby improving the safety of the photovoltaic system. Photovoltaic system embodiment

[0332] Based on the protection device applied to the photovoltaic system and provided in the above embodiments, an embodiment of the present application further provides a photovoltaic system, which will be described in detail below with reference to the accompanying drawings.

[0333] FIG. 24 is a schematic diagram of a photovoltaic power generation system according to an embodiment of the present application.

[0334] Photovoltaic system 2400 includes at least two photovoltaic units and a protection device.

[0335] The photovoltaic section is formed by connecting at least one photovoltaic component in series or parallel.

[0336] The protection device may be connected to the at least two photovoltaic units using an interface, and the at least two photovoltaic units are connected in parallel to a DC bus in the device to form at least two branches, with each branch being connected to at least one photovoltaic unit.

[0337] The protective switch of the protective device is configured, when in the open state, to allow up to three photovoltaic sections to be directly connected in parallel within the device to the DC busbar.

[0338] The protection device further includes a controller. For the description of the controller, please refer to the above embodiment. In this embodiment, details will not be described again.

[0339] Moreover, the protection device may further include a power circuit 201, which is configured to perform power conversion.

[0340] In some embodiments, the power circuit 201 may be a direct current-direct current (DC-DC) conversion circuit. When the power circuit 201 is a DC / DC conversion circuit, the DC / DC conversion circuit may be a boost circuit, a buck circuit, or a buck-boost circuit, among others. This application is not limited to any particular one.

[0341] In some embodiments, the power circuit 201 may be a direct current to alternating current (DC-AC) conversion circuit, ie, an inverter (also referred to as an inverter circuit), configured to convert direct current to alternating current for output.

[0342] In this embodiment, the device shown in Fig. 20 is used as an example. It can be understood that the solution provided in this embodiment may be used in the devices provided in the device embodiments 1 to 11, and the details will not be described again in this embodiment.

[0343] In summary, according to the photovoltaic system provided in this embodiment of the present application, when the protection device of the photovoltaic system is connected to multiple photovoltaic units using an interface, the controller can control the protection switch to an open state when the reverse current of the branch exceeds a first current value. In particular, when the absolute value of the current of any branch exceeds the absolute value of the current of the DC bus, or the current direction of any branch is opposite to the default current direction, the controller controls the protection switch to an open state, so that the current of any branch is less than the first current value, thereby protecting the photovoltaic unit and the line of the photovoltaic system. In addition, only the protection switch is added to the circuit, and the resistance of the protection switch is less than the resistance of the fuse, so that the loss rate and loss of the photovoltaic system are further reduced. In addition, since the fuse is no longer used, the Y harness, which is originally used for the built-in fuse, can be placed on the photovoltaic unit side instead of under the inverter or DC combiner box of the photovoltaic system, which further reduces the cable cost of the photovoltaic system.

[0344] The controller of the present embodiment of the present application may be an application-specific integrated circuit (ASIC), a programmable logic device (PLD), or a combination thereof. The PLD may be a complex programmable logic device (CPLD), a field-programmable gate array (FPGA), a generic array logic (GAL), or any combination thereof. The present embodiment of the present application is not limited to this.

[0345] In this application, it is to be understood that "at least one (item)" means one or more, and "plurality" means two or more. The term "and / or" is used to describe a relationship between related items and indicates that a three-way relationship may exist. For example, "A and / or B" may refer to three cases, where only A is present, only B is present, or both A and B are present, where A and B may be singular or plural. The symbol " / " usually indicates an "or" relationship between related items. "At least one of the described items" or similar expressions refers to any combination of these items, including any combination of a single item or multiple items. For example, at least one of a, b, or c may refer to a, b, c, "a and b," "a and c," "b and c," or "a, b, and c," where a, b, and c may be singular or plural.

[0346] In summary, the above embodiments are only intended to be used to describe the technical solutions of the present application, and are not intended to be used to limit the present application. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art will naturally understand that the technical solutions described in the above embodiments can be modified or some technical features can be equivalently substituted. Such modifications and substitutions do not cause the essential elements of the corresponding technical solutions to depart from the spirit and scope of the technical solutions of the embodiments of the present application. [Explanation of symbols]

[0347] 101 Photovoltaic Components 103 MPPT Components 101a1 Photovoltaic section 101a2 Photovoltaic section 101a3 Photovoltaic section 101a4 Photovoltaic section 101ai Photovoltaic Department 102a2 Photovoltaic section 102 DC Switch S 1 Protection Switch S 2 Protection Switch S M-2 Protection Switch S M-1 Protection Switch S N Protection Switch S M Protection Switch S M+N-2 Protection Switch S01 Protection switch S02 Protection switch S1 Protection Switch S2 Protection Switch S3 Protection Switch S4 Protection Switch S5 Protection Switch S6 Protection Switch 200 Protective devices 201 Power circuit Q protection part S2201 Step S2202 Step S2301 Step S2302 Step 2001 Power Converter 2400 Photovoltaic System A Detection point B Detection point C Detection point D Detection point E Detection point F Detection location G Detection location H Detection location

Claims

1. A photovoltaic inverter, the photovoltaic inverter comprising a plurality of interfaces, a plurality of protection switches, a plurality of interfaces, a DC bus, a power circuit, and a controller; The plurality of interfaces are respectively connected to a plurality of photovoltaic units, each of the photovoltaic units including a plurality of photovoltaic modules connected in series; the plurality of protection switches are connected to the interfaces; the DC bus is connected to the interface via the protection switch; the power circuit includes a direct current-to-direct current (DC-DC) conversion circuit or a direct current-to-alternating current (DC-AC) conversion circuit, the power circuit being connected to the DC bus; the photovoltaic unit is coupled to the DC bus and the protection switch using the interface to form a plurality of branches; The controller: Detecting that the photovoltaic inverter has a fault based on the parameter detection values ​​of the branch or the parameter detection values ​​of the DC bus; Based on detecting a fault in the photovoltaic inverter, controlling the plurality of protection switches to disconnect at least some of the branches from the DC bus, to disconnect photovoltaic units connected in parallel from each other, and to disconnect the branch in which the fault is located from the DC bus; A photovoltaic inverter, wherein some of said interfaces are connected to at least two photovoltaic sections, connected in parallel.

2. The plurality of photovoltaic units include at least four photovoltaic units connected to a DC bus by using the protection switch, When the protection switch is turned on and connected to the DC bus, the at least four photovoltaic units are connected in parallel to each other; The photovoltaic inverter of claim 1 , wherein when the protection switch is turned off and disconnected from the DC bus, only two photovoltaic units are directly connected in parallel.

3. A photovoltaic inverter as described in claim 1 or 2, wherein the positive or negative output ends of the multiple photovoltaic units are connected to the DC bus via N rotary DC switch disconnectors, and the other opposite polarity output ends of the multiple photovoltaic units are connected to the DC bus via more than N rotary series switch disconnectors, N representing at least one rotary DC switch disconnector.

4. 3. The photovoltaic inverter according to claim 1 or 2, wherein the protection switch is configured to disconnect all or some of the photovoltaic units from the DC bus to reduce the number of the photovoltaic units connected in parallel with each other so that there are only two photovoltaic units directly connected in parallel when a reverse current value of the branch or a parameter detection value of the DC bus is greater than a first current value.

5. 5. The photovoltaic inverter of claim 1, wherein the interfaces further include a third interface group including at least one interface, and wherein a number of photovoltaic units connected to one of the third interface group is greater than a number of photovoltaic units connected to one of the first interface group, and each of the interfaces is connected to a positive output end or a negative output end of at least one photovoltaic unit such that two of the protection switches carry different currents.

6. 6. The photovoltaic inverter according to claim 1, wherein the number of the protection switches connected to the positive or negative output end of the photovoltaic unit from the branch is greater than the number of the protection switches connected to the opposite polarity output end of the photovoltaic unit from the branch.

7. 7. A photovoltaic inverter according to claim 1, wherein the branches include at least one first branch and at least one second branch, each of the first branches including one photovoltaic unit connected to the at least one DC bus via two switches at two output ends of opposite polarity, and each of the second branches including two or three photovoltaic units grouped together and connected in parallel before being connected to the at least one DC bus via two switches at two output ends of opposite polarity.

8. 4. The photovoltaic inverter according to claim 3, wherein the positive or negative output ends of the multiple photovoltaic units (101) are grouped together and connected to the DC bus via one of the rotary DC switch disconnectors, and the other opposite polarity output ends of the two photovoltaic units (101) are connected to the DC bus via two or more rotary DC switch disconnectors, allowing up to three photovoltaic units to be directly connected in parallel in the event of a fault in the photovoltaic inverter.

9. The photovoltaic section is a first group (S １ , S Ｍ－２ ) and a second group of photovoltaic parts (S Ｍ－１ , S Ｍ ), and the first group (S １ , S Ｍ－２ ) comprises at least one photovoltaic section, and the second group (S Ｍ－１ , S Ｍ ) comprises at least two photovoltaic sections connected in series in parallel, and the first group (S １ , S Ｍ－２ ) the positive or negative output end of each photovoltaic unit is connected to the DC bus via one of the protection switches, and the second group (S Ｍ－１ , S Ｍ 9. The photovoltaic inverter according to claim 1 , wherein the positive or negative output ends of each of the two photovoltaic sections of the first photovoltaic section and the second photovoltaic section are both connected in series with another one of the protection switches connected to the DC bus.

10. The photovoltaic section is a first group (S １ , S Ｍ－２ ) and a second group of photovoltaic parts (S Ｍ－１ , S Ｍ ), the first group includes at least one photovoltaic section, the second group includes at least two photovoltaic sections, and the first group (S １ , S Ｍ－２ ) the positive or negative output end of each photovoltaic unit and one switch are connected in series to the at least one DC bus, and the second group (S Ｍ－１ , S Ｍ The positive or negative output end of each of the two photovoltaic units of the first group (S １ , S Ｍ－２ ) and the other opposite polarity output end of one of the photovoltaic units of the second group (S Ｍ－１ , S Ｍ 9. The photovoltaic inverter according to claim 1 , wherein the other output end of the at least one photovoltaic unit of the photovoltaic inverters having the opposite polarity is connected to the DC bus via the same one of the protection switches.

11. 11. The photovoltaic inverter of claim 10, further comprising: a third group (j) of photovoltaic sections connected using said interface; and a maximum of two or three photovoltaic sections of said third group (j) of photovoltaic sections being directly connected in parallel to said DC bus.

12. At least four photovoltaic sections (101, 101 ａ１ , 101 ａ２ , 101 ａ３ , 101 ａ４ ) is connected to the input interface, and each photovoltaic unit (101, 101 ａ１ , 101 ａ２ , 101 ａ３ , 101 ａ４ ) includes at least one photovoltaic string, and said at least four photovoltaic sections (101, 101 ａ１ , 101 ａ２ , 101 ａ３ , 101 ａ４ ) are gathered together at their positive or negative output ends, and then all are connected to a single protection switch (S １ ), and said at least four photovoltaic units (101, 101 ａ１ , 101 ａ２ , 101 ａ３ , 101 ａ４ ) each of the opposite polarity output ends of each protection switch (S １ , S ２ , S ３ , S ４ , S ５ , ... S Ｍ＋Ｎ ) or Three photovoltaic units (101, 101 ａ１ , 101 ａ２ , 101 ａ３ ) is connected to the input interface, and each photovoltaic unit (101, 101 ａ１ , 101 ａ２ , 101 ａ３ ) includes at least one photovoltaic string, and the three photovoltaic sections (101, 101 ａ１ , 101 ａ２ , 101 ａ３ The positive or negative output ends of the three photovoltaic units (101, 101) are brought together and then all connected to a single DC switch, ａ１ , 101 ａ２ , 101 ａ３ ) are connected to the protection switch (S １ , S ２ , S ３ , S ４ , S ５ , ... S Ｍ＋Ｎ ) and the three photovoltaic units (101 ａ１ , 101 ａ２ , 101 ａ３ ) the output end of each of the other opposite polarity switches (S １ , S ２ , S ３ , S ４ , S ５ , ... S Ｍ＋Ｎ ), or Four photovoltaic units (101, 101 ａ１ , 101 ａ２ , 101 ａ３ , 101 ａ４ ) are connected to the input interface (200), and each photovoltaic unit (101, 101 ａ１ , 101 ａ２ , 101 ａ３ , 101 ａ４ ) includes at least one photovoltaic string, and the four photovoltaic sections (101, 101 ａ１ , 101 ａ２ , 101 ａ３ , 101 ａ４ ) are gathered together at their positive or negative output ends, and then all are connected to a single protection switch (S １ ), and the four photovoltaic units (101, 101 ａ１ , 101 ａ２ , 101 ａ３ , 101 ａ４ ) have the same protection switch (S １ , S ２ , S ３ , S ４ , S ５ , ... S Ｍ＋Ｎ ), and each of the other two opposite polarity output ends is connected to a protection switch (S １ , S ２ , S ３ , S ４ , S ５ , ... S Ｍ＋Ｎ ) or Four photovoltaic units (101, 101 ａ１ , 101 ａ２ , 101 ａ３ , 101 ａ４ ) are connected to the interface, and each photovoltaic unit (101, 101 ａ１ , 101 ａ２ , 101 ａ３ , 101 ａ４ ) includes at least one photovoltaic string, and the four photovoltaic sections (101, 101 ａ１ , 101 ａ２ , 101 ａ３ , 101 ａ４ ) are brought together at the two positive or negative output ends, and then connected to the same protection switch (S １ ), and the positive or negative output ends of another two of the four photovoltaic units are brought together, and then another identical protection switch (S ３ ), and the four photovoltaic units (101, 101 ａ１ , 101 ａ２ , 101 ａ３ , 101 ａ４ ) have the same protection switch (S １ , S ２ , S ３ , S ４ , S ５ , ... S Ｍ＋Ｎ ), and the other two output ends of the opposite polarity are each connected to a protection switch (S １ , S ２ , S ３ , S ４ , S ５ , ... S Ｍ＋Ｎ ) or Four photovoltaic units (101, 101 ａ１ , 101 ａ２ , 101 ａ３ , 101 ａ４ ) is connected to the input interface, and each photovoltaic unit (101, 101 ａ１ , 101 ａ２ , 101 ａ３ , 101 ａ４ ) includes at least one photovoltaic string, and the four photovoltaic sections (101, 101 ａ１ , 101 ａ２ , 101 ａ３ , 101 ａ４ ) are gathered together, and then connected to the same protection switch (S １ ), and the positive or negative output end of another one of the four photovoltaic units is connected to another protection switch (S ３ ), and the four photovoltaic units (101, 101 ａ１ , 101 ａ２ , 101 ａ３ , 101 ａ４ ) have three identical protection switches (S １ , S ２ , S ３ , S ４ , S ５ , ... S Ｍ＋Ｎ ), and another output end of the opposite polarity is connected to a protection switch (S １ , S ２ , S ３ , S ４ , S ５ , ... S Ｍ＋Ｎ 11. A photovoltaic inverter according to claim 1 , connected to a

13. 13. The photovoltaic inverter of claim 1, wherein the protection switch comprises a rotary DC switch disconnector connected between the interface and the at least one DC bus bar for connecting or disconnecting a photovoltaic unit to or from the at least one DC bus bar.

14. Three photovoltaic units (101) among the plurality of photovoltaic units ａ１ ~101 ａ３ ) is connected to the DC busbar by means of the protection switch; The positive or negative output ends of the at least three photovoltaic units are all connected to a first protection switch (S １ ) connected to the DC bus line, and a first and a second photovoltaic unit (101) of the at least three photovoltaic units ａ１ , 101 ａ２ ) are brought together, and a second protection switch (S ２ ) connected to the DC bus line via a third photovoltaic unit (101) of the at least three photovoltaic units. ａ３ The other output end of the opposite polarity of the protection switch (S ３ ) connected to said DC busbar via The positive or negative output ends of at least four photovoltaic units are all connected to a first protection switch (S １ ) connected to the DC bus line, and a first and a second photovoltaic unit (101) of the at least four photovoltaic units ａ１ , 101 ａ２ ) are brought together, and a second protection switch (S ２ ) connected to the DC bus line, and a third and fourth photovoltaic section (101) of the at least four photovoltaic sections ａ３ , 101 ａ４ The other output end of the opposite polarity of the protection switch (S ３ , S ４ ) respectively connected to said DC busbar, or The first and second photovoltaic units (101) among the at least four photovoltaic units ａ１ , 101 ａ２ ) are brought together, and then the first one of the protection switches (S １ ) connected to the positive DC bus, and the first and second photovoltaic units (101 ａ１ , 101 ａ２ ) is connected to the fourth protection switch (S ４ ) to the negative DC bus, and a third photovoltaic unit (101) of the at least four photovoltaic units is connected to the negative DC bus using a ａ３ ) is connected to the positive output end of the first protection switch (S １ ) is connected to the positive DC bus, and the third photovoltaic unit (101 ａ３ ) is connected to the second protection switch (S ２ ) connected to the negative DC bus, and a fourth photovoltaic unit (101) of the at least four photovoltaic units ａ４ ) is connected to the third protection switch (S ３ ) is connected to the positive DC bus, and the fourth photovoltaic unit (101 ａ４ ) is connected to the negative output end of the fourth protection switch (S ４ ) to the negative DC bus, or First and second photovoltaic sections (101) among at least four photovoltaic sections ａ１ , 101 ａ２ ) are brought together, and then the first protection switch (S １ ) is connected to the DC bus, and the first and second photovoltaic units (101 ａ１ , 101 ａ２ The other output end of the opposite polarity of the protection switch (S ２ ) connected to the DC bus; The third and fourth photovoltaic sections (101) among the at least four photovoltaic sections ａ３ , 101 ａ４ ) are brought together, and a third protection switch (S ３ ) are respectively connected to the DC bus, and the third and fourth photovoltaic units (101) of the at least four photovoltaic units are ａ３ , 101 ａ４ The other output end of the opposite polarity of the protection switch (S ４ , S ５ 14. A photovoltaic inverter as claimed in claim 1 , wherein each of said photovoltaic inverters is connected to said DC bus using a respective one of said first and second inverters.

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