Photovoltaic inverter and photovoltaic string protection method

Abstract

The present invention provides a photovoltaic inverter, including a first switch group, a second switch group, an anti-reverse circuit, a DC / DC power conversion circuit, a bus capacitor and a controller. The first photovoltaic string is connected to the bus capacitor through the first switch group and the anti-reverse circuit in sequence. Multiple photovoltaic strings are connected to the DC / DC power conversion circuit through the second switch, and the multiple photovoltaic strings include the first photovoltaic string. The controller is used to close all switches in the second switch group, and when the current flowing through some switches in the second switch group is overcurrent, disconnect some switches in the second switch group where overcurrent occurs, or the controller is used to close all switches in the second switch group, and when the current flowing through some switches in the second switch group is a reverse current, disconnect some switches in the second switch group where reverse current occurs. With such a configuration, when the photovoltaic string is reversely connected, the reverse connection fault can be timely identified and eliminated, thereby improving the reliability and safety of the photovoltaic power station.

Description

Technical Field

[0001] The present application relates to the field of renewable energy power generation, and in particular to a photovoltaic inverter, a photovoltaic system, and a method for protecting a photovoltaic string. Background Art

[0002] In recent years, solar energy has been widely used as a clean and renewable energy source. In a photovoltaic power station, photovoltaic modules convert solar energy into direct current through the photovoltaic effect, and transmit the direct current to the photovoltaic inverter, which further converts the direct current into alternating current with the same frequency as the mains. When the photovoltaic inverter is connected to the grid for the first time, the user connects the photovoltaic array strings to the photovoltaic inverter. Due to improper operation, some or all photovoltaic strings may be reversely connected. If the controller of the photovoltaic inverter cannot obtain the abnormal situation of the reverse connection of the photovoltaic strings through sampling information in time, it may cause the photovoltaic strings or even the inverter to burn out, seriously affecting the safety of the photovoltaic power station. Summary of the invention

[0003] To solve the above problems, the embodiments of the present application provide a method for protecting a photovoltaic inverter and a photovoltaic string, so as to promptly identify the reverse connection fault and disconnect the short-circuit loop of the photovoltaic string when the photovoltaic string is partially or completely reversely connected, thereby improving the safety and reliability of the photovoltaic power station.

[0004] In a first aspect, an embodiment of the present application provides a photovoltaic inverter, comprising a first switch group, a second switch group, a DC / DC power conversion circuit, a bus capacitor, and a controller. One end of the first switch group is used to be connected to the first photovoltaic string, and the other end of the first switch group is used to be connected to the bus capacitor, so that when the first switch group is closed, the bus capacitor supplies power to the controller. One end of the second switch group is connected to the second photovoltaic string, and the other end of the second switch group is connected to the DC / DC power conversion circuit. After the controller has been powered on and the second switch group has been closed, the controller is used to disconnect the switch in the second switch group where the overcurrent occurs in response to the current flowing through the second switch group being overcurrent, or, after the controller has been powered on and the second switch group has been closed, the controller is used to disconnect the switch in the second switch group where the reverse current occurs in response to the current flowing through the second switch group including a reverse current.

[0005] Such a setting can ensure that the controller can work normally before the second switch group is closed, and after the second switch group is closed, the controller can promptly identify whether faults such as reverse connection of the photovoltaic string and short circuit of the photovoltaic module have occurred in the second photovoltaic string, and when the above faults occur, timely eliminate the fault by disconnecting the switch in the second switch group that has reverse current or overcurrent.

[0006] It is worth mentioning that the other end of the first switch group is used to connect to the bus capacitor, which means that the electric energy generated by the first photovoltaic string can be used to charge the bus capacitor through the first switch group, and then the bus capacitor can power the controller. In practical applications, there may be other components between the first switch group and the bus capacitor, such as a DC / DC power converter, etc., which is not limited in this application.

[0007] In addition, the first photovoltaic string can be a single photovoltaic string, and the single photovoltaic string includes a plurality of photovoltaic modules connected in series. The first photovoltaic string can also be a two-way or three-way photovoltaic string connected in parallel. The second photovoltaic string is a multi-way photovoltaic string, and each photovoltaic string includes a plurality of photovoltaic modules connected in series, wherein the output ends of the one, two or three photovoltaic strings are connected in parallel to a DC terminal of the photovoltaic inverter, and are connected to the second switch group through the DC terminal. In practical applications, a plurality of DC terminals are generally provided on the photovoltaic inverter, and each DC terminal can be connected to one, two or three photovoltaic strings, and this application does not impose any restrictions on this. It is worth mentioning that the first photovoltaic string can be part of the second photovoltaic string.

[0008] In a possible implementation, the photovoltaic inverter includes an anti-reverse circuit, wherein the anti-reverse circuit is located on the connection line between the first photovoltaic string and the bus capacitor. For example, one end of the anti-reverse circuit is used to connect to the first switch group, and the other end of the anti-reverse circuit is used to connect to the bus capacitor, or one end of the anti-reverse circuit is used to connect to the first photovoltaic string, and the other end of the anti-reverse circuit is used to connect to the first switch group. By setting the anti-reverse circuit, it can be ensured that the first photovoltaic string can be correctly connected to the photovoltaic inverter to charge the DC bus.

[0009] Specifically, before the photovoltaic inverter is connected to the grid, the user can manually close the first switch group to power the first photovoltaic string to the DC bus or bus capacitor. With this setting, the auxiliary source can further draw power from the DC bus or bus capacitor and power the controller to enable the controller to work normally. After the controller works normally, the electric energy of the multiple photovoltaic strings is input into the photovoltaic inverter by closing the second switch group. Among them, the second switch group can be controlled to close by the controller or manually closed by the user. After the second switch group is closed, if some of the multiple photovoltaic strings connected to the photovoltaic inverter are reversely connected, or if all the multiple photovoltaic strings connected to the photovoltaic inverter have a reverse connection fault, or if the current flowing through some switches in the second switch group is overcurrent, the controller can identify it in time and disconnect the corresponding switch in the second switch group connected in series with the reverse photovoltaic string. Therefore, such a setting can significantly improve the recognition rate of the reverse connection fault of the photovoltaic string and improve the reliability of the photovoltaic power station.

[0010] It is worth mentioning that in actual application, the number of photovoltaic strings in the first photovoltaic string can be changed, and this application does not limit this. For example, the first photovoltaic string includes N photovoltaic strings, and the output ends of the N photovoltaic strings are connected in parallel to the photovoltaic inverter and connected in series with the first switch group. In addition, in actual application, the number of photovoltaic units in each photovoltaic string is not limited. For example, the number of photovoltaic units in one photovoltaic string can be one or more.

[0011] It is worth mentioning that in actual application, the multi-way photovoltaic strings connected in series with the second switch group are generally connected in series with the second switch group through a port set on the photovoltaic inverter. For example, the multi-way photovoltaic strings connected in series with the second switch group are connected in series with the second switch group through M ports, wherein the number of the multi-way photovoltaic strings connected in series with the second switch group can be an integer greater than or equal to M. When the number of the multi-way photovoltaic strings connected in series with the second switch group is M, one photovoltaic string is connected in series with some switches in the second switch group through a port. When the number of the multi-way photovoltaic strings connected in series with the second switch group is greater than M, there may be at least two photovoltaic strings connected in series with some switches in the second switch group through a port, and this application does not limit this. It is worth mentioning that in this application, a port is a general term for function. In actual application, a port can be further divided into a positive port and a negative port, wherein the positive port is used to connect the positive pole of the photovoltaic string, and the negative port is used to connect the negative pole of the photovoltaic string.

[0012] It is worth mentioning that in actual application, the present application does not limit the number of switches in the first switch group, that is, there is at least one switch on the connection line between the first photovoltaic string and the DC / DC power converter, and the switch can achieve the effect of connecting and disconnecting the first photovoltaic string. For example, a switch can be connected in series at the positive output end of the first photovoltaic string, or a switch can be connected in series at the negative output end of the first photovoltaic string. Of course, switches can also be connected in series at both the positive output end and the negative output end of the first photovoltaic string, and the present application does not limit this.

[0013] It is worth mentioning that, in practical application, the present application does not limit the number of switches in the second switch group, that is, there is at least one switch on the connection line between each port and the DC / DC power converter, and the details are not repeated here.

[0014] In a possible implementation, after the controller is powered on and the second switch group is closed, if the current flowing through the second switch group does not have an overcurrent and the current flowing through the second switch group does not have a reverse current, the controller is used to disconnect the first switch group. If the controller does not identify the reverse connection fault of the photovoltaic string, it means that the connection state of the second photovoltaic string is normal. Therefore, in order to enable the multiple photovoltaic strings to better transmit energy to the photovoltaic inverter, the first switch group can be disconnected, so that the multiple photovoltaic strings can be powered normally. Specifically, when the connection state of the second photovoltaic string is normal, the direct current of the second photovoltaic string can be smoothly transmitted to the photovoltaic inverter and charge the bus capacitor. That is to say, even if the first switch group is disconnected at this time, the controller can work normally. Further, when the first photovoltaic string is part of the second photovoltaic string, since the first switch group is connected in series with the anti-reverse circuit, and the anti-reverse circuit usually includes devices such as resistors or diodes, if the first switch group is not disconnected for a long time, the energy transmitted by the first photovoltaic string to the photovoltaic inverter will be lost due to the diode or resistor in the anti-reverse circuit. Therefore, such a setting can improve the energy utilization efficiency of the photovoltaic string and increase the overall power generation of the photovoltaic power generation system. More importantly, in actual applications, for cost considerations, even if the first switch group has a remote disconnection mechanism, the first switch group is usually not equipped with a free tripping mechanism or an arc extinguishing chamber, while the second switch usually has a remote disconnection mechanism or a free tripping mechanism and an arc extinguishing chamber. For the first switch group that is not equipped with a free tripping mechanism, if the first photovoltaic string has a short circuit or overcurrent fault, when the handle corresponding to the first switch group is stuck, even if the controller sends a remote disconnection signal, the first switch group cannot be disconnected smoothly, and it is difficult to reliably eliminate the fault. For the first switch group that is not equipped with an arc extinguishing chamber, if the first photovoltaic string has a short circuit or overcurrent fault, the arc generated when the first switch group is disconnected is difficult to cool in time, which can easily lead to the burning of the second switch group, and in severe cases, it may even cause the photovoltaic inverter and the entire photovoltaic system to catch fire and explode. Therefore, when the first PV string is part of the second PV string, when the second switch group is closed and the connection between the second PV string and the PV inverter is normal, if the controller can promptly control the first switch to disconnect, even if the first PV string later has faults such as overcurrent or reverse current, the second switch group can safely and reliably eliminate the fault.

[0015] In a possible implementation, the photovoltaic inverter includes an indicator light. If the first switch group is closed so that the controller is powered on by the bus capacitor, the indicator light is on. The indicator light is used to instruct the user to close the second switch group. With this arrangement, the user can more intuitively perceive the state of the controller and manually close the second switch group when the controller is working normally, so that the energy of the second photovoltaic string is smoothly transmitted to the photovoltaic inverter.

[0016] In one possible implementation, after the second switch group is closed, the indicator light remains on, and the indicator light remains on to instruct the user to disconnect the first switch group after closing the second switch group. In practical applications, for cost considerations, the first switch group can also be set as an uncontrolled switch, that is, the closed or disconnected state of the first switch group can only be adjusted manually and cannot be adjusted by the controller. As mentioned above, the first switch group is usually not equipped with a free tripping mechanism and an arc extinguishing chamber, while the second switch group usually has a remote disconnecting mechanism or a free tripping mechanism and an arc extinguishing chamber. Therefore, after the second switch group is closed, that is, after the photovoltaic inverter is normally connected to the grid, if the first switch group is still closed, when a short-circuit fault occurs in the first photovoltaic string, the controller cannot promptly identify and disconnect the first switch group, resulting in a long-term short-circuit fault in the first photovoltaic string, and in severe cases, it may even cause the first photovoltaic string and the photovoltaic inverter to catch fire and explode. Based on this, by setting an indicator light, the user can more intuitively perceive the status of the controller, and then manually disconnect the first switch group after the second switch group is closed. Later, even if a short circuit or overcurrent fault occurs in the first photovoltaic string, the second switch group can promptly and reliably eliminate the fault, thereby improving the safety and reliability of the photovoltaic system.

[0017] In one possible implementation, the photovoltaic inverter includes an indicator light. If the first switch group is closed but the controller does not obtain power from the bus capacitor and is not powered on, the indicator light will not light up. The indicator light not lighting up is used to indicate that there is a fault, for example, to remind the user to check whether the first photovoltaic string is reversely connected or faulty. As described above, when the connection status of the first photovoltaic string is normal, that is, there is no reverse connection, the DC power output by the first photovoltaic string is smoothly transmitted to the DC bus or bus capacitor, thereby powering on the controller. By setting the indicator light, the user can more intuitively perceive the status of the controller, and then when the switch is not lit, it is known that the first photovoltaic string is likely to be reversely connected or have other faults, and the first photovoltaic string can be checked in a targeted manner, thereby ensuring the reliable power-on and grid connection of the photovoltaic inverter.

[0018] In a possible implementation, the anti-reverse circuit includes a resistor and a diode, wherein one end of the resistor is used to be connected to the positive electrode of the first photovoltaic string, the other end of the resistor is used to be connected to the DC / DC power conversion circuit, the cathode of the diode is used to be connected to the negative electrode of the first photovoltaic string, and the anode of the diode is used to be connected to the DC / DC power conversion circuit. By setting the anti-reverse circuit, the connection state of the first photovoltaic string can be guaranteed to be normal, so that the energy delivered by the first photovoltaic string can smoothly power the controller, thereby enabling the controller to have the ability to identify and troubleshoot faults. In practical applications, an indicator light can also be set for the photovoltaic inverter. If the controller is connected normally, the indicator light is on, and if the controller is not connected normally, the indicator light is off. Such a setting can promptly inform the user of the status of the controller, and then when the controller cannot be powered on, remind the user to check whether the first photovoltaic string has reverse connection or other faults, thereby improving the reliability and safety of the photovoltaic inverter.

[0019] It is worth mentioning that one end of the resistor is used to connect to the positive pole of the first photovoltaic string, which means that the first photovoltaic string can be directly connected to one end of the resistor, and the first photovoltaic string can also be connected to one end of the resistor through other components. This application is not limited by comparison. Similarly, the other end of the resistor is used to connect to the DC / DC power conversion circuit, which also means that the other end of the resistor can be directly connected to the DC / DC power conversion circuit, and the other end of the resistor can also be connected to the DC / DC power conversion circuit through other components. The connection relationship between the specific components in the following anti-reverse circuit and the first photovoltaic string and the DC / DC power conversion circuit is the same as the above relationship, which will not be repeated here.

[0020] In one possible implementation, the anti-reverse circuit includes a resistor and a diode, wherein one end of the resistor is used to be connected to the negative electrode of the first photovoltaic string, the other end of the resistor is used to be connected to the DC / DC power conversion circuit, the anode of the diode is used to be connected to the positive electrode of the first photovoltaic string, and the cathode of the diode is used to be connected to the DC / DC power conversion circuit. Based on the same principle, by swapping the positions of the resistor and the diode in the anti-reverse circuit, the effect of preventing the first photovoltaic string from being reversed can also be achieved, which will not be elaborated here. When the positions of the resistor and the diode are swapped, the cathode and anode of the diode also need to be flipped.

[0021] In a possible implementation, the anti-reverse circuit includes a first diode and a second diode, wherein the anode of the first diode is used to be connected to the positive electrode of the first photovoltaic string, the cathode of the first diode is used to be connected to the DC / DC power conversion circuit, the cathode of the second diode is used to be connected to the negative electrode of the first photovoltaic string, and the anode of the second diode is used to be connected to the DC / DC power conversion circuit. With such an arrangement, when a short circuit fault occurs in one of the diodes in the anti-reverse circuit, the anti-reverse circuit can still prevent the first photovoltaic string from being reversely connected, thereby improving the stability of the anti-reverse circuit.

[0022] In a possible implementation, the anti-reverse circuit includes a first bridge arm and a second bridge arm connected in parallel, wherein the first bridge arm includes a first diode and a second diode connected in series, and the second bridge arm includes a third diode and a fourth diode connected in series, the cathode of the first diode is connected to the cathode of the third diode, and the anode of the second diode is connected to the anode of the fourth diode. The series connection point of the first diode and the second diode is used to connect to the positive electrode of the first photovoltaic string, and the series connection point of the third diode and the fourth diode is used to connect to the DC / DC power conversion circuit. Based on the same principle, such an arrangement can also prevent the anti-reverse circuit from preventing the first photovoltaic string from being reversely connected when some diodes in the anti-reverse circuit have a short-circuit fault, thereby improving the stability of the anti-reverse circuit.

[0023] In a possible implementation, the anti-reverse circuit is connected to the DC input side of the DC / DC power conversion circuit, or the anti-reverse circuit is connected to the DC output side of the DC / DC power conversion circuit. When the anti-reverse circuit is connected to the DC input side of the DC / DC power conversion circuit, part of the DC / DC power conversion circuit can be reused, thereby reducing the use of wires and optimizing the internal space of the photovoltaic inverter.

[0024] In a possible implementation, the number of switches in the second switch group is less than or equal to the number of second photovoltaic strings connected to the photovoltaic inverter, and each photovoltaic string in the second photovoltaic string is connected to the DC / DC power conversion circuit through at least one switch in the second switch group. In other words, each photovoltaic string in the multiple photovoltaic strings is connected to the DC / DC conversion circuit of the photovoltaic inverter through at least one switch, and when the controller identifies the fault of reverse connection of the photovoltaic string, the transmission path of the reverse current or overcurrent can be cut off in time to eliminate the fault.

[0025] In a second aspect, the present application provides a photovoltaic system, comprising the photovoltaic inverter described in any one of the first aspects and multiple photovoltaic strings, wherein the multiple photovoltaic strings are connected to the DC input terminal of the photovoltaic inverter for inputting DC power to the photovoltaic inverter.

[0026] In a third aspect, the present application provides a method for protecting a photovoltaic string, the method comprising: closing all switches in the second switch group, and when the current flowing through some switches in the second switch group is overcurrent, disconnecting some switches in the second switch group where overcurrent occurs; or, closing all switches in the second switch group, and when the current flowing through some switches in the second switch group is a reverse current, disconnecting some switches in the second switch group where reverse current occurs. One end of the second switch group is used to be connected to the photovoltaic module, and the other end of the second switch group is used to be connected to the DC / DC power conversion circuit.

[0027] In a possible implementation, all switches in the second switch group are closed, and after a preset time interval, if the current flowing through the second switch group does not have an overcurrent and the current flowing through the second switch group does not have a reverse current, the first switch group is disconnected. One end of the first switch group is used to be connected to at least one photovoltaic string, and the other end of the first switch group is used to be connected to a DC / DC power conversion circuit.

[0028] In general, the photovoltaic inverter provided in this application can promptly identify and eliminate the reverse connection fault of the photovoltaic module through a simple circuit setting, thereby significantly improving the safety and reliability of the photovoltaic power station. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a network diagram of the optical storage system;

[0030] Figure 2a The current flow diagram when the photovoltaic string provided for this application is normally connected;

[0031] Figure 2b A current flow diagram for some photovoltaic strings reversely connected provided for this application;

[0032] Figure 2c The current flow diagram for all photovoltaic strings provided in this application when they are reversely connected;

[0033] Figure 3 A topological diagram of the DC side of a photovoltaic inverter capable of protecting photovoltaic strings provided in this application;

[0034] Figure 4a A topological diagram of the DC side of a photovoltaic inverter capable of protecting photovoltaic strings provided in this application;

[0035] Figure 4b A topological diagram of the DC side of a photovoltaic inverter capable of protecting photovoltaic strings provided in this application;

[0036] Figure 4c A topological diagram of the DC side of a photovoltaic inverter capable of protecting photovoltaic strings provided in this application;

[0037] Figure 4d A topological diagram of the DC side of a photovoltaic inverter capable of protecting photovoltaic strings provided in this application;

[0038] Figure 5 A topological diagram of the DC side of a photovoltaic inverter capable of protecting photovoltaic strings provided in this application;

[0039] Figure 6a A topological diagram of the DC side of a photovoltaic inverter capable of protecting photovoltaic strings provided in this application;

[0040] Figure 6bA topological diagram of the DC side of a photovoltaic inverter capable of protecting photovoltaic strings provided in this application;

[0041] Figure 6c A topological diagram of the DC side of a photovoltaic inverter capable of protecting photovoltaic strings provided in this application;

[0042] Figure 6d A topological diagram of the DC side of a photovoltaic inverter capable of protecting photovoltaic strings provided in this application; DETAILED DESCRIPTION

[0043] See also Figure 1 , Figure 1 This is a networking diagram of a photovoltaic storage system in an AC coupling scenario, in which photovoltaic modules convert solar energy into DC power through the photovoltaic effect, and the inverter converts the DC power output by the photovoltaic modules into AC power and further transmits the AC power to the box-type substation. After the box-type substation converts the low-voltage AC power output by the inverter into medium-voltage AC power, it further transmits the AC power to the booster station (grid) or the box-type substation corresponding to the energy storage system. The energy storage system is used to store unstable electrical energy from photovoltaic modules and output stable electrical energy to the grid through the energy storage inverter and the corresponding box-type substation.

[0044] As described in the background technology, when a photovoltaic inverter is connected to the grid for the first time, there may be a situation where the photovoltaic strings are partially or completely reversely connected. If not identified and handled in time, it may cause damage to the photovoltaic strings or even the photovoltaic inverter. Figure 2a , Figure 2b and Figure 2c The flow direction of DC power is analyzed when all PV strings are connected normally, when some PV strings are connected in reverse, and when all PV strings are connected in reverse.

[0045] First, see Figure 2a , Figure 2aThe figure is a flow diagram of the direct current generated by the photovoltaic strings when all photovoltaic strings are normally connected to the photovoltaic inverter. Among them, multiple photovoltaic strings are connected in parallel to the direct current / direct current (DC / DC) conversion circuit of the photovoltaic inverter through the DC side switch 10 of the photovoltaic inverter. The number of photovoltaic strings connected to the photovoltaic inverter is n, and n is a positive integer greater than or equal to 1. It is worth mentioning that a photovoltaic string may include one or more photovoltaic panels, and each photovoltaic panel is composed of multiple photovoltaic cells. PVn+ represents the positive pole of the nth photovoltaic string, and PVn- represents the negative pole of the nth photovoltaic string. When the photovoltaic module generates direct current, the direct current flows out from PVn+, and passes through the DC / DC conversion circuit and the positive DC bus in turn to charge the bus capacitors C1 and C2, and finally flows into PVn- through the negative DC bus to realize the current loop. It should be noted that, except for Figure 2a In addition to the DC side switch 10, the DC / DC conversion circuit and the bus capacitors C1 and C2 shown in the figure, in actual application, the photovoltaic inverter also includes Figure 2a The DC / AC conversion circuit, LCL filter, relay, etc. not shown are not described in detail in this application.

[0046] Below, see Figure 2b , Figure 2b The figure is the flow diagram of the direct current generated by the photovoltaic strings when some photovoltaic strings are reversely connected. Among them, the photovoltaic strings that are reversely connected are the first photovoltaic string and the second photovoltaic string. Figure 2a In comparison, PV1+ and PV1- are swapped, and PV2+ and PV2- are also swapped. In this case, when the DC side switch 10 of the photovoltaic inverter is closed, the DC power generated from PV(n-2)+ to PVn+ will be directly injected into PV1- and PV2-, and the DC power flowing out of PV1+ and PV2+ will enter PV(n-2)- to PVn-, forming a current loop, which will cause the DC bus to lose power, making it impossible for the auxiliary source of the photovoltaic inverter to draw power from the DC bus or from the bus capacitor and power the controller. Therefore, the controller of the photovoltaic inverter cannot promptly identify whether the photovoltaic string is reversely connected, and which photovoltaic string is reversely connected. Of course, the controller cannot promptly disconnect the switch in the DC side switch 10 of the photovoltaic inverter that is connected in series with the reverse photovoltaic string to eliminate the fault.

[0047] Continue to see Figure 2c , Figure 2c This is the flow diagram of the DC power generated by the photovoltaic strings when all photovoltaic strings are reversely connected. Figure 2aIn comparison, PVn+ and PVn- are swapped. In this case, when the DC side switch 10 of the photovoltaic inverter is closed, the DC power generated from PV1+ to PVn+ passes through the diode D1 in the Boost circuit of the DC / DC (direct current / direct current, DC / DC) conversion circuit, which is anti-parallel to the switch tube V1, forming a short circuit loop, which will also cause the DC bus to lose power, so that the auxiliary source of the inverter cannot take power from the DC bus or from the bus capacitor and power the controller. Similarly, the controller of the inverter cannot timely identify whether the photovoltaic string is reversely connected, and the specific location of the reverse connection of the photovoltaic string. Of course, the controller cannot timely disconnect the switch in the DC side switch 10 of the photovoltaic inverter that is connected in series with the reverse photovoltaic string, thereby eliminating the reverse connection fault.

[0048] Therefore, in order to solve the problem of reverse connection of some photovoltaic strings on the DC side of the photovoltaic inverter or reverse connection of all photovoltaic strings on the DC side of the photovoltaic inverter, the following will be specifically combined with the attached Figure 3 To Attachment Figure 6d , the embodiments of the present application are introduced and described.

[0049] First, see Figure 3 , Figure 3 A topology diagram of the DC side of a photovoltaic inverter that can timely protect photovoltaic strings is provided in this application. Figure 2a-2c The structure shown is different in that Figure 3 In the embodiment, the first photovoltaic string, namely PV1+ and PV1-, is also connected to the input end of the DC / DC power conversion circuit 12 through the first switch group S1 and the anti-reverse circuit 11. It is worth mentioning that in Figure 3 In the example, the second switch group S2 represents Figure 2a-2c The DC side switch 10 of the photovoltaic inverter. The working principle of this topology is that before the photovoltaic inverter is connected to the grid for the first time, the user first closes the first switch group S1. If the connection between PV1+ and PV1- is normal, that is, PV1+ and PV1- are not reversely connected, the anti-reverse circuit 11 can be normally turned on, the DC bus and the DC bus capacitors C1 and C2 are powered on, so that the auxiliary source can take power from the DC bus or the DC bus capacitors C1 and C2, and power the controller. Then, the second switch group S2 is closed. At this time, since the auxiliary source has powered the controller, the controller can determine in real time whether there is a reverse-connected photovoltaic string among all photovoltaic strings connected to the DC / DC power conversion circuit 12. If there is a reverse-connected photovoltaic string, the controller can disconnect the switch connecting the reverse-connected photovoltaic string and the DC / DC power conversion circuit 12 in the second switch group S2, thereby eliminating the reverse connection fault. If all photovoltaic strings are normally connected to the DC / DC power conversion circuit 12, the controller controls the first switch group S1 to be disconnected, and all photovoltaic strings are normally connected to the photovoltaic inverter, thereby realizing photovoltaic grid connection.

[0050] It is worth mentioning that after the user first closes the first switch group S1, if the connection between PV1+ and PV1- is normal, that is, PV1+ and PV1- are not reversely connected, an additional indicator light can be set in the photovoltaic inverter to remind the user that the controller in the photovoltaic inverter can work normally. Therefore, the user can continue to manually close the second switch group S2 and turn off the first switch group S1 to achieve photovoltaic grid-connected power generation. With this arrangement, even if there is a reverse connection fault in the photovoltaic string connected to the photovoltaic inverter, the controller in the photovoltaic inverter can identify it in time and eliminate the reverse connection fault in time. Of course, after the controller works normally, the second switch group S2 can also be directly closed by the controller to disconnect the first switch group S1, without the user manually closing the second switch group S2 and disconnecting the first switch group S1. This application does not limit this.

[0051] In addition, Figure 3 In the figure, for the convenience of description, this application only shows one photovoltaic string, that is, the first photovoltaic string PV1 is connected to the DC / DC power conversion circuit 12 in sequence through the first switch group S1 and the anti-reverse circuit 11. In actual applications, multiple photovoltaic strings can be set to be connected to the DC / DC power conversion circuit 12 in sequence through the first switch group S1 and the anti-reverse circuit 11, and this application does not limit this.

[0052] It should also be noted that in Figure 3 In the embodiment, the first switch group S1 includes two switches, wherein the two switches are connected to the anti-reverse circuit 11 through PV1+ and PV1- respectively. In practical applications, the number of switches in the first switch group S1 is not limited to two, that is, the number of switches in the first switch group S1 can be one or more, and the present application does not impose any restrictions on this. When the number of switches in the first switch group S1 is only one, the switch can be connected to either PV1+ or PV1-, and the present application does not impose any restrictions on this. Based on the same principle, in Figure 3 In the present application, there is no restriction on the number of switches in the second switch group S2, that is, there can be one switch or multiple switches on the connection line between each photovoltaic string and the DC / DC power conversion circuit 12.

[0053] Next, we will combine Figure 4a , the embodiments provided in this application are described. Figure 3 The difference is, Figure 4aA specific structure of the anti-reverse circuit 11 is shown. Among them, the anti-reverse circuit 11 includes a resistor R1 and a diode D1, one end of the resistor R1 is connected to PV1+, the other end of the resistor R1 is connected to the DC / DC power conversion circuit 12, the anode of the diode D1 is connected to the DC / DC power conversion circuit 12, and the cathode of the diode D1 is connected to PV1-. Such a setting can ensure that the access of the first photovoltaic string is normal, that is, the current output by the first photovoltaic string can flow through the DC bus and the DC bus capacitors C1 and C2, and then power on the controller through the auxiliary source, so that the controller has the ability to identify the reverse connection fault of the photovoltaic string. Based on the same principle, the structure of the anti-reverse circuit 11 can also refer to Figure 4b .and Figure 4a The structure shown is different in that Figure 4b In the embodiment, the anode of the diode D1 is connected to PV1+, the cathode of the diode D1 is connected to the DC / DC power conversion circuit 12, one end of the resistor R1 is connected to PV1-, and the other end of the resistor R1 is connected to the DC / DC power conversion circuit 12. At the same time, it is worth mentioning that Figure 4a and Figure 4b In the anti-reverse circuit 11 shown, the resistor R1 mainly functions to limit the current, and the diode D1 mainly functions to prevent a short circuit when the first photovoltaic string is reversely connected.

[0054] Next, we will combine Figure 4c , the embodiments provided in this application are described. Figure 4a and Figure 4b The structure shown is different in that Figure 4c The anti-reverse circuit 11 shown includes two diodes, namely, a diode D1 and a diode D2, wherein the anode of the diode D1 is connected to PV1+, the cathode of the diode D1 is connected to the DC / DC power conversion circuit 12, the anode of the diode D2 is connected to the DC / DC power conversion circuit 12, and the cathode of the diode D2 is connected to PV1-. By arranging two diodes in the anti-reverse circuit 11, even if one of the two diodes has a short-circuit fault, the anti-reverse circuit 11 can still work, that is, it is ensured that the current output by the first photovoltaic string can flow through the DC bus and the DC bus capacitors C1 and C2, and then the controller is powered on through the auxiliary source, so that the controller has the ability to identify the reverse connection fault of the photovoltaic string.

[0055] Next, we will combine Figure 4d , the embodiments provided in this application are described. Figure 4a , Figure 4b and Figure 4c The structure shown is different in that Figure 4dThe anti-reverse circuit 11 shown is a full-bridge circuit. Specifically, the anti-reverse circuit 11 includes a first bridge arm and a second bridge arm connected in parallel, the first bridge arm includes a diode D1 and a diode D2 connected in series, and the second bridge arm includes a diode D3 and a diode D4 connected in series, wherein PV1+ is connected to the series connection point of the diode D1 and the diode D2 through the first switch group S1, PV- is connected to the series connection point of the diode D3 and the diode D4 through the first switch group S1, the cathode of the diode D1 is connected to the cathode of the diode D3, and the parallel connection point of the diode D1 and the diode D3 is connected to the DC / DC power conversion circuit 12, the anode of the diode D2 is connected to the anode of the diode D4, and the parallel connection point of the diode D2 and the diode D4 is connected to the DC / DC power conversion circuit 12. Such a setting can also ensure that the current output by the first photovoltaic string can flow through the DC bus and the DC bus capacitors C1 and C2, and then the controller is powered on by the auxiliary source, so that the controller has the ability to identify the reverse connection fault of the photovoltaic string. Figure 4c The structure shown is similar in that even if one of the diodes D1 and D4 has a short circuit fault, the anti-reverse circuit 11 can still work normally. At the same time, it is worth mentioning that in actual applications, resistors can also be connected in series on the first bridge arm and the second bridge arm to achieve the function of current limiting, and this application does not limit this.

[0056] In the above embodiment, the first photovoltaic string, i.e., PV1+ and PV1-, are connected to the input end of the DC / DC power conversion circuit 12 through the first switch group S1 and the anti-reverse circuit 11. In practical applications, the first photovoltaic string, i.e., PV1+ and PV1-, can also be connected to the output end of the DC / DC power conversion circuit 12 through the first switch group S1 and the anti-reverse circuit 11. Figure 5 and Figure 6a-6d The embodiments of the present application are described.

[0057] First, see Figure 5 , Figure 5 A topological diagram of the DC side of a photovoltaic inverter that can timely identify the reverse connection of photovoltaic strings is provided in this application. Figure 2a-2c The structure shown is different in that Figure 5 In the embodiment, the first photovoltaic string, namely PV1+ and PV1-, is also connected to the output end of the DC / DC power conversion circuit 12 through the first switch group S1 and the anti-reverse circuit 11. It is worth mentioning that in Figure 5 In the example, the second switch group S2 represents Figure 2a-2cThe DC side switch 10 of the photovoltaic inverter. The working principle of this topology is that before the photovoltaic inverter is connected to the grid for the first time, the user first closes the first switch group S1. If the connection between PV1+ and PV1- is normal, that is, PV1+ and PV1- are not reversely connected, the anti-reverse circuit 11 can be normally turned on, the DC bus and the DC bus capacitors C1 and C2 are powered on, so that the auxiliary source can take power from the DC bus or the DC bus capacitors C1 and C2, and power the controller. Then, the second switch group S2 is closed. At this time, since the auxiliary source has powered the controller, the controller can determine in real time whether there is a reverse-connected photovoltaic string among all photovoltaic strings connected to the DC / DC power conversion circuit 12. If there is a reverse-connected photovoltaic string, the controller can disconnect the switch connecting the reverse-connected photovoltaic string and the DC / DC power conversion circuit 12 in the second switch group S2, thereby eliminating the reverse connection fault. If all photovoltaic strings are normally connected to the DC / DC power conversion circuit 12, the controller controls the first switch group S1 to be disconnected, and all photovoltaic strings are normally connected to the photovoltaic inverter, thereby realizing photovoltaic grid connection.

[0058] It is worth mentioning that after the user first closes the first switch group S1, if the connection between PV1+ and PV1- is normal, that is, PV1+ and PV1- are not reversely connected, an additional indicator light can be set in the photovoltaic inverter to remind the user that the controller in the photovoltaic inverter can work normally. Therefore, the user can continue to manually close the second switch group S2 and turn off the first switch group S1 to achieve photovoltaic grid-connected power generation. With this arrangement, even if there is a reverse connection fault in the photovoltaic string connected to the photovoltaic inverter, the controller in the photovoltaic inverter can identify it in time and eliminate the reverse connection fault in time. Of course, after the controller works normally, the second switch group S2 can also be directly closed by the controller to disconnect the first switch group S1, without the user manually closing the second switch group S2 and disconnecting the first switch group S1. This application does not limit this.

[0059] In addition, Figure 5 In the figure, for the convenience of description, this application only shows one photovoltaic string, that is, the first photovoltaic string PV1 is connected to the DC / DC power conversion circuit 12 in sequence through the first switch group S1 and the anti-reverse circuit 11. In actual applications, multiple photovoltaic strings can be set to be connected to the DC / DC power conversion circuit 12 in sequence through the first switch group S1 and the anti-reverse circuit 11, and this application does not limit this.

[0060] It should also be noted that in Figure 5In the embodiment, the first switch group S1 includes two switches, wherein the two switches are connected to the anti-reverse circuit 11 through PV1+ and PV1- respectively. In practical applications, the number of switches in the first switch group S1 is not limited to two, that is, the number of switches in the first switch group S1 can be one or more, and the present application does not impose any restrictions on this. When the number of switches in the first switch group S1 is only one, the switch can be connected to either PV1+ or PV1-, and the present application does not impose any restrictions on this. Based on the same principle, in Figure 5 In the present application, there is no restriction on the number of switches in the second switch group S2, that is, there can be one switch or multiple switches on the connection line between each photovoltaic string and the DC / DC power conversion circuit 12.

[0061] Next, we will combine Figure 6a , the embodiments provided in this application are described. Figure 5 The difference is, Figure 6a A specific structure of the anti-reverse circuit 11 is shown. Among them, the anti-reverse circuit 11 includes a resistor R1 and a diode D1, one end of the resistor R1 is connected to PV1+, the other end of the resistor R1 is connected to the DC / DC power conversion circuit 12, the anode of the diode D1 is connected to the DC / DC power conversion circuit 12, and the cathode of the diode D1 is connected to PV1-. Such a setting can ensure that the access of the first photovoltaic string is normal, that is, the current output by the first photovoltaic string can flow through the DC bus and the DC bus capacitors C1 and C2, and then power on the controller through the auxiliary source, so that the controller has the ability to identify the reverse connection fault of the photovoltaic string. Based on the same principle, the structure of the anti-reverse circuit 11 can also refer to Figure 6b .and Figure 6a The structure shown is different in that Figure 6b In the embodiment, the anode of the diode D1 is connected to PV1-, the cathode of the diode D1 is connected to the DC / DC power conversion circuit 12, one end of the resistor R1 is connected to PV1-, and the other end of the resistor R1 is connected to the DC / DC power conversion circuit 12. At the same time, it is worth mentioning that in Figure 4a and Figure 4b In the anti-reverse circuit 11 shown, the resistor R1 mainly functions to limit the current, and the diode D1 mainly functions to prevent a short circuit when the first photovoltaic string is reversely connected.

[0062] Next, we will combine Figure 6c , the embodiments provided in this application are described. Figure 6a and Figure 6b The structure shown is different in that Figure 6cThe anti-reverse circuit 11 shown includes two diodes, namely, a diode D1 and a diode D2, wherein the anode of the diode D1 is connected to PV1+, the cathode of the diode D1 is connected to the DC / DC power conversion circuit 12, the anode of the diode D2 is connected to the DC / DC power conversion circuit 12, and the cathode of the diode D2 is connected to PV1-. By arranging two diodes in the anti-reverse circuit 11, even if one of the two diodes has a short-circuit fault, the anti-reverse circuit 11 can still work, that is, it is ensured that the current output by the first photovoltaic string can flow through the DC bus and the DC bus capacitors C1 and C2, and then the controller is powered on through the auxiliary source, so that the controller has the ability to identify the reverse connection fault of the photovoltaic string.

[0063] Next, we will combine Figure 6d , the embodiments provided in this application are described. Figure 6a , Figure 6b and Figure 6c The structure shown is different in that Figure 6d The anti-reverse circuit 11 shown is a full-bridge circuit. Specifically, the anti-reverse circuit 11 includes a first bridge arm and a second bridge arm connected in parallel, the first bridge arm includes a diode D1 and a diode D2 connected in series, and the second bridge arm includes a diode D3 and a diode D6 connected in series, wherein PV1+ is connected to the series connection point of the diode D1 and the diode D2 through the first switch group S1, PV- is connected to the series connection point of the diode D3 and the diode D4 through the first switch group S1, the cathode of the diode D1 is connected to the cathode of the diode D3, and the parallel connection point of the diode D1 and the diode D3 is connected to the DC / DC power conversion circuit 12, the anode of the diode D2 is connected to the anode of the diode D4, and the parallel connection point of the diode D2 and the diode D4 is connected to the DC / DC power conversion circuit 12. Such a configuration can also ensure that the current output by the first photovoltaic string can flow through the DC bus and the DC bus capacitors C1 and C2, and then the controller is powered on by the auxiliary source, so that the controller has the ability to identify the reverse connection fault of the photovoltaic string. Figure 6c The structure shown is similar in that even if one of the diodes D1 and D4 is short-circuited, the anti-reverse circuit 11 can still work normally. At the same time, it is worth mentioning that in actual applications, resistors can also be connected in series with the first bridge arm and the second bridge arm to achieve current limiting, which is not limited in this application.

[0064] The above specific implementation methods further illustrate the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific implementation methods of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made on the basis of the technical solutions of the present invention should be included in the scope of protection of the present invention.

Claims

1. A photovoltaic inverter, characterized in that: The photovoltaic inverter includes a first switch group, a second switch group, a DC / DC power conversion circuit, a bus capacitor and a controller; wherein, The bus capacitor is connected to a DC input terminal or an output terminal of the DC / DC power conversion circuit; One end of the first switch group is used to be connected to the first photovoltaic string, and the other end of the first switch group is used to be connected to the bus capacitor, so that when the first switch group is closed, the controller is powered by the bus capacitor; One end of the second switch group is used to be connected to the second photovoltaic string, and the other end of the second switch group is used to be connected to the DC input end of the DC / DC power conversion circuit, wherein the first photovoltaic string is a part of the second photovoltaic string; After the controller is powered on and the second switch group is closed, the controller is used to, in response to an overcurrent of the current flowing through the second switch group, disconnect the switch in the second switch group where the overcurrent occurs; or After the controller is powered on and the second switch group is closed, the controller is configured to, in response to the current flowing through the second switch group including a reverse current, open a switch in the second switch group where a reverse current occurs.

2. The photovoltaic inverter according to claim 1, characterized in that: The photovoltaic inverter includes an anti-reverse circuit, which is connected in series between the first switch group and the bus capacitor, or the anti-reverse circuit is connected in series between the first switch group and the first photovoltaic string, and the anti-reverse circuit is used to prevent the reverse current from entering the bus capacitor when the first photovoltaic string is reversely connected.

3. The photovoltaic inverter according to claim 1, characterized in that: After the controller is powered on and the second switch group is closed, if the current flowing through the second switch group does not have an overcurrent and the current flowing through the second switch group does not have the reverse current, the controller is used to disconnect the first switch group.

4. The photovoltaic inverter according to claim 1, characterized in that: The photovoltaic inverter includes an indicator light. If the first switch group is closed so that the controller is powered on by the bus capacitor, the indicator light is on. The indicator light is used to instruct the user to close the second switch group.

5. The photovoltaic inverter according to claim 4, characterized in that: After the second switch group is closed, the indicator light remains on, and the indicator light remains on to instruct the user to close the second switch group and then disconnect the first switch group.

6. The photovoltaic inverter according to any one of claims 1 to 4, characterized in that: The photovoltaic inverter includes an indicator light. If the first switch group is closed and the controller does not obtain power from the bus capacitor and is not powered on, the indicator light will not light up. The indicator light not lighting up is used to indicate the presence of a fault.

7. The photovoltaic inverter according to any one of claims 1 to 5, characterized in that: The photovoltaic inverter includes an auxiliary source, which is connected to the bus capacitor. When the first switch group is closed, the auxiliary source is used to draw power from the bus capacitor to power the controller.

8. The photovoltaic inverter according to claim 2, characterized in that: The anti-reverse circuit is connected in series between the first switch group and the bus capacitor, and the anti-reverse circuit includes a diode, one end of the diode is connected to the positive or negative pole of the first photovoltaic string through the switch in the first switch group, and the other end of the diode is used to be connected to the DC / DC power conversion circuit, and the conduction direction of the diode is opposite to the direction of the reverse current.

9. The photovoltaic inverter according to claim 8, characterized in that: The anti-reverse circuit includes a resistor, one end of the resistor connected in series with the diode is connected to the first photovoltaic string through the switch in the first switch group, and the other end of the resistor connected in series with the diode is connected to the DC / DC power conversion circuit, or one end of the resistor is connected to the first photovoltaic string through the first switch group, and the other end of the resistor is connected to the DC / DC power conversion circuit.

10. The photovoltaic inverter according to claim 2, characterized in that: The anti-reverse circuit is connected in series between the first switch group and the bus capacitor, and the anti-reverse circuit includes a first diode and a second diode, wherein: The anode of the first diode is connected to the positive electrode of the first photovoltaic string through the switch in the first switch group, the cathode of the first diode is used to be connected to the DC / DC power conversion circuit, the cathode of the second diode is connected to the negative electrode of the first photovoltaic string through the switch in the first switch group, and the anode of the second diode is used to be connected to the DC / DC power conversion circuit.

11. The photovoltaic inverter according to claim 10, characterized in that: The anti-reverse circuit includes a resistor, wherein the resistor is connected in series with the first diode and connected to the first photovoltaic string and the DC / DC power conversion circuit through a switch in the first switch group, or the resistor is connected in series with the second diode and connected to the first photovoltaic string and the DC / DC power conversion circuit through a switch in the first switch group.

12. The photovoltaic inverter according to claim 10, characterized in that: The anti-reverse circuit includes two resistors, one of which is connected in series with the first diode and then connected to the first photovoltaic string and the DC / DC power conversion circuit through the switch in the first switch group, and the other resistor is connected in series with the second diode and then connected to the first photovoltaic string and the DC / DC power conversion circuit through the switch in the first switch group.

13. The photovoltaic inverter according to claim 2, characterized in that: The anti-reverse circuit includes a first bridge arm and a second bridge arm connected in parallel, wherein: The first bridge arm includes a first diode and a second diode connected in series, the second bridge arm includes a third diode and a fourth diode connected in series, the cathode of the first diode is connected to the cathode of the third diode, and the anode of the second diode is connected to the anode of the fourth diode; The series connection point of the first diode and the second diode is used to be connected to the positive electrode of the first photovoltaic string, and the series connection point of the third diode and the fourth diode is used to be connected to the DC / DC power conversion circuit.

14. The photovoltaic inverter according to claim 2, characterized in that: The anti-reverse circuit is connected to the DC output side of the DC / DC power conversion circuit, the bus capacitor is connected to the DC output side of the DC / DC power conversion circuit and is connected to the first photovoltaic string through the anti-reverse circuit and the first switch group, so that when the first switch group is closed, power is drawn from the first photovoltaic string to power on the controller.

15. The photovoltaic inverter according to claim 2, characterized in that: The anti-reverse circuit is connected to the DC input side of the DC / DC power conversion circuit, the bus capacitor is connected to the DC input side of the DC / DC power conversion circuit and is connected to the first photovoltaic string through the anti-reverse circuit and the first switch group.

16. The photovoltaic inverter according to claim 2, characterized in that: The anti-reverse circuit is connected in series between the first switch group and the first photovoltaic string. The anti-reverse circuit includes a diode, one end of the diode is connected to the positive pole or the negative pole of the first photovoltaic string, and the other end of the diode is used to be connected to the DC / DC power conversion circuit through the switch in the first switch group. The conduction direction of the diode is opposite to the direction of the reverse current.

17. The photovoltaic inverter according to claim 16, characterized in that: The anti-reverse circuit includes a resistor, one end of the resistor connected in series with the diode is used to be connected to the first photovoltaic string, and the other end of the resistor connected in series with the diode is connected to the DC / DC power conversion circuit through the switch in the first switch group, or one end of the resistor is used to be connected to the first photovoltaic string, and the other end of the resistor is connected to the DC / DC power conversion circuit through the switch in the first switch group.

18. A method for protecting photovoltaic strings, applied to photovoltaic inverters, characterized in that: The method comprises: Connecting the first photovoltaic string to the bus capacitor of the inverter through the first switch group to charge the bus capacitor to power on the controller of the inverter; After the controller is powered on and the second switch group is closed, in response to an overcurrent in a part of the switches in the second switch group, disconnecting the part of the switches in the second switch group where the overcurrent occurs; or, After the second switch group is closed, in response to the current flowing through some switches in the second switch group being a reverse current, some switches in the second switch group where the reverse current occurs are disconnected, wherein one end of the second switch group is used to be connected to a second photovoltaic string, and the other end of the second switch group is used to be connected to a DC / DC power conversion circuit, and the first photovoltaic string is a part of the second photovoltaic string.

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