Photovoltaic system, inverter and direct current arc detection method

Abstract

The invention discloses a photovoltaic system, an inverter and a direct current arc detection method. The system comprises the inverter, a controller and at least two converters. The controller controls the input current of the inverter to be reduced to realize arc extinguishing when detecting that the electric arc appears, and controls the output voltage of the at least one photovoltaic string to be reduced to a first preset voltage after arc extinguishing is realized, and the first preset voltage is lower than the input voltage of the inverter when detecting that the electric arc appears; or, the maximum value of the output current of at least one photovoltaic group string is controlled to be second preset current, and the second preset current is lower than the input current of the inverter when it is detected that the electric arc appears. The above two work recovery modes do not generate electric arc again, that is, secondary arc discharge is avoided in the process of confirming the electric arc, and damage to the photovoltaic system is avoided.

Description

[0001] This application is a divisional application. The application number of the original application is 202111056652.3, and the original application date is September 9, 2021. The entire contents of the original application are incorporated into this application by reference. Technical Field

[0002] The present application relates to the field of photovoltaic power generation technology, and in particular to a photovoltaic system, an inverter, and a method for detecting a DC arc. Background Art

[0003] An electric arc is a gas discharge phenomenon, specifically, an instantaneous spark is generated when an electric current passes through some insulating medium (such as air). The electric arc will generate high temperature, and when it is strong, it can produce open flames. The electric arc will not only cause the surrounding insulating materials to decompose or carbonize and lose their insulating effect, but also easily cause the surrounding materials to reach the ignition point and catch fire.

[0004] A certain voltage and current are required for the arc to maintain burning. If the voltage or current is low, the arc will extinguish quickly. Therefore, the arc protection function is clearly defined in the NEC 2017 690.11 standard. Arc detection can be exempted when the voltage is below 80V, that is, arc faults will not occur or the arc will be unstable and extinguished quickly when the voltage is below 80V.

[0005] DC arc detection mainly detects the frequency domain information of the arc current or voltage, such as frequency, energy, variation, etc. Since the equipment operating environment is complex and changeable, when the ambient noise is close to the spectrum characteristics of the arc, it is impossible to determine whether an arc has actually occurred, which can easily lead to false alarms of arc faults.

[0006] At present, most fire accidents in photovoltaic systems are caused by DC arc faults. The main causes of DC arc faults include: there are too many wiring terminals and the connection terminals are incompatible or the connection is unreliable, the cables are long and placed in the open air, which is prone to aging and damage, and the DC voltage is high.

[0007] However, with the development of module-level power electronics (MLPE) in photovoltaic systems, the high-frequency noise of the converter interferes with arc fault detection, resulting in the inability to accurately detect whether an arc fault has actually occurred. Summary of the invention

[0008] In order to solve the above technical problems, the present application provides a photovoltaic system, an inverter and a DC arc detection method, which can accurately detect whether an arc fault has occurred.

[0009] The photovoltaic system provided by the present application includes: an inverter, a controller and at least one converter; the input end of the inverter is connected to a photovoltaic string, each photovoltaic string includes at least one converter; the input end of each converter is connected to a corresponding photovoltaic module; when the controller detects that an arc occurs in the photovoltaic system, the input current of the inverter is controlled to be reduced to extinguish the arc, that is, the arc is extinguished first and then the work is restored to confirm whether an arc actually occurs. The restoration work can be carried out in the following two ways. If it can be restored, it indicates that there is no arc, otherwise it indicates that there is an arc;

[0010] The first method: controlling the output voltage of at least one photovoltaic string to be reduced to a first preset voltage, the first preset voltage being lower than the input voltage of the inverter when an arc is detected; that is, lowering the output voltage of the photovoltaic string to avoid causing an arc again during the arc confirmation process;

[0011] The second type: the maximum value of the output current of at least one photovoltaic string is controlled to be the first preset current, that is, the output current of the photovoltaic string is limited, that is, no matter how the voltage is controlled, the output current of the photovoltaic string is less than or equal to the first preset current, and the first preset current is lower than the input current of the inverter when the arc feature is detected. That is, the current is lowered to confirm whether an arc actually occurs. Since the current is reduced during the recovery process, the arc will not be caused again during the confirmation process.

[0012] If the above two methods can be successfully restored, it means that no arc has occurred and the detected arc is caused by other reasons. If the restoration cannot be successful, it means that an arc has actually occurred and the detected arc is caused by the arc itself. Whether it is the method of lowering the voltage or the method of lowering the current, the arc will not appear again during the recovery process, because the first preset current and the first preset voltage are both set to safe values ​​that will not cause arcs. In this way, the inverter avoids secondary arcing during the process of confirming the arc and avoids damage to the photovoltaic system.

[0013] In a possible implementation, the controller is further used to control the output voltage of at least one photovoltaic string to decrease to a first preset voltage, and then increase the input current of the inverter. Specifically, the input current of the inverter can be increased starting from the point where the arc is extinguished, and the specific current value to which it is increased is not specifically limited. For example, after the arc is extinguished, the controller controls the output voltage of at least one photovoltaic string to decrease to a first preset voltage, and increases the input current of the inverter to the input current of the inverter corresponding to the point where the arc is detected.

[0014] In a possible implementation, the controller is further used to control the maximum value of the output current of at least one photovoltaic string to be a first preset current, and then reduce the input voltage of the inverter. Specifically, the reduction can start from the input voltage of the inverter after the arc is extinguished, and the specific voltage value to which it is reduced is not specifically limited. For example, after the arc is extinguished, the controller controls the maximum value of the output current of at least one photovoltaic string to be the first preset current, and reduces the input voltage of the inverter to the input voltage of the inverter corresponding to when the arc is detected.

[0015] For example, when the controller detects the occurrence of an arc, it can first record the current operating point of the photovoltaic string, that is, record the output voltage and output current of the current photovoltaic string. It should be understood that the output voltage and output current here refer to the output voltage and output current after the converter is connected in series. For ease of understanding, the following embodiments are introduced by taking the second preset current as the input current of the inverter when the arc feature is detected, and the second preset voltage as the input voltage of the inverter when the arc feature is detected as an example. The second preset current can also be other current values, which can be less than the input current of the inverter when the arc feature is detected, and greater than the current when the arc is extinguished. The second preset voltage can also be other voltage values, which can be less than the input voltage of the inverter when the arc feature is detected.

[0016] In addition, there is no relationship between the first preset voltage and the second preset voltage, and there is no relationship between the second preset current and the first preset current. The first preset voltage and the second preset voltage are voltages in two different implementation schemes, and the second preset current and the first preset current are currents in two different implementation schemes.

[0017] In one possible implementation, the controller is specifically used to control the input current of the inverter to be reduced to zero to achieve arc extinguishing when the arc characteristics are detected. When the input current is 0, it works in an open circuit voltage working state. In addition, the input current of the inverter can also be controlled to be reduced to other values ​​as long as arc extinguishing can be achieved.

[0018] In order to restore the operation of the photovoltaic system after confirming that the detected arc is a false arc, for example, to perform maximum power tracking, the arc confirmation control is no longer performed. For the scheme of pulling down the voltage, the controller is also used to increase the input current of the inverter to the input current of the inverter when the arc is detected. After a preset time period, no arc is detected, and the output voltage of at least one photovoltaic string is no longer controlled to be reduced to a first preset voltage, that is, the voltage limitation is no longer performed. For the scheme of limiting current, the controller is also used to reduce the input voltage of the inverter to the input voltage of the inverter when the arc is detected. After a preset time period, no arc is detected, and the maximum value of the output current of at least one photovoltaic string is no longer controlled to be the first preset current, that is, the converter is no longer current limited.

[0019] In a possible implementation, the controller reduces the output voltage of at least one photovoltaic string to a first preset voltage, which can be achieved by controlling the output voltage of each converter in at least one photovoltaic string to be reduced. Since multiple converters are connected in series, if the total voltage after the series connection is reduced, the output voltage of each converter connected in series can be reduced for the convenience of control. Of course, the output voltage of some converters can also be reduced.

[0020] In one possible implementation, the controller reduces the output voltage of the photovoltaic string and can control the output voltage of the converter to reduce. In order to simplify the control, each converter can be controlled on average, that is, the output voltage of each converter is reduced to the same voltage value, that is, according to the first preset voltage V and the number n of converters included in at least one photovoltaic string, the output voltages of n converters are controlled to be reduced to V / n, where n is a positive integer greater than or equal to 2.

[0021] In one possible implementation, the controller is an inverter controller, which is used to send a voltage control instruction to n converters in at least one photovoltaic string, where the voltage control instruction carries V / n; the n converters all control the output voltage to V / n according to the V / n carried by the voltage control instruction.

[0022] In one possible implementation, the controller can ensure that there is no arcing during the recovery process by lowering the output current. In order to ensure that there is no arcing, since the output ends of the converters are connected in series, the current of each converter is equal, and the controller controls the maximum output current of each converter in at least one photovoltaic string to be a first preset current.

[0023] In one possible implementation, for the convenience of control, the technical solution provided in the present application can be completed by an inverter, that is, the controller is the controller of the inverter, and the controller is integrated inside the cabinet of the inverter.

[0024] In a possible implementation, the controller communicates with at least two converters via wired or wireless means; that is, the inverter controller is specifically used to send voltage control instructions to n converters via 485, PLC, WIFI or ZigBee.

[0025] In one possible implementation, the controller sends a current control instruction to each converter in the photovoltaic string. Since all converters in the photovoltaic string are connected in series, the output current of each converter is controlled to be the same, and each converter controls the output current to be less than or equal to a first preset current.

[0026] The first preset time period and the second preset time period may be the same or different, and are not specifically limited.

[0027] Based on the photovoltaic system provided above, the present application also provides an inverter and a method, which are introduced below. The advantages of each technical solution of the above photovoltaic system are also applicable to the following inverter and method.

[0028] The inverter includes: an inverter controller and a power conversion circuit; the input end of the power conversion circuit is connected to at least one photovoltaic string, each photovoltaic string in the at least one photovoltaic string includes at least one converter; the input end of each converter in the at least one converter is connected to the corresponding photovoltaic module; the inverter controller is used to control the input current of the inverter to reduce to achieve arc extinguishing when an arc is detected, and control the output voltage of at least one photovoltaic string to reduce to a first preset voltage, the first preset voltage is lower than the input voltage of the inverter when an arc is detected, or control the maximum value of the output current of at least one photovoltaic string to be the first preset current, the first preset current is lower than the input current of the inverter when an arc is detected.

[0029] In a possible implementation, the inverter controller is further used to control the maximum value of the output current of at least one photovoltaic string to be a first preset current, and then reduce the input voltage of the inverter to the input voltage of the inverter corresponding to the input voltage of the inverter when an arc is detected.

[0030] In a possible implementation, the inverter controller is further used to control the output voltage of at least one photovoltaic string to decrease to a first preset voltage, and then increase the input current of the inverter to the input current of the inverter corresponding to the input current of the inverter when an arc is detected.

[0031] In a possible implementation, each photovoltaic string in at least one photovoltaic string includes at least two converters; the input end of each converter in the at least two converters is connected to the corresponding photovoltaic module, and the output ends of the at least two converters are connected in series to the input end of the inverter;

[0032] The inverter controller is specifically used to control the output voltages of n converters to be reduced to V / n according to a first preset voltage V and the number n of converters included in at least one photovoltaic string, where n is a positive integer greater than or equal to 2.

[0033] In a possible implementation, the inverter controller is specifically configured to send a current control instruction to each converter in at least one photovoltaic string to control the maximum output current of each converter in at least one photovoltaic string to be a first preset current.

[0034] A possible implementation is to confirm that the detected arc is a false arc, so that the photovoltaic system resumes operation, such as performing maximum power tracking, and no longer performs arc confirmation control. That is, the controller is also used to increase the input current of the inverter to the point where the input current of the inverter runs for a first preset period of time when the arc is detected, and no arc is detected, and the output voltage of at least one photovoltaic string is no longer controlled to be reduced to the first preset voltage. Or, the controller is also used to reduce the input voltage of the inverter to the point where the input voltage of the inverter runs for a second preset period of time when the arc is detected, and no arc is detected, and the maximum value of the output current of at least one photovoltaic string is no longer controlled to be the first preset current.

[0035] The first preset time period and the second preset time period may be the same or different, and are not specifically limited. The first preset time period and the second preset time period may be set according to the safety requirements of the photovoltaic system and may be any values ​​under the premise of ensuring safety.

[0036] Based on the photovoltaic system and inverter provided above, the present application also provides a method for DC arc detection, which is applied to a photovoltaic system, wherein the photovoltaic system includes: an inverter and at least one converter; the input end of the inverter is connected to at least one photovoltaic string, each photovoltaic string in at least one photovoltaic string includes at least one converter; the input end of each converter in at least one converter is connected to the corresponding photovoltaic component; the method includes: judging whether an arc is detected; when an arc is detected, controlling the input current of the inverter to decrease to extinguish the arc; controlling the output voltage of at least one photovoltaic string to decrease to a first preset voltage, the first preset voltage being lower than the input voltage of the inverter when an arc is detected; or controlling the maximum value of the output current of at least one photovoltaic string to be a first preset current, the first preset current being lower than the input current of the inverter when an arc is detected.

[0037] A possible implementation method is to control the output voltage of at least one photovoltaic string to be reduced to a first preset voltage, specifically including: controlling the output voltage of each converter in at least one photovoltaic string to be reduced so that the output voltage of at least one photovoltaic string is reduced to the first preset voltage.

[0038] A possible implementation manner is to control the maximum value of the output current of at least one photovoltaic string to be reduced to a first preset current, specifically including: controlling the output current of each converter in at least one photovoltaic string to be less than or equal to the first preset current.

[0039] The photovoltaic system provided above is based on the application of the inverter in the field of photovoltaic power generation as an example. In addition, the technical solution provided by this application can also be applied to arc detection in other scenarios, that is, this application also provides a power supply system, including: an inverter, a controller and at least two converters; the input end of the inverter is connected to at least one DC source, and each DC source in at least one DC source includes at least two converters; the output ends of at least two converters are connected in series to the input end of the inverter; the DC source can be derived from photovoltaic power generation, hydropower generation, or wind power generation. The controller is used to control the input current of the inverter to reduce and extinguish the arc when the arc feature is detected, and resume work in any of the following ways. If it can be resumed, it indicates that there is no arc, otherwise it indicates that there is an arc; any one of the ways includes: controlling the output voltage of at least one photovoltaic string to be reduced to a first preset voltage, the first preset voltage is lower than the input voltage of the inverter when the arc feature is detected, and controlling the input current of the inverter to be a second preset current; or, controlling the output current of at least one photovoltaic string to be reduced to a first preset current, the first preset current is lower than the input current of the inverter when the arc feature is detected, and controlling the input voltage of the inverter to be a second preset voltage.

[0040] This application has at least the following advantages:

[0041] When the inverter detects the arc feature, the controller of the inverter first controls the input current to reduce to achieve arc extinguishing. For example, the input current can be controlled to reduce to zero. At this time, the output current of the photovoltaic string is 0, and each photovoltaic module works at the working point corresponding to the open circuit voltage, that is, the voltage when the arc is extinguished is relatively high. Specifically, the following two schemes can be used to verify whether an arc actually occurs. If it can be restored, it means that no arc fault has occurred. If it cannot be restored, it means that an arc fault has actually occurred. The first scheme: on the basis that the input current of the inverter continues to be the input current when the arc is extinguished, the output voltage of the photovoltaic string is controlled to be reduced to a first preset voltage, which is lower than the input voltage of the inverter when the arc is detected, that is, the output voltage of the photovoltaic string is pulled down to avoid causing the arc again during the arc confirmation process. The second scheme: on the basis that the input voltage of the inverter is the corresponding voltage when the arc is extinguished, the output current of the photovoltaic string is controlled to be reduced to a first preset current, which is lower than the input current of the inverter when the arc is detected, that is, the current is pulled down to confirm whether the arc actually occurs. Since the current is reduced during the recovery process, the arc will not be caused again during the confirmation process. Whether the voltage is lowered or the current is lowered, an arc will not occur again during the recovery process, because the first preset current and the first preset voltage are both set to safe values ​​that will not cause an arc. In this way, the inverter avoids secondary arcing during the arc confirmation process and avoids damage to the photovoltaic system. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1A schematic diagram of a photovoltaic system provided in an embodiment of the present application;

[0043] Figure 2 A schematic diagram of a power supply system provided in an embodiment of the present application;

[0044] Figure 3 A schematic diagram of another photovoltaic system provided in an embodiment of the present application;

[0045] Figure 4 This is the IV curve of the PV string during normal operation;

[0046] Figure 5 An IV curve of a photovoltaic string when an arc is confirmed provided in an embodiment of the present application;

[0047] Figure 6 Another IV curve of a photovoltaic string when an arc is confirmed provided in an embodiment of the present application;

[0048] Figure 7 A schematic diagram of another photovoltaic system provided in an embodiment of the present application;

[0049] Figure 8 A schematic diagram of another photovoltaic system provided in an embodiment of the present application;

[0050] Fig. 9 A schematic diagram of another photovoltaic system provided in an embodiment of the present application;

[0051] Fig.10 A schematic diagram of another photovoltaic system provided in an embodiment of the present application;

[0052] Fig.11 A schematic diagram of an inverter provided in an embodiment of the present application;

[0053] Fig.12 A flow chart of a method for DC arc detection provided in an embodiment of the present application. DETAILED DESCRIPTION

[0054] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application.

[0055] The terms "first", "second", etc. in the following description are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0056] In this application, unless otherwise clearly specified and limited, the term "connection" should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection or an indirect connection through an intermediate medium. In addition, the term "coupling" can be a way of achieving electrical connection for signal transmission. "Coupling" can be a direct electrical connection or an indirect electrical connection through an intermediate medium.

[0057] In order to enable those skilled in the art to better understand the technical solution provided by the embodiments of the present application, the application scenarios of the technical solution are first introduced below in conjunction with the accompanying drawings.

[0058] Photovoltaic system example

[0059] The embodiments of the present application relate to a photovoltaic system. Generally, the photovoltaic system includes an inverter and multiple photovoltaic strings. The multiple photovoltaic strings are connected to the input end of the inverter. The photovoltaic strings include multiple photovoltaic modules. In order to more flexibly configure the photovoltaic modules in the photovoltaic strings, a converter can be connected to each photovoltaic module, that is, the input end of the converter is connected to the corresponding photovoltaic module. The voltage of the photovoltaic module is the input voltage of the converter. The converter can adjust its own input voltage and then adjust the voltage of the photovoltaic module. Generally, the converter is a direct current / direct current (DC / DC) converter. The DC / DC converter can include a boost circuit, a buck circuit, or a buck-boost circuit. The converter connected to the photovoltaic module is also called an optimizer in the photovoltaic system.

[0060] The converter generally operates in Maximum Power Point Tracking (MPPT) mode.

[0061] MPPT mode: Under normal circumstances, the converter only controls the input voltage to operate at the maximum power point voltage (Vmpp) of the photovoltaic module to achieve the maximum power output of the photovoltaic module, without controlling the output voltage.

[0062] The following describes the architecture of a photovoltaic system provided by an embodiment of the present application in conjunction with the accompanying drawings.

[0063] See also Figure 1 , which is a schematic diagram of a photovoltaic system provided in an embodiment of the present application.

[0064] For the convenience of description, the photovoltaic system including at least two photovoltaic strings is described as an example in this embodiment: a first photovoltaic string 100 and a second photovoltaic string 200. In actual products, the input end of the inverter 300 can be connected to a larger number of photovoltaic strings, not limited to two photovoltaic strings. It should be understood that for a low-power photovoltaic system, the input end of the inverter 300 can also be connected to one photovoltaic string.

[0065] from Figure 1 It can be seen that the first photovoltaic string 100 includes n photovoltaic modules, and the second photovoltaic string 200 includes m photovoltaic modules. Wherein m and n are both integers greater than or equal to 2, and m and n can be different integers. It should be understood that m and n can also be the same integer, that is, when m and n are equal, the number of converters included in the two photovoltaic strings is the same. In order to facilitate the introduction and easily distinguish the first photovoltaic string 100 and the second photovoltaic string 200, the embodiment of the present application is introduced as an example of m and n being different integers, that is, the number of photovoltaic modules included in the first photovoltaic string 100 and the second photovoltaic string 200 is different, that is, the number of converters included is also different.

[0066] It should be understood that each photovoltaic string in the embodiments of the present application may also include only one converter. For ease of understanding, the embodiments of the present application are described by taking the example that each photovoltaic string includes multiple converters.

[0067] The input end of the converter 1-1 in the first photovoltaic string 100 is connected to the photovoltaic component 1-1, the input end of the converter 1-n is connected to the photovoltaic component 1-n, and the output ends of the converter 1-1 to the converter 1-n are connected in series to the input end of the inverter 300.

[0068] Similarly, the input end of the converter 2-1 in the second photovoltaic string 200 is connected to the photovoltaic component 2-1, the input end of the converter 2-m is connected to the photovoltaic component 2-m, and the output ends of the converter 2-1 to the converter 2-m are connected in series to the input end of the inverter 300.

[0069] The inverter 300 may include two stages or one stage, that is, the inverter 300 may be a string inverter or a centralized inverter.

[0070] When the inverter 300 includes two stages, including a DC / DC circuit and a direct current / alternating current (DC / AC) circuit, the inverter may include multiple DC / DC circuits, and the multiple DC / DC circuits correspond to multiple photovoltaic strings one by one, or one DC / DC circuit corresponds to multiple photovoltaic strings, for example, one DC / DC circuit corresponds to two photovoltaic strings. The output end of each photovoltaic string is connected to the input end of the corresponding DC / DC circuit, and the output ends of the multiple DC / DC circuits are all connected to the input end of the DC / AC circuit, that is, the output ends of the multiple DC / DC circuits are connected in parallel to the input end of the DC / AC circuit.

[0071] The inverter in the photovoltaic system involved in the embodiment of the present application is a single-stage inverter, that is, it only includes a DC / AC circuit but does not include a DC / DC circuit.

[0072] The output end of the inverter 300 is connected to the power grid 400. Generally, the inverter 300 is a three-phase inverter and the power grid 400 is a three-phase AC power grid. In addition, the inverter 300 can also be a single-phase inverter for household use, and the corresponding power grid 400 is a household AC power grid.

[0073] It should be understood that the DC arc detection solution provided in the embodiment of the present application is not only applicable to photovoltaic systems, but also to any occasions where a DC source exists, that is, the photovoltaic components in the above photovoltaic system can be replaced by any other DC source, such as wind power generation, hydropower generation or batteries. Figure 2 As shown, Figure 2 and Figure 1 The only difference is that Figure 2 The DC source in Figure 1 The photovoltaic components in the embodiment are the same as those in the embodiment, and other parts are the same, so they will not be described in detail here.

[0074] In actual operation, since the power supply system includes a converter, the converter includes a controllable switch tube, and the switching frequency of the controllable switch tube is relatively high, the high-frequency noise or environmental noise of the converter may be close to the spectrum characteristics of the arc, so it is impossible to effectively distinguish whether an arc fault has actually occurred. The inverter needs to further confirm the arc when the arc characteristics are detected to avoid false alarms of arc faults. The technical solution provided in the embodiment of the present application is based on the fact that the arc characteristics have been detected, and it is necessary to further confirm whether an arc fault has actually occurred to prevent false alarms of arc faults.

[0075] The technical solution provided by the embodiment of the present application is that when the inverter detects the arc feature, the inverter controls the input current to reduce to achieve arc extinguishing. For example, the input current can be controlled to zero. At this time, the output current of the photovoltaic string is 0, and each photovoltaic module operates at the working point corresponding to the open circuit voltage. Then the output voltage of the photovoltaic string is controlled to be reduced to a preset voltage, specifically by controlling each converter to reduce its own output voltage. A possible implementation method can restore the output current of the converter to the output current of the working point when the arc feature is detected. If it can be restored, it means that no arc fault has occurred. If it cannot be restored, it means that an arc fault has actually occurred. In addition, the output current of the photovoltaic string is controlled to be reduced to a preset current. By controlling each converter to reduce its own output current, a possible implementation method is to restore the output voltage of the converter to the output voltage of the working point when the arc feature is detected. If it can be restored, it means that no arc fault has occurred. If it cannot be restored, it means that an arc fault has actually occurred.

[0076] The photovoltaic system provided in the embodiments of the present application is described in detail below with reference to the accompanying drawings.

[0077] See also Figure 3 , which is a schematic diagram of another photovoltaic system provided in an embodiment of the present application.

[0078] The embodiment of the present application provides a photovoltaic system, including: an inverter 300, a controller 500 and at least two converters;

[0079] The input end of the inverter 300 is connected to at least one photovoltaic string, and each photovoltaic string in the at least one photovoltaic string includes at least two converters; the input end of each converter in the at least two converters is connected to the corresponding photovoltaic module, and the output ends of the at least two converters are connected in series to the input end of the inverter; Figure 3 As shown, taking the case where the input end of the inverter 300 is connected to two photovoltaic strings as an example, the first photovoltaic string 100 and the second photovoltaic string 200 include different numbers of photovoltaic modules, that is, the numbers of converters included are also different.

[0080] The input end of the converter 1-1 in the first photovoltaic string 100 is connected to the photovoltaic module 1-1, the input end of the converter 1-n is connected to the photovoltaic module 1-n, and the output ends of the converters 1-1 to 1-n are connected in series to the input end of the inverter 300. Similarly, the input end of the converter 2-1 in the second photovoltaic string 200 is connected to the photovoltaic module 2-1, the input end of the converter 2-m is connected to the photovoltaic module 2-m, and the output ends of the converters 2-1 to 2-m are connected in series to the input end of the inverter 300.

[0081] The inverter 300 may include two-stage power conversion circuits, namely, a DC / DC circuit and a DC / AC circuit; or may include only one-stage power conversion circuit, namely, only a DC / AC circuit. Figure 1 The specific implementation form of the inverter 300 has been introduced, and will not be repeated here.

[0082] The controller 500 is used to control the input current of the inverter to reduce to achieve arc extinguishing when arc characteristics are detected, for example, reducing the input current of the inverter to 0 to achieve arc extinguishing. In this embodiment, the input current of the inverter is not limited to being reduced to 0, and a smaller current can be used to achieve arc extinguishing. After arc extinguishing is achieved, the output voltage of at least one photovoltaic string is controlled to be reduced to a first preset voltage, and the first preset voltage is lower than the input voltage of the inverter when the arc is detected; or, the maximum value of the output current of at least one photovoltaic string is controlled to be a first preset current, and the first preset current is lower than the input current of the inverter when the arc is detected.

[0083] The controller 500 can determine whether an arc actually occurs in two ways. The first is based on whether the input current of the inverter is still the current when the arc is extinguished, that is, the input current of the inverter is relatively low and has not yet started to rise from the arc extinguishing current, and the output voltage of the photovoltaic string is reduced to the first preset voltage. The second is to control the maximum value of the output current of at least one photovoltaic string to be the first preset current after the arc is extinguished. In the above two methods, if the recovery can be successful, it means that no arc has occurred, and the detected arc characteristics are caused by other reasons. If the recovery cannot be successful, it means that an arc really occurred, and the detected arc characteristics are caused by a real arc. The two methods introduced in the embodiments of the present application are: the first is to pull down the voltage. When the voltage is low, no matter how large the current is, it will not cause an arc, that is, the pulled down voltage is a safe voltage, which ensures that no arc will be caused. The second is that the pulled down current is low enough, that is, under the pulled down current, no matter how large the voltage is, it will not cause an arc.

[0084] Among them, the first preset voltage is lower than the input voltage of the inverter when the arc feature is detected, and the first preset current is lower than the input current of the inverter when the arc feature is detected. The embodiment of the present application does not specifically limit the size of the first preset voltage, and can be set according to the actual voltage level of the photovoltaic system. In addition, it can also be set according to the provisions of the standard. For example, the standard mentions that when the voltage is below 80V, arc detection is not required. Therefore, even if an arc occurs, the arc will be extinguished by itself. It should be understood that the first preset voltage in the embodiment of the present application can be less than 80V or greater than 80V, as long as it is ensured that the arc will not be pulled out at the first preset voltage, and the first preset voltage is usually lower than the voltage corresponding to the working point when the arc feature is detected, because the working point when the arc feature is detected is generally the MPPT working point, and the corresponding voltage is relatively high. If the photovoltaic system restores the output voltage of the photovoltaic string to the voltage when the arc feature is detected after the arc is extinguished, then because the voltage is too high, if there is an arc fault, the arc will occur again due to the excessively high voltage, that is, secondary arcing may occur, causing the fault to spread and cause an electrical fire.

[0085] Similarly, the first preset current provided in the embodiment of the present application may also be a current that will not cause an arc. The embodiment of the present application does not specifically limit its value. Usually, the first preset current is lower than the current corresponding to the working point when the arc feature is detected. Therefore, the working point when the arc feature is detected is generally the MPPT working point, and the corresponding current is relatively large. If the photovoltaic system restores the output current of the photovoltaic string to the current when the arc feature is detected after the arc is extinguished, then because the current is too large, if there is an arc fault, the arc will occur again due to the excessively high current, that is, secondary arcing may occur, causing the fault to spread and cause an electrical fire.

[0086] The photovoltaic system provided in the embodiment of the present application performs arc confirmation when arc characteristics are detected. Specifically, the arc confirmation can be performed in two ways. The first is to control the output voltage of the photovoltaic string to a first preset voltage, and then increase the input current of the inverter to a second preset current; the second is to control the maximum value of the output current of the photovoltaic string to be the first preset current, and then reduce the input voltage of the inverter to the second preset voltage. If it succeeds, it means that there is no real arc; if it cannot be restored, it means that there is a real arc. Whether it is the first method or the second method, the arc will not appear again during the recovery process, because the first preset current and the first preset voltage are both set to safe values ​​that will not cause arcs. In this way, the inverter avoids secondary arcing during the process of confirming the arc, thereby avoiding damage to the photovoltaic system.

[0087] When the voltage is pulled down, that is, the controller is also used to control the output voltage of at least one photovoltaic string to decrease to a first preset voltage, and then increase the input current of the inverter starting from the input current of the inverter after arc extinguishing.

[0088] For example, the controller controls the output voltage of at least one photovoltaic string to decrease to a first preset voltage, and is also used to control the input current of the inverter to the input current of the inverter corresponding to when an arc is detected.

[0089] When the current is pulled down, the controller is further used to control the maximum value of the output current of at least one photovoltaic string to be a first preset current, and then reduce the input voltage of the inverter starting from the input voltage of the inverter when the arc is extinguished.

[0090] For example, after controlling the maximum value of the output current of at least one photovoltaic string to be the first preset current, the controller is also used to control the input voltage of the inverter to be the input voltage of the inverter corresponding to when an arc is detected.

[0091] For the convenience of description, the second preset current is the input current of the inverter when an arc is detected; the second preset voltage is the input voltage of the inverter when an arc is detected. When the controller detects the occurrence of an arc, the current operating point of the photovoltaic string can be recorded first, that is, the output voltage and output current of the current photovoltaic string can be recorded. It should be understood that the output voltage and output current here refer to the output voltage and output current after the converter is connected in series. For the convenience of understanding, the following embodiments are introduced by taking the second preset current as the input current of the inverter when an arc is detected, and the second preset voltage as the input voltage of the inverter when an arc is detected as an example. It should be understood that the second preset current can also be other current values, which can be less than the input current of the inverter when the arc feature is detected, and greater than the current when the arc is extinguished. Similarly, the second preset voltage can also be other voltage values, which can be less than the input voltage of the inverter when an arc is detected.

[0092] In addition, there is no relationship between the first preset voltage and the second preset voltage, and there is no relationship between the second preset current and the first preset current. The first preset voltage and the second preset voltage are voltages in two different implementation schemes, and the second preset current and the first preset current are currents in two different implementation schemes.

[0093] In order to enable those skilled in the art to better understand the advantages of the technical solution provided in the embodiments of the present application, the (current-voltage) IV curves of photovoltaic strings are compared and explained below.

[0094] See also Figure 4 , this figure is the IV curve of the photovoltaic string during normal operation.

[0095] In the embodiment of the present application, each photovoltaic string includes 10 photovoltaic modules connected in series. For the convenience of introduction, the parameters of all photovoltaic modules are the same, as follows: open circuit voltage V OC is 49.3V, short-circuit current I SCThe maximum power voltage VMP is 10.47A, the maximum power voltage VMP is 40.6V, the maximum power current IMP is 9.86A, and the IV curve of the photovoltaic string output after the converter is as follows: Figure 4 As shown, the optimal working point of the inverter is point B, at which the output voltage of each converter is 40.6V and the output current is 9.86A. The output voltage of the entire photovoltaic string at point B is the sum of the output voltages of the 10 photovoltaic modules, 406V, and the output current is the output current of each photovoltaic module, 9.86A.

[0096] When the inverter detects the arc feature, the inverter records the current working point B (406V / 9.86A); the inverter reduces the input current to achieve arc extinguishing, for example, controls the input current to zero, that is, the working point of the photovoltaic string is point A (493V / 0A), that is, the working point corresponding to the open circuit voltage. In the traditional technology, the inverter is restored to point B to confirm whether an arc fault occurs: if the work of point B can be restored, it means that the high-frequency noise or environmental noise of the converter in the photovoltaic system may cause the inverter to mistakenly detect the arc feature, and the inverter can continue to work normally; if it cannot be restored to point B, it means that a DC arc fault occurs in the photovoltaic system, and the inverter alarms a DC arc fault. The above is the process of the inverter confirming the arc fault in the traditional technology. Since the voltage and current are large when the inverter is restored to point B, it is easy to cause an arc for a second time, further spreading the fault range. Points C and D in the IV curve are not involved in this embodiment, so they are not introduced in detail.

[0097] The technical solution provided by the embodiment of the present application controls the photovoltaic string to output a lower voltage or a lower current in the process of confirming the arc, which is within the safe range, so that the arc will not be caused twice. In addition, the technical solution provided by the embodiment of the present application, in the process of confirming the arc, the controller sends control instructions to each converter by the inverter, and each converter controls its own output voltage or output current, thereby realizing the control of the output voltage or output current of the photovoltaic string. Among them, the controller and at least two converters can communicate by wired or wireless mode; the wired mode includes at least one of the following: 485 or PLC. The wireless mode includes at least one of the following: WIFI or ZigBee, and the controller of the inverter is specifically used to send voltage control instructions or current control instructions to n converters through 485, PLC, WIFI or ZigBee, for example, the voltage control instruction carries a first preset voltage, and the current control instruction carries a first preset current. With the continuous development of communication technology, the inverter and the converter can also communicate through other communication methods. As the communication rate becomes higher and higher, especially the wireless communication rate increases, when the communication between the inverter and the converter is faster, the technical solution provided in the embodiment of the present application can complete the arc confirmation in a shorter time, which takes very little time and does not affect the normal operation of the inverter.

[0098] The following describes in detail two methods of confirming an arc provided by the embodiments of the present application in conjunction with the accompanying drawings. First, the first implementation method is introduced.

[0099] The first method is that the controller first limits the output voltage of the PV string and then increases the output current.

[0100] Specifically, the controller controls the output voltage of each converter in at least one photovoltaic string to decrease so that the output voltage of at least one photovoltaic string decreases to a first preset voltage, and the first preset voltage is lower than the input voltage when the arc feature is detected. It should be understood that when the photovoltaic system provided in the embodiment of the present application includes multiple photovoltaic strings, the output voltage of each photovoltaic string can be controlled separately to determine whether an arc actually occurs. The confirmation mechanism provided in the following embodiment generally refers to any photovoltaic string.

[0101] It should be understood that when the controller confirms an arc, it only needs to control the output voltage of the photovoltaic string to be reduced to the first preset voltage. Specifically, the output voltage of the converter can be controlled to step down. When a photovoltaic string includes n converters, n is a positive integer greater than or equal to 2. The output voltages of the n converters may be the same or different, and are not specifically limited in the embodiments of the present application. For the convenience of control and description, the present embodiment is introduced as having the same output voltage of n converters, that is, n converters are voltage-balanced. Specifically, the controller controls the output voltages of the n converters to be reduced to V / n according to the first preset voltage V and the number n of converters included in at least one photovoltaic string.

[0102] The following is an introduction using the voltage balancing of n converters as an example.

[0103] See also Figure 5 , this figure is an IV curve of a photovoltaic string when an arc is confirmed provided in an embodiment of the present application.

[0104] In this embodiment, a photovoltaic string including 10 photovoltaic modules connected in series is used as an example for explanation. The parameters of each photovoltaic module are the same and are as follows: open circuit voltage V OC is 49.3V, short-circuit current I SC The maximum power MPP voltage is 10.47A. MP is 40.6V, maximum power MPP current I MP The output current and voltage curve (IV curve) of the photovoltaic string after the converter is 9.86A. Figure 5 As shown, the optimal operating point of the inverter is point B, at which point the output voltage of each converter is 40.6V and the output current is 9.86A.

[0105] When the controller detects arc characteristics, it performs the following arc confirmation process:

[0106] The controller records the current working point B (406V / 9.86A);

[0107] The controller controls the input current of the inverter to zero to extinguish the arc. At this time, the operating point is point A (493V / 0A);

[0108] The controller reduces the output voltage of the photovoltaic string by controlling the converter. For example, the output voltage of the photovoltaic string is reduced from the open circuit voltage to 50V. Since the photovoltaic string includes 10 converters in series, the output voltage of each converter is controlled to be 50V÷10=5V. At this time, the IV curve of the photovoltaic string after the converter is as follows: Figure 5 As shown, it works at point A1 (50V / 0A) at this time.

[0109] The controller controls the input current of the inverter to return to the working current (9.86A) of the working point B when the arc feature is detected, corresponding to Figure 5 Check point B1 in the IV curve to confirm whether a DC arc fault has occurred: If the operating current at point B1 can be restored, that is, it is working at point B1 (49.2V / 9.86A), it means that the high-frequency noise or environmental noise of the converter in the photovoltaic system has caused the controller to mistakenly detect the arc characteristics, and the converter is controlled to recover. Figure 4 The IV curve shown in the figure indicates that the inverter is working normally. If it cannot recover to work at point B1, it means that a DC arc fault has actually occurred in the PV system and the inverter will give an alarm for a DC arc fault.

[0110] In the photovoltaic system provided in this embodiment, since the controller controls the photovoltaic string to recover to the current when the arc feature is detected, the voltage corresponding to point B1 is only 49.2V, which is relatively low. The low voltage will not cause secondary arcing, thereby preventing the fault from spreading and causing an electrical fire.

[0111] Another method of arc confirmation provided by an embodiment of the present application is introduced below.

[0112] The controller is specifically used to control the maximum output current of each converter in at least one photovoltaic string to be a first preset current, that is, to limit the output current capability of the converter, so that the output current is less than or equal to the first preset current. No matter how the output voltage is controlled, the output current of the photovoltaic string will not exceed the first preset current, thereby ensuring that no secondary arc is caused.

[0113] See also Figure 6 , this figure is another IV curve of a photovoltaic string when an arc is confirmed provided in an embodiment of the present application.

[0114] In this embodiment, a photovoltaic string including 10 photovoltaic modules connected in series is used as an example for explanation. The parameters of each photovoltaic module are the same and are as follows: open circuit voltage V OC is 49.3V, short-circuit current ISC The maximum power MPP voltage is 10.47A. MP is 40.6V, maximum power MPP current I MP The output current and voltage curve (IV curve) of the photovoltaic string after the converter is 9.86A. Figure 6 As shown, the optimal operating point of the inverter is point B, at which point the output voltage of each converter is 40.6V and the output current is 9.86A.

[0115] When the controller detects arc characteristics, it performs the following arc confirmation process:

[0116] The controller records the current working condition point B (406V / 9.86A);

[0117] The controller controls the input current of the inverter to zero to extinguish the arc, that is, it works at point A (493V / 0A).

[0118] The following arc confirmation process is performed to reduce the current limit by controlling the converter. For example, if the string current is limited to 1A, each converter will output a maximum current of 1A. At this time, the IV curve of the photovoltaic string after the converter is as follows: Figure 6 As shown, it is working at point A2 (493V / 0A) at this time.

[0119] The working voltage at point B (406V) is restored to the previous working condition, corresponding to Figure 6 Check point B2 in the IV curve to confirm whether a DC arc fault has occurred: If the current can be restored to the current limit value of 1A after the working voltage at point B is restored, that is, it is working at point B2 (406V / 1A), it means that the high-frequency noise or environmental noise of the converter in the photovoltaic system has caused the inverter to mistakenly detect the arc characteristics, and the control converter is restored. Figure 4 The IV curve shown indicates that the inverter is working normally. If it cannot recover to point B2, it means that a DC arc fault has occurred in the PV system and the inverter will give an alarm for a DC arc fault.

[0120] Since the current corresponding to point B2 is only 1A, the low current will not cause secondary arcing, thus preventing the fault from spreading and causing an electrical fire.

[0121] In the photovoltaic system provided in each embodiment of the present application, the controller can be integrated inside the cabinet of the inverter, or can be located outside the cabinet of the inverter. The controller can be implemented by the controller of the inverter, or can be a controller independently provided from the controller of the inverter, which is not specifically limited in the embodiments of the present application.

[0122] The above embodiments are applicable to various topologies of inverters, which are described below in conjunction with the accompanying drawings.

[0123] The first one is that the inverter includes multiple DC / DC circuits inside, and the multiple DC / DC circuits inside the inverter correspond one-to-one to multiple photovoltaic strings.

[0124] See also Figure 7 , which is a schematic diagram of another photovoltaic system provided in an embodiment of the present application.

[0125] The inverter 300 in the photovoltaic system provided in this embodiment includes a plurality of DC / DC circuits. For the convenience of description, the inverter 300 is described below by taking as an example an example that the inverter 300 includes at least the following two DC / DC circuits: a first DC / DC circuit 300a1 and a second DC / DC circuit 300a2.

[0126] In this embodiment, the controller 500 is located inside the inverter 300 as an example for description, that is, the controller 500 in the inverter 300 communicates with the converters in each photovoltaic string.

[0127] like Figure 7 As shown, the first photovoltaic string 100 corresponds to the first DC / DC circuit 300a1, and the output end of the first photovoltaic string 100 is connected to the input end of the first DC / DC circuit 300a1. The second photovoltaic string 200 corresponds to the second DC / DC circuit 300a2, and the output end of the second photovoltaic string 200 is connected to the second DC / DC circuit 300a2.

[0128] In addition, the output ends of the first DC / DC circuit 300a1 and the second DC / DC circuit 300a2 are connected together to the input end of the DC / AC circuit 300b. The embodiment of the present application does not limit the internal topology implementation form of the DC / AC circuit 300b, which can be a two-level inverter circuit or a multi-level inverter circuit.

[0129] Since the inverter 300 includes multiple DC / DC circuits, when performing arc confirmation, the photovoltaic strings can be confirmed one by one, and when an arc fault actually occurs, the photovoltaic string with the arc fault can be locked. For example, the controller 500 first controls the output voltage or output current of each converter (1-1 to 1-n) in the first photovoltaic string 100 to perform arc confirmation, and then controls the output voltage or output current of each converter (2-1 to 2-m) in the second photovoltaic string 200 to perform arc confirmation, so as to determine whether an arc fault actually occurs, and when an arc fault actually occurs, it can be located whether the first photovoltaic string 100 has an arc fault or the second photovoltaic string 200 has an arc fault. The above is only an example that the controller 500 first performs arc confirmation on the first photovoltaic string 100, and then performs arc confirmation on the second photovoltaic string 200. It should be understood that the controller 500 can also first perform arc confirmation on the second photovoltaic string 200, and then perform arc confirmation on the first photovoltaic string 100.

[0130] above Figure 7 The photovoltaic system introduced here is based on the example that each DC / DC circuit corresponds to one photovoltaic string. The following will introduce that each DC / DC circuit can correspond to multiple photovoltaic strings. The following will introduce an example that one DC / DC circuit corresponds to two photovoltaic strings.

[0131] See also Figure 8 , which is a schematic diagram of another photovoltaic system provided in an embodiment of the present application.

[0132] In this embodiment, the inverter 300 includes two DC / DC circuits as an example, and may include more DC / DC circuits. Each DC / DC circuit is connected to multiple photovoltaic strings. In this embodiment, each DC / DC circuit is connected to two photovoltaic strings as an example, and may be connected to more photovoltaic strings.

[0133] The first DC / DC circuit 300 a connects the first photovoltaic string 100 and the second photovoltaic string 200 , and the second DC / DC circuit 300 b connects the third photovoltaic string 300 and the fourth photovoltaic string 400 .

[0134] Combine the following Fig. 9 The arc confirmation process when one DC / DC circuit corresponds to multiple PV strings is specifically introduced.

[0135] See also Fig. 9 , which is a schematic diagram of another photovoltaic system provided in an embodiment of the present application.

[0136] For the convenience of description, this embodiment is described by taking the inverter 300 including one DC / DC circuit as an example, and one DC / DC circuit is connected to multiple photovoltaic strings. In actual products, the inverter 300 may include multiple DC / DC circuits, each of which is connected to multiple photovoltaic strings corresponding to each other, which will not be described in detail here.

[0137] like Fig. 9As shown, the input end of the DC / DC circuit 300a is connected to the first photovoltaic string 100 and the second photovoltaic string 200. The controller 500 can first control the output voltage or output current of each converter (1-1 to 1-n) in the first photovoltaic string 100 to confirm the arc, and then control the output voltage or output current of each converter (2-1 to 2-m) in the second photovoltaic string 200 to confirm the arc, so as to determine whether an arc fault actually occurs, and when an arc fault actually occurs, it can be located whether the arc fault occurs in the first photovoltaic string 100 or the second photovoltaic string 200. The above is only an example that the controller 500 first confirms the arc on the first photovoltaic string 100 and then confirms the arc on the second photovoltaic string 200. It should be understood that the controller 500 can also first confirm the arc on the second photovoltaic string 200 and then confirm the arc on the first photovoltaic string 100.

[0138] The above descriptions are all based on the example of an inverter including a DC / DC circuit. The following descriptions are about the implementation of an inverter that does not include a DC / DC circuit but only includes a DC / AC circuit.

[0139] See also Fig.10 , which is a schematic diagram of another photovoltaic system provided in an embodiment of the present application.

[0140] The photovoltaic system provided in this embodiment does not include a DC / DC circuit inside the inverter 300, but includes a DC / AC circuit 300b, wherein the output ends of multiple photovoltaic strings are directly connected to the DC / AC circuit 300b. In this embodiment, two photovoltaic strings are taken as an example, and the output ends of the first photovoltaic string 100 and the second photovoltaic string 200 are both connected to the DC / AC circuit 300b.

[0141] The controller 500 can first control the output voltage or output current of each converter (1-1 to 1-n) in the first photovoltaic string 100 to perform arc confirmation, and then control the output voltage or output current of each converter (2-1 to 2-m) in the second photovoltaic string 200 to perform arc confirmation, so as to determine whether an arc fault actually occurs, and when an arc fault actually occurs, it can be located whether an arc fault occurs in the first photovoltaic string 100 or in the second photovoltaic string 200. The above is only an example that the controller 500 first performs arc confirmation on the first photovoltaic string 100 and then performs arc confirmation on the second photovoltaic string 200. It should be understood that the controller 500 can also first perform arc confirmation on the second photovoltaic string 200 and then perform arc confirmation on the first photovoltaic string 100.

[0142] In order to restore the operation of the photovoltaic system when it is confirmed that the detected arc is a false arc, for example, to perform maximum power tracking, the confirmation control of the arc is no longer performed. That is, the controller is also used to increase the input current of the inverter to the input current of the inverter when the arc is detected. After the first preset time period, no arc is detected, and it can be restored to the current when the arc is detected. The current runs for the first preset time period, which means that the work can be restored, which means that the previously detected arc is a false arc, not a real arc, and the output voltage of at least one photovoltaic string is no longer controlled to be reduced to the first preset voltage. Or, the controller is also used to reduce the input voltage of the inverter to the input voltage of the inverter when the arc is detected. After the second preset time period, it can be restored to the input voltage when the arc is detected. After a period of time, no arc is detected, which means that the previously detected arc is not a real arc, and the maximum value of the output current of at least one photovoltaic string is no longer controlled to be the first preset current. Among them, the first preset time period and the second preset time can be the same or different, and are not specifically limited.

[0143] Inverter Embodiment

[0144] Based on a photovoltaic system provided in the above embodiment, the embodiment of the present application further provides an inverter, which is described in detail below with reference to the accompanying drawings.

[0145] See also Fig.11 , which is a schematic diagram of an inverter provided in an embodiment of the present application.

[0146] The present application implements a provided inverter, including: an inverter controller 500 and a power conversion circuit 600;

[0147] The input end of the power conversion circuit 600 is connected to at least one photovoltaic string, and each photovoltaic string in the at least one photovoltaic string includes at least one converter; the input end of each converter in the at least one converter is connected to the corresponding photovoltaic module, and when the photovoltaic string includes at least two converters, the output ends of the at least two converters are connected in series to the input end of the power conversion circuit;

[0148] The inverter controller 500 is used to control the input current of the inverter to decrease to extinguish the arc when an arc is detected, and after the arc is extinguished, control the output voltage of at least one photovoltaic string to decrease to a first preset voltage, the first preset voltage is lower than the input voltage of the inverter when the arc is detected, or control the maximum value of the output current of at least one photovoltaic string to be the first preset current, the first preset current is lower than the input current of the inverter when the arc is detected.

[0149] The embodiment of the present application does not limit the specific structure of the power conversion circuit 600 in the inverter, but at least includes a DC / AC circuit and may also include a DC / DC circuit. For example, the architecture of the inverter can be referred to in Figure 7-10 The power conversion circuit 600 may include one DC / DC circuit, or may include at least two DC / DC circuits, and the input end of each DC / DC circuit in the at least two DC / DC circuits is connected to at least one photovoltaic string, that is, each DC / DC circuit may be connected to one photovoltaic string, or may be connected to multiple photovoltaic strings, which is not specifically limited in the embodiments of the present application.

[0150] When the voltage is pulled down, that is, after the inverter controller controls the output voltage of at least one photovoltaic string to be reduced to a first preset voltage, it is also used to increase the input current of the inverter from the input current of the inverter when the arc is extinguished to a value greater than the input current of the inverter corresponding to the arc extinguishing, that is, the second preset current.

[0151] For example, after the inverter controller controls the output voltage of at least one photovoltaic string to drop to a first preset voltage, it is also used to control the input current of the inverter to the input current of the inverter corresponding to when an arc is detected; then when the input current of the inverter is detected to be the input current of the inverter corresponding to when an arc is detected, it is determined that no arc has occurred, otherwise an arc has occurred.

[0152] When the current is pulled down, the inverter controller controls the output current of at least one photovoltaic string to be reduced to a first preset current, and is also used to reduce the input voltage of the inverter from the input voltage of the inverter when the arc is extinguished to a voltage lower than the corresponding input voltage of the inverter when the arc is extinguished, that is, a second preset voltage.

[0153] For the convenience of description, the second preset current can be the input current of the inverter when the arc feature is detected; the second preset voltage can be the input voltage of the inverter when the arc is detected. When the controller detects the occurrence of an arc, the current operating point of the photovoltaic string can be recorded first, that is, the output voltage and output current of the current photovoltaic string can be recorded. It should be understood that the output voltage and output current here refer to the output voltage and output current after the converter is connected in series. For the convenience of understanding, the following embodiments are introduced by taking the second preset current as the input current of the inverter when the arc is detected, and the second preset voltage as the input voltage of the inverter when the arc is detected as an example. It should be understood that the second preset current can also be other current values, which can be less than the input current of the inverter when the arc feature is detected, and greater than the current when the arc is extinguished. Similarly, the second preset voltage can also be other voltage values, which can be less than the input voltage of the inverter when the arc is detected.

[0154] The inverter provided in the embodiment of the present application performs arc confirmation when an arc is detected. Specifically, the arc confirmation can be performed in two ways. The first is to control the output voltage of the photovoltaic string to a first preset voltage and increase the input current of the inverter to a second preset current; the second is to control the maximum value of the output current of the photovoltaic string to the first preset current and reduce the input voltage of the inverter to the second preset voltage. If it succeeds, it means that there is no real arc; if it cannot be restored, it means that there is a real arc. Whether it is the first method or the second method, the arc will not appear again during the recovery process, because the first preset current and the first preset voltage are both set to safe values ​​that will not cause arcs. In this way, the inverter avoids secondary arcing and damage during the process of confirming the arc.

[0155] When the inverter provided in the embodiment of the present application performs arc confirmation, specifically, the inverter controller sends a control instruction to each converter in the photovoltaic string to make the converter change its own output voltage or output current. Specifically, the controller is specifically used to control the output voltage of each converter in at least one photovoltaic string to decrease, so that the output voltage of at least one photovoltaic string is reduced to a first preset voltage, and the first preset voltage is lower than the input voltage when the arc is detected.

[0156] It should be understood that the inverter controller can control each converter to output the same voltage, or control each converter to output different voltages. A possible implementation is described below, in which the inverter controller controls each converter to output the same voltage, that is, according to the first preset voltage V and the number n of converters included in at least one photovoltaic string, the output voltages of n converters are controlled to be reduced to V / n, where n is a positive integer greater than or equal to 2. For example, a photovoltaic string includes 10 photovoltaic modules and 10 converters, and the output voltage of the photovoltaic string is controlled to be reduced to 50V, that is, the output voltage of each converter is controlled to be 50V÷10=5V.

[0157] The above is the first arc confirmation mechanism for controlling the output voltage. The following introduces another arc confirmation mechanism, which is achieved by controlling the output current of the photovoltaic string. Specifically, the inverter controller controls the maximum output current of each converter in at least one photovoltaic string to be a first preset current, so that the input current of the inverter is reduced to the first preset current. The first preset current is lower than the input current when the arc feature is detected. Since the converters in the photovoltaic string are connected in series, the output currents of the converters are controlled to be the same.

[0158] In order to restore the operation of the photovoltaic system when it is confirmed that the detected arc is a false arc, for example, to perform maximum power tracking, the confirmation control of the arc is no longer performed. That is, the controller is also used to increase the input current of the inverter to the input current of the inverter when the arc is detected. After the input current of the inverter runs for the first preset time period, it can be restored to the current when the arc is detected. It runs for the first preset time period, which means that the work can be restored, which means that the previously detected arc is a false arc, not a real arc, and the output voltage of at least one photovoltaic string is no longer controlled to be reduced to the first preset voltage. Or, the controller is also used to reduce the input voltage of the inverter to the input voltage of the inverter when the arc is detected. After the input voltage of the inverter runs for a second preset time period, it can be restored to the input voltage when the arc is detected. It runs for a period of time, which means that the previously detected arc is not a real arc, and the maximum value of the output current of at least one photovoltaic string is no longer controlled to be the first preset current. Among them, the first preset time period and the second preset time can be the same or different, and are not specifically limited.

[0159] Method Embodiment

[0160] Based on a photovoltaic system and an inverter provided in the above embodiments, an embodiment of the present application further provides a method for detecting a DC arc, which is described in detail below in conjunction with the accompanying drawings.

[0161] See also Fig.12 , which is a flow chart of a method for DC arc detection provided in an embodiment of the present application.

[0162] The DC arc detection method provided in this embodiment is applied to a photovoltaic system, which includes: an inverter and at least two converters;

[0163] The input end of the inverter is connected to at least one photovoltaic string, and each photovoltaic string in the at least one photovoltaic string includes at least two converters; the input end of each converter in the at least two converters is connected to the corresponding photovoltaic module, and the output ends of the at least two converters are connected in series to the input end of the inverter;

[0164] The method includes:

[0165] S1201: When an arc is detected, the input current of the inverter is controlled to be reduced to extinguish the arc.

[0166] For example, the input current of the inverter is reduced to 0 to achieve arc extinguishing. In this embodiment, the input current of the inverter is not limited to being reduced to 0, and a smaller current can be used to achieve arc extinguishing. Due to the characteristics of the IV curve of the photovoltaic string, when the current is reduced, the voltage will naturally be pulled up.

[0167] S1202: Control the output voltage of at least one photovoltaic string to be reduced to a first preset voltage, where the first preset voltage is lower than the input voltage of the inverter when an arc is detected; or control the maximum value of the output current of at least one photovoltaic string to be a first preset current, where the first preset current is lower than the input current of the inverter when an arc feature is detected.

[0168] The method provided in the embodiment of the present application performs arc confirmation when an arc is detected. Specifically, the arc can be confirmed in two ways. The first is to control the output voltage of the photovoltaic string to a first preset voltage; the second is to control the maximum value of the output current of the photovoltaic string to be the first preset current. If it succeeds, it means that there is no real arc; if it cannot be restored, it means that there is a real arc. Whether it is the first method or the second method, the arc will not appear again during the recovery process, because the first preset current and the first preset voltage are both set to safe values ​​that will not cause arcs. In this way, the inverter avoids secondary arcing during the process of confirming the arc, which causes damage to the photovoltaic system.

[0169] Among them, a possible implementation manner is to control the output voltage of at least one photovoltaic string to decrease to a first preset voltage, specifically including:

[0170] The output voltage of each converter in at least one photovoltaic string is controlled to decrease, so that the output voltage of at least one photovoltaic string decreases to a first preset voltage.

[0171] Controlling the maximum value of the output current of the at least one photovoltaic string to be a first preset current specifically includes:

[0172] The output current of each converter in at least one photovoltaic string is controlled to be less than or equal to a first preset current.

[0173] The photovoltaic system provided in the embodiment of the present application performs arc confirmation when arc characteristics are detected. Specifically, the arc confirmation can be performed in two ways. The first is to control the output voltage of the photovoltaic string to a first preset voltage, and then increase the input current of the inverter to a second preset current; the second is to control the maximum value of the output current of the photovoltaic string to be the first preset current, and then reduce the input voltage of the inverter to the second preset voltage. If it succeeds, it means that there is no real arc; if it cannot be restored, it means that there is a real arc. Whether it is the first method or the second method, the arc will not appear again during the recovery process, because the first preset current and the first preset voltage are both set to safe values ​​that will not cause arcs. In this way, the inverter avoids secondary arcing during the process of confirming the arc, thereby avoiding damage to the photovoltaic system.

[0174] It should be understood that the second preset current can also be other current values, which can be less than the input current of the inverter when an arc is detected, and greater than the current when the arc is extinguished. Similarly, the second preset voltage can also be other voltage values, which can be less than the input voltage of the inverter when an arc is detected.

[0175] In order to restore the operation of the photovoltaic system when it is confirmed that the detected arc is a false arc, for example, to perform maximum power tracking, the confirmation control of the arc is no longer performed. That is, the controller is also used to increase the input current of the inverter to the point where the input current of the inverter runs for a first preset time period when the arc is detected, and can be restored to the current when the arc is detected for a first preset time period, which means that the operation can be restored. If it is a false arc, not a real arc, the output voltage of at least one photovoltaic string is no longer controlled to be reduced to the first preset voltage. Or, the controller is also used to reduce the input voltage of the inverter to the point where the input voltage of the inverter runs for a second preset time period when the arc is detected, and can be restored to the input voltage when the arc is detected for a period of time, which means that it is not a real arc, and the maximum value of the output current of at least one photovoltaic string is no longer controlled to be the first preset current. Among them, the first preset time period and the second preset time can be the same or different, and are not specifically limited.

[0176] It should be understood that in this application, "at least one (item)" means one or more, and "more" means two or more. Any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of this application without departing from the content of the technical solution of this application shall still fall within the scope of protection of the technical solution of this application.

Claims

1. A photovoltaic system, characterized in that: include: Power conversion circuits and controllers; The input end of the power conversion circuit is used to connect at least one photovoltaic string, each photovoltaic string in the at least one photovoltaic string includes at least one converter and a photovoltaic component corresponding to each converter; the input end of each converter is connected to the corresponding photovoltaic component; The controller is used to: When an electric arc is detected in the photovoltaic system, controlling the input current of the power conversion circuit to decrease to a first current value to extinguish the arc; After arc extinguishing is achieved, the output voltage of the at least one photovoltaic string is controlled to be reduced to a first preset voltage, and the input current of the power conversion circuit is controlled to be a second preset current; wherein the first preset voltage is lower than the input voltage of the power conversion circuit when an arc is detected, and the first preset voltage is a safe voltage that will not cause an arc, and the second preset current is the input current of the power conversion circuit when arc extinguishing is detected; if the input current of the power conversion circuit cannot reach the second preset current, a DC arc fault alarm is issued; or, After arc extinguishing is achieved, the maximum value of the output current of the at least one photovoltaic string is controlled to be a first preset current, and the input voltage of the power conversion circuit is controlled to be a second preset voltage; wherein the first preset current is lower than the input current of the power conversion circuit when an arc is detected and higher than the first current value, and the first preset current is a safe current that will not cause an arc, and the second preset voltage is the input voltage of the power conversion circuit when arc extinguishing is detected; if the input voltage of the power conversion circuit cannot reach the second preset voltage, a DC arc fault alarm is issued.

2. The photovoltaic system according to claim 1, characterized in that: The first current value is 0.

3. The photovoltaic system according to claim 1, characterized in that: The controller is further configured to: if the input current of the power conversion circuit reaches the second preset current and runs for a first preset time period, control the at least one photovoltaic string to resume normal operation.

4. The photovoltaic system according to claim 1, characterized in that: The controller is further configured to: if the input voltage of the power conversion circuit reaches the second preset voltage and operates for a second preset time period, control the at least one photovoltaic string to resume normal operation.

5. The photovoltaic system according to any one of claims 1 to 4, characterized in that: Each photovoltaic string in the at least one photovoltaic string includes at least two converters; the input end of each converter in the at least two converters is connected to the corresponding photovoltaic component, and the output ends of the at least two converters are connected in series to the input end of the power conversion circuit.

6. The photovoltaic system according to claim 5, characterized in that: The controller is specifically used to control the output voltage of each converter in the at least one photovoltaic string to decrease, so that the output voltage of the at least one photovoltaic string decreases to the first preset voltage.

7. The photovoltaic system according to claim 6, characterized in that: The controller is specifically used to control the output voltages of n converters to be reduced to V / n according to the first preset voltage V and the number n of converters included in the at least one photovoltaic string, where n is a positive integer greater than or equal to 2.

8. The photovoltaic system according to claim 7, characterized in that: The controller is specifically configured to send a voltage control instruction to n converters in the at least one photovoltaic string, wherein the voltage control instruction carries the V / n; The n converters are used to control the output voltage to be the V / n according to the V / n carried by the voltage control instruction.

9. The photovoltaic system according to claim 5, characterized in that: The controller is specifically used to send a current control instruction to each converter in the at least one photovoltaic string to control the output current of each converter in the at least one photovoltaic string to be less than or equal to the first preset current.

10. The photovoltaic system according to claim 8 or 9, characterized in that: The controller is specifically used to send the voltage control instruction or the current control instruction to the n converters through 485, PLC, WIFI or ZigBee to control the voltage output or current output of the converters.

11. A method for detecting a DC arc, characterized in that: Applied to a photovoltaic system, the photovoltaic system comprising: a power conversion circuit and at least one converter; The input end of the power conversion circuit is used to connect at least one photovoltaic string, each photovoltaic string in the at least one photovoltaic string includes at least one converter and a photovoltaic component corresponding to each converter; the input end of each converter is connected to the corresponding photovoltaic component; The method comprises: When an arc is detected in the photovoltaic system, the input current of the power conversion circuit is controlled to be reduced to a first current value to extinguish the arc; After arc extinguishing is achieved, the output voltage of the at least one photovoltaic string is controlled to be reduced to a first preset voltage, and the input current of the power conversion circuit is controlled to be a second preset current; wherein the first preset voltage is lower than the input voltage of the power conversion circuit when an arc is detected, and the first preset voltage is a safe voltage that will not cause an arc, and the second preset current is the input current of the power conversion circuit when arc extinguishing is detected; if the input current of the power conversion circuit cannot reach the second preset current, a DC arc fault alarm is issued; or, After arc extinguishing is achieved, the maximum value of the output current of the at least one photovoltaic string is controlled to be a first preset current, and the input voltage of the power conversion circuit is controlled to be a second preset voltage; wherein the first preset current is lower than the input current of the power conversion circuit when an arc is detected and higher than the first current value, and the first preset current is a safe current that will not cause an arc, and the second preset voltage is the input voltage of the power conversion circuit when arc extinguishing is detected; if the input voltage of the power conversion circuit cannot reach the second preset voltage, a DC arc fault alarm is issued.

12. The method according to claim 11, characterized in that The first current value is 0.

13. The method according to claim 11, characterized in that The method further comprises: If the input current of the power conversion circuit reaches the second preset current and runs for the first preset time period, the at least one photovoltaic string is controlled to resume normal operation.

14. The method according to claim 11, characterized in that The method further comprises: If the input voltage of the power conversion circuit reaches the second preset voltage and operates for a second preset time period, the at least one photovoltaic string is controlled to resume normal operation.

15. The method according to claim 11, characterized in that Each photovoltaic string in the at least one photovoltaic string includes at least two converters; and controlling the output voltage of the at least one photovoltaic string to decrease to a first preset voltage specifically includes: The output voltage of each converter in the at least one photovoltaic string is controlled to decrease, so that the output voltage of the at least one photovoltaic string decreases to the first preset voltage.

16. The method according to claim 11, characterized in that Each photovoltaic string in the at least one photovoltaic string includes at least two converters; and the controlling the maximum value of the output current of the at least one photovoltaic string to be a first preset current specifically includes: The output current of each converter in the at least one photovoltaic string is controlled to be less than or equal to the first preset current.

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