Inverter DC side fault identification method and photovoltaic system

Abstract

The present invention discloses a method for identifying faults on the DC side of an inverter and a photovoltaic system, and belongs to the field of photovoltaic technology. The DC side of the inverter of the photovoltaic system includes: multiple photovoltaic modules, multiple trip switches, multiple solar controllers, a first bus capacitor and a second bus capacitor; the method includes: obtaining various electrical parameters on the DC side of the inverter; wherein the electrical parameters include: the output voltage of each photovoltaic module, the output current of each photovoltaic module, the voltage across the first bus capacitor and the voltage across the second bus capacitor; determining the fault type on the DC side of the inverter according to the electrical parameters; for any fault type, when the fault parameter in the fault process reaches the protection action threshold corresponding to the fault parameter, the corresponding trip switch is controlled to perform a tripping action according to the fault type. The embodiment of the present invention can more comprehensively identify the fault on the DC side of the inverter and perform fault removal, while reducing the risk of false alarms to improve the safety of the photovoltaic system.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaic technology, and in particular to a method for identifying a fault on a DC side of an inverter and a photovoltaic system. Background Art

[0002] The global share of the new energy photovoltaic industry is increasing year by year, the scale of photovoltaic power generation is expanding, and new technologies are constantly being applied in the field of photovoltaic inverters. String-type grid-connected inverters have the advantages of high energy density, small size and light weight, simple topology and easy control. They are currently widely used in the field of solar photovoltaic power generation. As the specific energy of string-type grid-connected inverters continues to increase, the current on the DC side also increases. Once a short circuit or other fault occurs, if the photovoltaic panels cannot be disconnected in time, the energy continues to be input from the photovoltaic panels into the equipment, which may cause the machine to explode or even a fire, causing a large amount of property losses. Fault identification and protection on the DC side of the inverter has become a difficult problem that all photovoltaic inverter equipment manufacturers have to face. However, the existing inverter DC side protection is mostly limited to single faults such as reverse connection, backflow or short circuit, and the extraction of fault characteristic signals is relatively complex, which is prone to false alarms under harsh working conditions on site. Summary of the invention

[0003] The present invention provides a method for identifying a fault on the DC side of an inverter and a photovoltaic system, which can more comprehensively identify a fault on the DC side of an inverter and perform fault removal, while reducing the risk of false alarms to improve the safety of the photovoltaic system.

[0004] In a first aspect, an embodiment of the present invention provides a method for identifying a fault on the DC side of an inverter, in a photovoltaic system, the DC side of the inverter includes: a plurality of photovoltaic components, a plurality of trip switches, a multi-channel solar controller, a first bus capacitor, a second bus capacitor, a first DC bus and a second DC bus; every two photovoltaic components are connected to a corresponding solar controller through a set of switch contacts in a trip switch; each solar controller is connected to the first bus capacitor and the second bus capacitor, the first DC bus is connected to the first bus capacitor, and the second DC bus is connected to the second bus capacitor;

[0005] The inverter DC side fault identification method comprises:

[0006] Acquire various electrical parameters of the DC side of the inverter; wherein the electrical parameters include: the output voltage of each photovoltaic module, the output current of each photovoltaic module, the voltage across the first bus capacitor and the voltage across the second bus capacitor;

[0007] determining a fault type on a DC side of the inverter according to the electrical parameters;

[0008] For any fault type, when the fault parameter in the fault process reaches the protection action threshold corresponding to the fault parameter, the corresponding trip switch is controlled to perform a tripping action according to the fault type.

[0009] Optionally, controlling the corresponding trip switch to perform a tripping action according to the fault type includes:

[0010] Determine the fault level according to the fault type; wherein the fault types include: photovoltaic module reverse connection fault, photovoltaic module backflow fault, single bus short circuit fault, double bus short circuit fault and solar controller short circuit fault; the single bus short circuit fault, the double bus short circuit fault and the solar controller short circuit fault are all first-level faults, and the photovoltaic module reverse connection fault and the photovoltaic module backflow fault are both second-level faults;

[0011] For the primary fault, controlling all the trip switches on the DC side of the inverter to perform a tripping action;

[0012] For the secondary fault, the trip switch connected to the failed photovoltaic assembly is controlled to perform a tripping action.

[0013] Optionally, the fault type includes: photovoltaic component reverse connection fault, and the fault parameter includes: fault energy;

[0014] Determining the fault type of the DC side of the inverter according to the electrical parameter includes:

[0015] If the output voltage of any of the photovoltaic components is less than the first fault threshold voltage, and the output current of the same photovoltaic component is less than the first fault threshold current, it is determined that there is a photovoltaic component reverse connection fault on the DC side of the inverter; wherein the first fault threshold current is a negative value;

[0016] Controlling the corresponding trip switch to perform a tripping action according to the fault type includes:

[0017] Integrate the square of the output current of the faulty photovoltaic assembly over time, and when the integral value reaches a first preset threshold, determine that the fault energy in the reverse connection fault of the photovoltaic assembly reaches its corresponding protection action threshold;

[0018] Determining whether the inverter is running;

[0019] If so, a shutdown request is issued to control the inverter to shut down, and when the maximum value of the output currents of the photovoltaic assemblies connected to the trip switch connected to the faulty photovoltaic assembly is less than the preset trip current, the trip switch connected to the faulty photovoltaic assembly is controlled to perform a tripping action;

[0020] If not, the trip switch connected to the failed photovoltaic assembly is directly controlled to perform a tripping action.

[0021] Optionally, the fault type includes: photovoltaic component backflow fault, and the fault parameter includes: fault energy;

[0022] Determining the fault type of the DC side of the inverter according to the electrical parameter includes:

[0023] If the output voltages of the two photovoltaic modules connected to any solar controller are the same, but the output currents are one positive and one negative, the negative output current is used as the reverse current;

[0024] When the reverse current exceeds the safety threshold, it is determined that there is a reverse fault of the photovoltaic assembly on the DC side of the inverter;

[0025] Controlling the corresponding trip switch to perform a tripping action according to the fault type includes:

[0026] Integrate the square of the backfeed current over time, and when the integral value reaches a second preset threshold, determine that the fault energy in the backfeed fault of the photovoltaic component reaches its corresponding protection action threshold;

[0027] Determining whether the inverter is running;

[0028] If so, a shutdown request is issued to control the inverter to shut down, and when the maximum value of the output currents of the photovoltaic assemblies connected to the trip switch connected to the photovoltaic assembly with the fault is less than the preset trip current, the trip switch connected to the photovoltaic assembly with the fault is controlled to perform a tripping action;

[0029] If not, the trip switch connected to the faulty photovoltaic assembly is directly controlled to perform a tripping action.

[0030] Optionally, the fault type includes: single bus short circuit fault, and the fault parameter includes: fault energy;

[0031] Determining the fault type of the DC side of the inverter according to the electrical parameter includes:

[0032] Calculating a voltage difference between a voltage across the first bus capacitor and a voltage across the second bus capacitor;

[0033] When the voltage difference exceeds a voltage difference threshold, it is determined that a single bus short circuit fault exists on the DC side of the inverter;

[0034] Controlling the corresponding trip switch to perform a tripping action according to the fault type includes:

[0035] The square of the voltage difference is integrated over time, and when the integral value reaches a third preset threshold, it is determined that the fault energy in the single bus short circuit fault reaches its corresponding protection action threshold, and all the trip switches on the DC side of the inverter are controlled to perform a tripping action.

[0036] Optionally, the fault type includes: single bus short circuit fault, and the fault parameters include: fault time;

[0037] Determining the fault type of the DC side of the inverter according to the electrical parameter includes:

[0038] Calculating a voltage difference between a voltage across the first bus capacitor and a voltage across the second bus capacitor;

[0039] When the voltage difference exceeds a voltage difference threshold, it is determined that a single bus short circuit fault exists on the DC side of the inverter;

[0040] Controlling the corresponding trip switch to perform a tripping action according to the fault type includes:

[0041] When the duration of the voltage difference exceeding the voltage difference threshold reaches a first preset time, it is determined that the fault time of the single bus short circuit fault reaches its corresponding protection action threshold;

[0042] Determining whether the maximum value among the output currents of the photovoltaic modules is less than a preset tripping current;

[0043] If yes, all the trip switches on the DC side of the inverter are controlled to perform a tripping action;

[0044] If not, a shutdown request is issued to control the inverter to shut down, and when the maximum value of the output currents of the photovoltaic components is less than the preset tripping current, all the tripping switches on the DC side of the inverter are controlled to perform a tripping action.

[0045] Optionally, the fault type includes: double bus short circuit fault, and the fault parameters include: fault time;

[0046] Determining the fault type of the DC side of the inverter according to the electrical parameter includes:

[0047] In each sampling period, calculating a voltage sum between a voltage across the first bus capacitor and a voltage across the second bus capacitor as a bus voltage;

[0048] When the bus voltage in the current sampling period drops by more than a preset percentage threshold compared with the bus voltage in the previous sampling period, it is determined that a double bus short circuit fault exists on the DC side of the inverter;

[0049] Controlling the corresponding trip switch to perform a tripping action according to the fault type includes:

[0050] When the duration of the bus voltage maintaining the voltage value after the drop reaches a second preset time, it is determined that the fault time of the double bus short circuit fault reaches its corresponding protection action threshold, and all the trip switches on the DC side of the inverter are controlled to perform a tripping action.

[0051] Optionally, the fault type includes: a solar controller short circuit fault, and the fault parameters include: fault time;

[0052] Determining the fault type of the DC side of the inverter according to the electrical parameter includes:

[0053] If the output voltages of the two photovoltaic modules connected to any solar controller are both less than the second fault threshold voltage, and the output currents are both greater than the second fault threshold current, it is determined that there is a short circuit fault of the solar controller on the DC side of the inverter; wherein the second fault threshold current is a positive value;

[0054] Controlling the corresponding trip switch to perform a tripping action according to the fault type includes:

[0055] When the output voltages of the two photovoltaic modules connected to the solar controller are both lower than the second fault threshold voltage, and the duration of the output currents being higher than the second fault threshold current reaches a third preset time, it is determined that the fault time of the short-circuit fault of the solar controller reaches its corresponding protection action threshold, and all the trip switches on the DC side of the inverter are controlled to perform a tripping action.

[0056] In a second aspect, an embodiment of the present invention further provides a photovoltaic system, including:

[0057] A plurality of photovoltaic modules, a plurality of trip switches and a multi-channel solar controller; wherein every two photovoltaic modules are connected to a solar controller via a set of switch contacts in a trip switch; and at least one set of switch contacts is provided in a trip switch;

[0058] A first bus capacitor, a second bus capacitor, a first DC bus and a second DC bus; the first end of the first bus capacitor is connected to the first output end of each solar controller, the second end of the first bus capacitor and the first end of the second bus capacitor are both connected to the neutral point of each solar controller, and the second end of the second bus capacitor is connected to the second output end of each solar controller; the first DC bus is connected to the first end of the first bus capacitor, and the second DC bus is connected to the second end of the second bus capacitor;

[0059] An inverter, wherein a first input terminal and a second input terminal of the inverter are respectively connected to the first DC bus and the second DC bus;

[0060] A sampling module, used for collecting the output voltage of each photovoltaic assembly, the output current of each photovoltaic assembly, the voltage across the first bus capacitor and the voltage across the second bus capacitor;

[0061] A controller is connected to the sampling module and each of the trip switches, and the controller is used to execute the inverter DC side fault identification method provided by any embodiment of the present invention.

[0062] Optionally, the photovoltaic system further includes: a bypass circuit, respectively connecting the first DC bus, the second DC bus and the controller; the controller is also used to control the bypass circuit to discharge the first bus capacitor and the second bus capacitor after controlling all the trip switches on the DC side of the inverter to trip in the event of a primary fault.

[0063] In the inverter DC side fault identification method provided by the embodiment of the present invention, by acquiring a variety of electrical parameters on the inverter DC side, the fault feature collection of different key nodes on the inverter DC side can be fully realized to achieve accurate and comprehensive fault type discrimination. In addition, after determining the fault type, by further collecting the fault parameters and judging whether the fault parameters reach the protection action threshold, it can be confirmed whether the fault has actually occurred, so as to avoid false alarms and false actions as much as possible. And, when it is determined that the fault parameters reach the protection action threshold, the embodiment of the present invention also controls the corresponding trip switch to perform the tripping action, and disconnects the faulty equipment from the normal equipment in time, so as to avoid further spread of the fault. In summary, compared with the prior art, the embodiment of the present invention provides a comprehensive inverter DC side fault identification and protection method, which can more comprehensively identify the inverter DC side fault and perform fault removal, while reducing the risk of false alarms to improve the safety of the photovoltaic system.

[0064] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0066] Figure 1 is a schematic structural diagram of a photovoltaic system provided by an embodiment of the present invention;

[0067] Figure 2 It is a flow chart of a method for identifying a DC side fault of an inverter provided by an embodiment of the present invention;

[0068] Figure 3 This is a schematic diagram of a photovoltaic module reverse connection fault identification process provided by an embodiment of the present invention;

[0069] Figure 4 This is a schematic diagram of a photovoltaic module backflow fault identification process provided by an embodiment of the present invention;

[0070] Figure 5 This is a schematic diagram of a single busbar short circuit fault identification process provided by an embodiment of the present invention;

[0071] Figure 6 It is another schematic diagram of a single bus short circuit fault identification process provided by an embodiment of the present invention;

[0072] Figure 7 It is a schematic diagram of a double busbar short circuit fault identification process provided by an embodiment of the present invention;

[0073] Figure 8 It is a schematic diagram of a short-circuit fault identification process of a solar controller provided by an embodiment of the present invention;

[0074] Fig. 9 It is a schematic diagram of the structure of another photovoltaic system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0075] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0076] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions.

[0077] The embodiment of the present invention provides a method for identifying a DC side fault of an inverter, which can be applied to comprehensively identify and actively remove a DC side fault of a string-type grid-connected inverter, and the method can be executed by a controller in a photovoltaic system. In order to better explain the fault identification method, the structure of the DC side of the inverter in the photovoltaic system is first roughly described below.

[0078] Figure 1 is a schematic structural diagram of a photovoltaic system provided by an embodiment of the present invention, Figure 1 The DC side topology of a string grid-connected inverter is given as an example. Figure 1 The inverter DC side includes: a plurality of photovoltaic (PV) modules, a plurality of trip switches 20, a multi-channel solar controller 30, a first bus capacitor C1, a second bus capacitor C2, a first DC bus BUS1 and a second DC bus BUS2.

[0079] Wherein, every two photovoltaic modules are connected to a solar controller 30 through a set of switch contacts in a trip switch 20, forming a photovoltaic string. The photovoltaic system may include multiple photovoltaic strings, and each photovoltaic string may include the same structure. Figure 1 A photovoltaic string is given as an example for explanation. For the convenience of explanation, the two photovoltaic components in one photovoltaic string are respectively marked as the first photovoltaic component PV1 and the second photovoltaic component PV2, and a group of switch contacts in the trip switch 20 include the first switch S1 and the second switch S2. Specifically, the positive pole of the first photovoltaic component PV1 and the positive pole of the second photovoltaic component PV2 are both connected to the first end of the first switch S1, and the second end of the first switch S1 is connected to the first input end of the solar controller 30; the negative pole of the first photovoltaic component PV1 and the negative pole of the second photovoltaic component PV1 are respectively connected to the first end and the second end of the second switch S2, and the second end of the second switch S2 is also connected to the second input end of the solar controller 30. A photovoltaic component may include at least one photovoltaic panel. In order to ensure the operational safety of the photovoltaic component, bypass diodes can be connected in parallel at both ends of each photovoltaic component, for example Figure 1 The solar controller 30 may include a BOOST circuit, for example, a BOOST circuit with a three-level topology structure including a flying capacitor Cfly, based on the coordinated control of the first transistor Q1, the second transistor Q2, the inductor, each capacitor and each diode, to form an MPPT (Maximum Power Point Tracking) solar controller.

[0080] Exemplarily, at least one group of switch contacts is provided in a trip switch 20, and each group of switch contacts is connected to a solar controller 30. The output ends of each solar controller 30 share a first bus capacitor C1 and a second bus capacitor C2. For example, the first output end of each solar controller 30 is connected to the first end of the first bus capacitor C1 and the first DC bus BUS1; the second output end of each solar controller 30 is connected to the second end of the second bus capacitor C2 and the second DC bus BUS2; the neutral point of each solar controller 30 is connected to the second end of the first bus capacitor C1 and the first end of the second bus capacitor C2. The first DC bus BUS1 and the second DC bus BUS2 serve as the bus of the DC side input end of the inverter, for example, they are respectively connected to the first input end and the second input end of the inverter in the photovoltaic system.

[0081] To implement the method, a sampling module and a controller 10 are also provided in the photovoltaic system. Figure 1 The sampling range of the sampling module is exemplarily represented by a dotted line frame, and the sampling module is used to collect various electrical parameters on the DC side of the inverter, such as the output voltage of each photovoltaic module, the output current of each photovoltaic module, the voltage across the first bus capacitor C1, and the voltage across the second bus capacitor C2. The controller 10 is connected to the sampling module and each trip switch 20 respectively, and is used to execute the inverter DC side fault identification method, perform fault identification according to various electrical parameters, and control the working state of each trip switch 20 accordingly.

[0082] The following is an explanation of the inverter DC side fault identification method provided by an embodiment of the present invention. Figure 2 It is a flow chart of a method for identifying a DC side fault of an inverter provided by an embodiment of the present invention.

[0083] See also Figure 2 , the inverter DC side fault identification method comprises the following steps:

[0084] S110, obtaining various electrical parameters of the DC side of the inverter; wherein the electrical parameters include: the output voltage of each photovoltaic module, the output current of each photovoltaic module, the voltage across the first bus capacitor, and the voltage across the second bus capacitor.

[0085] The sampling module can collect various electrical parameters in real time based on a preset sampling frequency. For example, each voltage parameter can be collected based on a corresponding voltage sensor, and each current parameter can be collected based on a corresponding current sensor. The controller can obtain various electrical parameters through the sampling module when necessary.

[0086] S120: Determine the fault type on the DC side of the inverter according to the electrical parameters.

[0087] Among them, the fault types may specifically include PV module reverse connection fault, PV module backflow fault, single bus short circuit fault, double bus short circuit fault and solar controller short circuit fault. The types of electrical parameters and / or fault characteristic values ​​corresponding to the electrical parameters used to diagnose different fault types are different. By analyzing the measured values ​​of various electrical parameters and the relationship between the measured values ​​of different types of electrical parameters, comprehensive fault diagnosis of the inverter DC side can be performed to determine the cause and location of the fault, which is conducive to rapid fault removal and equipment maintenance.

[0088] S130. For any fault type, when the fault parameter in the fault process reaches the protection action threshold corresponding to the fault parameter, the corresponding trip switch is controlled to perform a tripping action according to the fault type.

[0089] Among them, different fault parameters can be used for measurement for different fault types, for example: whether the measurable fault energy in the photovoltaic module reverse connection fault and photovoltaic module backflow fault reaches the energy threshold; whether the measurable fault time in the single bus short circuit fault, double bus short circuit fault and solar controller short circuit fault reaches the time threshold; the specific protection action threshold corresponding to different fault types can be set according to the actual situation. For example, when the fault is serious and the impact is large, the protection action threshold can be set smaller accordingly to control the corresponding trip switch to trip as soon as possible and complete the active removal protection action. Setting the protection action threshold here is equivalent to setting the protection action condition. When the fault parameter reaches the corresponding protection action threshold, it indicates that this type of fault has indeed occurred and is continuing. At this time, the trip switch related to this type of fault is controlled to remove the faulty equipment, which can effectively avoid fault misjudgment caused by sampling errors or changes in environmental conditions. At the same time, by reasonably setting the protection action threshold, the fault removal speed can be guaranteed, the fault circuit can be reliably disconnected, the protection effect can be guaranteed, and the fault range can be avoided from spreading and the impact can be expanded.

[0090] In the inverter DC side fault identification method provided by the embodiment of the present invention, by acquiring a variety of electrical parameters on the inverter DC side, the fault feature collection of different key nodes on the inverter DC side can be fully realized to achieve accurate and comprehensive fault type discrimination. In addition, after determining the fault type, by further collecting the fault parameters and judging whether the fault parameters reach the protection action threshold, it can be confirmed whether the fault has actually occurred, so as to avoid false alarms and false actions as much as possible. And, when it is determined that the fault parameters reach the protection action threshold, the embodiment of the present invention also controls the corresponding trip switch to perform the tripping action, and disconnects the faulty equipment from the normal equipment in time, so as to avoid further spread of the fault. In summary, compared with the prior art, the embodiment of the present invention provides a comprehensive inverter DC side fault identification and protection method, which can more comprehensively identify the inverter DC side fault and perform fault removal, while reducing the risk of false alarms to improve the safety of the photovoltaic system.

[0091] On the basis of the above-mentioned embodiments, the fault levels corresponding to different fault types can be optionally pre-set according to the severity of the fault, and the response speed and fault removal range can be set based on different fault levels, so as to disconnect the faulty equipment from the photovoltaic panel in time and cut off the energy input to avoid secondary failure. For example, single bus short circuit fault, double bus short circuit fault and solar controller short circuit fault are all first-level faults, and the fault range affects the entire DC side; photovoltaic module reverse connection fault and photovoltaic module backflow fault are both second-level faults, and the fault range only affects the photovoltaic string where the faulty photovoltaic module is located.

[0092] Then, in S130, controlling the corresponding trip switch to perform a tripping action according to the fault type may include the following steps:

[0093] 1) Determine the fault level according to the fault type.

[0094] 2) Determine the removal range according to the fault level.

[0095] Specifically, for a primary fault, all the trip switches on the DC side of the inverter can be controlled to perform a tripping action to cut off the energy input of the inverter and protect the photovoltaic panels in each photovoltaic module. For a secondary fault, the trip switches connected to the faulty photovoltaic module can be controlled to perform a tripping action.

[0096] From the above analysis, it can be seen that there are many types of faults on the DC side of the inverter. The fault-related electrical parameters corresponding to various fault types, the fault judgment method, the fault parameters that need to be measured during the fault process, and the protection action thresholds corresponding to the fault parameters may all be different. The identification and protection processes of various types of faults are described separately below, but this is not intended to limit the present invention.

[0097] In one implementation, optionally, the fault type includes: a photovoltaic component reverse connection fault, and the fault parameter includes: a fault energy. Figure 3 is a schematic diagram of a photovoltaic module reverse connection fault identification process provided by an embodiment of the present invention. Figure 3 The process of identifying whether the k-th photovoltaic module has a reverse connection fault is given as an example, where k is a positive integer, and the reverse connection fault identification of each photovoltaic module can adopt this process. Figure 3 , the identification and protection process of PV module reverse connection fault includes:

[0098] S201, determine whether the tripping is enabled? If yes, execute S202; if no, end the fault identification.

[0099] This step is, for example, to detect the communication status between the controller and the trip switch, and to detect whether the controller can normally control the trip switch to perform a tripping action so that each switch is disconnected to ensure that subsequent processes can be carried out reliably.

[0100] S202: Initialize the integrator.

[0101] In this process, the fault energy is characterized based on the integration of the square of the fault current over time. The integrator may be an integral calculation component in the controller, and the integrator may be initialized before each integration.

[0102] S203. Determine whether VPVk≤V1&&IPVk≤I1. If yes, execute S204; if no, return to execute S202.

[0103] Where VPVk represents the output voltage of the kth PV module, IPVk represents the output current of the kth PV module, V1 is the first fault threshold voltage, and I1 is the first fault threshold current. When the positive and negative poles of the PV module are connected in reverse, its electric energy flows through the bypass diode. The fault is manifested in electrical parameters as follows: the output voltage suddenly drops below a certain value, and the output current reverses, that is, the output current is negative. Figure 1 For any photovoltaic string, when the first switch S1 and the second switch S2 are both closed, the first photovoltaic component PV1 and the second photovoltaic component PV2 are in parallel, and the output voltages of the two are the same; for the same photovoltaic string, the reverse connection fault can be divided into two categories: a single photovoltaic component is reversed and all photovoltaic components are reversed. When a single photovoltaic component is reversed, for example, the first photovoltaic component PV1 is reversed, the electric energy of the first photovoltaic component PV1 flows through the first bypass diode Dpv1. At this time, the first photovoltaic component PV1 is equivalent to the load of the second photovoltaic component PV2. The second photovoltaic component PV2 supplies power to the solar controller 30. Compared with the situation where both photovoltaic components supply power to the solar controller 30, the output voltage of the photovoltaic component will decrease, and for the first photovoltaic component PV1, the current flowing through it is reversed. When both photovoltaic components are reversed, the electric energy of the two photovoltaic components PV2 flows through the corresponding bypass diodes. At this time, the output voltages of the two photovoltaic components both decrease, and the currents are reversed. In summary, when any type of photovoltaic module reverse connection fault occurs, the output voltage of the faulty photovoltaic module will drop and the output current will reverse; based on this, the first fault threshold voltage V1 can be set to a smaller positive value, and the first fault threshold current I1 can be set to a negative value with a smaller absolute value.

[0104] This step is equivalent to determining that there is a photovoltaic component reverse connection fault on the DC side of the inverter and the kth photovoltaic component is a faulty component when the output voltage VPVk of the kth photovoltaic component is less than the first fault threshold voltage V1 and the output current IPVk of the kth photovoltaic component is less than the first fault threshold current I1.

[0105] S204, IPvk 2 Integrate over time.

[0106] This step is: integrating the square of the output current of the failed photovoltaic module over time.

[0107] S205. Is the integral value ≥ Nmax1? If yes, execute S206; if no, return to execute S203.

[0108] Among them, Nmax1 is a first preset threshold value, and its value can be set according to the protection requirements of the reverse connection fault of the photovoltaic module.

[0109] Exemplarily, the judgment of this step can be performed once every sampling cycle or every several sampling cycles. When the integral value reaches the first preset threshold value Nmax1, it can be determined that the fault energy in the reverse connection fault of the photovoltaic component reaches its corresponding protection action threshold, and the subsequent protection action is controlled to be executed. When the integral value does not reach the first preset threshold value Nmax1, return to S203 to determine whether the electrical parameters in the next sampling cycle still meet the characteristics of the reverse connection fault of the photovoltaic component; if so, continue to accumulate integrals; if not, jump out of the integration, initialize the integrator, and clear the integral value to prevent misjudgment and misoperation.

[0110] S206, determine whether the inverter is running; if so, execute S207; if not, execute S208.

[0111] The controller may include a communication terminal for communicating with the inverter and a main control platform in the photovoltaic system. The controller may obtain the operating status of the entire machine through the communication terminal and confirm whether the inverter is running.

[0112] If the inverter is not running, the trip switch connected to the faulty PV module can be directly controlled to perform a tripping action.

[0113] If the inverter is in operation, a shutdown request is first issued to control the inverter to shut down, and wait for the output current of each photovoltaic module to decrease. When the maximum output current of each photovoltaic module connected to the trip switch connected to the faulty photovoltaic module is less than the preset trip current, the trip switch connected to the faulty photovoltaic module is controlled to perform the tripping action to avoid arcing during the tripping process as much as possible, which may cause fire problems. Among them, the preset tripping current is the safe current threshold at which the trip switch can not produce arcing when tripping, which can be set according to the working characteristics of the trip switch.

[0114] S207, protection shutdown.

[0115] That is, a shutdown request is issued to control the inverter to shut down.

[0116] S208, reporting the reverse connection fault of the photovoltaic module; controlling the trip switch connected to PVk to trip.

[0117] Wherein, PVk is the kth photovoltaic module. While controlling the trip switch to trip, the controller can issue corresponding alarms such as sound, light, and text based on the fault type, and upload the alarm information to the main control platform of the photovoltaic system. In addition, the controller can upload the electrical parameters related to the fault to the main control platform for drawing and display.

[0118] This embodiment implements intelligent identification and protection of photovoltaic module reverse connection faults through S201-S208 based on the fault characteristics of the photovoltaic module reverse connection fault and combined with the safety shutdown logic judgment.

[0119] In another implementation, optionally, the fault type includes: photovoltaic component backflow fault, and the fault parameter includes: fault energy. Figure 4 The present invention provides a schematic diagram of a photovoltaic module backfeed fault identification process. Figure 4 The process of identifying whether the photovoltaic string where the k-th photovoltaic module is located has a backfeed fault is given as an example, k is a positive integer, and the backfeed fault identification of each photovoltaic string can adopt this process. Figure 4 , the identification and protection process of photovoltaic module backflow fault includes:

[0120] S301, determine whether the tripping is enabled? If yes, execute S302; if no, end the fault identification.

[0121] The explanation of this step can be found in S201 and will not be repeated here.

[0122] S302: Initialize the integrator.

[0123] The explanation of this step can be found in S202 and will not be repeated here.

[0124] S303. Determine whether VPVk≥V0&&IPVk≤I0. If yes, execute S304; if no, return to execute S302.

[0125] Wherein, V0 is the third fault threshold voltage, and I0 is the third fault threshold current. For any photovoltaic string, when a photovoltaic component backflow fault occurs, that is, the connection methods of the first photovoltaic component PV1 and the second photovoltaic component PV2 are correct, but the output voltage of one photovoltaic component is greater than the output voltage of the other photovoltaic component, and there is a potential difference, so that a backflow loop is formed between the first photovoltaic component PV1 and the second photovoltaic component PV2. At this time, the fault characteristics of the photovoltaic string in terms of electrical parameters are as follows: the output voltage of the photovoltaic component increases, and the output current of one photovoltaic component is negative.

[0126] Based on this, the third fault threshold voltage V0 can be set to a larger positive value; and the third fault threshold current can be set to a negative value. In this step, when the k-th photovoltaic component satisfies VPVk≥V0&&IPVk≤I0, it can be determined that there is a backflow fault in the photovoltaic string where the k-th photovoltaic component is located.

[0127] Alternatively, this step can be replaced by the following steps:

[0128] For any PV string:

[0129] First, determine whether the following situation exists: the output voltages of the two PV modules in the PV string are the same, but the output currents of the two PV modules are one positive and one negative; if so, the negative output current is used as the reverse current.

[0130] Then determine whether the reverse current exceeds the safety threshold; if so, it is determined that there is a reverse fault of the photovoltaic components on the DC side of the inverter, and the photovoltaic string is a faulty string; if not, the protection does not operate.

[0131] The safety threshold may be a third fault threshold current I0, which may be specifically set according to the characteristics of the photovoltaic module.

[0132] S304: Integrate the square of the reverse current over time.

[0133] S305. Is the integral value ≥ Nmax2? If yes, execute S306; if no, return to execute S303.

[0134] Among them, Nmax2 is a second preset threshold value, and its value can be set according to the protection requirements of the photovoltaic component backfeed fault.

[0135] Exemplarily, this step is equivalent to determining whether the fault energy in the photovoltaic component backfeed fault has reached its corresponding protection action threshold. The relevant explanations of S305-S308 can refer to the explanations of S205-S208, and will not be repeated here.

[0136] S306, determine whether the inverter is running; if so, execute S307; if not, execute S308.

[0137] S307, protection shutdown.

[0138] S308, reporting the reverse connection fault of the photovoltaic module; controlling the trip switch connected to PVk to trip.

[0139] This embodiment implements intelligent identification and protection of photovoltaic module backfeeding faults through S301-S308 based on the fault characteristics of photovoltaic module backfeeding faults and combined with safety shutdown logic judgment.

[0140] In yet another embodiment, optionally, the fault type includes: a single bus short circuit fault (or half-BUS short circuit fault), and the fault parameter includes: fault energy. Figure 5 Schematic diagram of a single busbar short circuit fault identification process provided by an embodiment of the present invention. Figure 5 , the identification and protection process of single busbar short circuit fault includes:

[0141] S401: Determine whether the tripping is enabled. If yes, execute S402; if no, end the fault identification.

[0142] The explanation of this step can be found in S201 and will not be repeated here.

[0143] S402: Initialize the integrator.

[0144] In this process, the fault energy is characterized based on the integration of the square of the fault voltage over time. The integrator may be an integral calculation component in the controller, and the integrator may be initialized before each integration.

[0145] S403. Determine whether the voltage difference is ≥ △Vmax. If yes, execute S404; if no, return to execute S402.

[0146] Wherein, △Vmax is a voltage difference threshold, and the voltage difference is a voltage difference between a voltage across the first bus capacitor and a voltage across the second bus capacitor. Exemplarily, in the calculation process, the voltage across the first bus capacitor and the voltage across the second bus capacitor may be subtracted from the larger of the two to obtain a positive voltage difference, or the absolute value of the voltage difference may be directly used for the determination in S403.

[0147] When both DC buses are normal, the voltage across the first bus capacitor is basically the same as the voltage across the second bus capacitor, and the voltage difference is close to 0; when either DC bus is short-circuited, the voltage difference increases. Based on this fault characteristic, the value of the voltage difference threshold △Vmax can be reasonably set. When the voltage difference exceeds the voltage difference threshold △Vmax, it can be determined that there is a single bus short-circuit fault on the DC side of the inverter.

[0148] S404: Integrate the square of the voltage difference over time.

[0149] S405. Is the integral value ≥ Nmax3? If yes, execute S406; if no, return to execute S403.

[0150] Among them, Nmax3 is the third preset threshold value, and its value can be set according to the protection requirement of single bus short circuit fault.

[0151] Exemplarily, the judgment of this step can be performed once every sampling cycle or every several sampling cycles. This step is equivalent to judging whether the fault energy in the single bus short circuit fault reaches its corresponding protection action threshold. If so, all the trip switches on the DC side of the inverter are directly controlled to perform the tripping action; if not, return to S403 to judge whether the electrical parameters in the next sampling cycle still meet the characteristics of the single bus short circuit fault; if so, continue to accumulate points; if not, jump out of the integration, initialize the integrator, and clear the integral value to prevent misjudgment and misoperation.

[0152] S406, report busbar short circuit fault; control all trip switches to trip.

[0153] This embodiment implements intelligent identification and protection of single bus short-circuit faults based on the fault characteristics of the single bus short-circuit faults through S401-S406.

[0154] The above implementation provides a protection process for a single bus short circuit fault measured by fault energy, but this is not intended to be a limitation of the present invention. In other implementations, optionally, the fault time can also be selected as a fault parameter in a single bus short circuit fault to determine when to start protection. Figure 6 FIG. 1 is another schematic diagram of a single busbar short circuit fault identification process provided by an embodiment of the present invention. Figure 6 In another embodiment, optionally, the single bus short circuit fault identification and protection process includes:

[0155] S501: Determine whether the tripping is enabled. If yes, execute S502; if no, end the fault identification.

[0156] The explanation of this step can be found in S201 and will not be repeated here.

[0157] S502, m=0; i=1.

[0158] This step is equivalent to initializing the timing parameters: m represents the number of sampling cycles for which fault time timing has been performed; i represents the sampling cycle count in the current timing cycle.

[0159] S503. Determine whether the voltage difference is ≥ △Vmax. If yes, execute S504; if no, return to execute S502.

[0160] The explanation of this step can be found in S403 and will not be repeated here.

[0161] S504, m=i++.

[0162] The following operations can be performed in this step: firstly, perform fault timing, and execute: m=i; then update the sampling cycle count, and execute i=i+1.

[0163] S505. Determine whether m≥m1. If yes, execute S506; if no, return to execute S503.

[0164] Among them, m1 is the number of sampling cycles corresponding to the first preset time, and its value can be set according to the protection requirements of the single bus short circuit fault. This step is equivalent to determining whether the fault time in the single bus short circuit fault reaches its corresponding protection action threshold. For relevant explanations, please refer to the explanation in S405 and will not be repeated here.

[0165] S506. Determine whether IPVmax is less than Iref. If so, execute S507; if not, execute S508.

[0166] Among them, IPVmax is the maximum value of the output current of each photovoltaic module, and Iref is the preset tripping current. This step is equivalent to judging whether the tripping can be performed safely. If so, all the tripping switches on the DC side of the inverter can be directly controlled to perform the tripping action; if not, a shutdown request is issued to control the inverter to shut down. When the maximum value of the output current of each photovoltaic module is less than the preset tripping current, all the tripping switches on the DC side of the inverter are controlled to perform the tripping action.

[0167] S507, report busbar short circuit fault; control all trip switches to trip.

[0168] The explanation of the controller fault report can be found in S208 and will not be repeated here.

[0169] S508, protection shutdown.

[0170] This embodiment provides another intelligent identification and protection process for a single bus short-circuit fault through S501-S508.

[0171] In yet another embodiment, optionally, the fault type includes: a double bus short circuit fault (or a whole BUS short circuit fault), and the fault parameters include: fault time. Figure 7 FIG. 1 is a schematic diagram of a double busbar short circuit fault identification process provided by an embodiment of the present invention. Figure 7 , the identification and protection process of double busbar short circuit fault includes:

[0172] S601: Determine whether the tripping is enabled. If yes, execute S602; if no, end the fault identification.

[0173] The explanation of this step can be found in S201 and will not be repeated here.

[0174] S602, m=0; i=1.

[0175] The explanation of this step can be found in S502 and will not be repeated here.

[0176] S603: Determine whether the bus voltage drop exceeds a preset percentage threshold. If yes, execute S604; if no, return to execute S602.

[0177] Among them, in each sampling period, the voltage sum between the voltage across the first bus capacitor and the voltage across the second bus capacitor can be calculated as the bus voltage. The difference between the bus voltage of the current sampling period and the bus voltage of the previous sampling period is calculated, and the bus voltage of the previous sampling period is used as a reference. When the bus voltage of the current sampling period drops by more than a preset percentage threshold (for example, 50%, which can be adjusted according to actual conditions) compared with the bus voltage in the previous sampling period, it can be determined that there is a double bus short circuit fault on the DC side of the inverter.

[0178] S604, m=i++; control the inverter to reduce output power according to the maximum step length.

[0179] In this step, m=i can be executed first, and then i=i+1 can be executed. Since the impact of the entire BUS short-circuit fault is relatively large, when the fault is determined to exist, the inverter can be controlled to reduce power to minimize the impact of the fault; if the subsequent electrical parameters continue to indicate a fault, the trip switch can be controlled to operate after a short delay.

[0180] S605. Determine whether m≥m2. If yes, execute S606; if no, return to execute S603.

[0181] Among them, m2 is the second preset time, and its value can be set according to the protection requirements of the double bus short circuit fault. This step is equivalent to determining whether the fault time of the double bus short circuit fault reaches its corresponding protection action threshold. If so, all the trip switches on the DC side of the inverter are immediately controlled to perform the tripping action; if not, return to execute S603. Among them, when S603 is executed again, the bus voltage of a sampling period before the first judgment that the bus voltage drops by more than the preset percentage threshold can be used as a reference value, that is, the same reference voltage is used as the sampling period in the current timing cycle when the bus voltage drops for the first time. In other words, in S605, it is to determine whether the voltage value of the bus voltage after the drop remains unchanged for the second preset time without rising again.

[0182] S606, report double bus short circuit fault; control all trip switches to trip.

[0183] This embodiment implements intelligent identification and protection of double bus short circuit faults based on the fault characteristics of the double bus short circuit faults through S601-S606.

[0184] In yet another embodiment, optionally, the fault type includes: a solar controller short circuit fault, and the fault parameter includes: a fault time. Figure 8 1 is a schematic diagram of a solar controller short circuit fault identification process provided by an embodiment of the present invention. Figure 8 , the identification and protection process of solar controller short circuit fault includes:

[0185] S701: Determine whether the tripping is enabled. If yes, execute S702; if no, end the fault identification.

[0186] The explanation of this step can be found in S201 and will not be repeated here.

[0187] S702, m=0; i=1.

[0188] The explanation of this step can be found in S502 and will not be repeated here.

[0189] S703: Determine whether the input PV voltage of a certain MPPT drops at the same time and the PV current rises at the same time? If yes, execute S704; if no, return to execute S702.

[0190] Among them, MPPT represents the solar controller, PV voltage represents the output voltage of any photovoltaic module connected to the solar controller, and PV current represents the output current of any photovoltaic module connected to the solar controller. In this step, the PV voltage and PV current of the previous sampling cycle can be used as a reference to determine the changes in the PV voltage and PV current in the current sampling cycle.

[0191] like Figure 1 As shown, for any photovoltaic string, when the solar controller 30 is short-circuited, for example, the first transistor Q1 and the second transistor Q2 are both short-circuited, causing the upper and lower bridges to be directly connected, the output voltages of the first photovoltaic component PV1 and the second photovoltaic component PV2 will also be extremely small, and the output currents will be approximately equal to the short-circuit current of the solar panel.

[0192] This step can be replaced by the following steps: Determine whether the following situation exists: the output voltages of the two photovoltaic modules connected to any solar controller are both less than the second fault threshold voltage, and the output currents are both greater than the second fault threshold current; wherein the second fault threshold voltage can be a small positive value, and the second fault threshold current is a large positive value, close to the current when the solar panel in the photovoltaic module is short-circuited. If so, it can be determined that a solar controller short-circuit fault occurs on the DC side of the inverter, and the solar controller in the photovoltaic string is a faulty solar controller.

[0193] S704, m=i++.

[0194] The explanation of this step can be found in S504 and will not be repeated here.

[0195] S705. Determine whether m≥m3. If yes, execute S706; if no, return to execute S703.

[0196] Among them, m3 is the third preset time, and its value can be set according to the protection requirements of the short-circuit fault of the solar controller. This step is equivalent to determining whether the fault time of the short-circuit fault of the solar controller reaches its corresponding protection action threshold. If so, all trip switches on the DC side of the inverter are immediately controlled to perform the tripping action; if not, return to execute S703.

[0197] When S703 is executed again, the same reference PV voltage and reference PV current as those used in the current timing cycle when the PV voltage drops and the PV current rises for the first time can be used. In other words, in S705, it is determined whether the duration after the output voltages of the two photovoltaic modules connected to the solar controller both drop and the output currents both rise reaches a third preset time.

[0198] S706: Report short circuit fault of solar controller; control all trip switches to trip.

[0199] This embodiment implements intelligent identification and protection of a solar controller short-circuit fault through S701-S706 based on the fault characteristics of the solar controller short-circuit fault.

[0200] In summary, the embodiments of the present invention can realize the identification and active removal functions of various faults by real-time acquisition of various electrical parameter signals on the DC side of the string-type grid-connected inverter. Specifically, based on the output voltage and output current of the photovoltaic module, PV reverse connection fault (i.e. photovoltaic module reverse connection fault), PV backflow fault (i.e. photovoltaic module backflow fault) and flying capacitor BOOST short circuit fault (i.e. solar controller short circuit fault) can be identified; based on the voltage across the first bus capacitor and the voltage across the second bus capacitor, bus voltage sampling can be realized to identify half-BUS short circuit fault and full BUS short circuit fault. After the controller identifies the fault according to the sampling signal, it controls the trip switch to perform tripping, disconnects the faulty equipment from the photovoltaic panel, and realizes protection.

[0201] The embodiment of the present invention also provides a photovoltaic system, which can apply the inverter DC side fault identification method provided by any embodiment of the present invention, and has corresponding beneficial effects. Exemplarily, the photovoltaic system may include: an inverter, multiple photovoltaic modules, multiple trip switches, a multi-channel solar controller, a first bus capacitor, a second bus capacitor, a first DC bus, a second DC bus, a sampling module and a controller. The controller is used to execute the inverter DC side fault identification method. Among them, the connection relationship between the above-mentioned devices can be referred to the explanation related to the photovoltaic system structure in the above-mentioned embodiments, which will not be repeated here.

[0202] Exemplarily, sampling circuits related to at least some parameters such as voltage, current, sound, light, dust, temperature, humidity and heat can be set in the sampling module as needed. The controller can be provided with a sampling unit, connected to the sampling module through an ADC interface, for obtaining the signal output by the sampling module; a communication circuit, communicating with the main control platform of the photovoltaic system through the communication interface; a trip control circuit, connected to each trip switch through an IO interface, for controlling the working state of each trip switch; and a main control unit, connected to other functional units in the controller, for realizing functions such as data processing and calculation in the inverter DC side fault identification method, and executing the fault identification and removal algorithm.

[0203] Exemplarily, the controller may be a DSP, or other logic controller including sampling, IO and other peripherals, such as a single-chip microcomputer, MCU and ARM.

[0204] For example, in addition to the above-mentioned devices, the photovoltaic system may also include components such as a photovoltaic shutoff box, a DC reverse switching circuit, a drive circuit, a system control circuit, an output filter circuit and a power grid to achieve photovoltaic power generation.

[0205] The following problems also exist in the prior art: most of the existing trip switches do not have the ability to extinguish arcs, and when the fault current is large, they are disconnected, which may cause arcing and fire. In response to the above problems, the embodiments of the present invention also set a bypass circuit on the DC side of the inverter, which can avoid arcing accidents caused by load tripping to a certain extent, thereby improving the safety of the system. Fig. 9 is a schematic diagram of the structure of another photovoltaic system provided by an embodiment of the present invention. Fig. 9, exemplarily, the bypass circuit 40 is respectively connected to the first DC bus BUS1, the second DC bus BUS2 and the controller (e.g., DSP 101). The controller is also used to control the bypass circuit 40 to operate after all the trip switches 20 on the DC side of the inverter are controlled to trip in the event of a primary fault, so as to discharge the first bus capacitor C1 and the second bus capacitor C2, bypass the inverter, avoid the arcing phenomenon generated during high current tripping, and enable each trip switch 20 to trip safely. Exemplarily, the bypass circuit 40 can be a bypass chopper circuit; the controller can be connected to the bypass circuit 40 through the GPIO interface to control the working state of the bypass circuit 40.

[0206] Exemplarily, the sampling module and controller are installed in the BOOST circuit of the photovoltaic inverter and used in conjunction with the internal circuit of the inverter. In addition, the technology can also be applied to other DCDC products with BOOST topology, such as off-grid inverters and other similar BOOST topology circuits, after adaptive adjustment.

[0207] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the present invention can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of the present invention can be achieved, and this document does not limit this.

[0208] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for identifying a fault on the DC side of an inverter, characterized in that: In a photovoltaic system, the DC side of the inverter includes: a plurality of photovoltaic components, a plurality of trip switches, a multi-channel solar controller, a first bus capacitor, a second bus capacitor, a first DC bus and a second DC bus; every two photovoltaic components are connected to a corresponding solar controller through a set of switch contacts in a trip switch; each solar controller is connected to the first bus capacitor and the second bus capacitor, the first DC bus is connected to the first bus capacitor, and the second DC bus is connected to the second bus capacitor; The inverter DC side fault identification method comprises: Acquire various electrical parameters of the DC side of the inverter; wherein the electrical parameters include: the output voltage of each photovoltaic module, the output current of each photovoltaic module, the voltage across the first bus capacitor and the voltage across the second bus capacitor; determining a fault type on a DC side of the inverter according to the electrical parameters; For any fault type, when the fault parameter in the fault process reaches the protection action threshold corresponding to the fault parameter, the corresponding trip switch is controlled to perform a tripping action according to the fault type; the fault parameter includes fault energy or fault time; for any fault type whose fault parameter is the fault energy, the fault energy is the integral of the square of the fault voltage or the fault current over time; the fault types include: photovoltaic component reverse connection fault, photovoltaic component backflow fault, single bus short circuit fault, double bus short circuit fault and solar controller short circuit fault; the fault parameters corresponding to the photovoltaic component reverse connection fault include fault energy; the fault parameters corresponding to the photovoltaic component backflow fault include fault energy; the fault parameters corresponding to the single bus short circuit fault include fault energy or fault time; the fault parameters corresponding to the double bus short circuit fault include fault time; the fault parameters corresponding to the solar controller short circuit fault include fault time.

2. The inverter DC side fault identification method according to claim 1, characterized in that: Controlling the corresponding trip switch to perform a tripping action according to the fault type includes: Determine the fault level according to the fault type; wherein the single bus short circuit fault, the double bus short circuit fault and the solar controller short circuit fault are all first-level faults, and the photovoltaic module reverse connection fault and the photovoltaic module backflow fault are both second-level faults; For the primary fault, controlling all the trip switches on the DC side of the inverter to perform a tripping action; For the secondary fault, the trip switch connected to the failed photovoltaic assembly is controlled to perform a tripping action.

3. The inverter DC side fault identification method according to claim 1, characterized in that: The fault type includes: photovoltaic module reverse connection fault, and the fault parameter includes: fault energy; Determining the fault type of the DC side of the inverter according to the electrical parameter includes: If the output voltage of any of the photovoltaic components is less than the first fault threshold voltage, and the output current of the same photovoltaic component is less than the first fault threshold current, it is determined that there is a photovoltaic component reverse connection fault on the DC side of the inverter; wherein the first fault threshold current is a negative value; Controlling the corresponding trip switch to perform a tripping action according to the fault type includes: Integrate the square of the output current of the faulty photovoltaic assembly over time, and when the integral value reaches a first preset threshold, determine that the fault energy in the reverse connection fault of the photovoltaic assembly reaches its corresponding protection action threshold; Determining whether the inverter is running; If so, a shutdown request is issued to control the inverter to shut down, and when the maximum value of the output currents of the photovoltaic assemblies connected to the trip switch connected to the failed photovoltaic assembly is less than the preset trip current, the trip switch connected to the failed photovoltaic assembly is controlled to perform a tripping action; If not, the trip switch connected to the failed photovoltaic assembly is directly controlled to perform a tripping action.

4. The inverter DC side fault identification method according to claim 1, characterized in that: The fault type includes: photovoltaic component backflow fault, and the fault parameter includes: fault energy; Determining the fault type of the DC side of the inverter according to the electrical parameter includes: If the output voltages of the two photovoltaic modules connected to any solar controller are the same, but the output currents are one positive and one negative, the negative output current is used as the reverse current; When the reverse current exceeds the safety threshold, it is determined that there is a reverse fault of the photovoltaic assembly on the DC side of the inverter; Controlling the corresponding trip switch to perform a tripping action according to the fault type includes: Integrate the square of the backfeed current over time, and when the integral value reaches a second preset threshold, determine that the fault energy in the backfeed fault of the photovoltaic component reaches its corresponding protection action threshold; Determining whether the inverter is running; If so, a shutdown request is issued to control the inverter to shut down, and when the maximum value of the output currents of the photovoltaic assemblies connected to the trip switch connected to the photovoltaic assembly with the fault is less than the preset trip current, the trip switch connected to the photovoltaic assembly with the fault is controlled to perform a tripping action; If not, the trip switch connected to the faulty photovoltaic assembly is directly controlled to perform a tripping action.

5. The inverter DC side fault identification method according to claim 1, characterized in that: The fault type includes: single bus short circuit fault, and the fault parameters include: fault energy; Determining the fault type of the DC side of the inverter according to the electrical parameter includes: Calculating a voltage difference between a voltage across the first bus capacitor and a voltage across the second bus capacitor; When the voltage difference exceeds a voltage difference threshold, it is determined that a single bus short circuit fault exists on the DC side of the inverter; Controlling the corresponding trip switch to perform a tripping action according to the fault type includes: The square of the voltage difference is integrated over time, and when the integral value reaches a third preset threshold, it is determined that the fault energy in the single bus short circuit fault reaches its corresponding protection action threshold, and all the trip switches on the DC side of the inverter are controlled to perform a tripping action.

6. The inverter DC side fault identification method according to claim 1, characterized in that: The fault type includes: single bus short circuit fault, and the fault parameters include: fault time; Determining the fault type of the DC side of the inverter according to the electrical parameter includes: Calculating a voltage difference between a voltage across the first bus capacitor and a voltage across the second bus capacitor; When the voltage difference exceeds a voltage difference threshold, it is determined that a single bus short circuit fault exists on the DC side of the inverter; Controlling the corresponding trip switch to perform a tripping action according to the fault type includes: When the duration of the voltage difference exceeding the voltage difference threshold reaches a first preset time, it is determined that the fault time of the single bus short circuit fault reaches its corresponding protection action threshold; Determining whether the maximum value among the output currents of the photovoltaic modules is less than a preset tripping current; If yes, all the trip switches on the DC side of the inverter are controlled to perform a tripping action; If not, a shutdown request is issued to control the inverter to shut down, and when the maximum value of the output currents of the photovoltaic components is less than the preset tripping current, all the tripping switches on the DC side of the inverter are controlled to perform a tripping action.

7. The inverter DC side fault identification method according to claim 1, characterized in that: The fault type includes: double bus short circuit fault, and the fault parameters include: fault time; Determining the fault type of the DC side of the inverter according to the electrical parameter includes: In each sampling period, calculating a voltage sum between a voltage across the first bus capacitor and a voltage across the second bus capacitor as a bus voltage; When the bus voltage in the current sampling period drops by more than a preset percentage threshold compared with the bus voltage in the previous sampling period, it is determined that a double bus short circuit fault exists on the DC side of the inverter; Controlling the corresponding trip switch to perform a tripping action according to the fault type includes: When the duration of the bus voltage maintaining the voltage value after the drop reaches a second preset time, it is determined that the fault time of the double bus short circuit fault reaches its corresponding protection action threshold, and all the trip switches on the DC side of the inverter are controlled to perform a tripping action.

8. The inverter DC side fault identification method according to claim 1, characterized in that: The fault type includes: solar controller short circuit fault, and the fault parameters include: fault time; Determining the fault type of the DC side of the inverter according to the electrical parameter includes: If the output voltages of the two photovoltaic modules connected to any solar controller are both less than the second fault threshold voltage, and the output currents are both greater than the second fault threshold current, it is determined that there is a short circuit fault of the solar controller on the DC side of the inverter; wherein the second fault threshold current is a positive value; Controlling the corresponding trip switch to perform a tripping action according to the fault type includes: When the output voltages of the two photovoltaic modules connected to the solar controller are both lower than the second fault threshold voltage, and the duration of the output currents being higher than the second fault threshold current reaches a third preset time, it is determined that the fault time of the short-circuit fault of the solar controller reaches its corresponding protection action threshold, and all the trip switches on the DC side of the inverter are controlled to perform a tripping action.

9. A photovoltaic system, characterized in that: include: A plurality of photovoltaic modules, a plurality of trip switches and a multi-channel solar controller; wherein every two photovoltaic modules are connected to a solar controller via a set of switch contacts in a trip switch; and at least one set of switch contacts is provided in a trip switch; A first bus capacitor, a second bus capacitor, a first DC bus and a second DC bus; the first end of the first bus capacitor is connected to the first output end of each solar controller, the second end of the first bus capacitor and the first end of the second bus capacitor are both connected to the neutral point of each solar controller, and the second end of the second bus capacitor is connected to the second output end of each solar controller; the first DC bus is connected to the first end of the first bus capacitor, and the second DC bus is connected to the second end of the second bus capacitor; An inverter, wherein a first input terminal and a second input terminal of the inverter are respectively connected to the first DC bus and the second DC bus; A sampling module, used for collecting the output voltage of each photovoltaic assembly, the output current of each photovoltaic assembly, the voltage across the first bus capacitor and the voltage across the second bus capacitor; A controller is connected to the sampling module and each of the trip switches, and the controller is used to execute the inverter DC side fault identification method according to any one of claims 1 to 8.

10. The photovoltaic system according to claim 9, characterized in that: Also includes: Bypass A circuit, respectively connecting the first DC bus, the second DC bus and the controller; The controller is also used to control the bypass circuit to operate so as to discharge the first bus capacitor and the second bus capacitor after controlling all the trip switches on the DC side of the inverter to perform a tripping action when a primary fault occurs.

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