Photovoltaic power generation system DC side protection control method and photovoltaic power generation system

Abstract

The invention is suitable for the technical field of photovoltaic power generation, and provides a photovoltaic power generation system direct current side protection control method and a photovoltaic power generation system.The method comprises the steps that electrical parameters of all input branches connected with an inverter are collected, and direct current side fault judgment is conducted based on the electrical parameters; if the direct current side fault exists, disconnecting the inverter, and detecting whether the inverter has an inverter built-in fault or not; if a fault occurs in the inverter, a circuit breaker in each combiner box connected with the inverter is controlled to be disconnected; and if the inverter internal fault does not occur, searching a target fault branch based on the electrical parameters, controlling a combiner box on the target fault branch to be broken, determining a target fault position based on a fault elimination result of the direct current side fault, and controlling and executing corresponding protection actions based on different target fault positions. According to the method, the specific fault position can be quickly judged, the safety and reliability of the system can be improved, and the possibility of systematic faults is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic power generation, and particularly relates to a protection control method for the DC side of a photovoltaic power generation system and a photovoltaic power generation system. Background Art

[0002] In a photovoltaic power generation system using a centralized photovoltaic inverter, on the DC side, generally multiple photovoltaic strings are connected in parallel through a busbar box and then connected to the DC side of the inverter. Each centralized inverter is connected to multiple busbar boxes, and each busbar box is connected to multiple photovoltaic strings. Therefore, all the photovoltaic strings in the entire system are in parallel. If a positive-negative short circuit or arcing fault occurs at any point, the current of all devices will flow to the fault point. If it cannot be cut off in time, accidents such as equipment damage may occur.

[0003] In the existing technical solutions, a fuse is installed on the DC side of the inverter to break the short-circuit current. When a short circuit or arcing fault occurs at any point in the photovoltaic series circuit, the fuse automatically cuts off, disconnecting the connection of the DC side of the inverter. However, in fact, due to the characteristics of the photovoltaic panel current source, after a short circuit or arcing fault occurs, the fault current is only slightly larger than the normal current, and sometimes the fuse cannot be blown, resulting in the inability to turn off the short-circuit current, leading to serious faults and low safety. Summary of the Invention

[0004] The present invention provides a protection control method for the DC side of a photovoltaic power generation system, aiming to solve the problem in the existing technology that after a short circuit or arcing fault occurs, the fault current is only slightly larger than the normal current, the fuse cannot be blown, resulting in the inability to turn off the short-circuit current, leading to serious faults and low safety.

[0005] The present invention is implemented as follows. In a first aspect, the present application provides a protection control method for the DC side of a photovoltaic power generation system, and the method includes:

[0006] Collect electrical parameters on each input branch connected to the inverter, and perform DC side fault judgment based on the electrical parameters;

[0007] If there is the DC side fault, disconnect the inverter and detect whether an in-inverter fault occurs in the inverter;

[0008] If the in-inverter fault occurs, control the circuit breakers in each busbar box connected to the inverter to trip;

[0009] If the in-inverter fault does not occur, perform target fault branch search based on the electrical parameters, control the circuit breaker in the busbar box on the target fault branch to trip, determine the target fault location based on the fault elimination result of the DC side fault, and control and execute corresponding protection actions based on different target fault locations.

[0010] Further, the electrical parameters include first electrical parameters. Collecting the electrical parameters on each input branch connected to the inverter and performing DC-side fault judgment based on the electrical parameters includes:

[0011] Collecting the first electrical parameters on each input branch connected to the inverter in real time;

[0012] Judging whether the DC-side fault occurs according to the change states of current and voltage in the first electrical parameters.

[0013] Further, the judging whether the DC-side fault occurs according to the change states of current and voltage in the first electrical parameters includes:

[0014] Judging whether current and voltage fluctuations occur based on the first electrical parameters, where the current and voltage fluctuations include voltage drop and current increase;

[0015] If the current and voltage fluctuations occur, judging that the DC-side fault occurs in the photovoltaic power generation system based on the first electrical parameters;

[0016] If the current and voltage fluctuations do not occur, judging that the DC-side fault does not occur in the photovoltaic power generation system based on the first electrical parameters.

[0017] Further, if there is the DC-side fault, disconnecting the inverter and detecting whether an in-inverter fault occurs in the inverter includes:

[0018] If it is detected that there is the DC-side fault, controlling the inverter to stop and disconnecting the DC switch and AC switch in the inverter;

[0019] Collecting multiple status parameters of the inverter itself and judging whether each of the status parameters is abnormal;

[0020] If at least one of the status parameters in the inverter is abnormal, judging that the in-inverter fault occurs in the inverter;

[0021] If each of the status parameters in the inverter is normal, judging that the in-inverter fault does not occur in the inverter.

[0022] Further, controlling the circuit breakers in each combiner box connected to the inverter to trip includes:

[0023] If the in-inverter fault occurs, generating a circuit breaker tripping instruction;

[0024] Sending the circuit breaker tripping instruction to the controllers in all combiner boxes, and controlling the circuit breakers in the combiner boxes to trip through the controllers.

[0025] Further, the method for finding the target fault branch based on the electrical parameters and controlling the circuit breaker in the combiner box on the target fault branch to trip includes:

[0026] Finding the target fault branch based on the first electrical parameters of each input branch collected by the inverter;

[0027] If it is determined that the current and voltage fluctuations occur according to the first electrical parameters, the inverter input branch corresponding to the occurrence of the current and voltage fluctuations is determined as the target fault branch;

[0028] Sending the circuit breaker trip command to the combiner box on the target fault branch through the inverter, and controlling the circuit breaker in the combiner box on the target fault branch to trip based on the circuit breaker trip command.

[0029] Further, the method for determining the target fault location based on the fault elimination result of the DC side fault and controlling corresponding protection actions to be executed based on different target fault locations includes:

[0030] After the circuit breaker in the combiner box on the target fault branch trips, detecting whether the DC side fault is cleared;

[0031] If the fault is cleared after the circuit breaker in the combiner box on the target fault branch trips, it is determined that the target fault location on the target fault branch is on the input side of the combiner box, and the inverter is started to operate;

[0032] If the fault is not cleared after the circuit breaker in the combiner box on the target fault branch trips, it is determined that the target fault location on the target fault branch is on the output side of the combiner box, and the circuit breaker trip command is sent to all the other combiner boxes, controlling the circuit breakers in all the other combiner boxes to trip.

[0033] Further, the method further includes:

[0034] Real-time collecting the second electrical parameters of each input branch connecting each combiner box;

[0035] Judging whether current and voltage fluctuations occur based on the second electrical parameters in each combiner box;

[0036] If current and voltage fluctuations occur, judging that the corresponding combiner box has the DC side fault based on the second electrical parameters;

[0037] If no current and voltage fluctuations occur, judging that the corresponding combiner box does not have the DC side fault based on the second electrical parameters.

[0038] Further, after determining that the corresponding busbar box has a DC-side fault based on the second electrical parameter when current and voltage fluctuations occur, the method further includes:

[0039] If the busbar box determines that there is a DC-side fault based on the collected second electrical parameter, wait to receive the breaker tripping instruction;

[0040] If the waiting duration exceeds a preset duration threshold and the breaker tripping instruction is not received, it is determined that there is a superior protection failure fault or a communication fault, and the breaker is automatically tripped and the fault information is uploaded.

[0041] In a second aspect, the present application provides a photovoltaic power generation system applicable to the protection control method for the DC side of the photovoltaic power generation system described in the first aspect above. The photovoltaic power generation system includes an inverter, a plurality of busbar boxes connected to the inverter, and a plurality of photovoltaic strings connected to each busbar box. The busbar box includes a breaker and a controller, and the controller is communicatively connected to the inverter and the photovoltaic power generation background system.

[0042] The beneficial effects achieved by the present invention: In the present application, the inverter collects the electrical parameters on each input branch connected thereto, determines the DC-side fault based on the electrical parameters, and not only controls the inverter to disconnect after detecting the DC-side fault, but also determines the fault location to determine whether the fault occurs inside the inverter or at the front end of the inverter. When it is at the front end of the inverter, the target fault branch can be determined based on the electrical parameters, and the breaker in the busbar box on the target fault branch can be controlled to trip in a timely manner. And based on the fault elimination result after disconnection, the target fault location can be determined, and it can be judged whether the fault occurs on the input side or the output side of the busbar box. Furthermore, according to different target fault locations, the fault can be selectively removed. It can not only quickly determine the specific fault location based on the electrical parameters, but also improve the system safety and reliability and reduce the possibility of systematic faults. Description of the Drawings

[0043] Figure 1 It is a flowchart of a protection control method for the DC side of a photovoltaic power generation system provided by an embodiment of the present invention;

[0044] Figure 2 It is a schematic diagram of the DC-side circuit of a photovoltaic power generation system provided by an embodiment of the present invention;

[0045] Figure 3 It is an optional inverter protection logic flowchart provided by an embodiment of the present invention;

[0046] Figure 4 It is an optional busbar box protection logic flowchart provided by an embodiment of the present invention. Detailed Embodiments

[0047] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0048] In this application, both the inverter and the busbar box collect the electrical parameters on each input branch connected thereto, perform DC-side fault judgment based on the electrical parameters, and strengthen the protection of the DC side through the multi-device linkage method, which is more conducive to improving the system safety. Moreover, the busbar box itself has a fault judgment mechanism and can be used as the backup protection of the system. In addition, it can also judge the fault location and determine whether the fault occurs inside the inverter or at the front end of the inverter. When it is at the front end of the inverter, the target fault branch can be determined based on the electrical parameters, so as to timely control the circuit breaker on the busbar box of the target fault branch to trip, and determine the target fault location according to the result of the fault elimination after disconnection, and judge whether the fault occurs on the input side or the output side of the busbar box, and then selectively cut off the fault according to different target fault locations, avoiding one-size-fits-all control. It can not only quickly judge the specific fault location based on the electrical parameters, but also improve the system safety and reliability and reduce the possibility of systematic faults.

[0049] Embodiment 1

[0050] Combined with Figure 1 as shown in Figure 1 is a flowchart of a protection control method for the DC side of a photovoltaic power generation system provided by an embodiment of the present invention. A protection control method for the DC side of a photovoltaic power generation system includes steps S1 to S4. The specific implementation principles of each step are as follows:

[0051] S1. Collect the electrical parameters on each input branch connected to the inverter, and perform DC-side fault judgment based on the electrical parameters.

[0052] In this embodiment, combined with Figure 2As shown, the inverter is connected to multiple combiner boxes (1, 2, ……, n), and each combiner box is connected to multiple photovoltaic strings. Combiner box 1 is connected to photovoltaic strings 1-1, ……, 1-N, combiner box 2 is connected to 2-1, ……, 2-N, and so on. Circuit breakers (K1~Kn) and controllers are installed in the combiner boxes. The circuit breakers are DC circuit breakers. The controller of the combiner box can communicate directly with the upper-level inverter through the PLC communication method, or communicate with the background system through communication methods such as RS485, WiFi, wireless 485, Lora, etc., and indirectly communicate with the inverter. The controller in the same combiner box can control its own DC circuit breaker. The inverter and the background system can control the controller in the combiner box. Circuit breakers and controllers are added to the combiner box, which can communicate remotely with the background system or directly with the inverter. Compared with the traditional manually operated disconnect switch, it is more convenient and the control method is more diverse.

[0053] Specifically, the above electrical parameters include voltage and current. The inverter can obtain the voltage and current input by each input branch connected between the combiner boxes and the inverter, and each combiner box can obtain the voltage and current input by the corresponding connected photovoltaic strings.

[0054] Further, when a DC short circuit or arcing and other faults occur in the line, the voltage and current will fluctuate, including that the voltage will drop sharply and the current will increase slightly at the moment of the fault. Therefore, according to the changes in the obtained voltage and current, it can be judged whether a DC side fault occurs in the photovoltaic inverter system.

[0055] In some optional embodiments, the above step S1 includes:

[0056] S11. Real-time collect the first electrical parameters on each input branch connected to the inverter;

[0057] S12. Judge whether a DC side fault occurs according to the change states of the current and voltage in the first electrical parameters.

[0058] Specifically, after the inverter collects the first electrical parameters in each input branch connected to it, the first electrical parameters can be processed and compared in the inverter, including voltage comparison and current comparison, to judge whether current and voltage fluctuations occur. According to the comparison results of the first electrical parameters, it can be judged whether faults such as DC short circuit or arcing occur.

[0059] In some optional embodiments, the above step S12 specifically includes:

[0060] S121. Judge whether current and voltage fluctuations occur based on the first electrical parameters. The current and voltage fluctuations include voltage drop and current increase;

[0061] S122. If current and voltage fluctuations occur, determine whether a DC-side fault occurs in the photovoltaic power generation system based on the first electrical parameter;

[0062] S123. If no current and voltage fluctuations occur, determine that the photovoltaic power generation system has not experienced a DC-side fault based on the first electrical parameter.

[0063] In some embodiments, when the photovoltaic power generation system is operating normally, the voltage and current in the first electrical parameter are output in a stable state. If the voltage drops sharply and the current increases slightly, it is considered that a DC-side fault has occurred, including a short circuit or arcing fault on the DC side of the photovoltaic power generation system. For example: the voltage on the input branch a connected to the inverter drops by 80% based on the normal voltage value, and the current increases by 2% based on the normal current value. If no current and voltage fluctuations occur, it is determined that the photovoltaic power generation system has not experienced a DC-side fault and is in a safe operating state.

[0064] In this embodiment, the inverter monitors the first electrical parameters on each input branch connected to it in real time. The inverter can obtain the first electrical parameters in real time, enabling the system to immediately sense the fluctuations of current and voltage, and timely determine whether a DC-side fault has occurred, facilitating timely intervention and control in the event of a DC-side fault, thereby avoiding the occurrence or expansion of the fault, enhancing the safety and reliability of the DC side of the photovoltaic power generation system, and facilitating subsequent accurate fault location.

[0065] S2. If a DC-side fault exists, disconnect the inverter and detect whether an in-inverter fault has occurred in the inverter.

[0066] In this embodiment, once it is determined that a DC-side fault exists, corresponding protection measures will be taken, such as inverter shutdown, alarm, etc., to prevent the further expansion of the fault and damage to the system. At the same time, the inverter will record the fault information for subsequent analysis and processing by maintenance personnel. To lock the fault location, further fault location search can be carried out.

[0067] In some alternative embodiments, as shown in Figure 2 and Figure 3 above, step S2 specifically includes:

[0068] If it is detected that a DC-side fault exists, control the inverter to shut down and disconnect the DC switch and AC switch in the inverter;

[0069] Collect multiple status parameters of the inverter itself and determine whether each status parameter is abnormal;

[0070] If at least one status parameter in the inverter is abnormal, it is determined that an in-inverter fault has occurred in the inverter;

[0071] If there are no abnormalities in the status parameters of the inverter, it is determined that no internal fault has occurred in the inverter.

[0072] In this embodiment, if a DC-side fault is detected, the inverter is immediately controlled to stop, and at the same time, the DC switch Kdc and the AC switch Kac in the inverter are disconnected to prevent the fault from expanding from the DC side to the AC side. At the same time, the status parameters of the inverter itself can be collected, and it is determined whether an internal fault has occurred according to the status parameters. The internal faults are such as Figure 2 the position of FAULT3 in. Among them, the status parameters of the inverter itself can include whether the display screen in the inverter is turned on, whether the parameters such as voltage, current, and power generation power on the display screen are normal, whether the display of the status light is normal, whether there are obvious physical damages on the appearance of the inverter, for example: whether there are cracks, charred marks or liquid leakage on the appearance of the inverter. It can also include whether the connection harness of the inverter is loose or damaged, whether the input power supply of the inverter is normal, whether the capacitor is working properly, whether the static resistance value and unidirectional conduction of the transistors in the inverter are normal, etc.

[0073] In this embodiment, after detecting a DC-side fault, the inverter not only stops but also determines the fault location. By obtaining the status parameters of the fuse in the inverter, it is further determined whether an internal fault has occurred, so as to timely control each busbar box to be disconnected in case of an internal fault, prevent the fault from expanding, and improve the safety of the system.

[0074] S3. If an internal fault occurs in the inverter, control the circuit breakers in each busbar box connected to the inverter to be disconnected.

[0075] In this embodiment, when an internal fault occurs in the inverter, in order to prevent the internal fault of the inverter from damaging the front-end busbar box, etc., the circuit breakers in each busbar box can be controlled to be disconnected after detecting the internal fault, so as to achieve the front-end protection of the inverter.

[0076] In some alternative embodiments, the above step S3 specifically includes:

[0077] If an internal fault occurs in the inverter, generate a circuit breaker disconnection command;

[0078] Send the circuit breaker disconnection command to the controllers in all busbar boxes, and control the circuit breakers in the busbar boxes to be disconnected through the controllers.

[0079] In this embodiment, if an internal fault occurs in the inverter, the inverter will generate a circuit breaker disconnection command, broadcast and send it to all the busbar boxes connected to it, control all the busbar boxes to be disconnected, and record and upload the fault information, and the fault information is uploaded to the background system. When an internal fault occurs in the inverter, timely controlling the DC circuit breakers in all busbar boxes to be disconnected can prevent the indirect spread of the fault and ensure the safety of the system.

[0080] S4. If no internal fault occurs in the inverter, the target fault branch is searched based on electrical parameters, the bus coupler on the target fault branch is controlled to trip, and the target fault location is determined based on the fault elimination result of the DC-side fault. Corresponding protection actions are executed based on different target fault locations.

[0081] In this embodiment, if no internal fault occurs in the inverter, it may be that a fault occurs on the input side or the output side of the bus coupler. In this case, it is necessary to determine which branch has a fault based on the collected electrical parameters, that is, search for the target fault branch. After locking the target fault branch, the bus coupler on the target fault branch is cut off in time, and it is judged whether the fault is eliminated after the bus coupler trips. The fault location, that is, the target fault location, is further determined according to whether the fault is eliminated or not.

[0082] In some alternative embodiments, in combination with Figure 3 As shown, in the above step S4, searching for the target fault branch based on electrical parameters and controlling the bus coupler on the target fault branch to trip includes:

[0083] Searching for the target fault branch based on the first electrical parameters of each input branch collected by the inverter;

[0084] If current and voltage fluctuations are judged according to the first electrical parameters, the inverter input branch corresponding to the current and voltage fluctuations is determined as the target fault branch;

[0085] Sending a breaker trip command to the bus coupler on the target fault branch through the inverter, and controlling the breaker of the bus coupler on the target fault branch to trip based on the breaker trip command.

[0086] Specifically, when voltage and current fluctuations occur in the voltage and current of each input branch obtained by the inverter, the input branch where the voltage and current fluctuations occur is correspondingly used as the target fault branch, and the specific location where the fault occurs on the target fault branch is further analyzed. Among them, after locking the target fault branch, the inverter sends a breaker trip command to the controller of the bus coupler on the target fault branch, or sends a breaker trip command to the controller of the bus coupler on the target fault branch through the background system. The controller of the bus coupler immediately executes the breaker trip action after receiving the breaker trip command.

[0087] As a possible implementation, the priority of instruction issuance can be set, and the priority of the inverter to issue instructions is higher than that of the background system to issue instructions. The background system can monitor various states of the inverter, including the situation of instruction issuance. If the inverter does not issue a circuit breaker tripping instruction to the busbar trunking unit within the set time, the background system will send a circuit breaker tripping instruction to the busbar trunking unit. For example, after finding the target fault branch, if the controller of the busbar trunking unit does not receive a circuit breaker tripping instruction within a certain time, it will be issued by the background system. By setting the priority of instruction issuance, the circuit breaker tripping in the busbar trunking unit can be accurately controlled, avoiding the situation of simultaneous or multiple issuances in a short time by the background system and the inverter, resulting in tripping confusion or operation errors.

[0088] In this embodiment, by finding the target fault branch according to the voltage and current fluctuations, the busbar trunking unit on the target fault branch can be timely controlled to cut off, ensuring system safety. Secondly, not only can the busbar trunking unit be controlled to trip by the inverter, but also the busbar trunking unit can be controlled to trip by the background system, realizing remote tripping, with higher controllability and flexibility.

[0089] In some alternative embodiments, as shown in Figure 3 In step S4, based on the fault elimination result of the DC-side fault, the target fault location is determined, and corresponding protection actions are controlled and executed based on different target fault locations, including:

[0090] After the circuit breaker of the busbar trunking unit on the target fault branch trips, detect whether the DC-side fault is removed;

[0091] If the fault is removed after the circuit breaker of the busbar trunking unit on the target fault branch trips, it is determined that the target fault location on the target fault branch is on the input side of the busbar trunking unit, and the inverter operation is started;

[0092] If the fault is not removed after the circuit breaker of the busbar trunking unit on the target fault branch trips, it is determined that the target fault location on the target fault branch is on the output side of the busbar trunking unit, and a circuit breaker tripping instruction is issued to all the other busbar trunking units to control the circuit breakers in all the other busbar trunking units to trip.

[0093] In this embodiment, after the circuit breaker in the busbar trunking unit on the target fault branch trips, the inverter can detect whether the DC-side fault is removed and further determine the target fault location. Specifically, after the circuit breaker in the busbar trunking unit on the target fault branch trips, the photovoltaic string connected to the busbar trunking unit is disconnected from the inverter. If the fault is removed after tripping the circuit breaker of the busbar trunking unit on the target fault branch, it indicates that the fault is on the photovoltaic string side of the input side of the busbar trunking unit, such as Figure 2 a fault occurs at FAULT1 in Figure 2 A fault occurs at FAULT2.

[0094] Furthermore, if the fault is cleared, the inverter restarts and continues to operate, and uploads the fault information to the background system. If disconnecting the combiner box on the target fault branch cannot completely clear the fault, the inverter issues a breaker tripping command to all other combiner boxes, ordering them to disconnect all breakers connected to them, and uploads the fault information to the background system.

[0095] It should be noted that FAULT1, FAULT2, and FAULT3 mentioned in the above embodiments refer to faults occurring in a certain interval, rather than fixed point faults in the figure. Figure 2 in

[0096] In this embodiment, when a fault occurs on the input side of a certain combiner box and does not affect the overall system, the inverter can automatically clear the fault and restart, maintaining the operation of the combiner boxes in the fault-free part to supply energy to the subsequent stage, which is beneficial to reducing power generation losses. When the fault is a fault in the subsequent stage of the combiner box, disconnecting all the combiner boxes connected in parallel can ensure the safety of the system.

[0097] In some alternative embodiments, the method further includes:

[0098] Real-time collect the second electrical parameters on each input branch connecting each combiner box;

[0099] Based on the second electrical parameters in each combiner box, determine whether current and voltage fluctuations occur;

[0100] If current and voltage fluctuations occur, based on the second electrical parameters, determine that the corresponding combiner box has a DC side fault;

[0101] If no current and voltage fluctuations occur, based on the second electrical parameters, determine that the corresponding combiner box has no DC side fault.

[0102] In this embodiment, while the inverter collects the first electrical parameters, each combiner box can also collect the second electrical parameters in the input lines of each photovoltaic string connected to it in real time. The second electrical parameters also include current and voltage. Since the combiner box includes a controller, the controller can not only control the DC breaker in the combiner box by itself to achieve backup protection, but also realize remote control with the background system, and the control method is more flexible.

[0103] Further, the second electrical parameters collected can be processed and compared in the junction box, and whether faults such as DC short - circuit or arcing occur can also be judged according to the comparison results of the second electrical parameters. Specifically, when the photovoltaic power generation system is operating normally, the voltage and current in the second electrical parameters are output in a stable state. If it is judged from the second electrical parameters that the voltage drops sharply and the current increases slightly, it is considered that a DC - side short - circuit or arcing fault has occurred. For example, if the voltage on the input branch A connected to the junction box drops by 70% based on the normal voltage value and the current increases by 3% based on the normal current value, it is considered that a DC - side fault has occurred in the junction box. Here, the normal value can refer to a standard reference value within the normal operating range.

[0104] In this embodiment, by separately collecting the second electrical parameters on the input branches where each photovoltaic string is connected to the corresponding junction box for DC - side fault judgment, it forms a multi - device linkage for fault detection with the inverter's DC - side fault judgment based on the first electrical parameters. This not only can strengthen the protection of the DC side of the photovoltaic inverter system, but also is more conducive to improving the system safety and the accuracy of judging DC - side faults.

[0105] In some alternative embodiments, as shown in Figure 4 After judging that the corresponding junction box has a DC - side fault based on the second electrical parameters if current and voltage fluctuations occur, the method further includes:

[0106] If the junction box judges that there is a DC - side fault according to the collected second electrical parameters, it waits to receive a circuit breaker tripping instruction.

[0107] If the waiting duration exceeds the preset duration threshold and the circuit breaker tripping instruction is not received, it is determined that there is a failure of the upper - level protection or a communication fault, and the circuit breaker is automatically tripped and the fault information is uploaded.

[0108] In this embodiment, the junction box itself has a mechanism for judging faults. If the junction box itself judges a fault but does not receive a tripping instruction within the waiting time, it will judge that there is a failure of the upper - level protection or a communication fault, automatically trip the circuit breaker and upload the fault information, which can be used as the backup protection of the system, making the protection more reliable.

[0109] Specifically, the controller of the junction box can be in a receiving state in real - time to receive the circuit breaker tripping instruction issued by the inverter or the background system at any time. If the tripping instruction is not received, the junction box automatically detects the DC - side fault. After the junction box detects the DC - side fault, it first waits for the circuit breaker tripping instruction issued by the inverter or the background system. During the waiting period, it is possible that the inverter or the background system detects the DC - side fault and issues a circuit breaker tripping instruction, or it may be unable to complete the issuance due to other faults.

[0110] Furthermore, if the waiting duration exceeds the preset duration threshold, there may be a failure of the upper-level protection or a communication failure, resulting in the inability to issue commands or a delay in issuing commands. At this time, the busbar box will automatically cut off the circuit breaker and upload the fault information to the background system and the inverter.

[0111] In this embodiment, the busbar box itself has a mechanism for judging faults. In the case of the failure of the inverter's fault detection mechanism / communication failure / delay, etc., it can automatically disconnect the circuit breaker, which can serve as the backup protection of the system and has higher reliability.

[0112] As an alternative implementation, determining whether a DC-side fault has occurred may further include:

[0113] Performing feature extraction on each first electrical parameter to obtain a first feature parameter, and performing feature extraction on each second electrical parameter to obtain a second feature parameter;

[0114] Judging whether a DC-side fault has occurred in the photovoltaic power generation system according to the feature parameters of the first feature parameter and the second feature parameter, where the feature parameters include amplitude and phase.

[0115] In this embodiment, when an arc occurs, it is equivalent to adding a dynamic resistance in the circuit, which will cause a sudden change in the current in the time-domain characteristics. During the arc combustion process, the high-frequency components in the current will also increase. In this regard, the inverter and the busbar box can also detect the fault arc using the current characteristics of the arc. By performing Fourier transform analysis on the current, the high-frequency components or harmonic signals in a specific frequency band generated by the arc are extracted and used as the fault arc feature parameters for judgment. In this case, the above-mentioned first electrical parameter and second electrical parameter are currents, and the first feature parameter and the second feature parameter are the fault arc feature parameters.

[0116] Specifically, extracting the fault arc feature parameters includes: performing current preprocessing on the first electrical parameter and the second electrical parameter, including steps such as filtering and denoising, to improve the quality of the parameters and the accuracy of the analysis. Performing Fourier transform on the preprocessed parameters to convert the parameters from the time domain to the frequency domain. Extracting the high-frequency components or harmonics in the specific frequency band in the converted parameters. In the frequency domain, analyzing the spectral characteristics of the current and extracting the high-frequency components or harmonic signals generated by the arc. Since the high-frequency components or harmonic signals are usually related to the combustion process of the fault arc, they can be used as the fault arc feature parameters. Reading the feature parameters of the high-frequency components or harmonic signals, where the feature parameters include features such as amplitude and phase. Comparing the features such as amplitude and phase with the corresponding set judgment thresholds respectively. If the judgment threshold is exceeded, it is judged that there is a fault arc; otherwise, it is judged as normal current, thereby realizing the distinction between normal current and current containing a fault arc in the first electrical parameter and the second electrical parameter.

[0117] In this embodiment, DC-side fault analysis is carried out based on the arc characteristics. By performing Fourier transform analysis on the current, the high-frequency components generated by the arc or harmonic signals in a specific frequency band are extracted as characteristic parameters, and the characteristic parameters of the characteristic parameters are compared with the set threshold values, which can effectively judge the existence of fault arcs, with high accuracy, strong real-time performance and anti-interference ability.

[0118] Embodiment 2 A photovoltaic power generation system is applicable to the protection control method for the DC side of the photovoltaic power generation system in the above embodiment. The photovoltaic power generation system includes an inverter, a plurality of busbar boxes connected to the inverter, and a plurality of photovoltaic strings connected to each busbar box. The busbar box includes a circuit breaker and a controller, and the controller is communicatively connected to the inverter and the photovoltaic power generation background system.

[0120] In this embodiment, the inverter includes a DC switch Kdc, an AC switch Kac, a DC-AC converter connected between the DC switch Kdc and the AC switch Kac, and fuses FUdc1, FUdc2,..., FUdcn connected in series on each input branch on the input side of the inverter. The DC side of the fuses of the inverter is connected to a plurality of busbar boxes (busbar boxes 1, 2,..., n), each busbar box is connected to a plurality of photovoltaic strings, and each photovoltaic string is connected in series with a fuse. Specifically, busbar box 1 is connected to photovoltaic strings 1-1,..., 1-N, where photovoltaic strings 1-1,..., 1-N are sequentially connected in series with fuses FU1-1,..., FU1-N; busbar box 2 is connected to photovoltaic strings 2-1,..., 2-N, where photovoltaic strings 2-1,..., 2-N are sequentially connected in series with fuses FU2-1,..., FU2-N, and so on. In addition to the fuses, DC circuit breakers (K1~Kn) and a control system (controller) are installed in the busbar box. The controller of the busbar box can communicate directly with the upper-level inverter through the PLC communication method, or communicate with the background system through communication methods such as RS485, WiFi, wireless 485, Lora, etc., and communicate indirectly with the inverter. The controller in the same busbar box can control its own DC circuit breaker. The inverter and the background system can control the controller in the busbar box.

[0121] The photovoltaic power generation system provided in this embodiment can perform DC-side fault detection and protection control through the protection control method for the DC side of the photovoltaic power generation system in the above embodiment. In the protection control method for the DC side of the photovoltaic power generation system, both the inverter and the busbar box collect the electrical parameters on each input branch connected to them respectively, and based on the electrical parameters, DC-side fault judgment is carried out. The protection of the DC side is strengthened through the multi-device linkage method, which is more conducive to improving the system safety. Moreover, the busbar box itself has a fault judgment mechanism and can be used as the backup protection of the system. After detecting a DC-side fault, it will not only control the inverter to disconnect, but also judge the fault location to determine whether the fault occurs inside the inverter or at the front end of the inverter. When it is at the front end of the inverter, the target fault branch can be determined based on the electrical parameters, so as to timely control the circuit breaker on the busbar box of the target fault branch to trip, and determine the target fault location according to the fault elimination result after disconnection, and judge whether the fault occurs on the input side or the output side of the busbar box. Then, the fault is selectively removed according to different target fault locations, which can not only reduce the power generation loss, but also improve the system safety and reliability. Therefore, the photovoltaic power generation system provided in this embodiment can also achieve the various embodiments provided by the above method and reach the corresponding effects, which will not be elaborated here.

[0122] The terms "first", "second", etc. in the specification and claims of the present invention or in the above drawings are used to distinguish different objects, rather than to describe a specific order. The mention of "embodiment" in this article means that the specific features, structures or characteristics described in connection with the embodiment may be included in at least one embodiment of the present invention. The appearance of this phrase at various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0123] It should be understood that in the present invention, "a plurality of" means two or more. "And / or" is only a variable relationship describing associated objects, indicating that there can be three relationships. For example, A and / or B means: A exists alone, A and B exist simultaneously, and B exists alone. The character " / " generally means that the associated objects before and after are in an "or" relationship. "Including A, B, and C", "including A, B, C" means that all of A, B, and C are included, "including A, B, or C" means including any one of A, B, and C, and "including A, B, and / or C" means including any one or any two or all three of A, B, and C.

[0124] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A protection and control method for the DC side of a photovoltaic power generation system, characterized in that: The method comprises: Collecting electrical parameters on each input branch connected to the inverter, and making a DC side fault judgment based on the electrical parameters; If the DC side fault exists, disconnect the inverter and detect whether an inverter internal fault occurs; If a fault occurs inside the inverter, the circuit breakers in the combiner boxes connected to the inverter are controlled to be disconnected; If the inverter internal fault does not occur, the target fault branch is searched based on the electrical parameters, the circuit breaker in the junction box on the target fault branch is controlled to disconnect, and the target fault location is determined based on the fault elimination result of the DC side fault, and corresponding protection actions are performed based on different controls of the target fault location.

2. A protection and control method for the DC side of a photovoltaic power generation system according to claim 1, characterized in that: The electrical parameters include a first electrical parameter, and the collecting of the electrical parameters on each input branch connected to the inverter and the DC side fault judgment based on the electrical parameters include: Real-time collection of first electrical parameters on each input branch connected to the inverter; Whether the DC side fault occurs is determined according to the change status of the current and voltage in the first electrical parameter.

3. A protection and control method for the DC side of a photovoltaic power generation system according to claim 2, characterized in that: The determining whether the DC side fault occurs according to the change state of the current and voltage in the first electrical parameter includes: determining whether current and voltage fluctuations occur based on the first electrical parameter, the current and voltage fluctuations comprising a voltage drop and a current increase; If the current and voltage fluctuations occur, determining that the photovoltaic power generation system has the DC side fault based on the first electrical parameter; If the current and voltage fluctuations do not occur, it is determined based on the first electrical parameter that the photovoltaic power generation system does not have the DC side fault.

4. A protection and control method for the DC side of a photovoltaic power generation system according to claim 1, characterized in that: If the DC side fault exists, disconnecting the inverter and detecting whether an inverter internal fault occurs in the inverter includes: If the DC side fault is detected, the inverter is controlled to shut down, and the DC switch and AC switch in the inverter are disconnected; Collect multiple status parameters of the inverter itself and determine whether each of the status parameters is abnormal; If at least one of the state parameters in the inverter is abnormal, it is determined that the inverter has an internal fault; If there is no abnormality in the state parameters of the inverter, it is determined that the inverter does not have the inverter internal fault.

5. A protection and control method for the DC side of a photovoltaic power generation system according to claim 3, characterized in that: The controlling of disconnecting the circuit breakers in the combiner boxes connected to the inverters comprises: If an internal fault of the inverter occurs, a circuit breaker disconnection instruction is generated; The circuit breaker disconnection instruction is sent to the controllers in all the combiner boxes, and the circuit breakers in the combiner boxes are controlled to disconnect by the controllers.

6. A protection and control method for the DC side of a photovoltaic power generation system according to claim 5, characterized in that: The searching for a target faulty branch based on the electrical parameters and controlling a circuit breaker in a combiner box on the target faulty branch to disconnect the target faulty branch includes: Searching for a target fault branch based on the first electrical parameters on each input branch collected by the inverter; If it is determined according to the first electrical parameter that the current and voltage fluctuations occur, the inverter input branch corresponding to the current and voltage fluctuations is determined as the target fault branch; The circuit breaker disconnection instruction is sent to the combiner box on the target fault branch through the inverter, and the circuit breaker disconnection of the combiner box on the target fault branch is controlled based on the circuit breaker disconnection instruction.

7. A protection and control method for the DC side of a photovoltaic power generation system according to claim 5, characterized in that: The determining of a target fault location based on a fault elimination result of the DC side fault, and performing corresponding protection actions based on different controls of the target fault location include: After the circuit breaker of the combiner box on the target fault branch is disconnected, detecting whether the DC side fault is removed; If the fault is removed after the circuit breaker of the combiner box on the target fault branch is disconnected, it is determined that the target fault position on the target fault branch is located at the input side of the combiner box, and the inverter is started; If the fault is not removed after the circuit breaker of the combiner box on the target faulty branch is disconnected, it is determined that the target fault position on the target faulty branch is located at the output side of the combiner box, and the circuit breaker disconnection instruction is sent to all other combiner boxes to control the circuit breakers in all other combiner boxes to disconnect.

8. A protection and control method for the DC side of a photovoltaic power generation system according to claim 5, characterized in that: The method further comprises: Real-time collection of second electrical parameters on each input branch connected to each combiner box; determining in each combiner box whether current and voltage fluctuations occur based on the second electrical parameter; If current and voltage fluctuations occur, determining that the DC side fault occurs in the corresponding combiner box based on the second electrical parameter; If no current and voltage fluctuation occurs, it is determined based on the second electrical parameter that the DC side fault does not occur in the corresponding combiner box.

9. A protection and control method for the DC side of a photovoltaic power generation system according to claim 8, characterized in that: After determining that the DC side fault occurs in the corresponding combiner box based on the second electrical parameter if current and voltage fluctuations occur, the method further includes: If the combiner box determines that the DC side fault exists according to the collected second electrical parameter, then waits to receive the circuit breaker disconnection instruction; If the waiting time exceeds the preset time threshold and the circuit breaker disconnection instruction is not received, it is determined that there is a superior protection failure or communication failure, and the circuit breaker is automatically disconnected and the fault information is uploaded.

10. A photovoltaic power generation system, applicable to the protection and control method for the DC side of the photovoltaic power generation system according to any one of claims 1 to 9, characterized in that: The photovoltaic power generation system includes an inverter, multiple junction boxes connected to the inverter, and multiple photovoltaic strings connected to each of the junction boxes. The junction boxes include a circuit breaker and a controller. The controller is communicatively connected to the inverter and the photovoltaic power generation background system.

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