Low-voltage DC system short-circuit fault protection system based on improved double-ring wavelet decomposition
Through the improved double-ring wavelet decomposition technology and linear fitting method, combined with multi-resolution wavelet decomposition, the early detection and selective breakdown of short-circuit faults in DC systems are achieved, and the problems of long detection time and poor reliability in the existing technology are solved, and the anti-interference ability and reliability of the system are improved.
Patent Information
- Application Number
- CN202411529977.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-30
- Publication Date
- 2025-03-07
AI Technical Summary
The short-circuit fault detection time in existing DC systems has long lead to the development of short-circuit voltage and current to a large extent, causing huge harm to power electronic devices. In addition, the traditional methods have weak anti-interference ability and poor reliability, which is prone to misjudgment and cross-step tripping.
The improved double-ring wavelet decomposition technology is adopted, combined with linear fitting method and multi-resolution wavelet decomposition, and the composite criterion is constructed to achieve early detection and selective breakdown. Through the CAN bus and RS485 communication, the central control module and the early detection module of short-circuit faults can be realized to quickly identify and remove short-circuit faults.
It effectively shortens the detection time of short-circuit faults, improves the reliability and robustness of the criterion, reduces damage to power electronic devices, avoids misjudgment and cross-step tripping, and improves the anti-interference ability of the system.
Smart Images
Figure CN119582103A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the field of early fault detection, and in particular to a low-voltage direct current system short-circuit fault protection system based on improved double-loop wavelet decomposition. Background Art
[0002] In the early stage of power development, the DC power supply and distribution system was limited by the fact that it was not easy to transform, not conducive to long-distance transmission, and not conducive to the formation of a large power grid, and the development was slow. However, with the development of power electronics technology, the defects of the AC distribution system have become more and more obvious: large line loss, difficult flow control, unable to achieve asynchronous interconnection, and the existence of power angle balance. At the same time, with the continuous improvement of the power generation rate of distributed power sources and the development of wind, light, and storage microgrids, the control system of the AC power grid has a huge impact. Compared with the AC distribution network, the DC distribution system has been continuously developed due to its advantages such as high power quality, strong ability to absorb DC loads, low line loss, diverse power supply methods, and closed-loop operation. However, once a short-circuit fault occurs in the DC distribution system, if the fault cannot be removed in time, the short-circuit impact current caused will cause great damage to the power electronic devices in the DC system, seriously endangering the service life of the power electronic equipment. At the same time, the DC short-circuit impact current has a high short-circuit current change rate and a large peak value, and there is no natural zero crossing point. If the fault cannot be removed in time, a large amount of heat will be generated, which is very easy to cause a fire accident.
[0003] At present, the detection method of DC short-circuit fault mainly adopts the comparison of fault voltage and current with the set threshold value. This method requires a long detection time. When the short-circuit fault is detected, the short-circuit voltage has dropped to a certain extent and the short-circuit current has developed to a large extent, which is extremely harmful to the power electronic device. At the same time, the DC circuit breaker will reduce its service life if it breaks a large short-circuit current. At the same time, this method may misjudge transient processes such as load switching and load starting, and has weak anti-interference ability and poor reliability.
[0004] In addition, when a short circuit occurs in the system, the short-circuit current is designed for each level of protective devices, which has a wide range of impact. Traditional selective protection only relies on the time-current curve of each protective device, and achieves selective protection between levels through parameter setting. If the short-circuit current is too large, the upper and lower level protective devices can detect the occurrence of short-circuit faults, and it is very easy to trip at the same time or trip across levels. Summary of the invention
[0005] In order to solve the above problems, the object of the present invention is to provide a low voltage DC system short circuit fault protection system based on improved double-loop wavelet decomposition.
[0006] To achieve the above object, the present invention adopts the following technical solutions:
[0007] A low-voltage DC system short-circuit fault protection system based on improved double-loop wavelet decomposition comprises a short-circuit fault early detection module and a central control module. When a short-circuit fault occurs in the system, the short-circuit fault early detection module detects the short circuit, and sends the hierarchical branch of the detected fault and the short-circuit fault current and voltage characteristics to the central control module through CAN bus communication. The central control module determines the short-circuit fault early detection module at the protection disconnection position and issues a disconnection instruction. The short-circuit fault early detection module issues a protection disconnection signal to the corresponding circuit breaker through RS485 to complete the selective disconnection of the short-circuit fault.
[0008] Furthermore, the short-circuit fault early detection module includes a voltage and current high-speed sampling module, an MCU calculation unit module and a CAN bus / RS485 communication module.
[0009] A short-circuit fault protection method for a low-voltage DC system based on improved dual-loop wavelet decomposition comprises the following steps:
[0010] The linear fitting method is used to fit the short-time window data of the low-voltage DC system voltage and current digital signals collected at high frequency by the MCU computing unit module to obtain the linear fitting parameters within the window, and the fitting parameters are brought back to obtain the estimated values of the current and voltage data. In this way, the interference of signal noise can be effectively filtered out without reducing the voltage and current short-circuit characteristics.
[0011] The filtered sampling signal is decomposed by multi-resolution wavelet to obtain the detail components and smooth components of voltage and current: U_cD4, U_S4, I_cD4 and I_S4, and the composite criterion of DC short circuit fault is formed through four eigenvalues;
[0012] The short-circuit fault detection start criterion is formed by the DC voltage and current detail components: I_cD4-U_S4>Fault set.1 ; Short circuit fault judgment criteria: U_S4 / I_S4 <Fault act.1 , when the start criterion is met, the short circuit judgment is started, and when the judgment takes effect, it is determined that a DC short circuit has occurred;
[0013] If the fault branch is a load branch, the early fault detection link will first trigger the action mechanism of the protective electrical appliance to disconnect, and then upload the fault information to the central control module;
[0014] If the faulty branch is a non-load branch, the fault information will be uploaded when the CAN bus is idle. If the locking information of the lower-level rapid detection link is received during this period, the system will enter the locking state and will not upload the fault information to the central control module. If only the starting criterion is greater than the threshold, the system will be judged to be abnormal and continuously monitored. If the short-circuit fault criterion is not met within a certain period of time and the short-circuit fault starting criterion disappears, it is determined that the system has transient processes such as load switching. If the short-circuit fault criterion is not met within a certain period of time and the short-circuit fault starting criterion still exists, it is determined that the system has an overcurrent problem.
[0015] Further, the straight line fitting method is as follows:
[0016] Assume that the functional relationship between x and y is as follows: y = kx + b; where k represents the slope and b represents the intercept; for N sets of data (x i ,y i ), i=1,2,3.....,N,x i The value is considered accurate and any error is related only to y i , the observed data is fitted into a straight line by the least squares method, requiring the observed value y i The weighted sum of squares of the deviations is minimized, that is, the following formula is minimized:
[0017]
[0018] Taking partial derivatives of k and b for the above formula, we can get the following system of equations:
[0019]
[0020] Solving the above equations can obtain the best estimated values of the straight line parameters k and b, which are as follows:
[0021]
[0022] Furthermore, when the central control module receives new fault information, it parses the information content and writes it into the decision space. In order to avoid information omissions caused by the transmission delay of fault information at each level and take into account the timeliness of information collection, the continuous idle time of the monitoring bus is set to 50us; the fault branch is judged according to the information in the decision space, and a disconnection instruction is issued; after sending the disconnection instruction, the update status of the fault information in the decision space is continuously monitored until the fault information in the decision space is completely cleared.
[0023] Furthermore, if a short circuit occurs in a branch of the low-voltage DC system, short-circuit current will exist in the layers and branches from the DC power supply output terminal to the fault point. The short circuit fault will be detected on each branch and the fault information will be sent to the protection decision terminal module; by setting the arbitration field identifier priority in the CAN bus protocol, the fault information uploaded close to the fault side has the highest priority.
[0024] Furthermore, the central control module collects the short-circuit faults detected by branches at all levels, sorts the fault information in the decision cache space according to the hierarchical branches, determines the short-circuit branch at the last level as the protection response branch, and finally issues a disconnection instruction to the corresponding short-circuit fault early detection module.
[0025] Furthermore, the short-circuit fault early detection module has a high-speed selective protection terminal mechanism, which makes an autonomous judgment after detecting a short circuit. If the faulty branch is a load branch, the early fault detection link will prioritize triggering the action mechanism of the protective electrical appliance to disconnect, and then upload the fault information to the central control module. If the faulty branch is a non-load branch, the fault information is uploaded when the CAN bus is idle. If the locking information is received from the lower-level rapid detection link during this period, it will enter the locking state and will not upload the fault information to the central control module.
[0026] The present invention has the following beneficial effects:
[0027] The present invention can effectively filter out the interference of signal noise without reducing the voltage and current short-circuit characteristics through least squares filtering; the composite criterion composed of voltage and current multi-resolution wavelet decomposition components fully considers transient processes such as load switching, and effectively improves the reliability and robustness of the criterion; through the coordination of the rapid detection module and the protection decision terminal, rapid detection and selective disconnection after a short-circuit fault can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Figure 1 It is a schematic diagram of the functions and interrelationships of the modules of the present invention;
[0029] Figure 2 A schematic diagram of a method flow in one embodiment of the present invention;
[0030] Figure 3 A system architecture diagram in one embodiment of the present invention;
[0031] Figure 4 This is a diagram of the information processing program of the short-circuit fault early detection module in one embodiment of the present invention;
[0032] Figure 5 A flowchart of the central control module coordinating analysis and issuing instructions in one embodiment of the present invention;
[0033] Figure 6The figure is a flow chart of composite criterion data processing for improving dual-loop wavelet decomposition in one embodiment of the present invention. DETAILED DESCRIPTION
[0034] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:
[0035] refer to Figure 1 In this embodiment, a low-voltage DC system short-circuit fault protection system based on improved dual-loop wavelet decomposition is provided, including a short-circuit fault early detection module and a central control module; when a short-circuit fault occurs in the system, the short-circuit fault early detection module detects the short circuit, and sends the hierarchical branch of the detected fault and the short-circuit fault current and voltage characteristics to the central control module through CAN bus communication. The central control module determines the short-circuit fault early detection module of the protection disconnection position and issues a disconnection instruction. The short-circuit fault early detection module sends a protection disconnection signal to the corresponding circuit breaker through RS485 to complete the selective disconnection of the short-circuit fault.
[0036] In this embodiment, the short-circuit fault early detection module includes a voltage and current high-speed sampling module, an MCU calculation unit module and a CAN bus / RS485 communication module.
[0037] In this embodiment, reference Figure 2 In this embodiment, a low voltage DC system short circuit fault protection method based on improved dual-loop wavelet decomposition includes the following steps:
[0038] The linear fitting method is used to fit the short-time window data of the low-voltage DC system voltage and current digital signals collected at high frequency by the MCU computing unit module to obtain the linear fitting parameters within the window, and the fitting parameters are brought back to obtain the estimated values of the current and voltage data. In this way, the interference of signal noise can be effectively filtered out without reducing the voltage and current short-circuit characteristics.
[0039] The filtered sampling signal is decomposed by multi-resolution wavelet to obtain the detail components and smooth components of voltage and current: U_cD4, U_S4, I_cD4 and I_S4, and the composite criterion of DC short circuit fault is formed through four eigenvalues;
[0040] Preferably, in the present embodiment, if only the composite criteria formed by the multi-resolution wavelet decomposition components of the DC voltage and current are greater than the threshold, it is determined that a short-circuit fault has occurred. If the fault branch is a load branch, the early fault detection link will give priority to triggering the action mechanism of the protective electrical appliance to disconnect, and then upload the fault information to the protection decision terminal module. If the fault branch is a non-load branch, the fault information is uploaded when the CAN bus is idle. If the locking information of the lower-level rapid detection link is received during this period, the lock is entered and the fault information is not uploaded to the protection decision terminal module. If only the startup criterion is greater than the threshold, the system is judged to be abnormal and continuously monitored. If the short-circuit fault criterion is not met within a certain period of time, and the short-circuit fault startup criterion disappears, it is determined that the system has transient processes such as load switching; if the short-circuit fault criterion is not met within a certain period of time, and the short-circuit fault startup criterion still exists, it is determined that the system has an overcurrent problem;
[0041] If the fault branch is a load branch, the early fault detection link will first trigger the action mechanism of the protective electrical appliance to disconnect, and then upload the fault information to the central control module;
[0042] If the faulty branch is a non-load branch, the fault information will be uploaded when the CAN bus is idle. If the locking information of the lower-level rapid detection link is received during this period, the system will enter the locking state and will not upload the fault information to the central control module. If only the starting criterion is greater than the threshold, the system will be judged to be abnormal and continuously monitored. If the short-circuit fault criterion is not met within a certain period of time and the short-circuit fault starting criterion disappears, it is determined that the system has transient processes such as load switching. If the short-circuit fault criterion is not met within a certain period of time and the short-circuit fault starting criterion still exists, it is determined that the system has an overcurrent problem.
[0043] In this embodiment, the straight line fitting method is as follows:
[0044] Assume that the functional relationship between x and y is as follows: y = kx + b; where k represents the slope and b represents the intercept; for N sets of data (x i ,y i ), i=1,2,3.....,N,x i The value is considered accurate and any error is related only to y i , the observed data is fitted into a straight line by the least squares method, requiring the observed value y i The weighted sum of squares of the deviations is minimized, that is, the following formula is minimized:
[0045]
[0046] Taking partial derivatives of k and b for the above formula, we can get the following system of equations:
[0047]
[0048] Solving the above equations can obtain the best estimated values of the straight line parameters k and b, which are as follows:
[0049]
[0050] In this embodiment, when a short circuit fault occurs in the system, the short circuit fault early detection module detects the short circuit within 1ms, and sends the hierarchical branch of the detected fault and the short circuit fault current and voltage characteristics to the protection decision terminal module through CAN bus communication. The protection decision terminal module determines the short circuit fault early detection module at the protection disconnection position and issues a disconnection instruction. The early detection module sends a protection disconnection signal to the corresponding circuit breaker through RS485 to complete the selective disconnection of the short circuit fault.
[0051] In this embodiment, when the central control module receives new fault information, it parses the information content and writes it into the decision space. In order to avoid information omissions caused by the transmission delay of fault information at each level and take into account the timeliness of information collection, the continuous idle time of the monitoring bus is set to 50us; the fault branch is judged according to the information in the decision space, and a disconnection instruction is issued; after sending the disconnection instruction, the update status of the fault information in the decision space is continuously monitored until the fault information in the decision space is completely cleared.
[0052] In this embodiment, a short circuit fault occurs in a branch of the low-voltage DC system. Short-circuit current will exist in the layers and branches from the DC power supply output terminal to the fault point. The occurrence of the short circuit fault will be detected on each branch, and the fault information will be sent to the protection decision terminal module; by setting the arbitration field identifier priority in the CAN bus protocol, the fault information uploaded close to the fault side has the highest priority.
[0053] In this embodiment, the central control module collects the short-circuit faults detected by branches at all levels, sorts the fault information in the decision cache space according to the hierarchical branches, determines the short-circuit branch at the last level as the protection response branch, and finally issues a disconnection instruction to the corresponding short-circuit fault early detection module.
[0054] In this embodiment, the short-circuit fault early detection module has a high-speed selective protection terminal mechanism. After detecting a short circuit, it makes an independent judgment. If the fault branch is a load branch, the early fault detection link will give priority to triggering the action mechanism of the protection electrical appliance to disconnect, and then upload the fault information to the central control module. If the fault branch is a non-load branch, the fault information is uploaded when the CAN bus is idle. If the locking information of the lower-level rapid detection link is received during this period, it will enter the locking state and will not upload the fault information to the central control module.
[0055] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.
[0056] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.
[0057] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.
[0058] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.
[0059] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.
Claims
1. A low voltage DC system short circuit fault protection system based on improved double-loop wavelet decomposition, characterized in that: It includes a short-circuit fault early detection module and a central control module; when a short-circuit fault occurs in the system, the short-circuit fault early detection module detects the short circuit and sends the hierarchical branch of the detected fault and the short-circuit fault current and voltage characteristics to the central control module through CAN bus communication. The central control module determines the short-circuit fault early detection module at the protection disconnection position and issues a disconnection instruction. The short-circuit fault early detection module sends a protection disconnection signal to the corresponding circuit breaker through RS485 to complete the selective disconnection of the short-circuit fault.
2. The low voltage DC system short circuit fault protection system based on improved dual-loop wavelet decomposition according to claim 1 is characterized in that: The short-circuit fault early detection module comprises a voltage and current high-speed sampling module, an MCU calculation unit module and a CAN bus / RS485 communication module.
3. A method for protecting a low voltage DC system short circuit fault system based on improved dual-loop wavelet decomposition according to claim 2, characterized in that: The linear fitting method is used to fit the short-time window data of the low-voltage DC system voltage and current digital signals collected at high frequency by the MCU computing unit module to obtain the linear fitting parameters within the window, and the fitting parameters are brought back to obtain the estimated values of the current and voltage data; The filtered sampling signal is decomposed by multi-resolution wavelet to obtain the detail components and smooth components of voltage and current: U_cD4, U_S4, I_cD4 and I_S4, and the composite criterion of DC short circuit fault is formed through four eigenvalues; The short-circuit fault detection start criterion is formed by the DC voltage and current detail components: I_cD4-U_S4>Fault set.1 ; Short circuit fault judgment criteria: U_S4 / I_S4 <Fault act.1 , when the start criterion is met, the short circuit judgment is started, and when the judgment takes effect, it is determined that a DC short circuit has occurred; If the fault branch is a load branch, the early fault detection link will first trigger the action mechanism of the protective electrical appliance to disconnect, and then upload the fault information to the central control module; If the faulty branch is a non-load branch, the fault information will be uploaded when the CAN bus is idle. If the locking information of the lower-level rapid detection link is received during this period, the system will enter the locking state and will not upload the fault information to the central control module. If only the starting criterion is greater than the threshold, the system will be judged to be abnormal and continuously monitored. If the short-circuit fault criterion is not met within a certain period of time and the short-circuit fault starting criterion disappears, it is determined that the system has transient processes such as load switching. If the short-circuit fault criterion is not met within a certain period of time and the short-circuit fault starting criterion still exists, it is determined that the system has an overcurrent problem.
4. The protection method according to claim 3, characterized in that: The straight line fitting method is specifically as follows: Assume that the functional relationship between x and y is as follows: y = kx + b; where k represents the slope and b represents the intercept; for N sets of data (x i ,y i ), i=1,2,3.....,N,x i The value is considered accurate and any error is related only to y i , the observed data is fitted into a straight line by the least squares method, requiring the observed value y i The weighted sum of squares of the deviations is minimized, that is, the following formula is minimized: Taking partial derivatives of k and b for the above formula, we can get the following system of equations: Solving the above equations can obtain the best estimated values of the straight line parameters k and b, which are as follows:
5. The protection method according to claim 3, characterized in that: When the central control module receives new fault information, it analyzes the information content and writes it into the decision space. In order to avoid information omission caused by the transmission delay of fault information at each level and take into account the timeliness of information collection, the continuous idle time of the monitoring bus is set to 50us; The faulty branch is determined according to the information in the decision space, and a disconnection command is issued; after the disconnection command is sent, the update status of the fault information in the decision space is continuously monitored until the fault information in the decision space is completely cleared.
6. The protection method according to claim 3, characterized in that: When a short circuit fault occurs in a branch of the low-voltage DC system, short-circuit current will exist in the layers and branches from the DC power supply outlet to the fault point. The occurrence of the short circuit fault will be detected on each branch, and fault information will be sent to the protection decision terminal module; By setting the arbitration field identifier priority in the CAN bus protocol, the fault information uploaded close to the fault side has the highest priority.
7. The protection method according to claim 3, characterized in that: The central control module collects the short-circuit faults detected by branches at all levels, sorts the fault information in the decision cache space according to the level branches, determines the short-circuit branch at the last level as the protection response branch, and finally issues a disconnection instruction to the corresponding short-circuit fault early detection module.
8. The protection method according to claim 3, characterized in that: The short-circuit fault early detection module is equipped with a high-speed selective protection terminal mechanism, which makes an autonomous judgment after detecting a short circuit. If the faulty branch is a load branch, the early fault detection link will prioritize triggering the action mechanism of the protective electrical appliance to disconnect, and then upload the fault information to the central control module. If the faulty branch is a non-load branch, the fault information will be uploaded when the CAN bus is idle. If the locking information of the lower-level rapid detection link is received during this period, the module will enter the locking state and will not upload the fault information to the central control module.