A fast microgrid protection method and device based on inverter PWM signal

Abstract

This invention provides a fast microgrid protection method and apparatus based on inverter PWM signals. The method includes: acquiring the internal PWM signal of the inverter; integrating the internal PWM signal to obtain the equivalent potential (EMP) of the actual output of the inverter; correcting the voltage of each inverter node in the microgrid according to the EMP of the actual output of the inverter to obtain the corrected node voltage; and performing segmented current direction-low voltage protection of the microgrid based on the corrected node voltage. By correcting the node voltage through integration, when a short-circuit fault occurs on the microgrid line, the segmented current direction-low voltage protection is activated to clear the fault, ensuring timely fault clearing when a fault occurs in the microgrid and preventing damage to the renewable energy power source.

Description

Technical Field

[0001] This invention relates to a fast microgrid protection method and device based on inverter PWM signals, belonging to the field of microgrid protection technology. Background Technology

[0002] With the advancement of new energy technologies and the increasing emphasis placed on environmental protection by the state, microgrids that integrate power generation, storage, and load are being used more and more frequently in power systems to meet the comprehensive needs of efficiently coordinating local load power consumption and new energy power generation.

[0003] Microgrids have two operating modes, and the fault current differs significantly between grid-connected and islanded modes. With the rapid development of microgrids, microgrid protection faces the challenge of determining whether a fault occurs inside or outside the microgrid in both grid-connected and islanded modes, while ensuring the reliability, speed, sensitivity, and selectivity of the protection systems installed in the microgrid.

[0004] Most power sources in microgrids are distributed generation. Distributed generation differs from traditional generation methods, being significantly affected by environmental factors, resulting in fluctuating and difficult-to-control output. Furthermore, the frequent switching of these power sources easily causes current fluctuations within the microgrid. Traditional distribution network structures are radial networks with a single power source, where power flow is unidirectional. They employ ungrounded neutral points or grounded via arc suppression coils to ensure power supply reliability. Therefore, overcurrent protection is generally used. The widespread application of microgrids and distributed generation has altered the fault characteristics of traditional distribution networks, impacting traditional overcurrent protection. This includes reduced sensitivity of line protection; the possibility of protection malfunctions when adjacent lines experience faults; decreased reclosing success rate; and a narrowed protection range.

[0005] Because microgrids typically have lower voltage levels, smaller areas, and shorter lines, the current changes during faults are limited by the power electronic devices, resulting in less noticeable fluctuations. This leads to less sensitive protection devices and difficulties in protection setting. Therefore, current protection widely used in large power grids is no longer suitable for microgrids. However, voltage changes at various points in the system are relatively significant, making low-voltage protection beneficial for ensuring the reliability of relay protection.

[0006] Considering the significant differences between microgrids and large power grids in terms of network configuration, operating mode, and spatial characteristics, relay protection in microgrids should adopt different methods than that in large power grids. To balance the fault characteristics of microgrid relay protection, the stable and safe operation of internal distributed power sources, and the unique operating state of microgrids, and to quickly determine the location of faults, a rapid protection method for microgrid power sources needs to be designed. This method should ensure timely detection and isolation of faults when they occur in the microgrid, guaranteeing that renewable energy sources are not damaged. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a fast microgrid protection method and device based on inverter PWM signals. By integrating the node voltage, the node voltage change is corrected, making the change more obvious and ensuring that faults in the microgrid can be detected in time, thus ensuring that the new energy power source is not damaged.

[0008] To achieve the above objectives, the present invention is implemented using the following technical solution:

[0009] In a first aspect, the present invention provides a fast microgrid protection method based on inverter PWM signals, comprising the following steps:

[0010] Obtain the internal PWM signal of the converter;

[0011] Based on the internal PWM signal of the converter, the equivalent electromotive force of the actual output of the converter is obtained by integration;

[0012] The voltage of each converter node in the microgrid is corrected based on the equivalent potential actually output by the converter to obtain the corrected node voltage.

[0013] Microgrid segmented current direction-low voltage protection is performed based on the corrected node voltage.

[0014] Furthermore, based on the internal PWM signal of the converter, the equivalent electromotive force of the actual output of the converter is obtained by integration, including:

[0015] Based on the half-wave integration method of the PWM signal inside the converter, the PWM signal is integrated by a sliding window with a width of π to obtain the internal potential of the converter.

[0016] The formula for calculating the half-wave integral of a PWM signal starting at any given time is:

[0017]

[0018] E=α1U dc

[0019] Where: α1 is the duty cycle of the PWM waveform obtained by half-wave integration; θ represents any time at the start of integration; f(wt) is the PWM waveform inside the converter; U dc E is the converter output voltage under normal operating conditions; E is the equivalent potential of the actual output of the converter.

[0020] Furthermore, based on the internal PWM signal of the converter, the equivalent electromotive force of the actual output of the converter is obtained by integration, including:

[0021] Based on the quarter-cycle integration method of the PWM signal within the converter's internal sliding window, the PWM signal starting at any time is integrated using a sliding window of width [value missing]. The calculation formula is as follows:

[0022]

[0023] E=α2U dc

[0024] Where: α2 is the duty cycle of the PWM waveform obtained by half-wave integration; A is the first PWM pulse width of the sliding-out window; B is the first PWM pulse width of the sliding-in window. θ represents any time at the start of integration; f(wt) is the PWM waveform inside the converter; U dc E is the converter output voltage under normal operating conditions; E is the equivalent potential of the actual output of the converter.

[0025] Furthermore, the voltage of each converter node in the microgrid is corrected based on the actual output equivalent potential of the converter, resulting in the corrected node voltage, including:

[0026] The voltages of each converter node in the microgrid are:

[0027] U k.i =E i -U dc.i

[0028] Among them: U k.i U is the corrected voltage at node i. dc.i E represents the output voltage with converter node i in normal system operation. i The equivalent electromotive force of the converter at node i is obtained by integration.

[0029] Furthermore, the method also includes:

[0030] Set the activation value U for the protection device Δ When the equivalent potential of the actual output of the converter obtained by integrating the PWM signal is lower than U... Δ If the fault is determined to be an external line fault, then the microgrid segmented current direction-low voltage protection will be activated; otherwise, the protection will not operate.

[0031] Startup quantity U Δ Set to 0.8 times the rated output voltage of the converter;

[0032] Furthermore, based on the corrected node voltage, segmented current direction-undervoltage protection for the microgrid is performed, including:

[0033] Step A: Obtain the adjusted three-stage undervoltage protection settings; the adjusted three-stage undervoltage protection settings include the settings for undervoltage protection stage I, undervoltage protection stage II, and undervoltage protection stage III.

[0034] Step B: When a fault occurs, if the corrected node voltage is less than the setting value of the low voltage protection section I of this line, it is determined that the fault occurred within the low voltage protection section I range of this line, and the protection will operate immediately; otherwise, the protection will not operate and will jump to step C.

[0035] Step C: If the node correction voltage is less than the setting value of the undervoltage protection stage II of this line, determine the current direction. If the current direction is determined to be positive, perform a short delay. If the voltage magnitude does not change when the delay ends, the undervoltage protection stage II of this line will operate to clear the fault. If the bus voltage rises to the voltage value under normal operating conditions when the delay ends, the corrected node voltage will be recalculated. If the current direction is reversed, the protection will not operate.

[0036] Step D: If the node correction voltage is less than the setting value of the undervoltage protection stage III for this line, and the current direction is positive, the protection will perform a short delay. If the node correction voltage is still lower than the setting value of the undervoltage protection stage III when the delay ends, the undervoltage protection stage III for this line will operate to clear the fault. If the bus voltage rises after the delay, it indicates that the fault or overload has ended, and the corrected node voltage will be recalculated. If the current direction is reversed, the protection will not operate.

[0037] Furthermore, the direction of the current is determined by the power direction element on the line.

[0038] Furthermore, the setting value of the undervoltage protection stage I is...

[0039]

[0040] In the formula, I k Z represents the fault current measured on the faulty line AB when a three-phase short-circuit fault occurs; AB The impedance is the total length of the line between the faulty busbars A and B. The reliability coordination factor for the low voltage stage I protection can be taken as 0.7-0.8;

[0041] The setting value of the low voltage protection stage II is

[0042]

[0043] In the formula, To ensure the reliability coordination factor of the low-voltage stage II protection, a range of 0.7-0.8 is generally selected; Z AC The line impedance between busbars A and C;

[0044] The setting value for stage III of the undervoltage protection is

[0045]

[0046] In the formula, The reliability coordination factor for the low-voltage stage III protection can be taken as 0.8-0.9; I L.max This is the maximum load current flowing through the line when the system is under maximum load.

[0047] Furthermore, Take 0.7-0.8; Choose 0.7-0.8; Take 0.8-0.9.

[0048] Secondly, the present invention provides a fast microgrid protection device based on inverter PWM signals, comprising:

[0049] Signal acquisition module: used to acquire the internal PWM signal of the converter;

[0050] Integration module: used to integrate the PWM signal inside the converter to obtain the equivalent electromotive force of the actual output of the converter;

[0051] Correction module: used to correct the voltage of each converter node in the microgrid based on the equivalent potential actually output by the converter, so as to obtain the corrected node voltage;

[0052] Protection module: used for segmented current direction-low voltage protection of the microgrid based on the corrected node voltage.

[0053] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0054] 1. The present invention proposes a fast microgrid protection method and device based on inverter PWM signal. The effective value of the inverter output voltage is obtained by integration. The voltage change is relatively obvious, which ensures that the fault can be cut off in time when a fault occurs in the microgrid, and ensures that the new energy power supply will not be damaged.

[0055] 2. This invention utilizes a sliding module to perform half-wave or quarter-cycle integration on the PWM signal inside the inverter to obtain the effective value of the inverter output voltage. This method can obtain the voltage within half a cycle or a quarter cycle. When a fault occurs in the system, the voltage will be too low. Therefore, by equipping the output voltage obtained based on integration with appropriate protection measures, it is possible to effectively balance the operational safety of power electronic equipment inside the microgrid and the relay protection characteristic quantity requirements of the microgrid.

[0056] 3. This invention addresses microgrids containing a large amount of renewable energy power sources by proposing a fast microgrid protection method based on the inverter's internal PWM signal. By referencing the traditional three-stage overcurrent protection method, a three-stage undervoltage protection method is incorporated within the microgrid. This method effectively improves protection performance by utilizing a significantly varying voltage as a relay protection characteristic, addressing the challenges of short electrical distances between electrical devices within the microgrid and the relatively insignificant changes in fault current.

[0057] 4. The fast microgrid protection method based on the internal PWM signal of the inverter proposed in this invention is designed based on the inverter component contained in all new energy power sources. It can be widely used in microgrids containing different types of new energy sources and has high versatility.

[0058] The fast microgrid protection method based on the inverter's internal PWM signal proposed in this invention can be applied to microgrids containing a large amount of renewable energy generation, improving the reliability and security of power supply and renewable energy generation in both grid-connected and off-grid modes. Attached Figure Description

[0059] Figure 1 This is a schematic diagram illustrating the principle of a fast microgrid protection method and device based on inverter PWM signals.

[0060] Figure 2 This is a schematic diagram of the protection method of the present invention. Detailed Implementation

[0061] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0062] Example 1:

[0063] This embodiment provides a fast microgrid protection method based on inverter signals for selectively disconnecting lines in a microgrid that have experienced short-circuit faults. It includes: (1) proposing a theoretical basis for using the half-wave integral or quarter-cycle integral of the internal PWM signal sliding window as a criterion; (2) proposing a node voltage correction algorithm using the internal PWM integral signal (involving multiple inverter power supplies within the microgrid); and (3) proposing a segmented current direction-low voltage protection method for correcting node voltages and its implementation method.

[0064] This method specifically includes:

[0065] The protection criterion is to use the half-wave or quarter-cycle integral of the PWM signal sliding window inside the converter as the protection criterion and to correct the node voltage. When a short-circuit fault occurs on the microgrid line, the fault is cleared by the segmented current direction-low voltage protection.

[0066] Specifically, due to the short distances between lines in a microgrid, the current changes in the lines are not significant enough when a fault occurs. Regardless of whether the microgrid is in grid-connected or off-grid mode, it is difficult to use traditional segmented current protection to determine which line is faulty. However, the voltage values ​​at each node in a microgrid change significantly during a fault. Using the characteristics of voltage values ​​as the protection criterion helps ensure the four characteristics of relay protection (reliability, sensitivity, selectivity, and speed).

[0067] Specifically, the PWM signal inside the inverter modulates the output current of the AC / DC converter by adjusting the pulse width. The PWM signal consists of high and low levels. This PWM signal is fed into an integrator, which integrates the PWM signal (the per-unit value of the converter output voltage) using a sliding window with a width of π to obtain the converter's internal potential. The formula for calculating the half-wave integral of the PWM signal starting at any given time is:

[0068]

[0069] E=α1U dc

[0070] Where: α1 is the duty cycle of the PWM waveform obtained by half-wave integration; θ represents any time at the start of integration; f(wt) is the PWM waveform inside the converter; U dc E is the converter output voltage under normal operating conditions; E is the equivalent potential of the actual output of the converter.

[0071] Specifically, the method based on the quarter-cycle integration of the PWM signal within the converter's internal sliding window shortens the signal processing time by integrating the PWM signal starting at any given time using a sliding window of a certain width. This method allows for unlimited sampling time of the PWM signal while ensuring the accuracy of the integration result. The integration calculation formula starting from any given time is as follows:

[0072]

[0073] E=α2U dc

[0074] Where: α2 is the duty cycle of the PWM waveform obtained by half-wave integration; A is the first PWM pulse width of the sliding-out window; B is the first PWM pulse width of the sliding-in window.

[0075] Specifically, the half-wave or quarter-cycle integral of the PWM signal sliding window is used as the equivalent electromotive force of the actual output of the converter with equivalent three-segment current direction-low voltage protection.

[0076] To ensure the reliability of the protection operation, a start-up value U is set for the protection device. Δ When the internal potential obtained by integrating the PWM signal is lower than U Δ The system is identified as having an external line fault and the protection system is activated.

[0077] The voltage change at the converter outlet after a short-circuit fault is used as the activation quantity for segmented undervoltage protection.

[0078] Specifically, for nodes connected to renewable energy sources, the connection of these sources affects the power flow of the system, causing abnormal voltage values, branch current values, and current directions at each node, leading to protection failures or maloperations. Therefore, it is necessary to correct the voltage of each converter node in the microgrid to eliminate the influence of the converter power supply on the node voltage and branch current during a microgrid fault, thus ensuring the reliability of the protection actions configured on the line. After a fault occurs, the corrected voltage of each converter node is as follows:

[0079] U k.i =E i -U dc.i

[0080] Among them: U k.i E is the corrected voltage at node i. i U is the actual output voltage of the converter at node i obtained by integration. dc.i This is the output voltage with converter node i in normal system operation.

[0081] Specifically, the setting method for segmented current direction-low voltage protection in microgrids is as follows:

[0082] When a three-phase short-circuit fault occurs in a microgrid, the voltage at the fault point is 0, and the voltage at the protection installation point closest to the short-circuit point is the lowest.

[0083] As attached Figure 1 As shown, taking protection 1 as an example, when a fault occurs in section AB, the voltage at bus A is the lowest point. When the power direction element installed on the line determines that the current direction is positive, the low-voltage protection stage I at protection 1 immediately operates, disconnecting the line without delay. Its operating setting value is...

[0084]

[0085] In the formula, I k Z represents the fault current measured on line AB when a three-phase short-circuit fault occurs; AB The impedance of the line between busbars A and B is the total length of the line. To ensure the reliability coordination factor of the low voltage stage I protection, a value of 0.7-0.8 can be used.

[0086] The undervoltage protection stage II of protection 1 should coordinate with the undervoltage protection stage I of line BC. That is, when a short-circuit fault occurs on line BC, the undervoltage protection stage I of protection 2 will operate to clear the fault. At this time, the power direction element determines that the current direction on line AC is from C to A. After a short delay, the undervoltage protection stage II of protection 1 will operate, and the operating setting value of the undervoltage protection stage II of protection 1 will be... for:

[0087]

[0088] In the formula, To ensure the reliability coordination factor of the low-voltage stage II protection, a range of 0.7-0.8 is generally selected; Z AC The line impedance between busbars A and C;

[0089] The undervoltage protection stage III of protection 1 is set for overload protection to ensure that the protection will not malfunction under maximum load. The setting value is... for:

[0090]

[0091] In the formula, To ensure the reliability coordination factor of the undervoltage stage III protection, a value of 0.8-0.9 can be adopted; L.max This is the maximum load current flowing through protection 1 in the line when the system load is at its maximum.

[0092] Specifically, the implementation steps for segmented current direction-undervoltage protection are as follows:

[0093] Step A: For nodes connected to converters, a quarter-cycle integration method based on the sliding window of the converter's internal PWM signal is used to quickly obtain the equivalent potential of the actual output of the converter at that node.

[0094] Step B: If the actual output equivalent potential of the converter at this node is lower than the starting value U Δ If the condition is met, the protection will be activated and the process will proceed to step C; otherwise, the process will proceed to step A. The voltage change at the converter outlet after a short-circuit fault is used as the activation parameter for the segmented undervoltage protection.

[0095] Step C: Correct the node voltage. Calculate the output voltage of the converter node, i.e., the corrected voltage, based on the equivalent potential of the actual output of the converter.

[0096] U k.i =E i -U dc.i

[0097] Reduce the impact of new energy power sources on protection actions;

[0098] Step D: If the node correction voltage is less than the setting value of the low voltage protection section I of this line, it is determined that the fault occurred within the low voltage protection section I range of this line, and the protection will operate immediately; otherwise, the protection will not operate and will jump to step E.

[0099] Step E: If the node correction voltage is less than the setting value of the undervoltage protection stage II of this line, the power direction element on the line determines the current direction. When the current direction is determined to be positive, a short delay is performed. When the voltage magnitude does not change at the end of the delay, the undervoltage protection stage II of this line will operate to clear the fault. If the bus voltage rises to the voltage value under normal operating conditions at the end of the delay, then step A is skipped.

[0100] Step F: If the node correction voltage is less than the setting value of the undervoltage protection stage III of this line, and the power direction element on the line determines that the current direction is positive, the protection will perform a short delay. If the voltage is still low when the delay ends, the undervoltage protection stage III of this line will operate to clear the fault. If the bus voltage rises when the delay ends, it indicates that the fault or overload has ended, and the process will jump to step A.

[0101] The segmented current direction-low voltage protection has three protection stages, I, II, and III, that work together in terms of timing. The operating time of stage II is longer than that of stage I, and the operating time of stage III is longer than that of stage II, thus ensuring the selectivity of the low voltage protection operation.

[0102] Note that in this invention, inverter and converter essentially mean the same thing, both being components that convert direct current to alternating current.

[0103] Example 2:

[0104] This embodiment provides a fast microgrid protection device based on inverter PWM signals, including:

[0105] Signal acquisition module: used to acquire the internal PWM signal of the converter;

[0106] Integration module: used to integrate the PWM signal inside the converter to obtain the equivalent electromotive force of the actual output of the converter;

[0107] Correction module: used to correct the voltage of each converter node in the microgrid based on the equivalent potential actually output by the converter, so as to obtain the corrected node voltage;

[0108] Protection module: used for segmented current direction-low voltage protection of the microgrid based on the corrected node voltage.

[0109] The apparatus in this embodiment can be used to implement the method described in Embodiment 1.

[0110] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied 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.

[0111] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0112] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0113] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0114] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A fast microgrid protection method based on inverter PWM signal, characterized in that, Includes the following steps: Obtain the internal PWM signal of the converter; Based on the internal PWM signal of the converter, the equivalent electromotive force of the actual output of the converter is obtained by integration; The voltage of each converter node in the microgrid is corrected based on the equivalent potential actually output by the converter to obtain the corrected node voltage. Microgrid segmented current direction-low voltage protection is performed based on the corrected node voltage. The method further includes: Set the activation amount for the protection device When the equivalent potential of the actual output of the converter obtained by integrating the PWM signal is lower than... If the fault is determined to be an external line fault, then the microgrid segmented current direction-low voltage protection will be activated; otherwise, the protection will not operate. Based on the corrected node voltage, segmented current direction-undervoltage protection for the microgrid is performed, including: Step A: Obtain the adjusted three-stage undervoltage protection settings; the adjusted three-stage undervoltage protection settings include the settings for undervoltage protection stage I, undervoltage protection stage II, and undervoltage protection stage III. Step B: When a fault occurs, if the corrected node voltage is less than the setting value of the low voltage protection section I of this line, it is determined that the fault occurred within the low voltage protection section I range of this line, and the protection will operate immediately; otherwise, the protection will not operate and will jump to step C. Step C: If the node correction voltage is less than the setting value of the undervoltage protection stage II of this line, determine the current direction. If the current direction is determined to be positive, perform a short delay. If the voltage magnitude does not change when the delay ends, the undervoltage protection stage II of this line will operate to clear the fault. If the bus voltage rises to the voltage value under normal operating conditions when the delay ends, the corrected node voltage will be recalculated. If the current direction is reversed, the protection will not operate. Step D: If the node correction voltage is less than the setting value of the undervoltage protection stage III of this line, and the current direction is positive, the protection will perform a short delay. When the node correction voltage is still lower than the setting value of the undervoltage protection stage III at the end of the delay, the undervoltage protection stage III of this line will operate to clear the fault. If the bus voltage rises at the end of the delay, it indicates that the fault or overload has ended, and the corrected node voltage will be recalculated. If the current direction is reversed, the protection will not operate.

2. The fast microgrid protection method based on inverter PWM signal according to claim 1, characterized in that, Based on the internal PWM signal of the converter, the equivalent electromotive force of the actual output of the converter is obtained by integration, including: Based on the half-wave integral method of the PWM signal sliding window inside the converter, a window with a width of The PWM signal is integrated using a sliding window to obtain the converter internal potential. The formula for calculating the half-wave integral of a PWM signal starting at any given time is: ； ； in: The duty cycle of the PWM waveform obtained by half-wave integration; This represents any time at which the integration begins; This is the PWM waveform inside the converter; This refers to the converter output voltage under normal operating conditions. This represents the equivalent potential of the actual output of the converter.

3. The fast microgrid protection method based on inverter PWM signal according to claim 1, characterized in that, Based on the internal PWM signal of the converter, the equivalent electromotive force of the actual output of the converter is obtained by integration, including: Based on the quarter-cycle integral method of the sliding window of the PWM signal inside the converter, a window with a width of A sliding window of / 2 integrates the PWM signal starting at any given time, and its calculation formula is as follows: ； ； in: The duty cycle of the PWM waveform obtained by half-wave integration; The width of the first PWM pulse when the window slides out; The width of the first PWM pulse entering the window; This represents any time at which the integration begins; This is the PWM waveform inside the converter; This refers to the converter output voltage under normal operating conditions. This represents the equivalent potential of the actual output of the converter.

4. The fast microgrid protection method based on inverter PWM signal according to claim 1, characterized in that, The voltages of each converter node in the microgrid are corrected based on the equivalent potential actually output by the converter, resulting in the corrected node voltages, including: The corrected voltages for each converter node in the microgrid are: ； in: For nodes Correction voltage, For those with converter nodes The output voltage, E, under normal system operating conditions i For nodes The actual output equivalent potential of the converter.

5. The fast microgrid protection method based on inverter PWM signal according to claim 1, characterized in that, The direction of the current is determined by the power direction element on the line.

6. The fast microgrid protection method based on inverter PWM signal according to claim 1, characterized in that, The setting value of the undervoltage protection stage I is : ； In the formula, This indicates the fault current measured on the faulty line AB when a three-phase short-circuit fault occurs; The impedance is the total length of the line between the faulty busbars A and B. The reliability coordination factor for the low voltage stage I protection is taken as 0.7-0.8; The setting value of the low voltage protection stage II is : ； In the formula, To ensure the reliability coordination factor of the protection for the low voltage stage II, a value of 0.7-0.8 is adopted. The line impedance between busbars A and C; The setting value of the undervoltage protection stage III is : ； In the formula, The reliability coordination factor for the low-voltage stage III protection is taken as 0.8-0.9; This is the maximum load current flowing through the line when the system is under maximum load.

7. A fast microgrid protection device based on inverter signals for performing the method as described in claim 1, characterized in that, include: Signal acquisition module: used to acquire the internal PWM signal of the converter; Integration module: used to integrate the PWM signal inside the converter to obtain the equivalent electromotive force of the actual output of the converter; Correction module: used to correct the voltage of each converter node in the microgrid based on the equivalent potential actually output by the converter, so as to obtain the corrected node voltage; Protection module: used for segmented current direction-low voltage protection of the microgrid based on the corrected node voltage.

Images