A microgrid power supply protection method and device using the internal PWM signal of the converter.

Abstract

This invention proposes a microgrid power supply protection method and device using an internal PWM signal from a converter. The method, based on a microgrid system including renewable energy sources, loads, and a converter, includes the following steps: acquiring the converter's output current; determining whether the current has reached a maximum current limit; if so, sampling the PWM signal based on the converter's internal PWM signal to obtain the effective value of the converter's output voltage; if the effective value of the converter's output voltage is less than the starting voltage, determining the fault location based on the effective value of the converter's output voltage and initiating undervoltage protection. This method is highly adaptable, has simple setting parameters, good robustness, and is well-suited for fluctuating renewable energy generation and grid-connected / off-grid switching.

Description

Technical Field

[0001] This invention relates to a fast protection method for microgrid power supplies using the internal PWM signal of the converter, belonging to the field of microgrid relay protection. Background Technology

[0002] Distributed energy generation has become an increasingly widespread application as an important component of the large power grid. Distributed generation offers many advantages that traditional power generation methods lack, such as being cleaner and having flexible and controllable scale. However, it also exhibits disadvantages such as high grid connection costs and difficulty in control. Distributed power sources are uncontrollable sources for the large power grid, and their output often exhibits randomness. To reconcile this contradiction, microgrid technology has emerged.

[0003] Microgrid protection differs significantly from traditional low-voltage distribution network single-source radial relay protection, mainly in the following aspects: microgrid power flow is bidirectional, employs a large number of distributed power sources of various types, and has more complex control strategies; the short-circuit current in microgrids differs greatly between grid-connected and islanded modes, making reliable operation of relay protection for internal faults a current challenge in microgrids.

[0004] Traditional distribution networks with unidirectional power flow rely on overcurrent protection for protection. However, since microgrids generally have lower voltage levels, smaller ranges, and shorter lines, the current is limited by the relevant power electronic devices when a fault occurs in the system, and the change is not significant enough. This results in the protection devices not being sensitive enough and makes protection setting difficult. Therefore, the current protection widely used in large power grids is no longer suitable for microgrids.

[0005] Meanwhile, microgrids typically use inverters connected to the grid for power supply. When a short-circuit fault occurs in the microgrid, the inverter controller employs a current-limiting strategy to reduce the output fault current by decreasing the PWM pulse width, thereby preventing the switching current from exceeding the limit. However, regardless of whether the microgrid is in grid-connected or off-grid mode, it lacks generator protection comparable to or similar to that of a traditional power grid, making it difficult to determine whether the fault lies within the microgrid network or the inverter power supply itself.

[0006] To take into account 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 to ensure that faults can be promptly isolated when they occur in the microgrid, thus preventing damage to renewable energy sources. Summary of the Invention

[0007] This invention provides a microgrid power protection method and device that uses the internal PWM signal of the converter. The effective value of the converter output voltage is obtained by integration, and the voltage change is relatively obvious, which ensures that the fault can be detected in time when a fault occurs in the microgrid, and ensures that the new energy power supply will not be damaged.

[0008] In a first aspect, the present invention provides a method for fast protection of microgrid power supply using an internal PWM signal of a converter, based on a microgrid system, the microgrid system including a new energy power supply, a load and a converter;

[0009] The method includes the following steps:

[0010] Obtain the current output from the converter;

[0011] When determining whether the current has reached the maximum current limit, if so, the PWM signal is sampled based on the internal PWM signal of the converter to obtain the effective value of the converter output voltage.

[0012] If the effective value of the converter output voltage is less than the starting voltage, the location of the fault is determined based on the effective value of the converter output voltage, and the undervoltage protection is activated.

[0013] Furthermore, the maximum current limit is 1.2-1.5 times the rated output current of the converter.

[0014] Furthermore, based on the internal PWM signal of the converter, PWM signal sampling is performed to obtain the effective value of the converter output voltage, including:

[0015] Obtain the internal PWM signal of the converter;

[0016] The general function f(wt) for a PWM signal waveform is given by:

[0017]

[0018] Where: H is the set of all time points where the signal is 1, Z is the set of all time points where the signal is 0, and L is the set of all time points where the signal is -1. The effective value E of the converter output voltage can be obtained by performing a half-wave integral on the waveform function.

[0019]

[0020] Among them: U dc This represents the converter output voltage under normal operating conditions. θ represents any moment at the start of integration; f(wt) is the PWM waveform inside the converter.

[0021] Furthermore, the startup voltage U Δ Set to 0.8 times the rated output voltage of the converter;

[0022] When the effective value of the converter output voltage E is lower than the starting voltage U Δ If a short circuit fault is detected, the location of the fault is determined by the effective value of the converter output voltage, and the undervoltage protection is activated; otherwise, the protection will not operate.

[0023] Furthermore, the location of the fault is determined based on the effective value of the converter output voltage, and undervoltage protection is activated, including:

[0024] When the effective value E of the converter output voltage is lower than the judgment voltage, it is judged as an internal fault of the converter, and the new energy power supply is directly cut off to protect the power supply.

[0025] When the effective value E of the converter output voltage is higher than the judgment voltage, it is judged as an external fault of the converter, and equivalent segmented undervoltage protection is implemented to achieve selective isolation of faults in different lines.

[0026] Furthermore, the judgment voltage is 0.2-0.3 times the rated output voltage of the converter.

[0027] Furthermore, equivalent segmented undervoltage protection is implemented to selectively isolate faults on different lines, including:

[0028] The effective value E of the converter output voltage is compared with the setting value of the converter's internal low voltage protection to determine the location of the fault, and each section of protection selectively delays the clearing of the fault.

[0029] Furthermore, the microgrid is equipped with bus C, bus D, bus E, and bus F, thereby dividing the lines into lines CD, DE, and EF; protection section I is the line between protection bus CD, protection section II is the line between protection bus CE, and protection section III is the line between protection bus CF.

[0030] The effective value E of the converter output voltage is compared with the internal undervoltage protection setting value of the converter to determine the location of the fault. Each protection stage selectively delays the clearing of the fault, including:

[0031] When the effective value E of the converter output voltage is less than the setting value of the protection stage I of this line, it is determined that the short circuit fault occurred on this line, and the protection stage I immediately operates to clear the fault; otherwise, the protection does not operate.

[0032] When the effective value E of the converter output voltage is less than the setting value of the protection stage II of this line, a short delay is performed. If the effective value of the converter output voltage rises to a level not lower than the setting value of protection stage II before the end of the delay, it indicates that the fault occurred on line DE or EF and has been cleared by other protections, and protection stage II will not operate. If the effective value of the converter output voltage is still lower than the setting value after the short delay, it indicates that the protection on line DE or EF fails to operate. In this case, protection stage II will operate as a remote backup protection for the next line to clear the fault.

[0033] When the voltage at bus C is less than the setting value of protection section III of this line, a short delay is performed. If the effective value of the converter output voltage rises to no less than the setting value of protection section III before the end of the delay, protection section III will not operate. If the effective value of the converter output voltage is still lower than the setting value of protection section III after the short delay, protection section III will operate as a remote backup protection to clear the fault.

[0034] Furthermore, the duration of the brief delay is 0.5 seconds.

[0035] Furthermore, the brief delay time limit is coordinated with the protection stages I and II of the next line to achieve selective protection operation.

[0036] Furthermore, the protection segment I setting value for:

[0037]

[0038] In the formula, I S This represents the normal output current of the converter under normal operating conditions; Z CD The line impedance of the transmission line between busbars C and D; The reliability coordination factor for the undervoltage protection stage I of protection 1;

[0039] The protection stage II setting value for:

[0040]

[0041] In the formula, To ensure the reliability coefficient of the undervoltage protection stage II of protection 1, The operating setting value for the undervoltage protection stage I of protection 2 on line DE;

[0042] The protection stage III setting value for:

[0043]

[0044] In the formula, To ensure the reliability factor of the undervoltage protection stage II of protection 1, I L.max Z represents the load current that may occur under system overload conditions. DE Z is the total impedance of line DE along its entire length; EF Let EF be the total impedance of the line.

[0045] Furthermore, Take 0.8-0.9;

[0046] Take 0.85;

[0047] Take 0.85.

[0048] Secondly, the present invention provides a microgrid power supply fast protection device employing an internal PWM signal of the converter, comprising:

[0049] Current module: Used to obtain the output current of the converter;

[0050] PWM integrator: Used to determine whether the current has reached the maximum current limit. If so, it samples the PWM signal based on the internal PWM signal of the converter to obtain the effective value of the converter output voltage.

[0051] Protection module: Used to activate undervoltage protection if the effective value of the converter output voltage is less than the starting voltage.

[0052] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0053] 1. This paper proposes a fast protection method for microgrid power supply using the internal PWM signal of the inverter. When the inverter output current limiting is detected, PWM signal sampling is started to prevent false protection. By performing half-wave integration on the internal PWM signal of the inverter, the effective value of the inverter output voltage is obtained. This method can quickly detect and integrate the inverter voltage within half a cycle. Based on this output voltage, appropriate protection measures are equipped. The voltage change is relatively obvious, which can greatly shorten the protection action time.

[0054] 2. This invention proposes a fast microgrid protection method based on inverter PWM signals. A judgment voltage is set for microgrid faults to determine whether the fault occurs inside or outside the converter. A three-stage equivalent undervoltage protection method is provided for external converter faults. During microgrid faults, due to the short electrical distances between electrical devices within the microgrid, the change in fault current is not significant, while the change in voltage is large. Therefore, using the output voltage as the protection activation criterion can improve the sensitivity and reliability of the protection action.

[0055] 3. The microgrid power supply fast protection method using the internal PWM signal of the converter proposed in this invention has strong versatility and can be well applied to microgrids with high or low proportion of new energy power.

[0056] 4. The device proposed in this invention uses the internal PWM integral signal of the converter as a criterion, which can not only adjust the output voltage of the inverter through PWM signal pulse width modulation, but also determine the fault location, cut off the renewable energy power supply, and improve the reliability and safety of power supply to users and clean energy generation.

[0057] 5. This invention sets a starting voltage. When the effective value of the converter output voltage obtained by integration is lower than the starting voltage, it is determined that a short circuit fault has occurred in the system, and the microgrid power supply needs to be protected. This improves the protection efficiency on the one hand, and prevents the protection from malfunctioning on the other. Attached Figure Description

[0058] Figure 1 This is a schematic diagram illustrating the principle of a fast power supply protection method for microgrids that uses the internal PWM signal of the converter.

[0059] Figure 2 This is a schematic diagram of the microgrid structure of the present invention;

[0060] Figure 3 This is a schematic diagram of the protective device structure and integral principle 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 protection method for microgrid power supply using the PWM signal inside the converter. It uses the half-wave integral of the PWM signal inside the converter as a criterion to determine whether the short-circuit fault occurs inside the converter or on the microgrid line, and clears the fault by different protection actions.

[0064] Specifically, because photovoltaic power generation is greatly affected by environmental weather, the output current fluctuates. To ensure relatively stable output, the input DC current and output AC current are controlled by a power electronic grid-connected control device. The output current of the AC / DC converter is modulated by the PWM signal inside the converter through pulse width adjustment, ensuring that the output of the switching transistor is stable and does not exceed the limit. When the converter output current limit is detected, PWM signal sampling is initiated. The current limiting factor is generally 1.2 to 1.5 times.

[0065] Specifically, the PWM signal inside the converter consists of high and low levels. The PWM signal is fed into an integrator and integrated half-wave to obtain the per-unit value of the effective output voltage within half a cycle. This per-unit value reflects the converter's output voltage level.

[0066] The general function f(wt) for a PWM signal waveform is given by:

[0067]

[0068] Where: H is the set of all time points where the signal is 1, Z is the set of all time points where the signal is 0, and L is the set of all time points where the signal is -1. Half-wave integration of the waveform function can reflect the effective value of the converter output voltage.

[0069]

[0070] Among them: U dc This is the converter output voltage under normal operating conditions.

[0071] Specifically, to ensure reliable operation of the protection, a starting voltage U is set for the fast protection of microgrid power supplies. Δ As a basis for judgment, the starting value can be set to 0.8 times the rated output voltage of the converter.

[0072] Specifically, when the effective value E of the converter output voltage obtained by integration is lower than the start-up voltage U... Δ When this occurs, it is determined that a short circuit fault has occurred in the system, and protection of the microgrid power supply is required.

[0073] Specifically, in order to determine whether a short-circuit fault occurs inside the converter or on the microgrid line, a judgment voltage needs to be set. The voltage value can be adjusted according to the actual situation, and is currently set to 0.2-0.3 times the rated output voltage of the converter.

[0074] Specifically, when the effective value E of the converter output voltage obtained by integration is less than the judgment voltage, it is judged as an internal fault of the converter. The circuit breaker in the photovoltaic grid-connected dual-loop controller directly cuts off the new energy power supply to protect the power supply. When the potential is higher than the judgment voltage, it is judged as an external fault of the converter. The corresponding line protection further judges the fault location, thereby avoiding protection maloperation.

[0075] Specifically, in order to protect against short-circuit faults in microgrid lines, a three-stage undervoltage protection system is installed inside the microgrid, referencing the three-stage overcurrent protection system.

[0076] Specifically, the half-wave integral of the PWM signal is used as the activation value for the equivalent three-stage undervoltage protection. The activation criterion method for undervoltage protection of circuit breakers within the zone (including the converter itself and the first line) is as follows:

[0077] As attached Figure 1 As shown, at this time, the effective value E of the converter output voltage under the low-voltage protection of the power electronic switch at the converter outlet is less than the converter output voltage setting value when the microgrid system is operating normally without line faults. Therefore, the switch trips the renewable energy power supply, and its setting value is U. set :

[0078] U set =K rel U s

[0079] Among them: U s This is the converter output voltage when the microgrid system is operating normally; This is the reliability coefficient for low voltage protection. Its value can be adjusted according to specific needs, and can be set to 0.7-0.8 to ensure that the protection does not fail to operate.

[0080] Specifically, the setting method for the three-stage undervoltage protection of microgrids is as follows:

[0081] As attached Figure 1 As shown, taking protection 1 as an example, the operating voltage value of the low voltage protection stage I of protection 1 must be less than the residual voltage at bus C when a short circuit fault occurs on line CD. Therefore, the operating setting value of the low voltage protection stage I of protection 1 is... for:

[0082]

[0083] In the formula, I S This represents the normal output current of the converter under normal operating conditions; Z CD The line impedance of the transmission line between busbars C and D; To ensure the reliability coordination factor of the undervoltage protection stage I for protection 1, it can generally be taken as 0.8-0.9;

[0084] Correspondingly, the undervoltage protection stage II of protection 1 needs to coordinate with the undervoltage protection stage I of the next line protection 2 to protect most of the next line DE. Therefore, the operating setting value of the undervoltage protection stage II of protection 1 is... for:

[0085]

[0086] In the formula, The reliability coefficient of the undervoltage protection stage II of protection 1 can generally be taken as 0.85; This is the operating setting value for the undervoltage protection stage I of protection 2 on line DE. The setting method is similar to that of the undervoltage protection stage I of protection 1.

[0087] The equivalent undervoltage protection III of protection 1 is designed for system overload operation. That is, the setting value of protection stage III should be less than the minimum residual voltage at bus C when the system is operating under overload conditions. Therefore, the operating setting value of the equivalent undervoltage protection III of protection 1... for:

[0088]

[0089] In the formula, To ensure the reliability coefficient of the undervoltage protection stage II for protection 1, a value of 0.85 is generally recommended. L.max Z represents the load current that may occur under system overload conditions. DE Z is the total impedance of line DE along its entire length; EF Let EF be the total impedance of the line.

[0090] Specifically, the three-stage undervoltage protection operation process is as follows:

[0091] When the effective value of the output voltage obtained by half-wave integration of the PWM signal inside the converter, that is, the voltage at bus C, is less than the setting value of the low voltage I-stage protection of this line, it is determined that the short circuit fault occurred on this line, and the first stage protection of the line immediately operates to clear the fault; otherwise, the protection does not operate.

[0092] If the voltage at bus C is less than the setting value of the protection stage II of this line, the protection will perform a short delay. If the voltage at bus C rises before the delay ends, it indicates that the fault occurred on line DE or EF and has been cleared by other protections. If the voltage at bus C is still lower than the setting value after the short delay, it indicates that the protection on line DE or EF has failed to operate. In order to protect the microgrid power supply, protection stage II of protection 1 should operate as a remote backup protection for the next line to clear the fault.

[0093] Meanwhile, in case of overload, an equivalent undervoltage protection stage III needs to be set. When the voltage at bus C is less than the setting value of protection stage III of this line, after a short delay, the overload is determined by whether the voltage at bus C changes at the end of the delay. Then, protection stage III of protection 1 is used as a remote backup protection to clear the fault.

[0094] The equivalent undervoltage protection stage I does not require a delay, while protection stages II and III require a short delay before operation. The operating time limit should be coordinated with the protection stages I and II of the next line to achieve selective operation of the protection.

[0095] Example 2:

[0096] This embodiment provides a microgrid power supply fast protection device that uses the internal PWM signal of the converter, including:

[0097] Current module: Used to obtain the output current of the converter;

[0098] PWM integrator: Used to determine whether the current has reached the maximum current limit. If so, it samples the PWM signal based on the internal PWM signal of the converter to obtain the effective value of the converter output voltage.

[0099] Protection module: Used to activate undervoltage protection if the effective value of the converter output voltage is less than the starting voltage.

[0100] Specifically, the protection device in this embodiment can be a photovoltaic grid-connected dual-loop control device that uses the internal PWM integral signal of the converter as the criterion.

[0101] The photovoltaic grid-connected dual-loop control device consists of a circuit breaker, a protection module, a PWM integrator, and a power electronic grid-connected control device. The power electronic grid-connected control device can perform closed-loop control of the output current. According to the change of the input current, it modulates the output current of the AC / DC converter (set between buses A and B) by adjusting the pulse width, thereby reducing the fluctuation of the output current caused by changes in environmental weather.

[0102] When the output current limit is detected, the power electronic grid-connected control device collects the PWM signal inside the converter and obtains the effective value of the converter output voltage by performing half-wave integration on the signal through an integrator.

[0103] The protection module compares the effective value of the converter output voltage obtained by integration with the starting voltage (0.2-0.3 of the rated output voltage) to determine whether the fault is on the line or inside the converter. For faults within the zone, the internal circuit breaker of the device will operate. For faults outside the zone, it will cooperate with the equivalent segmented undervoltage protection to achieve selective disconnection of faults on different lines.

[0104] The photovoltaic grid-connected dual-loop control device can collect the PWM signal inside the converter and obtain the effective value of the converter output voltage by performing half-wave integration on the signal through an integrator. The protection module compares this voltage with the output voltage under normal operation to determine whether a short circuit fault has occurred in the system.

[0105] In the event of a fault, the protection module can further determine the location of the fault. When a short-circuit fault occurs inside the converter, the circuit breaker included in the control device will immediately disconnect the renewable energy power supply without delay. When a fault occurs on the microgrid line, the photovoltaic grid-connected dual-loop control device can cooperate with the equivalent segmented undervoltage protection equipped on the line to achieve selective isolation of the short-circuit fault.

[0106] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only used to facilitate the description of the present invention and to simplify the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the scope of protection of the present invention.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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 method for fast protection of microgrid power supplies using internal PWM signals of the converter, characterized in that, Based on a microgrid system, the microgrid system includes new energy power sources, loads, and converters; The method includes the following steps: Obtain the current output from the converter; Determine whether the current has reached the maximum current limit. If so, sample the PWM signal based on the internal PWM signal of the converter to obtain the effective value of the converter output voltage. If the effective value of the converter output voltage is less than the starting voltage, the location of the fault is determined based on the effective value of the converter output voltage, and the undervoltage protection is activated. The effective value of the converter output voltage is obtained by sampling the PWM signal based on the internal PWM signal of the converter, including: Obtain the internal PWM signal of the converter; Give the general function of PWM signal waveform The expression is: ； in: The set of all time points where the signal is 1. The set of all time points where the signal is 0. The effective value of the converter output voltage E can be obtained by performing a half-wave integral on the waveform function, given the set of all time points where the signal is -1. ； in: This refers to the converter output voltage under normal operating conditions. This represents any time at which the integration begins; This is the PWM waveform inside the converter; Implement equivalent segmented undervoltage protection to selectively isolate faults on different lines, including: The effective value of the converter output voltage The fault location is determined by comparing the value with the internal low voltage protection setting of the converter, and each protection section selectively delays the clearing of the fault. The microgrid is equipped with bus C, bus D, bus E, and bus F, which divides the lines into lines CD, DE, and EF; and protects the lines between protection bus CD in section I, the lines between protection bus CE in section II, and the lines between protection bus CF in section III. The effective value of the converter output voltage The fault location is determined by comparing the fault location with the internal low-voltage protection setting of the converter. Each protection stage selectively delays the clearing of the fault, including: When the effective value of the converter output voltage When the value is less than the setting value of the protection stage I of this line, it is determined that the short circuit fault occurred on this line, and the protection stage I immediately operates to clear the fault; otherwise, the protection does not operate. When the effective value of the converter output voltage If the effective value of the converter output voltage is less than the setting value of the protection stage II of this line, a short delay will be performed. If the effective value of the converter output voltage rises before the end of the delay, it indicates that the fault occurred on line DE or EF and has been cleared by other protections, and protection stage II will not operate. If the effective value of the converter output voltage is still lower than the setting value after the short delay, it indicates that the protection on line DE or EF fails to operate. In this case, protection stage II will operate as a remote backup protection for the next line to clear the fault. When the voltage at bus C is less than the setting value of protection section III of this line, a short delay is performed. If the effective value of the converter output voltage rises to no less than the setting value of protection section III before the end of the delay, protection section III will not operate. If the effective value of the converter output voltage is still lower than the setting value of protection section III after the short delay, protection section III will operate as a remote backup protection to clear the fault.

2. The microgrid power supply fast protection method using the internal PWM signal of the converter as described in claim 1, characterized in that, The maximum current limit is 1.2-1.5 times the rated output current of the converter.

3. The microgrid power supply fast protection method using the internal PWM signal of the converter as described in claim 1, characterized in that, The start-up voltage Set to 0.8 times the rated output voltage of the converter; When the effective value of the converter output voltage Below the starting voltage If a short circuit fault is detected, the location of the fault is determined by the effective value of the converter output voltage, and the undervoltage protection is activated; otherwise, the protection will not operate.

4. The microgrid power supply fast protection method using the internal PWM signal of the converter as described in claim 1, characterized in that, The location of the fault is determined based on the effective value of the converter output voltage, and the undervoltage protection is activated, including: When the effective value of the converter output voltage If the voltage is lower than the threshold voltage, it is determined to be an internal fault in the converter, and the new energy power supply is directly disconnected to protect the power supply. When the effective value of the converter output voltage When the voltage exceeds the threshold voltage, it is determined to be an external fault of the converter, and equivalent segmented undervoltage protection is implemented to selectively disconnect faults from different lines.

5. The microgrid power supply fast protection method using the internal PWM signal of the converter according to claim 4, characterized in that, The protection I-stage setting value for: ； In the formula, This indicates the normal output current of the converter under normal operating conditions; The line impedance of the transmission line between busbars C and D; The reliability coordination factor for the undervoltage protection stage I of protection 1; The protection stage II setting value for: ； In the formula, To ensure the reliability coefficient of the undervoltage protection stage II of protection 1, The operating setting value for the undervoltage protection stage I of protection 2 on line DE; The protection stage III setting value for: ； In the formula, To ensure the reliability coefficient of the undervoltage protection stage II of protection 1, This refers to the load current that may occur under system overload conditions. Let DE be the total impedance of the line. Let EF be the total impedance of the line.

6. The microgrid power supply fast protection method using the internal PWM signal of the converter according to claim 5, characterized in that, Take 0.8-0.9; Take 0.85; Take 0.

85.

7. A microgrid power supply fast protection device employing an internal PWM signal of the converter for performing the method as described in claim 1, characterized in that, include: Current module: Used to obtain the output current of the converter; PWM Integrator: Used to determine whether the current has reached the maximum current limit. If so, it samples the PWM signal based on the internal PWM signal of the converter to obtain the effective value of the converter output voltage. Protection module: Used to activate undervoltage protection if the effective value of the converter output voltage is less than the starting voltage.

Images