Longitudinal differential protection method and device for micro-grid line and storage medium

Abstract

The invention discloses a longitudinal differential protection method and device for a micro-grid line and a storage medium. The method comprises the following steps: acquiring normal operation parameters and short-circuit operation parameters of a micro-grid line; according to the normal operation parameters and the short-circuit operation parameters, virtual short-circuit current output by the inverter is calculated; calculating virtual differential current and integer braking current of the micro-grid line according to the virtual short-circuit current; and determining whether the micro-grid line has a short-circuit fault or not according to the virtual differential current and the integer braking current. According to the technical scheme provided by the embodiment of the invention, the influence of relatively small short-circuit current on the sensitivity of the protection device is solved, the sensitivity of the protection device is effectively improved, a relay protection function with good performance can be realized in a micro-grid using an inverter for alternating current transmission, and relatively high engineering practicability is achieved.

Description

Technical Field

[0001] The present invention relates to the field of microgrid control technology, and in particular to a longitudinal differential protection method, device and storage medium for a microgrid line. Background Art

[0002] At present, my country is vigorously developing new energy, most of which are not fully controllable energy, such as wind power, solar energy, etc. Its frequency cannot be guaranteed to be completely consistent with the frequency of the normal power grid, so DC transmission and distribution can be used, so DC-AC-DC microgrids often appear.

[0003] In the microgrid, a three-phase voltage source is formed by controlling the pulse width modulation (PWM) of the inverter power supply, and the short-circuit current is controlled to reduce the short-circuit current when the AC part fails. However, because the short-circuit current is relatively small compared to the short-circuit current of the traditional microgrid line when the inverter power supply is not used, after passing through the current transformer, the longitudinal differential protection device will find it difficult to sensitively detect the occurrence of internal short-circuit faults. Therefore, in order to solve the above problems, a new longitudinal differential protection method is proposed for the microgrid structure using inverter power PWM control. Summary of the invention

[0004] The present invention provides a longitudinal differential protection method, device and storage medium for a microgrid line, so as to solve the problem of poor sensitivity of the longitudinal differential protection device in the prior art.

[0005] According to one aspect of the present invention, a longitudinal differential protection method for a microgrid line is provided, comprising:

[0006] Collect normal operation parameters and short-circuit operation parameters of microgrid lines;

[0007] Calculating a virtual short-circuit current output by the inverter according to the normal operating parameters and the short-circuit operating parameters;

[0008] Calculating a virtual differential current and a set braking current of a microgrid line according to the virtual short-circuit current;

[0009] Whether a short circuit fault occurs in the microgrid line is determined according to the virtual differential current and the set braking current.

[0010] Optionally, the calculating the virtual short-circuit current output by the inverter according to the normal operating parameter and the short-circuit operating parameter includes:

[0011] Calculating a virtual short-circuit current magnification factor according to the normal operating parameters and the short-circuit operating parameters;

[0012] The virtual short-circuit current output by the inverter is calculated according to the virtual short-circuit current amplification factor and the short-circuit operation parameter.

[0013] Optionally, the normal operating parameters include a first DC voltage, a second DC voltage, a first duty cycle, a second duty cycle, a first AC voltage, a second AC voltage, a first AC current, and a second AC current when the microgrid line is operating normally; the short-circuit operating parameters include a first DC voltage, a second DC voltage, a first duty cycle, a second duty cycle, a first AC voltage, a second AC voltage, a first AC current, and a second AC current when the microgrid line is operating in short circuit;

[0014] The calculating the virtual short-circuit current magnification factor according to the normal operating parameters and the short-circuit operating parameters comprises:

[0015] Calculating a first virtual short-circuit current leakage voltage ratio according to a first alternating current voltage, a first alternating current, and a first internal resistance when the microgrid line is operating normally;

[0016] Calculate a first short-circuit current leakage voltage ratio according to a first AC voltage, a first AC current and the first internal resistance when the microgrid line is in short-circuit operation;

[0017] Calculating a second virtual short-circuit current leakage voltage ratio according to a second alternating current voltage, a second alternating current, and a second internal resistance when the microgrid line is operating normally;

[0018] Calculate a second short-circuit current leakage voltage ratio according to the second AC voltage, the second AC current and the second internal resistance when the microgrid line is in short-circuit operation;

[0019] Calculate a first virtual short-circuit current amplification factor according to the first virtual short-circuit current leakage voltage ratio and the first short-circuit current leakage voltage ratio, a first half-wave integral signal calculated from a first duty cycle when the microgrid line is operating normally, and a first half-wave integral signal calculated from a first duty cycle when the microgrid line is short-circuited;

[0020] The second virtual short-circuit current amplification factor is calculated according to the second virtual short-circuit current leakage voltage ratio and the second short-circuit current leakage voltage ratio, the second half-wave integral signal calculated by the second duty cycle when the microgrid line is operating normally, and the second half-wave integral signal calculated by the second duty cycle when the microgrid line is short-circuited.

[0021] Optionally, calculating the virtual short-circuit current output by the inverter according to the virtual short-circuit current amplification factor and the short-circuit operation parameter includes:

[0022] Calculate a first virtual short-circuit current according to the first virtual short-circuit current amplification factor and a first alternating current when the microgrid line is in short-circuit operation;

[0023] The second virtual short-circuit current is calculated according to the second virtual short-circuit current amplification factor and the second alternating current when the microgrid line is in short-circuit operation.

[0024] Optionally, the calculating the virtual differential current and the set braking current of the microgrid line according to the virtual short-circuit current includes:

[0025] Calculating a virtual differential current of a microgrid line according to the virtual short-circuit current;

[0026] The setting braking current is determined according to the virtual differential current, the preset minimum virtual differential current, the preset minimum setting braking current and the virtual short-circuit current.

[0027] Optionally, determining the setting braking current according to the virtual differential current, the preset minimum virtual differential current, the preset minimum setting braking current and the virtual short-circuit current includes:

[0028] Determining whether the virtual differential current is less than the preset minimum virtual differential current; if so, determining the preset minimum setting braking current as the setting braking current;

[0029] If not, the absolute value of the difference between the primary-side virtual short-circuit current and the secondary-side virtual short-circuit current is determined as the adjustment braking current.

[0030] Optionally, determining whether a short circuit fault occurs in the microgrid line according to the virtual differential current and the set braking current includes:

[0031] Determine whether the virtual differential current is less than or equal to the set braking current. If so, determine that no short circuit fault occurs in the microgrid line, and return to the step of collecting normal operating parameters and current operating parameters of the microgrid line;

[0032] If not, it is determined that a short circuit fault occurs in the microgrid line, and a protection action is performed.

[0033] According to another aspect of the present invention, a longitudinal differential protection device for a microgrid line is provided, comprising:

[0034] A collection module, the collection module is used to collect normal operating parameters and short-circuit operating parameters of the microgrid line;

[0035] A first calculation module, the first calculation module is used to calculate a virtual short-circuit current output by the inverter according to the normal operating parameters and the short-circuit operating parameters;

[0036] A second calculation module, the second calculation module is used to calculate the virtual differential current and the set braking current of the microgrid line according to the virtual short-circuit current;

[0037] A determination module is used to determine whether a short circuit fault occurs in the microgrid line according to the virtual differential current and the set braking current.

[0038] Optionally, the first calculation module includes a virtual short-circuit current amplification factor calculation module and a virtual short-circuit current calculation module;

[0039] The virtual short-circuit current magnification calculation module is used to calculate the virtual short-circuit current magnification according to the normal operating parameters and the short-circuit operating parameters;

[0040] The virtual short-circuit current calculation module is used to calculate the virtual short-circuit current output by the inverter according to the virtual short-circuit current amplification factor and the short-circuit operation parameters.

[0041] According to another aspect of the present invention, a computer-readable storage medium is provided, wherein the computer-readable storage medium stores computer instructions, and the computer instructions are used to enable a processor to implement the longitudinal differential protection method for a microgrid line described in any embodiment of the present invention when executed.

[0042] The technical solution provided by the embodiment of the present invention collects the normal operating parameters and short-circuit operating parameters of the microgrid line; calculates the virtual short-circuit current output by the inverter according to the normal operating parameters and the short-circuit operating parameters; calculates the virtual differential current and the set braking current of the microgrid line according to the virtual short-circuit current; and determines whether the microgrid line has a short-circuit fault according to the virtual differential current and the set braking current. First, for a microgrid whose power supply is an inverter power supply, the limiting condition of the inverter power supply is judged by the PWM duty cycle; secondly, according to the half-wave integral of PWM and the DC side voltage of the inverter, the inverter is constructed as a voltage source type three-phase power supply, and its output current is virtualized as the external short-circuit output current of the voltage source; finally, an error braking standard is proposed. This method effectively solves the influence of a small short-circuit current on the sensitivity of the protection device by amplifying the short-circuit current measured by the protection device, effectively improves the sensitivity of the protection device, and can achieve a good performance relay protection function in a microgrid using an inverter for AC transmission, and has high engineering practicality.

[0043] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0045] Figure 1 A flow chart of a longitudinal differential protection method for a microgrid line provided by an embodiment of the present invention;

[0046] Figure 2 A schematic diagram of a microgrid circuit structure using inverter PWM signal control provided in an embodiment of the present invention;

[0047] Figure 3 A flow chart of another longitudinal differential protection method for a microgrid line provided by an embodiment of the present invention;

[0048] Figure 4 An equivalent circuit diagram of an inverter power supply provided by an embodiment of the present invention;

[0049] Figure 5 The equivalent structure diagram of the microgrid circuit provided in this embodiment;

[0050] Figure 6 The action characteristic curve diagram of the longitudinal differential protection device provided in the embodiment of the present invention;

[0051] Figure 7 A schematic structural diagram of a longitudinal differential protection device for a microgrid line provided in an embodiment of the present invention;

[0052] Figure 8 A schematic diagram of the structure of an electronic device for a longitudinal differential protection method for a microgrid line provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0053] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0054] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0055] Figure 1 This is a flow chart of a longitudinal differential protection method for a microgrid line provided by an embodiment of the present invention. This embodiment can be applied to longitudinal differential protection of a microgrid line controlled by an inverter PWM signal. The method can be executed by a longitudinal differential protection device for a microgrid line. The longitudinal differential protection device can be implemented in the form of hardware and / or software. The longitudinal differential protection device can be configured in any electronic device with a communication function. Figure 1 , the longitudinal differential protection method includes:

[0056] S110. Collect normal operating parameters and short-circuit operating parameters of the microgrid line.

[0057] The normal operating parameters include parameters such as voltage, current and duty cycle when the microgrid line is in normal operation, and the short-circuit operating parameters include parameters such as voltage, current and duty cycle when the microgrid line is in short-circuit operation. Specifically, the normal operating parameters and short-circuit operating parameters of the microgrid line are respectively collected through a voltage transformer, a current transformer and a duty cycle measuring device, wherein the duty cycle measuring device can be, for example, an oscilloscope, a single-chip microcomputer or a counter, and the present invention does not limit this.

[0058] S120. Calculate a virtual short-circuit current output by the inverter according to the normal operating parameters and the short-circuit operating parameters.

[0059] Figure 2 This is a schematic diagram of a microgrid line structure using an inverter PWM signal control provided by an embodiment of the present invention. Only under this structure can the microgrid line longitudinal differential protection method provided by an embodiment of the present invention be used to perform line longitudinal differential protection on the microgrid. Figure 2The structure includes two inverter power supplies, a microgrid line and two protection devices. The two inverters are connected through the microgrid line. One inverter power supply corresponds to one protection device. The first inverter power supply PWM1 is connected to the protection device 1, and the second inverter power supply PWM2 is connected to the protection device 2. The protection device 1 and the protection device 2 are connected through a communication optical fiber. Two voltage-type inverters are used as power supplies to realize the power supply of the microgrid system. The DC side power supplies Udc1 and Udc2 are constant and do not change during normal operation and fault operation. The control of the AC voltage and current waveform of the inverter power supply can be realized by controlling the PWM signal. The AC side current can be measured by the current transformer, and the current transformer can be integrated in the protection device. In addition, this system also needs a duty cycle measurement device, which can be integrated in the protection device to measure the time interval between the two rising edges of the PWM waveform and the time interval between a rising edge and a falling edge to obtain the duty cycle of the PWM waveform. Finally, the AC side current and duty cycle signal are input into the protection devices on both sides respectively. The protection devices then transmit the converted virtual current signal to the opposite side. After the logical judgment inside the protection device, it can be determined whether there is a short circuit fault inside the system and whether it is necessary to trip immediately to eliminate the fault.

[0060] S130. Calculate a virtual differential current and a set braking current of the microgrid line according to the virtual short-circuit current.

[0061] Among them, virtual differential current is generally a concept used in specific scenarios such as power system protection or electrical equipment monitoring. Generally, differential current refers to the difference between the current flowing into and out of the protected equipment (such as transformers, motors, etc.). However, virtual differential current is not the traditional differential current actually measured. It may be a value similar to differential current obtained through a specific algorithm, model or equivalent calculation. For example, in some intelligent protection devices or advanced monitoring systems, in order to improve the reliability and sensitivity of protection, various data and information may be used to construct a virtual differential current through complex calculations and analysis to determine whether the equipment has a fault or abnormal operating state. Virtual differential current can comprehensively consider multiple factors, such as equipment operating parameters, historical data, environmental conditions, etc., to more accurately reflect the actual operating status of the equipment and provide a basis for protection and control decisions. The set trip current is usually a current value set in an electrical protection device (such as a motor protection device, a line protection device, etc.). When the actual detected current reaches or exceeds this set trip current, the protection device will trigger the corresponding protection action, such as cutting off the circuit, issuing an alarm signal, etc. The setting of the adjustment braking current generally needs to be determined through comprehensive consideration and calculation based on factors such as the rated current, operating characteristics and possible fault conditions of the protected equipment, so as to ensure timely and effective protection when abnormal current occurs in the equipment, while avoiding false operation during normal operation.

[0062] S140. Determine whether a short circuit fault occurs in the microgrid line according to the virtual differential current and the set braking current.

[0063] The technical solution provided by the embodiment of the present invention collects the normal operating parameters and short-circuit operating parameters of the microgrid line; calculates the virtual short-circuit current output by the inverter according to the normal operating parameters and the short-circuit operating parameters; calculates the virtual differential current and the set braking current of the microgrid line according to the virtual short-circuit current; and determines whether the microgrid line has a short-circuit fault according to the virtual differential current and the set braking current. First, for a microgrid whose power supply is an inverter power supply, the limiting condition of the inverter power supply is judged by the PWM duty cycle; secondly, according to the half-wave integral of PWM and the DC side voltage of the inverter, the inverter is constructed as a voltage source type three-phase power supply, and its output current is virtualized as the external short-circuit output current of the voltage source; finally, an error braking standard is proposed. This method effectively solves the influence of a small short-circuit current on the sensitivity of the protection device by amplifying the short-circuit current measured by the protection device, effectively improves the sensitivity of the protection device, and can achieve a good performance relay protection function in a microgrid using an inverter for AC transmission, and has high engineering practicality.

[0064] Optionally, calculating the virtual short-circuit current output by the inverter according to the normal operating parameters and the short-circuit operating parameters includes:

[0065] The virtual short-circuit current amplification factor is calculated based on the normal operating parameters and the short-circuit operating parameters.

[0066] Among them, the normal operating parameters include the first DC voltage, the second DC voltage, the first duty cycle, the second duty cycle, the first AC voltage, the second AC voltage, the first AC current and the second AC current when the microgrid line is operating normally; the short-circuit operating parameters include the first DC voltage, the second DC voltage, the first duty cycle, the second duty cycle, the first AC voltage, the second AC voltage, the first AC current and the second AC current when the microgrid line is operating in short circuit.

[0067] Optionally, a first virtual short-circuit current leakage voltage ratio is calculated based on a first AC voltage, a first AC current and a first internal resistance when the microgrid line operates normally.

[0068] Specifically, the first virtual short-circuit current leakage voltage ratio is calculated using the following formula:

[0069] In the formula, δ 1 % is the first virtual short-circuit current leakage voltage ratio, I 1 is the first AC current when the microgrid line is operating normally, R s1 is the first internal resistance, U 1 It is the first AC voltage when the microgrid line operates normally.

[0070] A first short-circuit current leakage voltage ratio is calculated according to a first alternating current voltage, a first alternating current and the first internal resistance when the microgrid line is in short-circuit operation.

[0071] Specifically, the first short-circuit current leakage voltage ratio is calculated using the following formula:

[0072] In the formula, δ ‘ 1 % is the first short-circuit current leakage voltage ratio, I ′ 1 is the first AC current when the microgrid line is in short circuit operation, U ′ 1 It is the first AC voltage when the microgrid line is in short-circuit operation.

[0073] A second virtual short-circuit current leakage voltage ratio is calculated according to the second alternating current voltage, the second alternating current and the second internal resistance when the microgrid line operates normally.

[0074] Specifically, the second virtual short-circuit current leakage voltage ratio is calculated using the following formula:

[0075] In the formula, δ 2 % is the second virtual short-circuit current leakage voltage ratio, I 2is the second AC current when the microgrid line is operating normally, R s2 is the second internal resistance, U 2 It is the second AC voltage when the microgrid line operates normally.

[0076] The second short-circuit current leakage voltage ratio is calculated according to the second alternating current voltage, the second alternating current and the second internal resistance when the microgrid line is in short-circuit operation.

[0077] Specifically, the second short-circuit current leakage voltage ratio is calculated using the following formula:

[0078] In the formula, δ ‘ 2 % is the second short-circuit current leakage voltage ratio, I ′ 2 is the second AC current when the microgrid line is in short circuit operation, U ′ 2 It is the second AC voltage when the microgrid line is in short-circuit operation.

[0079] The first virtual short-circuit current amplification factor is calculated according to the first virtual short-circuit current leakage voltage ratio and the first short-circuit current leakage voltage ratio, the first half-wave integral signal calculated by the first duty cycle when the microgrid line is operating normally, and the first half-wave integral signal calculated by the first duty cycle when the microgrid line is short-circuited.

[0080] Among them, the first half-wave integral signal. ∫PWM=∑E k , k = 1, 2..., n, n is the number of PWM pulses in half wave, E k It indicates the electromotive force in the corresponding pulse time, and its size is related to the duty cycle. Therefore, ∫PWM is the numerical integration of the waveform. By measuring the duty cycle, ∫PWM can be calculated. The value is the area of ​​the half wave, which is related to the duty cycle. When the duty cycle increases, the area increases, and ∫PWM increases. The same is true for other half-wave integral signals.

[0081] Specifically, the first virtual short-circuit current magnification is calculated using the following formula:

[0082] In the formula, is the first virtual short-circuit current magnification factor, ∫PWM 1 is the first half-wave integral signal when the microgrid line is operating normally, ∫PWM ′ 1 It is the first half-wave integral signal when the microgrid is in short-circuit operation.

[0083] The second virtual short-circuit current amplification factor is calculated according to the second virtual short-circuit current leakage voltage ratio and the second short-circuit current leakage voltage ratio, the second half-wave integral signal calculated by the second duty cycle when the microgrid line is operating normally, and the second half-wave integral signal calculated by the second duty cycle when the microgrid line is short-circuited.

[0084] Specifically, the second virtual short-circuit current magnification is calculated using the following formula:

[0085] In the formula, is the second virtual short-circuit current magnification, PWM 2 It is the second half-wave integral signal when the microgrid is operating normally, PWM ′ 2 It is the second half-wave integral signal when the microgrid is in short-circuit operation.

[0086] The virtual short-circuit current output by the inverter is calculated according to the virtual short-circuit current amplification factor and the short-circuit operation parameters.

[0087] Specifically, the first virtual short-circuit current is calculated according to the first virtual short-circuit current amplification factor and the first alternating current when the microgrid line is in short-circuit operation.

[0088] The first virtual short-circuit current is calculated using the following formula:

[0089] In the formula, is the first virtual short-circuit current, I ′ 1 is the first AC current when the microgrid line is short-circuited. is the first virtual short-circuit current magnification factor.

[0090] The second virtual short-circuit current is calculated according to the second virtual short-circuit current magnification factor and the second alternating current when the microgrid line is in short-circuit operation.

[0091] The second virtual short-circuit current is calculated using the following formula:

[0092] In the formula, is the second virtual short-circuit current, is the second virtual short-circuit current magnification factor, I ′ 2 It is the second AC current when the microgrid line is in short-circuit operation.

[0093] Optionally, calculating the virtual differential current and the set braking current of the microgrid line according to the virtual short-circuit current includes:

[0094] The virtual differential current of the microgrid line is calculated based on the virtual short-circuit current.

[0095] Specifically, the virtual differential current of the microgrid line is calculated using the following formula:

[0096] In the formula, ΔI * is the virtual differential current.

[0097] The setting braking current is determined according to the virtual differential current, the preset minimum virtual differential current, the preset minimum setting braking current and the virtual short-circuit current.

[0098] Optionally, determining the setting braking current according to the virtual differential current, the preset minimum virtual differential current, the preset minimum setting braking current and the virtual short-circuit current includes:

[0099] Determine whether the virtual differential current is less than the preset minimum virtual differential current; if so, determine the preset minimum setting braking current as the setting braking current; if not, determine the absolute value of the difference between the primary side virtual short-circuit current and the secondary side virtual short-circuit current as the setting braking current.

[0100] Specifically, the virtual differential current ΔI is determined * Is it less than the preset minimum virtual differential current? when hour, Adjust according to actual data; Thereby, the protection device can accurately implement longitudinal differential protection action under different virtual differential current sizes.

[0101] Optionally, determining whether a short circuit fault occurs in the microgrid line according to the virtual differential current and the set braking current includes:

[0102] Determine whether the virtual differential current is less than or equal to the set braking current. If so, determine that no short-circuit fault occurs in the microgrid line, and return to the step of collecting the normal operating parameters and current operating parameters of the microgrid line; if not, determine that a short-circuit fault occurs in the microgrid line, and execute a protection action.

[0103] Specifically, the virtual differential current ΔI is determined * Is it less than or equal to the set braking current? when It is determined that there is no short circuit fault in the microgrid line, and the process returns to the step of collecting the normal operating parameters and current operating parameters of the microgrid line; when This means that the differential current is greater than the braking current, and a short circuit fault has occurred in the AC part, requiring protection action, that is, immediately tripping to cut off the faulty line.

[0104] The following is a specific example to introduce the longitudinal differential protection method for microgrid lines provided by an embodiment of the present invention. Figure 3 A flow chart of another longitudinal differential protection method for a microgrid line provided in an embodiment of the present invention.

[0105] During normal operation, the inverter power supply serves as the power supply of the system to realize the power supply of the microgrid system, the DC side power supply is constant, and the PWM waveform is constant. When a short circuit fault occurs inside the microgrid, the short circuit current will increase sharply when the duty cycle remains unchanged, but due to the influence of PWM control, its duty cycle changes, and the short circuit current will therefore decrease, ultimately making the short circuit current increase less than the working current during normal operation.

[0106] When the PWM duty cycle remains unchanged, using the Thevenin theorem, Figure 2 The two inverter power supplies are equivalent to a three-phase voltage source with internal impedance. The symmetrical three-phase can be simplified to a single-phase power supply, such as Figure 4 As shown, Figure 4 The equivalent circuit diagram of the inverter power supply provided by the embodiment of the present invention, and the formula ①K can be obtained 1 *∫PWM 1 *U dc1 =I 1 *R s1 +U 1 , where the DC voltage U dc1 , three groups of PWM half-wave integral signals ∫PWM 1 , three-phase current effective value I 1 , three-phase voltage source U 1 All of them can be directly measured by the device, only the ratio K 1 、Internal resistance R s1 Unknown. Similarly, simplifying the other side can form the following Figure 5 The equivalent circuit diagram shown is Figure 5 This is the equivalent structure diagram of the microgrid line provided in this embodiment. When a short circuit occurs between two voltage sources, the DC voltage U dc1 , U dc2 , internal impedance R s1 , R s2 However, since the PWM control of the inverter will limit the short-circuit current by controlling the duty cycle, it is necessary to re-measure the three sets of PWM half-wave integral signals ∫PWM ′ 1 ,∫PWM ′ 2 , three-phase short-circuit current effective value I ′ 1 ,I ′ 2 , thus constructing a three-phase voltage source U during short circuit′ 1 , U ′ 2 , for side 1, we can get formula ②K 1 *∫PWM ′ 1 *U dc1 =I ′ 1 *R s1 +U ′ 1 However, since the PWM control makes the short-circuit current small, it is not easy for the protection device to detect system abnormalities, which may cause the system to refuse to operate. Therefore, it is assumed that there is no PWM control, the duty cycle before and after the short circuit remains unchanged, and the three groups of PWM half-wave integral signals after the short circuit are still ∫PWM 1 , at this time, formula ③ can be obtained for side 1 By solving the formulas together, we can get in The same can be said

[0108] At this time, the amplified virtual short-circuit current can be used for longitudinal differential protection with proportional braking characteristics. The longitudinal differential protection with proportional braking characteristics takes the absolute value of the sum of the currents on both sides as the differential current, and the absolute value of the difference between the currents on both sides as the braking current. Its action characteristics are as follows: Figure 6 As shown, Figure 6 The longitudinal differential protection device action characteristic curve diagram provided in the embodiment of the present invention. In the inverter PWM signal microgrid embodiment targeted by the present invention, its virtual differential current is The virtual braking current is When the protection device determines When , it means that the differential current is greater than the braking current, and a short circuit fault has occurred in the AC part, which requires protection action to cut off the faulty line, otherwise continue to detect.

[0109] Compared with the prior art, the present invention has the following beneficial effects:

[0110] (1) The present invention proposes a method for longitudinal differential protection of a microgrid line using an inverter PWM signal. Compared with the traditional method of directly using the measured current for differential comparison, it takes into account the influence of the PWM control in the inverter on the short-circuit current and amplifies the tiny current difference. Therefore, after the microgrid is short-circuited, even if the short-circuit current is very small, the longitudinal differential current is also very small, and there is no need to improve the reliability of the protection by reducing the protection setting value. By amplifying the current, both reliability and sensitivity are guaranteed.

[0111] (2) The present invention proposes a method for longitudinal differential protection of a microgrid line using an inverter PWM signal. The existing grid current protection device can be used. The PWM half-wave signal, DC voltage, and three-phase current effective value can be directly read without changing the circuit structure. Only certain improvements need to be made to the internal program of the protection device to increase the calculation of the virtual current. In addition, the present invention adopts a differential protection with a proportional braking characteristic, which has higher reliability and sensitivity, certain adaptability, and high engineering practicality.

[0112] Figure 7 A schematic diagram of a longitudinal differential protection device for a microgrid line provided in an embodiment of the present invention is shown in FIG. Figure 7 The longitudinal differential protection device includes a collection module 710, a first calculation module 720, a second calculation module 730 and a de-rating module 740.

[0113] The acquisition module 710 is used to acquire normal operation parameters and short circuit operation parameters of the microgrid line;

[0114] The first calculation module 720 is used to calculate the virtual short-circuit current output by the inverter according to the normal operating parameters and the short-circuit operating parameters.

[0115] The second calculation module 730 is used to calculate the virtual differential current and the set braking current of the microgrid line according to the virtual short-circuit current.

[0116] The determination module 740 is used to determine whether a short circuit fault occurs in the microgrid line according to the virtual differential current and the set braking current.

[0117] Optionally, the first calculation module 720 includes a virtual short-circuit current amplification factor calculation module and a virtual short-circuit current calculation module;

[0118] The virtual short-circuit current magnification calculation module is used to calculate the virtual short-circuit current magnification according to the normal operating parameters and the short-circuit operating parameters;

[0119] The virtual short-circuit current calculation module is used to calculate the virtual short-circuit current output by the inverter according to the virtual short-circuit current magnification factor and the short-circuit operation parameters.

[0120] The longitudinal differential protection device for a microgrid line provided in an embodiment of the present invention can execute the longitudinal differential protection method for a microgrid line provided in any embodiment of the present invention, and has functional modules and beneficial effects corresponding to the execution method.

[0121] Figure 8A schematic diagram of the electronic device structure of a longitudinal differential protection method for a microgrid line provided in an embodiment of the present invention. The electronic device is intended to represent various forms of digital computers, such as laptop computers, desktop computers, workbenches, personal digital assistants, servers, blade servers, mainframe computers, and other suitable computers. The electronic device may also represent various forms of mobile devices, such as personal digital processing, cellular phones, smart phones, wearable devices (such as helmets, glasses, watches, etc.) and other similar computing devices. The components shown herein, their connections and relationships, and their functions are merely examples and are not intended to limit the implementation of the present invention described and / or required herein.

[0122] like Figure 8 As shown, the electronic device 10 includes at least one processor 11, and a memory connected to the at least one processor 11, such as a read-only memory (ROM) 12, a random access memory (RAM) 13, etc., wherein the memory stores a computer program that can be executed by at least one processor, and the processor 11 can perform various appropriate actions and processes according to the computer program stored in the read-only memory (ROM) 12 or the computer program loaded from the storage unit 18 to the random access memory (RAM) 13. In the RAM 13, various programs and data required for the operation of the electronic device 10 can also be stored. The processor 11, the ROM 12, and the RAM 13 are connected to each other through a bus 14. An input / output (I / O) interface 15 is also connected to the bus 14.

[0123] A number of components in the electronic device 10 are connected to the I / O interface 15, including: an input unit 16, such as a keyboard, a mouse, etc.; an output unit 17, such as various types of displays, speakers, etc.; a storage unit 18, such as a disk, an optical disk, etc.; and a communication unit 19, such as a network card, a modem, a wireless communication transceiver, etc. The communication unit 19 allows the electronic device 10 to exchange information / data with other devices through a computer network such as the Internet and / or various telecommunication networks.

[0124] The processor 11 may be a variety of general and / or special processing components with processing and computing capabilities. Some examples of the processor 11 include, but are not limited to, a central processing unit (CPU), a graphics processing unit (GPU), various special artificial intelligence (AI) computing chips, various processors running machine learning model algorithms, digital signal processors (DSPs), and any appropriate processors, controllers, microcontrollers, etc. The processor 11 executes the various methods and processes described above, such as a longitudinal differential protection method for a microgrid line.

[0125] In some embodiments, the longitudinal differential protection method of the microgrid line can be implemented as a computer program, which is tangibly contained in a computer-readable storage medium, such as a storage unit 18. In some embodiments, part or all of the computer program can be loaded and / or installed on the electronic device 10 via the ROM 12 and / or the communication unit 19. When the computer program is loaded into the RAM 13 and executed by the processor 11, one or more steps of the longitudinal differential protection method of the microgrid line described above can be performed. Alternatively, in other embodiments, the processor 11 can be configured to execute the longitudinal differential protection method of the microgrid line in any other appropriate manner (for example, by means of firmware).

[0126] Various implementations of the systems and techniques described above herein can be implemented in digital electronic circuit systems, integrated circuit systems, field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), application specific standard products (ASSPs), systems on chips (SOCs), load programmable logic devices (CPLDs), computer hardware, firmware, software, and / or combinations thereof. These various implementations can include: being implemented in one or more computer programs that can be executed and / or interpreted on a programmable system including at least one programmable processor, which can be a special purpose or general purpose programmable processor that can receive data and instructions from a storage system, at least one input device, and at least one output device, and transmit data and instructions to the storage system, the at least one input device, and the at least one output device.

[0127] Computer programs for implementing the methods of the present invention may be written in any combination of one or more programming languages. These computer programs may be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing device, so that when the computer program is executed by the processor, the functions / operations specified in the flow chart and / or block diagram are implemented. The computer program may be executed entirely on the machine, partially on the machine, partially on the machine and partially on a remote machine as a stand-alone software package, or entirely on a remote machine or server.

[0128] In the context of the present invention, a computer-readable storage medium may be a tangible medium that may contain or store a computer program for use by or in combination with an instruction execution system, device or equipment. A computer-readable storage medium may include, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices or equipment, or any suitable combination of the foregoing. Alternatively, a computer-readable storage medium may be a machine-readable signal medium. A more specific example of a machine-readable storage medium may include an electrical connection based on one or more lines, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0129] To provide interaction with a user, the systems and techniques described herein may be implemented on an electronic device having: a display device (e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor) for displaying information to the user; and a keyboard and a pointing device (e.g., a mouse or trackball) through which the user can provide input to the electronic device. Other types of devices may also be used to provide interaction with the user; for example, the feedback provided to the user may be any form of sensory feedback (e.g., visual feedback, auditory feedback, or tactile feedback); and input from the user may be received in any form (including acoustic input, voice input, or tactile input).

[0130] The systems and techniques described herein may be implemented in a computing system that includes backend components (e.g., as a data server), or a computing system that includes middleware components (e.g., an application server), or a computing system that includes frontend components (e.g., a user computer with a graphical user interface or a web browser through which a user can interact with implementations of the systems and techniques described herein), or a computing system that includes any combination of such backend components, middleware components, or frontend components. The components of the system may be interconnected by any form or medium of digital data communication (e.g., a communication network). Examples of communication networks include: a local area network (LAN), a wide area network (WAN), a blockchain network, and the Internet.

[0131] A computing system may include a client and a server. The client and the server are generally remote from each other and usually interact through a communication network. The client and server relationship is generated by computer programs running on the corresponding computers and having a client-server relationship with each other. The server may be a cloud server, also known as a cloud computing server or cloud host, which is a host product in the cloud computing service system to solve the defects of difficult management and weak business scalability in traditional physical hosts and VPS services.

[0132] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the present invention can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of the present invention can be achieved, and this document does not limit this.

[0133] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A longitudinal differential protection method for a microgrid line, characterized in that: include: Collect normal operation parameters and short-circuit operation parameters of microgrid lines; Calculating a virtual short-circuit current output by the inverter according to the normal operating parameters and the short-circuit operating parameters; Calculating a virtual differential current and a set braking current of a microgrid line according to the virtual short-circuit current; Determine whether a short circuit fault occurs in the microgrid line according to the virtual differential current and the set braking current.

2. The longitudinal differential protection method according to claim 1, characterized in that: Calculating the virtual short-circuit current output by the inverter according to the normal operating parameters and the short-circuit operating parameters includes: Calculating a virtual short-circuit current magnification factor according to the normal operating parameters and the short-circuit operating parameters; The virtual short-circuit current output by the inverter is calculated according to the virtual short-circuit current amplification factor and the short-circuit operation parameter.

3. The longitudinal differential protection method according to claim 2, characterized in that: The normal operating parameters include a first DC voltage, a second DC voltage, a first duty cycle, a second duty cycle, a first AC voltage, a second AC voltage, a first AC current, and a second AC current when the microgrid line is operating normally; The short-circuit operation parameters include a first DC voltage, a second DC voltage, a first duty cycle, a second duty cycle, a first AC voltage, a second AC voltage, a first AC current, and a second AC current when the microgrid line is in short-circuit operation; The calculating the virtual short-circuit current magnification factor according to the normal operating parameters and the short-circuit operating parameters comprises: Calculating a first virtual short-circuit current leakage voltage ratio according to a first alternating current voltage, a first alternating current, and a first internal resistance when the microgrid line is operating normally; Calculate a first short-circuit current leakage voltage ratio according to a first AC voltage, a first AC current and the first internal resistance when the microgrid line is in short-circuit operation; Calculating a second virtual short-circuit current leakage voltage ratio according to a second alternating current voltage, a second alternating current, and a second internal resistance when the microgrid line is operating normally; Calculate a second short-circuit current leakage voltage ratio according to the second AC voltage, the second AC current and the second internal resistance when the microgrid line is in short-circuit operation; Calculate a first virtual short-circuit current amplification factor according to the first virtual short-circuit current leakage voltage ratio and the first short-circuit current leakage voltage ratio, a first half-wave integral signal calculated from a first duty cycle when the microgrid line is operating normally, and a first half-wave integral signal calculated from a first duty cycle when the microgrid line is short-circuited; The second virtual short-circuit current amplification factor is calculated according to the second virtual short-circuit current leakage voltage ratio and the second short-circuit current leakage voltage ratio, the second half-wave integral signal calculated by the second duty cycle when the microgrid line is operating normally, and the second half-wave integral signal calculated by the second duty cycle when the microgrid line is short-circuited.

4. The longitudinal differential protection method according to claim 3, characterized in that: Calculating the virtual short-circuit current output by the inverter according to the virtual short-circuit current magnification factor and the short-circuit operation parameter includes: Calculate a first virtual short-circuit current according to the first virtual short-circuit current amplification factor and a first alternating current when the microgrid line is in short-circuit operation; The second virtual short-circuit current is calculated according to the second virtual short-circuit current amplification factor and the second alternating current when the microgrid line is in short-circuit operation.

5. The longitudinal differential protection method according to claim 1, characterized in that: The calculating of the virtual differential current and the set braking current of the microgrid line according to the virtual short-circuit current comprises: Calculating a virtual differential current of the microgrid line according to the virtual short-circuit current; The setting braking current is determined according to the virtual differential current, the preset minimum virtual differential current, the preset minimum setting braking current and the virtual short-circuit current.

6. The longitudinal differential protection method according to claim 5, characterized in that: Determining the setting braking current according to the virtual differential current, the preset minimum virtual differential current, the preset minimum setting braking current and the virtual short-circuit current includes: Determining whether the virtual differential current is less than the preset minimum virtual differential current; if so, determining the preset minimum setting braking current as the setting braking current; If not, the absolute value of the difference between the primary-side virtual short-circuit current and the secondary-side virtual short-circuit current is determined as the adjustment braking current.

7. The longitudinal differential protection method according to claim 1, characterized in that: The determining whether a short circuit fault occurs in the microgrid line according to the virtual differential current and the set braking current comprises: Determine whether the virtual differential current is less than or equal to the set braking current. If so, determine that no short circuit fault occurs in the microgrid line, and return to the step of collecting normal operating parameters and current operating parameters of the microgrid line; If not, it is determined that a short circuit fault occurs in the microgrid line, and a protection action is performed.

8. A longitudinal differential protection device for a microgrid line, characterized in that: include: A collection module, the collection module is used to collect normal operating parameters and short-circuit operating parameters of the microgrid line; A first calculation module, the first calculation module is used to calculate a virtual short-circuit current output by the inverter according to the normal operating parameters and the short-circuit operating parameters; A second calculation module, the second calculation module is used to calculate the virtual differential current and the set braking current of the microgrid line according to the virtual short-circuit current; A determination module is used to determine whether a short circuit fault occurs in the microgrid line according to the virtual differential current and the set braking current.

9. The longitudinal differential protection device according to claim 8, characterized in that: The first calculation module includes a virtual short-circuit current amplification factor calculation module and a virtual short-circuit current calculation module; The virtual short-circuit current magnification calculation module is used to calculate the virtual short-circuit current magnification according to the normal operating parameters and the short-circuit operating parameters; The virtual short-circuit current calculation module is used to calculate the virtual short-circuit current output by the inverter according to the virtual short-circuit current amplification factor and the short-circuit operation parameters.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer instructions, and the computer instructions are used to enable a processor to implement the longitudinal differential protection method for a microgrid line according to any one of claims 1 to 7 when executed.

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