Regional differential protection method and device for micro-grid system and storage medium

Abstract

The invention discloses a micro-grid system regionalization differential protection method and device 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 system according to the virtual short-circuit current; and determining whether the micro-grid system has a short-circuit fault 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 a relatively small short-circuit current on the sensitivity of the protection device is effectively solved, the selectivity, quickness, sensitivity and reliability of protection for a complex regional micro-grid structure are effectively improved, and the method has relatively high engineering practicability.

Description

Technical Field

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

[0002] With the miniaturization and lightness of photovoltaic and wind power, more and more enterprises, communities and other places will consider adding some photovoltaic and wind power generation during construction to reduce electricity consumption from the grid and carbon emissions. Except for some DC equipment, most of the equipment needs inverters to convert the above electricity into AC power, which eventually forms various microgrids. Microgrids are different from traditional power grids. They usually use inverter power supplies, which are controlled by pulse width modulation (PWM) controllers to convert DC into AC, resulting in the short-circuit current being less affected by PWM control. 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, and it is difficult to identify faults in complex microgrids composed of PWM-controlled inverter power supplies. Summary of the invention

[0003] The present invention provides a method, a device and a storage medium for regionalized differential protection of a microgrid system, so as to solve the problem of poor sensitivity of the longitudinal differential protection device in the prior art.

[0004] According to one aspect of the present invention, a method for regionalized differential protection of a microgrid system is provided, comprising:

[0005] Collect normal operating parameters and short-circuit operating parameters of the microgrid system;

[0006] Calculating a virtual short-circuit current output by the inverter according to the normal operating parameters and the short-circuit operating parameters;

[0007] Calculate a virtual differential current and a set braking current of the microgrid system according to the virtual short-circuit current;

[0008] Whether a short circuit fault occurs in the microgrid system is determined according to the virtual differential current and the set braking current.

[0009] 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:

[0010] Calculating a virtual short-circuit current magnification factor according to the normal operating parameters and the short-circuit operating parameters;

[0011] 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.

[0012] Optionally, the normal operating parameters include a first DC voltage, a second DC voltage, a third DC voltage, a first duty cycle, a second duty cycle, a third duty cycle, a first AC voltage, a second AC voltage, a third AC voltage, a first AC current, a second AC current and a third AC current when the microgrid system is operating normally; the short-circuit operating parameters include a first DC voltage, a second DC voltage, a third DC voltage, a first duty cycle, a second duty cycle, a third duty cycle, a first AC voltage, a second AC voltage, a third AC voltage, a first AC current, a second AC current and a third AC current when the microgrid system is operating in short circuit;

[0013] The calculating the virtual short-circuit current magnification factor according to the normal operating parameters and the short-circuit operating parameters comprises:

[0014] 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 system is operating normally;

[0015] 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 system is in short-circuit operation;

[0016] 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 system is operating normally;

[0017] 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 system is in short-circuit operation;

[0018] Calculating a third virtual short-circuit current leakage voltage ratio according to a third AC voltage, a third AC current and a third internal resistance during normal operation of the microgrid system;

[0019] Calculating a third short-circuit current leakage voltage ratio according to the third AC voltage, the third AC current and the third internal resistance when the microgrid system is in short-circuit operation;

[0020] 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 system is operating normally, and a first half-wave integral signal calculated from a first duty cycle when the microgrid system is short-circuited;

[0021] Calculate the second virtual short-circuit current amplification factor 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 system is operating normally, and the second half-wave integral signal calculated by the second duty cycle when the microgrid system is short-circuited;

[0022] The third virtual short-circuit current amplification factor is calculated according to the third virtual short-circuit current leakage voltage ratio and the third short-circuit current leakage voltage ratio, the third half-wave integral signal calculated by the third duty cycle when the microgrid system is operating normally, and the third half-wave integral signal calculated by the third duty cycle when the microgrid system is short-circuited.

[0023] Optionally, the virtual short-circuit current includes a first virtual short-circuit current, a second virtual short-circuit current, and a third virtual short-circuit current, and according to the virtual short-circuit current amplification factor and the short-circuit operation parameter, calculating the virtual short-circuit current output by the inverter includes:

[0024] Calculate a first virtual short-circuit current according to the first virtual short-circuit current magnification factor and a first alternating current when the microgrid system is in short-circuit operation;

[0025] Calculate the second virtual short-circuit current according to the second virtual short-circuit current magnification factor and the second alternating current when the microgrid system is in short-circuit operation;

[0026] The third virtual short-circuit current is calculated according to the third virtual short-circuit current magnification factor and the third alternating current when the microgrid system is in short-circuit operation.

[0027] Optionally, the calculating a virtual differential current and a set braking current of the microgrid system according to the virtual short-circuit current includes:

[0028] Calculating a virtual differential current of the microgrid system according to the virtual short-circuit current;

[0029] The set braking current is calculated according to the virtual short-circuit current and the braking current proportionality coefficient.

[0030] Optionally, determining whether a short circuit fault occurs in the microgrid system 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 system, and return to the step of collecting normal operating parameters and current operating parameters of the microgrid system;

[0032] If not, it is determined that a short circuit fault occurs in the microgrid system, and a protection action is performed according to the set braking current.

[0033] Optionally, the setting braking current includes a first setting braking current, a second setting braking current and a third setting braking current; and performing a protection action according to the setting braking current includes:

[0034] A protection action is performed according to a maximum value of the first setting braking current, the second setting braking current and the third setting braking current.

[0035] According to another aspect of the present invention, a longitudinal differential protection device for a microgrid line is provided, comprising:

[0036] A collection module, the collection module is used to collect normal operating parameters and short-circuit operating parameters of the microgrid system;

[0037] 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;

[0038] A second calculation module, the second calculation module is used to calculate a virtual differential current and a set braking current of the microgrid system according to the virtual short-circuit current;

[0039] A determination module is used to determine whether a short circuit fault occurs in the microgrid system according to the virtual differential current and the set braking current.

[0040] Optionally, the first calculation module includes a virtual short-circuit current amplification factor calculation module and a virtual short-circuit current calculation module;

[0041] 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;

[0042] 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.

[0043] 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 regionalized differential protection method for a microgrid system described in any embodiment of the present invention when executed.

[0044] 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 system according to the virtual short-circuit current; and determines whether a short-circuit fault occurs in the microgrid system according to the virtual differential current and the set braking current. First, for a microgrid whose power source 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, and effectively improves the selectivity, speed, sensitivity and reliability of the protection when facing a complex regionalized microgrid structure, and has high engineering practicality.

[0045] 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

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. 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.

[0047] Figure 1 A flow chart of a regionalized differential protection method for a microgrid system provided by an embodiment of the present invention;

[0048] Figure 2 A schematic diagram of the structure of a microgrid system provided in an embodiment of the present invention;

[0049] Figure 3 A flow chart of another microgrid system regional differential protection method provided by an embodiment of the present invention;

[0050] Figure 4 A polling control logic sequence diagram provided by an embodiment of the present invention;

[0051] Figure 5 A schematic diagram of the structure of a regionalized differential protection device for a microgrid system provided by an embodiment of the present invention;

[0052] Figure 6A schematic diagram of the electronic device structure of a regionalized differential protection method for a microgrid system 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 method for regionalized differential protection of a microgrid system provided by an embodiment of the present invention. This embodiment is applicable to the situation where it is difficult to identify the fault of a complex microgrid composed of a PWM controlled inverter power supply. The method can be executed by a regionalized differential protection device of a microgrid system. The regionalized differential protection device of a microgrid system can be implemented in the form of hardware and / or software. The regionalized differential protection device of a microgrid system can be configured in any electronic device with a communication function. Figure 1 , the regionalized differential protection method of the microgrid system includes:

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

[0057] Figure 2 A schematic diagram of the microgrid system structure provided by an embodiment of the present invention is shown in FIG. Figure 2The system is a microgrid system controlled by inverter PWM signal, which is composed of three inverter power supplies to form a ring network. Every two inverter power supplies are connected by a line. Each inverter power supply corresponds to a protection device. The first inverter power supply PWM1 is connected to the protection device 1, the second inverter power supply PWM2 is connected to the protection device 2, and the third inverter power supply PWM3 is connected to the protection device 3. Three voltage-type inverters are used as power supplies to realize the power supply of the microgrid system. The DC side power supplies Udc1, Udc2 and Udc3 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 three protection devices respectively collect the current, voltage and duty cycle information of the system under the current operating state through the current transformer, voltage transformer and duty cycle measurement device integrated in each of them. The duty cycle measurement device measures the time interval between the two rising edges of the PWM waveform and the time interval between a rising edge and a falling edge, thereby obtaining the duty cycle of the PWM waveform. The protection devices are connected to each other through communication optical fibers for signal transmission. In addition, the three protection devices need to be connected to a main controller through communication optical fiber so that the main controller can have an overall grasp of the system status to determine whether a fault has occurred in the system. If a fault occurs, the location of the fault needs to be determined and corresponding actions taken.

[0058] 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.

[0059] S120. Calculate a virtual short-circuit current output by the inverter according to the normal operating parameters and the short-circuit operating parameters.

[0060] S130. Calculate a virtual differential current and a set braking current of the microgrid system 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 system 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; 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 smaller short-circuit current on the sensitivity of the protection device by amplifying the short-circuit current measured by the protection device, and effectively improves the selectivity, speed, sensitivity and reliability of the protection when facing a complex regionalized microgrid structure, and has high engineering practicality.

[0064] Optionally, according to the normal operating parameters and the short-circuit operating parameters, calculating the virtual short-circuit current output by the inverter 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 third DC voltage, the first duty cycle, the second duty cycle, the third duty cycle, the first AC voltage, the second AC voltage, the third AC voltage, the first AC current, the second AC current and the third AC current when the microgrid system is operating normally; the short-circuit operating parameters include the first DC voltage, the second DC voltage, the third DC voltage, the first duty cycle, the second duty cycle, the third duty cycle, the first AC voltage, the second AC voltage, the third AC voltage, the first AC current, the second AC current and the third AC current when the microgrid system is operating in short circuit.

[0067] Figure 3 A flowchart of another microgrid system regional differential protection method provided by an embodiment of the present invention is shown in FIG. Figure 3 Specifically, the DC voltage U dc1 , U dc2 , U dc3 , three groups of PWM half-wave integral signals ∫PWM1, ∫PWM2, ∫PWM3, three-phase current effective values ​​I1, I2, I3, based on which after calculation, the inverter can be equivalent to a three-phase voltage source U1, U2, U3. ∫PWM=∑E k , k = 1, 2..., n, n is the number of PWM pulses in half wave, E k It represents 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 ​​half wave, which is related to the duty cycle. When the duty cycle increases, the area increases, and ∫PWM increases.

[0068] During normal operation, Figure 2 The first inverter power supply can be listed as formula ①K1*∫PWM1*U dc1 =I1*R s1 +U1, where K1 is the ratio of PWM control to DC voltage reduction, R s1 is the internal impedance of the first inverter power supply.

[0069] Collect three sets of PWM half-wave integral signals ∫PWM when a short circuit fault occurs in the microgrid system ′ 1. ∫PWM ′ 2. ∫PWM ′ 3. Three-phase current effective value I ′ 1.I ′ 2.I ′ 3. The three-phase voltage source U in the short-circuit state can be ′ 1. U ′2. U ′ 3 The construction is successful. Since the inverter power supply has not been replaced, the DC voltage U in the short-circuit state dc1 , U dc2 , U dc3 , internal impedance R s1 , R s2 , R s3 Still remains the same.

[0070] At this time Figure 2 The first inverter power supply can also be listed as formula ②K1*∫PWM ′ 1*U dc1 =I ′ 1*R s1 +U ′ 1. Modify the parameters in the formula to the voltage and half-wave integral signal of the system during normal operation, and then the formula ② can be transformed into the formula ③ in is the virtual short-circuit current.

[0071] Combining formulas ① and ③ in steps 1 and 2, we can solve:

[0072] in,

[0073] In the formula, is the virtual short-circuit current magnification factor, I ′ 1 is the first AC current when the microgrid system is in short-circuit operation, U ′ 1 is the first AC current when the microgrid system is in short-circuit operation, R s1 is the internal impedance, δ ‘ 1% is the short-circuit leakage voltage ratio, δ1% is the virtual short-circuit leakage voltage ratio, is the virtual short-circuit current.

[0074] Using the same method, we can obtain Figure 2 The relationship between the second inverter power supply and the third inverter power supply when the external short circuit occurs is as follows:

[0075] in,

[0076] in,

[0077] The main controller processes the various parameters of the microgrid system provided by each protection device, such as the PWM half-wave integral signal value, current value, etc., and obtains the virtual short-circuit current emitted by each inverter power supply. Right now

[0078] Optionally, according to the normal operating parameters and the short circuit operating parameters, calculating the virtual short circuit current magnification factor includes:

[0079] A first virtual short-circuit current leakage voltage ratio is calculated according to a first alternating current voltage, a first alternating current, and a first internal resistance when the microgrid system is operating normally.

[0080] Specifically, the first virtual short-circuit current leakage voltage ratio is calculated using the following formula:

[0081] Where δ1% is the first virtual short-circuit current leakage voltage ratio, I1 is the first AC current when the microgrid system is operating normally, and R s1 is the first internal resistance, and U1 is the first AC voltage when the microgrid system operates normally.

[0082] A first short-circuit current leakage voltage ratio is calculated according to a first alternating current voltage, a first alternating current and a first internal resistance when the microgrid system is in short-circuit operation.

[0083] Specifically, the first short-circuit current leakage voltage ratio is calculated using the following formula:

[0084] In the formula, δ ‘ 1% is the first short-circuit current leakage voltage ratio, I ′ 1 is the first AC current when the microgrid system is in short-circuit operation, U ′ 1 is the first AC voltage when the microgrid system is in short-circuit operation.

[0085] 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 system is operating normally.

[0086] Specifically, the second virtual short-circuit current leakage voltage ratio is calculated using the following formula:

[0087] Where δ2% is the second virtual short-circuit current leakage voltage ratio, I2 is the second AC current when the microgrid system is operating normally, and R s2 is the second internal resistance, and U2 is the second AC voltage when the microgrid system operates normally.

[0088] 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 system is in short-circuit operation.

[0089] Specifically, the second short-circuit current leakage voltage ratio is calculated using the following formula:

[0090] In the formula, δ ‘ 2% is the second short-circuit current leakage voltage ratio, I ′ 2 is the second AC current when the microgrid system is in short-circuit operation, U′ 2 is the second AC voltage when the microgrid system is in short-circuit operation.

[0091] The third virtual short-circuit current leakage voltage ratio is calculated according to the third alternating current voltage, the third alternating current and the third internal resistance when the microgrid system is operating normally.

[0092] Specifically, the third virtual short-circuit current leakage voltage ratio is calculated using the following formula:

[0093] Where δ3% is the third virtual short-circuit current leakage voltage ratio, I3 is the second AC current when the microgrid system is operating normally, and R s3 is the third internal resistance, and U3 is the third AC voltage when the microgrid system operates normally.

[0094] The third short-circuit current leakage voltage ratio is calculated according to the third alternating current voltage, the third alternating current and the third internal resistance when the microgrid system is in short-circuit operation.

[0095] Specifically, the third short-circuit current leakage voltage ratio is calculated using the following formula:

[0096] In the formula, δ ‘ 3% is the third short-circuit current leakage voltage ratio, I ′ 3 is the third AC current when the microgrid system is in short-circuit operation, U ′ 3 is the third AC voltage when the microgrid system is in short-circuit operation.

[0097] 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 system is operating normally, and the first half-wave integral signal calculated by the first duty cycle when the microgrid system is short-circuited.

[0098] Specifically, the first virtual short-circuit current magnification is calculated using the following formula:

[0099] In the formula, is the first virtual short-circuit current magnification factor, ∫PWM1 is the first half-wave integral signal calculated from the first duty cycle when the microgrid system is operating normally, and ∫PWM ′ 1 is the first half-wave integral signal calculated from the first duty cycle when the microgrid system is in short-circuit operation.

[0100] 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 system is operating normally, and the second half-wave integral signal calculated by the second duty cycle when the microgrid system is short-circuited.

[0101] Specifically, the second virtual short-circuit current magnification is calculated using the following formula:

[0102] In the formula, is the second virtual short-circuit current magnification factor, PWM2 is the second half-wave integral signal calculated from the second duty cycle when the microgrid system is operating normally, and PWM ′ 2 is the second half-wave integral signal calculated from the second duty cycle when the microgrid system is in short-circuit operation.

[0103] The third virtual short-circuit current amplification factor is calculated according to the third virtual short-circuit current leakage voltage ratio and the third short-circuit current leakage voltage ratio, the third half-wave integral signal calculated by the third duty cycle when the microgrid system is operating normally, and the third half-wave integral signal calculated by the third duty cycle when the microgrid system is short-circuited.

[0104] Specifically, the third virtual short-circuit current magnification is calculated using the following formula:

[0105] In the formula, is the second virtual short-circuit current magnification factor, PWM3 is the third half-wave integral signal calculated by the third duty cycle when the microgrid system is operating normally, and PWM ′ 3 is a third half-wave integral signal calculated from the third duty cycle when the microgrid system is in short-circuit operation.

[0106] 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.

[0107] The virtual short-circuit current includes a first virtual short-circuit current, a second virtual short-circuit current and a third virtual short-circuit current. According to the virtual short-circuit current magnification factor and the short-circuit operation parameters, calculating the virtual short-circuit current output by the inverter includes:

[0108] 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 system is in short-circuit operation.

[0109] The first virtual short-circuit current is calculated using the following formula:

[0110] In the formula, is the first virtual short-circuit current, I ′ 1 is the first AC current when the microgrid system is in short-circuit operation, is the first virtual short-circuit current magnification factor.

[0111] 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 system is in short-circuit operation.

[0112] The second virtual short-circuit current is calculated using the following formula:

[0113] In the formula, is the second virtual short-circuit current, is the second virtual short-circuit current magnification factor, I ′ 2 is the second AC current when the microgrid system is in short-circuit operation.

[0114] The third virtual short-circuit current is calculated according to the third virtual short-circuit current magnification factor and the third alternating current when the microgrid system is in short-circuit operation.

[0115] The third virtual short-circuit current is dissipated using the following formula:

[0116] In the formula, is the third virtual short-circuit current, is the third virtual short-circuit current magnification, I ′ 3 is the third AC current when the microgrid system is in short-circuit operation.

[0117] Optionally, calculating a virtual differential current and a set braking current of the microgrid system according to the virtual short-circuit current includes:

[0118] The virtual differential current of the microgrid system is calculated based on the virtual short-circuit current.

[0119] Specifically, the virtual differential current ΔI of the microgrid line is calculated based on the following formula using a proportional or margin method: * :

[0120] In the formula, ΔI * is the virtual differential current.

[0121] The set braking current is calculated based on the virtual short-circuit current and the braking current proportionality coefficient.

[0122] The setting braking current includes the first setting braking current Second set braking current The third set braking current And adjust the total braking current

[0123] The set brake current is calculated using the following formula:

[0124]

[0125] Among them, c1, c2, and c3 are braking current proportional coefficients selected according to actual needs.

[0126] Optionally, determining whether a short circuit fault occurs in the microgrid system according to the virtual differential current and the set braking current includes:

[0127] 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 system, and return to the step of collecting the normal operating parameters and current operating parameters of the microgrid system; if not, determine that a short-circuit fault occurs in the microgrid system, and perform protection actions according to the set braking current.

[0128] Specifically, the main controller compares ΔI * and The size of If the system is fault-free, the system returns to the step of collecting the normal operating parameters and current operating parameters of the microgrid system; otherwise, When the protection device determines that there is a fault in the system, it compares the set braking current The largest value among the three corresponds to the protection action tripping.

[0129] Optionally, the setting braking current includes a first setting braking current, a second setting braking current and a third setting braking current; and performing a protection action according to the setting braking current includes:

[0130] A protection action is performed according to a maximum value of the first setting braking current, the second setting braking current and the third setting braking current.

[0131] Specifically, a protection system combining a main controller and distributed control of each protection device is constructed for the microgrid system. While all virtual current signals are input into the main controller, each virtual current signal is also transmitted to the three protection devices, and the three protection devices also calculate the differential current ΔI * With braking current The size of the fault is used to determine whether there is any fault inside the system. If there is a fault, all three protection devices will be activated.

[0132] Then the protection devices 1, 2 and 3 are compared respectively. The size of the virtual current signal and the virtual braking current signal are processed and compared by the protection devices 1, 2, and 3 at the same time in the round. In the program, each protection device can first Calculate the data in the order of Compare and take the larger value By comparison, the maximum value among the three can be obtained, and a blocking command is issued to the protection device involved in the maximum virtual braking current. The above is called the polling process. For details, see Figure 4 , Figure 4 A polling control logic sequence diagram provided for an embodiment of the present invention.

[0133] Finally, since the polling process of the protection device itself is to ensure that the system can reliably cut off the fault in the event of a main controller failure, it is necessary to have a certain delay before the non-locked protection device can perform the longitudinal differential protection action.

[0134] The technical solution provided by the embodiment of the present invention is to avoid the error caused by a smaller short-circuit current that causes the protection device to refuse to operate or malfunction. Therefore, it is necessary to use a virtual short-circuit current method to amplify the short-circuit current to reduce the impact of the PWM controller on the short-circuit judgment. In addition, the embodiment of the present invention establishes a distributed competitive decision-making method to avoid the main controller from failing. In case of a failure, it can be used as a backup protection to determine whether a fault has occurred and the location of the fault and perform protective actions. Compared with traditional microgrid protection, the present invention only needs to add a main controller and add several logic comparison functions inside each protection device. It does not have a high construction cost, and it can improve the selectivity, speed, sensitivity, and reliability of protection when facing a complex regionalized microgrid structure, and has high engineering practicality.

[0135] The following describes in detail the regional differential protection method for a microgrid system provided by an embodiment of the present invention by taking a fault between lines 1 and 2 as an example.

[0136] During normal operation, the summary Figure 1 The formula is: ①K1*∫PWM1*U dc1 =I1*R s1 +U1, where K1 is the ratio of PWM control to DC voltage reduction, R s1 is the internal impedance of the inverter on side 1. For sides 2 and 3, we can get K2*∫PWM2*U in the same way. dc2 =I2*R s2 +U2、K3*∫PWM3*U dc3 =I3*R s3 +U3.

[0137] After a short circuit occurs, the three sets of PWM half-wave integral signals change, recorded as ∫PWM ′ 1. ∫PWM ′ 2. ∫PWM ′ 3. Three-phase current effective value I ′ 1.I ′ 2.I ′ 3. Construct a three-phase voltage source U under short-circuit condition ′ 1. U′ 2. U ′ 3. DC voltage U dc1 , U dc2 , U dc3 , internal impedance R s1 , R s2 , R s3 constant.

[0138] At this time, the abstract is attached Figure 1 The side formula is modified to ②K1*∫PWM ′ 1*U dc1 =I ′ 1*R s1 +U ′ 1. Modify the parameters in the formula to the voltage and half-wave integral signal of the system during normal operation, and then the formula ② can be transformed into the formula ③ in is the virtual short-circuit current. Similarly, the formulas on sides 2 and 3 become

[0139] For side 1, we can solve by combining formulas ①③:

[0140] in

[0141] Similarly, the relationship between sides 2 and 3 can be obtained:

[0142] in

[0143] in

[0144] The final solution

[0145] The above three virtual current calculations are calculated and saved in the three protection devices respectively. Then the three virtual currents are first transmitted to the main controller, which calculates the virtual differential current ΔI * And adjust the braking current

[0146] in

[0147] The main controller always keeps the ΔI * , For comparison, When the microgrid system is judged to have no fault, the main controller can continue the above steps to collect and compare. The main controller determines that there is a fault inside the microgrid system. Compare and find the maximum value to determine which line the fault is. When the maximum value is reached, the main controller commands protection devices 1 and 2 to operate. When a short circuit occurs between sides 1 and 3, Maximum, the main controller commands protection devices 1 and 3 to operate. When a short circuit fault occurs between sides 2 and 3, Maximum, the main controller instructs protection devices 1 and 3 to operate.

[0148] In addition, a polling function needs to be set on the protection device as a backup for the main controller failure. Each protection device obtains the above virtual short-circuit current After that, the virtual short-circuit current signal is transmitted to the other two protection devices, and the protection devices use the same method to detect the virtual differential current ΔI * And adjust the braking current Similarly, when a fault occurs on side 1 or 2, the protection device can determine When a fault occurs inside the system, all three protection devices start up and wait for the command from the main controller. By comparison, it was found The maximum, therefore, needs to send a blocking command to the protection device 3. If the protection does not return to non-blocking within t0 time after the protection is started, but no tripping command is received from the main controller, the two non-blocking protection devices will act immediately. Thus, the regional differential protection of the complex microgrid system is completed.

[0149] Compared with the prior art, the present invention has the following beneficial effects:

[0150] Firstly, the virtual short-circuit current can solve the problem of small short-circuit current caused by PWM control of the inverter power supply.

[0151] Secondly, adding a main controller that can perform the above-mentioned operations and logical analysis on the data can solve the short-circuit fault identification problem of the above-mentioned complex microgrid system, which has the advantages of high engineering practicality, low economic cost, and rapid fault identification.

[0152] Finally, the three protection devices are given a fault polling function as a backup for the main controller. By adding programs for data processing and communication, the reliability of this set of devices for complex microgrid system protection can be increased. Therefore, compared with traditional complex microgrid protection, the present invention has greater beneficial effects.

[0153] Figure 5A schematic diagram of a microgrid system regional differential protection device provided by an embodiment of the present invention is shown in FIG. Figure 5 The device includes a collection module 510, a first calculation module 520, a second calculation module 530 and a de-rating module 540.

[0154] The acquisition module 510 is used to acquire normal operation parameters and short circuit operation parameters of the microgrid system.

[0155] The first calculation module 520 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.

[0156] The second calculation module 530 is used to calculate the virtual differential current and the set braking current of the microgrid system according to the virtual short-circuit current.

[0157] The determination module 540 is used to determine whether a short circuit fault occurs in the microgrid system according to the virtual differential current and the set braking current.

[0158] Optionally, the first calculation module 520 includes a virtual short-circuit current amplification factor calculation module and a virtual short-circuit current calculation module;

[0159] The virtual short-circuit current magnification calculation module is used to calculate the virtual short-circuit current magnification according to the normal operation parameters and the short-circuit operation parameters.

[0160] 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.

[0161] 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.

[0162] Figure 6 A schematic diagram of the electronic device structure of a microgrid system regionalized differential protection method provided by 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 can 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.

[0163] like Figure 6As 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.

[0164] 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.

[0165] 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 dedicated 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 regionalized differential protection method for a microgrid system.

[0166] In some embodiments, the microgrid system regionalized differential protection method may 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 may 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 microgrid system regionalized differential protection method described above may be performed. Alternatively, in other embodiments, the processor 11 may be configured to execute the microgrid system regionalized differential protection method in any other appropriate manner (e.g., by means of firmware).

[0167] 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.

[0168] 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.

[0169] 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.

[0170] 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).

[0171] 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.

[0172] 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.

[0173] 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.

[0174] 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 regionalized differential protection method for a microgrid system, characterized in that: include: Collect normal operating parameters and short-circuit operating parameters of the microgrid system; Calculating a virtual short-circuit current output by the inverter according to the normal operating parameters and the short-circuit operating parameters; Calculate a virtual differential current and a set braking current of the microgrid system according to the virtual short-circuit current; Whether a short circuit fault occurs in the microgrid system is determined according to the virtual differential current and the set braking current.

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

4. The method for regionalized differential protection of a microgrid system according to claim 3, characterized in that: The virtual short-circuit current includes a first virtual short-circuit current, a second virtual short-circuit current and a third virtual short-circuit current. According to the virtual short-circuit current magnification factor and the short-circuit operation parameter, calculating the virtual short-circuit current output by the inverter includes: Calculate a first virtual short-circuit current according to the first virtual short-circuit current magnification factor and a first alternating current when the microgrid system is in short-circuit operation; Calculate the second virtual short-circuit current according to the second virtual short-circuit current magnification factor and the second alternating current when the microgrid system is in short-circuit operation; The third virtual short-circuit current is calculated according to the third virtual short-circuit current magnification factor and the third alternating current when the microgrid system is in short-circuit operation.

5. The microgrid system regionalized 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 system according to the virtual short-circuit current comprises: Calculating a virtual differential current of the microgrid system according to the virtual short-circuit current; The set braking current is calculated according to the virtual short-circuit current and the braking current proportionality coefficient.

6. The method for regionalized differential protection of a microgrid system according to claim 1, characterized in that: The determining whether a short circuit fault occurs in the microgrid system 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 system, and return to the step of collecting normal operating parameters and current operating parameters of the microgrid system; If not, it is determined that a short circuit fault occurs in the microgrid system, and a protection action is performed according to the set braking current.

7. The method for regionalized differential protection of a microgrid system according to claim 6, characterized in that: The setting braking current includes a first setting braking current, a second setting braking current and a third setting braking current; and performing a protection action according to the setting braking current includes: A protection action is performed according to a maximum value of the first setting braking current, the second setting braking current and the third setting braking current.

8. A regionalized differential protection device for a microgrid system, 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 system; 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 a virtual differential current and a set braking current of the microgrid system according to the virtual short-circuit current; A determination module is used to determine whether a short circuit fault occurs in the microgrid system according to the virtual differential current and the set braking current.

9. The microgrid system regionalized 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 microgrid system regionalized differential protection method according to any one of claims 1 to 7 when executed.

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