Isolated network stability discrimination method considering frequency voltage control

Abstract

The invention discloses an isolated network stability judgment method considering frequency voltage control, which is used for solving the problems that a traditional stability evaluation method based on a passive isolated network instantaneous disturbance frequency change rate is relatively tedious and an obtained result is not accurate enough. When the isolated network operation of the regional power grid occurs, obtaining the exchange power section, the equivalent inertia of the traditional unit, the high-frequency generator tripping amount and the low-frequency load shedding amount of the isolated network system of the regional power grid in the current operation mode; calculating an initial disturbance frequency change rate according to the exchange power section and the equivalent inertia of the traditional unit; performing disturbance judgment based on the initial disturbance frequency change rate and a preset disturbance condition, and recalculating the disturbance frequency change rate in combination with the high-frequency generator tripping amount and / or the low-frequency load shedding amount according to a disturbance judgment result to obtain a target disturbance frequency change rate; and performing stability judgment according to the target disturbance frequency change rate to obtain an isolated network stability judgment result of the isolated network system. Therefore, the process is simplified, and an accurate and stable judgment result is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of new power systems, and particularly to a method for judging the stability of an islanded power grid considering frequency and voltage control, a device for judging the stability of an islanded power grid considering frequency and voltage control, an electronic device, and a storage medium. Background Art

[0002] With the construction of new power systems and the structural reform of the energy supply side, the complementary coordination of various power sources such as wind, light, water, and energy storage in regional power grids can effectively improve the quality of energy and power development. This change is of great significance for promoting China's energy transformation and economic and social development.

[0003] In actual situations, a large number of regional power grids are rich in wind and solar new energy and small hydropower, and have a weak connection with the system. When the tie line or tie transformer between the regional power grid and the main grid trips, the regional power grid enters islanded operation and usually it is difficult to maintain stable operation, thus affecting the reliable power supply.

[0004] The load and installed capacity of the regional power grid are small, the moment of inertia is low, and there are problems such as large fluctuations in frequency and voltage and difficulties in stable control of reconnection during operation. The high proportion of new energy access makes the islanded power grid system exhibit high-frequency and fast dynamic characteristics such as low moment of inertia, high-speed switching of control strategies, and wide-band oscillation. This further affects the stable operation ability of the islanded power grid system. Considering the safe and stable operation of the islanded power grid system with a combination of various power sources such as wind, light, water, and energy storage, a suitable evaluation system is urgently needed. However, the traditional evaluation system for the stable operation ability of power systems is difficult to support the evaluation requirements of highly power-electronic islanded power grid systems. If the operating state of the islanded power grid cannot be accurately evaluated, it will seriously affect the formulation of control decisions and the setting of protection values for the islanded power grid system.

[0005] Traditionally, the inertia-frequency stability of power grids is mostly characterized by the rate of change of disturbance frequency to represent the power deficit (i.e., power section), system inertia, and other stable operation capabilities of the power grid. After the regional power grid operates in islanded mode, due to large fluctuations in voltage and frequency, a large number of security and automatic devices such as high-frequency generator tripping, under-frequency load shedding, and under-voltage load shedding configured in the regional power grid act disorderly, which may cause the islanded power grid system to suffer a secondary impact. Therefore, it is necessary to optimize and improve the traditional stable evaluation method based on the instantaneous disturbance frequency change rate of the passive islanded power grid to achieve a more accurate and quantitative evaluation of the stability of the islanded power grid. Summary of the Invention

[0006] The present invention provides a method for judging the stability of an islanded power grid considering frequency and voltage control, a device for judging the stability of an islanded power grid considering frequency and voltage control, an electronic device, and a storage medium, which are used to solve or partially solve the technical problem that the traditional stable evaluation method based on the instantaneous disturbance frequency change rate of the passive islanded power grid is relatively cumbersome and the results obtained are not accurate enough.

[0007] The present invention provides a method for judging the stability of an isolated power grid considering frequency and voltage control. The method includes:

[0008] When the isolated operation of the regional power grid occurs, obtain the exchange power section, the equivalent inertia of traditional units, the high-frequency generator tripping amount, and the low-frequency load shedding amount of the isolated power grid system of the regional power grid under the current operation mode;

[0009] Calculate the initial disturbance frequency change rate according to the exchange power section and the equivalent inertia of the traditional units;

[0010] Based on the initial disturbance frequency change rate and a preset disturbance condition, perform a disturbance judgment, and according to the disturbance judgment result, combine the high-frequency generator tripping amount and / or the low-frequency load shedding amount to recalculate the disturbance frequency change rate to obtain the target disturbance frequency change rate;

[0011] Perform a stability judgment according to the target disturbance frequency change rate to obtain the isolated power grid stability judgment result of the isolated power grid system.

[0012] Optionally, based on the initial disturbance frequency change rate and a preset disturbance condition, perform a disturbance judgment, and according to the disturbance judgment result, combine the low-frequency load shedding amount to recalculate the disturbance frequency change rate to obtain the target disturbance frequency change rate, including:

[0013] When the initial disturbance frequency change rate is less than or equal to the first preset disturbance frequency change rate, subtract the low-frequency load shedding amount from the absolute value of the exchange power section to obtain the power section after load shedding;

[0014] Obtain the rated capacity of each unit in the isolated power grid system and the unit output of each traditional unit, and calculate the in-region spinning reserve power of the isolated power grid system according to the rated capacity of each unit and the unit output of each traditional unit;

[0015] When the power section after load shedding is less than or equal to the in-region spinning reserve power, add the low-frequency load shedding amount to the exchange power section to obtain the first updated exchange power section;

[0016] Calculate the first target disturbance frequency change rate according to the first updated exchange power section and the equivalent inertia of the traditional units.

[0017] Optionally, the method further includes:

[0018] When the power section after load shedding is greater than the in-region spinning reserve power, determine that the system is unstable, which is used as the isolated power grid stability judgment result of the isolated power grid system.

[0019] Optionally, the high-frequency generator tripping amount includes the new energy generator tripping amount; performing disturbance judgment based on the initial disturbance frequency change rate and a preset disturbance condition, and according to the disturbance judgment result, recomputing the disturbance frequency change rate in combination with the high-frequency generator tripping amount to obtain a target disturbance frequency change rate, including:

[0020] When the initial disturbance frequency change rate is greater than or equal to a second preset disturbance frequency change rate and less than a third preset disturbance frequency change rate, subtracting the new energy generator tripping amount from the exchange power section to obtain a second updated exchange power section;

[0021] Updating the equivalent inertia of the conventional units based on the cut-off new energy generator tripping amount to obtain a first updated equivalent inertia;

[0022] Calculating a second target disturbance frequency change rate according to the second updated exchange power section and the first updated equivalent inertia.

[0023] Optionally, the high-frequency generator tripping amount includes the new energy generator tripping amount and the conventional unit generator tripping amount; performing disturbance judgment based on the initial disturbance frequency change rate and a preset disturbance condition, and according to the disturbance judgment result, recomputing the disturbance frequency change rate in combination with the high-frequency generator tripping amount and the low-frequency load shedding amount to obtain a target disturbance frequency change rate, including:

[0024] When the initial disturbance frequency change rate is greater than or equal to the third preset disturbance frequency change rate, subtracting the new energy generator tripping amount and the conventional unit generator tripping amount from the exchange power section and adding the low-frequency load shedding amount to obtain a third updated exchange power section;

[0025] Updating the equivalent inertia of the conventional units based on the cut-off conventional unit generator tripping amount to obtain a second updated equivalent inertia;

[0026] Calculating a third target disturbance frequency change rate according to the third updated exchange power section and the second updated equivalent inertia.

[0027] Optionally, the calculation formula of the disturbance frequency change rate is as follows:

[0028]

[0029] Wherein, represents the disturbance frequency change rate; represents the exchange power section, with the positive direction being the power transmission from the regional power grid; represents the system rated frequency; represents the equivalent inertia of the conventional units.

[0030] Optionally, the stability judgment is performed according to the target disturbance frequency change rate to obtain the islanding stability discrimination result of the islanded power system, including:

[0031] Determine whether the target disturbance frequency change rate is within the disturbance frequency change rate interval; the disturbance frequency change rate interval corresponds to the maximum frequency deviation interval when the isolated network system is stable;

[0032] If so, determine that the system is stable, which is used as the isolated network stability discrimination result of the isolated network system;

[0033] If not, determine that the system is unstable, which is used as the isolated network stability discrimination result of the isolated network system.

[0034] The present invention also provides an isolated network stability discrimination device considering frequency and voltage control, including:

[0035] A data acquisition unit, configured to acquire the exchange power section, the equivalent inertia of the traditional unit, the high-frequency generator tripping amount, and the low-frequency load shedding amount of the isolated network system of the regional power grid in the current operation mode when the regional power grid operates in an isolated network;

[0036] An initial disturbance frequency change rate calculation unit, configured to calculate the initial disturbance frequency change rate according to the exchange power section and the equivalent inertia of the traditional unit;

[0037] A target disturbance frequency change rate update unit, configured to perform disturbance judgment based on the initial disturbance frequency change rate and a preset disturbance condition, and according to the disturbance judgment result, recompute the disturbance frequency change rate in combination with the high-frequency generator tripping amount, and / or the low-frequency load shedding amount, to obtain the target disturbance frequency change rate;

[0038] A stability judgment unit, configured to perform stability judgment according to the target disturbance frequency change rate to obtain the isolated network stability discrimination result of the isolated network system.

[0039] The present invention also provides an electronic device, which includes a processor and a memory:

[0040] The memory is used to store program codes and transmit the program codes to the processor;

[0041] The processor is configured to execute the isolated network stability discrimination method considering frequency and voltage control as described in any one of the above according to the instructions in the program codes.

[0042] The present invention also provides a computer-readable storage medium, which is used to store program codes, and the program codes are used to execute the isolated network stability discrimination method considering frequency and voltage control as described in any one of the above.

[0043] It can be seen from the above technical solutions that the present invention has the following advantages:

[0044] A method for judging the stability of an isolated power grid considering frequency-voltage control is provided. When the regional power grid operates in an isolated power grid mode, the relevant parameters of generator tripping and load shedding of the isolated power grid system of the regional power grid under the current operation mode are obtained, and the initial disturbance frequency change rate is calculated. Based on the initial disturbance frequency change rate and the preset boundary judgment conditions, the disturbance is judged. According to the actual disturbance judgment result, the relevant parameters of generator tripping and load shedding are flexibly combined to recalculate the disturbance frequency change rate, and the stability is judged according to the new disturbance frequency change rate, so as to obtain the judgment result of the stability of the isolated power grid system of the isolated power grid. Therefore, when the regional power grid becomes an isolated power grid passively, only simple calculations are required, without a cumbersome modeling and simulation process. Compared with the traditional inertia-frequency evaluation method, it can quantitatively evaluate the stability of the regional power grid after isolated power grid operation in a more intuitive and rapid manner, which can not only simplify the calculation process, but also greatly improve the efficiency and accuracy of the evaluation of the stable operation of the isolated power grid, providing a useful reference for the arrangement of the power grid operation mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0046] Figure 1 It is a schematic diagram of the frequency stability characteristics of an isolated power grid operation;

[0047] Figure 2 It is a schematic diagram of the new energy fault ride-through recovery characteristics;

[0048] Figure 3 It is a flowchart of the steps of a method for judging the stability of an isolated power grid considering frequency-voltage control;

[0049] Figure 4 It is a schematic diagram of the overall process of a method for judging the stability of an isolated power grid considering frequency-voltage control;

[0050] Figure 5 It is a structural block diagram of a device for judging the stability of an isolated power grid considering frequency-voltage control. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0051] The embodiments of the present invention provide a method for judging the stability of an isolated power grid considering frequency-voltage control, a device for judging the stability of an isolated power grid considering frequency-voltage control, an electronic device and a storage medium, which are used to solve or partially solve the technical problems that the traditional stability evaluation method based on the initial disturbance frequency change rate of passive isolated power grid is relatively cumbersome and the obtained results are not accurate enough.

[0052] In order to make the object, features, and advantages of the present invention more obvious and understandable, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the embodiments described below are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0053] As an example, in the traditional power grid, the inertia-frequency stability is mostly characterized by the rate of change of disturbance frequency to represent the power grid power deficit (i.e., power section), system inertia, and other stable operation capabilities of the power grid. After the regional power grid operates in an islanded mode, due to large fluctuations in voltage and frequency, a large number of automatic safety devices such as high-frequency generator tripping, low-frequency load shedding, and low-voltage load shedding configured in the regional power grid operate disorderly, which may cause the islanded power grid system to suffer secondary impacts. Therefore, it is necessary to optimize and improve the traditional stability assessment method based on the instantaneous disturbance frequency change rate of the passive islanded power grid to achieve a more accurate and quantitative assessment of the islanded power grid stability.

[0054] Therefore, one of the core inventive points of the embodiments of the present invention is to propose a method for quantitatively assessing the stability of an islanded power grid based on the instantaneous disturbance frequency change rate considering frequency and voltage control. When the regional power grid operates in an islanded mode, obtain the relevant parameters of generator tripping and load shedding of the islanded power grid system of the regional power grid under the current operation mode, and calculate the initial disturbance frequency change rate; set corresponding boundary judgment conditions according to the corresponding relationship between the disturbance frequency change rate and the maximum frequency deviation, and perform disturbance judgment based on the initial disturbance frequency change rate. According to the actual disturbance judgment result, flexibly combine the relevant parameters of generator tripping and load shedding to perform corresponding protection actions, and recalculate the disturbance frequency change rate. Perform stability judgment based on the new disturbance frequency change rate to obtain the stability discrimination result of the islanded power grid system. The method provided by the embodiments of the present invention only requires simple calculations and does not require a cumbersome modeling and simulation process. Compared with the traditional inertia-frequency assessment method, it can quantitatively assess the stability of the regional power grid after islanded operation in a more intuitive and fast manner. It can not only simplify the calculation process but also greatly improve the efficiency and accuracy of the assessment of the stable operation of the islanded power grid, providing a useful reference for the arrangement of the power grid operation mode.

[0055] To enable those skilled in the art to better understand the technical solutions of the present invention, Figure 1 Fig. shows a schematic diagram of the frequency stability characteristics of islanded operation. According to the summary of a large number of typical accident cases of passive islanded operation of regional power grids with a high proportion of small hydropower and new energy, based on the change of the islanded power grid frequency, the system frequency response of the regional power grid after passive islanding can generally be divided into 5 stages.

[0056] (1) t0~t1 New energy fault ride-through stage:

[0057] After a short - circuit fault that causes the regional power grid to passively enter an islanded grid occurs, the voltage in the islanded grid drops instantaneously. According to the requirements for the voltage ride - through ability of new energy in current standards, the fault - ride - through recovery characteristic curves of new - energy active power and reactive power are as Figure 2 shown. At this time, the active power of the new - energy unit drops significantly during the fault, and the system frequency in the islanded grid does not increase.

[0058] After the fault is cleared, according to the standard requirements, the new energy should at least recover to the pre - fault value at a power of 20% . As the new - energy power recovers, the islanded - grid frequency rises rapidly. At this time, the main factors affecting the system frequency stability are the proportion of new energy in the islanded grid and the power - recovery rate after the new - energy voltage ride - through.

[0059] (2) Inertia - response stage from t1 to t2:

[0060] After the new - energy power recovers, at the moment when the system in the islanded grid is passively jumped into the islanded grid, the system frequency deviation is less than the primary - frequency - regulation dead zone of conventional units and new energy. The system frequency change rate is only related to the pre - accident tie - line power (interchange - power section) , the load change amount (low - frequency load - shedding amount) ( , are both per - unit values) and the system inertia . As shown in the following formula:

[0061]

[0062] In the formula, , and are the constant - impedance, constant - current, and constant - power load ratios respectively; is the per - unit value of the voltage change amount; is the total islanded - grid load power.

[0063] The system inertia includes the inertia of synchronous machines on the power - supply side, the inertia of asynchronous machines on the load side, and the virtual inertia of new energy, etc. Since the islanded - grid load is mainly civilian load, the inertia of asynchronous motors can also be ignored. Therefore, the system inertia can be approximately related to the inertia of synchronous machines in the islanded grid and the inertia of new energy . As shown in the following formula:

[0064]

[0065] In the formula, , is the The inertia constant and installed capacity of a small hydropower unit; , For the th new energy unit in the isolated grid, the equivalent inertia time constant and installed capacity of the new energy.

[0066] The magnitude directly affects the maximum frequency deviation of the isolated grid operation and the duration of frequency over-limit, etc. Since the inertia support provided by new energy is much smaller than that of traditional units, as the proportion of new energy increases, the system equivalent inertia decreases, which is not conducive to the stability of the isolated grid.

[0067] (3) Primary frequency regulation action stage from t2 to t3:

[0068] The system frequency in the isolated grid changes rapidly and will soon exceed the primary frequency regulation dead zone limit. Primary frequency regulation and inertia work together, and the power change amounts corresponding to the primary frequency regulation of traditional units and new energy units and can be calculated by the following formula:

[0069]

[0070] In the formula, represents the rated active power of the traditional unit; represents the rated active power of the new energy; represents the active frequency modulation coefficient of the new energy power station; represents the regulation differential coefficient of the traditional unit; represents the change amount of the system frequency; represents the system rated frequency; represents the frequency dead zone of the traditional unit.

[0071] In the actual system, due to the large frequency change during isolated grid operation, the primary frequency regulation capacity of traditional units and new energy units is also limited by the maximum or minimum value and the regulating ability of the prime mover.

[0072] (4) High-frequency action stage from t3 to t4:

[0073] When the isolated grid frequency satisfies , the high-frequency generator tripping configured in the isolated grid operates, and may operate in multiple rounds to trip off a part of the units, denoted as . During this period, when the frequency of the new energy unit exceeds 51.50 Hz, according to the standard requirements, the new energy unit is allowed to trip off. According to the different frequency and voltage tolerance capabilities of the units, the new energy may be disconnected one after another, and the disconnected capacity is denoted as . The disconnection of the new energy unit and the traditional unit reduces the power deviation , as shown in the following formula:

[0074]

[0075] Since the inertia effect provided by the unit gradually disappears at this time, it is difficult to quantitatively evaluate the high-frequency generator tripping and the off-grid capacity of new energy. The power deviation between the islanded power generation and the load may be negative. At the same time, the primary frequency regulation responds slower than the frequency mutation after generator tripping. The frequency generally overshoots and drops below 50 Hz. When the frequency reaches a certain value, the under-frequency load shedding action can be triggered.

[0076] (5) Stage when the system tends to be stable from t4 to t5:

[0077] After the under-frequency load shedding action, the power deviation becomes smaller. With the gradual adjustment of the primary frequency regulation of the remaining units, the system gradually tends to be stable.

[0078] As can be seen from the above several stages, if the arrangements of high-frequency generator tripping and under-frequency load shedding are unreasonable, it may lead to serious mismatches in generator tripping. Eventually, the system frequency and voltage fluctuate greatly, and the system becomes unstable. Therefore, to address this problem, the embodiment of the present invention proposes a method for judging the stability of an islanded power grid considering frequency and voltage control to achieve a more accurate quantitative evaluation of the stable operation of the passive islanded power grid in the regional power grid.

[0079] Refer to Figure 3 , which shows a flowchart of the steps of a method for judging the stability of an islanded power grid considering frequency and voltage control provided by the embodiment of the present invention, and specifically may include the following steps:

[0080] Step 301, when the regional power grid operates in an islanded mode, obtain the interchange power section, the equivalent inertia of traditional units, the high-frequency generator tripping amount, and the under-frequency load shedding amount of the islanded power grid system of the regional power grid under the current operating mode;

[0081] In a specific implementation, when the regional power grid operates in an islanded mode, obtain the interchange power section of the islanded power grid system of the regional power grid under the current operating mode , the equivalent inertia of traditional units , the high-frequency generator tripping amount, and the under-frequency load shedding amount .

[0082] Among them, the interchange power section is the power of the tie line before the accident, that is, the power deficit of the regional power grid operating in an islanded mode, with the outgoing direction of the regional power grid being positive.

[0083] The under-frequency load shedding amount refers to the load change amount, that is, the total under-frequency load shedding amount, corresponding to the active power output of the load to be cut when the under-frequency load shedding action is subsequently executed. That is to say, the load change amount in the inertia response stage is the total under-frequency load shedding amount in the subsequent stage.

[0084] The equivalent inertia of traditional units It is the equivalent inertia constant of traditional units in the islanded power grid (indicating that the system inertia does not consider the inertia provided by new energy units and loads at this time). It is expressed by the following formula:

[0085]

[0086] Wherein, represents the per-unit value of inertia of the th traditional unit in the islanded power grid system; represents the rated capacity of the th unit in the islanded power grid system; represents the proportion of new energy. This calculation formula is the same as the calculation formula introduced earlier. The difference is only that the previous calculation formula distinguishes the units into two types: small hydropower and new energy. When calculating, the two can be equivalently replaced and used.

[0087] The high-frequency generator tripping amount includes the new energy generator tripping amount and the traditional unit generator tripping amount . The new energy generator tripping amount represents the active power output of the new energy units that are tripped. The traditional unit generator tripping amount represents the active power output of the traditional power units that are tripped.

[0088] Step 302: Calculate the initial disturbance frequency change rate according to the exchange power section and the equivalent inertia of the traditional units;

[0089] According to the theoretical analysis results and practical experience, the disturbance frequency change rate can be calculated simply to quickly evaluate the stability of the islanded power grid. The calculation formula of the disturbance frequency change rate is as follows:

[0090]

[0091] Step 303: Based on the initial disturbance frequency change rate and the preset disturbance conditions, perform disturbance judgment, and according to the disturbance judgment result, combine the high-frequency generator tripping amount and / or the low-frequency load shedding amount to recalculate the disturbance frequency change rate to obtain the target disturbance frequency change rate;

[0092] The control objective of the embodiment of the present invention is to control the islanded power grid frequency (maximum frequency error or maximum frequency deviation) within a maximum allowable boundary range. According to different control objectives , the corresponding can be queried through Table 1 below:

[0093]

[0094] Table 1: and corresponding relationship

[0095] Based on the above corresponding relationship, an isolated network quantization evaluation method based on the change rate of multiple disturbance frequencies is proposed in an embodiment of the present invention. Specifically, the boundary of the isolated network frequency stability can be set as the frequency not greater than 55 Hz and not less than 47.5 Hz, that is, control . According to the shown in Table 1 and corresponding relationship, it is judged whether it is necessary to cut off new energy, high-frequency generator tripping or low-frequency load shedding, and the change amount thereof is superimposed on , and the inertia of the remaining units is updated.

[0096] In some embodiments, the process of performing disturbance judgment based on the initial disturbance frequency change rate and the preset disturbance condition, and recomputing the disturbance frequency change rate in combination with the low-frequency load shedding amount according to the disturbance judgment result to obtain the target disturbance frequency change rate can be implemented by executing the following sub-steps S01 to S04:

[0097] Step S01: When the initial disturbance frequency change rate is less than or equal to the first preset disturbance frequency change rate, subtract the low-frequency load shedding amount from the absolute value of the interchange power section to obtain the power section after load shedding;

[0098] Specifically, when , use the absolute value of the interchange power section Subtract the low-frequency load shedding amount to obtain the power section after load shedding .

[0099] Step S02: Obtain the rated capacity of each unit in the isolated network system and the output of each conventional unit, and calculate the in-region spinning reserve power of the isolated network system according to the rated capacity of each unit and the output of each conventional unit;

[0100] The in-region spinning reserve power of the isolated network system is calculated by the following formula:

[0101]

[0102] wherein, represents the output of the th conventional power unit in the isolated network system.

[0103] Step S03: When the power section after load shedding is less than or equal to the in-region spinning reserve power, add the low-frequency load shedding amount to the interchange power section to obtain the first updated interchange power section;

[0104] Judge the off-grid capacity before the accident (that is, the power section after load shedding) Subtract the total low-frequency load shedding amount (i.e., the low-frequency load shedding quantity). Whether it is greater than the in-region spinning reserve .

[0105] If , update the exchange power section, and keep the equivalent inertia unchanged. That is, use the exchange power section plus the low-frequency load shedding quantity to obtain the first updated exchange power section :

[0106]

[0107] Step S04: Calculate the first target disturbance frequency change rate according to the first updated exchange power section and the equivalent inertia of the traditional unit.

[0108] The calculation formula of the first target disturbance frequency change rate can be executed with reference to the calculation method of the disturbance frequency change rate in the foregoing embodiments, and will not be elaborated here.

[0109] When the power section after load shedding is greater than the in-region spinning reserve power, that is , it is determined that the system is unstable, which is the islanding stability discrimination result of the islanded power system.

[0110] In some embodiments, the process of performing disturbance judgment based on the initial disturbance frequency change rate and the preset disturbance conditions, and recalculating the disturbance frequency change rate in combination with the high-frequency generator tripping amount according to the disturbance judgment result to obtain the target disturbance frequency change rate can be implemented by executing the following sub-steps S11 to S13:

[0111] Step S11: When the initial disturbance frequency change rate is greater than or equal to the second preset disturbance frequency change rate and less than the third preset disturbance frequency change rate, subtract the new energy generator tripping amount from the exchange power section to obtain the second updated exchange power section;

[0112] Specifically, when and , calculate the second updated exchange power section through the following formula :

[0113]

[0114] Step S12: Update the equivalent inertia of the traditional unit based on the new energy generator tripping amount that has been cut off to obtain the first updated equivalent inertia:

[0115] The first updated equivalent inertia is calculated as shown in the following formula:

[0116]

[0117] Step S13: Calculate the second target disturbance frequency change rate according to the second updated power transfer section and the first updated equivalent inertia.

[0118] The calculation formula of the second target disturbance frequency change rate can be executed with reference to the calculation method of the disturbance frequency change rate in the foregoing embodiments, and will not be elaborated here.

[0119] In some embodiments, the process of performing disturbance judgment based on the initial disturbance frequency change rate and the preset disturbance conditions, and recalculating the disturbance frequency change rate in combination with the high-frequency generator tripping amount and the low-frequency load shedding amount according to the disturbance judgment result to obtain the target disturbance frequency change rate can be implemented by executing the following sub-steps S21 to S23:

[0120] Step S21: When the initial disturbance frequency change rate is greater than or equal to the third preset disturbance frequency change rate, subtract the new energy generator tripping amount and the conventional unit generator tripping amount from the power transfer section, and add the low-frequency load shedding amount to obtain the third updated power transfer section;

[0121] Specifically, when the third updated power transfer section is calculated by the following formula :

[0122]

[0123] Step S22: Update the equivalent inertia of the conventional unit based on the tripped amount of the conventional unit generator to obtain the second updated equivalent inertia;

[0124] The second updated equivalent inertia is calculated by the following formula:

[0125]

[0126] where and respectively represent the inertia and rated capacity of each tripped conventional unit.

[0127] Step S23: Calculate the third target disturbance frequency change rate according to the third updated power transfer section and the second updated equivalent inertia.

[0128] The calculation formula of the third target disturbance frequency change rate can be executed with reference to the calculation method of the disturbance frequency change rate in the foregoing embodiments, and will not be elaborated here.

[0129] Step 304, perform stability judgment according to the target disturbance frequency change rate to obtain the off-grid stability discrimination result of the off-grid system.

[0130] In a specific implementation, stability judgment is performed according to the change rate of the target disturbance frequency, and the islanding stability discrimination result of the islanded power system can be:

[0131] Judge whether the change rate of the target disturbance frequency is within the change rate interval of the disturbance frequency, that is, whether it satisfies ; where the change rate interval of the disturbance frequency corresponds to the maximum frequency deviation interval when the islanded power system is stable ;

[0132] If so, it is determined that the system is stable, which is used as the islanding stability discrimination result of the islanded power system;

[0133] If not, it is determined that the system is unstable, which is used as the islanding stability discrimination result of the islanded power system.

[0134] It should be noted that due to the particularity of small hydropower units, the islanded power grid can still operate at a relatively high frequency (such as 70 Hz) and can operate for a long time at the minimum power under the action of primary frequency regulation. Therefore, when the unit power is greater than the load, it is generally considered that the islanded power grid can maintain stable operation.

[0135] In the embodiment of the present invention, a method for quantitatively evaluating the islanding stability based on the instantaneous frequency change rate considering frequency-voltage control is proposed. When the regional power grid operates in islanding mode, the relevant parameters of generator tripping and load shedding of the islanded power system of the regional power grid in the current operation mode are obtained, and the initial disturbance frequency change rate is calculated; corresponding boundary judgment conditions are set according to the corresponding relationship between the disturbance frequency change rate and the maximum frequency deviation, and disturbance judgment is performed based on the initial disturbance frequency change rate. According to the actual disturbance judgment result, the relevant parameters of generator tripping and load shedding are flexibly combined to perform corresponding protection actions, and the disturbance frequency change rate is recalculated. Stability judgment is performed according to the new disturbance frequency change rate to obtain the islanding stability discrimination result of the islanded power system. The method provided by the embodiment of the present invention only needs to perform simple calculations and does not require a cumbersome modeling and simulation process. Compared with the traditional inertia-frequency evaluation method, it can quantitatively evaluate the stability of the regional power grid after islanding operation in a more intuitive and fast way. It can not only simplify the calculation process, but also greatly improve the efficiency and accuracy of the evaluation of the stable operation of the islanded power grid, providing a useful reference for the arrangement of the power grid operation mode.

[0136] For better illustration, referring to Figure 4 , a schematic diagram of the overall process of an islanding stability discrimination method considering frequency-voltage control provided by the embodiment of the present invention is shown. It should be noted that this embodiment only briefly describes the general process of islanding stability discrimination considering frequency-voltage control. The specific implementation process of each step can be understood by referring to the relevant content in the foregoing embodiments, and will not be elaborated here. It can be understood that the present invention places no restrictions on this.

[0137] When the regional power grid operates in an islanded mode, calculate the equivalent inertia of the islanded power grid system of the regional power grid under the current operating mode. , and count the high-frequency generator tripping amount (including the new energy generator tripping amount and the traditional generator tripping amount ) and the low-frequency load shedding amount ;

[0138] Calculate the initial disturbance frequency change rate according to the interchange power section ; ;

[0139] When , judge whether it meets ; if so, execute and then calculate the new disturbance frequency change rate ; if not, directly determine that the islanded power grid system is unstable or critically stable;

[0140] When , execute ;

[0141] Judge whether it simultaneously meets on the basis of ; if so, on the basis of , subtract , add , that is , update according to the generator tripping amount to obtain , and calculate the new disturbance frequency change rate ; if not, directly update according to the generator tripping amount to obtain , and calculate the new disturbance frequency change rate ;

[0142] Judge whether the new disturbance frequency change rate meets ; if so, determine that the islanded power grid system is stable; if not, determine that the islanded power grid system is unstable or critically stable.

[0143] To enable those skilled in the art to better understand the technical solution of the present invention, the following describes an embodiment of the present invention through a specific example.

[0144] Before the islanded operation of a certain regional power grid, the output power, inertia and power deviation at each stage of each unit are shown in Table 2 below:

[0145]

[0146] Table 2: Disturbance frequency change rate at each stage of the islanded power grid Calculate

[0147] Among them, the frequency protection action trips G12 unit (20 MW), G13 unit (18 MW), G14 unit (22 MW) and PMSG1 (100 MW), a total of 178 MW, and cuts the load by 44 MW.

[0148] According to the relevant calculation method provided by the embodiments of the present invention, the rate of change of frequency disturbance can finally be obtained is -0.85 Hz / s. That is to say, the islanded power system can operate stably. In addition, the correctness of the above calculation method can also be proved by the islanded operation simulation.

[0149] Referring to Figure 5 , a structural block diagram of an islanded power grid stability discrimination device considering frequency and voltage control provided by an embodiment of the present invention is shown, which may specifically include:

[0150] A data acquisition unit 501, configured to acquire the exchange power section, the equivalent inertia of the conventional units, the high-frequency generator tripping amount, and the low-frequency load shedding amount of the islanded power system of the regional power grid in the current operation mode when the regional power grid operates in an islanded mode;

[0151] An initial disturbance frequency change rate calculation unit 502, configured to calculate an initial disturbance frequency change rate according to the exchange power section and the equivalent inertia of the conventional units;

[0152] A target disturbance frequency change rate updating unit 503, configured to perform disturbance judgment based on the initial disturbance frequency change rate and a preset disturbance condition, and according to the disturbance judgment result, recompute the disturbance frequency change rate in combination with the high-frequency generator tripping amount, and / or, the low-frequency load shedding amount, to obtain a target disturbance frequency change rate;

[0153] A stability judgment unit 504, configured to perform stability judgment according to the target disturbance frequency change rate to obtain the islanded power grid stability discrimination result of the islanded power system.

[0154] In an optional embodiment, the target disturbance frequency change rate updating unit 503 includes:

[0155] A post-load-shedding power section calculation unit, configured to, when the initial disturbance frequency change rate is less than or equal to a first preset disturbance frequency change rate, subtract the low-frequency load shedding amount from the absolute value of the exchange power section to obtain a post-load-shedding power section;

[0156] An in-region spinning reserve power calculation unit, configured to obtain the rated capacity of each unit in the islanded power system and the unit output of each conventional unit, and calculate the in-region spinning reserve power of the islanded power system according to the rated capacity of each unit and the unit output of each conventional unit;

[0157] The first updated exchange power section calculation unit is used to, when the post - load - shedding power section is less than or equal to the spinning reserve power within the region, obtain the first updated exchange power section by adding the low - frequency load - shedding amount to the exchange power section.

[0158] The first target disturbance frequency change rate calculation unit is used to calculate the first target disturbance frequency change rate according to the first updated exchange power section and the equivalent inertia of the traditional units.

[0159] In an optional embodiment, the stability judgment unit 504 is specifically used for:

[0160] The system instability determination unit is used to determine that the system is unstable when the post - load - shedding power section is greater than the spinning reserve power within the region, as the islanded grid stability discrimination result of the islanded grid system.

[0161] In an optional embodiment, the high - frequency generator tripping amount includes the new - energy generator tripping amount; the target disturbance frequency change rate updating unit 503 includes:

[0162] The second updated exchange power section calculation unit is used to, when the initial disturbance frequency change rate is greater than or equal to the second preset disturbance frequency change rate and less than the third preset disturbance frequency change rate, obtain the second updated exchange power section by subtracting the new - energy generator tripping amount from the exchange power section.

[0163] The first updated equivalent inertia calculation unit is used to update the equivalent inertia of the traditional units based on the new - energy generator tripping amount that is cut off, to obtain the first updated equivalent inertia.

[0164] The second target disturbance frequency change rate calculation unit is used to calculate the second target disturbance frequency change rate according to the second updated exchange power section and the first updated equivalent inertia.

[0165] In an optional embodiment, the high - frequency generator tripping amount includes the new - energy generator tripping amount and the traditional - unit generator tripping amount; the target disturbance frequency change rate updating unit 503 includes:

[0166] The third updated exchange power section calculation unit is used to, when the initial disturbance frequency change rate is greater than or equal to the third preset disturbance frequency change rate, obtain the third updated exchange power section by subtracting the new - energy generator tripping amount and the traditional - unit generator tripping amount from the exchange power section and then adding the low - frequency load - shedding amount.

[0167] The second updated equivalent inertia calculation unit is used to update the equivalent inertia of the traditional units based on the traditional - unit generator tripping amount that is cut off, to obtain the second updated equivalent inertia.

[0168] A third target disturbance frequency change rate calculation unit is configured to calculate a third target disturbance frequency change rate according to the third updated power exchange section and the second updated equivalent inertia.

[0169] In an alternative embodiment, the calculation formula of the disturbance frequency change rate is as follows:

[0170]

[0171] Wherein, represents the disturbance frequency change rate; represents the power exchange section, with the positive direction being the power output from the regional power grid; represents the system rated frequency; represents the equivalent inertia of traditional units.

[0172] In an alternative embodiment, the stability judgment unit 504 is specifically configured to:

[0173] Judge whether the target disturbance frequency change rate is within the disturbance frequency change rate interval; the disturbance frequency change rate interval corresponds to the maximum frequency deviation interval when the islanded power grid system is stable;

[0174] If so, it is determined that the system is stable, which is used as the islanded stability discrimination result of the islanded power grid system;

[0175] If not, it is determined that the system is unstable, which is used as the islanded stability discrimination result of the islanded power grid system.

[0176] For the device embodiment, since it is basically similar to the method embodiment, the description is relatively simple. For the relevant parts, refer to the partial description of the foregoing method embodiment.

[0177] It should be noted that, in order to enable those skilled in the art to better distinguish data of the same type but with different actual meanings, in the embodiments of the present invention, some technical features are distinguished and described using terms such as first and second. The terms first and second are only used for data differentiation and have no other special meanings. It can be understood that the present invention places no restrictions on this.

[0178] The embodiments of the present invention further provide an electronic device, which includes a processor and a memory:

[0179] The memory is used to store program codes and transmit the program codes to the processor;

[0180] The processor is used to execute the islanded stability discrimination method considering frequency and voltage control according to the instructions in the program codes in any embodiment of the present invention.

[0181] An embodiment of the present invention also provides a computer-readable storage medium, which is used to store program codes for executing the isolated network stability discrimination method involving frequency and voltage control according to any embodiment of the present invention.

[0182] Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working processes of the above-described systems, devices, and units can refer to the corresponding processes in the foregoing method embodiments and will not be elaborated herein.

[0183] In several embodiments provided by the present invention, it should be understood that the disclosed systems, devices, and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of the units is only a logical function division, and there may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed couplings or direct couplings or communication connections to each other can be through some interfaces, and the indirect couplings or communication connections of the devices or units can be in electrical, mechanical, or other forms.

[0184] The units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they can be located in one place or distributed to multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0185] In addition, in each embodiment of the present invention, the functional units can be integrated into one processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above-mentioned integrated units can be implemented in the form of hardware or in the form of software functional units.

[0186] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memories (ROMs), random access memories (RAMs), magnetic disks, or optical discs that can store program codes.

[0187] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for judging the stability of an isolated power grid considering frequency and voltage control, characterized in that Including: When the regional power grid operates in an islanded mode, obtain the exchange power section, the equivalent inertia of traditional units, the high-frequency generator tripping amount, and the low-frequency load shedding amount of the islanded system of the regional power grid under the current operation mode; Calculate the initial disturbance frequency change rate according to the exchange power section and the equivalent inertia of the traditional units; Based on the initial disturbance frequency change rate and a preset disturbance condition, perform a disturbance judgment, and according to the disturbance judgment result, combine the high-frequency generator tripping amount, and / or, the low-frequency load shedding amount to recalculate the disturbance frequency change rate to obtain the target disturbance frequency change rate; Perform a stability judgment according to the target disturbance frequency change rate to obtain the islanded stability discrimination result of the islanded system; 2. The islanding stability discrimination method according to claim 1, wherein, Based on the initial disturbance frequency change rate and a preset disturbance condition, perform a disturbance judgment, and according to the disturbance judgment result, combine the low-frequency load shedding amount to recalculate the disturbance frequency change rate to obtain the target disturbance frequency change rate, including: When the initial disturbance frequency change rate is less than or equal to the first preset disturbance frequency change rate, subtract the low-frequency load shedding amount from the absolute value of the exchange power section to obtain the power section after load shedding; Obtain the rated capacity of each unit in the islanded system and the unit output of each traditional unit, and calculate the in-region spinning reserve power of the islanded system according to the rated capacity of each unit and the unit output of each traditional unit; When the power section after load shedding is less than or equal to the in-region spinning reserve power, add the low-frequency load shedding amount to the exchange power section to obtain the first updated exchange power section; Calculate the first target disturbance frequency change rate according to the first updated exchange power section and the equivalent inertia of the traditional units; 3. The isolated network stability discrimination method according to claim 2, wherein Also including: When the power section after load shedding is greater than the in-region spinning reserve power, determine that the system is unstable, which is used as the islanded stability discrimination result of the islanded system; 4. The method for judging the stability of an isolated network according to claim 1, characterized in that The high-frequency generator tripping amount includes the new energy generator tripping amount; based on the initial disturbance frequency change rate and a preset disturbance condition, perform a disturbance judgment, and according to the disturbance judgment result, combine the high-frequency generator tripping amount to recalculate the disturbance frequency change rate to obtain the target disturbance frequency change rate, including: When the initial disturbance frequency change rate is greater than or equal to the second preset disturbance frequency change rate and less than the third preset disturbance frequency change rate, subtract the new energy generator tripping amount from the exchange power section to obtain the second updated exchange power section; Based on the new energy generator tripping amount cut off, update the equivalent inertia of the traditional units to obtain the first updated equivalent inertia; Calculate the second target disturbance frequency change rate according to the second updated exchange power section and the first updated equivalent inertia; 5. The off-grid stability discrimination method according to claim 1, characterized in that, The high-frequency generator tripping amount includes the new energy generator tripping amount and the traditional unit generator tripping amount; based on the initial disturbance frequency change rate and a preset disturbance condition, perform a disturbance judgment, and according to the disturbance judgment result, combine the high-frequency generator tripping amount and the low-frequency load shedding amount to recalculate the disturbance frequency change rate to obtain the target disturbance frequency change rate, including: When the change rate of the initial disturbance frequency is greater than or equal to the third preset disturbance frequency change rate, subtract the new energy generator tripping amount and the conventional unit tripping amount from the exchanged power section, and add the low-frequency load shedding amount to obtain the third updated exchanged power section; Based on the tripping amount of the conventional unit that is cut off, update the equivalent inertia of the conventional unit to obtain the second updated equivalent inertia; Calculate the third target disturbance frequency change rate according to the third updated exchanged power section and the second updated equivalent inertia.

6. The method for judging the stability of an isolated network according to any one of claims 1 to 5, characterized in that The calculation formula of the disturbance frequency change rate is as follows: Among them, represents the disturbance frequency change rate; represents the exchange power section, with the positive direction being the power output from the regional power grid; represents the system rated frequency; represents the equivalent inertia of the traditional unit.

7. The method for judging the stability of an isolated network according to claim 6, characterized in that Judging stability according to the target disturbance frequency change rate to obtain the off-grid stability discrimination result of the off-grid system, including: Judging whether the target disturbance frequency change rate is within the disturbance frequency change rate interval; the disturbance frequency change rate interval corresponds to the maximum frequency deviation interval when the off-grid system is stable; If so, determine that the system is stable, which is used as the off-grid stability discrimination result of the off-grid system; If not, determine that the system is unstable, which is used as the off-grid stability discrimination result of the off-grid system.

8. A stand-alone network stability discrimination device considering frequency and voltage control, characterized in that Including: A data acquisition unit, configured to acquire the exchanged power section, the equivalent inertia of the conventional unit, the high-frequency generator tripping amount, and the low-frequency load shedding amount of the off-grid system of the regional power grid in the current operation mode when the regional power grid operates in an off-grid manner; An initial disturbance frequency change rate calculation unit, configured to calculate the initial disturbance frequency change rate according to the exchanged power section and the equivalent inertia of the conventional unit; A target disturbance frequency change rate update unit, configured to perform disturbance judgment based on the initial disturbance frequency change rate and a preset disturbance condition, and according to the disturbance judgment result, recompute the disturbance frequency change rate in combination with the high-frequency generator tripping amount, and / or, the low-frequency load shedding amount to obtain the target disturbance frequency change rate; A stability judgment unit, configured to judge stability according to the target disturbance frequency change rate to obtain the off-grid stability discrimination result of the off-grid system.

9. An electronic device, characterized in that, The device includes a processor and a memory: The memory is used to store program codes and transmit the program codes to the processor; The processor is configured to execute the off-grid stability discrimination method considering frequency and voltage control according to any one of claims 1-7 based on the instructions in the program codes.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium is used to store program codes, and the program codes are used to execute the off-grid stability discrimination method considering frequency and voltage control according to any one of claims 1-7.

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