CN117955120B - Load transient voltage instability discrimination method and system based on power factor positive feedback - Google Patents

Abstract

The invention provides a method and a system for judging the transient voltage instability of a load based on positive feedback of a power factor, which are used for deducing the transient voltage instability process of the load side based on a variable impedance model and determining the mechanism characteristic and the stability characteristic quantity of the transient voltage instability of the load side; carrying out measurable expression on the mechanism characteristic and the stable characteristic quantity by using bus power and a power factor angle cotangent value, and determining the response characteristic of transient voltage instability at a load side; and adding additional criteria to reduce the false judgment rate, constructing load transient voltage instability criteria based on positive feedback of the power factor, and judging whether the load transient voltage is unstable or not by using the criteria. The load transient voltage instability criterion based on the power factor positive feedback constructed by the invention directly starts from an instability mechanism, the selected response characteristic is easy to obtain in an actual power grid, and the misjudgment rate of a stable scene is lower on the premise of ensuring accurate identification of the load side voltage instability scene.

Description

Method and system for judging load transient voltage instability based on power factor positive feedback

Technical Field

The present invention belongs to the technical field of power grid stability determination, and in particular relates to a load transient voltage instability determination method and system based on power factor positive feedback.

Background Art

The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

As one of the important traditional stability forms, voltage stability has long received much attention. Among them, the effective identification of transient voltage instability has always been an important topic in voltage stability research. In recent years, with the increasing scale of my country's receiving systems and the large-scale penetration of power electronic equipment in the power grid, the problem of transient voltage stability in the power system has become more prominent. The shortcomings of the transient voltage stability identification and control technology of traditional plan-based event matching have gradually emerged. It is imperative to identify transient voltage instability based on response characteristics. It is generally believed that the common transient voltage instability scenario is an electromechanical transient process dominated by load factors. The power load often contains equipment that adjusts its own impedance according to the difference between the power obtained and the preset target. It is this kind of action mechanism that causes more load reactive power consumption and grid reactive power transmission in some cases, which may cause transient voltage instability.

In terms of judging transient voltage instability, the bus voltage amplitude can reflect the voltage level of the power system. Some scholars use the voltage amplitude change rate of key nodes to construct the Lyapunov index, and judge whether the system transient voltage is stable based on whether the index is greater than 0. Some foreign scholars realize voltage trajectory tracking through the time series of characteristic parameters. This method does not require a system model. On this basis, relevant researchers of the State Grid Corporation of China analyze the voltage amplitude change rate at the machine end-voltage amplitude deviation characteristic curve to construct a transient voltage instability judgment criterion. The above method only needs to measure the bus voltage to judge whether the transient voltage is unstable, but only using the bus voltage amplitude may have problems such as low judgment accuracy and long judgment time. Relevant researchers analyzed the challenges brought by new energy distributed grid connection and DC transmission to the load side transient voltage stability judgment. When a serious fault occurs in the traditional DC or it recovers from the fault, the DC inverter absorbs a large amount of reactive power from the receiving system under the action of the control system, resulting in a drop in the commutation bus voltage, causing the expansion of the instability domain of nearby variable impedance loads, and increasing the risk of transient voltage instability. Based on this, some scholars have established stability measurement indicators for the DC receiving end system by analyzing the changes in various electrical quantities in the inverter station when the voltage collapse occurs in the commutation bus. If the scale of new energy grid connection is large, but the number of reactive compensation devices in the system is insufficient, it will affect the transient voltage stability of the system. In order to accurately determine whether the system has transient voltage instability when new energy is involved, some scholars have defined indicators such as voltage severity and fault limit removal time.

Although the above studies have proposed methods for distinguishing transient voltage instability to a certain extent, these distinguishing methods are not based on the essential mechanism of transient voltage instability on the load side.

In order to improve the accuracy and timeliness of transient voltage instability criterion, some scholars combined real-time measurement information and used Thevenin theorem to construct equivalent circuits to propose transient voltage instability criterion, but it is difficult to construct equivalent circuits in power systems containing a large number of power electronic equipment. Other related researchers found that transient voltage instability on the load side can be accompanied by a positive feedback process of continuous decrease in line active power and continuous increase in line current. Therefore, it is proposed to judge stability by monitoring line current, line active power and bus voltage, but the reasons for the misjudgment of some stable cases and the omission of some instability cases by this criterion are not explained.

Summary of the invention

In order to overcome the shortcomings of the above-mentioned prior art, the present invention provides a method and system for judging load transient voltage instability based on power factor positive feedback, and constructs a voltage instability judgment criterion based on positive feedback of bus active power and bus power factor angular cotangent value, which directly starts from the most essential mechanism of transient voltage instability on the load side, thereby ensuring the practicality of the judgment criterion.

To achieve the above object, a first aspect of the present invention provides a method for determining load transient voltage instability based on power factor positive feedback, comprising:

Based on the variable impedance model, the transient voltage instability process on the load side is deduced to determine the mechanism characteristics and stability characteristic quantities of the transient voltage instability on the load side;

The mechanism characteristics and stability characteristic quantities are expressed measurably by using bus power and cotangent value of power factor angle to determine the response characteristics of transient voltage instability on the load side;

Additional criteria are added to reduce the false positive rate, the differential form in the response characteristics is converted into a differential form, a load transient voltage instability criterion based on power factor positive feedback is constructed, and the constructed load transient voltage instability criterion is used to determine whether the transient voltage on the load side is unstable.

Furthermore, based on the variable impedance model, the transient voltage instability process on the load side is deduced, and the mechanism characteristics of the transient voltage instability on the load side are determined, specifically:

When the variable impedance load enters the unstable domain and becomes unstable, there is a vicious positive feedback characteristic between the impedance change and the load absorbing active power; the load absorbs active power and changes impedance to obtain the preset active power target. The impedance change causes the load absorbing active power to further deviate from the preset active power target, thus forming a positive feedback process in which the load absorbs active power deviation, the load changes impedance, and the load absorbs active power further deviates.

Furthermore, based on the variable impedance model, the transient voltage instability process on the load side is deduced, and the stable characteristic quantity of the transient voltage instability on the load side is determined to be the equivalent impedance of the load bus, specifically:

The first-order differential model of variable impedance load is shown as follows:

Where, R _Load is the equivalent load resistance; is the recovery time constant of conductivity; P _L0 is the preset target of active power; P _Load is the active power absorbed by the load;

The stable characteristic quantity of transient voltage instability on the load side is determined as the bus equivalent impedance:

Where X _Load is the equivalent load reactance.

Furthermore, the bus power and the cotangent value of the power factor angle are used to implement a measurable expression of the mechanism characteristics and the stability characteristic quantity, and the response characteristics of the transient voltage instability on the load side are determined, specifically:

When the variable impedance load becomes unstable due to the vicious positive feedback process of impedance change and bus power deviation, the equivalent load impedance continues to decrease, resulting in a continuous decrease in the cotangent value of the power factor angle, thereby absorbing more reactive power and causing voltage collapse; the bus power factor angle cotangent value and the equivalent load impedance show a one-to-one correspondence, and the bus power factor angle cotangent value is easier to measure. Therefore, the bus power factor angle cotangent value is used to approximately characterize the change in load impedance, forming a measurable response characteristic.

Furthermore, the response characterization of transient voltage instability on the load side is determined as follows:

In the formula, P is the bus active power; Q is the bus reactive power; is the cotangent value of the bus power factor.

Furthermore, for the misjudgment scenario caused by the existence of more than two intersection points between the actual active power of the bus and the preset target active power curve, the method of setting the voltage safety threshold value is added to reduce the misjudgment rate; for the misjudgment scenario caused by the contraction of the unstable domain during the dynamic rise of voltage, the method of setting the judgment criterion duration threshold is used to reduce the misjudgment rate.

Furthermore, additional criteria are added to reduce the misjudgment rate, the differential form in the response characteristics is converted into a differential form, and a load transient voltage instability criterion based on power factor positive feedback is constructed, specifically:

Where, _Pk and _Qk are the bus active power and reactive power at the kth moment respectively; Pk _+N and _QktN are the bus active power and reactive power at the k+Nth moment respectively; t is the duration of the bus active power drop and the power factor cotangent value drop; _T1 is the judgment duration threshold; is the bus voltage at the k+N+ _T1 moment; _U1 is the voltage safety threshold.

A second aspect of the present invention provides a load transient voltage instability determination system based on power factor positive feedback, comprising:

The first determination module: a module for deducing the transient voltage instability process on the load side based on the variable impedance model, and determining the mechanism characteristics and stability characteristic quantities of the transient voltage instability on the load side;

The second determination module: a module for implementing a measurable expression of the mechanism characteristics and stability characteristic quantities by using bus power and cotangent value of power factor angle to determine the response characteristics of transient voltage instability on the load side;

Discrimination module: Add additional criteria to reduce the misjudgment rate, convert the differential form in the response characteristics into a differential form, construct a load transient voltage instability criterion based on power factor positive feedback, and use the constructed load transient voltage instability criterion to determine whether the transient voltage on the load side is unstable.

The third aspect of the present invention provides a computer device, comprising: a processor, a memory and a bus, wherein the memory stores machine-readable instructions executable by the processor, and when the computer device is running, the processor and the memory communicate via the bus, and when the machine-readable instructions are executed by the processor, a load transient voltage instability judgment method based on power factor positive feedback is executed.

A fourth aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, and when the computer program is executed by a processor, a method for determining load transient voltage instability based on positive feedback of power factor is executed.

One or more of the above technical solutions have the following beneficial effects:

The present invention determines the stable characteristic quantity of transient voltage instability on the load side based on the variable impedance model, reflects the transient voltage instability process caused by the combined action of multiple dynamic devices and static devices, and avoids the problem that a single dynamic device cannot accurately characterize transient voltage instability.

The response characteristic of transient voltage instability on the load side of the present invention measures the active power and reactive power on the bus, which is easy to obtain in an actual power grid, has a fast calculation speed, and can more intuitively characterize the transient voltage instability process on the load side.

The load transient voltage instability criterion based on power factor positive feedback constructed by the present invention starts directly from the instability mechanism and transforms the differential form that is prone to errors into a differential form. Under the premise of ensuring accurate identification of the load side voltage instability scene, the misjudgment rate of the stable scene is low.

Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

FIG1 is a variable impedance model circuit of a load in Embodiment 1 of the present invention;

2 is a schematic diagram showing the relationship between equivalent load impedance, active power absorbed by the load, bus voltage, and current flowing through the load in the first embodiment of the present invention;

FIG3 is a schematic diagram of the running trajectory of the running point when the running point is located in different areas in the first embodiment of the present invention;

4 is a schematic diagram showing a misjudgment caused by the presence of more than two intersection points between the actual active power and the preset target active power in the first embodiment of the present invention;

FIG5 is a schematic diagram of misjudgment caused by the contraction of the unstable region during the dynamic voltage rise process in the first embodiment of the present invention;

FIG6 is a schematic diagram of solving bus active power and reactive power in Embodiment 1 of the present invention;

FIG7 is a voltage image of three 220 kV stable nodes 1SB15222, 2SB10222, and 3SB032221 in Embodiment 1 of the present invention;

FIG8 is a determination result of three 220 kV stable nodes 1SB15222, 2SB10222, and 3SB032221 in Embodiment 1 of the present invention;

FIG9 is a voltage image of a 220 kV unstable node of 1RB07321 in Example 1 of the present invention;

FIG10 is a result of determining the 1RB07321 220 kV instability node in the first embodiment of the present invention;

FIG. 11 is a flow chart of a method for determining load transient voltage instability in Embodiment 1 of the present invention.

DETAILED DESCRIPTION

It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

It should be noted that the terms used herein are for describing specific embodiments only and are not intended to be limiting of exemplary embodiments according to the present invention.

In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

Embodiment 1

As shown in FIG11 , this embodiment discloses a method for determining load transient voltage instability based on power factor positive feedback, including:

Based on the variable impedance model, the transient voltage instability process on the load side is deduced to determine the mechanism characteristics and stability characteristic quantities of the transient voltage instability on the load side;

The mechanism characteristics and stability characteristic quantities are expressed measurably by using bus power and cotangent value of power factor angle to determine the response characteristics of transient voltage instability on the load side;

Additional criteria are added to reduce the false positive rate, and a load transient voltage instability criterion based on power factor positive feedback is constructed. The constructed load transient voltage instability criterion is used to determine whether the transient voltage on the load side is unstable.

The solution of this embodiment aims to extract the response characteristics of transient voltage instability on the load side according to the most essential mechanism of transient voltage instability on the load side, and use the load transient voltage instability criterion based on power factor positive feedback to determine whether the transient voltage on the load side is unstable.

The main implementation steps of the method of this embodiment are as follows:

Step 1: Determine the mechanism characteristics and stability characteristics of transient voltage instability on the load side

The AC circuit is constructed as shown in Figure 1, where R _Line and X _Line are the line resistance and reactance, R _Load and X _Load are the equivalent load resistance and reactance, and _Er is the single-machine infinite power supply potential.

The current flowing through the equivalent load is shown in formula (1):

The voltage across the equivalent load is shown in formula (2):

The active power absorbed by the load is shown in formula (3):

The reactive power absorbed by the load is shown in formula (4):

Assuming that the line impedance remains unchanged during the dynamic change of the system, formulas (1)-(3) are combined to obtain the equivalent load impedance-load absorbed active power, bus voltage, and load current relationship diagram as shown in Figure 2.

The first-order model of equivalent load resistance is shown in formula (5):

Where P _L0 is the preset target of active power, is the recovery time constant of the conductivity.

After the power system is greatly disturbed, if the load is between point O and point A, P _Load <P _L0 , the load increases its own active power consumption by reducing its own equivalent impedance, and finally stabilizes at point A; when the load is between point A and point C, P _Load >P _L0 , the load increases its own equivalent load impedance, the active power absorbed by the load increases between point C and point B, decreases between point B and point A, and finally stabilizes at point A. When the operating point is to the right of point C, P _Load <P _L0 , the load equivalent load impedance decreases, but the active power absorbed by the load further decreases, forming a positive feedback process.

In summary, the movement trajectory of the operating point when the marked operating point is between point O and point A, between point A and point C, and in the area to the right of point C is shown in Figure 3. It is found that the instability of the system load is accompanied by a continuous decrease in the equivalent load impedance, but the positive feedback process of the load absorbing active power continues to decrease. The expression of this process is shown in formula (6). Therefore, the load absorbing active power and the equivalent load impedance can be used as transient stability characteristic quantities.

Where P _Load is the active power absorbed by the load, and Z _Load is the equivalent load impedance, which is used as the stable characteristic quantity of transient voltage instability on the load side.

Step 2: Determine the response characteristics of transient voltage instability on the load side

In actual power grids, bus voltage amplitude and phase angle, bus active power, and bus reactive power can be measured, but equivalent load impedance cannot be measured. Therefore, the equivalent load impedance needs to be measurable in order to be effectively applied in actual power grids.

According to the AC circuit model constructed in Figure 1, the expression of the cotangent value of the bus power factor angle is shown in formula (7):

Where _R0 is the equivalent load resistance of the bus at the initial moment, _X0 is the equivalent load reactance of the bus at the initial moment, _vR is the decrease rate of the equivalent load resistance of the bus, and _vX is the decrease rate of the equivalent load reactance of the bus.

Assuming that v _R and v _X are not functions of time, let the cotangent value of the power factor be differentiated with respect to time, and we can get equation (8) as follows:

If the equivalent load impedance can be approximately represented by the cotangent value of the bus power factor angle, the relationship must be as shown in equation (9):

Under the condition of formula (9), the cotangent value of the bus power factor decreases as the equivalent load impedance decreases. This process may cause the load to absorb more reactive power, resulting in bus voltage collapse. Therefore, transient voltage instability can be described as a positive feedback process of continuous reduction of bus active power and continuous reduction of bus power factor cotangent value, thereby determining the response characterization of transient voltage instability on the load side as shown in formula (10):

Where: P is the bus active power, Q is the bus reactive power, is the cotangent value of the bus power factor.

Step 3: Construct a load transient voltage instability criterion based on power factor positive feedback

There are two misjudgment scenarios in equation (10): (1) there are more than two intersection points between the actual active power curve of the bus and the preset target active power curve; (2) the voltage rise in the dynamic process causes the unstable region to shrink.

When there are three intersections between the actual active power of the bus and the preset target active power curve, the operation trajectory of the operating point from point O to point A, point A to point B, point B to point C, and after point C is drawn as shown in Figure 4. Through the analysis of the operation trajectory of the operating point, the operating point can finally remain stable in each area. However, when the operating point is between point B and point C, there will be a process of reducing the equivalent load impedance and reducing the active power, which will lead to misjudgment.

For scenarios where there are more than two intersections between the actual active power of the busbar and the preset target active power curve, the method of setting a voltage safety threshold can be used to reduce the misjudgment rate. This method considers voltage safety issues and voltage stability issues together. When the voltage is a safe voltage, the judgment criteria will not be triggered, thereby avoiding misjudgment.

The schematic diagram of the contraction of the unstable domain during the dynamic voltage rise is shown in Figure 5. The operating point is initially located at point A, which is the unstable domain, and the operating point moves from point A to point B; when the operating point is at point B, the voltage rises, and the operating point moves from point B to point C, running from the unstable domain to the stable domain; after the operating point is at point C, if the voltage remains unchanged, the operating point will remain in the stable domain and eventually run to the stable point. However, when the operating point is in the unstable domain, the load transient voltage instability criterion based on power factor positive feedback has been triggered, resulting in a misjudgment.

For the misjudgment scenario caused by the contraction of the unstable region during the dynamic voltage rise, the method of setting the judgment duration threshold can be used to reduce the misjudgment rate. This method reduces the probability of misjudgment caused by the return of the operating point from the unstable region to the stable region by adding the judgment duration threshold in the judgment.

Therefore, on the basis of the original load transient voltage instability criterion based on power factor positive feedback, two additional criteria, namely voltage safety threshold value and criterion duration threshold value, are added to reduce the misjudgment rate. The load transient voltage instability criterion based on power factor positive feedback after adding the additional criteria is shown in formula (11):

Where U is the bus voltage; _U1 is the set voltage safety threshold; t is the duration of the bus active power drop and the power factor cotangent value drop (i.e., the first two lines of formula (11)); _T1 is the judgment duration threshold.

In order to reduce the errors caused by the power angle dynamics and measurement noise that may exist in the actual power grid, the time sliding window difference is used to replace the differential method. The final load transient voltage instability criterion based on power factor positive feedback is shown in formula (12):

Where, _Pk and _Qk are the bus active power and reactive power at the kth moment; Pk _+N and Qk _+N are the bus active power and reactive power at the k+Nth moment; is the bus voltage at the k+N+ _T1 moment.

Case analysis: The 10,000-node test system of the Electric Power Research Institute mainly includes two subsystems: the sending end test system and the receiving end test system. It includes 10,575 three-phase nodes: about 550 synchronous power supplies; 1,031 wind/solar renewable energy stations; total installed power capacity of 289.58 million kilowatts, 178.96 million kilowatts of conventional power installed capacity, and 110.62 million kilowatts of new energy installed capacity (accounting for 38.2% of the total installed capacity); 6 DC loops, of which the sending and receiving ends are connected through 3 8 million DC loops, 1 loop at the sending end is sent to other power grids, and 2 loops at the receiving end are fed from other power grids.

The sending-end test system is based on a 500 kV main grid and is divided into three zones: Zone 1S with a high proportion of new energy wind and fire bundled transmission; Zone 2S with conventional load centers; Zone 3S with a high proportion of hydropower transmission, with a weak connection section with the main grid. It includes 4,941 three-phase nodes; 295 synchronous power sources; 392 wind/solar renewable energy stations; total installed power capacity of 154.98 million kilowatts, 87.28 million kilowatts of conventional units, and 67.7 million kilowatts of new energy (55.05 million kilowatts of wind power and 12.65 million kilowatts of photovoltaic power, accounting for 43.68% of the total installed capacity; 4 DC (4 million kilowatts*1+8 million kilowatts*3).

The receiving end test system is based on a 500 kV main grid and is divided into four areas: Zone 1R is the receiving area; Zone 2R contains a high proportion of new energy; Zone 3R is a hybrid AC/DC receiving area; Zone 4R is a pure power supply base with a weak connection to the main grid. It includes 5,624 three-phase nodes, 8,767 branches; 255 synchronous power sources; 639 wind/solar renewable energy stations; total installed power capacity of 135.7 million kilowatts, conventional installed capacity of 92.78 million kilowatts, and new energy installed capacity of 42.92 million kilowatts (wind power installed capacity of 13 million kilowatts, photovoltaic installed capacity of 29.92 million kilowatts: 50% each for Class A and Class B photovoltaic); 5 DC feed-in lines, including 4 +800 kV UHV DC with a rated power of 8 million kilowatts, and 1 +660 kV DC with a rated power of 4 million kilowatts.

Under the peak 103 operation mode, the load is 7795.4 kilowatts. 5 DC lines feed in a total of 28 million kilowatts, and DC feed-in accounts for 35% of the load. Conventional units generate 39.3 million kilowatts of electricity, and new energy generates 10.6536 million kilowatts of electricity (933,600 kilowatts of wind power and 9.72 million kilowatts of photovoltaic power). New energy output accounts for 20% of power generation and 13.6% of load. Partition 1R is the load center, with a large proportion of AC power. The load is 17.36 million kilowatts, and the power generation is 8.55 million kilowatts (5.67 million conventional units and 2.88 million distributed new energy: accounting for 17% of the load); AC power is 8.81 million kilowatts, accounting for 50% of the power.

The bus voltage with load at the receiving end and its related line active power and line reactive power are monitored, and the active power and reactive power of the related lines are summed up to obtain the bus active power and reactive power. The load transient voltage instability criterion based on power factor positive feedback is applied to the bus. If one of the bus criterion is established, the system is judged as transient voltage instability.

Taking Figure 6 as an example, if we want to determine whether the transient voltage of the 220kV B node is stable, we need to obtain the bus active power and bus reactive power of the 220kV B node according to equations (13) and (14) respectively, and apply the load transient voltage instability criterion based on power factor positive feedback at this node to determine whether transient voltage instability occurs at this node.

P＝P ₁ +P ₂₁ +P ₂₂ +P ₃ (13)

Q＝Q ₁ +Q ₂₁ +Q ₂₂ +Q ₃ (14)

The voltage images of 220kV nodes such as 1SB15222, 2SB10222, and 3SB032221 are shown in Figure 7. The voltages of these nodes all recovered to above 0.8pu within 10s, so they are stable nodes. The three nodes were judged by the load transient voltage instability criterion based on power factor positive feedback, and the results are shown in Figure 8. The output "0" represents no trigger criterion, and the output "1" represents a trigger criterion. None of these three nodes triggered the criterion, so these three nodes can be correctly judged as stable.

The voltage image of the 1RB07321 node with a voltage level of 220kV is shown in Figure 9. The voltage of this node did not recover to above 0.8pu within 10s, so this node is an unstable node. The node was judged using the load transient voltage instability criterion based on power factor positive feedback. The result is shown in Figure 10. The judgment result outputs "1", so the node can be correctly judged as unstable.

Through the above analysis, the load transient voltage instability criterion based on power factor positive feedback can correctly determine whether the node is stable.

Embodiment 2

The purpose of this embodiment is to provide a load transient voltage instability judgment system based on power factor positive feedback, including:

The first determination module: a module for deducing the transient voltage instability process on the load side based on the variable impedance model, and determining the mechanism characteristics and stability characteristic quantities of the transient voltage instability on the load side;

The second determination module: a module for implementing a measurable expression of the mechanism characteristics and stability characteristic quantities by using bus power and cotangent value of power factor angle to determine the response characteristics of transient voltage instability on the load side;

Discrimination module: Add additional criteria to reduce the misjudgment rate, convert the differential form in the response characteristics into a differential form, construct a load transient voltage instability criterion based on power factor positive feedback, and use the constructed load transient voltage instability criterion to determine whether the transient voltage on the load side is unstable.

Embodiment 3

The purpose of this embodiment is to provide a computing device, including: a processor, a memory and a bus, wherein the memory stores machine-readable instructions executable by the processor, and when the computer device is running, the processor and the memory communicate through the bus, and the steps of the above method are performed when the machine-readable instructions are executed by the processor.

Embodiment 4

The purpose of this embodiment is to provide a computer-readable storage medium.

A computer-readable storage medium stores a computer program, which executes the steps of the above method when executed by a processor.

The steps involved in the apparatuses of the above embodiments 2, 3 and 4 correspond to the method embodiment 1, and the specific implementation methods can refer to the relevant description part of embodiment 1. The term "computer-readable storage medium" should be understood as a single medium or multiple media including one or more instruction sets; it should also be understood to include any medium that can store, encode or carry an instruction set for execution by a processor and enable the processor to execute any method in the present invention.

Those skilled in the art should understand that the modules or steps of the present invention described above can be implemented by a general-purpose computer device, or alternatively, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Technical personnel in the relevant field should understand that various modifications or variations that can be made by technical personnel in the field without creative work on the basis of the technical solution of the present invention are still within the scope of protection of the present invention.

Claims (4)

1. A method for determining load transient voltage instability based on power factor positive feedback, characterized by comprising: Based on the variable impedance model, the transient voltage instability process on the load side is deduced to determine the mechanism characteristics and stability characteristic quantities of the transient voltage instability on the load side; The load-side transient voltage instability process is deduced based on the variable impedance model to determine the mechanism characteristics of the load-side transient voltage instability, specifically: When the variable impedance load enters the unstable region and becomes unstable, there is a vicious positive feedback feature between the impedance change and the load absorbing active power acquisition; the load absorbs active power and changes impedance to obtain the preset active power target, and the impedance change causes the load to absorb active power further deviate from the preset active power target, thus forming a positive feedback process in which the load absorbs active power deviation, the load changes impedance, and the load absorbs active power further deviates; The transient voltage instability process on the load side is deduced based on the variable impedance model, and the stable characteristic quantity of the transient voltage instability on the load side is determined to be the equivalent impedance of the load bus, which is specifically: The first-order differential model of variable impedance load is: Where, R _Load is the equivalent load resistance; is the recovery time constant of conductivity; P _L0 is the preset target of active power; P _Load is the active power absorbed by the load; The stable characteristic quantity of transient voltage instability on the load side is determined as the bus equivalent impedance: Where, X _Load is the equivalent load reactance; The mechanism characteristics and stability characteristic quantities are expressed measurably by using bus power and cotangent value of power factor angle to determine the response characteristics of transient voltage instability on the load side; The bus power and the cotangent value of the power factor are used to implement a measurable expression of the mechanism characteristics and the stability characteristic quantity to determine the response characteristics of the transient voltage instability on the load side, specifically: When the variable impedance load loses stability due to the vicious positive feedback process of impedance change and bus power deviation, the equivalent load impedance continues to decrease, resulting in a continuous decrease in the bus power factor angular cotangent value, thereby absorbing more reactive power and causing voltage collapse; the bus power factor angular cotangent value and the equivalent load impedance show a one-to-one correspondence, and the bus power factor angular cotangent value is easier to measure; therefore, the bus power factor angular cotangent value is used to approximately characterize the change in the equivalent load impedance, forming a measurable response characteristic; The response characterization of transient voltage instability on the load side is determined as: In the formula, P is the bus active power; Q is the bus reactive power; is the cotangent value of bus power factor; Add additional criteria to reduce the false positive rate, convert the differential form in the response characteristics into differential form, construct a load transient voltage instability criterion based on power factor positive feedback, and use the constructed load transient voltage instability criterion to determine whether the transient voltage on the load side is unstable. Specifically: Where, _Pk and _Qk are the bus active power and reactive power at the kth moment respectively; Pk _+N and Qk _+N are the bus active power and reactive power at the k+Nth moment respectively; t is the duration of the bus active power drop and the power factor cotangent value drop; _T1 is the judgment duration threshold; is the bus voltage at the k+N+ _T1 moment; _U1 is the voltage safety threshold; For misjudgment scenarios caused by more than two intersections between the actual bus active power and the preset target active power curve, the method of setting a voltage safety threshold value is used to reduce the misjudgment rate; for misjudgment scenarios caused by the contraction of the unstable domain during the dynamic rise of voltage, the method of setting the judgment criterion duration threshold is used to reduce the misjudgment rate; The additional criteria are a voltage safety threshold value and a criterion duration threshold value. 2. A load transient voltage instability judgment system based on power factor positive feedback, characterized in that it includes: The first determination module: a module for deducing the transient voltage instability process on the load side based on the variable impedance model, and determining the mechanism characteristics and stability characteristic quantities of the transient voltage instability on the load side; The load-side transient voltage instability process is deduced based on the variable impedance model to determine the mechanism characteristics of the load-side transient voltage instability, specifically: When the variable impedance load enters the unstable region and becomes unstable, there is a vicious positive feedback feature between the impedance change and the load absorbing active power acquisition; the load absorbs active power and changes impedance to obtain the preset active power target, and the impedance change causes the load to absorb active power further deviate from the preset active power target, thus forming a positive feedback process in which the load absorbs active power deviation, the load changes impedance, and the load absorbs active power further deviates; The transient voltage instability process on the load side is deduced based on the variable impedance model, and the stable characteristic quantity of the transient voltage instability on the load side is determined to be the equivalent impedance of the load bus, which is specifically: The first-order differential model of variable impedance load is: Where, R _Load is the equivalent load resistance; is the recovery time constant of conductivity; P _L0 is the preset target of active power; P _Load is the active power absorbed by the load; The stable characteristic quantity of transient voltage instability on the load side is determined as the bus equivalent impedance: Where, X _Load is the equivalent load reactance; The second determination module: a module for implementing a measurable expression of the mechanism characteristics and stability characteristic quantities by using bus power and cotangent value of power factor angle to determine the response characteristics of transient voltage instability on the load side; The bus power and the cotangent value of the power factor are used to implement a measurable expression of the mechanism characteristics and the stability characteristic quantity to determine the response characteristics of the transient voltage instability on the load side, specifically: When the variable impedance load loses stability due to the vicious positive feedback process of impedance change and bus power deviation, the equivalent load impedance continues to decrease, resulting in a continuous decrease in the bus power factor angular cotangent value, thereby absorbing more reactive power and causing voltage collapse; the bus power factor angular cotangent value and the equivalent load impedance show a one-to-one correspondence, and the bus power factor angular cotangent value is easier to measure; therefore, the bus power factor angular cotangent value is used to approximately characterize the change in the equivalent load impedance, forming a measurable response characteristic; The response characterization of transient voltage instability on the load side is determined as: In the formula, P is the bus active power; Q is the bus reactive power; is the cotangent value of bus power factor; Discrimination module: Add additional criteria to reduce the misjudgment rate, convert the differential form in the response characteristics into differential form, construct a load transient voltage instability criterion based on power factor positive feedback, and use the constructed load transient voltage instability criterion to determine whether the transient voltage on the load side is unstable. Specifically: Where, _Pk and _Qk are the bus active power and reactive power at the kth moment, respectively; Pk _+N and Qk _+N are the bus active power and reactive power at the k+Nth moment, respectively; t is the duration of the bus active power drop and the power factor cotangent value drop; _T1 is the judgment duration threshold; is the bus voltage at the k+N+ _T1 moment; _U1 is the voltage safety threshold; For misjudgment scenarios caused by more than two intersections between the actual bus active power and the preset target active power curve, the method of setting a voltage safety threshold value is used to reduce the misjudgment rate; for misjudgment scenarios caused by the contraction of the unstable domain during the dynamic rise of voltage, the method of setting the judgment criterion duration threshold is used to reduce the misjudgment rate; The additional criteria are a voltage safety threshold value and a criterion duration threshold value. 3. A computer device, characterized in that it includes: a processor, a memory and a bus, the memory stores machine-readable instructions executable by the processor, when the computer device is running, the processor and the memory communicate through the bus, and when the machine-readable instructions are executed by the processor, the load transient voltage instability judgment method based on power factor positive feedback as described in claim 1 is executed. 4. A computer-readable storage medium, characterized in that a computer program is stored on the computer-readable storage medium, and when the computer program is executed by a processor, the load transient voltage instability judgment method based on power factor positive feedback as claimed in claim 1 is executed.