An analytical evaluation method for static voltage stability margin of a new energy multi-station transmission system

Abstract

The present invention discloses an analytical evaluation method for the static voltage stability margin of a new energy multi-station transmission system, which includes: obtaining the structure and parameters of the new energy multi-station transmission system, including line impedance and the power factor of new energy stations, splitting the structure of the original system, and transforming it into multiple simplified single-point transmission systems; obtaining the static stability power constraint conditions of each simplified single-point transmission system, which are the static stability power constraint conditions of the entire new energy multi-station transmission system; taking the equal sign for each power constraint condition simultaneously, solving the equations to obtain the power distribution of new energy stations in the limit state, and summing to obtain the power limit of the entire transmission system; combining the power of stations in the current state, calculating the power margin index, and evaluating the static voltage stability margin of the new energy multi-station transmission system. The present invention can quickly and accurately calculate the power limit of the entire transmission system, providing a very important decision-making basis for the safe and stable operation of the power grid.

Description

Technical Field

[0001] The present invention belongs to the field of power systems, and particularly relates to an analytical evaluation method for the static voltage stability margin of a new energy multi-station transmission system. Background Art

[0002] With the high-proportion grid connection of new energy and the large-scale application of power electronic devices, the complexity of the power system has been increasing day by day, and the probability of voltage instability has also increased significantly. To ensure the safe and stable operation of the power system, it is usually necessary to evaluate the static voltage stability margin of the system to facilitate decision-making by dispatchers. For example Figure 1 As shown in the figure of the new energy multi-station transmission system, existing methods generally evaluate the stability margin by estimating or calculating the static voltage stability limit of new energy stations and combining the limit value with the current operating state. However, the rapid growth in the number of new energy stations and the ever-changing operating state of the power system make the computational workload of monitoring each station one by one extremely large, and it is difficult to apply in practice. Summary of the Invention

[0003] In view of this, the present invention proposes an analytical evaluation method for the static voltage stability margin of a new energy multi-station transmission system, which solves the problem that existing evaluation methods are difficult to quickly and accurately calculate the power limit of the entire transmission system.

[0004] The technical solution adopted by the present invention is specifically as follows: An analytical evaluation method for the static voltage stability margin of a new energy multi-station transmission system, the steps are as follows:

[0005] Step 1: Obtain the structure and parameters of the new energy multi-station transmission system, including line impedance and the power factor of new energy stations, split the structure of the original system, and transform it into multiple simplified single-point transmission systems;

[0006] Step 2: Obtain the static stability power constraint conditions of each simplified single-point transmission system, which are the static stability power constraint conditions of the entire new energy multi-station transmission system;

[0007] Step 3: Simultaneously set each power constraint condition to an equal sign, solve the system of equations, obtain the power distribution of new energy stations in the limit state, and sum to obtain the power limit of the entire transmission system;

[0008] Step 4: Combine the power of stations in the current state, calculate the power margin index, and evaluate the static voltage stability margin of the new energy multi-station transmission system.

[0009] Further, Step 1 described above is specifically as follows: The new energy multi-station transmission system is radial. After several new energy stations are converged at the busbar, they are sent to the receiving system through a long-distance transmission line. Suppose there are n new energy stations in a certain transmission system. The active power and reactive power of the new energy station n are P n and Q n ; the total resistance and reactance of the line and transformer from it to the busbar are R n and X n ; the busbar is sent to the receiving system through a long-distance transmission line. The resistance and reactance of the transmission line are R m and X m ; the receiving system is regarded as an infinite bus, and its voltage is 1 p.u. The busbar is split step by step to decouple the system into n single-point transmission systems;

[0010] Taking j as the imaginary unit, the power of the station n is expressed as P n +jQ n ; the total impedance of the line, transformer and other components from the station n to the busbar is R n +jX n ; the impedance of the transmission line is R m +jX m ;

[0011] Keeping the voltage between the busbar and the infinite bus unchanged, split the impedance R m +jX m . According to the parallel impedance, the following formula is obtained:

[0012]

[0013] In the formula, R 1m +jX 1m , R 2m +jX 2m , …, R nm +jX nm are the n impedances after splitting;

[0014] Ensure that the power flowing through each split impedance is distributed according to P 1 ~P n . Since the voltages at both ends are the same, the power flowing through is inversely proportional to the split reactance, and the proportionality coefficients of each split branch are the same. The following formula is obtained:

[0015] P 1 X 1m =P 2 X 1m =ΛP n X nm =U 0 U m sinθ (2)

[0016] Where U 0 is the voltage amplitude of the busbar; U m is the voltage amplitude of the infinite grid; θ is the phase angle difference between the busbar and the infinite grid voltage;

[0017] Assume that the impedance ratio of each line is the same, that is, R n =μX n , μ is the ratio constant, and the split impedance R of the nth single-point system is obtained by combining equations (1) and (2): nm +jX nm The expression is as follows:

[0018]

[0019] Further, the method of step 2 as described above is as follows: based on the power flow equation of the decoupled single-point transmission system, the power limit is calculated, and the critical transmission power P of the decoupled system is cr It is expressed as follows:

[0020]

[0021] In the formula, Q is the reactive power delivered by the new energy station; R and X are the resistance and reactance values ​​of the decoupled system respectively; Z is the impedance modulus of the decoupled system; E is the voltage amplitude of the infinite power grid;

[0022] When the output power of the new energy station P≤P cr When , the system is stable; in the actual system, the new energy station is controlled by constant power factor, so Q = λP, λ is the ratio constant, and combined with R = μX, E = 1, equation (4) is further derived to obtain the following equation:

[0023]

[0024] The analytical expressions of critical transmission power, power factor of new energy station and line impedance are obtained by sorting out equation (5):

[0025]

[0026] In actual systems, the new energy station to the receiving system will go through multiple convergence processes. At this time, the decoupling and splitting are carried out step by step according to the method in step 1 to simplify the system into a single-point delivery system.

[0027] Furthermore, the power constraint formula of the entire system in step 3 as described above is as follows:

[0028]

[0029] Where, X jeqis the final equivalent reactance of the system obtained after decoupling the j-th new energy power station; P j is the transmission power of the j-th power station;

[0030] Equation (7) describes an n-dimensional inequality group. Let these n inequalities hold simultaneously, and solve the equations to obtain the critical transmission power P of each new energy power station 1cr , P 2cr , … P ncr . Further, sum the critical powers of these n power stations to obtain the critical transmission power P of the entire transmission system lim , which is the power limit of the entire transmission system.

[0031] Furthermore, the specific steps of step 4 are as follows: The power station powers of the new energy multi-power station transmission system under a certain operating state are P 1 , P 2 , … P n , then the expression of the static voltage stability margin K of the entire transmission system is as follows:

[0032]

[0033] Furthermore, the object of the present invention is realized by an analytical evaluation system for the static voltage stability margin of a new energy multi-power station transmission system, including: a memory, a processor, and a computer program stored on the memory and executable on the processor. When the computer program is executed by the processor, it realizes the above-mentioned analytical evaluation method for the static voltage stability margin of a new energy multi-power station transmission system.

[0034] Furthermore, the object of the present invention is realized by a computer-readable storage medium. An implementation program for information transmission is stored on the computer-readable storage medium. When the program is executed by a processor, it realizes the steps of the above-mentioned analytical evaluation method for the static voltage stability margin of a new energy multi-power station transmission system.

[0035] The present invention has the following advantages and beneficial effects: The present invention can establish analytical power constraint conditions according to the specific parameters of the new energy multi-power station transmission system, and can provide a method for quickly evaluating the static voltage stability margin; The present invention uses the power margin index as a measure of the static voltage stability margin of the new energy multi-power station transmission system, and can quickly and accurately calculate the power limit of the entire transmission system, providing a very important decision-making basis for the safe and stable operation of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a diagram of a new energy multi-power station transmission system;

[0037] Figure 2 is a flowchart of the evaluation method of the present invention;

[0038] Figure 3 It is a two - level system diagram;

[0039] Figure 4 It is an impedance splitting diagram;

[0040] Figure 5 It is a topological decoupling diagram;

[0041] Figure 6 It is a schematic diagram of a radial multi - substation power transmission system;

[0042] Figure 7 It is a general structure diagram of a radial multi - substation power transmission system;

[0043] Figure 8 It is a new - energy single - point power transmission system diagram;

[0044] Figure 9 It is a typical radial structure diagram of a new - energy multi - substation power transmission system;

[0045] Figure 10 It is the first splitting diagram;

[0046] Figure 11 It is a complete splitting diagram. Specific implementation manner

[0047] The present invention will be further described below with reference to the accompanying drawings and examples:

[0048] Example 1

[0049] As Figure 2 shown, an analytical evaluation method for the static voltage stability margin of a new - energy multi - substation power transmission system is as follows:

[0050] Step 1: Taking the system shown in Figure 3 as an example, split the topology.

[0051] Keeping the voltage between the bus - bar and the infinite - bus unchanged, split the impedance R m +jX m as shown in Figure 4 According to the parallel impedance, the following formula can be obtained:

[0052]

[0053] In the formula, R 1m +jX 1m , R 2m +jX 2m , …, R nm +jX nm are the n split impedances;

[0054] Ensure that the power flowing through each split impedance is distributed according to P 1 ~P n Since the voltages at both ends are the same, the power flowing through is inversely proportional to the split reactance, and the proportionality coefficients of each split branch are the same. The following formula is obtained:

[0055] P 1 X 1m =P 2 X 1m =ΛP n X nm =U 0 U m sinθ (2)

[0056] In the formula, U 0 is the voltage amplitude of the busbar; U m is the voltage amplitude of the infinite power grid; θ is the phase angle difference between the busbar voltage and the infinite power grid voltage;

[0057] Assume that the impedance ratios of each line are the same, that is, R n =μX n , where μ is a ratio constant. By combining formulas (1) and (2), the expression of the split impedance R nm +jX nm of the nth single-point system is obtained as follows:

[0058]

[0059] After the splitting process of step 1, the system shown in Figure 3 can be split into the n single-point sending-out systems shown in Figure 5 , realizing the decoupling of the topology.

[0060] The typical structure of an actual new energy multi-station sending-out system is radial. Generally, it goes through multiple levels of boosting and busbar connection processes and finally converges into the main grid at the same point, as shown in Figure 6 . In the figure, the black represents the new energy station nodes, which are also the starting nodes of power. The orange represents the busbar nodes, where the power inflow and outflow are the same. The red represents the main grid grid-connection nodes. For a general radial system as shown in Figure 7 , the impedances can be repeatedly split step by step according to formulas (1) to (3), and finally the system is transformed into the form of several single-point sending-out systems.

[0061] Step 2: As shown in Figure 8 , it is the general form of a single-point sending-out system. Based on this, calculate the power limit of each single-point sending-out system.

[0062] According to the power flow equation, the expression of the power limit of the new energy station is as follows:

[0063]

[0064] Wherein, Q is the reactive power output from the new energy power station; R and X are respectively the resistance and reactance values of the decoupled system; Z is the impedance modulus of the decoupled system; E is the voltage amplitude of the infinite power grid;

[0065] When the output power P of the new energy power station ≤ P cr , the system is stable; in the actual system, the new energy power station adopts constant power factor control. Therefore, let Q = λP, where λ is a ratio constant. Combining with R = μX and E = 1, the following formula can be further derived from formula (4):

[0066]

[0067] By arranging formula (5), an analytical expression for the critical transmission power in relation to the power factor of the new energy power station and the line impedance can be obtained:

[0068]

[0069] Step 3: Combining the critical transmission powers of the n single-point output systems obtained in Step 2, the power constraint condition formula for the entire system can be obtained as follows:

[0070]

[0071] Wherein, X jeq is the final equivalent reactance of the system obtained after decoupling the jth new energy power station; P j is the output power of the jth power station;

[0072] Formula (7) describes an n-dimensional inequality group. Let these n inequalities hold simultaneously and solve the equations to obtain the critical transmission powers P 1cr , P 2cr , … P ncr of each new energy power station. Further, sum up the critical powers of these n power stations to obtain the critical transmission power P lim of the entire output system, which is the power limit of the entire output system.

[0073] Step 4: Assume that the power station powers of the new energy multi-power station output system under a certain operating state are P 1 , P 2 , … P n , respectively. Then, the expression for the static voltage stability margin K of the entire output system is as follows:

[0074]

[0075] Example 2

[0076] Adopt Figure 9The system shown is used to illustrate the present invention. In the figure, the impedance ratios of each line are the same, all being 0.25, the power factors of each new energy power station are the same, all being 0.95, the active power is 100 MW, the voltage amplitude of the infinite power grid is 1, and the reactance parameters in the figure are shown in Table 1 (per-unit value, the base power is 100 MVA).

[0077] Table 1 Reactance Parameters

[0078]

[0079] In step 1, first, the impedance R 7 +jX 7 is split. Since there are two impedances R 5 +jX 5 , R 6 +jX 6 connected to bus 1, then R 7 +jX 7 should be split into two parts, namely R 71 +jX 71 , R 72 +jX 72 , as shown in Figure 10 .

[0080] Ensure that the impedance remains unchanged before and after splitting. According to the parallel impedance calculation formula

[0081]

[0082] Ensure that the power is still distributed according to P 5 , P 6 . From the power transmission in the power system, it can be known that

[0083]

[0084] By solving the equations simultaneously

[0085]

[0086] The obtained impedances are respectively combined with R 5 +jX 5 , R 6 +jX 6 . According to the same process as above for splitting, the system shown in Figure 9 can be finally split into the form shown in Figure 11 . In the figure, each impedance satisfies formula (11):

[0087]

[0088] In step 2, based on the four simplified systems after splitting, substituting equation (11) into equation (6), the static stability power constraint condition of the original system can be obtained as shown in equation (12).

[0089]

[0090] In step 3, let each inequality take the equal sign simultaneously to obtain a 4 - variable linear equation system. Solving it can get the corresponding power distribution modes of each substation under the power limit state. Substituting the data in Table 1 for solution, we can get

[0091]

[0092] The base power is 100 MVA. Therefore, the power limit P cr = 564.99 MW.

[0093] In step 4, the power of each substation is 100 MW. Substituting it into equation (7), the static voltage stability margin of the system can be obtained as shown in Table 2.

[0094] Table 2 Static voltage stability margin of the system

[0095]

[0096] It can be seen from Table 2 that the connection points of each new - energy substation meet the grid - connection requirements. Among them, the stability margin at substation 4 is the largest, and there is still room for power increase. The stability margin at substation 2 is the smallest, and close monitoring should be paid attention to during operation.

Claims

1. An analytical evaluation method for static voltage stability margin of a new energy multi-station transmission system, characterized in that: Here are the steps: Step 1: Obtain the structure and parameters of the new energy multi-station transmission system, including line impedance and new energy station power factor, split the structure of the original system, and convert it into multiple simplified single-point transmission systems; Among them, the new energy multi-station transmission system is radial, and several new energy stations converge at the busbar and then send them to the receiving system through long-distance transmission lines. Suppose there are n new energy stations in a certain transmission system, and the active power and reactive power of the new energy station n are P respectively. n and Q n The total resistance and reactance of the line and transformer to the busbar are R n and X n ; The busbar is sent to the receiving system through a long-distance transmission line. The resistance and reactance of the transmission line are R m and X m The receiving end system is an infinite node with a voltage of 1p.u. The busbar is split step by step to decouple the system into n single-point sending systems. Taking j as the imaginary unit, the power of station n is expressed as P n +jQ n The total impedance of the line and transformer from station n to the busbar is R n +jX n ; The impedance of the transmission line is R m +jX m ; Keep the voltage between the busbar and the infinite node constant and change the impedance R m +jX m After splitting, the following formula is obtained based on the parallel impedance: In the formula, R 1m +jX 1m ,R 2m +jX 2m ,…,R nm +jX nm is the n impedances after splitting; Ensure that the power flowing through each split impedance is P1~P n Distribution, since the voltages at both ends are the same, the power flowing is inversely proportional to the split reactance, and the proportional coefficients of each split branch are the same, resulting in the following formula: P1X 1m =P2X 1m =ΛP n X nm =U0U m sinθ (2) Where U0 is the voltage amplitude of the busbar; U m is the voltage amplitude of the infinite grid; θ is the phase angle difference between the busbar and the infinite grid voltage; Assume that the impedance ratio of each line is the same, that is, R n =μX n , μ is the ratio constant, and the split impedance R of the nth single-point system is obtained by combining equations (1) and (2): nm +jX nm The expression is as follows: Step 2: Obtain the static stable power constraint conditions of each simplified single-point transmission system, that is, the static stable power constraint conditions of the entire new energy multi-station transmission system; Step 3: Take all power constraints as equal at the same time and solve the equation group to obtain the power distribution of the new energy station under the limit state. The sum is the power limit of the entire transmission system. Step 4: Calculate the power margin index based on the current station power and evaluate the static voltage stability margin of the new energy multi-station transmission system.

2. According to claim 1, a method for analyzing and evaluating the static voltage stability margin of a new energy multi-station transmission system is characterized in that: Step 2 is as follows: Calculate the power limit of the decoupled single-point transmission system based on the power flow equation. The critical transmission power P of the decoupled system is cr It is expressed as follows: In the formula, Q is the reactive power delivered by the new energy station; R and X are the resistance and reactance values ​​of the decoupled system respectively; Z is the impedance modulus of the decoupled system; E is the voltage amplitude of the infinite power grid; When the output power of the new energy station P≤P cr When , the system is stable; in the actual system, the new energy station is controlled by constant power factor, so Q = λP, λ is the ratio constant, and combined with R = μX, E = 1, equation (4) is further derived to obtain the following equation: The analytical expressions of critical transmission power, power factor of new energy station and line impedance are obtained by sorting out equation (5): In actual systems, the new energy station to the receiving system will go through multiple convergence processes. At this time, the decoupling and splitting are carried out step by step according to the method in step 1 to simplify the system into a single-point delivery system.

3. According to claim 2, a method for analyzing and evaluating the static voltage stability margin of a new energy multi-station transmission system is characterized in that: The power constraint formula of the entire system in step 3 is as follows: Where, X jeq is the final equivalent reactance of the system after decoupling the jth renewable energy station; P j is the transmission power of the jth station; Formula (7) describes an n-dimensional inequality group. Let these n inequalities be equal at the same time, and solve the equation group to obtain the critical transmission power P of each new energy station. 1cr ,P 2cr ,…P ncr , further, the critical power of these n stations is summed to obtain the critical transmission power P of the entire transmission system lim , which is the power limit of the entire transmission system.

4. According to claim 3, a method for analyzing and evaluating the static voltage stability margin of a new energy multi-station transmission system is characterized in that: Step 4 is as follows: Under a certain operating state, the station powers of the new energy multi-station transmission system are P1, P2, ... P n , then the expression of the static voltage stability margin K of the entire transmission system is as follows:

5. An analytical evaluation system for static voltage stability margin of a new energy multi-station transmission system, comprising: A memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: when the computer program is executed by the processor, an analytical evaluation method for the static voltage stability margin of a new energy multi-station transmission system as described in any one of claims 1 to 4 is implemented.

6. A computer-readable storage medium having stored thereon a program for implementing information transmission, characterized in that: When the program is executed by a processor, the steps of an analytical evaluation method for a static voltage stability margin of a new energy multi-station transmission system as described in any one of claims 1 to 4 are implemented.

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