Reactive compensation capacitor configuration method for improving voltage stability of new energy grid-connected system

Abstract

The invention belongs to the field of power system stability analysis, and particularly relates to a reactive compensation capacitor configuration method for improving the voltage stability of a new energy grid-connected system. Most new energy bases are located at the tail end of a grid and present weak grid characteristics. In order to improve the voltage performance of a new energy grid-connected system, the voltage supporting capacity of the grid-connected system is generally improved by installing a reactive compensation capacitor. According to the method, on the basis of a new energy grid-connected model containing the reactive compensation capacitor, the voltage after the reactive compensation capacitor is additionally installed and new system equivalent impedance are obtained through station power voltage equation derivation, a new reference mode can be provided for the installation site of the reactive compensation capacitor by calculating a position-related short-circuit ratio index, and a new energy grid-connected model is provided for the installation site of the reactive compensation capacitor. And the improvement effect on the voltage stability after the reactive compensation capacitor is additionally arranged is evaluated.

Description

Technical Field

[0001] The present invention relates to the field of power system voltage stability, and in particular to a method for configuring reactive power compensation capacitors for improving voltage stability of a new energy grid-connected system. Background Art

[0002] For centralized renewable energy, most of its bases are located at the end of the grid, resulting in a relatively weak grid structure and exhibiting weak grid characteristics. To improve the voltage performance of the renewable energy grid-connected system, reactive power compensation capacitors are usually installed to increase the voltage support capacity of the grid-connected system.

[0003] Using parallel reactive power compensation capacitors can directly and quickly provide the reactive power required by the system and support the AC bus voltage. Currently, this method has been adopted in power systems worldwide. This patent proposes a reactive power compensation capacitor configuration method to improve the voltage stability of renewable energy grid-connected systems. A single-machine infinite system model including reactive power compensation capacitors is established. This model can conveniently solve the voltage, maximum active output, and system equivalent impedance of renewable energy grid-connected power systems after the reactive power compensation capacitors are installed. It also calculates the location-dependent short-circuit ratio and critical short-circuit ratio indicators in renewable energy grid-connected power systems that consider reactive power compensation capacitors. Unlike existing calculation methods for measuring the AC system's ability to accommodate high-voltage direct current transmission systems based on grid-commutated converters, the proposed method is based on a single-machine single-feed model including reactive power compensation capacitors. This method considers the supporting effect of reactive power compensation capacitors on the grid-connected point voltage and their impact on the system equivalent impedance. It can calculate the short-circuit ratio and critical short-circuit ratio indicators applicable to renewable energy grid-connected systems containing reactive power compensation capacitors, thereby characterizing the voltage support strength of renewable energy grid-connected systems. Summary of the Invention

[0004] The purpose of this invention is to provide a method for configuring reactive power compensation capacitors in a new energy grid-connected system. This method establishes a new energy grid-connected model that includes reactive power compensation capacitors. Furthermore, the voltage and power expressions for this new energy grid-connected model, which takes reactive power compensation capacitors into account, are derived, and a method for configuring reactive power compensation capacitors in a new energy grid-connected system is proposed. This method obtains the voltage at the grid-connected point of a new energy grid connected in parallel with reactive power compensation capacitors, introduces the system equivalent impedance of the parallel reactive power compensation capacitors, and incorporates the voltage support provided by the reactive power compensation capacitors into the calculation of the short-circuit ratio. Simulation examples verify the effectiveness and practicality of the proposed method.

[0005] The technical solutions for implementing the present invention are as follows:

[0006] A method for improving reactive power compensation capacitor configuration in a new energy grid-connected system, characterized by comprising the following steps:

[0007] Step 1: Establish a single-machine single-feed model including reactive compensation capacitors;

[0008] Step 2: Based on the established mathematical model and Kirchhoff's current law, derive the station power-voltage equation, solve the voltage and power expressions, and connect the susceptance of the reactive compensation capacitor in parallel with the system impedance to obtain the system equivalent impedance;

[0009] Step 3: Build a simulation model for the new energy base. Calculate the short-circuit ratio of the new energy station when reactive compensation capacitors are not put into use based on the operating voltage of the new energy grid connection point, the system equivalent impedance, and the actual active output.

[0010] Step 4: Based on the short-circuit ratio index required by the high-proportion new energy power system, the lowest point of the short-circuit ratio index is used as the installation location for the reactive power compensation capacitor, and the effect of installing the reactive power compensation capacitor on the short-circuit ratio index is evaluated. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0012] Figure 1 A flowchart provided for an embodiment of the present invention;

[0013] Figure 2 A single-machine infinite system model considering reactive compensation capacitance provided in an embodiment of the present invention;

[0014] Figure 3 A new energy base simulation model provided by an embodiment of the present invention;

[0015] Figure 4 The short-circuit ratio simulation results before and after the configuration of the reactive compensation capacitor provided in the embodiment of the present invention are shown. DETAILED DESCRIPTION

[0016] The following is a clear and complete description of the technical solutions in the embodiments of the present invention, in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0017] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. The specific analysis process is as follows:

[0018] Figure 1 The flow chart of the present invention comprises the following steps:

[0019] Step 1: Establish a single-machine infinite system model including reactive compensation capacitors;

[0020] For centralized renewable energy, most of its renewable energy bases are located at the end of the grid, and the grid structure is relatively weak, showing weak grid characteristics. In order to improve the voltage performance of the renewable energy grid-connected system, reactive power compensation capacitors are usually installed to improve the voltage support capacity of the grid-connected system. A single-machine infinite system model including reactive power compensation capacitors is established, including the AC large system, the renewable energy single-machine model, and the reactive power compensation capacitors at the renewable energy outlet. The simplified model is as follows: Figure 3 shown.

[0021] Step 2: Based on the established mathematical model and Kirchhoff's current law:

[0022]

[0023] In the formula is the current transmitted on the line, is the current passing through the reactive compensation capacitor.

[0024] Further get the power voltage equation

[0025] (1-2BX+B 2 Z 2 )U '4 -U '2 [E 2 +2(PR+QX-QBZ 2 )]+(P 2 +Q 2 )Z 2 =0 (2) According to the above station power voltage equation, the following voltage expression is solved:

[0026]

[0027] Let the discriminant of the quadratic equation be equal to zero and solve to obtain the maximum transmission power P max for:

[0028]

[0029] At this time, the critical voltage Uc is

[0030]

[0031] The system equivalent impedance of the parallel reactive capacitor is obtained by connecting the susceptance of the reactive compensation capacitor in parallel with the system Thevenin equivalent impedance:

[0032]

[0033] Step 3: In the steady-state operation of a high-proportion renewable energy power system, the short-circuit ratio and critical short-circuit ratio related to the station location are important indicators of voltage stability. The short-circuit ratio level before the reactive compensation capacitor is put into use is calculated according to the following formula:

[0034]

[0035] In the formula It is the operating voltage of the new energy grid. is the system's equivalent Thevenin impedance, P RE Make actual active contributions to new energy stations.

[0036] As the output of renewable energy stations continues to increase, the system's operating point transitions from the upper half of the PV curve to the lower half. At the nose point, the system reaches a critical stable state and the static voltage stability limit of the system. The critical short-circuit ratio can be calculated based on the maximum active output of renewable energy and the corresponding critical voltage at this time:

[0037]

[0038] Step 4. Use the lowest point of the short-circuit ratio index as the installation location for the reactive compensation capacitor. Substitute the voltage after the reactive compensation capacitor is installed in step 2, the new system equivalent impedance, and the actual active output of the new energy station into the short-circuit ratio calculation related to the station location to evaluate the improvement effect of installing the reactive compensation capacitor on the short-circuit ratio index.

[0039] Application Examples

[0040] Taking a 10-machine 39-node system as an example, the method of the present invention is demonstrated:

[0041] The position-related short-circuit ratio indicators of the system's new energy nodes before and after reactive power compensation are shown in the following table:

[0042] Table 1 Short-circuit ratio indicators of each new energy node position before and after reactive power compensation

[0043] node Pre-compensation indicators Post-compensation indicators 33 1.696 1.786 34 2.249 2.306 35 1.416 1.526 36 2.187 2.254 38 2.051 2.118

[0044] In this example, the new energy stations are 33, 34, 35, 36, and 38. When reactive compensation capacitors are installed at each grid-connected node, the relevant short-circuit ratios before and after compensation are obtained by calculation, and the effect of installing reactive compensation capacitors on improving the short-circuit ratio index is evaluated.

[0045] Figure 4 This is the short-circuit ratio indicator simulation result provided by the embodiment of the present invention.

[0046] It should be noted that the contents not described in detail in the embodiments of the present invention belong to the prior art known to those skilled in the art.

[0047] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for configuring reactive power compensation capacitors to improve voltage stability of new energy grid-connected systems. Its characteristics include the following steps: Step 1: Establish a single-machine infinite system model including reactive compensation capacitors; Step 2: Based on the established mathematical model and Kirchhoff's current law, derive the station power-voltage equation, solve the voltage and power expressions, and connect the susceptance of the reactive compensation capacitor in parallel with the system impedance to obtain the equivalent system impedance; Step 3: Build a simulation model for the new energy base. Based on the operating voltage of the new energy grid connection point, the system equivalent impedance, and the actual active power output, calculate the location-related short-circuit ratio level of the new energy station when the reactive compensation capacitor is not put into use. Step 4: Based on the short-circuit ratio index required by the high-proportion new energy power system, the lowest point of the short-circuit ratio index is used as the installation location for reactive power compensation capacitors, and the effect of adding reactive power compensation capacitors on the short-circuit ratio index is evaluated.

2. A method for configuring reactive power compensation capacitors to improve voltage stability in a high-proportion renewable energy power system according to claim 1, characterized in that: In the step 1, a single-machine infinite system model including a reactive compensation capacitor is established, including an AC large system, a new energy single-machine model, and a reactive compensation capacitor at the new energy outlet.

3. A reactive power compensation capacitor configuration method for improving voltage stability of a high-proportion renewable energy power system according to claim 1, characterized in that: In step 2, first, according to Kirchhoff's current law: In the formula is the current transmitted on the line, is the current passing through the reactive compensation capacitor. According to the above station power voltage equation, the following voltage expression is solved: The equivalent impedance of the system incorporating the reactive capacitor is obtained by connecting the susceptance of the reactive compensation capacitor in parallel with the system Thevenin equivalent impedance:

4. A method for configuring reactive power compensation capacitors to improve voltage stability in a high-proportion renewable energy power system according to claim 1, characterized in that: In step 3, in the steady-state operation of a high-proportion new energy power system, the short-circuit ratio and critical short-circuit ratio related to the station location are important indicators of voltage stability. The short-circuit ratio level before the reactive compensation capacitor is put into use is obtained according to the following calculation formula: In the formula It is the operating voltage of the new energy grid. is the system's equivalent Thevenin impedance, P RE Make actual active contributions to new energy stations.

5. A reactive power compensation capacitor configuration method for improving voltage stability of a high-proportion renewable energy power system according to claim 1, characterized in that: In step 4, based on the short-circuit ratio index required by the high-proportion new energy power system, the lowest point of the short-circuit ratio index is used as the installation location of the reactive compensation capacitor. The voltage after the reactive compensation capacitor is installed in step 2, the new system equivalent impedance and the actual active output of the new energy station are substituted into the short-circuit ratio calculation related to the station location to evaluate the improvement effect of the short-circuit ratio index after the installation of the reactive compensation capacitor.

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