Weak power grid voltage source modeling method suitable for online simulation

Abstract

The invention discloses a weak power grid voltage source modeling method suitable for online simulation. The method comprises the following steps: determining a shortest connecting line between a new energy power generation grid-connected converter and a superior substation and a shortest connecting line between the new energy power generation grid-connected converters; determining a common connection point based on the determined shortest connection line, calculating the line impedance of the common connection point, and calculating the output power and the coupling power of each new energy power generation grid-connected converter based on the line impedance of the common connection point; based on the output power and the coupling power of each grid-connected converter for new energy power generation, calculating the decoupling power of the corresponding grid-connected converter for new energy power generation; calculating the access capacity of the common connection point based on the decoupling power; calculating the voltage of a weak power grid voltage source based on the access capacity of the common connection point and the short-circuit ratio of the new energy station; and based on the swing equation of the synchronous generator, calculating the frequency of the voltage of the weak power grid voltage source, and completing weak power grid voltage source modeling suitable for online simulation.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy access to the distribution network, and particularly relates to a weak grid voltage source modeling method suitable for online simulation. Background Art

[0002] With the large-scale access of renewable energy and the rapid development of distributed generation, the traditional power system is transforming towards a more flexible, decentralized and intelligent direction, forming a so-called new power system. During this transformation process, the structure and operation mode of the power grid have changed significantly. The traditional strong grid mainly relies on large-scale centralized power generation and strong system inertia to ensure stability, while in the new power system, due to the increase in the proportion of new energy access, problems such as frequent power grid load fluctuations, unstable power generation, and insufficient system inertia often occur. These factors make the power grid more vulnerable to external disturbances, which may in turn cause phenomena such as voltage and frequency fluctuations, forming a so-called "weak grid" state. Summary of the Invention

[0003] To solve the above technical problems, the present invention proposes a weak grid voltage source modeling method suitable for online simulation, which can significantly reduce the number of nodes occupied by the modeling of new energy power generation access to a complex power grid.

[0004] To achieve the above object, the present invention provides a weak grid voltage source modeling method suitable for online simulation, including:

[0005] Determine the shortest connection line between the grid-connected converter of new energy power generation and the superior substation, and the shortest connection line between the grid-connected converters of new energy power generation;

[0006] Based on the determined shortest connection line, determine a common connection point, calculate the line impedance of the common connection point, and calculate the output power and coupling power of each grid-connected converter of new energy power generation based on the line impedance of the common connection point;

[0007] Based on the output power and coupling power of each grid-connected converter of new energy power generation, calculate the decoupling power for the corresponding grid-connected converter of new energy power generation;

[0008] Based on the decoupling power, calculate the access capacity of the common connection point; based on the access capacity of the common connection point and the short-circuit ratio of the new energy power station, calculate the weak grid voltage source voltage;

[0009] Based on the swing equation of the synchronous generator, calculate the frequency of the weak grid voltage source voltage, and complete the weak grid voltage source modeling suitable for online simulation.

[0010] Optionally, calculating the line impedance of the common connection point includes:

[0011]

[0012] where k n is the total number of power nodes between the converter numbered n and the common connection point; is the line impedance corresponding to the i-th node counted from the common connection point side; is the line impedance from the converter to the common connection point.

[0013] Optionally, calculating the output power of each grid-connected converter for new energy power generation based on the line impedance of the common connection point includes:

[0014]

[0015] where P nn , Q nn , E n and δ n are respectively the active power, reactive power, maximum voltage and power angle input by the converter numbered n to the power grid; E p is the maximum voltage of the common connection point; arg[·], Re[·] and Im[·] are respectively the argument, real part and imaginary part of a complex number; |·| is the absolute value of a real number or the modulus of a complex number; is the line impedance from the converter to the common connection point.

[0016] Optionally, calculating the coupling power of each grid-connected converter for new energy power generation based on the line impedance of the common connection point includes:

[0017]

[0018] where P xy , Q xy are respectively the active power and reactive power coupled by the converter numbered x to the converter numbered y; E x and δ x are respectively the maximum voltage and power angle input by the converter numbered x to the power grid; E y and δ y are respectively the maximum voltage and power angle input by the converter numbered y to the power grid.

[0019] Optionally, calculating the decoupling power for the corresponding grid-connected converters for new energy power generation includes:

[0020] P id = diag[P t ·(2J - I)];

[0021] Q id = diag[Q t ·(2J - I)];

[0022] Among them, P id and Q id are respectively the active power column vector and the reactive power column vector actually injected by the converter into the point of common coupling; P t and Q t are respectively the active power matrix and the reactive power matrix of the parallel converters; J is the identity matrix, with the dimension consistent with the total number of parallel converters; I is the all-ones matrix, with the dimension consistent with the total number of parallel converters; diag[·] takes the main diagonal elements of the matrix in the form of a column vector.

[0023] Optionally, calculating the access capacity of the point of common coupling based on the decoupled power includes:

[0024]

[0025] Among them, S p is the access capacity of the point of common coupling; P id and Q id are respectively the active power column vector and the reactive power column vector actually injected by the converter into the point of common coupling.

[0026] Optionally, calculating the voltage of the weak grid voltage source based on the access capacity of the point of common coupling and the short-circuit ratio of the new energy power station includes:

[0027]

[0028] Among them, is the voltage on the weak grid side; S p is the access capacity of the point of common coupling; R scr is the short-circuit ratio of the new energy power station; E n is the maximum voltage of the nth converter; is the line impedance from the nth converter to the PPC.

[0029] Optionally, calculating the frequency of the weak grid voltage source based on the swing equation of the synchronous generator includes:

[0030]

[0031] Among them, ω g is the weak grid voltage source frequency; J g and D g are respectively the inertia coefficient and the damping coefficient of the synchronous generator; ω ref is the grid frequency reference value; ΔG is the grid noise.

[0032] Technical effects of the present invention: The present invention discloses a weak grid voltage source modeling method suitable for online simulation, which integrates a multi-node distribution network model into a single-node or small-number-of-node distribution network model, and can significantly reduce the number of nodes occupied by modeling the access of new energy power generation to a complex power grid. Brief Description of the Drawings

[0033] The drawings constituting a part of this application are used to provide a further understanding of this application. The schematic embodiments of this application and their descriptions are used to explain this application and do not constitute an improper limitation of this application. In the drawings:

[0034] Figure 1 It is a schematic flowchart of a weak grid voltage source modeling method suitable for online simulation according to an embodiment of the present invention;

[0035] Figure 2 It is a schematic diagram of weak grid voltage source modeling according to an embodiment of the present invention. Detailed Embodiments

[0036] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The following will refer to the drawings and combine the embodiments to detail this application.

[0037] It should be noted that the steps shown in the flowchart of the drawings can be executed in a computer system such as a set of computer-executable instructions, and although the logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in a different order than here.

[0038] In the power system, grid nodes with a short-circuit ratio less than 3 are usually referred to as weak grids. In the experimental verification stage of developing a new power system, the state of a weak grid can be approximately simulated by building an IEEE standard multi-node distribution network scenario, but currently most experiments are usually completed through offline simulation. However, in response to this problem, the present invention proposes a weak grid voltage source modeling method suitable for online simulation, which can not only accurately simulate the state of a weak grid, but also achieve real-time monitoring and analysis, providing a new technical means for the research of dynamic control technologies of new power systems and the evaluation of weak grid characteristics.

[0039] As Figure 1 - Figure 2 shown, this embodiment provides a weak grid voltage source modeling method suitable for online simulation, including:

[0040] Determine the shortest connection line between the grid-connected converter of new energy power generation and the superior substation and the shortest connection line between the grid-connected converters of new energy power generation;

[0041] Based on the determined shortest connection line, determine a common connection point, calculate the line impedance of the common connection point, and calculate the output power and coupling power of the grid-connected converter for each new energy power generation based on the line impedance of the common connection point;

[0042] Based on the output power and coupling power of the grid-connected converter for each new energy power generation, calculate the decoupling power for the corresponding grid-connected converter of the new energy power generation;

[0043] Based on the decoupling power, calculate the access capacity of the common connection point; based on the access capacity of the common connection point and the short-circuit ratio of the new energy power station, calculate the voltage of the weak grid voltage source;

[0044] Based on the swing equation of the synchronous generator, calculate the frequency of the weak grid voltage source voltage to complete the modeling of the weak grid voltage source applicable to online simulation.

[0045] Further, calculating the line impedance of the common connection point includes:

[0046]

[0047] where k n is the total number of power nodes between the converter numbered n and the common connection point; is the line impedance corresponding to the i-th node counted from the common connection point side; is the line impedance from the converter to the common connection point.

[0048] Specifically, based on the new power system topology model and related parameters accessed by the new energy power generation, determine the shortest connection line between the grid-connected converter (REC) of the new energy power generation and the upper-level substation (or power plant). If there are multiple groups of new energy power stations in the distribution network, it is necessary to determine the shortest connection line between the grid-connected converters of each new energy power generation.

[0049] Based on the determined shortest connection line, determine a common connection point (PCC) for all grid-connected converters of the new energy power generation. If two or more grid-connected converters of the new energy power generation are connected to the same node, they are regarded as a group of parallel converters. Assuming that all new energy power stations adopt the grid-forming grid-connected control method, then the physical model of the grid-connected converter of the new energy power generation can be equivalent to a controlled voltage source.

[0050] Further, calculating the output power of the grid-connected converter for each new energy power generation based on the line impedance of the common connection point includes:

[0051]

[0052] where P nn 、Q nn 、E n and δn are the active power, reactive power, maximum voltage, and power angle input from the converter numbered n to the power grid; E p is the maximum voltage at the point of common coupling; arg[·], Re[·], and Im[·] are the argument, real part, and imaginary part of a complex number respectively; |·| is the absolute value of a real number or the modulus of a complex number; is the line impedance from the converter to the point of common coupling.

[0053] Furthermore, calculating the coupling power of each grid-connected converter for new energy power generation based on the line impedance at the point of common coupling includes:

[0054]

[0055] where P xy , Q xy are the active power and reactive power coupled from the converter numbered x to the converter numbered y respectively; E x and δ x are the maximum voltage and power angle input from the converter numbered x to the power grid respectively; E y and δ y are the maximum voltage and power angle input from the converter numbered y to the power grid respectively.

[0056] Furthermore, based on the access power expression of the converter, it is extended to t groups of parallel converters. The actual output power is defined in matrix form:

[0057]

[0058] In the formula, P t and Q t are the active power matrix and reactive power matrix of the parallel converters respectively.

[0059] Calculating the decoupling power for the corresponding grid-connected converters for new energy power generation includes:

[0060] P id = diag[P t ·(2J - I)];

[0061] Q id = diag[Q t ·(2J - I)];

[0062] where P id and Q id are the column vectors of the active power and reactive power actually injected by the converter into the point of common coupling respectively; P t and Q tThey are the active power matrix and reactive power matrix of the parallel converters respectively; J is the identity matrix with the same dimension as the total number of parallel converters; I is the all-ones matrix with the same dimension as the total number of parallel converters; diag[·] takes the main diagonal elements of the matrix in the form of a column vector.

[0063] Furthermore, calculating the access capacity of the point of common coupling based on the decoupled power includes:

[0064]

[0065] Among them, S p is the access capacity of the point of common coupling; P id and Q id are the column vectors of the active power and reactive power actually injected by the converters into the point of common coupling respectively.

[0066] Furthermore, calculating the voltage of the weak grid voltage source based on the access capacity of the point of common coupling and the short-circuit ratio of the new energy power station includes:

[0067]

[0068] Among them, is the voltage on the weak grid side; S p is the access capacity of the point of common coupling; R scr is the short-circuit ratio of the new energy power station; E n is the maximum voltage of the nth converter; is the line impedance from the nth converter to the PPC.

[0069] Furthermore, calculating the frequency of the weak grid voltage source based on the swing equation of the synchronous generator includes:

[0070]

[0071] Among them, ω g is the frequency of the weak grid voltage source; J g and D g are the inertia coefficient and damping coefficient of the synchronous generator respectively; ω ref is the grid frequency reference value; ΔG is the grid noise.

[0072] Aiming at the modeling problem of weak grids in the new power system, the present invention proposes an innovative simplified strategy for multi-node distribution networks, and combines the physical model of converters for new energy power generation to provide an efficient method for modeling the voltage and frequency of weak grids.

[0073] Multi-node distribution network simplification strategy: By reasonably simplifying the structure of the distribution network, the complexity of modeling is reduced while maintaining the key characteristics of the system. This strategy can significantly reduce the number of nodes when modeling weak power grids in multi-node power grids and adapt to the operating conditions in the online simulation platform.

[0074] Physical model based on renewable energy power converter: This model fully considers the physical characteristics of renewable energy power converters and establishes a power decoupling matrix based on this. Power decoupling can effectively separate the coupling power between converters, providing a more accurate basis for subsequent node access capacity calculation.

[0075] PCC access capacity calculation: PCC access capacity is further derived by decoupling power calculation. This method allows the dynamic characteristics and stability requirements of the system to be considered when evaluating the capacity of the access point between the power grid and the new energy station, ensuring that the power grid can remain stable during the new energy grid connection process.

[0076] Voltage model based on short-circuit ratio: In a weak power grid, the short-circuit ratio is an important indicator for measuring the stability of the power grid. Based on the short-circuit ratio of the new energy station, the present invention establishes a voltage model for the weak power grid. The model can reflect the voltage variation characteristics of the power grid under low short-circuit ratio, thereby providing a theoretical basis for voltage regulation of weak power grid power sources.

[0077] Frequency model of synchronous machine swing equation: Based on the swing equation of the synchronous machine, the present invention establishes a frequency model of a weak power grid. In a weak power grid, the frequency fluctuation is more severe due to the lack of sufficient inertial support. By establishing a frequency model, the frequency response of a weak power grid in the face of disturbances can be described more accurately, providing a new idea for frequency modeling of weak power grid power sources.

[0078] The present invention provides a novel weak power grid modeling method by combining new energy stations, short-circuit ratio, voltage and frequency models. This method can integrate the characteristics of multi-node distribution networks into a real-time simulation platform and has important application prospects.

[0079] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A weak grid voltage source modeling method suitable for online simulation, characterized in that: include: Determine the shortest connection line between the grid-connected converter of renewable energy power generation and the upper-level substation, and the shortest connection line between the grid-connected converters of renewable energy power generation; Based on the determined shortest connection line, a common connection point is determined, the line impedance of the common connection point is calculated, and the output power and coupling power of the grid-connected converter of each renewable energy power generation are calculated based on the line impedance of the common connection point; Based on the output power and coupling power of each grid-connected converter of renewable energy power generation, the decoupling power of the corresponding grid-connected converter of renewable energy power generation is calculated; Based on the decoupled power, calculating the access capacity of the common connection point; based on the access capacity of the common connection point and the short-circuit ratio of the new energy station, calculating the voltage of the weak power grid voltage source; Based on the synchronous generator swing equation, the frequency of the weak grid voltage source voltage is calculated to complete the weak grid voltage source modeling suitable for online simulation.

2. The weak grid voltage source modeling method suitable for online simulation according to claim 1, characterized in that: Calculating the line impedance at the point of common connection involves: Among them, k n is the total number of power nodes between the converter numbered n and the common connection point; The line impedance corresponding to the ith node is taken into account starting from the common connection point side; is the line impedance from the converter to the common connection point.

3. The weak grid voltage source modeling method suitable for online simulation according to claim 1, characterized in that: Calculating the output power of each grid-connected converter of renewable energy power generation based on the line impedance of the common connection point includes: Among them, P nn , Q nn 、E n and δ n are the active power, reactive power, maximum voltage and power angle input to the grid by the converter numbered n; E p is the maximum voltage at the common connection point; arg[·], Re[·] and Im[·] are the angle, real part and imaginary part of the complex number respectively; |·| is the absolute value of a real number or the modulus of a complex number; is the line impedance from the converter to the common connection point.

4. The weak power grid voltage source modeling method suitable for online simulation according to claim 1, characterized in that: Calculating the coupled power of each grid-connected converter of renewable energy generation based on the line impedance of the common connection point includes: Among them, P xy , Q xy are the active power and reactive power coupled from the converter numbered x to the converter numbered y; E x and δ x are the maximum voltage and power angle of the converter numbered x input to the grid; E y and δ y They are respectively the maximum voltage and power angle input to the grid by the converter numbered y.

5. The weak grid voltage source modeling method suitable for online simulation according to claim 1, characterized in that: The calculation of decoupling power for the grid-connected converter of the corresponding renewable energy power generation includes: P id =diag[P t ·(2J-I)]; Q id =diag[Q t ·(2J-I)]; Among them, P id and Q id are respectively the active power column vector and reactive power column vector actually injected by the converter to the common connection point; P t and Q t are the active power matrix and reactive power matrix of the parallel converters, respectively; J is the unit matrix, whose dimension is the same as the total number of parallel converters; I is the all-one matrix, whose dimension is the same as the total number of parallel converters; diag[·] is the main diagonal elements of the matrix taken in the form of column vectors.

6. The weak power grid voltage source modeling method suitable for online simulation according to claim 1, characterized in that: Based on the decoupled power, calculating the access capacity of the common connection point includes: Among them, S p is the access capacity of the public connection point; P id and Q id are respectively the active power column vector and reactive power column vector actually injected by the converter into the common connection point.

7. The weak grid voltage source modeling method suitable for online simulation according to claim 1, characterized in that: Based on the access capacity of the common connection point and the short-circuit ratio of the new energy station, calculating the voltage of the weak grid voltage source includes: in, is the voltage on the weak grid side; S p is the access capacity of the public connection point; R scr is the short-circuit ratio of the new energy station; E n is the maximum voltage of the nth converter; is the line impedance from the nth converter to PPC.

8. The weak grid voltage source modeling method suitable for online simulation according to claim 1, characterized in that: Based on the synchronous generator swing equation, calculating the frequency of the weak grid voltage source voltage includes: Among them, ω g is the frequency of the weak grid voltage source; J g and D g are the inertia coefficient and damping coefficient of the synchronous generator respectively; ω ref is the grid frequency reference value; ΔG is the grid noise.

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