Heterogeneous multi-source proportion configuration method

Abstract

The invention discloses a heterogeneous multi-source proportion configuration method for improving flexible direct-current power transmission capability by using network construction type renewable energy sources. The method comprises the following steps: firstly, obtaining a steady-state mathematical model and a small-signal model of a heterogeneous multi-source complementary flexible direct-current delivery system; secondly, according to the model, calculating multi-dimensional steady-state operation constraints influencing the flexible direct-current power transmission capability, wherein the multi-dimensional steady-state operation constraints comprise an electric energy quality index, flexible direct-current operation limitation and small signal stability constraints; scanning the multi-proportion configuration of the heterogeneous power supply at the sending end, analyzing the DC transmission power maximum value meeting the multi-dimensional steady-state operation constraint under different reactive power operation points of the flexible DC power supply, and obtaining the flexible DC power transmission capability of the heterogeneous multi-source at the sending end under different proportion configurations; and finally, summarizing the change trend of the direct-current power transmission capability under different output ratios of the network construction type renewable energy sources to obtain the heterogeneous multi-source proportion configuration method for improving the direct-current power transmission capability. According to the method provided by the invention, the configuration of different proportions of required network type / network construction type renewable energy sources and traditional energy sources for improving the flexible direct current power transmission capability can be quantitatively evaluated, and a reference basis is provided for realizing optimal configuration of resources and ensuring safe and stable operation of a system.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of power system stability analysis, and particularly relates to a heterogeneous multi-source proportion configuration method for improving the power transmission capacity of flexible direct current by grid-connected renewable energy. BACKGROUND

[0002] Due to the geographical location of China, large-scale wind power and photovoltaic power are mainly concentrated in the northwest of China, while the main load is concentrated in the southeast coastal areas, which requires large-capacity long-distance power transmission. The modular multilevel converter based high voltage direct current (MMC-HVDC) system has become an important part of the power system. However, when the sending end has a large proportion of grid-connected renewable energy, the system steady-state operating point changes, which may not meet the multi-dimensional constraint conditions for maintaining safe and stable operation of the system, and the grid-connected renewable energy has oscillation risk in weak power grids, which will all limit the direct current power transmission capacity. In order to improve the direct current power transmission capacity, grid-connected renewable energy with good applicability in weak power grids needs to be introduced.

[0003] Based on the necessity of introducing grid-connected renewable energy into the power system, we need to study a multi-type power source proportion configuration method that can improve the direct current power transmission capacity. With the grid connection of grid-connected renewable energy, the operating characteristics of the alternating current power grid are more complex and the operating conditions are more variable. It is necessary to comprehensively evaluate the direct current power transmission capacity from the aspects of power flow constraints, small signal stability constraints, power quality indicators and flexible direct current operation limits, and to study the direct current power transmission capacity under different output proportion configurations of grid-connected / grid-connected renewable energy and traditional energy, so as to provide a reference for realizing resource optimization and ensuring safe and stable operation of the system. SUMMARY

[0004] The present application aims to provide a heterogeneous multi-source proportion configuration method for improving the power transmission capacity of flexible direct current by grid-connected renewable energy, which takes into account both small signal stability constraints, power quality indicators and flexible direct current operation limits, and considers different output proportion configurations of grid-connected / grid-connected photovoltaic power, water and other multi-type power sources. It can simply and efficiently quantitatively evaluate the direct current power transmission capacity under different proportion configurations of multi-type power sources, so as to improve the system direct current power transmission capacity by optimizing the output proportion of grid-connected / grid-connected photovoltaic power, water and other power sources.

[0005] In order to achieve the above purpose, the present application provides a heterogeneous multi-source proportion configuration method for improving the power transmission capacity of flexible direct current by grid-connected renewable energy, characterized by the following steps: Step 1: Obtain the steady-state mathematical model and small signal model of the heterogeneous multi-source complementary flexible DC transmission system; Step 2: Calculate the multi-dimensional steady-state operation constraints affecting the flexible DC power transmission capacity based on the model, including power quality indicators, flexible DC operation limits, and small signal stability constraints; Step 3: Scan the sending end heterogeneous multi-source proportion configuration, analyze the maximum DC transmission power that meets the multi-dimensional steady-state operation constraints at different reactive power operating points of the flexible DC, and obtain the flexible DC power transmission capacity under different proportion configurations of the sending end heterogeneous multi-source. Step 4: Summarize the trend of DC power transmission capacity under different output ratios of network-type renewable energy sources, and obtain the heterogeneous multi-source proportion configuration method for improving DC power transmission capacity.

[0006] Further, the steady-state mathematical model of the system is established according to the system power flow equation and the MMC-HVDC steady-state equation.

[0007] Further, the small signal model is established according to the dynamic process of the system, which can be represented as: where A represents the system state matrix, B represents the input matrix; ΔX and ΔU represent the system state vector increment and input vector increment, respectively.

[0008] Further, the small signal stability constraint condition can be determined by the following method: the system minimum damping ratio ξmin is used to measure the small signal stability of the system, and the small signal stability constraint condition corresponding to the system minimum damping ratio ξmin can be represented as ξmin>0, where ξ represents the eigenvector of the state matrix A.

[0009] Further, the power quality constraints include AC bus voltage deviation constraints and renewable energy grid connection point power factor constraints: where the AC bus voltage deviation constraint can be represented as Umin≤UPCC≤Umax, where UPCC represents the AC bus voltage, Umin takes 0.95pu, and Umax takes 1.05pu; the renewable energy grid connection point power factor constraint can be represented as cosφ≥cosφmin, where cosφ represents the renewable energy grid connection point power factor, and cosφmin takes 0.95.

[0010] Further, the flexible DC operation limits include modulation ratio constraints and converter station current overload constraints: where the modulation ratio constraint can be represented as M≤Mmax, where M represents the modulation ratio and Mmax takes 1; the converter station current overload constraint can be represented as IMMC≤Imax, where IMMC represents the AC current flowing into the converter station, and Imax represents the maximum AC current of the converter station, taking 1.15Sbase / Ubase, where Sbase and Ubase represent the rated power and rated AC voltage of the converter station, respectively.

[0011] Furthermore, the heterogeneous multi-source includes grid-following photovoltaic, grid-building photovoltaic and hydropower.

[0012] Furthermore, the scanning of the heterogeneous multi-source ratio configuration at the sending end, analyzing the maximum DC transmission power that satisfies the multi-dimensional steady-state operation constraints under different reactive power operating points of the flexible DC, and obtaining the flexible DC power transmission capacity under different ratio configurations of the heterogeneous multi-source at the sending end include the following steps: Step 1: Given the hydropower output and grid-connected photovoltaic output, analyze the maximum DC transmission power that satisfies the multi-dimensional steady-state operation constraints under different reactive power operating points of the flexible DC system; Step 2: Change the grid-connected PV output and repeatedly calculate the maximum DC transmission power of the system under the corresponding working conditions. Obtain the flexible DC power transmission capacity of the grid-connected PV under different outputs when the hydropower output is constant; Step 3: Change the active output of hydropower and repeat step 2 to obtain the flexible DC power transmission capacity under different output ratios of hydropower and grid-connected photovoltaic.

[0013] Furthermore, given the hydropower output and the grid-connected photovoltaic output, analyzing the maximum value of the direct current transmission power that satisfies the multi-dimensional steady-state operation constraints at different reactive power operating points of the flexible direct current includes the following steps: Step 1: Given the hydropower output, grid-connected PV output, flexible DC reactive power operating point, and DC transmission power; Step 2: Obtain the grid-following photovoltaic power operating point and line flow according to the steady-state mathematical model, solve the state space matrix according to the small signal model, and determine whether the multi-dimensional steady-state operation constraints are met; Step 3: Scan different DC transmission powers and repeat step 2 to find all DC power transmission ranges that meet the steady-state operation constraints at this flexible DC reactive power operating point, and extract the maximum DC transmission power.

[0014] Step 4: Scan the flexible direct current at different reactive power operating points, repeat step 3, and obtain the maximum DC transmission power at different reactive power operating points of the flexible direct current, and obtain the maximum DC transmission power at the configuration point of the heterogeneous multi-source ratio of this group of sending ends.

[0015] Beneficial effects of the present invention: The present invention proposes a heterogeneous multi-source ratio configuration method for grid-type renewable energy to improve the flexible DC power transmission capacity. Compared with the existing sending-end heterogeneous multi-source ratio configuration calculation method, the present invention fully considers the small signal stability constraints, power quality indicators and flexible DC operation limitations and the limitations on DC power transmission capacity, uses the maximum feasible DC transmission power to realize the evaluation of DC power transmission capacity, and considers the impact of grid-type photovoltaic output configuration under different hydropower outputs on the DC power transmission range, providing a reference basis for achieving resource optimization configuration and ensuring safe and stable operation of the system. BRIEF DESCRIPTION OF DRAWINGS

[0016] The accompanying drawings illustrate exemplary embodiments of the present application and, together with the general description of the application given above, and the detailed description of the embodiments given below, serve to explain the principles of the present application. In these drawings:

[0017] Figure 1 Flow chart of a heterogeneous multi-source proportion configuration method for improving flexible DC power transmission capacity of a grid-forming renewable energy source according to an embodiment of the present application; Figure 2 Topology diagram of a grid-following / grid-forming photovoltaic and hydropower complementary flexible DC transmission system according to an embodiment of the present application; Figure 3 Steady-state equivalent circuit according to an embodiment of the present application; Figure 4 Equivalent structure diagram of a photovoltaic power station according to an embodiment of the present application; Figure 5 Grid-following control strategy block diagram of a photovoltaic power station according to an embodiment of the present application; Figure 6 Grid-forming control strategy block diagram of a photovoltaic power station according to an embodiment of the present application Figure 7 DC power transmission limit under different hydropower output and grid-forming photovoltaic output configurations according to an embodiment of the present application. DETAILED DESCRIPTION

[0018] In order to make the objectives, technical solutions and advantages of the present application clearer, the specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the related content and not limit the present application. In addition, it should be noted that only the parts related to the present application are shown in the accompanying drawings for ease of description.

[0019] It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other without conflict, and the technical solutions of the present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0020] The terms used herein are for the purpose of describing specific embodiments and are not limiting. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, to the extent that the terms "comprises," "includes," "contains," and / or "comprising," "including," and / or "containing" are used in the specification, these terms are used in the sense of providing an open range of meanings where the moieties listed before the term (e.g., "comprises"), the term itself, and the moieties listed after the term (e.g., "comprising") are intended to be interpreted as "including, but not limited to."

[0021] The flowchart of the heterogeneous multi-source proportion configuration method for improving the flexible DC power transmission capacity of the network-constructed renewable energy is described below with reference to the accompanying drawings.

[0022] As shown in the drawings, the heterogeneous multi-source proportion configuration method for improving the flexible DC power transmission capacity based on the network-constructed renewable energy specifically includes the following steps: Figure 1 Step 1: Obtain the steady-state mathematical model and the small-signal model of the heterogeneous multi-source complementary flexible DC external transmission system.

[0023] Specifically, the method of the present application is described by taking three power sources, i.e., grid-connected photovoltaic, network-constructed photovoltaic and hydropower, as examples. The following describes the method of the present application in combination with Figure 2 a photovoltaic-hydropower complementary flexible DC external transmission system topology diagram and Figure 3 a steady-state equivalent circuit. The steady-state mathematical model of the system is established according to the system power flow equation and the MMC-HVDC steady-state equation. The small-signal model is established according to the dynamic process of the system.

[0024] Step 2: Calculate the multi-dimensional steady-state operation constraints affecting the flexible DC power transmission capacity according to the model, including the power quality index, the flexible DC operation limit and the small-signal stability constraint.

[0025] Specifically, the multi-dimensional steady-state operation constraints include the power flow solution constraint, the power quality constraint, the flexible DC operation limit and the small-signal stability constraint. For the power quality constraint, it includes but is not limited to the AC bus voltage deviation constraint and the renewable energy grid-connected point power factor constraint. For the flexible DC operation constraint, it includes but is not limited to the modulation ratio constraint and the converter station current overload constraint. For the judgment index of the small-signal stability constraint, it includes but is not limited to the state space matrix modal damping ratio and the phase margin index.

[0026] For example, the state space matrix modal damping ratio is used to judge whether the system satisfies the small-signal stability constraint. When the modal damping ratio ξ is greater than 0, the system satisfies the small-signal stability. Further, when the minimum modal damping ratio ξmin is greater than 0, it indicates that the system damping ratio is greater than 0, satisfying the small-signal stability requirement.

[0027] Step 3: Scan the sending-end heterogeneous multi-source proportion configuration, analyze the maximum DC transmission power satisfying the multi-dimensional steady-state operation constraint under different reactive power operation points of the flexible DC, and obtain the flexible DC power transmission capacity under different proportion configurations of the sending-end heterogeneous multi-source.

[0028] ​Specifically, according to the scanning sending end heterogeneous multi-source proportion configuration, the maximum value of DC transmission power meeting the multi-dimensional steady-state operation constraint at different flexible and reactive power operation points is analyzed to obtain the flexible DC power transmission capacity under different proportion configurations of the sending end heterogeneous multi-source, including the following steps: (1) keeping the hydropower output, grid-connected photovoltaic output and converter station reactive power operation point unchanged, and giving the DC transmission power; (2) obtaining the grid-connected photovoltaic power operation point and line flow according to the steady-state mathematical model, solving the state space matrix according to the small signal model, and judging whether the power quality index, flexible DC operation limit and small signal stability constraint are met, if met, it means that under the proportion configuration of the sending end multi-type power source, the system can stably transmit power; (3) under the flexible DC multi-reactive power operation point, scanning the DC different transmission power, repeating step 2, obtaining the DC power transmission range meeting the multi-dimensional constraint condition, and extracting the maximum value of the DC transmission power to evaluate the DC power transmission capacity; (4) changing the grid-connected photovoltaic output, and repeating the calculation of the maximum value of the DC transmission power of the system under the corresponding working condition. The flexible DC power transmission capacity under different grid-connected photovoltaic outputs when the hydropower output is certain is obtained. (5) changing the hydropower active output, and repeating (4) to obtain the flexible DC power transmission capacity under different output proportions of the hydropower and grid-connected photovoltaic, and the calculation result is as shown in Figure 7

[0029] Step 4: Inducing the change trend of the DC power transmission capacity under different output proportions of the grid-connected renewable energy to obtain the heterogeneous multi-source proportion configuration method for improving the DC power transmission capacity.

[0030] Specifically, from Figure 7 It can be seen that the influence of the grid-connected photovoltaic on the DC power transmission limit under different hydropower outputs is different. Specifically, when the grid-connected photovoltaic output is small, the DC power transmission limit is restricted by the small signal stability and the converter station current overload constraint, and increases with the increase of the hydropower or grid-connected photovoltaic output; when the grid-connected photovoltaic output is large, the DC power transmission limit is restricted by the power factor constraint and the current overload constraint, and the increase of the grid-connected photovoltaic output will not improve the transmission limit. When the hydropower proportion is small, that is, 0.12pu, in order to make the DC feasible transmission power reach 1pu, the grid-connected photovoltaic output proportion needs to reach 0.11pu.

[0031] ​The application is not only suitable for the grid-connected type / grid-forming type photovoltaic and hydropower complementary flexible DC external transmission system in the same photovoltaic power station, but also suitable for the case of multiple areas corresponding to different types and inconsistent operating conditions of photovoltaic, especially for the power system with high photovoltaic power generation penetration rate, and provides a heterogeneous multi-source proportion configuration method for improving the power transmission capacity of the grid-forming renewable energy flexible DC system. Through the method, the power transmission capacity of the flexible DC external transmission system under different output proportions of the grid-forming photovoltaic can be quantitatively constructed, so that the improvement of the DC transmission capacity can be realized by optimizing the proportion configuration of multiple types of power sources.

[0032] The above examples only specifically demonstrate the embodiments of the application, but those skilled in the art should understand that various changes can be made to the application in form and detail without departing from the spirit and scope of the application defined in the appended claims, and all are within the protection scope of the application.

Claims

1. A method for configuring a proportion of multiple types of power sources for improving a DC power transmission capacity of a networked renewable energy, characterized in that, The method comprises the following steps: Step 1: obtaining a steady-state mathematical model and a small signal model of a heterogeneous multi-source complementary flexible DC transmission system; Step 2: calculating multi-dimensional steady-state operation constraints affecting the flexible DC power transmission capacity according to the model; Step 3: scanning the sending-end heterogeneous multi-source proportion configuration, analyzing the maximum DC transmission power meeting the multi-dimensional steady-state operation constraints at different reactive power operation points of the flexible DC, and obtaining the flexible DC power transmission capacity under different proportion configurations of the sending-end heterogeneous multi-source; Step 4: summarizing the change trend of the DC power transmission capacity under different output ratios of the grid-connected renewable energy, and obtaining the heterogeneous multi-source proportion configuration method for improving the DC power transmission capacity.

2. The heterogeneous multi-source proportion configuration method for networked renewable energy to improve the flexibility of HVDC power transmission capacity according to claim 1, wherein, The multi-dimensional steady-state operation constraints comprise power quality indicators, flexible DC operation limits and small signal stability constraints.

3. The heterogeneous multi-source proportion configuration method for networked renewable energy to improve the flexibility of HVDC power transmission capacity according to claim 1, wherein, The steady-state mathematical model of the system is established according to system power flow equations and MMC-HVDC steady-state equations.

4. The heterogeneous multi-source proportion configuration method for networked renewable energy to enhance the flexibility of HVDC power transmission capacity of claim 1, wherein, The small signal model can be expressed as: ; wherein A represents a system state matrix, B represents an input matrix; ΔX and ΔU represent system state vector increment and input vector increment, respectively.

5. The heterogeneous multi-source proportion configuration method for networked renewable energy to enhance the flexibility of HVDC power transmission capacity of claim 2, wherein The small signal stability constraint condition can be determined by the following method: The system minimum damping ratio ξ min measures the system small signal stability, the system minimum damping ratio ξ min corresponding to the small signal stability constraint condition can be expressed as ξ min > 0, wherein ξ represents an eigenvalue vector of the state matrix A.

6. The heterogeneous multi-source occupancy ratio configuration method for networked renewable energy to enhance the flexibility of HVDC power transmission capacity of claim 2, wherein The power quality constraints include an AC bus voltage deviation constraint and a renewable energy grid point power factor constraint; wherein the AC bus voltage deviation constraint can be expressed as U min ≤ U PCC ≤ U max , wherein U PCC represents an AC bus voltage, U min takes 0.95pu, and U max takes 1.05pu; the renewable energy grid point power factor constraint can be expressed as cosφ ≥ cosφ min , wherein cosφ represents an AC renewable energy grid point power factor, cosφ min takes 0.

95.

7. The heterogeneous multi-source occupancy ratio configuration method for networked renewable energy to enhance the flexibility of HVDC power transmission capacity of claim 2, wherein, The flexible direct operation limit includes a modulation ratio constraint and a converter station current overload constraint; wherein the modulation ratio constraint can be expressed as M≤M max , wherein M represents the modulation ratio, M max =1; the converter station current overload constraint can be expressed as I MMC ≤I max , wherein I MMC represents the AC current flowing into the converter station, I max represents the maximum AC current of the converter station, I base =1.15S base , wherein S base , U base respectively represent the rated power and the rated AC voltage of the converter station.

8. The heterogeneous multi-source proportion configuration method for networked renewable energy to improve the power transmission capacity of flexible DC according to any one of claims 1-7, wherein, The heterogeneous multi-source comprises grid-connected photovoltaic, grid-forming photovoltaic and hydropower.

9. The heterogeneous multi-source proportion configuration method for networked renewable energy to improve the power transmission capacity of flexible DC according to any one of claims 1-7, wherein, The scanning of the sending-end heterogeneous multi-source proportion configuration, the analysis of the maximum DC transmission power meeting the multi-dimensional steady-state operation constraints at different reactive power operation points of the flexible DC, and the obtaining of the flexible DC power transmission capacity under different proportion configurations of the sending-end heterogeneous multi-source comprise the following steps: Step 1: given the hydropower output and the grid-forming photovoltaic output, the maximum DC transmission power meeting the multi-dimensional steady-state operation constraints at different reactive power operation points of the flexible DC is analyzed; Step 2: the grid-forming photovoltaic output is changed, and the maximum DC transmission power of the system under the corresponding working condition is repeatedly calculated to obtain the flexible DC power transmission capacity under different grid-forming photovoltaic outputs when the hydropower output is certain; Step 3: the hydropower active output is changed, and step 2 is repeated to obtain the flexible DC power transmission capacity under different output proportions of the hydropower and the grid-forming photovoltaic.

10. The heterogeneous multi-source occupancy ratio configuration method for network-constructed renewable energy to enhance the flexibility of HVDC power transmission capacity according to claim 9, wherein, The given hydropower output and grid-forming photovoltaic output, and the analysis of the maximum DC transmission power meeting the multi-dimensional steady-state operation constraints at different reactive power operation points of the flexible DC comprise the following steps: Step 1: given the hydropower output, the grid-forming photovoltaic output, the flexible DC reactive power operation point and the DC transmission power; Step 2: the grid-connected photovoltaic power operation point and the line power flow are obtained according to the steady-state mathematical model, the state space matrix is solved according to the small signal model, and it is judged whether the multi-dimensional steady-state operation constraints are met; Step 3: the DC transmission power is scanned, step 2 is repeated, the DC power transmission range meeting the steady-state operation constraints at the flexible DC reactive power operation point is found out, and the maximum DC transmission power is extracted; Step 4: the flexible DC reactive power operation point is scanned, step 3 is repeated, the maximum DC transmission power at the flexible DC reactive power operation point is obtained, and the maximum DC transmission power at the sending-end heterogeneous multi-source proportion configuration point is obtained.

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