Economical-efficiency-based capacity matching method for network-following type-network-constructing type converter

Abstract

The invention provides an economical efficiency-based capacity matching method for a network following type-network constructing type converter, and belongs to the field of capacity planning of a new energy power generation system. Comprising the following steps: S1, constructing a capacity optimization objective function considering economy, and optimizing capacity configuration of the new energy converter; s2, calculating an initial value of a generalized short-circuit ratio according to network and equipment capacity, and determining a target value of the generalized short-circuit ratio according to system requirements; and S3, according to the relation between the generalized short-circuit ratio and the capacity ratio, the generalized short-circuit ratio initial value and the generalized short-circuit ratio target value, calculating to obtain the capacity ratio of the network-following type converter and the network-constructing type converter. Therefore, by considering the economical efficiency of the current transformer capacity configuration, the current transformer capacity configuration with the lowest cost is obtained under the constraint of the optimization objective function, and the construction cost of the system is reduced; and meanwhile, the safety ratio of the converter is obtained by researching the relationship between the generalized short-circuit ratio of the system and the network following-network constructing converter, so that the supporting capability of the local extremely-high-proportion new energy access system is effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of capacity planning of new energy power generation systems, and in particular to a capacity matching method of a grid-following type-grid-building type converter based on economy. Background Art

[0002] The "double high" trend of the new power system is constantly strengthening, and the installed capacity of new energy is increasing. By the end of 2023, my country's cumulative installed capacity of wind and solar power will exceed 1 billion kilowatts, and the total installed capacity will account for 36% of the total installed capacity in the society. The extremely high proportion of new energy has become a typical feature of regions rich in wind and light resources.

[0003] At present, photovoltaic and energy storage generally use grid-type converters based on current source converters, which have poor anti-disturbance ability, weak active support ability for the power grid, and instability under weak grid conditions. Compared with grid-type converters, grid-building converters have synchronous voltage source characteristics, which can effectively improve the stability of new power systems with power electronics, and can be used for the development of new energy access systems in areas with extremely high proportions of local new energy such as Gantang. However, on the one hand, grid-building equipment needs to build and maintain output voltage and frequency, and its technical complexity and equipment requirements are high, resulting in relatively high costs. On the other hand, grid-building equipment is prone to synchronous instability under large disturbances, and the current limiting characteristics of power electronics will also increase the risk of instability. Too many grid-building devices will affect the stability of the power system. Therefore, it is necessary to propose a safe matching method for grid-building devices, which can achieve stability complementarity between grid-building devices and grid-building devices while taking into account the economy, so that the access of grid-building converters can play a positive role in the stability of new power systems. Summary of the invention

[0004] In view of this, the present invention provides a capacity ratio matching method of a grid-following type-grid-building type converter based on economy, so as to achieve stability complementarity between the grid-building type device and the grid-following type device while taking economy into consideration.

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] A capacity matching method for a grid-following type and a grid-building type converter based on economy comprises the following steps:

[0007] S1. Construct a capacity optimization objective function that takes economic considerations into account and optimize the capacity configuration of new energy converters;

[0008] S2. Calculate the initial value of the generalized short-circuit ratio according to the network and equipment capacity, and determine the target value of the generalized short-circuit ratio according to system requirements, wherein the equipment capacity is determined according to the optimized new energy converter capacity configuration;

[0009] S3. Calculate the capacity ratio of the grid-following type and grid-forming type converters according to the relationship between the generalized short-circuit ratio and the capacity ratio, the initial value of the generalized short-circuit ratio and the target value of the generalized short-circuit ratio.

[0010] Preferably, in step S1, constructing a capacity optimization objective function considering economy includes:

[0011] The capacity optimization objective function consisting of converter cost, power failure loss and excess energy loss is established:

[0012] minC=min{C inv +C ls +C es}

[0013] In the formula, C inv represents the converter cost; C ls Represents power loss; C es Represents excess energy loss.

[0014] Preferably, the calculation formulas of Cinv, Cls and Ces are respectively:

[0015] C inv =C ini +C opr +C m +C r -C f

[0016]

[0017] In the formula, C ini is the investment cost of the converter, in yuan; C opr is the operating cost of the converter, in yuan; C m is the maintenance cost of the converter, in yuan; C r is the replacement cost of the converter, yuan; C f The residual value after the converter life ends, in yuan; C e is the unit electricity price, in yuan / kWh; C mp P is the unit load compensation cost after the load loses power, in yuan / kWh; ls (t) is the power loss at time t, in kW; P es (t) is the excess energy power at time t, in kW; C ls0 is the inherent power loss of the system, in yuan; C es0 is the inherent excess energy loss of the system, in yuan; n is the project life, in years.

[0018] Preferably, the constraint condition of the capacity optimization objective function is:

[0019]

[0020] Where P inv is the converter capacity; P e is the converter capacity under maximum and minimum β; P iload is the load power; C d To meet the power shortage coefficient; P rs For backup power capacity.

[0021] Preferably, in step S2, calculating the initial value of the generalized short circuit ratio according to the network and equipment capacity includes:

[0022] S21. Calculate the short-circuit capacity S of the grid-connected node of the system under study sc :

[0023]

[0024] Where U is the reference voltage of the grid-connected node; Z sc is the equivalent short-circuit impedance of the grid-connected node;

[0025] S22. Calculate the equivalent impedance Z of the grid-connected equipment eq1 ;

[0026] S23. Determine the generalized short-circuit capacity S of the system under study gsc :

[0027]

[0028] Arranged:

[0029]

[0030] S24. Calculate the initial value of the generalized short-circuit ratio based on the generalized short-circuit capacity and the rated capacity of the equipment:

[0031]

[0032] Where gSCR is the generalized short-circuit ratio; S is the rated capacity of the grid-connected equipment.

[0033] Preferably, in step S3, the generalized short circuit ratio and capacity ratio relationship is:

[0034]

[0035] Where, δ is the capacity ratio of grid-following type and grid-building type converter; gSCR0 is the initial value of generalized short-circuit ratio; gSCR d is the generalized short-circuit ratio target value; where:

[0036]

[0037] Preferably, in step S3, the capacity ratio of the grid-following type and grid-forming type converters is calculated according to the relationship between the generalized short-circuit ratio and the capacity ratio, the generalized short-circuit ratio initial value and the generalized short-circuit ratio target value, including the following steps:

[0038] S31. Obtain the impedance external characteristics of the grid-type converter by impedance measurement method and calculate its equivalent internal reactance Z eq2 ;

[0039] S32. Calculate the equivalent impedance Z of each transformer used in the original system Ti ;

[0040] S33, the generalized short circuit ratio initial value calculated in step S2, the generalized short circuit ratio target value determined according to system requirements, Z eq2 and Z Ti By substituting the generalized short-circuit ratio into the capacity ratio relationship, the capacity ratio of the grid-following type and grid-forming type converters can be calculated.

[0041] Preferably, the equivalent impedance Z Ti The calculation formula is:

[0042]

[0043] In the formula, Z Ti is the transformer equivalent impedance; Z T is the original impedance of the transformer; m is the equivalent quantity.

[0044] The present invention also provides a computer-readable storage medium, in which program instructions are stored. When the program instructions are executed, they are used to execute the above-mentioned economic-based grid-following-grid-building converter capacity ratio matching method.

[0045] The present invention also provides an economy-based grid-following-grid-building converter capacity ratio system, comprising the computer-readable storage medium as described above.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] The capacity matching method of the grid-type and grid-forming converter provided by the present invention based on economy first constructs the system capacity optimization objective function considering economy and optimizes the capacity configuration of the new energy converter; secondly, the generalized short-circuit ratio of the studied system is calculated according to the network and equipment capacity, and the target generalized short-circuit ratio value is determined according to the actual demand; finally, the capacity matching ratio of the grid-type converter and the grid-forming converter is calculated according to the generalized short-circuit ratio and capacity matching ratio relationship, the generalized short-circuit ratio initial value and the generalized short-circuit ratio target value. Thus, by considering the economy of the converter capacity configuration, the converter capacity configuration with the lowest cost is obtained under the constraint of the optimization objective function, and the construction cost of the system is reduced; at the same time, the relationship between the system generalized short-circuit ratio and the grid-forming converter is studied, and the safety matching ratio of the grid-type converter and the grid-forming converter is reversed through the generalized short-circuit ratio, so that the grid-forming device and the grid-type device can achieve stability complementarity, so that the access of the grid-forming converter plays a positive role in the stability of the new power system, and can effectively improve the support capacity of the local extremely high proportion of new energy access system. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a flow chart of the method of the present invention.

[0049] Figure 2 It is a flow chart for optimizing the capacity configuration of new energy converters.

[0050] Figure 3 This is the control schematic diagram of the grid-type converter.

[0051] Figure 4 It is the supply and demand power deviation diagram.

[0052] Figure 5 It is a schematic diagram of a multi-machine system.

[0053] Figure 6 This is the waveform diagram after the terminal voltage is applied to the modified 2.3% grid-type converter.

[0054] Figure 7 This is the waveform diagram after the terminal voltage is applied to the modified 6.8% grid-type converter. DETAILED DESCRIPTION

[0055] The technical solutions and technical effects of the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings of the present invention.

[0056] Please see Figure 1 A capacity matching method of a grid-following type-grid-building type converter based on economy comprises the following steps:

[0057] S1. Construct a capacity optimization objective function that takes economic considerations into account and optimize the capacity configuration of new energy converters;

[0058] S2. Calculate the initial value of the generalized short-circuit ratio according to the network and equipment capacity, and determine the target value of the generalized short-circuit ratio according to system requirements, wherein the equipment capacity is determined according to the optimized new energy converter capacity configuration;

[0059] S3. Calculate the capacity ratio of the grid-following type and grid-forming type converters according to the relationship between the generalized short-circuit ratio and the capacity ratio, the initial value of the generalized short-circuit ratio and the target value of the generalized short-circuit ratio.

[0060] The capacity ratio matching method of grid-following and grid-forming converters provided by the present invention based on economy firstly constructs a system capacity optimization objective function considering economy to optimize the capacity configuration of new energy converters; secondly, the generalized short-circuit ratio of the studied system is calculated according to the network and equipment capacity, and the target generalized short-circuit ratio value is determined according to actual needs; finally, the capacity ratio of the grid-following converter and the grid-forming converter is calculated according to the relationship between the generalized short-circuit ratio and the capacity ratio, the initial value of the generalized short-circuit ratio and the target value of the generalized short-circuit ratio. Therefore, by considering the economy of the converter capacity configuration, the converter capacity configuration with the lowest cost is obtained under the constraint of the optimization objective function, thereby reducing the construction cost of the system; at the same time, the relationship between the system's generalized short-circuit ratio and the grid-following and grid-building converters is studied, and the safety ratio of the grid-following converter and the grid-building converter is inferred through the generalized short-circuit ratio, so that the grid-building equipment and the grid-following equipment can achieve stability complementarity, so that the access of the grid-building converter has a positive effect on the stability of the new power system, and can effectively enhance the supporting capacity of the local extremely high proportion of new energy access systems, thereby ensuring the stability of the system while taking into account the economy.

[0061] In step S1, constructing a capacity optimization objective function considering economy includes:

[0062] Taking into account the system economy and reliability, a capacity optimization objective function consisting of converter cost, power failure loss and excess energy loss is established:

[0063] minC=min{C inv +C ls +C es}

[0064] In the formula, C inv represents the converter cost; C ls Represents power loss; C es Represents excess energy loss. Excess energy loss includes clean energy loss, such as wind and solar power abandonment. Therefore, by comprehensively considering converter cost, power loss and excess energy loss, the converter capacity configuration is optimized to obtain the most economical converter capacity configuration.

[0065] Furthermore, the converter cost includes investment cost, operation and maintenance cost, replacement cost and residual value; power failure loss includes power loss caused by insufficient converter capacity configuration and power failure compensation loss; excess energy loss refers to power generation loss caused by insufficient converter capacity configuration. Therefore, C inv , C ls , C es The calculation formulas are:

[0066] C inv =C ini +C opr +C m +C r -C f

[0067]

[0068] In the formula, C ini is the investment cost of the converter, in yuan; C opr is the operating cost of the converter, in yuan; C m is the maintenance cost of the converter, in yuan; C r is the replacement cost of the converter, yuan; C f The residual value after the converter life ends, in yuan; C e is the unit electricity price, in yuan / kWh; C mp P is the unit load compensation cost after the load loses power, in yuan / kWh; ls (t) is the power loss at time t, in kW; P es (t) is the excess energy power at time t, in kW; C ls0 is the inherent power loss of the system, in yuan; C es0 is the inherent excess energy loss of the system, in yuan; n is the project life, in years.

[0069] Furthermore, the proportion of time that the converter capacity meets the power exchange demand within a period of time is defined as the time probability of meeting the power exchange demand under grid connection, which is recorded as β. Since the system allows excess power generation, the converter capacity only needs to meet the power exchange demand at most times of the year. The constraint condition of the capacity optimization objective function can be expressed as:

[0070]

[0071] Where P inv is the converter capacity; P e is the converter capacity under maximum and minimum β; P iload is the load power; C d To meet the power shortage coefficient; P rsFor backup power capacity.

[0072] In some implementations, the new energy converter capacity configuration optimization process is as follows: Figure 2 As shown in the figure, firstly, considering the system economy and reliability comprehensively, the capacity optimization objective function consisting of converter cost, power loss and excess energy loss is established; then, the data is input, including the converter cost, power loss and excess energy loss obtained through analysis and calculation; at the same time, the objective function parameters are initialized, and the parameters mainly include the number of iterations; next, the exchange demand time probability is determined, and the constraints of the optimization objective function are set according to the above formula, and the objective function is calculated. When the termination condition is met, the optimization result is output, so that the optimal solution of the converter capacity configuration can be obtained according to the constraints and its own needs, that is, the converter capacity configuration with the lowest cost that meets the constraints is obtained.

[0073] In some embodiments, the termination condition is a constraint condition, that is, when the capacity configuration of the converter satisfies the constraint condition, it indicates that the calculation of the objective function satisfies the termination condition, and the corresponding optimization result can be output. In other embodiments, the termination condition can be the number of iterations, that is, when the number of iterations satisfies the set number, it indicates that the calculation of the objective function satisfies the termination condition, and the corresponding optimization result can be output.

[0074] In step S2, calculating the initial value of the generalized short circuit ratio according to the network and equipment capacity includes:

[0075] S21. Calculate the short-circuit capacity S of the grid-connected node of the system under study sc , that is, the capacity that the power grid can provide in the event of a short circuit in the system:

[0076]

[0077] Where U is the reference voltage of the grid-connected node; Z sc is the equivalent short-circuit impedance of the grid-connected node;

[0078] S22. Calculate the equivalent impedance Z of the grid-connected equipment eq1 ; Equivalent impedance includes the output impedance of power generation equipment and inverters, etc. This part of impedance affects the voltage support capacity of the grid to the grid-connected equipment. The equivalent impedance can be calculated according to the characteristics of the equipment, generally based on the principle of constant loss.

[0079] S23. Determine the generalized short-circuit capacity S of the system under study gsc :

[0080]

[0081] Arranged:

[0082]

[0083] The generalized short-circuit capacity is the result of the combination of the system short-circuit capacity and the equivalent impedance of the grid-connected equipment. Here, S gsc It is a comprehensive short-circuit capacity that takes into account the impedance of the grid-connected equipment and can more accurately reflect the voltage support capability of the grid-connected node.

[0084] S24. Calculate the initial value of the generalized short-circuit ratio based on the generalized short-circuit capacity and the rated capacity of the equipment:

[0085]

[0086] In the formula, gSCR is the generalized short-circuit ratio; S is the rated capacity of the grid-connected equipment. The rated capacity of the grid-connected equipment is the total capacity of the converter in the optimized new energy converter capacity configuration in step S1.

[0087] In step S3, the connection of the grid-connected converter will not affect the critical short-circuit ratio of the original system, and the generalized short-circuit ratio can be increased from the initial value gSCR0 to the target value gSCR d , the system strength is thus improved, and the generalized short-circuit ratio and capacity ratio relationship is:

[0088]

[0089] Where, δ is the capacity ratio of grid-following type and grid-building type converter; gSCR0 is the initial value of generalized short-circuit ratio; gSCR d is the generalized short-circuit ratio target value; where:

[0090]

[0091] According to the above formula, the capacity ratio of grid-following type and grid-building type converters can be calculated;

[0092] Furthermore, the higher the generalized short-circuit ratio, the stronger the system voltage support capability and the better the stability. The required generalized short-circuit ratio gSCR can be determined according to actual needs. d .

[0093] In the specific implementation process, in step S3, the capacity ratio of the grid-following type and grid-forming type converters is calculated according to the generalized short-circuit ratio and capacity ratio relationship, the generalized short-circuit ratio initial value and the generalized short-circuit ratio target value, including the following steps:

[0094] S31, grid-type converter control method such as Figure 3 As shown in the figure, the impedance external characteristic of the grid-type converter is obtained by the impedance measurement method, and its equivalent internal reactance Z is calculated. eq2 ;

[0095] S32. Calculate the equivalent impedance Z of each transformer used in the original system Ti, adopt the method of "capacity weighted, impedance series and parallel":

[0096]

[0097] In the formula, Z Ti is the transformer equivalent impedance; Z T is the original impedance of the transformer; m is the equivalent quantity.

[0098] S33, the generalized short circuit ratio initial value calculated in step S2, the generalized short circuit ratio target value determined according to system requirements, Z eq2 and Z Ti By substituting the generalized short-circuit ratio into the capacity ratio relationship, the capacity ratio of the grid-following type and grid-forming type converters can be calculated.

[0099] An embodiment is given below:

[0100] In order to verify the effectiveness of the proposed capacity optimization and ratio, a simulation model was built based on the MATLAB / SIMULINK platform. Based on the previous operating data of a new energy station in a certain area of ​​Ningxia, the supply and demand power difference data of 8760h (i.e. one year) was randomly sampled. Figure 4 Using this data to optimize the capacity configuration considering economy, the capacity range is [28.1kW, 64.8kW]. Therefore, the optimal capacity of the converter is 28.1kW, and the minimum total cost is 846,000 yuan.

[0101] Based on the above converter capacity configuration, build Figure 5 The transient simulation model of the multi-machine system is shown. The capacity of each new energy station converter is configured to be 28kW. The initial generalized short-circuit ratio of the power grid is about 1.0, and it is considered to increase the generalized short-circuit ratio to 1.2 and 1.5 respectively. The calculated grid-to-grid converter ratios are 44.45 and 14.03, respectively, which means that about 2.3% and 6.8% of the grid-to-grid converters are transformed into grid-to-grid converters, respectively. The modified system is simulated and verified. Specifically, at t=1s, a 5% terminal voltage drop is applied at the infinite bus and quickly cleared. For the simulation results, please refer to Figure 6 and Figure 7 , among which Figure 6 As shown in Figure 2, when 2.3% of the grid-type converters were modified, the three-phase voltage continued to oscillate and the system stability margin was low; while when 6.8% of the grid-type converters were modified, Figure 7 As shown, the three-phase voltage can be quickly restored and the system stability margin is high; thereby verifying the correctness and effectiveness of the capacity ratio calculated by the capacity ratio method of the present invention.

[0102] In addition, the present invention also provides a computer-readable storage medium, which stores program instructions. When the program instructions are executed, they are used to execute the above-mentioned economic-based grid-following type-grid-building type converter capacity ratio matching method.

[0103] In addition, the present invention also provides an economy-based grid-following-grid-building converter capacity matching system, comprising: the computer-readable storage medium as described above.

[0104] What is disclosed above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. A person skilled in the art can understand that all or part of the processes of the above embodiments and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A capacity matching method for grid-following and grid-building converters based on economy, characterized in that: The following steps are involved: S1. Construct a capacity optimization objective function that takes economic considerations into account and optimize the capacity configuration of new energy converters; S2. Calculate the initial value of the generalized short-circuit ratio according to the network and equipment capacity, and determine the target value of the generalized short-circuit ratio according to system requirements, wherein the equipment capacity is determined according to the optimized new energy converter capacity configuration; S3. Calculate the capacity ratio of the grid-following type and grid-forming type converters according to the relationship between the generalized short-circuit ratio and the capacity ratio, the initial value of the generalized short-circuit ratio and the target value of the generalized short-circuit ratio.

2. The capacity matching method of the grid-following type and grid-building type converter based on economy according to claim 1 is characterized in that: In step S1, constructing a capacity optimization objective function considering economy includes: The capacity optimization objective function consisting of converter cost, power failure loss and excess energy loss is established: minC=min{C inv +C ls +C es } In the formula, C inv represents the converter cost; C ls Represents power loss; C es Represents excess energy loss.

3. The capacity matching method of the grid-following type and grid-building type converter based on economy according to claim 2 is characterized in that: C inv , C ls , C es The calculation formulas are: C inv =C ini +C opr +C m +C r -C f In the formula, C ini is the investment cost of the converter, in yuan; C opr is the operating cost of the converter, in yuan; C m is the maintenance cost of the converter, in yuan; C r is the replacement cost of the converter, yuan; C f The residual value after the converter life ends, in yuan; C e is the unit electricity price, in yuan / kWh; C mp P is the unit load compensation cost after the load loses power, in yuan / kWh; ls (t) is the power loss at time t, in kW; P es (t) is the excess energy power at time t, in kW; C ls0 is the inherent power loss of the system, in yuan; C es0 is the inherent excess energy loss of the system, in yuan; n is the project life, in years.

4. The capacity matching method of the grid-following type and grid-building type converter based on economy according to claim 3 is characterized in that: The constraints of the capacity optimization objective function are: Where P inv is the converter capacity; P e is the converter capacity under maximum and minimum β; P iload is the load power; C d To meet the power shortage coefficient; P rs For backup power capacity.

5. The economical grid-following and grid-building converter capacity matching method according to claim 1 is characterized in that: In step S2, calculating the initial value of the generalized short circuit ratio according to the network and equipment capacity includes: S21. Calculate the short-circuit capacity S of the grid-connected node of the system under study sc : Where U is the reference voltage of the grid-connected node; Z sc is the equivalent short-circuit impedance of the grid-connected node; S22. Calculate the equivalent impedance Z of the grid-connected equipment eq1 ; S23. Determine the generalized short-circuit capacity S of the system under study gsc : Arranged: S24. Calculate the initial value of the generalized short-circuit ratio based on the generalized short-circuit capacity and the rated capacity of the equipment: Where gSCR is the generalized short-circuit ratio; S is the rated capacity of the grid-connected equipment.

6. The capacity matching method of the grid-following type and grid-building type converter based on economy as claimed in claim 1, characterized in that: In step S3, the generalized short-circuit ratio and capacity ratio are: Where, δ is the capacity ratio of grid-following type and grid-building type converter; gSCR0 is the initial value of generalized short-circuit ratio; gSCR d is the generalized short-circuit ratio target value; where:

7. The capacity matching method of grid-following type and grid-building type converter based on economy according to claim 6 is characterized in that: In step S3, the capacity ratio of the grid-following type and grid-forming type converters is calculated according to the generalized short-circuit ratio and capacity ratio relationship, the generalized short-circuit ratio initial value and the generalized short-circuit ratio target value, including the following steps: S31. Obtain the impedance external characteristics of the grid-type converter by impedance measurement method and calculate its equivalent internal reactance Z eq2 ; S32. Calculate the equivalent impedance Z of each transformer used in the original system Ti ; S33, the generalized short circuit ratio initial value calculated in step S2, the generalized short circuit ratio target value determined according to system requirements, Z eq2 and Z Ti By substituting the generalized short-circuit ratio into the capacity ratio relationship, the capacity ratio of the grid-following type and grid-forming type converters can be calculated.

8. The capacity matching method of grid-following type and grid-building type converters based on economy according to claim 7 is characterized in that: The equivalent impedance Z Ti The calculation formula is: In the formula, Z Ti is the transformer equivalent impedance; Z T is the original impedance of the transformer; m is the equivalent quantity.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores program instructions, and when the program instructions are executed, they are used to execute the economic-based grid-following-grid-building converter capacity ratio matching method described in any one of claims 1 to 8.

10. A capacity matching system of grid-following and grid-building converters based on economy, characterized in that: A computer-readable storage medium comprising the computer-readable storage medium of claim 9.

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