A method for power distribution of an ac-dc cross-region parallel grid ac-dc channel

Abstract

The application discloses a kind of AC-DC cross-regional parallel power grid AC-DC passage power distribution method, comprising: S1: arrange DC passage power transmission total power, obtain AC passage power;S2: power flow calculation is obtained the maximum power angle difference of generator and each line power in AC passage, when not meet the preset static stability condition, according to the first reduction amount, reduce the power of sending end generator, according to the first increase amount, increase the power of receiving end generator, repeat this step until meet the preset static stability condition;S3: calculate the system stability after the largest power transmission capacity DC occurs preset fault, when system does not meet transient stability standard, according to the second reduction amount, reduce the power of sending end generator, according to the second increase amount, increase the power of receiving end generator;S4: repeat execution S3 until system meets transient stability standard.The application can determine the maximum transmission power of AC passage under different DC passage power, realize AC-DC section power transmission power maximization.

Description

Technical Field

[0001] This invention relates to the field of power technology, and in particular to a method for power allocation of AC / DC channels in a cross-regional parallel AC / DC power grid. Background Technology

[0002] In recent years, the scale of single-circuit DC transmission has reached 8,000 to 12,000 MW, while the transmission capacity of AC channels has not been significantly improved due to the constraints of transmission corridors and substation land occupation. In order to ensure the reliability of the power grid, the regional power grids still maintain the AC interconnection mode, thus forming a long chain structure of inter-regional AC interconnection. The main problem with this structure is that when the power of AC and DC channels is too large, and a single-pole or double-pole blocking fault occurs in the large-capacity DC, the surplus power is transferred to the long chain AC channel, which leads to an increase in the power angle difference between the sending-end and receiving-end units, causing power angle instability in the synchronous grid. At the same time, large-scale power transfer causes large voltage oscillations in the AC channel, which can easily cause the regional power grid to lose synchronization and disconnect. Therefore, when making mode arrangements, operators need to reasonably control the power of AC and DC channels to avoid the above problems.

[0003] Due to the complex operation mode of large power grids, the previous arrangement of AC and DC section power was often based on experience. In order to ensure the safe operation of the power grid, a large margin was usually reserved based on experience, so it was impossible to maximize the AC and DC section power transmission. Summary of the Invention

[0004] The purpose of this invention is to provide a power allocation method for AC / DC channels in AC / DC inter-regional parallel power grids, so as to solve the technical problem that the existing technology cannot maximize the AC / DC cross-section power transmission power of AC / DC inter-regional parallel power grids.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for power allocation of AC / DC channels in an AC / DC inter-regional parallel power grid, comprising:

[0007] S1: Arrange the total power supply of the DC channel. The AC channel power is obtained by summing the maximum power supply capacity of a single DC circuit in the DC channel and the thermal stability value of all lines in the AC channel.

[0008] S2: Perform power flow calculations to obtain the maximum power angle difference of the generator and the power of each line in the AC channel. When the system does not meet the preset static stability conditions, reduce the power of the sending end generator according to the first reduction amount and increase the power of the receiving end generator according to the first adjustment increment. Repeat this step until the preset static stability conditions are met, and then execute S3.

[0009] S3: Calculate the system stability after a preset fault occurs in the DC with the largest power transmission capacity. When the system does not meet the transient stability standard, reduce the power of the sending end generator according to the second reduction amount and increase the power of the receiving end generator according to the second increment amount.

[0010] S4: Repeat S3 until the system meets the transient stability criterion, and obtain the maximum transmission power of the AC channel under the total power output of the DC channel.

[0011] Alternatively, the AC channel power can be calculated using the following formula:

[0012] P = Pac - 0.5 × P1;

[0013] Where P is the AC channel power, Pac is the sum of the line thermal stability values ​​of all lines in the AC channel, and P1 is the maximum power transmission capacity of a single DC circuit in the DC channel.

[0014] Optionally, the preset static stability condition is:

[0015] The generator has a maximum power angle difference greater than 90 degrees, and there is at least one overloaded line in the AC channel, wherein the overloaded line is the line whose power is greater than the line thermal stability value.

[0016] Optionally, before reducing the power output of the sending-end generator according to the first reduction amount, the following steps are also included:

[0017] Calculate the first reduction amount.

[0018] Optionally, before increasing the power of the receiving-end generator according to the first adjustment increment, the following steps are also included:

[0019] Calculate the first adjustment increment.

[0020] Optionally, the formula for calculating the first reduction is:

[0021] ΔP s =max{P s-r / 200×(maximum power angle difference-90), Σ(P overload -P N )};

[0022] Where, ΔP s For the first reduction, P s-r P is the difference between the output power of the sending end and the output power of the receiving end. overload P represents the power of the overloaded line. N This represents the thermal stability value of the overloaded circuit.

[0023] Optionally, the formula for calculating the first adjustment increment is:

[0024] ΔP r =ΔP s×95%;

[0025] Where, ΔP s For the first reduction, ΔP r This is the first adjustment increment.

[0026] Optionally, the second reduction amount is:

[0027] Maximum single-unit capacity of the power supply at the sending end.

[0028] Optionally, the second adjustment increment is:

[0029] Maximum single-unit capacity of the power supply at the sending end.

[0030] Optionally, the preset fault is:

[0031] Single-pole interlocking fault.

[0032] This invention provides a method for power allocation of AC / DC channels in a cross-regional parallel AC / DC power grid, comprising: S1: arranging the total power transmission of the DC channel, obtaining the AC channel power based on the sum of the maximum transmission capacity of a single DC circuit in the DC channel and the line thermal stability values ​​of all lines in the AC channel; S2: performing power flow calculations to obtain the maximum power angle difference of the generators and the power of each line in the AC channel. When the system does not meet the preset static stability conditions, reducing the power of the sending-end generator according to the first reduction amount and increasing the power of the receiving-end generator according to the first adjustment increment, repeating this step until the preset static stability conditions are met, and then executing S3; S3: calculating the system stability after a preset fault occurs in the DC circuit with the largest transmission capacity. When the system does not meet the transient stability criteria, reducing the power of the sending-end generator according to the second reduction amount and increasing the power of the receiving-end generator according to the second adjustment increment; S4: repeating S3 until the system meets the transient stability criteria, obtaining the maximum transmission power of the AC channel under the total power transmission of the DC channel.

[0033] Based on the above technical solution, the beneficial effects of this invention are:

[0034] This invention first arranges the total power transmission of the DC channel to obtain the power of the AC channel. When the preset static stability condition is not met, the power of the sending-end generator is reduced according to the first reduction amount, and the power of the receiving-end generator is increased according to the first increment amount, until the preset static stability condition is met. This continuously reduces the power angle difference between the sending-end and receiving-end generators, ensuring the stability of the power angle within the synchronous grid. The system stability is calculated after a preset fault occurs in the DC channel with the largest transmission capacity. When the system does not meet the transient stability standard, the power of the sending-end generator is reduced according to the second reduction amount, and the power of the receiving-end generator is increased according to the second increment amount. This process is repeated until the system meets the transient stability standard. This invention can reasonably control the power of the AC and DC channels, and can reasonably determine the maximum transmission power of the AC channel under different DC channel power levels, improving the efficiency of the mode arrangement and maximizing the power transmission of the AC and DC sections. Attached Figure Description

[0035] Figure 1 This is a schematic flowchart of the method of the present invention;

[0036] Figure 2 This is a schematic diagram of the method flow according to an embodiment of the present invention;

[0037] Figure 3 This is a schematic diagram of the AC / DC cross-regional parallel power grid structure in the method of the present invention. Detailed Implementation

[0038] This invention provides a method for power allocation of AC / DC channels in a cross-regional parallel AC / DC power grid, in order to solve the technical problem that the existing technology cannot maximize the AC / DC cross-section power transmission capacity of the cross-regional parallel AC / DC power grid.

[0039] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0041] Please see Figure 1 This invention provides an embodiment of a power allocation method for AC / DC channels in an AC / DC inter-regional parallel power grid, comprising:

[0042] S100: Arrange the total power supply of the DC channel. The AC channel power is obtained by summing the maximum power supply capacity of a single DC circuit in the DC channel and the thermal stability value of all lines in the AC channel.

[0043] S200: Perform power flow calculation to obtain the maximum power angle difference of the generator and the power of each line in the AC channel. When the system does not meet the preset static stability conditions, reduce the power of the sending end generator according to the first reduction amount and increase the power of the receiving end generator according to the first adjustment increment. Repeat this step until the preset static stability conditions are met, and then execute S300.

[0044] S300: Calculate the system stability after a preset fault occurs in the DC with the largest power transmission capacity. When the system does not meet the transient stability standard, reduce the power of the sending end generator according to the second reduction amount and increase the power of the receiving end generator according to the second increment amount.

[0045] S400: Repeat S300 until the system meets the transient stability criterion, and obtain the maximum transmission power of the AC channel under the total power output of the DC channel.

[0046] In step S100, the AC channel power is calculated using the following formula:

[0047] P = P ac -0.5×P1;

[0048] Where P is the AC channel power, P ac P1 is the sum of the thermal stability values ​​of all lines in the AC channel, and P1 is the maximum power transmission capacity of a single DC circuit in the DC channel.

[0049] In this embodiment, each line has a fixed thermal stability value, which is related to the line type and is fixed. For example, if an AC channel has three lines with thermal stability values ​​a, b, and c, then the sum of the thermal stability values ​​of all lines in the AC channel, P, is... ac = a + b + c.

[0050] It should be noted that the total power output of the DC channel arranged in step S100 is a condition for simulation calculation in steps S200 and S300, and it affects the power output limit of the AC channel.

[0051] In this embodiment, before reducing the power of the sending-end generator according to the first reduction amount, the method further includes: calculating the first reduction amount; before increasing the power of the receiving-end generator according to the first increase amount, the method further includes: calculating the first increase amount.

[0052] In step S200, when the maximum power angle difference of the generator is greater than 90 degrees, or when there is an overloaded line in the AC channel with a line power greater than the line thermal stability value, the power of the sending end generator is reduced according to the first reduction amount, and the power of the receiving end generator is increased according to the first adjustment increment. This step is repeated until the preset static stability condition is met.

[0053] In this embodiment, the preset static stability condition is:

[0054] The generator's maximum power angle difference is greater than 90 degrees, and there is at least one overloaded line in the AC channel. The overloaded line is the line whose power is greater than the line's thermal stability value.

[0055] In this embodiment, the formula for calculating the first reduction amount is:

[0056] ΔP s =max{P s-r / 200×(maximum power angle difference-90), Σ(P overload -P N )};

[0057] Where, ΔP s For the first reduction, P s-r P is the difference between the output power of the sending end and the output power of the receiving end. overload P represents the power of the overloaded line. N This represents the thermal stability value of the overloaded circuit.

[0058] The formula for calculating the first adjustment increment is:

[0059] ΔP r =ΔP s ×95%;

[0060] Where, ΔP s For the first reduction, ΔP r This is the first adjustment increment.

[0061] In step S300, the system stability is calculated after a preset fault occurs in the DC power transmission capacity with the largest capacity. In a preferred embodiment, the preset fault is a single-pole blocking fault. The calculation of system stability mainly involves simulating a single-pole blocking fault in the DC power transmission capacity with the largest capacity, and then observing: the maximum power angle difference of all generators in the network, the maximum power angle difference curve, and obtaining the attenuation damping, voltage of each substation in the AC channel, etc.

[0062] In this embodiment, the transient stability criterion for determining whether the system is in a transient stable state is: the maximum power angle difference of the generator does not exceed 180 degrees, the maximum power angle difference oscillation damping ratio is greater than 3%, and the time when the voltage of each substation in the AC channel is lower than 0.75pu is less than 1 second.

[0063] It should be noted that the transient stability standard is determined based on GB 38755-2019 "Guidelines for the Safety and Stability of Power Systems" and "Guidelines for the Safety and Stability of Regional Power Grids". In the maximum power angle difference of generators, 90 degrees is the static stability limit of the power system, and 180 degrees is the limit to prevent out-of-step oscillations between generator units.

[0064] It should be noted that single-pole interlocking is generally required by safety and stability guidelines, meaning that transient stability standards must be met without any measures. Bipolar interlocking can meet transient stability standards after measures are taken, and the method arrangement is generally based on single-pole interlocking as the assessment requirement.

[0065] In this embodiment, the second reduction amount is the maximum single-unit capacity of the sending-end power supply; the second increase amount is the maximum single-unit capacity of the sending-end power supply. At this time, the adjustment amount of the generator power at both the sending end and the receiving end is the maximum single-unit capacity of the sending-end power supply.

[0066] This invention first arranges the total power transmission of the DC channel to obtain the power of the AC channel. When the preset static stability condition is not met, the power of the sending-end generator is reduced according to the first reduction amount, and the power of the receiving-end generator is increased according to the first increment amount, until the preset static stability condition is met. This continuously reduces the power angle difference between the sending-end and receiving-end generators, ensuring the stability of the power angle within the synchronous grid. The system stability is calculated after a preset fault occurs in the DC channel with the largest transmission capacity. When the system does not meet the transient stability standard, the power of the sending-end generator is reduced according to the second reduction amount, and the power of the receiving-end generator is increased according to the second increment amount. This process is repeated until the system meets the transient stability standard. This invention can reasonably control the power of the AC and DC channels, and can reasonably determine the maximum transmission power of the AC channel under different DC channel power levels, improving the efficiency of the mode arrangement and maximizing the power transmission of the AC and DC sections.

[0067] Please see Figure 2 Another embodiment of the AC / DC channel power allocation method for AC / DC inter-regional parallel power grid provided by the present invention is described in detail below:

[0068] Step 1: Calculate the maximum power transmission capacity P1 of a single DC circuit in the DC channel, and the sum of the thermal stability values ​​P of all AC lines. ac Arrange the DC channel to transmit power P dc1 The AC channel power is P ac -0.5*P1.

[0069] Step 2: Calculate the maximum power angle difference of all generators in the network and the power of each line in the AC channel through power flow calculation.

[0070] Step 3: If the maximum power angle difference of the entire network is greater than 90 degrees, or if the power of a line in the AC channel is greater than the thermal stability value of the line, then reduce the power of the sending-end generator and increase the power of the receiving-end generator. The formula for calculating the power adjustment of the sending-end generator is shown in (1), and the formula for calculating the power adjustment of the receiving-end generator is shown in (2). Repeat steps 2 and 3 until the maximum power angle difference of the entire network is less than 90 degrees and the power of all lines in the AC channel is less than the thermal stability value.

[0071] ΔP s =max{P s-r / 200×(maximum power angle difference-90), Σ(P overload -P N )}(1)

[0072] ΔP r =ΔP s ×95%(2)

[0073] Where P s-r P is the difference between the output power of the sending end and the output power of the receiving end. overload P represents the power of the overloaded line. N This represents the thermal stability value of the overloaded circuit.

[0074] Step 4: Calculate the system stability after a single-pole blocking fault occurs in the DC power supply with the largest transmission capacity. If the system does not meet the transient stability criteria, reduce the power of the sending-end generator and increase the power of the receiving-end generator. The adjustment amount of the sending-end and receiving-end generator power is the maximum single-unit capacity of the sending-end power supply. Repeat step 4 until the system stabilizes after the single-pole blocking fault.

[0075] The criteria for judging transient stability are: the maximum power angle difference of the generator does not exceed 180 degrees, the damping ratio of the maximum power angle difference oscillation is above 3%, and the time when the voltage of each substation in the AC channel is below 0.75pu is less than 1 second.

[0076] The AC / DC channel power allocation method for AC / DC cross-regional parallel power grid provided by this invention can reasonably determine the maximum transmission power of AC channels under different DC channel power, improve the work efficiency of personnel in the mode arrangement, and maximize the power transmission of AC / DC sections.

[0077] The following example illustrates the function of the invention: an AC / DC inter-regional parallel power grid, such as... Figure 3 As shown.

[0078] Step 1: The maximum power transmission capacity of a single DC line in the DC channel is 12000MW, and the sum of the thermal stability values ​​of all AC lines is 15000MW.

[0079] Step 2: The total power output of the DC transmission channel is 25,000 MW, and the initial power output of the AC transmission channel is 15,000 - 12,000 / 2 = 9,000 MW. Through power flow calculation, the maximum power angle difference of the entire network is 97°, and two AC lines in the AC transmission channel exceed their thermal stability values.

[0080] Step 3: Since the power output difference between the sending end and the receiving end is 28571MW, and the sum of the overload of the two lines Σ(Poverload-PN) is 600MW, the power of the generator in the sending end grid is reduced by 1000MW according to formula (1), and the power of the generator in the receiving end grid is increased by 950MW according to formula (2). Through power flow calculation, the maximum power angle difference of the entire network is 89°, and all AC lines in the AC channel do not exceed the thermal stability value. At this time, the power transmission capacity of the AC channel is reduced to 8000MW.

[0081] Step 4: Calculate the simulated unipolar blocking fault for the DC transmission with the largest capacity (i.e., a DC transmission capacity of 12000MW) and analyze the system's transient stability. The calculation results show that the maximum power angle difference of the generators is 156°, and the damping ratio for the maximum power angle difference oscillation is 5%. However, the voltage at points A and B of the AC channel remains below 0.75 seconds for more than 1 second. Therefore, the generator power of the sending-end grid is reduced by 700MW, and the generator power of the receiving-end grid is increased by 700MW. The power flow calculation is then performed again. The maximum power angle difference of the entire network is 86°, and all AC lines in the AC channel do not exceed the thermal stability value. Then, a transient stability simulation of the simulated unipolar blocking fault for the DC transmission capacity of 12000MW is conducted. The simulation results show that the system meets the transient stability criteria, and the AC channel power after the power reduction is 7300MW. Therefore, when the total power transmission capacity of the DC channel is arranged to be 25000MW, the AC channel power should be controlled below 7300MW.

[0082] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0083] In the embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or electrical connection shown or discussed between each other can be through some interfaces; the indirect coupling or electrical connection between devices or units can be electrical, mechanical, or other forms.

[0084] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0085] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0086] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0087] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for power allocation of AC / DC channels in an AC / DC inter-regional parallel power grid, characterized in that, include: S1: Arrange the total power supply of the DC channel. The AC channel power is obtained by summing the maximum power supply capacity of a single DC circuit in the DC channel and the thermal stability value of all lines in the AC channel. S2: Perform power flow calculations to obtain the maximum power angle difference of the generator and the power of each line in the AC channel. When the system does not meet the preset static stability conditions, reduce the power of the sending end generator according to the first reduction amount and increase the power of the receiving end generator according to the first adjustment increment. Repeat this step until the preset static stability conditions are met, and then execute S3. S3: Calculate the system stability after a preset fault occurs in the DC with the largest power transmission capacity. When the system does not meet the transient stability standard, reduce the power of the sending end generator according to the second reduction amount and increase the power of the receiving end generator according to the second increment amount. S4: Repeat S3 until the system meets the transient stability criterion to obtain the maximum transmission power of the AC channel under the total power output of the DC channel; The preset static stability condition is: The generator's maximum power angle difference is greater than 90 degrees, and there is at least one overloaded line in the AC channel, wherein the overloaded line is the line whose power is greater than the line's thermal stability value. Before reducing the power output of the sending-end generator according to the first reduction amount, the following steps are also included: Calculate the first reduction amount; Before increasing the receiving-end generator power according to the first adjustment increment, the following also applies: Calculate the first adjustment increment; The formula for calculating the first reduction is: ； Where, ΔP s For the first reduction, P s-r P is the difference between the output power of the sending end and the output power of the receiving end. overload P represents the power of the overloaded line. N This represents the thermal stability value of the overloaded circuit. The formula for calculating the first adjustment increment is: ； Where, ΔP s For the first reduction, ΔP r This is the first adjustment increment; The second reduction amount is: Maximum single-unit capacity of the sending-end power supply; The second adjustment increment is: Maximum single-unit capacity of the power supply at the sending end.

2. The AC / DC channel power allocation method for AC / DC inter-regional parallel power grids according to claim 1, characterized in that, Calculate the AC channel power using the following formula: ； Where P is the AC channel power, Pac is the sum of the line thermal stability values ​​of all lines in the AC channel, and P1 is the maximum power transmission capacity of a single DC circuit in the DC channel.

3. The AC / DC channel power allocation method for AC / DC inter-regional parallel power grids according to any one of claims 1-2, characterized in that, The preset fault is: Single-pole interlocking fault.

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