New Energy Island Flexible DC Transmission Voltage Characteristics Evaluation Method

Abstract

In the new energy island flexible DC transmission voltage characteristic evaluation method provided by this application, according to the voltage characteristic evaluation model, as well as the voltage change ranges on the new energy side and the flexible DC side of the new energy island system, a system stable operation power circle is drawn. The voltage characteristic evaluation model is constructed based on the total impedance of the new energy island system, the flexible DC absorbed power, and the voltages on the new energy side and the flexible DC side. According to the maximum steady-state reactive power output of the flexible DC and the system stable operation power circle, the maximum transmission power of the new energy island system is calculated, and the system transmission power of the new energy island system is determined. If the system transmission power is not greater than the maximum transmission power, the reactive power compensation capacity of the transmission voltage of the new energy island system is calculated, and an evaluation result of system voltage stability is generated; otherwise, an evaluation result of system voltage instability is generated. In this way, the reactive power capacity of the flexible DC and the impedance of the new energy collection network can be comprehensively considered to accurately evaluate the voltage stability of the new energy power station.

Description

Technical Field

[0001] The present application relates to the technical field of flexible DC power transmission, and particularly to a method for evaluating the voltage characteristics of flexible DC transmission from a new energy island. Background Art

[0002] In recent years, with the increasing global demand for clean energy, the construction of new energy power stations has shown a booming trend. In large-scale new energy power stations, flexible DC technology has been introduced as the transmission channel for new energy, which can replace traditional rotating equipment to become the only stable AC voltage source in the system. However, in some remote areas such as "sand, gobi, and desert", due to the harsh geographical environment and the difficulty of site selection for power station construction, there is a long electrical distance between the new energy collection area and the flexible DC converter station. At the same time, affected by the resource distribution, the new energy power stations are widely distributed, and the collection electrical distance is also large.

[0003] The long electrical distance between the new energy unit and the flexible DC converter station will lead to a large amount of reactive power consumption, which will further cause the voltage at the power supply side to drop or even collapse unstably, thus limiting the active power transmission capacity of the new energy. Therefore, in order to ensure that the new energy in remote areas does not have the problem of power output limitation due to voltage stability, it is necessary to evaluate the voltage of the flexible DC transmission system, so as to adjust the configuration of the flexible DC transmission system for the new energy island power station according to the evaluation results. However, the current voltage characteristic evaluation method only equivalent the new energy power station to a PQ node, without considering the flexible DC reactive power capacity and the impedance of the new energy collection network. Summary of the Invention

[0004] The purpose of the present application aims to at least solve one of the above technical defects, especially the technical defect that only the new energy power station is equivalent to a PQ node in the prior art, without considering the flexible DC reactive power capacity and the impedance of the new energy collection network.

[0005] In the first aspect, the present application provides a method for evaluating the voltage characteristics of flexible DC transmission from a new energy island, the method comprising:

[0006] According to the constructed voltage characteristic evaluation model and the pre-determined voltage change ranges of the new energy side and the flexible DC side of the new energy island system, draw the system stable operation power circle of the new energy island system, where the voltage characteristic evaluation model is constructed based on the total impedance of the new energy island system, the power absorbed by the flexible DC, the voltage of the new energy side, and the voltage of the flexible DC side;

[0007] According to the pre-determined maximum steady-state reactive power output of the flexible DC of the new energy island system and the system stable operation power circle, calculate the maximum power output of the new energy island system, and determine the system power output of the new energy island system;

[0008] If the power output of the system is less than or equal to the maximum power output, the reactive power compensation capacity of the output voltage of the new energy island system is calculated according to the pre-determined system reactive power parameters, the new energy side voltage, and the flexible DC side voltage, and an evaluation result of system voltage stability is generated;

[0009] If the power output of the system is greater than the maximum power output, an evaluation result of system voltage instability is generated.

[0010] In one embodiment, the flexible DC absorbed power includes the flexible DC absorbed active power and the flexible DC absorbed reactive power;

[0011] The construction process of the voltage characteristic evaluation model includes:

[0012] The voltage characteristic evaluation model is constructed according to the following expression:

[0013]

[0014] In the formula, P c ′ represents the ratio of the flexible DC absorbed active power to the rated capacity of the new energy island system, that is, the relative active power. The rated capacity is the ratio of the square of the rated voltage of the new energy island system to the imaginary part of the total impedance. Q c ′ represents the ratio of the flexible DC absorbed reactive power to the rated capacity of the new energy island system, that is, the relative reactive power. K1 represents the ratio of the new energy side voltage to the rated voltage of the new energy island system, that is, the per-unit value of the power supply side voltage. K2 represents the ratio of the flexible DC side voltage to the rated voltage of the new energy island system, that is, the per-unit value of the flexible DC port voltage.

[0015] In one embodiment, the step of calculating the maximum power output of the new energy island system according to the pre-determined maximum steady-state reactive power output of the flexible DC of the new energy island system and the system stable operation power circle includes:

[0016] The maximum power output of the new energy island system is calculated according to the following expression:

[0017]

[0018] Among them, P cmax represents the maximum power output. S0 represents the rated capacity of the new energy island system. The rated capacity is the ratio of the square of the rated voltage of the new energy island system to the imaginary part of the total impedance. Q c0 represents the maximum steady-state reactive power output of the flexible DC. Q c ′0 represents the relative value of the maximum steady-state reactive power output of the HVDC, Q c ′ cr represents the relative value of the reactive power at the intersection of the system stable operation power circle.

[0019] In one embodiment, the system reactive power parameters include the reactive power consumed by the shunt reactors at both ends of the AC long line, the reactive power at the DC system ports, and the charging power of the AC long line;

[0020] The step of calculating the reactive power compensation capacity of the new energy island system output voltage according to the pre-determined system reactive power parameters, the new energy side voltage, and the HVDC side voltage includes:

[0021] Calculate the reactive power compensation capacity according to the following expression:

[0022]

[0023] In the formula, Q CG represents the reactive power compensation capacity, Q cr represents the reactive power consumed by the shunt reactors at both ends of the AC long line, Q c represents the reactive power at the DC system ports, Q LB represents the charging power of the AC long line, U s ∠0 ° represents the complex representation of the system side voltage of the AC long line, where U s is its amplitude, representing the new energy side voltage, ∠0 ° is its phase angle, U c ∠-δ represents the complex representation of the output voltage of the new energy island system, where U c is its amplitude, representing the HVDC side voltage, ∠-δ is its phase angle, X L represents the imaginary part of the total impedance.

[0024] In a second aspect, the present application provides a device for evaluating the characteristics of the output voltage of a new energy island flexible DC, the device includes:

[0025] A system stable operation power circle drawing module, configured to draw the system stable operation power circle of the new energy island system according to the constructed voltage characteristic evaluation model and the pre-determined change ranges of the new energy side voltage and the HVDC side voltage of the new energy island system, and the voltage characteristic evaluation model is constructed based on the total impedance, the HVDC absorption power, the new energy side voltage, and the HVDC side voltage of the new energy island system;

[0026] The maximum power output calculation module is used to calculate the maximum power output of the new energy island system according to the pre-determined maximum reactive power output in the steady state of the flexible DC of the new energy island system and the system stable operation power circle, and determine the system power output of the new energy island system;

[0027] The first voltage characteristic evaluation module is used to calculate the reactive power compensation capacity of the output voltage of the new energy island system according to the pre-determined system reactive power parameters, the new energy side voltage and the flexible DC side voltage if the system power output is less than or equal to the maximum power output, and generate an evaluation result of system voltage stability;

[0028] The second voltage characteristic evaluation module is used to generate an evaluation result of system voltage instability if the system power output is greater than the maximum power output.

[0029] In one embodiment, the flexible DC absorption power includes flexible DC absorption active power and flexible DC absorption reactive power;

[0030] The system stable operation power circle drawing module includes:

[0031] The voltage characteristic evaluation module construction unit is used to construct the voltage characteristic evaluation model according to the following expression:

[0032]

[0033] In the formula, P c ′ represents the ratio of the flexible DC absorption active power to the rated capacity of the new energy island system, that is, the relative active power. The rated capacity is the ratio of the square of the rated voltage of the new energy island system to the imaginary part of the total impedance. Q c ′ represents the ratio of the flexible DC absorption reactive power to the rated capacity of the new energy island system, that is, the relative reactive power. K1 represents the ratio of the new energy side voltage to the rated voltage of the new energy island system, that is, the per-unit value of the power supply side voltage. K2 represents the ratio of the flexible DC side voltage to the rated voltage of the new energy island system, that is, the per-unit value of the flexible DC port voltage.

[0034] In one embodiment, the maximum power output calculation module includes:

[0035] The maximum power output calculation unit is used to calculate the maximum power output of the new energy island system according to the following expression:

[0036]

[0037] Among them, P cmaxrepresents the maximum power output, S0 represents the rated capacity of the new energy island system, and the rated capacity is the ratio of the square of the rated voltage of the new energy island system to the imaginary part of the total impedance, Q c0 represents the maximum steady-state reactive power output of the flexible DC, Q c ′ 0 represents the relative value of the maximum steady-state reactive power output of the flexible DC, Q c ′ cr represents the relative value of the reactive power at the intersection of the system stable operation power circle.

[0038] In one embodiment, the system reactive power parameters include the reactive power consumed by the shunt reactors at both ends of the AC long line, the reactive power at the DC system port, and the charging power of the AC long line;

[0039] The first voltage characteristic evaluation module includes:

[0040] A reactive power compensation capacity calculation unit for calculating the reactive power compensation capacity according to the following expression:

[0041]

[0042] In the formula, Q CG represents the reactive power compensation capacity, Q cr represents the reactive power consumed by the shunt reactors at both ends of the AC long line, Q c represents the reactive power at the DC system port, Q LB represents the charging power of the AC long line, U s ∠0 ° represents the complex representation of the system-side voltage of the AC long line, where U s is its amplitude, representing the new energy side voltage, ∠0 ° is its phase angle, U c ∠-δ represents the complex representation of the output voltage of the new energy island system, where U c is its amplitude, representing the flexible DC side voltage, ∠-δ is its phase angle, X L represents the imaginary part of the total impedance.

[0043] In a third aspect, the present application provides a storage medium storing computer-readable instructions, which, when executed by one or more processors, cause the one or more processors to execute the steps of the new energy island flexible DC output voltage characteristic evaluation method according to any one of the above embodiments.

[0044] In a fourth aspect, the present application provides a computer device, including: one or more processors, and a memory;

[0045] The computer-readable instructions are stored in the memory, and when the computer-readable instructions are executed by the one or more processors, the steps of the new energy island flexible DC transmission voltage characteristic evaluation method described in any one of the above embodiments are executed.

[0046] As can be seen from the above technical solutions, the embodiments of the present application have the following advantages:

[0047] In a new energy island flexible DC transmission voltage characteristic evaluation method provided by the present application, according to the constructed voltage characteristic evaluation model, and the pre-determined voltage change range on the new energy side and the voltage change range on the flexible DC side of the new energy island system, the system stable operation power circle of the new energy island system is drawn. The voltage characteristic evaluation model is constructed based on the total impedance of the new energy island system, the flexible DC absorption power, the voltage on the new energy side, and the voltage on the flexible DC side; according to the pre-determined maximum steady-state reactive power output of the flexible DC of the new energy island system, and the system stable operation power circle, the maximum transmission power of the new energy island system is calculated, and the system transmission power of the new energy island system is determined; if the system transmission power is less than or equal to the maximum transmission power, then according to the pre-determined system reactive power parameters, the new energy side power parameters, and the flexible DC side power parameters, the reactive power compensation capacity of the transmission voltage of the new energy island system is calculated, and an evaluation result of system voltage stability is generated; if the system transmission power is greater than the maximum transmission power, an evaluation result of system voltage instability is generated. The voltage characteristic evaluation model in this method takes into account the flexible DC reactive power capability and the new energy collection network impedance, making the model closer to the actual situation, so as to be able to more accurately evaluate the voltage stability of the new energy power station; by calculating the maximum transmission power of the system, the operation limit of the system can be determined, so as to more accurately predict the relationship between the system transmission power and the maximum transmission power limit, and adjust the configuration of the new energy power station island flexible DC transmission system according to the evaluation result. Description of the Drawings

[0048] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0049] Figure 1 It is a schematic flow chart of the new energy island flexible DC transmission voltage characteristic evaluation method provided by the embodiments of the present application;

[0050] Figure 2 It is an equivalent circuit diagram of the voltage characteristic evaluation of the new energy island flexible DC transmission system provided by the embodiments of the present application.

[0051] Figure 3 One of the example diagrams of the system stable operation power circle of the new energy island system provided by the embodiment of the present application;

[0052] Figure 4 Another example diagram of the system stable operation power circle of the new energy island system provided by the embodiment of the present application;

[0053] Figure 5 Schematic diagram of the structure of the new energy island flexible DC transmission voltage characteristic evaluation device provided by the embodiment of the present application;

[0054] Figure 6 Internal structure diagram of the computer device provided by the embodiment of the present application. Specific implementation manners

[0055] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0056] The present application provides a method for evaluating the new energy island flexible DC transmission voltage characteristics. The following embodiments are described by taking the application of this method to a computer device as an example. It can be understood that the computer device can be various devices with data processing functions, and can be, but not limited to, a single server, a server cluster, a personal laptop computer, a desktop computer, etc. As Figure 1 shown, the method may include the following steps:

[0057] S101: According to the constructed voltage characteristic evaluation model, and the pre-determined voltage change range on the new energy side and the voltage change range on the flexible DC side of the new energy island system, draw the system stable operation power circle of the new energy island system.

[0058] Among them, the voltage characteristic evaluation model is constructed based on the total impedance, the flexible DC absorption power, the voltage on the new energy side, and the voltage on the flexible DC side of the new energy island system;

[0059] Among them, the new energy island system refers to a power system composed of large-scale new energy power stations, which can operate independently and supply power to the external power grid without relying on the support of the traditional power grid. The new energy side voltage variation range refers to the variation range of the AC voltage output by the new energy power station relative to its rated voltage in the new energy island system. The flexible DC side voltage variation range refers to the variation range of the AC voltage output by the flexible DC converter station relative to its rated voltage in the new energy island system. The system stable operation power circle refers to the power range that can maintain the steady-state operation of the system determined by comprehensively considering the voltage characteristics and equipment capacity limitations in the new energy island flexible DC transmission system. In one example, this power range is usually represented by drawing a power circle diagram, with the abscissa representing the active power and the ordinate representing the reactive power. The total impedance of the new energy island system refers to the system impedance composed of the AC line and the leakage reactance of the transformer between the new energy power station and the flexible DC converter station. The flexible DC absorbed power refers to the power absorbed by the flexible DC converter during the process of converting AC to DC or DC to AC in flexible DC power transmission. The new energy side voltage refers to the voltage in the power system connected to the new energy generation equipment. The flexible DC side voltage refers to the voltage in the power system connected to the flexible DC converter in the flexible DC power transmission system.

[0060] In this step, first, the new energy side voltage variation range and the flexible DC side voltage variation range can be determined. For example, assume that the new energy side voltage variation range is ±5% and the flexible DC side voltage variation range is ±3%. Combining the constructed voltage characteristic evaluation model, draw the system stable operation power circle of the new energy island system. In one example, on the complex plane, with the new energy side voltage as the horizontal axis and the flexible DC side voltage as the vertical axis, a voltage space diagram can be drawn, and according to the known conditions, the stable operation power circle of the new energy island system can be drawn on this diagram.

[0061] S102: Calculate the maximum power output of the new energy island system and determine the system power output of the new energy island system according to the pre-determined maximum steady-state reactive power output of the flexible DC in the new energy island system and the system stable operation power circle.

[0062] Among them, the maximum steady-state reactive power output of the flexible DC refers to the maximum reactive power that the flexible DC converter station can provide in the new energy island system. The maximum steady-state reactive power output of the flexible DC can usually be determined by the reactive power compensation device and control strategy inside the flexible DC station and the device tolerance. The maximum power output of the new energy island system refers to the maximum active power that the new energy island system can transmit to the external power grid on the premise of meeting the system stable operation power circle and the maximum steady-state reactive power output of the flexible DC. The system power output refers to the active power actually transmitted by the system to the external power grid at the current moment.

[0063] In this step, after determining the maximum steady-state reactive power output of the flexible DC in the new energy island system and the power circle for stable system operation, the maximum power output of the new energy island system can be calculated based on the maximum steady-state reactive power output of the flexible DC and the power circle for stable system operation. The power output of the system is affected by the demands and constraints of the external power grid and the internal electrical parameters of the system. In one example, the power output of the system can be determined by real-time monitoring and adjustment of the system operating state.

[0064] S103: If the power output of the system is less than or equal to the maximum power output, calculate the reactive power compensation capacity of the output voltage of the new energy island system based on the pre-determined system reactive parameters, the voltage on the new energy side, and the voltage on the flexible DC side, and generate an evaluation result of system voltage stability.

[0065] Among them, the system reactive parameters refer to the parameters that describe the system's demand for and tolerance of reactive power. Common system reactive parameters include power factor, reactive power, and reactive power margin, etc. The reactive power compensation capacity refers to the ability of the system to require reactive power.

[0066] In this step, when the power output of the system is less than or equal to the maximum power output, calculate the reactive power compensation capacity of the output voltage of the new energy island system through the system reactive parameters, the electrical parameters on the new energy side, and the electrical parameters on the flexible DC side, so as to configure a reactive power compensation device for the new energy island system according to the calculated reactive power compensation capacity, thereby maintaining voltage stability. At the same time, an evaluation result of system voltage stability can also be generated.

[0067] S104: If the power output of the system is greater than the maximum power output, generate an evaluation result of system voltage instability.

[0068] In this step, when the power output of the system is greater than the maximum power output, it indicates that the system voltage is unstable. Therefore, an evaluation result of system voltage instability can be generated. Further, if the power output of the island system is greater than the maximum power output, the system cannot maintain voltage stability and may undergo instability and collapse. Generating an evaluation result of system voltage instability can remind relevant personnel to re-conduct the configuration planning for the sending-end power grid and increase the AC system configuration to improve the voltage characteristics.

[0069] In the above embodiments, according to the constructed voltage characteristic evaluation model, and the pre-determined voltage change ranges on the new energy side and the flexible DC side of the new energy island system, the system stable operation power circle of the new energy island system is drawn. The voltage characteristic evaluation model is constructed based on the total impedance of the new energy island system, the flexible DC absorbed power, the voltage on the new energy side, and the voltage on the flexible DC side; according to the pre-determined maximum steady-state reactive power output of the flexible DC of the new energy island system, and the system stable operation power circle, the maximum power output of the new energy island system is calculated, and the system power output of the new energy island system is determined; if the system power output is less than or equal to the maximum power output, then according to the pre-determined system reactive power parameters, the new energy side power parameters, and the flexible DC side power parameters, the reactive power compensation capacity of the output voltage of the new energy island system is calculated, and an evaluation result of system voltage stability is generated; if the system power output is greater than the maximum power output, then an evaluation result of system voltage instability is generated. The voltage characteristic evaluation model in this method takes into account the flexible DC reactive power capacity and the new energy collection network impedance, making the model closer to the actual situation, so as to more accurately evaluate the voltage stability of the new energy power station; by calculating the maximum power output of the system, the operation limit of the system can be determined, so as to more accurately predict the relationship between the system power output and the maximum power transmission limit, and adjust the configuration of the new energy power station island flexible DC output system according to the evaluation result.

[0070] In one embodiment, the flexible DC absorbed power includes the flexible DC absorbed active power and the flexible DC absorbed reactive power;

[0071] The construction process of the voltage characteristic evaluation model includes:

[0072] Construct the voltage characteristic evaluation model according to the following expression:

[0073]

[0074] In the formula, P c ′ represents the ratio of the flexible DC absorbed active power to the rated capacity of the new energy island system, that is, the relative active power. The rated capacity is the ratio of the square of the rated voltage of the new energy island system to the imaginary part of the total impedance. Q c ′ represents the ratio of the flexible DC absorbed reactive power to the rated capacity of the new energy island system, that is, the relative reactive power. K1 represents the ratio of the voltage on the new energy side to the rated voltage of the new energy island system, that is, the per-unit value of the power supply side voltage. K2 represents the ratio of the voltage on the flexible DC side to the rated voltage of the new energy island system, that is, the per-unit value of the flexible DC port voltage.

[0075] Among them, the flexible DC absorption power includes the flexible DC absorption reactive power and the flexible DC absorption active power. The flexible DC absorption reactive power refers to the reactive power absorbed by the flexible DC converter station from the new energy power station or the external power grid. The flexible DC absorption active power refers to the active power absorbed by the flexible DC converter in the flexible DC transmission during the process of converting alternating current to direct current.

[0076] Specifically, based on the steady-state equivalent principle, a large-scale new energy power station is equivalently aggregated into 1 power source, and the steady-state voltage analysis of the flexible DC transmission system for a new energy island is carried out using the equivalent circuit shown as follows. Figure 2 In the figure, U Figure 2 is the voltage on the new energy side, U s is the voltage on the flexible DC side, Z c is the total system impedance between the power source side and the flexible DC side, including the AC line and the leakage reactance of the transformer. P L , P s , P c are the active power output by the power source and absorbed by the flexible DC respectively, and Q s , Q c are the reactive power output by the power source and absorbed by the flexible DC respectively. It is assumed that the phase angle of the voltage on the power source side is zero, and the phase angle of the voltage on the flexible DC side lags by δ. It should be noted that sufficient reactive power compensation devices will be configured inside the new energy power station to ensure that the voltage at the 220 kV grid connection point can vary between 0.95 and 1.05 times the rated voltage according to the grid dispatching instructions. Therefore, the voltage phasor at the 220 kV grid connection point of the new energy power station is the phasor of U s in the equivalent circuit. The collector lines between each power station and the collection station are reduced to the Z L total impedance according to the principle of consistent power loss.

[0077] Considering that Z L includes the leakage reactance of transformers at all levels and AC lines of 220 kV and above, and the overall reactance is much larger than the resistance. Therefore, the resistance is ignored, and Z L can be approximately equivalent to jX L . The power absorption model on the flexible DC side is established as shown in the following expression:

[0078]

[0079] The corresponding active power is as follows:

[0080]

[0081] The corresponding reactive power is as follows:

[0082]

[0083] Combining the active power and the reactive power, we can get:

[0084]

[0085] In the new - energy island - connected power transmission system, since the flexible DC will provide a stable AC voltage for the new energy through its own control, it can be assumed that U c is a determined value. Define the ratios of the voltages on the new - energy side and the flexible - DC side to the rated voltage, then:

[0086]

[0087] Let We can get:

[0088]

[0089] In one example, as Figure 3 shown, based on the voltage - characteristic evaluation model, the bus voltage on the new - energy side is generally controlled within 500 kV - 550 kV, and the bus of the flexible DC converter station is generally controlled within 525 kV - 535 kV. Then the range of K1 can be determined as 0.95 - 1.05, and the range of K2 can be determined as 1.0 - 1.02. Set K1 to three levels of 0.95, 1.00, and 1.05, and K2 to two levels of 1.0 and 1.02. Based on the voltage - characteristic evaluation model, draw the power circle for the stable operation of the system. Figure 2 In it, the solid lines and dashed lines from the outside to the inside represent the power - supply - side voltages of 1.05×525, 1.0×525, and 0.95×525 kV respectively, and the solid lines and dashed lines represent the flexible - DC - side voltages of 1.0×525 and 1.02×525 kV respectively.

[0090] In this embodiment, the voltage - characteristic evaluation model takes into account the influence of the impedance of the collector lines among new - energy power stations and collection stations, is closer to the characteristics of the actual new - energy island flexible - DC power - transmission system, and can more accurately describe the voltage characteristics of the new - energy power - transmission system.

[0091] In one embodiment, the step of calculating the maximum power output of the new - energy island system according to the pre - determined maximum steady - state reactive power output of the flexible DC in the new - energy island system and the power circle for the stable operation of the system includes:

[0092] Calculate the maximum power output of the new - energy island system according to the following expression:

[0093]

[0094] Where, P cmax represents the maximum power output, S0 represents the rated capacity of the new - energy island system, and the rated capacity is the ratio of the square of the rated voltage of the new - energy island system to the imaginary part of the total impedance. Q c0 represents the maximum steady - state reactive power output of the flexible DC, Q c ′0 represents the relative value of the maximum steady-state reactive power output of the flexible DC, Q c ′ cr The relative value of the reactive power at the intersection of the power circle where the system operates stably.

[0095] Specifically, as Figure 4 shown, considering the power output of the flexible DC multi-receiving island system in the actual new energy island flexible DC transmission system, and the reactive power absorbed or emitted by the flexible DC cannot be too large due to equipment capacity limitations, so the part of the operating power circle with the abscissa greater than zero and the ordinate greater than -1 is intercepted and magnified. Set the maximum reactive power output limit at ±Q c0 when the system operates stably, the power characteristic region of the system is Figure 4 the shaded area shown in, and the corresponding maximum transmission power is calculated using the voltage characteristic evaluation model as follows:

[0096]

[0097] where Q c ′ cr The expression of is as follows:

[0098]

[0099] In the formula, K 21 represents the minimum value of K2, which is 1.0, and K 22 represents the maximum value of K2, which is 1.02.

[0100] In this embodiment, when calculating the maximum power transmission limit, considering the limitation of the maximum steady-state reactive power output of the flexible DC based on equipment capacity is closer to the operating characteristics of the actual new energy island flexible DC transmission system.

[0101] In one embodiment, the reactive power parameters of the system include the reactive power consumed by the shunt reactors at both ends of the AC long line, the reactive power at the DC system port, and the charging power of the AC long line;

[0102] The step of calculating the reactive power compensation capacity of the output voltage of the new energy island system according to the pre-determined system reactive power parameters, the voltage on the new energy side, and the voltage on the flexible DC side includes:

[0103] Calculate the reactive power compensation capacity according to the following expression:

[0104]

[0105] In the formula, Q CG represents the reactive power compensation capacity, and Q cr represents the reactive power consumed by the shunt reactors at both ends of the AC long line, and Q cIndicates the reactive power magnitude of the DC system port, Q LB Indicates the charging power of the AC long line, U s ∠0 ° Indicates the complex representation of the system-side voltage of the AC long line, where U s Is its amplitude, indicating the new energy side voltage, ∠0 ° Is its phase angle, U c ∠-δ indicates the complex representation of the outgoing voltage of the new energy island system, where U c Is its amplitude, indicating the voltage on the flexible DC side, ∠-δ is its phase angle, X L Indicates the imaginary part of the total impedance.

[0106] In this embodiment, the system reactive power configuration requirements are proposed, which are closer to the actual operating characteristics of the new energy island flexible DC outgoing system.

[0107] Next, the new energy island flexible DC outgoing voltage characteristic evaluation device provided by the embodiment of the present application will be described. The new energy island flexible DC outgoing voltage characteristic evaluation device described below can be mutually corresponding and referred to the new energy island flexible DC outgoing voltage characteristic evaluation method described above. As Figure 5 Shown, a new energy island flexible DC outgoing voltage characteristic evaluation device, the device includes:

[0108] System stable operation power circle drawing module 201, configured to draw the system stable operation power circle of the new energy island system according to the constructed voltage characteristic evaluation model and the pre-determined new energy side voltage change range and flexible DC side voltage change range of the new energy island system, and the voltage characteristic evaluation model is constructed based on the total impedance, flexible DC absorption power, new energy side voltage and flexible DC side voltage of the new energy island system;

[0109] Maximum power output calculation module 202, configured to calculate the maximum power output of the new energy island system according to the pre-determined maximum steady-state reactive power output of the flexible DC of the new energy island system and the system stable operation power circle, and determine the system power output of the new energy island system;

[0110] First voltage characteristic evaluation module 203, configured to calculate the reactive power compensation capacity of the outgoing voltage of the new energy island system according to the pre-determined system reactive power parameters, the new energy side voltage and the flexible DC side voltage if the system power output is less than or equal to the maximum power output, and generate an evaluation result of system voltage stability;

[0111] Second voltage characteristic evaluation module 204, configured to generate an evaluation result of system voltage instability if the system power output is greater than the maximum power output.

[0112] In one embodiment, the HVDC absorption power includes the HVDC absorption active power and the HVDC absorption reactive power;

[0113] The system stable operation power circle drawing module 201 includes:

[0114] A voltage characteristic evaluation module construction unit, configured to construct the voltage characteristic evaluation model according to the following expression:

[0115]

[0116] In the formula, P c ′ represents the ratio of the HVDC absorption active power to the rated capacity of the new energy island system, that is, the relative active power, and the rated capacity is the ratio of the square of the rated voltage of the new energy island system to the imaginary part of the total impedance, Q c ′ represents the ratio of the HVDC absorption reactive power to the rated capacity of the new energy island system, that is, the relative reactive power, K1 represents the ratio of the voltage on the new energy side to the rated voltage of the new energy island system, that is, the per-unit value of the power supply side voltage, and K2 represents the ratio of the voltage on the HVDC side to the rated voltage of the new energy island system, that is, the per-unit value of the HVDC port voltage.

[0117] In one embodiment, the maximum power output calculation module 202 includes:

[0118] A maximum power output calculation unit, configured to calculate the maximum power output of the new energy island system according to the following expression:

[0119]

[0120] Among them, P cmax represents the maximum power output, S0 represents the rated capacity of the new energy island system, and the rated capacity is the ratio of the square of the rated voltage of the new energy island system to the imaginary part of the total impedance, Q c0 represents the maximum steady-state reactive power output of the HVDC, Q c ′ 0 represents the relative value of the maximum steady-state reactive power output of the HVDC, Q c ′ cr represents the relative value of the reactive power at the intersection of the system stable operation power circle.

[0121] In one embodiment, the system reactive power parameters include the reactive power consumed by the shunt reactors at both ends of the AC long line, the reactive power at the DC system port, and the charging power of the AC long line;

[0122] The first voltage characteristic evaluation module 203 includes:

[0123] A reactive power compensation capacity calculation unit for calculating the reactive power compensation capacity according to the following expression:

[0124]

[0125] In the formula, Q CG represents the reactive power compensation capacity, Q cr represents the reactive power consumed by the shunt reactor at both ends of the AC long line, Q c represents the reactive power at the DC system port, Q LB represents the charging power of the AC long line, U s ∠0 ° represents the complex representation of the system-side voltage of the AC long line, where U s is its amplitude, representing the new energy-side voltage, ∠0 ° is its phase angle, U c ∠-δ represents the complex representation of the outgoing voltage of the new energy island system, where U c is its amplitude, representing the voltage on the flexible DC side, ∠-δ is its phase angle, X L represents the imaginary part of the total impedance.

[0126] In one embodiment, the present application further provides a storage medium in which computer-readable instructions are stored. When the computer-readable instructions are executed by one or more processors, one or more processors are caused to execute the steps of the new energy island flexible DC outgoing voltage characteristic evaluation method as described in any one of the above embodiments.

[0127] In one embodiment, the present application further provides a computer device in which computer-readable instructions are stored. When the computer-readable instructions are executed by one or more processors, one or more processors are caused to execute the steps of the new energy island flexible DC outgoing voltage characteristic evaluation method as described in any one of the above embodiments.

[0128] Schematically, as Figure 6 shown, Figure 6 is an internal structure schematic diagram of a computer device provided by an embodiment of the present application. The computer device 300 can be provided as a server. Referring to Figure 6, the computer device 300 includes a processing component 302, which further includes one or more processors, and memory resources represented by a memory 301 for storing instructions executable by the processing component 302, such as application programs. The application programs stored in the memory 301 may include one or more modules each corresponding to a set of instructions. In addition, the processing component 302 is configured to execute instructions to perform the new energy island flexible DC output voltage characteristic evaluation method of any of the above embodiments.

[0129] The computer device 300 may further include a power supply component 303 configured to perform power management of the computer device 300, a wired or wireless network interface 304 configured to connect the computer device 300 to a network, and an input / output (I / O) interface 305. The computer device 300 may operate based on an operating system stored in the memory 301, such as Windows Server TM, Mac OS XTM, Unix TM, Linux TM, Free BSDTM or the like.

[0130] Those skilled in the art can understand that Figure 6 the structure shown in is only a block diagram of some structures related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine some components, or have different component arrangements.

[0131] Finally, it should also be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the element. In this article, "a", "one", "the", "this" and "its" may also include the plural form unless the context clearly indicates otherwise. Multiple means at least two cases, such as 2, 3, 5 or 8, etc. "And / or" includes any and all combinations of the related listed items.

[0132] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The various embodiments can be combined as needed, and the same or similar parts can be referred to each other.

[0133] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for evaluating the voltage characteristics of a flexible DC transmission from a new energy island, characterized in that, The method includes: According to the constructed voltage characteristic evaluation model, and the pre-determined voltage change ranges of the new energy side and the flexible DC side of the new energy island system, draw the system stable operation power circle of the new energy island system. The voltage characteristic evaluation model is constructed based on the total impedance, flexible DC absorbed power, new energy side voltage and flexible DC side voltage of the new energy island system. The flexible DC absorbed power includes flexible DC absorbed active power and flexible DC absorbed reactive power; The construction process of the voltage characteristic evaluation model includes: Construct the voltage characteristic evaluation model according to the following expression: Wherein, P c ′ represents the ratio of the active power absorbed by the VSC-HVDC to the rated capacity of the new energy island system, i.e., the relative active power. The rated capacity is the ratio of the square of the rated voltage of the new energy island system to the imaginary part of the total impedance. Q c ′ represents the ratio of the reactive power absorbed by the VSC-HVDC to the rated capacity of the new energy island system, i.e., the relative reactive power. K1 represents the ratio of the voltage on the new energy side to the rated voltage of the new energy island system, i.e., the per-unit value of the voltage on the power supply side. K2 represents the ratio of the voltage on the VSC-HVDC side to the rated voltage of the new energy island system, i.e., the per-unit value of the voltage at the VSC-HVDC port; According to the pre-determined maximum steady-state reactive power output of the flexible DC of the new energy island system and the system stable operation power circle, calculate the maximum power output of the new energy island system, and determine the system power output of the new energy island system; If the system power output is less than or equal to the maximum power output, calculate the reactive power compensation capacity of the output voltage of the new energy island system according to the pre-determined system reactive power parameters, the new energy side voltage and the flexible DC side voltage, and generate an evaluation result of system voltage stability; If the system power output is greater than the maximum power output, generate an evaluation result of system voltage instability.

2. The method for evaluating the voltage characteristics of a flexible DC transmission from a new energy island according to claim 1, characterized in that, The step of calculating the maximum power output of the new energy island system according to the pre-determined maximum steady-state reactive power output of the flexible DC of the new energy island system and the system stable operation power circle includes: Calculate the maximum power output of the new energy island system according to the following expression: Among them, P cmax represents the maximum power output, S0 represents the rated capacity of the new energy island system, and the rated capacity is the ratio of the square of the rated voltage of the new energy island system to the imaginary part of the total impedance, Q c0 represents the maximum steady-state reactive power output of the flexible direct current transmission, Q c ′ 0 represents the relative value of the maximum steady-state reactive power output of the flexible direct current transmission, Q c ′ cr represents the relative value of the reactive power at the intersection of the power circle for stable operation of the system.

3. The method for evaluating the voltage characteristics of a flexible DC transmission from a new energy island according to claim 1, characterized in that, The system reactive power parameters include the reactive power consumed by the shunt reactors at both ends of the AC long line, the reactive power at the DC system port, and the charging power of the AC long line; The step of calculating the reactive power compensation capacity of the output voltage of the new energy island system according to the pre-determined system reactive power parameters, the new energy side voltage and the flexible DC side voltage includes: Calculate the reactive power compensation capacity according to the following expression: Wherein, Q CG represents the reactive power compensation capacity, Q cr represents the reactive power consumed by the shunt reactor at both ends of the AC long line, Q c represents the reactive power at the DC system port, Q LB represents the charging power of the AC long line, U s ∠0 ° represents the complex representation of the system-side voltage of the AC long line, where U s is its amplitude, representing the new energy-side voltage, ∠0 ° is its phase angle, U c ∠-δ represents the complex representation of the outgoing voltage of the new energy island system, where U c is its amplitude, representing the voltage on the flexible DC side, ∠-δ is its phase angle, X L represents the imaginary part of the total impedance.

4. A device for evaluating the voltage characteristics of a flexible DC transmission from a new energy island, characterized in that, The device includes: A system stable operation power circle drawing module, configured to draw the system stable operation power circle of the new energy island system according to the constructed voltage characteristic evaluation model and the pre-determined voltage change ranges of the new energy side and the flexible DC side of the new energy island system. The voltage characteristic evaluation model is constructed based on the total impedance, flexible DC absorbed power, new energy side voltage and flexible DC side voltage of the new energy island system. The flexible DC absorbed power includes flexible DC absorbed active power and flexible DC absorbed reactive power; The system stable operation power circle drawing module includes: A voltage characteristic evaluation module construction unit, configured to construct the voltage characteristic evaluation model according to the following expression: wherein, P c ′ represents the ratio of the active power absorbed by the HVDC to the rated capacity of the new energy island system, i.e., the relative active power, and the rated capacity is the ratio of the square of the rated voltage of the new energy island system to the imaginary part of the total impedance; Q c ′ represents the ratio of the reactive power absorbed by the HVDC to the rated capacity of the new energy island system, i.e., the relative reactive power, K1 represents the ratio of the voltage on the new energy side to the rated voltage of the new energy island system, i.e., the per-unit value of the voltage on the power supply side, and K2 represents the ratio of the voltage on the HVDC side to the rated voltage of the new energy island system, i.e., the per-unit value of the voltage at the HVDC port; A maximum power output calculation module, configured to calculate the maximum power output of the new energy island system according to the pre-determined maximum steady-state reactive power output of the flexible DC of the new energy island system and the system stable operation power circle, and determine the system power output of the new energy island system; A first voltage characteristic evaluation module, configured to calculate a reactive power compensation capacity of the output voltage of the new energy island system and generate an evaluation result of system voltage stability according to pre-determined system reactive power parameters, the new energy side voltage, and the flexible DC side voltage if the power output by the system is less than or equal to the maximum power output; A second voltage characteristic evaluation module, configured to generate an evaluation result of system voltage instability if the power output by the system is greater than the maximum power output.

5. The device for evaluating the voltage characteristics of a flexible DC transmission from a new energy island according to claim 4, characterized in that, The maximum power output calculation module includes: A maximum power output calculation unit, configured to calculate the maximum power output of the new energy island system according to the following expression: Among them, P cmax represents the maximum power output, S0 represents the rated capacity of the new energy island system, and the rated capacity is the ratio of the square of the rated voltage of the new energy island system to the imaginary part of the total impedance, Q c0 represents the maximum steady-state reactive power output of the flexible DC, Q c ′ 0 represents the relative value of the maximum steady-state reactive power output of the flexible DC, Q c ′ cr represents the relative value of the reactive power at the intersection of the power circle for stable system operation.

6. The new energy island flexible DC transmission voltage characteristic evaluation device according to claim 4, wherein, The system reactive power parameters include the reactive power consumed by the shunt reactors at both ends of the AC long line, the reactive power at the DC system port, and the charging power of the AC long line; The first voltage characteristic evaluation module includes: A reactive power compensation capacity calculation unit, configured to calculate the reactive power compensation capacity according to the following expression: Wherein, Q CG represents the reactive power compensation capacity, Q cr represents the reactive power consumed by the shunt reactors at both ends of the AC long line, Q c represents the reactive power at the DC system port, Q LB represents the charging power of the AC long line, U s ∠0 ° represents the complex representation of the system-side voltage of the AC long line, where U s is its amplitude, representing the new energy-side voltage, ∠0 ° is its phase angle, U c ∠-δ represents the complex representation of the outgoing voltage of the new energy island system, where U c is its amplitude, representing the voltage on the flexible DC side, ∠-δ is its phase angle, X L represents the imaginary part of the total impedance.

7. A storage medium, characterized in that: The computer-readable instructions are stored in the storage medium, and when the computer-readable instructions are executed by one or more processors, the one or more processors are caused to execute the steps of the method for evaluating the output voltage characteristics of the new energy island flexible DC as described in any one of claims 1 to 3.

8. A computer device, characterized in that, Including: One or more processors, and a memory; The computer-readable instructions are stored in the memory, and when the computer-readable instructions are executed by the one or more processors, the steps of the method for evaluating the output voltage characteristics of the new energy island flexible DC as described in any one of claims 1 to 3 are executed.

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