Alternating current-direct current hybrid section rationality evaluation method and system

Abstract

The method comprises the following steps: constructing an AC / DC hybrid section rationality evaluation system, and calculating various indexes of the AC / DC hybrid section under the AC / DC hybrid section rationality evaluation system based on a target power grid structure and operation parameters; and coupling the calculated indexes by adopting an entropy weight method to obtain an AC / DC hybrid section rationality evaluation result. According to the method, through multi-dimensional evaluation indexes, controllable, safe and stable operation characteristics of the series-parallel section are guaranteed.

Description

Technical Field

[0001] The present invention belongs to the technical field of power systems, and in particular relates to a method and system for evaluating the rationality of an AC / DC hybrid section. Background Art

[0002] In order to meet the power transmission demand, the scale of the main AC grid is constantly expanding, and safety and stability issues such as excessive short-circuit current, DC commutation failure, and line overload will also appear with the expansion of the AC grid. Taking into account the power transmission demand and operational safety and stability of the power grid, a strategy of introducing embedded DC lines is proposed to build an AC / DC hybrid power grid structure. In order to ensure that the constructed section meets the power grid operation requirements, it is necessary to conduct a rationality assessment of the AC / DC hybrid section.

[0003] Regarding the rationality evaluation system of AC / DC hybrid sections, the existing literature "Research on Three Basic Constraints of Reasonable Scale of Synchronous Power Grids" pointed out that from the perspective of stability, there are three basic constraints that determine the reasonable scale of synchronous power grids, namely frequency stability constraint, low-frequency oscillation minimum frequency constraint and synchronous power support effect disappearance constraint. Later, some scholars further proposed the general principle of asynchronous separation of AC / DC synchronous power grids. However, this evaluation method only takes into account the stability requirements of the system, and does not constrain the flow control capability, short-circuit risk and other aspects. In addition to stability, the flow distribution relationship between AC / DC lines is also one of the important factors that determine the form of AC / DC hybrid network. In actual planning, it is necessary to avoid the occurrence of chain failures caused by the flow transfer caused by DC blocking.

[0004] With the increasing number of DC transmission lines, the operating characteristics of AC / DC hybrid power grids have become more complex. How to evaluate the complex operating characteristics of AC / DC hybrid power grids has always been a key issue that scholars have paid attention to. Summary of the invention

[0005] In order to solve the problems existing in the prior art, the present invention proposes a method and system for evaluating the rationality of an AC / DC hybrid section.

[0006] The technical solution of the present invention is as follows:

[0007] A method for evaluating the rationality of an AC / DC hybrid section, characterized by comprising:

[0008] Constructing an AC / DC hybrid section rationality assessment system, wherein the evaluation indicators of the AC / DC hybrid section rationality assessment system include a first indicator for assessing the power flow control capability of the AC / DC hybrid section, a second indicator for assessing the N-1 overload risk of the AC / DC hybrid section, a third indicator for assessing the risk of exceeding the short-circuit current of the AC / DC hybrid section, a fourth indicator for assessing the frequency stability of the AC / DC hybrid section, a fifth indicator for assessing the voltage stability of the AC / DC hybrid section, and a sixth indicator for assessing the synchronization stability of the AC / DC hybrid section;

[0009] Based on the target grid structure and operating parameters, calculate the various indicators of the AC / DC hybrid section under the AC / DC hybrid section rationality evaluation system;

[0010] The entropy weight method is used to couple the calculation indicators to obtain the rationality evaluation results of the AC / DC hybrid section.

[0011] Furthermore, the method for obtaining the first index θ for evaluating the AC / DC hybrid section power flow control capability is:

[0012] θ=nm-1

[0013] Where Θ is the first indicator, i.e., the uncontrollable power dimension of the AC / DC hybrid section; n is the number of transmission lines in the DC hybrid section; and m is the number of DC transmission lines in the DC hybrid section.

[0014] Furthermore, the second indicator S for evaluating the overload risk of the AC / DC hybrid section N-1 is ac，dc The method to obtain is:

[0015]

[0016] In the formula, S ac，dc The second index is the N-1 impact strength index; P dcj Deliver power to the jth DC transmission line; is the sum of the maximum transmission capacity of all AC transmission lines; It is the sum of all AC line power delivered under normal operation.

[0017] Furthermore, the method for obtaining the third indicator α for evaluating the risk of excessive short-circuit current in the AC / DC hybrid section is:

[0018]

[0019] In the formula, α is the third indicator, that is, the node short-circuit current margin in the system; is the maximum allowable short-circuit current of the ith node; I ai is the actual short-circuit current of the ith node.

[0020] Furthermore, the method for obtaining the fourth index for evaluating the AC / DC hybrid section frequency is:

[0021]

[0022] In the formula, β f The fourth index is the frequency stability margin index; ΔP max The maximum power deficit allowed for system frequency stability; P is the maximum power shortage that may actually occur in the system. ac,j is the power delivered by the jth DC transmission line, n ac is the total number of DC transmission lines;

[0023] Furthermore, the method for obtaining the fifth indicator for evaluating the voltage stability of the AC / DC hybrid section is as follows:

[0024] K vtg =U sys / U sys0

[0025] In the formula, K vtg is the fifth index, namely, system voltage stiffness; U sys is the voltage modulus on the network port; U sys0 It is the no-load voltage at any point when the network-connected device is not connected to the power grid.

[0026] Furthermore, the sixth index Q for evaluating the synchronization stability of the AC / DC hybrid section is ac,dc The method to obtain is:

[0027]

[0028] Furthermore, the specific method of using the entropy weight method to couple the calculation of various indicators to obtain the rationality evaluation result of the AC / DC hybrid section is:

[0029] Obtain the entropy weight coefficients corresponding to each indicator and construct the comprehensive weight matrix A of the evaluation indicators:

[0030] A=[A1 A2…A6]

[0031] For the third indicator used to evaluate the risk of short-circuit current exceeding the standard in AC / DC hybrid sections, the fourth indicator used to evaluate the frequency stability of AC / DC hybrid sections, the fifth indicator used to evaluate the voltage stability of AC / DC hybrid sections, and the sixth indicator used to evaluate the synchronization stability of AC / DC hybrid sections, the membership functions corresponding to the three evaluation levels of weak, medium, and strong are adopted, which are:

[0032]

[0033] In the formula, is the degree of membership of indicator i corresponding to comment level k, k = 1, 2, 3 correspond to poor, medium, and excellent comment levels respectively, i = 3, 4, 5, 6 correspond to the third indicator, the fourth indicator, the fifth indicator, and the sixth indicator respectively, e1, e2, and e3 are the values ​​of weak, medium, and strong indicators when the corresponding degree of membership is 1;

[0034] For the first indicator used to evaluate the power flow control capability of the AC / DC hybrid section and the second indicator used to evaluate the overload risk of the AC / DC hybrid section N-1, the membership function corresponding to the two evaluation levels of qualified and unqualified is adopted:

[0035]

[0036] In the formula, is the degree of membership of indicator i corresponding to comment level k, k = 0, 4 respectively represent the comment level as qualified and unqualified, i = 1, 2 respectively represent the first indicator and the second indicator; e0, e4 are the values ​​of qualified and unqualified indicators when the corresponding degree of membership of the indicator is 1;

[0037] Calculate the corresponding comment level score for each indicator:

[0038] For the third, fourth, fifth and sixth indicators, the corresponding scores for weak, medium and strong are 60, 80 and 100 respectively. The specific scoring rules are as follows:

[0039]

[0040] Where W i k is the score of the kth comment level corresponding to the i-th indicator;

[0041] For the first and second indicators, the corresponding scores for the qualified and unqualified levels are 100 and -∞, respectively. The specific scoring rules are as follows:

[0042]

[0043] Finally, the rationality score of AC / DC hybrid transmission section is comprehensively calculated as follows:

[0044]

[0045] Where, W is the rationality score of AC / DC hybrid section;

[0046] According to the calculated rationality score, equivalence classification is performed. When W<60, the rationality assessment level is unqualified; when 60≤W<80, the rationality assessment level is weak; when 80≤W<90, the rationality assessment level is medium; when 90≤W<100, the rationality assessment level is strong.

[0047] A rationality evaluation method for an AC / DC hybrid section includes a system construction module, an index calculation module, and a rationality evaluation result acquisition module; wherein:

[0048] The system construction module is used to construct an AC / DC hybrid section rationality evaluation system, and the evaluation indicators of the AC / DC hybrid section rationality evaluation system include a first indicator for evaluating the power flow control capability of the AC / DC hybrid section, a second indicator for evaluating the N-1 overload risk of the AC / DC hybrid section, a third indicator for evaluating the short-circuit current exceeding the standard risk of the AC / DC hybrid section, a fourth indicator for evaluating the frequency stability of the AC / DC hybrid section, a fifth indicator for evaluating the voltage stability of the AC / DC hybrid section, and a sixth indicator for evaluating the synchronization stability of the AC / DC hybrid section;

[0049] The index calculation module is used to calculate various indicators of the AC / DC hybrid section under the AC / DC hybrid section rationality evaluation system based on the target power grid structure and operating parameters;

[0050] The rationality evaluation result acquisition module is used to couple the calculation indicators using the entropy weight method to obtain the rationality evaluation result of the AC / DC hybrid section.

[0051] An electronic device comprises a memory and a processor, wherein the memory stores a computer program, and the processor is used to call and run the computer program stored in the memory to execute any of the methods described above.

[0052] A computer-readable storage medium stores a computer program, wherein the computer program implements the steps of any of the above methods when executed by a processor.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] The present invention proposes a method and system for evaluating the rationality of an AC / DC hybrid section. The method adopts a first indicator for evaluating the flow control capability of an AC / DC hybrid section, namely, an uncontrollable power dimension indicator, which can evaluate the rationality of the number of AC / DC lines and ensure the flow control capability of the section.

[0055] The present invention adopts a second indicator for evaluating the N-1 overload risk of the AC / DC hybrid section, namely the anti-N-1 impact strength indicator, which can evaluate the rationality of the capacity allocation relationship between the DC line and the AC line and avoid the N-1 overload risk of the AC line under fault conditions.

[0056] The present invention adopts a third indicator for evaluating the risk of excessive short-circuit current in an AC / DC hybrid section, namely a short-circuit current margin indicator, which can evaluate the rationality of the AC / DC hybrid section structure and avoid the risk of excessive short-circuit current under a short-circuit fault.

[0057] The present invention adopts the fourth index / fifth index for evaluating the frequency / voltage stability of the AC / DC hybrid section, namely the frequency stability margin index and the voltage stiffness index, which can evaluate the rationality of the AC / DC hybrid section structure and avoid the risk of excessive short-circuit current under short-circuit fault.

[0058] The present invention adopts a sixth index for evaluating the synchronization stability of the AC / DC hybrid section, namely the AC / DC channel strength index, which can evaluate the operating state of the AC line and avoid the risk of phase instability of the AC / DC hybrid system.

[0059] The present invention adopts an AC / DC hybrid section rationality evaluation method, which can evaluate the rationality of the AC / DC hybrid section and ensure the controllable, safe and stable operation characteristics of the hybrid section. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 It is a flow chart of the rationality evaluation method of AC / DC hybrid section in the embodiment;

[0061] Figure 2 The Thevenin equivalent principle diagram of the power grid in the embodiment;

[0062] Figure 3 The characteristic of the port voltage of the network access device changing with the short-circuit ratio after the network access device is connected to the power grid in the embodiment;

[0063] Figure 4 This is a structural diagram of the interconnected power grid of three transmission channels in the embodiment;

[0064] FIG5(a) is a curve diagram showing the frequency response of the group during DC locking corresponding to the AC / DC hybrid structure in the embodiment;

[0065] FIG5( b ) is a curve diagram showing the frequency response of the DC blocking group corresponding to the full DC asynchronous structure in the embodiment;

[0066] FIG6 (a) is a curve diagram showing the power angle response of the unit during a short circuit fault corresponding to the AC / DC hybrid structure in the embodiment;

[0067] FIG6( b ) is a curve diagram of the power angle response of the unit during a short circuit fault corresponding to the full DC asynchronous structure in the embodiment. DETAILED DESCRIPTION

[0068] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent modifications of the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0069] Embodiment 1:

[0070] A method for evaluating the rationality of an AC / DC hybrid section of the present invention is as follows: Figure 1As shown, the specific steps are as follows:

[0071] Constructing an AC / DC hybrid section rationality assessment system, wherein the evaluation indicators of the AC / DC hybrid section rationality assessment system include a first indicator for assessing the power flow control capability of the AC / DC hybrid section, a second indicator for assessing the N-1 overload risk of the AC / DC hybrid section, a third indicator for assessing the risk of exceeding the short-circuit current of the AC / DC hybrid section, a fourth indicator for assessing the frequency stability of the AC / DC hybrid section, a fifth indicator for assessing the voltage stability of the AC / DC hybrid section, and a sixth indicator for assessing the synchronization stability of the AC / DC hybrid section;

[0072] Based on the target grid structure and operating parameters, calculate the various indicators of the AC / DC hybrid section under the AC / DC hybrid section rationality evaluation system;

[0073] The entropy weight method is used to couple the calculation indicators to obtain the rationality evaluation results of the AC / DC hybrid section.

[0074] Embodiment 2:

[0075] This embodiment is further designed on the basis of the first embodiment in that the method for obtaining the first index θ used to evaluate the AC / DC hybrid section power flow control capability in this embodiment is:

[0076] θ=nm-1

[0077] Where Θ is the first indicator, i.e., the uncontrollable power dimension of the AC / DC hybrid section; n is the number of transmission lines in the DC hybrid section; and m is the number of DC transmission lines in the DC hybrid section.

[0078] For the fully AC interconnected power grid structure, the systems at both ends of the transmission and reception can change the power that needs to be exchanged by the systems at both ends by adjusting the power output or load size. Therefore, the total power of the AC transmission section is controllable. However, it is difficult to adjust the power distribution between different lines. It is necessary to change the position of the power and load distribution at the transmission and reception ends. The power and load distribution are usually determined by complex practical factors, and the unit startup method depends on the economic dispatch results. Therefore, for the AC / DC hybrid power grid structure, assuming that m of the n lines are DC transmission lines, since the DC system transmission power is completely controllable, the dimension of uncontrollable power in the AC / DC hybrid power grid structure is nm-1. For the fully DC asynchronous Internet structure, the power of any line in the section can be controlled, and the dimension of uncontrollable power is 0.

[0079] The total exchange power between the sending and receiving systems is controllable, and the DC line transmission power is controllable. Therefore, according to the AC line transmission power calculation expression, the AC line transmission power is also controllable, and the section flow is completely controllable.

[0080] Embodiment three:

[0081] This embodiment is further designed on the basis of the first embodiment in that this embodiment further involves a second indicator for evaluating the overload risk of the AC / DC hybrid section N-1, and the second indicator is used to determine the overload risk of N-1.

[0082] In the AC / DC hybrid network structure, if any one AC or DC line fails, the power will be transferred to the remaining AC lines, and the power of the remaining DC lines will remain unchanged. Therefore, in the planning stage of the AC / DC hybrid network, it is usually necessary to focus on checking the N-1 fault, especially to avoid the occurrence of strong DC and weak AC. In the all-DC asynchronous network structure, the DC system transmission power is determined by the command value, and there will be no overload problem after the N-1 fault.

[0083] Under N-1 fault, the power transfer determines the line transmission capacity constraint. For AC / DC hybrid grid, after the AC line N-1 fault, the power will not be transferred to the DC system. However, after the DC system N-1 fault, the power will be transferred to the AC line, causing power shock to the AC line. Therefore, under this grid structure, it is necessary to evaluate the ability of the AC channel in the transmission section to resist the impact of the DC channel power transfer. The second indicator S ac，dc The method to obtain is:

[0084]

[0085] In the formula, S ac，dc The second index is the N-1 impact strength index; P dcj Deliver power to the jth DC transmission line; is the sum of the maximum transmission capacity of all AC transmission lines; It is the sum of all AC line power delivered under normal operation.

[0086] The second index reflects the balance relationship between AC and DC power flows. In order to make the hybrid power grid meet the N-1 principle specified in the "Guidelines for Safety and Stability of Power Systems", the N-1 impact strength index S ac,dc Must be greater than 1.

[0087] Embodiment 4:

[0088] This embodiment is further designed on the basis of the first embodiment in that a third indicator for evaluating the risk of short-circuit current exceeding the standard in the AC / DC hybrid section is further designed in this embodiment, and the third indicator is used to judge the risk of short-circuit current exceeding the standard;

[0089] With the increasing load demand, the AC grid is constantly being strengthened. Considering the high reserve margin of the AC grid under N-1 and N-2 verification, the electrical distance between the power source and the load area is too close, and the problem of excessive short-circuit current in the power grid is gradually becoming prominent. If the AC line is replaced by a DC system, it will be beneficial to increase the electrical distance between the power source and the load node, reduce the short-circuit current, and reduce the risk of short-circuit current overload. Under the same transmission capacity, the higher the degree of DCization, the lower the risk of excessive short-circuit current in the system. Therefore, adding embedded DC lines and adopting an AC / DC hybrid power grid will greatly reduce the risk of excessive short-circuit current in the full AC power grid structure.

[0090] For the AC / DC hybrid power grid structure, the AC electrical connection between the sending and receiving end systems has been greatly weakened, and the short-circuit current problem can be alleviated to a large extent. At the same time, according to the contribution of each channel of the section to the short-circuit current of each node of the sending and receiving end system, the AC line with the lowest comprehensive contribution can be selected to be retained, and the remaining channels use the DC system. The specific method is to calculate the short-circuit current margin under various AC / DC hybrid section structures, and select the method with the largest short-circuit current margin. The method for obtaining the third indicator α used to evaluate the risk of excessive short-circuit current in AC / DC hybrid sections is:

[0091]

[0092] In the formula, α is the third indicator, that is, the node short-circuit current margin in the system; is the maximum allowable short-circuit current of the ith node; I ai is the actual short-circuit current of the ith node.

[0093] Embodiment five:

[0094] This embodiment is further designed on the basis of the first embodiment in that this embodiment is further designed to evaluate the fourth index of the AC / DC hybrid section frequency, and the fourth index is used to judge the frequency / voltage stability.

[0095] For all-AC interconnected power grid structures and AC / DC hybrid power grid structures, under any line N-1 fault, as long as there is an AC line connection between the two end systems, the entire power system will not have power imbalance problems and will not face the risk of frequency instability. For all-DC asynchronous interconnected power grid structures, there is no AC connection between the power grids at both ends of the DC transmission line. The N-1 fault of the DC system will bring power surplus to the sending end system and power shortage to the receiving end system, causing frequency fluctuations and destroying the system frequency stability.

[0096] Regarding frequency stability, in an AC / DC hybrid network, any N-1 or N-2 fault in the DC system will not cause a power shortage in the sending and receiving systems, and the power transmitted by the DC will be transferred to the AC line. Therefore, DC faults will not threaten the frequency stability of the AC / DC hybrid system. If an N-1 or N-2 fault occurs in the AC line, causing the sending and receiving systems to completely lose AC connection, the power transmitted by the original AC line will not be borne by the DC system, resulting in a power shortage in the sending and receiving systems. For the AC / DC hybrid section, the maximum power shortage that may occur at the sending and receiving ends is P acsum , which is the actual transmission power of the AC line. Since the AC line power is fully controllable, P acsum It can be limited to a very small range, or even 0. The fourth indicator is obtained as follows:

[0097]

[0098] In the formula, β f The fourth index is the frequency stability margin index; ΔP max The maximum power deficit allowed for system frequency stability; P is the maximum power shortage that may actually occur in the system. ac,j is the power delivered by the jth DC transmission line, n ac is the total number of DC transmission lines;

[0099] Embodiment six:

[0100] This embodiment is further designed on the basis of the first embodiment in that, in terms of voltage stability, the voltage strength in the AC / DC hybrid power grid system is measured by the voltage stiffness index. The voltage support strength at any point in the power grid is defined as the ability to maintain the voltage modulus at the access point close to the no-load voltage at the access point. The short-circuit ratio of the networked device at any point in the power grid is λ SCR , the voltage modulus U on the network port sys is related to the short-circuit ratio λ SCR and impedance angle and When the network equipment is not connected to the grid, the no-load voltage at any point is U sys0 In this example, the method for obtaining the fifth index used to evaluate the voltage stability of the AC / DC hybrid section is as follows:

[0101] K vtg =U sys / U sys0

[0102] In the formula, K vtg is the fifth index, namely, system voltage stiffness; U sys is the voltage modulus on the network port; U sys0It is the no-load voltage at any point when the network-connected device is not connected to the power grid.

[0103] When discussing the voltage support strength of the power grid, the object of investigation is the positive sequence network of the AC power grid at the fundamental frequency. Corresponding to this fundamental frequency positive sequence network, according to the Thevenin equivalent principle, when looking at the power grid from any point SYS in the power grid, the entire power grid can be represented by a Thevenin equivalent circuit, such as Figure 2 The Thevenin equivalent circuit is composed of the Thevenin equivalent potential E th =E th ∠θ th Thevenin equivalent impedance Thevenin equivalent potential E th Equal to the no-load voltage U on SYS when the network device is not connected to the grid sys0 =U sys0 ∠θ sys0 , where the horizontal line under the parameter represents a complex number. Thevenin equivalent impedance Z th It is equal to the equivalent impedance of the network viewed from point SYS when each independent power source in the fundamental frequency positive sequence network is reset to zero.

[0104] The short-circuit capacity S of the power grid at point SYS sc for:

[0105]

[0106] Assume the impedance of the network access device is The capacity of the network access equipment under rated voltage is:

[0107]

[0108] Click SYS corresponding to the network device Z device The short circuit ratio λ SCR for:

[0109]

[0110] Voltage U at point SYS sys for:

[0111]

[0112] Network access device Z device After connecting to the grid, the voltage modulus U sys is related to the short-circuit ratio λ SCR and impedance angle and Consider a typical case where the Thevenin equivalent impedance of the power grid is purely inductive, while the equivalent impedance of the network-connected equipment is purely resistive, that is, and U sysThe expression simplifies to:

[0113]

[0114] When SCR >>1: U sys ≈U N ; In other cases, U sys Always less than U N U sys With λ SCR The changing characteristics such as Figure 3 As shown. It can be seen that when λ SCR =5, U sys =0.98UN; when λ SCR =3, U sys =0.95U N ; When λ SCR =1, U sys =0.71U N Therefore, it is generally believed that when the short-circuit ratio is greater than 3, the access point SYS is a relatively strong access point because its voltage drop after loading is less than 5% of the rated voltage.

[0115] For new power systems, voltage stiffness is more accurate than the short-circuit ratio index in measuring the voltage stability of AC / DC hybrid power grids. The voltage stability of new power systems is the result of the combined effects of source, DC, and load. The source side includes synchronous power supplies and non-synchronous power supplies, the DC side includes the influence of DC's own characteristics and the interaction between DC and DC, and the load side includes static loads and motor loads. The following will analyze the advantages and disadvantages of short-circuit ratio and voltage stiffness in characterizing synchronous power supplies, non-synchronous power supplies, DC's own characteristics, the interaction between DC, static loads, and motors. Based on the above comparison, the comparison of the short-circuit ratio and voltage stiffness on the key parts of the new power system is summarized in Table 1.

[0116] Table 1 Comparison of short circuit ratio and voltage stiffness adaptability

[0117]

[0118] Embodiment seven:

[0119] This embodiment is further designed on the basis of the first embodiment in that a sixth index for evaluating the synchronization stability of the AC / DC hybrid section is further designed in this embodiment, and the sixth index is used to judge the synchronization stability of the AC / DC hybrid section.

[0120] For the transmitting and receiving systems, the closer the electrical distance between the two ends, that is, the stronger the AC transmission channel of the transmission section, the higher the frequency coupling degree, and the better the synchronization stability. Compared with the full AC grid, the synchronization stability of the AC / DC hybrid power grid is reduced. It is particularly important to judge the synchronization stability of the AC / DC hybrid section, and it is necessary to evaluate the degree of strong and weak AC in the AC / DC transmission channel. The sixth indicator Q for evaluating the synchronization stability of the AC / DC hybrid section ac,dc The method to obtain is:

[0121]

[0122] Generally, when Q ac,dc <0.5, the system shows strong tonic and weak crossover; when Q ac,dc >2, the system shows strong crossover and weak directivity; when 0.5 ac,dc When Q <4, the system presents AC and DC intensity balance. ac,dc The smaller the index is, the worse the system synchronization stability is. Therefore, when Q ac,dc Less than the minimum value allowed by AC and DC systems When the AC channel is disconnected, the sending and receiving power grids can operate independently and asynchronously.

[0123] In the real-time operation stage, the stability of the transmission and receiving end systems can be ensured by checking the phase margin of the transmission line transmission and receiving end grids. In the event of a serious fault, the AC tie line relay device detects the phase difference Δθ at both ends in real time. ac , the phase difference reaches a certain value θ th After that, the AC line is automatically disconnected, and the sending and receiving systems run asynchronously, and there is no need to maintain synchronization.

[0124] Embodiment eight:

[0125] This embodiment is further designed on the basis of the first embodiment in that the entropy weight method is used in this embodiment to couple the calculation of various indicators, and the specific method for obtaining the rationality evaluation result of the AC / DC hybrid section is:

[0126] Obtain the entropy weight coefficients corresponding to each indicator and construct the comprehensive weight matrix A of the evaluation indicators:

[0127] A=[A1 A2…A6]

[0128] For the third indicator used to evaluate the risk of short-circuit current exceeding the standard in AC / DC hybrid sections, the fourth indicator used to evaluate the frequency stability of AC / DC hybrid sections, the fifth indicator used to evaluate the voltage stability of AC / DC hybrid sections, and the sixth indicator used to evaluate the synchronization stability of AC / DC hybrid sections, the membership functions corresponding to the three evaluation levels of weak, medium, and strong are adopted, which are:

[0129]

[0130] ​In the formula, is the degree of membership of indicator i corresponding to comment level k, k = 1, 2, 3 correspond to poor, medium, and excellent comment levels respectively, i = 3, 4, 5, 6 correspond to the third indicator, the fourth indicator, the fifth indicator, and the sixth indicator respectively, e1, e2, and e3 are the values ​​of weak, medium, and strong indicators when the corresponding degree of membership is 1;

[0131] For the first indicator used to evaluate the power flow control capability of the AC / DC hybrid section and the second indicator used to evaluate the overload risk of the AC / DC hybrid section N-1, the membership function corresponding to the two evaluation levels of qualified and unqualified is adopted:

[0132]

[0133] In the formula, is the degree of membership of indicator i corresponding to comment level k, k = 0, 4 respectively represent the comment level as qualified and unqualified, i = 1, 2 respectively represent the first indicator and the second indicator; e0, e4 are the values ​​of qualified and unqualified indicators when the corresponding degree of membership of the indicator is 1;

[0134] Calculate the corresponding comment level score for each indicator:

[0135] For the third, fourth, fifth and sixth indicators, the corresponding scores for weak, medium and strong are 60, 80 and 100 respectively. The specific scoring rules are as follows:

[0136]

[0137] Where W i k is the score of the kth comment level corresponding to the i-th indicator;

[0138] For the first and second indicators, the corresponding scores for the qualified and unqualified levels are 100 and -∞, respectively. The specific scoring rules are as follows:

[0139]

[0140] Finally, the rationality score of AC / DC hybrid transmission section is comprehensively calculated as follows:

[0141]

[0142] Where, W is the rationality score of AC / DC hybrid section;

[0143] According to the calculated rationality score, equivalence classification is performed. When W<60, the rationality assessment level is unqualified; when 60≤W<80, the rationality assessment level is weak; when 80≤W<90, the rationality assessment level is medium; when 90≤W<100, the rationality assessment level is strong.

[0144] Embodiment nine:

[0145] The present invention provides a method for evaluating the rationality of an AC / DC hybrid section, comprising a system construction module, an index calculation module, and a rationality evaluation result acquisition module; wherein:

[0146] The system construction module is used to construct an AC / DC hybrid section rationality evaluation system, and the evaluation indicators of the AC / DC hybrid section rationality evaluation system include a first indicator for evaluating the power flow control capability of the AC / DC hybrid section, a second indicator for evaluating the N-1 overload risk of the AC / DC hybrid section, a third indicator for evaluating the short-circuit current exceeding the standard risk of the AC / DC hybrid section, a fourth indicator for evaluating the frequency stability of the AC / DC hybrid section, a fifth indicator for evaluating the voltage stability of the AC / DC hybrid section, and a sixth indicator for evaluating the synchronization stability of the AC / DC hybrid section;

[0147] The index calculation module is used to calculate various indicators of the AC / DC hybrid section under the AC / DC hybrid section rationality evaluation system based on the target power grid structure and operating parameters;

[0148] The rationality evaluation result acquisition module is used to couple the calculation indicators using the entropy weight method to obtain the rationality evaluation result of the AC / DC hybrid section.

[0149] Embodiment nine:

[0150] An electronic device comprises a memory and a processor, wherein the memory stores a computer program, and the processor is used to call and run the computer program stored in the memory to execute any of the methods described above.

[0151] A computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of any of the above methods are implemented.

[0152] Application examples:

[0153] In this case, Figure 4The three-transmission channel interconnected power grid structure shown in the figure simulates the implementation of the rationality evaluation method of the present invention. The power grid structure is constructed according to the IEEE two-zone four-machine system, and reasonable parameters are designed and auxiliary protection devices are configured. In this example, case analysis is carried out on three interconnection modes: full AC, AC / DC hybrid, and full DC. The operating characteristics are analyzed and studied from six dimensions, and the comprehensive characteristic evaluation results of the AC / DC hybrid section are obtained as "strong", while the comprehensive characteristic evaluation results of the full DC and full AC structures are "medium". Compared with the simulation results, the transient response characteristics of the power grid frequency and power angle under different interconnection modes are shown in Figures 5(a) and 5(b) and Figures 6(a) and 6(b), respectively. The operating characteristics obtained by simulation analysis are summarized in Table 2 below. It can be seen that the theoretical evaluation of the rationality of the AC / DC hybrid section is consistent with the simulation characteristics, which can truly and accurately reflect the actual operating characteristics of the AC / DC power grid, verifying the effectiveness of the rationality evaluation method of the AC / DC hybrid section, and providing a reliable rationality evaluation basis for the construction and optimization of the AC / DC hybrid network frame.

[0154] Table 2 Operation characteristics of three typical topological structures

[0155]

[0156]

[0157] The above is an evaluation scheme for the rationality of AC / DC hybrid power grid. Combining the characteristics of DC and AC transmission systems, it comprehensively evaluates the power grid's flow control capability, N-1 overload risk, short-circuit current exceeding risk, frequency / voltage stability, and synchronous stability operating characteristics, and proposes specific calculation indicators for each operating characteristic. It provides a theoretical basis for technical personnel in this field to conduct safety and stability evaluation of AC / DC hybrid power grids, which is conducive to in-depth research on the reasonable planning path of subsequent AC / DC hybrid power grids.

[0158] The above description is only a specific implementation of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a technician familiar with the technical field within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for evaluating the rationality of an AC / DC hybrid section, characterized in that: include: Constructing an AC / DC hybrid section rationality assessment system, wherein the evaluation indicators of the AC / DC hybrid section rationality assessment system include a first indicator for assessing the power flow control capability of the AC / DC hybrid section, a second indicator for assessing the N-1 overload risk of the AC / DC hybrid section, a third indicator for assessing the risk of exceeding the short-circuit current of the AC / DC hybrid section, a fourth indicator for assessing the frequency stability of the AC / DC hybrid section, a fifth indicator for assessing the voltage stability of the AC / DC hybrid section, and a sixth indicator for assessing the synchronization stability of the AC / DC hybrid section; Based on the target grid structure and operating parameters, calculate the various indicators of the AC / DC hybrid section under the AC / DC hybrid section rationality evaluation system; The entropy weight method is used to couple the calculation indicators to obtain the rationality evaluation results of the AC / DC hybrid section.

2. The AC / DC hybrid section rationality evaluation method according to claim 1 is characterized in that: The method for obtaining the first index θ for evaluating the AC / DC hybrid section power flow control capability is: θ=nm-1 Where Θ is the first indicator, i.e., the uncontrollable power dimension of the AC / DC hybrid section; n is the number of transmission lines in the DC hybrid section; and m is the number of DC transmission lines in the DC hybrid section.

3. The AC / DC hybrid section rationality evaluation method according to claim 1 is characterized in that: The second indicator S for evaluating the overload risk of the AC / DC hybrid section N-1 ac，dc The method to obtain is: In the formula, S ac，dc The second index is the N-1 impact strength index; P dcj Deliver power to the jth DC transmission line; is the sum of the maximum transmission capacity of all AC transmission lines; It is the sum of all AC line power delivered under normal operation.

4. The AC / DC hybrid section rationality evaluation method according to claim 1 is characterized in that: The method for obtaining the third indicator α for evaluating the risk of excessive short-circuit current in the AC / DC hybrid section is: In the formula, α is the third indicator, that is, the node short-circuit current margin in the system; is the maximum allowable short-circuit current of the ith node; I ai is the actual short-circuit current of the ith node.

5. The AC / DC hybrid section rationality evaluation method according to claim 1 is characterized in that: The method for obtaining the fourth index for evaluating the AC / DC hybrid section frequency is: In the formula, β f The fourth index is the frequency stability margin index; ΔP max The maximum power deficit allowed for system frequency stability; P is the maximum power shortage that may actually occur in the system. ac,j is the power delivered by the jth DC transmission line, n ac is the total number of DC transmission lines.

6. The AC / DC hybrid section rationality evaluation method according to claim 1 is characterized in that: The method for obtaining the fifth indicator for evaluating the voltage stability of the AC / DC hybrid section is as follows: K vtg =U sys / IN sys0 In the formula, K vtg is the fifth index, namely the system voltage stiffness; U sys is the voltage modulus on the network port; U sys0 It is the no-load voltage at any point when the network-connected device is not connected to the power grid.

7. The AC / DC hybrid section rationality evaluation method according to claim 1 is characterized in that: The sixth index Q for evaluating the synchronous stability of AC / DC hybrid sections ac,dc The method to obtain is:

8. The AC / DC hybrid section rationality evaluation method according to claim 1 is characterized in that: The specific method of using the entropy weight method to couple the calculation of various indicators and obtain the rationality evaluation result of the AC / DC hybrid section is: Obtain the entropy weight coefficients corresponding to each indicator and construct the comprehensive weight matrix A of the evaluation indicators: A=[A1 A2…A6] For the third indicator used to evaluate the risk of short-circuit current exceeding the standard in AC / DC hybrid sections, the fourth indicator used to evaluate the frequency stability of AC / DC hybrid sections, the fifth indicator used to evaluate the voltage stability of AC / DC hybrid sections, and the sixth indicator used to evaluate the synchronization stability of AC / DC hybrid sections, the membership functions corresponding to the three evaluation levels of weak, medium, and strong are adopted, which are: In the formula, is the degree of membership of indicator i corresponding to comment level k, k = 1, 2, 3 correspond to poor, medium, and excellent comment levels respectively, i = 3, 4, 5, 6 correspond to the third indicator, the fourth indicator, the fifth indicator, and the sixth indicator respectively, e1, e2, and e3 are the values ​​of weak, medium, and strong indicators when the corresponding degree of membership is 1; For the first indicator used to evaluate the power flow control capability of the AC / DC hybrid section and the second indicator used to evaluate the overload risk of the AC / DC hybrid section N-1, the membership function corresponding to the two evaluation levels of qualified and unqualified is adopted: In the formula, is the degree of membership of indicator i corresponding to comment level k, k = 0, 4 respectively represent the comment level as qualified and unqualified, i = 1, 2 respectively represent the first indicator and the second indicator; e0, e4 are the values ​​of qualified and unqualified indicators when the corresponding degree of membership of the indicator is 1; Calculate the corresponding comment level score for each indicator: For the third, fourth, fifth and sixth indicators, the corresponding scores for weak, medium and strong are 60, 80 and 100 respectively. The specific scoring rules are as follows: Where W i k is the score of the kth comment level corresponding to the i-th indicator; For the first and second indicators, the corresponding scores for the qualified and unqualified levels are 100 and -∞, respectively. The specific scoring rules are as follows: Finally, the rationality score of AC / DC hybrid transmission section is comprehensively calculated as follows: Where, W is the rationality score of AC / DC hybrid section; According to the calculated rationality score, equivalence classification is performed. When W<60, the rationality assessment level is unqualified; when 60≤W<80, the rationality assessment level is weak; when 80≤W<90, the rationality assessment level is medium; when 90≤W<100, the rationality assessment level is strong.

9. A method for evaluating the rationality of AC / DC hybrid sections, characterized in that: It includes system construction module, indicator calculation module and rationality evaluation result acquisition module; among them, The system construction module is used to construct an AC / DC hybrid section rationality evaluation system, and the evaluation indicators of the AC / DC hybrid section rationality evaluation system include a first indicator for evaluating the power flow control capability of the AC / DC hybrid section, a second indicator for evaluating the N-1 overload risk of the AC / DC hybrid section, a third indicator for evaluating the short-circuit current exceeding the standard risk of the AC / DC hybrid section, a fourth indicator for evaluating the frequency stability of the AC / DC hybrid section, a fifth indicator for evaluating the voltage stability of the AC / DC hybrid section, and a sixth indicator for evaluating the synchronization stability of the AC / DC hybrid section; The index calculation module is used to calculate various indicators of the AC / DC hybrid section under the AC / DC hybrid section rationality evaluation system based on the target power grid structure and operating parameters; The rationality evaluation result acquisition module is used to couple the calculation indicators using the entropy weight method to obtain the rationality evaluation result of the AC / DC hybrid section.

10. An electronic device, characterized in that: The electronic device comprises a memory and a processor, wherein the memory stores a computer program, and the processor is configured to call and run the computer program stored in the memory to execute the method according to any one of claims 1 to 7.

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