Method and system for analyzing influence of dc side fault of flexible dc power transmission on ac side

Abstract

The application discloses a method and system for analyzing the influence of DC side faults of flexible DC power transmission on AC side, and the method comprises the following steps: constructing a DC collection and sending system model according to a flexible DC power transmission network, and obtaining an equivalent model of the DC collection and sending system after equivalent transformation; inputting a pre-created DC side fault event into the equivalent model of the DC collection and sending system to obtain a corresponding fault equivalent circuit; obtaining each AC side sequence component network by equivalent transformation of the fault equivalent circuit according to the number relationship of harmonics between the AC side and the DC side; obtaining the interaction influence data of each DC side fault type in the AC side sequence component network; and determining the fault result of the flexible DC power transmission network based on the detected interaction influence data in the actual operation of the flexible DC power transmission network. The application can clearly show the characteristic change and fault development stage of the DC side fault on the AC side, accurately analyze the influence of the DC side fault on the AC side, and realize effective control of the AC side after the DC side fault.

Description

Technical Field

[0001] This invention relates to the field of DC power transmission and transformation technology, and in particular to a method, system, equipment and medium for analyzing the impact of DC-side faults on the AC side of flexible DC transmission. Background Technology

[0002] DC transmission is one of the effective ways to absorb renewable energy. MMC converter stations are key equipment connecting the AC and DC sides. The electrical quantities on the AC and DC sides are coupled and influence each other through the MMC converter station. A fault on one side can propagate to the other side through the MMC converter station, causing changes in electrical quantities. Undervoltage and overcurrent can pose safety hazards to system equipment. However, existing research lacks analysis of AC / DC side fault coupling, resulting in unclear characteristics and development stages of DC side faults on the AC side. With the increasing controllability of DC transmission, in the future, after a DC transmission fault, the MMC converter station may not be locked out and may directly enter the fault control stage, making effective post-fault control impossible.

[0003] Therefore, how to solve the problem of low accuracy in fault analysis and inability to effectively control faults in flexible DC transmission networks has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] This invention provides a method and system for analyzing the impact of DC-side faults on the AC side of flexible DC transmission networks, in order to solve the technical problems of low accuracy in fault analysis and inability to effectively control faults after they occur in flexible DC transmission networks. This invention aims to improve the accuracy of fault analysis in flexible DC transmission networks and enable effective control after DC-side faults occur.

[0005] In a first aspect, the present invention provides a method for analyzing the impact of DC-side faults on the AC side of a flexible DC transmission network, wherein the flexible DC network includes a DC side and an AC side connected via an MMC converter station, and the method includes:

[0006] Based on the flexible DC transmission network, a DC collection and transmission system model is constructed, and the DC collection and transmission system model is transformed into an equivalent model of the DC collection and transmission system.

[0007] By inputting the pre-created DC-side fault events of various types into the equivalent model of the DC collection and transmission system, the fault equivalent circuits of the flexible DC transmission network under different DC fault types are obtained.

[0008] Based on the harmonic order relationship between the AC side and the DC side, each fault equivalent circuit is equivalently transformed to obtain each AC side sequence component network, wherein the AC side sequence component network has a positive sequence network, a negative sequence network and a zero sequence network.

[0009] The interaction impact data of each DC fault type in the positive sequence network, the negative sequence network, and the zero sequence network are obtained respectively;

[0010] In the actual operation of the flexible DC transmission network, the fault results corresponding to the flexible DC transmission network are determined based on the detected interaction impact data.

[0011] Preferably, the step of performing an equivalent transformation on each fault equivalent circuit based on the harmonic order relationship between the AC side and the DC side to obtain each AC side sequence component network includes:

[0012] Based on the harmonic order relationship between the AC side and the DC side, the instantaneous value of the three-phase positive sequence voltage on the AC side corresponding to the equivalent model of the DC collection and transmission system is obtained.

[0013] Based on the aforementioned order relationship, the instantaneous values ​​of the three-phase positive sequence voltage on the AC side are mapped to each of the fault equivalent circuits to obtain each of the AC side sequence component networks.

[0014] Preferably, the step of acquiring the interaction impact data of each DC fault type in the positive-sequence network, the negative-sequence network, and the zero-sequence network includes:

[0015] Analyze the electrical characteristics of the positive-sequence network, the negative-sequence network, and the zero-sequence network;

[0016] Based on the electrical characteristics, first interaction data in the positive sequence network, the negative sequence network, and the zero sequence network are obtained when a DC-side unipolar fault occurs.

[0017] Based on the electrical characteristics, second interaction data in the positive sequence network, the negative sequence network, and the zero sequence network are obtained when there is a DC-side inter-pole fault.

[0018] Preferably, the analysis of the electrical characteristics of the positive-sequence network, the negative-sequence network, and the zero-sequence network includes:

[0019] Based on the positive-sequence network, the negative-sequence network, and the zero-sequence network, the following are obtained: the loop current equation of the MMC converter station; the first relationship between the DC-side outlet voltage and current of the MMC converter station; the second relationship between the AC-side current, DC-side current, and bridge arm current corresponding to the DC-side grounding with high resistance; the third relationship between the bridge arm voltage and bridge arm current; the equivalent resistance relationship between the DC-side and the AC-side; and the equivalent inductance relationship between the DC-side and the AC-side.

[0020] Substituting the equivalent resistance relationship and the equivalent inductance relationship into the MMC converter station loop current equation, respectively, yields the fourth relationship between the DC-side outlet voltage and the DC-side voltage of the MMC converter station.

[0021] Substituting the fourth relation into the second relation, we obtain the fifth relation for the AC side current, DC side current, and bridge arm current corresponding to the DC side grounded through high resistance.

[0022] Substituting the fifth relationship into the third relationship, we obtain the sixth relationship between the DC side current and the three-phase bridge arm current corresponding to the DC side grounded through high resistance.

[0023] Substituting the sixth relation into the fourth relation, we obtain the seventh relation between the capacitor voltages of the upper and lower bridge arms of phase A, the AC side voltage, and the DC side outlet voltage of the MMC converter station.

[0024] Substituting the third relation into the loop current equation of the MMC converter station, we obtain the eighth relation between the AC side outlet voltage and the AC side of the MMC converter station.

[0025] Substituting the seventh relation into the eighth relation, we obtain the first DC component contained in the AC side i-phase voltage and current in steady state.

[0026] The seventh relation and the first DC component are used as the electrical characteristics of the positive-sequence network, the negative-sequence network, and the zero-sequence network.

[0027] Preferably, the step of obtaining the first interaction data in the positive-sequence network, the negative-sequence network, and the zero-sequence network when a DC-side unipolar fault occurs based on the electrical characteristics includes:

[0028] Based on the seventh relation, the positive sequence network, the negative sequence network, and the zero sequence network are analyzed respectively, and the ninth relation of AC, DC and bridge arm capacitor voltage in the positive sequence network, the tenth relation of AC, DC and bridge arm capacitor voltage in the negative sequence network, and the eleventh relation of AC, DC and bridge arm capacitor voltage in the zero sequence network are obtained when the DC side unipolar fault occurs.

[0029] By analyzing the equivalent model of the DC collection and transmission system, the twelfth relationship between the DC side current and the fault point current corresponding to the DC side grounded through high resistance is obtained;

[0030] Based on the DC-side zero-resistance grounding, the equivalent model of the DC collection and transmission system is analyzed, and the thirteenth relationship between the DC-side outlet negative zero-sequence voltage and the DC-side zero-sequence current of the MMC converter station is obtained.

[0031] Substituting the thirteenth relation into the twelfth relation, we obtain the fourteenth relation between the DC side current and the fault point current corresponding to the DC side grounded through high resistance.

[0032] Based on the relationship between the amplitude and phase of the zero-sequence component, the fourteenth relationship is transformed to obtain the fifteenth relationship between the DC side current and the fault point current corresponding to the DC side grounded through high resistance.

[0033] Substituting the fifteenth relation into the thirteenth relation, we obtain the sixteenth relation between the negative electrode voltage and the lower bridge arm voltage.

[0034] Substituting the sixteenth relation and the value of the zero-sequence voltage of the DC side outlet of the MMC converter station into the eleventh relation, we obtain the simplified seventeenth relation for the AC, DC and bridge arm capacitor voltages in the zero-sequence network.

[0035] Substituting the voltage value in the positive sequence network during the DC-side unipolar fault into the ninth relational expression yields the first analysis result.

[0036] Substituting the voltage value in the negative sequence network during the DC-side unipolar fault into the tenth relational expression yields the second analysis result.

[0037] Substituting the voltage value in the zero-sequence network during the DC-side unipolar fault into the seventeenth relation, the third analysis result is obtained;

[0038] Based on the first analysis result, the second analysis result and the third analysis result, the first component of the AC side output voltage and current when there is a DC side unipolar fault is obtained;

[0039] The seventeenth relation and the first component are used as the first interaction data.

[0040] Preferably, the step of obtaining the first interaction data in the positive-sequence network, the negative-sequence network, and the zero-sequence network when a DC-side unipolar fault occurs based on the electrical characteristics further includes:

[0041] Based on the value of the equivalent resistance when the AC side is not grounded, the first component is analyzed to obtain the second component of the AC side output voltage and current corresponding to the AC side being ungrounded when the DC side is unipolar fault.

[0042] The second component is used as the first interaction impact data.

[0043] Preferably, the step of obtaining the second interaction data in the positive-sequence network, the negative-sequence network, and the zero-sequence network when there is a DC-side inter-pole fault based on the electrical characteristics includes:

[0044] The equivalent model of the DC collection and transmission system is analyzed to obtain the voltage component of the AC side outlet when there is a DC side inter-pole fault.

[0045] Substituting the relationship between phase voltage and zero-sequence voltage into the thirteenth relationship, we obtain the eighteenth relationship between the AC side outlet phase A voltage, the upper and lower arm voltages of phase A, and the DC side negative terminal voltage of the MMC converter station.

[0046] Substitute the voltage value of the positive sequence network during the DC-side inter-electrode fault into the eighteenth relation and the first DC component in sequence to obtain the second DC component of the AC-side outlet voltage and current of the MMC converter station corresponding to the DC-side inter-electrode fault.

[0047] Substitute the voltage value of the negative sequence network during the DC-side inter-pole fault into the tenth relation and the first DC component in sequence to obtain the third DC component of the AC-side outlet voltage and current of the MMC converter station corresponding to the DC-side inter-pole fault.

[0048] Based on the second DC component and the third DC component, the fourth DC component of the AC side outlet voltage and current of the MMC converter station when the inter-pole fault enters steady state is obtained.

[0049] The voltage component of the AC side outlet and the fourth DC component are used as the second interactive influence data.

[0050] Secondly, the present invention also provides a system for analyzing the impact of DC-side faults on the AC side of a flexible DC transmission network. The flexible DC transmission network includes a DC side and an AC side connected by an MMC converter station. The system includes: a system equivalent model construction unit, a fault equivalent circuit acquisition unit, an AC side sequence component network acquisition unit, an interactive impact data acquisition unit, and a fault analysis unit.

[0051] The system equivalent model construction unit is used to construct a DC collection and transmission system model based on the flexible DC transmission network, and to perform an equivalent transformation on the DC collection and transmission system model to obtain an equivalent model of the DC collection and transmission system.

[0052] The fault equivalent circuit acquisition unit is used to input pre-created DC-side fault events of various types into the DC collection and transmission system equivalent model to obtain the fault equivalent circuit of the flexible DC transmission network under different DC fault types.

[0053] The AC-side sequence component network acquisition unit is used to perform equivalent transformation on each fault equivalent circuit according to the harmonic order relationship between the AC side and the DC side to obtain each AC-side sequence component network, wherein the AC-side sequence component network has a positive sequence network, a negative sequence network and a zero sequence network.

[0054] The interaction impact data acquisition unit is used to acquire the interaction impact data of each DC fault type in the positive sequence network, the negative sequence network, and the zero sequence network.

[0055] The fault analysis unit is used to determine the fault result of the flexible DC transmission network based on the detected interaction impact data during the actual operation of the flexible DC transmission network.

[0056] Preferably, the AC side-order component network acquisition unit includes: a conversion unit and a mapping unit.

[0057] The conversion unit is used to obtain the instantaneous value of the three-phase positive sequence voltage on the AC side corresponding to the equivalent model of the DC collection and transmission system based on the harmonic order relationship between the AC side and the DC side.

[0058] The mapping unit is used to map the instantaneous values ​​of the three-phase positive sequence voltage on the AC side to each of the fault equivalent circuits based on the order relationship, so as to obtain each of the AC side sequence component networks.

[0059] Preferably, the interaction impact data acquisition unit includes: a first analysis unit, a second analysis unit, and a third analysis unit;

[0060] The first analysis unit is used to analyze the electrical characteristics of the positive-sequence network, the negative-sequence network, and the zero-sequence network;

[0061] The second analysis unit is used to obtain, based on the electrical characteristics, the first interaction data in the positive sequence network, the negative sequence network, and the zero sequence network when a DC-side unipolar fault occurs;

[0062] The third analysis unit is used to obtain second interaction data in the positive sequence network, the negative sequence network, and the zero sequence network when there is a DC-side inter-pole fault, based on the electrical characteristics.

[0063] Preferably, the first analysis unit includes: a first calculation unit, a second calculation unit, a third calculation unit, a fourth calculation unit, a fifth calculation unit, a sixth calculation unit, a seventh calculation unit, and a first determination unit;

[0064] The first calculation unit is used to obtain, based on the positive-sequence network, the negative-sequence network, and the zero-sequence network, the loop current equation of the MMC converter station, the first relationship between the DC side outlet voltage and current of the MMC converter station, the second relationship between the AC side current, DC side current, and bridge arm current corresponding to the DC side grounded through high resistance, the third relationship between the bridge arm voltage and bridge arm current, the equivalent resistance relationship between the DC side and the AC side, and the equivalent inductance relationship between the DC side and the AC side.

[0065] The second calculation unit is used to substitute the equivalent resistance relationship and the equivalent inductance relationship into the MMC converter station loop current equation to obtain the fourth relationship between the DC side outlet voltage and the DC side of the MMC converter station.

[0066] The third calculation unit is used to substitute the fourth relation into the second relation to obtain the fifth relation for the AC side current, DC side current and bridge arm current corresponding to the DC side grounded through high resistance.

[0067] The fourth calculation unit is used to substitute the fifth relationship into the third relationship to obtain the sixth relationship between the DC side current and the three-phase bridge arm current corresponding to the DC side grounded through high resistance.

[0068] The fifth calculation unit is used to substitute the sixth relation into the fourth relation to obtain the seventh relation between the upper and lower bridge arm capacitor voltages of phase A, the AC side voltage, and the DC side outlet voltage of the MMC converter station.

[0069] The sixth calculation unit is used to substitute the third relation into the MMC converter station loop current equation to obtain the eighth relation between the AC side outlet voltage and the AC side of the MMC converter station.

[0070] The seventh calculation unit is used to substitute the seventh relation into the eighth relation to obtain the first DC component contained in the AC side i-phase voltage and current in steady state.

[0071] The first determining unit is used to use the seventh relation and the first DC component as electrical characteristics of the positive-sequence network, the negative-sequence network, and the zero-sequence network.

[0072] Preferably, the second analysis unit includes: an eighth calculation unit, a ninth calculation unit, a tenth calculation unit, an eleventh calculation unit, a twelfth calculation unit, a thirteenth calculation unit, a fourteenth calculation unit, a fifteenth calculation unit, a sixteenth calculation unit, a seventeenth calculation unit, an eighteenth calculation unit, and a second determination unit;

[0073] The eighth calculation unit is used to analyze the positive sequence network, the negative sequence network and the zero sequence network respectively according to the seventh relation, and obtain the ninth relation of AC, DC and bridge arm capacitor voltage in the positive sequence network, the tenth relation of AC, DC and bridge arm capacitor voltage in the negative sequence network and the eleventh relation of AC, DC and bridge arm capacitor voltage in the zero sequence network when the DC side unipolar fault occurs.

[0074] The ninth calculation unit is used to analyze the equivalent model of the DC collection and transmission system to obtain the twelfth relationship between the DC side current and the fault point current corresponding to the DC side grounded through high resistance.

[0075] The tenth calculation unit is used to analyze the equivalent model of the DC collection and transmission system based on the DC side zero resistance grounding, and obtain the thirteenth relationship between the DC side outlet negative pole zero-sequence voltage and the DC side zero-sequence current of the MMC converter station.

[0076] The eleventh calculation unit is used to substitute the thirteenth relation into the twelfth relation to obtain the fourteenth relation between the DC side current and the fault point current corresponding to the DC side grounded through high resistance.

[0077] The twelfth calculation unit is used to transform the fourteenth relationship based on the relationship between the amplitude and phase of the zero-sequence component, and obtain the fifteenth relationship between the DC side current and the fault point current corresponding to the DC side grounded through high resistance.

[0078] The thirteenth calculation unit is used to substitute the fifteenth relation into the thirteenth relation to obtain the sixteenth relation between the negative electrode voltage and the lower bridge arm voltage.

[0079] The fourteenth calculation unit is used to substitute the sixteenth relation and the value of the zero-sequence voltage of the DC side outlet of the MMC converter station into the eleventh relation to obtain the simplified seventeenth relation of AC, DC and bridge arm capacitor voltages in the zero-sequence network.

[0080] The fifteenth calculation unit is used to substitute the voltage value in the positive sequence network when the DC-side unipolar fault occurs into the ninth relational expression to obtain the first analysis result.

[0081] The sixteenth calculation unit is used to substitute the voltage value in the negative sequence network when the DC-side unipolar fault occurs into the tenth relation to obtain the second analysis result;

[0082] The seventeenth calculation unit is used to substitute the voltage value in the zero-sequence network when the DC-side unipolar fault occurs into the seventeenth relation to obtain the third analysis result;

[0083] The eighteenth calculation unit is used to obtain the first component of the AC side outlet voltage and current when there is a DC side unipolar fault based on the first analysis result, the second analysis result and the third analysis result.

[0084] The second determining unit is used to take the seventeenth relation and the first component as the first interaction influence data.

[0085] Preferably, the second analysis unit further includes: a nineteenth calculation unit and a third determination unit;

[0086] The nineteenth calculation unit is used to analyze the first component based on the value of the equivalent resistance when the AC side is not grounded, and to obtain the second component of the AC side output voltage and current corresponding to the AC side being ungrounded when the DC side is a single-pole fault.

[0087] The third determining unit is used to use the second component as the first interaction influence data.

[0088] Preferably, the third analysis unit further includes: a twentieth calculation unit, a twenty-first calculation unit, a twenty-second calculation unit, a twenty-third calculation unit, a twenty-fourth calculation unit, and a fourth determination unit;

[0089] The twentieth calculation unit is used to analyze the equivalent model of the DC collection and transmission system to obtain the voltage component of the AC side outlet when there is a DC side inter-pole fault.

[0090] The 21st calculation unit is used to substitute the relationship between phase voltage and zero-sequence voltage into the 13th relationship to obtain the 18th relationship between the AC side outlet phase A voltage, the upper and lower arm voltages of phase A, and the DC side negative electrode voltage of the MMC converter station.

[0091] The 22nd calculation unit is used to substitute the voltage value of the positive sequence network when the DC-side inter-pole fault occurs into the 18th relation and the first DC component in sequence to obtain the second DC component of the AC-side outlet voltage and current of the MMC converter station corresponding to the DC-side inter-pole fault.

[0092] The 23rd calculation unit is used to substitute the voltage value of the negative sequence network when the DC-side inter-pole fault occurs into the 10th relation and the first DC component in sequence to obtain the third DC component of the AC-side outlet voltage and current of the MMC converter station corresponding to the DC-side inter-pole fault.

[0093] The 24th calculation unit is used to obtain the fourth DC component of the AC side outlet voltage and current of the MMC converter station when the inter-pole fault enters steady state, based on the second DC component and the third DC component.

[0094] The fourth determining unit is used to take the voltage component of the AC side outlet and the fourth DC component as the second interactive influence data.

[0095] Thirdly, the present invention also provides a computer device, the computer device including a memory, a processor and a transceiver, which are connected to each other via a bus; the memory is used to store a set of computer program instructions and data, and to transmit the stored data to the processor, the processor executes the program instructions stored in the memory to execute the above-described method for analyzing the impact of DC-side faults on the AC side of flexible DC transmission.

[0096] Fourthly, the present invention also provides a computer-readable storage medium storing a computer program that, when the computer program is run, implements the above-described method for analyzing the impact of DC-side faults on the AC side of flexible DC transmission.

[0097] This invention provides a method, system, equipment, and medium for analyzing the impact of DC-side faults on the AC side of flexible DC transmission lines. Compared with existing technologies, the beneficial effects of the embodiments of this invention are at least one of the following:

[0098] (1) Clearly define the characteristic changes and development stages of DC-side faults on the AC side, and accurately analyze the impact of DC-side faults on the AC side.

[0099] (2) Based on the impact of DC side faults on AC side electrical quantities, effective control of the AC side is achieved after a DC side fault. Attached Figure Description

[0100] Figure 1 This is a schematic diagram of the steps of a method for analyzing the impact of DC-side faults on the AC side of a flexible DC transmission system, provided in a preferred embodiment of the present invention.

[0101] Figure 2 This is a schematic diagram of a DC collection and transmission system model provided in a preferred embodiment of the present invention;

[0102] Figure 3 This is a schematic diagram of an equivalent model of a DC collection and transmission system provided in a preferred embodiment of the present invention;

[0103] Figure 4 This is a schematic diagram of the steps of the method for obtaining various AC side-order component networks provided in a preferred embodiment of the present invention;

[0104] Figure 5 This is a schematic diagram of the structure of a positive-order component network provided in a preferred embodiment of the present invention;

[0105] Figure 6 This is a schematic diagram of the structure of a negative-order component network provided in a preferred embodiment of the present invention;

[0106] Figure 7 This is a schematic diagram of the structure of a zero-order component network provided in a preferred embodiment of the present invention;

[0107] Figure 8 This is a schematic diagram of the steps for obtaining interaction impact data according to a preferred embodiment of the present invention;

[0108] Figure 9 This is a preferred embodiment of the present invention, showing the DC-side output voltage waveform of an MMC converter during an AC-side grounding fault with the DC-side positive terminal grounding.

[0109] Figure 10 This is a preferred embodiment of the present invention, showing the AC-side output voltage waveform of an MMC converter with a DC-side positive-to-ground fault when the AC side is grounded.

[0110] Figure 11 This is a preferred embodiment of the present invention, showing the DC-side output voltage waveform of an MMC converter with an AC-side ground fault during a DC-side inter-electrode fault.

[0111] Figure 12 This is a preferred embodiment of the present invention, showing the AC-side output voltage waveform of an MMC converter with a DC-side inter-electrode fault when the AC side is grounded.

[0112] Figure 13 This is a preferred embodiment of the present invention, which provides the AC / DC current amplitude of the zero-sequence network during an AC-side grounding fault on the DC side.

[0113] Figure 14 This is a preferred embodiment of the present invention, which provides the negative sequence network AC / DC current amplitude for a DC-side positive grounding fault during AC-side grounding.

[0114] Figure 15 This is a preferred embodiment of the present invention, which provides the AC / DC current amplitude of the positive sequence network for a DC-side positive electrode grounding fault when the AC side is grounded;

[0115] Figure 16 This is a preferred embodiment of the present invention, which provides the simulated and calculated values ​​of the AC side output voltage after a positive grounding fault;

[0116] Figure 17 This is a preferred embodiment of the present invention, which provides the simulated and calculated values ​​of the AC side outlet voltage after an inter-electrode fault.

[0117] Figure 18 This is the AC / DC current amplitude of the zero-sequence network during AC-side grounding provided in a preferred embodiment of the present invention;

[0118] Figure 19 This is the AC / DC current amplitude of the inter-electrode fault negative sequence network when the AC side is grounded, provided by a preferred embodiment of the present invention;

[0119] Figure 20 This is the AC / DC current amplitude of the positive sequence network for inter-electrode faults during AC side grounding provided in a preferred embodiment of the present invention;

[0120] Figure 21 This is a schematic diagram of a system for analyzing the impact of DC-side faults on the AC side of a flexible DC transmission line, provided in a preferred embodiment of the present invention.

[0121] Figure 22This is a schematic diagram of a computer device provided in a preferred embodiment of the present invention. Detailed Implementation

[0122] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. The embodiments are provided for illustrative purposes only and should not be construed as limiting the invention. The accompanying drawings are for reference and illustration only and do not constitute a limitation on the scope of protection of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of this invention. In the description of this invention, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," "third," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0123] In the description of this invention, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to communication within two components. The terms "vertical," "horizontal," "left," "right," "upper," "lower," and similar expressions used herein are for illustrative purposes only and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0124] In the description of this invention, it should be noted that, unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing specific embodiments only and is not intended to limit the invention. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0125] Please see Figure 1 In an embodiment of the present invention, a method for analyzing the impact of DC-side faults on the AC side of flexible DC transmission is provided, wherein the liquid hydrogen superconducting magnetic energy storage device includes at least a liquid hydrogen energy storage unit and a superconducting magnetic energy storage unit, and the method includes:

[0126] S1. Based on the flexible DC transmission network, construct a DC collection and transmission system model, and perform an equivalent transformation on the DC collection and transmission system model to obtain an equivalent model of the DC collection and transmission system.

[0127] S2. Input the pre-created DC-side fault events of various types into the equivalent model of the DC collection and transmission system to obtain the fault equivalent circuit of the flexible DC transmission network under different DC fault types.

[0128] S3. Based on the harmonic order relationship between the AC side and the DC side, perform equivalent transformation on each fault equivalent circuit to obtain each AC side sequence component network, wherein the AC side sequence component network has a positive sequence network, a negative sequence network and a zero sequence network.

[0129] S4. Obtain the interaction impact data of each DC fault type in the positive sequence network, the negative sequence network and the zero sequence network respectively.

[0130] S5. In the actual operation of the flexible DC transmission network, based on the detected interactive impact data, determine the fault result corresponding to the flexible DC transmission network.

[0131] In a preferred embodiment of the present invention, a DC collection and transmission system model is constructed based on a flexible DC transmission network, such as... Figure 2 The diagram shows the structure of a DC collection and transmission system. This system involves a DC power station directly connecting to the DC side and transmitting power to the AC side via an MMC converter station. DC power stations include renewable energy power stations such as photovoltaic and wind power plants. By performing an equivalent transformation on the DC collection and transmission system model, an equivalent model can be obtained. This equivalent model consists of a DC equivalent system and an AC equivalent system, as shown below. Figure 3 The diagram shown is an equivalent model of a DC collection and transmission system.

[0132] Based on historical faults on the DC side of the flexible DC transmission network, various types of DC fault events are created. These pre-created DC fault events are then input into the equivalent model of the DC collection and transmission system to obtain the corresponding fault equivalent circuits of the flexible DC transmission network under different DC fault types. These fault equivalent circuits serve as the basis for fault analysis.

[0133] In a preferred embodiment of the present invention, the amplitude of the positive sequence component of the power frequency AC electrical quantity F is set to F. (1) The magnitude of the negative-order component is F (2) The zero-sequence component amplitude is F (0)The equivalent model of the DC collection and transmission system is obtained. Based on the equivalent model of the DC collection and transmission system, the various types of DC-side fault events that were created beforehand are input into the equivalent model of the DC collection and transmission system to obtain the fault equivalent circuit of the flexible DC transmission network under different DC fault types. The positive and negative sequence components of the fault equivalent circuit are shown in Equation (1):

[0134]

[0135] Among them, F A(1) For the positive sequence component of a phase A DC fault, F B(1) For the positive sequence component of a phase B DC fault, F C(1) For the positive sequence component of a C-phase DC fault; F A(2) For the negative sequence component of a phase A DC fault, F B(2) For the negative sequence component of a phase B DC fault, F C(2) For the negative sequence component of a C-phase DC fault, F (1) For the peak value of the positive sequence component of a DC fault, F (2) This represents the peak value of the negative sequence component of a DC fault. ω represents the power frequency angular frequency, and t represents time.

[0136] Furthermore, based on the harmonic order relationship between the AC and DC sides, an equivalent transformation is performed on each fault equivalent circuit to obtain the sequence component networks of each AC side, such as... Figure 4 As shown, it includes the following steps:

[0137] S301. Based on the harmonic order relationship between the AC side and the DC side, obtain the instantaneous value of the three-phase positive sequence voltage on the AC side corresponding to the equivalent model of the DC collection and transmission system.

[0138] S302. Based on the aforementioned order relationship, the instantaneous values ​​of the three-phase positive sequence voltage on the AC side are mapped to each of the aforementioned fault equivalent circuits to obtain each of the aforementioned AC side sequence component networks.

[0139] The harmonic orders between the AC and DC sides have the following relationship:

[0140] k dc =±(k) ac -1) (2)

[0141] Where, k ac For the harmonic order of the AC side, k dc This represents the harmonic order on the DC side.

[0142] Based on equation (2), the instantaneous values ​​of the three-phase positive sequence voltage on the AC side are obtained, as shown in equation (3):

[0143]

[0144] Among them, EA(1) E is the positive sequence component of phase A of the instantaneous voltage on the AC side. B(1) E is the positive sequence component of phase B of the instantaneous voltage on the AC side. C(1) E is the positive sequence component of the C-phase instantaneous voltage on the AC side. m E represents the peak instantaneous voltage on the AC side. m For k ac The amplitude of the subharmonic electrical quantity.

[0145] Furthermore, in orthogonal networks, k ac =1, corresponding to k dc =0, at this time the positive sequence component on the AC side and the DC component on the DC side are mutually mapped, thus obtaining the positive sequence network as follows: Figure 5 As shown. In the negative order network, k ac =1, corresponding to k dc =2, at this time there is a mapping relationship between the negative sequence component on the AC side and the second harmonic on the DC side, so the negative sequence network is as follows: Figure 6 As shown. The zero-sequence component is related to the grounding method and fault type. The AC side zero-sequence component is as shown in equation (4). If there is also a grounding point on the DC side, the DC side zero-sequence current has the relationship shown in equation (5). The zero-sequence network is as follows. Figure 7 As shown.

[0146] F A(0) =F B(0) =F C(0) =F (0) sin(ωt+α) (4)

[0147] F dc(0) =3F (0) sin(ωt+α) (5)

[0148] Furthermore, the interaction data of each DC fault type in the positive-sequence network, negative-sequence network, and zero-sequence network are obtained separately, such as... Figure 8 As shown, it includes the following steps:

[0149] S401. Analyze the electrical characteristics of the positive-sequence network, the negative-sequence network, and the zero-sequence network.

[0150] S402. Based on the electrical characteristics, obtain the first interaction data in the positive sequence network, the negative sequence network, and the zero sequence network when a DC-side unipolar fault occurs.

[0151] S403. Based on the electrical characteristics, obtain the second interaction data in the positive sequence network, the negative sequence network, and the zero sequence network when there is a DC side inter-pole fault.

[0152] Based on the obtained ordered component networks, the electrical characteristics of the positive-order network, negative-order network, and zero-order network are analyzed, specifically:

[0153] Based on the sequence component network, the loop current equations for the MMC converter station are written as follows:

[0154]

[0155] Among them, u p The positive line voltage of DC, u n The DC negative line voltage, u A For the phase A voltage at the AC side collection point of the MMC converter station, u As For the AC side A-phase voltage, u Au The voltage of phase A on the DC side of the upper bridge arm converter valve, u Aa The voltage of phase A on the DC side of the lower arm converter valve, i A For the lower bridge arm A phase bridge arm current, i dc For DC side current, L ac For the AC side equivalent inductance, R dc This is the DC side resistance.

[0156] The equivalent resistance and equivalent inductance between the DC side and the AC side have the following relationship: R aca =2R ac +R arm L aca =2L ac +L arm Among them, R ac R is the equivalent resistance on the AC side. arm L is the equivalent resistance of the bridge arm. arm For the bridge arm reactance and inductance, L aca To account for the AC side grounding resistance, the equivalent inductance on the AC side, R aca The equivalent resistance of the AC side when considering the AC side grounding resistance.

[0157] Based on the above relationship between the equivalent resistance and equivalent inductance between the DC and AC sides, substituting this into the MMC converter station loop current equation, we obtain the fourth relationship between the DC-side outlet voltage and the DC side of the MMC converter station, as shown below:

[0158]

[0159] Among them, u Aa1 This is the voltage of the lower bridge arm.

[0160] Based on the sequence component network, the first relationship between the DC-side outlet voltage and current of the MMC converter station is written as follows:

[0161] u p =-R dcn (i p +i dc ),u n =-Rdcn (i n -i dc (8)

[0162] Among them, i p For DC side current, R dcn For DC side grounding resistance, i n This is the negative current on the DC side.

[0163] Based on the sequence component network, the second relationship between the AC side current, DC side current, and bridge arm current corresponding to the DC side being grounded through a high resistance is written as shown in equation (9). Because when the DC side is grounded through a high resistance, i p ≈-i n ≈i dc The relationship, equation (9), is shown below:

[0164]

[0165] Among them, i i For AC side current, i p i n DC side current, i iu For the upper bridge arm current and i i1 This represents the current in the lower bridge arm.

[0166] Substituting the fourth relationship into the second relationship, we obtain the fifth relationship for the AC side current, DC side current, and bridge arm current corresponding to the DC side being grounded through high resistance. Specifically, according to equations (8) and (9), we can obtain equation (10), which is the second relationship for the AC side current, DC side current, and bridge arm current corresponding to the DC side being grounded through high resistance. Equation (10) is shown below:

[0167]

[0168] Based on the sequence component network, the third relationship between the bridge arm voltage and the bridge arm current is written as follows:

[0169]

[0170] Among them, u Acu The voltage of the upper bridge arm of phase A, u Aau The voltage of the lower bridge arm of phase A, u Aa1 The voltage of the upper bridge arm capacitor is u. Ac1 C is the voltage across the lower bridge arm capacitor. Au For the upper bridge arm capacitor, C sm For the submodule capacitor, C A1 This is the capacitor for the lower bridge arm.

[0171] Substituting the fifth relationship into the third relationship, we obtain the sixth relationship between the DC-side current and the three-phase bridge arm current corresponding to the DC-side high-resistance grounding. Specifically, in the DC-side high-resistance grounding system, substituting equation (10) into (11), we obtain the relationship between the DC-side current and the three-phase bridge arm current corresponding to the DC-side high-resistance grounding, as shown in equation (12):

[0172]

[0173] Among them, u ic1 For the three-phase bridge arm current, i icu This is the DC side current.

[0174] Substituting the sixth relation into the fourth relation, we obtain the seventh relation between the capacitor voltages of the upper and lower bridge arms of phase A, the AC side voltage, and the DC side outlet voltage of the MMC converter station. Specifically, substituting equation (12) into the relation between the DC side outlet voltage and the DC side of the MMC converter station, i.e., equation (7), we obtain the relation between the capacitor voltages of the upper and lower bridge arms of phase A, the AC side voltage, and the DC side outlet voltage of the MMC converter station, as shown in equation (13):

[0175]

[0176] Where, N Au N represents the number of submodules deployed on the upper bridge arm. A1 The number of sub-modules to be deployed in the lower bridge arm.

[0177] Furthermore, substituting the third relation into the loop current equation of the MMC converter station, we obtain the eighth relation between the AC side outlet voltage and the AC side of the MMC converter station. Specifically, substituting (11) into loop equation (6), we obtain the relation between the AC side outlet voltage and the AC side of the MMC converter station, as shown in equation (14):

[0178]

[0179] Furthermore, substituting the seventh relation into the eighth relation, we obtain the first DC component of the AC side i-phase voltage and current in steady state. Specifically, the i-phase bridge arm capacitor voltage ui is obtained from equation (13). cu u icl Substituting this into equation (14) yields the output voltage u of phase i on the AC side. i Therefore, considering only the DC component, the DC components of the AC side i-phase voltage and current in steady state can be obtained as shown in equation (15):

[0180]

[0181] Among them, U p U is the positive voltage on the DC side. n This is the negative voltage on the DC side.

[0182] The seventh relation and the first DC component are used as the electrical characteristics of the positive sequence network, negative sequence network and zero sequence network, that is, the above equations (13) and (15) are used as the basis for subsequent fault analysis.

[0183] Based on electrical characteristics, the first interaction effect data of a DC-side unipolar fault in the positive-sequence, negative-sequence, and zero-sequence networks is obtained. The specific process is as follows:

[0184] Based on the seventh relation, i.e. equation (13), the positive sequence network, negative sequence network and zero sequence network are analyzed respectively, and the ninth relation of AC, DC and bridge arm capacitor voltage in the positive sequence network, the tenth relation of AC, DC and bridge arm capacitor voltage in the negative sequence network and the eleventh relation of AC, DC and bridge arm capacitor voltage in the zero sequence network are obtained when there is a DC side unipolar fault.

[0185] The ninth relation is shown in equation (16):

[0186]

[0187] Among them, u Asf|0| The voltage of phase A on the AC side before the fault, u Acuf(1) For the positive sequence component of the DC-side A-phase voltage of the upper bridge arm converter valve, u Ac1f(1) The positive sequence component of the DC-side A-phase voltage of the lower bridge arm converter valve, u pf(1) U is the positive DC-side voltage in the positive sequence network. As|0| For the steady-state upper bridge arm voltage, u as|0| The steady-state bridge arm voltage, u nf(1) This is the negative voltage on the DC side of the positive sequence network.

[0188] Negative-sequence networks have a similar relationship; by removing the equivalent voltage sources on the AC and DC sides, u... As =0, then the tenth relation is as shown in equation (17):

[0189]

[0190] Among them, u Acuf(2) For the negative sequence component of the DC-side A-phase voltage of the upper bridge arm converter valve, u Ac1f(2) For the negative sequence component of the DC-side A-phase voltage of the lower bridge arm converter valve, u pf(2) The negative sequence voltage of the positive DC line of the MMC after the fault, u nf(2) It is the negative sequence voltage of the negative pole line.

[0191] After a unipolar fault, if the AC side is grounded, a zero-sequence path exists. Similarly, the eleventh relation can be obtained, as shown in equation (18):

[0192]

[0193] Among them, u Acuf(0) For the zero-sequence component of the DC-side A-phase voltage of the upper bridge arm converter valve, u Ac1f(0) For the zero-sequence component of the DC-side A-phase voltage of the lower bridge arm converter valve, u pf(0) The zero-sequence voltage of the positive DC line of the MMC after the fault, u nf(0) This is the zero-sequence voltage of the negative pole line.

[0194] An analysis of the equivalent model of the DC collection and transmission system yields the twelfth relationship between the DC side current and the fault point current corresponding to the DC side grounding via high resistance, as shown in equation (19):

[0195]

[0196] Among them, i p(0) i represents the zero-sequence component of the DC-side current at the outlet of the positive converter valve. dc(0) i is the zero-sequence component of the positive DC side current. f(0) i represents the zero-sequence component of the DC-side fault point current. a(0) For the zero-sequence component of the A-phase current on the AC side, i i(0) This represents the zero-sequence component of the i-phase current on the AC side.

[0197] Based on the zero-resistance grounding of the DC side, the equivalent model of the DC collection and transmission system is analyzed, and the thirteenth relationship between the negative terminal zero-sequence voltage and the zero-sequence current of the DC side outlet of the MMC converter station is obtained, as shown in equation (20):

[0198]

[0199] Among them, L dc(0) R is the DC-side zero-sequence inductance. dc(0) This is the DC-side zero-sequence resistance.

[0200] Substituting the thirteenth relation into the twelfth relation, we obtain the fourteenth relation between the DC side current and the fault point current corresponding to the DC side grounded through high resistance. Specifically, substituting equation (20) into equation (19) yields equation (21).

[0201]

[0202] Among them, i pf(0) For the zero-sequence component of the DC current flowing through the positive commutator valve during a DC-side unipolar fault, i nf(0) For the zero-sequence component of the DC current flowing through the negative commutator valve during a DC-side unipolar fault, i g C is the fault current during a DC-side unipolar fault. sm(0) For the submodule capacitor, the zero-sequence capacitor, u icuf(0) For the zero-sequence component of the DC-side i-phase voltage of the upper arm converter valve, u icu1f(0)For the zero-sequence component of the DC-side i-phase voltage of the lower bridge arm converter valve, i 0 dcf This represents the zero-sequence component of the DC current.

[0203] Since the amplitude and phase of the zero-sequence component are equal, the fourteenth relationship is transformed based on the relationship between the amplitude and phase of the zero-sequence component to obtain the fifteenth relationship between the DC side current and the fault point current corresponding to the DC side grounding through high resistance. Specifically, equation (21) is rewritten as equation (22), which is shown below:

[0204]

[0205] Substituting the fifteenth relation into the thirteenth relation, we obtain the sixteenth relation between the negative electrode voltage and the lower bridge arm voltage. Specifically, substituting (22) into (20), we obtain the sixteenth relation between the negative electrode voltage and the lower bridge arm voltage, as shown in equation (23):

[0206]

[0207] Among them, U nf(0) This is the negative voltage.

[0208] Substituting the sixteenth relation and the value of the zero-sequence voltage at the DC-side outlet of the MMC converter station into the eleventh relation, we obtain the simplified seventeenth relation for the AC, DC, and bridge arm capacitor voltages in the zero-sequence network. Specifically, U... nf(0) Substituting 0 and equation (23) into equation (18), we obtain equation (24):

[0209]

[0210] Among them, L aca(0) R is the equivalent inductance on the AC side when considering the AC side grounding resistance in a zero-sequence network. a11(0) For the equivalent resistance in a zero-sequence network, L a11(0) It is an equivalent inductor in a zero-sequence network.

[0211] Substituting the voltage values ​​in the positive sequence network during a DC-side unipolar fault into the ninth relation, we obtain the first analytical result. Specifically, during a DC-side unipolar fault, in the positive sequence network, the positive voltage is 0, and the negative voltage is u. nf(1) =2u n|0| Substituting into equation (16), we obtain the first analysis result.

[0212] Substituting the voltage value in the negative-sequence network during a DC-side unipolar fault into the tenth relation yields the second analytical result. Specifically, during a DC-side unipolar fault, in the negative-sequence network, u As =0, u dc =0, substituting into equation (17), we obtain the third analysis result.

[0213] Substituting the voltage value in the zero-sequence network during a DC-side unipolar fault into the seventeenth relation yields the third analytical result. Specifically, during a DC-side unipolar fault, in the zero-sequence network, u As =0, u dc =0, substituting into equation (24), we obtain the third analysis result.

[0214] Based on the first, second, and third analysis results, the first components of the AC side output voltage and current during a DC-side unipolar fault are obtained, as shown in equation (25):

[0215]

[0216] Among them, U if I is the AC phase i-voltage of the converter valve during a DC-side unipolar fault. if U is the AC phase i-current of the converter valve during a DC-side unipolar fault. pf U is the positive DC voltage during a fault. nf This is the negative DC voltage during a fault.

[0217] The seventeenth relation and the first component are used as the first interactive influence data.

[0218] The first interactive impact data also includes the second components of the AC side output voltage and current corresponding to the AC side being ungrounded when there is a DC side unipolar fault. The method for obtaining these components is as follows:

[0219] Based on the equivalent resistance value when the AC side is ungrounded, the first component is analyzed to obtain the second component of the AC side output voltage and current corresponding to the AC side being ungrounded when there is a DC side unipolar fault. Specifically, when the AC side is ungrounded, R... acs The values ​​are relatively large, thus obtaining the second components of the AC side output voltage and current corresponding to the AC side being ungrounded when the DC side is in a unipolar fault, as shown in equation (26):

[0220] U if =(U pf +U nf ) / 2,I if =0 (26)

[0221] Based on electrical characteristics, the second interaction effect data of DC-side inter-pole faults in the positive-sequence, negative-sequence, and zero-sequence networks is obtained. The specific process is as follows:

[0222] The equivalent model of the DC collection and transmission system is analyzed to obtain the voltage component of the AC side outlet when there is an inter-pole fault on the DC side. Specifically, when there is an inter-pole fault, the DC side provides a short-circuit current flowing from the positive pole to the negative pole through the fault point. The equivalent impedance from the AC side outlet of the MMC converter station to the DC side decreases. The voltage component when the AC side voltage drops and stabilizes is shown in equation (27).

[0223]

[0224] Among them, Z dcf k is the DC-side equivalent impedance. f1 The impedance coefficient, For steady-state AC voltage, R f This is the transition resistance.

[0225] Substituting the relationship between phase voltage and zero-sequence voltage into equation thirteen, we obtain the eighteenth relationship between the AC side outlet phase A voltage, the upper and lower arm voltages of phase A, and the DC side negative electrode voltage of the MMC converter station. Specifically, during a DC side inter-electrode fault, the phase voltage and zero-sequence voltage exhibit a certain relationship. As =k f1 u Asf|0| Substituting the relationship between phase voltage and zero-sequence voltage into equation (20), we obtain the eighteenth relationship between the AC side outlet phase A voltage, the upper and lower bridge arm voltages of phase A, and the DC side negative terminal voltage of the MMC converter station, as shown in equation (28):

[0226]

[0227] During an inter-pole fault, the bridge arm capacitors discharge. Due to the different discharge sequence, the voltage of each phase bridge arm capacitor is unbalanced during the capacitor discharge. When the voltage exceeds the circulating current suppression control range, a bridge arm circulating current is generated, and a negative sequence network exists on the AC side. In this negative sequence network, the relationship between AC, DC and bridge arm capacitor voltages is the same as that in the case of a DC side unipolar fault, as shown in equation (17).

[0228] Substituting the voltage values ​​of the positive-sequence network during a DC-side inter-electrode fault into the eighteenth relation and the first DC component, we obtain the second DC component of the AC-side outlet voltage and current of the MMC converter station corresponding to the DC-side inter-electrode fault. Specifically, during an inter-electrode short circuit, there is no grounding point on the DC side, so there is no zero-sequence network. The voltage values ​​in the positive-sequence network during a DC-side inter-electrode fault have the following characteristics: In the positive-sequence network, the positive voltage is 0, and the negative voltage is u. nf(1) =2u n|0|Meanwhile, considering that the positive and negative voltages of the DC side of the MMC converter station are 0 after the fault enters steady state, the above characteristics are substituted into the eighteenth relationship between the AC side outlet voltage of phase A, the upper and lower arm voltages of phase A and the negative voltage of the DC side of the MMC converter station, i.e., equation (28). Then, the first DC component of the AC side i-phase voltage and current contained in steady state, i.e., equation (15), is substituted to obtain the second DC component of the AC side outlet voltage and current of the MMC converter station corresponding to the DC side inter-pole fault.

[0229] Substituting the voltage value of the negative-sequence network during the DC-side inter-electrode fault into the tenth relation and the first DC component, the third DC component of the AC-side outlet voltage and current of the MMC converter station corresponding to the DC-side inter-electrode fault is obtained. Specifically, during an inter-electrode short circuit, the voltage value in the negative-sequence network during a DC-side inter-electrode fault has the following characteristics: In the negative-sequence network, u As =0, u dc =0, and considering that the positive and negative voltages of the DC side of the MMC converter station are 0 after the fault enters steady state. Substituting the tenth relationship of AC, DC and bridge arm capacitor voltage in the above characteristic negative sequence network, i.e., equation (17), into the first DC component of the AC side i-phase voltage and current in steady state, i.e. equation (15), we obtain the third DC component of the AC side outlet voltage and current of the MMC converter station corresponding to the DC side inter-pole fault.

[0230] Based on the second and third DC components, the fourth DC component of the AC side outlet voltage and current of the MMC converter station when the inter-pole fault enters steady state is obtained, as shown in equation (29):

[0231] U if =0,I if =0 (29)

[0232] The voltage component at the AC side outlet and the fourth DC component are used as the second interactive influence data.

[0233] Furthermore, after acquiring the first and second interactive impact data, in the actual operation of the flexible DC transmission network, based on the actual detected interactive impact data, the corresponding fault result of the flexible DC transmission network is determined, thereby achieving effective control of the AC side after a DC-side fault.

[0234] In a preferred embodiment of the present invention, a DC collection and transmission system model is constructed based on a flexible DC transmission network. This model is then transformed into an equivalent model of the DC collection and transmission system. Pre-created DC fault events of various types are input into the equivalent model to obtain fault equivalent circuits for the flexible DC transmission network under different DC fault types. Based on the harmonic order relationship between the AC and DC sides, each fault equivalent circuit is transformed to obtain various AC-side sequence component networks, which include positive-sequence, negative-sequence, and zero-sequence networks. Interaction data for each DC fault type in the positive-sequence, negative-sequence, and zero-sequence networks are acquired. During the actual operation of the flexible DC transmission network, the fault outcome is determined based on the detected interaction data. The flexible DC transmission network method of the present invention clarifies the characteristic changes and fault development stages of DC-side faults on the AC side, accurately analyzes the impact of DC-side faults on the AC side, and, based on the impact of DC-side faults on the AC side, achieves effective control of the AC side after a DC-side fault.

[0235] In a specific embodiment of the present invention, the photovoltaic cell output voltage of a ±30kV / 1MW substation is taken as not exceeding 820V, and the photovoltaic cell output voltage of a 20kV / 500kW substation is taken as not exceeding 274V, i.e., the photovoltaic output voltage does not exceed 90% of the open-circuit voltage. Specific grid-connected converter parameters are shown in Table 1.

[0236] Table 1 Parameters of Grid-Connected Converter

[0237]

[0238] After a unipolar metallic short-circuit grounding, it's equivalent to moving the neutral point to the fault point. This slightly alters the photovoltaic output power. Figure 9 As shown in the waveform of the DC-side output voltage of the MMC converter during an AC-side ground fault (DC-side positive electrode grounding fault), the inter-electrode voltage at the DC-side output of the MMC converter station changes slightly, and the positive electrode voltage drops to 0, indicating that a positive electrode grounding fault has occurred. Because the inter-electrode voltage remains essentially unchanged, the arm capacitor voltage remains essentially unchanged, the arm current does not flow, the MMC converter station does not block, and the effective value of the AC-side output voltage remains essentially unchanged. Under the influence of the DC positive and negative electrode voltage imbalance, the AC-side voltage contains a DC component, and this DC component is approximately 1 / 2 of the inter-electrode voltage. Figure 10 The waveform shown is the AC side output voltage waveform of the MMC converter during an AC side grounding fault with the DC side positive terminal grounding. Under the control of the MPPT converter station, the DC side inter-electrode voltage drops to 38kV, as... Figure 11The diagram shows the DC-side output voltage waveform of an MMC converter during an AC-side ground fault. To maintain voltage balance with the inter-electrode voltage, the lower arm capacitor voltage rises. This voltage imbalance between the upper and lower arm capacitors leads to an abnormal AC-side output voltage, as shown in the diagram. Figure 12 The waveform of the AC side output voltage of the MMC converter during a DC side inter-electrode fault is shown.

[0239] Because the MMC converter station has no grounding point on the AC side, there is no zero-sequence network. For example... Figure 13 The diagram shows the AC and DC current amplitudes of the zero-sequence network during an AC-side ground fault with a DC-side positive terminal grounding. The AC-side zero-sequence current is 0, and the DC-side power frequency component amplitude is essentially the same as before the fault, indicating that there is no zero-sequence network in the system. After the fault, the voltage changes of the upper and lower bridge arm capacitors are essentially the same as before the fault, and the bridge arm capacitor voltages remain balanced, therefore there is no negative-sequence network, and the bridge arm current remains essentially unchanged. Figure 14 The AC and DC current amplitudes, AC negative-sequence current amplitude, and second harmonic content of the DC current in the negative-sequence network during an AC-side ground fault are consistent with those before the fault, indicating the absence of a negative-sequence network. Because the bridge arm voltage changes are consistent with those before the fault, the AC voltage amplitude remains essentially unchanged, but includes a DC component; therefore, the inter-electrode voltage remains essentially unchanged. Figure 15 The diagram shows the AC and DC current amplitudes in the positive-sequence network during an AC-side ground fault on the DC side. In the positive-sequence network, the AC and DC voltages drop by approximately 30kV almost simultaneously. Because there is no grounding point on the DC side during an inter-pole short circuit, there is no [further variation / effect]. Figure 18 The AC / DC current amplitudes of the zero-sequence network during AC-side grounding faults only exist as shown in the figure. Figure 19 The AC / DC current amplitudes of the negative sequence network during AC-side grounding faults are shown below. Figure 20 The AC / DC current amplitudes of the positive sequence network during AC-side grounding faults are shown.

[0240] When the MMC converter station is not locked, the presence of zero-sequence and negative-sequence components on the AC side affects the setting of the AC side fast protection. Simultaneously, from... Figure 16 The simulated and calculated values ​​of the AC side output voltage after a positive ground fault are shown. Figure 17 The simulated and calculated values ​​of the AC side outlet voltage after an inter-pole fault are shown. It can be seen that the difference between the calculated and simulated values ​​after the fault is small, especially in the steady-state stage of the fault, where the calculated values ​​are more accurate.

[0241] Accordingly, such as Figure 21As shown, based on a method for analyzing the impact of DC-side faults on the AC side of a flexible DC transmission network, this embodiment of the invention also provides an analysis of the impact of DC-side faults on the AC side of a flexible DC transmission network. The flexible DC transmission network includes a DC side and an AC side connected through an MMC converter station. The system includes: a system equivalent model construction unit 1, a fault equivalent circuit acquisition unit 2, an AC side sequence component network acquisition unit 3, an interaction impact data acquisition unit 4, and a fault analysis unit 5.

[0242] The system equivalent model construction unit 1 is used to construct a DC collection and transmission system model based on the flexible DC transmission network, and to perform equivalent transformation on the DC collection and transmission system model to obtain an equivalent model of the DC collection and transmission system.

[0243] The fault equivalent circuit acquisition unit 2 is used to input various types of pre-created DC-side fault events into the DC collection and transmission system equivalent model to obtain the fault equivalent circuit of the flexible DC transmission network under different DC fault types.

[0244] The AC-side sequence component network acquisition unit 3 is used to perform equivalent transformation on each fault equivalent circuit according to the harmonic order relationship between the AC side and the DC side to obtain each AC-side sequence component network, wherein the AC-side sequence component network has a positive sequence network, a negative sequence network and a zero sequence network.

[0245] The interaction impact data acquisition unit 4 is used to acquire the interaction impact data of each DC fault type in the positive sequence network, the negative sequence network and the zero sequence network respectively;

[0246] The fault analysis unit 5 is used to determine the fault result of the flexible DC transmission network based on the detected interaction impact data during the actual operation of the flexible DC transmission network.

[0247] In a preferred embodiment of the present invention, the AC side-order component network acquisition unit 3 includes: a conversion unit and a mapping unit.

[0248] The conversion unit is used to obtain the instantaneous value of the three-phase positive sequence voltage on the AC side corresponding to the equivalent model of the DC collection and transmission system based on the harmonic order relationship between the AC side and the DC side.

[0249] The mapping unit is used to map the instantaneous values ​​of the three-phase positive sequence voltage on the AC side to each of the fault equivalent circuits based on the order relationship, so as to obtain each of the AC side sequence component networks.

[0250] In a preferred embodiment of the present invention, the interaction impact data acquisition unit 4 includes: a first analysis unit, a second analysis unit, and a third analysis unit;

[0251] The first analysis unit is used to analyze the electrical characteristics of the positive-sequence network, the negative-sequence network, and the zero-sequence network;

[0252] The second analysis unit is used to obtain, based on the electrical characteristics, the first interaction data in the positive sequence network, the negative sequence network, and the zero sequence network when a DC-side unipolar fault occurs;

[0253] The third analysis unit is used to obtain second interaction data in the positive sequence network, the negative sequence network, and the zero sequence network when there is a DC-side inter-pole fault, based on the electrical characteristics.

[0254] In a preferred embodiment of the present invention, the first analysis unit includes: a first calculation unit, a second calculation unit, a third calculation unit, a fourth calculation unit, a fifth calculation unit, a sixth calculation unit, a seventh calculation unit, and a first determination unit;

[0255] The first calculation unit is used to obtain, based on the positive-sequence network, the negative-sequence network, and the zero-sequence network, the loop current equation of the MMC converter station, the first relationship between the DC side outlet voltage and current of the MMC converter station, the second relationship between the AC side current, DC side current, and bridge arm current corresponding to the DC side grounded through high resistance, the third relationship between the bridge arm voltage and bridge arm current, the equivalent resistance relationship between the DC side and the AC side, and the equivalent inductance relationship between the DC side and the AC side.

[0256] The second calculation unit is used to substitute the equivalent resistance relationship and the equivalent inductance relationship into the MMC converter station loop current equation to obtain the fourth relationship between the DC side outlet voltage and the DC side of the MMC converter station.

[0257] The third calculation unit is used to substitute the fourth relation into the second relation to obtain the fifth relation for the AC side current, DC side current and bridge arm current corresponding to the DC side grounded through high resistance.

[0258] The fourth calculation unit is used to substitute the fifth relationship into the third relationship to obtain the sixth relationship between the DC side current and the three-phase bridge arm current corresponding to the DC side grounded through high resistance.

[0259] The fifth calculation unit is used to substitute the sixth relation into the fourth relation to obtain the seventh relation between the upper and lower bridge arm capacitor voltages of phase A, the AC side voltage, and the DC side outlet voltage of the MMC converter station.

[0260] The sixth calculation unit is used to substitute the third relation into the MMC converter station loop current equation to obtain the eighth relation between the AC side outlet voltage and the AC side of the MMC converter station.

[0261] The seventh calculation unit is used to substitute the seventh relation into the eighth relation to obtain the first DC component contained in the AC side i-phase voltage and current in steady state.

[0262] The first determining unit is used to use the seventh relation and the first DC component as electrical characteristics of the positive-sequence network, the negative-sequence network, and the zero-sequence network.

[0263] In a preferred embodiment of the present invention, the second analysis unit includes: an eighth calculation unit, a ninth calculation unit, a tenth calculation unit, an eleventh calculation unit, a twelfth calculation unit, a thirteenth calculation unit, a fourteenth calculation unit, a fifteenth calculation unit, a sixteenth calculation unit, a seventeenth calculation unit, an eighteenth calculation unit, and a second determination unit;

[0264] The eighth calculation unit is used to analyze the positive sequence network, the negative sequence network and the zero sequence network respectively according to the seventh relation, and obtain the ninth relation of AC, DC and bridge arm capacitor voltage in the positive sequence network, the tenth relation of AC, DC and bridge arm capacitor voltage in the negative sequence network and the eleventh relation of AC, DC and bridge arm capacitor voltage in the zero sequence network when the DC side unipolar fault occurs.

[0265] The ninth calculation unit is used to analyze the equivalent model of the DC collection and transmission system to obtain the twelfth relationship between the DC side current and the fault point current corresponding to the DC side grounded through high resistance.

[0266] The tenth calculation unit is used to analyze the equivalent model of the DC collection and transmission system based on the DC side zero resistance grounding, and obtain the thirteenth relationship between the DC side outlet negative pole zero-sequence voltage and the DC side zero-sequence current of the MMC converter station.

[0267] The eleventh calculation unit is used to substitute the thirteenth relation into the twelfth relation to obtain the fourteenth relation between the DC side current and the fault point current corresponding to the DC side grounded through high resistance.

[0268] The twelfth calculation unit is used to transform the fourteenth relationship based on the relationship between the amplitude and phase of the zero-sequence component, and obtain the fifteenth relationship between the DC side current and the fault point current corresponding to the DC side grounded through high resistance.

[0269] The thirteenth calculation unit is used to substitute the fifteenth relation into the thirteenth relation to obtain the sixteenth relation between the negative electrode voltage and the lower bridge arm voltage.

[0270] The fourteenth calculation unit is used to substitute the sixteenth relation and the value of the zero-sequence voltage of the DC side outlet of the MMC converter station into the eleventh relation to obtain the simplified seventeenth relation of AC, DC and bridge arm capacitor voltages in the zero-sequence network.

[0271] The fifteenth calculation unit is used to substitute the voltage value in the positive sequence network when the DC-side unipolar fault occurs into the ninth relational expression to obtain the first analysis result.

[0272] The sixteenth calculation unit is used to substitute the voltage value in the negative sequence network when the DC-side unipolar fault occurs into the tenth relation to obtain the second analysis result;

[0273] The seventeenth calculation unit is used to substitute the voltage value in the zero-sequence network when the DC-side unipolar fault occurs into the seventeenth relation to obtain the third analysis result;

[0274] The eighteenth calculation unit is used to obtain the first component of the AC side outlet voltage and current when there is a DC side unipolar fault based on the first analysis result, the second analysis result and the third analysis result.

[0275] The second determining unit is used to take the seventeenth relation and the first component as the first interaction influence data.

[0276] In a preferred embodiment of the present invention, the second analysis unit further includes: a nineteenth calculation unit and a third determination unit;

[0277] The nineteenth calculation unit is used to analyze the first component based on the value of the equivalent resistance when the AC side is not grounded, and to obtain the second component of the AC side output voltage and current corresponding to the AC side being ungrounded when the DC side is a single-pole fault.

[0278] The third determining unit is used to use the second component as the first interaction influence data.

[0279] In a preferred embodiment of the present invention, the third analysis unit further includes: a twentieth calculation unit, a twenty-first calculation unit, a twenty-second calculation unit, a twenty-third calculation unit, a twenty-fourth calculation unit, and a fourth determination unit;

[0280] The twentieth calculation unit is used to analyze the equivalent model of the DC collection and transmission system to obtain the voltage component of the AC side outlet when there is a DC side inter-pole fault.

[0281] The 21st calculation unit is used to substitute the relationship between phase voltage and zero-sequence voltage into the 13th relationship to obtain the 18th relationship between the AC side outlet phase A voltage, the upper and lower arm voltages of phase A, and the DC side negative electrode voltage of the MMC converter station.

[0282] The 22nd calculation unit is used to substitute the voltage value of the positive sequence network when the DC-side inter-pole fault occurs into the 18th relation and the first DC component in sequence to obtain the second DC component of the AC-side outlet voltage and current of the MMC converter station corresponding to the DC-side inter-pole fault.

[0283] The 23rd calculation unit is used to substitute the voltage value of the negative sequence network when the DC-side inter-pole fault occurs into the 10th relation and the first DC component in sequence to obtain the third DC component of the AC-side outlet voltage and current of the MMC converter station corresponding to the DC-side inter-pole fault.

[0284] The 24th calculation unit is used to obtain the fourth DC component of the AC side outlet voltage and current of the MMC converter station when the inter-pole fault enters steady state, based on the second DC component and the third DC component.

[0285] The fourth determining unit is used to take the voltage component of the AC side outlet and the fourth DC component as the second interactive influence data.

[0286] For specific limitations regarding the analysis of the impact of a DC-side fault on the AC side of a flexible DC transmission line, please refer to the above-described limitations of the method for analyzing the impact of a DC-side fault on the AC side of a flexible DC transmission line, which will not be repeated here. Those skilled in the art will recognize that the various modules and steps described in conjunction with the embodiments disclosed in this invention can be implemented in hardware, software, or a combination of both. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this invention.

[0287] like Figure 22 As shown, an embodiment of the present invention provides a computer device including a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor. When the processor executes the computer program, it implements the steps described in the above embodiment of the method for analyzing the impact of DC-side faults on the AC side of flexible DC transmission, for example... Figure 1 Steps S1 to S5 as described above.

[0288] Those skilled in the art will understand that the illustrations Figure 22 This is merely an example of a computer device and does not constitute a limitation on the computer device. It may include more or fewer components than shown, or combine certain components, or different components. For example, the computer device may also include input / output devices, network access devices, buses, etc.

[0289] The processor can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor. The processor is the control center of the computer device, connecting various parts of the computer device via various interfaces and lines.

[0290] The memory can be used to store the computer programs and / or modules. The processor implements various functions of the computer device by running or executing the computer programs and / or modules stored in the memory and by calling data stored in the memory. The memory may mainly include a program storage area and a data storage area. The program storage area may store the operating system, at least one application program required for a function (such as sound playback function, image playback function, etc.), etc.; the data storage area may store data created according to the use of the mobile phone (such as audio data, phonebook, etc.). In addition, the memory may include high-speed random access memory, and may also include non-volatile memory, such as hard disk, memory, plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, at least one disk storage device, flash memory device, or other volatile solid-state storage device.

[0291] If the modules integrated into the computer device are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[0292] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. The storage medium can be a magnetic disk, optical disk, read-only memory (ROM), or random access memory (RAM), etc.

[0293] Accordingly, embodiments of the present invention provide a computer-readable storage medium comprising a stored computer program, wherein, when the computer program is executed, it controls the device containing the computer-readable storage medium to perform steps in the method for analyzing the impact of DC-side faults on the AC side of flexible DC transmission as described in the above embodiments, for example... Figure 1 Steps S1 to S5 as described above.

[0294] This embodiment provides a method, system, computer equipment, and storage medium for analyzing the impact of DC-side faults on the AC side of flexible DC transmission networks. It addresses the technical problem of low accuracy in fault analysis and the inability to effectively control faults after they occur in flexible DC transmission networks. The invention constructs a DC collection and transmission system model based on the flexible DC transmission network, performs an equivalent transformation on this model, and obtains an equivalent model of the DC collection and transmission system. Pre-created DC fault events of various types are input into the equivalent model to obtain the fault equivalent circuits of the flexible DC transmission network under different DC fault types. Based on the harmonic order relationship between the AC and DC sides, each fault equivalent circuit is equivalently transformed to obtain various AC-side sequence component networks, which include positive-sequence, negative-sequence, and zero-sequence networks. The interaction impact data of each DC fault type in the positive-sequence, negative-sequence, and zero-sequence networks are acquired. In the actual operation of the flexible DC transmission network, the corresponding fault result is determined based on the detected interaction impact data. The flexible DC transmission network method of the present invention clarifies the characteristic changes and fault development stages of DC-side faults on the AC side, accurately analyzes the impact of DC-side faults on the AC side, and achieves effective control of the AC side after a DC-side fault based on the impact of DC-side faults on the AC side.

[0295] The above-described embodiments are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various improvements and substitutions without departing from the principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention. Therefore, the scope of protection of this invention should be determined by the scope of the claims.

Claims

1. A method for analyzing the influence of DC side fault of flexible DC power transmission on AC side, the flexible DC power transmission grid comprising a DC side and an AC side connected through MMC converter stations, characterized in that, The method comprises: According to the flexible HVDC power grid, a DC collection and sending system model is constructed, and equivalent transformation is performed on the DC collection and sending system model to obtain a DC collection and sending system equivalent model; Each type of DC side fault event is input into the DC collection and sending system equivalent model to obtain a fault equivalent circuit of the flexible HVDC power grid corresponding to different DC fault types; According to the frequency relationship between the AC side and the DC side, each fault equivalent circuit is equivalent transformed to obtain each AC side sequence component network, wherein the AC side sequence component network comprises a positive sequence network, a negative sequence network and a zero sequence network; Interaction influence data of each DC fault type in the positive sequence network, the negative sequence network and the zero sequence network is obtained respectively; In actual operation of the flexible HVDC power grid, a fault result corresponding to the flexible HVDC power grid is determined based on the detected interaction influence data.

2. The method according to claim 1, wherein the method is characterized by, According to the frequency relationship between the AC side and the DC side, each fault equivalent circuit is equivalent transformed to obtain each AC side sequence component network, comprising: Based on the frequency relationship between the AC side and the DC side, AC side three-phase positive sequence voltage instantaneous values corresponding to the DC collection and sending system equivalent model are obtained; Based on the frequency relationship, the AC side three-phase positive sequence voltage instantaneous values are mapped with each fault equivalent circuit to obtain each AC side sequence component network.

3. The method of claim 1, wherein the method is characterized by: The interaction influence data of each DC fault type in the positive sequence network, the negative sequence network and the zero sequence network is obtained respectively, comprising: Electrical characteristics of the positive sequence network, the negative sequence network and the zero sequence network are analyzed; According to the electrical characteristics, first interaction influence data in the positive sequence network, the negative sequence network and the zero sequence network when a DC side single-pole fault occurs is obtained; According to the electrical characteristics, second interaction influence data in the positive sequence network, the negative sequence network and the zero sequence network when a DC side inter-pole fault occurs is obtained.

4. The method according to claim 3, wherein the method is characterized by, The electrical characteristics of the positive sequence network, the negative sequence network and the zero sequence network are analyzed, comprising: According to the positive sequence network, the negative sequence network and the zero sequence network, MMC converter station loop current equations, a first relationship between MMC converter station DC side outlet voltage and current, a second relationship between AC side current corresponding to DC side grounding through high resistance, DC side current and bridge arm current, a third relationship between bridge arm voltage and bridge arm current, an equivalent resistance relationship between the DC side and the AC side, and an equivalent inductance relationship between the DC side and the AC side are obtained respectively; The equivalent resistance relationship and the equivalent inductance relationship are substituted into the MMC converter station loop current equations to obtain a fourth relationship between MMC converter station DC side outlet voltage and DC side; The fourth relationship is substituted into the second relationship to obtain a fifth relationship between AC side current corresponding to DC side grounding through high resistance, DC side current and bridge arm current; Substituting the fifth relationship into the third relationship, a sixth relationship of the DC side current corresponding to the DC side grounding through high resistance and the three-phase bridge arm current is obtained; Substituting the sixth relationship into the fourth relationship, a seventh relationship among the upper and lower bridge arm capacitor voltages of phase A, the AC side voltage and the DC side outlet voltage of the MMC converter station is obtained; Substituting the third relationship into the MMC converter station loop current equation, an eighth relationship of the AC side outlet voltage of the MMC converter station and the AC side is obtained; Substituting the seventh relationship into the eighth relationship, a first DC component contained in the AC side i-phase voltage and current at the steady state is obtained; The seventh relationship and the first DC component are taken as the electrical characteristics of the positive sequence network, the negative sequence network and the zero sequence network.

5. The method according to claim 4, wherein the method is characterized by, According to the electrical characteristics, first interaction influence data in the positive sequence network, the negative sequence network and the zero sequence network at the time of the DC side single-pole fault is obtained, including: According to the seventh relationship, the positive sequence network, the negative sequence network and the zero sequence network are analyzed respectively, and a ninth relationship of the AC, DC and bridge arm capacitor voltage in the positive sequence network, a tenth relationship of the AC, DC and bridge arm capacitor voltage in the negative sequence network, and an eleventh relationship of the AC, DC and bridge arm capacitor voltage in the zero sequence network are obtained at the time of the DC side single-pole fault; The DC collection and sending system equivalent model is analyzed to obtain a twelfth relationship of the DC side current corresponding to the DC side grounding through high resistance and the fault point current; Based on the DC side zero resistance grounding, the DC collection and sending system equivalent model is analyzed to obtain a thirteenth relationship of the negative pole zero sequence voltage of the DC side outlet of the MMC converter station and the DC side zero sequence current; Substituting the thirteenth relationship into the twelfth relationship, a fourteenth relationship of the DC side current corresponding to the DC side grounding through high resistance and the fault point current is obtained; According to the relationship between the zero sequence component amplitude and the phase, the fourteenth relationship is converted to obtain a fifteenth relationship of the DC side current corresponding to the DC side grounding through high resistance and the fault point current; Substituting the fifteenth relationship into the thirteenth relationship, a sixteenth relationship of the negative pole voltage and the lower bridge arm voltage is obtained; Substituting the sixteenth relationship and the value of the negative pole zero sequence voltage of the DC side outlet of the MMC converter station into the eleventh relationship, a seventeenth relationship of the AC, DC and bridge arm capacitor voltage in the simplified zero sequence network is obtained; Substituting the voltage value in the positive sequence network at the time of the DC side single-pole fault into the ninth relationship, a first analysis result is obtained; Substituting the voltage value in the negative sequence network at the time of the DC side single-pole fault into the tenth relationship, a second analysis result is obtained; Substituting the voltage value in the zero sequence network at the time of the DC side single-pole fault into the seventeenth relationship, a third analysis result is obtained; According to the first analysis result, the second analysis result and the third analysis result, a first component of the AC side outlet voltage and current at the time of the DC side single-pole fault is obtained; The seventeenth relationship and the first component are taken as the first interaction influence data.

6. The method of claim 5, wherein the DC side fault of the flexible HVDC power transmission system is a DC side fault of a DC side of a DC / AC converter. The first interaction influence data in the positive sequence network, the negative sequence network and the zero sequence network during the DC side single-pole fault is obtained according to the electrical characteristics, and the method further includes: According to the value of the equivalent resistance when the AC side is not grounded, the first component is analyzed to obtain a second component of the AC side outlet voltage and current corresponding to the AC side not grounded during the DC side single-pole fault; The second component is taken as the first interaction influence data.

7. The method according to claim 6, wherein the method is characterized by, The second interaction influence data in the positive sequence network, the negative sequence network and the zero sequence network during the DC side inter-pole fault is obtained according to the electrical characteristics, and the method further includes: The DC collection and sending system equivalent model is analyzed to obtain a voltage component of the AC side outlet during the DC side inter-pole fault; The relationship between the phase voltage and the zero sequence voltage is substituted into the thirteenth relationship to obtain an eighteenth relationship of the MMC converter station AC side outlet A-phase voltage, A-phase upper and lower bridge arm voltage and DC side negative pole voltage; The voltage value of the positive sequence network during the DC side inter-pole fault is substituted into the eighteenth relationship and the first DC component in sequence to obtain a second DC component of the MMC converter station AC side outlet voltage and current corresponding to the DC side inter-pole fault; The voltage value of the negative sequence network during the DC side inter-pole fault is substituted into the tenth relationship and the first DC component in sequence to obtain a third DC component of the MMC converter station AC side outlet voltage and current corresponding to the DC side inter-pole fault; According to the second DC component and the third DC component, a fourth DC component of the MMC converter station AC side outlet voltage and current corresponding to the inter-pole fault entering a steady state is obtained; The voltage component of the AC side outlet and the fourth DC component are taken as the second interaction influence data. 8.A system for analyzing the influence of DC side fault of a flexible DC power transmission on an AC side, the flexible DC power transmission grid comprising a DC side and an AC side connected by an MMC converter station, characterized in that, The system includes a system equivalent model construction unit, a fault equivalent circuit acquisition unit, an AC side sequence component network acquisition unit, an interaction influence data acquisition unit and a fault analysis unit; The system equivalent model construction unit is configured to construct a DC collection and sending system model according to the flexible DC power transmission network, and to obtain a DC collection and sending system equivalent model by equivalent transformation of the DC collection and sending system model; The fault equivalent circuit acquisition unit is configured to input each type of DC side fault event created in advance into the DC collection and sending system equivalent model to obtain a fault equivalent circuit of the flexible DC power transmission network corresponding to different DC fault types; The AC side sequence component network acquisition unit is configured to perform equivalent conversion on each fault equivalent circuit according to the frequency relationship between the AC side and the DC side to obtain each AC side sequence component network, wherein the AC side sequence component network has a positive sequence network, a negative sequence network and a zero sequence network; The interaction influence data acquisition unit is configured to acquire interaction influence data of each DC fault type in the positive sequence network, the negative sequence network and the zero sequence network, respectively. The system includes a system equivalent model construction unit, a fault equivalent circuit acquisition unit, an AC side sequence component network acquisition unit, an interaction influence data acquisition unit and a fault analysis unit; The system equivalent model construction unit is configured to construct a DC collection and sending system model according to the flexible DC power transmission network, and to obtain a DC collection and sending system equivalent model by equivalent transformation of the DC collection and sending system model; The fault equivalent circuit acquisition unit is configured to input each type of DC side fault event created in advance into the DC collection and sending system equivalent model to obtain a fault equivalent circuit of the flexible DC power transmission network corresponding to different DC fault types; The AC side sequence component network acquisition unit is configured to perform equivalent conversion on each fault equivalent circuit according to the frequency relationship between the AC side and the DC side to obtain each AC side sequence component network, wherein the AC side sequence component network has a positive sequence network, a negative sequence network and a zero sequence network; The interaction influence data acquisition unit is configured to acquire interaction influence data of each DC fault type in the positive sequence network, the negative sequence network and the zero sequence network, respectively. The fault analysis unit is configured to determine a corresponding fault result of the flexible HVDC power grid based on the detected interaction data in actual operation of the flexible HVDC power grid.

9. The flexible DC power transmission DC side fault impact on AC side analysis system of claim 8, wherein, The AC side sequence component network acquisition unit comprises a conversion unit and a mapping unit. The conversion unit is configured to acquire an AC side three-phase positive sequence voltage instantaneous value corresponding to an equivalent model of the DC collection and sending system based on a frequency relationship of harmonics between the AC side and the DC side. The mapping unit is configured to map the AC side three-phase positive sequence voltage instantaneous value and each fault equivalent circuit based on the frequency relationship to obtain each AC side sequence component network.

10. The flexible HVDC DC side fault impact on AC side analysis system of claim 8, wherein, The interaction data acquisition unit comprises a first analysis unit, a second analysis unit and a third analysis unit. The first analysis unit is configured to analyze electrical characteristics of the positive sequence network, the negative sequence network and the zero sequence network. The second analysis unit is configured to acquire first interaction data in the positive sequence network, the negative sequence network and the zero sequence network when a DC side single-pole fault occurs based on the electrical characteristics. The third analysis unit is configured to acquire second interaction data in the positive sequence network, the negative sequence network and the zero sequence network when a DC side inter-pole fault occurs based on the electrical characteristics.

11. The flexible DC power transmission DC side fault impact on AC side analysis system of claim 10, wherein, The first analysis unit comprises a first calculation unit, a second calculation unit, a third calculation unit, a fourth calculation unit, a fifth calculation unit, a sixth calculation unit, a seventh calculation unit and a first determination unit. The first calculation unit is configured to obtain an MMC converter station loop current equation, a first relationship between an MMC converter station DC side outlet voltage and current, a second relationship between an AC side current corresponding to a DC side grounding through a high resistance, a DC side current and a bridge arm current, a third relationship between a bridge arm voltage and a bridge arm current, an equivalent resistance relationship between the DC side and the AC side, and an equivalent inductance relationship between the DC side and the AC side based on the positive sequence network, the negative sequence network and the zero sequence network. The second calculation unit is configured to substitute the equivalent resistance relationship and the equivalent inductance relationship into the MMC converter station loop current equation to obtain a fourth relationship between the MMC converter station DC side outlet voltage and the DC side. The third calculation unit is configured to substitute the fourth relationship into the second relationship to obtain a fifth relationship between the AC side current corresponding to the DC side grounding through the high resistance, the DC side current and the bridge arm current. The fourth calculation unit is configured to substitute the fifth relationship into the third relationship to obtain a sixth relationship between the DC side current and the three-phase bridge arm current corresponding to the DC side grounding through the high resistance. The fifth calculation unit is configured to substitute the sixth relationship into the fourth relationship to obtain a seventh relationship between the A-phase upper and lower bridge arm capacitor voltage, the AC side voltage and the MMC converter station DC side outlet voltage. The sixth calculation unit is configured to substitute the third relationship into the MMC converter station loop current equation to obtain an eighth relationship between the MMC converter station AC side outlet voltage and the AC side. The seventh calculation unit is configured to substitute the seventh relationship into the eighth relationship to obtain first direct current components contained in alternating current side i-phase voltage and current in a steady state; The first determination unit is configured to take the seventh relationship and the first direct current components as electrical characteristics of the positive sequence network, the negative sequence network and the zero sequence network.

12. The flexible DC power transmission DC side fault impact on AC side analysis system of claim 11, wherein, The second analysis unit comprises an eighth calculation unit, a ninth calculation unit, a tenth calculation unit, an eleventh calculation unit, a twelfth calculation unit, a thirteenth calculation unit, a fourteenth calculation unit, a fifteenth calculation unit, a sixteenth calculation unit, a seventeenth calculation unit, an eighteenth calculation unit and a second determination unit; The eighth calculation unit is configured to analyze the positive sequence network, the negative sequence network and the zero sequence network respectively according to the seventh relationship, and obtain a ninth relationship of alternating current, direct current and bridge arm capacitor voltage in the positive sequence network, a tenth relationship of alternating current, direct current and bridge arm capacitor voltage in the negative sequence network, and an eleventh relationship of alternating current, direct current and bridge arm capacitor voltage in the zero sequence network when the direct current side single-pole fault occurs. The ninth calculation unit is configured to analyze the direct current collection and sending-out system equivalent model to obtain a twelfth relationship of the direct current side current and the fault point current when the direct current side is grounded through a high resistance. The tenth calculation unit is configured to analyze the direct current collection and sending-out system equivalent model based on the direct current side zero-resistance grounding to obtain a thirteenth relationship of the MMC converter station direct current side outlet negative pole zero sequence voltage and the direct current side zero sequence current. The eleventh calculation unit is configured to substitute the thirteenth relationship into the twelfth relationship to obtain a fourteenth relationship of the direct current side current and the fault point current when the direct current side is grounded through a high resistance. The twelfth calculation unit is configured to convert the fourteenth relationship according to the relationship between the zero sequence component amplitude and the phase to obtain a fifteenth relationship of the direct current side current and the fault point current when the direct current side is grounded through a high resistance. The thirteenth calculation unit is configured to substitute the fifteenth relationship into the thirteenth relationship to obtain a sixteenth relationship of the negative pole voltage and the lower bridge arm voltage. The fourteenth calculation unit is configured to substitute the sixteenth relationship and the value of the MMC converter station direct current side outlet negative pole zero sequence voltage into the eleventh relationship to obtain a seventeenth relationship of alternating current, direct current and bridge arm capacitor voltage in the simplified zero sequence network. The fifteenth calculation unit is configured to substitute the voltage value in the positive sequence network when the direct current side single-pole fault occurs into the ninth relationship to obtain a first analysis result. The sixteenth calculation unit is configured to substitute the voltage value in the negative sequence network when the direct current side single-pole fault occurs into the tenth relationship to obtain a second analysis result. The seventeenth calculation unit is configured to substitute the voltage value in the zero sequence network when the direct current side single-pole fault occurs into the seventeenth relationship to obtain a third analysis result. The eighteenth calculation unit is configured to obtain first components of the alternating current side outlet voltage and current when the direct current side single-pole fault occurs according to the first analysis result, the second analysis result and the third analysis result. The second determining unit is configured to take the seventeenth relationship and the first component as the first interaction influence data.

13. The flexible DC power transmission DC side fault impact on AC side analysis system of claim 12, wherein, The second analyzing unit further includes a nineteenth calculating unit and a third determining unit. The nineteenth calculating unit is configured to analyze the first component according to the value of the equivalent resistance when the AC side is not grounded, to obtain a second component of the AC side outlet voltage and current corresponding to the single-pole fault of the DC side. The third determining unit is configured to take the second component as the first interaction influence data.

14. The flexible DC power transmission DC side fault impact on AC side analysis system of claim 13, wherein, The third analyzing unit further includes a twentieth calculating unit, a twenty-first calculating unit, a twenty-second calculating unit, a twenty-third calculating unit, a twenty-fourth calculating unit and a fourth determining unit. The twentieth calculating unit is configured to analyze the equivalent model of the DC collection and sending system to obtain a voltage component of the AC side outlet when the inter-pole fault of the DC side occurs. The twenty-first calculating unit is configured to substitute a relationship between phase voltage and zero sequence voltage into the thirteenth relationship to obtain an eighteenth relationship of the A-phase voltage of the AC side outlet of the MMC converter station, the upper and lower bridge arm voltages of the A phase and the negative pole voltage of the DC side. The twenty-second calculating unit is configured to substitute the voltage value of the positive sequence network when the inter-pole fault of the DC side occurs into the eighteenth relationship and the first DC component in sequence to obtain a second DC component of the AC side outlet voltage and current of the MMC converter station corresponding to the inter-pole fault of the DC side. The twenty-third calculating unit is configured to substitute the voltage value of the negative sequence network when the inter-pole fault of the DC side occurs into the tenth relationship and the first DC component in sequence to obtain a third DC component of the AC side outlet voltage and current of the MMC converter station corresponding to the inter-pole fault of the DC side. The twenty-fourth calculating unit is configured to obtain a fourth DC component of the AC side outlet voltage and current of the MMC converter station corresponding to the steady state of the inter-pole fault according to the second DC component and the third DC component. The fourth determining unit is configured to take the voltage component of the AC side outlet and the fourth DC component as the second interaction influence data.

15. A computer device, comprising: The computer device includes a memory, a processor and a transceiver which are connected through a bus; the memory is configured to store a set of computer program instructions and data, and transmit the stored data to the processor; the processor executes the program instructions stored in the memory to perform the flexible DC power transmission DC side fault influence analysis method of any one of claims 1 to 7.

16. A computer-readable storage medium, characterized in that: The computer readable storage medium stores a computer program, when the computer program is executed, the flexible DC power transmission DC side fault influence analysis method of any one of claims 1 to 7 is realized.

Images