Transient overvoltage suppression method and device for new energy system during asymmetric fault period

Abstract

The invention relates to a transient overvoltage suppression method and device for a new energy system during an asymmetric fault period. The method comprises the steps of obtaining a topological structure of the new energy system and a control strategy adopted during a fault ride-through period; establishing each sequence equivalent circuit of the new energy system and obtaining each sequence voltage equation; solving a voltage expression of a non-fault phase at the fault position based on each sequence voltage equation, and obtaining related control parameters; analyzing related control parameters to obtain key control parameters; calculating a current reference value based on the key control parameters and constraint conditions; and sending the current reference value to a current inner ring. According to the method, quantitative analysis is carried out on system transient overvoltage, the relation between negative sequence reactive current and non-fault phase overvoltage of a system fault point is obtained, and then key control parameters influencing the non-fault phase overvoltage are obtained, so that suppression of the system transient overvoltage is achieved, and the reliability of the system is improved. Effective suppression of the transient overvoltage of the new energy transmission system during the fault period is realized, and safe operation of the new energy transmission system is guaranteed.

Description

Technical Field

[0001] This application relates to the technical field of power safety, and specifically relates to a method and device for suppressing transient overvoltage of a new energy system during an asymmetric fault. Background Technique

[0002] With the gradual replacement of traditional power generation methods such as thermal power generation by new energy power generation such as wind power and photovoltaic power, a large number of new energy devices are connected to the power system, making the power system show the characteristics of "double highs", that is, a new generation of power system with high-penetration renewable energy and a high proportion of power electronic equipment. Generally, when an asymmetric short-circuit fault occurs in the power system, relatively serious transient overvoltage problems often occur in the non-fault phases of the new energy power system. When the system voltage is too high, it will affect the safe operation of the equipment in the power system and pose a serious threat to the new energy transmission capacity and the safe and stable operation of the power system. Therefore, it is very important to analyze the generation mechanism and influencing factors of transient overvoltage in the new energy transmission system, and to propose a transient overvoltage calculation method and suppression strategy that meet the engineering requirements.

[0003] At present, there is little analysis of the transient overvoltage level in the new energy AC transmission system under asymmetric faults. The existing literature 1 [Wu Linlin, Wang Xiao, Yang Yanchen, etc. Power frequency overvoltage during the unbalanced operation process after a single transient fault clearance in a new energy collection system [J]. High Voltage Engineering, 2022, 48(11): 4362-4373] analyzed the unbalanced operation of the new energy transmission system. This literature used the symmetrical component method to analyze the transient overvoltage during the fault but did not consider the detailed new energy control strategy, and this literature did not propose a method to suppress the transient overvoltage. When an asymmetric short-circuit fault occurs in the new energy power system, relatively serious transient overvoltage problems may occur in the non-fault phases at the fault point in the system. The existing literature 2 [Wang Shuang, Chen Xiaoyue, Zheng Zhihui, etc. Research on electromagnetic transients of asymmetric grounding and load shedding in a permanent magnet direct-drive wind turbine offshore wind power transmission system [J]. Proceedings of the Chinese Society of Electrical Engineering, 2024, 44(02): 827-838] only simulated the transient overvoltage of the system during two-phase grounding, but did not explain it through theoretical calculations, and did not give a detailed method to suppress the transient overvoltage. The existing methods cannot effectively suppress the transient overvoltage in the new energy system, posing a serious threat to the new energy transmission capacity and the safe and stable operation of the power system. Summary of the Invention

[0004] To overcome the deficiencies of the above-mentioned prior art, this application provides a method and device for suppressing transient overvoltage of a new energy system during an asymmetric fault, and specifically adopts the following technical solutions:

[0005] A method for suppressing transient overvoltage of a new energy system during an asymmetric fault, the method includes the following steps:

[0006] Obtain the topological structure of the new energy system and the control strategy adopted by the new energy system during fault ride-through; among them, the new energy grid-side converter adopts a positive and negative sequence double current loop control strategy, and the new energy grid-connected inverter adopts a control strategy based on grid voltage orientation and a positive and negative sequence double current loop control strategy.

[0007] Based on the topological structure of the new energy system, use the symmetrical component method to establish the equivalent circuits of each sequence of the new energy system respectively, where the new energy equipment is equivalent to a current source, and the output current of the new energy equipment is determined according to the corresponding control strategy;

[0008] Obtain the voltage equations of each sequence according to the equivalent circuits of each sequence of the new energy system;

[0009] Based on the voltage equations of each sequence, solve the voltage expressions of the non-fault phases at the fault location, and obtain the relevant control parameters affecting the transient overvoltage of the new energy system according to the voltage expressions of the non-fault phases at the fault location;

[0010] Based on the voltage equations of each sequence, analyze the change of the transient overvoltage of the non-fault phases at the fault point by the relevant control parameters, and obtain the key control parameters for suppressing the transient overvoltage of the new energy system;

[0011] Based on the key control parameters and the constraint conditions, calculate the current reference values of the new energy system under asymmetrical short-circuit faults;

[0012] Send the calculated current reference values to the current inner loop to achieve the suppression of the transient overvoltage of the new energy system.

[0013] Optionally: During asymmetrical short-circuit faults, the control strategy adopted by the new energy units in the new energy system is:

[0014] The positive-sequence reactive current reference value output by the new energy unit is controlled according to the voltage deviation;

[0015] The positive-sequence active current reference value output by the new energy unit is controlled in a constant current mode;

[0016] The negative-sequence reactive current reference value output by the new energy unit is controlled in a constant current mode;

[0017] The negative-sequence active current reference value output by the new energy unit is set to 0.

[0018] Optionally: The steps of solving the voltage expressions of the non-fault phases at the fault location based on the voltage equations of each sequence:

[0019] Among them, obtain the positive-sequence voltage equation, negative-sequence voltage equation and zero-sequence voltage equation respectively:

[0020] The positive-sequence voltage equation is:

[0021]

[0022] The negative-sequence voltage equation is as follows:

[0023]

[0024] The zero-sequence voltage equation is as follows:

[0025]

[0026] Where is the positive-sequence open-circuit voltage at the fault location; is the negative-sequence open-circuit voltage at the fault location; is the zero-sequence open-circuit voltage at the fault location; Z eq1 is the Thevenin equivalent impedance from the fault location in the positive-sequence equivalent circuit; Z eq2 is the Thevenin equivalent impedance from the fault location in the negative-sequence equivalent circuit; Z eq0 is the Thevenin equivalent impedance from the fault location in the zero-sequence equivalent circuit; X L1 is the line reactance on the grid side in the positive-sequence equivalent circuit; X L2 is the line reactance on the grid side in the negative-sequence equivalent circuit; X L0 is the line reactance on the grid side in the zero-sequence equivalent circuit; X T1 is the total reactance of the transmission line and transformer on the new energy side in the positive-sequence equivalent circuit; X T2 is the total reactance of the transmission line and transformer on the new energy side in the negative-sequence equivalent circuit; is the positive-sequence voltage phasor of the fault point to the ground; is the negative-sequence voltage phasor of the fault point to the ground; is the zero-sequence voltage phasor of the fault point to the ground; is the positive-sequence current phasor of the fault point to the ground; is the negative-sequence current phasor of the fault point to the ground; is the zero-sequence current phasor of the fault point to the ground; is the positive-sequence voltage phasor at the new energy terminal; is the negative-sequence voltage phasor at the new energy terminal; is the positive-sequence current phasor output by the new energy; is the negative-sequence current phasor output by the new energy; j is the imaginary unit;

[0027] Obtain the corresponding boundary conditions according to the asymmetrical short-circuit fault:

[0028]

[0029] Obtain the voltage expression of the unfaulted phase at the fault location according to each sequence voltage equation and the boundary conditions:

[0030]

[0031] Optionally, the step of analyzing the influence of relevant control parameters on the transient over-voltage change of the non-fault phase at the fault point based on the sequence voltage equations includes:

[0032] When only positive-sequence and negative-sequence reactive currents are output by the new energy units in the new energy system, and the positive-sequence and negative-sequence active currents are both zero, based on the sequence voltage equations and boundary conditions, it is obtained that the positive-sequence open-circuit voltage and the negative-sequence open-circuit voltage phasors at the fault location are collinear, and the positive-sequence open-circuit voltage is in the same phase as the positive-sequence phasor of the voltage source; or when the positive-sequence and negative-sequence reactive currents output by the new energy are not zero, and the positive-sequence active current is also not zero, based on the sequence voltage equations and boundary conditions, it is obtained that the positive-sequence open-circuit voltage and the negative-sequence open-circuit voltage phasors at the fault location are collinear;

[0033] When the new energy emits negative-sequence reactive power and positive-sequence reactive power, the positive-sequence open-circuit voltage and the negative-sequence open-circuit voltage at the fault location are in opposite directions. At this time, increasing the negative-sequence reactive current output by the new energy has an inhibitory effect on the transient over-voltage of the non-fault phase at the fault point.

[0034] Optionally, the key control parameter is the negative-sequence reactive current output by the new energy unit.

[0035] Optionally, the constraint conditions include a first constraint condition and a second constraint condition,

[0036] wherein the first constraint condition includes that the phase voltage amplitudes at the point of common connection of the new energy and the machine terminal of the new energy unit do not exceed the voltage constraint value V m ;

[0037] The second constraint condition includes that the phase current amplitudes output by the new energy converter do not exceed the current constraint value I m 。

[0038] Optionally, the step of calculating the current reference value of the new energy system under the asymmetrical short-circuit fault based on the key control parameter and the constraint conditions includes:

[0039] Obtaining the positive-sequence and negative-sequence voltage amplitudes at the point of common connection of the new energy based on the topological structure of the new energy system:

[0040]

[0041] Obtaining the phase voltage amplitude V at the point of common connection based on the positive-sequence and negative-sequence voltage amplitudes at the point of common connection of the new energy abc :

[0042]

[0043] Considering that there is a Dy11 transformer between the new energy unit and the point of common connection to the public, then the phase voltage amplitude V at the machine terminal of the new energyjabc is:

[0044]

[0045] The three-phase current amplitude I of the new energy output rabc is:

[0046]

[0047] where V 1 is the positive-sequence voltage amplitude of the common connection point; V 2 is the negative-sequence voltage amplitude of the common connection point; V g1 is the positive-sequence voltage amplitude of the system side; V g2 is the positive-sequence voltage amplitude of the system side; I r1 is the phasor of the new energy output current in the positive-sequence equivalent circuit; I r2 is the phasor of the new energy output current in the negative-sequence equivalent circuit; I d1 is the d-axis component of the positive-sequence current of the new energy output; I d2 is the d-axis component of the negative-sequence current of the new energy output; I q1 is the q-axis component of the positive-sequence current of the new energy output; I q2 is the q-axis component of the negative-sequence current of the new energy output; ω is the angular frequency; L is the inductance value; is the difference in the initial phase angles of the positive and negative sequence voltages; is the difference in the initial phase angles of the positive and negative sequence currents; represents the phase angle corresponding to the single-phase electricity;

[0048] Obtain the maximum value of I according to the three-phase current amplitude of the new energy output q2 of.

[0049] Optional: When calculating the current reference value of the new energy system under an asymmetrical short-circuit fault, the fmincon function in Matlab is used for solution.

[0050] Optional: The reference values of the positive and negative sequence voltages in the positive and negative sequence double current loop control strategy are:

[0051]

[0052] where k p1 is the proportional coefficient of the positive-sequence voltage; k i1 is the integral coefficient of the positive-sequence voltage; k p2 is the proportional coefficient of the negative-sequence voltage; k i2 is the integral coefficient of the negative-sequence voltage; is the reference value of the d-axis component of the positive-sequence voltage; is the reference value of the d-axis component of the negative-sequence voltage; is the reference value of the q-axis component of the positive-sequence voltage; is the reference value of the q - axis component of the negative - sequence voltage; is the reference value of the d - axis component of the positive - sequence current; is the reference value of the d - axis component of the negative - sequence current; is the reference value of the q - axis component of the positive - sequence current; is the reference value of the q - axis component of the negative - sequence current; L g is the inductor on the AC side of the converter; is the positive - sequence voltage at the new - energy grid - connection point; is the negative - sequence voltage at the new - energy grid - connection point; is the positive - sequence d - axis current output by the new - energy source; is the negative - sequence d - axis current output by the new - energy source; is the positive - sequence q - axis current output by the new - energy source; is the negative - sequence q - axis current output by the new - energy source; ω is the angular frequency of the grid voltage; t is the time integral.

[0053] In addition, this application also discloses a transient over - voltage suppression device for a new - energy system during an asymmetrical fault. The device includes:

[0054] A system acquisition module, configured to acquire the topological structure of the new - energy system and the control strategy adopted by the new - energy system during the fault - ride - through period. Among them, the new - energy grid - side converter adopts a positive - and - negative - sequence double - current - loop control strategy, and the new - energy grid - connection inverter adopts a grid - voltage - oriented and positive - and - negative - sequence double - current - loop control strategy.

[0055] An equivalent - circuit establishment module, configured to respectively establish the sequence equivalent circuits of the new - energy system based on the topological structure of the new - energy system by using the symmetrical component method. Among them, the new - energy equipment is equivalent to a current source, and the output current of the new - energy equipment is determined according to the corresponding control strategy;

[0056] A voltage - equation acquisition module, configured to obtain the sequence voltage equations according to the sequence equivalent circuits of the new - energy system;

[0057] A control - parameter acquisition module, configured to solve the voltage expression of the non - fault phase at the fault location based on the sequence voltage equations, and obtain the relevant control parameters affecting the transient over - voltage of the new - energy system according to the voltage expression of the non - fault phase at the fault location;

[0058] A key - parameter selection module, configured to analyze the change of the transient over - voltage of the non - fault phase at the fault point by the relevant control parameters based on the sequence voltage equations, and obtain the key control parameters for suppressing the transient over - voltage of the new - energy system;

[0059] A current - calculation module, configured to calculate the current reference value of the new - energy system under an asymmetrical short - circuit fault based on the key control parameters and the constraint conditions;

[0060] The control output module is used to send the calculated current reference value to the inner current loop to achieve transient overvoltage suppression of the new energy system.

[0061] Beneficial effects

[0062] The technical solution of this application has obtained the following beneficial effects:

[0063] The transient overvoltage suppression method of this application obtains the topological structure and control strategy of the new energy system, establishes the sequence equivalent circuits, and then quantitatively analyzes the transient overvoltage of the new energy system during asymmetric faults, obtains the relationship between the negative-sequence reactive current of the new energy and the overvoltage of the non-fault phase at the system fault point, and further obtains the key control parameters affecting the overvoltage of the non-fault phase at the system fault point. Based on the control of the key control parameters, the current reference value is calculated and sent to the inner current loop to achieve the suppression of the system transient overvoltage, effectively suppressing the transient overvoltage of the new energy transmission system during faults and ensuring the safe operation of the new energy transmission system. Description of the drawings

[0064] Figure 1 It is a flowchart of the transient overvoltage suppression method of the new energy system during asymmetric faults in the embodiment of this application.

[0065] Figure 2 It is a schematic structural diagram of the new energy system in the embodiment of this application.

[0066] Figure 3 It is a schematic structural diagram of the sequence equivalent circuits in the new energy system in the embodiment of this application.

[0067] Figure 4 It is a schematic flow diagram of solving the current reference value using the fmincon function in the embodiment of this application.

[0068] Figure 5 It is a simulation waveform diagram of the transient overvoltage of the non-fault phase at the system fault point in the embodiment of this application.

[0069] Figure 6 It is a waveform diagram of the non-fault voltage at the fault point under two working conditions in the embodiment of this application. Among them Figure 6 (a) is the waveform diagram of the non-fault voltage at the fault point under working condition 1; Figure 6 (b) is the waveform diagram of the non-fault voltage at the fault point under working condition 2.

[0070] Figure 7 It is a waveform diagram of the voltage at the PCC point under two working conditions in the embodiment of this application. Among them Figure 7 (a) is the waveform diagram of the voltage at the PCC point under working condition 1; Figure 7 (b) is the waveform diagram of the voltage at the PCC point under working condition 2.

[0071] Figure 8This is the three-phase voltage waveform diagram of the new energy machine terminal under two working conditions in the embodiment of the present application. Among them Figure 8 (a) in it is the three-phase voltage waveform diagram of the new energy machine terminal under working condition 1; Figure 8 (b) in it is the three-phase voltage waveform diagram of the new energy machine terminal under working condition 2.

[0072] Figure 9 This is the output current waveform diagram of the new energy converter under two working conditions in the embodiment of the present application. Among them Figure 9 (a) in it is the output current waveform diagram of the new energy converter under working condition 1; Figure 9 (b) in it is the output current waveform diagram of the new energy converter under working condition 2.

[0073] Figure 10 This is the structural diagram of the fault prediction device for the cooling system of the steam turbine generator in the embodiment of the present application.

[0074] Figure 11 This is the structural diagram of an electronic device in the embodiment of the present application. Specific embodiments

[0075] The present application will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application and cannot be used to limit the protection scope of the present application. It should be pointed out that the following detailed descriptions are all exemplary and are intended to provide further explanations for the present application.

[0076] Combined with Figure 1 As shown, the embodiment of the present application discloses a transient overvoltage suppression method for a new energy system during an asymmetric fault. The method includes the following steps:

[0077] Step 1: Obtain the topological structure of the new energy system and the control strategy adopted by the new energy system during the fault ride-through period; As Figure 2 shown, the topological structure of a general new energy system contains important information such as new energy units, converters, inverters, transmission lines, transformers, and various electrical connection relationships. Based on the above connection methods and structures, the electrical characteristics of the system during a fault can be obtained. Among them, the new energy grid-side converter adopts a positive and negative sequence dual current loop control strategy, which can effectively regulate the output power and voltage of the converter by precisely controlling the positive sequence current and negative sequence current respectively; The new energy grid-connected inverter adopts a grid voltage-oriented and positive and negative sequence dual current loop control strategy. Based on the grid voltage orientation, the inverter can better track the changes in the grid voltage. Combining the positive and negative sequence dual current loops control can improve the operating performance of the inverter under asymmetric faults.

[0078] In the positive and negative sequence double current loop control strategy of this embodiment, the positive and negative sequence electrical quantities are respectively transformed into the d and q coordinate systems of forward rotation and reverse rotation, so as to realize the decoupling control of the positive and negative sequence electrical quantities. Finally, the SPWM (sinusoidal pulse width modulation) signal is output to control the grid-side converter of the new energy. The positive and negative sequence voltage reference values given by the current loop are as follows:

[0079]

[0080] where k p1 is the proportional coefficient of the positive sequence voltage; k i1 is the integral coefficient of the positive sequence voltage; k p2 is the proportional coefficient of the negative sequence voltage; k i2 is the integral coefficient of the negative sequence voltage; is the reference value of the d-axis component of the positive sequence voltage; is the reference value of the d-axis component of the negative sequence voltage; is the reference value of the q-axis component of the positive sequence voltage; is the reference value of the q-axis component of the negative sequence voltage; is the reference value of the d-axis component of the positive sequence current; is the reference value of the d-axis component of the negative sequence current; is the reference value of the q-axis component of the positive sequence current; is the reference value of the q-axis component of the negative sequence current; L g is the inductor on the AC side of the converter; is the positive sequence voltage at the new energy grid connection point; is the negative sequence voltage at the new energy grid connection point; is the positive sequence d-axis current output by the new energy; is the negative sequence d-axis current output by the new energy; is the positive sequence q-axis current output by the new energy; is the negative sequence q-axis current output by the new energy; ω is the angular frequency of the grid voltage; t is the time integral.

[0081] In addition, during the asymmetric short-circuit fault, the control strategy adopted by the new energy units in the new energy system is as follows:

[0082] The reference value of the positive sequence reactive current output by the new energy unit is controlled according to the voltage deviation;

[0083] The reference value of the positive sequence active current output by the new energy unit is controlled in a constant current mode;

[0084] The reference value of the negative sequence reactive current output by the new energy unit is controlled in a constant current mode;

[0085] The reference value of the negative sequence active current output by the new energy unit is set to 0.

[0086] Step 2: Based on the topological structure of the new energy system, the sequence equivalent circuits of the new energy system are established respectively by using the symmetrical component method. As shown in Figure 3 , where the new energy equipment is equivalent to a current source, and the output current of the new energy equipment is determined according to the corresponding control strategy. In this embodiment, the case of a two-phase grounding fault occurring at the fault location on the AC transmission line is described, where Figure 3 (a) is the positive sequence equivalent circuit, Figure 3 (b) is the negative sequence equivalent circuit, Figure 3 (c) is the zero sequence equivalent circuit. Among them, Figure 3 , the subscripts 1, 2, and 0 represent positive, negative, and zero sequence electrical quantities respectively. I r is the phasor of the new energy output current, U r is the phasor of the voltage at the new energy terminal, U S is the positive sequence phasor of the infinite voltage source, X L is the reactance of the grid-side line, X T is the total reactance of the transmission line and transformer on the new energy side (when the fault point is located at a position close to the high-voltage side of the transformer on the transmission line, X T represents the reactance of the transformer on the new energy side), U is the phasor of the voltage of the fault point to the ground, and I is the phasor of the current of the fault point to the ground.

[0087] Step 3: Obtain the sequence voltage equations according to the sequence equivalent circuits of the new energy system. As shown in Figure 3 , the system equations of the sequence equivalent circuits can be written according to the symmetrical component method, that is, the corresponding voltage equations. It should be noted that in this embodiment, the positive sequence terminal voltage phasor of the new energy is set as U r1 ∠δ u1 , then the positive sequence output current phasor of the new energy is: I r1 ∠(δ u1 -Δδ 1 ). Among them, U r1 ∠δ u1 are all unknown quantities, I r1 and Δδ 1 are all known quantities and are determined by the new energy control. Δδ 1 = arctan(I q1 / I d1 ). And the negative sequence terminal voltage phasor of the new energy is set as U r2 ∠δ u2 , and the negative sequence reactive current phasor emitted by the new energy is I r2 ∠(δ u2 +Δδ 2 ) = I q2 ∠(δ u2 +Δδ 2), the negative - sequence current does not contain active - current components. Among them, U r2 ∠δ u2 is the quantity to be solved, I r2 and Δδ 2 are both known quantities and are determined by the new - energy negative - sequence control. Among them, Δδ 2 = 90°.

[0088] Specifically, in this embodiment, each - sequence voltage equation includes a positive - sequence voltage equation, a negative - sequence voltage equation, and a zero - sequence voltage equation:

[0089] The positive - sequence voltage equation is:

[0090]

[0091] The negative - sequence voltage equation is:

[0092]

[0093] The zero - sequence voltage equation is:

[0094]

[0095] Among them is the positive - sequence open - circuit voltage at the fault location; is the negative - sequence open - circuit voltage at the fault location; is the zero - sequence open - circuit voltage at the fault location; Z eq1 is the Thevenin equivalent impedance from the fault location in the positive - sequence equivalent circuit; Z eq2 is the Thevenin equivalent impedance from the fault location in the negative - sequence equivalent circuit; Z eq0 is the Thevenin equivalent impedance from the fault location in the zero - sequence equivalent circuit; X L1 is the line reactance on the grid side in the positive - sequence equivalent circuit; X L2 is the line reactance on the grid side in the negative - sequence equivalent circuit; X L0 is the line reactance on the grid side in the zero - sequence equivalent circuit; X T1 is the total reactance of the transmission line and transformer on the new - energy side in the positive - sequence equivalent circuit; X T2 is the total reactance of the transmission line and transformer on the new - energy side in the negative - sequence equivalent circuit; is the positive - sequence voltage phasor of the fault point to the ground; is the negative - sequence voltage phasor of the fault point to the ground; is the zero - sequence voltage phasor of the fault point to the ground; is the positive - sequence current phasor of the fault point to the ground; is the negative - sequence current phasor of the fault point to the ground; is the zero - sequence current phasor of the fault point to the ground; is the positive - sequence voltage phasor at the new - energy terminal; is the negative - sequence voltage phasor at the new - energy terminal; is the positive - sequence current phasor output by the new energy; is the negative - sequence current phasor output by the new energy; j is the imaginary unit.

[0096] Step 4: Solve the voltage expression of the non - fault phase at the fault location based on the sequence voltage equations, and obtain the relevant control parameters affecting the transient over - voltage of the new - energy system according to the voltage expression of the non - fault phase at the fault location. Specifically, the operation steps of solving the voltage expression of the non - fault phase at the fault location based on the sequence voltage equations in this step 4 include:

[0097] Obtain the positive - sequence voltage equation, negative - sequence voltage equation, and zero - sequence voltage equation respectively;

[0098] Obtain the corresponding boundary conditions according to the asymmetrical short - circuit fault:

[0099]

[0100] Obtain the voltage expression of the non - fault phase at the fault location according to the sequence voltage equations and the boundary conditions:

[0101]

[0102] Furthermore, in this embodiment, when a two - phase - to - ground fault occurs, it is generally approximately considered that Z eq1 = Z eq2 , then the voltage phasor of the non - fault phase at the fault location is:

[0103]

[0104] where k = Z eq0 / Z eq1 .

[0105] Based on the voltage expression of the non - fault phase at the fault location, it can be seen that during the asymmetrical fault, the transient over - voltage of the new - energy transmission system is related to the positive - and negative - sequence control parameters of the new energy and the system parameters.

[0106] Step 5: Analyze the change of the transient over - voltage of the non - fault phase at the fault point with respect to the relevant control parameters based on the sequence voltage equations, and obtain the key control parameters for suppressing the transient over - voltage of the new - energy system.

[0107] Specifically, when the new - energy units in the new - energy system only output positive - sequence reactive current and negative - sequence reactive current, and both the positive - sequence and negative - sequence active currents are zero, based on the sequence voltage equations and the boundary conditions, the positive - sequence open - circuit voltage and the negative - sequence open - circuit voltage phasors are collinear, and the positive - sequence open - circuit voltage and the positive - sequence phasor of the voltage source In-phase

[0108] When the new energy generates negative-sequence reactive power and positive-sequence reactive power, the positive-sequence open-circuit voltage and negative-sequence open-circuit voltage at the fault location are just in reverse. Therefore, during the asymmetrical fault, when increasing the negative-sequence capacitive reactive current output by the new energy, that is, increasing the amplitude of will cause the overall amplitude of to decrease, thereby reducing the transient overvoltage problem of the non-fault phases at the fault point; while if the new energy outputs inductive negative-sequence reactive power, it will exacerbate the overvoltage problem of the non-fault phases at the fault point. From the above analysis, it can be seen that increasing the negative-sequence reactive current output by the new energy at this time has an inhibitory effect on the transient overvoltage of the non-fault phases at the fault point.

[0109] Or, when the positive-sequence reactive current and negative-sequence reactive current output by the new energy are not zero, and the positive-sequence active current is also not zero, based on the voltage equations of each sequence and the boundary conditions, the positive-sequence open-circuit voltage and negative-sequence open-circuit voltage at the fault location are collinear;

[0110] When the new energy generates negative-sequence reactive power and positive-sequence reactive power, the positive-sequence open-circuit voltage and negative-sequence open-circuit voltage at the fault location are still in reverse. Therefore, when increasing the negative-sequence capacitive reactive current output by the new energy, the overvoltage problem of the non-fault phases at the fault point can also be reduced.

[0111] In summary, by making the new energy output a certain amount of negative-sequence reactive current, the effective suppression of the transient overvoltage of the non-fault phases at the system fault point can be achieved. Therefore, the key control parameter described in this embodiment uses the negative-sequence reactive current output by the new energy unit.

[0112] Step Six: Calculate the current reference value of the new energy system under the asymmetrical short-circuit fault based on the key control parameter and the constraint conditions.

[0113] During the asymmetrical short-circuit fault in this embodiment, since according to the national standard requirements, the new energy only absorbs a certain amount of negative-sequence reactive power, and the new energy needs to generate positive-sequence reactive power due to entering the low-voltage ride-through control. Therefore, after the asymmetrical grounding fault occurs in the new energy system, when there is a transient overvoltage problem in the non-fault phases at the fault point, the method of making the new energy output negative-sequence reactive current is considered to suppress this system transient overvoltage. However, at the same time, it is necessary to ensure that the phase voltage amplitude at the new energy grid connection point does not exceed the limit and the phase current of the new energy does not exceed the rated value.

[0114] Specifically, combined with Figure 3The topological structures of the positive and negative sequence equivalent circuits can obtain the positive and negative sequence voltage amplitudes at the new energy point of common connection:

[0115]

[0116] Based on the positive and negative sequence voltage amplitudes at the new energy point of common connection, the phase voltage amplitude V of the point of common connection is obtained abc :

[0117]

[0118] Considering that there is a Dy11 transformer between the new energy unit and the point of common connection to the public, and the positive and negative sequence voltage angles need to be deflected by 30° respectively, then the phase voltage amplitude V at the new energy machine terminal is jabc as follows:

[0119]

[0120] The three-phase current amplitude I output by the new energy is rabc as follows:

[0121]

[0122] where V 1 is the positive sequence voltage amplitude at the point of common connection; V 2 is the negative sequence voltage amplitude at the point of common connection; V g1 is the positive sequence voltage amplitude on the system side; V g2 is the positive sequence voltage amplitude on the system side; I r1 is the new energy output current phasor in the positive sequence equivalent circuit; I r2 is the new energy output current phasor in the negative sequence equivalent circuit; I d1 is the d-axis component of the positive sequence current output by the new energy; I d2 is the d-axis component of the negative sequence current output by the new energy; I q1 is the q-axis component of the positive sequence current output by the new energy; I q2 is the q-axis component of the negative sequence current output by the new energy; ω is the angular frequency; L is the inductance value; is the difference in the initial phase angles of the positive and negative sequence voltages; is the difference in the initial phase angles of the positive and negative sequence currents; represents the phase angle corresponding to the single-phase electricity;

[0123] Subsequently, according to the three-phase current amplitude output by the new energy in the above formula, a suitable current reference value can be selected to achieve the goal of controlling the phase voltage at the new energy PCC point and the phase current output by the new energy converter. It should be noted that during the asymmetrical short circuit in this embodiment, in order to ensure the safe grid connection of the new energy, a first constraint condition and a second constraint condition are set, where the first constraint condition includes that the phase voltage amplitudes at the new energy point of common connection and the new energy machine terminal do not exceed the voltage constraint value Vm ; The second constraint condition includes that the amplitude of the phase current output by the new energy converter does not exceed the current constraint value I m .

[0124] In order to limit the transient overvoltage of the non-fault phase at the fault point, the negative-sequence reactive current output by the new energy should be as large as possible. In this embodiment, the process of solving the current reference value is transformed into a constrained non-linear optimization problem, and the fmincon function in Matlab is preferably used to solve the current reference value, as Figure 4 shown. Therefore, the objective function of the non-linear optimization problem can be taken as obtaining the maximum value of I q2 , that is, max I q2 , so as to minimize the system overvoltage problem of the non-fault phase at the fault point to the greatest extent.

[0125] In addition, in this embodiment, the positive-sequence reactive current of the new energy is controlled according to the national standard as: I q1 = k 1 (0.9 - V 1 ), where k 1 is the positive-sequence reactive power proportion coefficient of the new energy. The positive-sequence active current of the new energy is set as a constant, and the negative-sequence active current of the new energy is 0 pu.

[0126] Step seven: Send the calculated current reference value to the current inner loop to achieve the suppression of the transient overvoltage of the new energy system.

[0127] Furthermore, in order to verify the above method in this embodiment, based on the Matlab simulation software, a system model as Figure 3 shown is built in the simulation, and the aggregated model of the direct-drive wind turbine is used to simulate the new energy power station. When operating normally, the active power output by the new energy is 200 MW, and the new energy is connected to the 220 kV infinite power grid through an AC line. All electrical quantities in the calculation are represented by per-unit values, and the reference capacity value is taken as 200 MW and the reference voltage is 220 kV.

[0128] First, analyze the influence of the negative-sequence reactive current of the new energy on the transient overvoltage to verify the influence of changing the negative-sequence reactive current of the new energy on the transient overvoltage of the non-fault phase in the system:

[0129] Among them, the simulation conditions are as follows: during the fault ride-through, set the positive-sequence active and reactive current reference values of the new energy to a fixed value and keep them unchanged, and change the reference value of the negative-sequence reactive current of the new energy to observe the change trend of the overvoltage. Among them, the transformer reactance is 0.05 pu, the parameters per unit length of the AC line are shown in Table 1, and the length of the AC line is taken as 150 km. Among them, the negative-sequence reactive current of the new energy takes 0, 0.1, and 0.3 pu respectively, the positive-sequence active current of the new energy is fixed at 0.2 pu, and the positive-sequence reactive current of the new energy is fixed at 0.4 pu. The simulation values and calculated values of the peak value of the transient overvoltage of the new energy are shown in Table 2. Set a two-phase grounding short circuit to occur on the transmission line at 0.4 s, and the duration is 0.4 s. The simulation results of the transient overvoltage of the non-fault phase at the system fault point are as Figure 5 shown, Figure 5 where the waveform in it is the fundamental voltage amplitude.

[0130] Table 1

[0131] Line sequence parameters Parameters per unit length (pu / km) Positive sequence reactance parameters of the line <![CDATA[2.1×10 -3 > Negative sequence reactance parameters of the line <![CDATA[2.1×10 -3 > Zero sequence reactance parameters of the line <![CDATA[7×10 -3 >

[0132] Table 2

[0133]

[0134]

[0135] It can be seen from Table 2 above that as the amplitude of the negative-sequence reactive current of the new energy increases, under the same short-circuit fault setting, the peak value of the transient overvoltage gradually decreases, which is consistent with the influence characteristic of the negative-sequence reactive current on the overvoltage proposed by the method of this embodiment. And the change trend of the theoretical calculated value and the simulation value of the overvoltage is basically the same. From the simulation results, in order to reduce the transient overvoltage, the amplitude of the negative-sequence reactive current of the new energy can be appropriately increased.

[0136] Subsequently, the transient overvoltage suppression method of this application is verified:

[0137] According to the above simulation analysis results, it can be seen that the negative-sequence reactive current of the new energy has an obvious influence on the transient overvoltage. Therefore, the transient overvoltage of the non-fault phase at the system fault point is adjusted by optimizing the value of the negative-sequence reactive current.

[0138] During this simulation process, the length of the 220 kv AC line is set to 100 km, and the line parameters are as shown in Table 1 above. A BC metal grounding fault occurs on the AC line near the system side, the fault occurs at 0.4 s, and the fault is cleared at 0.8 s. The current limit of the converter Im is taken as 1.15 pu; the phase voltage limit Vm is set to 1.1 pu. Two working conditions are set in this embodiment, and the system overvoltage during the short circuit is compared.

[0139] Condition 1: During the fault, the positive-sequence reactive power ratio coefficient k of the new energy1 = 1.2, the positive-sequence active current reference value is taken as 0.2 pu, and the negative-sequence current reference values of new energy are all 0 pu.

[0140] Condition 2: The positive-sequence current parameters of new energy are the same as those in Condition 1, and the negative-sequence reactive current reference values of new energy are calculated by the transient overvoltage suppression method of this application.

[0141] As Figure 6 shown, it is the non-fault voltage waveforms of the fault points in two conditions. As Figure 7 shown, it is the voltage waveforms at the PCC point in two conditions. As Figure 8 shown, it is the three-phase voltage waveforms at the machine terminals of new energy in two conditions. As Figure 9 shown, it is the output current waveforms of the new energy converters in two conditions.

[0142] Combined with Figures 6 - 9 it can be known that in Condition 1, when new energy does not output negative-sequence current, the non-fault phase voltage at the system fault point will exceed the 1.3 pu limit value, with serious overvoltage. While in Condition 2, after using the control method proposed in this application, it is ensured that the phase voltages at the machine terminals of new energy and the PCC grid connection points will not exceed the limit, the output current of new energy will not exceed the current limit value, and the overvoltage of the non-fault phase at the fault point is reduced to less than 1.3 pu to the greatest extent, and the system transient overvoltage problem is suppressed. Therefore, through the method proposed in this application, new energy outputs as much negative-sequence reactive current as possible, effectively suppressing the non-fault phase voltage at the system fault point.

[0143] In addition, as Figure 10 shown, this application also discloses a transient overvoltage suppression device for a new energy system during asymmetric faults. The device includes:

[0144] A system acquisition module, used to acquire the topological structure of the new energy system and the control strategy adopted by the new energy system during fault ride-through; among them, the new energy grid-side converter adopts a positive and negative sequence double-current-loop control strategy, and the new energy grid-connected inverter adopts a grid-voltage-oriented and positive and negative sequence double-current-loop control strategy.

[0145] An equivalent circuit establishment module, used to respectively establish the sequence equivalent circuits of the new energy system based on the topological structure of the new energy system by using the symmetrical component method, where the new energy equipment is equivalent to a current source, and the output current of the new energy equipment is determined according to the corresponding control strategy;

[0146] A voltage equation acquisition module, used to obtain the sequence voltage equations according to the sequence equivalent circuits of the new energy system;

[0147] A control parameter acquisition module, configured to solve the voltage expression of the non-fault phase at the fault location based on the sequence voltage equations, and obtain relevant control parameters affecting the transient overvoltage of the new energy system according to the voltage expression of the non-fault phase at the fault location;

[0148] A key parameter selection module, configured to analyze the change of the transient overvoltage of the non-fault phase at the fault point by the relevant control parameters based on the sequence voltage equations, and obtain the key control parameters for suppressing the transient overvoltage of the new energy system;

[0149] A current calculation module, configured to calculate the current reference value of the new energy system under the asymmetrical short-circuit fault based on the key control parameters and the constraint conditions;

[0150] A control output module, configured to send the calculated current reference value to the current inner loop to achieve the suppression of the transient overvoltage of the new energy system.

[0151] The device provided by the embodiment of the present application can implement Figure 1 each process implemented by the method embodiment. To avoid repetition, it will not be elaborated here.

[0152] As Figure 11 shown, the embodiment of the present application also provides an electronic device, including a processor and a memory, a program or instruction stored on the memory and executable on the processor, and when the program or instruction is executed by the processor, it implements each process of the method embodiment as shown in Figure 1 and can achieve the same technical effect. To avoid repetition, it will not be elaborated here.

[0153] The embodiment of the present application also provides a readable storage medium, on which a program or instruction is stored, and when the program or instruction is executed by the processor, it implements each process of the method embodiment described above Figure 1 and can achieve the same technical effect. To avoid repetition, it will not be elaborated here.

[0154] The embodiment of the present application also provides a computer program product, including computer instructions, and when the computer instructions are executed by the processor, it implements each process of the method embodiment described above Figure 1 and can achieve the same technical effect. To avoid repetition, it will not be elaborated here.

[0155] It should be understood that the "one embodiment" or "an embodiment" mentioned throughout the specification means that the specific features, structures or characteristics related to the embodiment are included in at least one embodiment of the present application. Therefore, the appearances of "in one embodiment" or "in an embodiment" throughout the specification do not necessarily refer to the same embodiment. In addition, these specific features, structures or characteristics may be combined in one or more embodiments in any suitable manner. It should be understood that in various embodiments of the present application, the magnitudes of the serial numbers of the above processes do not mean the order of execution, and the order of execution of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present application. The serial numbers of the embodiments of the present application above are only for description and do not represent the advantages or disadvantages of the embodiments.

[0156] It should be noted that in this text, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the element.

[0157] In several embodiments provided in the present application, it should be understood that the disclosed devices and methods can be implemented in other ways. The device embodiments described above are only illustrative. For example, the division of the units is only a logical function division, and there may be other division methods in actual implementation. For example, multiple units or components can be combined, or can be integrated into another device, or some features can be ignored, or not executed. In addition, the couplings, direct couplings or communication connections between the components shown or discussed with each other can be through some interfaces, and the indirect couplings or communication connections of the devices or units can be electrical, mechanical or other forms.

[0158] The units described above as separate components may or may not be physically separated, and the components shown as units may or may not be physical units; they can be located in one place or distributed to multiple network units; some or all of the units can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0159] In addition, each functional unit in the embodiments of the present application can be all integrated in a processing unit, or each unit can be separately used as a unit, or two or more units can be integrated in one unit; the above integrated units can be implemented in the form of hardware, or in the form of a combination of hardware and software functional units.

[0160] Those of ordinary skill in the art can understand that all or part of the steps to implement the above method embodiments can be completed by hardware related to program instructions. The foregoing program can be stored in a computer-readable storage medium. When the program is executed, it performs the steps including those of the above method embodiments; and the foregoing storage medium includes: removable storage devices, read-only memory (ROM), magnetic disks, or optical discs and other various media that can store program codes.

[0161] Alternatively, if the above integrated units of the present application are implemented in the form of software function modules and sold or used as independent products, they can also be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the embodiments of the present application, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a device (which can be a terminal or a platform, etc.) to execute all or part of the methods described in the various embodiments of the present application. And the foregoing storage medium includes: removable storage devices, ROM, magnetic disks, or optical discs and other various media that can store program codes.

[0162] The foregoing are only the preferred embodiments of the present application. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present application, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present application.

Claims

1. A method for suppressing transient overvoltage in a new energy system during an asymmetric fault, characterized in that: The method comprises the following steps: Obtain the topological structure of the new energy system and the control strategy adopted by the new energy system during fault ride-through; the new energy grid-side converter adopts a positive and negative sequence dual current loop control strategy, and the new energy grid-connected inverter adopts a grid voltage-oriented and positive and negative sequence dual current loop control strategy; Based on the topological structure of the new energy system, the symmetrical component method is used to establish the equivalent circuits of each sequence of the new energy system, in which the new energy equipment is equivalent to a current source, and the output current of the new energy equipment is determined according to the corresponding control strategy; Obtain the voltage equations of each sequence according to the equivalent circuits of each sequence of the new energy system; The voltage expression of the non-fault phase at the fault location is solved based on each sequence voltage equation, and the relevant control parameters affecting the transient overvoltage of the new energy system are obtained according to the voltage expression of the non-fault phase at the fault location; Based on the sequence voltage equations, the changes of transient overvoltage of non-fault phases at the fault point caused by relevant control parameters are analyzed to obtain the key control parameters for suppressing transient overvoltage of the new energy system. Calculate the current reference value of the new energy system under asymmetric short circuit fault based on key control parameters and constraints; The calculated current reference value is sent to the current inner loop to achieve transient overvoltage suppression in the new energy system.

2. The transient overvoltage suppression method according to claim 1, characterized in that: During an asymmetric short circuit fault, the control strategy adopted by the new energy unit in the new energy system is: The positive sequence reactive current reference value output by the new energy unit is controlled according to the voltage deviation; The positive sequence active current reference value output by the new energy unit is controlled in a constant current mode; The negative sequence reactive current reference value output by the new energy unit is controlled in a constant current manner; The reference value of the negative-sequence active current output by the new energy unit is set to 0.

3. The transient overvoltage suppression method according to claim 1, characterized in that: The step of solving the voltage expression of the non-fault phase at the fault location based on each sequence voltage equation is: The positive sequence voltage equation, negative sequence voltage equation and zero sequence voltage equation are obtained respectively: The positive sequence voltage equation is: The negative sequence voltage equation is: The zero-sequence voltage equation is: in is the positive sequence open circuit voltage at the fault location; is the negative sequence open circuit voltage at the fault location; is the zero-sequence open-circuit voltage at the fault location; Z eq1 is the Thevenin equivalent impedance from the fault position in the positive sequence equivalent circuit; Z eq2 is the Thevenin equivalent impedance from the fault position in the negative sequence equivalent circuit; Z eq0 is the Thevenin equivalent impedance from the fault position in the zero-sequence equivalent circuit; X L1 is the grid-side line reactance in the positive sequence equivalent circuit; X L2 is the grid-side line reactance in the negative sequence equivalent circuit; X L0 is the grid-side line reactance in the zero-sequence equivalent circuit; X T1 is the total reactance of the transmission line and transformer on the new energy side in the positive sequence equivalent circuit; X T2 is the total reactance of the transmission line and transformer on the renewable energy side in the negative sequence equivalent circuit; is the positive sequence voltage phasor from the fault point to the ground; is the negative sequence voltage phasor from the fault point to the ground; is the zero-sequence voltage phasor from the fault point to the ground; is the positive sequence current phasor from the fault point to the ground; is the negative sequence current phasor from the fault point to the ground; is the zero-sequence current phasor from the fault point to the ground; is the positive sequence voltage phasor at the renewable energy terminal; is the negative sequence voltage phasor at the new energy terminal; is the positive sequence current phasor of the new energy output; is the negative sequence current phasor of the new energy output; j is the imaginary unit; Obtain the corresponding boundary conditions based on the asymmetric short circuit fault: The voltage expression of the non-fault phase at the fault location is obtained according to the sequence voltage equations and boundary conditions:

4. The transient overvoltage suppression method according to claim 3, characterized in that: The step of analyzing the change of transient overvoltage of non-fault phases of the fault point by relevant control parameters based on each sequence voltage equation comprises: When the new energy generating units in the new energy system only output positive-sequence reactive current and negative-sequence reactive current, and the positive-sequence, sequence and negative-sequence active currents are all zero, the positive-sequence open-circuit voltage and negative-sequence open-circuit voltage phasors at the fault location are obtained to be collinear based on each sequence voltage equation and boundary conditions, and the positive-sequence open-circuit voltage is in phase with the positive-sequence phasor of the voltage source; or when the positive-sequence reactive current and negative-sequence reactive current output by the new energy are not zero, and the positive-sequence active current is not zero either, the positive-sequence open-circuit voltage and negative-sequence open-circuit voltage phasors at the fault location are obtained to be collinear based on each sequence voltage equation and boundary conditions; When renewable energy generates negative-sequence reactive power and positive-sequence reactive power, the positive-sequence open-circuit voltage and the negative-sequence open-circuit voltage at the fault location are opposite. At this time, increasing the negative-sequence reactive current output by renewable energy has a suppressive effect on the transient overvoltage of the non-fault phase at the fault point.

5. The transient overvoltage suppression method according to claim 4, characterized in that: The key control parameter adopts the negative sequence reactive current output by the new energy unit.

6. The transient overvoltage suppression method according to claim 1, characterized in that: The constraint conditions include a first constraint condition and a second constraint condition, The first constraint condition includes that the phase voltage amplitude between the new energy public connection point and the new energy generator end does not exceed the voltage constraint value V m ; The second constraint condition includes that the phase current amplitude output by the new energy converter does not exceed the current constraint value I m .

7. The transient overvoltage suppression method according to claim 6, characterized in that: The step of calculating the current reference value of the new energy system under an asymmetric short circuit fault based on the key control parameters and the constraint conditions includes: Based on the topological structure of the new energy system, the positive and negative sequence voltage amplitudes of the new energy public connection point are obtained: Based on the positive and negative sequence voltage amplitudes of the new energy public connection point, the phase voltage amplitude V of the public connection point is obtained. abc : Considering that there is a Dy11 transformer between the new energy unit and the public connection point, the phase voltage amplitude V at the new energy unit end is jabc for: Three-phase current amplitude I of new energy output rabc for: Where V1 is the positive sequence voltage amplitude of the common connection point; V2 is the negative sequence voltage amplitude of the common connection point; V g1 is the positive sequence voltage amplitude on the system side; V g2 is the positive sequence voltage amplitude on the system side; I r1 is the output current phasor of the new energy in the positive sequence equivalent circuit; I r2 is the output current phasor of the new energy in the negative sequence equivalent circuit; I d1 is the d-axis component of the positive sequence current output by the renewable energy; I d2 is the d-axis component of the negative sequence current output by the renewable energy source; I q1 is the q-axis component of the positive sequence current output by the renewable energy source; I q2 is the q-axis component of the negative sequence current output by the new energy source; ω is the angular frequency; L is the inductance value; is the difference between the initial phase angles of the positive and negative sequence voltages; is the difference between the initial phase angles of the positive and negative sequence currents; Represents the phase angle of the corresponding single-phase electricity; According to the three-phase current amplitude of the new energy output, I q2 The maximum value of .

8. The transient overvoltage suppression method according to claim 7, characterized in that: When calculating the current reference value of the new energy system under an asymmetric short-circuit fault, the fmincon function in Matlab is used for solution.

9. The transient overvoltage suppression method according to claim 1, characterized in that: The reference values ​​of the positive and negative sequence voltages in the positive and negative sequence dual current loop control strategy are: where k p1 is the proportional coefficient of the positive sequence voltage; k i1 is the integral coefficient of the positive sequence voltage; k p2 is the proportional coefficient of negative sequence voltage; k i2 is the integral coefficient of negative sequence voltage; is the reference value of the d-axis component of the positive sequence voltage; is the reference value of the d-axis component of the negative sequence voltage; is the reference value of the q-axis component of the positive sequence voltage; is the reference value of the q-axis component of the negative sequence voltage; is the reference value of the d-axis component of the positive sequence current; is the reference value of the d-axis component of the negative sequence current; is the reference value of the q-axis component of the positive sequence current; is the reference value of the q-axis component of the negative sequence current; L g is the inductance of the AC side of the converter; It is the positive sequence voltage of the renewable energy grid connection point; It is the negative sequence voltage of the renewable energy grid connection point; is the d-axis positive sequence current output by the new energy; It is the d-axis negative sequence current output by the new energy; is the q-axis positive sequence current output by the new energy; is the q-axis negative sequence current output by renewable energy; ω is the angular frequency of the grid voltage; t is the time integral.

10. A transient overvoltage suppression device for a new energy system during an asymmetric fault, characterized in that: The device comprises: The system acquisition module is used to obtain the topological structure of the new energy system and the control strategy adopted by the new energy system during fault ride-through; the new energy grid-side converter adopts a positive and negative sequence dual current loop control strategy, and the new energy grid-connected inverter adopts a grid voltage-oriented and positive and negative sequence dual current loop control strategy; An equivalent circuit establishment module is used to establish equivalent circuits of each sequence of the new energy system based on the topological structure of the new energy system by using the symmetrical component method, wherein the new energy device is equivalent to a current source, and the output current of the new energy device is determined according to the corresponding control strategy; A voltage equation acquisition module is used to obtain voltage equations of each sequence according to equivalent circuits of each sequence of the new energy system; A control parameter acquisition module is used to solve the voltage expression of the non-fault phase at the fault location based on each sequence voltage equation, and obtain relevant control parameters affecting the transient overvoltage of the new energy system according to the voltage expression of the non-fault phase at the fault location; The key parameter selection module is used to analyze the transient overvoltage changes of the non-fault phase of the fault point caused by the relevant control parameters based on the sequence voltage equations, and obtain the key control parameters for suppressing the transient overvoltage of the new energy system; A current calculation module is used to calculate the current reference value of the new energy system under an asymmetric short circuit fault based on key control parameters and constraints; The control output module is used to send the calculated current reference value to the current inner loop to achieve transient overvoltage suppression of the new energy system.

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