Closing resistor selection method considering zero loss phenomenon suppression and related system thereof

Abstract

The invention belongs to the technical field of transient stability of a power system, and discloses a closing resistor selection method considering a zero loss phenomenon and a related system thereof. According to the method, the current of the circuit breaker is solved through the Runge-Kutta method, a numerical solution of the current in a time domain is obtained, alternating-current and direct-current components of the current of the circuit breaker are obtained through fast Fourier transform, and the size relation of the alternating-current and direct-current components serves as a criterion to obtain a closing resistor feasible region for restraining the zero loss phenomenon. The defects of an existing closing resistor selection method for suppressing the zero loss phenomenon are overcome, the closing resistor selection efficiency is improved while the solving precision of the closing resistor for suppressing the zero loss phenomenon is guaranteed, complex simulation modeling is avoided, a closing resistor feasible region for suppressing the zero loss phenomenon is obtained, and the method is suitable for popularization and application. The defects of an existing closing resistor selection method for suppressing the zero loss phenomenon are overcome.

Description

Technical Field

[0001] The present invention belongs to the technical field of transient stability of power systems, and particularly relates to a closing resistor selection method considering suppression of zero point loss phenomenon and a related system thereof. Background Art

[0002] In the current construction of (ultra-)high-voltage (EHV) power grids, cables are gradually replacing overhead lines. Long-distance (ultra-)high-voltage (EHV) cable transmission lines have high capacitive charging power, and devices such as shunt reactors are often required for reactive power compensation. This reduces power frequency overvoltage, switching overvoltage, and capacitive current, achieving reactive power balance.

[0003] Highly compensated cable lines can cause zero-point loss during closing operations, meaning the current flowing through the circuit breaker fails to cross zero for several seconds. If a line fault occurs during this period or the circuit breaker needs to be opened, the healthy phase breaker may not extinguish the arc in time after reaching the open position. Continued arcing can damage components within the interrupter, degrade the SF6 gas, and even lead to more serious faults. Therefore, it is necessary to conduct in-depth research on measures to mitigate zero-point loss in lines equipped with parallel-compensated cables.

[0004] The fundamental cause of zero-point loss is that the reactor current cannot change suddenly. After the reactor is closed, the reactor current has a DC component. When the DC component of the current flowing through the circuit breaker is greater than the AC component, zero-point loss occurs. The decay rate of the DC component of the circuit breaker current is related to the resistance component in the cable system. Increasing the resistance component of the line increases the decay rate of the DC component of the current. By using a circuit breaker equipped with a closing resistor, the decay rate of the DC component of the circuit breaker current can be accelerated, thereby suppressing zero-point loss.

[0005] However, excessively large or small closing resistances are detrimental to suppressing zero-point loss. This is because the circuit breaker current shunt consists of a forward DC component and a reverse DC component. As the resistance increases, the reverse DC component increases, while the forward DC component decreases. Excessively large or small closing resistances generate a DC component with a large absolute value. Therefore, selecting the appropriate closing resistance value is crucial for suppressing zero-point loss in parallel-compensated cable lines.

[0006] Existing research on closing resistor selection methods for suppressing zero-point loss mainly focuses on the energy conservation method and the differential equation solution method. The energy conservation method equates the energy of the reactor decay during the closing resistor operation time with the energy consumed by the closing resistor, thereby obtaining a calculation formula for the closing resistor that suppresses zero-point loss. However, this method has many limitations and considers the DC component decay process in a relatively simple way, resulting in inaccurate closing resistance. The differential equation solution method equates the cable line to a π-type equivalent line, uses Kirchhoff's theorem to write a set of differential equations, and solves the frequency domain solution of the line breaker current. By comparing the steady-state amplitude of the line breaker current AC component with the amplitude obtained by the frequency domain solution, the closing resistor corresponding to the DC component decaying to zero is selected. However, this method can only calculate a single closing resistor value that suppresses zero-point loss, and cannot solve the feasible domain of the closing resistor, making it difficult to meet the needs of actual engineering for multi-objective optimization.

[0007] In summary, there is an urgent need for a closing resistance selection method for parallel-compensated cable lines that takes into account the suppression of zero-point loss. This method is applicable to all cable lines with parallel compensation and can solve the feasible domain of closing resistance that suppresses the zero-point loss phenomenon, thereby meeting the needs of actual engineering for multi-objective optimization. Summary of the Invention

[0008] The present invention provides a closing resistor selection method and a related system that considers the suppression of the zero point loss phenomenon, so as to solve the technical problem that the existing closing resistor selection method has simple considerations and strict criteria, resulting in the inability to solve the feasible domain of the closing resistor that suppresses the zero point loss phenomenon.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions: A method for selecting a closing resistor taking into account the suppression of zero point loss phenomenon comprises the following steps: Establish an equivalent circuit model for the AC cable system. Input the electrical parameters of the reactor and cable, the resistor input time, and the resistor value into the equivalent circuit model. Use Kirchhoff's theorem to write a differential equation system for the current-voltage relationship. Based on the differential equations of the current-voltage relationship, the time-domain numerical solution of the circuit breaker current is solved by the Runge-Kutta method. The time-domain numerical solution of the parallel line circuit breaker current is subjected to fast Fourier transform to extract the DC component and AC component of the reactor current. The DC component of the reactor current and the AC component of the reactor current are compared to obtain the closing resistance range that can suppress the zero point loss phenomenon.

[0010] The equivalent circuit model in step 1 is based on the Thevenin theorem, which equates the cable line to a π-type equivalent circuit, the parallel compensator to a series connection of resistance and inductance, and the power supply impedance to a series connection, thereby completing the establishment of the equivalent circuit model of the AC cable system.

[0011] The differential equations for the relationship between current and voltage are listed based on Kirchhoff's theorem. The differential equations are shown in the following formula:

[0012] Where, For time The voltage at is the total line current, is the resistance element in the circuit, is the inductor element, For inductance Road-related resistance, Through the inductor The current, is the capacitor element, is the voltage across the capacitor, is the resistance associated with the capacitor branch, is the current through the capacitor, is the inductance associated with the capacitive branch.

[0013] The differential equations do not have an analytical solution in the time domain. Based on the differential equations of current and voltage, the Runge-Kutta method is used to solve the numerical solution of the circuit breaker current in the time domain. The calculation method of the Runge-Kutta method is as follows: Given a first-order ordinary differential initial value problem: Where, is the current, For the initial moment The current value when .

[0014] Compute four slope estimates using the fourth-order Runge–Kutta method:

[0015] The weighted average iteration is performed on the slope estimation value obtained above, and the numerical solution of the circuit breaker current is obtained iteratively:

[0016] Where, is the step length, is the current time, is the current solution, For the next step solution.

[0017] The numerical solution of the circuit breaker current is obtained according to the Runge-Kutta method. The AC and DC components of the circuit breaker current are extracted using the fast Fourier transform. The calculation method of the fast Fourier transform is as follows:

[0018] Where, is a complex sequence in the frequency domain, is the imaginary unit ( ), is the rotation factor.

[0019] The DC component of the reactor current and the AC component of the reactor current are compared to obtain a closing resistance range that can suppress the zero point loss phenomenon. Specifically, if the AC component of the reactor current is greater than the DC component of the reactor current, there is no zero point loss phenomenon. Conversely, if the AC component of the reactor current is less than or equal to the DC component of the reactor current, there is a zero point loss phenomenon.

[0020] When the AC component of the reactor current is greater than the DC component, the amplitude of the AC component of the reactor current plus a small tolerance ε is greater than the DC component of the reactor current. Then the current has a zero crossing point and zero point loss does not occur at this time. This shows that the resistance value at this time can suppress zero point loss and belongs to the feasible domain of the closing resistance value.

[0021] An electronic device includes a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the processor implements the steps of a closing resistance selection method considering the suppression of zero point loss phenomenon.

[0022] A storage medium stores a computer program, which, when executed by a processor, implements the steps of a closing resistor selection method that takes zero point loss phenomenon suppression into consideration.

[0023] A computer program product for selecting a closing resistor taking into account the suppression of a zero point loss phenomenon includes a computer usable medium having computer program logic, wherein the computer program logic is used to implement the steps of a method for selecting a closing resistor taking into account the suppression of a zero point loss phenomenon, wherein the computer program logic includes: Establish an equivalent circuit model for the AC cable system. Input the electrical parameters of the reactor and cable, the resistor input time, and the resistor value into the equivalent circuit model. Use Kirchhoff's theorem to write a differential equation system for the current-voltage relationship. Based on the differential equations of the current-voltage relationship, the time-domain numerical solution of the circuit breaker current is solved by the Runge-Kutta method. The time-domain numerical solution of the parallel line circuit breaker current is subjected to fast Fourier transform to extract the DC component and AC component of the reactor current. The DC component of the reactor current and the AC component of the reactor current are compared to obtain the closing resistance range that can suppress the zero point loss phenomenon.

[0024] Compared with the prior art, the present invention has the following beneficial effects: Furthermore, the present invention can obtain the feasible domain of the closing resistor that accurately suppresses the zero point loss phenomenon without complex simulation modeling. While ensuring the calculation accuracy, it enhances the efficiency of closing resistor selection, reduces the difficulty of closing resistor selection, and facilitates the determination of the closing resistor value in actual engineering.

[0025] Furthermore, within the feasible closing region that suppresses zero-point loss, personnel can comprehensively consider line closing overvoltage, closing inrush current, and closing resistor heat absorption to perform multi-objective optimization of the closing resistor value, better meeting the requirements for safe and stable system operation. Previous closing resistor selection methods were unable to perform multi-objective optimization of closing resistor values, making them difficult to meet the needs of actual projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 : Circuit breaker structure diagram with closing resistor; Figure 2 : Cable circuit structure diagram for parallel compensation configuration; Figure 3 : Flowchart of the closing resistor selection method proposed in the present invention; Figure 4 : Parameters of the cable line in the simulation model; Figure 5 : Parameters of overhead lines in the simulation model; Figure 6 : PSCAD simulation model of 330kV cable-overhead line hybrid line; Figure 7 : Verification diagram of the accuracy of the closing resistor selection method proposed in the present invention; Figure 8 : Waveform diagram of the circuit breaker current (IBRK) when the present invention is not implemented; Figure 9 : Circuit breaker current (IBRK) waveform after implementation of the present invention; Figure 10 : Flowchart of the closing resistor selection method considering the suppression of zero point loss phenomenon; Figure 11 : Schematic diagram of the system hardware structure related to the closing resistor selection method considering the suppression of zero point loss phenomenon.

[0027] Explanation of reference numerals: 100, electronic device; 101, memory; 102, processor; 103, computer program; 104, communication bus. DETAILED DESCRIPTION

[0028] In order to further understand the content of the present invention, the present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the embodiments are only for explaining the present invention and are not intended to limit it.

[0029] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0030] Example 1 like Figure 10 As shown, this embodiment proposes a closing resistor selection method considering the suppression of zero point loss phenomenon, including the following steps: Establish an equivalent circuit model for the AC cable system. Input the electrical parameters of the reactor and cable, the resistor input time, and the resistor value into the equivalent circuit model. Use Kirchhoff's theorem to write a differential equation system for the current-voltage relationship. Based on the differential equations of the current-voltage relationship, the time-domain numerical solution of the circuit breaker current is solved by the Runge-Kutta method. The time-domain numerical solution of the parallel line circuit breaker current is subjected to fast Fourier transform to extract the DC component and AC component of the reactor current. The DC component of the reactor current and the AC component of the reactor current are compared to obtain the closing resistance range that can suppress the zero point loss phenomenon.

[0031] Example 2 Based on the configuration of parallel compensation cable lines, the present invention proposes a closing resistor selection method that takes into account the suppression of zero point loss phenomenon, which mainly includes two parts: solving the line circuit breaker current and solving and comparing the AC and DC components of the current.

[0032] In a parallel compensation cable line, the DC component of the circuit breaker current is mainly composed of the DC component of the reactor current. The attenuation rate of the DC component of the circuit breaker current depends on the ratio of the resistance and reactance of the reactor in parallel with the circuit breaker. When the loop resistance value is increased, the attenuation rate of the DC component of the current will increase accordingly, thereby suppressing the zero point loss phenomenon. Configuring a closing resistor in the circuit breaker can increase the loop resistance value. Therefore, using a circuit breaker configured with a closing resistor can speed up the attenuation rate of the DC component of the circuit breaker current, reducing the DC component of the circuit breaker current to below the AC component amplitude in a short time, thereby avoiding the problem of the current failing to cross zero for a long time, ensuring safe arc extinction when the circuit breaker is opened, and thus suppressing the zero point loss phenomenon. Configuring the closing resistor in the circuit breaker circuit structure, such as Figure 1The diagram in Figure 1 shows the structure of a circuit breaker equipped with a closing resistor. The closing resistor is connected in series with the auxiliary contacts and then in parallel with the main contacts. When in use, the auxiliary contacts are closed first, and the closing resistor is connected to the circuit. The connection time of the closing resistor is usually 8ms-11ms. At this time, the current mainly passes through the branch between the closing resistor and the auxiliary contacts. After a period of time, the main contacts are closed, the closing resistor is short-circuited, and the closing resistor is removed. At this time, the current mainly passes through the branch of the main contact. By configuring the closing resistor, the resistance of the circuit is increased. When the circuit breaker is closed, the resistor is used to limit the current, accelerating the attenuation of the DC component of the current. Then, the main contacts switch to normal operation, ensuring that the current can quickly recover the zero-crossing capability even under the most stringent zero-crossing closing conditions.

[0033] In order to consider the most serious case of zero point loss, the present invention models the parallel compensation cable line configured with a closing resistor circuit breaker. According to the Thevenin theorem, the parallel compensation cable line is equivalent to a π-type equivalent circuit, the parallel compensator is equivalent to a series connection of resistance and inductance, and the power supply impedance is equivalent to a series connection. An equivalent circuit model of the AC cable system is established, as shown in the following example: Figure 2 The cable and reactor are switched on simultaneously when the bus voltage crosses zero to verify the effectiveness of this measure.

[0034] Depend on Figure 2 As can be seen from the figure, when the main contacts are closed and the closing resistor is short-circuited, the removal of the closing resistor reduces the resistive component in the circuit, and the equivalent resistance of the reactor also decreases. The DC component of the circuit breaker current is primarily composed of the DC component of the reactor current. The DC component of the reactor current after the closing resistor is removed is used to represent the DC component of the circuit breaker current. The variation of the DC component of the current under different closing resistances provides a theoretical explanation for the feasible region of closing resistors that can suppress zero point loss.

[0035] The variation of the DC component of the current under different closing resistances is analyzed based on the reactor current value before and after the closing resistance is removed. The calculation method is as follows: The calculation method of is shown in the following formula (2).

[0036] (1) (2) Where, is the power supply voltage amplitude; is the power supply voltage angular frequency; is the closing phase angle, is the impedance angle of the reactor before the closing resistance is removed, is the impedance angle of the reactor after the closing resistance is removed, is the equivalent inductance of the reactor; is the equivalent resistance of the reactor before the closing resistance is withdrawn; is the equivalent resistance of the reactor after the closing resistance is removed; is the decay time constant of the DC component of the reactor current before the closing resistor exits, is the decay time constant of the DC component of the reactor current after the closing resistor is removed; The initial current value at the moment the closing resistor is removed; the decay time constant of the DC component of the reactor current before and after the closing resistor is removed and The calculation method is shown in the following formula (3).

[0037] (3) For the impedance angle of the reactor before the closing resistance is withdrawn , since the inductive reactance of the reactor is much larger than the equivalent resistance after the closing resistor is removed, that is, , according to formula (3) The calculation formula is: The value of is extremely large, ; For the impedance angle of the reactor after the closing resistance is removed When the closing resistor is connected, the equivalent resistance of the reactor before the closing resistor is removed is larger. is a finite value, so Since the reactor current cannot change suddenly before and after the closing resistor is removed, is the closing resistor input time (8-11ms), and the corresponding electrical angle range is: At the moment when the closing resistor exits, , the current during the closing resistor connection phase Current in the exit phase with closing resistance Equal, that is = Through the current boundary conditions, the initial current value at the moment of closing resistance exit is Solve to ensure the continuity of current before and after the closing resistor is removed, and provide initial conditions for analyzing the subsequent current transient process. The initial current value at the moment the closing resistor is removed The calculation formula is shown in the following formula (4): (4) Substitute formula (4) into formula (2) to obtain the expression of the DC component of the reactor current after the closing resistance is removed, and take the closing phase angle α = 0°, the DC component of the reactor current after the closing resistor is removed is expressed as As shown in the following formula (5).

[0038] (5) As shown in formula (5), the DC component of the reactor current consists of a positive DC component and a negative DC component. The amplitude of the negative DC component increases with the equivalent resistance of the reactor before the closing resistor is removed. The amplitude of the positive DC component increases with the increase of the equivalent resistance of the reactor before the closing resistance is withdrawn. In addition, when If it is too small, the impedance angle of the reactor before the closing resistance is withdrawn = 90°, then , the impedance angle of the reactor before the closing resistor exits The reverse DC component is smaller, and may even be transformed into a positive DC component, with the positive DC component being dominant. When it is too large, the impedance angle of the reactor before the closing resistance is withdrawn = 0°, at this time , the decay time constant of the DC component of the reactor current before the closing resistor exits is smaller, so the forward DC component is smaller and the reverse DC component dominates. And compared with other closing resistors, when =10ms, a larger reverse DC component will be generated. Therefore, the absolute value of the DC component of the reactor current shows a trend of first decreasing and then increasing with the change of the closing resistance. Therefore, there is a feasible region of the closing resistance that suppresses the zero point loss phenomenon. When the resistance value is less than the feasible region, increasing the resistance is conducive to reducing the DC component; when the resistance value exceeds the feasible region, increasing the resistance will cause the absolute value of the DC component to rise again.

[0039] like Figure 3 As shown in FIG, a flow chart of the closing resistance selection method proposed in the present invention is shown. num is the recording instruction of the closing resistance. When num=0, the closing resistance of this cycle is not recorded. When num=1, the closing resistance of this cycle is recorded. is the time after the circuit breaker is closed, is the time for the closing resistor to be put into operation, and are the AC and DC components of the circuit breaker current after the closing resistor is removed, respectively. ɛ is the cutoff value of the circuit breaker. To obtain the feasible region of the closing resistor, based on the established equivalent circuit model of the AC cable system, the electrical parameters of the reactor and cable, the resistor input time, and the closing resistor value are input into the equivalent circuit model. At this time, num=0. When the time after the circuit breaker is closed = Closing resistor input time When the Runge-Kutta method is used to calculate the circuit breaker current before the closing resistor is disconnected , the time after the circuit breaker is closed >Closing resistor input time At this time, the closing resistance is removed, and the Runge-Kutta method is used to calculate the circuit breaker current after the closing resistance is removed. The solution method for circuit breaker current and the criterion for zero-point loss are specified. Based on Kirchhoff's theorem, a differential equation system for the relationship between current and voltage is written. The differential equation system is shown in the following formula:

[0040] Where, For time The voltage at is the total line current, is the resistance element in the circuit, is the inductor element, For inductance Road-related resistance, Through the inductor The current, is the capacitor element, is the voltage across the capacitor, is the resistance associated with the capacitor branch, is the current through the capacitor, is the inductance associated with the capacitive branch.

[0041] When writing a differential equation system for the relationship between current and voltage based on Kirchhoff's theorem, since the switching on and off of the closing resistor will cause the circuit parameters to change, and there is a time-varying process in the circuit, the differential equation system does not have an analytical solution in the time domain. For differential equation systems without analytical solutions, the Runge-Kutta method is used to solve the numerical solution of the circuit breaker current in the time domain. The time is divided into several steps, and the slope estimates at different time points are calculated. The weighted average is then used to update the solution value, and the true solution is iteratively approximated. The calculation method of the Runge-Kutta method is as follows: Given an initial value problem of first-order ordinary differential: Where, is the current, For the initial moment The current value when .

[0042] Compute four slope estimates using the fourth-order Runge–Kutta method:

[0043] Perform weighted average iteration on the slope estimate obtained above, and the iterative solution is:

[0044] Where, is the step length, is the current time, is the current solution, For the next step solution.

[0045] Substitute the circuit breaker current into the iterative process and gradually calculate the current numerical solution for each time step, thus obtaining the numerical solution of the line current in the time domain after the closing resistor is removed. Perform a fast Fourier transform on the numerical solution of the circuit breaker current after the closing resistor is removed to extract the AC component of the reactor current. and DC component of the reactor , the calculation method of fast Fourier transform is as follows:

[0046] Where, is a complex sequence in the frequency domain, is the imaginary unit ( ), is the rotation factor.

[0047] The AC component of the reactor current separated by fast Fourier transform and DC component of the reactor , compare the AC component of the reactor current and DC component of the reactor When the AC component of the reactor current is greater than the DC component of the reactor, and the AC component of the reactor current amplitude plus a small tolerance Greater than the DC component of the reactor current, that is , the current crosses a zero point, and zero-point loss does not occur. This indicates that the resistance value at this point can suppress zero-point loss and falls within the feasible domain of closing resistor values. At this point, set num = 1, record the closing resistor value for this loop, add the resistance value to the input parameters in the equivalent circuit model, and continue the above steps, re-entering the resistance value of the closing resistor until the above conditions are no longer met. Conversely, if the AC component of the reactor current is less than or equal to the DC component, zero-point loss will occur. At this point, num remains at the initial value of 0, the loop ends, and the resistance value of the closing resistor to be closed is re-entered. Based on the comparison of the AC and DC components of the reactor current, the feasible domain of closing resistors that suppress zero-point loss is selected. This method avoids the complex simulation modeling process and directly solves the feasible domain of closing resistors that suppress zero-point loss.

[0048] In order to verify the accuracy of the feasible region of the closing resistance obtained by the present invention, the line parameters are R s= 3.099Ω, L s = 4.6604H, R c = 0.6541Ω, L c = 0.021H, C =1.5μF input to Figure 2 In the equivalent circuit model shown in FIG, the feasible region of the closing resistance under different resistor input times (8ms-11ms) is obtained. Based on the obtained resistance feasible region, the variation law of the AC and DC components of the circuit breaker current with the closing resistance under different input times is simulated in PSCAD for different resistors in the feasible region. The simulation model is shown in FIG. Figure 6 As shown in the figure, the simulation model is a hybrid line including cables and overhead lines. In order to verify the calculation results of the feasible domain of the resistance selection of the present invention, the overhead lines and cables are modeled separately using the frequency-dependent phase domain model (FDPM). The cable modeling is as follows: Figure 4 As shown. The modeling parameters of the cable are: the radius of the core conductor is: , the radius of the inner insulation layer is: , the radius of the metal sheath is: , the radius of the outer insulation layer is: Overhead line modeling Figure 5 As shown, the blue and orange lines are two overhead lines, and the purple line is the lightning protection line. : soil resistivity; : Split wire spacing; : conductor sag; : is the height of the lightning conductor. The conductor radius of the lightning conductor is , the conductor radius of the two overhead lines , overhead line DC resistance , relative magnetic permeability of overhead lines .

[0049] Figure 7 The comparison between simulation results and calculation results is shown, which is the comparison between simulation structure and calculation results under 8ms, 9ms, 10ms and 11ms. Figure 7 The horizontal axis of each subgraph in the figure represents the closing resistor value, and the vertical axis represents the current value. It was found that the AC and DC components of the circuit breaker current obtained by simulation and calculation are essentially identical for different resistor input times, confirming the validity of the calculated feasible region for closing resistance. The effective region in the figure indicates that within a specific resistance range, the AC component is greater than the DC component, suppressing zero point loss, confirming the validity of the calculated feasible region for closing resistance.

[0050] Figure 8 and Figure 9The following diagrams show the current waveforms of the circuit breaker when the busbar voltage is closed at zero crossing point for a 330 kV cable line equipped with parallel compensation before and after the implementation of the present invention. Figure 8 It can be seen that the current deviates from the zero axis for a long time after closing, showing a large DC component, and the current does not cross zero for a period of time. This shows that when the method of the present invention is not adopted, the zero point loss phenomenon is obvious, the current cannot cross zero normally, and it may cause arc extinguishing difficulties when the circuit breaker is opened. Figure 9 It can be seen that after implementation, the DC component of the current rapidly decays, the current quickly returns to a normal AC waveform, and is able to cross zero in a timely manner. This shows that the closing resistor selection method provided by the present invention effectively suppresses the zero-point loss phenomenon, ensures the normal zero-crossing characteristics of the current, and improves the safety and reliability of the circuit breaker when opening. Therefore, the closing resistor selection method provided by the present invention that suppresses the zero-point loss phenomenon can effectively avoid the problem of the circuit breaker current not crossing zero for a period of time after the cable line equipped with parallel compensation is closed.

[0051] The present invention solves the drawbacks of existing closing resistor selection methods for suppressing the zero point loss phenomenon. The AC and DC components of the circuit breaker are solved through the Runge-Kutta method and fast Fourier transform, and this is used as a criterion to optimize the closing resistor selection method for suppressing the zero point loss phenomenon, thereby determining the feasible domain of the closing resistor for suppressing the zero point loss phenomenon, and improving the efficiency of closing resistor selection for suppressing the zero point loss phenomenon while ensuring accuracy.

[0052] Example 3 like Figure 11 As shown, the present invention also provides an electronic device 100 for implementing a closing resistor selection method considering the suppression of zero point loss phenomenon; the electronic device 100 includes a memory 101, at least one processor 102, a computer program 103 stored in the memory 101 and executable on the at least one processor 102, and at least one communication bus 104.

[0053] The memory 101 can be used to store the computer program 103. The processor 102 implements the steps of the closing resistor selection method for suppressing zero point loss described in Example 1 by running or executing the computer program stored in the memory 101 and calling the data stored in the memory 101. The memory 101 can mainly include a program storage area and a data storage area, wherein the program storage area can store an operating system, an application required for at least one function (such as a sound playback function, an image playback function, etc.), etc.; the data storage area can store data (such as audio data) created based on the use of the electronic device 100. In addition, the memory 101 can include a non-volatile memory, such as a hard disk, a memory, a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, at least one disk storage device, a flash memory device, or other non-volatile solid-state storage device.

[0054] The at least one processor 102 may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The processor 102 may be a microprocessor or any conventional processor, etc. The processor 102 is the control center of the electronic device 100 and connects various parts of the entire electronic device 100 using various interfaces and lines.

[0055] The memory 101 in the electronic device 100 stores a plurality of instructions to implement a closing resistor selection method considering the suppression of zero point loss phenomenon. The processor 102 can execute the plurality of instructions to implement: Establish an equivalent circuit model for the AC cable system. Input the electrical parameters of the reactor and cable, the resistor input time, and the resistor value into the equivalent circuit model. Use Kirchhoff's theorem to write a differential equation system for the current-voltage relationship. Based on the differential equations of the current-voltage relationship, the time-domain numerical solution of the circuit breaker current is solved by the Runge-Kutta method. The time-domain numerical solution of the parallel line circuit breaker current is subjected to fast Fourier transform to extract the DC component and AC component of the reactor current. The DC component of the reactor current and the AC component of the reactor current are compared to obtain the closing resistance range that can suppress the zero point loss phenomenon.

[0056] Example 4 If the module / unit integrated in the electronic device 100 is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the process in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium, and the computer program can implement the steps of the above-mentioned method embodiments when executed by the processor. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form, etc. The computer-readable medium may include: any entity or device that can carry the computer program code, recording medium, U disk, mobile hard disk, magnetic disk, optical disk, computer memory and read-only memory (ROM, Read-Only Memory).

[0057] Example 5 This embodiment provides a computer program product for selecting a closing resistor with consideration for suppressing a zero point loss phenomenon, including a computer-usable medium having computer program logic. The computer program logic is configured to implement the steps of a method for selecting a closing resistor with consideration for suppressing a zero point loss phenomenon. The computer program logic includes: Establish an equivalent circuit model for the AC cable system. Input the electrical parameters of the reactor and cable, the resistor input time, and the resistor value into the equivalent circuit model. Use Kirchhoff's theorem to write a differential equation system for the current-voltage relationship. Based on the differential equations of the current-voltage relationship, the time-domain numerical solution of the circuit breaker current is solved by the Runge-Kutta method. The time-domain numerical solution of the parallel line circuit breaker current is subjected to fast Fourier transform to extract the DC component and AC component of the reactor current. The DC component of the reactor current and the AC component of the reactor current are compared to obtain the closing resistance range that can suppress the zero point loss phenomenon.

[0058] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0059] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0060] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0061] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0062] In addition, it should be understood that although this specification describes the embodiments, not every embodiment contains only one independent technical solution. This description is for clarity only. Those skilled in the art should consider the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only for the purpose of illustrating the technical concept of the present invention and cannot be used to limit the scope of protection of the present invention. Any changes made based on the technical solution in accordance with the technical concept proposed by the present invention fall within the scope of protection of the claims of the present invention.

Claims

1. A method for selecting closing resistance of a parallel compensation cable line considering the suppression of zero point loss, characterized in that: The following steps are involved: Establish an equivalent circuit model for the AC cable system. Input the electrical parameters of the reactor and cable, the resistor input time, and the resistor value into the equivalent circuit model. Use Kirchhoff's theorem to write a differential equation system for the current-voltage relationship. Based on the differential equations of the current-voltage relationship, the time-domain numerical solution of the circuit breaker current is solved by the Runge-Kutta method. The time-domain numerical solution of the parallel line circuit breaker current is subjected to fast Fourier transform to extract the DC component and AC component of the reactor current. The DC component of the reactor current and the AC component of the reactor current are compared to obtain the closing resistance range that can suppress the zero point loss phenomenon.

2. A method for selecting a closing resistor for a parallel compensation cable line considering the suppression of zero point loss according to claim 1, characterized in that: The equivalent circuit model in step 1 is based on the Thevenin theorem, which equates the cable line to a π-type equivalent circuit, the parallel compensator to a series connection of resistance and inductance, and the power supply impedance to a series connection, thereby completing the establishment of the equivalent circuit model of the AC cable system.

3. The method for selecting a closing resistor for a parallel compensation cable line considering the suppression of zero point loss according to claim 2, characterized in that: The differential equations for the relationship between current and voltage are listed based on Kirchhoff's theorem. The differential equations are shown in the following formula: Where, For time The voltage at is the total line current, is the resistance element in the circuit, is the inductor element, For inductance Road-related resistance, Through the inductor The current, is the capacitor element, is the voltage across the capacitor, is the resistance associated with the capacitor branch, is the current through the capacitor, is the inductance associated with the capacitive branch.

4. The method for selecting a closing resistor for a parallel compensation cable line considering the suppression of zero point loss according to claim 3, characterized in that: The differential equations do not have an analytical solution in the time domain. Based on the differential equations of current and voltage, the Runge-Kutta method is used to solve the numerical solution of the circuit breaker current in the time domain. The calculation method of the Runge-Kutta method is as follows: Given an initial value problem of first-order ordinary differential: Where, is the current, For the initial moment The current value when Compute four slope estimates using the fourth-order Runge–Kutta method: The weighted average iteration is performed on the slope estimation value obtained above, and the numerical solution of the circuit breaker current is obtained iteratively: Where, is the step length, is the current time, is the current solution, For the next step solution.

5. The method for selecting a closing resistor for a parallel compensation cable line considering the suppression of zero point loss according to claim 4, characterized in that: The numerical solution of the circuit breaker current is obtained according to the Runge-Kutta method. The AC and DC components of the circuit breaker current are extracted using the fast Fourier transform. The calculation method of the fast Fourier transform is as follows: Where, is a complex sequence in the frequency domain, is the imaginary unit ( ), is the rotation factor.

6. The method for selecting closing resistance of a parallel compensation cable line considering the suppression of zero point loss according to claim 1, characterized in that: The DC component of the reactor current and the AC component of the reactor current are compared to obtain a closing resistance range that can suppress the zero point loss phenomenon. Specifically, if the AC component of the reactor current is greater than the DC component of the reactor current, there is no zero point loss phenomenon. Conversely, if the AC component of the reactor current is less than or equal to the DC component of the reactor current, there is a zero point loss phenomenon.

7. A closing resistor selection method considering the suppression of zero point loss according to claim 6, characterized in that: When the AC component of the reactor current is greater than the DC component, the amplitude of the AC component of the reactor current plus a small tolerance ε is greater than the DC component of the reactor current. Then the current has a zero crossing point and zero point loss does not occur at this time. This shows that the resistance value at this time can suppress zero point loss and belongs to the feasible domain of the closing resistance value.

8. An electronic device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of a closing resistor selection method considering the suppression of zero point loss phenomenon according to any one of claims 1 to 7 are implemented.

9. A storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of a closing resistor selection method considering the suppression of zero point loss phenomenon according to any one of claims 1 to 7 are implemented.

10. A computer program product for selecting a closing resistor with consideration of zero point loss suppression, comprising a computer-usable medium having computer program logic, wherein the computer program logic is configured to implement the steps of the method for selecting a closing resistor with consideration of zero point loss suppression according to any one of claims 1 to 7, the computer program logic comprising: Establish an equivalent circuit model for the AC cable system. Input the electrical parameters of the reactor and cable, the resistor input time, and the resistor value into the equivalent circuit model. Use Kirchhoff's theorem to write a differential equation system for the current-voltage relationship. Based on the differential equations of the current-voltage relationship, the time-domain numerical solution of the circuit breaker current is solved by the Runge-Kutta method. The time-domain numerical solution of the parallel line circuit breaker current is subjected to fast Fourier transform to extract the DC component and AC component of the reactor current. The DC component of the reactor current and the AC component of the reactor current are compared to obtain the closing resistance range that can suppress the zero point loss phenomenon.

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