159 results about "Peak value" patented technology

The invention relates to the technical field of equipment maintenance, in particular to a distribution box remote diagnosis and maintenance system which comprises a voltage deviation detection module, a node hot stacking identification module, a channel stability classification module, a contact aging trend evaluation module and a period adjustment trigger module. According to the method, peak value change of effective voltage in each channel period in the distribution box is collected and compared with a preset criterion so as to accurately identify an abnormal discharge unit and accurately position a potential risk channel, and the change rate of equivalent series capacitance, contact conductance and contact resistance of a node is continuously sampled in a non-power-on state so as to accurately identify the potential risk channel. According to the method, multi-parameter same-trend change characteristics are determined, the contact aging process is accurately evaluated by integrating the parameter trend, the node trend and the maintenance plan period remaining time are subjected to cross comparison, the maintenance task advance opportunity is automatically judged, the maintenance plan is actively adjusted, the node fault missing detection risk is effectively reduced, and the maintenance timeliness and accuracy are remarkably improved.

The invention discloses a high-precision transformer fault detection method and system, relates to the technical field of transformer detection, is used for solving the problems of insensitive fault characterization and delayed diagnosis under a light load condition, and judges whether to enter a load judgment mechanism or not by acquiring input side access voltage information and counting low-load accumulated duration. When entering a load discrimination mechanism, detecting the start-stop behavior of a load branch and the temperature rise trend of a winding, calculating a light load index, identifying a light load state, carrying out region division on an iron core, collecting magnetic flux density data, and calculating iron loss balance characteristics aiming at iron loss deviation which is easy to occur under a light load condition; the insulation degradation coefficient is calculated by fusing the oil temperature peak value and the dielectric loss factor, and the abnormal index is generated with the iron loss balance characteristic, so that the early warning of the early hidden fault of the transformer can be realized in a light load scene in which the traditional temperature rise and current indexes are insensitive, and the operation reliability and maintenance efficiency of the transformer in a power distribution system are improved.

The invention relates to the technical field of direct current transmission detection, in particular to a device and method for testing power pipeline connection, and the device comprises a power parameter collection module which is used for collecting current signals and voltage signals in a power pipeline, measuring temperature values at a plurality of positions, obtaining insulation resistance at each node, and measuring grounding resistance of a plurality of grounding points; and summarizing the measurement data to generate an electric power parameter set. According to the invention, through integration and analysis of measurement data of current, voltage, temperature, insulation resistance and grounding resistance, comprehensive monitoring and evaluation of the state of the power pipeline are realized. After the data are integrated, by calculating the mean value, the variance and the peak value of the data and analyzing the spatial distribution of the temperature and the frequency characteristics of the grounding resistance, the understanding of the behavior of the power system is enhanced. According to the data analysis mode, the prediction capability of potential risks and the sensitivity of fault detection are improved, and serious equipment faults and service interruption are effectively avoided.

The invention discloses a turn ratio optimization method of an integrated three-phase Boost-LLC topology. The turn ratio optimization method comprises the following steps: acquiring a positive peak value and a negative peak value of Boost chopping inductive current; according to the positive peak value and the negative peak value, obtaining an effective value of the chopping inductive current; obtaining resonance current peak values of a Boost primary side and a Boost secondary side; according to the resonance current peak value, resonance current effective values of a primary side and a secondary side are obtained; when the output voltage is fixed, inductance values under different turn ratios are calculated; and according to the effective value of the chopping inductive current, the effective value of the resonance current and the inductance values under different turn ratios, obtaining the turn ratio with the minimum loss. According to the method, the problem that the turn ratio in the integrated three-phase Boost-LLC topology is difficult to design scientifically and efficiently is solved.

The invention is suitable for the technical field of grounding grid defect evaluation, and provides a transient electromagnetism-based grounding grid corrosion defect evaluation method and system, and the method comprises the steps: placing a sensor of a transient electromagnetic detection device above a to-be-detected region of a grounding grid, injecting a pulse current excitation signal into a conical focusing excitation coil, and carrying out the detection of the to-be-detected region of the grounding grid; acquiring an induced voltage time sequence signal through a receiving coil; extracting at least one characteristic parameter from the induced voltage time sequence signal, wherein the characteristic parameter comprises a signal peak value, peak value time, an attenuation rate or a signal integral quantity; inputting the characteristic parameters into a preset corrosion evaluation model, and performing inversion to obtain a residual thickness value or a corrosion depth value of the grounding grid in the to-be-detected area; generating and outputting a quantitative evaluation result containing the residual thickness value or the corrosion depth value; the method can be implemented in a non-stop state of the grounding grid, and an efficient and reliable decision basis is provided for safe operation and state maintenance of a power system.

The invention discloses an intelligent power supply control method adaptive to different loads, and the method comprises the following steps: starting up a power supply, carrying out the output in a constant voltage source mode, and relaxing a voltage and current loop; when more than two times of rated current occurs, the output voltage is reduced according to the output current signal, whether an overload phenomenon occurs or not is judged, and a dynamic response mode or a peak power mode is entered; if the power supply stays in a dynamic response mode or a peak power mode for a long time or enters an accumulated continuous different-place time for multiple times in a short time, entering a constant-current protection mode; and after the output voltage signal and the output current signal of the power supply return to normal, the constant current protection mode is quitted, and the constant voltage source mode is re-entered. The output of the power supply is controlled through the micro control unit (MCU), and different types of loads are intelligently detected and responded, so that the purposes of timely identification, timely protection and rapid and stable output are achieved, and the reliability and applicability of the power supply are enhanced.

The embodiment of the invention discloses a converter fault ride-through method and system based on a dynamic virtual impedance parameter, and relates to the technical field of power electronics, and the method comprises the steps: latching the virtual internal potential amplitude of a converter and the angular velocity of a system before a fault when the voltage amplitude of a grid-connected point is detected to be lower than a preset voltage threshold value; calculating d-axis and q-axis fault current components which are expected to flow through the converter by using latch data, a current grid-connected point voltage amplitude, a virtual impedance initial value before a fault and controller output delay, calculating to obtain a three-phase fault current maximum peak value, comparing the three-phase fault current maximum peak value with a maximum current which can be borne by the converter, and determining the current value of the converter. And according to a comparison result, an adjustment coefficient and an impedance proportionality coefficient, a virtual resistor and a virtual inductor are dynamically calculated and updated, new d-axis and q-axis current reference values are calculated together with a latched virtual internal potential amplitude and d-axis and q-axis voltages of the current grid-connected point, and the new d-axis and q-axis current reference values are input into a current inner loop controller to control the output of the converter.

The invention relates to the technical field of relay protection, in particular to a three-phase self-adaptive reclosing method and system for a wind power transmission line. The method comprises the following steps: when a fault is detected, collecting a secondary side voltage signal of a target fault phase of the wind power system; determining a fault phase voltage envelope value according to the peak value of the secondary side voltage signal; calculating energy in a plurality of time windows according to the fault phase voltage envelope value; sequentially calculating the energy ratio between the energy of the jth (j = 2, 3, 4,...) time window and the energy of the first time window; if the value of the energy ratio of at least three continuous time windows in the maximum discrimination time limit is greater than 1, determining a reclosing moment so as to output a circuit breaker closing signal after the reclosing moment is reached; otherwise, judging that the fault type is a permanent fault, and not outputting the circuit breaker closing signal. The objective of the invention is to solve the problem of how to identify the fault type of a wind power system before reclosing of a circuit breaker.

The invention relates to the technical field of power supply testing, in particular to a power supply testing system and method. Comprising the following steps: performing power supply demand simulation based on a load transition mechanism: performing deep analysis on a correlation relationship among components of a load by using demand analysis, and performing power supply demand simulation according to a deep analysis result; and constructing a power supply response state set based on the power supply demand simulation result and in combination with the load response characteristics, and carrying out the adaptability test of the power supply behavior through a power supply adaptability clustering algorithm according to the distribution characteristics of the load states under different configurations. According to the method, the instantaneous peak value, the stable power consumption and the load transition characteristics are extracted, the power supply response model is constructed in combination with the load state, and the fitting degree of the real power supply demand of each component is improved; and through a multi-round clustering center iteration verification and adjustment mechanism, it is ensured that the test covers the power supply threshold of all components, and the comprehensiveness and reliability of the power supply test are improved.

The invention discloses a method for modulating two parallel converters based on zero common-mode voltage and zero-sequence circulating current suppression, which comprises the following steps of: firstly, analyzing the influence of 64 switch combinations on zero-sequence circulating current and common-mode voltage, simultaneously considering common-mode voltage elimination and zero-sequence circulating current suppression, and screening out 18 optimal switch combinations; secondly, in order to eliminate the low-frequency zero-sequence circulating current, designing six switch sequence templates which are symmetrical in a quarter period, and limiting the average value of the zero-sequence circulating current of each switch period to be 0; then, on the basis of the sequence template, starting from the angle of zero-sequence circulating current peak value minimization and switching loss optimization, a vector plane is divided into six large sectors, each large sector comprises six sub-sectors, and the optimal switching sequence of each area is obtained; and finally, a modulation wave is calculated for the optimal switching time sequence, a switching action mode is designed, and a driving signal of the switch is obtained. According to the invention, the problems of low-frequency zero-sequence circulating current and large zero-sequence circulating current peak value existing in the existing zero common-mode voltage modulation algorithm are solved.

The invention discloses a multi-parameter collaborative optimization design method for a modular multilevel converter, and belongs to the technical field of modular multilevel converter design. In order to solve the problem of reasonable design of main parameters of the modular multilevel converter, a mathematical model of the modular multilevel converter is constructed; designing a capacitor voltage fluctuation model, a sub-module capacitor capacitance value model and a fluctuation quantity model, and analyzing the relationship between the capacitor voltage fluctuation and the operation condition and the relationship between the sub-module capacitor capacitance value and the operation condition; determining an upper limit value of the bridge arm inductance based on consideration of a system power operation range, determining a design initial value of the bridge arm inductance based on consideration of ring current suppression, determining a lower limit value of the bridge arm inductance based on consideration of resonance avoidance and fault current rise rate limitation, and obtaining a design range of the bridge arm inductance; adjusting the bridge arm inductance to obtain a design value of the designed bridge arm inductance; and according to the capacitance value of the sub-module capacitor and the design value of the designed bridge arm inductor, analyzing the peak voltage and the peak current of the power device IGBT to determine the parameter selection of the power device.

The invention relates to the technical field of electrical variable measurement, in particular to a filter fault detection method and system, and the method comprises the following steps: synchronously collecting an input current signal flowing through a filter and voltage time domain waveforms at the two ends of the filter based on a sine input voltage signal applied to the filter; the ratio of the peak voltage to the peak current in the initial stage is calculated, and the waveform transient amplitude ratio is obtained; and based on the waveform transient amplitude comparison, segmenting and sorting continuously acquired time domain waveforms according to a preset time window to generate an instantaneous electrical parameter sequence. An input current signal and voltage waveforms at the two ends are synchronously collected on the basis of application of a sine input voltage signal, the ratio of peak voltage to peak current is extracted to obtain waveform transient amplitude comparison, the sensitivity of waveform characteristics is improved, continuously collected time domain waveforms are divided through the waveform transient amplitude comparison, an instantaneous electrical parameter sequence is formed, and the accuracy of the waveform characteristics is improved. And the signal segmentation is more reliable.

The invention relates to a resonance grounding power distribution network grounding fault line selection method based on a zero sequence current ratio, and belongs to the technical field of power distribution network relay protection. The method comprises the following steps: acquiring neutral point zero-sequence voltage and phase current data of each outgoing line of the power distribution network, and judging whether a fault occurs or not according to whether the zero-sequence voltage exceeds a threshold value or not; if the zero-sequence voltage does not exceed the threshold value, the line selection process is not started, otherwise, the zero-sequence current of each outgoing line is calculated according to the phase current data; calculating the sum of total zero-sequence current of the power distribution network according to the zero-sequence current of each outgoing line, and comparing the zero-sequence current of a single outgoing line with the sum of the total zero-sequence current to obtain a zero-sequence current ratio of each outgoing line; and comparing the waveform of the zero-sequence current ratio, finding a first sharp peak value after the fault occurs, and if the sharp peak value of the outgoing line is opposite to that of other outgoing lines, judging that the outgoing line is a fault outgoing line. According to the method, the fault line with the high-resistance grounding fault in the resonance grounding power distribution network can be accurately identified, and the limitation that the high-resistance fault is difficult to identify in the existing method is overcome.

The invention discloses a driving control method of an interleaving parallel flyback micro inverter. The driving control method comprises the following steps: comparing the total output power of the interleaved parallel flyback micro inverter with the maximum output power of a single branch; when the total output power of the interleaved parallel flyback micro inverter is smaller than the maximum output power of a single branch, determining a time point corresponding to the maximum value according to the peak current reference value, and controlling the first transformer and the second transformer to work alternately based on the time point; and when the total output power of the interleaving flyback micro inverter is greater than or equal to the maximum output power of the single branch, determining a time interval corresponding to the condition that the total output power is greater than or equal to the maximum output power of the single branch, and controlling the first transformer and the second transformer to work at the same time in the time interval, and alternately working outside the time interval. According to the technical scheme, the aging difference of branch devices can be effectively reduced, and the situation that branch heat accumulation is serious is avoided.

A method for controlling pulse arc welding involving feeding a welding wire and applying a welding current by repeating a pulse cycle including: a peak rising period of applying a peak rising current increasing from a base current to a peak current; a peak period of applying the peak current; a peak falling period of applying a peak falling current decreasing from the peak current to the base current; and a base period of applying the base current. The feed speed of the welding wire is changed such that it beings to change from a reverse-feeding peak value toward a forward-feeding peak value at a point earlier by a first preceding period than the start of the peak rising period. Then, the feed speed reaches the forward-feeding peak value at a point earlier than an end of the peak rising period, and beings to change from the forward-feeding peak value toward the reverse-feeding peak value at a point earlier by a second preceding period than the start of the peak falling period, and reaches the reverse-feeding peak value at a point earlier than an end of the peak falling period.

The invention discloses a parallel energy storage array battery cluster adaptive parallel operation prediction method and system, and the method comprises the steps: estimating the total current of each battery cluster during parallel operation based on a parallel operation equivalent circuit model, and determining the estimated value of the total parallel operation current during each parallel operation according to a parallel operation sequence; based on the equivalent circuit model and the parallel operation equivalent circuit model, predicting the total voltage of the direct current bus during each parallel operation; based on a parallel operation peak current model, determining p and p + 1 times of parallel operation peak current; when the p parallel operation peak current is not greater than the closed peak current tolerance value of the parallel operation contactor, but the p + 1 parallel operation peak current is greater than the closed peak current tolerance value of the parallel operation contactor, calculating the voltage difference between the total voltage measured value and the direct current bus total voltage predicted value at the starting time and the ending time of the p and p + 1 parallel operation interval time; if the pressure difference at the starting moment is not greater than the pressure difference at the ending moment, judging that the (p + 1) th parallel operation cannot be executed; on the contrary, the p-th parallel operation interval period and the p + 1-th parallel operation interval period are prolonged, and battery cluster parallel operation prediction is achieved.

The invention discloses a scintillation pulse peak voltage sampling method and device and a computer storage medium, and the method comprises the steps: carrying out the peak holding processing of a scintillation pulse, and obtaining a peak holding signal, the size of the peak holding signal and the peak value of the scintillation pulse meeting a first pre-calibrated mapping relation; generating a reference signal, wherein the reference signal conforms to the prior model; comparing the reference signal with the peak holding signal to obtain time difference information when the reference signal crosses the peak holding signal, the time difference information and the peak holding signal conforming to a second pre-calibrated mapping relation, and the second pre-calibrated mapping relation being associated with the prior model; and according to the time difference information, the first pre-calibrated mapping relation and the second pre-calibrated mapping relation, reversely obtaining the peak voltage of the scintillation pulse. On one hand, the problems existing in existing PP-MVT can be solved, on the other hand, the method can be highly compatible with an existing framework of an MVT method, and sampling and restoring of flash pulse key information are completed.

The present invention discloses a method for generating the short - circuit breaking voltage and current waveforms of a circuit breaker and obtaining parameters, which is characterized in that by obtaining the positive - sequence reactance X1, positive - sequence resistance R1, and zero - sequence reactance X0 of the node where the circuit breaker is located, the total current, alternating - current component current, direct - current component current, and power - frequency recovery voltage during the short - circuit breaking process of the circuit breaker are calculated by applying a three - phase equivalent circuit model. Further, the parameters of the last half - wave of the short - circuit breaking current are obtained: the duration ΔT, the peak value I peak , the direct - current component p at the current zero - crossing point, and from p, the di / dt at the current zero - crossing point and the TRV parameters under the condition of modified asymmetrical short - circuit breaking can be calculated. The short - circuit breaking voltage and current parameters of the high - voltage alternating - current circuit breaker obtained by the method of the present invention can provide reference and basis for the evaluation of the breaking capacity of the circuit breaker and phase - selective breaking.

A start-up method for reducing inrush current to a transformer when closing a switching device. The method includes monitoring a voltage in one of the phases. The method also includes, for each of a sequence of iterations: at a same opening angle relative to a reference angle of the monitored voltage, opening the switching device; at a closing angle relative to the reference angle, which is shifted in relation to the closing angle of all other iterations in the sequence, closing the switching device; and obtaining a peak value of the overall inrush current resulting from the closing. The method also includes selecting for future use with said same opening angle, the closing angle of one of the iterations in which the overall inrush current is relatively low when compared with the other iterations of the sequence.

The invention relates to a power outer loop collaborative optimization virtual synchronous generator transient stability improvement method, and belongs to the technical field of virtual synchronous generator transient stability, and the method comprises the following steps: S1, building a virtual synchronous generator small signal power angle model; s2, performing active transient compensation and capacity constraint of power angle-frequency difference cooperative state feedback; s3, voltage deviation driven adaptive reactive power coefficient and active-reactive power combined current limiting are carried out; and S4, fault current impact suppression of the current-driven virtual impedance. The method can effectively reduce peak values and oscillation time of a power angle and a frequency difference, limit a fault current not to exceed a set upper limit, consider voltage support and active support capabilities, has good stability and robustness, and is suitable for controlling the grid-connected virtual synchronous generator under different short-circuit ratios and various fault working conditions.

The present application proposes a method for controlling the output voltage ripple of a dual active bridge and a related device, the method comprising: a controller obtaining a plurality of first circuit parameters and the n-1th ripple voltage peak-to-peak value under the current working condition, the plurality of first circuit parameters including a plurality of frequency-jittering-related frequency values ​​and a first phase shift angle; determining a phase shift angle control variable based on the n-1th ripple voltage peak-to-peak value; determining a second phase shift angle based on the phase shift angle control variable, the n-1th ripple voltage peak-to-peak value, the nth ripple voltage peak-to-peak value and the first phase shift angle; determining a target phase shift angle based on the second phase shift angle and a plurality of frequency-jittering-related frequency values; and performing a phase shift angle compensation operation based on the target phase shift angle when the frequency-jittering cycle reaches the n+1th frequency-jittering cycle. In this way, when a phase shift angle reverse compensation operation is performed based on the ripple voltage peak-to-peak value to offset the power transmission error caused by the frequency offset, the output power imbalance problem at the moment of frequency change is greatly alleviated, and the degree of deterioration of the output voltage ripple is reduced.

The present application provides a method for monitoring a through fault current. The method may involve: detecting a through fault; calculating an electrical stress, peak current, and duration of the through fault; determining two sets of percentage state changes associated with the through fault; assigning a respective set of weights and criticalities to each set of percentage state changes; calculating a mechanical state change based on the first set of percentage state changes and the first set of weights and criticalities; calculating a thermal state change based on the second set of percentage state changes and the second set of weights and criticalities; calculating a cumulative state change based on the mechanical and thermal state changes; and training a machine learning model using the electrical stress, peak current, duration, two sets of percentage state changes, and mechanical, thermal, and cumulative state changes.

The application discloses a kind of relay branch state detection method, device, medium and electric meter of three-phase electric meter, including obtaining the voltage digital signal after superposition of each phase branch of three-phase electric meter relay;According to the voltage digital signal after superposition, the voltage peak value of each phase branch and the timestamp corresponding to the voltage peak value are obtained;According to the voltage peak value and the timestamp and the preset state determination condition, the state result of the three-phase electric meter relay branch is obtained.The application solves the problem that the prior art can only judge the overall on-off state of three-phase power supply, resulting in a single state recognition function.

The invention provides a linearization control method and system for an energy storage system, and mainly provides a single-phase-shift frequency conversion modulation method applied to the linearization control method and system, the single-phase-shift frequency conversion modulation method is applied to a single-stage DAB type AC-DC converter, and the alternating current input voltage vac, the alternating current input current iac and the direct current output voltage Vdc of the single-stage DAB type AC-DC converter are sampled; based on the sampled alternating current input voltage vac, the alternating current input current iac and the direct current output voltage Vdc, a control variable theta is obtained through calculation; on the basis of the obtained control variable theta, at the moment when the leakage inductance peak current iLk has the maximum value, a mapping coefficient c of the leakage inductance peak current at the moment is obtained through a differential extreme value method; based on the obtained control variable theta and the mapping coefficient c, calculating to obtain a phase shift ratio D and a switching frequency fs; d = 1-c theta; fs = fa (c-c2theta); and based on the obtained phase shift ratio D and the switching frequency fs, a driving signal for single phase shift frequency conversion modulation is given.

The application relates to the technical field of electric variable monitoring, in particular to a safe power-on test method, device and system for a power distribution cabinet, which comprises the following steps: acquiring three-phase voltage signals of the power distribution cabinet in a safe power-on test process; analyzing the similarity between the three-phase voltage signals of the power distribution cabinet and the fluctuation degree of each-phase voltage of the power distribution cabinet, obtaining three-phase fluctuation characteristic values of the three-phase voltage signals, constructing a peak value difference rate between any two-phase voltage signals according to the peak value difference degree between the three-phase voltage signals, and then acquiring an electromagnetic interference factor of the three-phase voltage signals; and constructing an each-phase voltage abnormality judgment value according to the electromagnetic interference factor and the deviation degree of each-phase voltage, so as to judge the abnormal operation condition of the power distribution cabinet. The application can improve the safe power-on test precision of the power distribution cabinet.

The invention relates to the technical field of three-phase systems, and provides a three-phase voltage state estimation method and system based on virtual coordinates, and the method comprises the steps: calculating the voltage peak value of each phase for three-phase voltages, and determining that a phase is open if the peak voltage of a certain phase is lower than a threshold value in the three peak voltages; for three-phase voltage, virtual beta-axis voltage is generated through an all-pass filter, actual beta-axis voltage is obtained through Clark transformation, the product of the virtual beta-axis voltage and the actual beta-axis voltage serves as an evaluation function, and a positive sequence and a negative sequence are distinguished according to the positive and negative of the evaluation function. The system state can be accurately and effectively judged under the conditions of three-phase imbalance and voltage distortion, the anti-noise capability and the anti-harmonic interference capability are high, and safe and stable operation of equipment under the abnormal condition is ensured.

The invention relates to a method, implemented by a control system for an electrical converter, for controlling said converter, comprising the following steps: a step (40) of determining the peak-to-peak amplitude of the current in a low-frequency switching branch of the converter; a step (42) of comparing the peak-to-peak amplitude to a threshold current value; if the peak-to-peak amplitude is greater than or equal to the threshold current value, a step (44) of deactivating the switching branch; otherwise, a step (46) of determining whether a mathematical relationship is verified; if the verification is negative, corresponding to a discontinuous diode conduction mode, a step (48) of keeping the switching branch active; otherwise, a step (50) of keeping the switching branch active or deactivating it according to a predefined criterion. Abstract figure: Fig. 2

The invention relates to the technical field of electric energy meter quality detection, in particular to a data-driven single three-phase meter automatic verification system and method, and the method comprises the steps: obtaining a current sequence, a voltage sequence and an electromagnetic sequence of a single three-phase meter; acquiring peak values in all sequences; recording the current sequence and the voltage sequence as electric power sequences; obtaining an abnormal peak value in the power sequence; obtaining an abnormal factor of the power sequence according to whether the data dispersion degree in each peak neighborhood window in the power sequence is equal or not; according to the position and the fluctuation characteristic of each abnormal peak value in the power sequence, the total number of the abnormal peak values and the abnormal factors, obtaining a waveform deviation coefficient of the power sequence; obtaining the verification abnormity degree of the single-three-phase meter by combining the difference coefficient of each phase in the single-three-phase meter; and whether the single three-phase meter has a quality problem or not is judged. By analyzing the data characteristics of the single-three-phase meter, whether the single-three-phase meter has a quality problem can be accurately judged, so that the automatic verification precision is improved.

The invention discloses a zero-sequence component-based multi-criterion low-current grounding system fault line selection method, and mainly relates to the technical field of power grid grounding fault line selection. Comprising the following steps of collecting zero-sequence voltage U0 at a neutral point, judging whether line selection is started or not according to the value of U0, and if the line selection is judged to be started, collecting zero-sequence current of each outgoing line; performing CEEMDAN decomposition on the collected zero sequence current to obtain a modal component of each outgoing line; extracting an energy peak value of the intrinsic mode energy of the zero-sequence current of each outgoing line and a line mode energy total value by using a mode energy method; the method has the advantages that the grey wolf optimization algorithm GWO is introduced, the optimal combination of parameters is searched by optimizing the LSSVM, and therefore the line selection precision can be improved.