29 results about "Negative sequence current" patented technology

The present application relates to the technical field of power system relay protection, and particularly relates to a kind of offshore wind power through flexible low-frequency transmission system sending out line protection method, offshore wind farm is connected with modular multi-level matrix converter after being sent out by low-frequency through booster transformer, and is incorporated into large power grid after being frequency converted by M3C. When M3C of offshore wind farm fails, negative sequence current suppression and positive sequence current limiting strategy are adopted for fault ride-through, and relay protection devices are installed at both ends of low-frequency sending out line and communicate. The current sampling values before and after the fault on both sides of the line are reconstructed in phase space, and the difference between the permutation entropies is used to construct a protection scheme, which overcomes the problem of sensitivity reduction of traditional current differential protection for sending out line, reduces the amount of data interaction, and reduces the pressure of protection communication and the requirement of data synchronization. It is not affected by the control strategy of wind turbine and modular multi-level matrix converter at both ends of the line, fault ride-through mode, transition resistance and fault location, and has high reliability and good speed.

This application proposes a method and apparatus for detecting phase loss in a power plant starting transformer, relating to the field of power fault detection technology. The method includes: acquiring the signal energy distribution of the starting transformer; constructing an energy feature vector reflecting the relative energy relationship between the three-phase current signals and inputting it into a phase loss identification model to obtain the initial probability of phase loss faults in each phase; performing state inversion calculations by combining real-time calculated zero-sequence and negative-sequence current amplitudes to infer the changes in the equivalent circuit parameters of the transformer's internal windings and leads before and after the fault, thereby correcting the initial probability to obtain a confidence level, and finally generating a phase loss detection report including the fault phase and fault severity. This application comprehensively characterizes the energy correlation characteristics of the three-phase currents through energy feature vectors and corrects the initial probability of the model using changes in equivalent circuit parameters, eliminating random biases in the output of a single model, achieving accurate matching between the fault determination result and the actual fault state of the transformer, and improving the accuracy of fault phase identification.

The present application provides a method for determining a distance to a fault in a power systems network. The method may involve determining, based on a set of measured voltage samples, a set of processed voltage samples; determining, based on a set of measured current samples, a set of processed reactive current samples, a set of processed resistive current samples, a set of processed negative sequence current samples, and a set of processed zero sequence current samples; selecting, based on an indication from a faulty phase indicator, a selected processed voltage sample, a selected processed reactive current sample, a selected processed resistive current sample, and a selected processed negative or zero sequence current sample; determining, based on the selected processed reactive current sample, that no distortion has occurred due to current transformer (CT) saturation; and calculating, based on the determination that no distortion has occurred, the distance to the fault.

The method and system for identifying new energy power supply under asymmetric fault based on sequence impedance difference, the protection device collects three-phase current and three-phase voltage in real time, and calculates to obtain negative sequence current voltage, zero sequence current voltage and positive sequence current voltage; after the protection is started, the asymmetric fault type is judged; when the ground fault occurs, the modulus difference and impedance angle difference of the negative sequence impedance and the zero sequence impedance are compared to judge the fault characteristics of the power supply behind the protection; when the phase-to-phase fault occurs, the modulus difference of the negative sequence impedance and the positive sequence impedance is compared, and the impedance angle difference of the negative sequence impedance and the positive sequence impedance and the difference between the line positive sequence sensitive angle are combined to judge the fault characteristics of the power supply behind the protection; it is determined that the power supply behind the protection is a new energy power supply, the identification of the new energy power supply under asymmetric fault based on sequence impedance difference is realized, and the safety and reliability of the relay protection under the new energy access to the power system are improved.

The application discloses a converter fault ride-through control method based on circulating current compensation and negative sequence current injection, and belongs to the technical field of electric power control; the method comprises the following steps: collecting M3C bridge arm voltage and current in real time; performing positive and negative sequence decomposition on the collected voltage and current, and converting to the dq synchronous rotating coordinate system; calculating the imbalance power between the bridge arms according to each component of the voltage and current; calculating the required negative sequence current injection amount and circulating current injection amount according to the set power balance proportion coefficient and the imbalance power between the bridge arms, and converting the required negative sequence current injection amount and circulating current injection amount into voltage reference values; and generating a driving signal through nearest level approximation modulation. When an asymmetric fault occurs in a line, in order to balance the asymmetric voltage between each bridge arm in the M3C, the method realizes the M3C fault ride-through by injecting negative sequence current into the fault line and injecting circulating current between the converters, thereby reducing the control difficulty of the circulating current path, reserving part of the negative sequence current characteristics for line fault detection, and realizing the comprehensive optimization of the internal and external characteristics of the M3C during the fault.

This invention discloses a power regulation method and system for an intelligent traction power supply system; including: calculating real-time transfer power, and calculating compensation current in real time by combining power transfer error and negative sequence current; calculating current tracking value based on current inner loop command value and voltage synchronization signal; designing a feedforward-feedback composite controller to calculate feedforward compensation amount and feedback control amount respectively; calculating the total duty cycle of PWM modulation signal based on feedback control amount and feedforward compensation amount, and driving the railway power regulator to output the actual current value; the control method and system provided by this invention have low engineering implementation cost, are suitable for traction substation RPC application scenarios, and are easy to promote.

The application discloses a kind of offshore low-frequency wind power transmission line longitudinal protection method and system, after fault occurs, the control strategy of permanent magnet direct drive wind generator net side converter and modular multilevel matrix converter is switched, protection device is collected negative sequence current on line two sides;Wavelet transform denoising is carried out to the negative sequence current collected on line two sides, and mode component is extracted in combination with variable mode decomposition;The energy of each mode component obtained is calculated, and the largest energy characteristic mode is selected;The Hilbert transform is carried out to the selected characteristic mode, and the negative sequence current envelope line is extracted;The slope of negative sequence current envelope line is fitted using least square method;The protection direction identification value of line two sides is determined according to the positive and negative of slope;The protection direction identification value of line two sides is transmitted to the opposite side, when logic criterion F =1 is judged as internal fault, otherwise as external fault, the application meets power grid specification, and the noise resistance is strong, internal fault is sensitive action, and the safety of system is guaranteed.

This invention proposes a dual zero-sequence voltage injection cascaded H-bridge power control method combining levitation and energy storage. The device consists of m cascaded H-bridge modules equipped with supercapacitors (SC) and n cascaded H-bridge modules equipped with levitation capacitors (FC) connected in series. Under three-phase grid asymmetry, the negative-sequence current is first controlled to zero. Then, through hierarchical control, the reference voltage generated during grid operation is decomposed into active and reactive components. The SC module provides active power support by acting as an active voltage reference, while the FC module handles reactive power regulation in grid operation scenarios, achieving active-reactive decoupling control. By injecting zero-sequence voltage parallel to the current direction into the levitation and energy storage modules respectively, the DC bus voltage is stabilized. The short-time power response capability of the supercapacitors is fully utilized, improving the system's dynamic performance and reliability. This method is suitable for power quality regulation scenarios involving cascaded H-bridges with energy storage during grid operation.

This invention relates to an online detection method and apparatus for stator short-circuit faults in motors under transient operating conditions. The method includes: performing Clark transform on the three-phase currents to obtain α and β two-phase currents; calculating the current amplitude, estimating the fundamental frequency, and determining the target frequency band based on the two-phase currents; constructing two-phase current signals by combining historical data; obtaining new two-phase current signals through fast Fourier transform, Hilbert filtering, bandpass filtering, and inverse fast Fourier transform; extracting the new two-phase currents; calculating the negative sequence current, current amplitude, and short-circuit fault index based on the new two-phase currents; and performing fault early warning processing based on the short-circuit fault index and fault index threshold. This invention can improve the detection sensitivity and reliability of short-circuit fault detection under transient operating conditions.

The application provides a power plant starting transformer open-phase detection method and device, and relates to the technical field of power failure detection. The method comprises the following steps: acquiring signal energy distribution of the starting transformer, constructing an energy feature vector reflecting the relative energy relationship among three-phase current signals and inputting the energy feature vector into an open-phase identification model to obtain initial probabilities of each-phase open-phase failure; combining real-time calculated zero sequence and negative sequence current amplitudes to perform state inversion calculation, inferring the change amount of equivalent circuit parameters of transformer internal windings and lead wires before and after the failure, correcting the initial probabilities to obtain confidence, and further generating an open-phase detection report containing fault phase and fault severity. The application completely depicts the three-phase current energy correlation characteristics through the energy feature vector, corrects the initial probabilities of the model by using the change amount of the equivalent circuit parameters, eliminates the random deviation of the single model output, realizes accurate matching between the fault determination result and the actual fault state of the transformer, and improves the fault phase identification accuracy.

This disclosure provides a train operation control method, apparatus, electronic device, storage medium, program product, and train, applicable to the field of rail vehicle technology. The train operation control method includes: in response to receiving a first warning signal indicating a first-level short-circuit fault in the traction motor, generating a first control command for controlling the train to run at a first limited speed, wherein the first limited speed is less than the train's normal operating speed; the first warning signal is generated by the traction control unit in response to the detection of a first target current more than or equal to a first-time threshold number during a fault detection cycle; the first target current is a current including a negative-sequence current component greater than or equal to a first current threshold; and sending the first control command to the traction control unit and the braking control unit, so that the traction control unit and the braking control unit adjust their respective output forces to collaboratively control the train to run at the first limited speed.

The application provides a kind of energy router coordination method and system for new energy station voltage ride-through, belongs to the field of power electronics and new energy grid-connected control technology, its method includes, first, the voltage of grid-connected point is collected, the dynamic threshold set is calculated and the hysteresis logic is introduced;Then realize seamless switching of three operating modes according to the threshold, reconstruct power unit;Then decompose voltage and current sequence components, generate positive and negative sequence current instructions and superimpose virtual impedance limiting;Fusion deep reinforcement learning and transient energy function, adaptive setting control parameters;Finally, combined with related instructions, state and parameters, execute multi-port energy interaction dynamic coordination, improve the voltage ride-through performance of new energy station.The application realizes new architecture through dynamic multi-modal control+coordination current limiting support+intelligent adaptive parameter tuning+multi-port collaboration, significantly improves the ride-through performance of new energy station under grid voltage sag / fault, takes into account grid stability and equipment safety, has significant innovation and practical value.

The invention discloses an asymmetric fault current limiting method based on a network-forming type energy storage current converter. The asymmetric fault current limiting method comprises three core links of power parameter setting, internal potential primary compensation and internal potential secondary compensation. In the power parameter setting step, reference amplitudes of an active current and a reactive current are determined based on a fault current limiting range and active support characteristics of a reactive voltage loop of the grid-forming type energy storage converter; setting of power parameters is completed; the internal potential primary compensation is used for compensating the internal potential compensation amount of the negative-sequence current required to be suppressed to the original internal potential; and the internal potential secondary compensation is used for limiting transient overcurrent under an asymmetric fault on the basis of the internal potential primary compensation and power parameter setting. According to the method, through primary compensation of the internal potential, the aim of balancing the current is achieved by suppressing the negative sequence current and limiting the overall current under network-forming type control, and meanwhile, secondary compensation of the internal potential is further introduced, so that transient over-current limitation under an asymmetric fault is achieved.

This invention relates to the field of power system relay protection technology and discloses an adaptive relay protection threshold setting method for high-proportion distributed photovoltaic distribution networks, comprising the following steps: S1: The end-side protection device collects electrical signals of the protected line and extracts the current transient change rate di / dt and the negative sequence current change amount ΔI2 as mixed fault characteristic quantities; This adaptive relay protection threshold setting method for high-proportion distributed photovoltaic distribution networks extracts the current transient change rate and the negative sequence current change amount as mixed fault characteristic quantities through the end-side protection device, and calculates the dynamic current protection threshold by combining the inverter current limiting value, low voltage ride-through state, real-time output of distributed photovoltaic, system short-circuit capacity, total harmonic distortion rate of voltage, line rated current and maximum load current, so that the protection threshold can be adjusted according to the fault characteristics, photovoltaic penetration state and inverter current limiting capability, thereby improving the adaptability of relay protection threshold setting in high-proportion distributed photovoltaic access scenarios.

This application discloses a control method and device for energy storage converters based on positive and negative sequence decoupling, belonging to the field of energy storage converter control technology. The method includes: performing coordinate system transformation on the three-phase grid-connected voltage and three-phase grid-connected current of the energy storage converter under fault conditions to obtain first voltage components, second voltage components, first current components, and second current components under different axes; extracting positive sequence voltage and positive sequence current representing normal operation and rotating counterclockwise, and negative sequence voltage and negative sequence current representing fault disturbance and rotating clockwise, based on the above components; then employing independent control of positive and negative sequence dual channels to generate positive and negative sequence voltage reference commands respectively; and superimposing the two types of command vectors to generate a total voltage reference command to control the energy storage converter to perform voltage regulation actions. This application can achieve decoupling of positive and negative sequence components and realize independent power regulation and suppression of negative sequence current through dual channels, ensuring the grid-connected reliability of the energy storage system.

The application relates to the technical field of power grid management, in particular to a fault research and judgment method and system based on a transformer area intelligent terminal. The method comprises the following steps: acquiring three-phase current data of a low-voltage side of a distribution transformer, and performing feature extraction on the three-phase current data to obtain a fundamental wave zero-sequence current component, a fundamental wave negative-sequence current component and a third harmonic current component; determining a fault residual error energy index according to the fundamental wave negative-sequence current component and the third harmonic current component; acquiring three-phase voltage data of the low-voltage side of the distribution transformer, determining a zero-sequence voltage component according to the three-phase voltage data, and calculating a projection intensity index of the zero-sequence voltage component and the residual error current component; generating a fault research and judgment index according to the fault residual error energy index and the projection intensity index, and using the fault research and judgment index to research and judge whether a high-resistance grounding fault exists in a transformer area. Through the above technical scheme, the research and judgment of whether a high-resistance grounding fault exists in a transformer area can be more accurately realized.

This invention belongs to the field of power system technology and discloses a method and system for managing three-phase voltage imbalance in low-voltage distribution areas through a combination of composite commutation and active compensation. The method includes: acquiring and preprocessing three-phase voltage and current signals of the distribution area; tracking the grid phase and frequency through a phase-locked loop to generate discrete sampling steps; extracting the negative-sequence voltage component and calculating the imbalance index, then smoothing and anti-jittering to generate a management demand signal; calculating a reference value for the negative-sequence compensation current based on the negative-sequence voltage component and the equivalent negative-sequence impedance of the distribution area; using the error between the reference value and the actual negative-sequence current as input, employing a composite control strategy of fuzzy self-tuning PI and adaptive repetitive control in parallel to generate modulation commands to drive the parallel compensation device to inject negative-sequence current; and executing commutation scheduling when triggering conditions are met. This invention, through the coordinated management of commutation and active compensation, reduces the capacity occupancy of the compensation device and improves the tracking accuracy of the negative-sequence current and the adaptability to the grid frequency.

The application discloses a kind of interturn short circuit fault diagnosis methods of permanent magnet synchronous motor based on negative sequence current difference, it is related to motor interturn short circuit fault diagnosis technique relevant field, the method includes: obtaining the three-phase current and electric angle of two permanent magnet synchronous motors, according to the three-phase current and electric angle of two motors respectively, obtain dq axis negative sequence current;According to dq axis negative sequence current, obtain dq axis negative sequence current direct current component;According to dq axis negative sequence current direct current component, obtain negative sequence current amplitude;According to the negative sequence current amplitude of two motors, obtain negative sequence current difference;According to the amplitude and polarity of negative sequence current difference, realize the detection and positioning of interturn short circuit fault in double permanent magnet synchronous motor traction system.The technical problem that existing fault diagnosis method is difficult to make full use of the coupling and consistency constraint naturally existing between motor in double permanent magnet synchronous motor traction system is solved, the method does not need to increase zero sequence voltage detection hardware additionally, effectively reduces the cost and complexity of realization.

The application discloses a kind of double-fed network unit positive and negative sequence current collaborative control method and system, it is related to double-fed unit network control technical field, the method includes: S1.data acquisition;S2.coordinate transformation and positive and negative sequence separation;S3.negative sequence current collaborative enabling logic design and negative sequence current instruction distribution;S4.network loop control;S5.positive and negative sequence reference voltage synthesis and generation rotor reference voltage.The application aims to solve how to improve positive and negative sequence separation method to adapt to double-fed unit variable speed operation characteristics and combined with network control, and how to design the collaborative control strategy of machine network side negative sequence current ring, to realize the high stability, high reliability operation of double-fed unit under the condition of weak power grid and asymmetric power grid.

The present application relates to the technical field of grid-forming converter control, and provides a grid-forming converter fault current limiting method, system, device and medium, which comprises extracting positive and negative sequence current components from two-phase synchronous rotating coordinate system according to the obtained three-phase static coordinate system current signal of the converter, obtaining positive and negative sequence current components, after analyzing the positive and negative sequence virtual impedance voltage drop based on the obtained positive sequence current reference value, negative sequence current reference value and angle difference value of the outer loop voltage control output, obtaining positive and negative sequence impedance voltage drop, and combining the positive and negative sequence current components to perform voltage and current double closed loop control to obtain control output voltage and perform pulse width modulation. The present application can eliminate current amplitude calculation oscillation problem without current saturation limiter, ensure that the virtual impedance intervenes in advance and continues to act when the current approaches the limit value, effectively suppresses the fault current, maintains the voltage source characteristics, and further enhances the system stability.

The application discloses an asynchronous motor inter-turn short circuit diagnosis method based on global adaptive threshold fitting. By adjusting the three-phase input voltage of the motor (obtaining different negative sequence voltage amplitude ratios), collecting three-phase currents and detecting load working conditions, the negative sequence voltage amplitude ratio and the negative sequence current amplitude ratio are calculated; a linear function relationship between the two is established according to the asynchronous motor model, a few data are linearly fitted to obtain a global threshold, and a healthy motor adaptive fault threshold table is constructed; according to the negative sequence voltage amplitude ratio and the load working condition under the real-time operation, the corresponding healthy threshold is matched, the difference between the negative sequence current amplitude ratio under the real-time operation and the healthy threshold is taken as a fault feature, and if the difference is greater than 0, it is determined that there is an inter-turn short circuit, and if the difference is less than or equal to 0, it is healthy. The method can adaptively adjust the fault threshold, eliminate errors caused by differences in motor structure and design, and is suitable for all asynchronous motors, and realizes high-precision and high-universality online fault diagnosis.

A method, system and grid-connected converter for flexible compensation of negative sequence voltage and current considering current limiting protection, the method comprising: constructing a positive sequence control loop and a negative sequence control loop by positive and negative sequence decomposition of the electrical quantities of the converter, the positive sequence loop generating a positive sequence modulation voltage based on droop control and virtual admittance, and the negative sequence loop generating a negative sequence current command based on an equivalent voltage source model of the grid-connected converter, and implementing limiting to ensure the safety of the total current; and switching the control target by adjusting the value of an adjustable coefficient k v : when k v =1, the target is to achieve output current balance; when k v =0, the target is to achieve common coupling point voltage balance; and when the current command is out of limit, the adjustable coefficient is adjusted to maximize voltage compensation under the premise of current limitation. The invention solves the problems of easy overcurrent and single control mode in traditional negative sequence voltage control, and achieves safe and flexible compensation control.

The application provides a transformer short window negative sequence differential protection method and device based on a split-phase reference. The protection method comprises: obtaining current sampling values of each side of a transformer; calculating negative sequence current sampling values according to the current sampling values; calculating adjusted current sampling values according to the negative sequence current sampling values; calculating adjusted current effective values according to the adjusted current sampling values; calculating differential current effective values according to the adjusted current sampling values; calculating braking current effective values according to the adjusted current effective values; and determining whether to start a protection action based on the differential current effective values and the braking current effective values.

The application discloses a network-constructing doubly-fed wind power transient stability analysis method considering flux linkage safety constraint. The method establishes a transient mathematical model which explicitly considers rotor voltage limiting amplitude dynamics, reveals a new transient instability mechanism triggered by voltage limiting amplitude, which is different from traditional current limiting amplitude, due to considering flux linkage safety constraint. Based on the model, the application quantitatively determines the action law of positive sequence virtual impedance and negative sequence current injection strategy on critical clearing time, perfects the stability analysis theory of network-constructing doubly-fed wind power generator under specific fault conditions, and provides accurate theoretical basis and engineering guidance for improving fault ride-through capability and optimizing control parameters.

The application provides a kind of permanent magnet direct drive wind turbine multi-objective control method under power grid asymmetrical fault, solve the technical problem of power fluctuation suppression and current unbalance degree reduction control target coordination optimization in fault ride-through. Including the following steps: S1: establish the positive and negative sequence coordinate system model of permanent magnet direct drive wind turbine grid-side converter, separate the positive and negative sequence of grid-side converter voltage and current;S2: calculate the grid-side converter reference current instruction of three control targets;S3: construct the unified expression form of grid-side converter reference current;S4: select active power fluctuation suppression and negative sequence current suppression as the coordinated optimization control target for control;S5: construct multi-objective optimization function, obtain the converter current reference value, and carry out current closed-loop control on grid-side converter. The beneficial effects of the application are: the multi-objective coordinated optimization control of permanent magnet direct drive wind turbine under power grid voltage fault is realized, and the low voltage ride-through capability and grid-connected performance are enhanced.

This invention discloses a method and system for identifying single-phase grounding high-resistivity faults in new energy grids connected to flexible DC power grids. The method involves acquiring three-phase time-domain voltage and current signals, obtaining phasors through discrete Fourier transform, decomposing them into sequence components, and extracting the fault phase voltage and current phasors. Based on the fault phase voltage phasors and negative-sequence current components, and combining a sign function with a fuzzy region, an identification criterion for the same-phase section is calculated to identify the lead-lag state between the bus voltage and the fault point voltage. Based on the criterion results, the protection action equations are adaptively switched, and the adaptive negative-sequence reactor operating voltage is calculated using the fault phase electrical quantities and the set impedance. This completes the reliable identification of single-phase grounding high-resistivity faults both within and outside the protection zone. Compared with existing technologies, this invention solves the problem of difficult high-resistivity fault identification in power electronic grids and achieves reliable identification of high-resistivity faults both within and outside the protection zone.

This application relates to a low-voltage ride-through control method, apparatus, and equipment for a two-stage grid-connected photovoltaic inverter. By using valve-side reference data obtained from a first and second control method (both capable of controlling positive and negative sequence voltage and current) respectively, the positive and negative sequence voltages are controlled, exhibiting voltage source characteristics externally. It also controls the positive and negative sequence currents to flexibly manage fault currents. Through the coordinated control strategies of the front-stage boost circuit and the rear-stage inverter circuit, the low-voltage ride-through of the two-stage grid-connected photovoltaic inverter achieves a balance of photovoltaic output power during faults and a smooth transition back to grid-connected control after a fault. This solves the technical problem of large currents that can occur after a fault in existing power systems using photovoltaic inverters in grid-connected control technology, potentially jeopardizing power system operation.

The application provides a modular multilevel matrix converter capacitor voltage control method and system, and belongs to the field of power system relay protection. The method comprises the following steps: when an asymmetric fault occurs in a line, the negative sequence current of the fault line is suppressed to zero, and three-phase voltage and current at the low-frequency side and the power-frequency side are obtained, then the bridge arm power of each bridge arm is calculated, and the direct current component in the bridge arm power is extracted; the bridge arm power imbalance component is determined according to the direct current component, and then the circulating current compensation component is determined; the circulating current compensation component is converted into a circulating current reference value, the circulating current outer loop control of the modular multilevel matrix converter is carried out, the outer loop control of the power-frequency side and the low-frequency side is carried out, and the bridge arm voltage of the modular multilevel matrix converter is controlled according to the overall bridge arm voltage reference value, so that the capacitor voltage of the modular multilevel matrix converter is controlled under the asymmetric fault state, and the safe and stable operation of the modular multilevel matrix converter is ensured.