840 results about "Negative sequence current" patented technology

The invention discloses a distance measuring method and a type diagnostic method of the single-phase grounding fault of an electric transmission line. In the distance measuring method, an amplitude value is calculated by utilizing the voltage, the current, the negative-sequence current and the zero-sequence current (phi is a fault phase: A phase, B phase, C phase) of the fault phase in a formed vector triangle according to the side-angle relationship of the vector triangle, because the fault distance x from a single-phase grounding fault point to a protected installation position is a positive real number, the fault distance x is obtained by utilizing division, the transition resistance value of the single-phase grounding fault is further calculated, and then the type of the single-phase grounding fault is diagnosed according to the condition of the transition resistance value of the single-phase grounding fault.

The invention relates to a online testing process for shorted fault of asynchronous motor's stator winding, which is belong to Detecting Technology. It was designed to solve the detecting problem of stator winding. The project is that it figures out the voltage and current of negative sequence and positive sequence of the stator winding by collecting three-phase stator voltage, instantaneous-current signal. Then using of normal motor sample reference document estimated the filter value of the stator negative sequence, figured out the stator negative sequence current fault component. And then base on the threshold of the stator negative sequence current fault component educe failure exponent. Finally according to the index judge whether to exist short circuit failure or not. This invention also gave corresponding detection device. Not only can high sensitivity, high reliability and on-line measurement asynchronous motor stator windings at the beginning of the early short circuit fault, but also can judge short circuit phase. This can effectively ensure the asynchronous motor operating safely.

The invention discloses a line single-phase earth fault single-terminal location method based on positioning function amplitude characteristics. The method comprises the following steps of: measuring fault phase voltage, fault phase current, fault phase negative-sequence current and zero-sequence current at a protection installation position of a transformer substation as input variables; with the origin of a protected line as a start point, calculating the positioning function amplitude of each point on a fault phase line one by one in a way that step length increases gradually till a trip signal setting range is reached; if protection trip signals cannot be obtained, searching all over the protected line, taking the point with the smallest positioning function amplitude as a fault pointand setting the distance between the point and the line protection installation position. The method is not influenced by distributed capacitance, or load current or transition resistance, does not have the problems of false root existing in the method of solving equation or non-convergence existing in the iteration method and achieves very high practical value.

The disclosed protection method for internal fault of large power transformer comprises: the protector samples the secondary current of current transformers on power transformer sides to obtain current instantaneous value and calculate complex number form of electric values by Fourier algorithm, corrects phase of connection form, and balances amplitude of transformation ratio; then, it calculates the complex number form of negative sequence current according to three-phase ac complex form, and computes negative sequence differential current and break current as the negative sequence differential protection principle to decide asymmetric inside and outside fault and drop out all breakers. This invention also contains exactly the negative sequence differential rate breaking feature and protection criterion, the adjusting means for protection values, the positive sequence current breaking criterion, and the block function for error action protection.

A method for fault detection in a power transformer/autotransformer and/or interconnected power lines, which are within the zone protected by the differential protection, and particularly suitable for detecting turn-to-turn faults in power transformer/autotransformer windings. All individual instantaneous phase currents of the protected object are measured, individual phase currents as fundamental frequency phasors are calculated, the contributions of the individual protected object sides negative sequence currents to the total negative sequence differential current are calculated by compensating for the phase shift of an eventual power transformer within the protected zone, the relative positions of the compensated individual sides negative sequence currents in the complex plane are compared, in order to determine whether the source of the negative sequence currents, i.e. the fault position, is within the protected zone or outside of the protected zone, delimited with current transformer locations, the protected object is disconnected if determined that the source of the negative sequence currents is within the protected zone.

The invention discloses a power compensation method for unbalanced direct power control of a voltage controlled grid-connected inverter, which is suitable for direct power control (the conventional direct power control) without synchronous speed rotational coordinate transformation. The method comprises the following steps of extracting negative sequence voltage signals and positive sequence current signals by collecting voltage and current signals of a three-phase electric network; and computing compensation items of active and reactive power according to selected control targets. In the method of the invention, the compensation items of active and reactive power are injected in the power reference signals of the conventional direct power control according to required control targets so as to respectively eliminate negative sequence current, double frequency fluctuation of the active power and double frequency fluctuation of the reactive power in the electric network, caused by unbalanced voltage in the electric network, and fit different application situations. The invention has the advantages of enhancing the capabilities of control and uninterrupted operation of the voltage controlled grid-connected inverter when the electric network is in an unbalanced fault.

The invention provides a photovoltaic grid connected inverter island detection method based on negative sequence current injection, belonging to the technical field of power system relay protection and automatic control. According to the method, an inverter is started to inject negative sequence current when a voltage harmonic distortion rate is larger than a fixed value, common connection point voltage unbalanced degree and voltage harmonic distortion rate are detected, when both the common connection point voltage unbalanced degree and the voltage harmonic distortion rate are larger than the respective fixed value and the duration time exceeds a set time, the generation of island is determined, and the rapid detection of the island is realized. According to the method, the setting difficulty of a criterion is reduced, the improvement of the detection speed is facilitated, the interference on a power grid is reduced as much as possible in the condition that the normal operation is ensured, the influence of a power grid asymmetrical fault is avoided, and there is no detection blind area. The simulation verification is carried out in the condition that the island detection is most not facilitated, and an island operation state still can be rapidly and accurately detected according to the method. A good method is provided for the operation withdrawal of a distributed power supply in the island or the turning of power grid connected operation into island operation control mode power system safe operation and the detection.

The invention relates to a novel topological structure voltage source type inverter and an adjusting method. The structure is a star-like topological structure and is formed by connecting a three-phase bridge type inverter in series at a neutral point of cascaded inverters connected in a star shape. Compared with the conventional cascaded inverters connected in the star shape, the novel topological structure theoretically has a function of completely compensating negative sequence current; and compared with the conventional three-phase bridge type inverter, the novel topological structure can realize extended application under high voltage level without using a device cascade or MMC (Multilevel Converter) structure. In the novel topological structure, a direct current side of the three-phase bridge type inverter can be connected with a direct current network, energy storage equipment or a power grid through a current transformer; the inverter can be widely applied to the fields of flexible direct current power transmission, new energy connection, high voltage frequency converter and the like; and the application prospect of the voltage source type inverter in the corresponding field is expanded. The novel topological structure has good generalization performance based on mature unit cascade and three-phase inverter structure and control technology.

The present invention provides a high voltage crossing control method of a wind power full power converter. When the network voltage suddenly increases over 1.1 times rated voltage, the transient overvoltage is restrained through an off-load circuit connected with a direct circuit bus, inductive reactive current relative to the network voltage is output through a decoupled active and reactive positive-and negative-sequence current controller to reduce the amplitude of the network voltage, and the occurrence of overmodulation is avoided through dynamic regulation of the voltage reference value of the direct current bus. According to the invention, a converter can operate without being dissociated from the power grid free of complex mode switch in the condition of a network voltage not larger than 1.3 times rated value, and an effective inductive reactive output is provided.

The invention discloses a joint operating system of the static var compensator and active power filter and the control method, which is characterized in that an active power filter and a control device are added in the static var compensator. The control method of balance compensation of three-phase unbalanced loads is used to realize the compensation of load negative sequence current and the technology of specific subharmonic compensation is used to realize the decoupling control of SVC and APF, so as to guarantee the safe and stable operation of the joint operating system. The invention notonly has the basic functions of the SVC, but also improves the filtering performance of the passive filter through APF, suppresses possible resonance phenomena between the passive component and the power grid equivalent impedance, and can realize dynamic management on subharmonic waves.

The invention discloses a method for eliminating DC harmonic voltage for the grid-side converter of a double-fed wind power generator in the case of asymmetric power grid. The method adopts a phase-shift T/4 delay negative sequence fast separation method, which performs positive-negative sequence separation on the voltage and current of the three-phase power grid, wherein the positive-negative sequence separation method has simple calculation which only includes addition, subtraction, multiplication and division, fast response that the positive-negative sequence component can be worked out only in 5 m and small delay which facilitates the design of PI parameters. In order to obtain good control effect, the positive-negative double-dq current control with completely symmetric structure is adopted. Therefore, the positive-negative sequence current instructions are both DC components and the PI regulator can realize floating control.

The invention discloses a STATCOM unbalance compensation control method based on a modular multilevel converter (MMC). The method comprises a converter compensation current dead-beat control method and a converter interphase circular current active damping control method. A comprehensive compensation current dead-beat control part is used for compensating active loss in the MMC by controlling active current, reactive current and negative-sequence current which are output by the MMC so as to eliminate unbalance of the current of a power grid and compensate reactive power; the interphase circular current active damping control method is used for summing by detecting the bridge arm current of upper and lower bridge arms of each phase and multiplying by 0.5 to obtain the circular current of each phase, and superposing the output of three-phase current passing through an active damping controller to dead-beat control output so as to inhibit the alternating current component of the circular current, reduce the current stress of converter devices and reduce the loss of the converter. Through the adoption of the method provided by the invention, compensation of the negative-sequence current and reactive current of unbalanced load of the power grid is realized, inhibition of the interphase double frequency circular current of the MMC is simple, the response speed is high and the stability is high.

The invention discloses a direct-current bus inter-phase voltage balancing control method for a chained type triangular connection STATCOM (Static Synchronous Compensator). The chained type STATCOM is connected between a three-phase power source and a non-linear load. A main circuit of the chained type STATCOM is in a triangular connection manner. A zero-sequence component instruction is output through three phases of a triangular connection, so that voltage on three-phase direct-current bus voltage is balanced through three-phase additional zero sequence circular current of the triangular connection, and no negative-sequence current is additionally injected to a power grid.

The invention discloses a model prediction current control method based on an NPC topology grid connected inverter under asymmetric voltage, introducing the model prediction current control technology into the NPC grid connected inverter control. The model prediction current control method disclosed by the invention comprises steps of introducing decoupling double synchronization reference coordinate system phase-locked loop (DDSRF-PLL) phase lock technology to perform tracking on a positive sequence voltage phase angle in order to accurately track the positive sequence voltage phase angle under the condition that the power system has the asymmetric fault, on the basis, utilizing the DDSRF-PLL to decouple to obtain fundamental frequency voltage positive and negative sequence components, realizing a model prediction current control with the inhibition of the negative sequence current component, the active power oscillation and the reactive power oscillation as the control goal by combining with a instantaneous power theory, and adding a weight coefficient item into a cost function in order to guarantee the capacitor voltage balance on the DC side of the NPC grid connected inverter in the control process. In the whole control process, the invention reduces the usage of the PI controller, enhances the responding speed of the system, and enables the two sides of the grid connected inverter to have higher electric energy quality and stability.

The invention discloses a high-voltage direct-hanging type scalable vector graphics (SVG) comprehensive control device and an SVG comprehensive control method. The comprehensive control device is connected with an electric network. Each phase of the high-voltage direct-hanging type SVG comprehensive control device comprises an inductor-capacitor (LC) filter branch, a connection reactor and an H-bridge unit serial branch, wherein the H-bridge unit serial branch is connected in series with the connection reactor and then connected in parallel with the LC filter branch; the LC filter branch comprises an inductor and a capacitor; the H-bridge unit serial branch comprises N H-bridge units which are connected in series; N is more than or equal to 2; and each H-bridge unit comprises a bridge circuit which consists of four power elements. The comprehensive control method comprises a step of comprehensive control; and the step of comprehensive control further comprises a detection step, in which a detection method based on a plurality of synchronous rotational coordinates is adopted so as to carry out comprehensive control on a reactive current, a negative-sequence current and a harmonic current. The technical scheme of the invention has the advantages of simple structure, high response speed, good waveform of an output voltage, flexible control, convenience for modular manufacturing, and the like.

The invention provides an unbalance compensation control method of a cascaded power electronic transformer, comprising a control component and a transformer, wherein the transformer is composed of aninput rectifier stage, an isolation stage and an output inverter stage. The input stage is a three-phase star-connected cascaded H-bridge rectifier, the isolation stage is a plurality of independent dual-active-bridge converters, and the output stage is a single-phase PWM inverter. The control method of the present invention includes an input rectifier stage stratification control unit, a voltageclosed loop control unit of an isolation stage and a constant voltage and current sharing control unit of an output inverter stage. The input rectifier stage stratification control unit, is further divided into an upper control unit and a lower control unit, wherein the upper control unit is composed of a coordinate transformation, a positive sequence decoupling control and a negative sequence current suppression, and the lower control unit is an in-phase voltage sharing control. The control method provided by the invention can simultaneously solve the negative sequence current compensation problem of the PET when the voltage at the network side and the three-phase load are unbalanced, thereby promoting the application of the power electronic transformer in the engineering practice.

The invention discloses a circuit inter-phase fault single-end ranging method, which comprises the following steps of: measuring a fault inter-phase voltage phasor, a fault inter-phase current phasor and a fault inter-phase negative sequence current phasor serving as input quantities of a circuit at a transformer substation protection installation position; calculating the voltage phasor at a fault position by using protection measured electric quantity; sequentially calculating matching error data of each point on the circuit by gradual step length increment from the beginning end of the protected circuit till a setting range of emitting a trip signal; if the protective trip signal cannot be acquired, searching the overall length of the protected circuit; and taking the point corresponding to the minimum matching error datum value as a fault point, wherein the distance between the point and the circuit protection installation position is a fault distance. The method is not affected by distributed capacitors, load current, fault resistors and operation mode of a system, has no false root problem of solving an equation or non-convergence problem of an iteration method, and has strong practical value.

An easily implemented method of diagnosing both supply path, upstream, and load path, downstream, anomalies such as impedance events in machine or motor circuitry is accomplished by analyzing the across-the-line startup current and voltage time waveforms. No line of sight limitations exist and high accuracy exists. The techniques can be automated estimating poor contact resistance based on the voltage and current variation under a load change condition perhaps such as startup and/or shutdown of the load. Both, upstream and downstream problems from the point of voltage measurement can be monitored analyzing a load change condition. Additionally, downstream problems can be identified by using negative sequence current under steady state operation of the load.

The invention discloses a positive-negative sequence voltage feedforward method of three-phase PWM (pulse width modulation) converter which relates to a positive-negative sequence voltage feedforward method and is capable of lowering the influence of lagging and negative sequence voltage of three-phase PWM control on running of a converter caused by. The method comprises the steps of: carrying out phase-sequence separation on an acquired power grid voltage after carrying out Clarke conversion on the acquired power grid voltage so as to obtain a positive sequence voltage component and a negative sequence voltage component; carrying out phase-sequence separation on an acquired current after carrying out Park conversion on the acquired current so as to obtain a positive sequence current component and a negative sequence current component; calculating a positive sequence current loop set value and a negative sequence current loop set value by adopting a PWM control algorithm; carrying outforward-feeding decoupling control on the positive sequence current component and the negative sequence current component to obtain control set voltage of a PWM converter; calculating and respectively carrying out phase angle compensation on a positive sequence synchronous coordinate system and a negative sequence synchronous coordinate system according to angles needed to be compensated in feedforward of positive sequence power grid voltage and negative sequence power grid voltage; synthesizing the control set voltage of the PWM converter and the compensated phase angles after respectively carrying out Park inverse conversion on the control set voltage of the PWM converter and the compensated phase angles to obtain the final control set voltage of the PWM converter. The positive-negativesequence voltage feedforward method of the three-phase PWM converter is suitable for the control process of the three-phase PWM converter.

The invention discloses a line single-phase earth fault single-terminal location method implemented by the aid of zero-sequence voltage distribution characteristics. The line single-phase earth fault single-terminal location method includes sequentially computing an absolute value of the difference between an amplitude value of an equivalent zero-sequence voltage of each point on a power transmission line and an amplitude value of a zero-sequence voltage of the point by the aid of a one-dimensional search process and a zero-sequence voltage, a zero-sequence current, fault-phase negative-sequence voltages and fault-phase negative-sequence currents at a power transmission line protection mounting position until computation is performed on all points in the total length of the power transmission line; selecting the distance from the power transmission line protection mounting position to the point corresponding to the minimum absolute value of the difference between the amplitude value of the equivalent zero-sequence voltage of the point and the amplitude value of the zero-sequence voltage of the point as the fault distance. The line single-phase earth fault single-terminal location method has the advantages that power transmission line single-phase earth fault single-terminal location is implemented by the aid of the distribution characteristics of the zero-sequence voltages along the power transmission line, influence of transition resistance, fault positions and load currents on the location precision is eliminated in principle, and the location precision is high.

The invention discloses a double-feed wind power generator stator short circuit current calculating method under the condition of asymmetric faults. The method comprises the following steps: establishing a voltage equation and a flux linkage equation of a double-feed wind power generator, in the form of space vectors under a stator shaft system; establishing stator and rotor current expressions, and establishing a stator positive sequence flux linkage expression after the faults; establishing a rotor positive sequence flux linkage expression after the faults; establishing a stator positive sequence current expression of the double-feed wind power generator under the condition of an asymmetric fall of voltage at a machine end; establishing a stator negative sequence flux linkage expression after the asymmetric fall of the voltage at the machine end; establishing a rotor negative sequence flux linkage expression after the asymmetric fall of the voltage at the machine end; establishing a stator negative sequence current expression after the asymmetric fall of the voltage at the machine end; and finally obtaining a stator current expression after the asymmetric fall of the voltage at the machine end. According to the invention, the problems of affected relay protection and control accessed to a wind power field, affected safe and stable operation of a wind power generator set and the like, caused by lack of research on a simple and effective stator short-circuit current calculation method under the condition of the asymmetric faults in the prior art are solved.

The invention relates to a dc cophase power supply device of a railway traction based on symmetric transformation of three-phase serial voltage sources. The full three-phase input voltages are divided into a plurality of independent lower voltages to form power units, thereby recombined adjusting resource is formed. A single-phase ac output is formed by serial superposition after the rectification-energy storage filter-inversion transformation of each power unit, a negative sequence current is eliminated, the power factor is improved and the harmonic wave is eliminated by using multiple principles of the input and the output. The device can realize the cophase power supply of a railway traction, make fully use of the capacity of the circuit and device, reduce the damage to the power supply system from the reactive current and harmonic wave, decrease the loss, reduce the pollution to the environment, greatly improve the reliability of train and reduce the operation, management and maintenance cost. The device is convenient to apply, and is suitable for requirement of high speed and overloading development.

The invention discloses a control method for a virtual synchronous generator capable of being adapted to imbalanced power grid and load conditions. The control method comprises the following steps that 1) an active ring simulates the mechanical characteristics of a speed controller and a rotor to obtain an output positive sequence voltage frequency and a phase position instruction; 2) a reactive ring simulates a n excitation controller to obtain an output positive sequence voltage amplitude value instruction; 3) a voltage-control and virtual synchronous impedance ring simulates the electrical characteristics of a stator; 4) positive and negative sequence current rings carry out accurate tracking on the positive and negative sequence current instructions respectively, and eliminates the negative sequence current output; and 5) a modulation signal is obtained by the combination of the positive and negative sequence current rings, and then the modulation signal is subjected to PWM to obtain a switching signal. Compared with the prior art, the output active power fluctuation and frequency fluctuation caused by imbalance of the power grid can be eliminated; and in addition, it is ensured that the output current of the virtual synchronous generator is balanced constantly, so that overhigh electrical stress of a certain bridge arm of the inverter can be avoided.