70 results about "Third harmonic voltage" patented technology

A method to detect of generator stator of a single-phase ground fault belongs to relay protection. Methods are as follows: using of generators and adjacent to the neutral point zero sequence voltage, machine-zero-sequence current component consumption as a reference, current transformer and voltage transformer wiring form of a standard wiring; under generator-and-neutral fault component adjacent to the third harmonic voltage and phase angle at the same small impose a certain value to determine from the neutral point 50 percent of the internal generator stator single-phase ground fault; under generator terminal voltage and zero-sequence - current weight-zero sequence of phase angle relationship to determine from the neutral 50% -100% within the scope of the internal generator stator whether single-phase fault. This invention has high sensitivity and reliability.

Disclosed is a discriminated method of generator terminal voltage mutual inductor once-off-line. A protector detects negative sequence voltage of a generator terminal voltage mutual inductor, open-mouth triangle fundamental wave zero sequence voltage and zero sequence voltage or a zero sequence current of a neutral point of a generator. According to the following formula, the detectable quantities are respectively compared with corresponding constant values, namely, when the conditions that the terminal voltage (TV) negative sequence voltage is larger than a constant value or the TV open-mouth triangle fundamental wave zero sequence voltage is larger than a constant value, and meanwhile the zero sequence voltage or the zero sequence current of the neutral point of the generator is smaller than a constant value are satisfied, once-off-line of the TV appears and alarm signals are sent, third harmonic voltage-type stator grounding protection and harmonic voltage-type stator grounding protection of a generator are locked, and protection mal-operations are avoided.

Methods, system and apparatus are provided for controlling third harmonic voltages when operating a multi-phase machine in an overmodulation region. The multi-phase machine can be, for example, a five-phase machine in a vector controlled motor drive system that includes a five-phase PWM controlled inverter module that drives the five-phase machine. Techniques for overmodulating a reference voltage vector are provided. For example, when the reference voltage vector is determined to be within the overmodulation region, an angle of the reference voltage vector can be modified to generate a reference voltage overmodulation control angle, and a magnitude of the reference voltage vector can be modified, based on the reference voltage overmodulation control angle, to generate a modified magnitude of the reference voltage vector. By modifying the reference voltage vector, voltage command signals that control a five-phase inverter module can be optimized to increase output voltages generated by the five-phase inverter module.

The invention provides a method and device for suppressing difference of capacitor voltage fluctuation of a hybrid MMC sub-module. The method includes the steps: when a hybrid modular multilevel converter is running in a steady state through over-modulation, determining the third harmonic voltage correction according to the operating state of the system, then determining the circulating current suppression voltage correction, and finally determining the modulation wave voltage of the hybrid modular multilevel converter. The method and device for suppressing difference of capacitor voltage fluctuation of a hybrid MMC sub-module can suppress the difference of the capacitor voltage fluctuation of a full-bridge sub-module and a half-bridge sub-module of the hybrid modular multi-level converter, and at the same time, can reduce the fluctuation level of the capacitor voltage of the whole converter, and the light weight effect is obvious, and the hybrid modular multilevel converter can be running stably. The technical solution provided by the method and device for suppressing difference of capacitor voltage fluctuation of a hybrid MMC sub-module introduces the third harmonic voltage injection rate, and can effectively suppress the capacitor voltage fluctuation of the full-bridge sub-module and the half-bridge sub-module of the hybrid modular multi-level converter on the premise of maintaining the voltage of the DC bus and the transmission power unchangeable, and can reduce the sub-module capacitor voltage ripple level of the overall converter.

This invention disclose a method for discriminating the earth fault of generator stator windings by distinguishing neutral point voltage triple harmonic component and that of the generate end open-end triangle voltage including the following steps: a protection device samples the voltage waveform of the voltage mutual inductor to get a transient value, evaluating the complex, form of the triple-harmonic voltage by Fourier algorithm plus digital filter algorithm, computing out its varied volume and its potential, automatically entering into the improved dynamic regulation of its voltage differential criteria under heavy load, automatically entering into its voltage ratio criteria under light load before interconnection, protection is operated after a delay when aided criteria meet the needs simultaneously.

The invention discloses a method for detecting PT neutral line failure. Positive-sequence fundamental wave voltage is calculated according to ABC three-phase sampling values of a PT secondary side, zero-sequence third harmonic voltage is calculated according to a zero-sequence voltage sampling value of a PT secondary side, and when the zero-sequence third harmonic voltage is greater than a floating threshold and third harmonic in one phase or multiple phases is greater than the floating threshold when the third harmonic content of each phase of voltage of the PT secondary side is calculated in a Fourier algorithm, the PT neutral line failure is reported through delaying. When the neutral line failure appears between the PT secondary side and a protective device, excitation current of the neutral line can not flow so as to cause changes of excitation current in ABC three phases, and the third harmonic of each phase of measured voltage of the protective device can appear. The PT neutral line failure can be detected according to the third harmonic in the zero-sequence voltage.

The invention discloses a control method of a cascade photovoltaic solid-state transformer and is to solve the problem of envelope ripples of quadruple power frequency of resonance current of a preceding-stage two-level full-bridge LLC converter after compensation of third harmonic voltage for the system. The method mainly comprises the following steps: controlling the average value of DC capacitor voltage of all H-bridge converters and obtaining an active current instruction value; controlling grid current and calculating third harmonic voltage and compensating the third harmonic voltage forthe system; controlling output voltage of the two-level full-bridge LLC converter and suppressing resonance current quadruple power frequency envelope ripples; and controlling input bus voltage of a Boost converter to realize maximum power point tracking control of a preceding-stage photovoltaic array. Compared with the prior art, the method can realize suppression of quadruple power frequency envelope ripples of the preceding-stage two-level full-bridge LLC converter without adding any hardware device, thereby improving system performance.

The invention provides a method for reducing capacitance voltage fluctuation of a sub-module of a modular multilevel converter (MMC) under unbalanced grid voltage. When the grid voltage is asymmetrical, physical quantities such as positive and negative sequence modulation ratios after unbalance are determined, then amplitude values of third harmonic injection voltage and phase angles of three phases are separately calculated and obtained, and finally calculated third harmonic voltage is injected to the three phases through an injection controller, thereby reducing the fluctuation degree of capacitance and voltage of the sub-module of the MMC under the unbalanced grid voltage. The technical scheme provided by the method introduces the injection amount of the third harmonic voltage, and solves the problems that when the grid voltage is unbalanced, the fluctuation of the capacitance and the voltage of the sub-module increases and a conventional method of reducing the voltage fluctuation of the sub-module is not applicable to a situation of the unbalance of the grid voltage. The method combines the characteristics of economy and control flexibility, can make the fluctuation degree of the capacitance and the voltage of the sub-module greatly reduce under the premise of maintaining direct current bus voltage and conveying power unchanged, thereby reducing a requirement for a capacitance value of a capacitor of the sub-module, the volume and the cost of the capacitor of the sub-module are reduced, and the method is beneficial to achieve light weight of the modular multilevel converter.

The invention discloses a method for detecting the breakage of a PT neutral line. The method comprises a step of calculating a positive sequence fundamental voltage and various higher-harmonic voltages of each phase according to voltage sampling values of A, B and C phases of a secondary side of a PT, a step of calculating a zero-sequence third-harmonic voltage according to the zero-sequence voltage sampling value of the secondary side of the PT, a step of calculating and obtaining a voltage threshold 1 according to the positive sequence fundamental voltage, a step of calculating and obtaininga voltage threshold 2 according to the various higher-harmonic voltages of each phase, and a step of reporting that the PT neutral line is broken after a delay when the zero-sequence third-harmonic voltage is larger than the voltage threshold 1 and the zero-sequence third-harmonic voltage is larger than the voltage threshold 2. By using the method, the breakage of the PT neutral line can be judged, when various higher-harmonic voltages are generated due to operations of no-load main transformer and the like in a system, besides third-harmonic content is large, other-harmonic content is also large, and the misjudgment of the breakage of the PT neutral line can be prevented.

The invention discloses a third harmonic voltage stator grounding protection method. The third harmonic voltage stator grounding protection method comprises the steps of calculating a positive-sequence voltage of a power generator end, a third harmonic voltage of a neutral point and a zero-sequence third harmonic voltage of the generator end; judging whether a zero-sequence PT of the generator end is broken or not, and shunting protection if the zero-sequence PT of the generator end is broken; judging whether a neutral point voltage loop is broken or not, and shunting protection if the neutral point voltage loop is broken; synthesizing a differential voltage and a brake voltage according to the third harmonic voltage of the neutral point and the zero-sequence third harmonic voltage, corrected by an automatic adjustment system, of the generator end, and performing protection action when the differential voltage is larger than the brake voltage and the zero-sequence PT of the generator end and the neutral point voltage loop both are not broke; and comparing a specific value between the zero-sequence third harmonic voltage of the generator end and the neutral point third harmonic voltage with a protection fixed value, and performing protection action when the specific value is larger than the protection fixed value and the neutral point voltage loop is not broken. No maloperation is generated when the zero-sequence PT of the power generator end and the neutral point voltage loop are broken, and the third harmonic voltage stator grounding protection method is high in reliability.

Provided is a current control type electric force converter capable of improving the waveform distortion of an output current. A harmonic shifting part (4) obtains a triple-frequency harmonic voltage component (V3') obtained by shifting a triple-frequency harmonic voltage component (V3) by a prescribed time Deltat using a phase voltage waveshape (Vu) as a reference. A signal subtration part (5) obtains a subtration signal (DeltaI3) by multiplying the triple-frequency harmonic voltage component (V3') by a gain (K1), and three-phase modified current command signals (Iux - Iwx) are obtained by subtracting three-phase current command signals (Iu_ref - Iw_ref) for feedback control by the subtration signal (DeltaI3). A grid signal generating circuit (2) outputs grid signals to six semiconductorswitching elements of a three-phase inverter circuit (IV) according to the three-phase modified current command signals (Iux - Iwx).

The invention relates to the technical field of modular multilevel converters, in particular to a method and a system for reducing the capacitance value of a full-bridge type MMC (modular multilevel converter) sub-module. The objective of the invention is to reduce the capacitance value of the full-bridge type MMC sub-module. The method comprises the steps of: calculating the initial phase and theamplitude of an optimal third harmonic voltage; generating an optimal third harmonic voltage according to the initial phase and the amplitude; generating a full-bridge type MMC three-phase referencevoltage by closed-loop control, and further generating reference voltages of each bridge arm of the full-bridge type MMC according to a direct-current voltage reference value, the three-phase reference voltage and the optimal third harmonic voltage; and generating drive control signals switched in or switched on by the full-bridge sub-module in each bridge arm according to the reference voltage ofeach bridge arm to control switching-in or switching-off of all the sub-modules of the upper and lower bridge arms according to the control signals so as to effectively inhibit the fluctuation of thecapacitance voltage of the full-bridge MMC sub-module and further reduce the sub-module capacitance value of the full-bridge MMC.

The invention discloses a method and a device for measuring non-uniformity of critical current density of a surface layer of a high-temperature superconducting bulk material and belongs to the technical field of magnetic measurement. The measuring device comprises a magnet exciting coil, a secondary coil, a coil bracket, a to-be-measured sample platform, phase-locked amplifiers, a power amplifier, a precision resistor and an impedance regulation resistor; the measuring method comprises the following steps: firstly, fully cooling the to-be-measured sample platform, the magnet exciting coil, the secondary coil and to-be-measured high-temperature superconducting samples in absence of a magnetic field; then calculating to obtain an exciting current peak value and a tertiary harmonic voltage peak value of the secondary coil under the output voltage of each phase-locked amplifier; calculating critical current density values and transmission depths of the to-be-measured high-temperature superconducting samples under the exciting magnetic field strength and drawing a curve. The device and the method can be used for measuring the non-uniformity of critical current density of the surface layer of the high-temperature superconducting bulk material; the measurement error range is 10%; the voltage signals can be measured; the measurement precision is up to 1nV.

The present application provides a measuring circuit, a measuring system and a method for measuring thermal property parameters. The measuring circuit comprises: a first amplifying circuit, a second amplifying circuit, a differential amplifying circuit, an adjustable resistor and an electronic multiplier. At least one of the output terminals of the first amplifying circuit and the second amplifying circuit is connected to an input terminal of the differential amplifying circuit through the electronic multiplier; the adjustable resistor is used to adjust a fundamental frequency voltage difference between the two input terminals before the measurement, so that the pre-measurement fundamental frequency voltage difference is less than or equal to a first preset threshold. The electronic multiplier is used to adjust the fundamental frequency voltage of the input terminal connected to the electronic multiplier during measurement, so that the fundamental frequency voltage difference between the two input terminals of the differential amplifier is less than or equal to a second preset threshold, the second preset threshold is smaller than the first preset threshold. And the differential amplifying circuit is used to measure the fundamental frequency voltage and the third harmonic voltage, thereby improving the accuracy of the measured third harmonic voltage and improving a technical problem that low accuracy of thermal property measurement is caused by the fundamental frequency voltage.

The present invention includes a method for providing ground fault protection to a generator. The method includes determining the existing state of the generator and second, determining the updated alarm or trip conditions of a relay connected to the generator in view of the existing state of the generator. This includes estimating a ratio of the magnitude of the 3^rd harmonic neutral voltage to the magnitude of the 3^rd harmonic terminal voltage of a generator, along with calculating the residual 3^rd harmonic voltage from the estimated 3^rd harmonic ratio. From this, a comparison is made between the energy of the residual voltage with a fractional energy of the 3^rd harmonic neutral voltage. Based on this comparison, an alarm or trip condition is signaled when the energy of the residual voltage is greater than the fractional energy of the 3^rd harmonic neutral voltage. The invention further includes adaptive relays and systems utilizing the adaptive relays, along with methods of producing power using the adaptive relays.

The invention discloses a stator core winding of a high-voltage generator. The stator core winding comprises a front pressing ring, a rear pressing ring and a stator core, wherein the stator core is arranged between the front pressing ring and the rear pressing ring and formed by stacking a plurality of punching sheets, the punching sheets are made of cold rolling silicon steel sheets, and a stator winding is wound on the stator core. A tooth slot of the stator core is of a taper slot structure, the stator winding is a forming lap winding with the 2/3 pitch, and a plurality of reinforcing ribs are welded and fixed to the periphery of the stator core. By the adoption of the stator core winding of the high-voltage generator, harmonics can be effectively reduced, third harmonic voltages can be effectively eliminated, and waveform distortion of the voltages are improved; in parallel operation, large neutral harmonic currents can be restrained, and neutral voltages to earth are small; the strength of the end portion of the stator winding is enhanced, and the stator winding is not prone to deforming.

An embodiment of the invention discloses a parameter design and control method for a hybrid modular multilevel converter, which increases a modulation ratio of the hybrid modular multilevel converter to an optimal operation point through the coordination and cooperation of third harmonic voltage injection and a full-bridge sub-module negative level utilization method. The parameter design and control method comprises the steps of firstly, increasing the modulation ratio of the hybrid modular multilevel converter to the maximum extent through adopting a third harmonic voltage injection method, and secondly, increasing the modulation ratio to the optimal point through configuration of the cascade number of full-bridge sub-modules in bridge arms. When the hybrid modular multilevel converter outputs rated active power, the modulation ratio operates at an optimal operating point, so that a fundamental component of bridge arm power fluctuation can be changed into zero, the capacitance voltage fluctuation of the sub-module is greatly reduced, the capacitance use amount of the hybrid modular multilevel converter is greatly reduced, the number of required full-bridge sub-modules is reduced to the maximum extent, and the total cost and size of the device are reduced.

The invention discloses a high-sensitive third harmonic voltage differential stator grounding protection method, comprising the following steps: acquiring Un (k), Us (k), UA (k), UB (k), UC (k); Calculated as shown in the descrption; calculate. DELTA U3n (t) and. DELTA U3s (t); According to deltaU 3n (t) and deltaU 3s (t), it is judged whether the zero-sequence voltage of the generator is broken or not, and the protection is blocked if the generator is broken. U3d, U3r, U3d 'and U3r' were calculated. When the zero-sequence voltage of the generator is not broken, whether the operation conditionis satisfied or not is judged according to U3d, U3r, U3d 'and U3r'. If yes, the protection operation is delayed. The invention has the beneficial effects that the insulation of the stator winding tothe ground is reduced slowly, the zero-sequence voltage loop of the generator is broken without misoperation, and the reliability of the generator is improved.

The invention provides a device and method for on-site accurate testing of heat conductivity of energy-saving thermal insulation materials, and belongs to the technical field of energy-saving thermal insulation material thermal characteristic testing. The device comprises a self-adaptation thermal response detector, an electric signal collection module and a data processing module. The device is adopted for performing on-site testing on the energy-saving thermal insulation materials, fundamental wave voltage (V1omega)y and third harmonic voltage (V3omega)y of a to-be-tested sample are obtained; resistor temperature coefficient beta, core belt length l, substrate thermal conductivity ks of a calibrated thermal response temperature testing unit before usage and the fundamental wave voltage (V1omega)y and third harmonic voltage (V3omega)y of the to-be-tested sample are adopted for calculating the thermal conductivity of the to-be-tested sample. According to the device and method, the defects that an existing experimental system is not high in signal stability, not high in tested resistance precision and poor in differential signal can be overcome, and on-site accurate testing of the heat conductivity of thermal insulation materials is ensured.

The thirty-two-pole harmonic excitation medium-frequency generator is a small-medium three-phase brushless synchronous generator, and the 400Hz intermediate frequency electric energy is sent out through a 1500r / min diesel engine. , Excitation mode for harmonic excitation. The third harmonic voltage induced by the harmonic auxiliary winding of the stator is supplied to the automatic voltage regulator, and the automatic voltage regulator is used to supply the required current to the host, thus ensuring the whole generator running. Third harmonic is characterized by no-load third-harmonic voltage is very small; full load when the third harmonic voltage output voltage. The invention has the advantages that the harmonic excitation is strong with the non-linear load. It is an object of the present invention to provide a thirty-two-pole harmonic excitation intermediate-frequency generator which employs a harmonic excitation method and has the capability of super-starting an induction motor and having a nonlinear load.