391 results about "Frequency meter" patented technology

The invention discloses a self-adaptive fault reflection method and device based on adjustable excitation frequency, and belongs to the technical field of cable fault detection and positioning. The method comprises the following steps: injecting an excitation signal which can be adjusted in a range of 1kHz-10MHz through an adjustable impedance matching network; collecting a reflected signal and calculating an SNR (f) curve; optimizing by adopting a particle swarm optimization algorithm and taking maximization of a signal-to-noise ratio as a target, and determining an optimal excitation frequency; and finally, calculating the fault position and type based on the optimal frequency. The particle swarm optimization algorithm is adopted to perform adaptive optimization on the excitation frequency, and the adjustable impedance matching network is combined to form a closed-loop adaptive detection framework of excitation-acquisition-analysis-optimization-re-excitation, so that the excitation frequency can be automatically adjusted according to a real-time detection result, and the detection accuracy is improved. And the fault detection sensitivity, the positioning precision and the energy efficiency are obviously improved.

The invention belongs to the field of power distribution automation, and relates to a power grid equipment frequency adaptive resampling method based on a dynamic scale factor, and the method comprises the steps: carrying out the point compensation through employing a linear interpolation method when a power grid equipment detects that the number of continuous lost points is smaller than or equal to 3; selecting a voltage signal channel or a current signal channel to carry out zero crossing point detection and real-time frequency calculation; when the real-time frequency obtained through calculation deviates from the nominal frequency, the power grid equipment introduces a dynamic scale factor for resampling, sampling points are increased when the real-time frequency is higher than the nominal frequency, and sampling points are reduced when the real-time frequency is lower than the nominal frequency; writing data obtained by resampling into a calculation annular cache region of the power grid equipment; and performing FFT calculation on the data in the calculation annular cache region to obtain power grid parameters. The sampling interval of the data acquisition unit is dynamically adjusted by increasing or reducing the sampling points, so that the sampling time sequence and the actual signal period are synchronized, the sampling frequency and the real-time frequency are adaptively matched, and the sampling distortion problem under the power grid frequency fluctuation is solved.

The invention relates to the field of pulse signal generation, and discloses an integer frequency signal generation circuit and method for a microprocessor, and the circuit comprises a flipping register, a frequency division register, a counter, a frequency signal flipping module, an integer frequency calculation unit, and a time delay unit. The integer frequency calculation unit is used for calculating the delay series of the fractional part of the frequency division value when the enable signal 1 is valid, and sending the delay series to the delay unit; and the delay unit is used for carrying out delay less than one clock period on the frequency signal output by the frequency signal overturning module according to the delay series sent by the integer frequency calculation unit, and outputting an integer frequency signal. According to the integer frequency signal output circuit disclosed by the invention, the frequency division value and the delay series of the frequency division register are automatically changed through the integer calculation module and the delay series calculation module, and the delay series controls the one-out-of-256 selector to be used for selecting the frequency signal output of the corresponding delay module in the delay unit, so that the generation of the integer frequency signal is realized.

The invention relates to the technical field of anti-seismic performance detection, in particular to an anti-seismic performance detection method and system for an assembled steel-wood composite structure, and the method comprises the steps: arranging a multidirectional acoustic emission sensor in a steel-wood structure node area, applying simulated seismic vibration, and synchronously collecting acoustic emission signals; the method comprises the following steps: preprocessing collected acoustic emission signals, dividing the acoustic emission signals into signals corresponding to microcracks and contact slippage, respectively calculating an energy attenuation rate and a phase offset, and constructing a matrix; micro-impact is applied to the steel-wood node through an electromagnetic excitation device, a response signal is collected, resonant frequency is extracted, the drift distance between the resonant frequency and a reference value is calculated, and the severity of interface damage is determined according to the value of the drift distance; the damage correlation index calculation takes the characteristic value of the interface wave propagation characteristic matrix and the resonance frequency drift distance as input, the damage correlation index is calculated through the correlation coefficient, and the damage grade is divided according to the correlation coefficient. And differential characterization of different damage types is realized through the interface wave propagation characteristic matrix.

The invention discloses a fan frequency control method and device, electronic equipment and a computer medium, and belongs to the technical field of automatic incineration. According to the specific scheme, the method comprises the steps of obtaining a parameter sequence value of a control parameter of the automatic combustion control system in a historical period, a current flow value of main steam flow, a flow set value of the main steam flow, a real-time value of steam pocket pressure, a hearth material layer pressure difference value and a control variable sequence value in the historical period; calculating a flow predicted value of the main steam flow; calculating flow deviation; calculating the frequency of an intermediate fan; the steam drum fan frequency is calculated; the flow fan frequency is obtained; calculating a primary frequency given value; and the primary frequency set value is dynamically corrected, and the target primary fan frequency of the primary fan is obtained and adopted to control the primary fan. The response speed of the automatic combustion control system can be effectively improved, so that the control of the frequency of the extension set can be closer to the actual production condition.

The invention relates to the field of load control, in particular to a non-fixed load accurate removal method based on load control fairness and effectiveness consideration. Comprising the following steps: acquiring the frequency of a power grid system, calculating the frequency change rate, judging whether to send a'preparation for load shedding 'instruction to all substations by monitoring the frequency of the power grid system and the frequency change rate, entering a load shedding amount calculation stage, and calculating the load amount needing to be cut off in each region through a dynamic weighted load precise cutting algorithm, calculating a total load shedding amount; based on the load capacity needing to be cut off in each area, the substation optimizes the cut-off combination of the load lines in the areas, after optimization is completed, the substation executes cut-off, and the master station monitors the frequency and the frequency change rate of the power grid system after cut-off and judges whether a locking condition is met or not so as to stop further cut-off. The technical problems that power grid frequency monitoring mostly depends on low-sampling-rate equipment, the rapidly-changing frequency dynamic state is difficult to capture, and instability detection lags or misjudgments are caused are solved.

The embodiment of the invention relates to the technical field of transformer fault detection, and discloses a transformer winding fault detection method and system based on frequency response and a medium, and the method comprises the steps: determining the equivalent inductance and equivalent capacitance of a transformer winding; and calculating a first-order grounding coefficient of driving point admittance by using the peak frequency and the valley frequency when the neutral point is grounded, and calculating a first-order open-circuit coefficient by using the peak frequency and the valley frequency when the neutral point is open-circuit. A first difference function is constructed through the equivalent inductance, the scaling rate and the first-order grounding coefficient, and a second difference function is constructed through the equivalent capacitance and the first-order open circuit coefficient. And fault detection of the transformer winding is carried out according to a comparison condition between fluctuation of the first difference function and the second difference function and a preset threshold value, and early sensitive detection is realized.

The invention provides a short bolt axial stress detection method and device based on electromagnetic ultrasonic resonance, and relates to the technical field of industrial fastener stress detection. The method comprises the following steps: determining a preset period and frequency of an excitation signal according to material characteristics of a to-be-measured short bolt, and calibrating resonant frequency and stress to obtain a calibration curve; classifying the lengths of the short bolts to be measured to obtain bolts with known original lengths and in-service bolts with unknown original lengths; based on the determined preset period and frequency, first-order resonant frequency corresponding to the bolt with the known original length is obtained through an electromagnetic ultrasonic transducer and a single-wave resonance method; based on the determined preset period and frequency, first-order resonant frequency corresponding to the in-service bolt with the unknown original length is obtained through an electromagnetic ultrasonic transducer and a double-wave resonance method; and calculating the axial stress of the corresponding short bolt to be measured according to the calibration curve and the first-order resonant frequency. The problems that in the prior art, the energy conversion efficiency is low, and the short bolt detection effect is poor are solved.

The invention relates to the technical field of photovoltaic support monitoring, and discloses a photovoltaic support displacement safety monitoring method. The method comprises the steps that sensors are installed at different nodes of a photovoltaic support based on a stay wire displacement monitoring system, and horizontal displacement and vertical displacement are collected in real time; correcting the displacement data through multi-dimensional data fusion in combination with environmental factors; and calculating the vibration frequency of the bracket, monitoring the frequency change in real time, and generating a bracket health assessment report and an early warning signal. In the prior art, accurate monitoring of support displacement is difficult to realize under a complex environment condition, and especially under the condition of non-uniform support stress or foundation settlement, accurate displacement monitoring and early warning cannot be provided. According to the invention, through multi-node sensor data acquisition, environmental factor correction and dynamic vibration frequency calculation, accurate monitoring and early warning of the displacement of the photovoltaic support are realized, and the operation safety and reliability of a photovoltaic system are improved.

The invention provides a non-contact measuring device and method for medium pressure in a pipeline based on an ultrasonic surface wave array, and the device comprises an ultrasonic surface wave array transmitting module, an ultrasonic surface wave receiving module, a signal amplification circuit, a high-speed signal collection card, a drive circuit, and an industrial control computer. Respectively sending driving instructions to the driving circuit when the medium pressure in the test pipeline is zero and the test pipeline is in a working state; after the amplified ultrasonic surface wave signals are received, extracting frequency signals including a zero-pressure state ultrasonic surface wave array frequency f0 and a working state ultrasonic surface wave array frequency f, calculating to obtain an ultrasonic surface wave array frequency difference value, and calculating a pressure indicating value through a pressure calculation formula; based on the ultrasonic surface wave array, the pressure of the medium in the pipeline is inverted by measuring the frequency of the ultrasonic surface wave, high-precision non-contact measurement of the pressure of the medium in the pipeline can be realized, and the sensor belongs to a novel mechanical sensor.

The invention discloses an LLCL filter design method, and relates to the technical field of power electronics. The method comprises the following steps: acquiring an initial filter capacitance, an initial inverter side filter inductance, a power grid side filter inductance and a target frequency; calculating filtering branch inductance based on the filtering capacitance and the target frequency; calculating a positive harmonic peak frequency based on the filter capacitor, the inverter side filter inductor, the power grid side filter inductor and the filter branch inductor; calculating damping resistance, damping inductance and damping capacitance based on the positive harmonic peak frequency, the filter capacitance, the resonant frequency value constraint, the first value range constraint and the second value range constraint of the quality factor; and when the target parameter does not meet the grid-connected current harmonic standard, updating the filter capacitor and / or the inverter side filter inductance, and skipping to the step of calculating the filter branch inductance based on the filter capacitor and the target frequency so as to carry out iteration until the grid-connected current harmonic standard is met. According to the embodiment of the invention, the design optimization of the parameter value of the filter element in the LLCL filter is realized.

The invention discloses a ship signal adaptive time-frequency analysis method based on instantaneous frequency direction self-adjustment. The ship signal adaptive time-frequency analysis method comprises the steps of collecting ship signals to be subjected to time-frequency analysis and performing short-time Fourier transform; estimating the instantaneous frequency of the ship signal based on short-time Fourier transform time-frequency distribution in combination with time-frequency narrow-band features; calculating the instantaneous frequency and the optimal window length after smoothing; segmenting the smoothed instantaneous frequency in time, calculating time-frequency domain direction pre-guidance of each time period, and constructing a Chirp atomic direction over-complete dictionary; segmenting the ship signal in time, and calculating the matching direction of the ship signal in each time period so as to calculate and improve Chirplet transformation time-frequency distribution; and calculating the optimal short-time Fourier transform in combination with the optimal window length, and correcting and improving Chirplet transform time-frequency distribution. According to the method, the robustness of short-time Fourier transform and the anisotropy of improved Chirplet transform are utilized at the same time, and time-frequency distribution with high robustness and high time-frequency resolution is obtained.

The invention relates to a square wave generation method and system based on a DDS signal transmitter, and belongs to the technical field of digital electronic signal synthesis. The method comprises the following steps: calculating a digital analog signal sampling frequency based on a square wave output frequency set by a user, and obtaining a digital fundamental frequency phase signal according to a phase-locked loop precision range; mapping the digital fundamental frequency phase signal into a sinusoidal amplitude signal according to a digital phase accumulation mechanism to obtain a digital-analog conversion clock, binarizing the sinusoidal amplitude signal, and outputting a square wave output period; dividing a square wave output period into a low level region and a high level region according to the precision range of the phase-locked loop, reading a square wave output frequency set by a user through a random storage address, and outputting a non-offset phase-locked square wave; and constructing an error accumulation self-checking architecture to calculate a frequency control word, and when detecting that the frequency control word has a decimal discarding error, recalculating the frequency control word.

The invention relates to a verification method and system for a mutual inductor calibrator based on accurate frequency tracking. The method comprises the following steps: sampling output signals of a standard mutual inductor and a mutual inductor to be tested to obtain original signals; sequentially performing high-pass and low-pass digital filtering on the original signal to obtain a filtered signal; performing accurate frequency calculation on the filtering signal by adopting a mode of combining zero crossing point detection and a similar triangle interpolation method, and if an absolute value of a difference value between a current fundamental frequency obtained by calculation and a fundamental frequency measured last time is greater than a set value, updating a hardware sampling interval until the absolute value is smaller than the set value; and discrete Fourier transform calculation is carried out on the filtering signals of the standard mutual inductor and the mutual inductor to be detected respectively, fundamental wave amplitudes and fundamental wave phases of the corresponding signals are obtained, and a ratio difference and an angular difference are calculated to serve as verification results of the mutual inductor calibrator. According to the invention, spectrum leakage and a fence effect in the fundamental wave extraction process can be eliminated, and the verification precision of the angular difference and the ratio error of the mutual inductor calibrator is improved.

The invention relates to the technical field of electronic measurement and sensing, and discloses a capacitance monitoring method and system based on a sweep frequency resonance point, and the method comprises the steps: carrying out the coarse sweeping in an initial frequency range, obtaining an impedance spectrum, and recognizing a coarse resonance interval; carrying out fine scanning in the interval and calculating an accurate resonant frequency by adopting a quadratic interpolation method; calculating a capacitance value in combination with the mapping table; and dynamically adjusting the frequency sweeping window of the next period based on the historical resonant frequency. The system comprises an excitation signal generation unit, an impedance response acquisition unit, a coarse / fine scanning control unit, a resonant frequency calculation unit, a capacitance resolving unit and a dynamic frequency window updating unit, and integrates a temperature compensation and anomaly detection mechanism. Through the two-stage frequency sweeping and self-adaptive frequency window strategy, the monitoring period is shortened to 1 / 5 or below of that of a traditional method while it is guaranteed that the resonant frequency measurement precision is superior to 0.01 Hz, and the real-time performance, stability and environmental adaptability are remarkably improved.

The invention discloses a frequency measurement method, system and device and a computer readable storage medium, and belongs to the technical field of electricians. Acquiring a sampling value, and judging whether the sampling value is invalid or not based on the absolute value of the sampling value; determining a first frequency value based on the sampling value and the sampling frequency; determining an amplitude and a phase of a vector value of the signal based on the sampling value; determining a second frequency value according to the phase change; determining a frequency based on the first frequency value and the second frequency value; according to the frequency measurement method, system and device and the computer readable storage medium, a low-value locking technology, an extreme value anti-shake technology, a sampling zero crossing point anti-shake technology and a hysteresis frequency calculation technology are adopted, and sampling point frequency measurement and vector frequency measurement are organically combined, so that the frequency measurement precision when the signal frequency fluctuates in a large range under different working conditions is ensured; and the problem that the frequency measurement error is large when the signal frequency fluctuates in a large range is solved.

The invention relates to the technical field of signal frequency measurement, in particular to a low-frequency-band fixed square wave frequency high-precision measurement method based on a kernel clock, which is suitable for the field of embedded systems and digital signal processing, is mainly used for low-frequency and fixed-frequency-band high-precision frequency measurement, and is not a frequency meter method specially used for measuring frequency. The method is suitable for measuring the fixed output frequency in a test system and the like. According to the method, a kernel clock of an embedded system (such as an STM32 single-chip microcomputer) is mainly utilized, a time constant is calibrated by measuring the count value of the duration of high and low levels of a fixed time window, and therefore the square wave frequency is obtained through calculation.

The invention relates to a fault monitoring method and a fault monitoring system. The fault monitoring method comprises the steps that sound signals in a cab and one or more corresponding vibration signals of one or more monitoring positions in a power system are collected in real time; calculating a frequency response function between the sound signal and each vibration signal and obtaining a peak point frequency corresponding to a peak point of each frequency response function; calculating a coherent characteristic function between each vibration signal and the sound signal and obtaining an amplitude corresponding to a peak point frequency of each frequency response function; judging whether the amplitude corresponding to the peak point frequency of each frequency response function is greater than a preset threshold value or not; and when the amplitude corresponding to the peak point frequency of the one or more frequency response functions is greater than a predetermined threshold, determining that a fault occurs at the monitoring position of the vibration signal corresponding to the one or more frequency response functions. The fault monitoring method and the fault monitoring system have improved performance.

The invention discloses a receiving-end frequency supporting method based on a four-end flexible direct-current power transmission system. The method comprises the following steps: firstly, detecting the frequency and active power of an alternating-current side bus of a No.1 receiving-end converter station of the four-end flexible direct-current power transmission system and the voltage of the direct-current sides of two transmitting-end converter stations through a synchronous phasor measurement device; then determining a control mode and a topological connection mode of each converter station of the four-end flexible direct current power transmission system, and calculating the support power of the four-end flexible direct current system to the receiving end based on the real-time data of the receiving end system frequency; calculating changes of active instruction values of a No.3 sending end converter station and a No.4 sending end converter station in real time based on changes of the DC voltage of the sending end side of the four-end flexible DC power transmission system after disturbance; and finally, measuring the frequency of a new energy base AC bus connected with the No.3 sending end converter station, and calculating the total active power instruction of the new energy base. According to the invention, the problems of small inertia and poor frequency stability of a receiving end system accessed through long-distance direct-current power transmission in the prior art can be solved.

The invention provides a sampling signal compensation method of a power supply converter and a power supply conversion device. The sampling signal compensation method comprises the following steps: S1, acquiring a sampling signal from the power supply converter; s2, obtaining the frequency of the sampling signal; s3, a compensation parameter calling index number is obtained through calculation according to the frequency of the sampling signal, a pre-stored compensation parameter table is inquired according to the compensation parameter calling index number, and a discrete compensation parameter table is obtained; s4, the sampling signal is compensated through the discrete compensation parameter table, a feedback signal is obtained, and the compensation parameter table is a discrete corresponding data table of time and compensation amount obtained at the lowest frequency of the sampled signal.

The invention belongs to the technical field of cable insulation material aging detection, and relates to a cable aging degree judgment method based on an impedance spectrum and a related device. The method comprises the steps of obtaining a reflection coefficient curve based on an impedance spectrum curve; obtaining a reflection coefficient real part curve based on the reflection coefficient curve, and extracting a resonant frequency corresponding to a resonant point of the reflection coefficient real part curve; calculating a relative dielectric constant real part of an insulating medium of the cable to be measured under different resonant frequencies; outputting an attenuation constant curve based on the reflection coefficient curve and a cable reflection coefficient amplitude calculation model; extracting a plurality of attenuation constant values of the attenuation constant curve on the resonant frequency; substituting the attenuation constant value and the relative dielectric constant real part into a dielectric loss angle tangent value calculation model to obtain a dielectric loss angle tangent value of the to-be-measured cable under the resonant frequency; and carrying out aging degree judgment based on the dielectric loss angle tangent value. The problem that an existing method is long in time consumption or cannot acquire full-band dielectric information of a cable insulating material is solved.

The invention relates to the technical field of frequency converter resonance control, and provides a frequency converter long-line driving system resonance suppression method and device, and the method comprises the steps: obtaining time sequence data, carrying out the normalization processing, calculating a theoretical resonant frequency, and predicting the resonant frequency through an attention-enhanced long-short-term memory neural network. Calculating a frequency error compensation amount, and calculating a harmonic suppression comprehensive performance evaluation index according to the frequency error compensation amount and the predicted resonant frequency; the harmonic suppression effect is evaluated according to the harmonic suppression comprehensive performance evaluation index and the index threshold value, and the weight coefficient of the attention-enhanced long-short-term memory neural network is adjusted through an NSGA-II optimization algorithm; and adjusting the center frequency and bandwidth parameters of the frequency converter long-line driving system according to the predicted resonant frequency to realize resonance suppression of the frequency converter long-line driving system. According to the invention, the feature extraction capability of the LSTM network is enhanced through the attention mechanism, the accuracy of resonant frequency prediction is significantly improved, and the harmonic suppression effect is improved.

The application discloses a transformer operation state monitoring and fault early warning method based on state index calculation, relates to the technical field of transformer operation state monitoring, and aims to solve the problem of reduced accuracy of potential fault identification. In the transformer operation process, winding temperature is collected to calculate temperature rise trend and monitor vibration state, vibration frequency is obtained, operation stress coefficient is calculated in combination with the temperature rise trend and the vibration frequency, the electric conductivity of insulation oil in the oil circulation pipeline is detected, the state index is generated by comprehensively considering the electric conductivity and the operation stress coefficient, and the transformer operation state is classified accordingly. When the state is warning, multiple groups of different cooling powers are inputted, the monitoring time is set, the corresponding radiator outlet air temperature is collected, the power change amount and the outlet air temperature difference change amount are calculated after the cooling powers are sorted, the heat dissipation characteristics are comprehensively evaluated, and it is judged whether a fault warning signal is generated, so that early warning of potential faults of the transformer is realized, and operation safety and reliability are improved.

The invention provides an insulation monitoring evaluation method and device for a high-voltage direct-current system cable, electronic equipment and a storage medium, and relates to the technical field of cable insulation monitoring, and the method comprises the steps: obtaining the initial resonant frequency of the high-voltage direct-current system cable in an initial operation state, estimating the target real-time resonant frequency of the high-voltage direct-current system cable after the operation target period; calculating a difference value between the initial resonant frequency and the target real-time resonant frequency to obtain a target resonant frequency offset; based on the target resonant frequency offset and a preset proportionality coefficient, a target cable aging state quantity is calculated and obtained, the target cable aging state quantity is compared with a preset threshold value, and the aging condition of the cable is evaluated according to a comparison result; wherein the preset proportionality coefficient is calculated by fitting the linear relation between the resonant frequency offset and the aging degree in the cable models of different aging degrees. Through the method provided by the invention, online monitoring and real-time evaluation of the health state of the cable are realized.

The invention provides a dynamic phase compensation method based on double DDS modules, and belongs to the technical field of digital frequency synthesis. The invention provides the following technical scheme: 1, a dynamic phase inheritance mechanism: through alternate work of double DDS modules, seamlessly transmitting an integer part and a decimal remainder contained in a phase accumulated value of a main DDS to a standby DDS during switching, and combining a shared clock source and a high-speed multiplexer to ensure phase continuity; 2, remainder compensation closed-loop control is carried out, a remainder accumulator is designed to record truncation errors in real time, FTW is dynamically adjusted through a PID algorithm, and long-term frequency error closed-loop suppression is achieved in combination with feedback of an external frequency meter; 3, according to a dual-mode triggering strategy, time period triggering and phase threshold triggering are supported, switching logic is started when a triggering condition (a fixed period or a phase threshold theta th is set) is met, and the phase accumulated value theta 1 (t) and the remainder epsilon 1 of the DDS1 are transmitted to the DDS2. According to the invention, through dynamic phase synchronization and closed-loop compensation, the problems of DDS phase accumulative errors and switching discontinuity are systematically solved.

The invention discloses a surface acoustic wave hydrogen sensor based on a platinum and graphene composite film and a manufacturing method thereof, and belongs to the technical field of gas sensors, the surface acoustic wave hydrogen sensor comprises a piezo-electric crystal, the piezo-electric crystal is oppositely provided with a first interdigital transducer and a second interdigital transducer, a graphene film is deposited on the piezoelectric crystal and located on a sound propagation path between the first interdigital transducer and the second interdigital transducer, a platinum catalyst layer film is deposited on the surface of the graphene film, and the first interdigital transducer and the second interdigital transducer are connected with an external circuit through metal pins. The external circuit comprises a signal generator, a frequency meter and a data acquisition system, the signal generator generates an excitation signal and transmits the excitation signal to the first interdigital transducer through the metal pin, and a detection signal generated by the interdigital transducers is received by the data acquisition system and then is detected and compared through the frequency meter. The problems that an existing pure graphene hydrogen sensor is low in sensitivity, poor in selectivity and slow in response time can be solved.

The present invention discloses a method for identifying sudden ionospheric disturbance events based on ionospheric vertical sounding data, comprising the following steps: Step 1, collecting and organizing fmin and foF2 data from each ionospheric observation station during a historical M5.0 solar flare eruption that occurred during daytime in my country; Step 2, calculating the ratio of fmin to foF2 data at each ionospheric observation station at the corresponding time, statistically analyzing the distribution of fmin / foF2, and determining the different intensity levels of ionospheric absorption at each ionospheric observation station; Step 3, determining the intensity level of the sudden ionospheric disturbance event. The method for identifying sudden ionospheric disturbance events disclosed by the present invention utilizes the minimum echo frequency of the ionospheric vertical sounding ionogram and the ionospheric critical frequency to calculate an absorption index representing the degree of ionospheric absorption. This method can simply and directly characterize the degree of ionospheric absorption in a certain region and can provide ionospheric absorption information for different regions of my country for shortwave and other electronic information systems.

The invention belongs to the field of transformer test, and relates to a transformer field load measurement method based on a frequency-doubled power supply, which comprises the following steps: electrically connecting the output end of a variable-frequency power supply with the low-potential side of an intermediate transformer, electrically connecting the high-potential side of the intermediate transformer with the high-voltage side of a tested transformer, and short-circuiting the low-voltage side of the tested transformer; a compensation capacitor bank is connected in parallel to the high potential side of the intermediate transformer, and a current transformer and a power analyzer are connected in series to one branch of the intermediate transformer and the tested transformer; during testing, multiple frequencies are selected according to parameters of the variable-frequency power source, the load capacity of the whole loop is calculated according to the selected frequencies, the compensation capacitor bank is adjusted to enable the whole loop to be kept in a sub-resonance state, and the load loss converted to the reference temperature under the power frequency is calculated according to rated parameters of the tested transformer. According to the invention, the capacitance of the compensation capacitor bank is small during load test under frequency multiplication, the occupied space of equipment is small, a field test loop is simplified, and the test safety coefficient and the working efficiency are improved.

The present invention discloses a method for synchronous control of grid-on and off-grid switching based on a dual rotating coordinate system. The method is used to synchronize grid voltage and phase during grid connection and off-grid operation. The method collects the three-phase grid voltage and performs a Clark transform to calculate the phase angle of the grid voltage signal; calculates the phase angle increment, the angular frequency of the grid fundamental wave, and the output frequency; calculates the phase angle step size in the internal rotating coordinate system and the phase angle step size in grid-on mode; and calculates the grid-on phase angle #imgabs0# in a dual coordinate system formed by the grid phase rotating coordinate system and the internal rotating coordinate system. By performing a Clark transform on the three-phase grid voltage and applying a second-order generalized integral, the voltages #imgabs1# and #imgabs2# in the stationary coordinate system are phase-shifted by 90 degrees. The positive and negative sequence voltages are then separated, eliminating interference from the negative sequence component on phase estimation and improving phase-locking accuracy. The phase angle #imgabs3# in both the grid phase rotating coordinate system and the internal rotating coordinate system is calculated, achieving a faster, less-hysteresis phase-locking method and ensuring consistency in switching phase and frequency during grid connection and off-grid operation.

The invention provides a method for improving PT residual voltage frequency measurement accuracy based on rotation vector characteristics, and relates to the technical field of generator set rotation speed measurement. The method comprises the following steps: acquiring a three-phase voltage alternating current signal through a generator end PT; processing the three-phase voltage signal to obtain projections of a voltage rotation vector on alpha and beta static coordinate axes; frequency characteristics are extracted based on projection and voltage amplitude and can be realized through direct calculation or a phase locking link; performing low-pass filtering on the frequency characteristic direct current quantity; a generator speed is calculated based on the filtered frequency and provided to a governor. According to the method, the limitation that a traditional PT residual voltage method only depends on zero crossing point information is broken through, frequency characteristics are extracted through a complete voltage sequence, alternating current signal filtering distortion is avoided through direct current filtering, high measurement precision and high anti-interference capacity can still be kept under the low-speed working condition, the problems that an existing speed measurement method is insufficient in precision and weak in anti-interference capacity are effectively solved, and the method is suitable for popularization and application. And reliable guarantee is provided for safe and stable operation of a unit.