220 results about "Rate of change of frequency" patented technology

Disclosed herein is an apparatus for evaluating the safety of a building. The apparatus includes first and second measurement instruments which measure earthquake accelerations of the top and bottom stories, a fast Fourier transform unit which performs fast Fourier transform on the earthquake accelerations, an integration unit which double-integrates the measured earthquake accelerations and creates drift data of the top story and the bottom story, a maximum inter-story drift ratio calculation unit which calculates a maximum inter-story drift ratio, a natural frequency change rate calculation unit which determines a natural frequency of the building, and compares the natural frequency with an ambient natural frequency of the building so as to calculate a natural frequency change rate, and a building safety evaluation unit which compares the maximum inter-story drift ratio and the frequency change rate with preset evaluation criteria and outputs a result of evaluation in the safety of the building.

The invention provides a frequency offset estimation method for high-dynamic large-frequency-offset burst signals. The estimation method comprises burst frame capturing, estimation and correction of Doppler changing rate, basic frequency offset estimation, and Doppler frequency offset estimation, a burst signal frame is formed by a pilot frequency segment and a data segment, and a receiver employs the pilot frequency segment to realize frequency offset estimation. Firstly, the burst frame capturing is realized via a threshold comparison method; then the segmentation of pilot frequency data is realized, a DFT-assistant hierarchical iteration method is employed to estimate the Doppler changing rate, and the estimation value of the Doppler changing rate is used for dynamic compensation of the pilot frequency segment; later, DFT-assistant basic frequency offset estimation of signals after dynamic correction is realized; and finally, the estimation value of the Doppler changing rate and the basic frequency offset estimation value are combined to estimate the frequency offset of each symbol in the burst signal frame. According to the frequency offset estimation method, the data segment is compensated by the adoption of the frequency offset estimation result so that the data segment has small frequency changing rate and residual frequency offset, and bit synchronization, frame synchronization, and carrier synchronization can be realized.

A method, system, and apparatus for providing a stimulation signal comprising a variable ramping portion using an implantable medical device (IMD). The first electrical comprises a first ramping portion. The first ramping portion comprises a first parameter selected from the group consisting of an amplitude, a rate of change of the amplitude, a time period of a rate of change of the amplitude, a pulse width, a rate of change of the pulse width, a time period of a rate of change of the pulse width, a frequency, a rate of change of the frequency, a time period of a rate of change of the frequency, and a duration of a time period of the ramping portion, the first parameter having a first value. The first electrical signal is applied to a target location of the patient's body. A second electrical signal comprising a second ramping portion is generated. The second ramping portion comprises the first parameter having a second value that is different from the first value. The second electrical signal is applied to a target location of the patient's body.

The invention discloses a method for detecting a piconet island state according to the self-characteristic of a piconet. The method comprises the following steps of: (1) detecting electrical characteristic value when the piconet runs; (2) judging whether the voltage at a load end is higher than the definite value or not, if yes, entering step (3), and if not, considering that the piconet is not in the island state; (3) judging whether the frequency changing rate is higher than the upper limit of the definite value or not, if yes, sending out a trip signal and then finishing, and if not, entering step (4); (4) detecting and judging whether the frequency changing rate is higher than the lower limit of the definite value or not, if yes, judging whether the phase difference is more than the phase difference setting valve or not, if yes, finishing the detection and sending out the trip signal, and if not entering step (5); and (5) after delaying for a period of time, judging whether the phase difference is more than the phase difference setting valve or not, if yes, sending out the trip signal, and if not, considering that the piconet is in the island state. Compared with the existing detection method, the method has the characteristics of rapid and reliable detection, and guarantees comparatively high anti-interference capability at the same time.

The invention discloses a primary frequency modulation coordination control method for a wind turbine generator set, and the method comprises the following steps: 1, measuring the system frequency andfrequency change rate of the grid-connected point in real time; 2, performing load shedding control of the set through pitch changing, so that the wind turbine generator set has stable active frequency modulation capacity under different wind conditions; 3, introducing an additional torque compensation link through rotor kinetic energy control, and enabling the wind turbine generator set to havefast active response characteristics; 4, rotor kinetic energy and power backup coordinated control achieving the rapid and continuous response of the wind turbine generator set to the system frequency change trough the rotor kinetic energy and power standby coordination control. The method is applicable to each wind speed, and can achieve the same standby capacitor under different wind speeds, sothat the primary frequency modulation capability of a fan is no longer restricted by the wind speed.

A method for measuring a rate of change of frequency includes estimating at least one phasor value, estimating a frequency based on the estimated at least one phasor value, compensating the estimated at least one phasor value based on the estimated frequency, calculating a frequency based on the compensated at least one phasor value, and calculating a rate of change of the calculated frequency based on the calculated frequency.

A wind power penetration limit calculating method that considers frequency constraint and wind power frequency modulation; the method comprises the following steps: using a weight equivalence polymerization method to solve a wind power plant primary frequency modulation response transfer function model and a wind power primary frequency modulation active increment; considering a wind power virtualinertia control strategy, and solving a power system equivalent inertia time constant under different wind power penetration rates; calculating a load damping effect, building a power grid frequencyresponse model that is equivalent to a rotor swing equation, and using the model to describe power system frequency response characteristics; using the power system frequency stable state deviation boundary and frequency rate of change boundary as constraints, and proposing the power grid wind power penetration limit calculating method. The method introduces the real wind power virtual inertia response, the active increment formed by the primary frequency modulation response and the power system frequency constraint into the wind power penetration limit calculation, thus improving the power grid robustness under the wind power grid connection condition, ensuring the power grid to stable and safely operate, and providing important guiding meanings for wind power grid connection planning construction.

Ice accretion on a probe is detected by determining the change of frequency of a vibrating type ice detector or sensor as ice starts to build up. The rate of change of frequency is determined and is combined with parameters including air velocity and air temperature for providing a signal that indicates liquid water content in the airflow as well as ice accretion on the ice detector.

The invention discloses a phase difference correction method applied to self-adaptive sampling of a power grid having a wide range of frequency fluctuation. The method overcomes lower measurement precision of phase difference correction methods upon dynamic variation of a fundamental frequency by increasing computing of frequency change rate, predicting real-time fundamental frequency for each measurement, correcting sample frequency so as to carry out measurement. Therefore, the method herein effectively reduce spectral frequency leakage and increases measurement precision. The method herein conducts simulation analysis on variety-frequency power grid signals by using phase difference correction method which is based on Harming window, verifies the feasibility of self-adaptive sampling methods. The method can produce high magnitude and phase measurement precision when a frequency is stable, and can also reach IEC standard requirements for magnitude measurement precision when the fundamental frequency has wide range of fluctuation, so that the method herein effectively reduce phase difference errors, can real-time reflect state of a system, and is suitable for on-line monitoring harmonic waves of a power grid which has a wide range of frequency fluctuation.

Inertia control system for a wind turbine comprising a rotor (5), generator (12) driven by the rotor (5) that interacts with a power converter (13) to generate electricity, a wind turbine controller (15) that comprises a blade pitch controller (19) and a generated power controller (18), a controller for the power converter (14) that interacts with the wind turbine controller (15), characterized because it comprises an inertia emulation block (17) that generates an extra power signal (32) negatively proportional to the frequency change rate (23) that is added to the power reference of the wind turbine generated power controller (15) and adapts the rotational speed reference of the wind turbine controller (15) according to the grid frequency (21) to prevent distortion in the active power output after adding or subtracting power in proportion to the frequency change rate (23).

The invention relates to a string structure damage combination identification method based on modal parameters. The method is characterized in that an acceleration signal arranged at on a string structure is collected, inherent frequency before and after damage and a displacement modal of an upper truss part before and after damage of the structure can be respectively obtained, according to the inherent frequency before and after damage of a grid part, first five-order regularization frequency change rate index can be calculated, a frequency-position curve is drafted, a frequency fingerprint database is established, then the frequency fingerprint parameter under practical damage condition can be calculated, positioning is carried out on the fingerprint curve of the corresponding frequency,and the damage position corresponding to each frequency fingerprint is found and then screening is carried out, first three-order curvature difference modal indexes are respectively calculated according to the curvature modals before and after damage of the truss part, and according to the curvature difference modal indexes, a first three-order curvature difference-position curve is drafted, a curve mutation position which is the damage position is found, and the mutation is larger, the damage degree is larger. According to the invention, the string structure is subjected to damage positioning for single damage and multiple damage conditions in an effective mode, and the damage degree can be accurately indentified.

Systems and methods for evaluating the stability of an islanded electrical system (off-grid) using high-speed frequency measurements of the electrical signal supplied by an alternate power source in the islanded electrical system. Additional inputs may include status signals from an automatic transfer switch, a generator, and loads within the islanded electrical system. The high-speed frequency measurements have a resolution sufficient to enable analysis of any combination of the frequency magnitude (e.g., sudden increase), frequency slew rate (e.g., frequency rate of change), frequency rate of recovery (e.g., frequency recovery time), or frequency oscillations (e.g., frequency ringing around the nominal value before settling) to indicate the presence of an actual or impending instability of the islanded electrical system. The frequency referred to herein corresponds to the frequency at which an alternating current supplied by the alternate power source is cycling.

Method and module for measuring the rate of change of frequency of a waveform related to a converter unit of a wind turbine generator, comprising: measuring an instantaneous value of said rate of change of frequency of the waveform, calculating a first filtered value of said rate of change of frequency, said first filtered value having good accuracy but low time response, and calculating a second filtered value of said rate of change of frequency said second filtered value having a good time response but low accuracy, comparing said first and second filtered values and selecting that an output value of said measured rate of change is based on said first or second filtered values depending on said comparison.

The invention discloses a least square fitting dynamic frequency measurement method. The method comprises steps that A / D conversion sampling of power grid continuous signals is carried out to form equal time interval discrete signals; an FIR digital filter is employed to extract relatively pure fundamental wave discrete signals, and a sampling matrix is formed; a binary function Taylor expansion is utilized, frequency deviation and frequency change deviation of the power grid signals are extracted, and a constant coefficient matrix is calculated in an offline mode; the least square method is utilized to solve an unknown parameter matrix containing frequency deviation and frequency change deviation; dynamic frequency of each sampling point in the data window is solved. The method is advantaged in that based on the multivariate Taylor series, a power grid signal measurement matrix equation is established, the least square method is utilized to solve an equation linearity fitting problem, on the condition that frequency tracking is realized, a frequency change rate can be further monitored, and high accuracy, good timeliness and strong interference immunity are realized.

The invention discloses an AGC emergency control method and an AGC emergency control system based on frequency change rate. The method comprises the following steps: monitoring the frequency change rate of the system in real time, judging whether the monitored frequency change rate is greater than a set threshold of a special emergence area, entering the special emergence area and performing next step if the monitored frequency change rate is greater than the set threshold of the special emergence area, and continuing monitoring if the monitored frequency change rate is not greater than the set threshold of the special emergence area; in the special emergence area, calculating the power deficiency of the system according to the frequency change rate of the system measured at the moment of disturbance; and judging whether the difference between the active power deficiency of the system and the standby active power of the system is greater than a set threshold according to the power deficiency of the system, if the difference is greater than the set threshold, starting load shedding, and if the difference is not greater than the set threshold, starting an AGC invocation strategy of the special emergence area, and using an AGC optimal invocation model based on shortest recovery time to allocate the power deficiency of system to AGC units. The method and the system have the advantages of fast frequency recovery and high efficiency, and can be widely used in the field of power control.

The invention discloses a method for controlling a wind turbine to participate in power grid frequency modulation based on virtual inertia and a pitch angle. The method comprises the following steps:when a frequency deviation exists between the rated power of a system power grid and the current frequency, calculating a proportionality factor of a tracking curve of the sub-optimal rotating speed-active power of the wind turbine under the control of the virtual inertia; calculating a reference power of an inverter at a rotor side under the control of the virtual inertia; calculating an introduced electromagnetic power at the rotor side inverter according to the frequency change rate, and accumulating the introduced electromagnetic power and the reference power to obtain a total electromagnetic power of the rotor side inverter; calculating the rotating speed deviation of the wind turbine, and adopting the rotating speed deviation of the wind turbine to calculate the electromagnetic powervariation of the rotor side inverter; obtaining an active power of a pitch angle mechanism according to the total electromagnetic power and the electromagnetic power variation, and calculating the pitch angle of the pitch angle mechanism by adopting the active power of the pitch angle mechanism; and controlling the wind turbine to increase captured wind energy and inject the active power into thepower grid according to the pitch angle.

Ultrasound-assisted contactless stirring of liquids in a resonator cell by microparticles is achieved by repeated creating and destruction of nodal patterns associated with standing waves of various resonance frequencies causing continuous movements of microparticles inside the cell. Swept-frequency sonication technique includes using constant or variable rate of frequency change as well as a stepwise change of frequency of the transducer within a predefined range. Other useful provisions include initial detection of the set of resonance frequencies and periodic refreshing of that set. Control systems are described including means to automatically detect the resonance frequencies and maintain the operation of the transducer thereon. Advantageous designs of the apparatus are described for use in microstirring, mixing of liquids using magnetic microbeads, microbubbles, microtiter plates, microarray plates, etc.

The invention discloses an island detection method and device for an electric power system. The island detection method for the electric power system comprises the steps of calculating the frequency change rate of the distributed electric power system, calculating a voltage difference value of the distributed electric power system, comparing the frequency change rate and a first threshold value and comparing the voltage different value and a second threshold value, and detecting that the island effect exists in the electric power system if the frequency change rate is larger than the first threshold value and the voltage difference value is smaller than the second threshold value. By means of the method and the device, the problem that in the related technology, an island detection dead zone is too large in the electric power system is solved, and then the effect of reducing the island detection dead zone in the electric power system is achieved.

The invention pertains to the field of power system microgrid protection and control, and relates to a microgrid non-destructive island detection method based on adaptive reactive disturbance. The method comprises the following steps: periodic reactive disturbance is added on the reference value of IBDG reactive output, the peak value selection of a triangular wave reactive disturbance portion is related to the IBDG operating mode and the system frequency when the reactive disturbance value is zero in the last disturbance period; and if the absolute value of the frequency change rate is detected to be equal to a preset value, and the duration time reaches a time setting value, then the island state is judged. The method of the invention is simple and practicable, and can be used to minimize the total disturbance and the influences of the disturbance on the quality of electric energy.

The invention relates to a frequency measurement apparatus which is arranged in such a way as to obtain an amplitude, chord length and rotation phase angle of a voltage rotation vector by means of an integration method, and furthermore, obtain a change rate of the rotation phase angle, and a rotational acceleration change rate of the rotation vector, and measure a dynamic frequency by determining a frequency change rate for every step.

The invention discloses an islanding detecting method which comprises the following steps: acquiring a voltage waveform of a common coupling point and measuring a frequency value, calculating the average change rate in a certain period to obtain a judging signal, comparing the judging signal with the preset change rate threshold value, outputting a control signal, selecting an outputted reference signal of an inverter by the control signal, introducing reference current after phase deviation under the condition that islanding possibly exists by a frequency change rate detection method, realizing further detection according to a sliding mode frequency deviation method, otherwise, introducing non-deviation reference current, and achieving normal operation of the system. The islanding detecting method has the advantages of reducing detection blind zones and impact on the system power quality and increasing the detection speed.

A method and an arrangement are disclosed for detecting islanding operation of a distributed power generator. The method can include determining a frequency of a grid to which the distributed power generator is connected, measuring a rate of change of the frequency of the grid at an output of the distributed power generator, determining a threshold value for an alteration speed, comparing the rate of change of the frequency of the grid with the threshold value, and detecting islanding operation when the measured rate of change of the frequency exceeds the threshold value for a certain time period.

The invention discloses an adaptive synchronous phasor measurement method based on signal identification. The method comprises the steps of establishing a dynamic phasor model, and simulating dynamic changes of phasor amplitude, phase angle, frequency and frequency change rate by means of a two-order Taylor series; by means of the established dynamic phasor model, obtaining a behavior rule of phasor model parameters in a power system typical static / dynamic process; according to the behavior rule of the obtained phasor model parameters, performing signal type identification, thereby identifying electric power signal transient change, a static process which does not comprise noise, a static process which comprises the noise, and a dynamic process; and aiming at the identified electric signal transient change, the static process which does not comprise the noise, the static process which comprises the noise, and the dynamic process, respectively performing adaptive construction of a time window before and after the transient change, noise inhibition and dynamic phasor compensation. The adaptive synchronous phasor measurement method can realize accurate and quick phasor measurement on the condition that the static signal or the dynamic signal is input.

The invention belongs to the technical field of air conditioner control and provides an air conditioner running control method and device. The air conditioner running control method includes detecting temperature of an indoor heat exchanger and acquiring a temperature value of the indoor heat exchanger; acquiring refrigerating or heating temperature difference deviation value according to the temperature value of the indoor heat exchanger, a preset air outlet temperature value and a refrigerating or heating temperature attenuation compensation value; acquiring a refrigerating or heating frequency changing rate from refrigerating or heating temperature difference changing tendency according to the refrigerating or heating temperature difference deviation value; acquiring refrigerating or heating correction output frequency according to current compressor running frequency and the refrigerating or heating frequency changing rate; according to a relationship between the refrigerating or heating correction output frequency and a preset output frequency interval, controlling a compressor to run according to the refrigerating or heating correction output frequency or maximum refrigerating or heating output frequency, thereby enabling air outlet temperature to be constantly maintained at a preset air outlet temperature value set by a user by adjusting running frequency of the compressor. By the air conditioner running control method and device, power consumption can be reduced correspondingly to achieve the objectives of energy conservation and emission reduction.

The invention discloses a burst signal detection and carrier synchronization method under rotor shielding, and belongs to the technical field of satellite communication. The method comprises the stepsof burst signal detection, frequency offset and frequency change rate estimation and phase offset estimation. Burst signal detection and carrier synchronization are sequentially completed based on dispersedly inserted pilot symbols, the signal receiving problem under the conditions of high Doppler dynamics, low link signal-to-noise ratio and rotor shielding is solved, and the method has a wide application prospect in helicopter satellite communication.

The invention discloses a virtual synchronous generator-based rotational inertia optimization control method, and belongs to the control field of distributed power generation. When frequency offset exceeds an allowable range, the rotational inertia is adjusted to slow down frequency change; and when the frequency change rate is in a zero passage reversion state, the rotational inertia is adjustedto realize frequency recovery. By virtue of the method, a microgrid inverter adopts a control strategy of the virtual synchronous generator, so that an optimization algorithm of the rotational inertiaof the virtual synchronous generator is realized; meanwhile, by improvement of a speed adjustment link, a voltage current phase angle is obtained by adopting a control mode to calculate the phase angle; and by adoption of the method, the inertia advantage of the conventional synchronous generator can be embodied completely, the inherit dynamic performance and stability of the inverter can be taken into consideration, and the economical efficiency of the power grid operation can be improved.

The invention provides a control method and system for a photovoltaic power station participating in system frequency modulation, wherein the method comprises the following steps: calculating an active power regulation amount of a photovoltaic power station according to grid-connected point frequency and a frequency change rate of a photovoltaic power station; correcting the initial command valueof active power of photovoltaic power station according to the active power regulation quantity of photovoltaic power station to obtain the final reference value of active power of photovoltaic powerstation; and based on the final active power reference value of the photovoltaic power station, controlling the active power of the grid-connected point of the photovoltaic power station. The technical scheme provided by the invention judges the disturbance magnitude of the power network through the frequency change rate, and adopts the emergency control to immediately increase or decrease different fixed active powers to regulate the active powers of the photovoltaic power station, thereby strengthening the support strength of the power network frequency, reducing the frequency fluctuation amplitude of the power network and increasing the stability of the power network.

The invention relates to a method for measuring liquid capacity of a pipeline based on ultrasonic guided wave technology, belonging to the technical field of testing and measuring and nondestructive testing. The method selects a longitudinal mode of the ultrasonic guided wave for measuring the liquid capacity of the pipeline, wherein, the longitudinal mode of the ultrasonic guided wave has an absolute value of group velocity at an excitation frequency position lower than 0.002m along with frequency variation rate, an average value of liquid distribution of axial displacement in the pipeline is more than 30 percent of the average value distributed on the pipeline wall, and the group velocity is monotonically increasing or reducing along with liquid flow rate in the pipeline. The method can measure the volume of the liquid capacity in a pipeline, in particular to a pipeline with small diameter, quickly and effectively.