417 results about "Harmonic analysis" patented technology

The invention relates to an axial circular runout and total runout single displacement error separation device and method, and belongs to the technical field of micro-nanometer ultra-precise measurement. In the method, an axial circular runout and total runout measurement device and an error separation system are organically integrated into a whole, a proper displacement angle alpha is selected in an error separation process, so that a workpiece performs a single small-angle displacement of a corresponding angle relative to a rotary main shaft, total harmonic separation of z(n) and g(n) in a harmonic range of between 1 and 100upr by measuring comprehensive errors A(n) and B(n) including a workpiece axial circular runout error g(n) and a main shaft rotary error z(n) before and after displacement of the workpiece, and utilizing fast Fourier series transform, harmonic analysis and other mathematic processing methods. According to the device and the system, when an existing error separation method is used for circular runout error separation, the defects that an error introduced by a rotary shaft cannot be completely separated, error separation time is long, various larger drifts are easily introduced and the like can be overcome, and the error separation device and the error separation process can be greatly simplified.

An inspection method for inspecting beads provided on a tire building drum in process of production a pneumatic tire includes measuring a displacement amount in a radial direction on each of the beads lying axially on both sides of the drum with a distance sensor such as an eddy current sensor while rotating the drum, synthesizing displacement amounts so obtained on the beads on both the sides, calculating a harmonic of the displacement amounts in the radial direction of the beads by performing harmonic analysis on a resultant synthesized displacement amount, and determining whether the magnitude of the harmonic so calculated falls within a predetermined range.

The invention discloses a harmonic modal analysis method for an offshore wind farm. The method comprises the steps of 1) building a system harmonic model according to an offshore wind farm system, namely a connection relationship between each component and a cable; 2) establishing a network admittance matrix of the system according to the system harmonic model, solving a modal impedance frequency spectrum of the system by utilizing a modal method, calculating a participation factor of each node, and determining a real occurrence position of harmonic vibration; 3) assessing the sensitivity of electric parameters of components of the system; and 4) assessing the sensitivity of design parameters of the system. According to the method, an equivalent model is built according to the parameter of each component of the wind farm, the harmonic performance of the system under different topological parameters, cable parameters, transformer parameters and other parameters is studied by applying the modal analysis method, and the topological design and component model selection of the wind farm can be optimized.

The invention discloses a frequency domain interpolation electric power harmonic wave analysis method based on discrete Fourier transform. The method comprises the following steps: (1) conducting time domain continuous signal discretization; (2) selecting an appropriate cosine-class window to weight a discrete sampling sequence according to measuring requirements; (3) performing fast Fourier transform on the sequence; (4) finding the two longest spectral lines close to harmonic waves in the form of spectrum peak searching, and calculating a spectrum value ratio between the two lines; (5) obtaining a frequency deviation according to a Newton interpolation method; and (6) further solving the amplitude, frequency and initial phase of sub-harmonic waves on the basis of the obtained frequency deviation. A fast interpolation based on table look-up is independent of a window function. The method is universally applied, and can be combined with any window function to conduct harmonic wave analysis. Meanwhile, no complex operation exits, the computational complexity is low, and the method is easy to realize in an embedded system.

The invention discloses a real-time monitoring and estimating system of power quality based on CAN bus for electric system and each class of power distribution system, which comprises the following network structures: data gathering layer as the first layer, which groups multiple stations to manage and transmits all the electric power network signal into standard voltage to the data gathering card; data disposing layer as the second layer, which converses the electric parameter by data gathering layer to realize the calculation and analysis of electric quality such as voltage fluctuation, harmonic analysis, flicker and so on; data transmitting layer as the third layer, which utilizes CAN bus to establish high-reliability opened data communicating circuit and realizes the conversion of order and data between middle control chamber PC set and working control machine; user layer as the fourth layer, which builds friend operational interface to provide display, storage, analysis and estimation function of the monitored data and makes the user to observe real-time data of wind electric-field operation directly.

The invention discloses a fault arc detection method. The method comprises the following steps that current signals are collected and subjected to harmonic analysis, the higher harmonic ratio is calculated, the higher harmonic ratio in a current time period is obtained by collecting signals within the time period set before and after switch-on and switch-off of a circuit, and then a time-related mathematical model of the higher harmonic ratio of the circuit is obtained; the change of the higher harmonic ratio of the circuit at the moment of being switched off is calculated and compared with the actual change of the higher harmonic ratio of the circuit; if the frequency that the actual higher harmonic ratio is higher than a theoretical higher harmonic ratio is larger than a threshold value, it is regarded that a fault arc happens. The fault arc detection method has the advantages that a unique model for the circuit is obtained by analyzing the circuit, and analysis in advance is not needed.

The invention belongs to the technical field of micro-grid signal processing, and relates to a micro-grid harmonic and inter-harmonic analysis method based on cubic spline interpolation waveform reconstruction. The method comprises the following steps of: sampling the original measuring signal at a given sampling frequency to acquire the original sampled signal; analyzing the original sampled signal to determine the actual fundamental frequency of a system by using a Hanning windowed double interpolation fast Fourier transform (FFT) algorithm; obtaining the corrected sampling frequency according to the actual fundamental frequency of the system; reconstructing a sampling waveform by using a cubic spline interpolation algorithm; processing the reconstructed signal sequence to determine fundamental waves and all harmonic components by using the Hanning windowed double interpolation FFT algorithm; subtracting the solved fundamental waves and each harmonic component from the original sampled signal; and determining each inter-harmonic component by using the Hanning windowed double interpolation FFT algorithm. By the method, spectrum leakage and a picket fence effect which are generated during harmonic analysis can be effectively reduced, and micro-grid harmonic and inter-harmonic analysis accuracy is improved.

A method for separating roundness error of single transposition includes selecting proper transposition angle a for carrying out single small angle transposition in relevant angle to rotation major axis and realizing complete harmonic separation of z(n) and g(n) as in scope of 1-100 upr harmonic wave by measuring workpiece error g(n) and major axis transposition error z(n) before and after workpiece transposition as well as utilizing quick. Fourier series transform and harmonic analysis.

The invention discloses a cascade inverter H-bridge unit short circuit fault detecting method based on harmonic analysis of switching frequency, which is suitable for a carrier phase-shifting PWM (pulse width modulation) manner based on the harmonic analysis to output phase voltage and comprises three parts, namely output alternating voltage sampling, extracting and processing of harmonic wave close to the switching frequency, and fault judging and fault locating. Three-phase output voltage of a cascade inverter is respectively subjected to low-pass filtering and A/D (analog-to-digital conversion) sampling, and is subjected to discrete Fourier transformation to obtain characteristic harmonic; a comparison result of the characteristic harmonic amplitude and a fault threshold is utilized as the evidence of fault judging, wherein the fault threshold is obtained by carrying out a series of calculation on command voltage. The fault locating is determined through a phase angle range of the harmonic of the switching frequency. According to the cascade inverter H-bridge unit short circuit fault detecting method based on the harmonic analysis of the switching frequency, which is disclosed by the invention, the three-phase output voltage of the inverter is collected, and no other hardware circuit is additionally arranged, so that the cost is reduced, and the efficiency is improved; the application capability is strong, and the application value in the study on the real time fault detection of the cascade inverter exists.