120 results about "Spectral leakage" patented technology

The invention discloses a method for measuring electric network voltage flicker, and discloses a high-accuracy rapid flicker calculating method aiming at a non-integral cycle low sampling rate by taking account of errors probably caused by harmonic waves and electric network frequency. The core of the calculating method is that: a low fixed sampling rate is adopted to perform non-integral cycle sampling on electric network voltage waveforms, a cosine window is used for performing a fast Fourier transform algorithm (FFT), then the flicker frequency component is accurately extracted through a double-spectral line interpolation algorithm and a frequency spectrum searching algorithm, and the instantaneous flicker visual sensitivity is obtained through calculation. By using the method, under the condition of non-integral cycle low sampling rate, the errors caused by frequency spectrum leakage and harmonic wave aliasing are overcome, the frequency resolution is improved, the complexity of flicker calculation is effectively simplified, and a flicker measurement result is acquired quickly. By using the method, the performance requirement of hardware of an analog-digital converter, a processor and the like is reduced, thus the cost of a flicker measuring instrument is reduced, and simultaneously the measuring accuracy is improved; and besides, the method is applicable to fast low-cost measurement of the electric network voltage flicker, and has a very good effect.

The invention discloses a power system interharmonic wave detection method based on MUSIC spectrum estimation and a HBF neural network, comprising the steps of getting sampling data of detected signals by an analog-to-digital converter, getting various harmonic waves and interharmonic wave frequency contained in the signals through MUSIC spectrum estimation, and getting amplitudes and phases of the harmonic waves and the interharmonic waves through the adaptive adjustment of weights of the HBF neural network. The invention first provides the power system interharmonic wave measurement method based on the MUSIC spectrum estimation and the HBF neural network. The invention has the advantages of high frequency resolution without causing frequency spectrum leakage, high measurement precision of frequency, amplitudes and phases of the harmonic waves and the interharmonic waves, and high learning speed of the weights of the neural network, and is adaptive to on-line monitoring and off-line testing of interharmonic waves in the power system.

The invention discloses a high-accuracy sinusoidal signal measuring device for removing frequency spectrum leakage, comprising an analog signal pre-processing unit, a data acquisition unit, a digital signal processing unit, a measuring result display unit, and a communication interface unit, wherein the analog signal pre-processing unit is connected with the data acquisition unit through multipath signal wires, and the digital signal processing unit is connected with the data acquisition unit, the measuring result display unit and the communication interface unit respectively through an SPI (Serial Peripheral Interface) bus. The measuring method comprises the steps of: 1, continuously sampling a signal to be measured to obtain sequences S1 and S2; 2, carrying out fast Fourier transform onthe S1, extracting a peak frequency spectrum and obtaining the peak frequency spectrum of the S2 through recursion; 3, calculating the frequency of the signal to be measured by applying the peak frequency spectrums of the S1 and the S2; 4, calculating the phase of the signal to be measured according to the phase angle information of the peak frequency spectrums of the S1 and S2; 5, solving an equation set relevant to positive and negative frequency spectrum amplitudes to obtain the measured value of the amplitude of the signal to be measured; and 6, removing the influence of the frequency spectrum leakage to obtain the accurate measured valve of a direct-current component.

The invention provides a harmonic detection method based on Nuttall window four-spectral-line interpolation FFT (fast Fourier transform). The method comprises steps as follows: (1), a time-domain signal is subjected to discrete sampling, a discrete signal sequence is obtained, a four-term three-derivative Nuttall window is selected to perform windowing processing on the discrete signal sequence, FFT analysis is performed, and a value of each discrete frequency point is obtained; (2), a maximum frequency point value and a submaximal frequency point value are selected nearby each peak frequency point spectral line according to the value of each discrete frequency point, a maximum amplitude spectral line and a submaximal amplitude spectral line nearby each peak frequency point spectral line as well as two peripheral spectral lines are found out according to the maximum frequency point value and the submaximal frequency point value, and amplitudes of the four spectral lines are obtained; (3), a amplitude correction formula, a frequency correction formula and a phase correction formula of four-spectral-line interpolations are derived according to the amplitude information of the four spectral lines. The spectrum leakage inhibition effect is good, the correction errors are small, and the harmonic analysis precision is high.

The invention provides a power system frequency calculation method of windowing spectral line interpolation. The method includes the following steps that 1, voltage sampling data of ten continuous sampling cycles of a public connection point are obtained through a voltage measurement circuit; 2, time domain windowing function processing is conducted on the voltage sampling data; 3, local discrete Fourier transformation is conducted on the data obtained after windowing, and voltage amplitude values of specific harmonic wave times are obtained; 4, for the calculated specific voltage amplitude values, interpolation is conducted between the two adjacent maximal amplitude values; 5, calculation is conducted through a polynomial curve fitting method, a frequency coefficient is obtained, and thus fundamental wave frequency of a power grid is determined. By means of the method, a blackman window function is applied to N sampling points, local discrete Fourier transformation (DFT) is only conducted on designated harmonic frequency , it is proved through experiments that by means of the method, the spectrum leakage inhibition effect is good, the calculation speed is high, the calculation process is simple, precision is high, universality is high, and the method can be used for high-precision electric energy metering and electric energy quality analysis.

A synchrophaser measurement method applied to a P Class Phasor Measurement Unit (PMU), and is based on the dynamic phasor mathematical model. The method includes providing a low pass digital filter for phasor factors and applying Discrete Fourier Transform, so that the spectrum leakage caused by the dynamic phasor inputs is eliminated, and the raw phasor measurements after the spectrum leakage being eliminated can be obtained. In addition, the dynamic phasor inputs are fitted by using the second order Taylor series and the linear relationship between the measurement errors causing the Discrete Fourier Transform averaging effect and the second order coefficients of the Taylor series is explored. The linear relationship is used to correct for the raw measurement errors under a dynamic condition, and the accurate dynamic phasor measurements can thus be obtained. This measurement method can measure phasor accurately and rapidly under both static and dynamic conditions.

The invention relates to a method which reduces the orthogonal frequency division multiplexing signal spectrum leakage, belongs to the technical field of wireless and wire communications using orthogonal frequency division multiplexing (OFDM) signals, and aims at having lower achievement complexity, causing only small inference to the data sub-carrier of the OFDM signals and effectively reducing the signal spectrum leakage. The input data of the invention can obtain a time-domain sequence si(n) of the OFDM signals through serial-parallel conversion, inverse discrete fourier transform and parallel-serial conversion, plus cyclic prefix and guard interval, and generate a time-domain sequence ci(n) of the optimal offset signals to the si(n), and then superimpose the ci(n) and the si(n) which are then transmitted by a transmitter. In order to reduce compute complexity and reduce the interference of the offset signals to the data sub-carrier in the si(n), two offset signal producing methods are provided; the method of the invention reduces the OFDM signal spectrum leakage, improves the spectrum resource utilization rate, and can also be applied to the communication system using the multi-carrier technology.