Papers by Keyword: Harmonic Detection

Abstract: The extensive usage of power electronic equipments makes harmonic problem increasingly serious. In unbalanced three-phase system, traditional p-q, d-q method ignores the zero sequence currents, resulting in zero sequence harmonic leakage error. This article is based on the basic principle of instantaneous reactive power theory, it proposes a new type of harmonic detection algorithm, this algorithm does not need phase-locked loop nor do a matrix transformation, and can effectively avoid the zero order harmonic leakage error caused by coordinate transformation.In the end, using Matlab/Simulink environment to build models of traditional algorithm and improved algorithm .Through comparison, the simulation result shows that the improved algorithm is more accurate and more effective than the traditional one.

Abstract: In this paper, a new approach for harmonic detection in power signals based on fast modified S-transform (FMST) is proposed, which combines the advantages of the incomplete S-transform and the modified S-transform. Initially, the Fast Fourier Transform was performed and dynamic measurement values were obtained from the envelope of power spectrum, then the valid harmonic frequency points were detected by selecting the dynamic measurement values which were larger than the set thresholds. Further, the FMST was specifically performed on these major frequency points and a complex matrix was generated. The row vectors of the matrix reflected the phase and the time location information of harmonic disturbances, while the column vectors reflected the amplitude-frequency characteristics. And the feature vectors extracted from the complex matrix were used to detect the harmonic amplitude, phase and transient information. Simulation results validate the high accuracy, strong noise immunity and rapidity of the proposed approach.

Abstract: The excellent time–frequency resolution of the modified S-transform (MST) makes it an attractive candidate for analysis and detection of harmonic in micro-grid. This paper presents a new approach for micro-grid harmonic detection based on the MST. Firstly, the MST was performed for the harmonic signal, and then the feature vectors were extracted from the resulting time-frequency matrix. Finally, the frequency, amplitude and phase of the harmonic were obtained by analyzing and processing these feature vectors. Simulation results show that the proposed approach can detect the harmonic in micro-grid with high accuracy and strong noise immunity.

Abstract: Traditional FFT show good trait in steady-state harmonic testing, while it turn low accuracy when testing harmonic with voltage sag or transient, and can not illustrates the information on amplitude-time plane. The discrete wavelet transform is suitable for transient harmonic signals. However it is not intuitive and has more computing than FFT. Since both steady-state and transient components exist in power system, a new method of harmonic analysis algorithm based on Kaiser windowed FFT combing with Daubechies wavelet transform is proposed. The simulation results demonstrate this method possesses high accuracy and flexibility in harmonic detection.

Abstract: Distributed renewable energy connected to the power grid in the form of micro-grid, which makes a great impact on the power quality of the grid. Active Power Filter (APF) is a kind of effective device, which can improve the power supply quality and purify the power pollution. It‘s particularly significant to improve the APF’s performance. Based on the selective harmonic current control strategy, which is used to solve the problem, that the main times of the harmonic current is not sufficiently compensated, this paper considers to adopt the LCL filter on the grid-side to further improve the compensation performance of active power filter. This improvement can reduce the high frequency harmonics caused by the way of PWM high frequency modulation. Finally a case study simulated by PSIM software verifies the superiority of the proposed measure.

Abstract: As we all know FFT(Fast Fourier Transform) can be used analyze and calculate linear and stationary signals, while signals in reality are always nonlinear and transient, so we use HHT(Hilbert-Huang Transform) to detect them. In the past,scholars detect harmonics by applying ARM accompany with FFT. In this article, we use the development board S3C6410-as hardware platform. our processor is ARM, while the main algorithm is HHT.

Abstract: A new harmonic detection algorithm is proposed in this paper. According to characteristics of the electric power harmonic, identified harmonic model is obtained based on Fourier series, and introduced a bounded disturbance in the model. When the parameter in the model is identified, firstly the interference value is estimated by the output error, and then the identification error is estimated and used it to update parameters of the model. By using the interference estimation and identification error estimation, the parameters convergence speed is accelerated and the identification accuracy is improved, numerical examples simulation verify this.

Abstract: Based on DFBLD (Distributed Feedback Laser Diode) and harmonic detection technique, a novel fiber-optic methane detection system is constructed. The system can be applied to broad-range concentration detection of methane. Based on the approximation express of the law of Beer-Lambert, detection of methane with various concentration from 0% to 20% is completed using subtraction of background and ratio processing method, as the atmosphere surroundings are treated as background noise. The direct absorption spectra for various concentration is measured using GRIN gas cell, combined with DFBLD. The R5 line of the 2v3 band of methane is selected as the absorption peak. The system is tested online during gas mixing process and the linear relationship between system indication and concentration variation is validated. Also the stability and dynamic response characteristics are confirmed by the experiments. The sensitivity of the system can be adjusted according to the concentration level of various field environments by changing the prism distance using step motor. In the range of 0% to 20% the sensitivity of methane detection can arrive at 0.001%. So the system can be applied to various application fields and adopted as monitoring instruments for coalmine tunnel and natural pipeline.

Abstract: Aiming at the features of complexity, poor real-time and Low-accuracy of single-phase Active Power Filter (APF), and the problem of impossible parallel computation in the traditional DSP software realization, new design method of APF Based on FPGA is proposed, This paper focuses on the study of the harmonic current detecting method and improves control method of compensate current, it builds an experimental platform with FPGA EP1C12Q240C8 as the controller, the experimental results all support the effectiveness and correctness of the control methods and design methods of APF.

Abstract: Harmonic detection is one of the most important core part of Active Power Filter,which can quickly and accurately detect the harmonic current that is the premise of circuit to quickly output harmonic compensation current,therefore the pros and cons of the detection method,a direct impact on the effect of harmonic compensation.Time compensation method is to add a specific time compensation angle based on the method of instantaneous reactive power compensation,so that it can accurately detect the harmonic currents at the same time,minimize the low-pass filter time delay.By MATLAB simulation,the results show high detection accuracy.And to ensure detection and compensation,while fully to improve the real-time function of the filter.