Single Low-pass Filter Research Articles

SOGI-FLL Grid Frequency Monitoring with an Error-Based Algorithm for a Better Response in Face of Voltage Sag and Swell Faults

The SOGI-FLL (second-order generalized-integrator frequency-locked-loop) is a well-known and simple adaptive filter that allows estimation of the parameters of the grid voltage with a small computational burden. However, this structure has shown to be sensitive to the events of voltage sags and swell faults, especially to voltage sags that deeply distort the estimated frequency. In this paper an algorithm is proposed to face the fault that modifies the SOGI-FLLs gains in order to achieve a better transient response with a reduced perturbation in the estimated frequency. The algorithm uses the SOGI’s instantaneous and absolute error to detect the fault and change the SOGI-FLL gains during the fault. Moreover, the average of the absolute error is used for returning to normal operating conditions. The average value is obtained by means of a single low pass filter (LPF). The approach is easy to implement and represents a low computational burden for being implemented into a digital processor. The performance is evaluated by using simulations and real-time Typhoon Hardware in the Loop (HIL) results.

Improved harmonic detection method based on ip-iq theory

Based on the traditional ip-iq harmonic detection theory, the accuracy of harmonic detection is easily affected by the phase-locked loop (PLL) output phase error, and the single low-pass filter (LPF) detection accuracy and filtering effect cannot be simultaneously. In this paper, an improved harmonic detection method based on the second-order generalized integrator-frequency locked loop (SOGI-FLL) technique is proposed to generate sine and cosine signals with the same frequency as the grid voltage; The traditional low-pass filter and average filter are used in series to improve the response speed and accuracy. Through theoretical analysis of the improved harmonic detection method and simulation in MATLAB environment, the theory and simulation results prove the effectiveness of the improved method.

The features of the use of energy storage devices in the railway power supply system

The pulsating mode of the power consumption in the railroad power supply network is the cause of the occurrence of voltage pulsations in the contact network. This leads to a decrease in the efficiency of the energy system. The purpose of this work is to develop means to improve the quality of the electrical energy of the railroad power supply system and formulate recommendations for their use. To compensate power fluctuations in the electric power supply network of the railway, it is proposed to use hybrid electric energy storage devices. The use of two-channel additional traction power station with an appropriate control system was proposed. The basis of the mathematical model is the data of real measurements. To suppress the power pulsations in the power supply system of the railway, it was proposed to use two-channel additional traction power station. The paper presents DC-DC converter with CF and VF terminals. As a result, dynamic losses are reduced and higher operating frequencies could be achieved. The possibility to transfer power in both directions allows the topology to be applied in high power battery applications. The possibility of using a single low-pass filter for the generation of control signals for both low-frequency and high-frequency channels of system is proven. The use of effective methods of balancing voltage levels in accumulators’ stack makes it possible to reduce the power of losses in the converter by 10-15%

Multi-D Wavelet Filter Bank Design Using Quillen-Suslin Theorem for Laurent Polynomials

In this paper we present a new approach for constructing the wavelet filter bank. Our approach enables constructing nonseparable multidimensional non-redundant wavelet filter banks with FIR filters using the Quillen-Suslin Theorem for Laurent polynomials. Our construction method presents some advantages over the traditional methods of multidimensional wavelet filter bank design. First, it works for any spatial dimension and for any sampling matrix. Second, it does not require the initial lowpass filters to satisfy any additional assumption such as interpolatory condition. Third, it provides an algorithm for constructing a wavelet filter bank from a single lowpass filter so that its vanishing moments are at least as many as the accuracy number of the lowpass filter.

Sequence detection in nonlinear channels: a convenient alternative to analog predistortion

A new maximum-likelihood sequence detection receiver for spectrally efficient linear modulations on bandlimited bandpass nonlinear channels is proposed. The receiver is based on oversampling the received signal corrupted by noise and nonlinear distortion. Contrary to other solutions in the literature, in the proposed technique there is no need for a bank of matched filters, and the receiver front end reduces to a single lowpass filter. For a given peak power level, a performance gain can be achieved over more traditional approaches to transmission on nonlinear channels, such as those based on predistortion, if a moderate spectral expansion is allowed. To analyze the receiver performance, the concept of distance spectrum is employed, since the minimum distance alone cannot account for a reliable performance evaluation. Both analysis and simulation are carried out for realistic narrowband nonlinear channels, possibly employing reduced-state sequence detection. Appreciable gain margins are confirmed to be possible in these realistic cases.

Automatic Recording Instrument for Measuring Optical Transfer Functions

An instrument is described which is capable of recording automatically both the amplitude and the phase of the O. T. F., as would be required by a test laboratory. A simplified version permits a continuous display on a C. R. T. and this is suitable for rapid workshop assessment of lens performance. The basic system consists of an object generator, an image analyser, and an electronic processing unit. By imaging part of a rotating radial grating on to a slit and then varying the orientation of the lines with respect to the slit it is possible to generate a periodic test pattern of constant contrast but in which the spatial frequency varies over a range of 100 to 1 and includes zero c/mm. The image of this object produced by the lens under test drifts at a constant rate over an analysing slit and photo-multiplier. A single low pass filter selects the fundamental of the photo-multiplier signal and this is proportional to the amplitude of O. T. F. of the lens under test. A reference optical system and photo-multiplier is used to measure phase and to provide a facility for null measurement by phase coherent detection.