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APPLICATION OF DIGITAL COMPUTERS TO POWER SYSTEM PROTECTION.
... The proposed algorithm can locate the fault without line parameter values and resists the influence of data error due to measurement, background noise, and fundamental component calculation using a DFT (discrete Fourier transform [20]) algorithm to some degree. ...
... Therefore, the solving of the equations can be transformed into a minimization problem in the form of Equation (20), where ‖ ( )‖ = ( ) × ( ) : ...
T-type transmission lines have been increasingly used in distribution networks because of the distributed generation integration, but inaccurate line parameters will cause significant error in the results of most existing fault location algorithms for this kind of line. In order to improve the precision, this paper proposes a new fault location algorithm taking line parameters as unknowns. The fault is assumed to occur on each section, and corresponding ranging equations can be built based on one set of three-terminal post-fault synchronous measurements, without using line parameters as inputs. Then, more sets of measurements are utilized to increase the redundancy of equations to resist the influence of data error. The reliable trust-region algorithm is used to solve each group of equations, but only equations of the assumed faulty section with the actual fault point can give the reasonable solutions, accordingly identifying the fault point. The performance of the proposed method is thoroughly investigated with MATLAB/Simulink. The results indicate that the algorithm has a high accuracy and is basically unaffected by fault position, fault resistance, unbalanced fault type, line parameter, and data error.
... 2) Algoritmo Recursivo de Fourier O algoritmo de Fourier de ciclo completo foi primeiramente proposto em [9] com a finalidade de determinar a amplitude e a fase a partir de suas medições uniformemente amostradas. . ...
... para a k-ésima fase. Considerando-se, cada função de contorno como uma função de cosseno [9], o perfil da corrente f k (θ) individual de fase pode ser determinado a partir dos requisitos do conjugado e do perfil da indutância. ...
... Thus, smart Signal Processing Techniques (SPTs), especially focused on the signals analysis together with digital signal processors, data storage broad, fast communication, and others, new methodologies could be proposed. In this context, several research projects, not only assuming the disturbance signal to be sinusoidal [40,41] but also proposed protection algorithms based on the detection of signal peak values were proposed. However, this assumption is not always true, especially if one considers distortion due to transient signals especially to lightning strokes. ...
The automatic location of lightning stroke impact point on transmission lines is one of the most crucial factors related to the behavior of Electric Power Systems, which can improve the swift recovery of electric power. The usual location of this phenomenon has been based on distance protection relays, which requires operation times of approximately one cycle. This paper presents a high-speed protection approach for the lightning-caused transient automated location on transmission lines or on ground. This work is based on the synchronized initial voltage-travelling waves at both ends of high voltage transmission lines. Lightning strikes at different sections along the 220. kV transmission line are detected at both protection relays by using an algorithm based on the ellipsoidal pattern previously presented in another research project. That methodology uses the projection of original signals. Thus, if these signals are located along the ellipsoidal pattern, the electric power system is operated under normal conditions. Unlike the aforementioned case, if the projected signals are located outside of the ellipsoidal pattern, it represents the presence of lightning strokes. After those signals are detected, initial voltage traveling waves measured by protection relays located at both ends of the transmission line are used in order to localize the lighting stroke impact point. At the instant that a lightning stroke hits either on the phase conductor or the ground, travelling waves propagate along the transmission line. Later on, depending on the impact point of atmospheric discharges, different time instances, which the travelling waves require to arrive at their respective ends, are determined. These times are used to calculate the distance from the impact point to both protection relays. Therefore, this paper presents a concise simple methodology for lightning stroke location on transmission lines or ground based in data mining to perform the signal detection and travelling wave times to determine the location along the transmission line. Simulations of lightning stroke signals on a 220. kV transmission line are carried out in the Alternative Transients Program (ATP). The results show that the behavior of the work is swift and effective in order to locate the impact point, especially in situations where flash current values, inception angles, distances from the impact point to protection relays, direct and indirect lightning and other factors, are considered, since it is immune to flash currents and other features. Finally, the proposed work could be considered as an alternative routine for protection relay algorithms.
... Over the last two decades various digital protection techniques have been developed aiming at overcoming the limitations of conventional distance relays [4][5][6][7][8][9][10][11][12]. In these techniques voltage and current samples are used to extract the fundamental voltage and current components to estimate the apparent impedance seen by the relay up to the fault location. ...
This paper presents a neural network based approach for three-zone distance protection of transmission lines. The proposed neural-network distance relay comprises three modular identical feedforward neural networks. The first unit is trained for main protection of a transmission line section, whereas the other two units are trained to provide back-up protection for the adjacent line sections. Each neural network is fed with the fundamental frequency voltage and current magnitudes. The output of each neural unit (1 or 0) thus determines if a fault is internal or external to its protection zone. Coordination of the three neural networks and initiation of the tripping signal is implemented through a digital logic circuit. The simulation results presented in this paper show that the proposed neural-network distance relay is very effective in detection and classification of the fault location, and therefore can be considered as a good tool for main and backup digital distance protection.
... Therefore their settings have to be reset for changes in the network configuration.123. Over the last two decades various digital protection techniques have been developed aiming at overcoming the limitations of conventional distance relays456789101112. In these techniques voltage and current samples are used to extract the fundamental voltage and current components to estimate the apparent impedance seen by the relay up to the fault location. ...
This paper presents a neural network based approach for three-zone distance protection of transmission lines. The proposed neural-network distance relay comprises three modular identical feedforward neural networks. The first unit is trained for main protection of a transmission line section, whereas the other two units are trained to provide back-up protection for the adjacent line sections. Each neural network is fed with the fundamental frequency voltage and current magnitudes. The output of each neural unit (1 or 0) thus determines if a fault is internal or external to its protection zone. Coordination of the three neural networks and initiation of the tripping signal is implemented through a digital logic circuit. The simulation results presented in this paper show that the proposed neural-network distance relay is very effective in detection and classification of the fault location, and therefore can be considered as a good tool for main and backup digital distance protection.
... Over the last three decades various digital protection techniques have been developed aiming at overcoming the limitations of conventional distance relays [2][3][4][5][6]. In these techniques voltage and current samples are used to extract the fundamental voltage and current components to estimate the apparent impedance seen by the relay up to the fault location. ...
This paper presents an artificial neural network (ANN) based approach for three-zone distance protection of transmission lines. The proposed neural network-based distance relay has multilayer feedforward architecture with two inputs and three trip/(no trip) output signals. The first output is responsible for main protection of the transmission line section, whereas the other two outputs provide back-up protection for the adjacent line sections. The input features of the neural network are the fundamental frequency voltage and current magnitudes extracted by discrete-Fourier transform. In this paper, the backpropagation training technique has been used for off-line training of the proposed ANN distance relay. The input-output patterns were simulated for faults covering the three zones of protection at different locations, operating conditions, and fault inception angles. The simulation results presented in this paper show that the proposed ANN distance relay is very effective in detection and classification of line faults and therefore can be considered as a good tool for main and backup digital distance protection.
... Larson implemented the FIR algorithm for protection of a 500VA power transformer using 14C6800 microprocessor. The relay discriminated the error between 1.25 to 1.5 cycles [9]. Degens used least square curve fitting in order to determine the ratio of the second harmonic to the first one in differential current for detecting inrush current. ...
In order to analyze a signal, wavelet transform can be applied as well as Fourier transform. Fourier transform and its inverse can transform a signal between the time and frequency domains. Therefore, it is possible to view the signal characteristics either in time or frequency domain, but not the combination of both domains. Differently from the case of Fourier transform, the Wavelet Analysis (WT) provides a varying time-frequency resolution in the time frequency plane. In this paper, a new method for protecting power transformers based on the energy of differential-current signals is introduced. The simulation results show that it is possible to detect different kinds of internal faults using this method. Furthermore, it is possible to distinguish such faults from magnetizing inrush current.
... B Decompose circulating current phasor Ramamoorthy[10] first proposed that the desired fundamental voltage or current be extracted from the distorted signal by correlating one cycle of data samples with the stored samples of reference fundamental sine and cosine waves. According to this method, the R axis component and Q axis component of circulating current phasor are derived. ...
Parallel multi-inverter systems can be designed to have the advantages of expandable output power, improved reliability, and easy N+X redundancy operation. However, a current-sharing control scheme has to be employed to enable the inverters to share the load current equally. The concept of circulating impedance is proposed in the paper, and introduced into current-sharing control scheme in parallel multi-inverter systems. The mathematical model of circulating impedance is set up. By introducing circulating-impedance control regulator, the characteristic of circulating-impedance is controlled to be similar to that of the pure resistance or inductance. Then the relationship between the circulating-current phasor and the amplitude, the phase of inverter module's output voltage reference is decoupled. Experimental 220 Vac/3 KVA inverter modules are built and parallel operated. The results of experiment verify that the current-sharing scheme based on circulating impedance is available and efficient.
... This is the phasordomain approach where voltage and current phasors are either compared [2,3], or used for measuring the fault impedance [4][5][6][7][8][9][10][11][12]. Phasors are computed by using some of the well-known methods of signal processing, such as: Fourier method [13][14][15], least error squares [16][17][18][19], wavelet method [20][21][22][23], and Newton's method [24][25][26]. ...
In this paper we propose a distance relay algorithm based on a time-domain phase comparator with a smaller computational burden than the traditional phasor-domain based algorithms. The phase comparator used in the time-domain algorithm is based on the average power on a half and full-cycle data window. The algorithm includes a filter which mitigates decaying DC-offset in the current as well as the capacitive coupled voltage transformer transients. The algorithm is compared to an algorithm based on the phasor-domain approach with full-cycle DFT. Both algorithms are tested on various fault locations, fault resistances, load directions, inception angles and SIR. This paper also includes analysis of the complex frequency response of the complete time-domain algorithm, and how the protected zone for a chosen operating characteristic depends on the line load and SIR.
... High frequency signal components, such as the third harmonic, affect the performance of the algorithm too. Ramamoorty [7] and Phadke et al. [8] correlate the sample data with those obtained from a reference sinusoid using, respectively, a complete cycle and a half cycle to extract the fundamental current and voltage from the transient. The full-cycle correlation yields high accuracy at a slow speed, while the half-cycle method improves the speed at the cost of reduced accuracy, especially when d.c.-offsets and harmonics are present in the signal. ...
... The parameter of interest for the relaying application is contained in the waveform description. The appropriate algorithms for the waveform model include Fourier algorithms [2], Wash type algorithms [3] and Curve fitting algorithms [4]. COMTRADE format record is categorized in this category. ...
This paper describes the process of extracting the fault information from common format for transient data exchange (COMTRADE) record. The COMTRADE format record was obtained from the distance relay recording device, provided by the Protection Department of Tenaga Nasional Berhad (TNB). A graphical user interface (GUI) simulation program using MATLAB was developed which implements the one-cycle cosine filter relaying algorithm to digitally filter out the unwanted signals at system's fundamental frequency from the COMTRADE record. This work aims to help the TNB protection engineer to have a faster solution in parameter extraction from protective relay recorded from substations in COMTRADE format.
Digital filters made with the use of discrete Fourier Transform are applied in most microprocessor protections produced both in the home country and abroad. When the input signal frequency deviates from the value to which these filters are configured, a signal is generated at their output with oscillation amplitude that is proportional to the deviation of the signal frequency from the specified one. The article proposes an algorithm for compensating the oscillations of orthogonal components of the output signals of digital filters implemented on the basis of a discrete Fourier transform, when the input signal frequency deviates from the nominal one. A mathematical model of the proposed digital filter with an algorithm for compensating the oscillations of its orthogonal components, as well as a signal model for reproducing input effects, is implemented in the MatLab-Simulink dynamic modeling environment. The digital filter model is provided with two channels, viz. a current channel and a voltage channel, which makes it possible to simulate their operation in relation to protections that use one or two input values, for example, for current and remote protection. Verification of the functioning of the digital filter model with compensation for fluctuations in its output signal was carried out with the use of two types of test effects, viz. a sinusoidal signal with a frequency of 48–51 Hz (idealized effect), and the effects that are close to the real secondary signals of measuring current transformers and voltage transformers in case of short circuits accompanied by a decrease in frequency. The conducted computational experiments with deviation of frequency from the nominal one, revealed the presence of undamped oscillations at the output of standard digital Fourier filters and their almost complete absence in the proposed digital filters. This makes us possible to recommend digital filters based on a discrete Fourier transform supplemented by an algorithm for compensation of fluctuations in the amplitudes of the output signals for the use in microprocessor protection.
On lines outgoing from the busbars of power stations or sub-stations of power systems, it is often necessary according to the stability conditions to clear faults within the entire protected line without time delay. This leads to the concept of unit protection whereby sections of the power systems are protected individually without reference to other sections. One of the relays that performs this function is the longitudinal biased differential relay.
This paper presents the theory and simulation results of a new fault-distance identification algorithm for transmission line distance protection using computer. Following a brief introduction indicating the increasing importance of digital relaying, the derivation of the proposed algorithm is given, wherein it is shown that the time curve of the fault current for a line section of unit length can be formulated in terms of the line voltage-time curve and the line longitudenal parameters, namely, the resistance and inductance. Thus, an estimate of the distance to the fault is computed from the division of line's actual fault current by the corresponding values of the theoretical current for a fault at the end of the unit-length line, using the same voltage signals for both currents. The analysis includes also the derivation of the algorithm's frequency response.
A phasor estimation algorithm, which uses orthogonal full-cycle filters in conjunction with an adaptive filtering of the decaying DC component, is presented in this paper. The full-cycle orthogonal filters are designed using a technique which combines the maximum overlap discrete wavelet transform and the least error square algorithm. The decaying DC component elimination is performed using an adaptive digital mimic filter. The frequency and time responses of the proposed algorithm are compared with those of other full cycle algorithms reported in the literature on the subject. The obtained results reveal that the proposed algorithm rejects all harmonics, is less sensitive to interharmonics, presents better transient responses and can be faster than other full cycle algorithms.
This paper reports the development of two computationally simple expressions (suitable for implementation on microprocessor) for extracting the fundamental frequency components present in distance relaying signals. The original expressions based on Fourier series and Walsh and Haar functions involve multiplication complexity, and have been simplified without adversely affecting the frequency response. The resistance and reactance computed with the proposed simplified expressions do not show any significant change over those computed with unmodified expressions.
Currently, most industrial power modules, even IPEMs (Intelligent Power Electronics Modules), are interconnected in a planar way, and interconnections are made with bonding wires. This paper presents a three dimensional interconnection solution based on the idea to flip chip the gate driver directly on the surface of the power device, simplifying and optimizing the packaging and the interconnections among the two devices and improving the overall performances. Various approaches and interconnection solutions will be presented in this paper, and the advantages of the chosen approach will be discussed. Then the technological process for the realization of the interconnections will be explained, and practical realizations will be shown.
A scheme for detection, classification and location of transmission line faults, which combines the wavelet multi-resolution analysis approach and the differential equation approach, is presented. While detection and classification of faults is carried out by a wavelet analysis based algorithm, fault location is determined by a differential equation based algorithm. Using EMTP and MATLAB, studies have been carried out on two simulated power system models. The models are subjected to different types of faults while operating at different operating conditions and the performance of the proposed scheme is evaluated. The results of the simulation studies, which are presented, confirm the feasibility of the proposed scheme.
Most protective relaying schemes use single frequency information from transient current/voltage signals to discriminate faults. In microprocessor based protective relaying, digital filtering is an attractive method of extracting effective frequency components. This paper presents three digital filtering methods based on frequency-spectral analysis for microprocessor based protective relaying: unit-combined filters, assigned zero-points filters and narrow band-pass filters. Test results are also presented.
The performance assessment of a symmetrical component based fault impedance estimation method that has previously been proposed by the authors is discussed in this paper. A brief review of the proposed method is given. The personal computer based Alternative Transient Program was used in these performance assessment studies. Voltage and current signals for various fault conditions were generated by simulating different types of fault on a selected transmission line of a sample power system. These signals were processed, sampled, and used in the proposed method. The apparent impedance of the protected transmission line from the relay location up to the fault point was calculated using the proposed method. These impedance estimates were inserted in R − X plane characteristics to determine the suitability of the proposed method for digital distance protection of the second and third zones. The results of these performance assessment studies are presented and discussed in the paper.
System impedance calculation for distance relaying requires extraction of fundamental frequency components from highly distorted post-fault relaying signals. Many algorithms are available for extracting the fundamental frequency component, but most of them involve a large amount of computation, whilst others have low accuracy, or poor convergence, or both. This paper describes two algorithms based on the Hartley transform. They are computationally simple, have good frequency response and give fast convergence in the calculation of resistance and reactance. Their efficacy has been examined using representative voltage and current relaying signals. The results obtained and presented here are gratifying.
A distance protection scheme for transmission lines based on analyzing the measured voltage and current signals at the relay location using fast orthogonal search (FOS) is presented in this paper. FOS has the ability to accurately provide fast estimate of the voltage and current fundamental frequency phasors that are required for a digital distance relay. Compared to the conventional FFT, FOS can estimate the fundamental phasors with higher accuracy and less number of samples. The proposed scheme has been tested on a transmission line model to verify the merit of this approach. The tests presented include solid ground faults, phase faults, and high impedance faults at different fault locations and loading conditions. The proposed scheme can classify all fault cases in less than one cycle after the inception of the faults.
The objective of this work is to present an algorithm for estimating the distance to the fault location for use in digital protection of transmission lines. The proposed scheme is based on the observation that for a line with zero shunt admittance, the fault current is inversely proportional to the fault distance. Assuming the current for a fault occurring at a distance of unity is available, the unknown distance to the fault can be estimated from the ratio of the assumed unity-distance fault current and the actual fault current. A detailed derivation of the algorithm is presented, and simulated test results on a 345 kV line are included. A comparison of the computational requirements, and hence the complexity of implementation and speed of response, is made vis-a-vis some of the well known approaches.
This work presents performance comparisons and evaluations of six different digital distance relay algorithms. In this work, steady state and transient behavior of the algorithms are evaluated. For this purpose, a digital distance relay is simulated by a digital computer. Different faults have been generated by EMTDC software and fault voltage and current waveforms have been given to the distance relay. Operation of the distance relay has been investigated for different faults and the operation of different algorithms are compared.
This paper presents the novel single-phase 3-level PWM inverter to
alleviate the harmonic components of output voltage and current under
the conditions of identical supply DC voltage and switching frequency to
the conventional inverter. The operational principles and analysis are
performed and the switching functions are derived. The deadbeat
controller is also designed and implemented for the inverter to keep the
output voltage sinusoidal and to have high dynamic performances even in
the cases of load variations and the partial magnetization in the filter
inductor. The validity of the proposed inverter is proved from the
simulated and experimented results
A load sharing control based on the frequency and voltage droop
concept for parallel operation of two three-phase uninterruptible power
supply (UPS) systems with no control interconnection lines is presented
in this paper. First of all, due to the use of active power and reactive
power as control variables, the characteristics of output powers
according to amplitude and phase differences between output voltages of
two UPS systems are analyzed. Secondly, simulation results with
different line impedance are demonstrated the feasibility of the
wireless load sharing control. Finally, experiments are presented to
verify the theoretical discussion with two three-phase 20 kVA UPS
systems employed TMS320C32, a kind of real time digital signal processor
(DSP)
In order to maintain a high quality output voltage, conventional
UPS systems use complex filters with large passive components. To
overcome this drawback, real-time feedback control schemes have been
investigated. However, these techniques require a high inverter
switching frequency to dynamically adapt to changing load conditions and
reduce harmonics of the output voltage, thereby rendering the system
inadequate for high power applications. This paper presents real-time
digital signal processor (DSP) control of a UPS system feeding nonlinear
loads to provide sinusoidal inverter output voltage. The control scheme
is composed of an RMS voltage regulator, the load current harmonics
regulator for the cancellation of output voltage harmonics and the
output voltage harmonics regulator for system stability. The controller
employs a Texas Instruments TMS320C40GFL50 DSP
Filtering requirements for power system distance relays are very
critical, because they must estimate precisely and quickly the
electrical distance to the fault, even with highly distorted input
signals. A number of digital filtering algorithms for distance relays
have been proposed and some of them are in use in practical relays;
however, power system evolution increases the corruption level of
signals and imposes the necessity of continuing the research efforts in
this area. In the present paper, a comparative evaluation of different
digital filtering algorithms for distance protection is performed. An
evaluation method is proposed, which gives comprehensive information
about filter transient behavior over a wide frequency range of noise.
The discussion is focused in well-known algorithms based on Fourier and
Walsh transforms, and includes a recently proposed combined sine-cosine
filter
The authors describe the design and implementation of a novel
microprocessor-based relay for transmission line protection. The design
incorporates two digital relaying techniques which operate in parallel.
Their outputs are fed to a voter logic which is programmed to achieve a
high level of dependability. The performance of the relay was evaluated
using fault data generated by the Electro-Magnetic Transient Program.
The results of the tests show that the proposed relay provides
reasonable outputs for all types of fault. The profile of the trip
counter also shows that the relay performs satisfactorily. With a
threshold of five, the voter logic module issued a trip command in less
than one cycle
This paper describes a new probabilistic technique for fault classification to be used in digital distance protection of power systems. The new technique is based on an adaptive Kalman filter using voltage measurements. The voltage data of each phase is processed in two Kalman filter models simultaneously. One Kalman filter assumes the features of a faulted phase while the other has the features of an unfaulted phase. The condition of the phase, faulted or non-faulted, is then decided from the computed a posteriori probabilities.
This paper develops state models for estimating the optimum performance of analog and computer impedance relays in the presence of noise due to non-fundamental frequency components. An Extended Kalman filter is used to determine the optimum estimates and error covariance of impedance magnitude and phase angle. lt is shown that impedance relays have performance limits dependent upon the amount of noise present. The effects of sampling rate of input signals, data-window used for fault detection, and cut-off frequency of anti-aliasing filter on the performance of a computer relay are also investigated. Digital computer simulation results for both analog and computer impedance relays are presented.
During the first cycle following a power system fault, a high speed computer relay has to make a decision usually based on the 60 Hz information, which is badly corrupted by noise. The noise in this case is the nonfundamental frequency components in the transient current or voltage, as the case may be. For research and development purposes of computer relaying techniques, the precise nature of the noise signal is required. The autocorrelation function and variance of the noise signal was obtained based on the frequency of occurrence of the different types of faults, and the probability distribution of fault location. A new technique for modelling the signal and the measurements is developed based on Kalman Filtering theory for the optimal estimation of the 60 Hz information. The results indicate that the technique converges to the true 60 Hz quanitities faster than other algorithms that have been used. The new technique also has the lowest computer burden among recently published algorithms and appears to be within the state of the art of current microcomputer technology.
A stand-alone digital relay has been designed and implemented. The
relay can be modified easily to accommodate the protection of different
types of transformers by changing the software only. Presented in this
paper are the real-time experimental results of five selected algorithms
implemented using this digital relay. These algorithms are: discrete
Fourier transform, Walsh function, rectangular transform, finite impulse
response and least-square. Based on the experimental results, the
discrete Fourier transform (DFT) algorithm is found to be the best
algorithm in terms of accuracy and speed for digital implementation of
the differential relay for power transformers
A distance relay for the protection of transmission lines is
usually designed on the basis of fixed settings. The reach of such
relays is therefore affected by the changing network conditions. The
implementation of a pattern recognizer for power system diagnosis can
provide great advances in the protection field. This paper demonstrates
the use of an artificial neural network as a pattern classifier for a
distance relay operation. The scheme utilizes the magnitudes of three
phase voltage and current phasors as inputs. An improved performance
with the use of an artificial neural network approach is experienced
once the relay can operate correctly, keeping the reach when faced with
different fault conditions as well as network configuration
changes
The author presents a technique which can effectively compute
transmission line impedances. The algorithm assumes that the input is
composed of a fundamental frequency component, a decaying DC-offset
transient and a number of nonharmonic components with unknown
frequencies. The decay rate is not assumed in advance because it is
affected by the resistance of the arc at the fault point, and the
effective resistance of the system. To indicate the degree of
improvement in impedance measurements obtained by using the technique as
compared to earlier techniques, the Fourier algorithm was selected as a
reference of comparison. The technique was tested using simulated data
generated from a software program, and data recorded at a 220 kV
switching station. Some of the test results are included
Filtering requirements for distance relays are very critical,
because they must estimate precisely and quickly the electrical distance
to the fault, even with highly distorted input signals. A number of
digital filtering algorithms for distance relays have been proposed and
some of them are in use in practical relays; however, power system
evolution increases the corruption level of signals and imposes the
necessity of continuing the research efforts in this area. In the
present paper, a comparative evaluation of different digital filtering
algorithms for distance protection is performed. An evaluation method is
proposed, which gives a comprehensive information about filter transient
behavior on a wide frequency range of noise. The discussion is focused
in well-known algorithms based on Fourier and Walsh transforms, and
includes a recently proposed combined sine-cosine filter
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