Patricio G. Donato

Variable Sampling Period Filter PLL for Distorted Three-Phase Systems

This paper proposes a novel variable sampling period filter phase-locked loop (VSPF-PLL) for use in the general area of three-phase systems. It is based on the concept of variable sampling period, which allows to automatically adjust the sampling frequency to be NPLL times the line frequency. Conventional three-phase PLL are based on synchronous reference frames (SRFs) to estimate the phase error between the PLL and the input signals. However, SRF transform fail when the voltage waveforms are distorted. In this paper, a sliding-Goertzel-transform- based filter is used in the loop to reject disturbances, such as unbalanced voltage and harmonics. It allows to detect the positive sequence present in the systems without errors. Characteristics of VSPF-PLL, including its mathematical model as well as steady state and dynamic responses, are discussed in this paper. The method is implemented in a DSP and tested using typical disturbances, such as frequency steps, unbalances, harmonics, saturation, and line-to-ground fault. Comparative simulations are performed between the proposed VSPF-PLL and some of the most common three-phase PLL described in the literature. Advantages of the proposed system over the methods analyzed are also discussed. Structural simplicity, robustness, and harmonics rejection are other attractive features offered by the proposed system.

Frequency Adaptive PLL for Polluted Single-Phase Grids

This paper proposes a frequency adaptive phase-locked loop (PLL) for use in single-phase systems. The main objective is to obtain a reliable synchronization signal even in polluted grids, where the fundamental frequency is contaminated with harmonics, or present variations in phase, amplitude, and/or frequency. The proposed PLL is based on the concept of a variable sampling period technique, already implemented in a three-phase digital synchronization method proposed by the authors. This single-phase method allows us to automatically adjust the sampling frequency to be an integer multiple of the line frequency. In this case, the phase error is calculated just by one multiplication, thereby reducing implementation. A sliding Goertzel transform-based filter is also used in the loop to reject the undesired effects of this phase error detector and line disturbances, such as harmonics. To stabilize the loop, a controller that maximizes the bandwidth with an acceptable transient is introduced. The characteristics of the proposed single-phase PLL are described and the experimental results obtained from a DSP implementation are presented. A set of comparative simulations between the proposed PLL and some single-phase PLL described in the literature are conducted to validate the method. The advantages of the proposed system over other methods analyzed are also dealt with. The robustness of the system is verified by the experimental tests conducted as well as by the harmonic filtering properties. The system is also characterized by its simple architecture, which allows us to provide a high dynamic response with a very much reduced number of calculations.

Modular Architecture for Efficient Generation and Correlation of Complementary Set of Sequences

Golay sequences and complementary sets of sequences have been long studied for their application in multisensor and communication systems. The feasibility of these systems strongly depends on the design of an efficient generator and correlator with the aim of reducing the computational load and hardware complexity. Recursive algorithms, which allow efficient architectures, are available in the case of complementary pairs of sequences and complementary sets of four sequences. This work presents a generalization of these algorithms with the purpose of obtaining complementary sets of M sequences with length L, the number of sequences M being a power of two (M=2m), and the length L a power of M (L=2mN) with m,Nisin N-{0}. This fact allows an ideal Kroumlnecker delta function of weight MmiddotL in the addition of the autocorrelation functions of the M sequences of the set. Furthermore, the generation of M different mutually orthogonal sets can be obtained. This fact makes their application suitable in simultaneous multiemission systems. With the proposed algorithm, an effective reduction in the number of operations necessary to implement the correlator can be obtained, if it is compared with the straightforward implementation. Also, a regular structure is provided that allows implementation of the generator and/or the correlator for complementary sets of M sequences, based on the structure for complementary sets of M/2 sequences The sequence length can also be easily extended to any multiple of M. Finally, the generation and correlation of M different mutually orthogonal complementary sets of M sequences can be immediately derived

Harmonics Measurement With a Modulated Sliding Discrete Fourier Transform Algorithm

Accurate harmonics estimation has become a key issue in power quality assessment. This paper deals with a discrete Fourier transform (DFT)-based measurement technique, which can be easily employed to accurately determine the harmonic components of a distorted signal, i.e., voltage or current. The proposed method is based on a modulated sliding DFT algorithm, which is unconditionally stable and does not accumulate errors due to finite precision representation, and a variable sampling period technique (VSPT) to achieve a frequency adaptive mechanism. It is worth noting that the VSPT changes the sampling period for a variable grid frequency condition, leading to a constant sampling frequency under steady-state conditions. The proposed method provides: 1) high degree of accuracy; 2) structural/performance robustness; and 3) frequency adaptability. Given the modular nature of the method, it is implemented on a field programmable gate array. Simulations and experimental tests are shown to verify the performance of the proposed method.

IR sensor array configuration and signal processing for detecting obstacles in railways

This work describes a sensor array based on optical emitters, which allows to detect obstacles in railways. The sensorial system consists of a barrier of emitters and another of receivers, placed at opposite sides of the railway. Apart from the disposition of the sensorial system, it is necessary a codification method for the emission in order to detect the reception or the non-reception of transmissions between an emitter and a receiver. The method is based on a signal codification using complementary sequence pairs, suitably adapted for their simultaneous emission through the transmission channel. A high reliability under adverse conditions is achieved with the developed system, being possible to detect the presence of obstacles, and to inform about their situation.

Simultaneous correlation of complementary set of sequences using a transpose generation approach

Complementary sets of sequences are currently being applied to signal coding, radar, and multi-user systems, among others. Their particular mathematical properties make them adequate for multi-emission and noisy environments. Nowadays sustained efforts are being devoted to reduce the calculations involved in the generation and/or correlation of these signals by means of recursive algorithms. Some authors have proposed efficient algorithms that are based on modular architectures made up of adders, multipliers and delays. This work introduces a new approach to correlation algorithms of complementary sets of sequences, which is based on a transposition of the generation process. This approach allows to notoriously reduce calculations, and enables the simultaneous correlation of M sequences, without adopting time multiplexing schemes or complex parallel implementations. The correlation algorithm is theoretically demonstrated and its calculation performance is evaluated in a hardware reconfigurable platform. A comparison with other algorithms is included, considering the amount of calculations as a function of the length of the sequences.

Complementary sets of sequences-based coding for ultrasonic array sensor

In this paper, an improved ultrasonic system for detection of falling objects or alive beings intrusion in railways is presented. The basic ultrasonic array sensor is composed of four emitters and six receivers and can be easily extended to a higher coverage area repeating this elementary structure. The receivers are able to distinguish among the signals coming from the four different emitters thanks to the signal coding with complementary sets of sequences, which also gives to the reception module an excellent process gain. The signal processing has been accomplished by means of the efficient set of sequences correlator which has been recently developed by the authors.

Train wheel detection without electronic equipment near the rail line

The reliable detection of the passage of railway units by certain points of the railway line is very important for a safe circulation. Thus, the system proposed in this work makes the detection with the sensor located next to the railway, without additional electronics in this place. All the electronic process equipment is concentrated in a point that can be far away from the rail. Moreover, the proposed sensor is capable of detecting the sense of circulation. In order to compensate for the attenuation in wires and the external noise, we use a signal codified with Golay complementary sequences.

Use of coded signals to wheel train detection

The detection of the passage of railway units by certain points of the railway line (mainly in the junctions or bifurcations of the routes), of reliable way, is a functionality of great importance for the safe management of the circulation. Most of the existing systems to that end bases of its operation on the detection of the disturbance that undergoes a magnetic flux (generated by means of coils) to the passage of the wheel of the train. With the system proposed here, we make this detection with the coils located next to the rail of the route, but without additional electronics located in this place. All the electronic systems are concentrated in a point that can be to a considerable distance from the rail. This makes easier the tasks of maintenance of the equipment, in addition to protecting it from the noises and aggressions of the environment. In order to compensate the attenuation of signal in the wires and the external noise, we propose a codification of the signal sent to the emitting coil by means of pairs of Golay complementary sequences.

Analysis of multiple scattering and multiphonon contributions in inelastic neutron scattering experiments

Abstract We present a method of analysis of inelastic neutron scattering (INS) experiments aiming at obtaining the density of phonon states in an absolute scale, as well as a reliable value of the mean-square displacement of the atoms. This method requires the measurement of the neutron total cross section of the sample as a function of energy, which provides a normalization condition for the INS experiment, as well as a value of the mean-square displacement. The method is applied in the case of an incoherent neutron scattering system, viz. the Ti–52wt.% Zr alloy. The applicability of this method to the study of metal alloys and other systems is discussed.