Frequency Domain Analysis Method Research Articles

Frequency performance analysis of proportional integral-type active disturbance rejection generalized predictive control for time delay systems

To improve the performance of the Active Disturbance Rejection Control (ADRC) in systems which have large time delay, reduce online computation for Proportional Integral-type Generalized Predictive Control (PI-GPC) method, the Proportional Integral-type Active Disturbance Rejection Generalized Predictive Control (PI-ADRGPC) based on Controlled Auto Regression and Moving Average (CARMA) model is designed. The frequency domain analysis method is used to analyse the stability of the PI-ADRGPC based on CARMA model. By using the open-loop transfer function of the PI-GPC discrete form, the influence of parameter changes on the PI-ADRGPC performance is analysed. The performance of the PI-ADRGPC and ADRC algorithm is compared through the application in a second-order time delay system and distillation column system. The research results show that compared with the ADRC algorithm, the PI-ADRGPC method has a shorter rise time and better performance.

Frequency domain analysis method of tuned liquid damper controlled multi-degree of freedoms system subject to earthquake excitation

Tuned liquid damper (TLD) is a typical passive device to control structural response under wind and earthquake excitation. At present, TLD is often used to control single-mode of structure. Hence, the design theory of TLD is often based on single-degree of freedom (SDOF) system in frequency domain, which is hard to accurately evaluate seismic performance of TLD-installed multi-degree of freedoms (MDOFs) with consideration of higher mode. In this work, a frequency domain transfer function for TLD controlled MDOFs system is established through the concept of substructure to evaluate overall seismic performance of TLD-installed MDOFs. The accuracy of the transfer function is verified by real-time hybrid testing. Using this transfer function, the effect of TLD on the seismic performance of MDOFs was discussed in frequency domain by parametric analysis. The analytical results indicated that, based on the design theory for single-mode, the TLD with large mass ratio cannot enhance the seismic performance effectively comparing with small mass ratio. In order to improve the control efficiency of relatively large mass TLD, a design method for multi-mode control is established based on the developed frequency domain transfer function. The simulation results showed that, with same TLD mass, the multi-mode method performed smaller structural acceleration response and similar displacement response relative to the single mode method.

Global matrix method for frequency-domain stability analysis of hydropower generating system

Safe and stable operation of hydropower plants is the basis and prerequisite of great importance for clean energy production and integration of renewables. To better analyze the operating stability of hydropower generating systems (HGSs), a novel frequency-domain method (global matrix method) is proposed in this paper. First, the principle of the new method and the mathematical models of each common hydraulic component in HGSs are presented. Second, three general steps for deriving the global matrix of an arbitrary system and order-reduction and numerical calculation of the matrix are illustrated in detail. In two case studies of HGS stability analysis, the transfer function method (TFM) suitable for time-frequency domain analysis is applied to evaluate the global matrix method. For simple single-unit system, the new method is compared by the TFM from both frequency domain and time domain. For complicated multi-unit system, the TFM is not applicable to the frequency-domain stability analysis, and only the time-domain simulation is applied to verify the new method. The results indicate that the stability regions by the two methods are in good agreement, verifying the accuracy of the new approach. The proposed method can replace the TFM for stability analysis of HGSs in frequency domain, outperforming the latter in applicability, flexibility, and quantification function.

Rotating consensus for double-integrator multi-agent systems with communication delay

In this paper, the rotating consensus problem for the multi-agent systems of double-integrator dynamic is mainly considered with and without communication delay. A fully distributed control strategy is given on the more general complex plane. For the case without communication delay, we design a distributed control protocol with the help of local relative information and obtain the sufficient and necessary condition with the lower bounded control parameter for the directed communication topology. Furthermore, with taking communication delay into consideration, the sufficient and necessary condition with the upper bounded communication delay is obtained with the help of frequency domain analysis method. Compared with some existing results, the communication topology considered is a more general directed graph. Finally, some simulation examples are presented to clarify the correctness of our results.

Research on vibration reduction of semi-active suspension system of quarter vehicle based on time-delayed feedback control with body acceleration

In this paper, the mechanical model of two-degree-of-freedom vehicle semi-active suspension system based on time-delayed feedback control with vertical acceleration of the vehicle body was studied. With frequency-domain analysis method, the optimization of time-delayed feedback control parameters of vehicle suspension system in effective frequency band was studied, and a set of optimization method of time-delayed feedback control parameters based on “equivalent harmonic excitation” was proposed. The time-domain simulation results of vehicle suspension system show that compared with the passive control, the time-delayed feedback control based on the vertical acceleration of the vehicle body under the optimal time-delayed feedback control effectively broadens the vibration absorption bandwidth of the vehicle suspension system. The ride comfort and stability of the vehicle under random road excitation are significantly improved, which provides a theoretical basis for the selection of time-delayed feedback control strategy and the optimal design of time-delayed feedback control parameters of vehicle suspension system.

Spatial-noise subdivision evaluation model of uncooled infrared detector

In this study, a spatial-noise subdivision evaluation model of an infrared detector is introduced. The spatial noise was classified into five independent noise components according to their graphic features. A frequency domain analysis method was used to accurately separate the spatial noise components and calculate their spatial noise equivalent temperature difference. By testing the spatial noise components of the mainstream uncooled infrared detector, we found that the main components were high and low spatial frequency noise. The effects of spatial noise on the performance of the infrared system were also analyzed for two typical applications of imaging and temperature measurements. We found that spatial high-frequency noise is the main factor affecting the minimum resolvable temperature difference performance of the infrared imaging system, whereas spatial low-frequency noise is the main factor affecting the accuracy of temperature measurements in the infrared temperature measurement system. The results indicate directions for further studies on the spatial noise of uncooled infrared detectors.

Ensemble Learning-Based Pulse Signal Recognition: Classification Model Development Study.

BackgroundIn pulse signal analysis and identification, time domain and time frequency domain analysis methods can obtain interpretable structured data and build classification models using traditional machine learning methods. Unstructured data, such as pulse signals, contain rich information about the state of the cardiovascular system, and local features of unstructured data can be extracted and classified using deep learning.ObjectiveThe objective of this paper was to comprehensively use machine learning and deep learning classification methods to fully exploit the information about pulse signals.MethodsStructured data were obtained by using time domain and time frequency domain analysis methods. A classification model was built using a support vector machine (SVM), a deep convolutional neural network (DCNN) kernel was used to extract local features of the unstructured data, and the stacking method was used to fuse the above classification results for decision making.ResultsThe highest average accuracy of 0.7914 was obtained using only a single classifier, while the average accuracy obtained using the ensemble learning approach was 0.8330.ConclusionsEnsemble learning can effectively use information from structured and unstructured data to improve classification accuracy through decision-level fusion. This study provides a new idea and method for pulse signal classification, which is of practical value for pulse diagnosis objectification.

Numerical Study on Pressure Pulsation in a Slanted Axial-Flow Pump Device under Partial Loads

The 30° slanted axial-flow pump device is widely used in agricultural irrigation and urban drainage in plains areas of China. However, during the actual operation process, the 30° slanted axial-flow pump device is prone to vibration, noise, cracks in the blades, and other phenomena that affect the safe and stable operation of the pump device. In order to analyze the flow pressure pulsation characteristics of the 30° slanted axial-flow pump device under different flow conditions, the time–frequency domain analysis method was used to analyze the pressure pulsation of each flow structure of the 30° slanted axial-flow pump device. The results showed that the internal pulsation law of the elbow oblique inlet flow channel is similar. At the 1.2 Qbep condition, the amplitude fluctuation of the pressure pulsation was small, and the main frequency is 4 times the rotating frequency. The monitoring points at the outlet of the elbow oblique inlet flow channel were affected by the impeller rotation, and the pressure pulsation amplitude was larger than that inside the elbow oblique inlet flow channel. The pressure fluctuation of each monitoring point at the inlet surface of the impeller was affected by the number of blades. There were four peaks and four valleys, and the main frequency was 4 times the rotating frequency. The amplitude of pressure fluctuation increased gradually from the hub to the rim. The main frequency of pressure fluctuation at each monitoring point of the impeller outlet surface was 4 times of the rotating frequency, and the low frequency was rich. The amplitude of pressure fluctuation was significantly lower than that of the impeller inlet. With the increase of flow rate, the peak fluctuation of pressure coefficient decreased gradually, and the amplitude of pressure fluctuation tended to be stable. Under 0.8 Qbep and 1.0 Qbep conditions, the large fluctuation of the pressure fluctuation amplitude on the outlet surface of the guide vane was mainly affected by the low-frequency fluctuation. Under the 1.2 Qbep condition, the pressure fluctuation amplitude changed periodically.

Comparison of lock-in correlation and a novel periodogram method for experimental multi-harmonic thermoelastic analysis

Lock-in correlation is a simple, efficient and widely employed method for thermoelastic stress analysis under cyclic loading. Frequency domain analysis of the thermoelastic signal using the Fourier transform has been also valuable for researchers, even though it presents some drawbacks. In this paper, a new frequency-domain method for thermoelastic analysis through periodograms using Welch’s averaging method has been developed. This method supplies the lack of phase shift information of the simple Fourier transform for thermoelastic signals and considerably reduce the data size. This work evaluates its performance against lock-in correlation through two experiments with opposite features for multi-harmonic analysis. One experiment consisted in the analysis of the thermoelastic signal in a plate with a centred hole, exhibiting a stress concentration and using the second harmonic as an indicator of the non-linearities. The second experiment consisted in the characterisation of mode shapes thermal maps during the simultaneous excitation of multiple specimen resonances. In comparison with the stress concentrator experiment, here the level of the thermal signal is lower and the number of frequencies to analyse is higher. The analysis of the thermal maps by both methods revealed that they yield practically identical results for any experiment. However, the evaluation of the computation efficiency highlights that the periodogram method has fewer memory requirements whereas, in terms of computation time, lock-in correlation is more efficient to analyse fewer frequencies in short image sequence tests, being the periodogram method more efficient for the opposite case.

Containment Control of First-Order Multi-Agent Systems under PI Coordination Protocol

This paper investigates the containment control problem of discrete-time first-order multi-agent system composed of multiple leaders and followers, and we propose a proportional-integral (PI) coordination control protocol. Assume that each follower has a directed path to one leader, and we consider several cases according to different topologies composed of the followers. Under the general directed topology that has a spanning tree, the frequency-domain analysis method is used to obtain the sufficient convergence condition for the followers achieving the containment-rendezvous that all the followers reach an agreement value in the convex hull formed by the leaders. Specially, a less conservative sufficient condition is obtained for the followers under symmetric and connected topology. Furthermore, it is proved that our proposed protocol drives the followers with unconnected topology to converge to the convex hull of the leaders. Numerical examples show the correctness of the theoretical results.

Study on the frequency of acoustic emission signal during crystal growth of salicylic acid

AbstractBased on the results of the previous experiment, this article studied the acoustic emission (AE) signals released during the crystallization of salicylic acid to establish the relationship between the AE signal and the particle size. A tremendous amount of acoustic data was analyzed using time–frequency domain analysis methods in order to extract the valuable contents. Based on the diffusion theory, the vibratory model between the AE signal and the crystal particle size was established. This article mainly studies the process of small particles diffusing to the growth point by impact, adding to the lattice, and the crystal releases energy. The impact of the growth unit on particle aggregate is equivalent to a linear elastic vibration system with one end fixed and the other end free. The vibration frequency is 200–355 kHz when the particle size is between 600 and 1,100 µm. The calculated vibration frequency is in good agreement with the measured frequency.

Geometric resistant polar quaternion discrete Fourier transform and its application in color image zero-hiding

As a typical frequency-domain analysis method, quaternion discrete Fourier transform (QDFT) has been widely used in information hiding in color images. However, due to the sensitivity of QDFT to geometric attacks, existing QDFT-based information hiding schemes have limited ability in resisting geometric attacks. In this study, a kind of novel geometrically resilient polar QDFT (PQDFT) is constructed and the properties of the proposed PQDFT are analyzed. Subsequently, a PQDFT-based color image zero-hiding scheme robust to geometric attacks is proposed for lossless copyright protection of color images, which experimentally shows reasonable resistance against geometric and common attacks, indicating better robustness compared with the existing QDFT-based information hiding schemes and other leading-edge zero-hiding schemes.

Frequency-Domain Analysis and the Effect on Voltage Distribution of the HTS SMES

The high-frequency PWM pulse voltage of SMES power conditioning system (PCS) transmitted to the HTS magnet will influence the security of the magnet. Therefore, to analyze the dynamic response of the magnet with the interaction of the PWM pulse voltage is necessary for the SMES operation. This paper proposes a frequency-domain analysis method for the transient characteristic of the HTS magnet, which can be utilized to analyze the voltage distribution and the frequency response characteristic of the magnet. To evaluate the effectiveness of the proposed method, a sample HTS magnet is assembled to measure its voltage distribution characteristic. Furthermore, the results of amplitude-frequency characteristics coincide with the trend of magnet voltage variation.

Stationary average-tracking problem of unmatched constant reference signals based on delayed-state feedback

Stationary average-tracking problems of unmatched constant reference signals are investigated for first-order multi-agent systems, and an integral-type average-tracking algorithm with delayed-state feedback is constructed. With identical communication delays and different introduced self-delays, sufficient conditions are obtained for the agents converging to the average-value of unmatched reference signals asymptotically by using the frequency-domain analysis method. To our delight, introducing delayed-state feedback improves the robustness to communication delay and unmatched reference signals. Simulation results show the effectiveness of our proposed algorithm.

Experimental Research on Pressure Pulsation and Stability of Giant Francis Turbine

Pressure pulsation is an important factor affecting the stability of the turbine. The test studied the characteristics and laws of pressure fluctuations of giant hydraulic turbines to provide guidance for the design and stable operation of giant hydraulic turbines. The test used time-domain analysis and frequency-domain analysis methods to test and analyze the pressure pulsating real machine of giant hydraulic turbine. The test results show that the amplitude of pressure pulsation has a negative correlation with active power. The active power ranges from no-load to 40%P, and the pressure pulsation is mainly expressed as a high-frequency waveform with a frequency conversion of 8.8 to 24.4 times. The active power ranges from 40%P to 75%P, and the pressure pulsation mainly manifests as a low-frequency waveform with a frequency conversion of 0.19 to 0.28 times. Active power range from 75%P to 100%P, the amplitude of pressure pulsation decreases significantly. The above three load areas coincide with the vibration area of the unit, indicating that the hydraulic factor is the main factor affecting the stability of the unit.

Design and Parameter Tuning of Nonlinear Active Disturbance Rejection Controller for Permanent Magnet Direct Drive Wind Power Converter System

When the permanent magnet direct-drive wind power converter system is disturbed by the grid side and the motor side, the output voltage of the converter and the DC bus voltage will change suddenly, and the power quality of the grid will deteriorate. The nonlinear active disturbance rejection controller (NLADRC) is used in the grid-connected inverter control system. Because of its ability to estimate and compensate disturbances, it can effectively improve the system's anti-disturbance ability and tracking accuracy. However, NLADRC still has problems such as many parameters to be adjusted and unclear physical meaning. This article explores the influence of various parameters on the dynamic performance of the entire system, and summarizes the direction and law of parameter tuning. At the same time, the frequency domain analysis method is used to express the gain parameter in the expanded state observer in the form of bandwidth, which provides a basis for parameter adjustment in actual engineering. The control algorithm proposed in this article is applied to the 3MW permanent magnet direct-drive wind power experimental platform. The experimental results under various working conditions show that NLADRC can effectively improve the anti-interference performance of the grid-connected inverter.

The Correlation Study of Cun, Guan and Chi Position Based on Wrist Pulse Characteristics

To analyze the correlation of pulse characteristics at different acquisition positions, the pulse parameters that can identify different pulse and physiological information are given. In this paper, the relevance and difference of wrist pulse characteristics at Cun, Guan and Chi position were studied by pulse diagnosis instrument and time-frequency, frequency-domain and time-frequency domain analysis methods etc. Firstly, the pulse information of Cun, Guan and Chi position is collected from 206 healthy adults. The 66 pulse characteristics of each sampled location are extracted. In addition, the 66 feature indexes of each position are used to calculate the Spearman correlation coefficients among Cun, Guan, Chi position as well as the both hands in detail. Finally, the relevance and difference of wrist pulse at Cun, Guan and Chi position were studied and analyzed by significance test. The pulse characteristics with high correlation at Cun-Guan-Chi position of left and right hands are mainly power spectrum characteristics and time-frequency characteristics, while the features with high correlation between both hands mostly concentrate in the time domain characteristics. This work has studied the relationship between the position of pulse acquisition from quantitative and qualitative aspects, and laid a foundation for the objective diagnosis of pulse condition and the comprehensive disclosure of pulse information.

A Recognition Method for Time-domain Waveform Images of Electric Traction Network Overvoltage Based on Deep Learning

A large amount of time-domain waveform images of overvoltage of electric traction network are collected during the on-board test of EMU. The traditional time-domain or frequency-domain analysis and classification method can’t be directly applied to time-domain waveform images. In order to analyze these images, firstly, image preprocessing is carried out. Then, the data set of time-domain waveform images is established. Finally, the CNN (convolutional neural network) classification model is trained based on data set. The results show that the sensitivity of recognition is above 81%, and this method is suitable for the time-domain waveform image of overvoltage of electric traction network.

Gyro-Sensor-Based Vibration Control for Dynamic Humanoid-Robot Walking on Inclined Surfaces.

An efficient motor-control system for stable walking of the lightweight humanoid robot KONDO KHR-3HV on inclined surfaces is investigated. The motor-control system is based on the angular velocity of the pitch motion of the robot, which is detected by a gyro sensor attached to the robot torso and referred to as the angular-pitch velocity. The robot gait is analyzed for different downslopes with and without the motor-feedback control. A novel method of frequency-domain analysis of the angular-pitch velocity is proposed for explaining the reasons behind the instabilities of dynamic humanoid-robot walking on inclined surfaces. The results show, that a nonlinear nature of the motor torque, due to a force induced by the slope, gives rise to harmonics of the fundamental walking frequency of 1.73 Hz. These harmonics are the origin of the unstable robot walking. Additionally, the feedback-gain parameters KA and KH affect the amplitudes of the harmonics, which give rise to vibrations at a higher surface inclination. Increased surface friction allows a reduction of the feedback gain, which reduces this specific contribution to the harmonics and thus stabilizes the robot. To improve the walking stability on inclined surfaces, it is found that the damped natural frequency of the motor-control system must be kept lower than the fundamental walking frequency.

An frequency domain analysis method of thermal parameters unsteady-state detection of building wall

ABSTRACT The in-situ inspection technology of thermal properties of building wall is an important technical guarantee to achieve the goal of building energy conservation. However, there is still a lack of fast, simple, and accurate unsteady-state detection method under natural conditions. This paper focuses on the thermal performance test and analysis method of building wall under natural condition. Two frequency domain analysis methods were developed for the thermal conductivity, as well as volume specific heat and thermal inertia of homogeneous wall along with the harmonic reaction method and the frequency domain analysis theory. The frequency response relationship between the internal and external surface temperature waves and indoor air temperature waves was established, and the relationship contains thermal performance parameters of wall. The thermal conductivity and specific volume heat of wall can be solved by using the response relation. Numerical simulation verification of the method was completed by using ANSYS software and the experimental verification by using wall insulation materials were accomplished in the laboratory. The maximum relative error of numerical simulation results is 1.48%, and that of laboratory experiment results is 8.75%. The implications of these results with respect to the influence on the in-situ inspection technology of building wall are discuss.