1,178,340 research outputs found

    Universal direct tuner for loop control in industry

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    This paper introduces a direct universal (automatic) tuner for basic loop control in industrial applications. The direct feature refers to the fact that a first-hand model, such as a step response first-order plus dead time approximation, is not required. Instead, a point in the frequency domain and the corresponding slope of the loop frequency response is identified by single test suitable for industrial applications. The proposed method has been shown to overcome pitfalls found in other (automatic) tuning methods and has been validated in a wide range of common and exotic processes in simulation and experimental conditions. The method is very robust to noise, an important feature for real life industrial applications. Comparison is performed with other well-known methods, such as approximate M-constrained integral gain optimization (AMIGO) and Skogestad internal model controller (SIMC), which are indirect methods, i.e., they are based on a first-hand approximation of step response data. The results indicate great similarity between the results, whereas the direct method has the advantage of skipping this intermediate step of identification. The control structure is the most commonly used in industry, i.e., proportional-integral-derivative (PID) type. As the derivative action is often not used in industry due to its difficult choice, in the proposed method, we use a direct relation between the integral and derivative gains. This enables the user to have in the tuning structure the advantages of the derivative action, therefore much improving the potential of good performance in real life control applications

    Identification and verification of frequency-domain models for XV-15 tilt-rotor aircraft dynamics

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    Frequency-domain methods are used to extract the open-loop dynamics of the XV-15 tilt-rotor aircraft from flight test data for the cruise condition (V = 170 knots). The frequency responses are numerically fitted with transfer-function forms to identify equivalent model characteristics. The associated handling quality parameters meet or exceed Level 2, Category A, requirements for fixed-wing military aircraft. Step response matching is used to verify the time-domain fidelity of the transfer-function models for the cruise and hover flight conditions. The transient responses of the model and aircraft are in close agreement in all cases, except for the normal acceleration response to elevator deflection in cruise. This discrepancy is probably due to the unmodeled rotor rpm dynamics. The utility of the frequency-domain approach for dynamics identification and analysis is clearly demonstrated

    Model predictive control of permanent magnet synchronous machine with reduced torque ripple

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    The conventional direct torque control (DTC) method features fast dynamic response, but it also has notable drawbacks such as high torque and flux ripples, variable switching frequency and acoustic noise. The proposed DTC scheme based on model predictive control (MPC) is studied in the paper for permanent magnet synchronous machine drive. The paper aims to reduce the torque and flux ripple. Firstly one- and two-step delay MPC methods are employed with or without the torque/flux and switching frequency compensation. Furthermore linear extrapolations N-step delay MPC method is taken into account. Compared to simulation results, the two-step delay DTC scheme is better than the one-step scheme in the steady response and dynamic performance, at the same time the torque and frequency compensations can reduce switching frequency from high value to a low constant one. Simulation results are presented to validate the effectiveness of the proposed schemes in this paper. © 2013 IEEE

    Control of a Nonlinear System by Linearization

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    In today’s linear control systems, exact solutions can be obtained by the use of Laplace Transforms in the frequency domain. In dealing with nonlinear systems, exact solutions are not always achievable. For this reason, it is necessary to linearize the system and then apply frequency response methods. This paper shows the comparison of a nonlinear system with the linearized model of the same system. For both proportional and proportional-integral control, the response to a unit step change in the set point showed minimal difference between the linearized and nonlinear system

    A simultaneous frequency and time-domain approximation method for discrete-time filters

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    金沢大学理工研究域 電子情報学系A simultaneous frequency- and time-domain approximation method for discrete-time filters is proposed in this paper. In the proposed method, transfer function coefficients are divided into two subsets,X_{1}andX_{2}, which are employed for optimizing a time response and a frequency response, respectively. Frequency and time responses are optimized through the iterative Chebyshev approximation method and a method of solving linear equations, respectively. At therth iteration step, the maximum frequency response error, which appeared at the(r - 1)th step, is minimized, andX_{2}^{(r- 1)}becomesX_{2}^{(r)})cdot X_{1}^{(r)}is obtained from linear equations includingX_{2}^{(r)}as a constant. The frequency response at the rth step is evaluated using the above obtainedX_{1}^{(r)}andX_{2}^{(r)}. This means the optimum time response is always guaranteed in the frequency-response approximation procedure. A design example of a symmetrical impulse response shows the new approach is more efficient than conventional methods from the filter order reduction viewpoint

    Vibration of a beam on continuous elastic foundation with nonhomogeneous stiffness and damping under a harmonically excited mass

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    In this paper, a method of analysis of a beam that is continuously supported on a linear nonhomogeneous elastic foundation and subjected to a harmonically excited mass is presented. The solution is obtained by decomposing the nonhomogeneous foundation properties and the beam displacement response into double Fourier summations which are solved in the frequency–wavenumber domain, from which the space–time domain response can be obtained. The method is applied to railway tracks with step variation in foundation properties. The validity of this method is checked, through examples, against existing methods for both homogeneous and nonhomogeneous foundation parameters. The effect of inhomogeneity and the magnitude of the mass are also investigated. It is found that a step variation in foundation properties leads to a reduction in the beam displacement and an increase in the resonance frequency for increasing step change, with the reverse occurring for decreasing step change. Furthermore, a beam on nonhomogeneous foundation may exhibit multiple resonances corresponding to the foundation stiffness of individual sections, as the mass moves through the respective sections along the beam

    Simultaneous frequency and time-domain approximation method for discrete-time filters

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    金沢大学大学院自然科学研究科情報システム金沢大学工学部A simultaneous frequency- and time-domain approximation method for discrete-time filters is proposed. In the method, transfer function coefficients are divided into two subsets, X//1 and X//2, which are employed for optimizing a time response and a frequency response, respectively. Frequency and time responses are optimized through the iterative Chebyshev approximation method and a method of solving linear equations, respectively. At the rth iteration step, the maximum frequency response error, which appeared at the (r minus 1)th step, is minimized, and X//2**(**r** minus **1**) becomes X//2**(**r**). X//1**(**r**) is obtained from linear equations including X//2**(**r**) as a constant. The frequency response at the rth step is evaluated using the above obtained X//1**(**r**) and X//2**(**r**). This means the optimum time response is always guaranteed in the frequency-response approximation procedure. A design example of a symmetrical impulse response shows the new approach is more efficient than conventional methods from the filter order reduction viewpoint

    Correlative confocal Raman and scanning probe microscopy in the ionically active particles of LiMn 2 O 4 cathodes

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    In this contribution, a correlative confocal Raman and scanning probe microscopy approach was implemented to find a relation between the composition, lithiation state, and functional electrochemical response in individual micro-scale particles of a LiMn 2 O 4 spinel in a commercial Li battery cathode. Electrochemical strain microscopy (ESM) was implemented both at a low-frequency (3.5 kHz) and in a high-frequency range of excitation (above 400 kHz). It was shown that the high-frequency ESM has a significant cross-talk with topography due to a tip-sample electrostatic interaction, while the low-frequency ESM yields a response correlated with distributions of Li ions and electrochemically inactive phases revealed by the confocal Raman microscopy. Parasitic contributions into the electromechanical response from the local Joule heating and flexoelectric effect were considered as well and found to be negligible. It was concluded that the low-frequency ESM response directly corresponds to the confocal Raman microscopy data. The analysis implemented in this work is an important step towards the quantitative measurement of diffusion coefficients and ion concentration via strain-based scanning probe microscopy methods in a wide range of ionically active materials. © 2019 by the authors

    Design Considerations for a Digital Audio Equalizer

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    The objective of this thesis is to consider a method for designing a digital audio equalizer. The primary design criteria is minimum audible frequency response error between a digital and a reference analog equalizer throughout the entire audio frequency range from 20 Hz to 20 Khz. The first step is to obtain a set of analog filters that suitably represent the reference equalization. From these filters, digital filter coefficients are generated using the bilinear transformation. Then, the digital filters are combined with anti-aliasing and D/A reconstruction filters and a zero-order hold to complete the design. Analysis of methods to minimize frequency axis warping effects on the response of the high frequency filters is presented. The problems associated with realizing a filter with low natural frequency and a very high sample rate is also studied
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