Browsing by Subject "Nonlinear systems"

Now showing 1 - 5 of 5

Open Access
H∞-performance analysis of robust controllers designed for AQM
(IEEE, 2003) Yan, P.; Özbay, Hitay
It has been shown that the TCP connections through the congested routers with the Active Queue Management (AQM) can be modeled as a nonlinear feedback system. In this paper, we design H∞ robust controllers for AQM based on the linearized TCP model with time delays. For the linear system model exhibiting LPV nature, we investigate the H∞-performance with respect to the uncertainty bound of RTT (round trip time). The robust controllers and the corresponding analysis of H∞-performance are validated by simulations in different scenarios.
Open Access
Inductorless realisation of Chua oscillator
(IET, 1995) Morgül, Ö.
An inductorless realisation of a Chua oscillator, which exhibits chaotic behaviour is presented. This new realisation consists of the Wien bridge oscillator, coupled in parallel with the same nonlinear resistor used in the standard realisation of a Chua oscillator. This new circuit is shown experimentally to also exhibit similar chaotic behaviour.
Open Access
Multiple electrically tunable parametric resonances in a capacitively coupled electromechanical resonator for broadband energy harvesting
(Institute of Physics Publishing Ltd., 2021-03-12) Surappa, S.; Erdoğan, Tuna; Degertekin, L. F.
Parametric excitation (PE) has widely been employed as a method of mechanical pre-amplification in nonlinear vibration energy harvesting systems. However, despite their advantages, most current PE systems are limited to degenerate parametric operation within a narrow frequency band around the primary instability tongue. In this paper, we simulate and experimentally demonstrate a parametrically driven capacitive electromechanical resonator having multiple electrical degrees of freedom. Multiple modes allow for several frequency bands in which the electrical resonator is driven into nondegenerate (combination) parametric resonance (PR) in addition to degenerate resonance, thereby enabling operation over a broader range of frequencies while maintaining the same mechanical footprint. These frequency bands and PR thresholds are tunable by simply changing the electrical circuit parameters and PR can be achieved in the presence of high mechanical damping making the method more adaptable than purely mechanical approaches. Experimental results are extended by simulations indicating that proper selection of operating parameters can enable the merging of instability tongues to produce a broadband region of PR for elastic wave energy harvesting thereby obtaining superior performance when compared to an equivalent single degree of freedom PE energy harvester.
Open Access
Nonlinear identification and optimal feedforward friction compensation for a motion platform
(Elsevier, 2020) Güç, Ahmet Furkan; Yumrukçal, Z.; Özcan, Onur
In this study, we present a method of nonlinear identification and optimal feedforward friction compensation for an industrial single degree of freedom motion platform. The platform has precise reference tracking requirements while suffering from nonlinear dynamic effects, such as friction and backlash in the driveline. To eliminate nonlinear dynamic effects and achieve precise reference tracking, we first identified the nonlinear dynamics of the platform using Higher Order Sinusoidal Input Describing Function (HOSIDF) based system identification. Next, we present optimal feedforward compensation design to improve reference tracking performance. We modeled the friction using the Stribeck model and identified its parameters through a procedure including a special reference signal and the Nelder–Mead algorithm. Our results show that the RMS trajectory tracking error decreased from 0.0431 deg/s to 0.0117 deg/s when the proposed nonlinear identification and friction compensation method is utilized.
Open Access
Nonlinear identification and optimal feedforward friction compensation for a motion platform
(2020-06) Güç, Ahmet Furkan
We present a method of nonlinear identiﬁcation and optimal feedforward friction compensation procedure for an industrial single degree of freedom motion platform. The platform suﬀers from nonlinear dynamic eﬀects, such as friction and backlash in the driveline, along with precise reference tracking requirements. In order to eliminate the nonlinear dynamic eﬀects and obtain precise reference tracking, we ﬁrst identiﬁed the system using nonparametric identiﬁcation with Best Linear Approximation (BLA). Next, the feedback controller is implemented as a classical PI controller and it is designed using loop shaping techniques so that the system meets the linear system requirements. Then, we identiﬁed the nonlinear dynamics of the platform using Higher Order Sinusoidal Input Describing Function (HOSIDF) based system identiﬁcation and we present optimal feedforward compensation design to improve reference tracking performance. We modeled the friction characteristics using the Stribeck friction model and identiﬁed through a procedure with a special reference signal and the Nelder-Mead algorithm. Results indicate that the RMS trajectory error decreased from 0.0431 deg/s to 0.0117 deg/s, and standart deviation of speed reference error integral decreased from 0.0382 deg to 0.0051 deg, when the proposed nonlinear identiﬁcation and friction compensation method is used.