• The Transactions of the Korean Institute of Electrical Engineers
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• v.43 no.3
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• pp.447-457
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• 1994

This paper presents a compensation method for discrete-time control systems with saturation nonlinearities to cope with the reset windup phenomena. The proposed ARW (Anti-Reset Windup) method is motivated by the concept of the equilibrium point. The design parameter of the ARW scheme is explicitly derived by minimizing a reasonable performance index. The resulting dynamics of the compensated controller exhibits the reduced model form of the unsaturated system which can be obtained by the singular perturbational model reduction method. An example is given to illustrate the effectiveness of the proposed method.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.1
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• pp.211-224
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• 2019

This paper deals with a nonlinear controller based on saturation functions with variable parameters for set-point regulation and trajectory tracking control of an Autonomous Underwater Vehicle (AUV). In many cases, saturation functions with constant parameters are used to limit the input signals generated by a classical PD (Proportional-Derivative) controller to avoid damaging the actuators; however this abrupt bounded harms the performance of the controller. We, therefore, propose to replace the conventional saturation function, with constant parameters, by a saturation function with variable parameters to limit the signals of a PD controller, which is the base of the nonlinear PD with gravitational/buoyancy compensation and the nonlinear PD + controllers that we propose in this paper. Consequently, the mathematical model is obtained, considering the featuring operation of the underwater vehicle LIRMIA 2, to do the stability analysis of the closed-loop system with the proposed nonlinear controllers using the Lyapunov arguments. The experimental results show the performance of an AUV (LIRMIA 2) for the depth control problems in the case of set-point regulation and trajectory tracking control.

• Current Optics and Photonics
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• v.6 no.3
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• pp.304-312
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• 2022

Digital images of cultural relics captured using line scan cameras present limitations due to uneven intensity and low contrast. To address this issue, this report proposes a colour linear array image enhancement method that can maintain a constant colour. First, the colour linear array image is converted from the red-green-blue (RGB) colour space into the hue-saturation-intensity colour space, and the three components of hue, saturation, and intensity are separated. Subsequently, the hue and saturation components are held constant while the intensity component is processed using the established intensity compensation model to eliminate the uneven intensity of the image. On this basis, the contrast of the intensity component is enhanced using an improved local contrast enhancement method. Finally, the processed image is converted into the RGB colour space. The experimental results indicate that the proposed method can significantly improve the visual effect of colour linear array images. Moreover, the objective quality evaluation parameters are improved compared to those determined using existing methods.

• ETRI Journal
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• v.39 no.6
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• pp.771-781
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• 2017

For efficient spectral utilization of satellite channels, a shared band transmission technique is introduced in this paper. A satellite transmits multiple received signals from a gateway and terminal in the common frequency band by superimposing the signals. To improve the power efficiency as well as the spectral efficiency, a travelling wave tube amplifier in the satellite should operate near the saturation level. This causes a nonlinear distortion of the superimposed transmit signal. Without mitigating this nonlinear effect, the self-interference cannot be properly cancelled and the desired signal cannot be demodulated. Therefore, an adaptive compensation scheme for nonlinearity is herein proposed with the proper operation scenario. It is shown through simulations that the proposed shared band transmission approach with nonlinear compensation and self-interference cancellation can achieve an acceptable system performance in nonlinear satellite channels.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.52 no.7
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• pp.387-392
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• 2003

During a fault the remanent flux in a current transformer (CT) may cause severe saturation of its core. The resulting distortion in the secondary current could cause the mal-operation of a protection relay. This paper proposes an algorithm for compensating for the errors in the secondary current caused by CT saturation and the remanent flux. The algorithm compensates the distorted current irrespective of the level of the remanent flux. The second-difference function of the current is used to detect when the CT first starts to saturate. The negative value of the second-difference function at the start of saturation, which corresponds to the magnetizing current, is inserted into the magnetization curve to obtain the core flux at the instant. This value is then used as an initial flux to calculate the actual flux of the CT during the course of the fault with the secondary current. The magnetizing current is then estimated using the magnetization curve and the calculated flux value. The compensated secondary current can be estimated by adding the magnetizing current to the secondary current. Test results indicate that the algorithm can accurately compensate a severely distorted secondary current signal.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.7
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• pp.1332-1340
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• 1992

A novel approach based on a nonlinear compensator is prposed to prevent 'windup', which is caused by the saturation of the acutator and the integral action of the controller. The anti-windup compensator is located between the conventional linear controller, designed neglecting the saturation, and the actuator. It was proven based on the describing function method that, if the closed loop control systems are stable assuming no saturation, then there may exist a range of compensator gain which prevents any limit-cycle. The computer simulation results show that the compensator proposed in the manuscript can eliminate the limit cycle and improve the transient response.

• Korean Journal of Optics and Photonics
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• v.14 no.1
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• pp.12-16
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• 2003

This paper presents a compensation method for a temperature-dependent gain tilt in L-band erbium-doped fiber amplifier using a voltage-controlled attenuator. The gain tilts in the L-band of 1570-1605 nm due to a temperature change have negative slopes, whereas they have positive slopes for the increasing optical input powers in a saturation region. The proposed method utilizes these opposite gain variations to compensate for the gain tilt over a wide range of temperature. While applying forty channels with a channel spacing of 100 GHz in the L-band and changing the ambient temperature from 0 to $50^{\circ}C$, the compensation method maintained the gain deviation within 1 dB.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.12
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• pp.5998-6016
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• 2017

In thin-film transistor liquid-crystal displays (TFT-LCDs), which are most commonly used in mobile devices, the backlight accounts for about 70% of the power consumption. Therefore, most low-power-related studies focus on realizing power savings through backlight dimming. Image compensation is performed to mitigate the visual distortion caused by the backlight dimming. Therefore, popular techniques include pixel compensation for brightness recovery and contrast enhancement, such as histogram equalization. However, existing pixel compensation techniques often have limitations with respect to blur owing to the pixel saturation phenomenon, or because contrast enhancement cannot adequately satisfy the human visual system (HVS). To overcome these, in this study, we propose a novel dimming technique to achieve both power saving and HVS-awareness by combining the pixel compensation and histogram specifications, which convert the original cumulative density function (CDF) by designing and using the desired CDF of an image. Because the process of obtaining the desired CDF is customized to consider image characteristics, histogram specification is found to achieve better HVS-awareness than histogram equalization. For the experiments, we employ the LIVE image database, and we use the structural similarity (SSIM) index to measure the degree of visual satisfaction. The experimental results show that the proposed technique achieves up to 15.9% increase in the SSIM index compared with existing dimming techniques that use pixel compensation and histogram equalization in the case of the same low-power ratio. Further, the results indicate that it achieves improved HVS-awareness and increased power saving concurrently compared with previous techniques.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.5B no.3
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• pp.253-257
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• 2005

By using a coupled circuit, time-stepping, two-dimensional finite element method (2-D FEM), the performance of a stand-alone permanent-magnet synchronous generator (PMSG) with inset rotor can be computed without involving the classical two-axis model. The effects of interpolar air gap length and armature resistance on the load characteristics are investigated. It is shown that the interpolar flux density, and hence the amount of voltage compensation, is affected by magnetic saturation. Validity of the coupled circuit and field analysis is confirmed by experiments on a prototype generator. The machine exhibits an approximately level load characteristic when it is supplying an isolated unity-power-factor load.

• Journal of Institute of Control, Robotics and Systems
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• v.2 no.4
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• pp.248-256
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• 1996

This paper presents an anti-reset windup (ARW) compensation method for saturating control systems with multiple controllers and/or multiloop configuration. The proposed ARW method is motivated by the concept of equilibrium point. The design parameters of the ARW scheme is derive explicitly by minimizing a reasonable performance index. In the event of saturation, the resulting dynamics of the compensated controller reflects the dynamics of the linear closed-loop system. The proposed method guarantees the total stability o fthe resulting control systems under a certain condition. An illustrative example is given to show the effectiveness of the proposed method. The paper is an extension of the results in Park and Choi[10].