• Journal of Power Electronics
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• v.19 no.2
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• pp.569-579
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• 2019

A robust controller is designed based on feedback linearization and sliding mode control to damp sub-synchronous control interaction (SSCI) in doubly fed induction generator (DFIG) wind power plants (WPPs) interfaced with the grid. A feedback-linearized sliding mode controller (FLSMC) is developed for the rotor-side converter (RSC) through feedback linearization, design of the sliding mode controller, and parameter tuning with the use of particle swarm optimization. A series-compensated 100-MW DFIG WPP is adopted in simulation to evaluate the effectiveness of the designed FLSMC at different compensation degrees and wind speeds. The performance of the designed controller in damping SSCI is compared with proportional-integral controller and conventional sub-synchronous resonance damping controller. Besides the better damping capability, the proposed FLSMC enhances robustness of the system under parameter variations.

• Journal of Sensor Science and Technology
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• v.28 no.4
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• pp.246-250
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• 2019

In this study, in conjunction with a SIMULINK program based on system modeling of a voice-coil-actuator (VCA)-driven balancing scale, a proportional-integral-derivative control algorithm is implemented, and weighing characteristics are investigated through experiments and simulations. The extent to which the back electromotive force induced in the VCA-driven circuit and the magnetic damping induced by the coil wound bobbin of VCA affect the weighing speed is also investigated.

• Earthquakes and Structures
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• v.26 no.2
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• pp.163-174
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• 2024

Dynamic equilibrium equations for finite element analysis were derived for the free field one-dimensional shear wave propagation through the horizontally layered soil deposits with the elastic half-space. We expressed Rayleigh's viscous damping consisting of mass and stiffness proportional terms. We considered two cases where damping matrices are defined in the total and relative displacement fields. Two forms of equilibrium equations are presented; one in terms of total motions and the other in terms of relative motions. To evaluate the performance of new equilibrium equations, we conducted two sets of site response analyses and directly compared them with the exact closed-form frequency domain solution. Results show that the base shear force as earthquake load represents the simpler form of equilibrium equation to be used for the finite element method. Conventional finite element procedure using base acceleration as earthquake load predicts exact solution reasonably well even in soil deposits with unrealistically high damping.

• Transactions of the Korean Society of Automotive Engineers
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• v.2 no.3
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• pp.75-84
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• 1994

In general direct-operated pressure reducing valves have been gardly applied to a dynamic control system such as active suspension control because of their poor control stability. But they are more robust than pilot-operated type and do not need pilot control flow. In this paper development of a new direct-operated proportional pressure reducing valve for low-band type active suspension control is reported. By means of a special damper directly linked to the valve spool, the control stability could be effectively improved without drawback in response time. The linearity error was less than $\pm$3.5%. Applied to an experimental active suspension system the new valve showed the $-90^{\circ}$ phase delay at 4Hz with 20% sinusoidal signal input and could control the suspension system with almost same performance as that with a pilot-operated type valve.

• Journal of Ocean Engineering and Technology
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• v.20 no.1 s.68
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• pp.1-6
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• 2006

The effects of microstructure on the damping capacity and tensile properties of 316L stainless steel were investigated. Increasing the degree of cold working, the volume fraction of $\varepsilon-martensite$ decreased after rising to maximum value at specific level of cold working, the volume fraction of d-martensite slowly increased and then dramatically increased from the point of decreasing $\varepsilon-martensite$ volume fraction. Increasing the degree of cold working, the behnvior of damping capacity is similar to that of the $\varepsilon-martensite$. After the damping capacity showing the maximum value at about $20\%$ of cold rolling, damping capacity was decreased with the volume fraction of $\varepsilon-martensite$. Tensile strength was proportional to the volume fraction of d-martensite, and elongation steeply decreased in the range low volume fraction of a'-martensite, then slowly decreased in range the above $10\%$ volume fraction of d-martensite. The damping capacity and elongation is strongly controlled by the volume fraction of $\varepsilon$ martensite with liner relationship. However, the effect of the volume fraction of d-martensite and austenite phase on the damping capacity was not observed. Tensile strength was governed by the volume fraction of d-martensite.

• Journal of Power Electronics
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• v.18 no.2
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• pp.511-521
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• 2018

Proportional capacitor current feedback active damping (CCFAD) has a limited valid damping region in the discrete time domain as (0, $f_s/6$. However, the resonance frequency ($f_r$) of an LCL-type filter is usually designed to be less than half the sampling frequency ($f_s$) with the symmetry regular sampling method. Therefore, ($f_s/6$, $f_s/2$) becomes an invalid damping region. This paper proposes an improved CCFAD method to extend the valid damping region from (0, $f_s/6$ to (0, $f_s/2$), which covers all of the possible resonance frequencies in the design procedure. The full-valid damping region is obtained and the stability margin of the system is analyzed in the discrete time domain with the Nyquist criterion. Results show that the system can operate stably with the proposed CCFAD method when the resonance frequency is in the region (0, $f_s/2$). The performances at the steady and dynamic state are enhanced by the selected feedback coefficient H and controller gain $K_p$. Finally, the feasibility and effectiveness of the proposed CCFAD method are verified by simulation and experimental results.

• Journal of Power Electronics
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• v.13 no.3
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• pp.469-478
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• 2013

This paper proposes a novel scheme for the current controller for the grid-side converter (GSC) of permanent-magnet synchronous generator (PMSG) wind turbines to eliminate the high-order harmonics in the grid currents under grid voltage disturbances. The voltage unbalance and harmonics in three-phase systems cause grid current distortions. In order to mitigate the input current distortions, multi-loop current controllers are applied, where the positive-sequence component is regulated by proportional-integral (PI) controllers, and the negative-sequence and high-order harmonic components are regulated by proportional-resonance (PR) controllers. For extracting the positive/negative-sequence and harmonic components of the grid voltages and currents without a phase delay or magnitude reduction, composite observers are applied, which give faster and more precise estimation results. In addition, an active damping method using PR controllers to damp the grid current component of the resonant frequency is employed to improve the operating stability of VSCs with inductor-capacitor-inductor (LCL) filters. The validity of the proposed method is verified by simulation and experimental results.

• Journal of Power Electronics
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• v.15 no.4
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• pp.994-1005
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• 2015

This paper presents a novel power control strategy for PWM current-source rectifiers (CSRs) in the stationary frame based on the instantaneous power theory. In the proposed control strategy, a virtual resistance based on the capacitor voltage feedback is used to realize the active damping. In addition, the proportional resonant (PR) controller under the two-phase stationary coordinate is designed to track the ac reference current and to avoid the strong coupling brought about by the coordinate transformation. The limitations on improving steady-state performance of the PR controller is investigated and mitigated using a cascaded lead-lag compensator. In the z-domain, a straightforward procedure is developed to analyze and design the control-loop with the help of MATLAB/SISO software tools. In addition, robustness against parameter variations is analyzed. Finally, simulation and experimental results verify the proposed control scheme and design method.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.6
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• pp.583-590
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• 2016

This paper presents a dynamic crack propagation algorithm with Rayleigh damping effect based on the MLS(Moving Least Squares) Difference Method. Dynamic equilibrium equation and constitutive equation are derived by considering Rayliegh damping and governing equations are discretized by the MLS derivative approximation; the proportional damping, which has not been properly treated in the conventional strong formulations, was implemented in both the equilibrium equation and constitutive equation. Dynamic equilibrium equation including time relevant terms is integrated by the Central Difference Method and the discrete equations are simplified by lagging the velocity one step behind. A geometrical feature of crack is modeled by imposing the traction-free condition onto the nodes placed at crack surfaces and the effect of movement and addition of the nodes at every time step due to crack growth is appropriately reflected on the construction of total system. The robustness of the proposed numerical algorithm was proved by simulating single and multiple crack growth problems and the effect of proportional damping on the dynamic crack propagation analysis was effectively demonstrated.

• Journal of Power Electronics
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• v.14 no.6
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• pp.1322-1333
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• 2014

To track the sinusoidal current under stationary frame and suppress the effects of low-order grid harmonics, the multi-resonant quasi-proportional plus resonant (PR) controller has been extensively used for digitally controlled LCL-type pulse-width modulation (PWM) converters with capacitor-current-feedback active damping. However, designing the controller is difficult because of its high order and large number of parameters. Moreover, the computation and PWM delays of the digitally controlled system significantly affect damping performance. In this study, the delay effect is analyzed by using the Nyquist diagrams and the system stability constraint condition can be obtained based on the Nyquist stability criterion. Moreover, impact analysis of the control parameters on the current loop performance, that is, steady-state error and stability margin, identifies that different control parameters play different decisive roles in current loop performance. Based on the analysis, a simplified controller design method based on the system specifications is proposed. Following the method, two design examples are given, and the experimental results verify the practicability and feasibility of the proposed design method.