• IEIE Transactions on Smart Processing and Computing
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• v.5 no.1
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• pp.35-42
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• 2016

Developments in power electronics have enabled the widespread application of Pulse Width Modulation (PWM) inverters, notably for connecting renewable systems to the grid. This study demonstrates that a high-quality power can be achieved using a stand-alone inverter, whereby the comparison between the power quality of the stand-alone inverter with battery storage (off-grid) and the power quality of the utility network is presented. Multi-loop control techniques for a single phase stand-alone inverter are used. A capacitor current control is used to give active damping and enhance the transient and steady state inverter performance. A capacitor current control is cheaper than the inductor current control, where a small current sensing resistor is used. The output voltage control is used to improve the system performance and also control the output voltage. The inner control loop uses a proportional gain current controller and the outer loop is implemented using internal model control proportional-integral-derivative to ensure stability. The optimal controls are achieved by using the Sisotool tool in MATLAB/Simulink. The outcome of the control scheme of the numerical model of the stand-alone inverter has a smooth and good dynamic performance, but also a strong robustness to load variations. The numerical model of the stand-alone inverter and its power quality are presented, and the power quality is shown to meet the IEEE 519-2014. Furthermore, the power quality of the off-grid system is measured experimentally and compared with the grid power, showing power quality of off-grid system to be better than that of the utility network.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.5
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• pp.521-532
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• 2007

Elastic wave propagations in the semi-infinite transversely isotropic cylinder under various kinds of longitudinal impact loads are analyzed using the axisymmetric finite element method and Houbolt time-integration scheme. For which the finite element program is newly constructed and verified through the comparison of present numerical results with those by other researchers. E-type glass-epoxy composite cylinders with different fiber volume fractions are adopted and studied in detail with dynamic responses of the isotropic cylinder. Three dimensional wave motions are given in graphic form to show the realistic view of the wave propagation. Nondimensionalized dynamic characteristic variables which relate the size of finite element mesh, the time step, and the wave speed are presented for obtaining accurate and stable numerical results.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.18 no.3
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• pp.470-487
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• 1996

The purpose of this study was to investigate the dynamic response of the mandible to impact and provide insight into the fracture mechanism of the mandible, by 3-dimensional finite element method. The finite element model of the mandible was developed and calculated using NASTRAN/XL (MSC co. U.S.A.) and the linear dynamic transient analysis was performed according to the impulsive force direction, force type and impulse time to the mandible. At first, the load was applied on the mandibular symphysis, body, angle and subcondylar area in the horizontal mandibular plane and the computed stress-time histories at 14 locations of the mandible were obtained. Secondly, the impulsive force was directed to the symphyseal area with changing the force magnitude and impulse time, and calculated the node displacement at 8 locations of mandible. The conclusions from from this study were as follows. 1. The appearance of impulsive energy transmission was different to the direction of impulse to the mandible. 2. The impulsive stress and deformation were larger in lingual or medial side than buccal or lateral in the mandible. 3. The velocity, appearance of energy transmission and the fracture pattern in mandible were affected rather impulse time than force. 4. The horizontal impact to the one side of mandible did not have effect on the stress and displacement of contralateral mandible. From the above results, fracture pattern in symphysis can be showed as simple or comminuted, multiple or associated in body and angle and solitary in subcondyle area.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.6
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• pp.144-150
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• 2007

In recent years, the particle number emissions rather than particulate mass emissions in automotive engine have become the subject of controversial discussions. Recent results from the health effects studies imply that it is possible that particulate mass does not properly correlated with the variety of health effects attributed to diesel exhaust. So, the concern is instead now focusing on nano-sized particles emitted from I. C. engine. This study has been performed for the better understanding about the engine nano-particle for 3-measurement systems with different measuring principle. Firstly, EEPS is a newly introduced instrument for size distribution measurement of engine exhaust particles. It can measure nano-particles with an adequate resolution and in real time. In this study, the characteristics of EEPS were compared with ELPI and SMPS. As a research results, EEPS showed a same effect of engine load on the size distribution with ELPI and SMPS. But the quantitative results of EEPS were more similar to SMPS than ELPI, because the EEPS and SMPS use a same principle for classifying particles by size. The capability for transient measurement of EEPS was equivalent to that of ELPI.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.10
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• pp.1432-1441
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• 2012

In this study, an improved LCCT(Inductor-Capacitor-Capacitor-Trans) Z-source inverter(Improved LCCT ZSI) with characteristics of Quasi Z-source inverter(QZSI) and LCCT Z-source inverter(LCCT ZSI) is proposed. The proposed inverter can also reduce the voltage stress and input current/capacitor voltage ripples compared with conventional LCCT ZSI and Quasi ZSI. A two winding trans in Z-impedance network of the conventional LCCT ZSI is replaced by a three winding trans in the proposed inverter. To verify the validity of the proposed inverter, a DSP controlled hardware was made and PSIM simulation was executed for each method. Comparing the current and voltage ripples of each method under the condition of input DC voltage 70[V] and output AC voltage 76[Vrms], the input current and capacitor voltage ripple factors of the proposed inverter were low as 11[%] and 1.4[%] respectively. And, for generation of the same output AC voltage of each method, voltage stress of the proposed inverter was low as 175[V] under the condition of duty ratio D=0.15. As mentioned above, we could know that the proposed inverter have the characteristics of low voltage stress, low ripple factor and low operation duty ratio compared with the conventional methods. Finally, the efficiency according to load change/duty ratio and the transient state characteristics were discussed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.6
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• pp.619-627
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• 2014

An optimization method is proposed for the simultaneous design of structural and control systems using the equivalent static loads. In the past researches, the control parameters of such feedback gains are obtained to improve some performance in the steady-state. However, the actuators which have position and velocity feedback gains should be designed to exhibit a good performance in the time domain. In other words, the system analysis should be conducted for the transient-state in dynamic manner. In this research, a new equivalent static loads method is presented to treat the control variables as the design variables. The equivalent static loads (ESLs) set is defined as a static load set which generates the same displacement field as that from dynamic loads at a certain time. The calculated sets of ESLs are applied as multiple loading conditions in the optimization process. Several examples are solved to validate the proposed method.

• Journal of Korean Society of Steel Construction
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• v.24 no.6
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• pp.637-645
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• 2012

The composite action in truss beam is generally achieved by providing shear connectors between the steel top chord of the truss and the concrete slab. The composite sections have greater stiffness than the sum of the individual stinesses of the slab and truss. Therefore, steel trusses that act compositely with concrete slabs can carry larger load and are stiffer and less prone to transient vibration. The crack pattern and deflection of the beam of the composte truss were investigated by using of 600MPa class steel in this study. The test results were compared with the results for the noncomposite trusses. Test results were also compared with the results of composite trusses by using of 400MPa class steel. It was ascertained that the case of high strength steel is more efficient compared with the case of SS400 steel for T-shaped steel.

• Journal of Mechanical Science and Technology
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• v.19 no.3
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• pp.778-791
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• 2005

A novel pneumatic artificial muscle actuator (PAM actuator), which has achieved increased popularity to provide the advantages such as high strength and high power/weight ratio, low cost, compactness, ease of maintenance, cleanliness, readily available and cheap power source, inherent safety and mobility assistance to humans performing tasks, has been regarded during the recent decades as an interesting alternative to hydraulic and electric actuators. However, some limitations still exist, such as the air compressibility and the lack of damping ability of the actuator bring the dynamic delay of the pressure response and cause the oscillatory motion. Then it is not easy to realize the performance of transient response of pneumatic artificial muscle manipulator (PAM manipulator) due to the changes in the external inertia load with high speed. In order to realize satisfactory control performance, a variable damper-Magneto­Rheological Brake (MRB), is equipped to the joint of the manipulator. Superb mixture of conventional PID controller and a phase plane switching control method brings us a novel controller. This proposed controller is appropriate for a kind of plants with nonlinearity, uncertainties and disturbances. The experiments were carried out in practical PAM manipulator and the effectiveness of the proposed control algorithm was demonstrated through experiments, which had proved that the stability of the manipulator can be improved greatly in a high gain control by using MRB with phase plane switching control method and without regard for the changes of external inertia loads.

• Journal of Electrical Engineering and Technology
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• v.12 no.4
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• pp.1442-1448
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• 2017

Recently, electric power systems have been operating with tight margins and have reached their operational limits. Many researchers consider a microgrid as one of the best solutions to relieve that problem. The microgrid is generally powered by renewable energies that are connected through power converters. In contrast to the rotational machines in the conventional power plants, the converters do not have physical rotors, and therefore they do not have rotational inertia. Consequently, a stand-alone microgrid has no inertia when it is powered by the only converter-based-generators (CBGs). As a result, the relationship between power and frequency is not valid, and the grid frequency cannot represent the power balance between the generator and load. In this paper, a superconducting flywheel energy storage system (SFESS) is applied to an inertia-free stand-alone (IFSA) microgrid. The SFESS accelerates or decelerates its rotational speed by storing or releasing power, respectively, based on its rotational inertia. Then, power in the IFSA microgrid can be balanced by measuring the rotor speed in the SFESS. This method does not have an error accumulation problem, which must be considered for the state of charge (SOC) estimation in the battery energy storage system (BESS). The performance of the proposed method is verified by an electromagnetic transient (EMT) simulation.

• Journal of Korean Society of Environmental Engineers
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• v.28 no.1
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• pp.97-103
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• 2006

In this paper, a control method of a mini ozone generator is proposed, and also a cooling technique is described which is cooling down the flowing air gap into a silent discharger to $2^{\circ}C$ to generate ozone of high density and diffusing power. As the digital control system for this method, a double feedback loop is designed which detects the voltage and current of equivalent capacitor of the discharger and compensates for the poor power waveform caused by the noise at high discharging frequency. During the plant modeling of this system, computing time factor is considered as a unique parameter of the power system to improve the transient responses with regard to fluctuating load and to replenish the computing time delay of the controller. Through the experiment, sinusoidal input current for discharger can be acquired and all the effectiveness of this accurate control system over unstable ozone discharger are proved.