• Journal of Power Electronics
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• v.19 no.4
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• pp.980-988
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• 2019

When compared with traditional power frequency generators, the frequency of a super high-speed permanent magnet generator (SHSPMG) is a lot higher. In order to study the influence of frequency on the electromagnetic field of SHSPMGs, a 60000rpm, 117kW SHSPMG was taken as a research object. The two-dimensional finite element model of the generator was established, and the two-dimensional transient field of the generator was simulated. In addition, a test platform of the generator was set up and tested. The reliability of the simulation was verified by comparing the experiment data with that of the simulation. Then the generator electromagnetic field under different frequencies was studied, and the influence mechanism of frequency on the generator electromagnetic field was revealed. The generator loss, voltage regulation rate, torque and torque ripple were analyzed under the rated active power load and different frequencies. The influences of frequency on the eddy current density, loss, voltage regulation rate and torque ripple of the generator were obtained. These conclusions can provide some reference for the design and optimization of SHSPMGs.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.1
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• pp.16-22
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• 2015

As the development of Battery Energy Storage System(BESS) and the increasing of intermittent energy sources like wind power and photovoltaic, the application of BESS in load frequency control is considered as an effective method. To evaluate the effectiveness of BESS application in frequency control, we defined a governor free model of BESS to conduct dynamic simulation. Using the BESS dynamic model, we implemented the power system dynamic model including steam, gas and hydro turbine generators. In this paper we study the control performance of BESS in primary frequency control. The effect of BESS speed regulation rate and response time on governor free operation is investigated. In addition, we compared BESS from steam turbine generator in view point of frequency regulation.

• Journal of Biosystems Engineering
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• v.21 no.2
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• pp.155-166
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• 1996

A direct injection sprayer was designed using the concepts of injection mixing and total flow control, flowrate-based system compensating for the variation of forwarding speed. A metered rate, proportionally to the actual diluent flow rate, of a tracer chemical was injected directly into the diluent stream. The injection of chemical may improve the precision and safety of chemical application process. The control system was evaluated for the variables of the control interval, tolerances and sensitivities of flow regulation valve and injection pump. Performance of the system was assessed as that the response time of flow rate, response time of injection rate, absolute steady state error, and the coefficient of variance(C.V.) of concentration were 8.5 and -0.53 seconds, 0.067 lpm(0.8%) and 3.15%, respectively, at optimal parameters of control interval of 1.0 sec, fast sensitivity of flow regulation valve, medium sensitivity of injection pump and medium tolerance of flow rate. Performance of the system can be improved by increasing the sensitivity of flow regulating valve and employing a high resolution velocimeter, such as Doppler radar.

• Journal of Power Electronics
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• v.19 no.5
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• pp.1203-1215
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• 2019

Sensorless brushless DC (BLDC) motor drive systems are often subjected to inaccurate commutation signals and can produce high current peaks and conduction consumption. To achieve accurate commutation, a fast commutation shift regulation method for sensorless BLDC motor drive systems considering the influence of the inductance freewheeling process is presented to compensate inaccurate commutation signals. The regulation method is effective in both steady speed and variable speed operations. In the proposed method, the commutation error is gained from the line-voltage difference integral in a 60 electrical-degree conduction period and the outgoing phase current before commutation. In addition, the detection precision of the commutation error is improved due to the consideration of the freewheeling period. The commutation error is directly obtained, which avoids successive optimization and accelerates the convergence rate of the proposed method. Moreover, the commutation error features a positive or negative sign, which can be utilized as an indicator of advanced or delayed commutation. Finally, experiments are conducted to validate the effectiveness and feasibility of the proposed method. The results obtained show that the proposed method can accurately regulate commutation signals.

• Journal of the Korean Society of Industry Convergence
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• v.7 no.2
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• pp.153-159
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• 2004

The purpose of this research is to investigate the performance of swirl combustion chamber diesel engine by changing the jet passage area, the depth and shape of the piston top cavity (main chamber). The performance of diesel engine with newly changed swirl combustion chamber was tested through the experimental conditions as engine speed, load and injection timing etc. The test results were compared and analyzed. And another purpose of this research is to make a new diesel engine that is satisfied fuel consumption and regulation value of exhaust gas. 1. The rate of fuel consumption was affected significantly by the jet passage area at the high speed and load than low speed and low load. The influence of jet passage large area was proven to decrease the rate of fuel consumption. 2. Smoke was affected significantly by the depth of the piston top cavity, but exhaust temperature and the rate of fuel consumption wasn't affected. The rate of fuel consumption was affected by changing injection timing. 3. The rate of fuel consumption, exhaust temperature and Smoke were affected significantly by the shape of the piston top cavity from rectangular to trapezoid. That is we have all high value. The exhaust smoke density and exhaust gas temperature depended sensitively on variation of the injection timing rather than the shape of the combustion chamber within the experimental conditions. 4. We made a new diesel engine that is satisfied design target values(sfc=190 g/hr, NOx + THC=6.0 g/KWh, PM=0.3 KWh), the rate of fuel consumption and emission standard etc., through changing injection timing at the maximum torque point and rated power point. Although we have a little high NOx value.

• The Korean Journal of Physiology and Pharmacology
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• v.6 no.2
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• pp.81-85
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• 2002

Conventional views of synaptic transmission generally overlook the possibility of 'postfusional-control' the regulation of the speed or completeness of transmitter release upon vesicular fusion. However, such regulation often occurs in non-neuronal cells where the dynamics of fusion-pore opening is critical for the speed of transmitter release. In case of synapses, the slower the transmitter release, the smaller the size and rate-of-rise of postsynaptic responses would be expected if postsynaptic neurotransmitter receptors were not saturated. This prediction was tested at hippocampal synapses where postsynaptic AMPA-type glutamate receptors (AMPAR) were not generally saturated. Here, we found that the small miniature excitatory postsynaptic currents (mEPSCs) showed significantly slower rise times than the large mEPSCs when the sucrose-induced mEPSCs recorded in cyclothiazide (CTZ), a blocker for AMPAR desensitization, were sorted by size. The slow rise time of the small mEPSCs might result from slow release through a non-expanding fusion pore, consistent with postfusional control of neurotransmitter release at central synapses.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.2
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• pp.182-189
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• 2003

We have found that the damage of the front part for a vehicle and that of the rear part for a vehicle are the majority of frequency experienced by the traffic accidents. In conventional bumper system was designed by safety standard regulation at low speed crash. For example there are 2.5 mile and 5 mile bumper. The conventional bumper system was the crash from max 5.5 mile to 3 mile low speed occurs most frequently and results in the highest rate of repairing cost in statistically. On this study, in order to check the damageability and repairability of gas tube bumper system RCAR 15 km/h 40 % offset frontal crash test was adopted in low speed and we have a gas tube bumper parts test and vehicle test with gas tube bumper, we can find gas tube bumper system definitely can improve the damageability and repairability of the vehicles and contribute to down the repairing cost.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.8
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• pp.1173-1182
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• 2001

Recent noticeable advances of CNC machine tools have considerably improved productivity and precision in manufacturing processes. However, in the respect of productivity some defects still remain because selection of machining conditions entirely depends on the experiences of programmers. Usually, machining conditions such as feed rate and spindle speed have been selected conservatively by considering the worst cases, and it has brought the loss of machining efficiency. Thus, the improvement of cutting force controller has been done to regulate cutting force constantly and to maximize feedrate simultaneously in case that machining conditions change variously. In this study, sliding mode control with boundary layer is applied to milling process for cutting force regulation and in a commercial CNC machining center data transfer between PC and PMC (programmable machine controller) of CNC machine is done using a standard interface method. And in the cutting force measurement, an indirect cutting force measuring system using current signal of AC servo is adopted in order not to use high-priced equipment like tool dynamometer. The purpose of this study is to maximize the productivity in milling process, thus its results can be applied to cases such as rough cutting process.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3294-3299
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• 2007

These days the exhaustion of petroleum resources and environmental problems are getting serious. Many researchers are focused on low emission and high performance vehicles. Therefore, we should concern about emission regulation when we design a new car. In this study, we investigated the characteristics of the traditional mechanical engine cooling systems which control the engine temperature using engine speed and wax type thermostat. This experiment used three components which are Radiator fan, water pump and water valve controlled by an electronic system based on the engine status (load, speed). We elucidated how different between traditional mechanical cooling system and electronic cooling system which control coolant temperature and coolant flow rate in a DI diesel engine in this paper. The results revealed a fuel saving and an emission (CO, HC) reduction on NEDC cycle.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.8
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• pp.1480-1486
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• 2002

In this study, the cross-coupling control (CCC) with three new features is proposed to maintain contour precision in high-speed nonlinear contour machining. One is an improved contour error model that provides almost exact calculation of the errors. Another is the utilization of variable controller gains based on the instantaneous curvature of the contour and the variable command. For this scheme, a stability is analyzed. As a result, the stability region is obtained, and the variable gains are decided within that region. The other scheme in the proposed CCC is a real-time feedrate adaptation module to regulate cutting force fur better surface finish through regulation of material removal rate (MRR). The simulation results show that the proposed CCC system can provide better precision than the existing method particularly in high-speed machining of nonlinear contours.