• Journal of Power Electronics
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• v.14 no.2
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• pp.249-256
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• 2014

A novel topology generation method for the no dead-time three-phase AC/DC converter is proposed in this study. With this method, a series of no dead time topologies are generated and their operation principles are analyzed. The classic three-phase bridge AC/DC converter can realize a bidirectional operation. However, dead-time should be inserted in the driving signals to avoid the shoot-through problem, which would cause additional harmonics. Compared with the bridge topology, the proposed topologies lack the shoot-through problem. Thus, dead time can be avoided. All of the no dead time three-phase AC/DC converters can realize bidirectional operation. The operating principles of the converters are analyzed in detail, and the corresponding control strategies are discussed. Comparisons of waveform distortion and efficiency among the converters are provided. Finally, 9 KW DSP-based principle prototypes are established and tested. Simulation and experimental results verify the theoretical analysis.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.9
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• pp.699-705
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• 2002

The present study discusses the deviation from the pure dead-time model of passive scalars such as temperature and concentration in the Poiseulle flow Even in the case of no thermal diffusion, there exists a substantial amount of damping and large deviation of phase lag from that computed by the traditional dead-time model after only 10 diameter downstream. These are caused by the phase difference of temperature in the radial direction due to the nonuniform velocity distribution. In the presence of thermal diffusion, damping is more pronounced.

• Journal of Power Electronics
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• v.9 no.3
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• pp.438-446
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• 2009

The performance of direct torque controlled (DTC) interior permanent magnet (IPM) machines is poor at low speeds due to a few reasons, namely limited accuracy of stator voltage acquisition and the presence of offset and drift components in the acquired signals. Due to factors such as forward voltage drop across switching devices in the three phase inverter and dead-time of the devices, the voltage across the machine terminals differ from the reference voltage vector used to estimate stator flux and electromagnetic torque. This can lead to instability of the IPM drive during low speed operation. Compensation schemes for forward voltage drops and dead-time are proposed and implemented in real-time control, resulting in improved performance of the space vector modulated DTC IPM drive, especially at low speeds. No additional hardware is required for these compensators.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.2B no.3
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• pp.81-89
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• 2002

The sensorless AC motor drive is a popular topic of study due to the cost and reliability of speed and position sensors. Most sensorless algorithms are based on the mathematical modeling of motors including electrical variables such as phase current and voltage. Therefore, the accuracy of such variables largely affects the performance of the sensorless AC motor drive. However, the output voltage of the SVPWM-VSI, which is widely used in sensorless AC motor drives, has considerable errors. In particular, the SVPWM-VSI is error-prone in the low speed range because the constant DC link voltage causes poor resolution in a low output voltage command and the output voltage is distorted due to dead time and voltage drop. This paper investigates a novel high-performance strategy for overcoming these problems in a sensorless ac motor drive. In this paper, a variation of the DC link voltage and a direct compensation for dead time and voltage drop are proposed. The variable DC link voltage leads to an improved resolution of the inverter output voltage, especially in the motor's low speed range. The direct compensation for dead time and voltage drop directly calculates the duration of the switching voltage vector without the modification of the reference voltage and needs no additional circuits. In addition, the proposed strategy reduces a current ripple, which deteriorates the accuracy of a monitored current and causes torque ripple and additional loss. Simulation and experimentation have been performed to verify the proposed strategy.

• Journal of Korean Society of Water and Wastewater
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• v.23 no.2
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• pp.199-205
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• 2009

It is very important to differentiate of DNA derived from live or dead bacteria within mixed microbial communities in aquatic environments. Ethidium monoazide (EMA) is a DNA intercalating agent and the treatment of EMA with strong visible light cleaves the genomic DNA of bacteria. In dead bacterial cells, EMA intercalates into the genomic DNA, induces the cleavage of DNA, and inhibits the PCR amplification. In this study, we developed the EMA-PCR and EMA real-time PCR to detect the DNA derived from viable Escherichia coli (E.coli) in mixed cultures of live and dead E.coli. The treatment of EMA, $50{\mu}g/mL$, and 650 W visible halogen light exposure for 2 minutes cleaved the genomic DNA derived from heat killed E.coli but did not those of live E.coli. EMA-PCR could detect the DNA from live E.coli in mixed culture samples of live and dead E.coli at various ratio and there was no DNA amplification in only dead E.coli cultures. Similar results were observed in EMA real-time PCR. Further studies are needed to develop various EMA-PCR methods to detect viable waterborne pathogens such as Helicobacter pylori, Giardia lamblia, and so on.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.4
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• pp.509-518
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• 2014

Though various techniques have been studied as a way of adjusting parameters of PID controllers, no perfect method of determining parameters is available to date. Especially the deign of PID controller for unstable processes with dead time(UPWDT) is even more difficult due to various reasons. Generally the existing design procedures for UPWDT involve deriving formulas to meet gain and phase margin specifications, or using inner loop to stabilize UPWDT before applying PID controller. In this paper, the dual-input describing function(DIDF) method is proposed, by which the performance and robustness of the closed-loop system can be improved. The method is based on moving the critical point (-1+j0) of Nyquist stability to a new position arbitrarily selected on the complex plane. This can be done by determining appropriate coefficients of the DIDF. As a result, we can easily determine parameters of PID-type controller by using existing conventional tuning methods for stable or unstable systems. Simulation results are included to show the effectiveness of the proposed method.

• Journal of Power Electronics
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• v.9 no.2
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• pp.232-242
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• 2009

In this paper, a matrix converter with improved low frequency output performance is proposed by achieving a one-step commutation owing to a general commutation circuit applicable to n-phase to m-phase matrix converters. The commutation circuit consists of simple resister and capacitor components, leading to a very stable, reliable and robust operation. Also, it requires no extra sensing information to achieve commutation, allowing for a one-step commutation like a conventional dead time commutation. With the dead time commutation strategy applied, the distortion caused by commutation delay is analyzed and compensated, therefore leading to better output linear behavior. In this paper, detailed commutation procedures of the R-C commutation circuit are analyzed. A selection of specific semiconductor switches and commutation circuit components is also provided. Finally, the effectiveness of the proposed commutation method is verified through a two-phase to single-phase matrix converter and the feasibility of the compensation approach is shown by an open loop space vector modulated three-phase matrix converter with a passive load.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.1007-1011
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• 2003

In this paper, a design of I-PDA controller by CDM to control a flow process whose structure is first order lag plus a dead time is introduced. The factor of dead time of the process is approximated by second order Pade approximation in order to get a third order system. The simulations show that both of the transient and steady state specifications can be fulfilled. However, the transient response of the I-PDA control system still has long rise time. Then, a feedforward controller (FFC) with two adjustable parameters and one derivative time is introduced into I-PDA control system for improving the speed of the system response. It is shown, from the simulation results, that the performance of the I-PDA control system with suitable FFC has shorter rise time and no overshoot, while settling time remains almost the same. The performance comparison of the proposed control system with the PI control system with and without FFC is also made.

• Toxicological Research
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• v.31 no.2
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• pp.203-211
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• 2015

Trichloroacetonitrile is used as an intermediate in insecticides, pesticides, and dyes. In Korea alone, over 10 tons are used annually. Its oral and dermal toxicity is classified as category 3 according to the globally harmonized system of classification and labelling of chemicals, and it is designated a toxic substance by the Ministry of Environment in Korea. There are no available inhalation toxicity data on trichloroacetonitrile. Thus, the present study performed inhalation tests to provide data for hazard and risk assessments. Sprague-Dawley rats were exposed to trichloroacetonitrile at concentrations of 4, 16, or 64 ppm for 6 hour per day 5 days per week for 13 weeks in a repeated study. As a result, salivation, shortness of breath, and wheezing were observed, and their body weights decreased significantly (p < 0.05) in the 16 and 64 ppm groups. All the rats in 64 ppm group were dead or moribund within 4 weeks of the exposure. Some significant changes were observed in blood hematology and serum biochemistry (e.g., prothrombin time, ratio of albumin and globulin, blood urea nitrogen, and triglycerides), but the values were within normal physiological ranges. The major target organs of trichloroacetonitrile were the nasal cavity, trachea, and lungs. The rats exposed to 16 ppm showed moderate histopathological changes in the transitional epithelium and olfactory epithelium of the nasal cavity. Nasal-associated lymphoid tissue (NALT) and respiratory epithelium were also changed. Respiratory lesions were common in the dead rats that had been exposed to the 64 ppm concentration. The dead animals also showed loss of cilia in the trachea, pneumonitis in the lung, and epithelial hyperplasia in the bronchi and bronchioles. In conclusion, the no-observed-adverse-effect level (NOAEL) was estimated to be 4 ppm. The main target organs of trichloroacetonitrile were the nasal cavity, trachea, and lungs.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.7 s.262
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• pp.588-595
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• 2007

The water transport inside a polymer electrolyte fuel cell (PEFC) varied according to the anodic supply mode. The performance characteristics of a PEFC which can be affected by the water transport were observed with the anodic supply mode. In the flow-through and recirculation mode the performance showed no reduction with time because the flow in the anode was not stagnated. In the dead-end mode, without any discharged gas, the water remains inside of the anode, which caused the reduction of the performance with the lapse of time. However, even in the dead-end mode, little reduction of the performance with time was shown when only the anode was humidified externally. It means that the back-diffusion was the major factor to the accumulation of water in the anode rather than external humidification.