• Journal of Power System Engineering
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• v.3 no.2
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• pp.26-33
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• 1999

Pressure pulsation Inside the discharge and suction cavity of rotary and scroll compressor are often a major source of objectionable noise and vibration. The key factor of these noise and vibration is due to the cavity resonance. It is not only necessary to understanding the characteristics of pulsation in order to reduce the excitation force of gas to the cavity but also to verifying the phenomena of cavity resonance. For the purpose of these understandings, measurement and simulation of cavity resonance can lead to a better understandings how they occur and be very important to identify the ways to reduce the noise efficiently. In this paper, modeling of the cavity(internal acoustics inside the shell) is discussed and simulated using FEM. Results from the simulation are compared with those measurement in experiments. In describing of cavity mode by experiments, it is very important to specify the exact conditions under which they are measured. Finally, this paper shows the one example of reduced cavity resonance in the compressor.

• Journal of Electrical Engineering and Technology
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• v.11 no.3
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• pp.560-574
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• 2016

This paper presents a novel method for power system harmonic estimation based on the Park transform. The proposed method firstly extends the signal to a group of three-phase signals in a-b-c coordinate. Then, a linear fitting based method is adopted to estimate the fundamental frequency. Afterwards, the Park transform is utilized to convert the three-phase signals from a-b-c coordinate to d-q-0 coordinate. Finally, the amplitude and phase of a harmonic component of interest can be calculated using the d-axis and q-axis components obtained. Simulation studies have been conducted using matrix laboratory (MATLAB) and power system computer aided design/electromagnetic transients including direct current (PSCAD/EMTDC). Simulation studies in MATLAB have considered three scenarios, i.e., no-frequency-deviation scenario, frequency-deviation scenario and the scenario in the presence of inter-harminics. The results have demonstrated that the proposed method achieves very high accuracy in frequency, phase and amplitude estimation under noisy conditions, and suffers little influence of the inter-harmonics. Moreover, comparison studies have proved that the proposed method is superior to FFT and Interpolated FFT with the Hanning Window (IpFFTHW). Finally, a popular case in PSCAD/EMTDC has been employed to further verify the effectiveness of the proposed method.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.55 no.9
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• pp.384-391
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• 2006

The harmonic currents generated along with the operating speed of electrical railroad traction are very difficult to analyze because of its nonlinear characteristics. This paper therefore presents probabilistic approach for the evaluation of harmonic currents about the operating speed of the arbitrary single traction. To use probabilistic method for railroad system, PDF(Probability Density Function) using measuring data based on the realistic h 따 monic currents per operating speed is calculated. Measuring data of harmonic current per operating speed is obtained using the result data of PSCAD/EMTDC dynamic simulation based on an IAT(Intra Airport Transit) in Incheon International Airport. The means(expected values) and variances of harmonic currents of single traction also are obtained by the PDF of the operating traction speed and harmonic currents. The uncertainty of harmonic currents can be calculated through the mean and variance of PDF. The probability of harmonic currents generated with the operating of arbitrary many tractions is calculated by the convolution of functions. The harmonics of different number of tractions are systematically investigated to assess the TDD(Total Demand Distortion) for the railroad system. The calculation of TDD was carried out using Monte-Carlo Simulations(MSCs) and the results of TDD evaluation of the power quality in the IAT power feeding system.

• Proceedings of the KIEE Conference
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• 2002.04a
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• pp.228-230
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• 2002

Recently, electric power reliability of our country has been improved. However, there are still remaining problems which are short-duration variations like instantaneous and momentary interruption and voltage sag by nature calamity ; typhoon, lightning, snow, etc. Besides, power quality ; harmonics, caused by using power electronics equipments, become a hot issue Malfunction of controller and stop machinery, and losing the important data are caused by poor power quality at a couple of second. Due to those, UPS, which is made up battery, has being used, but there are several disadvantages ; long charge and discharge time, environmental problem by acid and heavy metal, and short life time. As generally know, micro-SMES is a method to settle those mentioned. However, there need huge system apparatuses in order to verify the effect of system efficiency and stability considering the size of micro-SMES, the sort of converter type, and various conditions ; inner temperature, magnetic field, quench characteristic of micro-SMES, and etc. In this paper, in order to bring the mentioned above to a settlement, a micro-SMES is modeled with characteristics of micro-SMES is interfaced to EMTOC program using Fortran program interface method. We obtained hopeful answers and made the simulation model of micro SMES.

• Journal of the Korean Society for Railway
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• v.15 no.2
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• pp.129-134
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• 2012

In this paper, speed control of IPMSM drives for the next generation domestic high speed railway system using NPC 3-level inverters is presented. The NPC multilevel inverter is suitable for the high-voltage and high-power motor drive system because it has advantages in that the voltage rating of the power semiconductor devices and output current harmonics are reduced. For the speed control of IPMSM using NPC 3-level inverters, maximum torque control is applied in the constant torque region, and filed weakening control is applied in the constant power region. Simulation programs based on MATLAB/Simulink are developed. Finally the designed system is verified and their characteristics are analyzed by the simulation results.

• JSTS:Journal of Semiconductor Technology and Science
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• v.16 no.4
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• pp.451-462
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• 2016

Photovoltaic energy conversion becomes main focus of many researches due to its promising potential as source for future electricity and has many advantages than the other alternative energy sources like wind, solar, ocean, biomass, geothermal etc. In Photovoltaic power generation multilevel inverters play a vital role in power conversion. The three different topologies, diode-clamped (neutral-point clamped) inverter, capacitor-clamped (flying capacitor) inverter and cascaded h-bridge multilevel inverter are widely used in these multilevel inverters. Among the three topologies, cascaded h-bridge multilevel inverter is more suitable for photovoltaic applications since each pv array can act as a separate dc source for each h-bridge module. This paper presents a single phase Cascaded H-bridge five level inverter for grid-connected photovoltaic application using sinusoidal pulse width modulation technique. This inverter output voltage waveform reduces the harmonics in the generated current and the filtering effort at the input. The control strategy allows the independent control of each dc-link voltages and tracks the maximum power point of PV strings. This topology can inject to the grid sinusoidal input currents with unity power factor and achieves low harmonic distortion. A PID control algorithm is implemented in Arm Processor LPC2148. The validity of the proposed inverter is verified through simulation and is implemented in a single phase 100W prototype. The results of hardware are compared with simulation results. The proposed system offers improved performance over conventional three level inverter in terms of THD.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.5
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• pp.412-418
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• 2002

In this paper, the authors present the simulation results and the experimental considerations on the effects of the effects of the VCO oscillation characteristics caused by varying the length of the MSL and the composition capacitance of LC resonation circuity. Simulation was accomplished by nonlinear RF circuit simulator for designing and analyzing the RF characteristis of VCO. The samples with 3 different MSL lengths of which the length is 140mil, 280mil and 560mil respectively were fabricated by screen printing process. The oscillation frequency of each sample(VCO) was tuned to UHF band (750MHz~900MHz) by varying the capacitance of LC resonator circuit. The experimental results showed that the values of phase noise were -82, -93, -97[dBc/Hz] at 50[kHz] offset frequency, the pushing figures were 114, 94, 318[kHz] at applied voltage of $3\pm0.15$[V] and the harmonics were -21, -16, -13[dBc] for MSL lengths of 140mil 280mil, 560mil respectively. The frequency and output variation width were 779~898[MHz], -36~-33[dBm] for MSL with 140mil length; 818~836[MHz], -27.19~27.06[dBm] for 280mil; 751.54~751.198[MHz], -33.44~-33.31[dBm] for 560mil.

• Journal of Power Electronics
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• v.10 no.2
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• pp.138-145
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• 2010

This paper presents a single phase multilevel inverter for using as a voltage harmonic source. First, a single phase multilevel inverter system is presented and the structural parts of the inverter are described. In order to obtain multilevel output voltage waveforms, a switching strategy based on calculating switching angles is explained and an improved formula for determining switching angles is given. Simulation and experimental results of multilevel voltage waveforms are given for 15, 31 and 127 levels. The proposed topology does not only produce output voltages with low THD values. It also produces the required harmonic components on the output voltage. For this purpose, equations for switching angles are constituted and the switching functions are obtained. These angles control the output voltage as well as provide the required specific harmonics. The proposed inverter structure is simulated for various functions with the required harmonic components. The THD values of the output voltage waves are calculated. The simulated functions are also realized by the proposed inverter structure. By using a harmonic analyzer, the harmonic spectrums, which belong to the output voltage forms, are found and the THD values are measured. Simulation and experimental results are given for the specific functions. The proposed topology produces perfectly suitable results for obtaining the specific harmonic components. Therefore, it is possible to use the structure as a voltage harmonic source in various applications.

• Journal of Power Electronics
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• v.18 no.1
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• pp.81-91
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• 2018

This paper proposes a double line voltage synthesis (DLVS) strategy for three-to-five phase direct matrix converters. In the proposed strategy, the input and expected output voltages are divided into 6 segments and 10 segments, respectively. In addition, in order to obtain the maximum voltage transfer ratio (VTR), the input line voltages and "source key" should be selected reasonably according to different combinations of input and output segments. Then, the corresponding duty ratios are calculated to determine the switch sequences in different segment combinations. The output voltages and currents are still sinusoidal and symmetrical with little lower order harmonics under unbalanced or distorted input voltages by using this strategy. In addition, the common mode voltage (CMV) can be suppressed by rearranging some of the switching states. This strategy is analyzed and studied by a simulation model established in MATLAB/Simulink and an experimental platform, which is controlled by a DSP and FPGA. Simulation and experimental results verify the feasibility and validity of the proposed DLVS strategy.

• Journal of Power Electronics
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• v.17 no.6
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• pp.1683-1693
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• 2017

This paper analyses the harmonic pollution to power grids caused by thyristor-controlled devices. It also formulates a mathematic derivation for the voltage spikes in thyristor-controlled branches to explain the harmonic and EMI derived from the reverse-recovery characteristics of the thyristor. With an equivalent nonlinear time-varying voltage source, a detailed simulation model is established, and the periodic dynamic switching characteristic of the thyristor can be explicitly implied. The simulation results are consistent with the probed results from on-site measurements. An improved trigger system with gate-shorted circuit structure is proposed to reduce the voltage spikes that cause EMI. The experimental results indicate that a prototype with the improved trigger system can effectively suppress the voltage spikes.