• The Transactions of the Korean Institute of Electrical Engineers B
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• v.52 no.2
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• pp.68-79
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• 2003

We estimated harmonics on power system of AC railway based on quantitatively measured harmonics and investigated the need of facilities for harmonics reduction. In order to analysis harmonics which inflow into power system due to increase in collector voltages and harmonic currents generated from the train when the railway is in operation, the railway system Is sectioned into power supply, railway line, AT, sectioning Post and subsectioning post. For analysis of extension of currents resulting from the railway loads, PWM converter, VVVF inverter and the feeder system are modeled based on the dynamic node technique(DNT). In order to test the usefulness of the DNT for analysis of harmonic effects, the measured harmonic currents and harmonic magnification ratios at the S/K substation are compared with simulation results using DNT modelling, which include the results for two cases with and without filters for suppression of harmonic currents. When 8 cars(4M4T) are in operation, the total sum of harmonic currents resulting from the train at M and T phases, which inflow into the substation along with the railway line, is calculated. Using the harmonics analysis program for railway feeder system with these data, the total harmonic distortion factor(710) at the outgoing point of KEPCO substation is computed. The calculation shows that when the maximum THD at the receiving point of H/K substation was 0.0443% which is much lower than 1.5% which is the allowable value of KEPCO at 154kV as well as IEEE-519 above 132kV This result indicates that any measure for harmonics reduction in Incheon International Airport Railway is not needed.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.1
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• pp.45-52
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• 2021

The space vector control based voltage control method for a three-phase PWM rectifier requires a lot of effort to design an optimal switching pattern since a switching pattern for the switching section must be designed. In this study, a D-Q control based SPWM output voltage control algorithm was studied for the three-phase six-pulse CVS type rectifier. In the output voltage control algorithm, three-phase reference signals are obtained from the D-Q transformation based on the space vector representation method, instead of the switching pattern, SPWM method is used to generate rectifier switching control signals. Next, a three-phase six-pulse CVS PWM rectifier based on D-Q transformation and SPWM was modeled using EMTP-RV. Finally, the validity of the D-Q control-based SPWM voltage control algorithm was confirmed by comparing the output voltage waveform obtained through EMTP-RV simulation works with a reference value and confirming that the output voltage accurately follows the reference voltage.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.51 no.3
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• pp.120-125
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• 2002

The switching-mode power converter has been widely used because of its features of high efficiency and small weight and size. These features are brought by the ON-OFF operation of semiconductor switching devices. However, this switching operation causes the surge and EMI(Electromagnetic Interference) which deteriorate the reliability of the converter themselves and entire electronic systems. This problem on the surge and noise is one of the most serious difficulties in AC-to-DC converter. In the switching-mode power converter, the output voltage is generally controlled by varying the duty ratio of main switch. When a converter operates in steady state, duty ratio of the converter is kept constant. So the power of switching noise is concentrated in specific frequencies. Generally, to reduce the EMI and improve the immunity of converter system, the switching frequency of converter needs to be properly modulated during a rectified line period instead of being kept constant. Random Pulse Width Modulation (RPWM) is performed by adding a random perturbation to switching instant while output-voltage regulation of converter is performed. RPWM method for reducing conducted EMI in single switch three phase discontinuous conduction mode boost converter is presented. The more white noise is injected, the more conducted EMI is reduced. But output-voltage is not sufficiently regulated. This is the reason why carrier frequency selection topology is proposed. In the case of carrier frequency selection, output-voltage of steady state and transient state is fully regulated. A RPWM control method was proposed in order to smooth the switching noise spectrum and reduce it's level. Experimental results are verified by converter operating at 300V/1kW with 5%~30% white noise input. Spectrum analysis is performed on the Phase current and the CM noise voltage. The former is measured with Current Probe and the latter is achieved with LISN, which are connected to the spectrum analyzer respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.6
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• pp.2722-2728
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• 2011

3Phase PWM rectifier has become increasingly popular due to its capability of nearly sinusoidal waveform of the input current, and nearly unity power factor operation as a AC/DC rectifier of high capacity telecommunication power supply system. Generally, PI controller is used as a voltage controller of PWM rectifier and voltage controller must be designed to have low overshoot in transient state to get a reliability and stable operation. However, in the application of telecommunication in which load condition is varied very fast, the voltage controller must have a large bandwidth to reduce output voltage variation. The PI controller with large bandwidth arouse the excessive overshoot of the output voltage, and this large output voltage variation degrades the reliability of communication power of the three-phase PWM Rectifier. In this paper, new IP voltage controller for 3 phase PWM rectifier is proposed which has relatively low transient output voltage variation. The improved output characteristics of the transient state voltage responses of the starting and at load changes of the proposed voltage controller are proved by simulations and experiments.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.2
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• pp.360-369
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• 2008

The solar cells should be operated at the maximum power point because its output characteristics were greatly fluctuated on the variation of insolation, temperature and load. It is necessary to install an inverter among electric power converts by means of the output power of solar cell is DC. The inverter is operated supply a sinusoidal current and voltage to the load and the interactive utility line. In this paper, the proposes a photovoltaic system is designed with a step up chopper and single phase PWM voltage source inverter. Synchronous signal and control signal was processed by one-chip microprocessor for stable modulation. The step up chopper is operated in continuous mode by adjusting the duty ratio so that the photovoltaic system tracks the maximum power point of solar cell without any influence on the variation of insolation and temperature for solar cell has typical dropping character. The single phase PWM voltage source inverter is consists of complex type of electric power converter to compensate for the defect, that is, solar cell cannot be develop continuously by connecting with the source of electric power for ordinary using. It can be cause the efect of saving electric power, from 10 to 20%. The single phase PWM voltage source inverter operates in situation, that its output voltage is in same phase with the utility voltage. The inverter are supplies an ac power with high factor and low level of harmonics to the load and the utility power system.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.11B no.4
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• pp.169-174
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• 2001

A novel simulation scheme of transient phenomenon for the photovoltaic (PV) generation system under the real weather conditions has been proposed in this paper. A grid connected PV array is simulated using PSCAD/EMTDC. The transient changes of the output current of PV array under the real weather conditions is described and the output current of DC/AC converter flowing through the utility power network is also analyzed with the PWM switching width. Moreover, the MPPT control of PV generation system is combined to the system during the simulation for the comparison purposes of the control schemes. The outcome of the simulation demonstrates the effectiveness of the proposed simulation scheme. The result shows that the cost effective verifying for the efficiency or availability and stability of PV generation systems and the comparison research of various control schemes like MPPT under the same real whether conditions are eventually possible.

• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.1058-1060
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• 2002

This paper to overcome the peak power problems in summer and to endure good AC input characteristics, solar air conditioning system using the PWM converter is proposed and while the proposed circuit uses smaller ones and a small reactor not to boost the output voltage but improve the input current waveform. A high input power factor of 97[%] and an efficiency of 98[%] are also obtained.

• The Transactions of the Korean Institute of Power Electronics
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• v.4 no.5
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• pp.413-422
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• 1999

Auto-connected multipulse(12/24pulse) rectifier schemes are cost effective methods for reducing line current hamonics in PWM drive systems. Employing these schemes to enhance utility power quality requires careful attention to several design considerations In particular, excursion of dc-link voltage at no load, effect of pre-existing voltage distortion, impedance mismatches, unequal diode drops on rectifier current sharing and performance, are fully analyzed, Several corrective measures to improve the performance of 12/24­pulse rectifier systems are also discussed. Finally, experimental results on a 460V, 60Hz 400kVA commercial ASD, retrofitted with 12/24pulse rectifier systems are discussed in detail.

• Journal of Electrical Engineering and Technology
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• v.7 no.5
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• pp.714-723
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• 2012

A new Z-source inverter (ZSI) topology is developed to improve voltage boost ability. The proposed topology is modified from the switched inductor topology by adding some more inductors and diodes into inductor branch to the conventional Z-source network. The modulation methods developed for the conventional ZSI can be easily utilized in the proposed ZSI. The proposed ZSI has an ability to obtain a higher voltage boost ratio compared with the conventional ZSI under the same shoot-through duty ratio. Since a smaller shoot-through duty ratio is required for high voltage boost, the proposed ZSI is able to reduce the voltage stress on Z-source capacitor and inverter-bridge. Theoretical analysis and operating principle of the proposed topology are explicitly described. In addition, the design guideline of the proposed Z-source network as well as the PWM control method to achieve the desired voltage boost factor is also analyzed in detail. The improved performances are validated by both simulation and experiment.

• Proceedings of the KIEE Conference
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• 2003.04a
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• pp.338-340
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• 2003

This paper proposes a stand-alone adjustable speed wind Power generation system using a cage-type induction generator. Indirect vector control is used, where the q-axis current controls the generator speed and the d-axis current controls the excitation level. The generator speed is adjusted according to the wind speed so as to produce the maximum output power. The generated power is charged in the battery bank through ac/dc PWM converter. The proposed scheme has been verified by the experimental results.