• Journal of Electrical Engineering and Technology
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• v.10 no.1
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• pp.280-287
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• 2015

Three-level PWM rectifiers applied in medium voltage applications usually operate at low switching frequency to keep the dynamic losses under permitted level. However, low switching frequency brings a heavy cross-coupling between the current components $i_d$ and $i_q$ with a poor dynamic system performance and a harmonic distortion in the grid-connecting current. To overcome these problems, a mathematical model based on complex variables of the three-level voltage source PWM rectifier is firstly established, and the reasons of above issues resulted from low switching frequency have been analyzed using modern control theory. Then, a novel control strategy suitable for the current decoupling control based on the complex variables for $i_d$ and $i_q$ is designed here. The comparisons between this kind of control strategy and the normal PI method have been carried out. MATLAB and experimental results are given in detail.

• The Transactions of the Korean Institute of Power Electronics
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• v.10 no.1
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• pp.70-77
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• 2005

A new converter to transfer energy from a low-voltage AC current source to a battery is proposed. It is focused to find operational modes of the converter. The low-voltage AC current source is an equivalent of the piezoelectric generator, which converts the mechanical energy to the electric energy. The converter consists of a full-bridge MOSFET rectifier and a MOSFET boost converter in order to make the converter small and efficient. The operational principle and modes of the converter are investigated with the consideration of effects of the parasitic capacitances of MOSFETs and diode. The results are proved with simulation studies using PSIM and Pspice.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.51 no.4
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• pp.210-220
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• 2002

We analysised the effect of harmonics on electric machines of substation power system barred on quantitatively measured harmonics and proposed the methods for prevention of harmonics through checking on transformer, rectifier and cable's capacities against harmonics with reference to KEPCO's electricity service standard. In order to analysis harmoninics of silicon rectifier that is power source in DC substation, computer simulations for a substation with TR of high voltage distribution switchboard are performed. Simulation results show that the total harmonic distortion factor becomes smaller for TR primary and receiving points in order rather than silicon rectifier which is harmonic generation source so that the harmonics generated frets each rectifier are outflowed to power supply and high voltage distribution switchboard The result of higher distortion factors of voltage and current for rectifier with 100% load than those with 50 % and 30% indicates that the waveform of voltage and current for the real substation power system at the office-going and the closing hours with heavy loads might be more distorted. As proposed methods for harmonic reduction, the conventional 6 pulse-type for substation is required to be replaced by 12 pulse-type for reduction of 5th and 7th harmonics. The active filter rather than the passive filter is more effective due to severe variance of rectifier loads, but the high cost is price to be paid. In view of installation area and costs, the use of 12 pulse-type transformer is desirable and then the parallel transformer and the rectifier within the substation must be replaced at the same time. Other substations with parallel feeder can use 6 pulse-type transformer.

• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.365-366
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• 2015

Shunt active power filter is a complete current source which can provide an effective and adjustable solution for elimination of harmonic currents in power system. Its performance depends on strategy employed in reference current generation, control technique and topology of converter used in the design.[1-2]. In this paper Three Phase Six switch Z-source rectifier with active power filtering capability based on instantaneous reactive power theory is described. Thanking to the theory power factor and THD value are significantly improved. Experiment results and conclusions are presented.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.32 no.3
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• pp.76-83
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• 1983

This paper describes the method of operating the phase controlled rectifier by controlling the firing angle in III, IV quadrant to absorb the lrading reactive power and of improving the waveform of ac current by driving dual converter. The system is intended to compensate the reactive power for any lagging load. Also, by the above method this paper enables us to improve the power factor and waveform referred to the source current and the dc output voltage in the converter.

• Proceedings of the KIPE Conference
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• 2002.07a
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• pp.257-262
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• 2002

Water-Electrolyzed gas is a mixed gas has the constant volume ratio 2 1 Hydrogen and Oxygen gained from electrolyzed water, and it has better characteristics in the field of economy, efficiency of energy, and environmental intimacy than acetylene gas and LPG used for existing gas welding equipment. So nowdays many studies of Water-Electrolyzed gas are progressed, and commercially used as a source of thermal energy for gas welding in the industry. For Water-Electrolyzed Source, it was used diode rectifier or SCR rectifier for get DC source. This method which is not looking to improve a source for impossible current control or voltage and limited control intervals. In this paper, it was relized and designed In source of pulse type for complementing existing - DC source type, also by experiment it was acquired producting characteristics of Hydrogen -Oxygen Gas through feature of source

• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.4
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• pp.472-476
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• 2012

In this paper, a sensorless control scheme for a three-phase bi-directional voltage-type PWM rectifier in wind power generation system that operates without the input AC voltage sensors (generator side) is described. The basic principles and classification of the PWM rectifier are analyzed, and then the three-phase mathematical model of the input AC voltage sensorless PWM rectifier control system is established. The proposed scheme has been developed in order to lower the cost of the three-phase PWM rectifier but still achieve excellent output voltage regulation, limited current harmonic content, and unity input power factor.

• Proceedings of the KIPE Conference
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• 2010.11a
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• pp.17-19
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• 2010

In this paper, new PWM method is proposed to reduce input current THD of PWM Rectifier. In general, the carrier comparison PWM method is used for PWM rectifier in which triangle wave is used as a carrier wave. However, large d-axis current ripple by this method can be a source of large THD. In this paper, new carrier comparison PWM method is proposed in which sawtooth wave is used as a carrier wave. Depending on the phase of the voltage commands, the rising or falling sawtooth wave is selected to reduce the THD. The simulation results verified the performance of the proposed method.

• Journal of Power Electronics
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• v.15 no.4
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• pp.994-1005
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• 2015

This paper presents a novel power control strategy for PWM current-source rectifiers (CSRs) in the stationary frame based on the instantaneous power theory. In the proposed control strategy, a virtual resistance based on the capacitor voltage feedback is used to realize the active damping. In addition, the proportional resonant (PR) controller under the two-phase stationary coordinate is designed to track the ac reference current and to avoid the strong coupling brought about by the coordinate transformation. The limitations on improving steady-state performance of the PR controller is investigated and mitigated using a cascaded lead-lag compensator. In the z-domain, a straightforward procedure is developed to analyze and design the control-loop with the help of MATLAB/SISO software tools. In addition, robustness against parameter variations is analyzed. Finally, simulation and experimental results verify the proposed control scheme and design method.

• Journal of Power Electronics
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• v.18 no.5
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• pp.1325-1335
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• 2018

This paper presents a discontinuous pulse width modulation (DPWM) method to reduce switching losses in an indirect matrix converter (IMC) drive. The IMC has a number of power semiconductor switches. In other words, it consists of a rectifier stage and an inverter stage for AC/AC power conversion, which are composed of 12 and 6 switching devices, respectively. Therefore, the switching devices of the IMC suffer from high switching losses in the IMC drives. Various topologies to reduce switching losses have been studied by eliminating a number of switches from the rectifier stage. In this study, in contrast to prior research, a DPWM method is presented to reduce the switching losses of the inverter stage. The effectiveness of the proposed method to reduce switching losses in IMC drives is verified by simulations and experimental results.