• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제55권1호
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• pp.27-32
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• 2006

In this paper, a new scheme of current programmed control for three phase PWM AC-AC converter is presented. Compared to duty-ratio voltage control, current programmed control has several advantages such as reduction of system order, inherent current protection and robust output. By considering only the magnitude components, a similar scheme in the DC-DC converter can be extended to the three phase PWM AC-AC converter. The proposed current programmed control will be well adopted into various converter topologies though three phase PWM AC-AC boost converter is treated as an example. The converter analysis is carried out by applying the vector DQ transformation to obtain physical insight into the converter operation and to establish some important characteristic equations for control purpose. The experiment results show the validity of the proposed scheme.

• 수산해양기술연구
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• 제16권1호
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• pp.43-47
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• 1980

The author designed and tested the high sensitive three-phase power factor meter and relay circuit, and dealt with the circuit to detect the phase of the current and the voltage. An operational amplifier comparator circuit and two single-phase transformers are used to control and detect the phase angle between the current and the voltage. The results obtained are as follows: 1. Converting the sine wave input current into the constant amplitude rectangular wave form by using a transistor chopper circuit, the power factor can be measured precisely over the load current of 0.08 A. 2. Using the moving coil type current meter, the power factor meter can be read in uniform . scale all over the range. 3. Using the three-phase power factor meter, the power factor relay which works at any power factor can be made.

• 전기학회논문지
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• 제66권3호
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• pp.587-592
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• 2017

In the three-phase four-wire low-voltage power distribution equipment, single-phase and three-phase load have been used mainly mixed. Also linear and nonlinear loads have been used together in the same conditions. In a three-phase four-wire distribution line, the current distribution of three-phase linear load is almost constant in each phase during driving or stopping, but the single-phase load is different from each other for each phase in accordance with the operation and stop. So that the voltage unbalance is caused by the current difference of each phase. In the three-phase four-wire distribution system, non-linear load is used with linear load. The presence of single-phase nonlinear loads can produce an increase in harmonic currents in three-phase and neutral line. It can also cause voltage unbalance. In the present study, we analyzed for the voltage unbalance fluctuations by the operation pattern of the single and three-phase linear and non-linear load in three-phase four-wire low voltage distribution system.

• Journal of Power Electronics
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• 제3권4호
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• pp.249-258
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• 2003

This paper presents a high-efficient and cost effective three-phase AC/DC-DC/AC power conversion system with a single two-switch type active Auxiliary Resonant DC Link (ARDCL) snubber circuit, which can minimize the total power dissipation. The active ARDCL snubber circuit is proposed in this paper and its unique features are described. Its operation principle in steady-state is discussed for the three phase AC/DC-DC/AC converter, which is composed of PWM rectifier as power factor correction (PFC) converter, sinewave PWM inverter. In the presented power converter system not only three-phase AC/DC PWM rectifier but also three-phase DC/AC inverter can achieve the stable ZVS commutation for all the power semiconductor devices. It is proved that the proposed three-phase AC/DC-DC/AC converter system is more effective and acceptable than the previous from the cost viewpoint and high efficient consideration. In addition, the proposed two-switch type active auxiliary ARDCL snubber circuit can reduce the peak value of the resonant inductor injection current in order to maximize total system actual efficiency by using the improved DSP based control scheme. Moreover the proposed active auxiliary two-switch ARDCL snubber circuit has the merit so that there is no need to use any sensing devices to detect the voltage and current in the ARDCL sunbber circuit for realizing soft-switching operation. This three-phase AC/DC-DC/AC converter system developed for UPS can achieve the 1.8% higher efficiency and 20dB lower conduction noise than those of the conventional three-phase hard-switching PWM AC/DC-DC/AC converter system. It is proved that actual efficiency of the proposed three-phase AC/DC-DC/AC converter system operating under a condition of soft switching is 88.7% under 10kw output power.

• 전력전자학회논문지
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• 제20권4호
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• pp.375-387
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• 2015

This study investigates an economic and highly efficient power-converter topology and its modulation scheme for 60 kW rapid EV charger system. The target system is a three-phase three-switch buck-type rectifier topology. A new carrier-based PWM scheme, which is characterized by simple implementation using logic gates, is introduced in this paper. This PWM scheme replaces the diode rectifier equivalent switching state with an active switching state to produce the same effective current flowing path. As a result, the distortion of input current during the polarity reversal of capacitor line voltage can be mitigated. The proposed modulation technique is confirmed through simulation verification. The proposed modulation technique and its implementation scheme can expand the operation range of the three-phase three-switch buck-type rectifier with high-quality AC input and capacitor ripple current.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 추계학술대회 논문집 Vol.18
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• pp.165-166
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• 2005

In this paper, we investigated the quench generation of HTSC elements in fault types according to inductance variation in the integrated three-phase flux-lock type SFCL. The integrated three-phase flux-lock type SFCL was the upgrade version of the single-phase flux-lock type SFCL. The structure of the integrated three-phase flux-lock type SFCL consisted of three-phase flux-lock reactor wound on an iron core with the ratio of the same turn between coil 1 and coil 2 in each phase. When the SFCL is operated under the normal condition, the flux generated in the iron core is zero because the flux generated between two coils of each single phase is canceled out. Therefore, the SFCL's impedance is zero, and the SFCL has negligible influence on the power system. However, if a fault occurs in any single-phase among three phases, the flux generated in the iron core is not zero any more. The flux makes HTSC elements of all phases quench irrespective of the fault type, which reduces the current of fault phase as well as the current of sound phase. It was observed that the fault current limiting characteristics of the suggested SFCL were dependent on the quench characteristics of HTSC elements in all three phases.

• Journal of Power Electronics
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• 제6권4호
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• pp.356-365
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• 2006

This paper presents an improved three-phase PFC power rectifier with a three-phase diode rectifier cascaded four-switch boost converter. Its operating principle contains the operating principle of two conventional three-phase PFC power rectifiers: one switch boost converter type and a two switch boost converter type. The operating characteristics of the four switch boost converter type three-phase PFC power rectifier are evaluated from a practical point of view, being compared with one switch boost converter type and two switch boost converter topologies.

• 전기학회논문지
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• 제65권6호
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• pp.940-945
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• 2016

In this paper, zero sequence equivalent circuit of Yg-Yg three phase core-type transformer is analyzed. Many problems by iron core structure of the three phase transformer due to asymmetric three phase lines, which includes line disconnection, ground fault, COS OFF, and unbalanced load are reported in the distribution system. To verify a feasibility of zero sequence impedance of Yg-Yg type three phase transformer, fault current generation in the three phase core and shell-type Yg-Yg transformer is compared by PSCAD/EMTDC when single line ground fault is occurred. As a result, shell-type transformer does not affect the flow of fault current, but core-type transformer generate an adverse effect by the zero sequence impedance. The adverse effect is explained by the zero sequence equivalent circuit of core-type transformer and Yg-Yg type three phase core-type transformer supplies a zero sequence fault current to the distribution system.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제49권2호
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• pp.123-129
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• 2000

This paper proposes a novel current control method of three-phase PWM rectifiers using estimated currents without phase current sensors. The phase currents are reconstructed from switching states of the rectifier and the measured dc output currents. To eliminate the calculation time delay effect of the microprosessor, the current at the next sampling instant are predicted by a predictive state observer and then are used for feedback control. Experimental results show that the control performance of the proposed system is almost the same as that of the phase current sensor-based system.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제48권8호
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• pp.440-447
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• 1999

This paper proposes a control method for three-phase PWM rectifier with only single current sensor in DC link side. A PWM modulation strategy for reconstructing three phase currents from the DC link current is given. The states of the retifier switch are modified so that all phase currents can be reconstructed in a switching period although one or two of active vectors is applied only for a short time. Therefore, a new current control using an adjustment scheme of the modulation signal for three-phase PWM rectifier will be discussed, and verified the experimental results.