• The Transactions of the Korean Institute of Power Electronics
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• v.15 no.3
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• pp.226-234
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• 2010

This paper proposes an improved feed-forward controller that calculates the gain value by estimating the changed boost inductance in practical operating condition of transformer. The boost inductance is estimated by the measurement of input current and voltage. The estimated boost inductance is optimized by the least square method. The proposed feed-forward controller can be achieved the robust control through the gain value calculating the estimated boost inductance despite of the changed condition of transformer and can minimize the interference phenomenon by reducing the harmonics of input current. The validity of proposed technique is verified through the simulation and experiment.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.37 no.6
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• pp.64-72
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• 2000

This paper deals with the parallel operation of two PWM converters for auxiliary block of high speed train. The parallel operation of AC/DC PWM converter controlled by 3-level PWM switching method to operate switching devices to realize a high power factor and reduce the primary side of the transformer current harmonics is proposed. In this paper, it is presented the phase shift technique between two converters switching phase, solution to eliminate the coupling effects due to the transformer and zero crossing detection method for synchronized with the source and controller. Experimental results for laboratory system with TMS320C31 microprocessor and 10［kVA］PWM converter confirm the validity of the proposed algorithm.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.5
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• pp.88-95
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• 2009

This paper is the research on the development of power conversion system for the fuel cell. In composing the DC/DC converters which have high boost voltage ratio, unlike the conventional method a new multi DC/DC converter system is proposed that the diode and the condenser and the reactor can be reduced by connecting the secondary side output of the transformer. In this system the rectifier part and the filter part of the secondary side in the power transformer that is connecting in series are composed into a single module, which is the strong advantage and the number of level can be easily increased. A new variable shift phase switching method is also suggested that it makes possible to reduce the output voltage ripples in the proposed system. All the factors mentioned above have been verified through simulations and experiments, and the proposed converter is considered very useful in the demanded load which requires a wide of the output.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.51 no.6
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• pp.267-272
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• 2002

This Paper deals with the short circuit tests of the three-Phase DC reactor type fault current limiter (FCL) in changing of turns ratio of transformers. The experiment of this paper is a preliminary step to develop the FCL's faculties for an application to high voltage transmission line. So, superconducting coil was made of Nb-Ti, low temperature superconductor, and the ratings of the power system of experimental circuit are 400V/7A class. A three-phase DC reactor type FCL consists of three transformers, six diodes, one superconducting coil and one cryostat. The important point of experimental analysis is transient period, the operating lagging time of circuit breaker. As the results of the experiment, the values are referred to the limitation rate about 77% and 90% when the turns ratio of transformer was 1:1 and 2:1 respectively.

• Journal of Advanced Marine Engineering and Technology
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• v.16 no.4
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• pp.102-112
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• 1992

The three-phase full(6-pulse) bridge controlled rectifier is one of the most widely used types of solid-state converters in DC drive applications for higher performance. In most of the previous designs, the gate control circuits of the converter have been designed with analog method which can be easily affected by noise. Nowdays with advances of microelectronics and power electronics, microprocessor and pheripal LSIs are increasingly used for eliminating this problems. In this paper, a novel general-purpose microprocessor -based firing system and control scheme for a three-phase controlled rectifier bridge has been developed and tested. Using the phase relations between ${\Delta}$-Y transformer in power operation part, gate pulse of the converter is generated with real time process so that microprocessor may share its time to control algorithms efficiently. The firing angle of the converter is smoothly controlled in the range of 0 $^{\dirc}$ to 180$^{\dirc}$ with a fast respone and a constant open loop gain, even for the case where the converter is fed by a weak AC system of unregulated frequency. The hardware and software control circuit implementation built around a 80286 microprocessor is discussed, and the experimental results are given. This scheme uses less hardware components and has higher dynamic performance in variable speed DC drive applications.

• Journal of Power Electronics
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• v.5 no.3
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• pp.224-232
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• 2005

A new three phase three-level Pulse Width Modulation (PWM) Switched Voltage Source (SVS) inverter with zero neutral point potential is proposed. It consists of three single-phase inverter modules. Each module is composed of a switched voltage source and inverter switches. The major advantage is that the peak value of the phase output voltage is twice as high as that of a conventional neutral-point-clamped (NPC) PWM inverter. Thus, the proposed inverter is suitable for applications with low voltage sources such as batteries, fuel cells, or solar cells. Furthermore, three-level waveforms of the proposed inverter can be achieved without the switch voltage imbalance problem. Since the average neutral point potential of the proposed inverter is zero, a common ground between the input stage and the output stage is possible. Therefore, it can be applied to a transformer-less Power Conditioning System (PCS). The proposed inverter is verified by a PSpice simulation and experimental results based on a laboratory prototype.

• The Transactions of the Korean Institute of Power Electronics
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• v.19 no.5
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• pp.475-480
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• 2014

This study proposes a new synthetic test circuit (STC) for HVDC thyristor valve tests. The conventional STC with a 2-phase chopper requires a 3-phase transformer, a 3-phase diode rectifier, and an IGBT to facilitate the off state of an auxiliary thyristor. In the proposed STC, these three components are replaced with one diode and one resistor, which result in the simplified implementation of the hardware of the STC. Simulation and experimental results demonstrate the validity of the proposed scheme.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.6
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• pp.1283-1290
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• 2003

Recently, PWM Buck AC-AC Converter is widely employed in various industrial applications such as voltage and power regulator, electronic transformer, phase shifter and so on. This paper presents static and dynamic modeling and complete characteristic analysis of a PWM Buck AC-AC converter. Firstly, the three phase converter system is modelled by using DQ transformation whereby we can obtain basic characteristic equations such as voltage gain and power factor as well as state equation and transfer function for control. Secondly, based on the analysis, the feedforward-feedback control technique is also proposed to obtain instantaneous duty level change whereby very fast dynamic response is achieved. Finally, the experimental results show the validity of the modeling, analysis and control.

• Journal of Power Electronics
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• v.14 no.3
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• pp.413-420
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• 2014

The conventional Phase-Shift Full-Bridge (PSFB) converter has a serious voltage spike because of the ringing between the leakage inductance of the transformer and the parasitic output capacitance of the secondary side rectifier switches. To overcome this problem, an asynchronous active clamp technique employing an auxiliary DC/DC converter has been proposed. However, an exact analyses for designing the auxiliary DC/DC converter has not been presented. Therefore, the amount of power that is supposed to be handled in the auxiliary DC/DC converter is calculated through a precise mode analyses in this paper. In addition, this paper proposes a lossy snubber circuit with hysteresis characteristics to reduce the burden that the auxiliary DC/DC converter should take during the starting interval. This technique results in optimizing the size of the magnetic component of the auxiliary DC/DC converter. The operational principles and the theoretical analyses are validated through experiments with a 48V-to-30V/15A prototype.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.53 no.7
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• pp.397-404
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• 2004

This paper describes a study of transient characteristics in 765kV untransposed transmission lines. As the 765(kV) system can carry bulk power, some severe fault on the system nay cause large system disturbance. The large shunt capacitance and small resistance of 765kv transmission line make various difficulties for its protection. These problems including current difference between sending and receiving terminals on normal power flow, low order harmonic current component in fault current and current transformer saturation due to the long DC time constant of the circuit etc. must be investigated and solved. The analysis of transient characteristics at sending terminal has been carried out for the single phase to ground fault and 3-phase short fault, etc. The load current, charging current in normal condition and line flows, fault current, THD(Total Harmonic Distortion) of harmonics, time constants have been analysed for the 765kV untransposed transmission line systems.