• Proceedings of the KIEE Conference
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• 1999.07a
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• pp.111-114
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• 1999

This paper deals with the rated output power using grid-connected Doubly-Fed Induction Generator(DFIG) in the supersynchronous speed regions. The rated output power is controlled by both magnitude and frequency of the voltage fed to the rotor. And this rotor voltage is controlled by control of inverter switching frequency and fire angle. A DFIG generating characteristic is analyzed by simulation of steady-state algebraic equation of equivalent circuit using numerical analysis. And it is compared with results of experiment. Consequently, This paper presented to control method for rated output power of DFIG in variable wind speed.

• Journal of Power Electronics
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• v.9 no.2
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• pp.146-155
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• 2009

The static frequency converter (SFC) systems are used as a method of driving large synchronous machines in many power and industrial plants. In this paper, new control algorithms of SFC systems for starting gas turbo sets are proposed for a four quadrant operation: start-up at standstill; an acceleration up to the speed of the rated voltage; field weakening to reach the rated speed; synchronization to the main alternating current (AC) source; and dynamic braking to stop safely within the rating of the synchronous machine. Experimental results show that the proposed algorithms are proper and effective.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.1
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• pp.65-72
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• 2008

This paper describes the development of a novel islanding detection method, which uses the signal cross-corelation scheme between the injected reactive current and the power frequency deviation. The existing method, which injects the reactive current of 2.5-5% to the rated current and detects the frequency deviation directly, brings about lowing the power quality due to the harmonic pollution. The proposed method eliminates the weak point of the existing method, because it injects the reactive current less than 1% to the rated current. The operational feasibility was verified through computer simulations with PSCAD/EMTDC software, and experimental works with a 10kVA hardware prototype. The proposed method can detect the islanding status effectively without lowing the power quality of interconnected distributed generation system.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.48 no.12
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• pp.686-691
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• 1999

In a switching power supply, the high frequency switching makes the passive components small, but the losses and the stresses of switches are increased by the switching frequency. Therefore, zero crossing technology using resonant is used to improve defect in high switching. In generally, zero crossing switching consists of Zero Current Switching(ZCS) and Zero Voltage Switching(ZVS). This paper proposes A Buck ZC-ZVS Converter with Reduced Conduction Losses. Comparing with a conventional Buck ZC-ZVS Converter, the proposed converter operates with the smaller rated power. This is achieved by changing the auxiliary switch position, which reduces its rating power. Simulation results using Pspice program about test circuit with rated 160W(30V, 5.3A) at 30kHz and experiment result under same condition were described in the paper.

• Journal of Power Electronics
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• v.15 no.4
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• pp.876-885
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• 2015

High frequency alternating current (HFAC) has been widely used in a wide range of power distribution systems (PDS) due to its superior performance. A high frequency AC/DC converter plays the role of converting HFAC voltage to DC voltage. In this paper, a new LCL-T resonant AC/DC converter has been proposed, and an easier control method based on input voltage comparison is presented, without the complicated calculation of the zero-crossing point. Both a low distortion and near-to-unity power factor can be achieved by the proposed resonant converter and control strategy. The operational principle and steady-state analysis are given for the proposed resonant converter. A simulation model and experimental prototype are implemented with an operation frequency of 25kHz and a rated power of 20W. The simulation and experimental results verify the accuracy of the analysis and the excellent performance of the proposed topology.

• Proceedings of the KIEE Conference
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• 2000.07b
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• pp.693-695
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• 2000

Wide operating range and speed control is needed for wind power generating and a Doubly Fed Induction Generator(DFIG) has good adaptivity for that purpose. This paper deals with power and power factor control using the Grid connected DFIG in the wide speed regions, by controlling frequency and voltage fed to the rotor. Power flow of the DFIG and steady-state algebraic equations of the equivalent circuit are analyzed. For a normal operating region, in which the generator ratings were not exceeded, the rotor current was either less than or equal to the rated value. Accordingly, the optimal power factor can be selected relative to the permissible rated current at the rotor coil which controls the magnitude of the injected rotor voltage to the rotor according to a given rotor frequency.

• Journal of Power Electronics
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• v.5 no.4
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• pp.272-281
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• 2005

In this paper, a simple power control scheme for a constant frequency Class-D inverter with a variable duty cycle is proposed. It is more suitable and acceptable for high- frequency induction heating (IH) jar applications. The proposed control scheme has the advantages of not only wide power regulation range but also ease of control output power. Also it can achieve a stable and efficient Zero-Voltage-Switching (ZVS) in a whole load range. The control principles of the proposed method are described in detail and its validity is verified through simulated and experimental results on 42.8kHz IGBT for induction heating rated on 1.6kW with constant frequency variable power.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.14 no.4
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• pp.31-38
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• 2000

Wide operating range and speed control is needed for wind power generating and a Doubly Fed Induction Generator(DFIG) has good adaptivity for that purpose. This paper deals with the speed, power, and power factor control using the Grid connected DFIG in the super-synchronous speed regions, by controlling frequency and voltage fed to the rotor. Power flow of the DFIG and steady-state algebraic equations of the equivalent circuit are analyzed. The wind turbine speed and constant stator power were controlled by the rotor exciting frequency. For a normal operating region, in which the generator ratings were not exceeded, rotor exciting frequency. For a normal operating region, in which the generator ratings were not exceeded, the rotor current was either less than or equal to the rated value. Accordingly, the optimal power factor can be selected relative to the permissible rated current at the rotor coil which controls the magnitude of the injected rotor voltage to the rotor according to a given rotor frequency. Consequently, it is possible to determine the optimal drive of a DFIG for wind power generation application.

• The Transactions of the Korean Institute of Power Electronics
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• v.24 no.2
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• pp.105-110
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• 2019

This study proposed a reactive power variation (RPV) method equipped with positive feedback (PF) for detecting the islanding operation of distributed generation systems. The proposed RPV consists of the constant reactive power component and a certain reactive power term and uses the frequency deviation between the rated and the measured frequencies. The constant reactive power is injected from distributed generation system and power factor is to 0.9975 in grid-connected operation. PF is activated from generation of the frequency deviation and the injected reactive power is continuously increased due to PF when islanding occurs. Consequently, the increasing reactive power causes the point of common coupling frequency to deviate from the maximum/minimum threshold level. Performance of the proposed RPV is verified in a 1.7 kW T-type inverter, and the detection times are 53 and 150 ms.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.1
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• pp.24-31
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• 2018

An induction heating (IH) resonant converter, as well as its coil design method, is proposed in this study to improve the heat capability of low- and high-resistance IH vessels. Conventional IH resonant converters have been designed only for heating high-resistance containers designed for IH application. Thus, the primary current in the resonant tank becomes extremely high to transfer the rated power when the converter heats the low-resistance vessel. As a result, the rated power cannot be transferred due to overcurrent flows against the rated switch current. Hence, the optimal number of coil turns and proper operating frequency to heat high- and low-resistance vessels are proposed in this study by analyzing an IH load model. Simulation and experimental results using a 2.4 kW prototype resonant converter and its IH coil validate the proposed design.