• 전력전자학회논문지
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• 제3권2호
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• pp.118-124
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• 1998

This paper describes a relationship of a space vector PWM and a sinusoidal PWM and presents that the space vector PWM can produce linearly the output voltage to the unity MI(modulation index). At first, reference angles and holding angles are derived from expanding a Fourier series of the reference voltage waveform and then the angles are used for the inverter switching to linearize transfer characteristics of the inverter. In addition, the harmonic components of the output voltage are analyzed and on-line control is shown to be feasible by approximating in piecewise-linearization the reference and holding angles versus the MI. In V/f control of the induction motor, it is verified by the experiment that the motor current is changed smoothly for the variation of the inverter input voltage and the change of the reference voltage.

• Journal of Electrical Engineering and Technology
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• 제12권4호
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• pp.1484-1494
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• 2017

We present a two-stage inverter with high step-up conversion ratio engaging modified finite-set Model Predictive Control (MPC) for utility-integrated photovoltaic (PV) applications. The anticipated arrangement is fit for low power PV uses, the calculated efficiency at 150 W input power and 19 times boosting ratio was around 94%. The suggested high-gain dc-dc converter based on Cockcroft-Walton multiplier constitutes the first-stage of the offered structure, due to its high step-up ability. It can boost the input voltage up to 20 times. The 3S current-source inverter constitutes the second-stage. The 3S current-source inverter hires three semiconductor switches, in which one is functioning at high-frequency and the others are operating at fundamental-frequency. The high-switching pulses are varied in the procedure of unidirectional sine-wave to engender a current coordinated with the utility-voltage. The unidirectional current is shaped into alternating current by the synchronized push-pull configuration. The MPC process are intended to control the scheme and achieve the subsequent tasks, take out the Maximum Power (MP) from the PV, step-up the PV voltage, and introduces low current with low Total Harmonic Distortion (THD) and with unity power factor with the grid voltage.

• Journal of Power Electronics
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• 제17권5호
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• pp.1363-1371
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• 2017

In this paper, an improved Direct Power Control (DPC) algorithm is presented for grid connected three phase PWM rectifiers. The new DPC approach is based on two main tasks. First the optimization of the look-up table, which is well-known in conventional DPC, is outlined for selecting the optimum converter output voltage vectors. Secondly a very simple and effective method is used to directly calculate their duty cycles from the power errors. Therefore, the measured active and reactive powers are made to track their references using hysteresis controllers. Then two vectors are selected and applied during one control cycle to minimize both the active and reactive power ripples. The main advantages of this method are that there is no need of linear current controllers, coordinates transformations or modulators. In addition, the control strategy is able to operate at constant switching frequencies to ease the design of the power converter and the AC harmonic filter. The control exhibits a good steady state performance and improves the dynamic response without any overshoot in the line current. Theoretical principles of the proposed method are discussed. Both simulation and experimental results are presented to verify the performance and effectiveness of this control scheme.

• 전기학회논문지
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• 제67권3호
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• pp.398-405
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• 2018

LLC resonant converter is popular with industrial fields because it can be achieved high efficiency by zero voltage switching (ZVS). As interest grew, analysis of characteristics in LLC resonant converter have been actively studied. Generally, characteristic of LLC resonant converter is analyzed based on first harmonic approximation(FHA). The FHA analysis represents the characteristics of LLC resonant converter by obtaining the series resonant operation. FHA analysis of LLC resonant converter in load condition is correct. but it is not correct in no load condition. This paper proposed analysis of characteristics considering the parasitic components to overcome the limitation of FHA and analyze no-load characteristics. The validity of the proposed method has been investigated by simulation and experimental results.

• Journal of Power Electronics
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• 제16권4호
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• pp.1316-1323
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• 2016

Multilevel inverters (MLIs) have been preferred over conventional two-level inverters due to their inherent properties such as reduced harmonic distortion, lower electromagnetic interference, minimal common mode voltage, ability to synthesize medium/high voltage from low voltage sources, etc. On the other hand, they suffer from an increased number of switching devices, complex gate pulse generation, etc. This paper develops an ingenious symmetrical MLI topology, which consumes lesser component count. The proposed level dependent sources concoction multilevel inverter (LDSCMLI) is basically a multilevel dc link MLI (MLDCMLI), which first synthesizes a stepped dc link voltage using a sources concoction module and then realizes the ac waveform through a conventional H-bridge. Seven level and eleven level versions of the proposed topology are simulated in MATLAB r2010b and prototypes are constructed to validate the performance. The proposed topology requires lesser components compared to recent component reduced MLI topologies and the classical topologies. In addition, it requires fewer carrier signals and gate driver circuits.

• 전자공학회논문지T
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• 제35T권3호
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• pp.128-133
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• 1998

본 논문은 클록 초기치 누적 방식의 직접 디지털 주파수 합성기를 이용한 변조기의 성능해석에 관하여 연구한 것이다. 기존에는 랜덤한 주파수 도약을 실현하기 위하여 PLL 방식이나 디지털 주파수 합성 방식이 사용되어 왔다. 븐 논문에서는 두 방식의 단점을 개선하기 위하여 클록 초기치 누적 방식의 DDFS를 이용한 변조기 시스템을 구성하여 순시적인 주파수 도약 상태와 위상제어의 가능성 등을 확인하였다. 실험 결과 합성된 출력 주파수는 주파수 Index에 따라 기준주파수에 정확히 정수배가 되며, 합성된 정현파형의 스펙트럼은 기본파와 여러 고조파의 크기가 50 [㏈] 이상의 차이가 남으로서 고조파 성분들이 상당히 감소되었고, PN 코드를 사용한 순시적인 주파수 도약 상태는 스위칭 시간이 빠르기 때문에 주파수 도약 특성이 뛰어남을 알 수 있었다. 또한, 누산기의 set/reset상태변화에 따라 위상이 변한다는 사실도 입증하였다.

• 전기학회논문지
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• 제64권6호
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• pp.885-890
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• 2015

LLC resonant converter has been widely used because of its high efficiency and high energy density. In this paper, we designed a LLC resonant converter as the main power supply of the Nd:YAG pulse laser. First harmonic approximation (FHA) is used to model the LLC resonant converter. FHA equivalent circuit model and the transfer function of the LLC resonant converter is proposed. Soft start technology is also used to suppress the surge current. The laser output simulation test result is identical with the practical test, the laser energy of every pulse can reach up to 2.5J, and the pulse per second (PPS) can be adjusted from 6 to 18. The power system is verified stable and reliable by both of the simulation and experiment results.

• Journal of Power Electronics
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• 제9권2호
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• pp.215-223
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• 2009

A design methodology for transformers including integrated and center-tapped structures for LLC resonant converters is proposed. In the LLC resonant converter, the resonant inductor in the primary side can be merged in the transformer as a leakage inductance. And, the absence of the secondary filter inductor creates low voltage stress on the secondary rectifiers and is cost-effective. A center-tapped structure of the transformer secondary side is widely used in commercial applications because of its higher efficiency and lower cost than full-bridge structures in the rectifying stages. However, this transformer structure has problems of resonance imbalance and transformer inefficiency caused by leakage inductance imbalance in the secondary side and the position of the air-gap in the transformer, respectively. In this paper, gain curves and soft-switching conditions are derived by first harmonic approximation (FHA) and operating circuit simulation. In addition, the effects of the transformer including integrated and center-tapped structures are analyzed by new FHA models and simulations to obtain an optimal design. Finally, the effects of the air-gap position are analyzed by an electromagnetic field simulator. The proposed analysis and design are verified by experimental results with a 385W LLC resonant converter.

• 한국전자파학회논문지
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• 제28권4호
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• pp.347-350
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• 2017

본 연구에서는 TMA(Time-Modulated Array)와 USRP(Universal Software Radio Peripheral)를 이용하여 2.4 GHz 대역에서 동작하는 실시간 방향탐지 시스템을 구현하였다. 구현된 시스템은 2개의 상용 모노폴 안테나, 자체 제작한 스위치 보드, 그리고 하나의 USRP로만 구성되며, LabVIEW로 연동하여 실시간으로 특정 신호원의 입사 각도를 탐지할 수 있었다. 구현결과, $30^{\circ}$의 범위 내에서 최대 $4^{\circ}$의 오차 이내로 방향탐지가 가능함을 확인하였다. 제안한 시스템은 기존의 다중수신기를 갖는 방향탐지 시스템에 비해 하드웨어 구성이 간단할 뿐만 아니라, 주엽과 첫 번째 부엽 신호의 크기만을 이용하는 간단한 계산으로 방향탐지가 가능하다는 장점이 있다.

• Journal of Electrical Engineering and Technology
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• 제12권3호
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• pp.1090-1100
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• 2017

This paper presents the comparison of starting current characteristics of a three-phase induction motor fed by two types of soft starters. The first soft starter under investigation is a conventional AC voltage controller on the basis of a phase-control technique. The other is the proposed asynchronous PWM AC chopper which is developed from the conventional synchronous PWM AC chopper. In this paper, the proposed asynchronous PWM AC chopper control scheme is developed by generating only two asynchronous PWM signals for a three-phase main power circuit (6 switching devices) from a single voltage control signal which is compared with a single sawtooth carrier signal. By this approach, the PWM signals are independent and easy to implement since the PWM signals do not need to be synchronized with a three-phase voltage source. Details of both soft starters are discussed. The experimental and simulation results of the starting currents are shown. It is found that the asynchronous PWM AC chopper efficiently works as a suitable soft starter for the three-phase induction motor due to that the starting currents are reduced and are sinusoidal with less harmonic contents, when being compared with the starting current waveforms using the conventional phase-control starting technique. Also the proposed soft starter offers low starting electromagnetic torque pulsation.