• Journal of Positioning, Navigation, and Timing
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• 제2권1호
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• pp.59-65
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• 2013

The signal broadcast from a GPS satellite experiences code delay and carrier phase advance while passing through the ionosphere, which causes a signal error. Many ionosphere models have been studied to correct this ionospheric delay error. In this paper, the ionosphere modeling for the Korean Peninsula was carried out using a spherical harmonics based model. In contrast to the previous studies, we considered a real-time ionospheric delay correction model using fewer number of basis functions. The modeling performance was evaluated by comparing with a grid model. Total number of basis functions was set to be identical to the number of grid points in the grid model. The performance test was conducted using the GPS measurements collected from 5 reference stations during 24 hours. In the test result, the modeling residual error was smaller than that of the existing grid model. However, when the number of measurements was small and the measurements were not evenly distributed, the overall trend was found to be problematic. For improving this problem, we implemented the modeling with additional virtual measurements.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1990년도 추계학술대회 논문집 학회본부
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• pp.295-300
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• 1990

This paper describes a new method to increase the fundamental output of PWM inverter by adding all triplen-harmonics to sinusoidal reference wave. As a result, the amplitude of the fundamental component is increased upto 21 percent compared with the conventional SPWM method, and hence the conversion efficiency of dc link is higher. Also as the commutation number of the inverter is decreased to two-thirds, the heating of the switch devices is reduced. In addition random carrier modulation is adopted to lower the acoustic noise at given frequency modulation index.

• Journal of Electrical Engineering and Technology
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• 제9권6호
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• pp.1914-1920
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• 2014

In this paper, characteristics of blushless direct current (BLDC) motor including core loss are analyzed considering pulse width modulation (PWM) of inverter. Input voltage of BLDC motor due to PWM is calculated considering duty ratio and carrier frequency of inverter in order to control torque or speed of BLDC motor. For the calculation of core loss, the input current with harmonics due to PWM voltage is calculated by using equivalent circuit model of BLDC motor according to switching pattern and carrier frequency. Next, core loss is analyzed by inputting the currents as a source of BLDC motor for FEM. Characteristics including core loss are compared with ones without PWM waveform according to reference speed.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2003년도 춘계전력전자학술대회 논문집(2)
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• pp.630-634
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• 2003

This paper proposes a Carrier-Rotation PWM technique that is new solution for the voltage unbalancing problem of flying capacitors in the Flying Capacitor Multi-level Inverter (FCMI).The proposed PWM technique equalizes the utilization of phase leg voltage redundancies corresponding to the charging and the discharging state of flying capacitors during one switching period of all the switches. it also has the same switch utilization and the reduced harmonics of output voltage. Hence, it is more suitable for the FCMI compared with the conventional solutions. Experimental results on the laboratory prototype flying capacitor 3-level inverter confirm the validity of the proposed PWM technique.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 추계학술대회 논문집 학회본부A
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• pp.121-124
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• 1998

Front end AC to DC converters of the boost type are used in traction applications for generating the DC link for the inverters. A GTO based converter is usually switched with a switching frequency of 300 to 500Hz, resulting in low frequency harmonic problems. In order to avoid this, multiple converters with Phase shifted carrier waveforms are used to suppress the low frequency harmonics. A detailed study of an AC to DC converter, with two converters parallely operated with Phase shifted carrier wave farms is Presented in this paper.

• 전기학회논문지
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• 제62권10호
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• pp.1383-1389
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• 2013

There were telecommunication noise and malfunctions of the electronic devices occurred over a wide area due to the high harmonic voltage and/or current levels of the Back-to-back converter in the DFIG wind power system even though the magnitude of all harmonics is within the international standards. The triangular carrier signals of the PWM used in the power converter system is related to the telecommunication noise because they are in the range of audible frequencies and amplified by a variety of the standing waves that were excited by harmonic voltage sources in the weak grid system such as a long distance distribution transmission lines. This paper describes the characteristics of the harmonics in the wind turbine-generator, numerical analysis and simulation of the harmonics resonance phenomena in the distribution lines as well as measuring induced voltage of the telecommunication lines in parallel with power lines in order to verify the root cause of the telecommunication noise. These noise problems can occur in a wind turbine power system with a non-linear converter at any time, as well as photovoltaic power system. So, the preliminary review of suitable filter devices and switching frequencies of the PWM have to be required by considering the stability of the controller at the design stage but as part of the measures the effect of the telecommunication cable shields was analyzed by comparing the measured data between multi-conductor with/without shields so as to attenuate the sources of the harmonics voltage induced into the telecommunication lines and to apply the most cost-effective measures in the field.

• Journal of Advanced Marine Engineering and Technology
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• 제38권9호
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• pp.1131-1136
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• 2014

현재 LNG 운반선, 쇄빙선 등의 특수선박과 해양플랜트에 설치되는 전력변환 장치에는 다이오드를 이용하는 정류기가 많이 사용된다. 하지만 정류에 의한 비선형 부하의 입력전류에 많은 고조파가 포함되어 공급 전압파형의 왜곡을 초래한다. 전압파형의 왜곡은 발전기, 변압기, 부하기기 등의 오동작과 전력품질을 저하시키게 된다. 본 논문에서는 정류기 사용시의 전류왜곡을 감소시키기 위해서 직류 파형 정형화 회로를 사용하여 개선함으로써 부하에 인가되는 교류 파형을 정확한 정현파로 만든다. 그 결과 전력계통의 전류와 전압 파형에 포함되는 고조파를 저감할 수 있으며 이를 시뮬레이션을 통해 입증한다.

• 전력전자학회논문지
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• 제10권5호
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• pp.443-449
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• 2005

본 논문에서는 연료 전지 시스템을 위한 Z-소스 인버터로 구성된 병렬 운전 시스템을 제시 하였다. PWM 방식으로는 Carrier phase shifted SPWM을 적용하였으며 이 방식은 출력 전류의 고조파 성분을 줄일 수 있는 장점을 갖는다. 그러나 이 기법을 Z-소스 인버터로 구성된 병렬 운전 시스템에 적용하는 경우 추가적으로 순환 전류를 발생한다. Z-소스 인버터로 구성된 병렬 운전 시스템이 동작 시 발생하는 순환 전류를 분석하고 순환 전류를 감소시키며, 부하전류에 낮은 고조파 성분을 가질 수 있도록 순환 전류 리액터를 사용하였다. 이에 대한 적합성을 시뮬레이션과 실험을 통해 입증하였다.

• 한국통신학회논문지
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• 제39A권9호
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• pp.497-507
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• 2014

본 논문은 3GPP REL-12 에서 논의하는 반송파 집성(Carrier aggregation, CA) 기술의 표준 동향, 이를 지원하기 위한 단말요구 사항 정의, 그리고 이를 바탕으로 예측한 향후 기술 발전의 방향에 관한 것이다. 이는 REL-12에서 논의되는 상향 링크(Uplink, UL)에서의 2UL CA, 하향 링크(Downlink, DL)에서 3개의 반송파를 집성하는 3DL CA, TDD와 FDD를 결합하는 TDD-FDD CA 등이 포함되며, 또한 단말 RF 단에서 필요한 공존 이슈, 대역외 방사 이슈를 비롯한 여러 RF 요구사항을 분석 및 실험 결과들을 포함한다. 또한 CA 진화의 한 축인 비면허 대역과 LTE 운용 주파수 대역과의 반송파 집성기술인 LTE-U를 포함한 CA 진화 방향에 대해서도 기술한다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2005년도 전력전자학술대회 논문집
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• pp.298-301
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• 2005

The flying capacitor voltage control of the flying capacitor multi-level inverter (FCMLI) is very important for safe operation. The voltage unbalancing of flying capacitors caused serious problems in safety and reliability of system. In the FCMLI, balancing problem of the flying capacitor has its applications limited. The voltage unbalance is occurred by the difference of each capacitors charging and discharging time applied to FCMLI. This paper investigates and analyzes multi-carrier PWM methods to solve capacitor voltage balancing problem. The Phase-Shift PWM (PSPWM) method that is commonly used, The Modified Carrier-Redistribution PWM (MCRPWM) method and The Saw-Tooth-Rotation PWM (STRPWM) method are discussed and compared with respect to switching state, balancing voltage of capacitors and output waveform. These three PWM methods are analyzed by using a flying capacitor three-level inverter and provided result through simulation. Finally, the harmonics about the output voltages of their methods are compared using the harmonic distortion factor (HDF).