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선영식,이창석,김시경,김창봉,Sun, Young-Sik,Lee, Chang-Seok,Kim, Si-Kyung,Kim, Chang-Bong 대한전자공학회 2000 電子工學會論文誌-SD (Semiconductor and devices) Vol.37 No.1
고장에 대한 강인성, 높은 출력 전류 특성 및 모듈화의 용이성 때문에 병렬 인버터 시스템은 그활용도가 점차 높아지고 있다. 이러한 병렬 인버터 시스템에서 전체 시스템 전력균형 제어는 주로 주파수 드롭과 전압 드룹 제어 또는 유효전력 과 무효전력 제어를 통하여 이루어지고 있다. 그러나 이러한 제어방법들은 시스템 변수 변동 및 부하변동에 따라 늦은제어 응답특성을 가지는 단점을 가지고 있다. 이러한 단점을 해결하기위해, 본논문에서는 병렬 인버터 시스템의 각모듈 출력전력을 균등화 시키는 새로운 제어기를 제안하였다. 제안한 제어기는 하드웨어 구현의 용이성, 피크전류 차단 기능들의 특성을 가진다. 또한 본논문에서는 제안한 제어기의 설계 절차를 기술하였으며, 여러 부하조건 및 시스템 파라미터 변동조건에 따라 순시전력균형제어기 동작 특성의 효용성을 컴퓨터 시뮬레이션 및 실험을 통하여 확인 하였다. The parallel inverter is widely utilized because of its fault-tolerance capability, high-current output at constant voltages and system modularity. The conventional paralled inverter usually employes an active and reactive power control or a frequency and voltage droop control. However, these approaches have the disadvantages that the response time of parallel inverter control is slow against load and system parameter variation to calculate active, reactive power, frequency and voltage. This paper describes novel control scheme for equalization of output power between the parallel connected inverters. The proposed scheme has a fast power balance control response, a simplicity of implementation, and inherent peak current limiting capability since it employes a instantaneous current/voltage control with output voltage and current balance and output voltage regulation. A design procedure for the proposed parallel inverter controller is presented. Futhermore, the proposed constrol scheme is verified through the simulation in various cases such as the system parameter variation, the control parameter variation and the nonlinear load condition.
A New and Efficient UTD Based Near Field Scanning Technique for Antenna Radiation Pattern Analysis
선영식,명노훈,Probhakar H. Pathak 에스케이텔레콤 (주) 1997 Telecommunications Review Vol.7 No.5
A new method is presented for computing far field antenna patterns from spherical near field antenna measurement data. The method utilizes a novel Uniform Geometrical Theory of Diffraction(UTD) based transformation of spherically scanned antenna tangential electric (or magnetic) near field measured values to present to obtain the antenna far field more efficiently. If the measured tangential near fields on the spherical measurement surface S which completely encloses the antenna under test(AUT) are only of the electric type, then the field external to S can be expressed, via an appropriate equivalence theorem, directly as the field produced by an equivalent magnetic surface current source distribution on S that is now made into a perfect electric conductor(PEC). The equivalent magnetic surface current density on the PEC sphere S (PECS) is exactly related to the measured tangential electric field on the original surface S. The field external to the PECS due to an equivalent magnetic surface current distribution on the same PECS can thus be expressed as an integral of the dot product of an appropriate dyadic Green′s function. A highly accurate and relatively simple asymptotic high frequency UTD form of this special dyadic Green′s function is available in essentially closed form. Examples illustrating the accuracy and speed of UTD based spherical near to far field transformations for large to moderately large antennas are presented.
선영식,명노훈 대한전자공학회 1995 전자공학회논문지-A Vol.32 No.11
The problem of amplitude-and frequency-modulated waveforms is analyzed when a linearly polarized electromagnetic wave is scattered by a slowly rotating rotor with metal plates. ECM in conjunction with a quasi-stationary method is used to analyze the modulated waveforms. The modulated waveforms depend on the orientation and dimension of the object. its rotation speed, and very strongly on the incident and scattering directions. The modulate waveforms of a rotating non-skewed metal plate and a rotor with two blades are functions of twice the rotating frequency of those. Similar results are discussed for a rotating skewed metal plate, but the modulated waveforms is a function of the rotating frequency. Numerical results based on our ECM are presented and compared with those of Sikta's and PO solution.