• Journal of Electrical Engineering and Technology
• /
• 제13권5호
• /
• pp.1956-1964
• /
• 2018

Since the stator winding of High-Speed Permanent Magnet Generator (HSPMG) has few winding turns and low inductance value, it is more prone to be influenced by harmonic current. Moreover, the operation efficiency and the torque stability of HSPMG will be greatly influenced by harmonic current. Taking a 117 kW, 60 000 rpm HSPMG as an example, in order to analyze the effects of harmonic current on HSPMG in this paper, the 2-D finite element electromagnetic field model of the generator was established and the correctness of the model was verified by testing the generator prototype. Based on the model, the losses and torque of the generator under different frequency harmonic current were studied. The change rules of the losses and torque were found out. Based on the analysis of the influence of the harmonic phase angle on torque ripple, it is found that the torque ripple could be weakened through changing the harmonic phase angle. Through the analysis of eddy current density in rotor, the change mechanism of the rotor eddy current loss was revealed. These conclusions can contribute to reduce harmonic loss, prevent demagnetization fault and optimize torque ripple of HSPMG used in distributed power supply system.

• Journal of Power Electronics
• /
• 제18권6호
• /
• pp.1670-1682
• /
• 2018

The further improvement of submarine propulsion is associated with the modularity of accumulator-fed inverters, such as cascaded inverters (CIs). CI technology guarantees smooth output voltages with reduced switch frequencies under linear loads. However, the output voltages of CIs are distorted under rectifier loads. This distortion requires harmonic suppression technology. One such technology is the repetitive controller (RC), which is commonly applied but suffers from poor performance in propulsion systems. In this study, the FFT spectrum of a CI under rectifier load is analyzed, and the harmonic contents are uneven in magnitude. For the purpose of harmonic suppression, the control gains at each harmonic frequency should be seriously considered. A RC with a specific harmonic gain compensation (SHGC) for CIs is proposed. This method provides additional control gains at low-order harmonic frequencies, which are difficult to achieve with conventional RCs. This SHGC consists of a band-pass filter (BPF) and proportional element and is easy to implement. These features make the proposed method suitable for submarine propulsion. Experimental results verify the feasibility of the improved RC.

• 조명전기설비학회논문지
• /
• 제23권4호
• /
• pp.29-38
• /
• 2009

GHP(Gas Heating Pump) 시스템은 가스 엔진으로 구동되는 압축기로 구성되는 효율적인 냉/난방기이고, 학교나 사무용 빌딩에 널리 쓰이고 있다. GHP는 느린 응답, 큰 시정수와 시간에 따라 변하는 시스템으로 제어하기가 어렵다. 이들 비선형 부하는 고조파 전류를 발생시키고, 전력계통의 정현파 전압을 왜곡시킨다. 고조파 측정 결과로 고조파는 시간에 따라 변하는 특성이 관측되었다. 시간에 따라 변하는 고조파를 해결하기 위해서 쓰이는 가장 보편적인 방법은 누적확률을 사용하는 것이다. 본 논문에서는 GHP부하의 고조파 특성, IEC 61000-3-2에 의한 고조파 평가와 사례연구 시스템의 고조파 시뮬레이션 및 고조파 필터 적용을 심도있게 다루고자 하였다.

• 한국음향학회지
• /
• 제20권5호
• /
• pp.35-47
• /
• 2001

본 논문에서는 하모닉 부호화기와 CELP(Code Excited Linear Prediction) 부호화기의 장점을 고려한 효율적인 저 전송률 하모닉-CELP 음성 부호화기를 제안한다. 제안된 하모닉-CELP 부호화기에서는 프레임 단위 유/무성음 판별에 따라 무성음 구간에서는 고속 CELP방식으로 부호화하고 유성음 구간에서는 개선된 하모닉 부호화를 수행한다. 제안된 부호화기는 무성음 부호화를 위한 RP-VSELP(Regular Pulse Vector Sum Excited Linear Prediction), 유성음 부호화를 위한 간단한 정수 피치 검색, 정수 단위 피치에서의 고속 하모닉 추정, 가변 차원 하모닉 벡터 양자화, 주파수 해상도를 반영한 인지 가중치, 고속 하모닉 합성, 대역별 유성음 정도에 따른 자연성 제어, 다중 모드 등을 주요한 특징으로 하며, 이러한 특징들로 인해 기존의 HVXC(Harmonic Vector eXeited Coder) 부호화기에 비해서 매우 낮은 복잡도를 갖는다. 주관적인 음질 평가 결과, 제안된 2.4 kbps 하모닉-CELP 부호화기는 낮은 지연과 적은 계산량으로 양호한 음질을 얻을 수 있음을 확인하였다.

• 전력전자학회논문지
• /
• 제22권1호
• /
• pp.67-74
• /
• 2017

This study proposes a novel random pulse-width modulation (PWM) technique with a constant switching frequency utilizing a random offset voltage. The proposed PWM technique spreads switching harmonics by varying the position of an active voltage vector without a switching frequency variation. The implementation of the proposed PWM technique is simple because it does not require additional hardware and complex algorithm. The proposed random PWM technique is compared with the conventional PWM technique on the factors of harmonic spectrum, total harmonic distortion, and harmonic spread factor to confirm the harmonic spread effect. The validity of the proposed method is verified by simulations and experiments on a three-phase inverter drive system.

• 한국전자통신학회논문지
• /
• 제2권1호
• /
• pp.1-9
• /
• 2007

In this paper, a third-order harmonic mixer is designed using frequency multiplier theory for the Ka-band. The gate bias voltage is selected by frequency multiplier theory to maximize the third-order harmonic element ofthe fundamental LO frequency in the proposed mixer. The designed mixer has a gate mixer structure composed of a gate terminal input for the fundamental local signal ($f_{LO}$), RF signal (${RF}$) and a drain terminal output for the harmonic frequency ($3f_{LO}-f_{RF}$) respectively. The Ka-band harmonic mixer is designed and fabricated using a commercial GaAs MESFET device with a plastic package. The proposed mixer will provide a solution for the problems found in the high cost, complex circuitry in a conventional Ka-band mixer. The 33.5 GHz harmonic mixer has a -10 dB conversion gain by pumping 11.5 GHz LO with a +5 dBm level.

• 대한수학회지
• /
• 제54권4호
• /
• pp.1189-1208
• /
• 2017

In this paper, we study vanishing properties for $L^2$ harmonic 1-forms on a gradient shrinking Ricci soliton. We prove that if (M, g, f) is a complete oriented noncompact gradient shrinking Ricci soliton with potential function f, then there are no non-trivial $L^2$ harmonic 1-forms which are orthogonal to df. Second, we show that if the scalar curvature of the metric g is greater than or equal to (n - 2)/2, then there are no non-trivial $L^2$ harmonic 1-forms on (M, g). We also show that any multiplication of the total differential df by a function cannot be an $L^2$ harmonic 1-form unless it is trivial. Finally, we derive various integral properties involving the potential function f and $L^2$ harmonic 1-forms, and handle their applications.

• 대한수학회지
• /
• 제39권5호
• /
• pp.731-743
• /
• 2002

Let M be a Riemannian manifold with asymptotically non-negative curvature. We study the asymptotic behavior of the energy densities of a harmonic map and an exponentially harmonic function on M. We prove that the energy density of a bounded harmonic map vanishes at infinity when the target is a Cartan-Hadamard manifold. Also we prove that the energy density of a bounded exponentially harmonic function vanishes at infinity.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 2005년도 ICCAS
• /
• pp.782-785
• /
• 2005

This article introduces technique to reduce harmonic by using the $5^{th}$ and $7^{th}$ harmonic tune filter and line reactor in the comparison to the technique of intervening firing method at the pulse of the 6-pulse phase-controlled converter in every 1/6 period. The design of the technique introduced in this article is to reduce the harmonic distortion of the current and the voltage resulted from three-phase thyristor phase-controlled converter. The waveform obtained from the experiment was analyzed on the spectrum of the current, voltage and the total harmonic distortion. The double firing method causes zero vectors of output voltage and input current. Designing the mechanism of the converter based on the idea of Park Vector Theory, the number of harmonic distortion in the intervening firing method were compared to those in normal firing method.

• The Journal of the Acoustical Society of Korea
• /
• 제20권4E호
• /
• pp.24-30
• /
• 2001

This paper describes a fast harmonic estimation, referred to as Delta Adjustment (DA), using a low resolution pitch. The presented DA method is based on modification of the Generalized Dual Excitation (GDE) technique[1] which was proposed to improve speech enhancement performance. We introduce the GDE technique and modify it to be suitable for low bit rate harmonic coding that uses only an integer pitch estimate. Unlike the GDE, the DA matches a frequency-warped version of the original spectrum that conforms to a fixed pitch at all harmonic bands. In addition, complexity and performance of the presented method are described in comparison with those of the conventional Fractional Pitch (FP) based harmonic estimation. Experimental results showed that the DA algorithm significantly reduces the complexity of the FP method while maintaining the performance.