• Title/Summary/Keyword: Frequency control

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Optimal Hysteresis Control for CCM Driving of a Single-Stage PFC Flyback Converter for LED Lightings (LED 구동용 단일단 PFC CCM 플라이백 컨버터의 히스테리시스 최적 제어)

  • Kim, Choon-Tack
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.65 no.4
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    • pp.586-592
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    • 2016
  • The current control of Continuous Conduction Mode(CCM) can be implemented by several methods: peak current control; average current control; and hysteresis control. Among these methods, the hysteresis current control is popularly applied in various converter applications because of its simplicity of implementation, fast current control response and inherent peak current limiting capability. However, a current controller with conventional hysteresis band which multiplies the current reference has the disadvantage that the modulation frequency varies in one cycle of the input voltage and, as a result, generates high switching frequency in the low input voltage section. Also it is complicated to design the input filter due to varying switching frequency. This paper proposed an optimum hysteresis-band current control method where the band is generated by using both multiplication method and sum method to maintain the modulation frequency to be nearly constant. This approach can solve the high switching frequency in the low input voltage section, and achieve easy design of input filter. The performance of the proposed converter is verified with the simulation and the experimental works.

Load Frequency Control of Multi-area Power System using Auto-tuning Neuro-Fuzzy Controller (자기조정 뉴로-퍼지제어기를 이용한 다지역 전력시스템의 부하주파수 제어)

  • Jeong, Hyeong-Hwan;Kim, Sang-Hyo;Ju, Seok-Min;Heo, Dong-Ryeol;Lee, Gwon-Sun
    • The Transactions of the Korean Institute of Electrical Engineers A
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    • v.49 no.3
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    • pp.95-106
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    • 2000
  • The load frequency control of power system is one of important subjects in view of system operation and control. That is even though the rapid load disturbances were applied to the given power system, the stable and reliable power should be supplied to the users, converging unconditionally and rapidly the frequency deviations and the tie-line power flow one on each area into allowable boundary limits. Nonetheless of such needs, if the internal parameter perturbation and the sudden load variation were given, the unstable phenomenal of power system can be often brought out because of the large frequency deviation and the unsuppressible power line one. Therefore, it is desirable to design the robust neuro-fuzzy controller which can stabilize effectively the given power system as soon as possible. In this paper the robust neuro-fuzzy controller was proposed and applied to control of load frequency over multi-area power system. The architecture and algorithm of a designed NFC(Neuro-Fuzzy Controller) were consist of fuzzy controller and neural network for auto tuning of fuzzy controller. The adaptively learned antecedent and consequent parameters of membership functions in fuzzy controller were acquired from the steepest gradient method for error-back propagation algorithm. The performances of the resultant NFC, that is, the steady-state deviations of frequency and tie-line power flow and the related dynamics, were investigated and analyzed in detail by being applied to the load frequency control of multi-area power system, when the perturbations of predetermined internal parameters. Through the simulation results tried variously in this paper for disturbances of internal parameters and external stepwise load stepwise load changes, the superiorities of the proposed NFC in robustness and adaptive rapidity to the conventional controllers were proved.

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Phase Control Loop Design based on Second Order PLL Loop Filter for Solid Type High Q-factor Resonant Gyroscope (고체형 정밀 공진 자이로스코프를 위한 이차 PLL 루프필터 기반 위상제어루프 설계)

  • Park, Sang-Jun;Yong, Ki-Ryeok;Lee, Young-Jae;Sung, Sang-Kyung
    • Journal of Institute of Control, Robotics and Systems
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    • v.18 no.6
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    • pp.546-554
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    • 2012
  • This paper suggests a design method of an improved phase control loop for tracking resonant frequency of solid type precision resonant gyroscope. In general, a low cost MEMS gyroscope adapts the automatic gain control loops by taking a velocity feedback configuration. This control technique for controlling the resonance amplitude shows a stable performance. But in terms of resonant frequency tracking, this technique shows an unreliable performance due to phase errors because the AGC method cannot provide an active phase control capability. For the resonance control loop design of a solid type precision resonant gyroscope, this paper presents a phase domain control loop based on linear PLL (Phase Locked Loop). In particular, phase control loop is exploited using a higher order PLL loop filter by extending the first order active PI (Proportion-Integral) filter. For the verification of the proposed loop design, a hemispherical resonant gyroscope is considered. Numerical simulation result demonstrates that the control loop shows a robust performance against initial resonant frequency gap between resonator and voltage control oscillator. Also it is verified that the designed loop achieves a stable oscillation even under the initial frequency gap condition of about 25 Hz, which amounts to about 1% of the natural frequency of a conventional resonant gyroscope.

Improved Frequency Mitigation of a Variable-Speed Wind Turbine (개선된 가변속 풍력발전기의 주파수 평활화)

  • Li, Mingguang;Yang, Dejian;Kang, Yong Cheol;Hong, Junhee
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.67 no.6
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    • pp.695-701
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    • 2018
  • For a power grid that has a high wind penetration level, when wind speeds are continuously fluctuating, the maximum power point tracking (MPPT) operation of a variable-speed wind turbine (VSWT) causes the significant output power fluctuation of a VSWT, thereby significantly fluctuating the system frequency. In this paper, an improved power-smoothing scheme of a VSWT is presented that significantly mitigates the frequency fluctuation caused by varying wind speeds. The proposed scheme employs an additional control loop based on the frequency deviation that operates in combination with the MPPT control loop. To improve the power-smoothing capability of a VSWT in the over-frequency section (OFS), the control gain of the additional loop, which is set to be inversely proportional to the rotor speed, is proposed. In contrast, the control gain in the under-frequency section is set to be proportional to the rotor speed to improve the power-smoothing capability while avoiding over-deceleration of the rotor speed of a VSWT. The proposed scheme significantly improves the performance of the power-smoothing capability in the OFS, thereby smoothing the frequency fluctuation. The results clearly demonstrate that the proposed scheme significantly mitigates the frequency fluctuation by employing the different control gain for the OFS under various wind penetration scenarios.

Design of multivariable learning controller in frequency domain (주파수 영역에서 다변수 학습제어기의 설계)

  • 김원철;조진원;이광순
    • 제어로봇시스템학회:학술대회논문집
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    • 1993.10a
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    • pp.760-765
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    • 1993
  • A multivariable learning control is designed in frequency domain. A general to of feedback assisted learning scheme is considered and an inverse model based learning algorithm is derived through convergence analysis in frequency domain. Performance of the proposed control method is evaluated through numerical simulation.

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Microcomputer에 의한 3상유도전동기의 속도제어에 관한 연구

  • 정연택;이사영
    • 전기의세계
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    • v.31 no.4
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    • pp.303-307
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    • 1982
  • This paper describes how to improve a induction moter efficiency by a slip frequency control. Digital filter controlled by microcomputer is introduced in control system of a constant speed-drive and it has prove that the moter can be drived with a high efficiency at a constant slip frequency. The constant slip frequency control method has a merit of simplness.

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Circuit Design and Performance Analysis of CCFL Dimming Controller With Frequency Modulation

  • Kim, Cherl-Jin;Ji, Jae-Geun;Yoon, Shin-Yong
    • KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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    • v.4B no.4
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    • pp.201-205
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    • 2004
  • The CCFL dimming control methods are generally used lamp current regulation or average current adjustment method feeding the CCFL inverter. Inverter operation frequency is higher than resonant frequency for safe operation. In this study, we design the half-bridge type series and parallel resonant converter circuit that switches at variable frequency modulation methods to control the output power. This method has advantages such as low EMI and reduced harmonics, and it is convenient for dimming control using a microprocessor. The validity of this study is confirmed from the simulation and experimental results.

Current Decoupling Control for the Three-level PWM Rectifier with a Low Switching Frequency

  • Yuan, Qing-Qing;Xia, Kun
    • Journal of Electrical Engineering and Technology
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    • v.10 no.1
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    • pp.280-287
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    • 2015
  • Three-level PWM rectifiers applied in medium voltage applications usually operate at low switching frequency to keep the dynamic losses under permitted level. However, low switching frequency brings a heavy cross-coupling between the current components $i_d$ and $i_q$ with a poor dynamic system performance and a harmonic distortion in the grid-connecting current. To overcome these problems, a mathematical model based on complex variables of the three-level voltage source PWM rectifier is firstly established, and the reasons of above issues resulted from low switching frequency have been analyzed using modern control theory. Then, a novel control strategy suitable for the current decoupling control based on the complex variables for $i_d$ and $i_q$ is designed here. The comparisons between this kind of control strategy and the normal PI method have been carried out. MATLAB and experimental results are given in detail.

An integral square error-based model predictive controller for two area load frequency control

  • Kassem, Ahmed M.;Sayed, Khairy;El-Zohri, Emad H.;Ali, Hossam H.
    • Advances in Energy Research
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    • v.5 no.1
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    • pp.79-90
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    • 2017
  • The main objective of load frequency control (LFC) is to keep the frequency value at nominal value and force deviation of the frequency to zero in case of load change. This paper suggests LFC by using a model predictive control (MPC), based on Integral Square Error (ISE) method designed to optimize the damping of oscillations in a two-area power system. The MPC is designed and simulated with a model system in state space, for robust performance in the system response. The proposed MPC is tuned by ISE to achieve superior efficiency. Moreover, its performance has been assessed and compared with the PI and PID conventional controllers. The settling time and overshoot with MPC are extremely minimized as compared with conventional controllers.

A Speed and Power Control of DFIG Using the Exciting Frequency for Wind Power Generating (풍력발전용 권선형 유도발전기의 회전자 여자주파수를 이용한 속도와 출력제어)

  • Lee, U-Seok;O, Cheol-Su
    • The Transactions of the Korean Institute of Electrical Engineers B
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    • v.48 no.7
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    • pp.349-356
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    • 1999
  • 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 and power 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. For the speed control analysis, torque simulation is performed whereby the different slip between operating motor driving frequency and synchronous frequency of M-G system applied. To keep the output rating of the generator, the exciting frequency and voltage attenuation are applied.

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