• Title/Summary/Keyword: frequency control

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Improved Hysteresis Current Control Regulator for High-efficiency Switching (고효율 스위칭을 위한 개선된 히스테리시스 전류제어기)

  • Hong, Sun-Ki;Park, Jin-Ho
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.61 no.11
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    • pp.1606-1610
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    • 2012
  • Hysteresis current regulator has been used widely because of its simple principle and structure. However, when the current band width is too narrow or the applied voltage is relatively too high, the switching frequency may increase abruptly and it generates a large amount of heat. Thus, this study will suggest a better and simple method to reduce the switching frequency. For single phase current control, the proposed hysteresis current control is executed by adding 0 mode state and comparing the slope of the current reference. This simple method decreases the generated switching frequency and significantly reduces the generated heat. This proposed method was proved with simulations and experiments comparing with the classical hysteresis current control method.

Control Valve Positioner and Its effect on a Gas Turbine MW Control (공정제어루프 최종 조작부의 동작특성에 관한 연구)

  • Kim, Jong-An;Shin, Yoon-Oh
    • Proceedings of the KIEE Conference
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    • 1998.07b
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    • pp.728-730
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    • 1998
  • The control valve positioner is a high gain plain proportional controller which measures the valve stem position and compares it to its setpoint which is the primary controller output. The positioner in effect is the cascade slave of the primary controller. In order for a cascade slave to be effecttive, it must be fast enough compared to the speed of its set point change. This paper describes the positioner transfer function and its effect on the entire control loop characteristic based on the simulation results. The result showed that the control valve and positioner determined the gain and phase angle in the high frequency range, while the primary controller and process determined those of the low frequency range. We can also anticipate the combined characteristics in the whole frequency range when each element's frequency response is known.

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Active Vibration Control of Fixed-Fixed Beam Using Piezoelectric Sensor and Actuator (압전 감지기와 작동기를 이용한 양단 고정보의 능동 진동 제어)

  • 한상보;곽문규;최이호;윤신일
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 1996.10a
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    • pp.260-265
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    • 1996
  • Active control of forced vibration response of a fixed-fixed beam implementing PZT sensor/actuator was conducted. Among various control scheme, PPF control was chosen due to its amenability and natural robustness. For a single frequency excitation, the PPF control provided reasonable controllability with the appropriate damping ratio of the compensator. Without increasing actuator voltage, best controllability can be obtained by the exact tuning between the natural frequency of the structure and the cut-off frequency of the compensator. Even the multi-frequency excitation, the PPF provided good vibration suppression for corresponding mode of interest, even though residual modes should be controlled with independent compensators for each mode.

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A Study on a Current Control Based on Model Prediction for AC Electric Railway Inbalance Compensation Device (교류전력 불평형 보상장치용 모델예측기반 전류제어 연구)

  • Lee, Jeonghyeon;Jo, Jongmin;Shin, Changhoon;Lee, Taehoon;Cha, Hanju
    • The Transactions of the Korean Institute of Power Electronics
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    • v.25 no.6
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    • pp.490-495
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    • 2020
  • The power loss of large-capacity systems using single-phase inverters has attracted considerable attention. In this study, optimal switching sequence model prediction control at a low switching frequency is proposed to reduce the power loss in a high-power inverter system, and a compensation method that can be utilized for model prediction control is developed to reduce errors in accordance with sampling values. When a three-level, single-phase inverter using a switching frequency of 600 Hz and a sampling frequency of 12 kHz is adopted, the power factor is improved from 0.95 to 0.99 through 3 kW active power control. The performance of the controller is also verified.

Effect Analysis for Frequency Recovery of 524 MW Energy Storage System for Frequency Regulation by Simulator

  • Lim, Geon-Pyo;Choi, Yo-Han;Park, Chan-Wook;Kim, Soo-Yeol;Chang, Byung-Hoon;Labios, Remund
    • KEPCO Journal on Electric Power and Energy
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    • v.2 no.2
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    • pp.227-232
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    • 2016
  • To test the effectiveness of using an energy storage system for frequency regulation, the Energy New Business Laboratory at KEPCO Research Institute installed a 4 MW energy storage system (ESS) demonstration facility at the Jocheon Substation on Jeju Island. And after the successful completion of demonstration operations, a total of 52 MW ESS for frequency regulation was installed in Seo-Anseong (28 MW, governor-free control) and in Shin-Yongin (24 MW, automatic generation control). The control system used in these two sites was based on the control system developed for the 4 MW ESS demonstration facility. KEPCO recently finished the construction of 184 MW ESS for frequency regulation in 8 locations, (e.g. Shin-Gimjae substation, Shin-Gaeryong substation, etc.) and they are currently being tested for automatic operation. KEPCO plans to construct additional ESS facilities (up to a total of about 500 MW for frequency regulation by 2017), thus, various operational tests would first have to be conducted. The high-speed characteristic of ESS can negatively impact the power system in case the 500 MW ESS is not properly operated. At this stage we need to verify how effectively the 500 MW ESS can regulate frequency. In this paper, the effect of using ESS for frequency regulation on the power system of Korea was studied. Simulations were conducted to determine the effect of using a 524 MW ESS for frequency regulation. Models of the power grid and the ESS were developed to verify the performance of the operation system and its control system. When a high capacity power plant is tripped, a 24 MW ESS supplies power automatically and 4 units of 125MW ESS supply power manually. This study only focuses on transient state analysis. It was verified that 500 MW ESS can regulate system frequency faster and more effectively than conventional power plants. Also, it was verified that time-delayed high speed operations of multiple ESS facilities do not negatively impact power system operations. It is recommended that further testing be conducted for a fleet of multiple ESSs with different capacities distributed over multiple substations (e.g. 16, 24, 28, and 48 MW ESS distributed across 20 substations) because each ESS measures frequency individually. The operation of one ESS facility will differ from the other ESSs within the fleet, and may negatively impact the performance of the others. The following are also recommended: (a) studies wherein all ESSs should be operated in automatic mode; (b) studies on the improvement of individual ESS control; and (c) studies on the reapportionment of all ESS energies within the fleet.

Electronic-hydraulic Hitch Control System for Agricultural Tractor -Draft Control- (트랙터의 전자유압식(電子油壓式) 히치 제어(制御) 시스템에 관한 연구(硏究)(II) -견인력제어(牽引力制御)-)

  • Yoo, S.N.;Ryu, K.H.;Yun, Y.D.
    • Journal of Biosystems Engineering
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    • v.14 no.4
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    • pp.229-241
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    • 1989
  • The purposes of this study were to develop an electronic-hydraulic draft control system for tractor implements, to investigate the control performance of the system and the possibility of adaptation to the conventional tractor. Experiments were carried out to investigate the responses of the system to the step and sinusoidal inputs in draft control. The effects of control mode, hydraulic flow rate, reference deadband, and proportional constant on control performance of the system were investigated. Moreover, the effects of filtering signals from draft sensor were also investigated. The following conclusions were derived from the study; 1. In draft control, there were hunting problems in controlling the implement without filtering the draft signals. Filtering was performed by a control program of electronic controller and the control performance and stability of the system were improved significantly. 2. For the draft control system operated on on-off control mode, draft was controlled within ±27±55kgf to the reference draft when the hydraulic flow rates were 5-15 l/min. For the draft control system operated on PWM control, draft was controlled within ±27kgf to the reference draft regardless of hydraulic flow rates. 3. In the frequency responses of the draft control system, control performance on PWM control mode was not better than on on-off control mode because of characteristics of hydraulic valve and drafe sensor. As the hydraulic flow rates increased for the system operated on on-off control mode, the corner frequency of amplitude attenuation increased, but the corner frequency of phase-angle change remained nearly the same. But, the system was unstable beyond the frequency of 3.1 rad/s. 4. The electronic-hydraulic hitch control system developed in this study showed superior control performance, stability and convenience compared to conventional mechanical-hydraulic hitch control system. It is considered to be a superior replacement for the conventional mechanical-hydraulic hitch control system.

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Frequency Follow-up Control System of Resonant Load MOSFET Inverter using PLL (PLL을 이용한 공진부하 MOSFET 인버어터의 주파수 추종제어계)

  • Kim, Joon-Hong;Joong-Hwan kim
    • The Transactions of the Korean Institute of Electrical Engineers
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    • v.35 no.7
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    • pp.272-277
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    • 1986
  • The system that follows to the resonance frequency of high frequency MOSFET inverter and varies according to the changes of load characteristics is proposed. Also we suggested a method how to select the resonant load type between series and parallel circuit for a given inverter type. It leads to the conclusion that in the case of high impedance loads, parallel resonant circuits are preferable, on the other hand, for low impedance loads, series resonant circuits are more preferable. For frequency tracking, a PLL circuit is used as main control element to detect the phase difference of current and voltage of load. The realized apparatus composed of control circuit and voltage type full-bridged MOSFET elements as main parts of inverter. A stable frequency follow-up characteristics are obtained for 1.2MHz, 1.5KW high frequency output and power is always supplied to the load with unity power factor.

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Control of Matching Frequency of Ferrite Composite Microwave Absorber Consisted of Two Kinds of Ferrites (2종의 Ferrite가 혼합된 복합 Ferrite 전파흡수체의 정합주파수 제어)

  • 권형주;신재영;오재희
    • Journal of the Korean Ceramic Society
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    • v.30 no.10
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    • pp.823-828
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    • 1993
  • The performance of ferrite composite microwave absorber has been evaluated as the matching frequency, the matching thickness and the band width. Especially, matching frequency is very important in application of microwave absorber because it determines operating frequency range. In this study, the ferrite composite microwave absorbers consisted Ni-Zn ferrite and Zn2Y ferroxplana were prepared in order to control matching frequency. Then, the variation of the material constants and microwave absorbing characteristics were investigated with various ferrite mixing ratio. The material constants of ferrite composite microwave absorber could be controlled by variation ferrite mixing ratio. Therefore, it was confirm that matching frequency of microwave absorber could be shifted by control of material constants.

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Dynamic change of frequency after a generator outage in an Interconnection considering the primary control (연계계통에서 발전기 정지에 따른 주파수의 동적 변화)

  • Stanojevic, Vladimir;Moon, Y.H.;Yoon, J.Y.
    • Proceedings of the KIEE Conference
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    • 2001.05a
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    • pp.95-99
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    • 2001
  • Frequency is the unique physical value for all the interconnected systems. Therefore. the load frequency control is in the responsibility of all members in the interconnection power unbalance in one of the interconnected system can cause the problems in others. In the following text a brief description and the role of frequency in an interconnected system will be presented. Following is the short description of the Balkan Interconnection (UCTE Second Synchronous Zone) with schematic diagram. A Power-Frequency (P-f) dynamic model of a control area wil1 be shown. Model gives the analytical solution for frequency change versus a time after outage of a generator in the power system. This model will be applied to the Balkan Interconnection and compared with numerical approach. Advantages and drawbacks of the analytical method will be discussed Purpose of using this model is to investigate if the pumps in reversible hydropower plant will be underfrequency shed after the outage of the biggest generator unit in the interconnection, according %o (n-1) security postulate.

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A new broadband energy harvester using propped cantilever beam with variable overhang

  • Usharani, R.;Uma, G.;Umapathy, M.;Choi, S.B.
    • Smart Structures and Systems
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    • v.19 no.5
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    • pp.567-576
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    • 2017
  • Design of piezoelectric energy harvester for a wide operating frequency range is a challenging problem and is currently being investigated by many researchers. Widening the operating frequency is required, as the energy is harvested from ambient source of vibration which consists of spectrum of frequency. This paper presents a new technique to increase the operating frequency range which is achieved by designing a harvester featured by a propped cantilever beam with variable over hang length. The proposed piezoelectric energy harvester is modeled analytically using Euler Bernoulli beam theory and the effectiveness of the harvester is demonstrated through experimentation. The results from analytical model and from experimentation reveal that the proposed energy harvester generates an open circuit output voltage ranging from 36.43 V to 11.94 V for the frequency range of 27.24 Hz to 48.47 Hz. The proposed harvester produces continuously varying output voltage and power in the broadened operating frequency range.