• Title, Summary, Keyword: constant capacitance model

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Response Characteristics for Low Voltage Liquid Crystal Display Employing a Constant Charge Model

  • Kim, Mi-Soon;Huh, Su-Jung;Suh, Duck-Jong;Ahn, Yi-Joon;Lee, Kyung-Jin;Ahn, Seon-Hong;Kim, Kyeong-Hyeon;Kim, Sang-Soo
    • 한국정보디스플레이학회:학술대회논문집
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    • pp.228-230
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    • 2008
  • The response time characteristic of low voltage liquid crystals (LCs) is investigated and a new simulator for low voltage LCs is proposed. In order to enable low voltage operation, it is important to minimize Vth of LCs and variation of pixel voltage caused by dynamic capacitance operation of LC Display. Because dynamic capacitance variation is much larger for low voltage LC operation compared to that of conventional LC material, it is necessary to make a better model for dynamic capacitance operation. A proposed minimizing Vth of LCs and variation of pixel voltage study results through a new constant charge model improve response characteristics for low voltage LCs operation.

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Development of a variable resistance-capacitance model with time delay for urea-SCR system

  • Feng, Tan;Lu, Lin
    • Environmental Engineering Research
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    • v.20 no.2
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    • pp.155-161
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    • 2015
  • Experimental research shows that the nitric oxides ($NO_X$) concentration track at the outlet of selective catalytic reduction (SCR) catalyst with a transient variation of Adblue dosage has a time delay and it features a characteristic of resistance-capacitance (RC). The phenomenon brings obstacles to get the simultaneously $NO_X$ expected to be reduced and equi-molar ammonia available to SCR reaction, which finally inhibits $NO_X$ conversion efficiency. Generally, engine loads change frequently, which triggers a rapid changing of Adblue dosage, and it aggravates the air quality that are caused by $NO_X$ emission and ammonia slip. In order to increase the conversion efficiency of $NO_X$ and avoid secondary pollution, the paper gives a comprehensive analysis of the SCR system and tells readers the key factors that affect time delay and RC characteristics. Accordingly, a map of time delay is established and a solution method for time constant and proportional constant is carried out. Finally, the paper accurately describes the input-output state relation of SCR system by using "variable RC model with time delay". The model can be used for a real-time correction of Adblue dosage, which can increase the conversion efficiency of $NO_X$ in SCR system and avoid secondary pollution forming. Obviously, the results of the work discover an avenue for the SCR control strategy.

Determining Method of Minimum-capacitance for Self-excited Induction Generator (자기 여자 유도 발전기의 최소 커패시턴스의 결정법)

  • Jin, Chung-Min;Jwa, Chong-Keun
    • Proceedings of the KIEE Conference
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    • pp.729-731
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    • 2000
  • This paper presents a simple method for determining the minimum value of capacitance required for initiating self excitation in three-phase self-excited induction generator. Based on the steady-state equivalent circuit model, this paper presents simple and direct method to find the minimum capacitance requirement under R-L load. Using the loop impedance and nodal admittance. the minimum capacitance is determined by self excitation condition. These computed values can be used to predict practically the minimum value of the terminal voltage required for self-excitation. To maintain a constant terminal voltage, a method for determining the frequency, terminal capacitance, and exciting reactance is also described.

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Application of Generalized Transmission Line Models to Mixed Ionic-Electronic Transport Phenomena

  • Ahn, Pyung-An;Shin, Eui-Chol;Kim, Gye-Rok;Lee, Jong-Sook
    • Journal of the Korean Ceramic Society
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    • v.48 no.6
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    • pp.549-558
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    • 2011
  • Application of a generalized equivalent circuit including the electrode condition for the Hebb-Wagner polarization in the frequency domain proposed by Jamnik and Maier can provide a consistent set of material parameters, such as the geometric capacitance, partial conductivities, chemical capacitance or diffusivity, as well as electrode characteristics. Generalization of the shunt capacitors for the chemical capacitance by the constant phase elements (CPEs) was applied to a model mixed conducting system, $Ag_2S$, with electron-blocking AgI electrodes and ion-blocking Pt electrodes. While little difference resulted for the electron-blocking cell with almost ideal Warburg behavior, severely non-ideal behavior in the case of Pt electrodes not only necessitates a generalized transmission line model with shunt CPEs but also requires modelling of the leakage in the cell approximately proportional to the cell conductance, which then leads to partial conductivity values consistent with the electron-blocking case. Chemical capacitance was found to be closer to the true material property in the electron-blocking cell while excessively high chemical capacitance without expected silver activity dependence resulted in the electron-blocking cell. A chemical storage effect at internal boundaries is suggested to explain the anomalies in the respective blocking configurations.

Reduced-order Mapping and Design-oriented Instability for Constant On-time Current-mode Controlled Buck Converters with a PI Compensator

  • Zhang, Xi;Xu, Jianping;Wu, Jiahui;Bao, Bocheng;Zhou, Guohua;Zhang, Kaitun
    • Journal of Power Electronics
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    • v.17 no.5
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    • pp.1298-1307
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    • 2017
  • The constant on-time current-mode controlled (COT-CMC) switching dc-dc converter is stable, with no subharmonic oscillation in its current loop when a voltage ripple in its outer voltage loop is ignored. However, when its output capacitance is small or its feedback gain is high, subharmonic oscillation may occur in a COT-CMC buck converter with a proportional-integral (PI) compensator. To investigate the subharmonic instability of COT-CMC buck converters with a PI compensator, an accurate reduced-order asynchronous-switching map model of a COT-CMC buck converter with a PI compensator is established. Based on this, the instability behaviors caused by output capacitance and feedback gain are investigated. Furthermore, an approximate instability condition is obtained and design-oriented stability boundaries in different circuit parameter spaces are yielded. The analysis results show that the instability of COT-CMC buck converters with a PI compensator is mainly affected by the output capacitance, output capacitor equivalent series resistance (ESR), feedback gain, current-sensing gain and constant on-time. The study results of this paper are helpful for the circuit parameter design of COT-CMC switching dc-dc converters. Experimental results are provided to verify the analysis results.

Zirconium Titanate Thin FIlm Prepared by Surface Sol-Gel Process and Effects of Thickness on Dielectric Property

  • Kim, Chy-Hyung;Lee, Moon-Hee
    • Bulletin of the Korean Chemical Society
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    • v.23 no.5
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    • pp.741-744
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    • 2002
  • Single phase of multicomponent oxide ZrTiO4 film could be prepared through surface sol-gel route simply by coating the mixture of 100 mM zirconium butoxide and titanium butoxide on $Pt/Ti/SiO_2Si(100)$ substrate, following pyro lysis at $450^{\circ}C$, and annealing it at 770 $^{\circ}C.$ The dielectric constant of the film was reduced as the film thickness decreased due to of the interfacial effects caused by layer/electrode and a few voids inside the multilayer. However, the dielectric property was independent of applied dc bias sweeps voltage (-2 to +2 V).The dielectric constant of bulk film, 31.9, estimated using series-connected capacitor model was independent of film thickness and frequency in the measurement range, but theoretical interfacial thickness, ti, was dependent on the frequency. It reached a saturated ti value, $6.9{\AA}$, at high frequency by extraction of some capacitance component formed at low frequency range. The dielectric constant of bulk ZrTiO4 pellet-shaped material was 33.7 and very stable with frequency promising as good applicable devices.

Impedance Spectroscopy Models for X5R Multilayer Ceramic Capacitors

  • Lee, Jong-Sook;Shin, Eui-Chol;Shin, Dong-Kyu;Kim, Yong;Ahn, Pyung-An;Seo, Hyun-Ho;Jo, Jung-Mo;Kim, Jee-Hoon;Kim, Gye-Rok;Kim, Young-Hun;Park, Ji-Young;Kim, Chang-Hoon;Hong, Jeong-Oh;Hur, Kang-Heon
    • Journal of the Korean Ceramic Society
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    • v.49 no.5
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    • pp.475-483
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    • 2012
  • High capacitance X5R MLCCs based on $BaTiO_3$ ceramic dielectric layers exhibit a single broad, asymmetric arc shape impedance and modulus response over the wide frequency range between 1 MHz to 0.01 Hz. Analysis according to the conventional brick-layer model for polycrystalline conductors employing a series connection of multiple RC parallel circuits leads to parameters associated with large errors and of little physical significance. A new parametric impedance model is shown to satisfactorily describe the experimental spectra, which is a parallel network of one resistor R representing the DC conductivity thermally activated by 1.32 eV, one ideal capacitor C exactly representing bulk capacitance, and a constant phase element (CPE) Q with complex capacitance $A(i{\omega})^{{\alpha}-1}$ with ${\alpha}$ close to 2/3 and A thermally activated by 0.45 eV or ca. 1/3 of activation energy of DC conductivity. The feature strongly indicate the CK1 model by J. R. Macdonald, where the CPE with 2/3 power-law exponent represents the polarization effects originating from mobile charge carriers. The CPE term is suggested to be directly related to the trapping of the electronic charge carriers and indirectly related to the ionic defects responsible for the insulation resistance degradation.

An Accelerated Degradation Test of Electric Double-Layer Capacitors (전기이중층커패시터의 가속열화시험)

  • Jung, Jae-Han;Kim, Myung-Soo
    • Journal of Applied Reliability
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    • v.12 no.2
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    • pp.67-78
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    • 2012
  • An electric double-layer capacitor(EDLC) is an electrochemical capacitor with relatively high energy density, typically hundreds of times greater than conventional electrolytic capacitors. EDLCs are widely used for energy storage rather than as general-purpose circuit components. They have a variety of commercial applications, notably in energy smoothing and momentary-load devices, and energy-storage and kinetic energy recovery system devices used in vehicles, etc. This paper presents an accelerated degradation test of an EDLC with rated voltage 2.7V, capacitance 100F, and usage temperature $-40^{\circ}C{\sim}65^{\circ}C$. The EDLCs are tested at $50^{\circ}C$, $60^{\circ}C$, and $70^{\circ}C$, respectively for 1,750hours, and their capacitances are measured at predetermined times by constant current discharge method. The failure times are predicted from their capacitance deterioration patterns, where the failure is defined as 30% capacitance decrease from the initial one. It is assumed that the lifetime distribution of EDLC follows Weibull and Arrhenius life-stress relationship holds. The life-stress relationship, acceleration factor, and $B_{10}$ life at design condition are estimated by analyzing the accelerated life test data.

A Thermal Model for Electrothermal Simulation of Power Modules

  • Meng, Jinlei;Wen, Xuhui;Zhong, Yulin;Qiu, Zhijie
    • Journal of international Conference on Electrical Machines and Systems
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    • v.2 no.4
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    • pp.441-446
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    • 2013
  • A thermal model of power modules based on the physical dimension and thermal properties is proposed in this paper. The heat path in the power module is considered as a one-dimensional heat transfer in the model. The method of the parameters extraction for the model is given in the paper. With high speed and accuracy, the thermal model is suit for electrothermal simulation. The proposed model is verified by experimental results.