Voltage Transient Response Research Articles

Shuffled frog leaping algorithm‐based static synchronous compensator for transient stability improvement of a grid‐connected wind farm

The shuffled frog leaping algorithm (SFLA) is presented, to optimally design multiple proportional-integral (PI) controllers of the static synchronous compensator (STATCOM) system with the purpose of improving the transient stability of a grid-connected wind farm. The control strategy of the STATCOM system depends on a sinusoidal pulse width modulation voltage source converter, which is controlled by the cascaded PI control scheme. The response surface methodology is used to establish a second-order fitted model of the transient voltage responses at the point of common coupling in terms of PI controllers' parameters. For realistic responses, a three-mass drive train model is used for the wind turbine generator system because of its great influence on the dynamic analyses. The SFLA code is built using MATLAB software. The effectiveness of optimised PI-controlled STATCOM by the SFLA is then compared to that optimised by genetic algorithms technique taking into consideration symmetrical and unsymmetrical fault conditions. The proposed control scheme is applied to a real grid-connected wind farm system at Hokkaido Island, Japan. The validity of the proposed system is verified by the simulation results, which are performed using PSCAD/EMTDC software environment. With the proposed SFLA-based STATCOM, the transient stability of a grid-connected wind farm can be enhanced.

An Energy-Based Approach to Extract the Dynamic Instability Parameters of Dielectric Elastomer Actuators

An energy-based approach is presented to extract the thresholds on the transient dynamic response of step voltage driven dielectric elastomer actuators (DEAs). The proposed approach relies on establishing the energy balance at the point of maximum stretch in an oscillation cycle followed by the application of an instability condition to extract the dynamic instability parameters. Explicit expressions are developed for the critical values of maximum stretch and the corresponding nominal electric field, thus circumventing the need to perform iterative time-integrations of the equation of motion. The underlying principles of the approach are enunciated for the neo-Hookean material model and further extended to analyze relatively complex multiparameter hyperelastic models (Mooney–Rivlin and Ogden) that are employed prevalently for investigating the behavior of DEAs. The dynamic instability parameters predicted using the energy method are validated by examining the time-history response of the actuator in the vicinity of the dynamic instability. The development of dynamic instability parameters is complemented by energy-based extraction of static instability parameters to facilitate a quick comparison between the two. It is inferred quantitatively that the nominal electric field sufficient to cause the dynamic instability and the corresponding thickness stretch is lower than those corresponding to the static instability. A set of representative case studies for multiparameter material models is presented at the end, which can be used as an input for further experimental corroboration. The results of the present investigation can find their potential use in the design of DEAs subjected to transient loading.

A New Control Strategy Based Multi Converter UPQC Using Fuzzy Logic Controller to Improve the Power Quality Issues

A design of multiconverter unified power quality conditioner to improve the power quality issues is presents in this paper. Modified SRF theory and fuzzy logic controller technique are incorporated in this modelling. This newly designed controller is connected to a source in order to compensate voltage and current in the two feeders. The expanded concept of UPQC is multi converter-UPQC; this system has two series voltage source converter (VSC) and one shunt VSC connected back to back. In the proposed system, the power can be conveyed from one feeder to another in order to mitigate the voltage sag, swell, interruption and transient response of the system. The control strategies of multi converter-UPQC are designed based on the modified synchronous reference frame theory with fuzzy logic controller. The transient response of the fuzzy logic controller in dc-link voltage controller will be very fast. The relevant simulation and compensation performance analysis of multi converter-UPQC with fuzzy logic controller is performed using MATLAB/Simulink software.

Limiting Integral Loop Digital Control for DC–DC Converters Subject to Changes in Load Current and Source Voltage

A new digital control technique is proposed to improve the speed of both load current and source voltage transient responses for dc-dc converters operating in continuous conduction mode (CCM). The key structure of the proposed control technique is a combination of a limiting integral loop and related arithmetic operations to produce the desired switching sequence during transient condition. The limiting integral loop is built as a novel structure for capacitor charge balance operation. In contrast to previous approaches, the proposed control technique is valid for three basic converters: 1) buck; 2) boost; and 3) buck-boost. Moreover, since the transient period is forced to be an integer multiple of the switching cycle, the advantage of fixed switching frequency is inherently provided. Simulation and experimental results from a noninverting synchronous buck-boost converter prototype are given to validate the effectiveness of the proposed solution.

Electro-optical effects and temperature-dependent electrical properties of LuFe2O4 thin films

We report electro-optical and temperature-dependent electrical-transport properties of LuFe2O4 (LFO) thin films. The LFO thin films at 78K showed the electro-optical effects of size up to 5% near the Fe2+d to d on-site electronic transition. In the three-dimensional charge-ordered state of LFO, we observed hysteresis in dc voltage–current measurements and nonlinear voltage–current relationship in transient response of voltage under current pulses. The electro-optical and electrical properties of LFO thin films are interpreted in terms of the field-induced changes of the charge-ordered state mediated by the spin–charge–lattice coupling effect. We also discuss possible mechanisms of the complex electrical properties and electro-optical effects in conjunction with the Maxwell–Wagner effects.

Influence of Operation Parameters on the Response of a PEMFC with Electrodeposited Pt‐WO3 Cathode

AbstractPt‐WO3 electrodes for proton exchange membrane fuel cells (PEMFC) have been prepared by electrodeposition on microporous carbon substrates. The electrodes have been studied as cathode in single cells under different operation conditions, including gas humidification, stoichiometry, and cell temperature. Polarization curves show a response qualitatively different from that observed with standard Pt/C cathodes, dominated by properties of the WO3 phase. At low current densities, below ca. 400 mA cm–2, the response is limited by protonic resistance and electrochemical kinetics in the cathode catalyst layer; at high current densities, large water retention by the hydrophilic cathode catalyst layer may cause anode flooding. Chemical changes in WO3 phase accelerate at high temperature and under dry cathode conditions, compromising cell stability in the long term. Therefore, continuous and stable operation requires low humidification in the anode and high in the cathode. Also, a pronounced transient voltage response to current demand steps is observed at low cell voltage, which we attribute to the transition of the cathode potential to a mixed potential value, laying between the oxygen reduction and the hydrogen adsorption/desorption equilibrium mediated by spillover from Pt to the WO3 phase. Basic kinetics considerations show how the height of the voltage transient is related with H spillover rate. Pt‐WO3 cathode catalyst layer may have a practical interest as cathode for PEMFC when dry hydrogen inlet conditions are imposed, for instance, by the use of a metal hydride hydrogen storage system.

A discrete Fourier transform-based fuel concentration and permeation sensing scheme for low temperature fuel cells

Due to the fuel permeation phenomenon, fuel cells of low temperature suffer limitations in power density and energy density. It is especially crucial to a direct methanol fuel cell. Controlling the fuel concentration within an appropriate range thus becomes significant. This paper proposes a practical sensing scheme to estimate the methanol concentration and permeation fluxes. It can also serve as a gas sensor to measure the oxygen concentration as well. By acquiring the transient response of the open-circuit voltage under oxygen starvation conditions, a measurement index is derived via the Discrete Fourier Transform (DFT) and thereby performs the estimation. The approach takes only 3s to sample the transient open-circuit voltages, while a root mean square error of the estimated methanol concentration is 1.4% relative to the maximum measurement magnitude of 2.5M. It is also validated for a wide range of oxygen concentration in the illustrative examples. There is no strict requirement for the data acquisition unit. A sampling frequency of 5Hz is enough, and this enhances its feasibility and reduces its cost. Based on the pre-established data, it makes the estimation of methanol permeation fluxes portable without carrying delicate equipments. Finally, an area-oriented index deduced from the zero-frequency term of the DFT serves as an alternative measurement basis that provides more pathways to evaluate the sensing results. The notion proposed in this paper is not only suggested for small portable fuel cells. It possesses potential for developing other kinds of electrochemical sensors as well.

The effect of overpotentials on the transient response of the 300 W SOFC cell stack voltage

This paper presents the results of an experimental investigation of transient characterizations of 300W planar type Solid Oxide Fuel Cell (SOFC) cell stack during load change. It indicates the transient characterization obtained during a ramped electric current with a Current-Based Fuel Control (CBFC) strategy. The fuel utilization factor is chosen for a reference of the CBFC strategy and is kept constant to the ramping electric current. The fuel utilization factor can be described as a ratio of consumed fuel (expressed as a function with an applied electric current) to supplied fuel. For the simplification of discussion, hydrogen was used as fuel by mixing it with nitrogen in order to satisfy the constant gas residential time in all cases and instances. The transient response of the cell voltage obtained under several thermal conditions was shown for discussion. The effect of overpotentials, associated with the cell’s operating temperature, on the transient response of the cell voltage is primarily discussed. The paper indicates that reducing the fuel flow rate, namely, setting a higher set-point for the fuel utilization factor, may decrease the OCV, increase concentration polarization and finally degrade cell performance. This paper also pointed out the importance of operating temperature management on both improving the steady-state cell performance and eliminating the negative effect of the overpotentials that appear on the transient response of the cell voltage.

Analysis of the Dielectric Loss in the Transmission Line Based on Time Domain BLT Equation

Dielectric loss is caused due to imperfect dielectric insulation, in order to study the impact of the dielectric loss consider a uniform loss transmission line with leak conductance. The BLT equation from the frequency domain to time domain is derived to improve the time domain BLT equation, and the aim of using the time domain BLT equation to calculate load voltage of the transmission line with transient signal source, through the calculation results to analyze the impact of the dielectric loss. The results showed that the attenuation of the terminal load transient response voltage occurred when the dielectric loss exists, and this effect is nonlinear.

Square of Voltage Out-Loop Based Feedback Linearization Control of Voltage Source Converter (VSC) in SMES

To improve the response characteristic of the VSC in SMES (Superconducting Magnetic Energy Storage) with wide load disturbance, a new square of voltage out-loop based feedback linearization control strategy is proposed for the control of VSC. The input variable was controlled by a combining of square of voltage out-loop based direct voltage control and current inner-loop control to achieve fast stabilization of DC bus voltage and accurate tracking of power of PCC. Stability and dynamic response characteristics of the system were verified by simulation results. It is shown that the proposed strategy can improve the DC bus voltage transient response with load step change, with simplified control variable expression and reduced calculating burden.

Control Design for Multiphase Synchronous Buck Converters Based on Exact Constant Resistive Output Impedance

This paper describes a control design methodology based on output impedance analysis for multiphase synchronous buck converters. This design leads to an optimal output voltage transient response. Two design alternatives are proposed. The first alternative uses an equivalent single-phase converter to design the control parameters. This approximation is valid as long as the deviations between the phases of the converter are within the usual tolerance limits. The second one achieves exact constant resistive output impedance regardless of the differences that exist between the phases. Simulation and experimental results are reported in order to validate the two design approaches.

Temperature-dependent photovoltaic behavior of CdSe quantum dots/P3HT hybrid thinfilm

An organic–inorganic hybrid solar cell based on CdSe quantum dots (QDs) and poly(3-hexylthiophene) (P3HT) was fabricated. Its temperature-dependent photovoltaic behaviors, such as I–V characteristic curves and open circuit voltage (Voc) transient response, were measured. The photovoltaic behavior of this hybrid thin film device was similar with that of organic thin film solar cells, according to analysis results based on the equivalent circuit method. The exact carrier lifetime was remarkably different between under low-temperature region and under temperature above 197K.

An MPC-PI Approach for Buck DC-DC Converters and Its Implementation

This paper describes a new model predictive control method for buck DC-DC converters. The objective is to achieve a good trade-off between fast response and low overshoot in the transient response of the output voltage. In the well-known PWM-PI method, such a trade-off is difficult to attain. The proposed model predictive control is based on an analytic algorithm that can be easily implemented online. Further, a PI outer loop is introduced to improve the robustness against load uncertainty. Moreover, the advantage of the proposed model predictive control is verified experimentally. The experimental results show that the proposed method outperforms the PWM-PI method.

Application-Specific Instruction-Set Processor for Control of Multi-Rail DC-DC Converter Systems

Conventional digital signal processor (DSP) based digital controllers are not specifically optimized for multi-rail DC-DC converter applications. A new application-specific instruction-set processor (ASIP) that overcomes the shortcomings of existing controllers has thus been designed, implemented, and evaluated. The proposed dual multiply-accumulate (MAC) architecture has been implemented using a field programmable gate array and verified in a closed-loop power converter system. The benefits of the proposed ASIP are illustrated through a comparison with a conventional single MAC processor architecture. Experimental results demonstrate improved output voltage transient response compared with existing DSP-based controllers when controlling multiple DC-DC converters. In the case of multiple converters that have a non-integer switching frequency ratio more significant improvements in transient response are obtained due to the processor's interrupt controller.

Non-singular terminal sliding-mode control of DC–DC buck converters

This paper presents a non-singular terminal sliding mode control (NTSMC) method for DC–DC buck converters. The NTSMC method eliminates the singularity problem which arises in the terminal sliding mode due to the fractional power and assures the finite time convergence of the output voltage error to the equilibrium point during the load changes. It is shown that the NTSMC method has the same finite time convergence as that of the terminal sliding mode control (TSMC) method. The influence of the fractional power on the state trajectory of the converter is investigated. It is observed that the slope of the sliding line becomes larger with decreasing value of the fractional power which leads to a faster transient response of the output voltage during the load changes. The theoretical considerations have been verified both by numerical simulations and experimental measurements from a laboratory prototype.

Comparative Evaluation of the HVDC and HVAC Links Integrated in a Large Offshore Wind Farm—An Actual Case Study in Taiwan

This paper mainly focuses on the transient voltage and frequency responses of a large offshore wind farm integrated system in Taiwan. It adopts a simulation study by using different submarine cable technologies and wind turbine types, including high-voltage direct current (HVDC) link based on line-commutated converter (LCC), high-voltage alternating current (HVAC) link, and three types of wind turbines. In addition, it utilizes an actual system that connects the Taiwan grid and a 200-MW offshore wind farm in the Penghu area via two submarine cables. The aim of this paper is to analyze the transient characteristics of both the HVDC and the HVAC connected wind power systems. According to the simulation results, it shows that the HVDC link can provide better voltage and frequency responses, which are independent on the types of wind turbines. Moreover, the HVDC link can alleviate the effect of grid faults on the wind farm and provide the wind farm better voltage and frequency stability.

Adaptive terminal sliding-mode control strategy for DC–DC buck converters

This paper presents an adaptive terminal sliding mode control (ATSMC) strategy for DC–DC buck converters. The idea behind this strategy is to use the terminal sliding mode control (TSMC) approach to assure finite time convergence of the output voltage error to the equilibrium point and integrate an adaptive law to the TSMC strategy so as to achieve a dynamic sliding line during the load variations. In addition, the influence of the controller parameters on the performance of closed-loop system is investigated. It is observed that the start up response of the output voltage becomes faster with increasing value of the fractional power used in the sliding function. On the other hand, the transient response of the output voltage, caused by the step change in the load, becomes faster with decreasing the value of the fractional power. Therefore, the value of fractional power is to be chosen to make a compromise between start up and transient responses of the converter. Performance of the proposed ATSMC strategy has been tested through computer simulations and experiments. The simulation results of the proposed ATSMC strategy are compared with the conventional SMC and TSMC strategies. It is shown that the ATSMC exhibits a considerable improvement in terms of a faster output voltage response during load changes.

A quasi-three-dimensional non-isothermal dynamic model of a high-temperature proton exchange membrane fuel cell

A quasi-three-dimensional non-isothermal dynamic model of a high-temperature proton exchange membrane fuel cell, operating with a polybenzimidazole membrane, has been developed. In the model, dynamic equations of energy conservation, species conservation and electrochemical reaction are solved within a simplified quasi-three-dimensional geometry. With this simplified geometry, the model can predict the distribution of fuel cell characteristics and physical phenomena in a high-temperature proton exchange membrane fuel cell during the steady and the transient states within minutes, without using a computational fluid dynamics program. The simulation results of the current–voltage polarization curve are validated with the experimental data reported in the literature. The simulation results show a good agreement with the experimental data and show that the variation of temperature strongly affects the fuel cell’s performance. In particular, the simulation results show that the transient response of the cell voltage is dependent upon that of the cell temperature.

Evaluation of a MEMS-Based Dual Metal-Layer Thin-Film Microelectrode Array for Suprachoroidal Electrical Stimulation

A double metal-layer thin-film platinum microelectrode array was fabricated for implantation between sclera and choroid based on MEMS processing techniques and photosensitive polyimide material. The array was composed of 60 stimulating sites (6 × 10) and four selectable returning electrodes. The diameter of each stimulating electrode was 350 μ m with a center-to-center spacing of 750 μm. The transient voltage responses of the electrode to current pulse stimulation indicated a charge-injection capacity greater than 52.1 μ C/cm (2) . Acute in vivo animal experiments showed that the implicit time of electrically evoked potentials (EEPs) was 17.09±1.45 ms at a threshold current of 25.55 ±5.43 μA for a full-row of simultaneously stimulated electrodes (i.e., current applied simultaneously to each of the 10 electrodes). Individual electrode stimulation threshold was 48.57 ±6.90 μA. The corresponding threshold charge densities were 13.28 ±2.82 μC/cm (2) and 25.24 ±3.59 μC/cm (2) , respectively. The spatial spread of the maximally recorded P1 response in the EEPs indicated a correspondence between the retinal stimulation site and the focal response location in the cortex. This method of array fabrication is suitable for acute suprachoroidal stimulation, and has a potential use for the fabrication of a visual prosthesis.

LiPB Battery SOC Estimation Using Extended Kalman Filter Improved with Variation of Single Dominant Parameter

This paper proposes the State-of-charge (SOC) estimator of a LiPB Battery using the Extended Kalman Filter (EKF). EKF can work properly only with an accurate model. Therefore, the high accuracy electrical battery model for EKF state is discussed in this paper, which is focused on high-capacity LiPB batteries. The battery model is extracted from a single cell of LiPB 40Ah, 3.7V. The dynamic behavior of single cell battery is modeled using a bulk capacitance, two series RC networks, and a series resistance. The bulk capacitance voltage represents the Open Circuit Voltage (OCV) of battery and other components represent the transient response of battery voltage. The experimental results show the strong relationship between OCV and SOC without any dependency on the current rates. Therefore, EKF is proposed to work by estimating OCV, and then is converted it to SOC. EKF is tested with the experimental data. To increase the estimation accuracy, EKF is improved with a single dominant varying parameter of bulk capacitance which follows the SOC value. Full region of SOC test is done to verify the effectiveness of EKF algorithm. The test results show the error of estimation can be reduced up to max 5%SOC.