Transient Step Response Research Articles

Towards an optimal frequency and time response of singe-tube pressure measurement systems under continuum-flow conditions

The pressure transmission tube, as part of a pressure measurement system, generally has a considerable influence on its dynamic characteristics. The paper deals with the mathematical modelling of the dynamic behaviour of pressure transmission tubes with the aim of providing guidelines for the optimal design of such systems in the frequency and time domains. The mathematical models used are based on linear wave theory and continuum flow mechanics with no-slip and isothermal boundary conditions. The frequency responses were evaluated in terms of frequency bandwidth and the transient step responses in terms of settling and rise times. Following a systematic analysis of these characteristic parameters, we derived an analytically formulated optimisation objective function defining the transition between the low-wavenumber and high-wavenumber pressure waves in the pressure transmission tubes. The demanded dynamic behaviour in the frequency and time domains can be achieved through an appropriate ratio between the actual tube radius and the so-called transition tube radius, which was derived as a function of the tube length, end volume and fluid properties.

Molecular Structure Effect on the Epoxidation of 1-Butene and Isobutene on the Titanium Silicate Catalyst under Transient Conditions in a Trickle Bed Reactor.

Epoxidation of two butane isomers (1-butene and isobutene) on the commercial titanium silicate (TS-1) catalyst was studied in a laboratory-scale trickle bed reactor. The transient step response technique was used as the main tool in the investigation. The transient responses revealed different dynamics of product formation in continuous operation. The study of isomers showed the impact of the molecular structure on the transient and stationary states of the system. The four-carbon chain present in 1-butene displayed a dynamic behavior with a prominent maximum of the conversion as a function of time-on-stream. On the contrary, the behavior of isobutene was displayed to be closer to ethene and propene under similar conditions reaching a steady state after ca. 2 h. The structure of the epoxide was an important factor in order to achieve a high epoxide selectivity. In isobutene epoxidation, the primary product 1,2-epoxy-2-methylpropane was highly reactive, giving a spectrum of parallelly formed byproducts. Therefore, the selectivity of the epoxide from isobutene was limited to ca. 70%. In the epoxidation of 1-butene, 1,2-epoxybutane was displayed to be a highly stable product with a selectivity close to 99%. Based on the transient and stationary data, a reaction mechanism was proposed for the epoxidation and ring-opening reactions present in the system.

Design and Control of a Quasi-Z Source Multilevel Inverter Using a New Reaching Law-Based Sliding Mode Control

The rapid growth in renewable energies has given rise to their integration into the grid system. These renewable and clean energy sources are dependent on external conditions such as wind speed, solar irradiation, and temperature. For a stable connection between these sources and power grid systems, a controller is necessary to regulate the system’s closed-loop dynamic behavior. A sliding mode control (SMC) using a new reaching law is proposed for the integration of a Modified Capacitor-Assisted Extended Boost (MCAEB) quasi-Z Source 7 level 18 switch inverter with the grid. An SMC-based controller was implemented to regulate the current flow between the inverter and the grid. SMC has the advantages of ease of implementation, robustness, and invariance to disturbance. The simulation results of SMC and the proportional integral (PI) controller are compared in terms of settling time, steady-state error, and total harmonic distortion (THD) during transient response, steady-state response and step response under different operating conditions. A hardware-in-loop (HIL)-based experimental setup of MCAEB quasi-Z source multilevel inverter was implemented using OPAL-RT. The performance of the proposed controller was further validated by implementing it on DSPACE-1202.

Shaping transient response of nonlinear systems to satisfy a class of integral constraints

AbstractWe consider the problem of shaping the transient step response of nonlinear systems to satisfy a class of integral constraints. Such constraints are inherent in hybrid energy systems consisting of energy sources and storage elements. While typical transient specifications aim to minimize overshoot, this problem is unique in that it requires the presence of an appreciable overshoot to satisfy the foregoing constraints. The problem was previously studied in the context of linear systems and this article extends that work to nonlinear systems. A combined integral and feedforward control, that requires minimal knowledge of the plant model, is shown to make the system amenable to meeting such constraints. Broadly, the compensation is effective for nonlinear plants with stable open‐loop step response and a positive DC gain. However, stability of the resulting closed‐loop system mandates bounds on the integral gain. In this regard, we state and prove generalized stability theorems for first and higher‐order nonlinear plants.

Research on Self-Adaptive Algorithm of Transient Performance Analysis for DC Electronic Instrument Transformer Calibration

DC electronic instrument transformers (DCEIT) are widely used in the voltage source converter based high voltage direct current transmission (VSC-HVDC) system to measure the bus voltage or current, and should be of accurate and quick transient response. The transient performance of the DCEIT need to be calibrated using a calibrator. The existing schemes are difficult to recognize different transient step responses automatically, and usually require human intervention, which limits their flexibility and applicability. Besides, the accuracy of the calculated results is affected by human factors. A self-adaptive algorithm of transient performance analysis is proposed. It recognizes the characteristics of the transient step response based on wavelet analysis, and distinguishes the steady-state and step intervals automatically. Then it evaluates and finds the stable data segments in the steady-state intervals adaptively to calculate the high and low steady-state values. Finally, the data in the step interval are interpolated to search the feature points of the waveform, and then the transient response parameters are calculated according to the coordinates of feature points. In the validation stage, six kinds of step response waveforms are generated by MATLAB to test the performance of the proposed algorithm. Compared with the boundary window method, the proposed algorithm could recognize the characteristics of the tested waveforms automatically and achieve a more accurate analyses of transient performance. In addition, a calibrator prototype based on the proposed algorithm is developed, and some tests are carried out at the National Center for High Voltage Measurement (NCHVM) in China, whose results verify the feasibility of the algorithm.

Adaptive On-Time Control Buck Converter with a Novel Virtual Inductor Current Circuit

This study presents a new virtual inductor current circuit to reduce circuit complexity, which is not necessary to sense inductance current directly. The buck converter was designed to produce an output voltage of 1.0–2.5 V for a 3.0–3.6 V input voltage. The load current range was from 100 mA to 500 mA. It was simulated and verified by SIMPLIS and MathCAD. The simulation results of this buck converter show that the voltage error is within 1%, and the recovery time is smaller than 2 ms for step-up and step-down load transients. Additionally, it achieves less than 26 mV overshoot at full-load step transient response. The circuit topology would be able to fabricate using TSMC 0.35 mm 2P4M CMOS technology. The control mechanism, implementation, and design procedure are presented in this paper.

Experimental Evaluation of Optimal Tuning for PID Parameters in an AVR System

Automatic Voltage Regulator (AVR) is employed to stabilize the output voltage of the generators in the electric power plants. However, reliable performance of AVR depends on professional tuning of its PID controller’s parameters. Therefore, different optimization algorithms are used to determine those parameters. The objective of the optimization is defined as minimizing the characteristics of transient step response such as settling time, rise time, overshoot, and steady state error. Then, to verify the optimization results, a simulator is built experimentally for AVR and PID system that can also be used for other studies on AVR systems. The experimental results are compared with those of MATLAB and Pspice Software. Close agreement between the simulation and experimental results confirms the success of the optimization.

Evaluation of Impulse-Oscillometric Extravasation Prevention

Infusion liquid extravasation occurs in up to 6% of all intensive care patients and up to 78% for neonates. Currently, emerging extravasation cannot be detected. An impulse-oscillometric method to detect the onset of extravasation is tested and evaluated in vitro.A pinch valve compresses the infusion line, an impulse is formed, and the pressure response is recorded at the peripheral vein catheter. The response of this catheter-sensor-system is analysed by measuring the transient-step response (n = 10) for an opened and closed pinch valve. Trials utilising porcine shanks (n = 15) are performed with venous and extravasational catheter placement. The fundamental frequency, maximum amplitude, damping and decay constant of the pressure response are tested for differences between venous and extravasational placement.The response of the catheter-sensor-system shows no significant differences between an opened or closed pinch valve. The maximum amplitude, frequency, damping and decay constant of the pressure response differ highly significant for venous and extravasational catheter placement (p < .001). The parameters also differ depending on the presence of infusion liquid flow (p < .001).The method enables the detection of the onset of extravasation. Further tests are performed to investigate the relationships between impulse response and hydraulic impedance.

Multiple-order moments of the transient electromagnetic response of a one-dimensional earth with finite conductance – theory

The concept of moments of the electromagnetic response is useful in electromagnetic interpretation. Analytic formulae exist for low-order moments of a few conductivity models, enabling source parameters such as time constant, depth, conductance and conductivity to be estimated from the measured moments of the electromagnetic response. However, most models for which analytic formulae exist have conductivity varying abruptly as a function of depth or position. In this paper, we have derived a procedure that allows moments of any order to be calculated for a conductivity which has finite conductance but can otherwise vary arbitrarily with depth. The horizontal loop transient electromagnetic step response is computed as a sum of residues. Integration of the step response over time yields a mathematical expression for a moment of any order. We illustrate the procedure for a Gaussian conductivity function which varies smoothly with depth. The Gaussian model produces results that agree in specific limits with the thin sheet, thick sheet and half-space cases.

Order reduction of a wind turbine energy system via the methods of system balancing and singular perturbations

In this paper we study the order reduction of a wind turbine model using the methods of balancing transformation and singular perturbations. We show that the order of the considered wind turbine model can be reduced from eight to six via the balancing transformation. Further reduction via the aforementioned method results in a significant jump in the error bound. In contrast, the method of singular perturbations shows that the order of the model can be further reduced to four, or two, and still provide very good approximations to the system model, in terms of its transient step response. Moreover, we show that the reduction in model order achieved via singular perturbations is superior to that achieved via balancing, when the linear-quadratic near-optimal controllers are considered and when wind turbulence and a large-signal disturbance are applied to the system.

General Diffraction Mechanism Interpretation of Electromagnetic Transient Scattering From Large Scatterers by Time-Domain Aperture Integration Technique

The diffraction mechanisms of electromagnetic (EM) transient scattering from large scatterers are examined by applying a general time-domain aperture integration (TD-AI) technique when the scatterer is illuminated by an incident EM field. This incident field exhibits a transient-step field response and can be the radiation from a relatively arbitrary EM source located at any place. The mechanism is interpreted by considering an equal time-delay curved aperture (ETDCA) where a set of EM equivalent current sources are defined to radiate the scattering field. The transient responses at any instant time are then found by considering the effects of equal net time-delay in propagation when the incident wave propagates to the field point via EM scattering from the scatterer. A contributing contour in the radiation integral of the equivalent currents define on the ETDCA by its intersection with a time-varying equal path-length sphere defined by the field point is therefore extracted to reduce the surface integral into a line one. The characteristics of this contributing contour are employed to interpret the EM scattering mechanisms. Practical numerical examples are presented to demonstrate the validity and feasibility of this general TD-AI technique.

A Generalized Physical Optic-Based Diffraction Mechanism Analysis of Transient Scattering From Perfectly Conducting Surfaces

This paper presents a general quasi-analytical analysis of time domain (TD) electromagnetic (EM) scattering from a perfecting conducting object when it is illuminated by the radiation of a relatively arbitrary EM source with a transient-step TD response. In particular, the EM scattering mechanism is interpreted by using TD physical optic (PO) approximation to result in a contributing (integration) contour for the radiation integral. A fast numerical algorithm is also developed to find the EM scattering field. This TD-PO solution can be further applied via a time convolution to derive the early-time transient fields scattered from the same scatterer when it is illuminated by a realistic astigmatic finite-energy pulse. Practical numerical examples are presented to demonstrate the physical phenomenon of scattering mechanisms.

Consistent Device Simulation Model Describing Perovskite Solar Cells in Steady-State, Transient, and Frequency Domain.

A variety of experiments on vacuum-deposited methylammonium lead iodide perovskite solar cells are presented, including JV curves with different scan rates, light intensity-dependent open-circuit voltage, impedance spectra, intensity-modulated photocurrent spectra, transient photocurrents, and transient voltage step responses. All these experimental data sets are successfully reproduced by a charge drift-diffusion simulation model incorporating mobile ions and charge traps using a single set of parameters. While previous modeling studies focused on a single experimental technique, we combine steady-state, transient, and frequency-domain simulations and measurements. Our study is an important step toward quantitative simulation of perovskite solar cells, leading to a deeper understanding of the physical effects in these materials. The analysis of the transient current upon voltage turn-on in the dark reveals that the charge injection properties of the interfaces are triggered by the accumulation of mobile ionic defects. We show that the current rise of voltage step experiments allow for conclusions about the recombination at the interface. Whether one or two mobile ionic species are used in the model has only a minor influence on the observed effects. A delayed current rise observed upon reversing the bias from +3 to -3 V in the dark cannot be reproduced yet by our drift-diffusion model. We speculate that a reversible chemical reaction of mobile ions with the contact material may be the cause of this effect, thus requiring a future model extension. A parameter variation is performed in order to understand the performance-limiting factors of the device under investigation.

Parameter estimation of arbitrary-shape electrical cables through an image processing technique

A novel numerical estimation of power electrical parameters with arbitrary-shape cross sections using a here implemented image processing technique is presented in this paper. This begins with the acquisition of the photograph of the cross section of the cable. Then, the photograph is preprocessed with filters for removal of artifacts and to correct anomaly conditions during the image acquisition. The estimated resistance and inductance loops obtained in this paper are accurate with respect to the ones calculated with the coaxial transmission line theory for concentric cables and with the finite element method for non-concentric three-phase and sector-shaped cables. To test the accuracy of the cable parameters the voltage transient step-response at the remote-end of different cable geometries is simulated in the time domain and synthesized in the frequency domain. Finally, the obtained transient step-responses are validated with actual measurements from scaled prototype experiments developed in the laboratory.

Study on Ability of Desalination System to Compensate Renewable Energy Fluctuation

SUMMARYThe installation of renewable energy sources in island grids is focused on as a large part of island power generation whose power fluctuations should be compensated. A desalination system is given consideration as a controllable load. This paper proposes a model for such a desalination system, then estimates the controllable ranges under various constraints and evaluates the capacity for power fluctuation suppression. The model calculates the pressure, flow rate, and power consumption. The parameters in the model are fitted using tests with an experimental system. Next, the controllable ranges for power consumption under constraints involving the membrane or other factors are simulated using both tests and the model. The controllable ranges with the valve opening fixed are estimated to be 27% to 43% of the rated power. Finally, in order to evaluate transient response, step and ramp response tests and photovoltaic (PV) output suppression tests are performed. Most of the fluctuations in PV output are suppressed when PV output is within the controllable range.

Dynamic and Control of an Absorber - Desorber Plant at Heilbronn

The present work is based on an MEA absorption test campaign performed November 2013–January 2014 at EnBW's amine test pilot located in Heilbronn, Germany. The test campaign included transient step responses in steam, exhaust gas, solvent flow rate and in exhaust gas CO2 concentration. In addition, a test with simultaneous steps in all flow rates (exhaust gas, solvent and steam) was included.A dynamic model of the Heilbronn plant was then implemented in the dynamic simulator K-Spice® and tested against the step responses at the plant. In spite of some stead state deviations, the model was able to capture the process dynamics very well. For dynamic studies one can therefore assume that the model is representative for the plant. In the work presented here, two different control configurations were tested: 1) Ratio control in combination with a slow feed back control on the CO2 out of the absorber and 2) Control of CO2 out of the absorber by lean liquid flow rate and a temperature sensor up in the desorber packing. Both structures involve only simple PID control loops and are thus easy to implement. The proposed control configurations were tested by simulations with 30% changes in flue gas flow and composition. Both configurations showed good performance during the simulation testing, but the second one was superior as well as excellent with respect to tight CO2 recovery control. This may be an important property in supervisory control schemes.

Simultaneous dynamic optimization of valves timing and waste gate to improve the load step transient response of a turbocharged spark ignition engine

A result of adding a turbocharger for downsizing of spark ignition engines is slower transient response of the engine in comparison to the naturally aspirated engine. Until recently, it was impossible to use turbocharger in spark ignition engines due to self-ignition problems. However, with the waste gate technology, the turbine speed and hence the boost pressure level are regulated for reduction of self-ignition and increase of torque. In this paper, the engine simulation is done in one-dimensional software GT-POWER and the torque transient response is being focused. For optimization, the coupling between two softwares GT-POWER and MATLAB SIMULINK is used to find an appropriate setting to utilize variable valve timing and waste gate technologies simultaneously during the transient. Variable valve timing in this study refers to opening and closing timings of inlet and exhaust valves. The optimization target is to maximize the torque integral during time interval of the transient. The transient in this paper is the one in which the engine speed is constant and the load increases rapidly and suddenly to a special value (step increase of load). Improved genetic algorithm is used for optimization. With this optimization, the mean improvement percentage in torque integral is about 6.46% for speed 1900 rpm and about 9.33% for speed 2500 rpm. The studied engine is 1.65 L EF7-TC which is a spark ignition engine equipped with turbocharger.

Model-based control using interval type-2 fuzzy logic systems

Type-2 fuzzy logic introduced new formalisms capable of overcoming the inherent uncertainties of approximating real-world processes by computational models. Yet, despite increasingly present in the nonlinear modeling literature, model-based control theory does not seem to be taking full advantage of the improvements that type-2 fuzzy logic provides. Therefore, the present work proposes the development of a new control methodology based on the generalized predictive control theory supported by interval type-2 Takagi---Sugeno fuzzy logic systems. The developed control system is based on locally linear approximations of the type-2 Takagi---Sugeno model and will be evaluated using a nonlinear process based on the yeast fermentation reaction. For comparison purposes, two additional generalized predictive control implementations based on a linear auto-regressive model with exogenous inputs and a type-1 Takagi---Sugeno fuzzy model will be used. The performance of the closed loop systems will be evaluated by subjecting the process to quick changes in the operation regime and to unmeasured external disturbances. The mean squared error, control effort and typical transient step response metrics (overshoot and settling time) will provide the benchmark criteria. The results achieved demonstrate that at the expense of a small increase in the computational effort, type-2 fuzzy logic systems improve the transient behavior of the closed loop system, presenting significant advantages when the controlled process is subject to unmodeled disturbances.

Analysis of Finite-Control-Set Model Predictive Current Control With Model Parameter Mismatch in a Three-Phase Inverter

It is well known that predictive control methods can be affected by the presence of modeling errors. The extent to which finite-control-set model predictive control (FCS-MPC) is influenced by parametric uncertainties is a recurrent concern at the moment of evaluating the viability of this method for power electronics applications. This paper proposes an analytic approach to examine the influence of model parametric uncertainties on the prediction error of FCS-MPC for current control in a three-phase two-level inverter. The analysis shows that the prediction error is not only determined by parametric mismatch but also by the instantaneous values of load current and inverter output voltage. This implies that within each sampling period of the predictive algorithm several conditions of prediction error are generated, as multiple voltage vectors are evaluated. Simulation and experimental results are provided and discussed showing the effects of inaccuracies in the modeling of load resistance and inductance parameters on the performance of FCS-MPC. Even though steady-state performance is noticeably affected with parameter changes, especially when the load inductance is overestimated by the model, its fast transient step response is less affected by parameter changes.

Experimental and Theoretical Investigation of SO2 Adsorption over the 1,3-Phenylenediamine/SiO2 System

The reversible adsorption of SO2 on 1,3-phenylenediamine was investigated using the step transient response technique coupled with operando infrared spectroscopy, mass spectrometry, UV–vis spectrometry, and density functional theory (DFT). At 50 °C, the reaction of SO2 at the amine site resulted in fixation of sulfur as hydrogen-bonded SO32– (sulfite) and SO42– (sulfate) species. Simulated infrared and UV–vis spectra at the DFT B3LYP/6-31G(d,p) level were compared to the experimental results to help characterize the infrared spectra, molecular interactions, and bonding of the adsorbing species. The theoretically calculated binding energies revealed the sulfite and sulfate species bind stronger at the ammonium sites as compared to the amine site, which agrees with the infrared spectroscopic observations. Temperature-programmed desorption showed a capacity of 1.39 mol SO2/mol sorbent for pure 1,3-phenylenediamine and 2.8 mol SO2/mol sorbent for the SiO2 supported sorbent. The presence of sulfite and sulfate...