Search

In this short note, the relative stability results (based on root locus and Bode analyses) reported in "Optimal tuning of sigmoid PID controller using nonlinear sine cosine algorithm for the automatic voltage regulator system" (Suid and Ahmad, 2022) are analyzed. It is shown that the use of closed-loop transfer functions (CLTFs) should be avoided in relative stability analysis since they may lead to less accurate stability results. The present study affirms that the results of relative stability analysis obtained using loop transfer functions (LTFs) are more reliable and accurate. • Relative stability results reported in [ISA Trans 128(B) (2022) 265–86] are analyzed. • It is found that instead of LTF, CLTF was used for relative stability analysis. • The use of CLTF led to less accurate relative stability results. • Relative stability analysis is more reliable and accurate with LTF. [ABSTRACT FROM AUTHOR]

The selection of uncertainty structures is an important aspect of system identification for robust control. The aim of this paper is to provide insight into uncertain multivariable systems for robust control. A unified method for visualizing model sets is developed by generating Bode plots of multivariable uncertain systems, both in magnitude and phase. In addition, these model sets are compared from the viewpoint of the control objective, allowing a quantitative analysis as well. An experimental case study on an automotive transmission application demonstrates these connections and confirms the importance of the developed framework for control applications. In addition, the experimental results provide new insights into the shape of associated model sets by using the presented visualization procedure. Both the theoretical and experimental results confirm that a recently developed robust‐control‐relevant uncertainty structure outperforms general dual‐Youla‐Kučera uncertainty, which in turn outperforms traditional uncertainty structures, including additive uncertainty. [ABSTRACT FROM AUTHOR]

This work details the performance and behaviour of the suspension system by varying the suspension-damping coefficient for different vehicle speed over a sinusoidal bump. For this analysis 2-DoF quarter car suspension model is used. Governing equations of motion of the system are developed using Newton's law. Suspension system functions like sprung mass acceleration, suspension deflection, and tire deflection are developed using a transfer function model. Bode plot of the various transfer functions is simulated using Matlab/Simulink tool. [ABSTRACT FROM AUTHOR]

In this paper, linear quadratic regulator (LQR) control is applied to a Cuk converter, and mathematical modeling of the converter is done using state space averaging (SSA) in continuous conduction mode (CCM). The primary focus is to design a controller for the converter and maintain output voltage within 1% of the prescribed value when there is a unit step disturbance in the input. The design done by using MATLAB improved control of the converter from that with a conventional controller when tested with disturbances. The controller did not influence the system's stability, when assessed from the Bode plot. Despite the existence of disturbances, the findings prove the efficacy of the suggested approach, and the proposed controller can track the desired output voltage in less than 14 ms. The LQR control was developed for various applications of the Cuk converter, such as in a photovoltaic system and a wind system.

Depending upon charge and chemical affinity, interplay between resistances of membrane (Rmem) and membrane–solution interface (Rmem) may lead to preferential transport of an ion. Here, intermittent in-situ electrochemical impedance spectroscopy (EIS) was done during electrodriven transport (radiotracer based) to analyze the transport selectivity of Cs+ over Na+ in different membranes. Preference of the membranes for Cs+ was reflected in the time-dependent Nyquist plots itself. Bode plot analysis also indicated dominant Cs+ transport in terms of phase and frequency shift in crown ether (DB21C7) based membrane. In Cs+ selective polymer incluion membranes, irrespective of carrier, Rmem contributed majorly to overall resistance. However, time dependence of Rmem/Rmem was carrier as well as ion dependent. Interestingly, for nonselective ionic carrier, Rmem/Rmem was majorly close to 1 and a reverese transport order than previous membranes were obtained. A higher Na+ transport (than Cs+ ) was also obtained for DB21C7 loaded Nafion, where, due to ion templating effect, Rmem was the governing factor. EIS spectral nature of a mixed feed solution follows that of the most preferred ion, thus suggesting that EIS can be used to study prospective real-life systems and can be used as a significant tool in designing ion-selective membranes. [ABSTRACT FROM AUTHOR]

In this paper, linear quadratic regulator (LQR) control is applied to a Cuk converter, and mathematical modeling of the converter is done using state space averaging (SSA) in continuous conduction mode (CCM). The primary focus is to design a controller for the converter and maintain output voltage within 1% of the prescribed value when there is a unit step disturbance in the input. The design done by using MATLAB improved control of the converter from that with a conventional controller when tested with disturbances. The controller did not influence the system's stability, when assessed from the Bode plot. Despite the existence of disturbances, the findings prove the efficacy of the suggested approach, and the proposed controller can track the desired output voltage in less than 14 ms. The LQR control was developed for various applications of the Cuk converter, such as in a photovoltaic system and a wind system. [ABSTRACT FROM AUTHOR]

Isolated AC-DC solid-state transformers widely use the front and rear multi-stage cascade structure of the bidirectional converter. Due to the difference in the control bandwidth of the front and rear stages, the transmission power of the two stages is different. When the power suddenly changes, the difference will seriously threaten the operational safety of this type of SST. In view of this problem, this study analyzes the mechanism of the power difference between the stages, summarizes various control strategies to reduce the power fluctuations between the stages, and derives the mathematical model of the load disturbance on the voltage between the two stages under different strategies. Using MATLAB, the closed-loop Bode plots of various typical control strategies and the corresponding step responses in the time domain are obtained, and the advantages and disadvantages of various strategies are compared horizontally. Finally, simulation and experiment results verify the correctness and validity of the analysis and comparison results. [ABSTRACT FROM AUTHOR]

Due to the increasing number of direct current (DC) loads in electric vehicles (EVs), DC–DC converters are widely used in EV applications. Hence, a DC distribution system with DC–DC converters is more efficient. A three-phase interleaved step-up DC–DC converter (ISC) has been proposed for use in electric vehicles. Other uses of the proposed ISC converter include aircraft, satellites, industrial, and traction drives. The proposed converter is subjected to a thorough frequency response study, which is explained in detail. The design technique recommends the proper quantity of switches to be used in the system. The reduction in the number of switches results in a 94% increase in the efficiency of this converter. The economic aspects of ISC, such as cost analysis and its procedure, have been discussed. Design models were checked using MATLAB/Simulink, which was interfaced with the real-time simulator OPAL-RT (OP5700) to ensure that they were appropriate. The results have been presented in detail.

The problem of creating mathematical models of nonlinear dynamical systems does not have an unambiguous solution and requires the creation of a separate synthesis method for each such object. To develop a method for synthesizing mathematical models of an extensive class of nonlinear dynamical systems with polynomial nonlinearities. The work uses a method based on the solution of the Volterra integral equation in the ideology set forth in Van Trees H.L., according to which the structure of a nonlinear dynamical object present47s a series connection of the linear part, characterizing the inertial properties of the system, and the nonlinear element, given by static characteristic. The difference of the suggested version of the method from the classical one, proposed in the works of Van Trees H.L., is an expansion of their input and output signals into Fourier series and a representation of the inertial part of these systems by their Bode plots, connected into one structure with input and output signals and non-linearity by Volterra integral equation. The algorithm of the proposed method is disclosed by the example of solving the problem of identifying a nonlinear dynamical system which impulse response of the inertial part satisfies the separability requirement, the order of the polynomial nonlinearity is three, and the model of the input signal has the form of a sinusoid "raised" over the time axis on a priori given constant level. A computational experiment was carried out on the example of nonlinear dynamical systems with the third order of the nonlinear characteristic and the first and second orders of the model of the inertial part of these systems with the specified algorithms of their parametric identification. The suggested method allows to synthesis the mathematical model of a nonlinear dynamical system with the polynomial static characteristic to the case when the input signal has an arbitrary number of harmonics, and the model of the inertial part and the nonlinear polynomial function have an arbitrary order.

The aim of this work is the analysis, design and hardware implementation of the fractional-order point kinetics (FNPK) model along with its closed-loop controller. The stability and closed-loop control of FNPK models are critical issues. The closed-loop stability of the controller-plant structure is established. Further, the designed PI/PD controllers are implemented in real-time on a DSP processor. The simulation and real-time hardware studies confirm that the designed PI/PD controllers result in a damped stable closed-loop response.

The paper proposes a complex domain control and robustness analysis approach to damping of Sub-Synchronous Control Interactions (SSCI) in the IEEE first and second benchmark models and is applied to wind farms with Doubly-Fed Induction Generators (DFIG). Two complex pole-placement control laws are proposed to eliminate oscillations at different levels of compensation as well as at varying speed conditions. The complex domain framework reduces the system dimensions by half and facilitates the direct placement of the system poles in the left-half plane, ensuring stability and performance. An observer is designed to estimate the variables that would be difficult to measure at a high sampling rate but are useful to stabilize the systems. Time-domain simulations in MATLAB/Simscape show that the proposed controllers are successful in eliminating oscillations. By leveraging a complex domain representation, the feedback system is analyzed as a single-input single-output (SISO) system. This simplifies the visualization of the robustness of the controllers and makes it possible to compute the gain, phase, and delay margins of the feedback system. These margins are validated in simulations on the full-scale model. The proposed complex pole-placement controller is then compared to other excitation control-based approaches to demonstrate its effectiveness. [ABSTRACT FROM AUTHOR]

This paper deals with a two‐stage high‐power light‐emitting diode (LED) driving solution for an isolated LED load. The first‐stage DC–DC power conversion is using a nonisolated Zeta converter operating in critical conduction mode to reduce component stress and switching power loss. This power stage is accountable for the power factor correction (PFC) under the universal AC voltage operation and developed a constant DC‐bus voltage for the second stage. In the second stage, half‐bridge LLC resonant converter is dedicated to deliver ripple‐free DC voltage to an isolated LED load. A new primary‐side regulation (PSR) technique is implemented in series with the resonant tank to reduce the component counts in the feedback loop. The stability of the DC‐bus voltage is verified by the state‐space analysis for the critical conduction mode (CrCM) Zeta converter. A 150 W load is driven by a prototype with a nearly unity power factor (PF) and low harmonics distortion in the input current. [ABSTRACT FROM AUTHOR]

The paper presents the analysis of dynamic properties of pneumatic systems such as: cascade connection of membrane pressure transmitters and a pneumatic membrane actuator by means of differential equations of integer and non-integer order. The analyzed systems were described from the time perspective by means of step response, and in terms of frequency with the help of the Bode plot, i.e. logarithmic magnitude and phase responses. Each response was determined using differential equations of non-integer order. To determine the responses, the interactive Simulink package was an irreplaceable programming tool built on the basis of the MATLAB program, which enables the analysis and synthesis of continuous dynamic systems.

Anubhav Bussooa BHF Cardiovascular Research Centre, University of Glasgow, Glasgow G12 8TA, UKCorrespondence: Anubhav BussooaBHF Cardiovascular Research Centre, University of Glasgow, Glasgow G12 8TA, UKEmail abussooa@gmail.comIntroduction: Biological research relies on the culture of mammalian cells, which are prone to changes in phenotype during experiments involving several passages of cells. In regenerative medicine, specifically, there is an increasing need to expand the characterisation landscape for stem cells by identifying novel stable markers. This paper reports on a novel electric cell-substrate impedance sensing-based electroanalytical diagram which can be used for the “electrical characterisation” of cell monolayers consisting of smooth muscle cells, endothelial cells or co-culture.Materials and Methods: Interdigitated electrodes were microfabricated using standard cleanroom procedures and integrated into cell chambers. Electrochemical impedance spectroscopy data were acquired for 2 vascular cell types after they formed monolayers on the electrodes.Results and Discussion: A Mean impedance per unit area vs Mean phase plots provided a reproducible, visually obvious and statistically significant method of characterising cell monolayers. This electroanalytic diagram has never been used in previous papers, but it confirms findings by other research groups using similar approaches that the complex impedance spectra of different cell type are different. Further work is required to determine whether this method could be extended to other cell types, and if this is the case, a library of “signature spectra” could be generated for “electrical characterisation” of cells.Keywords: impedance sensors, electrochemical impedance spectroscopy, Bode plot, Nyquist diagram, electroanalytical plot

Ionic liquids have interesting properties because they have several advantages compared to conventional organic solvents, such as high thermal stability, high viscosity, good solvent properties, non-flammable, and non-volatile. In electrochemistry, ionic liquids can be used as solvents without the addition of electrolytes. However, ionic liquids still have resistivity properties (uncompensated resistance), thus ohmic drop measurements are needed for a potential correction. Imidazole-based ionic liquids, which are known for their high conductivity and commonly used as a solvent, have been measured of their resistivity as a function of temperature, and type of their cations/anions. Electrochemical Impedance Spectroscopy (EIS) method was chosen to measure the resistivity of ionic liquids and Bode plot was generated for the analysis of the results. The measured resistivities of ionic liquids are in the range of 420 to 1500 ohm. It is concluded that the resistivity of the imidazole-based ionic liquid is influenced by the size of their constituent ions, the viscosity, and the resistance is decreased with increasing temperature.

The aim of the study is to propose a diagnostics method based on blade's vibration model in frequency domain. Amplitude spectrum A(ω) and phase spectrum φ(ω) have been experimentally identified which define transfer function G(jω) = P(ω) + jQ(ω) and their real P(ω) and imaginary Q(ω) parts. Transfer function G(jω) and resulting frequency, amplitude, phase characteristics and real P(ω) and imaginary Q(ω) parts are parts of blade's diagnostics model. Changes in those characteristics are directly related to changes in the technical condition of the blades. It has been noticed that small changes in the technical condition cause large changes in frequency characteristics, which proves their usefulness in the diagnosis process. [ABSTRACT FROM AUTHOR]

Summary: This paper deals with a two‐stage LED (light emitting diode) driver on the basis of front‐end boost converter operating in critical conduction mode (CrCM) and second stage LLC resonant converter for driving an LED lighting load. The boost converter operates in the valley switching mode to reduce switching power loss with less component stress. The ZVS (zero voltage switching) operation of both the half‐bridge semiconductor switching devices reduces the switching losses, which improves the system efficiency. Moreover, to ensure the stability of the DC‐bus voltage, state‐space analysis is also carried out for the CrCM boost converter. The first stage provides the power factor correction (PFC) over the universal AC mains and maintains a constant DC‐bus for the next stage. The second‐stage converter maintains a ripple‐free output voltage to an LED load. This circuit has reasonably minimized the design complexity as compared with single‐stage variable DC‐bus PFC integrated resonant converters and also gives improved efficiency in an isolated configuration. In order to validate the system, a 150‐W prototype is investigated, and experimental findings are analyzed in‐line with theoretical results at universal AC mains. [ABSTRACT FROM AUTHOR]

Summary: This paper deals with a power factor corrected (PFC) flyback converter for high‐power light emitting diode lighting applications. This flyback converter is designed to operate in critical conduction mode to achieve improved power quality at universal AC mains and high efficiency with the low component count. The converter is analyzed using state‐space analysis with closed‐loop stability under varying input and output conditions. The PFC converter is designed and implemented with wide input and wide output variations. The performance of the prototype is also investigated for improved power quality such as power factor and harmonics distortion of AC mains current at universal AC mains of 85 to 265 V. The achieved efficiency of this converter is 92% and total harmonic distortion is less than 6% over universal AC mains for a prototype of 100 W, which are much improved results as compared to discontinuous conduction mode operation of the same converter. [ABSTRACT FROM AUTHOR]

Bioelectric impedance spectroscopy (BIS) has been widely used to study the electrical properties of biological tissue based on the characteristics of the complex electrical impedance dispersions. One of the problems in using the BIS method is the length of time required for the data acquisition process and possibly data analysis as well. In this research, a compact and work rapidly BIS instrumentation system has been developed at a low cost. It is designed to work in the frequency range of 100 Hz to 100 kHz, which is generally used in the fields of biophysics and medical physics. The BIS instrumentation system is built using several integrated modules. The modules are an AC current source to produce a selectable injection current; a data acquisition system to measure voltage, current, and phase difference rapidly and simultaneously; and software to calculate and display measurement results in the form of Bode and Nyquist plots in real time. The developed BIS system has been validated using a simple RC circuit as the sample being tested. The average time needed in the process of data acquisition and analysis until the formation of impedance dispersion curves in the form of Bode and Nyquist plots, for 54 sample frequencies, is less than one minute. The system is able to identify R and C values of the sample with a maximum error of 1.5%. In addition, some simple application examples are also presented in this paper. [ABSTRACT FROM AUTHOR]