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The phase locked loop (PLL) will introduce the negative resistance near the fundamental frequency, which deteriorates the stability of doubly fed induction generators (DFIG) system under the inductive weak grid. This article develops the impedance model of the DFIG system based on direct power control without PLL, and analyzes the frequency coupling characteristic of established impedance model. The phase margin around the fundamental frequency is enhanced after cancelling the PLL. However, there will be a high-frequency resonance issue related to the frequency coupling characteristic. Based on the simplified high-frequency impedance model and the Bode diagram of equivalent single-input single-output impedance, it can be found that the DFIG system is more prone to have stability issues when the degree of frequency coupling is enhanced. An impedance reshaping control strategy is proposed to reduce the degree of frequency coupling at high frequency and suppress the high-frequency resonance. The experimental results validate the availability of the proposed reshaping control strategy.

A tapped-inductor buck dc–dc converter uses the tapped-inductor to further step-down the output voltage. This article presents a small-signal model of a tapped-inductor buck dc–dc converter by using the circuit averaging technique. The obtained nonlinear model is linearized to derive its linear large-signal, small-signal, and dc models. The small-signal model is then used to derive open-loop transfer functions namely, control-to-output voltage transfer function and the input-to-output voltage transfer function. MATLAB was used to obtain their respective Bode plots and later validated experimentally using a gain-phase network analyzer.

Direct power control (DPC) can reduce the complexity of a controller and enhance the dynamic response for doubly fed induction generators (DFIG) system. The high-frequency resonance (HFR) issues will be analyzed for the DFIG system based on DPC under inductive weak grid in this article. Based on the simplified high-frequency impedance model of the DFIG system based on DPC and the Bode diagram of equivalent single-input single-output impedance, it is found that a strong frequency coupling related to the components of system delay in off-diagonal admittance will cause the high-frequency phase to change periodically for the DFIG system. Therefore, the DFIG system will show capacitive or even negative resistance to introduce potential risk of HFR at high frequency. The stability of a DFIG system will be further deteriorated as the system delay increases. An impedance reshaping control strategy is proposed to reduce the degree of frequency coupling at high frequency for eliminating the negative effects of system delay, so that HFR can be suppressed. The experimental results validate the availability of the proposed reshaping control strategy.

A current-mode control, which can be applied to three basic single-inductor dual-output (SIDO) dc–dc converters to suppress cross-regulation, is proposed in this article. The control circuits and operation principles under different inductor current trends and switch sequences are introduced. The SIDO boost converter operating in continuous conduction mode (CCM) is taken as an example to establish the complete and accurate small-signal model in detail. Based on which, the optimal compensators design are presented in this article. And then, the cross-regulation and transient performance are analyzed via Bode plots, and the SIMPLIS simulation results are presented to validate the small signal model. In addition, the stability condition for current mode controlled CCM SIDO boost converter is studied by using Routh–Hurwitz criterion. Finally, experimental results verify the correctness of the theoretical analysis. The research results indicate that the proposed current-mode control significantly reduces the cross-regulation of SIDO dc–dc converter compared with the existing control schemes.

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.

In this study, a dynamic model is used for the position control of an ionic polymer-metal composite (IPMC) actuated underwater propulsor. A time trace of actuation parameters versus voltage input is observed. The transfer function between the applied voltage and tip displacement is almost linear and flat before the cut-off frequency because of the mechanical damping. Also, a transfer function between the applied voltage and tip velocity is taken and this particular transfer function shows a sudden rise while approaching resonant frequency. This observation is clear to suggest that at this stage, highest vibration velocity is achieved by the fin tip. It can be seen from bode plots that the optimal range of actuation frequency can be identified and it will be helpful in getting maximum thrust production. Since Reynolds number depends on the length and width of IPMC, consideration of the length of IPMC propulsor is an important factor. The length of the IPMC propulsor is considered to be small as one of the objectives of the present study is to design miniaturized propulsor. Power consumption by the propulsor is an important factor, and it has also been considered in this study. Further, swimming speed is calculated for various input sinusoidal voltages. Power spent during actuation is calculated for various conditions. A parametric study is done by taking different fluid viscosities, IPMC strip lengths, widths of IPMC strip, and different voltage inputs to compare the results for different conditions. It can be seen that the average thrust and Reynolds number values depend on the length and width of IPMC strip as well as on input voltage. In order to give controlled input and obtain controlled system response, a proportional integral derivative (PID) control is implemented on the transfer functions. In this study, the displacement of 2 mm is considered as the desired value of deflection for the particular input and it is achieved via controlled input voltage. It was found that the system can be controlled for displacement by controlling the input voltage using a PID closed-loop position control. Also, a comparison is done with a fuzzy controller with improved controlled parameters like overshoot, settling time, and steady-state error.

Previously linearised plug-in electric vehicle (PEV) models are adopted in automatic generation control functioning. However, lesser attention is given towards the exact designing of a PEV unit con...

The prime motive of this research article is to construct a new mathematical approach for approximation of higher-order discrete interval system into its corresponding lower-order discrete interval model (LODIM). In this approach, a stable approximation technique for discrete interval system is derived with the help of integrated derivative technique. The key feature of this approach is that it is eliminating both the reciprocal transformation and normalization process as carried out in existing methods. Additionally, it assures stability retention of LODIM and upholds the steady-state value of original system. In order to show the accuracy and effectiveness of the proposed approach, a standard sampled test system is taken from the literature. The proposed technique is compared with the recent and relevant techniques of model order reduction. Further, step response and Bode diagram are plotted to prove the efficacy of proposed approach. A comparative study is also undertaken to conclude the same.

In the weak current network environment, the existence of power network impedance will reduce the current control stability margin of LCL grid connected inverter, the stability margin will gradually deteriorate as the inductive component of the power network impedance increases, leading to system instability. In this paper, an improved weighted average current control strategy is proposed, which is based on the active damping control of the voltage feedforward of the charged network. In the new control strategy, with the zero-pole cancellation method, a new weighting coefficient related only to the parameters of LCL filter is obtained, which reduces the order of the system, suppresses the influence of power network impedance, and improves the stabilization of the system, getting better inverter output current quality. Then the influence of power network impedance on the control system of grid connected inverter is analyzed, and the feed-forward control of grid voltage is improved to improve the stability of inverter in weak current network. The Bode diagram analysis and MATLAB simulation results proved that the proposed control strategy is feasible.

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 frequency frame is used to tune fractional order proportional–integral​ controllers for stability, performance and robustness of third order plus time delay plants. Such plants are frequently used in describing thermal processes such as an air heater or a fired boiler. The aim is to tune the controller to meet some frequency domain properties. As robustness is an indispensable issue for thermal processes, main inspiration of the paper comes from flattening the phase curve in the Bode plot to provide improved robustness for the system. In spite of some existing studies, flattening is not realized by equalizing the phase derivative to zero at a given frequency value. Firstly, gain and phase crossover frequency points are enclosed with a rectangular frame. Then, lengths of the edges of this frame are changed to tune phase and gain margins. Curves inside the frame can be flattened by proper tuning of the edges. This will enhance the robustness and also ensure the iso-damping property. Equations to obtain the controller are given with two theorems. Demonstrations are made on two different thermal plants which are a novel electrical air heater and a bagasse fired boiler and the results are given on detailed illustrations. The results proved that preferred gain and phase properties are successfully obtained and improved performance and robustness are provided for related systems.

The distribution static synchronous compensator (D-STATCOM) has the characteristics of non-linearity, multivariable and strong coupling. Based on the analysis of the D-STATCOM mathematical model, in order to improve the performance of the linear active disturbance rejection controller (LADRC), solve the coupling problem between the d-axis and q-axis current and improve the dynamic tracking response speed and anti-interference ability. A controller with LADRC that compensates the error of the total disturbance is proposed, and the stability of the improved first-order LADRC is proved by the Lyapunov stability theory. Then the output of the full interference channel is corrected to improve the anti-interference ability of the system and the interference observation ability of the linear extended state observer (LESO) to high-frequency noise. Through the analysis of the Bode diagram in the frequency domain, compared with the traditional LADRC, the improved LADRC proposed in this paper has better anti-interference performance. Finally, the improved first-order LADRC is used to replace the traditional D-STATCOM control strategy for current inner loop control, which effectively reduces the disturbance observation error of LESO. The experimental results show that the improved LADRC control performance is better than the proportional integral (PI) controller, and it has better tracking performance and anti-interference performance.

The power electronic converter that supplies power to the unmanned ship's servers can cause self-excited oscillation of the LC input filter under heavy load. To suppress voltage oscillation, an input impedance shaping method based on a sliding mode disturbance observer is presented. The self-excited oscillation mechanism of the LC filter caused by the buck converter's positive feedback is analyzed by using the small-signal model. The sliding mode disturbance observer calculates the input voltage according to the output voltage, inductance current and duty cycle of the buck converter. The feedforward compensation of the observed voltage reshapes the input admittance of the buck converter, making the system not meet the conditions of self-excited oscillation and suppressing the voltage oscillation of the LC filter. The phase shaping of input admittance is compared with the traditional amplitude shaping by the Bode diagram and Nyquist diagram. The experimental results show that the phase shaping method could better suppress the LC filter's self-excited oscillation and the sliding mode disturbance observer reduced the hardware cost.

Modal analysis is a tool to predict the vibration characteristics such as natural frequencies, mode shapes and viscous damping coefficients of the structures. These characteristics play an important role in engineering design and analysis. In this paper, the prediction of vibration characteristics or modal-modal of cantilever beam made of neat epoxy and various natural fiber composites carried out by using finite element analysis software ANSYS 20.0. In this study, the natural fibers such as jute, banana, coconut coir, hemp and kenaf fibers are used as reinforcement in the epoxy matrix. The size of beam is 160 mm × 20 mm × 3 mm. The volume fraction of fiber is 33.33% taken for all natural fiber composite materials. The natural frequencies, damping factor and frequency response function bode plot are obtained with the help of ANSYS software. The damping factor is found out using half power bandwidth method from frequency response function bode plot. The natural frequency and damping factors of different natural fiber composites are compared with epoxy material. It is found from this analytical study that the damping factor values for each natural fiber composite material have higher values corresponding to each mode than that of epoxy material. Hence, it is concluded that the natural fiber composites have better damping properties than epoxy material. Hemp and kenaf fiber composite materials have similar values of natural frequencies for lower modes (1st mode and 2nd mode) and at higher modes (5th mode and 6th mode) respectively.

Low frequency oscillation (LFO) in the electric multiple units (EMUs)-traction network cascade system (ETNCS) can lead to traction blockade and abnormal operation. Using the Chinese CRH3 EMUs as an example, a new LFO suppressing method by applying the energy storage (ES) device on EMUs is proposed in this paper and the ES is connected to the DC-link on board. The equivalent model of the ETNCS is established at first. The critical condition of LFO in the ETNCS is analyzed via impedance ratio criterion and Bode diagram. Then, the proposed on-board bidirectional DC-DC converter integrated with the ES system is controlled via a virtual DC machine (VDCM) strategy, and the VDCM small signal model derivation and the parameter design are carried out. Using the Bode diagram of the impedance ratio, the system stability with the ES device controlled by the proposed VDCM scheme is analyzed again; simulation results verify the effectiveness of the control algorithm to suppress the LFO adaptively. Compared with the traditional PI controller, the system steady-state and dynamic performance can be improved with the proposed method, including decreased overshoot, fluctuation, response time, and increased gain margin of the DC-link voltage.

For the controller design and stability analysis of power electronic converters, the Bode stability criterion and its subsequent revisions are the most practical tools. However, even though the control of the power converter is usually implemented in a microprocessor, none of these methods is infallible when applied to a discrete system. This article therefore proposes a new stability criterion, named the Discrete Generalized Bode Criterion (DGBC). This method is based on the Nyquist criterion but developed from the open-loop Bode diagram, evaluated also at 0 Hz and at the Nyquist frequency. The proposed criterion combines the advantages of the Nyquist and Bode criteria, since it is always applicable and provides an interesting and useful tool for the controller design process. The method is applied to design an active damping control of an inverter with LCL filter, showing how the proposed criterion accurately predicts stability, in contrast to the existing Bode criteria. The theoretical analysis is validated through experimental results performed with a three-phase inverter and an LCL filter. This work was supported in part by the Agencia Estatal de Investigación (AEI) under Grant PID2019-110956RB-I00/AEI/10.13039/501100011033, and in part by the Ingeteam Power Technology.

Terminalia chebula, Rubia tinctorum and Biancaea sappan are used here as sensitizers on TiO2 hollow-sphere. Anatase-rutile TiO2 hollow-spheres were synthesized using carbon spheres template assisted method. Structural, shape and purity of the prepared TiO2 hollow-spheres are confirmed through XRD, SEM measurements. Absorbance spectra are used to analyze the spectral response of the sensitizers. From the J-V measurements, it is found that Terminalia chebula shows a better performance of open circuit voltage (VOC) ∼ 0.47 V, short circuit current (JSC) ∼ 0.11 mA/cm2 and fill factor 40% compared to all others. The charge transfer resistance and life-time are investigated through Nyquist and Bode plots.

For a grid-connected inverter requiring the ac voltage magnitude and the active power control, both vector control and power synchronization control can be applied. The stability comparison based on the dq impedance stability analysis between both control are carried out via three factors including the grid impedance, the inner current loop and the virtual impedance. The dq impedances of the inverter based on both control are derived. The determinant of the impedance ratio matrix is used for the stability analysis. The bode plot of the grid impedance and the inverter impedance are present to assist the stability analysis and explain their interactions. It is found that increasing the grid impedance and the cut-off frequency of the current loop stabilize the inverter with the power synchronization control, which is converse to the vector control. Furthermore, the inverter with the power synchronization control may suffer the instabilities when connecting to a strong grid. The virtual inductor and resistor are proposed to enhance the stability for the vector control and the power synchronization control respectively. The simulation validation using Matlab/Simulink is performed.

A control-oriented circuit model of an inductive power transfer system is needed to design a high-performance controller. In this article, a dq synchronous reference frame model of a series–series tuned resonant inductive power transfer system is proposed. A single-phase dq modeling technique for a resonant converter is used to derive the model. The proposed control-oriented model clearly demonstrates the cross- and mutual-coupling between the state variables of the wireless power transfer system. It is interesting to note that the proposed model is similar to a dq synchronous reference frame model of a three-phase induction motor. The well-known controller design methods, such as proportional-integral controller design, manipulated input decoupling, disturbance input decoupling, state observers, and disturbance observers, etc. can be extended to the inductive power systems with the proposed model. The large- and small-signal responses of the transmitter current versus its input voltage are identified. Considering the frequency response, a new transmitter current controller that has a control bandwidth of 500 Hz is designed to show the validity of the proposed model. The proposed model and the controller are evaluated using simulated and experimental results. The simulated open- and closed-loop frequency responses of the model agree well with the theoretical bode plots of them. Also, the experimental results show that the proportional-integral with feedforward input controller regulates the transmitter current within 1 ms for three conditions: a step change of the reference, a step change of the load, and a step change of the mutual-coupling.

Although the stability of a speed adaptive full-order observer (AFO) has been studied for a sensorless induction motor (IM) ultralow speed operation, few researchers concern its dynamic performance simultaneously. To address this problem, this article proposed a novel feedback gain selection principle of an AFO considering both stability and dynamic performance. Compared with the conventional stability-based feedback gain selection, the proposed method applied the zero-point locus diagram and Bode diagram to further limit the range of stabilized feedback gain, leading to improved dynamic performance. Moreover, the robustness of the AFO is guaranteed with the proposed feedback gain under IM parameter mismatch. The validity of the proposed method is confirmed by comparative experiments.

Heterostructure photocatalysts with a built-in electric field have become one of the most promising strategies to enhance photogenerated electron-hole pair separation. However, close contact between the two active components of heterogeneous photocatalysts remains a problem. Herein, the in-situ fabrication of an SnO2/SnS2 heterostructure photocatalyst was performed; the structure showed enhanced photocatalytic performance resulting from the tight-contact heterostructures. The results of photoelectrochemical measurements further verified that a tight-contact heterostructure improved the separation of photogenerated electron-hole pairs. The results of EIS Bode plots also demonstrated that such in-situ fabricated SnO2/SnS2 samples exhibited the longest carrier lifetime (41.6 μs) owing to the intimate interface of SnO2/SnS2 heterostructures.

The effect of adding 5 and 10% of TiB2 on the corrosion of Udimet 700 (U700) in 1 M HCl including altered concentrations of organic compounds was considered at 25°C by electrochemical methods: potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) methods. Microstructure characterization of these alloys was studied by X-ray diffractometer. Tafel plots confirmed that the appearance of examined components had a slight effect on the polarization curves. The Nyquist plots demonstrated that the charge transfer resistance (Rct) increase for the examined compounds was much higher with compound II compared to compound I. Bode plot revealed that, the total impedance raised with increasing inhibitor concentration and the constant increment in the phase angle shift was clearly related to increasing of the inhibitor concentration adsorbed on alloy species. EFM results showed an agreement with PP and EIS.

Introduction 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.

In the last past year researchers have relied on the ability of Laplace transform to solve partial, ordinary linear equations with great success. Important analysis in signal analysis including the transfer function, Bode diagram, Nyquist plot and Nichols plot are obtained based on the Laplace transform. The output of the analysis depends only on the results obtained from Laplace transform. However, one weakness of Laplace transform is that the Laplace transform of even function is odd while the Laplace transform of an old function is even which is lack of conservation of properties. On the other hand there exist a similar integral transform known as Sumudu transform has the ability to conserve the properties of the function from real space to complex space. The question that arises in the work, is the following: Can we apply the Sumudu transform to construct new transfer functions that will lead to new Bode, Nichols and Nyquist plots? this question is answered in this work.

This paper intends to tune fractional order proportional derivative controller for the performance, stability and robustness of second order plus time delay plant. The tuning method is based on the previously proposed “frequency frame” which is a rectangular frame enclosing gain and phase margins limited with gain and phase crossover frequencies in the Bode plot. Edges of the frame are tuned to achieve desired crossover frequencies and margins. By shaping the curves of the Bode plot, improvements are observed in the performance and robustness of the second order plus time delay system controlled by a fractional order proportional derivative controller. Generalized equations to obtain the parameters of the fractional order proportional derivative controller for second order plus time delay plant are given. In contrast to existing studies, this method reduces mathematical complexity when providing desired properties. Three examples are considered and effectiveness of the frequency frame is shown.

In a commercial greenhouse, variables, such as temperature and humidity, should be controlled with minimal human intervention. A systematically designed climate control system can enhance the yield of commercial greenhouses. This study aims to formulate a nonlinear multivariable transfer function model of the greenhouse model using thermodynamic laws by taking into account the variables that affect the Greenhouse Climate Control System. To control its parameters, Mamdani model-based Fuzzy PID is designed which is compared with the performance of proportional-integral (PI) and proportional-integral-derivative (PID) controllers to achieve a smooth control action. The Fuzzy logic based PID provides robust control actions eliminating the need for conventional tuning methods. The robustness analysis is performed using values obtained from real-time implementation for the greenhouse model for Fuzzy based PID, PI and PID controllers by minimizing the Integral Absolute Error (IAE) and Integral Square Error (ISE). The greenhouse model has strong interactions between its parameters, which are removed by Relative Gain Array (RGA) analysis, thereby providing an effective control strategy for complex greenhouse production. Further, the stability analysis of non-linear greenhouse model is conducted with the help of the bode plot and Nyquist plot. Results show that good control performance can be achieved by tuning the gain parameters of controllers via step responses such as small overshoot, fast settling time, less rise time, and steady-state error. Also, smoother control action was obtained with Fuzzy based PID making the Greenhouse Climate Control System stable.

In the literature, Bode plots and Nyquist diagrams are used extensively in stability analysis for admittance-based models. In this letter, we demonstrate that eigenvalues obtained from the total admittance lead to accurate prediction of stability while Bode plots and Nyquist diagrams show limitations. A voltage source converter with weak grid interconnection is used as an illustrative example to demonstrate the pros and cons of the three methods applied to $dq$ -frame admittance matrices.

Rotordynamics is a very challenging field because of machine complexities. Many internal and external factors contribute toward change in the structural dynamic characteristics. One of these factors is broad-band high-vibration amplitudes. In this article, a similar high vibration issue on a gas turbine is investigated using bode, orbit, and shaft centerline plots. Data from proximity probes installed on turbine generator system are captured and analyzed against any factor contributing toward high vibration issue. Fish bone diagram was used for root cause investigation. Main components investigated for the root cause of high vibration issue include generator rotor and casing. Rotor behavior has been examined by capturing orbit and shaft centerline diagrams, whereas casing contribution has been investigated by conducting operating deflection shape analysis. A comparison is drawn between a machine suffering from high vibration issue and a normal machine. Resonance was identified as the root cause, and stiffness enhancement was recommended to change the natural frequency of casing. Based on investigations, recommendations are given and a final comparison is drawn after structural modification was done. In addition to early fault finding, reduction in maximum vibration was 38% after implementation of the fix that confirmed the accuracy of the root cause investigation process.

Small-signal instability issues of interconnected converter systems can be addressed by the impedance-based stability analysis method, where the impedance ratio at the point of common connection of different subsystems can be regarded as the open-loop gain, and thus the stability of the system can be predicted by the Nyquist stability criterion. However, the right-half plan (RHP) poles may be present in the impedance ratio, which then prevents the direct use of Nyquist curves for defining stability margins or forbidden regions. To tackle this challenge, this paper proposes a general rule of impedance-based stability analysis with the aid of Bode plots. The method serves as a sufficient and necessary stability condition, and it can be readily used to formulate the impedance specifications graphically for various interconnected converter systems. Experimental case studies validate the correctness of the proposed method.

This work is focused on the dynamic alternating current equivalent electric circuit (AC-EEC) modeling of the polycrystalline silicon wafer-based photovoltaic cell and module under various operational and fault conditions. The models are drawn from the impedance changes observed using electrochemical impedance spectroscopy. Vital considerations for valid impedance data and appropriate parameter extraction were also discussed. In this work, cell-level tests were carried out at different voltage bias levels under illumination, dark, uniform partial shading, and cell-mismatch conditions. The cell characterization procedure was then used as a basis for developing the photovoltaic (PV) module level model. Normal illumination and partial shading tests were carried out at the module/panel level. The AC-EEC model for both the levels was obtained from the associated Nyquist and Bode plots. These models were then used to extract the internal cell/module parameters and the associated trends were observed. Results obtained demonstrates that the variations of the ac model give several parameters that show distinct variation such that they can be used for inline characterization and real-time condition monitoring of the photovoltaic cells/module under the different operational and fault conditions.

The nutation mode is an obstacle to the stability improvement of a magnetic-bearing-supported rotor system with significant gyroscopic effects. This article explores a parameter design method of the filter cross feedback for the nutation mode suppression of asymmetric rotor systems supported by active magnetic bearings (AMBs). First, the coupled multi-input multi-output model of the asymmetric AMB rotor system is converted into an equivalent complex single-input single-output model. The equivalent transformation aims at easing the system analysis and extending the classical stability criterion to the complex coefficient frequency domain. Then, the double-frequency bode plot and the Nyquist criterion are used for analyzing the stability of the AMB rotor system and designing the parameters of the filter cross feedback exactly. Simulation results show that the designed filter cross-feedback method has a good performance for suppression of the nutation mode. Finally, the power spectrum level of the nutation component is below $-$ 60 dB after the filter cross-feedback method is implemented in the controller of a large-scale magnetically suspended turbomolecular pump. The experimental results validate the effectiveness of the proposed method.

In this paper, the reduced-order active disturbance rejection control (RADRC) is studied for marine engine speed control. The benefits of using RADRC are demonstrated by bode diagram method with the transfer function between input disturbance and system output. Discrete RADRC and active disturbance rejection control (ADRC) are designed for marine engine speed control by adopting variable sampling rate control method. The proposed method is assessed by experiment on a hard-in-loop (HIL) engine test platform. Except the step-response indexes, ADRC and RADRC are compared in more indexes. The results demonstrate that RADRC has superiority during the sudden load varying process. For steady-state, a single smaller observer bandwidth in RADRC can make a good compromise for a wide range engine speed. It also has been found that the index of total variation (TV) in control input for RADRC is inferior to the ADRC. Overall, RADRC is a promising method for marine engine speed control.

The ultra-low frequency oscillation (ULFO) problem reappears in China recently. Different from the classical low frequency oscillation (LFO), the generators in ULFO have the same mode shapes, namely oscillating in the same pace. To reveal the reason why ULFO generators do not oscillate inversely as classical LFO does, this paper investigates the mechanism of ULFO based on improved Philips-Heffron model of two-machine system. Through this model, the phase angle relationship between different generators is obtained. Based on the bode diagram, it is found that the phase angle difference of the two machines is around zero in ultra-low frequency band however the generator parameters change. On the contrary, the situation is different in classical low frequency band, which reveals the mechanism that generators in ULFO always oscillate in the same pace. Finally, the analysis above is validated through a 2-area 4-machine system and a 6-machine system established in PSASP software.

Most of the controlled plants in the industrial field are complex in structure and the models are difficult to obtain, thus tuning of the controller parameters without a detailed model is critical in practice. This paper proposes a specific parameter tuning formula for second-order linear active disturbance rejection controller (LADRC) based on step response curves of the controlled plant. The proposed tuning formula is only related to the two special points on the step response curve of the plant. Simulation results for a wide range of systems show that the proposed method can achieve satisfactory performance in disturbance rejection and robustness, and the Bode plots show that this tuning method also performs well in noise suppression. The effect is also verified with a practical heater temperature control experiment.

With the world's energy shortage, the scholars all over the world have done a lot of research work on the efficient use of energy, energy-saving emission reduction, and the development of new energy. Turbine generators have a wide range of applications in energy recovery. In this study, a new type of turbine generator structure is proposed. Four disc-type permanent magnet motors are symmetrically mounted on the shafting, and are supported by gas hydrostatic bearing. The vibration tests of the shafting were carried out. The vibration characteristics of the shafting were analysed by using the bode diagram, the time-waterfall map, the bifurcation diagram, the shaft orbits at the typical speeds, and the Poincare maps, which can provide references for developing high-speed turbine generators.

Power system stability is improved through using Automatic Voltage Regulator (AVR) to adjust the terminal voltage of synchronous generator. Proportional-Integral-Derivative (PID) and Proportional-Integral-Derivative-Acceleration (PIDA) controllers are used in AVR for excitation control. Whale optimization algorithm (WOA) technique is used in this paper to tune the controllers’ parameters. WOA using PID and PIDA controllers show its superiority through comparison with several optimization techniques. Then comparison between both controllers is carried out and shows that PIDA controller is better than PID controller. Therefore, WOA using PIDA controller is the best system. Robustness analysis is performed to check terminal voltage response with load variation and proved again the superiority of WOA-PIDA system. The contribution of the paper is mainly in analysis by using Root Locus and Bode diagram beside using new optimized controller system in this application. Keywords: Whale optimization, PID controller, PIDA controller, AVR

Purpose Potassium silicate sealer was applied on solvent-cleaned, acid-pickled, dacromet-coated steel to improve its corrosion resistance. The purpose of this paper is to study the corrosion behavior of dacromet-coated steel. Design/methodology/approach Potassium silicate sealer was applied on solvent-cleaned, acid-pickled, dacromet-coated steel to improve its corrosion resistance. Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and salt spray were carried out. SEM was used to study the morphological appearance of the surface. Findings The EIS behavior indicated that solvent-cleaned dacromet-coated steel sealed with potassium silicate showed that the corrosion current density was 2.664E − 5 A.cm2 which was reduced to 8.752E − 6 A.cm2 and the corrosion rate, which was 2.264E − 2 mm.year−1, was reduced to 7.438E − 3 mm.year−1 in NaCl 3.5 wt.per cent. EIS was used in NaCl 3.5 wt.%, and the Bode plot characteristics showed that the corrosion protection of solvent-cleaned, dacromet-coated steel was enhanced when sealed with potassium silicate. The EDS results of salt-sprayed, solvent-cleaned samples after 10 days indicated that the main corrosion products are composed of SiO2, ZnO and Al2O3. Research limitations/implications The detection of Li element in EDS was not possible because of the device limitation. Originality/value The current paper provides new information about the sealing properties of potassium silicate and its effects on the corrosion resistance of dacromet coating, which is widely used in many industries such as the automobile industry.

Over the past decade, memristors have been extensively studied for a number of applications, almost exclusively with DC characterization techniques. Studies of memristors in AC circuits are sparse, with only a few examples found in the literature, and characterization methods with an AC input are also sparingly used. However, publications concerning the usage of memristors in this working regime are currently on the rise. Here we propose a "technology agnostic" methodology for memristor testing in certain frequency bands. A measurement process is initially proposed, with specific instructions on sample preparation, followed by an equipment calibration and measurement protocol. This article is structured in a way which aims to facilitate the usage of any available measurement equipment and it can be applied on any type of memristive technology. The second half of this work is centered around the representation of data received from following this process. Bode plot and Nyquist plot representations are considered and the information received from them is evaluated. Finally, examples of expected behaviors are given, characterizing simulated scenarios which represent different internal device models and different switching behaviors, such as capacitive or inductive switching. This study aims at providing a cohesive way for memristor characterization, to be used as a good starting point for frequency applications, and for understanding physical processes inside the devices, by streamlining the measuring process and providing a frame in which data representation and comparison will be facilitated.

We demonstrate a simple method to fabricate all solid state, thermally reduced graphene oxide (TRGO) microsupercapacitors (µ-SCs) prepared using the atmospheric pressure chemical vapor deposition (APCVD) and a mask-free axiDraw sketching apparatus. The Fourier transform infrared spectroscopy (FTIR) shows the extermination of oxygen functional groups as the reducing temperature (RT) increases, while the Raman shows the presence of the defect and graphitic peaks. The electrochemical performance of the µ-SCs showed cyclic voltammetry (CV) potential window of 0–0.8 V at various scan rates of 5–1000 mVs−1 with a rectangular shape, depicting characteristics of electric double layer capacitor (EDLC) behavior. The µ-SC with 14 cm−2 (number of digits per unit area) showed a 46% increment in capacitance from that of 6 cm−2, which is also higher than the µ-SCs with 22 and 26 cm−2. The TRGO-500 exhibits volumetric energy and power density of 14.61 mW h cm−3 and 142.67 mW cm−3, respectively. The electrochemical impedance spectroscopy (EIS) showed the decrease in the equivalent series resistance (ESR) as a function of RT due to reduction of the resistive functional groups present in the sample. Bode plot showed a phase angel of −85° for the TRGO-500 µ-SC device. The electrochemical performance of the µ-SC devices can be tuned by varying the RT, number of digits per unity area, and connection configuration (parallel or series).

Hafnia zinc oxide (HfxZn1−xO) nanorod-like structures were processed for photoswitching applications through a facile chemical strategy. Their crystalline structure and phase purity were examined by X-ray diffraction and Raman analysis. The evolution of HfxZn1−xO in rod-like configuration was inferred through scanning and transmission electron microscopy. The band gap values of HfxZn1−xO were estimated using Tauc's plot to be around 2.89–3.11 eV. The association of multiple defects within the hafnia based nanorods was further substantiated through luminescence results via sub-band signals in near visible region. Nyquist and bode plots of HfxZn1−xO nanorods were extracted from the electrochemical impedance spectroscopic results to evaluate the role of grain boundaries on their conductivity values. The electrical properties of HfxZn1−xO nanorods including their carrier density were estimated by capacitance vs. voltage (1/C2 vs. V) measurements. The photoswitching potential of n-HfxZn1−xO was investigated by spin casting the nanostructures on p-Si and investigating the diode's charge transfer characteristics. The Hf composition in the respective diode architecture was found to influence their corresponding photocurrent values.

One promising solution for future large wind turbine power conversion is to use medium-voltage power conversion systems for high efficiency and high power-density, e.g., by using a cascaded structure presented in this paper. However, a medium-frequency (MF) oscillation issue was observed while testing the experimental prototype of the above system. Given the complex multivariable coupling models of the multiwinding transformer and multiple inverters, conventional single-variable theories are not suitable. Therefore, this paper presents a new decoupling analysis method. Using a proposed linear transformation matrix, the output currents of multiple inverters can be transformed to a summation (grid) current and difference currents, where the former is the summation of inverter currents and the latter are the differences between currents of any two inverters. This transformation has enabled the use of single-variable theories, e.g., Bode diagram to analyze the summation current and difference current separately. It was found that the MF oscillation issue is caused by the equivalent impedance of the summation current being much larger than that of the difference current. Specifically, using small controller parameters cannot ensure the grid current quality and using large parameters may cause oscillation in the difference current. The proposed method can provide guidelines to design the parameters of current regulators and filters in multiple-inverter systems. Experimental results of a downscaled wind energy conversion system are presented to verify the proposed method.

The paper presents the results of study of corrosion resistance of Vanadis 6 steel after conventional heat treatment and sub-zero treatment at-140 °C for 17 h. It was found that sub-zero treatment leads generally to decrease in corrosion current, which is in turn reflected in lower corrosion rate of the material subjected to this kind of treatment. The corrosion potential of sub-zero treated specimens was more anodic, suggesting their more noble behavior in 3.5 % NaCl water solution. This behavior was ascribed to the presence of a huge number of small globular carbides in SZT specimens, which seemed to stabilize the protective oxide films on the surfaces. Tempering reduces the corrosion resistance of the steel since this treatment produces fine precipitates of alloyed carbides that deplete the matrix by chromium and thereby destabilizes the protective films on the steel surface.

This paper is focused on a dual-loop current control method (grid current loop and fundamental current loop) for digitally controlled LCL -type shunt active power filters (APFs). Normally, a proportional-resonant (PR) unit is used as the fundamental current controller, where the proportional part of PR unit actually serves as the proportional feedback of inverter-side current and provides a certain degree of damping for LCL resonance. However, its valid damping region is only up to one-sixth of the sampling frequency ( fs /6), which leads to less robustness to the grid impedance. To address this issue, a delay-compensation control link is proposed in this paper to replace the proportional part of the PR fundamental current controller and widen the effective damping region. As a result, the system robustness is improved without adding extra sensors or introducing an extra active damping loop. Theoretical analysis proves that it can obtain a wider damping region of (0, fs /4). Moreover, a systematic controller parameter design criterion is studied. In particular, a numerical optimization algorithm is developed to optimize damping property, and a design method based on root locus plot and Bode diagram is presented to enhance harmonic compensation accuracy. Finally, experimental results implemented on a 30 kVA APF prototype have validated the feasibility of the proposed current controller and parameter design criterion.

Development of asymptotic magnitude Bode plots for integer-order transfer functions is a well-established topic in the control theory. However, construction of such plots for the fractional-order transfer functions has not received much attention in the existing literature. In the present paper, we investigate in this direction and derive the procedures for sketching asymptotic magnitude Bode plots for some of the popular fractional-order controllers. In addition, we deduce these plots for general fractional commensurate-order transfer functions as well. As applications of this work, we illustrate the analysis of the designed fractional-control loop, and the identification of fractional-order transfer function from a given plot.

Multiple loops have been used extensively to enhance the system performance in various applications. However, the increasing complexity of multi-loop systems also makes them much more difficult to analyze and implement. In this paper, a new methodology to analyze multi-loop system is proposed. In the proposed framework, multi-loop systems are regarded to be built upon of sub-modules of cascade, parallel adding, and feedback units, and then, they are simplified following a certain procedure based on the correlation of the Bode characteristics of the segmented sub-modules. Applying this methodology, the Bode plot and the transfer function of the system can be easily obtained with the system properties of gains, zeros, and poles. Two examples are provided as demonstrators, including a multi-loop low-dropout regulator (LDO) from literature, and a newly designed multi-loop LDO aiming at enhancing the stability over a wide load range, which show that the Bode plot and the transfer function can be obtained more intuitively and rapidly. Excellent agreements among theory, simulations, and measurements are confirmed, which verify the proposed method. It can help designers to gain more intuitions and insights on multi-loop systems from both circuit and device perspectives, which is also an effective tool for both stability analysis and circuit design.

In this paper, electrochemical impedance spectroscopy (EIS) is used as a non-destructive testing method for investigating the cracking behavior of two kinds of cement-based materials with/without fiber, which are engineered cementitious composites (ECC) and plain mortar. The experimental results show that the cracking patterns and deflection-load curves of plain mortar and ECC are different when the external load reaches to the first-cracking load and ultimate load. The EIS results show that the parameter value of Rct and plural modulus value Z in fractured mortar increase several hundred times compared with correspondingly origin plain mortar. Moreover, the semi-circle presents in the fractured mortar at high frequency and the diagonal lines are deviated from less than 45 deg at low frequency, and the phase angle (θ°) in cracked mortar decreases as the frequency decreases in Bode plots. However, the values of Rct and Z in cracked ECC increase dozens of times compared to origin ECC, and the phase angle decreases as the frequency decreases. The variation of Rct in Nyquist plots, and the stability and smoothness of Bode plot sensitively reflect the cracking degree of cementitious system. In this paper, it is proposed that as a non-destructive method, electrochemical impedance measurement can be used to evaluate the cracking behavior of cement-based materials.

With regard to heavy-duty automatic transmission vehicles, precise control and fast response of clutch pressure, as well as transient high flow capacity, are central to shifting performance. In order to reduce fuel consumption and improve shift quality, a novel mathematical model for electro-hydraulic actuator used in heavy-duty automatic transmission is proposed to predict the response performance of a wet clutch in this paper. Firstly, the governing equations of a proportional solenoid valve (PSV) excited by the current of pulse width modulation (PWM), a pressure reducing valve (PRV) pilot operated by PSV and a simplified clutch model are derived by means of integration technology. Moreover the transfer function of PRV to the clutch is deduced to draw Bode plots. Then, the experimental date obtained from a real test bench is compared with the numerical results to validate the applicability of the mathematical model. Finally, simulations are performed on the forces, displacement, velocity, flow rate, clutch pressure, pressure deviation, response deviation and flow force. Numerical results indicate that the proposed model is valuable for the performance analysis and optimization of clutch actuator.

The rotor critical speed of turbine generator unit when the amplitude of the rotor increases sharply, bring to unit certain harm, rotor critical speed calculation method often results with the actual error is bigger. Through Bode diagram method and frequency spectrum analysis method, the rotor critical speed measurement was carried out. Through the experimental results it was concluded that two methods the test results are basically identical, and bode diagram was determined the selection method of measuring rotor critical speed more accurate. By changing the rotor on the quality of the wheel and position change, the use of Bode diagram method for rotor critical speed measurement. It was concluded that with the increase of the quality of the rotor critical speed decreased, the impact is not big in the center of the deviation from the rotor position far; The same quality case, the farther wheel deviating from the center of rotor, the rotor critical speed increases faster. The test results can guide the engineering practice, for the calculation of the rotor critical speed, the simulation and experiment have certain reference function.

[EN] The main goal of this contribution is to introduce a new procedure in order to analyse properly SISO dual-rate systems (DRS) and to provide straightforward answers to some common general questions about this kind of systems. Frequency response analysis based on DRS lifting modelling can lead to interesting results about stability margins or performance prediction. As a novelty, it is explained how to understand DRS frequency response and how to handle it for an easy computation of magnitude and phase margins keeping classical frequency domain methods. There are also some repetitive questions about DRS that can be analysed and answered properly using the results from this contribution: what the optimum relation between sampling periods is or what effects does delay have in a DRS. Every step is illustrated with examples that should clarify the understanding of the text.

The existing literature demonstrates the application of neuro-fuzzy based control techniques to load frequency control in interconnected power systems. However, their performance has not been evaluated in the combined presence of renewable resources and system non-linearities. The focus of this paper is to present the design and simulation of an Adaptive Neuro Fuzzy Inference System (ANFIS) controller for a power network possessing non-linearities such as boiler dynamics, generation rate constraint, governor dead-band and time delay. A proportional integral (PI) controller was tuned with the Bode plot approach to obtain the training data set for the proposed controller. In the simulation model, multiple scenarios of wind and solar penetration levels in a two-area system were considered. The dynamic performance of the ANFIS controller was found to be superior when compared to a conventional controller in regards to peak overshoot and settling time.