Operating Region Research Articles

A Phase-Shift-Modulated Resonant Two-Switch Boosting Switched-Capacitor Converter and Its Modulation Map

In this paper, a Phase-shift-modulated (PS) Resonant Two-switch Boosting Switched-capacitor Converter (RTBSC) and its modulation map are proposed. Compared with the traditional RTBSC, all diodes are replaced by active switches and then phase-shift modulation is applied. The advantages of the modified topology are obtained as follow. 1) The voltage gain can be regulated efficiently either below or above the nominal value even at light-load condition, making it suitable for applications with voltage fluctuations; 2) The conduction loss is reduced by replacing all diodes in RTBSC with low turn-on resistance transistors, especially for high-order and high-gain configuration; 3) All switches achieve the zero-voltage-switching (ZVS) turn-on operation; 4) The soft-charging property smooths the current profile. Aside from the topology modification, a comprehensive analysis of operation principle, voltage gain, component stress and ZVS region is given. On the basis, a modulation map with the optimal operation region is proposed. It provides a guideline to operate and design such converters in the target gain range, low component stress and ZVS region, making up for the lack of modulation map and design guideline in aforementioned literatures. A 120W prototype with low-voltage side 43-60V and high-voltage side 150V was designed to verify the above analyses.

Hybrid Energy Storage System Based on a Multioutput Multilevel Converter

Energy Storage Systems (ESSs) allow improving the stability and efficiency of the electrical grids with a high penetration of renewable energy sources. Moreover, the use of Hybrid Energy Storage Systems (HESSs) enable storage solutions with both high-energy and high-power densities, by combining different storage technologies such as diverse battery chemistries, ultracapacitors, or hydrogen fuel cells to name a few. In this paper, an HESS-based Multi-Output Multilevel Converter is presented. The proposed topology enables decoupled control of each AC converter voltage outputs. The internal switching states further allow the use of different storage units and high-quality multilevel voltage in each AC outputs. The mathematical model of the proposed topology and the defined operation region of the system, besides a model-predictive control strategy are developed. Finally, simulation and experimental results validate the performance of the proposed topology.

A Comprehensive Review of Flexible Power-Point-Tracking Algorithms for Grid-Connected Photovoltaic Systems

The rapid increase in the penetration of photovoltaic (PV) power plants results in an increased risk of grid failure, primarily due to the intermittent nature of the plant. To overcome this problem, the flexible power point tracking (FPPT) algorithm has been proposed in the literature over the maximum power point tracking (MPPT) algorithm. These algorithms regulate the PV power to a certain value instead of continuously monitoring the maximum power point (MPP). The proposed work carries out a detailed comparative study of various constant power generation (CPG) control strategies. The control strategies are categorized in terms of current-, voltage-, and power-based tracking capabilities. The comparative analysis of various reported CPG/FPPT techniques was carried out. This analysis was based on some key performance indices, such as the type of control strategy, irradiance pattern, variation in G, region of operation, speed of tracking, steady-state power oscillations, drift severity scenario, partial shading scenario, implementation complexity, stability, fast dynamic response, robustness, reactive power, cost, and tracking efficiency. Among existing FPPT algorithms, model-based control has a superior performance in terms of tracking speed and low steady-state power oscillations, with a maximum tracking efficiency of 98.57%.

Controlled transition to different proton acceleration regimes: Near-critical-density plasmas driven by circularly polarized few-cycle pulses

A controlled transition between two different ion acceleration mechanisms would pave the way to achieving different ion energies and spectral features within the same experimental set up, depending on the region of operation. Based on numerical simulations conducted over a wide range of experimentally achievable parameter space, reported here is a comprehensive investigation of the different facets of ion acceleration by relativistically intense circularly polarized laser pulses interacting with thin near-critical-density plasma targets. The results show that the plasma thickness, exponential density gradient, and laser frequency chirp can be controlled to switch the interaction from the transparent operating regime to the opaque one, thereby enabling the choice of a Maxwellian-like ion energy distribution with a cutoff energy in the relativistically transparent regime or a quasi-monoenergetic spectrum in the opaque regime. Next, it is established that a multispecies target configuration can be used effectively for optimal generation of quasi-monoenergetic ion bunches of a desired species. Finally, the feasibility is demonstrated for generating monoenergetic proton beams with energy peak at E≈20–40 MeV and a narrow energy spread of ΔE/E≈18%–28.6% confined within a divergence angle of ∼175 mrad at a reasonable laser peak intensity of I0 ≃ 5.4 × 1020 W/cm2.

The inversion of multiresponse partial least squares models, a useful tool to improve analytical methods in the framework of analytical quality by design

Analytical Quality by Design (AQbD) is the adaptation of Quality by Design (QbD) when it is applied to the development of an analytical method. The main idea is to develop the analytical method in such a way that the desired quality of the Critical Quality Attributes (CQAs), stated via the analytical target profile (ATP), is maintained while allowing some variation in the Control Method Parameters (CMPs).The paper presents a general procedure for selecting factor levels in the CMPs to achieve the desired responses, characterized by the CQAs, when liquid chromatographic methods are to be used for the simultaneous determination of several analytes. In such a case, the CMPs are usually the composition of the ternary mobile phase, its flow rate, column temperature, etc., while typical CQAs refer to the quality of the chromatograms in terms of the resolution between each pair of consecutive peaks, initial and final chromatographic time, etc. The analytical target profile in turn defines the desired characteristics for the CQAs, the reason for the whole approach.The procedure consists of four steps. The first is to construct a D-optimal combined design (mixture-process design) to select the domain and levels of the CMPs. The second step is to fit a PLS2 model to predict the analytical responses expressed in the ATP (the good characteristics of the chromatogram) as a function of the CMPs. The third step is the inversion of the PLS2 model to obtain the conditions necessary to obtain the preset ATP in the corresponding CQAs. The inversion is performed computationally in order to estimate the Pareto front of these responses, namely, a set of experimental conditions to perform the chromatographic determination for which the desired critical quality attributes are met. The fourth final step is to obtain the Method Operable Design Region (MODR), that is, the region where the CMPs can vary while maintaining the quality of the CQAs.The procedure has been applied to some cases involving different analytes, all of which are regulated by the European Union due to their toxicity to human health, namely five bisphenols and ten polycyclic aromatic hydrocarbons.

Principles of White Analytical Chemistry and Design of Experiments to Stability-Indicating Chromatographic Method for Simultaneous Estimation of Thiocolchicoside and Lornoxicam.

A variety of chromatographic methods have been published for the stability evaluation of thiocolchicoside and lornoxicam. Nevertheless, the development of chromatographic methods requires the use of neurotoxic and teratogenic organic solvents that are detrimental to the environment and harmful to human life. Using the principles of design of experiments (DoE), a novel white analytical chemistry-driven stability-indicating high-performance thin layer chromatographic (SI-HPTLC) method has been developed for the concurrent stability study of thiocolchicoside (THC) and lornoxicam (LNX). To protect the environment and human life, the stability-indicating HPTLC method was developed using safe organic solvents. Potential analytical method risk parameters (AMRPs) and analytical method performance attributes (AMPAs) were screened using the fractional factorial design. The response surface analysis and optimization of critical AMRPs and AMPAs was carried out using full factorial design. Navigation of the method operable design region (MODR) was used to develop the SI-HPTLC technique. The developed method was validated as per ICH (International council for harmonization) Q2(R1) guideline. The developed method's greenness was evaluated using AGREE (Analytical Procedure Greenness) tool and ESA (Eco-Scale Assessment). The Blue (B) model was used to assess the proposed method's cost and time efficiency and user-friendlyness. For the stability studies of THC and LNX, the twelve principles of WAC (White Analytical Chemistry) were used to evaluate the published and proposed chromatographic techniques. As compared to previously published chromatographic techniques for studying the stability of THC and LNX, the suggested approach was found to be more affordable, environmentally friendly, and user-friendly. Development of stability-indicating HPTLC method using a novel white analytical chemistry approach and organic solvents with low toxicity potential. Application of the developed method for analysis of the forced degraded sample and fixed-dose combinations of THC and LNX.

Mathematical modelling and simulation of a wideband PLL for application in frequency synthesizers

In this paper the mathematical modelling of the Voltage Controlled Oscillator, Phase Frequency Detector, Low Pass Filter, Charge pump for designing a PLL circuit is proposed. Based on the modelling schematics are designed and proposed for the application in frequency synthesizer. The main design feature of this modelling is that VCO tunning switches are controlled digitally. The behaviour of PLL under its region of operation is simulated. The effect of temperature variations and insufficient bandgap overlapping on the output frequency of PLL is also presented and discussed. To avoid the current mismatching and residual phase errors the charge pump is modelled as to calibrate by its own circuit. Various simulations are done for the performance analysis of wideband PLL. The proposed design will have its application in frequency synthesizers suitable for multi band transceivers.

A spectral-domain wave-to-wire model of wave energy converters

Wave-to-Wire models play an important role in the development of wave energy converters. They could provide insight into the complete operating process of wave energy converters, from the power absorption stage to the power conversion stage. In order to cover a set of relevant nonlinear effects, wave-to-wire models are predominately established in the time domain. However, the low computational efficiency of time-domain modeling is hindering the extensive application of wave-to-wire models, especially in early-stage design and optimization where a large number of iterations are required. To address this issue, a spectral-domain wave-to-wire model is proposed, and the nonlinear effects are incorporated by stochastic linearization. This model can significantly reduce the computational load and maintain good accuracy. The reference concept studied in this paper is defined as a heaving point absorber coupled with a linear permanent-magnet generator. Four representative nonlinear effects involved in both the hydrodynamic stage and the electrical stage of the concept are considered. The proposed model is verified against a corresponding nonlinear time-domain wave-to-wire model, and a good agreement is observed. The relative error of the proposed spectral-domain wave-to-wire model is around 2 % in typical operational regions and is still within 7 % for wave states with large significant wave heights, regarding the estimate of the power conversion efficiency. Meanwhile, the computational load of the spectral-domain wave-to-wire model is reduced by 2 to 3 orders of magnitudes compared with the conventional time-domain approach. Finally, a case study of tuning the PTO damping to maximize power production is conducted to demonstrate the performance of the proposed spectral-domain wave-to-wire model.

Reduction of DC Capacitor Size in Three-Phase Input/Single-Phase Output Power Cells of Multi-Cell Converters through Resonant and Predictive Control: A Characterization of Its Impact on the Operating Region

Cascaded H-bridge drives require using a significant-size capacitor on each cell to deal with the oscillatory power generated by the H-bridge inverter in the DC-link. This results in a bulky cell with reduced reliability due to the circulating second harmonic current through the DC-link capacitors. In this article, a control strategy based on a finite control set model predictive control and a proportional-resonant controller is proposed to compensate for the oscillatory power required by the H-bridge inverter through the cell’s input rectifier. With the proposed strategy, a DC-link second harmonic free operation is achieved, allowing for the possibility of reducing the capacitor size and, in consequence, the cell dimensions. The feasibility of the proposed control scheme is verified by experimental results in one cell of a cascade H-bridge inverter achieving an operation with a capacitance 141 times smaller than required by conventional control approaches for the same voltage ripple.

Assessing safety functionalities in the design and validation of driving automation

This paper aims to contribute to the comprehensive and systematic safety assessment of Automated Driving Systems (ADSs) by identifying unknown hazardous areas of operation. The current methodologies employed in this domain typically involve estimating the distributions of situational variables based on human-centered field test, crash databases, or expert knowledge of critical values. However, due to the lack of a-priori knowledge regarding the influential factors, their critical ranges, and their distributions, these approaches may not be entirely suitable for the assessment of emerging automated driving technologies. To deal with this challenging problem, here we propose a testing methodology incorporating realistic yet unobserved driving conditions, distinguished by numerous situational variables, so to encompass unknown unsafe conditions comprehensively. Our methodology utilizes stochastic simulation and uncertainty modeling techniques to account for the variability of realistic driving conditions and their impact on ADSs' performances. By doing so, we aim to identify unsafe operational regions and triggering conditions that can lead to hazardous behaviors, thus improving the development and safety of automated driving functions. For our purposes, the Latin Hypercube Sampling technique and the recently proposed PAWN density-based sensitivity analysis method are employed. We apply this methodology for the first time in the specific field of ADSs design and validation, using an exemplificative use case. We discuss and compare the results obtained from our approach with those obtained from a traditional approach.

Düşey Milli Eksenel Bir Pompada Zamana Bağlı Akışın Deneysel Olarak İncelenmesi

Due to the changes in the system characteristics, pumps may have to be operated far away from the design point, such as in part-load or over-load operating points. Operating the pumps far away from the design point may cause fluctuations in the flow. As a result of the fluctuations mechanical problems in the pump structure may occur. In order to overcome the problem, the operating characteristics of the pump must be determined at part load operating conditions as well as design point operating condition. In this study, flow inside a vertical shaft axial flow pump is investigated experimentally. The experimental setup is designed and constructed for the laboratory tests. The pump which is designed and manufactured is tested in the test setup. The performance of the pump is determined by measuring the flow rate, inlet and outlet pressures, rotational speed and power input of the pump. The part load and over load operating regions are determined. Pressure variations are measured at various performance points with the piezoelectric pressure transducer placed in between impeller and diffuser blade passage. Simultaneously, comparisons are made with the vibration spectrums obtained in the pump.

Combustion Characteristics of a Novel Ammonia Combustor equipped with Stratified Injection for Low Emissions

Ammonia – a carbon-free fuel- is being considered by various research groups and organizations as a potential alternative fuel to tackle some global warming issues of the 21st century. However, ammonia faces some challenges as a fuel, particularly, the production of unwanted NOx and unburned ammonia traces at the back end of combustion systems accompanied by unstable flame regimes. Therefore, new concepts are currently being developed to address these challenges whilst also providing stable, high-power operation. This work presents a newly designed stratified combustion system for gas turbines capable of operating with both premixed and stratified modes. The system has been initially evaluated using these two modes employing solely hydrogen and ammonia. Increase of hydrogen stratification resulted in the reduction of NO and NO2, while N2O slightly increased due to the reduction of fuel in the premixed system. Further tests were conducted to evaluate the potential of the systems to replace fossil fuels. Previous work done using methane as the fuel-to-be-replaced has shown interesting trends in terms of emissions and stability. Thus, to progress on the subject, the work conducted here attempted propane/ammonia/hydrogen using this innovative strategy. Results denoted how stratification has a strong impact on NOx production at the flame front, whilst the mechanism of flame stabilization of the new burner enables large operability regions under a great variety of fuel combinations. Strategic injection setups were identified, whilst the best propane/ammonia/hydrogen blends for stability and emissions reduction are also detailed for further implementation in larger systems.

ZVS Soft Switching Operation Region Analysis of Modular Multi Active Bridge Converter Under Single Phase Shift Control

Modular multi active bridge (MMAB) converter can provide multiple dc ports using modular H-bridge. When voltage conversion ratios of each port are not equally balanced, zero-voltage-switching (ZVS) turn-on of power semiconductors in the MMAB converter cannot be secured under single phase shift (SPS) control, increasing power loss and leading to lower efficiency. To estimate the efficiency of the converter in various conditions, ZVS operation region of MMAB converters under SPS is comprehensively derived based on steady-state time domain with superposition theorem. Voltage conversion ratios are taken as main variables for ZVS region analysis and influences of them are comprehensively analyzed. Full ZVS regions and constrained ZVS regions are obtained by ZVS discriminants. Simulation and experimental results for a three-port MMAB prototype are given to verify the theoretical analysis of ZVS operation region.

Conditional Droop Adjustment for Reliability-Oriented Power Sharing in Microgrids

Power electronic systems are facing the challenge to function more safely and reliably. Reliability-oriented power sharing is thereby employed in multi-converter systems to reduce the cost of end-of-life maintenance. One typical approach is to adaptively adjust the droop gains of the converters solely based on the accumulated damage to the power devices. However, this does not always hold throughout the entire loading profile, possibly ending up with a contradiction from higher reliability. Hence, this paper generalizes the reliability-oriented power sharing by necessitating the adjustment of active droop gains considering the nominal power. Two operation regions are formalized by the nominal point, where the adjustment goes into opposite directions. The principle is validated by short-term experiments and long-term simulations estimating the B10 lifetime (10% probability of failure), revealing the improvement of system-level reliability especially under fluctuating loads or operator commands.

Discontinuous Space Vector Pulse Width Modulation for Six Switch Converter With Independent Control of Phase Voltages and Switching Device Stress Alleviation

This paper presents a discontinuous space vector pulse width modulation (DSVPWM) for the six-switch inverter. To provide a broader alternative of DSVPWM for the six-switch inverter, the space vector method employing three zero vector partitioning parameters has been used to generate the modulation signals. A simple mathematical transformation is applied to the resulting modulation signals. This, along with the switching logic results in the accurate synthesis of the phase voltages in both the linear and non-linear regions of operation. The operating modes are chosen to ensure independent phase voltages. Furthermore, the use of the three zero vector partitioning parameters for the DSVPWM not only alleviate the switching stresses of the devices but ensures even distribution of the stress in the top, middle and bottom devices in a leg of the converter. An application of the converter is the symmetrical two-phase induction motor (STPIM) drive. Experimental results validate the theory and analysis including an open loop v/f operation of the STPIM drive.

Load- and Renewable-Following Control of Linearization-Free Differential Algebraic Equation Power System Models

Electromechanical transients in power networks are mostly caused by a mismatch between power consumption and production, causing generators to deviate from the nominal frequency. To that end, feedback control algorithms have been designed to perform frequency and load/renewable-following control. In particular, the literature addressed a plethora of grid-and frequency-control challenges with a focus on linearized, differential equation models whereby algebraic constraints i.e., power flows (PFs) are eliminated. This is in contrast to the more realistic nonlinear differential algebraic equation (NDAE) models. Yet, as grids are increasingly pushed to their limits via intermittent renewables and varying loads, their physical states risk escaping operating regions due to either a poor prediction or sudden changes in renewables or demands—deeming a feedback controller based on a linearization point virtually unusable. In lieu of linearized differential equation models, the objective of this article is to design a simple, purely decentralized, linearization-free, feedback control law for the NDAE models of power networks. The aim of such a controller is to primarily stabilize frequency oscillations after a significant, unknown disturbance in renewables or loads. Although the controller design involves advanced NDAE system theory, the controller itself is as simple as a decentralized proportional or linear quadratic regulator (LQR) in its implementation. Case studies demonstrate that the proposed controller is able to stabilize dynamic and algebraic states under significant disturbances.

Throughput Maximization of Wireless-Powered Communication Network With Mobile Access Points

In order to mitigate the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">double near-far effect</i> , we focus on a mobile wireless-powered communication network (WPCN), where sensor nodes harvest energy from the radio frequency (RF) signal of the mobile energy access point (EAP), and transmit data to the mobile data access point (DAP) by using the harvested energy. Only the sensor nodes with energy larger than a threshold, which is mainly determined by the energy consumption of one transmission, have opportunities to transmit data. Due to the mobility of the EAP and DAP, the distance between the EAP and DAP changes over time. When the DAP moves into the operation region of the EAP, the EAP and DAP could not work simultaneously due to the severe interference, and an energy harvesting probability is employed to denote the probability that the EAP works in this scenario. The purpose of this paper is to identify the optimal transmission policy, i.e., the optimal pairing of the energy consumption of one transmission and the energy harvesting probability, that maximizes the throughput of the WPCN under an energy causality constraint. By analyzing the energy causality constraint, we show that the WPCN could be divided into an energy-sufficient state and an energy-limited state by the pairing of the energy consumption of one transmission and the energy harvesting probability. Since the energy consumption of one transmission and the energy harvesting probability are jointly intertwined with the energy causality constraint, making the joint optimization problem intractable, we divide the throughput maximization problem into two layers. In the inner problem, we investigate the optimal energy consumption of one transmission with a given energy harvesting probability. In the outer problem, we derive the optimal energy harvesting probability based on the obtained optimal energy consumption of one transmission. According to the aforementioned investigations, we propose a two-layer algorithm to obtain the specific solution. Numerical results are conducted to validate the theoretical results and the efficiency of the proposed two-layer algorithm.

Application of the Analytical Procedure Lifecycle Concept to a Quantitative 1H NMR Method for Total Dammarane-Type Saponins.

Dammarane-type saponins (DTSs) exist in various medicinal plants, which are a class of active ingredients with effects on improving myocardial ischemia and immunomodulation. In this study, a quantitative 1H NMR method of total DTSs in herbal medicines was developed based on the analytical procedure lifecycle. In the first stage (analytical procedure design), the Ishikawa diagram and failure mode effects and criticality analysis were used to conduct risk identification and risk ranking. Plackett-Burman design and central composite design were used to screen and optimize critical analytical procedure parameter. Then, the method operable design region was obtained through modeling. In the second stage (analytical procedure performance qualification), the performance of methodological indexes was investigated based on analytical quality by design. As examples of continued procedure performance verification, the method was successfully applied to determine the total DTSs in herbal pharmaceutical preparations and botanical extracts. As a general analytical method to quantify total DTSs in medicinal plants or pharmaceutical preparations, the developed method provides a new quality control strategy for various products containing dammarane-type saponin.

Tunable elastic wave modulation via local phase dispersion measurements of a piezoelectric metasurface with signal correlation enhancement

Tunable piezoelectric metasurfaces have been proposed as a means of adaptively steering incident elastic waves for various applications in vibration mitigation and control. Bonding piezoelectric material to thin structures introduces electromechanical coupling, enabling structural dynamics to be altered via tunable electric shunts connected across each unit cell. For example, by carefully calibrating the inductive shunts, it is possible to implement the discrete phase shifts necessary for gradient-based waveguiding behaviors. However, experimental validations of localized phase shifting are challenging due to the narrow bandgap of local resonators, resulting in poor transmission of incident waves and high sensitivity to transient noise. These factors, in combination with the difficulties in experimental circuitry synthesis, can lead to significant variability of data acquired within the bandgap operating region. This paper presents a systematic approach for extracting localized phase shifts by taking advantage of the inherent correlation between the incident and transmitted wavefronts. During this procedure, matched filtering greatly reduces noise in the transmitted signal when operating in or near bandgap frequencies. Experimental results demonstrate phase shifts as large as −170° within the locally resonant bandgap, with an average 28% reduction in error relative to a direct time domain measurement of phase, enabling effective comparison of the dispersive behavior with corresponding analytical and finite element models. In addition to demonstrating the tunable waveguide characteristics of a piezoelectric metasurface, this technique can easily be extended to validate localized phase shifting of other elastic waveguiding metasurfaces.

Offshore wind power generation system control using robust economic MPC scheme

With the increasing penetration of wind power in the modern power system, the economic model predictive control (EMPC) has been widely employed in the control of the offshore wind power generation system for promoting the dynamic economy. A robust EMPC strategy, aiming to minimizing damage to the turbine while maximizing the electric power output, is developed in this paper to enhance the dynamic economic performance under uncertain wind speed variation. A linear model is utilized to approximate the original nonlinear behavior of the wind power generation system, while the consequent linearization error is taken as the external disturbance of the control system. A linear feedback controller with a robust control invariant set is designed to restrict the deviation between the nominal linear system and the actual nonlinear wind power generation system. Plant simulations, as well as NREL FAST code testing, are given to demonstrate the proposed controller's effectiveness throughout the overall operating region.