Search Results (23)

This study explores the use of artificial intelligence (AI) in religious leadership in Germany, focusing on the interplay between technological innovation, theological principles, and human interaction. Drawing on qualitative methods, 23 Christian leaders and experts were interviewed to examine their perceptions, assessments, and potential applications of AI and related technologies in their work, alongside ethical and theological considerations. The findings reveal a prevailing ambivalence towards AI: while it is generally accepted as a tool for administrative tasks, its use in pastoral contexts encounters resistance due to ethical concerns and theological tensions. Despite predominantly neutral to positive attitudes, many leaders lack proactive engagement in exploring AI’s transformative potential—pointing to a marked lack of agency. Digital competence among leaders emerges as a significant factor influencing the openness to AI adoption. This study identifies key barriers to the integration of AI into religious practice and underscores the need for strategic education and planning. It advocates for a balanced approach to leveraging AI in ways that align with religious values while embracing innovation in a digitalizing society. Full article

The main purpose of this research is to develop an improved space vector pulse-width modulation (SVPWM) algorithm for three-level (3L) neutral point clamped (NPC) voltage source inverters (VSIs). The results of experiments conducted on the three-level power converter laboratory setup showed that the proposed SVPWM algorithm with a seven-stage switching sequence (SS) can reduce a VSI’s switching frequency by 43.48% compared to the SVPWM algorithm with the base SS. It also improves the neutral point (NP) voltage balance in the VSI DC link by 4.2% by controlling the duty factor of distributed base vectors in each SVPWM period based on phase load currents. It reduced the values of the 5th- and 7th-order harmonics of the VSI output voltage by 19% and 15.7%, respectively. The results show that the usage of the improved SVPWM algorithm helps increase the efficiency of a 3L NPC VSI by 0.6% and reduce the higher harmonics. The obtained results confirm the efficiency of the suggested algorithm and its great potential for power converters in industry. Full article

The neutral-point potential balance issues in three-level converters have obtained great attention. The popular view thinks that the neutral-point voltage deviation can be suppressed by regulating the injected zero-sequence component, whether via carrier modulation or space vector modulation techniques. However, this paper presents a novel finding: the efficacy of different frame controllers on the self-balancing of neutral-point potential in three-level converters differs when a comprehensive analysis of zero-sequence dynamics, including neutral-point current and PWM modulation, is conducted. That is, the proportional-resonant (PR) controller in the abc frame effectively introduces a zero-axis PR control of the zero-sequence component, which subsequently degrades the stability of neutral-point potential self-balancing. In contrast, the PI control in the dq frame does not incorporate any additional control of the zero-sequence component, thereby enhancing the self-balancing capability of the neutral-point potential. To substantiate this novel finding, a series of simulations and experimental validations were performed. Full article

Currently, the escalating integration of renewable energy sources is causing a steady weakening of grid strength. When grid strength is weak, interactions between inverters or those between inverters and grid line impedance can provoke widespread oscillations in the power system. Additionally, the diverse DC voltage application characteristics of power converter systems (PCS) may lead to over-modulation, generating narrow pulse issues that further impact control of the midpoint potential balance. Existing dead-time elimination methods are highly susceptible to current polarity judgments, rendering them ineffective in practical use. PCS, due to inherent dead-time effects, midpoint potential imbalances in three-level topologies, and narrow pulses, can elevate low-order harmonic content in the output voltage, ultimately distorting grid-connected currents. This is particularly susceptible to causing resonance in weak grids. To enhance the output voltage waveform of PCS, this article introduces a comprehensive compensation control strategy that combines dead-time elimination, midpoint potential balance, and narrow pulse suppression, all based on an active neutral point clamped (ANPC) three-level topology. This strategy gives precedence to dead-time elimination and calculates the upper and lower limits of the zero-sequence available for midpoint potential balance while fully compensating for narrow pulses. By prioritizing dead-time elimination, followed by narrow pulse suppression and finally midpoint potential balance, this method decouples the coupling between these three factors. The effectiveness of the proposed method is validated through semi-physical simulations. Full article

PWM (pulse width modulation) is the most widely applied current conversion technology, but the high-frequency harmonics it causes have a significant negative impact on inverter system performance. This paper focuses on the three-phase T-type three-level inverter as the research object and addresses existing PWM voltage noise and midpoint potential imbalance issues by proposing an improved random SVPWM strategy, named Neutral Point Potential Balance Random Space Vector PWM (NPB–RSVPWM). The NPB–RSVPWM strategy includes three main steps: (1) introducing a midpoint potential balancing control loop to adjust the synthesis timing of the effective vectors to generate pulse signals, optimizing midpoint potential balance; (2) employing a randomly varying carrier frequency in place of the carrier used in the SVPWM strategy to generate the driving signals for switching devices; and (3) controlling the inverter through the driving pulse signals. This strategy optimizes the synthesis sequence of traditional SVPWM strategy vectors and incorporates random frequency modulation techniques. The mathematical model analyzes PWM harmonic expressions corresponding to fixed switching frequencies, and a random frequency carrier is chosen to suppress these PWM harmonics. The effective vector’s equivalent circuit is analyzed, proposing a technique for optimized vector synthesis timing. The simulation and experimental results verify that the NPB–RSVPWM technique can disperse PWM harmonic energy, reduce voltage noise, and optimize midpoint potential balance. Under the NPB–RSVPWM strategy, the line voltage spectrum becomes uniform, the maximum harmonic content is greatly reduced, and the fluctuation in the DC side midpoint potential is significantly improved. Compared with the traditional SVPWM strategy and random PWM strategy, the NPB–RSVPWM strategy has a lower voltage noise, smaller total harmonic distortion, and a more stable midpoint potential. The effectiveness and feasibility of the NPB–RSVPWM strategy are verified by simulation and experimental results. Full article

Three-level NPC inverters have been widely used in grid-connected systems due to their superior performance compared with two-level inverters, but more switches lead to high fault probability. Meanwhile, the neutral point potential (NPP) fluctuation of the DC link is an inherent problem of three-level NPC inverters. To keep the three-level NPC inverter running stably after single-arm failure, a fault-tolerant control strategy based on an optimised space vector pulse width modulation (SVPWM) is proposed in this paper. Firstly, the common-mode voltage (CMV) of the postfault three-level NPC inverter is analysed and then the preliminary synthesis principles of the reference voltage vector are determined. Then, in order to ensure the NPP balance and the quality of the grid-connected currents, the reference voltage vector synthesis rules are optimised, a low-pass filter (LPF) and a hysteresis comparator are designed, respectively, to ensure the quality of grid-connected currents and effectively decrease the DC link NPP deviation. Finally, the simulation results show that the proposed fault-tolerant control strategy can realize the stable and reliable operation of the grid-connected three-level NPC inverter after single-arm failure, and the CMV can be reduced significantly, the quality of grid-connected currents is also improved. The proposed fault-tolerant strategy also shows good performance when the grid-connected currents change. Full article

In the field-weakening region, the traditional field-weakening method for induction motor drives based on model predictive control (MPC) is to take a no-load operation as the premise and adjust the flux reference in the cost function proportional to the inverse of the rotor speed, which leads to poor torque output. This paper presents a novel field-weakening method for IM drives based on MPC. Considering the induction motor field-weakening limiting conditions and according to the speed adaptive field-weakening strategy with a voltage closed-loop, the speed adaptive field-weakening controllers were designed to optimize the references of the excitation current and torque current. In the rotor field-orientation d–q coordinate system, the stator flux amplitude and torque reference values were optimized by the optimal distribution current. Then, according to the dead-beat control principle, they were converted into an equivalent stator flux vector reference. Moreover, the stator voltage vector reference can be obtained. For an induction motor fed by a three-level neutral point clamped (3L-NPC) inverter, the cost function was constructed by combining all the constraints, including the voltage vector, the neutral potential balance, and the switching frequency. In this way, the high-performance field-weakening operation for the induction motor based on a model predictive control can be realized. The simulation and experiment results show that the proposed method can increase the torque output by 22% in the field-weakening region; at the same time, the steady characteristics and the dynamic response performance can be maintained well. Full article

The objective of this study is to evaluate assets’ performance by considering the exit time within the risk measurement framework alongside Shannon entropy and, alternatively, excluding these factors, which can be used to create a portfolio aligned with short- or long-term objectives. This portfolio effectively balances the potential risks and returns, guiding investors to make decisions that are in line with their financial goals. To assess the performance, we used data envelopment analysis (DEA), whereby we utilized the risk measure as an input and the mean return as an output. The stop point probability–CVaR (SPP-CVaR) was the risk measurement used when considering the exit time. We calculated the SPP-CVaR by converting the risk-neutral density to the real-world density, calibrating the parameters, running simulations for price paths, setting the stop-profit points, determining the exit times, and calculating the SPP-CVaR for each stop-profit point. To account for negative data and to incorporate the exit time, we have proposed a model that integrates the mean return and SPP-CVaR, utilizing DEA. The resulting inefficiency scores of this model were compared with those of the mean-CVaR model, which calculates the risk across the entire time horizon and does not take the exit time and Shannon entropy into account. To accomplish this, an analysis was conducted on a portfolio that included a variety of stocks, cryptocurrencies, commodities, and precious metals. The empirical application demonstrated the enhancement of asset selection for both short-term and long-term investments through the combined use of Shannon entropy and the exit time. Full article

Direct power control (DPC) has gained increasing attention in recent years as a simple and efficient control strategy for pulse width modulation (PWM) rectifiers. In this paper, the idea of DPC is introduced into the three-phase coupled inductor-based bipolar-output active rectifier (TCIBAR) for the first time, and a virtual vector-based direct power control (VVB-DPC) strategy is proposed for TCIBAR to realize the bipolar DC power supply for more electric aircraft (MEA). First, the mathematical model of the TCIBAR is deduced, and the basic principle of the classic DPC strategy is reviewed. On this basis, the limitations of the classic DPC strategy in TCIBAR control are analyzed. Second, a set of virtual vectors are derived to establish a novel virtual-vector switching table. Based on the virtual-vector switching table, the hysteresis power control of TCIBAR can be realized without affecting the DC-side neutral-point potential of TCIBAR. Finally, a neutral-point potential control method based on DPC architecture is studied and integrated into the VVB-DPC strategy to maintain the bipolar DC voltage balance of TCIBAR under unbalanced load conditions. The VVB-DPC strategy is experimentally studied on a TCIBAR prototype, and the experimental results verify the feasibility and effectiveness of the proposed strategy. Full article

Three-phase three-level dual-active-bridge (3L-DAB3) converters are a potential topology for high-voltage and high-power applications. Neutral-point voltage balancing is a complex and important issue for three-level (3L) circuits. Compared with the single-phase 3L dual-active-bridge converter, the self-balancing capability of the 3L-DAB3 is limited. To guarantee the reliability of the converter, a neutral-point voltage balancing method for the 3L-DAB3 is proposed in this paper. First, the neutral-point voltage balancing principle of the 3L-DAB3 is analyzed. Then, the relationship between the duty ratio adjustment and injected neutral-point charge is described. In order to guarantee accurate neutral-point voltage balance, the proposed balancing method adopts a sign-hysteresis control with a dead zone. The dead zone is responsible for whether the duty ratio adjustment is activated, and the sign-hysteresis control guarantees a correct adjustment direction. The proposed neutral-point voltage balancing method only needs to sample the capacitor voltages, thus avoiding a complex parameter design and making it easy to implement. The transmission power of the converter is not affected during the adjustment process. The proposed balancing method has a rapid response speed and does not have problems with respect to stability. Finally, experiments were conducted on a 3.6 kW laboratory prototype. The validity and performance of the proposed neutral-point voltage balancing method were verified on the basis of the simulation and experimental results. Full article

The study sets a baseline for split DC link capacitance values and voltage set points in three-phase three-level AC/DC (or DC/AC) converters operating with unity power factor. In order to equalize the average values of partial DC link voltages, the controller generates a zero-sequence containing DC components only while employing neither dedicated DC link capacitance balancing hardware nor high-order zero-sequence component injection. Such a baseline is required in order to evaluate the effectiveness of different DC link capacitance reduction methods proposed in the literature. Unlike most previous works, utilizing neutral point current based on cumbersome analytical expressions to determine neutral point potential oscillations, the instantaneous power balance-based approach is employed in this paper, resulting in greatly simplified and more intuitive expressions. It is demonstrated that while the total DC link voltage is low-frequency ripple-free under unity power factor balanced AC-side operation, split DC link capacitors absorb triple-fundamental frequency power components with one-sixth load power magnitude. This yields significant opposite phase partial voltage ripples. In such a case, selection of DC link capacitances and voltage set points must take into account the expected values of AC-side phase voltage magnitude and split DC link capacitor voltage and current ratings. Simulation and experimental results validate the proposed methodology by application to a 10 kVA T-type converter prototype. Full article

The quasi-Z-source T-type inverter is a new type of three-level inverter. Compared with other three-level inverters, the quasi-z-source T-type inverter is characterized by its fault tolerance capability and boost capability. In the inverter, the modulation strategy greatly affects the performance. Aiming at the problems in three-level inverters such as excessive common-mode voltage and unbalanced neutral point potential, a space vector pulse width modulation (SVPWM) for a quasi-z-source T-type three-level inverter based via line voltage coordinate is proposed in this paper. The main research work and achievements of this paper include: (1) based on the existing research results, an SVPWM modulation strategy for the quasi-Z-source T-type inverter is proposed. The modulation method proposed by this paper can effectively reduce the common-mode voltage and balance the neutral point voltage. (2) This paper analyzes the principle of the line voltage coordinate system and makes some modifications to the line voltage coordinate system so that the proposed modulation scheme can be applied to the line voltage coordinate system. Compared with the traditional $\alpha \beta$ coordinate system, the SVPWM algorithm in the line voltage coordinate system has the characteristic of simple calculation. The simulation and experiment results show that the control method has good performance under the conditions of dynamic response and imbalance. Full article

In this study, we combined all-atom MD simulations, the ensemble-based mutational scanning of protein stability and binding, and perturbation-based network profiling of allosteric interactions in the SARS-CoV-2 spike complexes with a panel of cross-reactive and ultra-potent single antibodies (B1-182.1 and A23-58.1) as well as antibody combinations (A19-61.1/B1-182.1 and A19-46.1/B1-182.1). Using this approach, we quantify the local and global effects of mutations in the complexes, identify protein stability centers, characterize binding energy hotspots, and predict the allosteric control points of long-range interactions and communications. Conformational dynamics and distance fluctuation analysis revealed the antibody-specific signatures of protein stability and flexibility of the spike complexes that can affect the pattern of mutational escape. A network-based perturbation approach for mutational profiling of allosteric residue potentials revealed how antibody binding can modulate allosteric interactions and identified allosteric control points that can form vulnerable sites for mutational escape. The results show that the protein stability and binding energetics of the SARS-CoV-2 spike complexes with the panel of ultrapotent antibodies are tolerant to the effect of Omicron mutations, which may be related to their neutralization efficiency. By employing an integrated analysis of conformational dynamics, binding energetics, and allosteric interactions, we found that the antibodies that neutralize the Omicron spike variant mediate the dominant binding energy hotpots in the conserved stability centers and allosteric control points in which mutations may be restricted by the requirements of the protein folding stability and binding to the host receptor. This study suggested a mechanism in which the patterns of escape mutants for the ultrapotent antibodies may not be solely determined by the binding interaction changes but are associated with the balance and tradeoffs of multiple local and global factors, including protein stability, binding affinity, and long-range interactions. Full article

Considering the disadvantages of the traditional development pattern in an embedded control system for an inverter, that is, the single-process thinking and separation of software and hardware, a novel method, which is a model-based design, for developing a double closed-loop control system for the diode-clamped three-level inverter was proposed. System control models, including the PWM control algorithm model, the voltage control model, the neutral-point potential balancing model, and the frequency control model, were built with the MATLAB platform. The code-generation capacity and the operation effect were verified through a series of tests. The inverter with diode clamp and neutral-point potential control was developed. Codes were generated automatically and downloaded to the eZdsp28335 control chip. Experimental waveforms of the phase voltage, line voltage and current were analyzed under regulating the voltage and frequency. The experimental results demonstrate that the models and the generated codes are correct. Further studies have proven the feasibility of the system development model. Full article

Dietary fibres are an integral part of a balanced diet. Consumption of a high-fibre diet confers many physiological and metabolic benefits. However, fibre is generally avoided by individuals with gastrointestinal motility disorders like gastroparesis due to increased likelihood of exacerbated symptoms. Low-viscosity soluble fibres have been identified as a possible source of fibre tolerable for these individuals. The aim of this study is to determine the rheological properties of 10 common commercially available soluble fibres in chemically simulated digestive conditions and evaluate their suitability for individuals with mild to moderate gastroparesis, a gastric motility disorder. Rheological testing under neutral condition (distilled water pH 7) and chemically simulated gastric digestion were evaluated to determine the yield point and relative viscosity of each fibre. Our results reveal two rheological categories of soluble fibres; pseudoplastic and dilatant. Simulated digestion was shown to significantly alter the yield-points of psyllium husk, iota-carrageenan, beta-glucan, apple-fibre pectin, and inulin. Gum Arabic and partially hydrolysed guar gum showed the lowest viscosities and were not affected under simulated digestion, characteristics that make them potential candidate fibres for patients with gastroparesis. Altogether, our results demonstrate that digestion can have a significant impact on fibre viscosity and should be taken into consideration when evaluating the suitability of fibres for patients with gastric motility disorders. Full article