Search Results (142)

Interconnecting grid-following (GFL) and grid-forming (GFM) converters help stabilize weak grids with a high penetration of power electronics, but dynamic interactions can induce high-frequency oscillations (HFOs). The HFO mechanism within interconnected grid-forming battery energy storage (GFM-BESS) and grid-following VSC-HVDC systems remains unresolved, with viable suppression strategies yet to be established. To address this, this study utilizes harmonic linearization to derive small-signal frequency-domain impedance models for both devices. The models are developed for high-frequency-oscillation analysis: the GFM-BESS model retains all control loops, while the GFL-HVDC model retains the current loop and the phase-locked loop, with the slow outer loop omitted as justified within the high-frequency band. Frequency-coupled $2\times 2$ impedance matrices are established to capture the frequency coupling introduced by the power loops and the phase-locked loop. Stability is established by the argument principle, the exact Nyquist encirclement count and the roots of the closed-loop characteristic function. At a nominal control delay of 50 μs, the voltage-loop proportional gain has two finite stability boundaries: insufficient proportional action fails to damp the integral-loop mode, whereas excessive proportional action destabilizes the delay-affected filter mode. The resulting two-sided admissible interval is $0.0771<k_{vp}<0.5261$ p.u.; a robust engineering range of 0.15–0.30 p.u., with $k_{vp}=0.22$ p.u. as the nominal value, is recommended. Frequency-sweep results validate the impedance models, while the independently evaluated root locus and Nyquist count give identical stability classifications. Time-domain gain-step tests further verify both sides of the interval: changing $k_{vp}$ from 0.60 to 0.22 suppresses the HFO, whereas a further decrease of 0.15 p.u. to 0.07 re-excites it. Full article

The complex and nonlinear load characteristics of Hall thrusters remain a key challenge in the design of propulsion power-supply output stages. In existing power-supply simulations for electric propulsion systems, the Hall thruster is often simplified as a fixed impedance or a prescribed current source, which makes it difficult to capture the time-synchronized interaction during simulation between the power-supply output stage and the thruster discharge process. To address this issue, this study encapsulates a one-dimensional discharge model as an externally callable thruster slave and proposes a HallThruster.jl–Simulink–Saber co-simulation method. The proposed method enables synchronized bidirectional exchange between the power-port voltage $V_{cmd}$ and the thruster discharge current $I_{out}$. The results show that the discharge current under the co-simulation condition exhibits a sustained low-frequency response at approximately 15.0 kHz. Compared with a fixed-voltage standalone simulation, the co-simulation preserves the same principal oscillation band and overall internal-field structures, while small but observable differences remain in instantaneous phase, local waveform shape, harmonic amplitudes, and high-gradient regions of the internal fields. The proposed method provides a computational framework for investigating dynamically coupled port behavior between a Hall thruster and a representative power-supply output stage. Full article

Hybrid systems integrating grid-following (GFL) and grid-forming (GFM) inverters are increasingly deployed in renewable-energy-dominated power systems. However, impedance coupling between the two inverter types may induce low-frequency oscillations and high-frequency resonances, particularly under weak-grid conditions and varying power injections. This paper clarifies the stability mechanism of a hybrid GFL/GFM inverter system and develops a frequency-segmented active damping strategy. Small-signal impedance models are first derived for the GFL inverter, the GFM inverter, and the overall hybrid system, incorporating the control loops, digital delay, LC filters, interconnection branch impedances, and external grid impedance. Impedance decomposition, Bode plots, and Nyquist criteria are then employed to quantify the influence of power operating points and grid strength on system stability. The results indicate that increasing the GFL inverter output power weakens the stability margins in both low- and high-frequency ranges, whereas variations in the GFM inverter output power provide only limited impedance reshaping in the targeted oscillation bands. On this basis, a low-frequency damping loop is designed on the GFM inverter side, while a high-frequency damping loop based on capacitor-current feedback is implemented on the GFL inverter side. Simulation results confirm that the proposed strategy suppresses low-frequency oscillations and high-frequency harmonic components, maintains stable operation in the hybrid system under high GFL power injection, and reduces the THD of the PCC current from 14.52% to 0.62%. Full article

This paper presents a low-power 30/60 GHz dual-band CMOS voltage-controlled oscillator (VCO) for 5G applications. The design employs an LC-VCO core that simultaneously generates differential fundamental-frequency outputs and a single-ended second-harmonic output. To improve second-harmonic spectral purity, a second-harmonic quarter-wavelength (λ/4) transmission line is inserted in the V_DD bias path of the VCO core. A body-to-ground-with-resistor (B-to-GND-with-R_B) NMOS varactor configuration is adopted to provide a wide, monotonic tuning range while suppressing substrate leakage and noise coupling. In addition, a fundamental-frequency λ/4 transmission line is introduced in the control-voltage bias path to improve AC grounding of the differential varactor center node. The VCO consumes 2.19 mW and achieves a tuning range of 24.59–30.5 GHz (21.5%). At 27.48 GHz, it exhibits a phase noise of −117.69 dBc/Hz at a 10 MHz offset, corresponding to a figure of merit (FoM) of 189.72 dBc/Hz. The second-harmonic output covers 49.18–61 GHz, with the same fractional tuning range. The VCO core occupies a compact chip area of only 0.021 mm². Full article

The study investigates the nonlinear dynamics of a harmonically excited Duffing oscillator coupled with an unforced two-degrees-of-freedom nonlinear energy sink. The external excitation is applied only to the primary oscillator; meanwhile, the NES response is induced through nonlinear internal coupling. The governing nonlinear ordinary differential equations are analyzed using the proposed non-perturbation approach, which does not rely on small-parameter assumptions or Taylor-series expansions. The formulation is used to obtain amplitude-dependent equivalent linear representations and analytical approximations of the coupled system. The analytical results are compared with direct numerical simulations, showing overall agreement with the full nonlinear model. The stability of the steady-state solutions is examined under variations of the main system parameters. The results indicate that the nonlinear coupling and stiffness parameters significantly affect the response amplitudes, stability characteristics, and overall dynamical behavior. Additional analyses using bifurcation diagrams, Lyapunov exponents, Poincaré maps, and basins of attraction reveal transitions between periodic, quasi-periodic, and chaotic regimes, as well as the presence of multi-stability and sensitivity to initial conditions. The proposed framework provides a useful analytical tool in studying the dynamics and stability of nonlinear oscillatory systems over a wide range of operating conditions. Full article

The increasing integration of electric vehicle (EV) charging infrastructure is reshaping the operational and stability characteristics of modern power systems. Unlike conventional load growth, large-scale EV charging introduces converter-interfaced, time-varying, and controllable demand that affects the grid across multiple temporal and spatial scales. This review examines the static, dynamic, and electromagnetic interactions between EV charging infrastructure and power systems, with emphasis on stability mechanisms, converter-control effects, modeling methods, and mitigation strategies. Static impacts are reviewed in terms of voltage deviation, feeder and transformer loading, reactive power demand, phase imbalance, and hosting capacity constraints. Dynamic interactions are discussed from the perspectives of voltage stability, transient response, small-signal oscillation, and converter control coupling. Electromagnetic issues, including harmonic emission, resonance, impedance-based stability, and interoperability among heterogeneous charger topologies, are also assessed. In addition, the review summarizes key mitigation approaches such as coordinated charging, adaptive converter control, hierarchical energy management, and grid-supportive operation. Finally, major research gaps are identified in multi-timescale modeling, stability-aware planning, control co-design, and standardized technical assessment frameworks, and recommendations for future research are presented. Full article

In receiving-end modular multilevel converter (MMC)-based flexible high-voltage direct current (HVDC) grid-connected systems, high-frequency oscillation can significantly increase the peak values of the point of common coupling (PCC) voltage and grid current. To address this issue, this paper proposes a coordinated suppression strategy for high-frequency oscillation in receiving-end MMC grid-connected systems. First, an MMC impedance model is established based on harmonic linearization, and its frequency-domain interaction with the grid impedance is analyzed to clarify the formation mechanism of high-frequency oscillation and its main influencing factors. Then, considering the different roles of the voltage feedforward and current feedback channels in the target frequency band, a coordinated suppression strategy combining band-stop filtering in the voltage feedforward path with low-pass filtering and lead compensation in the current feedback path is designed. Hardware-in-the-loop experimental results show that the proposed method effectively identifies and suppresses high-frequency oscillation. Under the validated operating condition, the oscillation-induced peak increases in the PCC voltage and grid current are limited to within 20% and 12.5%, respectively, thereby suppressing further oscillation growth and reducing the risk of approaching the overvoltage and overcurrent protection thresholds. Full article

Hysteretic nonlinear vibration systems can exhibit jumps, coexisting attractors, and strong dependence on the initial state, particularly when material hysteresis is coupled with geometric nonlinearity. This paper investigates the global nonlinear dynamics of a harmonically forced single-degree-of-freedom oscillator incorporating pseudoelastic shape memory alloy (SMA) wires in a perpendicular geometric configuration. Cyclic force–displacement tests on pseudoelastic SMA wires are used to calibrate the constitutive response, after which steady-state dynamics are analyzed using time integration, numerical continuation (COCO), and basin-of-attraction computations over representative excitation frequencies, pre-tension levels, and the number of wires. The calibrated model predicts rich response regimes including jump phenomena, coexisting stable solutions, multistability, asymmetric periodic responses, and the pronounced dependence of the achieved steady response on initial conditions and internal state. Basin computations reveal sensitive partitioning of the state space between competing attractors, highlighting the influence of the initial and internal state in oscillators that combine pseudoelastic hysteresis with geometric stiffening. Additional numerical exploration of a negative pre-tension extension indicates transitions to more complex responses, including quasi-periodic and chaotic behaviour, but these are presented as secondary results outside the directly validated tension-wire regime. The results clarify how calibrated SMA hysteresis and geometric nonlinearity jointly shape multistability and basin structure in pseudoelastic oscillators. Full article

The quantum motion of a photon in an arbitrary medium was considered within the framework of the gauge symmetry group $SU\left(2\right)\otimes U\left(1\right)$ using the Yang–Mills (Y-M) equations for Abelian fields. A system of second-order partial differential equations (PDEs) for the vector wave function of a photon is derived using the first-order Y-M equations as identities. The full wave function of a photon was defined as the arithmetic mean of the components of the wave function. In a particular case, an equation is obtained for its full wave function, taking into account the structure of space-time in a plane perpendicular to the direction of propagation of the photon. The quantum state of a photon in a nanowaveguide was investigated, and it is shown that under certain conditions, it is reduced to the problem of two coupled 1D quantum harmonic oscillators (QHO) with variable frequencies. An explicit expression is obtained for the wave function of a photon, which is characterized by two vibrational quantum numbers. A quantum theory of a photon for a dissipative medium has been developed taking into account the processes of absorption and emission of photons. The mathematical expectation (ME) of the photon wave function is constructed as the product of two 2D integral representations in which the integrand is the solution of a system of two coupled second-order PDEs. The ME of the probability amplitude of the transition of a single-photon state into one of the two-photon entangled Bell states is constructed. Finally, it was proven that, in addition to frequency, spin, momentum and polarization, the photon also has a spatial structure responsible for the cross sections of processes in which this massless fundamental particle participates. Full article

An analytical solution is presented for transient heat conduction in a two-layer composite cylinder subjected to outer-surface convection with a general time-dependent ambient temperature. Using Duhamel’s principle, closed-form series expressions are derived and then specialized to harmonic ambient fluctuations, recovering the classical constant-ambient solution in the zero-frequency limit. A parametric study shows that the ratio of the inner layer conductivity to the conductivity of the outer layer strongly shapes interfacial gradients and mean-temperature evolution, with sensitivity concentrated at small ratios and diminishing when the ratio is larger than 0.1. Increasing Biot number accelerates the heat transfer and approaches the isothermal-surface limit as it becomes extremely large. The geometric aspect ratio is most influential when the inner layer is resistive, and becomes weak for large conductivity ratio, supporting thin-coating approximations. Under harmonic ambient fluctuations, the response rapidly reaches a periodic steady state; higher frequency decreases amplitude and increases phase lag, while larger Biot numbers amplify oscillations and reduce delay. The coupled effects of the aspect ratio and the conductivity ratio govern penetration and phase behavior. Full article

We study the fundamental limitations of implementing time-dependent Hamiltonian protocols when “time” is provided by a quantum clock rather than an external classical parameter. For a parametric harmonic oscillator controlled through a shortcut-to-adiabaticity (STA) schedule and coupled to a minimal clock degree of freedom, tracing out the clock yields an effective reduced dynamics that is a mixture of unitary Gaussian trajectories. Within a noise-dominated regime, we compute the energetic deviation from the target STA outcome and its fluctuations, together with the fidelity to the target evolution and the purity loss of the reduced state, for vacuum and coherent initial states. Combining these observables produces a thermodynamic-uncertainty-type tradeoff that links achievable precision to an irreducible loss of purity set by the clock precision and the protocol sensitivity. Full article

The harmonic equivalent method is a non-perturbative approach to nonlinear vibration issues, aiming to create linearly coupled systems from coupled vibrations. However, there is still much to be discovered about managing interconnected nonlinear components. This paper examines the nonlinear components of a fractal-connected system and offers suggestions. This paper explores insights into the principles and uses of nonlinear systems in science and engineering by investigating the dynamic behavior of a connected cubic–quintic damping fractal system analytically using an innovative approach to analytical examination. A two-scale transformation and reformulation of the system into fractal form simplify its governing equations for dynamic and stability analysis. Two analytical scopes are presented: one decouples nonlinear systems using weighted averaging functions, and the other converts even nonlinearities into odd terms using El-Dib’s frequency formulas for linear representation, enabling an equivalent linear representation of the system. The resilience of the decoupled system is verified by numerical simulations using Mathematica, which shows high agreement and minimal relative errors. It also accurately reflects dynamic behavior. Additionally, the work uses the bridging techniques of El-Dib and Elgazery to convert a linear damping fractal coupled system into a classical continuous-space form. A scaling fractal factor is made possible by re-expressing the fractal structure using pseudo-dimensional parameters. The linearly linked damping system has an exact analytical solution. The paper provides valuable insights into the design and control of coupled nonlinear oscillatory systems by validating analytical solutions through numerical simulations using Mathematica. Full article

Screw compressors are critical equipment in oil and gas production and transportation, where efficiency losses caused by rotor geometry, inlet pressure pulsations, and harsh climatic conditions can accumulate into substantial annual energy penalties and reliability degradation. This study provides a quantitative assessment of these coupled effects within a unified multiphysics framework that combines time-accurate transient CFD simulations based on a fixed Cartesian immersed-boundary formulation with a climate-calibrated offline physics-based digital twin—functioning as a digital shadow with one-way data flow from archival SCADA records—a reduced-order seasonal model with no real-time updating, calibrated against a full calendar year of SCADA records and validated against a held-out cold-season dataset (October–December 2022, T_amb = −15 to +8 °C); summer-period predictions rely on calibrated extrapolation beyond the validation window—an integration not previously demonstrated for oil-flooded screw compressors. Two rotor profile configurations (Type A and Type B) were analyzed to quantify geometry-driven differences in static pressure distribution, leakage tendency, and pulsation sensitivity. Transient suction conditions were modeled using harmonic and quasi-random inlet pressure disturbances to evaluate pressure amplification, phase lag, leakage intensification, and efficiency degradation. Seasonal performance was assessed by integrating temperature-dependent gas properties, oil viscosity behavior, and external heat transfer into an annual climatic load framework. The results show that inlet oscillations are amplified inside the chambers (pressure amplification factor П_p ≈ 1.95; П_p up to 2.3 under quasi-random excitation), reducing mass flow and volumetric efficiency by 8–10% and decreasing polytropic efficiency from 0.78 to 0.69–0.71, while increasing leakage by up to 27% and raising peak contact pressures to 167–171 MPa. Seasonal variability (+30 to −30 °C) increased suction density by 38% but raised drive power by ~9% due to viscosity-driven mechanical losses, producing an energy penalty up to 10.8% and an estimated annual additional consumption of approximately 186 MWh per compressor, decomposed as: cold-season contribution ~113 MWh (±10 MWh, directly field-validated against October–December 2022 SCADA data) and summer-season contribution ~51 MWh (calibrated extrapolation; additional uncertainty unquantified and not included in the ±10 MWh bound). The full annual figure of 186 MWh should be interpreted as a model-based estimate rather than a fully validated result. These findings demonstrate that rotor design optimization and mitigation of nonstationary suction effects, coupled with climate-aware offline physics-based digital shadow operation, represent high-priority levers for improving efficiency and reducing energy penalties in field conditions; reliability implications require further validation against summer-season field measurements. Full article

Efficient energy harvesting from open-channel flows offers a sustainable solution for powering distributed sensing systems in water infrastructure. This study investigates a piezoelectric wake-excited membrane vortex-induced vibration (VIV) energy harvester through a combined numerical and mechanical approach. The device features an upstream cylindrical bluff body that generates a periodic vortex street, exciting a downstream flexible membrane equipped with surface-mounted piezoelectric patches. A one-way coupled CFD–FEM framework implemented in ANSYS was employed to assess the effects of membrane length, material stiffness, and flow conditions on hydrodynamic loading, structural deformation, and deformation power. Results show that membrane length mainly affects oscillation amplitude and force levels, whereas material stiffness has a stronger influence on membrane deformation and RMS mechanical power. Among the investigated materials, low-stiffness polyethylene yields the highest deformation power, while none of the analysed configurations reaches a full lock-in condition within the explored parameter range. Complementary mechanical analysis revealed that the stiffness of commercial piezoelectric patches significantly reduces local strain, thereby constraining the practically harvestable energy in the present baseline configuration. Spectral power density analysis identified the dominant shedding frequency and its harmonics, confirming that the flow response is governed by a coherent periodic excitation. These findings highlight key design trade-offs in wake-excited membrane harvesters and provide useful guidance for the future optimisation of self-powered hydraulic monitoring systems. Full article

An integrated nonlinear dynamic model was developed to investigate resonance in a four-cylinder engine mounted on a viscoelastic foundation. A coupled lumped-parameter formulation captures vertical and torsional responses under unbalanced inertial forces, combustion torque, and stochastic base excitation. Time-domain simulations show that at low rotational speeds the vertical displacement reaches transient amplitudes before converging to periodic oscillations, whereas higher excitation speeds reduce steady-state amplitudes. Torsional motion exhibits initial angles near 0.05 rad that decay below 0.01 rad in steady state, with further reduction at higher speeds. Frequency-domain analysis indicates that vibration energy is concentrated in engine-order harmonics between approximately 8 and 50 Hz, while components above 60 Hz are strongly attenuated, yielding a dynamic range exceeding 50 dB. Finite element modal analysis identifies the first four structural modes between 18 Hz and 666 Hz, revealing an increasingly dominant overall translational mode and a localized directional behavior at higher frequencies. A high-dimensional kernel density spectrogram integrates modal and spectral features to map resonance regions. Results indicate that increasing rotational excitation enhances inertial stiffening, systematically reduces displacement amplitudes, and preserves bounded periodic dynamics without instability. Full article