Search Results (26)

Virtual synchronous generator (VSG) control has been increasingly utilized for the grid integration of the voltage source inverter (VSI). Under large disturbances, such as voltage sags and grid faults, the VSG synchronization dynamic is highly nonlinear and cannot be evaluated by small-signal-based approaches. Conventionally, the equal area criterion (EAC) is utilized to analyze the transient stability of a synchronous machine or a VSG. However, it is found that the EAC is only valid under special scenarios when the damping effect is ignored. In this case, the EAC will provide conservative predictions and therefore put stringent requirements on the fault-clearing time. This paper reveals that the motion of a pendulum is essentially the same as the VSG swing equation. Due to this, the phase portrait approach, which was used to predict the pendulum motion, can be similarly applied for the VSG transient stability study. Based on the analogical phase portrait analysis, a damping coefficient tuning guideline is proposed, which always guarantees the synchronization stability as long as an equilibrium exists. The aforementioned theoretical findings are finally verified through a grid-connected VSG under the hardware-in-loop (HIL) environment. Full article

Several challenges hinder accurate and physically consistent dynamic parameter estimation in power systems, particularly under scenarios involving limited measurements, strong system nonlinearity, and high variability introduced by renewable integration. Although data-driven methods such as Physics-Informed Neural Networks (PINNs) provide a promising direction, they often suffer from poor generalization and training instability when faced with complex dynamic regimes. To address these challenges, we propose a Residual Physics-Informed Neural Network (Res-PINN) framework, which integrates a residual neural architecture with the swing equation to enhance estimation robustness and precision. By replacing the traditional multilayer perceptron (MLP) in PINN with residual connections and injecting normalized time into each network layer, the proposed model improves temporal awareness and enables stable training of deep networks. A physics-constrained loss formulation is employed to estimate inertia and damping parameters without relying on large-scale labeled datasets. Extensive experiments on a 4-bus, 2-generator power system demonstrate that Res-PINN achieves high parameter estimation accuracy across various dynamic conditions and outperforms traditional PINN and Unscented Kalman Filter (UKF) methods. It also exhibits strong robustness to noise and low sensitivity to hyperparameter variations. These results show the potential of Res-PINN to bridge the gap between physics-guided learning and practical power system modeling and parameter identification. Full article

It is vital to study the stability of power systems under small perturbations to prevent blackouts. This study presents a load-shedding strategy that has been incorporated within the swing equation to reduce instability and delay the onset of chaotic dynamics. The objective of this study was to identify the minimal load reductions required after disturbances to maintain the frequency above a critical value. Analytical techniques such as eigenvalue analysis and perturbation methods can also be supported with numerical simulations using bifurcation diagrams, Lyapunov exponents, and the Simulink model. When compared to the conventional stepwise load-shedding method, the proposed approach allows for dynamic adjustments and presents a 49% increase in stable regions and a 45% reduction in recovery time. Performance was also analysed under different damping, inertia, and load scenarios. These results suggest that the strategy demonstrated in this research provides a robust and computationally practical solution for modern power system applications. Full article

The swivel system of a hydraulic excavator is susceptible to pressure impact during start and stop, which significantly impacts the service life of the excavator. In this investigation into how varying speeds affect the dynamic characteristics of a swing motor’s buffer relief valve (BRV), the AMESim simulation model of the whole swing motor was established, and its validity was confirmed through experimental testing. The pressure overshoot rate and start–stop impact time of the BRV of a swing motor at 1000 rpm, 1500 rpm, and 2000 rpm, under different spring stiffnesses, were analyzed. Based on the mathematical model of the BRV, the influence of the main structural parameters of the BRV on its dynamic characteristics were analyzed using an AMESim simulation model of the whole swing motor. The results show that an increase in the rotational speed of the electric motor, while maintaining a constant spring stiffness, affects the pressure overshoot rates of both the buffer relief valve of the swing motor inlet (BRVSMI) and the buffer relief valve of the swing motor outlet (BRVSMO); specifically, when the set pressure is established at 20 MPa, the pressure overshoot rate is observed to be higher, and the start–stop impact time exceeds 25 MPa. During the start phase of the swing motor, the start impact time for the BRVSMI remains relatively constant at approximately 2.5 s, with the pressure overshoot rate stabilizing at around 0.8. Conversely, in the stop phase of swing motor, both the stop impact time and the pressure overshoot rate of the BRVSMO exhibit variability in their response to the structural parameters of the BRV. Under conditions of comparatively high pressure, it is recommended to increase the diameter of the spool damping hole, the mass of the valve core, and the viscous damping coefficient, while simultaneously reducing the guide rod diameter of the buffer plunger, as these modifications can effectively enhance the start–stop impact time and mitigate the pressure overshoot rate. Full article

The proper design and configuration of the swing drive mechanism of a hydraulic excavator are crucial to improve energy consumption and efficiency and ensure operational stability. This paper analyzes the influence of the relationship between the parameters of a hydraulic motor and a reducer, which form the integrated transmission of a swing drive, the dynamic characteristics of a hydraulic excavator on loading, and the dynamic stability of the drive. The analysis deals with an excavator model that has the same parameters of the kinematic chain members, the same parameters of the upper structure drive mechanisms, and two variants of the swing drive that, with different integrated transmission parameters, provide the upper structure with the identical number of revolutions and equal rotating moment. One swing drive variant possesses an integrated transmission with a hydraulic motor with a low specific flow and a reducer with a high transmission ratio, while the other drive variant has the opposite parameters. Understanding this relationship is essential for optimizing the design of excavators to achieve better performance and dynamic stability under varying operational conditions. As an example, this paper provides the analysis results regarding the influence of the relationship between the parameters of the integrated transmission hydraulic motor and reducer on the loading and dynamic stability of the swing drive in a tracked hydraulic excavator of 100,000 kg in mass and 4.4 m³ in loading bucket volume, as obtained from the developed dynamic mathematical models of the excavator using the MSC ADAMS program. The results indicate that the dynamic loads on the swing drive’s axial bearing are higher in the variant with a low-specific-flow motor and high transmission ratio reducer during the acceleration and deceleration phases. However, this configuration demonstrated better dynamic stability, with lower oscillation amplitudes and shorter damping times compared to the variant with a high-flow motor and low transmission ratio. Those findings provide valuable criteria for the optimal synthesis of swing drive mechanisms in large hydraulic excavators using multi-criteria optimization methods. Full article

The cooperative transportation of a cable-suspended load by two unmanned rotorcraft is analyzed. Initially, the equations describing a system composed of three point masses and two rigid cables are derived. The model is then linearized about the hovering condition, and analytical expressions are derived to describe the eigenstructure of the open-loop system. Thanks to the specific parameterization of the problem, the different dynamic modes are outlined and discussed within an analytical framework. A novel controller is designed to enable the UAVs in the formation to perform trajectory tracking, maintain formation geometry, and stabilize payload swing simultaneously. A preliminary investigation of closed-loop stability is conducted using a linear approach. Validation is performed in a realistic simulation scenario where two drones are modeled as rigid bodies under the effect of external disturbances and rotor-generated forces and moments, as obtained by Blade Element Theory. The proposed method demonstrates relative simplicity and significantly improves the flying qualities of delivery operations while minimizing hazardous payload oscillations and reducing energy demand. Full article

The ability to power low-power devices and sensors has drawn a great deal of interest to energy harvesting from ambient vibrations. The application of variable-length pendulum systems in conjunction with piezoelectric or electromagnetic energy-harvesting devices is examined in this thorough analysis. Because of their changeable length, such pendulums may effectively convert mechanical vibrations into electrical energy. This study covers these energy-harvesting systems’ basic theories, design concerns, modeling methods, and performance optimization strategies. This article reviews several studies that look at dynamic models, the effects of damping coefficients, device designs, and excitation parameters on energy output. The advantages and disadvantages of piezoelectric and electromagnetic coupling techniques are demonstrated by comparative research. This review also looks at technical advances and future research prospects in variable-length, pendulum-based energy harvesting. An expanded model for an energy harvester based on a variable-length pendulum derived from the modified, swinging Atwood machine is more specifically presented. This model’s numerical simulations, estimated current and voltage outputs, and produced power from the electromagnetic and piezoelectric devices integrated at various points in a 4-DOF variable-length pendulum model all indicate encouraging results. This necessitates extra study, changes, and optimizations to improve the usefulness of the proposed model. Finally, important dynamic models on developing variable-length, pendulum-based energy harvesters for usage in a range of applications to create sustainable energy are summarized. Full article

During the walking process of lower limb exoskeleton rehabilitation robots, inevitable collision impacts will occur when the swinging leg lands on the ground. The impact reaction force from the ground will induce vibrations in the entire robot’s body from bottom to top. To address this phenomenon, considering the limitations of traditional active compliance and passive compliance methods, a variable stiffness and damping actuator (VSDA) leg structure using a magnetorheological damper (MRD) is proposed. Firstly, experimental methods are used to obtain the ground reaction force (GRF) exerted on a normal person during walking. Then, a mathematical model of the VSDA leg structure is constructed, and its working principle is analyzed. Based on human mass and dimensions, a 3D model is designed and selected. Finally, a simulation model is built in the MATLAB/Simulink environment using the fuzzy switch damping control strategy to simulate the acceleration and displacement of the human body under sinusoidal and random excitations. The results indicate that under sinusoidal excitation, employing fuzzy switch damping control optimizes human displacement by 72.47% compared to the high stiffness and high damping system, and by 16.95% compared to the switch damping system. Human acceleration is optimized by 52.09% compared to the high stiffness and high damping system, and by 25.2% compared to the switch damping system. Under random excitation, adopting fuzzy switch damping control optimizes human displacement by 59.09% compared to the high stiffness and high damping system, and by 21.74% compared to the switch damping system. Human acceleration is optimized by 78.74% compared to the high stiffness and high damping system, and by 31.66% compared to the switch damping system. This validates the VSDA design structure and control method, demonstrating certain advantages in improving the compliance and stability of lower limb exoskeleton rehabilitation robots. Full article

Accurate knowledge of oscillation parameters (i.e., frequency, amplitude, phase, and damping factor) is crucial for control strategies of power systems under power swing. This paper presents a method for the parameter estimation of power system oscillation signals under power swing based on Clarke–DFT. The proposed method provides accurate parameter estimation of damped sinusoidal signals for both balanced and unbalanced systems, which performs well even in the presence of harmonics. In the meantime, the negative frequency components in the spectra of the damped sinusoidal signals, which are caused by system imbalance, are calculated accurately using complex-valued interpolated DFT. To verify the performance of the proposed method, simulations are performed under balanced and unbalanced conditions. The results of the simulations confirm the effectiveness of the proposed method either in unbalanced or harmonic conditions. Full article

A method is proposed to estimate the swing state of a suspended payload in multirotor drone delivery scenarios. Starting from the equations of motion of the coupled slung load system, defined by two point masses interconnected by a rigid link, a recursive algorithm is developed to estimate cable swing angle and rate from acceleration measurements available from an onboard Inertial Measurement Unit, without the need for extra sensors. The estimation problem is addressed according to the Extended Kalman Filter structure. With respect to the classical linear formulation, the proposed approach allows for improved estimation accuracy in both stationary and maneuvering flight. As an additional contribution, filter performance is enhanced by accounting for aerodynamic disturbance force, which largely affects the estimation accuracy in windy flight conditions. The validity of the proposed methodology is demonstrated as follows. First, it is applied to an octarotor platform where propellers are modeled according to blade element theory and the load is suspended by an elastic cable. Numerical simulations show that estimated swing angle and rate represent suitable feedback variables for payload stabilization, with benefits on flying qualities and energy demand. The algorithm is finally implemented on a small-scale quadrotor and is investigated through an outdoor experimental campaign, thus proving the effectiveness of the approach in a real application scenario. Full article

The effect of microchannel height on acoustic streaming velocity and capacitive micromachined ultrasound transducer (CMUT) cell damping was investigated. Microchannels with heights ranging from 0.15 to 1.75 mm were used in experiments, and computational microchannel models with heights varying from 10 to 1800 micrometers were simulated. Both simulated and measured data show local minima and maxima of acoustic streaming efficiency associated with the wavelength of the `bulk acoustic wave excited at 5 MHz frequency. Local minima occur at microchannel heights that are multiples of half the wavelength (150 μm), which are caused by destructive interference between excited and reflected acoustic waves. Therefore, microchannel heights that are not multiples of 150 μm are more favorable for higher acoustic streaming effectiveness since destructive interference decreases the acoustic streaming effectiveness by more than 4 times. On average, the experimental data show slightly higher velocities for smaller microchannels than the simulated data, but the overall observation of higher streaming velocities in larger microchannels is not altered. In additional simulation, at small microchannel heights (10–350 μm), local minima at microchannel heights that are multiples of 150 μm were observed, indicating the interference between excited and reflected waves and causing acoustic damping of comparatively compliant CMUT membranes. Increasing the microchannel height to over 100 μm tends to eliminate the acoustic damping effect as the local minima of the CMUT membrane swing amplitude approach the maximum value of 42 nm, which is the calculated amplitude of the freely swinging membrane under the described conditions. At optimum conditions, an acoustic streaming velocity of over 2 mm/s in a 1.8 mm-high microchannel was achieved. Full article

This paper presents a simplified mathematical model of a pumped hydrofoil (PH)—a surfboard elevated above water surface and connected to a tandem of hydrofoils by a strut. The PH is operated by a rider who stands on the surfboard and produces swinging up-and-down motions resulting in forward propulsion of the device. In the present paper, the description of the vertical motion of the PH is reduced to a linear oscillator excited by an oscillating mass coupled with the requirement that the weight is supported by dynamic lift of the foil(s). The inertial and damping influence of the hydrofoil(s) is accounted for by expanding unsteady lift force on the foil(s) in terms of kinematic parameters. The restoring term of the oscillator is associated with the phenomenon of automatic stabilization of shallowly submerged hydrofoils. The latter effect manifests itself in that when a hydrofoil approaches free surface, its lift decreases, and when it moves away from free surface, its lift increases. The analytical solution of the pumping foil mass-spring type forced oscillations equation allows one to calculate the flapping motion of the foil(s) and, thereafter, the period-averaged thrust generated by the PH. The resulting speed has been estimated on an assumption that the device enters its cruising mode when the thrust becomes equal to the drag, the latter comprising viscous, wave, and induced drag components. The model under discussion allows one to relate the main parameters of the system to its performance and, hopefully, provides further insight into the pumped hydrofoil phenomenon, its design methodology, and operation strategy. The review part of the paper focuses on two aspects of the problem: hydrodynamic behavior of the hydrofoil(s) in proximity to free water surface and their propulsion due to oscillations. Full article

This paper presents a current literature review (from the years 2017–2022) on issues related to the application of power system stabilizers (PSSs) for damping electromechanical swings in power systems (PSs). After the initial selection of papers found in the databases used, over 600 publications were qualified for this review, of which 216 were subjected to detailed analysis. In the review, issues related to the following problems are described: applications of classic PSSs, applications of new stabilizer structures based on new algorithms (including artificial intelligence), development of new methods for tuning PSSs, and operation of PSSs in PSs with high power generation by renewable sources. Describing individual papers, the research methods used by the authors (simulations, measurement methods, and a combination of both) are specified, attention is paid to the waveforms presented in the papers, and reference is made to the types of PSs in which PSSs (large multimachine, reflecting real systems, smaller standard multimachine New-England type, and simplest single-machine) operate. The tables contain detailed comments on the selected papers. The final part of the review presents general comments on the analyzed papers and guidelines for future PS stability studies. Full article

In previous studies, the meshing force of a gear system is usually treated as being uniformly distributed for the convenience of analysis. In practical applications, however, it is nonuniformly distributed along the line of action due to machining errors, assembly errors, misalignment errors, etc. When a nonuniformly distributed meshing force is coupled with the shaft deformation, dynamic center distance, and time-varying meshing stiffness, the transmission performance of the gear system will be seriously degraded. Therefore, a nonuniformly distributed meshing force cannot be ignored when considering the gear systems used in complicated working conditions. In this study, the gear’s nonuniformly distributed meshing force is analyzed. Then, an 18 degrees-of-freedom bending-torsion-swing-coupled dynamic model of a pair of involute spur gears is put forward. Through this model, the coupling relationship between the nonuniformly distributed meshing force, shaft bending deformation, and dynamic center distance is accurately described. The influence of meshing frequency, stiffness excitation, damping, and error excitation on the nonlinear dynamic characteristics of the gear system was researched through bifurcation diagrams, phase diagrams, Poincaré maps, and time-domain diagrams. Various complicated nonlinear dynamic behaviors, such as quasiperiodic motion, bifurcation, chaotic motion, and chaotic banding, are revealed. Reasonable parameter ranges that guarantee the gear system is in a stable motion were extracted. By evading complicated nonlinear dynamic behavior, the transmission performance of a gear system was improved. This research will contribute to reducing the vibration and noise of gear systems. Full article

To achieve a more sustainable supply of electricity and reduce dependency on fuels, the application of renewable energy sources-based distribution systems (DS) is stimulating. However, the intermittent nature of renewable sources reduces the overall inertia of the power system, which in turn seriously affects the frequency stability of the power system. A virtual synchronous generator can provide inertial response support to a DS. However, existing active power controllers of VSG are not optimized to react to the variation of frequency changes in the power system. Hence this paper introduces a new controller by incorporating GA-ANFIS in the active power controller to improve the performance of the VSG. The advantage of the proposed ANFIS-based controller is its ability to optimize the membership function in order to provide a better range and accuracy for the VSG responses. Rate of change of frequency (ROCOF) and change in frequency are used as the inputs of the proposed controller to control the values of two swing equation parameters, inertia constant (J) and damping constant (D). Two objective functions are used to optimize the membership function in the ANFIS. Transient simulation is carried out in PSCAD/EMTDC to validate the performance of the controller. For all the scenarios, VSG with GA-ANFIS (VOFIS) managed to maintain the DS frequency within the safe operating limit. A comparison between three other controllers proved that the proposed VSG controller is better than the other controller, with a transient response of 22% faster compared to the other controllers. Full article