Search Results (289)

In the vector control of permanent magnet synchronous motor (PMSM), non-periodic disturbances such as cross-coupling between axes and variations in electrical parameters, along with periodic harmonic disturbances caused by inverter nonlinearities and magnetic field harmonics, influence the dq-axis currents. To address these challenges, this paper proposes a current loop disturbance rejection strategy based on a Resonant Control Periodic Disturbance Observer (RC-PDOB). First, this paper constructs a disturbance observer-based current loop decoupling model that mitigates dq-axis current coupling due to parameter variations and reduces the impact of non-periodic disturbances. Then this paper introduces proportional–resonant terms into the disturbance observer to suppress the 6th and 12th harmonics of the dq-axis, thereby reducing periodic current disturbances. This paper analyzes the disturbance rejection mechanism of RC-PDOB in detail and presents the design methodology and stability criteria of the proposed observer. Finally, experimental results demonstrate the effectiveness of the proposed approach. Full article

This paper addresses the challenges encountered by grid-connected photovoltaic (PV) systems, including the stochastic behavior of the system, harmonic distortion, and variations in grid impedance. To this end, an in-depth technical and pedagogical analysis of three linear multivariable current control strategies is performed: proportional-integral (PI), proportional-resonant (PR), and deadbeat (DB). The study contributes to theoretical formulations, detailed system modeling, and controller tuning procedures, promoting a comprehensive understanding of their structures and performance. The strategies are investigated and compared in both the rotating ($dq$) and stationary ($\alpha \beta$) reference frames, offering a broad perspective on system behavior under various operating conditions. Additionally, an in-depth analysis of the PR controller is presented, highlighting its potential to regulate both positive- and negative-sequence components. This enables the development of more effective and robust tuning methodologies for steady-state and dynamic scenarios. The evaluation is conducted under three main conditions: steady-state operation, transient response to input power variations, and robustness analysis in the presence of grid parameter changes. The study examines the impact of each controller on the total harmonic distortion (THD) of the injected current, as well as on system stability margins and dynamic performance. Practical aspects that are often overlooked are also addressed, such as the modeling of the inverter and photovoltaic generator, the implementation of space vector pulse-width modulation (SVPWM), and the influence of the output LC filter capacitor. The control structures under analysis are validated through numerical simulations performed in MatLab^® software (R2021b) using dedicated computational routines, enabling the identification of strategies that enhance performance and ensure compliance of grid-connected photovoltaic systems. Full article

The study of vibration characteristics and suppression methods in integrated electric drive systems of electric vehicles is of critical importance. To investigate these characteristics, both current harmonics within the motor and nonlinear factors within the drivetrain were considered. A 17-degree-of-freedom nonlinear torsional–planar dynamic model was developed, with electromagnetic torque and output speed as coupling terms. The model’s accuracy was experimentally validated, and the system’s dynamic responses were analyzed under different working conditions. To mitigate vibrations caused by torque ripple, a coordinated control strategy was proposed, combining a quasi-proportional multi-resonant (QPMR) controller and a full-frequency harmonic controller (FFHC). The results demonstrate that the proposed strategy effectively suppresses multi-order current harmonics in the driving motor, reduces torque ripple by 45.1%, and enhances transmission stability. In addition, the proposed electromechanical coupling model provides valuable guidance for the analysis of integrated electric drive systems. Full article

LCL (inductor–capacitor–inductor) filters are widely used in grid-connected inverters, particularly in electric vehicle (EV) battery-to-grid systems, for harmonic suppression but introduce resonance issues that compromise stability. This study presents a novel sensorless active damping strategy based on μ-synthesis control for EV batteries connected to the grid via LCL filters, eliminating the need for additional current sensors while preserving harmonic attenuation. A comprehensive state–space and process noise model enables accurate capacitor current estimation using only grid current and point-of-common-coupling (PCC) voltage measurements. The proposed method maintains robust performance under ±60% LCL parameter variations and integrates a proportional-resonant (PR) current controller for resonance suppression. Hardware-in-the-loop (HIL) validation demonstrates enhanced stability in dynamic grid conditions, with total harmonic distortion (THD) below 5% (IEEE 1547-compliant) and current tracking error < 0.06 A. Full article

The research demonstrates, through simulation and laboratory validation, the development of a low-voltage DC-link (LVDC) back-to-back converter system that enables multi-frequency power transfer. The system operates in two distinct modes, which include a three-phase grid-connected converter transferring fundamental and 5th and 7th harmonic power to a three-phase residential inverter supplying a clean 50 Hz load and another mode that uses a DC–DC buck–boost converter to integrate a battery storage unit for single-phase load supply. The system allows independent control of each harmonic component and maintains a clean sinusoidal voltage at the load side through DC-link isolation. The LVDC link functions as a frequency-selective barrier to suppress non-standard harmonic signals on the load side, effectively isolating the multi-frequency power grid from standard-frequency household loads. The proposed solution fills the gap between the multi-frequency power systems and the single-frequency loads because it allows the transfer of total multi-frequency grid power to the traditional household loads with pure fundamental frequency. Experimental results and simulation outcomes demonstrate that the system achieves high efficiency, robust harmonic isolation, and dynamic adaptability when load conditions change. Full article

Due to the complex mineral composition, low clay content, and strong heterogeneity of the mixed sedimentary shale in the Xinjiang Salt Lake Basin, the wettability characteristics of the reservoir and their influencing factors are not yet clear, which restricts the evaluation of oil-bearing properties and the identification of sweet spots. This paper analyzed mixed sedimentary shale samples from the Lucaogou Formation of the Jimsar Sag and the Fengcheng Formation of the Mahu Sag. Methods such as petrographic thin sections, X-ray diffraction, organic matter content analysis, and argon ion polishing scanning electron microscopy were used to examine the lithological and mineralogical characteristics, geochemical characteristics, and pore space characteristics of the mixed sedimentary shale reservoir. Alternating imbibition and nuclear magnetic resonance were employed to quantitatively characterize the wettability of the reservoir and to discuss the effects of compositional factors, lamina types, and pore structure on wettability. Research findings indicate that the total porosity, measured by the alternate imbibition method, reached 72% of the core porosity volume, confirming the effectiveness of alternate imbibition in filling open pores. The Lucaogou Formation exhibits moderate to strong oil-wet wettability, with oil-wet pores predominating and well-developed storage spaces; the Fengcheng Formation has a wide range of wettability, with a higher proportion of mixed-wet pores, strong heterogeneity, and weaker oil-wet properties compared to the Lucaogou Formation. TOC content has a two-segment relationship with wettability, where oil-wet properties increase with TOC content at low TOC levels, while at high TOC levels, the influence of minerals such as carbonates dominates; carbonate content shows an “L” type response to wettability, enhancing oil-wet properties at low levels (<20%), but reducing it due to the continuous weakening effect of minerals when excessive. Lamina types in the Fengcheng Formation significantly affect wettability differentiation, with carbonate-shale laminae dominating oil pores, siliceous laminae contributing to water pores, and carbonate–feldspathic laminae forming mixed pores; the Lucaogou Formation lacks significant laminae, and wettability is controlled by the synergistic effects of minerals, organic matter, and pore structure. Increased porosity strengthens oil-wet properties, with micropores promoting oil adsorption through their high specific surface area, while macropores dominate in terms of storage capacity. Wettability is the result of the synergistic effects of multiple factors, including TOC, minerals, lamina types, and pore structure. Based on the characteristic that oil-wet pores account for up to 74% in shale reservoirs (mixed-wet 12%, water-wet 14%), a wettability-targeted regulation strategy is implemented during actual shale development. Surfactants are used to modify oil-wet pores, while the natural state of water-wet and mixed-wet pores is maintained to avoid interference and preserve spontaneous imbibition advantages. The soaking period is thus compressed from 30 days to 3–5 days, thereby enhancing matrix displacement efficiency. Full article

Focusing on the common problems of phase-locked loop dependence, multiple current sensor requirements, a large number of controllers, and complex settings in traditional parallel active power filter (APF) control methods, this paper proposes a harmonic compensation control strategy based on an improved proportional resonant (PR) controller. The proposed method introduces an instantaneous power theory to construct a reference current model, which relies solely on grid voltage and current signals, does not require load-side current detection and phase-locked loop modules, and effectively simplifies the sensor configuration and system structure. At the same time, compared with the traditional solution that requires PR modules to be configured for each order of harmonics, this study only uses one set of PR controllers for fundamental current tracking, which has advantages in terms of compactness and computing resource occupation. To guide the controller parameter setting, this paper systematically discusses the influence of changes in K_p and K_r on pole distribution and dynamic performance based on discrete domain modeling and root locus analysis methods. The results were verified on the MATLAB/Simulink simulation platform and the 1 kVA experimental platform and compared with the traditional control method that requires the use of phase-locked loops (PLLs), load current sensors, and multiple PR controllers. The simulation and experimental results show that the proposed method has achieved a certain degree of optimization in terms of harmonic suppression effect, dynamic response performance, and system structure complexity. Full article

This paper presents a modern spectroscopic characterization of the synthetic oil from oil sands of Beke, Munaily-Mola, and Dongeleksor. The pyrolysis process was carried out at temperatures up to 580 °C with a controlled heating rate, and the products obtained were analyzed using Fourier transform infrared spectroscopy (FTIR), gas chromatography–mass spectrometry (GC–MSD), and nuclear magnetic resonance (NMR) spectroscopy. The FTIR spectra showed a predominance of aliphatic hydrocarbons in the sample from Munaily-Mola synthetic oil, while the content of aromatic compounds was higher in the sample from Beke. GC–MSD analysis revealed significant differences in the distribution of hydrocarbons between the samples, with the Munaily-Mola sample containing a higher proportion of heavy hydrocarbons. NMR spectroscopy provided additional information about the structural composition of the extracted oil. The results indicate the potential of pyrolysis as an effective method for processing oil sands, while the composition of the product varies depending on the geological origin of the raw materials. These findings provide valuable information for optimizing oil sands processing technologies and improving the efficiency of synthetic oil production. Full article

High oil content in breaded fried small yellow croaker (BFYC) was reduced using composite batter gels consisting of tapioca starch, wheat flour, and different concentrations of cassia gum (CG; 0%, 0.2%, 0.4%, 0.6%, 0.8%, 1%). The effects of CG on the oil absorption capacity of BFYC and potential mechanisms were investigated. Dynamic rheological analysis revealed that CG addition could enhance the viscoelasticity of the batter by increasing its storage modulus and loss modulus. Furthermore, FTIR and X-ray diffraction results demonstrated that CG interacts with starch through noncovalent interactions, increasing the relative crystallinity from 9.29% to 16.49%, which promoted the formation of a gel layer. This structural improvement effectively inhibited oil absorption. Differential scanning calorimetry analysis showed that within the 0–0.8% CG range, the batter’s denaturation temperature increased from 78.23 °C to 82.08 °C with higher CG concentrations, indicating prolonged gelatinization and enhanced thermal stability that further reduced oil penetration. Low-field nuclear magnetic resonance analysis revealed that CG increased the proportion of tightly bound and weakly bound water in the batter, thereby improving water retention capacity and reducing moisture loss during frying. Microscopic structural observations and Sudan Red-staining tests confirmed that at 0.8% CG concentration, the crust exhibited the lowest porosity with approximately 40% reduction in surface fat content compared to the control group. In conclusion, CG addition significantly improves batter properties and reduces oil content in fried products, providing theoretical support for the development of low-fat fried foods. Full article

Vehicle-to-home (V2H) technology enables electric vehicles (EVs) to supply power to residential loads, offering enhanced energy self-sufficiency and backup capabilities. Accurate voltage regulation is essential in such systems, especially under nonlinear and time-varying load conditions. The control method for three-phase four-wire (3P4W) converters plays a vital role in addressing these challenges. In the control configuration of such systems, the non-ideal proportional-resonant (PR) controller stands out due to its ability to reject periodic disturbances. However, the comprehensive study on the discretization of this controller for digital implementation in 3P4W systems has not been available in the literature to date. This paper presents a comparative study of several discretization methods for non-ideal PR controllers. The continuous-time complete transfer function of the integral term of non-ideal PR controllers is discretized using techniques such as Forward Euler, Backward Euler, Tustin, Zero-Order Hold, and Impulse Invariance. Additionally, the discretization methods based on two discrete integrators for the non-ideal PR controller, such as Forward Euler and Backward Euler, Backward Euler and Backward Euler plus computational delay, and Tustin and Tustin, are also evaluated. In the MATLAB/Simulink platform, through evaluating the performance of the non-ideal PR controllers, which are discretized using the above discretization methods, in controlling the output voltage of the 3P4W converter in the V2H application under nonlinear load scenarios, including substantial and sudden changes in load, the discretization method Backward Euler and Backward Euler plus delay is recommended. Full article

This paper investigates the system architecture and circuit topology of grid-connected inverters with embedded energy storage (EES), encompassing their modulation strategies and control methodologies. A mathematical model for an EES grid-connected inverter is derived based on capacitor current feedback control, from which the expression for the inverter’s output impedance is obtained. Building on this foundation, this study analyzes the influence of control parameters—such as the proportional coefficient, resonant coefficient, and switching frequency—on the inverter’s output impedance. Subsequently, the stability of single and multiple inverter grid-connected systems under various operating conditions is assessed using impedance analysis and the Nyquist criterion. Finally, the validity of the stability analysis based on the established mathematical model is verified through simulations conducted on the Matlab/Simulink platform, where models for both a single inverter and a two-inverter grid-connected system are constructed. Full article

In this study, the Proportional and Derivative Controller (PD) is presented as a modified control that combines features of the Proportional Controller (P-Controller) and the Derivative Controller (D-Controller) to suppress the vibrations of the Smooth and Discontinuous Oscillator (SD). The investigated model has been derived as a one-degree-of-freedom. The frequency response equation of the controlled system has been obtained using the perturbation technique up to a second approximation. The influence of the P-Controller, the D-Controller, and the PD-Controller on the SD-Oscillator amplitude has been studied by plotting the time histories. The numerical and approximate simulation established that the PD-Controller can inhibit the system vibration. Finally, there is high closeness between the numerical solutions (from time histories) and the approximate solutions (from perturbation analysis). Full article

Many studies aim to suppress vibrations in vibrating dynamic systems, such as bridges, highways, and aircraft. In this study, we scrutinize the primary resonance of a cantilever beam excited by an external force via a proportional fractional-order derivative controller (PFD). The average method is used to obtain the approximate solution of the vibrating system. The stability of the control system is illustrated using the Routh–Hurwitz criterion. We investigate the performance of some chosen parameters of the studied system to generate response curves. The performance of the linear fractional feedback control is studied at different values of the fractional order. Full article

Achieving excellent speed control in permanent magnet synchronous motors (PMSMs) relies on the simultaneous suppression of both aperiodic and periodic disturbances. This paper presents an enhanced Active Disturbance Rejection Control (ADRC) strategy specifically designed to address these disturbances in single-rotor compressors (SRCs). To achieve simultaneous suppression, a Recursive Gauss–Newton (RGN) algorithm is implemented in parallel with the conventional extended state observer (ESO) to enhance the ADRC framework. The RGN algorithm iteratively estimates the amplitude and phase information of periodic disturbances, while the ESO primarily observes the system’s aperiodic disturbances. In contrast to existing methods, the proposed angle-based approach demonstrates superior performance during speed transients. Detailed convergence and decoupling analyses are provided to facilitate parameter tuning. The effectiveness of the proposed method is validated through simulations and experiments conducted on a 650 W SRC, demonstrating its superiority over proportional–integral (PI) control, conventional ADRC, and quasi-resonant controller-based ADRC (QRC-ADRC) under both steady-state and dynamic conditions. Full article

Thermal energy storage (TES) is likely to play a significant role in the decarbonisation of domestic heat, allowing consumers to shift their energy consumption away from peak demand periods and reducing overall strain on the grid. Phase change materials (PCMs) are a promising option for TES, in which energy can be stored in the latent heat of the melting of the PCM; these offer greater storage densities than sensible heat TES and have the benefit of releasing stored heat at a consistent temperature (the crystallisation temperature of the PCM). One of the key difficulties for PCM-based TES is state of charge (SoC) estimation (the estimation of the proportion of energy stored in the TES unit up to its maximum capacity), particularly during idle periods while the unit is storing heat. SoC estimation is key to the implementation of TES, as it enables the effective control of the units. The use of a resonator within the PCM for SoC estimation could potentially provide a global estimate of the SoC, since the resonator passes through the full depth of the PCM in the unit. The SoC could be inferred by measuring the vibrational response of the resonator under excitation, which varies depending on the melt state of the PCM. This paper presents findings from a test rig investigating this proposal, including discussions on the features required from the resonator response for SoC inference. Full article