Search Results (28)

Carbon deposits on the crown of engine pistons can markedly reduce combustion efficiency and shorten service life. Conventional cleaning techniques often fail to simultaneously ensure a high carbon removal efficiency and maintain optimal surface integrity. To enable efficient and precise carbon removal, this study proposes the application of hybrid laser cleaning—combining continuous-wave (CW) and pulsed lasers—to piston carbon deposit removal, and employs response surface methodology (RSM) for multi-objective process optimization. Using the N52B30 engine piston as the experimental substrate, this study systematically investigates the combined effects of key process parameters—including CW laser power, pulsed laser power, cleaning speed, and pulse repetition frequency—on surface roughness (Sa) and carbon residue rate (RC). Plackett–Burman design was employed to identify significant factors, the method of the steepest ascent was utilized to approximate the optimal region, and a quadratic regression model was constructed using Box–Behnken response surface methodology. The results reveal that the Y-direction cleaning speed and pulsed laser power exert the most pronounced influence on surface roughness (F-values of 112.58 and 34.85, respectively), whereas CW laser power has the strongest effect on the carbon residue rate (F-value of 57.74). The optimized process parameters are as follows: CW laser power set at 625.8 W, pulsed laser power at 250.08 W, Y-direction cleaning speed of 15.00 mm/s, and pulse repetition frequency of 31.54 kHz. Under these conditions, the surface roughness (Sa) is reduced to 0.947 μm, and the carbon residue rate (RC) is lowered to 3.67%, thereby satisfying the service performance requirements for engine pistons. This study offers technical insights into the precise control of the hybrid laser cleaning process and its practical application in engine maintenance and the remanufacturing of end-of-life components. Full article

The electrical grid is undergoing increasing integration of decentralized power sources connected to the low-voltage network. In this context, the concept of a microgrid has emerged as a system comprising small-scale energy sources, loads, and storage devices, coordinated to operate as a single controllable entity capable of functioning in either grid-connected or islanded mode. The microgrid may be organized in a centralized configuration, such as a master-slave scheme, wherein the centralized converter, i.e., the grid-forming converter (GFC), plays a pivotal role in ensuring system stability and control. This paper introduces a plug-in repetitive controller (RC) strategy tuned to even harmonic orders for application in a three-phase GFC, diverging from the conventional approach that focuses on odd harmonics. The proposed control is designed within a synchronous reference frame and is targeted at centralized AC microgrids, particularly during islanded operation. Simulation results are presented to assess the microgrid’s power flow and power quality, thereby evaluating the performance of the GFC. Additionally, the proposed control was implemented on a Texas Instruments TMS320F28335 digital signal processor and validated through hardware-in-the-loop (HIL) simulation using the Typhoon HIL 600 platform, considering multiple scenarios with both linear and nonlinear loads. The main results highlight that the RC improves voltage regulation, mitigates harmonic distortion, and increases power delivery capability, thus validating its effectiveness for GFC operation. Full article

This paper presents an enhanced bipolar control strategy for 400 Hz three-phase inverters in aviation ground power supplies, with a focus on maintaining symmetry in power output under unbalanced load conditions. The strategy integrates Linear Active Disturbance Rejection Control (LADRC) for robust positive sequence voltage regulation, Proportional Integral with repetitive control (PI + RC) for harmonic suppression in positive sequence currents, and a Quasi-Proportional Resonance (QPR) controller for negative sequence components in the static coordinate system. By doing so, it simplifies negative sequence control and combines PI + RC to improve the dynamic response and eliminate periodic errors. In the context of symmetry, the proposed strategy effectively reduces the total harmonic distortion (THD) and the three-phase current imbalance degree. Simulation results show significant improvements: under balanced loads, THD is reduced by 41.5% (from 1.95% to 1.14%) compared to traditional PI control; under single-phase and three-phase unbalanced loads, THD decreases by 52.7% (2.56% to 1.21%) and 48.1% (2.39% to 1.24%), respectively. The system’s settling time during load transients is shortened by over 30%, and the three-phase current imbalance degree is reduced by 60–70%, which validates the strategy’s effectiveness in enhancing power quality and system stability, thus restoring and maintaining the symmetry of the power output. Full article

In this paper, a discrete-time design of a fractional internal model-based repetitive controller with a sliding mode approach is presented for uncertain linear systems subject to repetitive trajectory and periodic disturbance. The proposed algorithm, named a fractional delay-based repetitive sliding mode controller (FD-RSMC), aims to enhance tracking accuracy, transient response, and robustness against parametric variations beyond what is offered by conventional repetitive controllers. First, a fractional delay-based repetitive controller (FD-RC) that allows the periodic delay steps to be noninteger is presented to improve the trajectory tracking accuracy and good disturbance compensation of multiple periodic signals. Second, a sliding mode control (SMC) with a discrete-time reaching law is systematically incorporated into FD-RC to improve transient response, especially during the learning period of FD-RC, and also to provide system robustness against model uncertainties. Finally, the stability proof of the closed-loop system with the proposed controller is assessed based on a delayed-sliding mode-reaching condition. Finally, comparative simulation studies are presented to demonstrate the superior performance of the proposed controller. Full article

Repetitive control (RC) has been widely used in many fields due to its excellent ability to suppress periodic disturbances. However, when the permanent magnet synchronous motor (PMSM) operates at variable speeds, the speed loop sampling frequency is usually not equal to an integer multiple of the fundamental frequency of speed ripple, which prevents disturbances from being completely suppressed. In addition, the open-loop gain of the motor control system with RC is too large at certain frequencies, resulting in excessive speed overshoot during startup and loading. To solve these two problems, this paper proposes a fractional order repetitive control (FORC) strategy with dynamically adjustable gain. A fractional order delay link is introduced to make up for the shortcomings of the conventional repetitive controller (CRC) in its ability to suppress periodic speed ripples when the sampling frequency is not an integer multiple of the fundamental frequency of the motor. Then, to weaken the speed overshoot caused by RC, a nonlinear function fal(e,α,δ) is added in the front of the FORC to dynamically adjust the FORC gain. Simulation and experimental results verify the effectiveness of the proposed method. Full article

To reduce computational load and memory consumption, multirate repetitive control (MRC) with downsampling rates provides a flexible and efficient design for proportional-integral multi-resonant repetitive control (PIMR-RC) systems for grid-tied inverters. However, in MRC systems, repetitive controllers with low sampling rates produce low delay periods, and integer-order phase lead compensation may cause undercompensation or overcompensation. These imprecise linear phase lead compensations may result in deteriorated control performance. To address these problems, based on an infinite impulse response (IIR) filter, a fractional-order phase lead proportional-integral multi-resonant multirate repetitive control (FPL-PIMR-MRC) is proposed for grid-tied inverters in this paper. The proposed method can provide a suitable fractional phase lead step to achieve a wide stability region, minor tracking errors, and low hardware costs. The IIR fractional-order lead filter design, stability analysis, and the step-by-step parameter tuning of the FPL-PIMR-MRC system are derived in detail. Finally, simulation performed confirms the feasibility and effectiveness of the proposed scheme. Full article

The integer-order delay of proportional–integral multi-resonant-type repetitive control (PIMR-RC) cannot provide excellent control performance for grid-tied inverters when the grid frequency fluctuates. To address this issue and reduce control errors, a fractional delay PIMR-RC (FD-PIMR-RC) scheme is proposed. In addition, to reduce the computational load and memory consumption, a Farrow-structure fractional delay (FFD) filter is adopted. The digital filter with the Farrow structure is flexibly and efficiently used for fractional delay. For each new fractional delay, a large number of calculations and storage for the FFD filter coefficients are avoided, which significantly reduces the computational load and memory consumption. The parameter design of the FD-PIMR-RC scheme is provided in detail, including the implementation of fractional delay based on the Farrow structure. Then, a system stability analysis and parameter optimization are presented. Finally, simulations for the steady-state and dynamic responses are presented, and the validity of the proposed method is demonstrated. Full article

A new oligostilbene trimer, malaysianol F (1), together with ten known stilbenes (2–11), were successfully separated and purified from the acetone extract of the lianas of Gnetum microcarpum. Malaysianol D (2) was isolated for the first time in Gnetum plants. The tanninless crude extract (52.5 g) was fractionated using a vacuum liquid chromatography (VLC) technique to give five major fractions. Fraction 2 (4.68 g), 3 (4.79 g) and 4 (9.29 g) were all subjected to further isolation and purification using VLC, column chromatography (CC) and repetitive radial chromatography (RC) techniques with the best solvent system to yield malaysianol F (1) (6.2 mg), malaysianol D (2) (62.5 mg), malaysianol E (3) (2.4 mg), ε-viniferin (4) (10 mg), resveratrol (5) (6.5 mg), gnetol (6) (3.5 mg), gnetucleistol C (7) (12.2 mg), isorhapontigenin (8) (8 mg), cuspidan B (9) (3.2 mg), parvifolol D (10) (4.8 mg) and gnetifolin M (11) (2.5 mg). Their structures were determined on the basis of the analysis of spectral evidence by extensive NMR data analyses and comparison with the related published data. Several compounds were tested for anti-inflammatory activity. Their inhibitory effect on Prostaglandin E₂ (PGE₂) was tested using radioimmunoassay techniques. Compound 6 exhibited significant concentration-dependent inhibitory effects on PGE₂ production with IC₅₀ values of 1.84 µM comparable with the positive control, indomethacin (IC₅₀ 1.29 µM). Full article

In this article, we propose and demonstrate an ultrashort light pulse regenerative shaper based on a closed-loop double-stage Mamyshev regenerator with an electrically controllable acousto-optic switch. This setup allowed us to apply an initial pulse from an external pulse source and to reshape the pulse to an ultrashort, high-quality, compressible one, the parameters of which were determined by the parameters of the regenerative circuit (RC), due to repeated pulse round-trips in the closed-loop RC. It was found that after 3–7 round-trips the energy of the regenerated pulse was almost independent of the energy of the initial pulse. However, at least 20 round-trips in the RC were required to shape the steady repetitive pulse. In addition, we demonstrated, both experientially and numerically, that the generation of periodic pulse sequences with limited pump power can lead to a rearrangement of the pulse sequences, which results in variations in the length of the pulse sequence from period to period. Full article

In recent years, modular multilevel converters (MMCs) have been increasingly used in the field of electric vehicle charging and discharging due to their unique performance advantages. However, the unique cascade structure of MMCs raises the problem of the circulating current. Due to chemical processes, aging effects, etc., the capacitance parameters of the upper and lower bridge arms will be asymmetric, which will introduce odd harmonics into the circulating current, increasing system losses and threatening the system reliability. To address this phenomenon, this paper proposes a circulating current suppression strategy with additional virtual impedance (VI) based on a repetitive controller (RC). The corresponding simulation models were built for the comparative study of different circulating current suppression strategies. The results show that the VI-RC circulating current suppression strategy can significantly reduce the odd and even harmonics in the circulating current under asymmetric conditions, and the total harmonic distortion (THD) of the bridge arm current is only 0.98%, which verifies the effectiveness of the proposed strategy. Full article

Repetitive control (RC), which can track any periodic signal with a known integer period with zero steady-state error, is widely used for current control of grid-tied inverters in microgrids. However, the inherent one fundamental period time delay, leads to poor dynamic performance. Furthermore, the performance of conventional RC (CRC) will degrade when operating at a high variation grid frequency. Therefore, this paper proposes a frequency adaptive improved RC (FA-IRC) for grid-tied inverters. The improved RC (IRC) consists of a repetitive controller with a modified internal model filter, plus a proportional controller. In comparison to the CRC, the IRC has a good dynamic response, because it provides a higher gain and a wider bandwidth at the resonant frequency. Moreover, to achieve the frequency adaptability of the IRC, a fractional delay, based on a finite impulse response (FIR) filter, is built into the IRC system, to ensure that the resonant frequency of the IRC is approximately equal to the actual grid frequency and harmonic frequency. Stability analysis and characteristic analysis of the FA-IRC system are reported in this paper. Simulations are conducted, to demonstrate the validity of the proposed method. Full article

Repetitive controllers (RCs) are linear control structures based on the internal model principle. This control strategy is known for its ability to control periodic reference signals, even if these signals have many harmonic components. Despite being a solution that results in a good performance, several parameters of the repetitive controller need to be correctly tuned to guarantee its stability. Among these parameters, one that has high impact on the system performance and stability is the finite impulse response (FIR) filter, which is usually used to increase the stability domain of RC-based controllers. In this context, this paper presents a complete tutorial for designing the zero-phase FIR filter, which is often used to stabilize control systems that use RC-based controllers. In addition, this paper presents a Matlab^® application developed for performing the stability analysis of RC systems and designing its FIR filter. Simulation and experimental results of a shunt active power filter are used to validate the algorithm and the Matlab^® application. Full article

In this paper, a composite control method combining repetitive control (RC) and deadbeat predictive control (DPC) is proposed to reduce the harmonic content of output voltage and improve the quality of voltage waveform, in order to solve the problem of voltage distortion caused by linear and nonlinear loads at the common grid-connected point of microgrid. First, the mathematical model of three-phase Z-source inverters is established, and the model is transformed into a state space expression. Then, Lyapunov’s theory is used to find the design conditions of the state feedback control law based on linear matrix inequality. Finally, the parameters of the controller are solved by linear matrix inequality (LMI), and the parameter design of the improved repetitive controller is optimized. Furthermore, the system response speed is improved, and the system stability and robustness are guaranteed by combining the deadbeat predictive control technology. The simulation and experimental results verify the accuracy and superiority of the proposed deadbeat predictive repetitive control (DPRC) based on parameter optimization. Full article

The paper presents a design of repetitive control (RC) in the current control system of a three-phase grid-tied converter. The goal of the control system is to provide sinusoidal input filter currents under the conditions of distorted and asymmetrical grid voltage. A novel design of the RC is presented, in which the repetitive part is not excited by sharp and non-periodic changes of the reference signal, but it enables high-quality performance under periodic disturbance conditions. In the proposed system. RC cooperates with a discrete state feedback controller. An innovative approach to tuning is proposed in which parameters of the repetitive, as well as the state feedback controller, are selected as a result of the optimization process with the use of a particle swarm algorithm. The proposed control system is verified experimentally on a laboratory test bench. The achieved results confirm the high-quality system performance. Full article

In this paper, a periodic signal suppression method in position domain based on repetitive control (RC) is proposed to realize high-precision speed control for the gimbal servo system of the single gimbal control moment gyro (SGCMG). To reduce the volume and weight while outputting large torque, the gimbal servo system usually needs to install the harmonic drive. However, the nonlinear transmission characteristics of the harmonic drive are also introduced into the gimbal servo system and make the speed fluctuate. Considering the speed fluctuation signal shown as a fixed frequency in the position domain, a position domain RC method combined with acceleration feedback is designed to realize the speed fluctuation minimization. The position domain RC improves the dynamic characteristics, while the acceleration feedback increases the damping of the system. To analyze the stability, the position domain RC is converted into the time domain through the domain transformation method, and a phase compensator is designed to improve the stability and increase the bandwidth of the position domain RC by compensating for the phase lag of the middle and low frequency, respectively. The feasibility and effectiveness of the proposed method are verified by the simulation and experimental results. These results illustrate that after applying the proposed approach, the output speed fluctuation and harmonic components decrease more than 20% and 24.1%, respectively. Full article