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Resonant pole cancelation is usually adopted in the current control or active damping to tackle the filter resonance in the LCL -type grid-connected inverter. However, its potential impact on the system stability has not been adequately assessed. This article provides a comprehensive investigation on three typical control schemes that utilize resonant pole cancelation. An important finding is drawn that the resonant pole cancelation violates the so-called internal stability, which can give rise to the undesired harmonic oscillation in grid current. From the physical insights, it is revealed that the resonant pole cancelation does not essentially eliminate the LCL resonance but merely “hide” it in the system, which can still be triggered and, thereby, turns into the culprit of the harmonic oscillation. The theoretical expectation is validated by the simulation and experimental results.

Owing to simplicity, lower total harmonic distortion, and higher power factor benefits, the 12-pulse uncontrolled rectifiers with a coupling interphase reactor are widely used as the power factor correction (PFC) converters, which are inserted between the power grid and the non-linear loads. However, the key parameters of the 12-pulse rectifier, such as transformer ratio, coupling coefficient and self-inductance of interphase reactor, and the capacitance of filter capacitor, are generally designed by trial and error, which is complicated and inefficient. In order to offer a useful reference for engineers to design the 12-pulse rectifier, a simply design program is proposed considering current ripple and output voltage ripple. Subsequently, optimized parameters of the 12-pulse rectifier are obtained after running the design program. Therefore, the rectifier can work in high performance with smaller size. Finally, the correctness of the theoretical analysis and the effectiveness of the proposed design program are validated by simulation results.

Thanks to sensor-less and simplicity benefits, the filter-based active damping, being directly plugged into the current regulator, is attractive for the $LCL$ -filtered grid-connected inverter. Typically, the notch filter (NF) is employed and yields a good damping effect when the notch frequency $f_{n}$ is placed higher than the $LCL$ resonance frequency $f_{r}$ . However, for the frequencies above $f_{n}$ , excessive phase lead is provided, worsening the damping effect and giving rise to limited robustness. To address this issue, a quasi-notch filter (QNF) is proposed in this paper, which provides suitable phase compensation to cover a wide range of $f_{r}$ up to the Nyquist frequency $(f_{s/2)}$ . As a result, the high robustness against the variations of $LCL$ parameters and grid impedance can be achieved. The effectiveness of the proposed method is validated by experimental results.

The single-loop weighted average current (WAC) control is attractive for the LCL-type grid-connected inverter owing to its inherent active damping. High robustness can be naturally harvested without any additional damping methods, but it requires two current sensors. Depending on the different weight values, a family of the splitting current single-loop control schemes with the associated filter configurations is developed in this paper, where only one current sensor is needed. As a result, high robustness, high-quality grid current and cost-efficiency can be concurrently achieved. Finally, experimental results from a 6-kW setup confirm the effectiveness and practicality of the splitting current single-loop control.

The main shortcomings of the software-based power engineering education are a lack of physical understanding of phenomena and hands-on experience. Existing scaled-down analogous educational power system platforms cannot be widely used for experiments in universities due to the high cost, complicated operation, and huge size. An integrated power distribution system laboratory platform (PDSLP) using modular miniature physical elements is proposed in this paper. The printed circuit board (PCB) and microelectronic technology are proposed to construct each physical element. Furthermore, the constructed physical elements are used to set up an integrated PDSLP based on modular assembly technology. The size of the proposed cost-efficient PDSLP is significantly reduced, and the reliability of the proposed PDSLP can be improved greatly because the signal transmission path is shortened and a number of welding points are reduced. A PDSLP for fault location in neutral non-effectively grounded distribution systems (NGDSs) is selected as a typical experimental scenario and one scaled-down distribution network with three feeders is subsequently implemented and discussed. The measured zero-sequence currents by our proposed PDSLP when a single-phase earth fault occurred can reveal the true features of the fault-generated signals, including steady-state and transient characteristics of zero-sequence currents. They can be readily observed and used for students to design corresponding fault location algorithms. Modular renewable energy sources and other elements can be designed, implemented and integrated into the proposed platform for the laboratory education of the active distribution networks in the future.

This study presents the results of hybrid energy storage system (HESS) and improved maximum power point tracking (MPPT) algorithm simulation analysis undertaken to improve the smoothing performance of solar photovoltaic (PV) plant installed in the ship power system. Frequency hierarchical control algorithm is used to assign high-frequency oscillation part to the supercapacitor and low-frequency oscillation part to the battery. Meanwhile, improved MPPT algorithm is also used to limit the maximum output power of PV plant, which can reduce the necessary installed capacity of HESS further. The effectiveness of the proposed method was verified under a typical ship power system model.

Laser welding with filler wire makes welding more cost efficient due to its properties. However, fluctuation of welding parameters seriously affects the stability of welding process and the quality of deposition layer. Based on the high speed camera system and welding process test, this paper focuses on effects of welding parameters on the laser-wire coupling behavior, the transition behavior of molten metal and the characteristics of deposition layer. The results showed that the transition behaviors of liquid metal were decomposed into globular transition behavior, liquid-bridge transition behavior and spreading transition behavior, among which the liquid-bridge transition behavior was most stable relatively. Different dynamic welding processes in different circumstances were established to interpret the laser-wire coupling behaviors and the transition behaviors of liquid metal while the D was zero. It was found that the coupling behavior and the transition behavior of liquid metal belonged to different dynamic process with the variable welding parameters. The optimized welding parameters were obtained by analyzing the stability of welding process and the characteristics of deposition layer.

Polyamines (PAs) induce nitric oxide (NO) generation in plant tissues; however, their mechanism is still unclear. In the present study, suspension cells of soybean cotyledon-node callus were employed. Using a NO-specific fluorescent dye, DAF-FM-DA (3-amino, 4-aminomethyl-2', 7'-difluorescein, diacetate), and laser confocal scanning microscopy, changes in NO generation induced by exogenous PAs were examined. The results of this study showed that NO fluorescence was significantly induced above endogenous levels when callus cells were treated with 0.05 mM PAs. However, putrescine (Put) was the most active PA. The observed NO release by PAs was rapid and without an apparent lag phase. The response was quenched when the suspension cells were treated with the NO-specific scavenger cPTIO (2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-1-oxy-3-oxide). When 0.01 mM l-aminoguanidine (L-AG) was applied prior to the PA treatments, the NO fluorescence was diminished, and the inhibition of NO fluorescence was correlated with a decrease in diamine oxidase (DAO) activity. When callus cells were incubated with 0.1 mM catalase (CAT) and 1.0 mM N'N-dimethylthiourea (DMTU) prior to PA application, NO release was significantly reduced. In sum, our data provided evidence for PA-induced NO generation in suspension cells of soybean cotyledon node callus and demonstrated that peroxide, potentially derived from PA oxidative degradation, was involved in NO release induced by PAs.

In order to analyze the relationship between polyamine oxidative degradation induced by light and the Lignin synthesis in cell walls, the activities of diamine oxidases and peroxidase, the contents of H2O2 and lignin, and the growth of hypocotyls in soybean [Glycine max (Linn.) Merr.] grown under tight or in darkness were investigated. In comparison with the dark treatment, light irradiation significantly inhibited the growth of soybean hypocotyls and promoted the activities of diamine oxidases and peroxidase as well as the accumulation of H2O2 and lignin. Treatments with the different concentrations of diamine oxidase inhibitors (2-hydroxyethylhydrazine and aminoguanidine) under the light condition inhibited diamine oxidase activity, and decreased the contents of H2O2 and lignin. The results provide evidence for the hypothesis that light irradiation could promote the accumulation of H2O2 and lignin in cell walls by activating polyamine oxidative degradation mediated by diamine oxidases.