Search

Non-functional scars commonly form after cutaneous injuries. At present, most clinical treatments for scar eradication typically have long treatment courses, low curative effects, and are expensive. In this research, three hydrogels, namely chitin hydrogel, β-glucan hydrogel, and hybrid hydrogel composed of chitin and β-glucan, were successfully prepared, and they exhibited good shear thinning property and bioadhesiveness. In a full-thickness skin defect mouse model, the three hydrogels were found to effectively promote wound closure and inhibit scar formation. Through the immunohistochemistry staining and immunofluorescence staining of the wound tissues, the hydrogels could significantly promote the formation of collagen III, the regeneration of hair follicles, and the expression of keratin K14 and K15. They could also regulate the production of VEGF and immune factors such as IL-10 and IL-12, and inhibit the expression of the fibroblast regulatory factor En-1 in the wound site, which correlated well with their improved wound healing promoting effect and anti-scarring effect. Among all the hydrogels, the hybrid hydrogel was the best to promote wound healing and inhibit scarring. This study, for the first time, proved the excellent therapeutic effect of chitin and β-glucan hydrogels in the management of wound healing and skin regeneration without scar formation, which will lay a solid foundation for the development of skin regeneration medication and future clinical transformation.

The third-harmonic injection two-stage matrix converter (3TSMC) not only possesses the advantages of a TSMC, but also enhances the input reactive power control capability. Due to the input current deviation caused by the voltage ripple across the input filter capacitors, the mains currents of the 3TSMC are distorted at sector boundaries. To improve mains current quality, this article proposes a mains current distortion suppression method for a 3TSMC, which adds a prefilter to the output side of the input voltage selector to reduce the input current harmonics. As a result, the input filter capacitor voltage ripple and the input current deviation are reduced. The details of design of the prefilter are explained mathematically. To compensate for the dc-link voltage variation after topology improvement, an algorithm based on calculation of the voltage drops across the prefilter inductors is proposed, which can further improve the mains current performance. The feasibility of the proposed method is verified by simulation and experimental results.

This article investigates and compares the electromagnetic performance of two novel hybrid-magnetic-circuit variable flux memory machines (HMC-VFMMs) with different hybrid permanent magnet (PM) configurations. The investigated HMC-VFMMs are both geometrically characterized by a combination of series and parallel magnetic circuit topologies, but with different positions of series and parallel PM branches. The developed HMC design can combine the merits of wide flux adjustment range in parallel structure and excellent unintentional demagnetization withstand capability in series structure. The topologies, features, and working principles of the studied HMC-VFMMs with different hybrid magnet configurations are described, respectively. The magnetic circuit model is utilized to analytically reveal the performance metrics of the two machines. The electromagnetic characteristics of the radially magnetized (RM) and circumferentially magnetized LCF types of HMC-VFMMs are evaluated and compared by the finite-element method. Furthermore, the performance comparison of the proposed RM-type HMC-VFMM with a benchmark interior PM machine is conducted. The experiments on RM-type HMC-VFMM prototype with RM-structure are carried out to validate the FE analyses.

For the direct matrix converter (DMC) applied to permanent-magnet synchronous motor (PMSM) drives, a novel modulation scheme is proposed in this article, which could reduce the control complexity and improve the efficiency while achieving zero common-mode voltage (CMV). Only three counterclockwise or clockwise rotating vectors are adopted to operate the DMC. The proposed scheme has the inherent ability to generate sinusoidal input currents without explicit control in the modulation. The duty cycle expressions for the three vectors are quite simple without any trigonometric operations. The switching pattern is fixed, saving the need for sector and sequence determination. Therefore, compared with the conventional modulation scheme which also uses only rotating vectors, the proposed scheme could reduce the execution time by over 80%. In addition, it achieves higher efficiency benefiting from the reduced switching actions. Its validity is verified by experimental results on a 2.4-kW DMC-fed PMSM drive prototype.

The three-phase buck rectifier (3ph-BR) is suitable for applications where a voltage step down function is required. In this paper, an improved 3ph-BR topology is proposed to reduce the voltage stress on the transistors. The freewheeling diode in the conventional topology is split into two diodes in series and the input neutral point is connected to the common point of the two diodes. With the proposed topology and the correspondingly modified modulation scheme, the transistors only need to withstand the input phase voltage instead of the line-to-line voltage, bringing about the significant reduction of voltage stress. The proposed topology enables a more cost-efficient and flexible selection of the transistors. Experimental results have verified the validity of the modified topology and associated modulation scheme.

A matrix converter (MC) with model predictive control based on the source reactive power control usually fails to show sinusoidal source currents. The analysis presented in this paper shows that this common combination of a converter and control has the inherent inability to suppress some harmonics in the source currents, even with additional passive or active damping control. Direct source current control can be implemented to give sinusoidal source currents and intrinsic active damping. However, the issue of steady-state error in output currents then arises, as the MC topology does not allow of the independent control of source and output currents. Therefore, feedback control of load active power is proposed to address this issue without degrading the fast dynamic performance. Benefiting from the direct source current control, a simplified implementation is also proposed to decrease the number of candidate switching states from 27 to 5, which significantly reduces the computational burden. Experimental results have verified the theoretical analysis and the effectiveness of the proposed control scheme.

Fault location of the distribution network is an important direction in the construction of distribution automation. For the problem of slow convergence of intelligent optimization algorithms and easy to fall into local optimality, the multi-population particle swarm optimization algorithm is proposed. The algorithm is compared with single population particle swarm algorithm on IEEE69 node model, it is proved that the new algorithm can find fault location faster. Then the effectiveness of the algorithm in a variety of distribution network fault location scenarios is verified, including single fault location and multiple fault location, and the algorithm can also accurately locate when the input information is distorted which shows good fault tolerance.

For matrix converter (MC), real-time correction of duty cycles is a good solution to eliminate the effects of input voltage disturbances on output performance. However, MC adopting this solution suffers from stability deterioration. The typical active stabilization method is based on modifying output voltage reference with the filtered input voltage. In this paper, its performance is evaluated under input voltage disturbances. It is found that this method will introduce extra low-frequency harmonics into output reference voltage, degrading the output quality. The reason lies in the inability of the adopted digital high-pass filter to block the disturbances. To maintain a good output performance, the improved active stabilization method is proposed, which utilizes resonant controllers to eliminate the extra low-frequency harmonics. The principle and the implementation of the improved method are presented. The consideration of input frequency variation and the influence on input power quality are also discussed. Experimental results have verified the correctness of the performance evaluation and effectiveness of the proposed improvement.

This study proposes an improved hybrid modular multilevel converter (MMC) topology with enhanced fault ride-through capability and fast pre-charging strategies. This improved MMC topology mainly consists of the half-bridge sub-modules (HBSMs), the modified series connected double sub-modules (MSDSMs), and the adjustable damping sub-module (ADSM). In the improved topology, in addition to being configured on the MMC AC-side, resistors are also configured in MSDSMs and ADSM, respectively, in the MMC. This type of resistance configuration based on the improved MMC topology benefits adjusting the value of the total equivalent current limiting resistance during the pre-charging process, leading to a higher pre-charging speed and a lower SM voltage drop risk. Three different pre-charging strategies can cope with changes in resistance configuration caused by the increasing number of SMs. Furthermore, the resistances in MSDSM and ADSM also help dissipate the energy caused by the DC short-circuit fault so that the fault ride-through capacity is enhanced. The simulation and experimental results validate the effectiveness of the proposed topology and the corresponding pre-charging strategies.

The addition of Hermetia illucens larvae meal (HILM) to the feed could contribute to particular antimicrobial and intestinal health in animal husbandry. This study was conducted to investigate the effects of HILM on intestinal morphology and microbial diversity in different intestinal segments of Xuefeng black-bone chickens. All of 432 birds (45 weeks old) were randomly assigned to four equal groups with six replicates and 18 hens in each replicate: (A) basal diet, (B) basal diet with 1% HILM, (C) basal diet with 3% HILM, and (D) basal diet with 5% HILM. The results showed that, compared with the basal diet group, the HILM supplement significantly increased the abundance-based coverage estimator (ACE) and Chao index in cecum (p < 0.05). Diet with 1% HILM significantly increased the villus height (VH) of the duodenum (p < 0.05) and cecum microbial diversity as represented by the Simpson index (p < 0.05). In particular, 1% HILM displayed a markedly increase in the genus unclassified Bacteroidales (cecum, p < 0.05). A basal diet with 3% HILM markedly increased the beneficial genus Romboutsia (jejunum, p < 0.05). Also, principal component analysis (PCA) cluster analysis showed that 3% of HILM was more individual than other groups (p < 0.05). However, 5% HILM decreased the VH and the ratio of villus height to crypt depth (VH/CD) of the jejunum and increased beneficial bacteria such as Staphylococcus (p < 0.05), which was regarded as pathogenetic genera. In conclusion, we found that HILM improved intestinal morphology and increased microbiological diversity and species abundance. Together, dietary supplementation of 1 or 3% HILM might benefit the intestinal morphology and intestinal microbiota of Xuefeng black-bone chicken. However, the addition of 5% HILM could decrease VH and the ratio of VH/CD of the jejunum and increased pathogenetic genera. HILM was an excellent protein substitute for Xuefeng black-bone chickens, which could meet the nutritional requirements under the condition of less feed. These results provide information for HILM meal as an alternative source of soybean meal in Xuefeng black-bone chickens’ feed.

Antibiotics are commonly overused to prevent livestock from diseases and to increase production performance. As potential substitutes of antibiotics, plant extracts have attracted the attention of researchers. It was known to all that addition of Macleaya cordata extract (MCE) to the food could advance immunity, intestinal health and animal performance. Thus, it was conducted to investigate the influence of MCE (0, 100, 150 and 200 mg/kg, with six replicate pens/treatment and 24 hens/pen) on intestinal morphology and microbial diversity in different intestinal segments in Xuefeng black-boned chicken in this study. The results showed that MCE supplement (100, 150 and 200 mg/kg) significantly diminished (P

The pulse frequency modulation with a constant on-time can be adopted for the series resonant converter operating in discontinuous conduction mode to regulate the output voltage. It is found for the first time that there are two different operation cases with different magnetic flux density (MFD) values. The boundary condition for the two cases is found out and the exact MFD expression of each case is derived. The MFD has smallest value under lowest switching frequency and increases with the increase of switching frequency for both cases, indicating the high-power transformer can be designed at highest switching frequency. A transformer turns ratio design guideline can be easily obtained to avoid the higher maximum MFD case. The theoretical analysis is verified by the simulation and experimental results.

The existing power electronic transformer (PET) topologies based on modular multilevel converter (MMC) can provide multiple voltage ports. However, these PET topologies need four power conversion stages, which leads to complex circuit structure and large size. A multiport PET topology based on MMC with resonant circuit for DC distribution has been proposed in this paper. A mixed-frequency modulation strategy is adopted and a group of LC resonant circuit is connected in parallel with each MMC arm, to realize power decoupling between MVDC and LVDC ports. The proposed PET topology can provide the required four ports with only three power conversion stages, which has the advantages of simplified circuit structure and smaller size. Finally, the simulation results verify that the proposed PET is feasible and effective.

This paper presents a design scheme of distributed energy storage system (ESS) which is used to improve the automatic generation control. Based on the constraints of ESS and the manual of supercapacitor, the selection of supercapacitor methods are described in detail, and the common product combinations are listed. Because of the large number of energy storage units and output levels, half-bridge topology is advised which enables to save switching devices. Due to the high loss, insufficient advantages of carrier phase-shifting PWM and output distortion of nearest level modulation in ESS application, carrier disposition modulation is recommended and convenient to realize power-sharing under low switching loss. Based on carrier disposition modulation, voltage balance algorithm and grid-connected algorithm are designed, and detailed trigger block diagrams of each switch device are presented. Finally, the feasibility of the proposed design method is verified by Simulink simulation.

Accurately locating forced oscillations (FOs) disturbance source in a large-scale power system is a challenging task. In this paper, a localisation method featuring system-level and area-level localisation is proposed. Compared with traditional localisation methods which process the FOs signals only in control centre phasor data concentrator (PDC), the proposed method can not only relieve the data communication pressure, but also meets the data privacy and confidentiality requirements of utility companies. Besides, with the two-stage deep transfer learning, high accuracy of localisation can be realised with far less training. Firstly, by adopting principle component analysis (PCA) to extract the most representative information at system-level and smooth pseudo Wigner-Ville distribution (SPWVD) to characterize FOs signals, graphical representations of FOs at system-level and area-level are obtained respectively, transforming the localisation problem to image recognition problem. Subsequently, a two-stage deep transfer learning (DTL) algorithm is developed to locate FOs disturbance source. The first stage involves repurposing the learnt features from a pre-trained deep convolutional neural network (previously trained for universal image recognition) to improve the learning of system-level localisation. In a similar logic, the second stage entails transferring the knowledge acquired from the first stage is exploited to aid area-level localisation learning. Case studies carried out on the WECC 179-bus system demonstrate that the proposed method achieves a significantly higher accuracy in the presence of measurement noise, topology variation and load disturbances of the system with respect to the traditional machine learning method. The proposed method also exhibits a more favorable computational performance and learning efficiency due to the employment of the tactfully designed two-stage DTL approach.

Due to the absence of bulky dc-link capacitors, the matrix converter (MC) is a prospective candidate to replace the conventional two-stage ac–ac converter, especially in some applications which require high reliability. In order to enhance the reliability during system operation, this paper investigates an open-circuit fault detection technology for indirect MC. First, combining with the characteristics of the space vector modulation technique, this paper presents analysis work during the appearance of an open-circuit fault. Then, a novel fault diagnosis approach is proposed based on the circuit analysis. The proposed method establishes a unique corresponding relationship between switches and modulation sectors, and the faulty switch can be discriminated exactly by measuring the three-phase output voltages and the dc-link voltage. This method, which can locate the failure that occurs in rectifier stage or inverter stage correctly, offers favorable antidisturbance ability. The experiments are carried out to verify the feasibility and validity of the proposed fault detection method.

With the integration of renewable energy resources and variable loads into power grid, power oscillations caused by persistent external fluctuating forces are becoming more prevalent. Termed as “forced oscillations (FO)”, such phenomena could happen even when the grid is with good damping characteristics. Therefore, conventional mitigation methods based on improving damping are rendered less effective. By leveraging the new control capability offered by static synchronous compensator with energy storage (E-STATCOM), a novel approach to mitigate FOs is proposed in this paper. A control strategy based on resonant controllers is adopted to modulate active and reactive power supplied by E-STATCOM. It is theoretically shown that FOs propagating from the disturbed area to other areas can be effectively eliminated by this method. Besides, we derived the analytical relationship among the location, the capacity of E-STATCOM and the suppression performance. Case studies demonstrate the effectiveness of the proposed method.

Forced oscillations (FOs), which are caused by sustained cyclic disturbances, threaten the safe and stable operation of power system. The most effective way to eliminate FOs is to locate the oscillation source and take corresponding measures. In this paper, a two-level method for forced oscillations source location is proposed. First, the energy structure of the generator is analyzed based on Hamiltonian function. The energy injected into generator is divided into two parts, i.e., energy injected by the prime mover system and excitation system. Then, as to the energy injected into power grid, the phasor relation between the variances of branch variables is analyzed to identify the energy flow direction. Based on the former analysis, the proposed method includes two levels. The bus level location of the oscillation source is realized according to the energy flow direction obtained with phasor analysis. Furthermore, the control device level location within the generator is realized according to the injected energy of the prime mover system and excitation system of generator. This method has good robustness for the measurement of data quality issue and is able to locate multimode oscillations with multiple disturbances. The simulation results in four-machine two-area system, East China power grid and the WECC 179-bus system as well as the comparison with classic energy-based method demonstrate the effectiveness and improvement of the proposed method.

With the continuous improvement of the automation level of the distribution network, more and more switches can be controlled remotely. The reliability of switch remote control directly affects the stability of the entire distribution network system, so it is very important to test the switch regularly to ensure that it can be operated remotely in an emergency. At present, the switch test scheme is mainly artificially generated, which is very inefficient, and the review process is simple, which is easy to cause safety problems. This paper proposes an automatic generation system for switch test scheme based on topology analysis, which greatly improves the efficiency of scheme generation, and adds multiple roles for review, which improves the accuracy of the scheme. This system has been applied in practice and achieved good results.

Indirect matrix converter (IMC)'s source current may contain low-order harmonics caused by asymmetric modulation in a variable-speed-constant frequency generation system. However, without capacitor/inductor decoupling effect, IMC's source current depends on loads and cannot be controlled independently. In this paper, the expressions of source current harmonics in the synchronous rotating reference frame are analyzed first. It leads to the conclusions that the only uncontrollable part of the source current is its d -axis dc component, and the quality of the source current can be improved by suppressing the harmonics. On the basis of above analysis, a novel source current control strategy is proposed for an IMC with asymmetric modulation, which can improve the source current quality and correct the input power factor. Self-tuning resonant controllers and a proportional integral controller are employed to achieve above goals. The stability of the system is also analyzed considering the change of input impendence after adding the source current control, which can be used as the guidance for the selection of control parameters. Finally, the validity and the feasibility of the control strategy are verified via experiments.