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Objective: Gastric cancer (GC) is a malignant tumor rooting in the gastric mucosal epithelium, ranking the first among various malignant tumors. Therefore, the influence of microRNA-128-3p (miR-128-3p) by regulation of Tuftelin1 (TUFT1) on GC cells was investigated. Methods: The expression levels of miR-128-3p and TUFT1 in GC tissues and cells were detected. The correlation between miR-128-3p expression and overall survival of GC patients was analyzed. Human GC cells MGC803 were transfected with miR-128-3p or TUFT1-related oligonucleotides to figure their roles in viability, apoptosis, invasion, as well as epithelial-mesenchymal transition (EMT). The relationship between miR-128-3p and TUFT1 was validated. Results: miR-128-3p expression was low and TUFT1 expression was high in GC tissues. miR-128-3p expression was positively correlated with the overall survival of patients with GC. miR-128-3p targeted TUFT1. Up-regulated miR-128-3p or suppressed TUFT1 repressed viability, invasion, and EMT, and accelerated apoptosis of GC cells. Overexpressed TUFT1 reduced miR-128-3p-mediated growth inhibition of GC cells. Conclusion: The study stresses that miR-128-3p can inhibit TUFT1 expression, thereby repressing GC cell activities. [ABSTRACT FROM AUTHOR]

Insulated gate bipolar transistor (IGBT) module is one of the most prone-to-fail components in the wind power converter (WPC). The reduction of the junction temperature swing by thermal management can improve the reliability of a WPC. Due to the lack of an applicable selection criterion, not many studies on the control target of junction temperature swing were reported. This article proposes a thermal management strategy to find the control target of junction temperature swing. The proposed strategy considers the return on investment (ROI) of thermal management as a quantitative indicator to guide the control target selection. The selected control target enables optimal benefit of the thermal management. Results show that a 1% increase in the total harmonic distortion would extend the lifetime of IGBT module by 0.144 years. Success of the proposed scheme lies in the efficient regulation of the junction temperature swing. Case studies with different mission profiles and experimental tests on a three-phase two-level inverter are presented to validate the proposed method. [ABSTRACT FROM AUTHOR]

Multi-terminal modular multilevel converter (MMC) power transmission is the current development trend in DC transmission. However, owing to its fast control and dynamic characteristics, it may interact with the other inductive devices or the grid and cause stability issues. This paper describes the use of the impedance analysis method in the frequency domain to analyze system stability. First, the multi-harmonic linearization method is used to model the impedance of a three-terminal MMC system. To make the model more accurate, the modeling considers the effect of frequency coupling caused by an asymmetric controller and the AC sampling site position. This paper then proposes an equivalent method of the grid impedance for the three-terminal system that can accurately judge the stability of the grid-connected system when the AC side is coupled. This work provides a theoretical basis for the prediction and suppression of the oscillation of MMC grid-connected system with coupling on the AC side. Finally, a three-terminal MMC model is built in Matlab/Simulink and the Nyquist stability criterion is used to verify the correctness of the analysis. [ABSTRACT FROM AUTHOR]

The junction temperature of power semiconductors is a critical parameter during reliability evaluation. The incorporation of long-term mission profiles, such as power loadings and ambient temperature, into lifetime and reliability evaluations of power semiconductors increases the computational burden. Thus, there is an urgent need for a more accurate method for junction temperature acquisition. Current methods for junction temperature calculation are computationally inefficient and do not comprehensively incorporate long-term factors into junction temperature calculation and power semiconductor reliability evaluation. Here, a junction temperature calculation method is proposed that enables reliability evaluation for insulated gate bipolar transistor (IGBT) power semiconductors. This approach calculates the IGBT module junction temperature on the basis of an electro-thermal analogy using Gauss–Seidel iteration. When compared with electrical–thermal simulation and other numerical calculation methods, the proposed method guarantees accuracy, while greatly reducing the computational time and load. A performance comparison between the proposed method, electro-thermal simulation based on a Fuji IGBT simulator, and experimental results was carried out using a three-phase DC/AC inverter as a case study. [ABSTRACT FROM AUTHOR]

Wide bandgap (WBG) devices offer the advantages of high frequency, high efficiency, and high power density to power converters due to their excellent performance. However, their low parasitic capacitance and fast switching speed also make them more susceptible to switching oscillations. The switching oscillations can cause voltage and current overshoots, shoot-through, electromagnetic interference, additional power loss, and even device damage, which can seriously affect the performance of power converters and systems. However, a comprehensive and in-depth overview is lacking on this topic. This article reviews the types, the causes and negative effects, the effects of parasitic parameters and suppression methods of these switching oscillations, which is helpful for practical engineering. First, the switching oscillations are divided into different types, and their causes and negative effects are reviewed. Then, the effects of different parasitic parameters on the switching oscillations are overviewed. It is found that due to the different physical structures of silicon carbide metal-oxide-semiconductor field-effect transistors, enhancement-mode gallium nitride high-electron mobility transistors (eGaN HEMTs), and cascode GaN HEMTs, the effects are also different. Finally, the main methods of suppressing the switching oscillations are summarized, and the advantages and disadvantages of these methods are presented. Furthermore, future research works on this topic and the conclusion of this paper are drawn, which will help readers deepen their understanding of the switching oscillations of WBG devices, and inspire readers to better use WBG devices for high-frequency and high-efficient power conversion. [ABSTRACT FROM AUTHOR]

When the impedance-based stability criterion is used to analyze the stability of a three-phase inverter-grid system, the impedance of the grid-connected inverter has to be known. This article proposes an inverter impedance measurement method in stationary frame using the off-shelf frequency response analyzer (FRA). In small-signal representation, inverter impedance can be represented by the equivalent admittance, which enables accurate representation of the inverter frequency response. The admittance expression in the stationary frame contains frequency coupling components. These components include the response current or voltage at frequency different from the perturbation frequency. But, the existing FRA only measures the response current and voltage having the same frequency as the perturbation frequency. The proposed method constructs three intermediate variables to overcome this limitation. These variables can be obtained by the measured data from FRA. Then the equivalent admittance under different grid impedances can be expressed by them. Since the equivalent admittance considers the frequency coupling effect, accurate stability analysis of the inverter-grid system can be guaranteed. Simulation and experimental results are presented to demonstrate the effectiveness of the proposed impedance measurement method. [ABSTRACT FROM AUTHOR]

Recently, wind power technology has been developed rapidly. The interaction between the wind turbine generator and the grid may cause the stability issue and threats the reliable operation of the power system. So, it is vital to analyze the stability of the wind power grid-connected system. Due to the fluctuation of wind speed, the operation characteristics of the system vary, and the system exhibits different stability characteristics at the varied operating points. Thus, it is important to analyze the system stability in the entire operation space. The impedance-based analysis is an effective tool for the stability analysis of the grid-connected system. However, it is difficult to apply the conventional impedance/admittance model to characterize the system performance due to the fact that the system operating point often varies continually. To overcome this challenge, this paper proposes a two-variable admittance model that incorporates the wind speed into the conventional admittance model. In addition, a new stability criterion based on the magnitude and phase contour plot is developed to enable the stability analysis. Simulation and experimental results are presented to demonstrate that the proposed two-variable admittance model and the stability criterion are effective tools for stability analysis of the wind power grid-connected system. [ABSTRACT FROM AUTHOR]

Cardiomyocyte hypertrophy is the adaptive response of the heart to various physiological or pathological stresses. To combat this type of disease, more effective drugs are still needed. Wedelolactone is the main ingredient extracted from the medicinal plant Daylily and have effects such as immunomodulatory, anti-fibrosis, and anti-inflammation. However, the role and mechanism of Wedelolactone in myocardial hypertrophy are still unclear. Here, H9C2 cells were treated with Ang II to construct a cardiomyocyte hypertrophy cell model. We found Wedelolactone suppressed the survival of Ang II-induced cardiomyocytes. Wedelolactone further restrained the progression of Ang II-induced cardiomyocyte hypertrophy. Wedelolactone suppressed the oxidative stress of Ang II-induced cardiomyocytes, and restrained the apoptosis. Mechanically, Wedelolactone restrained the progression of Ang II-induced cardiomyocyte hypertrophy via Nuclear factor erythroid 2-related factor 2/Heme oxygenase-1 pathway (Nrf2/HO-1 pathway). In summary, Wedelolactone attenuates angiotensin II-induced hypertrophy and apoptosis in cardiomyocytes. Wedelolactone attenuates angiotensin II-stimulated hypertrophy and apoptosis in cardiomyocytes. [ABSTRACT FROM AUTHOR]

Drought stress, a major abiotic stress, significantly affects wheat (Triticum aestivum L.) production globally. To identify genes and metabolic pathways crucial for responding to short-term drought stress, we conducted transcriptomic and metabolomic analyses of winter wheat cultivar Jimai 418 at four developmental stages: jointing (GS31), booting (GS45), anthesis (GS65), and 8 days after anthesis (DAA8). Transcriptomic analysis identified 14,232 differentially expressed genes (DEGs) under drought stress compared to the control. Specifically, 1387, 4573, 7380, and 892 DEGs were identified at the four developmental stages, respectively. Enriched pathways associated with these DEGs included plant hormone signal transduction, mitogen-activated protein kinase (MAPK) signaling, galactose metabolism, and starch and sucrose metabolism. Totals of 222, 633, 358, and 38 differentially accumulated metabolites (DAMs) were identified at the four stages, respectively. Correlation analysis of both datasets revealed DEGs and DAMs associated with plant hormone signal transduction, arginine and proline metabolism, ABC transporters, and amino acid biosynthesis. These findings offer significant insights into Jimai 418's molecular response to short-term drought stress. The identified DEGs, DAMs, and enriched pathways contribute to our understanding of wheat drought tolerance. This research will facilitate further investigations into drought tolerance mechanisms and guide the breeding of wheat varieties with enhanced drought resistance. [ABSTRACT FROM AUTHOR]

The forced air cooling system plays an important role in the safe operation of power converters. Condition monitoring its health status can improve the reliability of power converter and reduce the cost of unscheduled maintenance due to over-heating. This letter proposed to use the natural frequency of thermal network as an indicator to monitor the aging process of cooling system. We show that the degradation of the cooling system can be monitored by detecting the variation of thermal network natural frequency. Experimental tests on a three-phase dc/ac converter with forced air cooling system are performed to verify the effectiveness of proposed method. This method is simple to implement and does not need to measure the power loss. Moreover, it enables the concurrent monitoring of multiple components in the cooling system. [ABSTRACT FROM AUTHOR]

This paper proposes a thermal network parameter estimation method for insulated-gate bipolar transistor (IGBT) modules using the junction temperature cooling curve. The proposed method finds the RC parameters of a fourth-order Cauer network by establishing a relationship between RC parameters and time constants of junction temperature response curves. Experimental tests are performed to validate the accuracy of the developed method. Results show that the difference of total thermal resistance between the proposed method and IEC standard is below 2%. Advantages of the proposed method over the existing methods are that the proposed method does not need 1) to know the power loss information of IGBT and 2) to heat the IGBT module up to thermal steady state. In addition, we show that the identified RC parameters can be used for condition monitoring and junction temperature estimation. [ABSTRACT FROM AUTHOR]

In this paper, we propose to monitor the thermal parameters of insulated gate bipolar transistor (IGBT) module using the case temperature. This method works during the shutoff period of IGBT module where the case temperature is in the cooling phase By establishing the relationship between the Cauer-type thermal RC parameters and the time constants of case temperature cooling curves, thermal parameters of the IGBT module can be identified. The proposed method is able to eliminate the influence of thermal interface material (TIM) degradation on the monitored results, which is quite challenging for the current case temperature monitoring methods. Moreover, it enables the detection of thermal resistance and thermal capacitance of the TIM and that of the IGBT module at the same time. Experimental tests are performed to validate the accuracy and feasibility of the proposed method. Moreover, impacts of the junction temperature, case temperature sensing position, and thermal coupling on the monitored results are analyzed. [ABSTRACT FROM AUTHOR]

• The limitation of the recent control methods (FCIN and FCOUT) are analyzed by analytical expressions. • The proposed method greatly improves the system stability, since it overcomes the limitation that the recent control methods do not consider the duty cycle perturbations. • The proposed method is simple and readily realized in the traditional control structure because it constructs an integrator and a high pass filter path outside the PLL. The interaction between the inverter and the grid in weak grids may produce resonances that lead to reduced power quality and instability concern. The recently proposed control methods based on eliminating disturbances in the control loop avoid the challenging control parameter design faced by the existing stability-enhancing control methods. They are effective to overcome the instability concern, but may not be able to maintain stable operation of the system in certain situations. Moreover, they affect the steady-state output current of the system under the fluctuation of the grid. This paper proposes a phase feed-forward method in the dq-frame to overcome the problems encountered by these control methods, such as duty cycle perturbation and grid phase jump. The proposed method constructs an integrator and a high pass filter path outside the PLL. It is simple and readily realized in the traditional control structure. Simulation and experimental results are presented to demonstrate the effectiveness of the proposed control method. [ABSTRACT FROM AUTHOR]

The dc-link capacitors are important components that tend to be one of the weakest part of power converters. Thus, it is necessary to monitor the aging parameters of dc-link capacitors in valuable power electronic systems. This paper proposes a simple yet effective variable electrical network (VEN) condition monitoring method for dc-link capacitors in three-phase pulsewidth modulation (PWM) ac–dc–ac power converters. The capacitance (C) and equivalent series resistance of dc-link capacitors are estimated through the designed VEN unit during the discharging process. This VEN method does not need the current sensor or injecting signals into the control loop. The above property is favorable for the hardware and controller design. Besides, the designed monitoring circuit can be an external unit or a built-in unit which offers a flexible solution for electrical devices. When the designed VEN is used as an external unit, neither the hardware design nor the programs in the controller needs to change, which is practical and economic for electrical devices in use. Experiments are carried out in a 55 kW ac–dc–ac inverter with different capacitors. The experiment results prove the method to be effective and accurate. [ABSTRACT FROM AUTHOR]

Improvement of cotton fibre yield and quality is challenging due to the narrow genetic base of modern cotton cultivars, which emphasizes the great need to effectively explore the existing germplasm resources. With major objective to assess the genetic diversity and population structure at DNA level, 302 elite upland cotton germplasm accessions (253 Chinese and 49 different exotic origins), were genotyped using 198 simple sequence repeats (SSRs) markers. Each of the 198 markers differed greatly in its ability to detect variations in the panel of cotton germplasm. The SSRs amplified 897 alleles, of which 77.7% were polymorphic. The number of alleles varied from 2 to 12 (mean 4.53). Gene diversity ranged from 0.020 to 0.492 with a mean of 0.279. The polymorphic information content (PIC) values ranged from 0.371 to 0.019 (mean 0.225). Genetic distances in the whole cotton germplasm ranged from 0.451 to 0.052 (mean 0.270), demonstrating relatively wider genetic diversity range. Chinese-origin cotton germplasm showed the highest level of SSR polymorphisms (gene diversity = 0.268, PIC = 0.218), whereas American-origin revealed the highest mean genetic distance (0.274). Model-based Bayesian analysis clustered the whole cotton germplasm into three subpopulations, and the highest molecular variation ws revealed between subpopulations (4%, P<0.001). The SSRs revealed moderate level of genetic diversity at DNA level, identified three structured subpopulations, suggesting a potential use of these markers for genomewide association mapping studies and for identifying and conserving useful alleles in upland cotton germplasm. [ABSTRACT FROM AUTHOR]

Ox-LDL-induced endothelial cells injury has been reported to play an important role in the development of atherosclerosis (AS). MicroRNAs have been identified to regulate their target genes post-transcriptionally and they are able to participate in the various diseases, including AS. However, the role of miR-410 in ox-LDL-triggered abnormal function of endothelial cells remains to be elaborated. Hence, our current study was to find out the underlying mechanism of miR-410 in AS. Here, we observed that ox-LDL can inhibit HUVECs growth and lead to a great cell apoptosis both dose-dependently and time-dependently. Meanwhile, it was exhibited that miR-410 expression was remarkably elevated in ox-LDL-indicated HUVECs. miR-410 knockdown was able to induce cell proliferation and alleviate HUVECs apoptosis subjected to ox-LDL. Reversely, signal transducer and activator of transcription 3 (STAT3) expression was greatly decreased in ox-LDL-incubated HUVECs in a time and dose dependent manner. Additionally, these findings exhibited that STAT3 was a target of miR-410, which was validated by a dual-luciferase assay in our study. Additionally, we observed that overexpression of STAT3 rescued ox-LDL induced AS events in vitro. Taken these together, our current study implied that miR-410 silence can inhibit the ox-LDL-induced HUVECs proliferation and rescue cell apoptosis through activating STAT3 in vitro. [ABSTRACT FROM AUTHOR]

Drought stress is the main limiting factor to spring maize production in the North China Plain (NCP). However, amounts of soil water and precipitation evaporate unproductively during the long fallow season before sowing spring maize. Therefore, sub-surface plastic mulching (PM) and straw mulching (SM) were conducted to reduce evaporation following the harvest of the previous season's crop in this three-year study. PM resulted in less water evaporation during the fallow season compared with SM and the control without mulching (CK). Thus, more water was stored in the soil under PM. Similarly, evapotranspiration from sowing to the sixth-leaf stage (V6) in CK and SM was increased by 18.5–43.1% compared with PM. Conversely, evapotranspiration of PM was higher than that of CK and SM during the V6-silking period. During the grain filling stage, there was no significant difference in evapotranspiration among treatments owing to abundant rainfall. Correlation analysis indicated that excessive soil water used during the fallow season and seedling stage exacerbated the yield reduction. However, more water employed from V6 to silking increased yield. PM increased soil temperature during the seedling stage, thus accelerating spring maize growth, but without significantly affecting grain yield. PM could increase leaf area index, thus improving the biomass accumulation. Finally, the kernel setting rate was elevated under PM compared to CK and SM. Grain yield, water use efficiency (WUE), and annual WUE of PM were increased by 9.3–15.2%, 8.7–15.6%, and 16.7–25.8% relative to CK and SM, respectively. In conclusion, sub-surface plastic mulching stored water for spring maize growth and development, and enhanced water availability during the critical stage of water demand, thus increasing grain yield and WUE and reducing annual evapotranspiration. • Sub-surface plastic mulching (PM) reduced water use in fallow season. • PM can store more soil water for spring maize kernel setting around silking. • PM obviously increased spring maize yield and WUE and reduced annul ET. [ABSTRACT FROM AUTHOR]

Power semiconductors in the wind turbine power converter system suffer from two-scale thermal loadings, the fundamental frequency thermal cycling caused by the output frequency of converter and the low frequency thermal cycling due to the variation of long-term wind speed. These two-scale thermal loadings introduce different consumed lifetimes. Accurate lifetime estimation in the wind power application is desired for reliability prediction and health management. This paper adopts the Bayerer lifetime model to evaluate the consumed lifetime of power semiconductors in wind power converter systems based on a numerical junction temperature calculation method. Lifetime estimation can be improved by taking into account the ambient temperature. Studies show that fluctuations of the ambient temperature increase the consumed lifetime due to the low frequency thermal cycling, but have little effect on the consumed lifetime due to the fundamental frequency thermal cycling. Our results also show that the consumed lifetime due to fundamental frequency thermal cycling mainly falls on the high wind speed area, whereas the consumed lifetime due to low frequency thermal cycling is clustered in the area due to large low frequency junction temperature fluctuations. The resulting distribution characteristics can be used in the thermal management for reliability improvement. [ABSTRACT FROM AUTHOR]

Against the background of long-term climate change, quantifying the response of maize growth and development to climate change during critical growth stages will contribute to future decision-making in maize production. However, there have been few reports on the impact of climate change on maize dry matter accumulation and yield formation using long-term field trial data. In this study, field trial data from 13 agricultural meteorological stations in the Beijing–Tianjin–Hebei region from 1981 to 2017 were analyzed using partial correlation analysis and multiple regression models to investigate the effects of climate change on maize growth and yield. The results showed that the average temperature (Tavg) and accumulated effective precipitation (EP) during the maize growing season increased while the accumulated solar radiation (SRD) decreased from 1981 to 2017. During the seedling stage (GS1, VE-V8) and ear development stage (GS2, V8-R1), Tavg increased by 0.34 °C and 0.36 °C/decade, respectively, and EP increased by 1.83 mm and 3.35 mm/decade, respectively. The significant increase in Tavg during GS1 was the main reason for the inhibitory effect of climate change on maize growth, development, and biomass accumulation. However, the increase in SRD during the grain formation stage (GS3, R1–R3) and grain filling stage (GS4, R3–R6) was favorable for yield formation, increasing the grain number per ear (GN) and grain weight (GW) by 5.00% and 2.84%, respectively. SRD significantly increased after the silk stage, partially offsetting the adverse effects of temperature on maize yield formation, but the final result was a 0.18% and 0.94% reduction in maize plant dry weight (TDW) and grain yield (GY), respectively, due to the combined effects of the three climate factors. Spatially, climate change mainly had a negative impact on maize in the eastern and western parts of the central region of Beijing–Tianjin–Hebei, with a maximum GY reduction of up to 34.06%. The results of this study can provide a scientific basis for future decision-making in maize production against the background of climate change. [ABSTRACT FROM AUTHOR]

Synchronization with the grid voltage is critical in the control of grid-connected power converters. Under unbalanced grid condition, the conventional synchronous reference frame phase-locked loop (SRF-PLL) does not work well due to the effect of the fundamental negative sequence component. This paper proposes a new synchronization method, the sinusoidal amplitude integrator based phase locked loop (SAI-based PLL), to efficiently eradicate the effect of the fundamental negative sequence component. As a result, it can accurately and quickly estimate the amplitude and phase angle of the fundamental components of grid voltages in unbalanced grid conditions. In addition, when dc offset and harmonics are contained in the grid voltage, a multi-SAI-based PLL method is developed to extract the synchronization signal. The proposed SAI-based PLL incorporates the sinusoidal amplitude integrator into the conventional SRF-PLL. Its operation is analyzed using the complex-vector notation. Simulation and experimental results on the performance of the proposed SAI-based PLL and comparison with other synchronization methods are presented. [ABSTRACT FROM AUTHOR]

In this paper, a dc link active power filter (APF) for three-phase diode rectifier is proposed. The proposed dc link APF, which is composed of two series-connected bidirectional boost converters, intends to eliminate the input current harmonics. It is paralleled at the dc link of the diode rectifier and is coupled to the ac input with three line-frequency switches. Compared with the full power processed power factor correction (PFC) solution, the dc link APF is partially power processed in that it only compensates for the harmonic current component at the dc link. Thus, it features with lower power processing. Moreover, it exhibits better total harmonic distortion of the ac line current when compared with the traditional ac side shunt APF. Voltage and current loop models are developed for average current control, and the selection of the current loop bandwidth is presented. Switching stresses of the ac APF, the dc link APF, and the six-switch PFC are also calculated and analyzed. Experimental and simulation results demonstrate the effectiveness of this dc link APF. [ABSTRACT FROM PUBLISHER]

This letter proposes a hybrid modulation scheme for the average current control (ACC) of the series-type single-phase power factor correction (PFC). The series PFC is a newly developed harmonic correction method for single-phase diode rectifier. It is composed of a hybrid full-bridge inverter and is in cascade between the dc terminal of the diode rectifier and the dc load. When the conventional ACC is applied, due to the large duty-ratio variation at the low-frequency transition points, the line current waveforms exhibit large distortion at the low-frequency switching points. A hybrid scheme, which combines the leading-edge and the trailing-edge modulation, is developed to overcome this problem. The reference signal selection and control logic design are discussed and implemented. Experimental results show that the proposed hybrid approach is able to reduce the harmonic distortion in the line current significantly, as compared with the conventional ACC control. [ABSTRACT FROM AUTHOR]

This paper presents a new current control method for three-phase pulse width modulation rectifiers with active power factor correction (PFC). Conventional three-phase PFC control requires sensing of at least two input phase currents. Since the input line must be isolated from the control circuitry, current transformers or Hall effects current sensors are required for sensing the phase currents, which are bulkier and more expensive than resistive current sensors. Such electromagnetic current sensors are also difficult to integrate with the rest of the control circuitry, representing a major barrier for low-cost integrated PFC control development. The proposed current control method solves these problems by using only the dc-rail current as the feedback signal. The dc-rail current can be easily sensed by a shunt resistor, and the sensed signal can be directly used by the control circuitry without isolation or level shifting. The control method is developed based on a nonlinear average current control principle and avoids the steady-state phase error of conventional linear PI control. [ABSTRACT FROM AUTHOR]

• A quasi-online condition monitoring technique for wind power converter is proposed. • This method enables concurrent health monitoring of power module and cooling system. • This approach does not need to measure the power loss and junction temperature. The power converter plays an important role in the energy conversion and management of wind turbine system. It is one of the core components in the system, but also one of the most prone to fail components according to industry-wide survey. Condition monitoring of power converter can improve the reliable operation of wind turbine system and reduce its unscheduled downtime. In this paper, a novel quasi-online monitoring technique based on the time-constants of heat sink temperature is proposed to check the health status of wind power converter. Advantages of the proposed technique include: (1) This approach enables the monitoring of power module degradation and cooling system deterioration in the converter simultaneously. (2) This method does not need to measure the junction temperature and power loss which reduces the cost and complexity of operation. Experimental tests were conducted to verify the effectiveness of this technique. Results also indicate that the maximum coefficient of variation of time-constants is below 1.7% under different converter operating conditions and ambient temperatures. In addition, the maximum error of time-constants in the application of condition monitoring is less than 3.1%. [ABSTRACT FROM AUTHOR]

• A lifetime extension strategy for power module in wind energy system is proposed. • This strategy is based on the optimal effectiveness of the thermal management. • The effectiveness gives the choice criteria about temperature swing control target. • Each application of temperature control can improve as much lifetime as possible. • Disturbance on the regular operation of wind energy system is greatly reduced. The power module plays a vital role in the renewable energy conversion. But it is one of the most prone to fail components in the wind energy system. The thermal management has been proved to be a cost-effective mean to improve the reliability of wind energy system, but it has a dual nature. To balance the benefit and risk of thermal management, a lifetime extension strategy is proposed. This strategy considers the minimum junction temperature fixed to the lowest ambient temperature and the allowed maximum junction temperature determined by the predefined temperature swing. Then the related wind speeds of predefined temperature swing can be concentrated in a part wind speed area and the effectiveness of thermal management under each predefined temperature swing is calculated. The optimal effectiveness is chosen as a quantitative evaluation criterion to design the working range of thermal management and control target of junction temperature in a long time scale. As a benefit, the economic performance of thermal management is greatly improved in that each application of temperature control can reduce as much consumed lifetime of power module as possible. Case studies and experiments are presented for performance verification of proposed strategy. Results show that the consumed lifetime reduced by each application of temperature control is 6.04 × 10-3%. The expected lifetime of power module is extended from 7.55 years to 22.08 years which meets the target lifetime of wind power generation system (20 years). In addition, this method only needs to be applied in the specified working range where the wind speed is higher than 9.30 m/s. Thus, the disturbance on the system's normal operation is significantly alleviated. [ABSTRACT FROM AUTHOR]

The LLC resonant converters commonly adopt frequency modulation (FM) or combination of FM with phase-shift modulation to regulate its output voltage. However, in these control schemes, a variable switching frequency range is required, which makes the magnetic components design complicated. Therefore, in this article, magnetic control (or variable inductor control) is adopted to make the converter operating at constant switching frequency and constant duty cycle. The fundamental harmonic analysis is commonly used because of its characteristic of simplicity. However, the accuracy of this method is reduced and considerable errors occur when the switching frequency or output power changes. Therefore, an optimal design methodology based on time-domain analysis of the LLC resonant converter with magnetic control is proposed in this article. The proposed methodology can assure that the converter will operate in PO or OPO modes within the whole operating range, and zero voltage switching operation for primary switches and zero current switching operation for secondary rectifier will be guaranteed. In addition, by limiting the resonant tank root-mean-square current, the system efficiency is improved. A 200-W experimental prototype is built and the effectiveness of the proposed optimal design methodology is verified. [ABSTRACT FROM AUTHOR]

In this paper, a dual half-bridge LLC resonant converter with magnetic control is proposed for the battery charger application. The primary switches are shared by two LLC resonant networks, and their outputs are connected in series. One of the LLC resonant converters is designed to operate at the series resonant frequency, which is also the highest efficiency operating point, and the constant output voltage characteristic is achieved at this operating point. The second LLC resonant converter adopts magnetic control to regulate the total output current and voltage during both constant current charge mode and constant voltage charge mode. Meanwhile, the function decoupling idea is adopted to further improve the system efficiency. The significant amount of the power is handled by the LLC resonant converter operating at the series resonant frequency, whereas the second LLC resonant converter fulfills the responsibility to achieve closed-loop control. By carefully designing the resonant networks, the zero-voltage switching for primary switches and zero-current switching for secondary diodes can be achieved for whole operation range. A 320-W experimental prototype is built to verify the theoretical analysis, and the maximum efficiency is measured about 95.5%. [ABSTRACT FROM AUTHOR]

Optimization of the electronic properties of crystalline organic semiconductors is important for the evolution of organic optoelectronic devices. One method of tuning the electronic properties is by applying external pressure to semiconducting molecular crystals. A recent dispersion-inclusive density functional theory (DFT) investigation regarding the effect of pressure up to 20 GPa on herringbone polycyclic aromatic hydrocarbons (PAHs) has revealed anomalous pressure dependence of the electronic properties of six systems [J. Phys. Chem. C 122, 23828 (2018)]. Here, we use intermolecular electronic coupling values (H ab), calculated by fragment orbital DFT (FO-DFT) to elucidate the pressure dependence of the electronic properties. We show that discontinuities in the pressure dependence of the band structures are correlated with pressure-dependent discontinuities in the electronic couplings of certain molecular dimers. H ab is shown to be a useful descriptor for gaining insight into the pressure dependence of the electronic properties of crystalline organic semiconductors. [ABSTRACT FROM AUTHOR]

This letter presents a theory for the creation of harmonics by resonance in converter-grid systems. A harmonic of this type is usually not present or observable under normal operation, but may suddenly appear, with a growing magnitude and at a frequency that coincides with a system resonance frequency. The growth may be unbounded, leading eventually to a shutdown of the converter or other components in the system due to protection or physical damage, but often it stops after certain time and the harmonic sustains itself at a constant magnitude. The latter is the focus of this work and is identified as a result of system operation changing from an initially unstable mode to a critically stable mode achieved via a self-adjusting process. Small-signal sequence impedance models are used to explain this self-adjusting process and to determine the resulting harmonic responses. Experimental measurements are presented to validate the theory and to demonstrate the characteristics of this new type of harmonics. [ABSTRACT FROM AUTHOR]

The increase in wind power penetration leads to the risk of energy supply interruption in integrated electricity‐heat energy systems (IHES). This paper presents an analytical‐based approach for the efficient operational reliability evaluation of the IHES. The wind power distribution characteristic model considering correlation is constructed based on Hidden Markov Model (HMM). To reduce computational complexity, a critical system state identification (CSSI) method is proposed that characterises both random device failures and wind power uncertainty. Under each critical system state, the analytical function relationship between the reliability index and the uncertainty factors is established based on the virtual stochastic response surface (VSRS) method. The analytical function can directly calculate the reliability index when the wind power output varies, avoiding a large number of repeated calculations of the optimal load‐shedding model of the system and reducing the time required for reliability assessment. This allows the operator to evaluate the operational reliability of the integrated energy system in real‐time. The numerical simulation of the test system combining the IEEE 33‐node distribution system and the existing 28‐node heating system proves the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Phased warming in late winter and early spring can increase winter wheat grain yield. However, the effects of different durations of warming during this period on winter wheat grain yield and quality are not yet clear. Therefore, this study conducted field warming experiments in a movable polyethylene greenhouse during the late winter and early spring stages of the three wheat growing seasons from 2019 to 2022. The results showed that the accumulated growing degree days (GDD) of the warming treatment during the warming period were increased by 87.3–215.7 °C d compared to the control (CK). The warming treatment advanced and prolonged the duration of vegetative growth and spike differentiation after regreening, promoted spike and flower development, and increased grain length, grain width, and grain area. During the three growing seasons, the longer the warming duration (WD) of the warming treatment, the more obvious were the observed promoting effects on the kernel number per spike and 1000-kernel weight. From 2019 to 2021, compared to the CK, the spike number per unit area and grain yield of the warming treatments increased with the prolongation of WD. However, in the 2022 growing season the spike number per unit area and grain yield of the warming treatment were increased with longer WD, reaching the maximum at WD of 56 days and then gradually decreasing with longer WD. Compared to CK, the grain protein content, wet gluten content, and sedimentation value of the warming treatment decreased with the prolongation of WD. The promotion effect of longer WD on grain starch content and protein yield was more significant. In summary, the accumulated GDD during the warming period compared to CK was 155.8–181.2 °C d, and at WD of 50–56 days a relatively higher grain yield and protein yield could be obtained. [ABSTRACT FROM AUTHOR]

Insulated-gate bipolar transistor (IGBT) modules and dc-link capacitors are important parts in the majority of power electronic converters which contribute to cost, size, and failure rate on a considerable scale. This paper presents an online condition monitoring method for both IGBT modules and dc-link capacitors of power converters based on short-circuit current of an IGBT module, which is a good condition indicator according to the theory analysis. The failure prediction of dc-Link capacitor is realized by equivalent series resistance, which can be calculated by short-circuit current and a step voltage, and the bond wires fatigue can also be identified by the short-circuit current. The proposed method is capable for detecting small changes in the failure indicators of IGBT modules and electrolytic capacitors, and its effectiveness is validated by a confirmatory experiment. The novelty of the proposed method is that the degradations of IGBT modules and capacitors can be identified simultaneously, and has the merits of low cost and circuit simplicity [ABSTRACT FROM PUBLISHER]

Finding and replacing the defective insulated-gate bipolar transistor (IGBT) module timely by monitoring the ageing state of IGBT can improve the reliability of a power converter and reduce the loss caused by IGBT failure. A method for detecting the condition of bond wires in IGBT module by identifying the short-circuit current of IGBT module is presented in this paper. It is based on the fact that parasitic parameters of IGBT module are affected by the local damage induced by ageing over time, and these changes can be easily detected by monitoring the difference of short-circuit current. The study results indicate that short-circuit current of IGBT module decreases with module ageing over time, and the difference of short-circuit current caused by junction temperature is much smaller than that caused by bond wires fatigue on a specific gate driving voltage. Therefore, the IGBT module in the power converter can be diagnosed by detecting the difference of short-circuit current without considering the effects of junction temperature. Finally, a confirmatory experiment is carried out, and the correctness of the method proposed in this paper is verified. [ABSTRACT FROM AUTHOR]

With the widespread application of lithium-ion battery packs, it calls for efficient balancing methods to improve the performance of these battery systems. The relevant research has focused on the design of equalization circuits and control strategies while neglecting quantitative analysis and comparison of battery active equalization structures from the systematic level. In this paper, we propose an improved system-theoretic modeling approach for active equalization structures that takes into account the battery's constraints, including equalization current rate and SOC operation range. Accordingly, the mathematical models of various active equalization structures are derived that can describe their equalization dynamic behavior. Then, the analytical algorithms are developed to estimate the balancing time of active equalization structures online. Finally, extensive numerical simulations are conducted to evaluate and compare the average performance of these equalization systems in term of equalization time. It then comes up with a comprehensive comparison among them. Consequently, the Multicell-to-Multicell (MC2MC) balancing structure benefits the fast balancing speed and the lowest sensitive to initial batteries’ SOCs. The global structure has the lowest implementation cost and the series structure benefits the simplest control. Moreover, the module-based structures have faster balancing speed when each module contains about 4–6 batteries. [ABSTRACT FROM AUTHOR]

This letter proposes an indirect power dissipation level short circuit protection (IPDL-SCP) method for silicon carbide (SiC) metal-oxide semiconductor field-effect transistors (mosfets). Due to differences between normal conducting and short-circuit (SC) conditions, this method is triggered by the voltage oscillation vss at the parasitic inductance (Lss) of the source and directly monitoring vds of SiC mosfet. For verification, the short circuit protection circuit is tested and proved functional on the SC test bench. Experimental results show that the protection circuit can respond to both hard switching fault (HSF) and fault under load (FUL), while the fastest response delays are 75 ns for HSF and 170 ns for FUL. Comparisons with other commonly used SC protection methods have also been made, which show that the proposed IPDL-SCP method has better performance in shorter protection delays. [ABSTRACT FROM AUTHOR]

Due to global warming, high temperature stress severely impacts maize growth and development, especially during the early filling stage. Supplemental irrigation is an effective measure to mitigate high temperature stress in maize. However, the underlying mechanism for alleviating transient high temperature stress during the early grain-filling stage is still unclear. A two-year field experiment involving high temperature during the early filling stage (HT), supplemental irrigation under high temperature stress (HTW), supplemental irrigation under control condition (W), and control treatment (CK) by using heat-tolerant variety ZD958 and heat-sensitive variety XY335 was conducted. Compared with the CK treatment, the HT treatment significantly decreased the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). HT also significantly reduced the Pn, soluble sugar content in stem, and dry matter accumulation, thus reducing kernel number per ear and yield by 11.2–17.6% and 23.4–23.7% in the both variety, respectively. However, compared with HT, the HTW treatment reduced the daily mean canopy temperature of ZD958 and XY335 by 2.6 °C and 2.8 °C, respectively. Accordingly, HTW increased SPAD value, photosynthetic performance, starch and soluble sugars content in stems and leaves, and antioxidant enzymes activities, but reduced the malondialdehyde (MDA). Moreover, HTW increased the grain sink capacity, prolonged the effective filling days by 1.4–6.5 d, and increased the average filling rate by 14.8–41.0% compared with HT. Finally, grain yield of HTW was increased by 15.8–22.3% compared with HT. Therefore, supplemental irrigation could effectively enhanced maize heat resistance by reduce canopy temperature. This study provides important insights into enhancing maize resistance and yield stability under a warming climate. • Supplemental irrigation (SI) reduced the canopy temperature under heat stress (HT). • SI improved the antioxidant defense of maize under HT. • SI improved the photosynthesis and assimilate accumulation under HT. • SI increased assimilates availability thus improving kernel number per ear and yield. [ABSTRACT FROM AUTHOR]

Gate-oxide degradation has been one of the critical reliability concerns of silicon carbide (SiC) metal–oxide–semiconductor-field-effect transistors (mosfets), which could be monitored through aging-sensitive parameters. In this article, an online gate-oxide degradation monitoring method for planar SiC mosfets is proposed by extracting gate charge time at a specific range of gate voltage. It is based on the findings that the input capacitances of planar SiC mosfets change significantly over gate-oxide degradation, which is theoretically analyzed and experimentally verified. The capacitance variations are converted into the gate charge time as the new aging-sensitive parameter. The new parameter measurement circuit is proposed and integrated into the gate driver module. The article results indicate that the new parameter varies noticeably with gate-oxide degradation and the difference of this parameter caused by junction temperature is much smaller than that caused by degradation. Besides, the parameter is immune to package degradation and load current. The condition monitoring method can be implemented online since the parameter is extracted during the off-state of SiC mosfet devices, which does not affect normal operation. The confirmatory experiment is carried out to verify the correctness of the proposed method. [ABSTRACT FROM AUTHOR]

The survival benefit for patients with gastric cancer (GC) is modest due to its high transfer potential. Targeted therapy for metastasis-related genes in GC may be a viable approach, however, inhibitors specifically targeting GC are limited. In this study, GC patient-derived xenografts (PDX) with metastatic burden were established via orthotopic transplantation. PCR-Array analysis of primary and metastatic tumors revealed EPH receptor B2 (EPHB2) as the most significantly upregulated gene. The interaction between the EPHB2 receptor and its cognate-specific EFNB1 ligands was high in GC and correlated with a poor prognosis. Fc-EFNB1 treatment increased the invasion and migration abilities of GC cells and induced a high EPHB2 expression. EPHB2 knockdown in GC cells completely abolished the ephrin ligand-induced effects on invasion and migration abilities. Signal transduction analysis revealed Wnt/β-catenin and FAK as downstream signaling mediators potentially inducing the EPHB2 phenotype. In conclusion, the observed deregulation of EPHB2/EFNB1 expression in GC enhances the invasive phenotype, suggesting a potential role of EPHB2/EFNB1 compound in local tumor cell invasion and the formation of metastasis. [Display omitted] • EPHB2 and EFNB1 are co-expressed in gastric cancer cells and tissues. • The interaction between EPHB2 and EFNB1 significantly promoted gastric cancer metastasis. • EPHB2/EFNB1 compounds are potential indicators for the diagnosis of gastric cancer metastasis. [ABSTRACT FROM AUTHOR]

Background: Upland Cotton (Gossypium hirsutum L.) has few cotton varieties suitable for mechanical harvesting. The plant height of the cultivar is one of the key features that need to modify. Hence, this study was planned to locate the QTL for plant height in a 60Co γ treated upland cotton semi-dwarf mutant Ari1327. Results: Interestingly, bulk segregant analysis (BSA) and genotyping by sequencing (GBS) methods exhibited that candidate QTL was co-located in the region of 5.80–9.66 Mb at D01 chromosome in two F2 populations. Using three InDel markers to genotype a population of 1241 individuals confirmed that the offspring's phenotype is consistent with the genotype. Comparative analysis of RNA-seq between the mutant and wild variety exhibited that Gh_D01G0592 was identified as the source of dwarfness from 200 genes. In addition, it was also revealed that the appropriate use of partial separation markers in QTL mapping can escalate linkage information. Conclusions: Overwhelmingly, the results will provide the basis to reveal the function of candidate genes and the utilization of excellent dwarf genetic resources in the future. [ABSTRACT FROM AUTHOR]

In order to further improve the efficiency of dual-active-bridge (DAB) converter, a hybrid five-variable modulation scheme with minimal root mean square (rms) current is proposed in this article, which combines the traditional phase-shift and pulsewidth modulation schemes. By adopting the proposed optimal scheme, a wider zero-voltage switching (ZVS) operation range and lower rms current level are achieved simultaneously when compared with other modulation schemes, which significantly improves the efficiency of the DAB converter. Moreover, for the complexity of the proposed modulation scheme with five variables, the Fourier decomposition based analytical expressions are derived for the converter and a generalized performance analysis results are presented. Besides, in order to avoid the analysis error, especially at light-load condition, the optimization strategy takes the rms current as the optimal objective, which includes the eight harmonic component of the inductor current rather than just considers the fundamental component. And an offline particle swarm optimization algorithm is introduced to acquire the optimal operating points for the whole power range. To substantiate the effectiveness of the proposed modulation scheme, a comprehensive comparison among related works in terms of the rms value and ZVS range were carried out under various operation condition. Finally, a 1.2 kW experimental platform was built and the highest experimental efficiency under the proposed modulation scheme reaches 96.8%. [ABSTRACT FROM AUTHOR]

In this article, an online condition monitoring (CM) method is proposed for the bond wire degradation of insulated-gate bipolar transistor (IGBT) modules in a single-phase or three-phase three-level neutral-point-clamped (3LNPC) dc–ac, ac–dc converter. The proposed method has the ability to detect the whole IGBTs in a 3LNPC converter, based on finding the idle on-state IGBTs under the specific load current direction and switching sequence of a leg. The detection time is short (0.2 ms) and the influence of online CM on load current can be completely neglected as long as the insertion areas for CM test are chosen reasonably. Meanwhile, an advanced bond wire CM module is designed to conduct the CM test. This module can generate and inject the current pulse trains into IGBT modules, with the high current for CM test and low current for temperature-sensitive electrical parameter measurement, and sample the collector–emitter on-state voltage (VCE ON) stably and precisely. Finally, the experimental work was carried out to verify the effectiveness of the proposed method and the practicality of the developed CM module. [ABSTRACT FROM AUTHOR]

Gallium nitride (GaN) devices are widely used due to their excellent performance when integrated into power electronics applications. However, owing to their low parasitic parameters and fast switching speed, they are more prone to instability than the silicon devices. The sustained oscillation discussed in this article is one of the instability problems, which may result in overshoot or even more serious device breakdown; thus, it is pretty necessary to suppress it effectively in practical applications. It is the first time to adopt an RC snubber to suppress the sustained oscillation in this article, which is very simple and cheap but effective. First, the sustained oscillation modeling based on a double pulse circuit is carried out. Then, the RC region is established quantitatively according to the root locus analysis results, which makes up for the defects of these qualitative methods before. Furthermore, it is first found that the sustained oscillation can be fully suppressed due to the existence of dipoles. Finally, the oscillation suppression effect within the RC region is compared with that outside the region by the simulation and experimental results, which are consistent with the theoretical analysis. Additionally, the possible negative influence of the added RC snubber is also discussed in this article, which shows that it has a little impact on the switching speed and energy loss, while the sustained oscillation is well suppressed. [ABSTRACT FROM AUTHOR]

In the current study, a novel mixed-ligand coordination polymer, {[Co(L)(dpe)]·(ClO4)} (1) (H2LCl = 3-carboxy-1-(3-carboxybenzyl)pyridin-1-ium, dpe = (E)-1,2-di(pyridin-4-yl)ethene), was synthesized under hydrothermal conditions by a zwitterionic organic ligand and fully characterized by the single crystal X-ray diffraction, powder X-ray diffraction, elemental analysis along with the FT-IR. Furthermore, the treatment activity of the compound on the ulcerative colitis was evaluated and the related mechanism was explored. First, the level of the tumor necrosis factor (TNF)-α and superoxide dismutase (SOD) released by the colon tissue into the plasma was measured with enzyme-linked immunosorbent assay (ELISA) detection kit. In addition to this, the activation level of the JAK2/STAT3 signaling pathway in the colonic epithelial cells was also determined with western blot. With the help of molecular docking simulation, the potential interacting gestures between the complex and the protein have been revealed. [ABSTRACT FROM AUTHOR]

Asymmetric duty modulation (ADM), as a recently proposed modulation scheme, provides new chance to improve the performance of dual active bridge (DAB) converter. On this basis, an optimal ADM (OADM) scheme is proposed in this article to minimize the inductor peak-to-peak current over the whole voltage and power range. First, the DAB converter adopting ADM scheme is analyzed in frequency-domain and time-domain, and four operating modes are established. Then, the minimum peak-to-peak inductor current for each operating mode is obtained under Karush–Kuhn–Tucker condition, and the corresponding optimal closed-loop control with low calculation complexity is derived. Then, the key values and features of the OADM scheme are compared with recent state of the art, mainly including the inductor root mean square current and soft-switching performance. Finally, an experimental prototype was built to validate the efficiency enhancement of the converter by adopting the proposed OADM scheme. [ABSTRACT FROM AUTHOR]

In this article, an efficiency-oriented hybrid duty modulation (HDM) scheme is proposed for the dual active bridge (DAB) converter that can reduce the inductor root-mean-square (rms) current and extend the switch soft-switching range. First, a complete description of the combination forms of different modulation schemes is presented considering the allocation of the zero-voltage portion. A unified description for these combination forms is obtained in the frequency domain. Second, the symmetric–symmetric duty modulation (SSDM) scheme and asymmetric–symmetric duty modulation (A2SDM) scheme are established to minimize the inductor rms current by considering its fundamental component. Third, the characteristics of SSDM, A2SDM, and the traditional phase shift modulation schemes are compared from several aspects, mainly including the inductor rms current and the soft-switching performance. Furthermore, the loss breakdown analysis results for the three modulation schemes are presented and compared. According to these results, the HDM scheme is proposed to improve the overall efficiency of the DAB converter. Finally, an experimental prototype was built with a peak efficiency of 97%, which validates the effectiveness of the proposed modulation scheme. [ABSTRACT FROM AUTHOR]

Monitoring the defective multichip insulated gate bipolar transistor (IGBT) module is a cost-effective approach to improve the quality of customer service. A method using time duration of the gate charge is proposed to monitor bond wires fatigue of the multichip IGBT modules when the modules are in the off-state. It is based on the fact that failure of the chip branch due to bond wires fatigue changes the gate input capacitance of the multichip IGBT module. The health state of bond wires can be converted into the change of time duration of gate charge under the constant gate current. A driver containing the constant current source is proposed. The study results indicate that the time duration of the gate charge decreases significantly when the failure of the chip branch occurs, and the effect of junction temperature can be ignored within the special range of gate voltage. Condition monitoring can be implemented during the off-state of the multichip module and without considering the effects of junction temperature. The confirmatory experiment is carried out to verify the correctness of the proposed method. [ABSTRACT FROM AUTHOR]

Multiple output LED drivers are necessary to achieve better performance and higher reliability in street lighting, tunnel lighting and LCD background lighting applications. Based on LCL-T constant-current characteristics, a modular multiple output LED driver is proposed in this paper. The LCL-T rectifiers are connected to the same voltage bus and work like current sources. However, since there are much higher voltage harmonics in the AC square bus voltage, it is very important to quantitatively analyze how these harmonics influence the precision of the output currents. In addition, all of the switches can achieve Zero Voltage Switching (ZVS) by proper design of the LCL-T network. Finally, a 200-W prototype with five channels is established with an efficiency of 92.25%. [ABSTRACT FROM AUTHOR]

Grid-connected current quality is seriously affected by the low-order background harmonics in the gird-inverter dynamic system. The point of common coupling voltage feedforward impedance reshaping method of the grid-connected inverter is generally applied to solve this problem, however about 90° phase lag of the inverter output impedance is brought in, which would deteriorate the adaptability of the inverter to the weak grid. To solve this problem, this article proposes a novel frequency-division virtual impedance shaping method, which shapes the output impedance of the grid-connected inverter with different coefficients in different frequency bands, respectively. The basic principles, parameters design, and application analysis are studied in detail. With the proposed scheme, the grid-connected inverter can be equipped with strong adaptability to a wide range of grid impedance and suppression ability to the background voltage harmonics simultaneously. Theoretical analysis and experimental results confirm the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Aluminum electrolytic capacitor (AEC) is one of the most age-affected components in ac–dc conversion, and its equivalent series resistance (ESR) is an important index for reflecting the healthy condition of AEC. In AEC-used boost power factor correction (PFC) converters, ESR of AEC causes a small jump in the switching ripple of output voltage at switching moments, especially at turn-off moments. This small jump is hardly observed at line-frequency scale, either using time-domain analysis or frequency-domain analysis. However using time–frequency analysis this jump is very prominent due to its singularity. In this article, an online ESR estimation method of AEC is proposed by using the wavelet transform (WT) based time–frequency analysis. The relationship between ESR and the jump amount of output voltage at turn-off moments is analyzed first, and then the ESR calculation model is derived using WT with the wavelet basis of the first derivative of Gaussian function. An appropriate sampling interval for the output voltage and the inductor current is determined. Besides, the online ESR estimation scheme is implemented including the hardware and software designs. Furthermore, a prototype of boost PFC converter with 220 V ac input and 360 V dc output is built, where an average current mode control chip UC3854 is used. Four factors are discussed for estimation accuracy in the experiment, and the estimated results are consistent with the results measured by LCR meter with a relative error less than 10%. [ABSTRACT FROM AUTHOR]