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A more complete understanding of the molecular mechanisms that support milk synthesis is needed to develop strategies to efficiently and sustainably meet the growing global demand for dairy products. With the postulate that coding gene transcript abundance reflects relative importance in supporting milk synthesis, we analyzed the global transcriptome of early lactation cows across magnitudes of normalized RNA-Seq read counts. Total RNA was isolated from milk samples collected from early-lactation cows ( n = 6) following two treatment periods of postruminal lysine infusion of 0 or 63 g/day. Twelve libraries were prepared and sequenced on an Illumina NovaSeq6000 platform using paired end reads. Normalized read counts were averaged across both treatments, because EBseq analysis found no significant effect of lysine infusion. Approximately 10% of the total reads corresponded to 12,730 protein coding transcripts with a normalized read count mean ≥5. For functional annotation analysis, the protein coding transcripts were divided into nine categories by magnitude of reads. The 13 most abundant transcripts (≥50K reads) accounted for 67% of the 23M coding reads and included casein and whey proteins, regulators of fat synthesis and secretion, a ubiquitinating protein, and a tRNA transporter. Mammalian target of rapamycin, JAK/STAT, peroxisome proliferator-activated receptor alpha, and ubiquitin proteasome pathways were enriched with normalized reads ≥100 counts. Genes with ≤100 reads regulated tissue homeostasis and immune response. Enrichment in ontologies that reflect maintenance of translation, protein turnover, and amino acid recycling indicated that proteostatic mechanisms are central to supporting mammary function and primary milk component synthesis.

For the grid-connected inverter which acts as the key interface in renewable energy power generation systems, the gird current quality and the robustness are important indicators of the system behaviors. The low-frequency voltage harmonics existed in the grid voltage are mainly responsible for the current distortion, and the feedforward of the voltage at the PCC (point of common coupling) can effectively suppress low-order current harmonics. However, in the weak grid, the voltage feedforward may amplify the low-order current harmonics and endanger the robustness due to the high grid impedance. During the last decade, some studies have indeed discussed some improved feedforward methods; however, the comparative study is still lacking and it is not easy for engineers to choose suitable feedforward methods for the application. Therefore, based on the impedance-based modelling and stability criterion, this study deeply discusses the impact of different feedforward strategies (including proportional feedforward, full feedforward, fundamental feedforward, bandpass filter-based feedforward, and low-pass filter feedforward) on the system robustness and grid current quality, while the behavior of SOGI-PLL is considered. The features and merits of different feedforward strategies are reviewed, and the applicable occasions are discussed.

Traditional half-bridge converters often suffer from the neutral point voltage fluctuation which may result in unequal voltage stress on switching devices, common mode interference, and poor power quality. Therefore, a voltage-competing flyback-based balancer is proposed, and it simultaneously serves as the auxiliary power supplier and the neutral point voltage balancer with the limited power devices. Since the excessive power of the capacitor with the higher voltage is stored and transferred to the other one through the same primary winding, additional power loss caused by the leakage inductor is avoided. Meanwhile, the output voltage of the secondary winding has a close relation with the lower voltage of the DC-link capacitor, which can be utilized to monitor the capacitor voltage difference without paying the price for the isolated sampling of the DC-side voltage. Compared to the traditional switching balancing methods or the auxiliary-circuit-based balancing methods, the proposed balancer not only alleviates the control burden but also reduces the hardware complexity. The experiments are finally conducted on a balancer with 24V auxiliary power output to verify the effectiveness of the proposed balancer in equalizing the capacitor voltages of the half-bridge-type converters.

Swiss-rectifier (SR) is a novel type of rectifier structure which contains a three phase unfolder circuit and two symmetric DC-DC converters. In order to implement a simplified isolated rectifier system, two forward converters or phase-shift full bridge converters are used to achieve power factor correction (PFC). However, this kind of replacement requires two same transformers. Using more than one transformer is not conducive to the reduction of the volume. Therefore, an optimized isolated Swiss forward rectifier (OSFR) is proposed. Only one double-forward structure is used when the power is transmitting. Two voltage clamp branches are used to implement the PFC principle of the SWISS-rectifier. The principle of the operation is discussed specifically. The performances of the proposed converter are verified on a prototype with 90kHz switching frequency.

Small RNAs (smRNAs) are important regulators of many biologic processes and are now most frequently characterized using Illumina sequencing. However, although standard RNA sequencing library preparation has become routine in most sequencing facilities, smRNA sequencing library preparation has historically been challenging because of high input requirements, laborious protocols involving gel purifications, inability to automate, and a lack of benchmarking standards. Additionally, studies have suggested that many of these methods are nonlinear and do not accurately reflect the amounts of smRNAs in vivo. Recently, a number of new kits have become available that permit lower input amounts and less laborious, gel-free protocol options. Several of these new kits claim to reduce RNA ligase-dependent sequence bias through novel adapter modifications and to lessen adapter-dimer contamination in the resulting libraries. With the increasing number of smRNA kits available, understanding the relative strengths of each method is crucial for appropriate experimental design. In this study, we systematically compared 9 commercially available smRNA library preparation kits as well as NanoString probe hybridization across multiple study sites. Although several of the new methodologies do reduce the amount of artificially over- and underrepresented microRNAs (miRNAs), we observed that none of the methods was able to remove all of the bias in the library preparation. Identical samples prepared with different methods show highly varied levels of different miRNAs. Even so, many methods excelled in ease of use, lower input requirement, fraction of usable reads, and reproducibility across sites. These differences may help users select the most appropriate methods for their specific question of interest.

Additional file 3: Table S3. List of primers used in the RT-qPCR validation.

In the renewable power generation systems, ensuring the synchronization of the inverter and the power grid is crucial for the stable operation of grid-connected inverters. Nowadays, the phase-locked loop (PLL) technology has become a widely used grid synchronization method because of its simple implementation and robustness under various grid conditions. Even though a lot of PLLs have been proposed, the overview and comparative analysis of multiple PLLs can be helpful for the practical applications. In addition, the weak grid condition is a great challenge for the system. Therefore, this study firstly presents an overview of the existing PLLs together with their general structures and basic working principles. Depending on the implementation of the phase detector, the PLL can be divided into three categories: power-based PLL (pPLL), orthogonal-signal-generator-based PLL (OSG-PLL) and adaptive-filter-based PLL (AF-PLL). Then, from the above classification, seven typical single-phase PLLs are selected for further study. Finally, some test results are given, and a comprehensive evaluation of the selected PLLs under different grid conditions is conducted.

SUMMARY Abscisic acid (ABA) is an important phytohormone controlling responses to abiotic stresses and is sensed by proteins from the PYR/PYL/RCAR family. To explore the genetic contribution of PYLs toward ABA-dependent and ABA-independent processes, we generated and characterized high-order Arabidopsis mutants with mutations in the PYL family. We obtained a pyl quattuordecuple mutant and found that it was severely impaired in growth and failed to produce seeds. Thus, we carried out a detailed characterization of a pyl duodecuple mutant, pyr1pyl1/2/3/4/5/7/8/9/10/11/12. The duo-decuple mutant was extremely insensitive to ABA effects on seed germination, seedling growth, stomatal closure, leaf senescence, and gene expression. The activation of SnRK2 protein kinases by ABA was blocked in the duodecuple mutant, but, unexpectedly, osmotic stress activation of SnRK2s was enhanced. Our results demonstrate an important role of basal ABA signaling in growth, senescence, and abscission and reveal that PYLs antagonize ABA-independent activation of SnRK2s by osmotic stress., In Brief Zhao et al. generated duodecuple and quattuordecuple Arabidopsis PYL ABA receptor mutants. Characterization of the mutants revealed that the ABA receptors are critical for plant growth and development and negatively regulate ABA-independent SnRK2 activity by interacting with and inhibiting osmotic stress-activated SnRK2 protein kinases.

Silicon carbide (SiC) devices have attracted widespread attention because of their superior characteristics. However, not only the higher slew rate of drain–source voltage but also the higher slew rate of reverse recovery current can result in a more serious crosstalk problem than Si-based devices in a half-bridge application. Crosstalk suppression should be integrated into the gate driver to ensure the safe operation of SiC devices. Therefore, a specific mathematical analysis is done in this paper to figure out the crosstalk phenomenon. The limitations of the existing suppression methods are illustrated. Thus, a gate driver based on the magnetic coupling is proposed to ensure the gate–source voltage within the safe range, even when the positive and negative spurious pulse voltages appear. The proposed gate driver uses three ring transformers to insulate the control signal and driver power supply. So, it is feasible to drive a half-bridge circuit in the medium or high power applications. By saving optical couplers and isolated drive power supplies, the gate driver can realize fully galvanic isolation and generate the positive and negative gate–source driving voltage simply. The results derived from the proposed mathematical analysis and the effectiveness of the proposed driver in suppressing the spurious pulse voltage are verified by the experiments.

The developing human brain is uniquely vulnerable to methylmercury (MeHg) resulting in lasting effects especially in developing cortical structures. Here we assess by single-cell RNA sequencing (scRNAseq) persistent effects of developmental MeHg exposure in a differentiating cortical human-induced pluripotent stem cell (hiPSC) model which we exposed to in vivo relevant and non-cytotoxic MeHg (0.1 and 1.0 μM) concentrations. The cultures were exposed continuously for 6 days either once only during days 4–10, a stage representative of neural epithelial- and radial glia cells, or twice on days 4–10 and days 14–20, a somewhat later stage which includes intermediate precursors and early postmitotic neurons. After the completion of MeHg exposure the cultures were differentiated further until day 38 and then assessed for persistent MeHg-induced effects by scRNAseq. We report subtle, but significant changes in the population size of different cortical cell types/stages and cell cycle. We also observe MeHg-dependent differential gene expression and altered biological processes as determined by Gene Ontology analysis. Our data demonstrate that MeHg results in changes in gene expression in human developing cortical neurons that manifest well after cessation of exposure and that these changes are cell type-, developmental stage-, and exposure paradigm-specific.

Random variables could be dependent, and so could interval variables. To accommodate dependent interval variables, this work develops an efficient hybrid reliability analysis method to handle both random and dependent interval input variables. Due to the dependent interval variables, the reliability analysis needs to perform the probability analysis for every combination of dependent interval variables. This involves a nested double-loop procedure and dramatically decreases the efficiency. The proposed method decomposes the nested double loops into sequential probability analysis (PA) loop and interval analysis (IA) loop. An efficient IA algorithm based on the cut-HDMR (High Dimensional Model Representation) expansion is developed and a sampling strategy with the leave-one-out technique without extra calls of the limit-state function is proposed. The proposed method has good accuracy and efficiency as demonstrated by two engineering examples.

The performance of the grid-connected inverter was affected by the uncertainty of the grid conditions including the background distortion and the grid impedance. Typically, the feedforward of the grid voltage at the point of common coupling (PCC) highly suppressed the grid current harmonics caused by the grid voltage distortion; however, the PCC grid usually had a nonnegligible grid impedance, and the PCC voltage feedforward aroused serious grid current harmonics or instability. This study proposes a novel adaptive algorithm for the PCC voltage feedforward to work well with the varied grid impedance. In the proposal, the band-pass filters at the harmonic frequencies are used to detect the variation of the grid impedance as well as to facilitate the adaptive PCC voltage feedforward. It is not necessary to inject an additional harmonic to estimate the grid impedance. The basic principles as well as the realization and logic of the proposed algorithm are detailed, and some selected waveforms are provided to verify the superior performance. Compared with the typical robust design or adaptive control, the proposed algorithm does not have to sacrifice the dynamic or the harmonics rejection performance, or to use the on or offline grid impedance estimation.

Grid-connected LCL-filtered inverters are commonly used for distributed power generators. The LCL resonance should be treated properly. Recently, many strategies have been used to damp the resonance, but the relationships between different damping strategies have not been thoroughly investigated. Thus, this study analyses the essential mechanisms of LCL-resonance damping and reviews state-of-the-art resonance damping strategies. Existing resonance damping strategies are classified into those with single-state and multi-state feedback. Single-state feedback strategies damp the LCL resonance using feedback of a voltage or current state at the resonance frequency. Multi-state feedback strategies are summarized as zero-placement and pole-placement strategies, where the zero-placement strategy configures the zeros of a novel state combined by multi-state feedback, while the pole-placement strategy aims to assign the closed-loop poles freely. Based on these mechanisms, an investigation of single-state and multi-state feedback is presented, including detailed comparisons of the existing strategies. Finally, some future research directions that can improve LCL-filtered inverter performance and minimize their implementation costs are summarized.

In this paper, the inverter output impedance is passivized for solving the harmonic and the stability problems in the multiparallel inverters. The harmonics are easily aroused because of the disturbances, and the system stability is challenged by the grid impedance. Based on the simplified equivalent impedance model, the two problems are analyzed in the low-frequency (LF) band and the high-frequency (HF) band, respectively. Aiming at improving the LF performance, the weighted-proportional grid voltage feedforward and the harmonic quasi-resonant controller with phase compensation are proposed. The dynamic performance is enhanced with an additional current reference generation scheme. In order to improve the HF performance, a novel digital phase lead filter which brings the system back to a minimum-phase case is proposed. By the proposed control method, the high modulus of each inverter output impedance $Z_{o}$ is guaranteed, while the phase angles of $Z_{o}$ over the entire frequency band are avoided to be lower than −90°. The experiments based on four-parallel inverters have been conducted to validate the effectiveness of the proposed control method.

An LCL -filter draws much attention in grid-connected applications, but the design faces challenges. The LCL and controller parameters are interdependent and inter-restricted as the grid current quality and control stability rely on the parameters of them both. In the past, researchers found that extra sensors or complex algorithms were required for the stability when the LCL parameters were designed independently. Consequently, the system cost and complexity were increased. Indeed, the LCL -filter with the delay-dependent single-loop current control can be stable if the LCL parameters are properly selected. Based on this thought, this study proposes to design the LCL parameters by considering their impact on the stability and dynamic of the inverter. Extra sensors or complex algorithms are no longer required. Based on establishing the model of the single-loop inverter-side current controlled inverter, the criteria of LCL design are obtained in order to improve the stability and the rejections of low-order and switching current harmonics. Based on those design criteria, a step-by-step procedure is proposed. Selected results have been provided to demonstrate the effectiveness of the proposed design.

Transposons are generally kept silent by epigenetic mechanisms including DNA methylation. Here, we identified a pair of Harbinger transposon-derived proteins (HDPs), HDP1 and HDP2, as anti-silencing factors in Arabidopsis. hdp1 and hdp2 mutants displayed an enhanced silencing of transgenes and some transposons. Phylogenetic analyses revealed that HDP1 and HDP2 were co-domesticated from the Harbinger transposon-encoded transposase and DNA-binding protein, respectively. HDP1 interacts with HDP2 in the nucleus, analogous to their transposon counterparts. Moreover, HDP1 and HDP2 are associated with IDM1, IDM2, IDM3 and MBD7 that constitute a histone acetyltransferase complex functioning in DNA demethylation. HDP2 and the methyl-DNA-binding protein MBD7 share a large set of common genomic binding sites, indicating that they jointly determine the target specificity of the histone acetyltransferase complex. Thus, our data revealed that HDP1 and HDP2 constitute a functional module that has been recruited to a histone acetyltransferase complex to prevent DNA hypermethylation and epigenetic silencing.

Salt stress is a major environmental factor limiting plant growth and productivity. We recently discovered an important new salt tolerance pathway, where the cell wall leucine-rich repeat extensins LRX3/4/5, the RAPID ALKALINIZATION FACTOR (RALF) peptides RALF22/23 and receptor-like kinase FERONIA (FER) function as a module to simultaneously regulate plant growth and salt stress tolerance. However, the intracellular signaling pathways that are regulated by the extracellular LRX3/4/5-RALF22/23-FER module to coordinate growth, cell wall integrity and salt stress responses are still unknown. Here, we report that the LRX3/4/5-RALF22/23-FER module negatively regulates the levels of jasmonic acid (JA), salicylic acid (SA) and abscisic acid (ABA). Blocking JA pathway rescues the dwarf phenotype of the lrx345 and fer-4 mutants, while disruption of ABA biosynthesis suppresses the salt-hypersensitivity of these mutants. Many salt stress-responsive genes display abnormal expression patterns in the lrx345 and fer-4 mutants, as well as in the wild type plants treated with epigallocatechin gallate (EGCG), an inhibitor of pectin methylesterases, suggesting cell wall integrity as a critical factor that determines the expression pattern of stress-responsive genes. Production of reactive oxygen species (ROS) is constitutively increased in the lrx345 and fer-4 mutants, and inhibition of ROS accumulation suppresses the salt-hypersensitivity of these mutants. Together, our work provides strong evidence that the LRX3/4/5-RALF22/23-FER module controls plant growth and salt stress responses by regulating hormonal homeostasis and ROS accumulation.

In the inverter-grid interconnected system, the impedance model which breaks the entire system into two independent subsystems is widely adopted to facilitate the stability analysis. This paper shows that the inverter output impedance Z o may be erroneously estimated if the frequency coupling effect of the phase-locked loop (PLL) is overlooked. To fully capture the dynamic interactions between the single-phase inverter and the grid, a multifrequency admittance matrix is proposed based on the linearized small-signal PLL model. Further on, a developed single-frequency output impedance model characterized by clear physical meaning is derived to facilitate the resonance identification and the stability assessment. It is found that Z o also depends on the grid impedance, which significantly influences the interconnected system stability under the weak grid. Using the impedance-based stability criterion, the stability of the single-phase grid-tied inverter system can be clearly identified. The close match between the theoretical output impedance curve and the measurement result validates the correctness of the proposed impedance model. The experimental waveforms also verify that the dynamic interactions contributed by the frequency-coupling effect of the PLL and the grid impedance.

In the distributed power generation system (DPGS), the dynamic performance and stability of grid-connected inverter are endangered by the non-ideal factors at the point of common coupling (PCC), including the grid impedance, the grid voltage fluctuation and the grid fault. This study focuses on the instability issue under the grid voltage fluctuations or faults. It is found that the reduction of voltage value can affect the loop gain of the phase-locked loop (PLL). Consequently, the inverter output impedance under the non-nominal grid voltage is affected, and the closed-loop poles of the overall grid-connected system with the grid impedance can move toward the unstable region. Hence, the inverter can be unstable if the magnitude of the grid voltage sags deeply in the weak grid. As a result, the protection can be triggered before the voltage supporting strategy comes into effect, and yields the failure of low-voltage ride-through. Test results have been provided to demonstrate the correctness of the presented analysis.

Grid-connected inverters are widely used in the distributed power generation systems (DPGSs). The grid voltage fluctuations or grid faults are considerably harmful to the inverter and even the DPGSs. To cope with the demand of high- or low-voltage ride-through, many fault voltage support strategies were proposed. Note that an important issue, i.e., the current or voltage overshoot before the supporting strategy took over, was not deeply discussed. Instead, the system elements including the capacitors and switches with high voltage or current ratings have to be used, which might not be cost-effective. Hence, this study analyzes the transient behavior of a grid-connected LCL-filtered inverter while the grid voltage varies. The impacts of system parameters on the overshoots have been discussed. It has been shown that the LCL filter parameters can have considerable impacts. Consequently, a novel design method has been proposed to suppress the transient overshoots. Hence, because of the reduced overshoots, the voltage or current level of inverter components can be reduced.

In the battery energy storage systems, the existing isolated bidirectional DC/DC converters fail to achieve high-efficiency because it is difficult to achieve soft-switching and low current stress simultaneously in the full operation range. A novel current-fed isolated bidirectional dc-dc converter with two transformers and two half bridges at the high voltage side is proposed to solve the problem. The PWM plus dual phase shift modulation (PPDPS) with voltage-match control is applied to keep peak and rms current of the transformers low. ZVS for most switches can be ensured by the control strategy, while practical ZVS for the rest switches is achieved by the magnetizing currents of the transformers. Therefore, low conduction losses and switching losses can be obtained in the proposed converter. The theoretical analysis and the soft-switching capability of the proposed converter are verified by the experimental results.

The injected current quality of the multi-parallel grid-connected inverters is challenged by the circulating resonant currents which usually locates beyond the control bandwidth. Taking the digital control and the nonlinear PWM into consideration, this paper analyzes the resonant characteristics of the circulating currents. Firstly, assuming that the modulated wave is polluted with harmonics, based on the one-dimensional spectrum analysis method, the harmonic spectra of the bridge voltage is mathematically deduced. The multifrequency model of the parallel single-phase grid-connected inverters is then proposed. Applying the generalized Nyquist stability criterion to the proposed model, the resonant frequency of the circulating currents can be predicted, and the influence of the carrier phase on the parallel system stability is revealed. Finally, it is pointed out that the enlargement of the modulus of the output impedance contributes to suppress the circulating currents. The experimental results verified the correctness and effectiveness of the proposed model.

Phase-locked loops (PLLs) are the key technique for inverters to be synchronized with the PCC voltage. Typically, in the single-phase applications, the delay-based PLL is being widely used. However, for nowadays applications where the inverter may be connected to the PCC with large grid impedance, the inverter performance can be endangered, and harmonics or even instabilities are aroused. Although there are some relevant literatures, the solutions for solving the adverse impacts of delay-PLL on the system performance are still not well documented. Therefore, this paper aims to study the limitations of delay-based PLL and provide an improved approach. Through the inverter output impedance modelling, the reason why the delay-based PLL causes the instability in the weak grid case has been clearly explained. Then, the way to solve the instability caused by the PLL has been discussed, and an improved delay-based PLL has been proposed to improve the weak grid compatibility of inverters. The single-phase inverter system can then work well when the grid impedance varies widely.

Swiss-rectifier is a family of high efficient AC-DC topologies. It's a combination of an input voltage selector and two symmetric DC-DC converters. In order to obtain an isolated single-stage rectifier system, the forward converter is used to replace the DC-DC converter in the recently study. However, the hard switching operation of forward converter is unfavorable to increase the working frequency of the magnetic elements. By replacing the forward converter with the phase-shifted full-bridge, the intensive stress of switches is released and the ZVS condition of high-frequency switches can be achieved. Compared with the currently Swiss-forward rectifier, the soft switching modulation mode and duty cycle loss must be considered into the new control scheme of the Swiss phase-shift full-bridge rectifier (SPFR). As a result, the control scheme design is shown in this paper and its characteristics are verified by the experimental results of a prototype.

The upper and lower power switches of sub modules (SMs) in Modular Multilevel Converter (MMC) could be switched on simultaneously by disturbances which could destroy the SM circuit and cause damage to MMC. To improve reliability, this paper proposes a novel SM topology based on the combinational power circuit. It consists of three circuits: the half-bridge circuit, clamping circuit and energy-transfer circuit. It overcomes the shoot-through problem using the impedance-source network. The fluctuation of SM capacitor voltages can be controlled by the hysteresis control strategy in each SM. The SMs are self-balanced by making the fluctuation of each SM capacitor voltage consistent. The circulating harmonic current can be small even without any circulating current suppression strategy (CCSS). Without the need for voltage balancing control and CCSS, it greatly reduces the computation load. Finally, a five-level single-phase experimental platform is established to verify the feasibility of MMC based on the proposed SM topology.

The hard-switching operation and the intensive stress of switches are two common problems in current Swiss rectifiers, which seriously affect the characteristics of the power rate and the power density. In order to improve the power density in high power applications, a novel isolated Swiss rectifier, named Swiss phase-shift full-bridge rectifier (SPFR), is presented. A novel modulation strategy is also proposed to realize the soft switching in SPFR. The principle of the soft-switching is discussed in detail. The characteristic of the soft-switching in SPFR are verified by the experimental results of a prototype rated at 10kW.

To improve the operation reliability of modular multilevel converters (MMCs), a fault-tolerant control method based on model predictive control (MPC) for MMC without redundant submodules (SMs) is proposed in this paper. It is sequenced by two steps. First, the AC current was conducted with optimal control. Second, multi-objective optimal control was carried out for circulating current and AC current. The calculation amount of the proposed method is 8 times. MMC can have good static and dynamic performance by the proposed control method not only under the normal condition but also under the faulty condition that the arm is asymmetric. The feasibility and advantages of the proposed method had been validated by the experimental results of a 5-level prototype.

In the distributed power generation systems, to suppress the switching harmonics, LCL filter combined with LC trap is attracting wide attention. However, in the digital control system, due to the folding effect of extra resonance poles, such LCL -LC- Trap filter behaves quite different from LCL filter. If the design and control of LCL -LC- Trap filter do not seriously consider the folding effect, the inverter can even be unstable. It is quite necessary to formulate a robust design and control dedicated for LCL -LC- Trap filter. First, this study analyzes the resonance of LCL -LC- Trap filter and shows the difference from LCL filter. To suppress the extra peak and phase sag caused by the folding effect, a passive resistor is then added. Unlike the typical passive damping, power loss of the passive resistor for suppressing the folding effect is minimal. By solving the folding effect, LCL -LC-Trap filter is treated as LCL filter within the Nyquist frequency. Then, a stability-oriented design based on resonance-frequency selection is provided, with which the inverter with LCL -LC- Trap filter can achieve the optimal phase margin in the default case while being robust for filter parameters variation. At last, results have been provided to verify the analysis and design.

The LCL filter has excellent high-frequency harmonics attenuation capability, However, due to the inherent resonance of LCL filter, it is necessary to add damping strategy. Although there are many passive damping schemes, such as series R, series RL, shunt RC and shunt RLC, there are few studies on the performance comparisons of these passive damping schemes. Besides, it is hard to know which one is cost-effective, given that higher-order damping methods complicate the power circuit and require more components. Therefore, this paper aims to study the performances, merits and applicable occasions of various types of passive damping schemes. At first, based on the traditional LCL filter parameter design method, combined with the design criteria derived from the view of improving the system dynamic, the unified design flowchart of the LCL filter with various passive damping is proposed. Then, for a 5kW single-phase grid-connected inverter, the parameters of LCL filter with above four passive damping schemes are selected. Their performances are evaluated from the aspects of damping loss, volume and weight. Finally, comparative results have shown the applicable occasions of different passive damping schemes.

The dynamic sag correctors are used at the sensitive load terminals of the centralized power supply in order to avoid the grid voltage sag. This paper focuses on the correction of grid voltage swell/sag in large range and the quality of compensated voltage. A wide correction range dynamic voltage corrector is proposed for solving above problems with low cost. The operation principle, the voltage corrector range, and the design consideration of key parameters are analyzed. The increase of dc-link voltage broadens the voltage sag correction range, while the realization of the voltage swell correction benefits from the bidirectional energy flow. The simulation and experimental results verify the validity of the theoretical analysis. A prototype which applies to the centralized power supply-based ground power unit for aircrafts has been developed. It is characterized as small size, light weight, high compensation efficiency, good dynamic performance, and high quality of output waveform.

For grid-connected LCL-filtered inverters, dual-loop current control with an inner-loop active damping (AD) based on capacitor current feedback is generally used for the sake of current quality. However, existing studies on capacitor current feedback AD with a control delay do not reveal the mathematical relation among the dual-loop stability, capacitor current feedback factor, delay time and LCL parameters. The robustness was not investigated through mathematical derivations. Thus, this paper aims to provide a systematic study of dual-loop current control in a digitally-controlled inverter. At first, the stable region of the inner-loop AD is derived. Then, the dual-loop stability and robustness are analyzed by mathematical derivations when the inner-loop AD is stable and unstable. Robust design principles for the inner-loop AD feedback factor and the outer-loop current controller are derived. Most importantly, ensuring the stability of the inner-loop AD is critical for achieving high robustness against a large grid impedance. Then, several improved approaches are proposed and synthesized. The limitations and benefits of all of the approaches are identified to help engineers apply capacitor current feedback AD in practice.

The three tandemly arranged CBF genes, CBF1, CBF2, and CBF3, are involved in cold acclimation. Due to the lack of stable loss-of-function Arabidopsis (Arabidopsis thaliana) mutants deficient in all three CBF genes, it is still unclear whether the CBF genes are essential for freezing tolerance and whether they may have other functions besides cold acclimation. In this study, we used the CRISPR/Cas9 system to generate cbf single, double, and triple mutants. Compared to the wild type, the cbf triple mutants are extremely sensitive to freezing after cold acclimation, demonstrating that the three CBF genes are essential for cold acclimation. Our results show that the three CBF genes also contribute to basal freezing tolerance. Unexpectedly, we found that the cbf triple mutants are defective in seedling development and salt stress tolerance. Transcript profiling revealed that the CBF genes regulate 414 cold-responsive (COR) genes, of which 346 are CBF-activated genes and 68 are CBF-repressed genes. The analysis suggested that CBF proteins are extensively involved in the regulation of carbohydrate and lipid metabolism, cell wall modification, and gene transcription. Interestingly, like the triple mutants, cbf2 cbf3 double mutants are more sensitive to freezing after cold acclimation compared to the wild type, but cbf1 cbf3 double mutants are more resistant, suggesting that CBF2 is more important than CBF1 and CBF3 in cold acclimation-dependent freezing tolerance. Our results not only demonstrate that the three CBF genes together are required for cold acclimation and freezing tolerance, but also reveal that they are important for salt tolerance and seedling development.

Random and interval variables often coexist. Interval variables make reliability analysis much more computationally intensive. This work develops a new hybrid reliability analysis method so that the probability analysis (PA) loop and interval analysis (IA) loop are decomposed into two separate loops. An efficient PA algorithm is employed, and a new efficient IA method is developed. The new IA method consists of two stages. The first stage is for monotonic limit-state functions. If the limit-state function is not monotonic, the second stage is triggered. In the second stage, the limit-state function is sequentially approximated with a second order form, and the gradient projection method is applied to solve the extreme responses of the limit-state function with respect to the interval variables. The efficiency and accuracy of the proposed method are demonstrated by three examples.

From the perspective of output voltage control stability, this study investigates the stable operating area of photovoltaic (PV) cells feeding the DC–DC converter in output voltage regulation (OVR) mode. In this study, the boost interface converter is taken as an example, and its control system arrangements, small-signal model including the dynamic equivalent circuit of PV cells and the closed-loop transfer functions with different control loop formation are deduced at first. After that, according to the Hurwitz criterion, the essential condition for output voltage control stability is analysed and the relations between control loop formation of the interface converter in OVR mode and the stable operating area are obtained. The validity of the theoretical analysis has been verified by the experiment and simulation results of a 150 W prototype. The investigation shows that: (i) no matter what kind of control loop formation is adopted, the PV cells cannot output the maximum power when the PV interface converter operates in OVR mode; (ii) when the interface converter operates in OVR mode, PV cells can only operate stably in voltage area or current area. Moreover, the type of operating area entirely depends on the converter's output voltage control loop formation.

In single phase grid-tied inverter application, the phase of the current reference is usually synchronized with the grid voltage with the aid of the phase-locked loop (PLL). If the PLL is not well designed, large low-order harmonics of the injected current may be observed under the inductive grid impedance. To reveal the influence of the PLL on the inverter's stability, this paper builds the multi-frequency model of the PLL. By embedding the PLL model into the inverter output impedance, the frequency coupling phenomenon is revealed, and the phase of the inverter output impedance declines more around the synchronous frequency. The simulation and the experimental results validated the proposed multi-frequency model.

Grid harmonic suppression and robustness to the grid impedance are two major concerns for grid-connected inverters under weak grid. Traditional Grid Voltage Feedforward compensation and Harmonic Quasi Resonant controllers are adopted for harmonic suppression and output impedance reshaping. However, control effect is unsatisfied and instability maybe triggered due to the non-negligible grid impedance. Therefore, this paper proposes to insert a UPQC-based converter in series with the grid-connected inverter. In this way, both high modulus and passivity of output impedance are guaranteed, which ensures better performance on wide range of harmonic suppression and robustness to grid impedance. Application can be extended to n-parallel inverters to enlarge stable operation region. The validation of the proposed method is verified by simulation.

For the grid-connected LCL-filtered inverter, for the purpose of using a minimal number of sensors, the grid current feedback active damping (GCFAD) based closed-loop control was widely discussed. However, the performance with such control was seriously affected by the grid conditions at the point of common coupling (PCC), especially the large grid impedance. Thus, in this study, the stability with GCFAD in the weak grid is discussed first and the relations between the robustness and system parameters are derived by mathematic derivations. The contradiction between the control bandwidth and the robustness is found. Based on the above analysis, a novel phase shaping method has been proposed for GCFAD to maintain a high robustness with a desired bandwidth. Selected simulation and experimental waveforms are provided to show the correctness of the analysis and the effectiveness of the improved control approach.

In grid-connected inverter applications, the phase-locked loop (PLL) and the feedforward of the grid voltage at the point of common coupling (PCC) were commonly used to ensure a high-quality grid current with unity power factor and low grid current distortion. However, when the inverter is linked to the PCC with a large grid impedance (specifically, with a low short-circuit-ratio (SCR) less than 5), the inverter performance and the stability were seriously endangered. Through theoretical analysis, it has been found that the cause of such phenomenon was that the inverter output impedance was improperly shaped because the grid impedance voltage was involved in the input single of PLL. Therefore, this study proposes an adaptive control method for the PLL. Based on online grid impedance estimation, the signal used as the input of the PLL is carefully modified to solve the instability caused by the large grid impedance. The principle of the proposed method is briefly explained, and selected waveforms are provided to demonstrate the effectiveness of the proposal.

The passive output impedance of the grid-connected inverters is proposed to suppress the harmonics and instabilities under either the capacitive or the inductive grid condition. The presented control method, the weighted proportional grid voltage feed-forward (WP-GVF) and the active damping delay compensation, wipe out the capacitive and the inductive non-dissipative regions of the inverter output impedance. Moreover, a reactive RC damping branch is placed in parallel with the inverter to provide the sufficient phase margin (PM) above the Nyquist frequency. By the proposed control and reactive method, the output impedance is passivized with the satisfied PM starting from the 5th harmonic frequency, and the inverter-grid system stability is guaranteed in the complicated grid. The effectiveness of the proposed method is validated by the experimental results on a T-NPC LCL-filtered grid-connected inverter.

High voltage gain and low current ripple on the low-voltage side can be achieved by both the new isolated bidirectional DC/DC converter based on the Cuk converter(I-DCuk-BDC) and the existing current-fed half-bridge converter(I-DBoost-BDC), so both are suitable for the battery energy storage system. Based on the analysis of the operating principles, the power transfer characteristic, the soft-switching ranges are analyzed, and the power losses are compared in terms of the 48V/400V battery energy storage application. The analysis results reveal that the power loss of the I-DBoost-BDC is less than that of the I-DCuk-BDC, which means the I-DBoost-BDC is superior to the I-DCuk-BDC in this application. The good characteristics of the I-DBoost-BDC has also been verified by the simulation and experimental results.

For the grid-connected LCL-filtered inverter in the distributed generations, the current control with one current feedback only is attracting a wide attention for the use of minimal sensors. Even though, it is found that the typical inverter-side current control with the filter-based active damping faces several problems, including 1) a contradiction between high bandwidth and stability, 2) a poor robustness under parameters variations and 3) a weak rejection of grid current low-order harmonics. To solve these problems while reserving the merit of using minimal number of sensors, this study proposes an inverter-side current control with reduced control delay and improved grid-voltage feedforward. By placing the PWM reference reloading instant at the moment the computation of control algorithm is finished, the digital control delay time is negligible so that the mentioned contradiction and the poor robustness are solved. With an extra first-order derivative feedforward of grid voltage, the limitation of inverter output impedance magnitude no longer exists so that the rejection of grid current low-order harmonics can be much strengthened. Finally, simulations and experiments prove that the improved inverter-side current control works much better than the typical inverter-side current control.

A MOSFET’s gate driver based on magnetic coupling is investigated. The gate driver can meet the demands in applications for wide range of duty cycles and high frequency. Fully galvanic isolation can be realized, and no auxiliary supply is needed. The driver is insensitive to the leakage inductor of the isolated transformer. No gate resistor is needed to damp the oscillation, and thus the peak output current of the gate driver can be improved. Design of the driving transformer can also be made more flexible, which helps to improve the isolation voltage between the power stage and the control electronics, and aids to enhance the electromagnetic compatibility. The driver’s operation principle is analyzed, and the design method for its key parameters is presented. The performance analysis is validated via experiment. The disadvantages of the traditional magnetic coupling and optical coupling have been conquered through the investigated circuit.

Although researchers have established that DNA methylation and active demethylation are dynamically regulated in plant cells, the molecular mechanism for the regulation of active DNA demethylation is not well understood. By using an Arabidopsis (Arabidopsis thaliana) line expressing the Promoter RESPONSIVE TO DEHYDRATION 29A:LUCIFERASE (ProRD29A:LUC) and Promoter cauliflower mosaic virus 35S:NEOMYCIN PHOSPHOTRANSFERASE II (Pro35S:NPTII) transgenes, we isolated an mbd7 (for methyl-CpG-binding domain protein7) mutant. The mbd7 mutation causes an inactivation of the Pro35S:NPTII transgene but does not affect the expression of the ProRD29A:LUC transgene. The silencing of the Pro35S:NPTII reporter gene is associated with DNA hypermethylation of the reporter gene. MBD7 interacts physically with REPRESSOR OF SILENCING5/INCREASED DNA METHYLATION2, a protein in the small heat shock protein family. MBD7 prefers to target the genomic loci with high densities of DNA methylation around chromocenters. The Gypsy-type long terminal repeat retrotransposons mainly distributed around chromocenters are most affected by mbd7 in all transposons. Our results suggest that MBD7 is required for active DNA demethylation and antisilencing of the genomic loci with high densities of DNA methylation in Arabidopsis.

This paper presents a novel combined-synchronous-rectifier high-frequency-link (CSR-HFL) inverter. Three types of conventional HFL inverters are analyzed and their performance is summarized. According to one of the conventional HFL inverters, i.e., cycloconverter-type HFL (CHFL) inverter, a combined rectifier topology is deduced. To prevent a shorted circuit, two additional switches are used in the new topology. The operation mode of the CSR-HFL inverter is analyzed and the mathematical relationships are given. The difference and correlation, and advantages and disadvantages, are analyzed between the CSR-HFL inverter and the conventional HFL inverter. The relevant grid-connected inverter, ac/ac converter, and full-wave CSR-HFL inverter are also given. The experimental results verify that the proposed CSR-HFL inverter has excellent performance and high efficiency.

With two controllable switches, the efficiency of the two-switch buck-boost converters can be optimised by adopting appropriate control schemes. Among the control schemes, when only one switch works at high frequency, losses of the converter can be reduced effectively, but the complicated control logic and compensation technique are needed for step-up/down smooth transitions; when both switches operate at high frequency, the efficiency of these converters are low for high-voltage applications because of the serious switching losses. In this study, the coupled inductor is introduced to reduce the switching losses of these converters for high-voltage application and an asynchronous control scheme is proposed to reduce the losses much more. Based on the designed prototype, theoretical calculation, experiment results and loss analysis are provided to compare the traditional converter adopting single-winding inductor and the proposed circuit with the coupled inductor. And the comparisons of the converter adopting coupled-inductor with the tradition synchronous control scheme and that with the proposed asynchronous control scheme are also presented. The analysis and experimental results show that the efficiency of the converter adopting coupled inductor with the proposed asynchronous control scheme is the highest one. Moreover, the smooth transitions between step-up and step-down are also guaranteed by the proposed asynchronous control scheme.

Current-controlled LCL-filtered inverters are usually paralleled together for interconnecting the renewable energy resources into the grid. When the inverter output impedance is not well designed, the harmonic circulating currents out of the control bandwidth may be easily aroused. To reveal this resonant phenomenon and to enhance the stability of the parallel system, this paper builds the parallel system model with the consideration of the asynchronous carrier wave. Aiming at optimizing the inverter output impedance around the resonant frequency, a simple control method, which cascades the classical active damping loop with a proportional resonant controller with phase compensation, is proposed for the parallel inverter system. Each inverter is carefully designed with a minimum phase behavior by tuning the control parameters. Both the high modulus and the passivity of the output impedance are guaranteed to mitigate the circulating resonant currents. The effectiveness of the proposed control method is experimentally validated by a three-parallel inverter system.

To improve the reliability of modular multilevel converter (MMC), the fault submodules must be isolated rapidly. In this paper, a new fast fault diagnosis method is proposed containing two steps: fault detecting and fault locating. Fault detection step finds failures by improved predictive model which detects the fault by comparing the difference between the predictive value and the measured one of the arm current with the threshold value. Then the failures are located by the proposed location method which contains two process: feature mining and fault location. The proposed method could locate multiple submodule failures without additional sensors rapidly and can be easily implemented with a microprocessor. The proposed method has been validated by the simulation results.

In order to improve the robustness of fault diagnosis method based on model in the modular multilevel converter, an improved predictive model of the circulating current is established. A correction method is proposed to compensate for the uncertainties of the parameters and the measurement errors, and the disturbances are eliminated by using multi-step prediction method. The fault detection method detects faults through comparing the average value of difference between the measured value and the predictive one with the threshold value, and the fault location pinpoints faults by comparing the difference between the capacitor voltage of submodule and the average voltage of submodules with the threshold value. The simulation results verify that the proposed method is characterized with strong robustness.

Silicon carbide (SiC) devices attract widespread attention of scholars because of their superior characteristics. However, the interaction between the upper and lower devices during the switching process in the bridge circuit will affect the safe operation of SiC devices. To suppress the crosstalk spurious voltage, this paper proposes a gate driver circuit based on magnetic coupling for SiC devices to adjust the gate-source voltage to the safe range when the positive and negative spurious pulse voltages appear. Compared with the existent gate drivers for crosstalk suppression, the proposed circuit can realize fully galvanic isolation and generate the positive-negative gate-source voltage without auxiliary power supplies. As a result, the gate driver circuit is simplified and conducive to the integration. Based on the experimental results, the performance of the proposed circuit is evaluated.