This paper introduces a new MMC topology, in which each phase leg consists of four arms. Two of the arms consists of cascaded connected submodules and are just like single phase leg in traditional MMC topology. Another two arms are formed by series switches such as high voltage IGBT, which are only activated when the ac voltage changes polarity. And then three phase legs are series connected in vertical direction to support the DC bus voltage. The major advantage of proposed topology are as follows: (1) The total number of required submodules are reduced to 1/3 compared with traditional MMC topology. (2) The energy ripple in each arm is calculated to be smaller than the traditional 3-phase MMC. Therefore, the total capacitor size can be reduced. A detailed 20 MW simulation has been conducted and the related results of proposed topology have been presented. What's more, The SM prototype and preliminary experiments are also demonstrated and analyzed.
Salt stress adversely affects the growth and yield of crops. Glutathione S-transferases (GSTs) are involved in plant growth and responses to biotic and abiotic stresses. In this study, 400 mM NaCl stress significantly induced the expression of Glutathione S-transferase U43 (SlGSTU43) in the roots of the wild-type tomato (Solanum lycopersicum L.) plants. Overexpressing SlGSTU43 enhanced the ability of scavenging reactive oxygen species (ROS) in tomato leaves and roots under NaCl stress, while SlGSTU43 knock-out mutants showed the opposite performance. RNA sequencing analysis revealed that overexpressing SlGSTU43 affected the expression of genes related to lignin biosynthesis. We demonstrated that SlGSTU43 can regulate the lignin content in tomato through its interaction with SlCOMT2, a key enzyme involved in lignin biosynthesis, and promote the growth of tomato plants under NaCl stress. In addition, SlMYB71 and SlWRKY8 interact each other, and can directly bind to the promoter of SlGSTU43 to transcriptionally activate its expression separately or in combination. When SlMYB71 and SlWRKY8 were silenced in tomato plants individually or collectively, the plants were sensitive to NaCl stress, and their GST activities and lignin contents decreased. Our research indicates that SlGSTU43 can enhance salt stress tolerance in tomato by regulating lignin biosynthesis, which is regulated by interacting with SlCOMT2, as well as SlMYB71 and SlWRKY8. This finding broadens our understanding of GST functions.
Abstract Background: Transcriptome sequencing was conducted to screen out genes that actively respond to exogenous 5-aminolevulinic acid (ALA) induction under low temperature stress. The study used two versions of the tomato genome database to strictly screen and identify tomato glutathione S-transferase (GST) gene families and carried out the related bioinformatics analysis of tomato GST gene family. The expression pattern of SlGST genes induced by exogenous application ALA under low temperature stress was also analysed. Related physiological indicators were determined, and related chemical stains were performed.Results: RNA sequencing (RNA-seq) results showed that the expression of SlGST gene was different under various treatments, and a large number of SlGST genes widely responded to ALA induction under low temperature stress. Sixty-nine full-length GST genes were identified by screening the two versions of tomato genome databases combined with protein domain analysis. Analysis of gene family phylogenetic tree divided the tomato GST gene family into eight subfamilies. Tandem replication of genes is one of the driving forces for the evolution of tomato GST gene family, and a large number of cis-acting elements are related to stress resistance on the promoter of the GST gene family. Exogenous ALA application under low temperature stress induces a broad response of tomato leaf SlGST gene (qRT-PCR verification), increases GST activity and decreases reactive oxygen species (ROS) accumulation.Conclusions: RNA sequencing results revealed that a large number of tomato GST genes are differentially expressed, and Sixty-nine GSTs are identified in the tomato genome. Tandem replication of genes is the driving force for 68 the evolution of tomato GST family, and the promoter contains a large number of cis-acting elements related to stress resistance. Test results show that exogenous ALA induces the expression of SlGST genes under low temperature stress, thereby increasing GST activity to eliminate the ROS produced under low temperature stress and increase the tomato tolerance.
$LLC$ and $CLLC$ resonant converters are good candidates for the isolated dc–dc stage in electric vehicle (EV) onboard chargers (OBCs) due to their capability of achieving zero-voltage-switching (ZVS) at full load range. The synchronous rectifier (SR) is usually utilized to reduce the conduction loss and improve the system efficiency compared with the conventional diode bridge rectifier. In this article, a high-dv/dt-immune, fine-controlled, and parameter-adaptive gate driving scheme is presented for GaN-based SR in EV OBCs. A novel self-driven SR drain-to-source voltage sensing circuit is proposed. The circuit provides a low-impedance bypassing path for the displacement current induced by the high dv/dt, which addresses the overvoltage and oscillation issues for the controller input. The detailed operating principles and the design considerations of the novel sensing circuit are discussed as well. Moreover, the adaptive SR ON-time tuning algorithm is implemented, which avoids the influence from the loop stray inductance and the propagation delay in the path and reaches the SR zero-current turn-off moment with fine accuracy. A 3.3-kW, 500-kHz $CLLC$ resonant converter prototype is built to validate the proposed SR gate driving scheme. With the employment of the proposed gate driving scheme, the SR almost achieves zero-current turn-off for the whole operating frequency range. The prototype demonstrates the peak efficiency of 97.6% and the power density of 130 W/in 3 .
Modular multilevel converter (MMC) has become the basic building block for multi-terminal direct current (MT-DC) system and dc grids. To effectively control the power flow of the ac-dc MMC systems, the dual-loop power decoupling control based on $dq$ reference frame is employed, which needs accurate phase information of ac grid through phase-locked loop (PLL). However, the control system may fail due to unstable PLL. In this paper, a novel power flow control approach based on $\alpha\beta 0$ reference frame without PLL is proposed, which consists of an inner loop for power decoupling and an outer loop for tracking power reference. Nonlinear state feedback is employed to eliminate time-varying and nonlinear terms through full-state linearization for constructing the inner loop. PI controller and feedforward compensation are used to build classical second-order damping elements for keeping fast dynamic response and tracking power reference in the outer loop. Performance of the proposed grid-connected control strategy for an high voltage MMC station is evaluated based on simulation studies in the PSCAD/EMTDC software environment. The study results illustrate the effectiveness of the proposed strategy for controlling the grid-connected MMC.
Pulse power supply is an important field of high-frequency power electronics. In advanced applications, such as ultrasonic sensors, Lidar waves, and laser generators, the voltage supply with high amplitude and high frequency is required to achieve sufficient technical performance. Meanwhile, the high power quality is pursued in some sensor applications to obtain better performance. This article develops a ±1000-V/1.5-MHz LCC resonant pulse inverter for electromagnetic acoustic transducer. First, the LCC filter is optimized to achieve the goals of low total harmonics distortion (THD), small gain variation, and zero-voltage soft-switching (ZVS) in a wide load range. The design guideline of LCC filter for nonresistive load conditions is proposed, and the design considerations for burst mode converters are summarized. Second, the startup and ending transients occur repetitively, which is a common problem for burst mode converters. The proposed precharging and damping strategy solves this transient problem. Moreover, by analyzing the circuit state equations, this strategy provides a general method for eliminating transients of resonant converters. Next, the signal receiving circuit uses depletion mode MOSFETs to attenuate the high transmitting load voltage while amplifying microvolt receiving signals. Finally, the experimental results under four worst case conditions validate the LCC filter design. A control experiment with or without the proposed transient mitigation method has been conducted to verify the effectiveness of the proposed strategy.
This paper proposes a novel multilevel topology “Modular-Isolated-Multilevel-Converter” which achieves almost zero low frequency capacitor voltage fluctuation. It inherits the structure of MMC but replaces the half bridge module by the newly proposed Isolated Half-Bridge (IHB). The fundamental and 2nd order harmonic frequency current originally in the MMC module capacitor have been eliminated through connecting the secondary sides of the IHB at the same level of the three phases together. The elimination is due to that the 1st and 2nd order components in the arm current are 120° phase shifted in three phases. Therefore, the module capacitance is reduced by more than 10 times since it only carries switching frequency ripple. Moreover, the arm inductance can also be significantly reduced since the 2nd order harmonic current disappears. The topology is specifically suitable for variable frequency drive application, because its capacitance and inductance are not affected by the output frequency. The challenges of zero frequency start-up when MMC is adopted for VSD can be addressed here. In the paper, the operation principle of the proposed MIMC is fully analyzed and the mathematical model is built. Moreover, a methodology of capacitor sizing and arm inductor design for general MMC topology is proposed. The detailed design considerations for MIMC are also discussed and presented. The plant modeling and control strategy have been proposed for MIMC. A 55-kW simulation is carried out to verify the theoretical analysis. And a 6-kW downscaled hardware prototype is also developed to demonstrate the benefits of the new topology over the traditional MMC.
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