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The demand for energy continues to increase as the global economy continues to grow. The role of oilfield chemicals in the process of oil and gas exploration, development, and production is becoming more and more important, and the demand is rising year by year. The support of national policies and the formulation of environmental protection regulations have put forward higher requirements for oilfield chemical products, which has promoted the innovative research and development and market application of oilfield chemicals. Polyformaldehyde glycol ether polymer (PGEP) is simple to synthesize, easily biodegradable, green and environmentally friendly, and in line with the development trend of chemicals used in oil and gas development. The interfacial tension performance of PGEP after compounding with different surfactants can reach as low as 0.00034 mN/m, which meets the requirements of the oilfield (interfacial tension ≤ 5 × 10−3 mN/m). The best oil washing efficiency performance of PGEP compounded with different surfactants reached 78.2%, which meets the requirements of the oilfield (oil washing efficiency ≥ 40%). The fracturing fluid drainage efficiency of PGEP after compounding with different surfactants reaches 22%, which meets the requirements of the oilfield (drainage efficiency ≥ 15%). The surface interfacial tension of the system remains constant after the concentration exceeds 0.2% and decreases with lower concentrations. The drainage efficiency increases with increasing concentrations in the range below 0.6%. It was determined that PGEP can be used as a surfactant instead of fatty-alcohol ethoxylates (FAE) in oilfield development. [ABSTRACT FROM AUTHOR]

The attitude of the Chinese government towards social organizations (SOs) is crucial, as it affects the management rule and development tendency of SOs. To research the rule of SOs' participation in social governance in China, this study used a new historical perspective, the institutional development perspective, to conduct its exploration. This perspective provides an accurate measure of the reality of the SOs' participation, as it involves a mixed research methodology using continuous data from 73 years of reports and content mining, as well as topic clustering analysis to reveal a macroscopic and multi-line picture. Using a co-word analysis of hundreds of reports, from 1949–2021, in the People's Daily, an official newspaper of the Communist Party of China, this study quantified changes in intensity, emotion, and content regarding social organization participation in social governance through topic distribution. Three trends were revealed: (1) "social-oriented character" and "organized-oriented character" were identified during the change in SOs; (2) the extent of being managed gradually strengthened and shifted from the Communist Youth League of China to the Community Party of China; (3) the goals of SOs shifted from general to innovated function in special charitable organizations. The institutional development perspective can complement the focus event perspective, including a new method, co-word analysis, to examine official Chinese media and validate the Administrative Absorption of Society (AAS) theory by identifying two lines of topic clustering trends. The attention distribution analysis in official media from an institutional development perspective can help explore the role of official media reports in analyzing the allocation of national attention and provide new analytical methods for big data mining to establish the social and organizational natures of SOs to optimize their roles. It offers a basis for modern social governance policy innovation in China. [ABSTRACT FROM AUTHOR]

Although metals (Fe(III)) loaded with BC (MBC) exhibited good catalytic reactivity, the structural evolution process of MBC with pyrolysis and the evaluation of electron transfer capacity of MBC during persulfate oxidation were typically overlooked. Results of this study indicated that increasing pyrolysis temperature could promote the carbonization of biomass and lead to the formation of a well-developed microporous structure. Large numbers of functional groups and Fe species were formed by pyrolysis, but the content varies greatly under different pyrolysis temperatures. MBC prepared at pyrolysis temperature of 300 °C (MBC300) exhibited an excellent activation capacity, and the removal efficiency of 2,4-dinitrotoluene reached 83.7% within 5 h of the reaction by adding in 2.5 mmol/L persulfate and 0.5 g/L MBC300. Sulfate radical (SO4·-) and hydroxyl radical (·OH) participated in the reaction, but ·OH was mainly responsible for the degradation of 2,4-dinitrotoluene. Multiple characterization methods confirmed that Fe(III) maghemite and Fe 2p1/2 in MBCs mainly promoted the activation of persulfate, and oxygen-containing functional groups as an electronic shuttle accelerated the electron transfer in the persulfate/MBC system. Compared to that of biochar, the electron donating and electron accepting capacity of MBC were increased by an order of magnitude. This result is of significance for the preparation of green activation material used in the remediation of organically polluted groundwater with persulfate oxidation. [ABSTRACT FROM AUTHOR]

Risk assessment has been recognized as an important tool for evaluating heavy metal pollution and providing risk-based information for decision makers. In order to accurately assess the risk of heavy metals in contaminated soil to human health, it is necessary to conduct bioavailability studies on heavy metals in soil. Bioavailability of heavy metals in soils and the implications for risk assessment and land management/remediation has evolved over the decades and now has considerable practical and economic implications internationally. This article aims to explore its evolution by undertaking a bibliometric analysis of the research fields which have addressed heavy metal bioavailability in soils, with a focus on the risk assessment of contaminated land and human exposure to soil-borne metals. Bibliometric analysis techniques are applied to monitor and assess the changing research literature on the bioavailability of heavy metals in contaminated soils. Over 5000 articles were found for the period 1979–2020. The purpose was not to perform an exhaustive literature review, but to draw out trends and patterns in the literature, and to make observations on past and current priorities. Key words were extracted from the analysis and the roles of different countries in driving the research literature identified. Three phases in literature/subject development were identified. Between 1979 and 2000 (initial phase, 213 articles), studies used extraction procedures and solubility studies to investigate the roles of soil properties on metal form/speciation and focused on bioavailability to (crop) plants in agricultural soils. Between 2001 and 2010 (slow development phase, 1105 articles), attention switched to metals introduced in soil amendments and wastes, metal impacts on soil microbial processes, and incorporating bioavailability in risk assessment. More rigorous techniques were being used, such as the diffusive gradients in thin films technique, to better understand kinetic and metal speciation in soils and the quantitative relationship to bioavailability. By 2011–2020 (rapid development phase, 3137 articles), research was being conducted in many countries (site specific, often industrially contaminated and urban sites), with a focus shift to health risk assessment, remediation, and bioavailability to various ecological receptors (e.g., humans and animals), with the development of many methods of bioavailability (e.g., simulated gastrointestinal tract enzymolysis methods). Some priorities for research on soil heavy metal bioavailability are identified. [ABSTRACT FROM AUTHOR]

The hybrid modular multilevel converter (MMC) consisting of half-bridge submodules (HBSMs) and full-bridge submodules (FBSMs) is a promising solution for overhead lines high-voltage direct current systems (HVDC) due to the advantages of direct current short circuit fault ride-through (DC-FRT) capability. This paper proposes an improved phase-disposition pulse width modulation (PDPWM) method for the hybrid modular multilevel converter. The number of carriers can be reduced from 3N (N is the number of submodules in each arm) to 6. The theoretical harmonic analysis of the improved PDPWM method for hybrid MMC is performed by using double Fourier integral analysis. The influence of three carrier displacement angles between HBSMs and FBSMs in the upper and lower arms on harmonic characteristics is investigated. The output voltage harmonics minimization PDPWM scheme and circulating current harmonics cancellation PDPWM scheme can be achieved by selecting the optimum carrier displacement angles, respectively. The proposed method for hybrid MMC is verified by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

Understanding the influence of soil microstructure on light non-aqueous phase liquids (LNAPLs) behavior is critical for predicting the formation of residual LNAPLs under spill condition. However, the roles of soil particle and pore on LNAPLs migration and residue remains unclear. Here, the experiment simulated an LNAPLs (diesel) spill that was performed in fourteen types of soils, and the key factors affecting diesel behavior are revealed. There were significant differences between fourteen types of soils, with regard to the soil particle, soil pore, and diesel migration and residue. After 72 h of leakage, the migration distance of diesel ranged from 3.42 cm to 8.82 cm in the soils. Except for sandy soil, diesel was mainly distributed in the 0–3 cm soil layer, and the residual amounts were 7.85–26.66 g/kg. It was further confirmed from microstructure that the consistency of soil particle and volume of soil macropores (0.05–7.5 μm) are important for diesel residue in the 0–1 cm soil layer and migration distance. The large soil particles corresponding to 90% of volume fraction and volume of soil mesopores (<0.05 μm) are key factors affecting diesel residue in the 1–3 cm soil layer. The result helps to further comprehend the formation mechanism of residual LNAPLs in the soil. [ABSTRACT FROM AUTHOR]

Promoting the diffusion of remediation technologies is an attractive solution to environmental protection and urban sustainability challenges. To better understand technology diffusion, we reviewed the engineering practices of cement kiln co-processing (CKC) of contaminated soil and obtained diffusion parameters using the Bass model in three provinces of China. Our results show that CKC has been adopted for the disposal of multiple contaminants and that the optimal feed rate of contaminated soil is 4–5%. The obtained diffusion parameters can be used to analyze and predict CKC diffusion. Driving factors analysis suggest that CKC diffusion is regulation-driven and obeys the S-curve pattern. Policies at the national level shape the basic pattern of the diffusion curve, while local policies, market scales, and contaminant types produce variations in diffusion rates across provinces. Results also reveal that the co-processing quota management on contaminated soil has little impact on CKC adoption. This study provides insights into contaminated soil remediation technology diffusion and the effectiveness of environmental policy implementation at home and abroad. [ABSTRACT FROM AUTHOR]

The modular multilevel railway power conditioner (MM-RPC) can effectively improve the power quality of the railway power grid. However, since the operating conditions of MM-RPC frequently vary with the traction load, the junction temperatures of semiconductor devices fluctuate very drastically. Severe junction temperature swings can easily affect the service lifetime and reliability of the MM-RPC. In this article, a power hysteresis based on incomplete compensation control strategy is proposed. The proposed control can effectively reduce junction temperature fluctuations under complex mission profiles and increase the overall life of the system while meeting the power quality requirements. Furthermore, the effectiveness of the proposed control is verified in MATLAB/PLECS electrothermal cosimulation under a section of the load curve of the Beijing–Shanghai high-speed railway traction substation. Finally, the experimental thermal platform is built to validate the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

In high-power applications, different multilevel voltage source converter (VSC) topologies are usually applied. The hybrid parallel multiconverters, which is a combination of multiactive and hybrid VSCs connecting in parallel, can be a promising solution in a high-power grid. In this article, the fusion VSC topology concept is proposed in which fusion VSC takes the advantages of both active (inductive coupling) VSC and hybrid (capacitive coupling) VSC. It corresponds to overcoming the insufficient-capacity problems when active VSCs are employed alone and vice versa. This article proposes fusion active power filter topology by combing active and hybrid power VSC through their equivalent model for power quality compensation. With the proposed VSC's equivalent model, it can reduce the converter rating by 17%–80% compared with the conventional approaches. Additionally, the corresponding control algorithm is proposed for the FAPF for power quality compensation. Finally, the simulation and real-time digital simulator hardware-in-the-loop experimental results of the proposed FAPF topology are given to demonstrate the validity and effectiveness for reducing its capacity and power loss compared with the conventional multi-VSC in power quality compensation. [ABSTRACT FROM AUTHOR]

In this article, a new three-level cascaded noninverting buck–boost converter (TL-CNIBB) is proposed, which has a superior adaptation for a wide-range voltage input of renewable energy access. Firstly, the operation principle is analyzed for TL-CNIBB and it is mainly divided into four modes, namely buck mode with the voltage ratio below or above 0.5, boost mode with the voltage ratio below or above 2. Due to multilevel and multimode features, several fundamental issues are required to be settled, such as a dead zone between buck mode and boost mode, capacitor voltage unbalance on both sides, and subharmonics at the edge of modes. For dead zone and capacitor voltage balance problems, a systematic control strategy is proposed, and four kinds of smooth transition technologies are proposed to deal with different cases. Furthermore, to avoid the chattering and subharmonics at the edge of modes, a modified hysteretic transition method is proposed. Finally, a prototype of TL-CNIBB system is constructed, and the experiments are carried out to verify the performance of the proposed system with high viability and flexibility. [ABSTRACT FROM AUTHOR]

In the current power system, the conversion between dc and ac is widely existing and the dc-side harmonic problem is prominent. To suppress the second-harmonic current at the dc side of a single-stage single-phase inverter, a dc hybrid active power filter (DC-HAPF) structure is presented, which composes of a bidirectional dc–dc circuit-based active power filter (APF) and a CL passive filter. In this article, the CL passive filter is used to mitigate the high-frequency harmonics and the APF is applied to compensate the low-frequency harmonic current. Meanwhile, the influence of the filter parameters on the harmonic suppression is analyzed based on the average switching model. In addition, for the control of the DC-HAPF, a nonlinear unified controller via feedback linearization is proposed, where the voltage and current dual-loop control is converted to a single-loop control of energy. By analyzing the control system stability and DC-HAPF's performance, appropriate control parameters are selected. To verify the feasibility of the proposed topology and control strategy, a 500-W single-stage single-phase inverter with the DC-HAPF is built and a good performance of the dc-side harmonic suppression has been achieved. [ABSTRACT FROM AUTHOR]

The fatigue energy consumption of independent gestures can be obtained by calculating the power spectrum of surface electromyography (sEMG) signals. The existing research studies focus on the fatigue of independent gestures, while the research studies on integrated gestures are few. However, the actual gesture operation mode is usually integrated by multiple independent gestures, so the fatigue degree of integrated gestures can be predicted by training neural network of independent gestures. Three natural gestures including browsing information, playing games, and typing are divided into nine independent gestures in this paper, and the predicted model is established and trained by calculating the energy consumption of independent gestures. The artificial neural networks (ANNs) including backpropagation (BP) neural network, recurrent neural network (RNN), and long short-term memory (LSTM) are used to predict the fatigue of gesture. The support vector machine (SVM) is used to assist verification. Mean square error (MSE), root mean square error (RMSE), and mean absolute error (MAE) are utilized to evaluate the optimal prediction model. Furthermore, the different datasets of the processed sEMG signal and its decomposed wavelet coefficients are trained, respectively, and the changes of error functions of them are compared. The experimental results show that LSTM model is more suitable for gesture fatigue prediction. The processed sEMG signals are appropriate for using as the training set the fatigue degree of one-handed gesture. It is better to use wavelet decomposition coefficients as datasets to predict the high-dimensional sEMG signals of two-handed gestures. The experimental results can be applied to predict the fatigue degree of complex human-machine interactive gestures, help to avoid unreasonable gestures, and improve the user's interactive experience. [ABSTRACT FROM AUTHOR]

How complex interactions of genetic, environmental factors and aging jointly contribute to dopaminergic degeneration in Parkinson's disease (PD) is largely unclear. Here, we applied frequent gene co‐expression analysis on human patient substantia nigra‐specific microarray datasets to identify potential novel disease‐related genes. In vivo Drosophila studies validated two of 32 candidate genes, a chromatin‐remodeling factor SMARCA4 and a biliverdin reductase BLVRA. Inhibition of SMARCA4 was able to prevent aging‐dependent dopaminergic degeneration not only caused by overexpression of BLVRA but also in four most common Drosophila PD models. Furthermore, down‐regulation of SMARCA4 specifically in the dopaminergic neurons prevented shortening of life span caused by α‐synuclein and LRRK2. Mechanistically, aberrant SMARCA4 and BLVRA converged on elevated ERK‐ETS activity, attenuation of which by either genetic or pharmacological manipulation effectively suppressed dopaminergic degeneration in Drosophila in vivo. Down‐regulation of SMARCA4 or drug inhibition of MEK/ERK also mitigated mitochondrial defects in PINK1 (a PD‐associated gene)‐deficient human cells. Our findings underscore the important role of epigenetic regulators and implicate a common signaling axis for therapeutic intervention in normal aging and a broad range of age‐related disorders including PD. [ABSTRACT FROM AUTHOR]

Although nonionic surfactant is widely used for petroleum-contaminated soil washing, there is no definite conclusion on the main soil factors which determine the removal of petroleum hydrocarbons from the soil. In this study, the influences of soil properties on Triton X-100-aided soil washing were investigated using 12 soils in China. The sorption characteristic of Triton X-100 on soils was described as well. The sorption isotherms of Triton X-100 on 12 typical soils were fitted to the Langmuir adsorption model, and the maximum sorption amount of Triton X-100 (Qmax) varied from 1.54 to 15.15 mg/g. The removal rates of diesel for 12 soils were well fitted to the modified Michaelis-Menten equation, and the maximum removal rate of diesel (φmax) ranged from 62.92 to 90.36%. The correlation analysis indicated that the φmax is significantly correlated with the Qmax. The soil factors affecting diesel removal from soils followed the order of sand content > cation exchange capacity (CEC) > organic matter (OM) content > silt and clay content > SSA >> pH. The prediction model based on CEC, silt content, and pH explained 83.1% of variance of diesel removal from soils. This study will have important implication for successfully remediating organic-contaminated soil using nonionic surfactant-based soil washing. [ABSTRACT FROM AUTHOR]

The underwater electroacoustic transduction system is widely used in underwater navigation, ranging, and communication. However, it is difficult to control the current of the giant magnetostrictive transducer (GMT) for a voltage mode amplifier, because nonsinusoidal waves without constant fundamental frequencies may be required, and the load parameters of the GMT vary greatly with its working frequency, current, and condition. A parameter online identification algorithm is proposed for the GMT, where only one matrix inversion and one filtering for a two-dimensional matrix are required. A discretized switched control is derived, which selects the subsystem minimizing the Lyapunov function of tracking error in each control period. In addition, a switching state selection method making the switching frequencies lower and consistent is also used to cooperate with the switched control. Finally, the adaptive switched control is experimentally verified on the designed 1-kW electroacoustic transduction platform. [ABSTRACT FROM AUTHOR]

In this paper, a railway power conditioner (RPC) based on a modular multilevel converter (MMC) with a split supercapacitor energy storage system (SCESS) is studied. In this case, the MMC-SCESS-based RPC could not only provide normal negative-sequence current compensation, but also reduce the impact of power fluctuations caused by the locomotive braking or startup on the electric grid. First, this paper analyzes the power flow patterns and deduces the reference circulating current under different operation modes of the MMC-SCESS-based RPC. Then, the control objectives of the MMC-SCESS-based RPC are divided into two categories—the balance control and the current tracking control. The balance control methods are developed for the submodule capacitor voltages and the state of charge of the supercapacitor, which are associated with the operation modes. To ensure the current tracking performance, a model-predictive direct current control method is presented for the MMC and the bidirectional energy converter. Finally, the effectiveness of the proposed control methods is verified by the experimental results of a downscaled prototype. [ABSTRACT FROM AUTHOR]

Due to the train load stochastic jumps, negative sequence currents (NSCs) are unpredictably brought into power grid, which may attack the power system and damage vital devices. To enhance the compensation capacities and improve the power quality, a hybrid scheme is studied in consideration of load stochastic jumps, composed of railway power conditioner, thyristor switched capacitor, and thyristor switched reactor. First, the load discrete jump model and its compensation principle of V/v railway traction system are analyzed to design the hybrid compensators and the capacities. Then, based on the attack-defense game theory, a two-level optimized hybrid controller is proposed to keep the power system affirmative for any train load attacks. In the hybrid system, defender 1 is a discrete strategy that can be early executed by finite logic to minimize the power demands, and defender 2 is a continuous strategy that can be lately controlled by optimal control to minimize NSCs. By this dynamic game, an optimized hybrid compensation can be realized. Finally, simulations and experiments are completed to prove the compensation abilities of the hybrid system and the effectiveness of the hybrid control strategy. [ABSTRACT FROM AUTHOR]

Medium-voltage dc (MVdc) distribution system is considered as the promising power architecture of future shipboard power system. Fault-tolerance ability is of great importance for power system on ships. In this paper, zonal dc–dc conversion system based on modular multilevel converter (MMC) and three-phase bridge rectifier are proposed with its hierarchical fault-tolerant scheme. The topology configurations of the front-end MMC with multiwinding medium frequency transformer under normal and postfault circumstances are presented. The reconfiguration scheme and fault-tolerant control strategy are also proposed to ride-through submodule (SM) level fault, phase level fault and bus level fault. Based on the hierarchical fault-tolerant scheme, redundant configuration of the MMC SM is further analyzed with the hierarchical reliability modeling. The effectiveness of the proposed control strategy is verified by the experimental results. [ABSTRACT FROM AUTHOR]

To manage the power quality of a high-speed V/v traction system, a multilevel railway power conditioner (MRPC) is researched. According to the structure and equivalent models of the MRPC, basically the MRPC is a symmetrical system, and its four clusters can be divided into two cluster groups. According to the ac equivalent mathematical models of cluster groups, it can be considered as the relationships in the αβ frame, but not completely symmetrical, so the positive- and negative-sequence dq models for cluster groups can be derived. As the fluctuation and randomness of the locomotive loads, a sliding mode control system based on the exponential reaching law in the dq frame is explored to control the cluster ac currents, which can improve the dynamic performance and keep a good tolerance against parameter mismatches. Finally, an experimental prototype is developed, and the results show the feasibility and the robustness of the system. [ABSTRACT FROM AUTHOR]

Asymmetric voltage sags often occur at the point of common coupling, which connects industrial active distribution networks to the utility grid. Distributed generations face the challenges of riding through and supporting the voltage under the grid faults. In order to tackle these challenges, a hybrid control strategy, combined with the frequency droop with passivity-based switch function, is proposed. By adopting the proposed strategy, the positive/negative sequence active/reactive power is injected to recover the voltage. The novel PBSF is enhanced by including both control components of inverter's output current and output voltage based on the Euler–Lagrange model. The novel frequency droop is applied to achieve the positive/negative sequence active/reactive power injection with a satisfied sharing accuracy among the coordinated operation of parallel connected multiple inverters. Extensive simulation and experimental results have validated the effectiveness of the proposed strategy with an effective dynamic response performance and stability. [ABSTRACT FROM AUTHOR]

In recent years, railway power conditioner (RPC) has been used to improve the power quality of a traction power system. In engineering application of RPC, mismatches between parameters used in controller and actual values are inevitable, which will increase the difficulty of current controller design and deteriorate compensation performance. In this paper, a passivity-based control (PBC) system is studied for multilevel RPC to enhance its tolerance for mismatches. According to the topology of multilevel RPC, equivalent electrical and mathematical models are developed. To employ PBC, Euler–Lagrange system model of RPC is established by Park (αβ/dq) transformation, and the passivity of RPC and stability of PBC are proved. On this basis, the robustness of PBC is analyzed and criteria for damping selection are derived. Finally, simulation and experiments have been carried out to verify the structure and control method in the paper. [ABSTRACT FROM PUBLISHER]

In this study, a novel method for the treatment of polycyclic aromatic hydrocarbon -contaminated soil using cement-activated persulfate was developed. The removal of PAHs in soil rose with increasing initial persulfate concentration, initial Portland cement (PC) concentration, and oxidation reaction time. At an initial persulfate and PC concentration of 19.20 mmol/kg and 10% of soil weight and a reaction time of 2 h, the removal rate of PAHs reached 57.3%. Residual PAHs were mainly adsorbed within the soil granules and thus became less available. The mechanism of PC facilitating the oxidation reaction was that PC addition can increase the pH and temperature of the system. When the soil was stabilized/solidified by 10% of PC, the leaching concentration of PAHs and TOC was significantly higher than that leached from untreated soil. Persulfate oxidation decreased the leaching concentration of PAHs but increased the leaching concentration of TOC in solidification/stabilization products. The addition of activated carbon can decrease the leaching concentrations of both PAHs and TOC. Freeze-thaw durability tests revealed that the leachability of PAHs was not affected by freeze-thaw cycles. The unconfined compressive strength (UCS) of treated soil samples after 12 freeze-thaw cycles was only 49.0% of that curing for 52 days, but the UCS was still > 1 MPa. The treated soil samples can resist disintegration during the process of freeze-thaw cycles. [ABSTRACT FROM AUTHOR]

With the rapid development of modern electrified railway, negative-sequence current minimization is one of the most important considerations in the high-speed railway traction system. In the past, many multiple or multilevel topologies with high compensation capacity have been introduced for railway power conditioner (RPC). This paper presents a simplified quantitative comparison of five previous modular RPC topologies for negative sequence compensation in V/V and SCOTT traction systems, aiming for an optimal selection of the compensators. Performance criteria such as transformer requirement, voltage stress and current stress of a power switch, numbers of the power switches and capacitor are derived by analytical methods. Moreover, the numerical comparison of operating controllers is completed for modular RPCs. In addition, power losses of five modular RPCs are obtained by theoretical analysis, IPOSIM calculation as well as PSIM simulation. These calculations are validated via simulations results in PSIM. The main conclusion is that presented modular RPCs can be divided into general purpose RPC and special purpose RPC in terms of the behavior and efficiency. It is helpful to choose the appropriate topology for specific applications. [ABSTRACT FROM AUTHOR]

In this paper, the full bridge-based modular multilevel converter (MMC) is discussed for the application of tundish induction heating power supply (TIHPS). TIHPS features three-phase to single-phase ac/ac conversion and variable output frequency, and has intense demand for the power transmission stability and output current control precision. MMC is suitable for this application and especially the bulky and costly transformer and ac filter in the conventional topology can be dispensable. Therefore, it is interesting to investigate the applicable control method for MMC-TIHPS. According to the instantaneous power theory, a hierarchical direct power control based on the improved deadbeat current control is presented to assure the energy balance inside and outside MMC-TIHPS and reduce the sensitiveness of the current controller to parameter uncertainties. The proposed control strategy dispenses with the phase-locked loop, and does not exist the coupling among control variables of internal and external currents. Then, parameters design of energy controller is studied for stability analysis. Finally, MMC-TIHPS and proposed control method are verified by experimental results of a down-scaled physical prototype. [ABSTRACT FROM AUTHOR]

To enhance the power quality in the medium/high-voltage distribution power systems, a single-phase unified power quality conditioner (UPQC) based on the modular multilevel matrix converter (M3C) is presented in this paper. The M3C-UPQC is comprised of four identical multilevel converter arms and associated filtering inductors. According to the established equivalent circuit of M3C-UPQC, its operation principle and power balance of each arm are analyzed theoretically, and the parameters’ design for the arm inductance as well as submodule capacitance is studied. Then, an integrated control method for M3C-UPQC in which the dc circulating current is used to balance the instantaneous active power of each arm is proposed to prevent the capacitor voltages from divergence inter- and intra-arms, so as to achieve voltages balance of M3C-UPQC. Finally, the effectiveness of the proposed control method is verified by a prototype rated at 8 kVA. [ABSTRACT FROM AUTHOR]

To meet the requirements of high‐power compensating occasion such as electrochemical industries, a multifunctional hybrid active power converter (HAPC) with LC series filter is studied to effectively integrate functions of rectification and power compensation. HAPC can be used as a high‐power pulse width modulation rectifier to supply its dc load, meanwhile, it can also compensate large amount of reactive and harmonic current without increasing the voltage rating of itself. A compound current control method for HAPC is introduced so as to improve the dynamic tracking performance. The current and voltage dual closed‐loop system of HAPC is built in s domain, and the detailed control parameters are designed to tune control performance further. Finally, a set of 800 kVA HAPC system for electrolytic copper‐foil is developed. The results show that the HAPC system can achieve expected operation performance and largely improves power quality of power grid. [ABSTRACT FROM AUTHOR]

In the rapid development process of a high-speed electrified railway, power quality problems in traction power grid have become increasingly deteriorative. In order to ensure a three-phase balanced traction power grid, a modular multilevel converter based railway traction power conditioner (RTPC) is presented. The RTPC consists of four H-Bridge clusters and filter inductors, and it can be directly connected to traction feeders in a co-phase traction system without insulation transformers. According to the equivalent circuit analysis of RTPC system, it can be considered as four single-phase inversion systems. Based on the equivalent control model of each single-phase cluster, the relationship between the multilevel output voltage and current slopes in a control period is analyzed, and an improved model predictive control is proposed. Moreover, a linear combination of two different output levels is proposed to improve tracking performance of cluster current control, and enhance the waveform quality of ac current. Finally, both simulation and experiment results are presented to verify the effectiveness of the structure and its control method. [ABSTRACT FROM AUTHOR]

Cascaded static var generators (SVG) with delta-configuration is discussed for a compensation of reactive, negative-sequence and harmonic currents. According to phasor analysis of negative-sequence current compensation, the role of zero-sequence circulating current for power balance is analysed. According to power analysis, the analytical expressions of zero-sequence circulating current and 2nd frequency ripples of dc-link voltages are derived. On the basis of this, the phase-current reference detection and the simplified control method of SVG for negative-sequence current compensation are proposed, which is concise and can achieve power balance of three-phase clusters by superimposing a zero-sequence circulating current without additional controllers. Finally, the simulation and experimental results have effectively verified the proposed method. [ABSTRACT FROM AUTHOR]

Two new species, Castanopsis praefissa R.Y. Li et B.N. Sun sp. nov. and Castanopsis praeouonbiensis R.Y. Li et B.N. Sun sp. nov., are described from fossil specimens collected from the upper Miocene Shengxian Formation, Zhejiang Province, Southeast China. The fossil leaves are obovate to elliptical with serration mostly confined to the upper 1/3 of the lamina, pinnate venation, straight anticlinal walls and cyclocytic stomata. The fossil cupule is globose with fasciculate and branched spines, and a broadly ovate nut scar. The fossil leaves and cupule have been compared with those extant and other fossil species hitherto described in this genus. Castanopsis praefissa shows the closest affinity to C. fissa, and C. praeouonbiensis closely resembles C. ouonbiensis. Castanopsis fissa has toothed leaves and scaly cupules, whereas C. ouonbiensis has untoothed leaves and spiny cupules. Furthermore, they were not collected from the same site. So it is reasonable to assign them to two different species, rather than to one. Castanopsis praeouonbiensis and C. praefissa became extinct in this area because of the cooling climate from the late Miocene to the present day in Zhejiang Province. [ABSTRACT FROM AUTHOR]

Fossil bamboo leaves and pollen from Upper Miocene deposits of the Shengxian Formation in Tiantai and Ninghai counties, eastern Zhejiang, China represent a rare record in Asia. The distinctive pseudopetiole and parallel venation of the leaf blades and the clearly thickened annulus of the pollen aperture place them in the subfamily Bambusoideae. Morphological analysis supports the determination of these fossil leaves as belonging to the genus Bambusium and two new species are described. Bambusium latipseudopetiolus Q.J. Wang et B.N. Sun sp. nov. has a distinctly wide pseudopetiole of 0.23 cm in width and 0.40 cm in length, several vascular bundles on parallel veins, and 5-8 lateral veins on both sides of the midrib. Bambusium longipseudopetiolus Q.J. Wang et B.N. Sun sp. nov. has a distinctly long pseudopetiole of 0.60 cm in length and 0.10 cm in width, several vascular bundles on the pseudopetiole, and 6 lateral veins on both sides of the midrib. Pollen grains from the same layer provide additional evidence of bamboos. They are characterized by 32.0-51.0 μm in diameter, a round pore 3.0-4.0 μm in diameter with a broad thickened annulus 2.5-3.5 μm around, and several conspicuous secondary folds on the exine surface. The morphological analysis leads to their assignment to Graminidites bambusoides Stuchlik. These fossils are important for the study of bamboo phytogeography in China. They demonstrate that there were bamboos growing in southeastern China during the Late Miocene and that bamboos in Zhejiang begin to diversify no later than the Late Miocene. In combination with bamboo fossils from other places, it seems that bamboos had a wide distribution across southern China during the Miocene, ranging from southwestern Yun'nan to southeastern Zhejiang. [ABSTRACT FROM AUTHOR]

In this study, 39 leaf samples of three angiosperms ( Betula albo-sinensis, tree species; and Caragana jubata and Berberis diaphana, shrub species) were collected in the middle-east parts at 2300-3640 m asl of the Qilian Mountains to study the variations of leaf characteristics of angiosperms with altitude change in inland high-altitude regions of China. Five leaf indexes, viz. epidermal cell density (ED), stomatal density (SD), stomatal index (SI), leaf vein density (VD) and carbon isotopic ratio ( δC), were analyzed in laboratory. The results show that there are significant or even very significant linear correlations between the five indexes and altitude, of which SD, SI and VD exhibit a negative correlation with altitude, while ED and δC exhibit a positive correlation with altitude. Such a correlation assemblage is quite different from the situation in the low-altitude humid environment. Generally, only an assemblage of positive correlations can be observed between the indexes (viz. SD, SI and δC, etc.) and the altitude in the low-altitude humid environment, which were caused mainly by the plants' responses to the change of atmospheric CO concentration ( C). However, an assemblage of the negative and positive correlations found here may be attributed mainly to the plants' responses to the change of physiological drought caused by change of low temperature, and here it is preliminarily called the inland high-altitude pattern of plant leaf variations. [ABSTRACT FROM AUTHOR]

This paper presents a three-leg voltage-source inverter topology for two-phase orthogonal power supply used for driving electromagnetic stirring. Compared with the conventional two two-leg inverter, the three-leg structure reduced the loss of power module and switching. The improved structure has an inductor in series between two-phase orthogonal power supply and the common phase of electromagnetic stirring, which make it possible to apply deadbeat current control method to two-phase orthogonal power supply, thus the controller design is simplified, the current adjustment speed is enhanced, and the current waveform is improved. A control strategy with reactive power compensation is proposed for enhancing the utilization rate of a three-phase pulsewidth modulation (PWM) rectifier in two-phase power supply, which makes it possible that the three-phase PWM rectifier not only operating rectification status but also operating reactive power compensation status. Hence, the reactive compensation cost of enterprises will be decreased. At last, simulation and industrial application results are provided to verify the effectiveness of the proposed topology and control strategy. [ABSTRACT FROM PUBLISHER]

With the rapid development of high-speed and high-power railway system in China, power quality such as the negative sequence current and harmonic current caused by electric locomotives becomes more and more critical. This paper proposes a half-bridge-converter-based railway static power conditioner (RPC) (HBRPC) which consists of two half-bridge converters connected by two capacitors in series. Compared with the traditional RPC, the HBRPC requires only a pair of power switch legs and two capacitors. Under the premise of accomplishing the same function of RPC, the proposed conditioner can reduce half of the power switches, which can make it with lower cost and hardware complexity. A double-loop control is proposed for HBRPC to keep the dc-link voltage stable and achieve the dynamic tracking of the current reference signals, while a balanced voltage control is proposed to eliminate the error of two capacitor voltages and maintain the normal operation of HBRPC. Finally, simulation and experiment results have verified the proposed structure and its control method effectively. [ABSTRACT FROM PUBLISHER]

Static var compensators (SVCs) are used for voltage and reactive power control in power systems. In this paper, we will consider the structure of SVCs that mainly consists of Y-connection of mechanically-switched capacitor (MSC) and delta connection of thyrister-controlled reactor (TCR). First, the control model of SVC was established in this paper. Then, a novel optimal nonlinear voltage controller for SVCs is proposed. The proposed SVC voltage controller consists of a nonlinear function and a conventional PI controller. The improved simplex method (SPX) is presented to adjust and optimize the parameters of the nonlinear PI controller in real-time, and to make transient state response procedure of SVC optimum. The integration of time multiplied absolute error (ITAE) is adopted as the optimized objective function of SPX. Simulation and engineering application results show that the proposed voltage control method is able to track reference voltage value of SVC immediately. It also demonstrates that the whole SVC control system can synthetically compensate reactive power. [ABSTRACT FROM AUTHOR]

In order to eliminate the negative-sequence and harmonic currents in the high-speed train traction systems with three-phase V/V transformers, a compensation strategy based on the railway static power conditioners (RPC) is proposed in this paper. An RPC contains two converters that are connected back to back by sharing the same dc link. In this paper, the structure and principle to compensate negative-sequence currents for the RPC with a three-phase V/V transformer are explained, and a strategy to provide the compensation references for negative-sequence and harmonic currents is proposed. Also, a method to separate active current, reactive current, and harmonic current references from the total negative-sequence and harmonic current references is given. Moreover, a controller is proposed to maintain the dc-link voltage and to compensate the negative-sequence and harmonic currents. Simulation and experimental results are provided to demonstrate that the proposed strategy is very effective. [ABSTRACT FROM AUTHOR]

For power quality in V/V traction system of the 350-km/h high-speed railway, a kind of railway static power conditioner (RPC) is discussed, which is used to carry out the comprehensive compensation of negative sequence and harmonic currents in the traction substation. In order to improve the control effect and performance of RPC, a dual-loop control strategy is constructed for RPC. Taking into account the disturbance and variation of electrified railway environment, a recursive proportional-integral control based on fuzzy algorithm is adopted to realize a fast and smooth tracking to the reference current. An energy-balance control is proposed to suppress the fluctuation of dc-link voltage and maintain the stability of RPC, which is an accurate and adaptive feedback control based on corresponding parameters. Finally, the correctness of the analysis proposed in this paper has been confirmed by the simulation and experiment results. [ABSTRACT FROM AUTHOR]

To relieve the contradiction between supply and demand, a multi-port power conditioner (MP-PC) and control strategy with renewable energy access for a railway traction system is presented, which is mainly composed of full-bridge-based MMC and isolated DC/DC converters. As for the full-bridge-based MMC, the equivalent model is established and its novel voltage control method is proposed, which can provide a medium/low-voltage DC-link. A renewable energy system is connected to the system through the DC-link, so the MP-PC can achieve on-site consumption and balance between the load power and output power of RESs. Meanwhile, with the proposed control strategy, MP-PC can achieve three-phase power balance control and improve the operation performance of the railway traction system. Finally, the traction power platform and simulation model are established in the lab, and the topology and control strategy of MP-PC are verified effectively. [ABSTRACT FROM AUTHOR]

Despite the important niche and broad applicability of thermal remediation (TD), little work has been done to discuss chemical reactions of methylnaphthalene contaminated soil. The 2-methylnaphthalene desorption amount (MDA) of TD is studied here under different conditions, and the carbonation (chemically polymerized or condensed) behavior of 2-methylnaphthalene is explained by analyzing the changes of soil organic carbons (SOCs), off-gas products, and surface chemical properties. It indicates that the influence sequence of MDA from high to low is heating time, heating temperatures, and flow rates of carrier gas. MDA increases steadily with the increase of temperatures (200–300 °C) but decreases slightly after 300 °C; the reason may be the chemical conversion of 2-methylnaphthalene. GC-MS analysis of off-gas confirms that partial 2-methylnaphthalene is polymerized to form 2-methylbenzo[b]thiophene and 2,4-di-tert-butylpheno at 400 °C, which is the first step of carbonization process. The x-ray photoelectron spectroscopy results of soil indicate that the C content decreases, but C–(C, H) chemical structure increases, indicating that new carbonaceous substances are generated. A layer of "char" is seen by scanning electron microscope to be left on the surface of the soil particles. As the temperature increases (200–400 °C), the SOCs generally decreases from 1.14 to 0.82%, which is the result of the equilibrium between SOCs pyrolysis and 2-methylnaphthalene carbonization. Therefore, partial 2-methylnaphthalene turns into smaller organic molecules in desorption gas of TD, meanwhile is accompanied by its chemical conversion to non-volatile products, which are attached to remediated soils and then improve soil properties and increase their fertility. [ABSTRACT FROM AUTHOR]