Parallel three-level T-type inverters (3LT 2 Is) can effectively increase the power rating. However, when multiple 3LT 2 Is are connected to a single dc bus, the zero-sequence circulating current ...(ZSCC) will occur. The ZSCC will distort the output currents and increase the system loss. To overcome this drawback, this paper proposes a novel deadbeat control scheme for the ZSCC suppression. A generalized model for analyzing ZSCC in parallel 3LT 2 Is is developed for designing the deadbeat control method. The proposed deadbeat control scheme is realized by real time adjusting the dwell time of small vectors in each space vector modulation. Compared to the conventional PI control method, the influence of different sector is eliminated, thus, improving the output current waveform and reducing the ZSCC. The effectiveness of the proposed method is verified by simulation and experiments.
In high-power applications, selective harmonic elimination pulsewidth modulation (SHEPWM) method is widely used to eliminate low-order harmonics in three-level inverters with low power losses. ...However, it faces the challenges that the conventional optimization methods for solving harmonic elimination equations in SHEPWM are easy to be trapped in local optimum. Moreover, the neutral point (NP) voltage of three-level inverter cannot be balanced under low-voltage ride-through (LVRT) condition with conventional SHEPWM method. To address these problems, a SHEPWM scheme is proposed, which is on the basis of an improved particle swarm optimization (IPSO) algorithm to solve the harmonic elimination equations and an enhanced NP balance control method in LVRT operation. First, an IPSO algorithm is proposed to calculate the switching angles of the transcendental equations for harmonic elimination. The IPSO algorithm defines a nonlinear negative exponential inertia weight considering the current and optimal fitness value, which can dynamically adjust the local and global searching speed and step size according to the actual situation, greatly improving the convergence speed and solution accuracy and avoiding falling into the local optimum. Then, by increasing the degree of freedom of the output current direction and combining with the NP voltage deviation, an enhanced NP voltage balance control method of SHEPWM in LVRT operation is proposed. The validity of the proposed method is proved by simulation and experimental results.
In this paper, a new modulation method is proposed for a Z-source three-level T-type inverter (3LT 2 I). The Z-source 3LT 2 I combines the merits of the Z-source two-level inverter and the advantages ...of the Z-source neutral-point-clamped inverter. Although the previous literature has proved that the space vector modulation (SVM) technique for Z-source 3LT 2 I produces the desired voltage transfer gain with minimized switching loss, it cannot deal with the neutral-point (NP) potential balance issue. Therefore, an improved SVM method addressing this problem for Z-source 3LT 2 I is proposed. The method simplifies the space-vector diagram of a Z-source 3LT 2 I into that of a Z-source two level inverter. In order to obtain NP potential balance, the pattern of the conventional symmetric SVM is changed by properly adding or subtracting a percentage of the minimum gate-on time. The upper and lower shoot-through states can be inserted into the improved symmetric SVM, thus offering av few advantages, including boosting ability, NP potential balance, and low switching loss. The considerate stable NP voltage and the boosting gain have been experimentally proven by results from a prototype inverter.
•Soil metal pollution with different e-waste recycling activities was determined.•In general, the soils were contaminated heavily with Cd, Cu, Pb and Sb.•Levels of Pb, Cr, Sb, Cd and Hg in the ...abandoned site were relatively lower.•Metal levels in the sites of acid leaching, dismantling, and burning, were high.
Heavy metal pollution of the environment caused by e-waste recycling is of increasing concern, but little information is available on metal emissions during e-waste processing activities. Here, the concentrations of nine metals in soil at four contaminated sites in Qingyuan (an e-waste recycling area in China) and the risks posed were investigated. Soil at the sites was polluted with metals, particularly Cd, Cu, Pb, and Sb, the concentrations of which were 2.83–2306, 2.17–1880, 0.96–1971, and 9.28–5607 times higher, respectively, than local background concentrations. The Cd, Cr, Hg, Pb, and Sb concentrations were significantly lower in soil at an abandoned site than at acid-leaching, dismantling, and burning sites. The risks posed by metals in soil to human and environmental health were much higher at the acid-leaching and burning sites than the dismantling and abandoned sites. Source assessments indicated the differences in metal concentrations at the different sites were caused by different e-waste recycling activities at the sites. The results indicated crude e-waste processing is an important source of heavy metals to soil and should be of great concern. Pollution control measures and risk management strategies specific to soil contaminated through e-waste processing activities should be developed.
Organic ultraviolet absorbents (OUVAs) in the environment have been of increasing concern because of their potential hazards. However, the OUVAs in waters is far from being well studied and little is ...known about their occurrence in small urban rivers. This study investigated the concentrations and distribution of eleven OUVAs in the sediments from five small urban rivers of Tianjin, China, and found total concentrations in the range of 11.6–189 ng/g dry weight. Relative to other rivers and lakes, no high concentrations of sediment OUVAs were observed in the small rivers. Benzophenone, homosalate and octocrylene were the dominant OUVAs, representing medians of 13.3%, 12.4% and 12.3% of the total concentrations, respectively. Our observed composition profiles of these chemicals were different from those found in most of other waters. The sediment OUVAs may originate more from industrial activities than the use of cosmetics and personal care products in this area. The risk to aquatic organisms from exposure to the sediment OUVAs in these small urban rivers was considered low, except for benzophenone. However, more researches are needed to investigate the pollution and associated risks of these chemicals in urban rivers due to the complexity of their toxicity to aquatic organisms.
•First report of the distribution of OUVAs in the sediments from small urban rivers.•The OUVA concentrations were comparable to those found in other rivers and lakes.•Sediment OUVAs attributed more to industrial activities than specific product usage.•Most of OUVAs in sediments from the small rivers have low risks to aquatic species.
Genetic variants in the asialoglycoprotein receptor 1 (ASGR1) are associated with a reduced risk of cardiovascular disease (CVD) in humans. However, the underlying molecular mechanism remains ...elusive. Given the cardiovascular similarities between pigs and humans, we generated ASGR1-deficient pigs using the CRISPR/Cas9 system. These pigs show age-dependent low levels of non-HDL-C under standard diet. When received an atherogenic diet for 6 months, ASGR1-deficient pigs show lower levels of non-HDL-C and less atherosclerotic lesions than that of controls. Furthermore, by analysis of hepatic transcriptome and in vivo cholesterol metabolism, we show that ASGR1 deficiency reduces hepatic de novo cholesterol synthesis by downregulating 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR), and increases cholesterol clearance by upregulating the hepatic low-density lipoprotein receptor (LDLR), which together contribute to the low levels of non-HDL-C. Despite the cardioprotective effect, we unexpectedly observed mild to moderate hepatic injury in ASGR1-deficient pigs, which has not been documented in humans with ASGR1 variants. Thus, targeting ASGR1 might be an effective strategy to reduce hypercholesterolemia and atherosclerosis, whereas further clinical evidence is required to assess its hepatic impact.
ZBED6 (zinc finger BED domain containing protein 6) is a transcription factor unique to placental mammals and its interaction with the IGF2 (insulin-like growth factor 2) locus plays a prominent role ...in the regulation of postnatal skeletal muscle growth. Here, we generated lean Bama miniature pigs by generating ZBED6-knockout (ZBED6.sup.-/-) and investigated the mechanism underlying ZBED6 in growth of muscle and internal organs of placental mammals. ZBED6.sup.-/- pigs show markedly higher lean mass, lean mass rate, larger muscle fiber area and heavier internal organs (heart and liver) than wild-type (WT) pigs. The striking phenotypic changes of ZBED6.sup.-/- pigs coincided with remarkable upregulation of IGF2 mRNA and protein expression across three tissues (gastrocnemius muscle, longissimus dorsi, heart). Despite a significant increase in liver weight, ZBED6.sup.-/- pigs show comparable levels of IGF2 expression to those of WT controls. A mechanistic study revealed that elevated methylation in the liver abrogates ZBED6 binding at the IGF2 locus, explaining the unaltered hepatic IGF2 expression in ZBED6.sup.-/- pigs. These results indicate that a ZBED6-IGF2-independent regulatory pathway exists in the liver. Transcriptome analysis and ChIP-PCR revealed new ZBED6 target genes other than IGF2, including cyclin dependent kinase inhibitor 1A (CDKN1A) and tsukushi, small leucine rich proteoglycan (TSKU), that regulates growth of muscle and liver, respectively.
T-NNPC inverter is an attractive topology with fewer switches and good withstand voltage for medium voltage applications. In order to effectively achieve five-level output, the conventional method is ...an MPC strategy that can quickly track current, ensuring good output performance under fundamental frequency conditions. However, the flying capacitor voltage fluctuates, especially under low-frequency conditions. In addition, the CO-PWM is a potential method for this topology due to the broader voltage level distribution in the vertical direction. Nevertheless, the flying capacitor voltage balancing cannot be guaranteed under the high modulation indexes. To improve voltage balance under various modulation indexes and current frequencies, this paper proposes an improved CO-PWM (ICO-PWM) method whose voltage level distribution is modified to better apply in the T-NNPC topology. Compared to the conventional MPC method, the flying capacitor voltage is more stable, and the fluctuation is reduced by more than five times, especially under low-frequency conditions. The effectiveness of the proposed ICO-PWM method is verified by the simulations and experiments.
Compared with a conventional three‐levelconverter, a reduced switch counts three‐level neutral point clamped (RSC‐3LNPC) inverter uses only 10 switching devices to achieve three‐leveloutput at a ...lower cost. However, in the RSC‐3LNPC inverter, the common modevoltage (CMV) reduction and neutral point voltage (NPV) balance are mutuallycoupled, and the buck switching module eliminates medium vectors, making conventional modulation methods no longer applicable. To address this problem, this paperdevelops a generation mechanism of the voltage and switching vectors for RSC‐3LNPC inverter and proposes a switching decomposition pulse width modulation (SDPWM) scheme. First, a virtual medium vector with two large vectors having the samedwell time is introduced. Then, the small and zero vectors with low CMV, along with the large and virtual medium vectors, are adopted, and by adjusting their dwell time, the NPV is balanced while reducing CMV. In addition, to reduce computational burden, the switching vector isdecomposed into a buck switching vector and a two‐level switching vector. Both switching vector sequences with transformed duty cycles are carefully designed to achieve only three switching transactions per switching period. Finally, validation and correctness of the proposed SDPWM scheme for RSC‐3LNPC inverterare verified by simulation and experiments.
Parallel photovoltaic inverters system can increase the power rating and efficiency. However, the zero-sequence circulating current (ZSCC) will be generated under unbalanced conditions. Therefore, ...this paper proposes a ZSCC control scheme for the M-paralleled (<inline-formula> <tex-math notation="LaTeX">M \ge 3 </tex-math></inline-formula>) inverters under unbalanced grid voltage and unbalanced filter parameters. Based on the analysis with the proposed generalized model of parallel inverters, it is observed that the ZSCC of the ith inverter is influenced by the output currents, filter parameters, duty cycles and ZSCCs of the ith and first inverters. To eliminate these adverse effects on the ZSCC control loop, a decoupled controller consisting of modified input type PI-quasi-resonant and the feed-forward controller is proposed. The modified input type PI-quasi-resonant controller mitigates the effects of the output currents, filter parameters, and ZSCCs, meanwhile, the feed-forward controller is employed to eliminate the difference of duty cycles. Compared with the conventional PI control method, the ZSCC is effectively suppressed with the proposed scheme, thus improving the quality of the currents. Moreover, the reliability of the paralleled system is improved because such scheme only needs the information of the ith and the first inverters. Simulation and experimental results obtained from three-paralleled inverters validate the effectiveness of theoretical analysis and the proposed method.
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