A novel dual closed-loop control scheme based on repetitive control for grid-connected inverters with an LCL filter.

Grid-connected inverters with LCL filters need high steady-state control accuracy, fast dynamic response performance, and strong robustness to guarantee the power quality. However, there are many problems in traditional control strategies that restrict improvements to control system performance, such as poor dynamic performance of traditional single-repetitive control, large ripples, low steady-state accuracy of inverter current feedback based repetitive dual-loop control or grid-current feedback based single-loop proportional-integral control. In this paper, a novel dual closed-loop repetitive control strategy based on grid current feedback is proposed for single-phase grid-connected inverters with LCL filters. The proportional-integral inner loop is stabilized by using an inherent one-beat delay achieved by digital controller. Based on the inner loop system, a detailed design scheme of a repetitive controller is presented, through which direct control of the grid current is realized, the reference is tracked perfectly to a zero phase shift, and high-attenuation gain is achieved in the high frequency range. In particular, the gird-voltage feed forward control and current reference feedforward control are adopted to suppress grid-voltage disturbance and increase dynamic tracking performance. Finally, the simulation and experimental results show that the proposed method has the advantages of high steady-state accuracy, fast dynamic response, and anti-disturbance ability.

Tracing the evolution of venom phospholipases A2 in Gloydius strauchii and related pitvipers: A tale of two acidic isozymes.

Two acidic Asp49-PLA2s with Glu6 substitution and a neutral Lys49-PLA (designated Gst-K49) were cloned from G. strauchii venom glands, their full amino acid sequences were deduced. The predominant acidic PLA2 (designated Gst-E6a) contains 124 residues and the M18W30 substitutions, while the minor acidic PLA2 (designated Gst-E6b) contains 122 residues and the V18A30 substitutions. Their sequences are most similar to those of the respective orthologous PLA2s of G. intermedius venom. Gst-E6a and Gst-E6b appear to be paralogs and possibly have different predatory targets or functions. The LC-MS/MS results indicate the presence of only three PLA2 gene products in the crude venom, the relative expression levels were in the order of Gst-E6a â‰« Gst-E6b > Gst-K49, as confirmed by qPCR results. In contrast to other Gloydius, G. strauchii venom does not contain neurotoxic or basic anticoagulant Asp49-PLA2s, but Gst-K49 is the first Lys49-PLA2 identified in Gloydius venoms. However, its venom content is relatively low and its pI value 7.3 is much lower than those of other Lys49-PLA2s and. The Lys49-PLA2 genes appear to regress in the venom of most of Gloydius and related rattlesnake, and this evolutionary regression occurred before the dispersal of Asian pitvipers to the New World.

[Survey on intestinal nematode infections among school students in Tengchong County].

One primary school and one middle school were selected from Gudong Town, Tengyue Town and Puchuan Township of Tengchong County, respectively, by using the lamination stochastic group sampling method. The intestinal parasite infections were investigated with the iodine-stained direct smear method and modified Kato-Katz thick smears method. A total of 1 134 students were investigated and the total infection rate of intestinal nematodes was 12.4% (141/1 134). The infection rate of Ascaris lumbricoides, Trichuris trichura, and hookworm was 9.4% (106/1 134), 2.8% (32/1 134), and 0.3% (3/1 134), respectively. The prevalence of intestinal nematodes among the students of urban (2.2%, 8/363) was lower than those of rural (17.3%, 133/771) (P < 0.01). The infection rate in students from Gudong Town was higher than those of Tengyue (2.2%, 8/363) and Puchuan County (2.3%, 8/35) (P < 0.01), whereas the economy level of Gudong Town (29.9%, 123/412) was the best in the three towns. After all, the infection rate of the middle school students (13.7%, 59/432) was higher than that of pupils (11.7%, 82/702) (P < 0.01). Compared with 2003, the prevalence of nematode infection among the school students in Tengchong County decreased significantly in 2013.