Analysis and mitigation of dead time harmonics in the single-phase full-bridge PWM converters with repetitive controllers

In order to prevent the power switching devices (e.g., the Insulated-Gate-Bipolar-Transistor, IGBT) from shoot through in voltage source converters during a switching period, the dead time is added either in the hardware driver circuits of the IGBTs or implemented in software in Pulse-Width Modulation (PWM) schemes. Both solutions will contribute to a degradation of the injected current quality. As a consequence, the harmonics induced by the dead time (referred to as "dead time harmonics" hereafter) have to be compensated in order to achieve a satisfactory current quality as required by standards. In this paper, the emission mechanism of dead time harmonics in single-phase PWM inverters is thus presented considering the modulation schemes in details. More importantly, a repetitive controller has been adopted to eliminate the dead time effect in single-phase grid-connected PWM converters. The repetitive controller has been plugged into a proportional resonant-based fundamental current controller so as to mitigate the dead time harmonics and also maintain the control of the fundamental frequency grid current in terms of dynamics. Simulations and experiments are provided, which confirm that the repetitive controller can effectively compensate the dead time harmonics and other low-order distortions, and also it is a simple method without hardware modifications

Capturing Topology in Graph Pattern Matching

Graph pattern matching is often defined in terms of subgraph isomorphism, an NP-complete problem. To lower its complexity, various extensions of graph simulation have been considered instead. These extensions allow pattern matching to be conducted in cubic-time. However, they fall short of capturing the topology of data graphs, i.e., graphs may have a structure drastically different from pattern graphs they match, and the matches found are often too large to understand and analyze. To rectify these problems, this paper proposes a notion of strong simulation, a revision of graph simulation, for graph pattern matching. (1) We identify a set of criteria for preserving the topology of graphs matched. We show that strong simulation preserves the topology of data graphs and finds a bounded number of matches. (2) We show that strong simulation retains the same complexity as earlier extensions of simulation, by providing a cubic-time algorithm for computing strong simulation. (3) We present the locality property of strong simulation, which allows us to effectively conduct pattern matching on distributed graphs. (4) We experimentally verify the effectiveness and efficiency of these algorithms, using real-life data and synthetic data.Comment: VLDB201

Clinical observation of bio-amnion implantation used in combined trabeculectomy for refractory glaucoma

AIM: To observe the clinical effect of bio-amnion implantation used in combined trabeculectomy for refractory glaucoma METHODS: Totally 86 eyes of 80 glaucoma patients were randomly divided into 2 groups. In experimental group, 43 eyes underwent trabeculectomy combined with bio-amnion implantation. In control group, 43 eyes only underwent trabeculectomy combined. The intraocular pressure(IOP), filtrative bleb and complications were observed. RESULTS: Following-up for 12 months, IOP: there was significant difference between the average IOP(15.5±1.1mmHg)in experimental group and the average IOP(19.7±2.5mmHg)in control group(P<0.05). Filtrative bleb: the incidence of the functional filtering bleb(86%)in experimental group was more than the one in control group(67%), there was significant different between the two groups(P<0.05). The incidence of complications of post-operation(shallow anterior chamber, choroidal detachment and bleb leaking)was lower than the one of the control group obviously. CONCLUSION: Combined trabeculectomy with bio-amnion implantation can increase the rate of success and reduce the incidence of complications