Switching Loss Reduction for an MMC-Fed AC/DC Converter

Medium-voltage connected ultra-fast chargers are getting more popular for charging electric vehicles with large battery capacities. Here, the solution based on a modular multilevel converter is more promising, since the isolation stage can be realized as a single medium-frequency transformer interconnecting the modular multilevel converter to a single-phase ac/dc converter. A new operating scheme is proposed for this converter, enabling zero-voltage switching and nearly zero-current switching across the entire load range. In contrast to the conventional phase-shift control method, the proposed scheme effectively reduces the reactive power through the ac/dc converter, leading to decreased turn-off switching losses in the ac/dc converter and a lower RMS current stress in the power path. A control scheme, integrating the operating principle, is developed for the modular multilevel converter. The method is verified through simulation and measurements on a scaled-down prototype. The results validate the theoretical analysis and practical feasibility of the proposed operating principle and the developed control scheme

Switching Loss Reduction for an MMC-Fed AC/DC Converter

Medium-voltage connected ultra-fast chargers are getting more popular for charging electric vehicles with large battery capacities. Here, the solution based on a modular multilevel converter is more promising, since the isolation stage can be realized as a single medium-frequency transformer interconnecting the modular multilevel converter to a single-phase ac/dc converter. A new operating scheme is proposed for this converter, enabling zero-voltage switching and nearly zero-current switching across the entire load range. In contrast to the conventional phase-shift control method, the proposed scheme effectively reduces the reactive power through the ac/dc converter, leading to decreased turn-off switching losses in the ac/dc converter and a lower RMS current stress in the power path. A control scheme, integrating the operating principle, is developed for the modular multilevel converter. The method is verified through simulation and measurements on a scaled-down prototype. The results validate the theoretical analysis and practical feasibility of the proposed operating principle and the developed control scheme

DC-bias Current Detection and Mitigation for a Three-Phase Transformer-Connected Converter through DC-Link Measurement

DC-bias of the magnetic flux is a common challenge for transformer-connected converters, leading to increased losses and potential converter malfunction. This paper presents a novel strategy to detect and mitigate DC-bias currents through the transformer. It detects DC-bias currents from the presence of a switching-frequency harmonic component in the DC-link current and successively regulates it to zero. Stability analysis demonstrates the robustness of the proposed method against phase errors in the current measurement circuit. Experimental measurements are conducted to validate both the theoretical analysis and effectiveness of the detection and mitigation method

Disruption of CDK-resistant chromatin association by pRB causes DNA damage, mitotic errors, and reduces Condensin II recruitment

Organization of chromatin structure is indispensible to the maintenance of genome integrity. The retinoblastoma tumor suppressor protein (pRB) mediates both transcriptional repression and chromatin organization, but the independent contributions of these functions have been difficult to study. Here, we utilize a synthetic Rb1 mutant allele (F832A) that maintains pRB association at cell cycle gene promoters, but disrupts a cyclin-dependent kinase (CDK)-resistant interaction with E2F1 to reduce occupancy of pRB on intergenic chromatin. Reduced pRB chromatin association increases spontaneous γH2AX deposition and aneuploidy. Our data indicates that the CDK-resistant pRB-E2F1 scaffold recruits Condensin II to major satellite repeats to stabilize chromatin structure in interphase and mitosis through mechanisms that are distinct from silencing of repetitive sequence expression

Sequence-decoupled resonant control of three-phase grid-interfacing inverter for local voltage support under unbalanced load

This paper considers a three-phase four-wire grid-interfacing voltage-source inverter with local unbalanced and distorting loads. A sequence-decoupled resonant control strategy is proposed to support the local voltage on top of conventional active power regulation. The local voltage at the point of common connection, which is traditionally used for grid synchronization for distributed generators, is also used for sensing unbalanced and harmonic voltages. Therefore, measurements of load currents for unbalanced and harmonic compensation can be eliminated with the proposed approach.</p

Pragmatic rules for comparability of biological medicinal products

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Formal and informal social participation of the 'young-old' in the Netherlands in 1992 and 2002

The study compares the formal and informal social participation of 60-69 year olds in The Netherlands in 1992 and 2002, and examines which attributes of the two cohorts favour social participation. Using data from the Longitudinal Aging Study Amsterdam, it was found that cohort differences in formal participation (as members of organisations, in volunteer work and in religious organisations) and in informal participation (having a large social network, and in cultural and recreational activities) associated with cohort differences in individual characteristics (level of education, health, employment status and marital status). Descriptive analyses showed an increase between 1992 and 2002 in all forms of participation except religious involvement. The 2002 cohort members were more educated and more engaged in employment, but in worse health and had a higher prevalence of divorce than the 1992 cohort members. Logistic regression analyses showed that the positive effect on social participation of the recent cohort's higher educational level was suppressed by the negative effect of their worse health. Being divorced had mixed effects on formal and informal participation, but the difference in the number of divorcees did not explain cohort differences in social participation. Interaction effects showed that the influence of sex and health on volunteer work and religious involvement changed over time. The paper concludes with a discussion of the prospects for higher levels of formal and informal social participation among future cohorts of young-older people. © 2010 Cambridge University Press