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For the traditional low voltage ride through control under asymmetrical faults, due to the limited control degrees of freedom, the grid-connected inverter control suffers from the problem of not being able to simultaneously realize the output current negative-sequence component suppression and the DC side voltage double-frequency fluctuation suppression. In this regard, a multiple-objective decoupling control strategy is proposed for low voltage ride through of two-stage grid-connected photovoltaic system under asymmetrical faults. The strategy sets the control objective of the inverter as the negative-sequence component suppression of the output current and gives a reference value calculation method for the inner current loop considering the inverter output current limit and reactive power output demand. The super-capacitor is connected to both ends of the DC bus capacitor through the bidirectional Buck-Boost converter to maintain its voltage stability, and the DC side voltage double-frequency fluctuation is transferred to the super-capacitor side. The simulation results show that under the proposed control strategy, the unbalance between three phases of the inverter is reduced and the output current distortion is improved. The double frequency fluctuation of the DC side voltage is reduced significantly compared with the traditional control method.

Qipanzhou Yangtse River Bridge is of long span, light and soft structure. Its design and construction are extremely sensitive to strong wind. Therefore, an automatic observation station, Qipanzhou automatic weather station, is established near the bridge to observe the characteristics of the wind at the bridge. On the basis of the wind data observed at Qipanzhou weather station and data collected from Huangshi whether station from Feb. 2011 to Jan. 2012, the mean wind speed, extreme wind speed, extreme wind speed are analyzed in details in this paper. The results indicate: 1) most of the time, the monthly average wind speed, maximum wind speed and extreme wind speed at Qipanzhou weather station are larger than Huangshi weather station; 2) As the wind speed increases, the correlation between the daily maximum wind speed at bridge and Huangshi weather station decline gradually until irrelevant; 3) the predominate wind directions at Qipanzhou weather station are converging SSE and NW, in some degree different from those at Huangshi weather station, which are E and NW and non-converging. [ABSTRACT FROM AUTHOR]