Drought and Waterlogging Characteristics during the Growth Period of Summer Maize in Luxi Plain Areas

In summer maize growth period,the water supply and demand ratio is regarded as the evaluation index of drought and waterlogging for the summer maize in Liaocheng City. Using GIS,statistics,agrometeorology and other methods,we analyze the precipitation during the summer maize growth period in Luxi Plains from 1961 to 2011. Through the calculation of drought and waterlogging index,it indicates that the disasters of drought and waterlogging frequently occur during the summer maize growth period,mainly affected by the drought; the frequency of occurrence of drought accounts for 80. 4%,that is,it is very prone to serious drought phenomenon,seriously affecting the normal growth and development of summer maize during the seedling period. With global warming,the industrial and domestic water demand is increasing year by year,so it is extremely difficult to increase the water diversion to solve the problem of water shortage for the growth of summer maize. Finally we put forth the following recommendations:( i) Selecting drought-resistant varieties,and improving the water resource use efficiency;( ii)Promoting the water and fertilizer coupling,sprinkler irrigation,drip irrigation,micro-irrigation and other water-saving irrigation technologies,and improving the water use efficiency;( iii) Promoting the ditch,ridge and laminating cultivation technology,reducing the field evapotranspiration,keeping warming and conserving moisture,and saving water resources;( iv) Strengthening the construction of water conservancy facilities,so that it can be irrigated during drought and drained during waterlogging;( v) During dry season,timely organizing artificial rainfall operation,and increasing precipitation in arid areas to ease drought;( vi) Rationally exploiting the groundwater,and improving the underground water use efficiency.

A partial compensation scheme for MMC-based railway cophase power supply

This paper presents a partial compensation scheme for V/v transformer cophase traction power supply in high-speed railway systems.The scheme compensates variable traction load current,and controls the current phase at the secondary side of the V/v transformer for power factor correction and negative sequence current reduction.To achieve this,the grid side current phase angles are optimized while satisfying the grid code on the power factor and voltage unbalance limits.The optimized phase angles are then used to design control references under varying load conditions.The compensation control action is updated regularly based on real-time measurements of the traction load,and the required currents are controlled by a 25-level single-phase back-to-back MMC power conditioner to achieve the compensation target.Static and dynamic load compensation performances are verified based on the simulation studies.