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Background Stress is a common contributing factor for irritable bowel syndrome (IBS). This study was to evaluate the efficacy of the centralized health education program in improving the quality of life (QOL) of middle school students with IBS who experienced the Wenchuan earthquake on May 12, 2008. Methods A multi-center, randomized and open evaluation study design was adopted. A total of 584 students...
To suppress the common mode current flowing into the grid effectively, this paper presents a novel active clamping inverter topology with non-isolated single-phase photovoltaic grid inverters. This topology can provide freewheeling path and separate solar panels from the grid at the freewheeling stage. In addition, a series resistor in the clamping channel of the new structure is added, which can...
Modular Multilevel Converter (MMC) is the latest achievement in terms of the main circuit topology in flexible HVDC, which has the merits of high modular, low harmonic content of output waveform and long maintenance interval. On the basis of analysis of topology and working principle, a strategy which adopts carrier phase shift modulation (CPS-SPWM), is proposed in this paper. Under low devices switching...
In the existing photovoltaic power generating system, life-span of the storage battery cannot be attained very well, which is a constraint on further development of photovoltaic industry. Aiming at the characteristics of the battery and photovoltaic module in charging system, one type of intelligent photovoltaic charging control strategy and system based on the chip of PIC16F877A is presented and...
The principle of photovoltaic grid-connected generation system is analyzed, and the research on PWM control strategy is done based on the power output side of photovoltaic grid-connected generation system. The direct current control strategy of photovoltaic grid-connected inverter is presented. The control fashion of applying fixed switch frequency and the feedforward compensation control of utility...
The principle of photovoltaic grid-connected generation system is analyzed, and the research on PWM control strategy is done based on the power output side of photovoltaic grid-connected generation system. The direct current control strategy of photovoltaic grid-connected inverter is presented. The control fashion of applying fixed switch frequency and the feedforward compensation control of utility...
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