Study On Grid-connected Inverters Of Renewable Energy Generation Based On One-cycle Control

With the deterioration of environment and depletion of conventional resource,the development of new energy is promoted. As a new type of energy, renewable energy has got more and more attention. At present, many countries of the whole world take the renewable energy generation grid-connected system measures like wind power and photovoltaic power generation. Wind power generation needs the rectifiers to convert alternating current into direct current, and then reverse to AC. Photovoltaic power generation needs the inverter to convert DC to AC and then connected to the grid. Grid-connected inverter has become a research focus as the interface unit which connects power generation system with grid. It has become keystone of research that people study novel topology and control methods which can make high quality output power while it increase the systems efficiency at the same time.Deficiency of soft-switching technique and the multi-level technique was pointed out on the basis of analysising and improving the grid-connected inverter systems efficiency. Dual-frequency inverter based on one-cycle control in the renewable energy generation provided a new way to increase the systems efficiency. Meanwhile, with the shoot-through problem in conventional bridge-type inverters, this paper analyzed dual buck grid-connected inverter and utilized the dual buck grid-connected inverter based on one-cycle control to grid-connected system in order to improve the output power quality and reduce witching losses simultaneously.The thesis expatiated the basic principle of one-cycle control, summarized the characteristics of one-cycle control technique, and established the one-cycle control circuit model of Buck. Computer simulation analysis of one-cycle control technique for anti-disturbance ability helps to get good simulation results.Dual-frequency buck converter circuit theory was analyzed in the thesis. The dual-frequency inverter was applied to the renewable generation system. The mode of grid-connected inverter with single-phase dual-frequency half-bridge and single-phase dual-frequency full-bridge inverter ware established and their working principle ware explained. And then taking an example of single-phase dual-frequency half-bridge grid-connected inverter, its working mode was analyzed, one-cycle control equations ware derived and simulation analysis was conducted. The results show that the single-phase dual-frequency grid-connected system has good dynamic and static performance. The performance of single-phase dual-frequency grid-connected inverter output current waveform is almost the same as a single high-frequency grid-connected inverter. Low-frequency switch shunts the high- frequency switch and lets the current of high-frequency switch down to reduce the switching loss, so that it can improve the system efficiency on the premise of ensuring the system performance and can increase the power rating and volume at the current level of power device. Hardware of single-phase dual-frequency half-bridge grid-connected inverter was designed based on theoretical analysis,and part of the experimental analysis was carried out in the paper。Furthermore, the three-phase dual-frequency grid-connected inverter based on one-cycle control was applied in the large or medium-power grid-connected system. The thesis analyzed the work principle and established the average model on the basis of deriving the average model of traditional three-phase grid-connected inverter. Then the one-cycle control method of three-phase dual-frequency grid-connected inverter was analyzed and discussed, and the one-cycle control model was established. The simulation results illustrate that the efficiency of the inverter is greatly increased compared with the single high-frequency grid-connected inverter.By comprehensively analyzing the structure and working principle of the dual buck grid-connected inverter, one-cycle control thought and its model was proposed. As to the three-phase dual buck grid-connected inverter, the thesis built up the one-cycle control model with vector operation mode and conducted simulative studies to prove the correctness of theoretical analysis. At last, the superior performance of one-cycle controller with vector operation is proved by comparative analysis to the traditional hysteresis control.