| ABSTRACT:As environmental and energy problems have become the focus in the global scope, and the new energy technology has developed rapidly, distributed generation has been widely applied in microgrid component with the represent of photovoltaic energy storage system. This paper focus on the related technology research of grid inverter grid-connected/islanding seamless transfer, based on the analysis of photovoltaic energy storage system model, system energy management, and control strategies.First of all, builds the model of grid inverter and analyses the basic control strategies of on and off grid working conditions, the output characteristics of photovoltaic and the corresponding MPPT control method of the Boost circuit are studied, the Buck-Boost circuit principle and control strategy of the energy storage are introduced, carries on the comparison and analysis of the different structures of photovoltaic energy storage system. From the whole perspective of the photovoltaic energy storage system, lists every part corresponding control strategies according to the different working conditions, carries on the analysis of the coordination control and simulation research of several selected typical operating conditions.Secondly, dual mode grid-connected/islanding is analyzed in detail. Islanding to grid-connected and grid-connected to islanding are analyzed respectively.analyses the problems of general dual mode grid-connected/islanding switch.and refers to the corresponding solution measures to solve these problems.The theoretical analysis of dual mode grid-connected/islanding switch is verified by modeling and simulation.Again, based on the contrast analysis of the dual mode switch this paper adopts single mode switch control strategy.which is grid-connected and islanding all adopt droop control strategy. On the basis of droop control has the current source output characteristic when operating grid-connected by adjusting the droop curve, the droop control single mode realizes grid-connected/islanding switch, which offsets the disadvantages of dual mode switch and improves the switching effect greatly. At the same time the traditional droop curve is improved by nonlinear droop curve,the inverter’s power output is more stable when parallel operates with grid compared to traditional droop curve and the effect of grid-connected/islanding switch is better.Finally based on the above theoretical analysis, this paper has designed the hardware circuit of three-phase grid-connected inverter. According to the power level of the whole system, it has completed the parameter design of key elements such as power switch,capacitance, inductance. It also has designed a control system based on digital signal processor TMS320F28335, mapped the printed circuit board, setted up the experimental platform,and carries on the experimental verification, analyzes the dual and single mode switch control strategys by the experiment waveforms,the validity of the proposed theory and the effectiveness of the proposed control strategy are verified, realized grid-connected/islanding seamless switching. |
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