Research On Control Strategy Of Stand-alone DC Distributed System With Multi-Photovoltaic Modules

Energy crisis and environmental problems have become a serious problem which must be faced and solved in the world today. In order to realize the sustainable development of our human beings, the solar photovoltaic based distributed power generation technology has been rapidly developed. Promoting the engineering and practical applications of solar photovoltaic power generation system have a important theoretical and practical significance. The realization of coordinated control and optimal operation of distributed photovoltaic power generation system according to its characteristics is a main way to achieve the promotion.This paper takes photovoltaic based DC distributed power generation system(DPGS) as the research object and deeply studies on four aspects: the system structure, coordinated control strategy of the system, optimization control strategy of the distributed multi-photovoltaic units and optimization control strategy of the distributed battery energy storage system(DBESS). First of all, through the study of the existing photovoltaic generation system structures, this paper proposes a novel stand-alone DC distributed multi-photovoltaic power architecture which is composed by distributed multiple photovoltaic modules, DBESS and the local loads. The structure of the system has the advantage of being able to achieve energy exchange between local areas to solve the problem of energy excess and deficiency of local areas. Then the coordinated control strategy of DPGS was detailedly studied and the voltage hierarchical coordinated control strategy which is based on DC voltage variations was used to achieve the coordinated control of each power electronic converter and ensure the safe and stable operation of the system in different conditions.Secondly, the scheduling strategy of distributed multi-photovoltaic units that installed in different local areas was researched, proposing the concepts of synchronous scheduling and step by step scheduling. Aiming at the step by step scheduling, this paper puts forward a photovoltaic interface converter control method based on EIM+DBS. In addition, the optimization control of DBESS was studied and a concept of “public load system” and “distributed load system” was proposed, the respective characteristics of the two kinds of system were researched. Then this paper makes decrease of system network loss as the object of optimal control, analyzing the principle of the traditional droop control in reducing the system network loss. At the same time, this paper has studied on the problem of state of charge(SOC) imbalance of DBESS and proposed a battery terminal voltage based droop control method for alleviating the SOC imbalance degree of DBESS.At the end of each chapter, simulations were make to verify the correction of theoretical analysis based on MATLAB/Simulink environment. Finally, a experiment prototype was implemented for the experimental demonstration of photovoltaic units control methods.