Research Of Control Method For Distributed Generation In A Micro-grid With Unbalanced Loads

As an effective carrier of Distributed Generator(DG), microgrid become one of the popular research fields in recent years for its high energy efficiency and well economic performance. The most common power quality problem of micro-grid is voltage unbalance, which is caused by the many unbalanced loads in microgrid. So how to eliminate the impact on the power quality of micro-grid and distribution network by the unbalanced loads and ensure the normal operation of micro-grid has important significance. This paper focus on the control and operation of Inverter Interfaced Distributed Generator(IIDG) under unbalanced loads, meanwhile, design a control system of IIDG under unbalanced loads.Firstly, after a comprehensive analysis of the background and research status of the subject, this dissertation analyzes the topology and working principle of the IIDG in micro-grid, and study the control method for different types of IIDG in grid-connected mode under normal conditions. Secondly, introduces the fundamental of symmetrical components and designs a method which can be used to extract the positive and negative sequence component of electromagnetic calorimeter in system under unbalanced conditions. Meanwhile, a detailed study has been put on the mathematical model of IIDG’s grid-connected inverter and sliding-mode control technology. Then, proposed a compensation strategy based on the sliding mode control for IIDG in micro-grid with unbalanced loads to implemented on the balanced output voltage and stable output positive sequence active and reactive power. The power sliding mode controller based on the integral-type switching function is given to directly regulate the output active and reactive power of grid-connected inverters; Besides, proposed the current sliding mode controller based on index reaching law to compensate for the negative sequence current component generated by the unbalanced loads of the microgrid. Through MATLAB/Simulink simulation of the proposed control method in balanced and unbalanced conditions, the stability and effective can be verified by compared with the conventional PQ control method.In additon, with considering the connection mode of DG and the position of unbalanced loads, this dissertation gives a coordination compensation control method based on sliding mode control for Multi-IIDGs interconnected micro-grid system. The coordination between IIDGs achieved by decomposition of negative sequence in target mode and distribution of compensation. Finally, the effective of the coordination compensation control method can be verified by simulation of a typical micro-grid system including unbalanced loads in the MATLAB/Simulink environment. This control method can improve the operational capabilities of micro-grid system under unbalanced conditions.