| In order to cope with the crisis of energy and optimize energy structure, the micro-grid has obtained a rapid development in recent years. A series of key technologies associated with micro-grid has become hot, power quality analysis and control is one of the key technologies of these. Due to the particularity of micro-grid system, its power quality is not only related to the operation characteristics of internal distributed power, storage device and load, but also has interactive effects with external distribution network. Based on the feature of micro-grid power quality, multifunctional inverter is used to comprehensive control of micro-grid power quality, the detection and control strategy is studied to improve micro-grid power quality based on multifunctional inverter in this paper.Firstly, the basic structure of micro-grid system is introduced and the control strategy of distributed generation is studied. According to these, different control strategies of micro-grid are formulated, the control principle and goal to improve micro-grid power quality are further clarified.Secondly, the detection method of instruction voltage and current signals for multi-function inverter output is researched. It is difficult to apply traditional phase-locked loop when distribution network voltage has unbalance and distortion, the two detection methods of instruction voltage based on Park transformation and resonant control without phase-locked loop are researched in this paper. In order to cope with the inherent time delay of digital system, the detection method of instruction current based on adaptive prediction is studied. A detection method of instruction current for the graded compensation is proposed, which is suitable for three-phase unbalanced load that contain any harmonic component. The direct and indirect prediction methods of instruction current for full compensation are compared from the two aspects of steady-state accuracy and dynamic response speed respectively. For the power fluctuations of micro-grid caused by intermittent power, the influence mechanism of PCC voltage quality by the power fluctuation is studied.Finally, the multi-objective control strategy to improve the power quality of micro-grid based on multifunction inverter is researched. The voltage tracking control strategy based on adaptive triangular carrier is studied, the capacitors on the DC side of multifunction inverter is equalizing controlled at the same time. To stabilize the micro-grid power fluctuations and improve the quality of the PCC voltage, the double loop control strategy of two bidirectional DC/DC converters in the hybrid energy storage unit is studied. According to the different characteristics of super capacitor and batteiy, an energy management method of hybrid energy storage unit is designed. It can not only exert respective advantage of the energy storage components but also control the operation of energy storage components in the safe range. The stabilize effect of micro grid is improved.In order to verify the effectiveness of the proposed control strategy in this paper, the simulation model is builded in Matlab/Simulink environment. By setting different conditions, the simulation research has been carried on from four aspects of improving voltage quality, current quality, stabilizing power fluctuations and management of important node. From the simulation results, the control strategy in this paper to improve power quality of micro-grid based on multifunction inverter is effective and feasible. |
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