| In recent years,with rapid development of renewable energy sources,the micro-grid technology has experienced two stages successively:the stage of feasibility study and verification of micro-grid technology and the stage of the research and maturity of micro-grid system control methods.Currently,micro-grid technology research has successfully stepped into the research stage of multi-micro-grid interaction method.The proposal of hierarchical control system framework of the micro-grid and hybrid control methods are important products at the second stage of the micro-grid,and are also the prerequisite foundation for stepping into the third stage.Study on the hybrid hierarchical control system framework has important milestone significance for future development of micro-grid technology.Hierarchical control framework of traditional micro-grid is divided into five control levels,and all levels are connected in series via modern Internet communication technology to form complete micro-grid control system network.The hybrid control system mainly relies on communication technology to achieve information fusion of various types of variables,hybrid control of different types of control methods,and collaborative control of different types of power supply and control levels.Therefore,the hybrid control theory under this framework can be divided into two directions of the research and communication of control method and the research of data processing method.For the research of control methods,there are still the accuracy of power distribution among power supply nodes,the improvement of static-dynamic response performance of the output of each node,economic utilization of various distributed resources throughout the grid and other problems.For long term,the problem of accuracy of micro-grid node power distribution is staying in the research and improvement of methods at the first and second levels all the time,and there is still limitation in the improvement of overall performance of micro-grid control system.The static-dynamic response performance of the output of each node not only directly influences static-dynamic performance of overall control system of the micro-grid and the economy and reliability of scheduling strategy of whole grid resources in specific implementation process,but also indirectly influences the accuracy of power distribution of each node.However,the research on output control method of each node of the micro-grid has not been able to solve the problem very well.In addition,the research on overall relevance problem of VSIs control network composed of these nodes is still relatively weak.Although such problem that,the correlation generated via transmission line impedance between different levels and control systems of different micro-grids will reduce internal control stability margin of the micro-grid,has been well known,it is still a blank space of the research on micro-grid control systems and methods to explore essential cause of such problem from the perspective of control science.In view of above problems,(1)major influencing factors to influence output response performance of each node,i.e.,controller parameters,the delay between hierarchies,the uncertainty of interconnection line parameters and the relevance of control system of interconnection nodes,have been analyzed by overall modeling for complete control system of single VSI node including various control levels.(2)In view of the mode of conventional way to improve response performance of the node by adjusting controller parameters,two kinds of setting methods of parameters of VSI node output controller,the offline optimization and online self-adjusting,have been designed utilizing Fruit Fly Optimization Algorithm.It has been discovered via comparative study that,there is certain limitation of this traditional method under the condition not changing the structure of control system.(3)Adopting further dynamic matrix predictive control theory,this paper has improved the design of internal output controller of VSI node,having comprehensively enhanced output response performance of single VSI node.(4)In view of multi-VSI node relevance problem of VSIs control network,from the perspective of control science,essential cause that node relevance influences controller performance via interconnection line parameters has been discovered via the analysis on multi-VSIs-node and multi-hierarchy complete control model,i.e.,because of the addition of the item of interconnection line parameters and the item of control model of adjacent nodes,in the control model,original control system model of each node has been changed,thereby pole distribution of VSI node is shifted,causing the reduction of stability margin of VSI node controller.(5)The matrix containing relevance parameters consisting of interconnection line parameters have been constructed with state space model.On this basis,a kind of multi-node cooperative output control method for VSIs control network has been designed adopting DMC-based control theory.By comparing and simulating of VSIs network composed of multi VSI nodes independently controlled by DMC control system,VSIs control network composed of VSI nodes controlled by traditional PI and VSIs control network DMC-based cooperative control under the same environment,the effectiveness of this collaborative control method to reduce relevance influence in VSIs control networks has been verified.(6)This paper has carried out model construction and study in view of interconnection interface equipment in multi-micro-grid interaction process.Considering overall consistency of VSIs control network,similarly,adopting DMC control method,this paper has designed internal output controller of interconnection interface equipment and verified its output response performance by experiment. |
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