Research On Fault Diagnosis Of Grid-connected Inverters Of Wind Turbine

It has a very vast development prospects for wind power technology in the new energy research. Especially along with the uninterrupted growth of wind power technology and high-power self-turn-off device, grid-connected converters of wind turbines are getting more and more in-depth research. In wind turbine systems, if the power switching device of high-power converters/inverters break down and cannot be timely diagnosed and recovered, it will bring about huge economic losses obviously. So it’s very important and also has practical significance that taking research on fault diagnosis and tolerant control for grid-connected converters of wind power system in order to ensure the reliability and safety of wind turbines.Based on this consideration, after thorough analysis on performance of high power converters, this paper mainly describes a system for modeling and discusses the fault analysis of three phase grid-connected inverters of wind turbines, mainly focusing on stuck-open faults and short-circuit faults.First of all in the modeling method on the selection, considering high-power inventers contain both continuous dynamics and discrete dynamics, which take the system on complex mixed properties owning to the above two characteristics. In order to realize fault diagnosis for hybrid system, the model must cover the two characteristics, namely the continuous dynamics and discrete dynamics. Thus, for the modeling of this kind of system, it is very complex and liable to make mistakes if using general mathematical method. Besides, the inhomogeneity of mathematics due to the isomerism of physical system often slip up, even can’t solved by numerical method. While, the method-divide the overall system into multiple subsystems and each subsystem is modeled by ordinary principles of mechanics or electromagnetism, then assemble these subsystems into unified equations and then transform into state equations is also hard to realize in technology, vulnerable to associated variables and missing modality. To make this problem come out effectively and guarantee the model can response its performance accurately, in this paper, from the view of energy, put forward a new bond graph-based modeling approach. As for switched power devices, a new concept named switched power junction (SPJ) is presented and a model is developed for the inverters analysis using SPJ.Secondly, taking three-phase grid-connected inverters for subjects, in this paper the bond graph model based on SPJ was established and also carried out simulation on20-sim. The response curves of the system were also obtained without any faults of each power devices. In this case, the unique superiority of BG-based modeling, which regarded as some advanced modeling tool in three-phase grid-connected inverters, was testified.At last, the fault diagnostic methods for switching power devices, mainly focused on stuck-open faults and short-circuit faults, is designed and described under Fault Tree Analysis (FTA). Steps are as follows:Develop time causal graph (TCG) from BG modeling to describe the causalities between variables.When observation produce deviations, establish the system’s fault trees by the method of TCG backtracking.Create hypothesis fault set on basis of fault trees. According to TCG, predict the future changes of each fault element. Comparing with new observation, correct the fault set and get the diagnosis.Thus, system’s fault state and fault cause have been analyzed relying on fault tree. And our proposed model is verified through experimental study on20-sim software. Compared with quantitative analysis, this approach has some advantages, such as less computation and low model precision etc.The major thrust of the paper are not only to widen out the fault analysis approaches of power electronics based on bond graph, but to provide feasibility for band graph using in hybrid system modeling.