| Due to the shortage and exhaustion of non-renewable energy sources such as coal and oil,renewable energy such as wind power generation and ocean power generation have flourished.Wave energy generation,as a renewable energy source with the highest energy density and new renewable energy generation method with great development potential,has become the focus of attention,meanwhile,it also has the characteristics of randomness,volatility and intermittence similar to other renewable energy power generation.As the interface between generator side and power grid side,wave energy converter plays an important role in the process of power conversion.Due to the influence of random fluctuation of power,intermittent operation and operating environment temperature,the fatigue aging of power semiconductors caused by thermal stress directly affects the safe and reliable operation of converters.Therefore,the research on life evaluation of power semiconductors in wave energy converters is extremely urgent.This thesis mainly focuses on the life prediction of power semiconductors of wave energy power generation converters.The main work of the thesis is as follows:Firstly,the analytical expression of the output characteristics model of the wave energy converter is established.It is the first step to obtain the long-term power loss profile of power semiconductors in wave energy converter.The output characteristics of the wave energy converter under regular waves and irregular waves are deduced and theoretically analyzed in detail,combined with WEC-Sim simulation for verification.Taking a certain sea state as an example,the simulation verifies the correctness of the derived output characteristics model of wave energy converter,such as power output,voltage and current,which provides theoretical support for obtaining the long-term electrical profile of power semiconductors(take one year of sea conditions as an example),and lays the foundation for calculating the long-term loss profile of power semiconductors.Then,the numerical method for extracting the junction temperature of the power semiconductors in wave energy power generation converter considering the dynamic of junction temperature equilibrium process is proposed.Based on the power loss model considering the electrical and thermal coupling,combined with the power semiconductors characteristics to obtain the power loss profile of the power semiconductors.Based on digital filter and electro-thermal analogy theory,the proposed method is used to calculate the thermal loading of power semiconductors under a certain working condition,meanwhile,junction temperature obtained by Fuji IGBT electro-thermal simulator and three-phase DC/AC converter experimental platform based on infrared thermal imager is used to verify the accuracy of junction temperature and its dynamic balance process.Through the comparison of simulation and experiments results,the proposed method can realize the thermal loading extraction considering the dynamic balance process of the junction temperature of the power semiconductors,and this method can ensure the accuracy of thermal load extraction while greatly reducing computation burden and improving calculation efficiency,which provides a new method to extract the long-term thermal loading of power semiconductors in wave energy converter.Finally,the method for lifetime evaluation of power semiconductors in wave energy converter under long-term scale and short-term thermal loading is proposed.Based on the numerical thermal loading extraction method,the thermal loading of the power semiconductors of wave energy converter is distributed in a short-term scale of fundamental frequency junction temperature fluctuation and sea states changes of longterm scale,meanwhile,the thermal loading of different time scales is analyzed and calculated.The damage accumulation of power semiconductors caused by different time scales is analyzed and calculated.The service lifetime of power semiconductors in wave energy converter is evaluated.And the influence of sea states sample rate on lifetime consumption accumulation of power semiconductors is studied.The sampling rate can directly reflect the relationship between prediction accuracy and calculation efficiency in the process of power semiconductors lifetime prediction,at same time,the cumulative lifetime consumption of wave energy converter at different stations is also analyzed.The theoretical evaluated lifetime of power semiconductors of different stations is compared,which provides guidance for layout and planning of wave energy generation system. |
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